Luminous Landscape Forum
Equipment & Techniques => Cameras, Lenses and Shooting gear => Topic started by: allegretto on January 16, 2012, 12:25:32 pm
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Perhaps, maybe certainly, this has been addressed previously. But I see it everywhere I turn in Cameradom. m4/3; "this 24mm lens is a 48mm in 35mm equivalent" and so on..
When I see the pictures, NO, IT'S NOT!!! It is indeed a 24mm lens. It may occupy the space that a 48mm lens would in a FF sensor photo, but it suffers from (or benefits from, whatever the situation) the same distortions of any 24mm lens. Or a least that's the way it looks to me. Portraits shot with small-sensor cameras and short focal length lenses make faces look pear-shaped and noses big. It seems many of the gear peddlers try to avoid this being noticed by playing with the image or lighting, making it "artsy" but distorted just the same.
Is my impression correct, or am I missing something?
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The "equivalent" is referring to field of view (angle of view) only.
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Amen Brother.
I'm a moderator on another photography forum and it seems to me that there is a lot of misinformation floating around about the dreaded 'crop factor'.
Actually, I think that a lot of people do have a decent understanding of it...but they way they express it, is often incorrect...and on a medium like an internet forum, that can lead to a lot of other people getting the wrong ideas.
It does bother me when I read people saying that a 50mm lens is an 80mm lens on ________ camera. ::)
No it's not (I shout in my head)...it's a 50mm lens and the camera is only seeing a certain portion of the frame (field of view) that is similar to what an 80mm lens would see on a 35mm film (of full frame) camera.
As we get farther and farther away from 'the old standard' of 35mm film...I think we should put the 'crop factor' to rest. Most of the people on photography internet forums (the one I mod for especially) have never used a 35mm film SLR, so the crop factor has no meaning to them...except to confuse them.
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The "big nose effect" is caused by short distance.
You may use a compact camera at 40 cm distance or a full format at 40 cm. It's just the same and it's called perspective.
Ciao, Walter
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"it's a 50mm lens and the camera is only seeing a certain portion of the frame (field of view) that is similar to what an 80mm lens would see on a 35mm film (of full frame) camera."
Except that an 80mm lens on a full frame has slightly more compression than the 50mm.
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... Except that an 80mm lens on a full frame has slightly more compression than the 50mm.
Care to define "compression'?
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... Portraits shot with small-sensor cameras and short focal length lenses make faces look pear-shaped and noses big...
Not correct. As Walter pointed out, it has nothing to do with sensor size or focal length, but everything to do with the distance from the object.
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Let's pose this another way...
If I was shooting a 50mm lens on 35mm, to swap my camera to 6x6 cm, I'd be shooting with about a 75-80mm lens. For 6x9 cm, I'd need maybe a 90-105mm, for 4x5, a 150mm is the lens. That's the was we figured before digital.
Today, with the 4/3, DX, etc., we're implying the same idea, but using a little different terminology. A 50mm on 35mm would work on a DX frame as though we were shooting with a 75mm to 80mm lens and on 4/3 as though we were shooting with a 100mm lens on the 35mm/FX/Full-frame. The meaning is about the same, though those of us from the glorious days of film (1990s) sometimes get picky...
As for me, I'm shooting both full-frame and DX and it's second nature what lenses I need and use to have a similar angle of view between the two formats.
Neither good nor bad, just a mind set. No reason to take offense or get bent out of shape. As for me, I'd rather be shooting than arguing. So now stop worrying about the terminology and simply go out and create a nice image!
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As folks have pointed out, perspective is created by distance; it is the relationship between different objects in the scene being photographed front to back (foreground, midground, background). Focal length determines magnification and field of view. Neville Maude at Amateur Photography magazine used to speak of steep vs shallow perspective.
A thought experiment:
Pinocchio asks you to take a corporate portrait (he’s in PR these days, but keeps in the background due to his *problem*). He poses 1m from your camera; his nose when tumescent is 500mm long which means it is half the distance to the lens than where his head is. Thus the *distortion ratio* (just made that up) is 50%. You have used use a standard 50mm lens, but think the effect is a little *in-your-face*, so you switch to a 135mm and back off to 2.7m. Pinocchio’s head will fill the same amount of the frame, but the ratio between the end of his wooden hooter and his face will have changed, relative to the greater distance. Do the sums for the 135: distance to face is 2.7m; distance to end of nasal stick is 2.7m – 500mm = 2.2m. Result 0.814 (three figures).
Or you could read this (http://www.mactalk.com.au/20/101271-portrait-lens.html#post1102666).
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Not correct. As Walter pointed out, it has nothing to do with sensor size or focal length, but everything to do with the distance from the object.
Hmmm
Isn't a 25 mm lens a 25mm lens regardless of sensor size?
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Yes, it is.
Ciao, Walter
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if the focal length had this effect cell phone cameras or 8x10" would be absolutely unusable for portraits.
it really only is the perspective.
the exact same discussion was very popular a few years ago (at least in the german speakin community) when the first (crop)dslrs became affordable. unfortunately I can't find one of those comparison that show absolutely no difference for different focal lengths with the same perspective (except resolution or things like that of course).
if you don't believe it just try it out. do a blind test, otherwise might see what you want to see.
simon
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Hmmm
Isn't a 25 mm lens a 25mm lens regardless of sensor size?
Yes.
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Hmmm
Isn't a 25 mm lens a 25mm lens regardless of sensor size?
of course, but a 25mm can be an extreme wide angle with a large image circle (medium format) or a rather long tele lens with a very small image circle (ps with small sensor).
maybe another thought experiment helps. take a camera with a lens and take a picture, now think of the exact same camera just 1:10 of the size. would you expect the shrunk camera to produce a different image that the big one? (I know, diffraction, noise and stuff will be different, but that can be "easily" explained, and that's not what I mean)
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As we get farther and farther away from 'the old standard' of 35mm film...I think we should put the 'crop factor' to rest. Most of the people on photography internet forums (the one I mod for especially) have never used a 35mm film SLR, so the crop factor has no meaning to them...except to confuse them.
The "35mm equivalent" is extremely useful shorthand for figuring out that a 24mm is a wide angle lens on a full-frame camera but a normal lens (ish) on a Micro Four Thirds camera. Without that short-hand we'd have to know what the crop factor of each camera is (and we're back to square one), or be experts at every single camera system (crop factor) out there, which is not feasible.
I'm not aware of a better and more intuitive way to compare lenses and focal lengths of cameras across formats, especially the ones we don't use regularly.
More on the subject here (http://www.luminous-landscape.com/essays/Equivalent-Lenses.shtml).
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Well if one uses the 25mm lens at 3M then yes, it doesn't get what I'll just call 'perspective distortion" (I just made that up and perhaps there is a better expression).
but I don't think that is what happens to the average amateur photographer. They want to fill the frame and thus get closer. No? And I just think that camera manufacturers don't want to do much to overcome that tendency. In fact, the "35mm equivalent" talk promotes it to folks who don't know better.
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The "35mm equivalent" is extremely useful shorthand for figuring out that a 24mm is a wide angle lens on a full-frame camera but a normal lens (ish) on a Micro Four Thirds camera. Without that short-hand we'd have to know what the crop factor of each camera is (and we're back to square one), or be experts at every single camera system (crop factor) out there, which is not feasible.
I'm not aware of a better and more intuitive way to compare lenses and focal lengths of cameras across formats, especially the ones we don't use regularly.
I agree with that 100% and wonder why 'old' experience should be discarded just because some neophyte doesn't understand. I'm quite sure that, should mankind last that long, by the time nobody around ever worked with full 135 format, then the 'new' way of mental adjustments will happen at is own speed; now is not yet the time.
As for bringing cellphone optics into it - be real; they have different applications and are not likely ever to offer real interchangeable lenses; easier to buy several cellphones equipped with different focal lengths, if you just use a cellphone to do your shots. Now that would be a new market for the 'phone makers!
Rob C
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@allegretto: You lost me. Maybe it's because I'm not a native speaker but I'm not able to understand what your point is.
Have we reached common ground about your statement in the first post? Your conception about small sensor problems was wrong.
Ciao, Walter
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As for bringing cellphone optics into it - be real; they have different applications and are not likely ever to offer real interchangeable lenses; easier to buy several cellphones equipped with different focal lengths, if you just use a cellphone to do your shots. Now that would be a new market for the 'phone makers!
Rob, prepare to have your mind blown (http://iprolens.com/). It takes pro-grade pictures *wink wink nudge nudge*.
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@allegretto: You lost me. Maybe it's because I'm not a native speaker but I'm not able to understand what your point is.
Have we reached common ground about your statement in the first post? Your conception about small sensor problems was wrong.
Ciao, Walter
Thank you Walter. I don't think I'm getting the proper point across and I'm trying to figure out the right way to phrase the question. I'm thinking about the optics and divergence of differing focal lengths.
How's this question;
Is a 4/3 with a 24mm lens merely a crop of the center of the same scene shot with a 24mm lens on a FF? Is it the "same" as a 48mm shot on a FF? Or is there a further consideration? A photo is a two-dimensional rendition of a three dimensional event (OK, let's leave M-theory and General Relativity out of it ;)). as a Mercator projection introduces linear distortions of the relative sizes of the continents, is there another factor attributable to product? It seems a possible paradox to me that the perspective is unchanged when the field of view is changed. But that's why I'm here.
Is that question more clear?
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It seems a possible paradox to me that the perspective is unchanged when the field of view is changed.
Cropping a photo doesn't change perspective, and changing the field of view (without moving the camera) likewise doesn't change perspective — it's equivalent to cropping.
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Is a 4/3 with a 24mm lens merely a crop of the center of the same scene shot with a 24mm lens on a FF?
Putting aside diffraction, resolution, noise: Yes, if both are placed at the same spot.
Is it the "same" as a 48mm shot on a FF?
Going further on and putting aside the different sensor ratio, depth of field, background separation, too: Yes, if both cameras are placed at the same spot.
Or is there a further consideration?
If depth of field, background separation have to be considered: Yes, there is.
Because that's the part where it differs.
A photo is a two-dimensional rendition of a three dimensional event (OK, let's leave M-theory and General Relativity out of it ;)). as a Mercator projection introduces linear distortions of the relative sizes of the continents, is there another factor attributable to product? It seems a possible paradox to me that the perspective is unchanged when the field of view is changed.
Take a look around in the room and fix a point of your choice. Relax and let the picture sink in. Now take a piece of paper and cut a hole in it. Look at the very point as before and move the paper back and forth. Perspective remains the same. (You have to look through the hole in the paper, of course)
Now move yourself nearer to the point or farther away. Perspective changes.
Further reading: Feininger, take a look at the book store or library.
Ciao, Walter
PS: If it comes to ultra wide focal length there will be strange perspective effects when 3-dimensional objects are involved. But this is a very different story not to be mixed up with this discussion.
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Alternatively, you might want to read a 50-page treatise (http://www.josephjamesphotography.com/equivalence/) on the subject.
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Boy, this is a topic.
The ratio of image sizes of two or more objects in a frame is directly proportional to the object distances. This however does not describe perspective, or only in comparing image from the same format.
Perspective, the apparent depth in the 2-D image, is a little more difficult. Given the same field of view and object distance, the perspective will be the same. This is the idea of equivalent focal length.
However, cropping or changing the focal length while maintain the object distance will change perspective. This is because the image to reach its final display size will be enlarged proportionally more. You can look at to two ways, either the foreground and background are not the same in the uncropped and cropped image meaning the ratio of object distances to the foreground and background are different in each image and so have different perspective, or the infinity points (used in linear perspective) are displaced giving different perspective in each image. So a 50mm lens on a 35mm camera will create an uncropped image with a different perspective as an uncropped image made with 50mm lens on an APS camera. Don't believe me? On the left is an uncropped image, to the right is a crop taken from the image and enlarged to the same size. The red line clearly show perspective has changed. (Yes, if I reduced the crop in size it will match the set on in the uncropped image, but we do not scale images to some absolute scale based on FoV and format size--magnification is the bit folks forget.)
BTW, while I am sure folks will be shocked, but this is not new nor radical. This is how it has always worked, but folks have been confusing the ratio of image size to the ratio of object distance as a rule about perspective for a very long time when there is not a direct link.
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Perhaps this issue can be more clearly understood if we start from the beginning.
As I understand, all cameras without exception are cropped-format cameras. If the camera didn't crop the image projected by the lens, one would see a circular image that is progressively dimmer towards the circumference to the point where it would be near black.
The difference between what is called a "full frame 35mm" camera and what is termed a "cropped format" camera is that the cropped-format camera simply crops the image projected by the lens to a greater degree. As a consequence the field of view is narrower but everything within that narrower field of view is the same in images from both cameras, provided pixel quality and pixel density is the same and provided the shots were taken with the same lens from the same position.
A good example of this could be demonstrated by comparing the Canon 5DMkII with the earlier cropped-formats Canon 20D & 30D. Because pixel density and pixel quality is approximately the same for all 3 cameras, the so-called 'cropped formats' 20D and 30D provide no IQ advantage over the 5D2 in any circumstance.
In other words, the usual advantages of the so-called 'cropped format' in terms of longer "effective" focal length and better image quality towards the edges and corners can be achieved with the 5D2 by simply cropping the 5D2 image in post processing to the same field of view as the 20D shot, having used the same lens from the same position with all cameras.
Hope this has clarified the issue.
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... the so-called 'cropped formats' 20D and 30D provide no IQ advantage over the 5D2 in any circumstance...
Your sentence above, when properly read, claims the opposite of what you were trying to say: that the cropped formats do have IQ advantage over FF cameras of the same generation.
