Any links to the original threads? This seems to make little sense by itself.
I agree, people should be clear about what they are referring to, unless their intention is to start all over.
This is what sparked Ray's urge to start this new thread:
Does a photo give spatial information (the nose job)? (http://www.luminous-landscape.com/forum/index.php?topic=61388.0)
and presumably
This puzzling business of "35mm lens equivalent" (http://www.luminous-landscape.com/forum/index.php?topic=61222.0)
Cheers,
Bart
There has recently been a bit of controversy on 'perspective' in another couple of threads, one entitled, 'This puzzling business of 35mm lens equivalent", and the other 'Does a photo give spatial information?'
There seems to be a mantra that perspective is related only to distance beteen the observer (photographer) and subject, which is difficult to break through. It's almnost like a religion.
I really think the matter should be sorted out. There seems to be so much confusion on the issue.
Below I'm attempting to enumerate all the relevant points that have occurred to me during the recent discussion in those threads I mentioned above..
(1) There's a mathematical and geometric definition of perspective which is useful and necessary for all sorts of drafting and sketching and the creation of computerised programs to convert 3-D into 2D, or to stitch images together etc etc.
(2) There's a human experience of perspective which may be at odds with that scientific definition of perspective.
(3) There's a reason for the discrepancy. Human vision is enormously complicated. Simple geometric rules cannot encompass it.
(4) I'm reminded of the current controversy over Mark Dubovoy's article in which he claims that 'Everything Matters'. This is relevant to the discussion on perspective, as experienced in the human mind.
Mark's point, as I understood it, was that seemingly trivial details can have a surprisingly significant effect. We shouldn't ignore them.
(5) Those who claim adamantly that perspective can only be changed by a change in distance to subject should make clear that they are referring to a mathematically and geometrically abstract defintion which does not necessarily encompass the human experience which is plain and simply, and unavoidably, biased in accordance with its own sense of brain-wired perspective.
(6)The classic example of proof for the statement that perspective cannot be altered without a change in position, is the cropping of a wide-angle shot to the same angle of view as a telephoto shot.
The adherents of this simplistic approach to perspective will point out that the cropped wide-angle shot will have the same perspective as the telephoto shot, as evidenced by the same broad size and shape of objects and angles apparent in both shots.
However, those of us who don't lack a subtle apprehension of detail, will notice that the cropped wide-angle shot is a bit fuzzy and lacking in detail, compared with the telephoto shot, which is sharp and clear.
Such indistinctness in the cropped wide-angle shot is indicative of greater distance. Clarity and sharpness, or to quote Mark Dubovoy, hyper-realism, is indicative of closeness.
Great painters realise this fact. If you want to depict something as being rather distant, the last thing you do is make it sharp and detailed, which a telephoto lens does.
I could go on, but I'll leave it at that for the sake of brevity.
PS Having just re-read another part of one of the mentioned threads, I think you are also stating something that is very obvious about 'apparent' perspective. So let us say that I shoot a group of distant building with a 200mm lens so that the buildings pretty much fill the image. If I show you that picture you have no real way of knowing how far away they are unless I tell you the focal length of the lens and you could then make an educated guess. If I also take a picture with a 21mm lens from the same spot and show that to you, it will become immediately obvious that the buildings are quite a long way off because you can see everything that is between the lens and the buildings. I think that is what you mean by perspective - am I right? But that is a different scene with a different lens, and if you crop down they will look the same, and if you could project outwards the lines from the 200mm shot you would get the same perspective.
Fred,
That's an excellent reiteration of the mantra that only position affects perspective. However, I'm speaking from the human perspective.
There are lots of issues other than 'real' distance that influence the sense of perspective in the human brain. I mentioned one of them, specifically resolution, which you completely ignored.
Do I have to repeat that sharp objects appear closer, to the human brain, than fuzzy and indistinct objects, despite the geometry.
Do I need to mention that large objects visible in the foreground tend to make other objects that are further away, seem even further away than they actually are?