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Your sentence above, when properly read, claims the opposite of what you were trying to say: that the cropped formats do have IQ advantage over FF cameras of the same generation.
Not true! The opposite of what I'm trying to say would only be apparent from an improper reading of what I wrote.
What I wrote was that the cropped format usually has certain advantages in respect of 'effective' increase in focal length and sharper edges to the frame. This is true because the pixel density of the 'so-called' cropped formats always lead. The pixel densities of the so-called full frame formats eventually catch up with those of much earlier so-called cropped format models, as is the case with my examples of the 5D2 compared with the 20D.
In other words, the usual advantages of the so-called cropped formats, compared with the lesser-cropped full frame formats, are entirely due to the greater pixel densities of the cropped format. Without such greater pixel density, there's no IQ advantage in any respect, using the same lenses of course.
The current 18mp Canon 7D and 60D have far greater pixel density than the 5D2, so the usual advantages would apply.
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Is a 4/3 with a 24mm lens merely a crop of the center of the same scene shot with a 24mm lens on a FF?
Yes, exactly that.
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Rob, prepare to have your mind blown (http://iprolens.com/). It takes pro-grade pictures *wink wink nudge nudge*.
It's blown!
Rob C
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The problem is that with such a variety of formats, you can't tell if a 24mm lens is "wide" or not. Yes, 24mm is 24mm - but the real question is how wide (or how long) is it, and the focal length alone is not sufficient to answer that. Talking about 35mm equivalent at least eliminates most of the uncertainty.
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The problem is that with such a variety of formats, you can't tell if a 24mm lens is "wide" or not. Yes, 24mm is 24mm - but the real question is how wide (or how long) is it, and the focal length alone is not sufficient to answer that. Talking about 35mm equivalent at least eliminates most of the uncertainty.
Unless you have never used 35mm...
And there is confusion as the normal on 35mm is 43mm, not 50mm that many people assume.
I find the easiest way is dividing the focal length by the diagonal of the format. The product is the magnification factor. I used all kinds of formats and I never had to convert them to another format I did not use to understand its FoV. You really should be working in the format you are using.
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Back in the darkest days of film, Pop Photography, or Modern, ran an article that explained it quite well. They put a wide angle lens on a camera and then put the image through a series of crops up to a 200mm equivalent. They also took a shot with a 200mm telephoto...same camera, location, and subject. When placed side by side, both the 200mm full frame and wide cropped to 200mm were both identical in depth of field and perspective.
The use of 35mm equivalents gives the manufacturers a common reference point that most people with even a rudimentary knowledge of photography can understand. Most point and shoots are labeled with their actual focal lengths, and without a reference point there's no way to translate that to real world.
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The use of 35mm equivalents gives the manufacturers a common reference point that most people with even a rudimentary knowledge of photography can understand. Most point and shoots are labeled with their actual focal lengths, and without a reference point there's no way to translate that to real world.
I am meeting more and more people who have no experience with 35mm. There was a compact camera being sold in Japan with the sales point that is was a 28mm wide. I asked a friend what they thought that meant. They had no idea. I really don't see the 35mm reference becoming anymore than a curiosity in the future.
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... sales point that is was a 28mm wide. I asked a friend what they thought that meant. They had no idea...
And they would if you told them it is, say, a 6mm lens!? Using ignoramuses as a yardstick!? Oh, my... :(
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And they would if you told them it is, say, a 6mm lens!? Using ignoramuses as a yardstick!? Oh, my... :(
Thank you for insulting my friends. It is nice to be in the presence of such intellect.
The point is that a 35mm reference is archaic. It is no longer a dominant format where people can identify with it.
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Sorry, but Slobodan has a point. He may be rude, but your argument is invalid and that's exaktly what he has pointed out.
Your friends ignorance doesn't validate anything.
The majority of people I know don't know anything about planet orbits. But this isn't a valid argument to defend or deny Keppler's laws.
Ciao, Walter
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And the ignorance that comes from not being able to work in a format and have to convert to another to understand it, that is something to write home about?
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However, cropping or changing the focal length while maintain the object distance will change perspective. This is because the image to reach its final display size will be enlarged proportionally more. .....
If you believe that then your definition of perspective is much different than mine and that of most photographers.
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If you believe that then your definition of perspective is much different than mine and that of most photographers.
But I provided the proof.
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But I provided the proof.
And that's the point. You made a statement and delivered a proof for it.
To argue your proof it would be wise to show an example, too. And I can't deliver it right now. Not because it is impossible, but it has to be done properly.
The point of view is not without pitfalls when discussing perspective. SCNR, this thread is born for bad puns.
Ciao, Walter
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... It is nice to be in the presence of such intellect...
You are welcome, thewiseguywitha645d.
But you evaded my question: would your friend have any idea what they are talking about if they told him the lens is 6mm? I sincerely doubt. The plethora of different nail sized-sensor dimensions in digital compacts makes it even more difficult to visualize what a 6mm lens is.
Btw, why would you perceive what I said as an insult? If, in your own words, your friend did not have a clue what they are talking about, that makes him, by definition, ignorant (at least in the field under discussion). Nothing wrong with that, there are thousands of fields where I am an absolute ignoramus as well and I take no offense when someone points it out.
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... The point is that a 35mm reference is archaic. It is no longer a dominant format where people can identify with it.
Which one is it then? APS-C? If so, is it:
1.3x (Canon)
1.52x (Nikon, Fuji, Sony)
1.53x (Pentax, some)
1.54x (Pentax, some)
1.6x (Canon)
1.7x (Sigma)
1.85x (Canon G1X)
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And that's the point. You made a statement and delivered a proof for it.
To argue your proof it would be wise to show an example, too. And I can't deliver it right now. Not because it is impossible, but it has to be done properly.
The point of view is not without pitfalls when discussing perspective. SCNR, this thread is born for bad puns.
Ciao, Walter
Walter, are your saying that the example image I posted shows a change in perspective because of the crop, yet you are going to show an example which will show that the image, while showing a change in perspective, is not showing a change in perspective????
You may find most photographer have never studied perspective. So why they would be an authority. There is nothing in my argument that has any pitfalls as it is a pretty standard stuff about perspective.
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But I provided the proof.
Unfortunately your proof is unconvincing. The ratio of the vertical dimensions of any two objects is the same in both images, and would remain the same at any enlargement or crop. What am I missing?
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Walter, let me give you a hand. Here is a standard definition of perspective from a standard reference: The Focal Encyclopedia of Photography, Third Edition, page 548-55:
PERSPECTIVE Perspective refers to the appearance of depth when a three-dimensional object or scene is represented in a two-dimensional image, such as a photograph, or when the subject is viewed directly.
If you are simply going to shoot something from a fixed distance with different focal lengths and show the image is the same, then I can save you time. I wouldn't bother--that really does not explain perspective enough and is not my point. But go back and reread my post.
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Would it be tolerable for you to wait for what I like to show you and discuss this afterwards rather than to discuss your opinion about what you think I might have to show?
Your proof might lead to the conclusion that size matters. It does but (playing the devil's advocate) in consequence you may take any painting and resize it. And then I will take your proof to prove that the perspektive of the painting has changed.
And I suppose this is the point which vexed "mouse" a lot.
EDIT: ops, overlap. I wrote before reading your last post. But I really have to go to bed now.
Ciao, Walter
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Unfortunately your proof is unconvincing. The ratio of the vertical dimensions of any two objects is the same in both images, and would remain the same at any enlargement or crop. What am I missing?
You are missing that perspective is not defined by image size ratios. Perspective is not a comparative quality decided on some king of absolute frame or specific objects in the frame. Perspective is the global appearance of depth in an image.
In linear perspective, the rate lines converge define the degree of perspective. This is pretty well known. The lines do not converge at the same rate and so the appearance of depth of the image changes
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Which one is it then? APS-C? If so, is it:
1.3x (Canon)
1.52x (Nikon, Fuji, Sony)
1.53x (Pentax, some)
1.54x (Pentax, some)
1.6x (Canon)
1.7x (Sigma)
1.85x (Canon G1X)
What happened to the old fashioned why of describing angle of view in degrees? For a photographer, in an earlier post I showed how to calculate angular magnification.
I won't give you a hard time about calling my friend names, but the crop factor thing has lots of people confused. Does the aperture change kind of thing.
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Would it be tolerable for you to wait for what I like to show you and discuss this afterwards rather than to discuss your opinion about what you think I might have to show?
Your proof might lead to the conclusion that size matters. It does but (playing the devil's advocate) in consequence you may take any painting and resize it. And then I will take your proof to prove that the perspektive of the painting has changed.
And I suppose this is the point which vexed "mouse" a lot.
EDIT: ops, overlap. I wrote before reading your last post. But I really have to go to bed now.
Ciao, Walter
Walter, I am quite happy to discuss perspective without you doing a lot of work. If it is necessary, we can then talk about examples.
Sure, I can take any image, taken at any distance, with any focal length and match the radial lines of linear perspective. But there is a common frame, standard viewing distance which is the distance equal to the diagonal of the display area--I think Michael will be happy if I don't post huge images. So no matter what size I display and image, the standard viewer will see the same image. This is why both original and cropped image are the same size. (No one prints to an absolute frame depending on format, object distance, focal length, etc. People make 8x10s or 16x20s or whatever regardless of how the image was taken.)
(Yes, viewing distance will alter perspective as well, but lets take one thing at a time. But my basic point does not alter that.)
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I am meeting more and more people who have no experience with 35mm. There was a compact camera being sold in Japan with the sales point that is was a 28mm wide. I asked a friend what they thought that meant. They had no idea. I really don't see the 35mm reference becoming anymore than a curiosity in the future.
You (and others) keep bringing up that point. While people with no experience with 35mm format don't know what 50mm equivalent is, it is nevertheless useful shorthand to compare. We can't continue dumbing things down to the lowest common denominator.
Even for those who don't what 35mm equivalent means, it's a matter of explaining 50mm+ equivalent is tele, 50mm- is wide. I guarantee that's much easier than trying to explain different crop factors and how to compare the focal lengths of J1, E-PL3 and NEX-5 to a novice about to buy his first non-P&S.
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In linear perspective, the rate lines converge define the degree of perspective. This is pretty well known. The lines do not converge at the same rate and so the appearance of depth of the image changes
I still fail to see how any amount of cropping (with or without subsequent enlargement) can change the rate at which lines converge.
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... continue dumbing things down...
Ooopps! You did it again! Insulted his friend, that is ;)
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I still fail to see how any amount of cropping (with or without subsequent enlargement) can change the rate at which lines converge.
Did you see the image I posted? The lines following the linear features in the image do not converge at the same rate for the uncropped image compared to the cropped image. Without the enlargement, the radial lines would be the same, but because we crop and enlarge, the rate this lines converge changes.
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You (and others) keep bringing up that point. While people with no experience with 35mm format don't know what 50mm equivalent is, it is nevertheless useful shorthand to compare. We can't continue dumbing things down to the lowest common denominator.
Even for those who don't what 35mm equivalent means, it's a matter of explaining 50mm+ equivalent is tele, 50mm- is wide. I guarantee that's much easier than trying to explain different crop factors and how to compare the focal lengths of J1, E-PL3 and NEX-5 to a novice about to buy his first non-P&S.
Actually, 43mm+ is tele and 43mm- is wide. I guess this 35mm equivalency is not really very good.
Some would say the whole crop factor thing is dumbing down.
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I tend to agree with guywitha645d on this issue of perspective. There certainly is a lot of confusion about the relationship between focal length of lens, shooting distance and perspective distortion.
Most people who use a camera have probably experienced the effect of perspective distortion when taking a portrait from really close up using a wide-angle lens. The nose appears too large in relation to the rest of the face.
The question thus arises when using a cropped-format camera with a 50mm lens versus a full-frame camera with an 80mm lens from the same position, will the wider lens on the cropped format cause some degree of perspective distortion which is not apparent with the 80mm lens on the full-frame camera.
The simple answer is no, provided apertures are adjusted on each lens to ensure equal DoF.
Unfortunately, some photographers, perhaps to demonstrate how expert they are, go overboard on this issue and make absurd claims that perspective has nothing to do with focal length of lens and everything to do with shooting distance. This is clearly nonsense.
One of the first things that most photographers learn is that wide-angle lenses tend to enlarge the foreground in relation to the background, and that telephoto lenses tend to compress the foreground in relation to the background. The effect is very obvious, and that effect clearly represents a change in perspective resulting from the focal length of lens, despite the shooting distance being the same.
However, the counter argument generally goes something like this. If you crop the wide angle shot so it has the same field of view as the telephoto shot, then the perspective will look the same, if both shots were taken from the same position.
Now this statement is also perfectly true (setting aside resolution and DoF limitations), but what has been overlooked is the fact that cropping a shot taken with a wide-angle lens turns it into a less-wide lens, or even a telephoto lens, 'effectively'.
Well, who would have thought that! Taking shots of the same scene from the same position using the same 'effective' focal length of lenses results in the same perspective. How profound! ;D
The lesson here is that changing the field of view by cropping, whether such cropping is performed in-camera or through post-processing, increases the 'effective' focal length of the lens, whatever lens is used.
Considering the plethora of different camera formats now on the market, knowing the 35mm format focal length equivalent is very useful. It's not necessary to have used a 35mm camera in order to understand that 14mm equivalent is really wide and that 600mm equivalent is really long, or that 24mm equivalent is wider than 28mm equivalent.
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One of the first things that most photographers learn is that wide-angle lenses tend to enlarge the foreground in relation to the background, and that telephoto lenses tend to compress the foreground in relation to the background. The effect is very obvious, and that effect clearly represents a change in perspective resulting from the focal length of lens, despite the shooting distance being the same.
However, the counter argument generally goes something like this. If you crop the wide angle shot so it has the same field of view as the telephoto shot, then the perspective will look the same, if both shots were taken from the same position.
Now this statement is also perfectly true (setting aside resolution and DoF limitations), but what has been overlooked is the fact that cropping a shot taken with a wide-angle lens turns it into a less-wide lens, or even a telephoto lens, 'effectively'.
How exactly do you reconcile these two statements? Are you saying that by cropping the image from a wide angle lens you then can reproduce the "compression of the foreground in relation to the background" which would be produced by a telephoto lens?
From Wikipedia, perhaps not the ultimate authority but usually pretty accurate:
Note that perspective distortion is caused by distance, not by the lens per se – two shots of the same scene from the same distance will exhibit identical perspective distortion, regardless of lens used. However, since wide-angle lenses have a wider field of view, they are generally used from closer, while telephoto lenses have a narrower field of view and are generally used from further away. For example, if standing at a distance so that a normal lens captures someone's face, a shot with a wide-angle lens or telephoto lens from the same distance will have exactly the same perspective on the face, though the wide-angle lens may fit the entire body into the shot, while the telephoto lens captures only the nose. However, crops of these three images with the same coverage will yield the same perspective distortion – the nose will look the same in all three.
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I am too late for this discussion but I have to say that I agree with those that believe that still there's no better parameter for comparing the zillion different formats we have now than the old 135/35/24X36/FF. Even medium format back manufacturers refer sometimes to the 24X36 (as in being a 0.60 x crop for just an example).
I would gladly and immediately adopt a better one if someone comes with it.
Perhaps something based on the diagonal of the format. A 1X lens in the case of 35 format has to be a 43mm lens. A 0.5-2-0 zoom lens would always be a zoom lens that goes from half the diagonal to twice the diagonal. In the case of 24X36, it's a 21-86mm zoom lens. For 4/3 it translates to a 10.8-43.2mm zoom lens. Is this of some help?
How about just declaring the actual angle of view in degrees and forgetting completely the FL? "104-57 zoom lens". Or it could be used in reverse. First the coverage at the tele position. "57-104 zoom lens"
For 24X36, do you know which zoom lens I'm referring to?
Just my 2 cents. Please don't feel forced to adopt any of these two just yet. ;D
Eduardo
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How exactly do you reconcile these two statements? Are you saying that by cropping the image from a wide angle lens you then can reproduce the "compression of the foreground in relation to the background" which would be produced by a telephoto lens?
From Wikipedia, perhaps not the ultimate authority but usually pretty accurate:
The question you should ask is 'which foreground' in 'which image'? When the wide-angle shot is cropped to the same FoV as the telephoto shot, you are not necessarily compressing the foreground in the wide-angle shot but perhaps displaying the distant background which is already compressed. If you were to crop the foreground in the wide-angle shot, you would possibly exclude the distant background, or at least part of it, so that there would be no sense, or less sense, of an enlarged foreground in relation to the background. Size is relative. Big is big only in relation to something smaller.
The Wikipedia article sounds a bit confused to me. It is not sensible to compare issues of perspective in essentially different images of different FoV and therefore different compositions. Imagine if we were to compare the DoF in two images taken with different focal lengths of lens from the same position using the same f stop, then crop one or both images to exclude any apparent differences in DoF for the purpose of claiming that DoF is the same. Would you think that sensible? I know that situation is not strictly analagous because it would not work for all areas cropped. However, my point is, the composition of an image is important in order to create a specific sense of perspective, or DoF.
To turn a wide angle lens into a telephoto lens through cropping in order to claim that focal length has no bearing on perspective sounds like chicanery to me. A big nose in relation to a small face looks different to that same nose cropped, in relation to nothing but a plain background.
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Perspective in an image depends solely on the distance from the subject, and is uninfluenced by lens focal length or the field of view, the size of the sensor/negative, or what portion of the captured image is used to produce the final print, or the size of such print.
A reasonable sampling of internet discussions on this subject makes it apparent that this concept is a hard sell. All manner of reasoning and rationalization have been invoked to show that this should not be so. Nevertheless I have yet to read anything that has convinced me that I, along with the vast majority of much wiser authorities, are wrong.
When one looks at a scene photographed from the same position, with both a short and long focal length lens, and subsequently printed at the same size, it is abundantly clear that the images are vastly different. And part of that difference is that the wider angle view contains much additional content which may serve to convey what one may legitimately describe as a greater feeling of depth. But perspective, properly defined, does not depend on added content nor upon a feeling of depth. The ultimate proof of this is a crop of a wide angle shot to show only the area captured by the longer lens will have precisely the same perspective (distortion) measured by any parameters you care to apply.
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Perspective in an image depends solely on the distance from the subject, and is uninfluenced by lens focal length or the field of view, the size of the sensor/negative, or what portion of the captured image is used to produce the final print, or the size of such print.
A reasonable sampling of internet discussions on this subject makes it apparent that this concept is a hard sell. All manner of reasoning and rationalization have been invoked to show that this should not be so. Nevertheless I have yet to read anything that has convinced me that I, along with the vast majority of much wiser authorities, are wrong.
When one looks at a scene photographed from the same position, with both a short and long focal length lens, and subsequently printed at the same size, it is abundantly clear that the images are vastly different. And part of that difference is that the wider angle view contains much additional content which may serve to convey what one may legitimately describe as a greater feeling of depth. But perspective, properly defined, does not depend on added content nor upon a feeling of depth. The ultimate proof of this is a crop of a wide angle shot to show only the area captured by the longer lens will have precisely the same perspective (distortion) measured by any parameters you care to apply.
Absolutely.
Problem comes because people tends to use different lenses in different situations: wides when near the subject, and teles when far from the subject; and they tend to associate the different perspective (caused by the different distances) to the difference in focal length. For example, if I am making a headshot, and I want to fill the frame with the subject, I will move forwards and backwards as I change the focal length; and thus I will be changing the perspective, with my feet.
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But perspective, properly defined, does not depend on added content nor upon a feeling of depth. The ultimate proof of this is a crop of a wide angle shot to show only the area captured by the longer lens will have precisely the same perspective (distortion) measured by any parameters you care to apply.
Really! You reckon the ultimate proof is to effectively convert the wide angle lens to the same focal length as the longer lens in order to prove that differences in focal length have no bearing on perspective? That doesn't sound like a proof relating to perspective, to me. It sounds more like a proof demonstrating that cropping an image produces an identical effect to using a longer focal length.
The sort of proof that would convince me is if someone were to take a few dozen portraits of a number of people from really close up, using a very wide angle lens (say 12mm in 35mm format terms from a distance of 8"), then present to some viewers a number of prints of cropped noses without face, and uncropped noses which include the entire face as background.
To make the experiment as soundly scientific as possible, one would take portraits of a variety of people with different size noses, big honkers, small pudgy noses, thin aquiline noses, and average noses etc. Also, one should not present prints of the same cropped nose that also features in another print with the full face, in order to be as objective as possible. One should also mix in a few cropped noses from images taken with longer lenses from a greater distance. For example, the guy with the big honker might be shot with a 50mm lens from a distance of a couple of feet.
One would then ask the viewers participating in the experiment to identify the images that show the greatest perspective distortion.
My guess would be that all viewers would correctly identify the uncropped images with full face as showing significant perspective distortion, but fail in correctly identifying the cropped noses as showing perspective distortion. What do you reckon?
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I have to say that I am behind Mouse on this one. Wider angle lenses only tend to distort perspective because you have to move in closer to a subject to fill the frame. The perspective is entirely dependant on the relative position of the lens to the subject. I can shoot exactly the same head and shoulder shot with my 35mm lens as I can with an 85mm lens from say 8 foot range. The perspective will be exactly the same regarding noses etc. It is just with the 35mm lens I will need to crop out a lot of the image, which is a waste of pixels/resolution etc.
With a 24mm lens and a theoretical unlimited resolution I believe I could shoot almost any scene including sports, wildlife etc. All that would be needed would be to crop the pictures heavily in some cases. This is of course not practical, but I think the theory is correct. Depth of field of course is another matter.
On the subject of terminology, I think that an angle of view number would be much more useful than 35mm equivalents. Whilst I have no problem as things are, as has been pointed out fewer and fewer people have the old reference points of 35mm photography ingrained into their heads. Anyone brought up with three prime lenses on a 35mm camera has very fixed reference points regarding focal length, but with zoom lenses and the plethora of formats around I think confusion is becoming the norm for newer photographers. Perhaps I just empathise with people who are easily confused! :)
Jim
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To turn a wide angle lens into a telephoto lens through cropping in order to claim that focal length has no bearing on perspective sounds like chicanery to me. A big nose in relation to a small face looks different to that same nose cropped, in relation to nothing but a plain background.
But here you neglect the fact that the big nose only comes from being very (or too) close the the subject. If you take a picture with a wide angle from further away, as you would do with a telephoto lens, and then crop it, it will look exactly the same. Mouse is absolutely correct.
EDIT: Sorry, Jim was typing faster.
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I would gladly and immediately adopt a better one if someone comes with it.
For compact cameras and lenses that will only be used on a given sensor-size:
"this camera/lense will cover 15 degrees of your scene horizontally"
I think that is more intuitive to the novice camera users.
Unfortunately, when the same lense may be used on "FF" and "crop" sensors, this explanation has less value.
-h
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But here you neglect the fact that the big nose only comes from being very (or too) close the the subject. If you take a picture with a wide angle from further away, as you would do with a telephoto lens, and then crop it, it will look exactly the same. Mouse is absolutely correct.
EDIT: Sorry, Jim was typing faster.
I do indeed neglect that fact, because I don't regard it as a fact. I can make the nose as big or as small as I want whatever the lens I've used from whatever distance, simply by interpolating or downsampling the cropped image of the nose and making either a big print or a small print.
The size of the nose itself, separate from its background, is not the issue regarding perspective. That's the point I'm trying to get across. It's the size of the nose in relation to its background of other facial features and in relation to other more distant features behind the person, that contribute to a sense of distorted perspective.
If one crops away all the background stuff that is necessary to provide the sense of distorted perspective that a wide-angle lens can produce from close up, then you have not only effectively converted the wide-angle lens to a longer focal length, but have also lost much (if not all) of that sense of distorted perspective.
This all seems very clear to me. I can't understand your difficulty. Cropping any image reduces the angle of view and effectively converts the lens used to a longer focal length. There's no dispute about that whatsoever. However, if you were given an assignment to produce amusing photos of people with distorted perspective and big noses, I suspect you would choose a wide-angle lens. I'd be very susrprised if you were to take this so-called authoritative advice that perspective has nothing to do with choice of focal length and pick any lens at random.
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[...]However, if you were given an assignment to produce amusing photos of people with distorted perspective and big noses, I suspect you would choose a wide-angle lens.[...]
No: I would choose to get very close to the subject; and to get all the face inside the frame, I would probably need a wider lens, or a larger sensor, or several shots merged together, ... . The distorted perspective that you mention does not come from the focal length, it comes from the distance; the focal length only serves to get back the angle of view that you lost by moving the camera.
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If distance is the sole criteria for perspective then why do the lines in my example converge at different rates--this is a pretty fundamental concept in linear perspective where changing the rate of convergence is changing perspective. And you can look at each image and see the apparent depth of each image is different. Seeing is believing.
The problem with using the ratio of image size/object distance is which two object define perspective. And my example show that perspective is changing, yet the image size ratio is held constant.
The crop comparison is a false argument simply because you are no longer comparing the uncropped to cropped image. You are comparing two identical images which naturally would look the same. You need to compare the cropped to the uncropped because the the change in relative scale is important.
(The other problem is, perspective in photography is not simply defined be the ratio of image size. I did git a source and you will note that the entry covers 7-8 pages.)
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BTW, the image size and distance is a ratio, not just a single distance. If the ratio of images sizes is 2:1, to keep that ratio I can actually do that in an unlimited number of object distances as long as I maintain a 2:1 ratio of object distances.
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If distance is the sole criteria for perspective then why do the lines in my example converge at different rates--this is a pretty fundamental concept in linear perspective where changing the rate of convergence is changing perspective. And you can look at each image and see the apparent depth of each image is different. Seeing is believing.
[...]
But the lines in your example do not converge at different rates (because they are the same lines). Do not believe me? Open both images on separate layers, and make the top one semi-transparent; if you move it properly, you can see how the lines match.
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But the lines in your example do not converge at different rates (because they are the same lines). Do not believe me? Open both images on separate layers, and make the top one semi-transparent; if you move it properly, you can see how the lines match.
You are not following the conversation. The difference in magnification does matter--you don't print your cropped images proportionally smaller than your uncropped images; no, you want an 8x10 or 16x20. By your definition, I can take any image, taken at any distance, with any lens and rescale it to fit any radial lines you would like--linear perspective is radial, but it is the relative rate of convergence that determines our perception of depth, not an absolute one.
At the scale they are presented in my example, the lines are converging at different rates. You can even see the angles are different. Perspective has changed and a viewer will perceive those differences.
Perspective is the apparent depth in a 2-D image; how a viewer perceives depth. It is not an absolute measure in an absolute frame.
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[...]By your definition, I can take any image, taken at any distance, with any lens and rescale it to fit any radial lines you would like[...]
No, you can't: unless you distort the image by changing the aspect ratio, the angles are not going to change, no matter how you crop or rescale the image.
[...]You can even see the angles are different.[...]
No, they aren't; just try it, measure them: 29 degrees, give or take, on both images.
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I am appalled that there is such widespread misunderstanding among photographers about this. Any of you that understand simple geometry will realize that Mouse is absolutely correct.
Conversely, those of you who dispute Mouse do not understand geometry (or the nature of "perspective").