Do I also need to mention if those larger objects in the foregrounds are cropped out of the image, the perspective of the remaininmg image has changed?
Fred, you are just repeating a false notion which you have been taught but which you have never questioned, it seems to me.
Human visual perception is in many ways very complex and not as "objective" as imaging by a machine. Witness the many optical illusions that play on the brain's processing of visual information and the fact that we exist and process things in a temporal environment (mentioned, I think, in another thread). Of course one's psychological state at any given moment will affect perception, i.e. when under stress or in a "fight or flight" situation, your brain's visual filtering will be quite different than when you're relaxed and taking in the scenery on a sunny day. Are you using the term "perspective" to mean "perception"?
Let's just address this issue above. Optical illusions certainly exist, and they are quite amazing. But one essential point about these illusions is that they seem to apply to everyone.
If you wish to make the point that various factors other than mere distance, that might affect the human brain's perception of perspective, are purely an illusion, then we are into a branch of philosophy rather than photography, which I'm quite willing to discuss.
Are you making the point that the extreme and contrived examples that trick the eye, such as people simultaneously walking up and down a staircase which is on the same level, are what we normally see in photographic images? In other woerds, everything is an illusion except the geometry of perspective?
Perhaps the confusion results from a lack of a clear definition of perspective. The general definition of perspective is perhaps too narrow in the sense that it only addresses distances and angles.
It seems that resolution, texture, Dof, FoV have no bearing on this geometric definition of perspective
... that most people on this forum seen to slavishly accept, but I suspect their eyes don't.
I would question the value of bringing this aspect of "perspective" into the topic of equivalent focal lengths... and would not be so derisive of geometric perspective in that context.
"Perspective is affected only by distance to subject"
Noooo..... Arrghh.
;D Then you have no other option than to ask the gods themselves. (the responsible "thing" whatever it is of this universe and its laws).
Well, I do have the option of just ignoring the theoretical rules of geometry and doing what I damned well please. ;D
The rules of projective geometry are not a theory, they are based on axioms (http://en.wikipedia.org/wiki/Projective_geometry#Axioms_of_projective_geometry).
If you don't agree, well, how about ignoring the 'theory of gravity'. I wish you a speedy recovery ;)
Cheers,
Bart
Why should they? Why isn't the burden on you to make clear what you are referring to when you talk of perspective? Why is it that you own the definition of that word?Because Ray is an ardent follower of that eminent philosopher Humpty Dumpty: “When I use a word,’ Humpty Dumpty said in rather a scornful tone, ‘it means just what I choose it to mean — neither more nor less.’" (Lewis Carroll)
Because Ray is an ardent follower of that eminent philosopher Humpty Dumpty: “When I use a word,’ Humpty Dumpty said in rather a scornful tone, ‘it means just what I choose it to mean — neither more nor less.’" (Lewis Carroll)
Eric ;D
Ray, you're essentially arguing nonsense, and I think you know it.
Of course the perception of perspective may differ from person to person, but the fact that my vision is 20-40 and you wear glasses to correct an astigmatism and the third guy is blind has nothing to do with the way a camera operates. All three of us could push the button on a camera, one after the the other, and we'd get the same photo. I doesn't depend on how we feel or what we think. The fact that there is fog in the valley doesn't change the lens. Perspective is determined by position, period. Perspective is not a philosophical concept, or an artificial construct, or negotiated in any way, it just is. (Unless, of course, you're a Republican, in which case we may need a new thread.)
What you're arguing is basically semantics. You're saying that because somebody somewhere may have misused the word "perspective," and their culture is as good as ours, then it's okay to say that perspective changes. No.
Wide-angle shots make close objects appear closer, and distant object more distant. Didn't you know that?
Goodness gracious me! ;D
Ray, Since you are so interested in what our eyes have to tell us, I have an experiment for you to perform. Secure the cardboard tube from the center of a roll of paper towels. Go outside and find a distant object and a close object. Hold the cardboard tube up to your eye and look at those two objects. Now remove the tube (thus converting your narrow angle vision thru the tube to a wide angle vision). Did the close object suddenly appear closer; or the distant object more distant? If they did, you need to visit your ophthalmologist.