Eric
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No, you can't: unless you distort the image by changing the aspect ratio, the angles are not going to change, no matter how you crop or rescale the image.
Sure I can. Your have never worked with radial lines and linear perspective.
No, they aren't; just try it, measure them: 29 degrees, give or take, on both images.
But there are two line, how can you get one number?
Left image:
Top line: 11.9 degrees
Bottom line: -17.6 degrees
Right image:
Top line: 11.5 degrees
Bottom line: -16.9 degrees
Measured in Photoshop extended CS5.5. Measured twice to smooth errors. And yes, the difference is great enough to be perceived.
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I am appalled that there is such widespread misunderstanding among photographers about this. Any of you that understand simple geometry will realize that Mouse is absolutely correct.
Conversely, those of you who dispute Mouse do not understand geometry (or the nature of "perspective").
Eric
Agreed. I think part of the problem is that a few people here are arguing different points without realising it.
Jim
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I am appalled that there is such widespread misunderstanding among photographers about this. Any of you that understand simple geometry will realize that Mouse is absolutely correct.
Conversely, those of you who dispute Mouse do not understand geometry (or the nature of "perspective").
Eric
Expressing indignation is not an argument. And the fact you dismiss the example image shows you don't understand geometry, let alone perspective.
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Agreed. I think part of the problem is that a few people here are arguing different points without realising it.
Jim
Jim, it goes deeper than that. Many people don't know what they are arguing, but just trying to affirm a tidbit of "knowledge" they picked up somewhere.
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But there are two line, how can you get one number?
I always get one number when I measure angles... I do not use PS, but you are probably measuring the angle of each line with respect to an (imaginary) horizontal line; just make a subtraction and you should get the same number as me.
Left image:
Top line: 11.9 degrees
Bottom line: -17.6 degrees
Right image:
Top line: 11.5 degrees
Bottom line: -16.9 degrees
Measured in Photoshop extended CS5.5. Measured twice to smooth errors. And yes, the difference is great enough to be perceived.
Please, repeat your test: grab the full-res version of the image, draw the lines on it, and measure the angle; now crop and enlarge at will (be very sure to preserve the aspect ratio), and measure the same lines again.
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This discussion reminds me of an old joke: a guy enters a highway in the opposite direction. Police spotted him and broadcasts a warning: "Attention all drivers... There is one idiot driving in the opposite direction." The guy heard the warning as well and says to himself: "Ha! Just one!? Look how many there are!"
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But then you know I can take any image regardless of objective distance, focal length, etc. and match them to one set radial lines by simple scaling...
But you have already proven the opposite, haven't you? You took an image, scaled it at your will, and obtained the same set of lines; how do you plan to obtain a different set of lines now?
Let's suppose your lines measured 30 degrees on the original; you cropped and scaled the image yourself, and the resulting lines where also 30 degrees apart. Could you make them measure 15 or 45 degrees? Without changing the aspect ratio?
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No: I would choose to get very close to the subject; and to get all the face inside the frame, I would probably need a wider lens,
You are not sure?? You think you might need a wide-angle lens, but stitching images with a moderate telephoto lens with a macro facility might be a sensible alternative?
The distorted perspective that you mention does not come from the focal length, it comes from the distance;
It comes from the distance to what, precisely? The distance to the nose? The distance to the eyes? The distance to the ears? The distance to some background object outside the FoV of a longer focal length lens?
the focal length only serves to get back the angle of view that you lost by moving the camera
Who's moving the camera? I thought we were talking about perspective from the same shooting position using different focal lengths of lenses. If you crop the wide-angle shot to the same FoV as the telephoto shot, you've effectively increased the focal length of that wide-angle lens. If you stitch images to increase the FoV, you've effectively reduced the focal length of the system and created a wide-angle lens equivalent, or at least a wider-angle lens equivalent.
If your point is that the actual and nominated focal length marked on the lens has in itself no fixed and unchangeable bearing on the perspective of a processed image, from a given shooting position, if one can use various strategies to either effectively increase or reduce focal length, such as applying cropping or stitching a number of images together, then I agree completely.
It's the effective focal length that always counts, not the nominated FL marking on the lens. That's understood surely. The effective focal length of the lens depends not only on the nominated focal length of the lens but the size of the sensor and the final FoV of the processed image.
In summary, the sense of perspective in any image is largely dependent upon two factors; the shooting position and the effective focal length of the lens, often described in 35mm format terms.
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How can one argue that a, say, 30-degree angle is not a 30-degree angle just because he measures it enlarged, is beyond me. You really do not need to measure it, it is based on the principles of geometry from several thousand years ago. A 30-degree angle is a 30-degree angle is a 30-degree angle.
However, if one insists on measuring it, then he should be aware that any difference in the measured result can only be possible due to the precision of the measuring device and/or the operator.
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No, folks my mistake. The angle does not change.
The vanishing point does. The object distances from foreground to background do. The image shows a change in perspective. Just keep me away from architectural drawing.
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You are not sure?? You think you might need a wide-angle lens, but stitching images with a moderate telephoto lens with a macro facility might be a sensible alternative?
Sensible!? No, not at all: it would be stupid; theoretically possible, but completely absurd in practice.
Who's moving the camera? I thought we were talking about perspective from the same shooting position using different focal lengths of lenses. If you crop the wide-angle shot to the same FoV as the telephoto shot, you've effectively increased the focal length of that wide-angle lens. If you stitch images to increase the FoV, you've effectively reduced the focal length of the system and created a wide-angle lens equivalent, or at least a wider-angle lens equivalent.
If your point is that the actual and nominated focal length marked on the lens has in itself no fixed and unchangeable bearing on the perspective of a processed image, from a given shooting position, if one can use various strategies to either effectively increase or reduce focal length, such as applying cropping or stitching a number of images together, then I agree completely.
I am not very fond of this "effective focal length" concept, but I think we agree on the basics.
Sorry if my post was confusing.
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Sensible!? No, not at all: it would be stupid; theoretically possible, but completely absurd in practice.
Tell that to Mr. Hockney :D
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...If your point is that the actual and nominated focal length marked on the lens has in itself no fixed and unchangeable bearing on the perspective of a processed image, from a given shooting position, if one can use various strategies to either effectively increase or reduce focal length, such as applying cropping or stitching a number of images together, then I agree completely....
So, let me rephrase your statement based on the bold parts (i.e., just removing the rhetorical fluffiness):
"I agree ... focal length... has... no... bearing on the perspective... if... applying cropping..."
At the same time, thewiseguywitha645d said:
The [cropped] image shows a change in perspective.
Could you two reconcile the opposing statements before you turn against the rest of us again? I mean, I am used to you two contradicting yourselves, but contradicting yourselves and each other simultaneously is a bit too much for me ;)
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So I did some more research and it appears Walter is right about the change in perspective being a viewing distance issue.
From Materials and Processes of Photography, Stroebel et al, page 158-59
4.10 Viewing Distance
It would seem that the distance at which we view photographs should have no effect on linear perspective, since a 2:1 size ratio of images of objects at different distances will not be altered by changes in viewing distance. In practice, however, changes in viewing distance can have a significant effect on the perspective, provided the photograph has good depth clues…those containing dominant objects in the foreground and background or receding parallel lines can change dramatically...
…The correct viewing distance for a 12-inch lens for a contact print of an 8x10-inch negative exposed with a 12-inch focal length lens is 12 inches. Since we tend to view photographs from a distance about equal to the diagonal, the perspective would appear normal to most viewers. If the 12-inch lens were replaced with a 6-inch focal length lens, the print would have to be viewed from 6-inches from the perspective to appear normal. When the print is viewed from the comfortable distance of 12-inches, the perspective will appear too strong. Conversely, the perspective in a photograph made with a 24-inch focal length lens would appear too weak when viewed from 12 inches. It is fortunate that people tend to view photographs from standardized distances rather than adjusting the viewing distance to make perspective appear normal, for that would deprive photographers of one of their most useful techniques for making dramatic and effective photographs.
So I just have it in the wrong end of the process. But this is what is happening when we crop and enlarge or change focal length.
Walter, I hope you have not gone to any work over this.
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Expressing indignation is not an argument. And the fact you dismiss the example image shows you don't understand geometry, let alone perspective.
I don't argue about facts, especially mathematical ones. I have a Ph. D. in mathematics. Do you?
Eric
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Agreed. I think part of the problem is that a few people here are arguing different points without realising it.
Jim
I think you are right about that.
Eric
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This discussion reminds me of an old joke: a guy enters a highway in the opposite direction. Police spotted him and broadcasts a warning: "Attention all drivers... There is one idiot driving in the opposite direction." The guy heard the warning as well and says to himself: "Ha! Just one!? Look how many there are!"
;D
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I don't argue about facts, especially mathematical ones. I have a Ph. D. in mathematics. Do you?
Eric
No, and I have put my mea culpa in the thread and so I apologize.
But I do have a science degree in imaging and have been trying to find a solution to this problem that has been nagging me. Particularly in regards to perspective drawing, and the issues in drafting and photography are different enough to make it tricky.
One thing I do know is our perception of perspective in a cropped image is different from the uncropped. And perception and vision is not my field, although I have assisted a number of researchers in making illusions--I am doing some stuff on reverse perspective at the moment. However, I have just posted the solution to the problem above.
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Could you two reconcile the opposing statements before you turn against the rest of us again? I mean, I am used to you two contradicting yourselves, but contradicting yourselves and each other simultaneously is a bit too much for me ;)
Perhaps you just need to put in a bit of effort. The cynic is an easy position. Beside, if you knew the change in perspective was a viewing distance issue, why did you not tell us?
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Perhaps you just need to put in a bit of effort. The cynic is an easy position. Beside, if you knew the change in perspective was a viewing distance issue, why did you not tell us?
I think you need another mea culpa:
Not correct. As Walter pointed out, it has nothing to do with sensor size or focal length, but everything to do with the distance from the object.
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I've been reading this thread and can't help feeling some what confuse. I use aps-c and micro 4/3 (don't think ever justify a FF body).
the image seen by the camera, is a cropped version of the same seen in a full frame with the same lens? or does it correspond to the image viewed in a ff with a bigger focal lenght?? (ie. 20mm m4/3 and 40mm on ff).
thanks
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I think you need another mea culpa:
You are not Walter and what you are quoting is not what I am talking about. Walter eluded to print size, he has yet to expound on it...
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I've been reading this thread and can't help feeling some what confuse. I use aps-c and micro 4/3 (don't think ever justify a FF body).
the image seen by the camera, is a cropped version of the same seen in a full frame with the same lens? or does it correspond to the image viewed in a ff with a bigger focal lenght?? (ie. 20mm m4/3 and 40mm on ff).
thanks
Don't mind us. Just work in your format with the lenses you have. None of this is really something you need to know to take pictures.
What we are talking about, at least that is what I think we are talking about, is if you put a 40mm lens on a FF and a m4/3, will those images have the same perspective. The relative size of the objects will stay the same, but will the perspective stay the same? Naturally, the field of view (or angle of view) will be different for each camera.
The answer, which is posted above, is the perspective will change depending on the viewing distance. If both images are printed to the same size and viewed from the same distance, the perspective will appear weaker in the m4/3 image as it goes through more magnification resulting from a different "correct" viewing distance.
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You are not Walter and what you are quoting is not what I am talking about. Walter eluded to print size, he has yet to expound on it...
Jesus, thewiseguywitha645d, you do not give up, do you? Walter did not "allude" [sic] to print size, but quite directly and explicitly to perspective. The same thing I was talking about. As for what you are talking about, I am not sure anymore even you know.
But you got one thing right in this debate: I am not Walter ;)
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Jesus, thewiseguywitha645d, you do not give up, do you? Walter did not "allude" [sic] to print size, but quite directly and explicitly to perspective. The same thing I was talking about. As for what you are talking about, I am not sure anymore even you know.
But you got one thing right in this debate: I am not Walter ;)
Slobadanto, why are you even taking part in this thread? Surely your charms would be better suited elsewhere.
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Don't mind us. Just work in your format with the lenses you have. None of this is really something you need to know to take pictures.
What we are talking about, at least that is what I think we are talking about, is if you put a 40mm lens on a FF and a m4/3, will those images have the same perspective. The relative size of the objects will stay the same, but will the perspective stay the same? Naturally, the field of view (or angle of view) will be different for each camera.
The answer, which is posted above, is the perspective will change depending on the viewing distance. If both images are printed to the same size and viewed from the same distance, the perspective will appear weaker in the m4/3 image as it goes through more magnification resulting from a different "correct" viewing distance.
Maybe you are right, is better just to keep taking pictures and don't think about that, either way you end up framing the picture the way you want it and backing off the necesary distance to make it happen (or zooming out).
thanks
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Mouse is 100% correct. Why anyone would spend any efforts in trying to contradict facts is beyond me.
As to "35mm lens equivalent"; this is just a useful yardstick, a reference with roots in photographic history.
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Actually, 43mm+ is tele and 43mm- is wide. I guess this 35mm equivalency is not really very good.
You're being pedantic. While I believe that is indeed the technically correct definition, 50mm is universally considered a normal lens in 35mm format. My point remains either way.
Some would say the whole crop factor thing is dumbing down.
I'm sure. Nevertheless, it is unreasonable to expect anyone to know the crop factors of all the different formats, from mirrorless cameras from Samsung, Sony, Olympus/Panasonic and Nikon, to SLRs from Sony, Canon and Nikon, to Medium Format cameras from Leica, Phase, Pentax. And I haven't even mentioned the endless P&S and phone camera formats.
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... Surely your charms would be better suited elsewhere.
Thank you!
Finally someone to recognize my usual curmudgeon persona as charming ;)
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Jesus, thewiseguywitha645d, you do not give up, do you? Walter did not "allude" [sic] to print size, but quite directly and explicitly to perspective. The same thing I was talking about. As for what you are talking about, I am not sure anymore even you know.
But you got one thing right in this debate: I am not Walter ;)
Excuse me while I pee my pants.
Thanks all for the best belly laugh in a long time (after reading the whole thread start to end).
But I don't know if I should be laughing or crying.
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Slobodan, Eric, and others,
Thank you for coming to my aid. I was beginning to despair. I realize that perspective is a subject which many beginning photographers fail to grasp. However, I was surprised by the number of respondents who, when presented by simple facts, fought so hard to deny the facts in order to confirm their beliefs. Dare I say it; it reminds me of many of the arguments about evolution. One starts with a belief and searches desparately for facts to support that belief.
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So, let me rephrase your statement based on the bold parts (i.e., just removing the rhetorical fluffiness):
"I agree ... focal length... has... no... bearing on the perspective... if... applying cropping..."
Can we offer you an award for the greatest degree of out-of-context quoting, Slobodan? ;D
Most people who engage in out-of-context quoting, such as certain journalists, just omit a few qualifying sentences, or perhaps the occasional explanatory paragraph. But you've taken this art-form to a new level by actually omitting numerous words within a single sentence in order to convey a meaning quite different to what was intended.
However, I guess this is to be expected from someone who thinks one can convincingly demonstrate that focal length has no bearing on perspective by cropping out all the clues in the wider-angle shot that might suggest the perspective is different. You are at least behaving in character. ;D
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I am not very fond of this "effective focal length" concept, but I think we agree on the basics.
Sorry if my post was confusing.
You could experience a bit of trouble or confusion if you don't like or understand the 'effective focal length' concept. For many of us, our first digital camera was a cropped-format DSLR which we used with lenses designed for our full-frame 35mm film cameras.
These issues of focal length equivalents and F/stop equivalents for equal DoF were thrashed out years ago.
Basically, the crop factor, or ratio of larger sensor to smaller sensor, should be divided into the actual focal length of the lens designed for the larger format, in order to determine the 'focal length equivalent' for the smaller sensor. The same applies to F/stop number in order to achieve DoF equivalence.
For example, many photographers who use a full-frame 35mm DSLR might be in the habit of using an 80mm lens for portraits. If they wish to get the same (or more precisely, similar) results with a cropped-format, say a Canon cropped format, using the same techniques and shooting from the same distances, using a particular F/stop for a particular shallow DoF, say F2.8, then they need to use a 50mm lens at F1.8 on the cropped-format. (80/1.6=50 and 2.8/1.6=1.75)
Now clearly different models of lenses have different qualities with regard to resolution, distortion and bokeh etc. Even different lenses of the same model can vary in performance, so one can't expect to get exactly the same result using an equivalent lens. My own experiments have indicated that sometimes the distance to the subject can affect DoF equivalence. A divisor of 1.6 might be okay for distant objects, but for close-up shots a divisor of 2 might give a more accurate DoF equivalent, ie. it might be necessary to use F1.4 instead of F1.8 on the equivalent lens on the cropped-format camera.
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Whatever happened to Walter? I think he jumped ship. And even theguywith... has backed down.
But not Ray; he's still hanging in there. ;)
However, I guess this is to be expected from someone who thinks one can convincingly demonstrate that focal length has no bearing on perspective by cropping out all the clues in the wider-angle shot that might suggest the perspective is different. You are at least behaving in character. ;D
Now ordinarily this wouldn't bother me. But this comes from a senior member with over 7500 posts. Makes one wonder. :(
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Whatever happened to Walter? I think he jumped ship. And even theguywith... has backed down.
But not Ray; he's still hanging in there. ;)
Now ordinarily this wouldn't bother me. But this comes from a senior member with over 7500 posts. Makes one wonder. :(
Well, I'm Rob not Walter, but when you have spent a lifetime on the job, such idiot arguments simply don't concern you further. You just know. You state that knowledge, and if others find it doesn't fit their mindset, then that's perfectly fine; it's their problem and your own life continues unaffected. What would affect your life, though, is wasting precious time of it trying to convince.
Rob C
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Whatever happened to Walter? I think he jumped ship.
No, I tumbled into a life boat by accident ...
Work, householding duties and - of course - second thoughts about the merits participating in this thread.
There are things left to discuss, I believe. But it would be a lot easier could be done in a conference room with our gear around. Second best: Video conference.
Anyone brought up what happens in the border area of ultra wide angle lenses? This surely will be a messy online discussion, judging by the way the much easier "crop" question has developed here and now.
Ciao, Walter
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It's a bit odd how on one of the most knowledgeable photography forums on the interwebs some people manage to dispute trivial linear, geometrical optic understood since 1600 AD. :-\
To add some usefulness to this reply: There is a very simple and nicely written book called "The INs and OUTs of FOCUS" about all these issued we're discussing about which can be downloaded for free.
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Hi,
You are essentially wrong. The angle of view of a 24 mm lens on 4/3 (Panasonic/Olympus) is similar to a 48 mm lens on full frame 135. The optical construction would probably be similar to (a double gauss design). Perepective is dependent on lens to subject distance only, so that is not dependent on focal length.
Angle of view is 2*atan((sensor width/2//focal length), so halving focal length and sensor size would give same angle of view.
On the other hand, on some cameras vignetting and distortion is not optically compensated but done in software instead.
Best regards
Erik
Perhaps, maybe certainly, this has been addressed previously. But I see it everywhere I turn in Cameradom. m4/3; "this 24mm lens is a 48mm in 35mm equivalent" and so on..
When I see the pictures, NO, IT'S NOT!!! It is indeed a 24mm lens. It may occupy the space that a 48mm lens would in a FF sensor photo, but it suffers from (or benefits from, whatever the situation) the same distortions of any 24mm lens. Or a least that's the way it looks to me. Portraits shot with small-sensor cameras and short focal length lenses make faces look pear-shaped and noses big. It seems many of the gear peddlers try to avoid this being noticed by playing with the image or lighting, making it "artsy" but distorted just the same.
Is my impression correct, or am I missing something?
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Can we offer you an award for the greatest degree of out-of-context quoting, Slobodan? ;D
I would have cropped that quote differently, so as to muddy the waters even more than Slobodan did:
"I... has... no... perspective... if... cropping..."
Now isn't that better? :D
Eric
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Perepective is dependent on lens to subject distance only, so that is not dependent on focal length.
Erik,
You're a very sensible and scientific sort of guy. Can you offer any proof that the perspective of a photographic image or composition is dependent only on the distance from the lens to the subject?
So far, in this thread the only proof that has been offered is the fact that converting a wide-angle shot to a narrow angle shot of the same effective focal length, through cropping, results in identical images.
Well that doesn't seem like proof to me, the fact that two lenses of equal focal length produce identical pictures when used from the same position. That's pretty obvious, isn't it.
The problem as I see it, is the absurdity of claiming that non-identical pictures can have identical perspective, as in the two examples attached.
The wide angle shot was taken with a 24mm lens. The image of the sign was taken with a 140mm lens equivalent. Whether I took the shot of the sign with an actual 140mm lens attached to my D700, or cropped the 24mm image to simulate a 140mm lens, possibly makes no difference, except in resolution, but maybe it does. This is something I hope you can clarify.
(1) If I had used a real 140mm lens for the shot of the sign, from the same position, I would have needed to turn slightly to the left in order to capture it. Would that have changed the angle between the top of the sign and the top of the frame?
(2) In the full-frame shot it is surely evident that a fairly wide-angle lens was used. Experienced photographers would guess that the lens used was somewhere between 20mm and 28mm, based on the perspective evident in the image.
Would experienced photographers be able to guess the focal length of the lens used to capture the sign only. Does the perspective in the image of the sign only, give any clues?
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I would have cropped that quote differently, so as to muddy the waters even more than Slobodan did:
"I... has... no... perspective... if... cropping..."
Now isn't that better? :D
Eric
No. Poor grammar, Eric. Slobodan retains the title. ;D
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No, I tumbled into a life boat by accident ...
Walter, vada a bordo, cazzo!
Or, in translation: go back on board, &^%*$!!! ;D
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Can we offer you an award for the greatest degree of out-of-context quoting, Slobodan? ;D
Most people who engage in out-of-context quoting, such as certain journalists, just omit a few qualifying sentences, or perhaps the occasional explanatory paragraph. But you've taken this art-form to a new level by actually omitting numerous words within a single sentence in order to convey a meaning quite different to what was intended...
It is all a matter of perspective, Ray... I just came closer (to the essence of your sentence).
You see, Ray, we are all photographers here... in contrast to painters, who face a blank canvas and add things to it at will, we photographers face a messy and chaotic world in our viewfinders (not unlike your posts) and then we have to simplify, eliminate, reposition, recompose, change perspective, etc. in order to reveal the underlying beauty or meaning.
And that is exactly what I did: I simplified, eliminated, repositioned, recomposed your messy post to ultimately reveal the inner beauty of your thoughts. ;)
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You mean, like in less is more, Slobodan?
Rob C
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(1) If I had used a real 140mm lens for the shot of the sign, from the same position, I would have needed to turn slightly to the left in order to capture it. Would that have changed the angle between the top of the sign and the top of the frame?
(2) In the full-frame shot it is surely evident that a fairly wide-angle lens was used. Experienced photographers would guess that the lens used was somewhere between 20mm and 28mm, based on the perspective evident in the image.
This is my understanding, but since I do not claim to be experienced this might be right or wrong ;):
(1) If you change the camera angle this will change "the angle between the top of the sign and the top of the frame". If you turn the camera and use the 24mm and then change to 140mm the perspective is identical. It should be noted that if you point the camera in another direction you take a different photo, NOT a different crop, and it makes no sense comparing.
(2) No, not based on perspective. A wide captures a larger angle of view (with same perspective as a tele). This 3-D is transformed to a 2-D representation. The objects of the outer edges of a wide will appear "strange" in 2-D since they are transformed from 3-D to 2-D, but this is pure geometry, and the perspective is the same. Also the relative sizes of objects in picture will hint to wide or not.
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It is all a matter of perspective, Ray... I just came closer (to the essence of your sentence).
You see, Ray, we are all photographers here... in contrast to painters, who face a blank canvas and add things to it at will, we photographers face a messy and chaotic world in our viewfinders (not unlike your posts) and then we have to simplify, eliminate, reposition, recompose, change perspective, etc. in order to reveal the underlying beauty or meaning.
And that is exactly what I did: I simplified, eliminated, repositioned, recomposed your messy post to ultimately reveal the inner beauty of your thoughts. ;)
Paraphrased: Our posts = RAW. Slobodan = RAW developer.
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This is my understanding, but since I do not claim to be experienced this might be right or wrong ;):
(1) If you change the camera angle this will change "the angle between the top of the sign and the top of the frame".
This is more or less how I imagine the situation to be, and following from this situation are two puzzling factors in relation to the claim that only distance to subject has any bearing on perspective.
As I've mentioned before, the proof offered so far to demonstrate that focal length of lens used has no bearing on perspective is the situation in the two images I've prsented above. Or to put it another way, the proof offered so far is in this thread, is essentially a very obvious statement to the effect if one takes two shots of identical scenes from the same position using identical lenses, then the resulting images will be identical.
Now I pride myself on having at least a reasonable grasp of logic, and I fail to see how an experiment demonstrating that effectively identical lenses used from the same position produce the same sense of perspective, is proof that non-identical lenses used from the same position also produce the same result.
If we agree that in order to shoot that sign with a different lens, say a 140mm lens, I would have to turn slightly to the left and by doing so would change the perspective of the sign in relation to the sign as cropped from the 24mm shot, then surely that demonstrates that focal length of lens does have a bearing on perspective.
Bear in mind that by turning slightly to the left in order to take the shot of the sign, I have not changed the distance from the camera to the sign and have therefore not stepped outside of that definition that perspective is only affected by distance to subject.
So, if we agree that these points are true, it follows that the statement "perspective is only affected by distance to the subject and has nothing to do with focal length of lens", cannot be true.
It should be noted that if you point the camera in another direction you take a different photo, NOT a different crop, and it makes no sense comparing.
Good point! If you don't point the camera in a different direction but use a different focal length of lens instead, have you not also taken a different photo?
Why would it makes sense to compare two photos that are very different in content and composition, as a result of the focal length of lenses used being different, but not make sense to compare two photos of precisely the same subject taken from the same distance, with the shot using the longer focal length being turned at a slight angle out of necessity?
Perhaps the definition should be changed along the lines, "Perspective in photographic images is affected by both distance to the subject and angle of view." ;D
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Good point! If you don't point the camera in a different direction but use a different focal length of lens instead, have you not also taken a different photo?
When standing at a given point in space and pointing your camera towards another point, I do not think that any lense will be able to "see around corners" or to make visible objects that are occluded by others. For that, you need to change your viewpoint (or take out your chainsaw).
I guess that the "big nose syndrome" when using wide-angles close-up to capture persons is due to the relative distance from camera to eye vs from camera to nose becoming very different (while at greater distances, the relative distance is almost the same)
-h
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Good point! If you don't point the camera in a different direction but use a different focal length of lens instead, have you not also taken a different photo?
Why would it makes sense to compare two photos that are very different in content and composition, as a result of the focal length of lenses used being different, but not make sense to compare two photos of precisely the same subject taken from the same distance, with the shot using the longer focal length being turned at a slight angle out of necessity?
Perhaps the definition should be changed along the lines, "Perspective in photographic images is affected by both distance to the subject and angle of view." ;D
If you point the camera in the same direction and change focal lenght you take the same photo with a different crop. You might also take a different photo due to different DoF and different real-world characteristics of different lenses but thats not whats being discussed.