It once occurred to me that the human eye is more akin to a fish-eye perspective than it is to a rectilinear perspective, even though we very much need the latter to interpret 2D images...
How do we know that changing the 'effective' FL of lens, at the same position, changes our sense of perspective? Because our eyes tell us it has changed. Wide-angle shots make close objects appear closer, and distant object more distant. Didn't you know that?
However this is a separate issue from the general effect that wide-angle lenses make objects more distant, and telephoto lenses make objects appear closer.
.... we can only change the orientation (direction of observation) of a given shot, never its perspective in terms of what is seen and what is hidden.[/li]
[/list]
So, where is the discussion? ??? all this just seems a semantic discussion to me.
This is my kitchen shot from a tripod without changing the direction of observation. Of course the visual perception of the 10mm frame is different to that of the 17mm and 20mm shots, but nobody denies this, one picture shows more things than the other!. And of course the cropped content (geometrical perspective) is the same in all three shots. So?
The perspective of what precisely is hidden?? This is the core of the nonsense. You are stating that the perspective of that which isn't there, which doesn't exist, which isn't in the photo, has not changed.
So, if you make the stuff in your 10mm shot hidden (by cropping), your microwave looks closer to the viewer, whoever that viewer may be.
No Ray, not the perspective of what is hidden, the perspective of what is seen, which is the only perspective that can be judged on both images. All this seems so obvious to me that I wonder if you are just making a joke.
Yes, you get an image where the microwave looks closer; in fact you get the same image as you got with the 22mm. Again: are you asking all these things seriously? ???
If what is seen in both images is different, how can the perspective be the same. It is you who is making a joke, right? ;D
I'm glad you agree. ;D
The longer you insist in mixing both conceps (the geometrical perspective which solely depends on subject distance, vs the visual perception which depends both on subject distance and FOV), the longer it will take you to realize we are talking about the same thing and we all agree.
Now, what you pointed, the subjective factors that actually fool the eyes (atmosphere is one) and alter our perception of the perspective is correct. So both, what you are pointing, and the geometry are correct and not in contradiction at all.
Exactly true! Good analogy! The perspective was the same because the focal length was the same, that is, the focal length of my eyes did not change simply because I was peering through a cardboard tube.Ray,
Camera lenses are not cardboard tubes. They are lenses, as our eyes are lenses, but different in some ways of course. If instead of using a cardboard tube, I'd used my D700 with a standard 50mm lens, I'd have got a similar effect, but not with a different focal length on my D700.
Let me try to explain what I think may be happening in this issue by providing additional clarification on this aspect of inclusion and exclusion.
One of the problems that scientific enquiry faces, which presents a problem in the formulation of theories and the confirmation or falsification of theories, is selection bias. One can collect a huge quantity of data on a particular subject, but the data one chooses to include or exclude will either confirm or refute the results one may hope to achieve, or the theory one is trying to either refute or substantiate
However, there's an additional problem because bias by its very nature is something we are not fully aware of. To be aware of one's biases is to be unbiased.
To behave in a biased manner in science, despite being aware one is biased on a specific issue, is tantamount to scientific fraud. Through a process of careful exclusion of specific data which doesn't support one's hypothesis, and the inclusion only of the data which does support one's hypothesis, one can prove or disprove almost anything.
So let's apply the above principle to this issue of the sense of perspective that a viewer experiences, when viewing an image of a scene through different focal lengths of lenses, from the same position.
If one wishes to test this in a scientific manner, one should take a number of shots from the same position actually using different focal lengths of lenses, then compare the images.
When I do this it is clear to me that a wide angle shot produces a different sense of perspective to a telephoto shot. However, since I have a fair understanding of this principle of 'selection bias', I know that I can turn these results on their head by excluding data from the wide-angle shot that gives the impression that the perspective is different. I do this by cropping out the offending data.