The difference between two photos with different focal lengths is that tele one has a subset of of the content, with exactly equal composition and perspective as the wide (DoF might differ). And nobody else than the ones ignorant of perspective would want to compare these, since the result is given as most of us know.
If you change the angle of the camera you change the distance to subjects since its a 2-D representation of 3-D. You actually tilt the angle of the 2-D plane capturing the 3-D. Try this: point the camera directly towards a building so that vertical lines of building are parallel. Then slowly tilt the camera up or downwards. What happens? The lines start to not be parallel. This is not because the building are starting to tilt when you move the camera.
So you don't need to state "by both distance to the subject and angle of view" since changing the angle means changing the distance.
I'm sorry to say that you are arguing with the last 1000 years or so of knowledge on simple geometry ;D.
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"Bear in mind that by turning slightly to the left in order to take the shot of the sign, I have not changed the distance from the camera to the sign and have therefore not stepped outside of that definition that perspective is only affected by distance to subject."
But you have, Ray, you have changed everything.
The entire concept of the thing is about a single shot. The moment you introduce movement, you might as well use a ciné camera and go the whole way. Or just a paintbrush.
The matter of equivalent focal lengths isn't about moving cameras, it's about difference or sameness within a single exposure. Anything else is another matter and irrelevant to the question being posed.
But you already knew that, you advocating devil!
;-)
Rob C
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Erik,
You're a very sensible and scientific sort of guy. Can you offer any proof that the perspective of a photographic image or composition is dependent only on the distance from the lens to the subject?
So far, in this thread the only proof that has been offered is the fact that converting a wide-angle shot to a narrow angle shot of the same effective focal length, through cropping, results in identical images.
Well that doesn't seem like proof to me, the fact that two lenses of equal focal length produce identical pictures when used from the same position. That's pretty obvious, isn't it.
The problem as I see it, is the absurdity of claiming that non-identical pictures can have identical perspective, as in the two examples attached.
The wide angle shot was taken with a 24mm lens. The image of the sign was taken with a 140mm lens equivalent. Whether I took the shot of the sign with an actual 140mm lens attached to my D700, or cropped the 24mm image to simulate a 140mm lens, possibly makes no difference, except in resolution, but maybe it does. This is something I hope you can clarify.
(1) If I had used a real 140mm lens for the shot of the sign, from the same position, I would have needed to turn slightly to the left in order to capture it. Would that have changed the angle between the top of the sign and the top of the frame?
(2) In the full-frame shot it is surely evident that a fairly wide-angle lens was used. Experienced photographers would guess that the lens used was somewhere between 20mm and 28mm, based on the perspective evident in the image.
Would experienced photographers be able to guess the focal length of the lens used to capture the sign only. Does the perspective in the image of the sign only, give any clues?
Ray, by picking a 140mm lens to compare with you are making it obvious that you would have to swing the camera to get the sign in. A better example would be to have used a 35mm lens and then the sign would appear in the top left of the image without having to move the camera. I think you would find the perspective would then be exactly the same. Less extreme example but one that proves the point.
Jim
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But you have, Ray, you have changed everything.
Rob C
C,mon Rob. Let's be sensible ;D . I haven't changed everything. I haven't necessarily changed the camera body for a start, and I haven't changed the distance to an object that appears in the top right-hand corner of a 14mm frame simply by turning the camera, with a longer focal length of lens attached, slightly to the right, and slightly upwards. Nor have I changed my clothes.
I'm addressing the oft quoted maxim that focal length of lens has nothing to do with perspective, only distance from lens to subject. If I turn slightly on the same spot, in order to photograph with a telephoto lens an object which would appear at the edge in a wide-angle shot, I have not changed the distance between the camera and that object.
In fact, if I turn around 360 degrees on the same spot, I haven't changed the distance between myself and any objects surrounding me, unless I wobble a bit, of course.
Now it's clear to me, in practice, using existing of state-of-art lenses, that angle of view also has some bearing on perspective. Distance to subject is not the only factor.
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... Nor have I changed my clothes....
Bingo! You finally grasped what ceteris paribus is all about! ;D
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C,mon Rob. Let's be sensible ;D . I haven't changed everything. I haven't necessarily changed the camera body for a start, and I haven't changed the distance to an object that appears in the top right-hand corner of a 14mm frame simply by turning the camera, with a longer focal length of lens attached, slightly to the right, and slightly upwards. Nor have I changed my clothes.
I'm addressing the oft quoted maxim that focal length of lens has nothing to do with perspective, only distance from lens to subject. If I turn slightly on the same spot, in order to photograph with a telephoto lens an object which would appear at the edge in a wide-angle shot, I have not changed the distance between the camera and that object.
In fact, if I turn around 360 degrees on the same spot, I haven't changed the distance between myself and any objects surrounding me, unless I wobble a bit, of course.
Now it's clear to me, in practice, using existing of state-of-art lenses, that angle of view also has some bearing on perspective. Distance to subject is not the only factor.
Congratulations. Your the only person so far that has been able to move without moving ;D ;D ;D. I recommend you to study the meaning of "move", "turn", "rotate" and so on, and try to do this without moving ;D ;D ;D. The last time I looked into moving it was to change the position relative to something.
You should also contemplate what distance between camera and object means. When stating "camera" one usually means the sensor. This is not a sphere nor a 0-D point that records light from all around you so that rotating doesn't influence , but a 2-D rectangle. When you rotate or otherwise move the camera you move this rectangle relative to all objects around you. Any movement will change distance, thats what movement is.
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Now it's clear to me, in practice, using existing of state-of-art lenses, that angle of view also has some bearing on perspective. Distance to subject is not the only factor.
Aha! Now we're getting to the heart of the matter. I think some of the other factors that just might have some bearing on perspective are equally worthy of lengthy discussion in the forum. Here are a few possibilities:
1. Now that you mentioned clothes, how do we know that changing clothes might or might not have some effect on perspective? Can you offer some proof either way?
2. Or how about carbon fibre vs. a wooden tripod?
3. Or whether or not the photographer in question knows enough Latin to be able to understand the meaning of ceteris paribus, all other things being equal?
4. Or whether Michael will have to buy a new hard drive just to hold this thread? That might have some effect on his perspective on the issue.
etc. :D
Eric
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It's a bit odd how on one of the most knowledgeable photography forums on the interwebs some people manage to dispute trivial linear, geometrical optic understood since 1600 AD. :-\
It's actually worse than that: this topic is brought up every few months, and every time it's just as controversial.
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Ray,
Could you try this experiment:
1. Take a "head shot" portrait with a 35mm camera and a wide focal length, say 28mm or less, used close enough to have the face fill the frame: this should achieve the big-nose effect.
2. Repeat with the same focal length on a smaller format camera, moving back from the subject to get the same framing.
3. Repeat again with that smaller format camera but reducing the focal length so as to get the same framing with the same camera position as in 1.
Ideally, the format size difference would be extreme, like 35mm format vs a small sensor compact.
And to avoid any misinterpretation, willful or otherwise, I mean same faming of the subject in the complete, uncropped images delivered by the cameras.
My high school geometry and photographic experience both tell me that 1. and 3. (same camera-subject distance, different focal length) will be equally big-nosy, while 2. (greater camera-subject distance, equal focal length as in 1.) will be less big-nosy.
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At the risk of adding to a thread which is already gone too far ...
Perspective as I understand it refers to the spatial relationship of objects in a scene, which of course varies with the viewpoint from which the scene is observed. Perspective is a real physical property of the scene, and does not depend on the apparatus (human eye or camera lens) used to record the scene. The big nose in a close-up picture taken with a wide-angle lens is an actual property of the face as viewed from that camera position. The size of the (close) nose relative to the (more distant) eye depends on the camera position and not on the lens focal length.
I think others in this forum are using the term perspective to include what I would call lens distortion. Pictures taken from the same location with different lenses will look somewhat different, even when cropped to the same size or angular coverage, because the lenses have different amounts of distortion. Lens distortion changes the mapping of a scene (with its inherent perspective) to a flat sensor plane. Pincushion or barrel distortion will make objects look different, both in size and orientation, depending on where they appear in the image. But calling this effect a change in "perspective" caused by the lens is confusing terminology, and that is what many posters here are objecting to.
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Ray,
Could you try this experiment:
1. Take a "head shot" portrait with a 35mm camera and a wide focal length, say 28mm or less, used close enough to have the face fill the frame: this should achieve the big-nose effect.
2. Repeat with the same focal length on a smaller format camera, moving back from the subject to get the same framing.
3. Repeat again with that smaller format camera but reducing the focal length so as to get the same framing with the same camera position as in 1.
Ideally, the format size difference would be extreme, like 35mm format vs a small sensor compact.
And to avoid any misinterpretation, willful or otherwise, I mean same faming of the subject in the complete, uncropped images delivered by the cameras.
My high school geometry and photographic experience both tell me that 1. and 3. (same camera-subject distance, different focal length) will be equally big-nosy, while 2. (greater camera-subject distance, equal focal length as in 1.) will be less big-nosy.
BJL,
You should understand better than anyone on this site that I know quite well that distance to subject affects perspective. This matter was discussed years ago. I'm certainly not disputing this fact. What gave you that idea?
What I'm disputing is that distance to subject is the only consideration as regards perspective. I think you also know, because I have the impression you have a scientific frame of mind, that one can prove that almost anything is true if one is selective in the data.
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You should also contemplate what distance between camera and object means. When stating "camera" one usually means the sensor. This is not a sphere nor a 0-D point that records light from all around you so that rotating doesn't influence , but a 2-D rectangle. When you rotate or otherwise move the camera you move this rectangle relative to all objects around you. Any movement will change distance, thats what movement is.
Distances are usually measured from point to point. I agree that a camera or sensor is not a theoretical point, nor am I. Nevertheless, if one wishes to be pedantic and absolutely precise about distance one needs to specify a point, or an average of numerous points.
So, for the sake of the exercise, shall we take a point in the centre of the sensor for measuring distances, or would you prefer to take an average of numerous points covering the whole sensor, representing the average distance of the sensor to any particular point in the scene?
Either way, I think you will agree that it is possible to rotate the sensor without changing the distance beteen a specified point in the far right of the scene and a specified point at the centre of the sensor.
Likewise, if one were to use the average of say 100 points spread evenly across the whole sensor, as the measuring point, one could rotate or tilt the sensor in such a way that the distance from that average to a specified point in the right of the scene was unchanged.
In other words, in rotating the sensor to the right, the left edge of the sensor becomes closer to the specified point in the right of the scene, and the right edge of the sensor becomes further away by the same degree. The average is: no change in distance. But we certainly get a change in perspective.
So, whilst I'd agree that there has been some miniscule alteration in distances to parts of the sensor, of the nature of 5mm or so, when I rotate the sensor to capture a part of the scene which can be captured with a wide-angle lens without rotation, the distance to the sensor as a whole has not changed.
I would think that such changes to parts of the sensor are best described as changes in angle of view, rather than changes in distance.
Below is the view out of my hotel window in Bangkok. You should be able to tell from the resolution which is the 14mm shot (cropped) and which is the 120mm shot (180mm equivalent because I used my Nikon D7000 for the telephoto shot).
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Hi,
I started to put together a small article on the issue: http://echophoto.dnsalias.net/ekr/index.php/photoarticles/64-lnses-in-perspective
Best regards
Erik
Ray, by picking a 140mm lens to compare with you are making it obvious that you would have to swing the camera to get the sign in. A better example would be to have used a 35mm lens and then the sign would appear in the top left of the image without having to move the camera. I think you would find the perspective would then be exactly the same. Less extreme example but one that proves the point.
Jim
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Perspective as I understand it refers to the spatial relationship of objects in a scene, which of course varies with the viewpoint from which the scene is observed. Perspective is a real physical property of the scene, and does not depend on the apparatus (human eye or camera lens) used to record the scene. The big nose in a close-up picture taken with a wide-angle lens is an actual property of the face as viewed from that camera position. The size of the (close) nose relative to the (more distant) eye depends on the camera position and not on the lens focal length.
I'm sorry but this just doesn't make sense to me, apart from the first sentence. I agree that perspective refers to the appearance of the spatial relationships in a scene from the point of view of the observer. However, surely it must be obvious that without an observer there is no perspective. Perspective cannot therefore be a real physical property of a scene independent of an an observer. If there's no observer, whether real person, or camera or recording device of some despription, there's no perspective.
The big nose effect in a close-up picture taken with a wide-angle lens is surely not an actual property of the face as viewed from that camera position. You could get into serious trouble telling your girlfriend what a big nose she has when you try to kiss her.
The actual size of her nose remains unchanged whatever position you're in. Perspective is an illusion. Isn't that obvious?
What the wide-angle lens does in photography is to create a sense of perspective in an image which is impossible for us to see in reality because the natural angle-of-view of our eyes is too narrow. What happens when we attempt to view a face from close-up is that we cannot simultaneously focus on the nose and the background. We have to shift our gaze from one part of the scene to another, therefore we don't get that direct comparison of the spatial relationship between different objects that are both inside and outside of the eyes' narrow FoV. Big is big only in relation to something that is perceived as being smaller.
This is I why I object to the claim that perspective has nothing to do with focal length of lens. If we try to simulate a wide-angle effect by stitching a number of shots taken with a short telephoto, similar in focal length to our eyes for example, then none of the individual shots prior to stitching will have an unusual perspective. The big nose in one image will only appear unusual in relation to the small ears in another image.
It's not until the images are stitched that the distorted perspective becomes apparent. However, after the images are stitched we have in effect a wide-angle shot. In other words, in order to get the rather amusing and absurd perspective of a very close-up portrait, one absolutely needs a wide-angle lens, or a wide-angle lens 'equivalent'.
That's why I claim that perspective is affected by both distance to subject and angle of view. I haven't yet figured out a way to get that distorted perspective effect from close-up without using a wide-angle lens, whether actual or effective through stitching.
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Distances are usually measured from point to point. I agree that a camera or sensor is not a theoretical point, nor am I. Nevertheless, if one wishes to be pedantic and absolutely precise about distance one needs to specify a point, or an average of numerous points.
So, for the sake of the exercise, shall we take a point in the centre of the sensor for measuring distances, or would you prefer to take an average of numerous points covering the whole sensor, representing the average distance of the sensor to any particular point in the scene?
Either way, I think you will agree that it is possible to rotate the sensor without changing the distance beteen a specified point in the far right of the scene and a specified point at the centre of the sensor.
Likewise, if one were to use the average of say 100 points spread evenly across the whole sensor, as the measuring point, one could rotate or tilt the sensor in such a way that the distance from that average to a specified point in the right of the scene was unchanged.
In other words, in rotating the sensor to the right, the left edge of the sensor becomes closer to the specified point in the right of the scene, and the right edge of the sensor becomes further away by the same degree. The average is: no change in distance. But we certainly get a change in perspective.
So, whilst I'd agree that there has been some miniscule alteration in distances to parts of the sensor, of the nature of 5mm or so, when I rotate the sensor to capture a part of the scene which can be captured with a wide-angle lens without rotation, the distance to the sensor as a whole has not changed.
I would think that such changes to parts of the sensor are best described as changes in angle of view, rather than changes in distance.
Below is the view out of my hotel window in Bangkok. You should be able to tell from the resolution which is the 14mm shot (cropped) and which is the 120mm shot (180mm equivalent because I used my Nikon D7000 for the telephoto shot).
You are incorrect. To consider the photo you need to take into account all points that make up the photo. If you change one point its a different photo. The photo of an object (except an ideal point with no size) will have points representing the real objects on the 2-D sensor. When you move that sensor (any kind of movement) you change the distance of these points on the sensor relative to their points at the object. Its possible to rotate the sensor along an axis so that a point or even a line will not change distance to a given line or point at the object. But all other points distances will change, so you will change the distances and hence perspective for the photo by any kind of movement.
The average of the distances is of no importance to this.
And with this Im do not want to give any more education lessons of subjects that should be obvious at ground school levels, and that the Greeks mastered more than 2000 years ago (and probably other cultures before that).
As to "do there need to be an observer". Thats more philosophical question. I would say that if you set a camera to take a photo by timer the photo will be in the camera from he exposure. Others will claim that there is a potential for many photos, and that this potential is realized by an observer. But for this discussion the normal geometry is "good" enough, and we do not need to consider quantum physics.
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Ray, you seem to have missed, will fully or otherwise, the point of my 1. vs 3. comparison, which is about getting equal perspective from possibly very different focal lengths when used from at the same position relative to the subject. That is the issue arising from the misunderstanding of the original post, and to the myth that using a smaller format and proportionately shorter focal lengths will produce undesirable results like making portraits "big-nosy" even when using a lens that gives equal angular FOV to get the same framing.
But my scientific observations also include:
- once a person has posted more than a couple of times repeatedly defending a position against numerous posts full of contrary arguments, the participants' opinions almost never change in subsequent posts. Or in other words, once the arguments have been made enough that an open-minded person has the information needed to reach a reasonable decision, it is quixotic to push on in pursuit of unanimous agreement.
- threads this long are past their useful lifespan, unless they contain lots of nice photos.
I have no nice, relevant photos to post, and so I am signing of now.
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You are incorrect. To consider the photo you need to take into account all points that make up the photo. If you change one point its a different photo.
I might well be incorrect. I've never heard of anyone who wasn't incorrect on at least a few points. But I fail to see how I am incorrect on the basis that I haven't taken into account all the points that make up the photo.
My argument so far has consistently been that the reason the wider angle shot has a different perspective, and from really close-up an obviously distorted perspective, is because it is a different photo from another taken from the same shooting position and same angle, using a longer lens.
The wide angle shot has many more points and many more clues about spatial relationships than the narrow angle shot. One cannot get the 'big nose effect' with a long lens shot taken from the same close distance as a wide-angle shot.
Obviously one does get essentially the same picture of the nose, barring lens imperfections, but no clues as to the perspective of the nose in relation to other points which simply don't exist in the narrow angle shot.
If you arrange for those points (and clues to perspective) to exist, by stitching a number of shots, you are then very slightly changing the position of the sensor with each shot, which, according to you, represents a change in distance, however small that change may be.
Nevertheless, I'm not one for nitpicking. I accept that within reason it is possible to emulate a wide-angle lens with a narrow lens through stitching. And I accept also that much of the differences in my comparison image above, if not all, are due to lens imperfections.
My main thesis here is that the wide-angle shot can provide a different perspective because there are more objects or points in the scene for the eye and brain to construct a sense of spatial relationships. Cropping the wide-angle shot makes it a narrower angle shot.
And with this Im do not want to give any more education lessons of
subjects that should be obvious at ground school levels, and that the Greeks
mastered more than 2000 years ago (and probably other cultures before
that).
The ancient Greeks! They weren't all that good at the scientific method, were they! Didn't they believe that we see, in part, because our eyes shine a light on the object we are looking at.
Didn't they tend to believe that the sun, and the entire observed universe, revolved around the earth?
Even Aristotle, one of the greatest of Greek thinkers, was confused about the number of teeth in a female human. He thought males had a greater number of teeth. Maybe his wife was abnormal, teeth-wise, or maybe he'd never bothered checking.
I can't help feeling compassion for all those countless individuals who, for over a thousand years, accepted everything that Aristotle wrote as being gospel, when we now know that most of what he wrote is sheer bunkum.
I'm reminded to some extent of the posters in this thread who blindly accept that focal length has nothing to do with perspective because certain renouned experts have said so. ;D
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Ray, you seem to have missed, will fully or otherwise, the point of my 1. vs 3. comparison, which is about getting equal perspective from possibly very different focal lengths when used from at the same position relative to the subject. That is the issue arising from the misunderstanding of the original post, and to the myth that using a smaller format and proportionately shorter focal lengths will produce undesirable results like making portraits "big-nosy" even when using a lens that gives equal angular FOV to get the same framing.
Nope. Didn't miss your point at all BJL. We discussed this about 10 years ago. Distance to subject affects perspective, and a difference in focal length is required to maintain equal FoV when sensor size is different.
The issue is, if a different focal length is not provided and the FoV of the shot is therefore different, is perspective entirely the same? Can one sensibly talk about perspective being equal in shots with a different FoV?
- once a person has posted more than a couple of times repeatedly defending a position against numerous posts full of contrary arguments, the participants' opinions almost never change in subsequent posts. Or in other words, once the arguments have been made enough that an open-minded person has the information needed to reach a reasonable decision, it is quixotic to push on in pursuit of unanimous agreement.
You are probably right. Maybe I'm just an incurable optimist. If one re-phrases the argument in numerous ways, perhaps the penny will eventually drop. On the other hand, perhaps it's me who is wrong. Perhaps someone will rephrase the argument in such a way that it becomes apparent to me that I'm wrong.
- threads this long are past their useful lifespan, unless they contain lots of nice photos.
I have no nice, relevant photos to post, and so I am signing off now.
Nor have I. Nice photos are not my speciality, but I post them anyway for the sake of their meaning rather than their niceness. ;D
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The wide angle shot has many more points and many more clues about spatial relationships than the narrow angle shot. One cannot get the 'big nose effect' with a long lens shot taken from the same close distance as a wide-angle shot.
You get exactly the same big nose effect. Position the nose inside the tele, then change to wide without moving sensor and the nose will appear identical. What I assume (but might be wrong) you are taking about is that the nose will appear different in the outer end of an wide. Well, thats simply the effect of trying to capture 3-D in 2-D. Its not possible to get a 2-D representation of an 3-D object without loosing something. So perfect round objects will appear oval in the outer end of photos by wides. This is called perspective. This does not mean that wides have different perspectives, just that they are wide.
Obviously one does get essentially the same picture of the nose, barring lens imperfections, but no clues as to the perspective of the nose in relation to other points which simply don't exist in the narrow angle shot.
If you arrange for those points (and clues to perspective) to exist, by stitching a number of shots, you are then very slightly changing the position of the sensor with each shot, which, according to you, represents a change in distance, however small that change may be.
Nevertheless, I'm not one for nitpicking. I accept that within reason it is possible to emulate a wide-angle lens with a narrow lens through stitching. And I accept also that much of the differences in my comparison image above, if not all, are due to lens imperfections.
My main thesis here is that the wide-angle shot can provide a different perspective because there are more objects or points in the scene for the eye and brain to construct a sense of spatial relationships. Cropping the wide-angle shot makes it a narrower angle shot.
If you are stitching several tele photos you to correspond to one wide photo each of these stitched photos will have a different content and perspective since you have moved the sensor, and the final stitched picture will be different and have a different perspective than the wide picture. You can also avoid "the nose effect" seen at the outer end of the wide photo since you are making a different photo with a different perspective by making a "tele nose photo" (since you have moved the sensor).
In fact you don't need a tele to do this. You can use the wide and point this in different directions and take several photos, and then make a crop in the center corresponding to taking these with a tele. If you stich these the result will be exactly the same as with the stitched teles (except resolution), but different to the original un-stiched wide, proving again that wides and tele gives the same perspective and that only changing position matters in terms of perspective.
So by stitching photos you are NOT emulating a wide, but you are making a new photo that can have the same angle and more or less the same content as the wide, but will have a different perspective.
My thesis is: the photos has exactly the same perspective independent of focal length as long as the position of the sensor is not changed.
The "sense of spatial relationships" is a another discussion that needs a separate thread. You will of course get different information form different pictures (such as a tele versus a wide). This has nothing to do with perspective.
P.S. Sorry to all about keeping this alive, for me this is obvious, but not all might agree that its obvious. To disagree on facts is anther issue. No-one can agree on the issue of perspective since it is inherent in our reality ;)
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You get exactly the same big nose effect. Position the nose inside the tele, then change to wide without moving sensor and the nose will appear identical.
Of course it will. The nose remains the same as long as the lens is wide enough to capture it. What changes with the angle of view, as you change the zoom lens to wide, without altering your position, is the perspective, ie. the relationship between the size of the nose and other objects that come into view as you zoom to wide.
Without those other objects, ears, eyes, people standing behind the head, houses, trees etc, there is little sense of perspective. I wouldn't claim there's no sense of perspective. The nose itself, even though divorced from its background, still has a certain perspective, from tip to base.
However, when the nose is placed in a different context of smaller than expected eyes and ears and pathetically small back ground objects, as a result of the zoom moving to wide mode, the perspective of the nose as a whole changes. It then appears as an exceedingly large nose. Got it?
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Of course it will. The nose remains the same as long as the lens is wide enough to capture it. What changes with the angle of view, as you change the zoom lens to wide, without altering your position, is the perspective, ie. the relationship between the size of the nose and other objects that come into view as you zoom to wide.
Without those other objects, ears, eyes, people standing behind the head, houses, trees etc, there is little sense of perspective. I wouldn't claim there's no sense of perspective. The nose itself, even though divorced from its background, still has a certain perspective, from tip to base.
However, when the nose is placed in a different context of smaller than expected eyes and ears and pathetically small back ground objects, as a result of the zoom moving to wide mode, the perspective of the nose as a whole changes. It then appears as an exceedingly large nose. Got it?
Ray, I think you've just talked yourself in to my corner! Having got there by yourself, then perhaps you'll now accept the basic truth of what some of us have been saying all along?
Thank God for that; the world can rest easy!
Extend your new credo a smidgen: imagine that neither the camera nor lens has moved, but imagine that the very same lens is now covering a different sensor (smaller or, conversely, larger) at the focal plane inside the camera. There you are: exactly the same perspective and depth of field, but a larger or smaller area of the scene covered.
So, using that very same focal length on any size of sensor at the same image size returns an identical image except for what’s cut off by the smaller section of the circle covered. Or, of course, the other way around if you are starting your experiment on a sensor that’s smaller than the one with which you are making the comparison. Naturally, you need to do this with a lens that covers the area of the larger sensor.
Perspective has not been altered at all; in the case of the larger sensor (for the sake of example and clarity, assume a 50mm lens on FF 135) the lens is seen to be whatever it says on the barrel or the box (50mm); when used with the smaller sensor, the lens is the same lens and you can believe the box. But, it is acting in a manner that makes it seem a longer lens (a 75mm on cropped format). But, it really is the same old 50mm can of worms it always was.
But, try to cover the same subject area with both sensors, and you will then have to get closer or further away than when using the other sensor size; that change in distance is what controls perspective, and not the focal length which, as we have just seen, is the same as ever it was. Whew, I feel I'm back in my back row at last! For which delusion, many thanks!
;-)
Rob C
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Of course it will. The nose remains the same as long as the lens is wide enough to capture it. What changes with the angle of view, as you change the zoom lens to wide, without altering your position, is the perspective, ie. the relationship between the size of the nose and other objects that come into view as you zoom to wide.
My final post in this, I promise :).
Make up your mind, do the nose remains the same or not? Since the nose itself is a object its proportions either stays the same or changes by zooming. I claim that the proportions at the 2-D photo stays the same. This is also called perspective. You claim that its proportions stays the same and do not stay the same.
Please fell free to approach the Nobel institute with groundbreaking news on the physical world view.
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I don't know why this subject causes so much consternation every time it comes up; it's really just basic geometry. Well, OK, maybe that's why ;D
To see the effect of crop factor, focal length, etc, it is useful to ask what one needs to do to take the same image using different formats. This establishes a baseline; once you know what scaling of each image parameter is required to take the same image, one can examine how the image will differ when the parameters are changed away from those equivalent values.