If I have two sets of data which are different, one set being larger than the other, and I exclude from the larger set all the data that is different to the smaller set, then I'm obviously left with two identical sets of data.
Such is the proof that focal length has no bearing on perspective.
Really! Pull the other leg. ;D
The longer you insist in mixing both conceps (the geometrical perspective which solely depends on subject distance, vs the visual perception which depends both on subject distance and FOV), the longer it will take you to realize we are talking about the same thing and we all agree.
Ray,
with apologies and please don't take any offense, but on this subject you really should leave it alone. You just can't get past the idea that distortion is not perspective. The point is when you remove the tube, you see more, but the perspective of the objects you saw with only the tube doesn't change. The only way to change that is move your position in relation to those objects. Make a framing guide from a piece of matt board and find a set of telephone poles receding in the distance. Frame an image with the rectangle and note the perspective of the poles to each other. When you remove the guide, that doesn't change. You see more, and that's all focal length on a lens does. Any other effect(distortion) is unintentional ( and now almost all of us correct it with software).
This insistence on this concept (you do realize that may be the ONLY one that believes this) reflects poorly on your credibility.
The point is when you remove the tube, you see more, but the perspective of the objects you saw with only the tube doesn't change.
After giving this matter some more thought, I think now see the reason for this difference of opinion about perspective and focal length of lens.
Whenever I compare technical qualities in images, such as resolution, noise or DoF etc, I always compare equal size images or prints, because that's the sensible thing to do.
I've been assuming all along that that's what everyone else does, but it seems this isn't the case.
Guillermo's example of his microwave taken with a 10mm lens, showing the crop lines for 17mm and 22mm can only demonstrate that perspective doesn't change provided the smaller images resulting from the cropping are not enlarged, and providing all the different sized images or prints are viewed from the same distance, which they are in his example.
However, this effect is not what happens when one looks through the camera's viewfinder using different focal lengths of lenses. The viewfinder remains the same size, but the objects viewed become enlarged as a result of any increase in focal length of lens.
Likewise, when making prints to hang on one's wall, or to sell to customers, one would not choose to make the size of the print inversely proportional to focal lengthof lens used, in order to maintain the original perspective, although one could if one so chose.
I think most of us would agree that it would be a very odd thing to do, if a photographer of wildlife were to exhibit his prints at postage-stamp size on the grounds that he wanted to maintain the original perspective before raising camera to eye, with telephoto lens attached, to take the shot.
Most of us want to exploit that potential of the telephoto lens to change perspective and make things look closer. We revel in the close-up view with its extra detail and hyper-realism.
Magnification, showing more detail is not perspective. Perspective is not angle of view either. Angle of view is related to magnification.
Please give an example of a change of perspective which does not involve a change in angle of view.Example:
Example:
Find two trees or other large objects that are a good 100 feet or more apart. Take a camera with your favorite fixed-focal length lens with you and go to a position where you are at least 500 feet from the nearer tree and where the more distant tree is still visible (that is, you are a little ways off from a straight line joining the trees, so you can see both of them. Take a picture of the two trees with a small lens opening and focused on the nearer tree.
Then, walk toward the nearest tree until you are about 20 feet from it, with the more distant tree still showing behind it. Don't forget to bring your camera and the same lens with you. Without changing the focus or lens opening from the first picture, take another picture of the two trees.
Since you used the same lens on the same camera, the viewing angle is identical in both images. But the perspective (as well as your invention of the "perception of perspective") will have changed.
Isn't this obvious? Please note that distortion will not have any different effect in the two images, since you used the same camera, lens, focus, and aperture for both pictures. Of course, the sun may have moved a little, or even gone behind a cloud between photos 1 and 2, but I hope even you won't consider exposure to be related to perspective.
Eric
So, my question to you, Guillermo, is do you agree with the following statements, and if not why not?
(1) Without the rest of the face visible, the size of the nose in relation to the eyes and ears, cannot be gauged in the telephoto shot. We cannot determine whether or not the nose is unusually large or not.
Correct. Both images would be undistinguishable.
(2) If we crop the wide-angle shot to the same FoV as the telephoto shot, we have effectively changed the focal length of the lens, thus demonstrating the principle that different lenses on different format cameras can have the same effective focal length. I've always argued that it's the effective focal length that counts, not the lens per se.
Incorrect. The focal length of a lens is a physical optical parameter, measured in mm. By cropping you only change the FOV. Different lenses on different formats can have the same FOV, not the same focal length. The term 'effective focal length' is incorrect, there is not such thing. There is just a FOV produced by the combination of a given focal length + sensor format. The term 'equivalent focal length' could be acceptable IMO, even if it doesn't refer to a focal length but to the FOV the lens would produce in a 35mm format.
(3) Whether the perspective distortion is caused by a change in focal length or a change in distance, it is a distortion in both cases, or an illusion if you like. Agreed?
The combination of perspective (which solely depends on distance) plus FOV (determined by the combination of focal length + sensor format) can make use perceive distorted subjects. The reason for this is basically because our visual system doesn't project images linearly nor has such a wide FOV as a wide angle lens can produce. This is why wide angle images look weird to us many times, because our eyes never produce them in real life. A wide angle image showing distortion is not incorrect, it's just a mathematical projection our visual system cannot produce by itself. Is this an illusion? I would rather consider it a mismatch between the image produced in the camera vs the images we are used to observe in real life.
(4) When I photograph a bird sitting on the branch of a tree from a distance of say 30 metres, using a telephoto lens, the image, or final print, really does give the impression the shot of the bird was taken from close up. If something in an image appears closer to the viewer than it actually was in reality, is that not perspective distortion? If not, what type of distortion or illusion would you call it?
Incorrect. It is not perspective, it is magnification, and as Fine_Art explained well this is related to FOV.
(5) I'm sure we can both agree that the big nose effect from a wide-angle lens is a distortion or illusion. But what happens when the subject for the portrait really does have a huge nose in reality? Well, we can create the opposite effect by taking the portrait with a 300mm or even 600mm lens (35mm format equivalent) from a great distance. The nose might then appear normal, and that would be an illusion, although probably a nice illusion.
Correct. Perspective (i.e. subject distance) can be used to fake the perception of nose's size in a portrait. You can take a picture of a big nosed guy from a long distance, and make it look a smaller nose than a wide angle shot taken from a very short distance from a guy with a regular nose.
Ray,Excellent request. I tried to answer quite explicitly the exact question that Ray asked, namely "Please give an example of a change of perspective which does not involve a change in angle of view."
Would it be possible for you to upload a couple of pictures which demonstrate the effect you're talking about, so we can understand it by comparison?
Ray,This has been the issue with Ray and perspective all along in the other threads. He wants to roll other things into the concept of "perspective" and redefine it, and while I suppose if you go by the broad definition of perspective it might be understandable, the term is very well defined and accepted in visual arts. Trying to explain other phenomenon as part of perspective goes against the accepted definition, as this thread as so aptly pointed out. Trying to roll FoV, distortion and perspective into one catchall concept of perspective seems illogical, especially since all three and their relationships are pretty well defined and understood by photographers (and others involved in visual arts), and understanding them separately is important and beneficial whereas lumping them together doesn't accomplish anything.
I think you have a very interesting point of view on this subject. However, I keep coming back to what others have stated: this is all about the definition. ...
Dave
Really! This is getting curiouser and curiouser. It seems pretty obvious to me that a change in the position of the viewer, whether the viewer is looking at 3-dimensional objects in a real scene or at a picture of that real scene hanging on the wall, will cause a change in angle between the line of sight from the eye to the proportions of the objects being viewed.