Imagine taking a 35mm format camera/lens and shrinking everything by a factor of two in every linear dimension:
1. The sensor is now 18mm x 12 mm, the focal length is half, the aperture is half (so the f/ratio, which is the ratio of focal length/aperture diameter, remains the same). The angle of view remains the same -- we went wider in focal length but then cropped to a smaller portion of the image, and the two effects exactly compensate.
2. Because the f/ratio is the same, the physical depth of field of the image is the same. But the imager is twice smaller; we need the depth of field to be half of what it was in order to get the same image on our shrunken platform. Therefore we need to open up the aperture, and make the f/ratio half what it was for 35mm, so that the DoF is shrunk in the same proportion to the camera. In other words, objects at the edge of the DoF are focused a small distance in front or behind the sensor plane, and this distance should be shrunk by the same factor as the camera so that everything about the imaging process is in proportion to the smaller format.
3. If we want the same degree of motion blur in the image, we want objects that move across some angle relative to the angle of view during the exposure to traverse the same angle; since nothing has changed about the angle of view, using the same shutter speed will result in the same amount of motion blur.
4. With half the f/ratio and the same shutter speed, the sensor receives four times the light during the exposure; the ISO should be dropped by a factor of four to to keep the raw data in the same range of values (in particular to avoid blowing out highlights).
So, the same photo results on the half-size format using the same shutter speed, half the f/ratio, half the focal length and one quarter the ISO (if available). Change any one of these parameters, and a different image results. So for instance if one doesn't halve the f/ratio, the DoF will be deeper and the sensor receives less light, increasing the appearance of noise. Differences between the formats most often arise at the limits of the available range of parameters; for instance the 35mm format image taken at a base ISO of 100 will have no equivalent in the half-size format unless the camera goes down to ISO 25, which such cameras typically do not. And sufficiently wide angle, wide aperture lenses may not be available relative to their 35mm equivalents, etc.
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ejmartin -
See two post above: Snap!
Rob C
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One interesting thing about this argument -- okay, maybe it's not *that* interesting -- is that it could have been settled for anyone with a camera and two different lenses in less time than it took to type out some of the contrary arguments.
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John, that would never do; what would be left about which to argue?
Rob C
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So, using that very same focal length on any size of sensor at the same image size returns an identical image except for what’s cut off by the smaller section of the circle covered.
There are many images of very different scenes, Rob, which are identical, except for the parts that are different. If there are parts that are different, the scenes are not identical, period. Almost everything has something in common. Even you have a few genes which are identical to mine, but don't worry about it. ;D
In digital photography, the degree of commonality is far greater. Most digital images, whether portraits, or landscapes with distant mountain views, will have certain components that are identical, such as pixels with the same value, such as R=50, G=150, B=79.
One could argue that a particular 'head-and-shoulders' portrait is identical to a particular mountain scene, except for the parts that are different.
You should have noticed throughout this thread that I've always argued that it's the 'equivalent' or 'effective' focal length that affects perspective. The Wikipedia article quoted by Mouse was correct in the sense that it stated, 'it's not the 'lens per se' that influences perspective'. However, the Wikipedia article should have added, 'It's the effective focal length that has a bearing on perspective'.
If I could attribute a single cause of confusion in this thread, it's the failure to understand that 'effective' focal length is what counts. Nominal focal length (as stated on the lens) does not necessarily have any effect of perspective, but real world effective focal length does.
Ciao!
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I don't know why this subject causes so much consternation every time it comes up; it's really just basic geometry. Well, OK, maybe that's why ;D
To see the effect of crop factor, focal length, etc, it is useful to ask what one needs to do to take the same image using different formats. This establishes a baseline; once you know what scaling of each image parameter is required to take the same image, one can examine how the image will differ when the parameters are changed away from those equivalent values.
Imagine taking a 35mm format camera/lens and shrinking everything by a factor of two in every linear dimension:
1. The sensor is now 18mm x 12 mm, the focal length is half, the aperture is half (so the f/ratio, which is the ratio of focal length/aperture diameter, remains the same). The angle of view remains the same -- we went wider in focal length but then cropped to a smaller portion of the image, and the two effects exactly compensate.
2. Because the f/ratio is the same, the physical depth of field of the image is the same. But the imager is twice smaller; we need the depth of field to be half of what it was in order to get the same image on our shrunken platform. Therefore we need to open up the aperture, and make the f/ratio half what it was for 35mm, so that the DoF is shrunk in the same proportion to the camera. In other words, objects at the edge of the DoF are focused a small distance in front or behind the sensor plane, and this distance should be shrunk by the same factor as the camera so that everything about the imaging process is in proportion to the smaller format.
3. If we want the same degree of motion blur in the image, we want objects that move across some angle relative to the angle of view during the exposure to traverse the same angle; since nothing has changed about the angle of view, using the same shutter speed will result in the same amount of motion blur.
4. With half the f/ratio and the same shutter speed, the sensor receives four times the light during the exposure; the ISO should be dropped by a factor of four to to keep the raw data in the same range of values (in particular to avoid blowing out highlights).
So, the same photo results on the half-size format using the same shutter speed, half the f/ratio, half the focal length and one quarter the ISO (if available). Change any one of these parameters, and a different image results. So for instance if one doesn't halve the f/ratio, the DoF will be deeper and the sensor receives less light, increasing the appearance of noise. Differences between the formats most often arise at the limits of the available range of parameters; for instance the 35mm format image taken at a base ISO of 100 will have no equivalent in the half-size format unless the camera goes down to ISO 25, which such cameras typically do not. And sufficiently wide angle, wide aperture lenses may not be available relative to their 35mm equivalents, etc.
I agree that it’s to do with geometry. To bring in aperture size, though, merely confuses the issue, with so many already confused from the outset!
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I have never read so much crap and confusion.
Perspective is dependant on distance. Period.
Lens focal length, combined with camera imaging area, permit greater or smaller parts of the scene before the camera to be recorded.
And why some posters introduce aperture into this discussion I do not understand.
Geometry may be used to compare lens focal length on different formats; by area, by diagonal or by formats adjusted for aspect ratio. This is the only way, in my view, to consider the subject in a practical, real-world manner.
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I agree that it’s to do with geometry. To bring in aperture size, though, merely confuses the issue, with so many already confused from the outset!
The sense of perspective, and the factors that influence it, are many. There's no doubt that DoF contributes to the appearance of perspective.
Consider two scenes of a huge rock against a background of palm trees on a distant shore. One image has the foreground rock in total focus, but the distant shore blurred.
The other image has the foreground rock blurred, but the distant shore as sharp as a tack. Is there really no difference in perspective between the two images?
I get a sense in this thread there's a confusion between the geometricaly theoretical and abstract definition of perspective, and the 'real-world' experience and perception of perspective using our very round eyeballs.
It seems that some people will stick to the abstract, geometrical definition of perspective come what may. Maybe it's a type of religion.
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You're close, but a more accurate statement would be: "Perspective is dependent only on the relative position in 3-dimensional space between the observer and subject" You can move spherically around the subject and always be the same distance from it, but the perspective between you and the subject will change (assuming only you, the observer is moving), so more variables than distance alone are needed to define perspective.
If you are Ray, who is swinging his camera around, he should be swinging it around the nodal point of his lens, so that the points in the 3-dimensional scene retain their relative positions when they hit his sensor in his many images taken for stitching. The "stretching" of objects towards the periphery of the image are simply the result of "projection" onto a flat imaging plane, but "perspective" or relative position of points within the scene translated to the imaging surface will remain the same. This is what will allow him to stitch the images together later, stretching and compressing them to match up the points in different images and form various types of "projections" - i.e. pretending that his sensor was spherical or his lens was not rectilinear, and so on.
I have never read so much crap and confusion.
Perspective is dependant on distance. Period.
Lens focal length, combined with camera imaging area, permit greater or smaller parts of the scene before the camera to be recorded.
And why some posters introduce aperture into this discussion I do not understand.
Geometry may be used to compare lens focal length on different formats; by area, by diagonal or by formats adjusted for aspect ratio. This is the only way, in my view, to consider the subject in a practical, real-world manner.
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The sense of perspective, and the factors that influence it, are many. There's no doubt that DoF contributes to the appearance of perspective.
Consider two scenes of a huge rock against a background of palm trees on a distant shore. One image has the foreground rock in total focus, but the distant shore blurred.
The other image has the foreground rock blurred, but the distant shore as sharp as a tack. Is there really no difference in perspective between the two images?
I get a sense in this thread there's a confusion between the geometricaly theoretical and abstract definition of perspective, and the 'real-world' experience and perception of perspective using our very round eyeballs.
It seems that some people will stick to the abstract, geometrical definition of perspective come what may. Maybe it's a type of religion.
Ha, ha, well, the perspective will change a bit if you refocus your lens ;). Far from being "religion", the geometrical definition of perspective is very important, as it relates to the design of imaging devices, software and production of images at various times during the past millenium. Your "sense" of perspective is subjective and is itself a perspective on perspective, so to speak, so I wouldn't expect everyone to have the same opinion and lively discussion should ensue. Whenever the subject of perspective comes up, though, a lot of misconceptions about the math stuff get thrown around and bog down the discussion about the subjective. False statements about the objective don't make for good arguments about the subjective, IMO.
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I have never read so much crap and confusion.
You must be new around here!
Against my better judgement, let me give a brief summary of what people like me mean when they say that perspective depends on distance only, and does not change in the way that some people fear when using a smaller format and proportionately shorter focal length.
If you take several photographs of the same subject from the same position (with all the subjects in the same positions too!), each photograph using a combination of focal length and format size that records the same field of view, then the relationships of size and position between objects in the scene will be the same, even if the focal lengths are very different.
(And for extra credit, if the effective aperture diameter (focal length divided by aperture ratio) are equal, then out--of-focus effects will be very close to equal, deviating only in some extremes like for objects that are very close to the camera --- that enters the other even more hotly debated part of "equivalency", or "when and how can I reproduce in one format the compositional details that I know how to achieve in another format?")
Using different definitions of the terms involved can of course change the truth of a statement by changing its meaning, so I wanted to clarify what people mean when they talk about perspective depending on distance, not focal length.
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And why some posters introduce aperture into this discussion I do not understand.
Forgive me, but it seemed that much of the to and fro seemed to revolve around whether different formats took different images. If one establishes what shooting parameters in two different formats take the same image, then that question is answered, and one can move on to the next bone of contention. In particular, it shows that cameras with different formats can achieve images with the same perspective when the image is taken from the same point.*
Since aperture is part of the answer to that question, I included it in the discussion.
* Unless, as BJL states, there are objects so close to the lens that it substantially affects the ray paths that make up the images in the two formats. When the subject distance is much larger than the entrance pupil of the lens, that is not an issue; otherwise it might be.
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One interesting thing about this argument -- okay, maybe it's not *that* interesting -- is that it could have been settled for anyone with a camera and two different lenses in less time than it took to type out some of the contrary arguments.
Indeed. It reminds me of a scene from the Sesame Street kid's TV program of many years ago. The two-headed monster was arguing with itself about why it was so cold in the room (the windows and dorrs were all open and snow was flying in). But eventually the two heads came up with the brilliant idea of cooperating, and once they did, they figured out that they should close the windows and doors.
;D
Eric
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One interesting thing about this argument -- okay, maybe it's not *that* interesting -- is that it could have been settled for anyone with a camera and two different lenses in less time than it took to type out some of the contrary arguments.
Not necessarily, John. After performing the required experiments with different lenses, the results have to be interpreted. It's frequently the case that the same data can be interpreted in different ways. This is a very common problem in science.
Having carried out such experiments myself many times, there's is no confusion in my mind about perspective. I will summarise my findings.
The conditions for identical perspective in two or more photographic images of the same scene are dependent primarily on 3 factors.
(1) Equal distance to the same subject.
(2) Use of equal, or effectively equal (or equivalent), focal length of lenses.
(3) Use of appropriate settings on each lens to ensure equal DoF and equal focussing.
If one changes any one of those 3 factors, one will change to some degree the sense of perspective that the viewer of the photographs will experience. By viewer I mean a subjective human being, rather than a robot that has been programmed to see only the parts that two or more images have in common.
I say that these are the primary factors, but I believe there are other perhaps more subtle factors such as light, shade, color and contrast which can affect our sense of perspective.
This issue is noted in the following article at: http://csmt.uchicago.edu/glossary2004/perspective.htm
Leonardo da Vinci, writing soon after the invention of scientific perspective, dismissed it as perspectiva accidentalis, and in his work Trattora della Pittura noted the distortive effects of perspective in wide angles and the various visual manipulations and elisions that occur from arbitrarily moving the constructed vanishing point in a painting. Leonardo encouraged painters instead to focus on parallel developments in aerial perspective – gradations in color, shadow, and texture to denote three-dimensional relations.
Elsewhere in the article the differences between the linear perspective of photography and our own vision are also addressed as follows:
This discrepancy between camera and physical eye is accounted for in part by the fact that in our eyes, light projects not onto a flat surface, but the curved inner surface of our eyeballs. Furthermore, a large portion of our perception comes from having two eyes that can triangulate relative depth (known as stereopsis, which is a form of parallax), and the ability to move our heads to accrete multiple views of a single object.
Parallels exist between the functioning of our vision and photography or linear perspective, but because our vision exists not only in the light that enters our eyes, but also the passage of time, and the interweaving of binocular pictures of the world by our brains in conjunction with our mental image of what we expect to see, the parallel becomes problematic. Artistic practice that developed contemporaneously with photography, such as impressionism and cubism, in many ways reflects this difference.