For example, if I view a tall building from such a distance that it looks very small, a mere detail in the landscape, the angle between the rays of light from the top of the building to my eyes, and the rays of light from the bottom of the building to my eyes, will be very narrow indeed. Agreed?
If I move up really close to the building, which will cause a change in perspective (I've never denied that. I'm not silly), then the angle between those rays reflecting from the top and bottom of the building to my eyeballs will be very wide indeed. Agreed!
How can you claim that perspective is not related to angle of view?
Please give an example of a change of perspective which does not involve a change in angle of view.
I answer over your text:
Incorrect. The focal length of a lens is a physical optical parameter, measured in mm. By cropping you only change the FOV. Different lenses on different formats can have the same FOV, not the same focal length. The term 'effective focal length' is incorrect, there is not such thing. There is just a FOV produced by the combination of a given focal length + sensor format. The term 'equivalent focal length' could be acceptable IMO, even if it doesn't refer to a focal length but to the FOV the lens would produce in a 35mm format.
equivalence | equivalency:
The fact of being the same, effectively the same, or interchangeable with something else.
You take a picture from the sidewalk. It looks a bit cramped. You check for cars then move your tripod at right angles to take the shot from the middle of the street. You have changed your perspective. Your angle of view has not changed. The building is still the same size in relation to the other buildings.
Ray,
Are you talking about the difference between the two attached images (when seen opened at full size)? To clarify, the pixel relationship between the toy dog and the distant building is exactly the same, the only difference is the presence or absence of surrounding detail.
John
So here are the two shots, taken earlier today, using the same camera from the same position and angle, displayed at the same size, and presumably viewed from the same distance. The only significant difference is the focal length of the lenses used.And the "perspective" in both pictures is the same, although the difference in "field of view" makes things look closer in one than the other. Is this the effect you have recently been calling "perception of perspective?" The "effect of field of view" might be a better term, but if you want to define a term in a non-standard way, you would help your cause if you provided a clear definition of it.
when referring to similarities in the focal length of lenses and other matters. The terms are synonymous. "Effectively the same" means "equivalent". If you disagree, I would describe that as a semantic quibble.transform and warp.
Your entire discussion about perspective IS about semantics.Yes! Absolutely!
Your entire discussion about perspective IS about semantics.
Your entire discussion about perspective IS about semantics.
What is the authoritative scholarly source (read: a book) which someone could refer to settle this? I'm positive these things have been put on paper hundred plus years ago. Having such drawn out and controversial threads on some of the most basic subjects of optics on a supposedly pro photography and pixel peeper forum is truly incomprehensible, and frankly embarrassing.A little embarrassing (for ray anyway). I guess embarrassing for others because keep bashing our heads against it and keep the thing alive. I'm not sure about "scholarly" source, but there are probably 100's of places that talk about "perspective" as it relates to photography (including threads like this which contributors have made it pretty clear), and ray is the only person I've ever seen try to "redefine" the accepted understanding of the photographic world (and other visual arts for that matter).
And the "perspective" in both pictures is the same, although the difference in "field of view" makes things look closer in one than the other. Is this the effect you have recently been calling "perception of perspective?" The "effect of field of view" might be a better term, but if you want to define a term in a non-standard way, you would help your cause if you provided a clear definition of it.
And the "perspective" in both pictures is the same, although the difference in "field of view" makes things look closer in one than the other. Is this the effect you have recently been calling "perception of perspective?" The "effect of field of view" might be a better term, but if you want to define a term in a non-standard way, you would help your cause if you provided a clear definition of it.
The most useful definition of perspective for media studies found in the Oxford English Dictionary is, “The art of drawing solid objects on a plane surface so as to give the same impression of relative position, size, or distance, as the actual objects do when viewed from a particular point.”
Your entire discussion about perspective IS about semantics.
But your particular view of what 'focal length' means is not a semantic discussion, you are simply wrong in this concept. There is no such thing as 'equivalent focal length' or whatever (no matter how many badly informed photographers use that term), because the focal length of a lens is UNIQUE. It is a physical parameter of the optics and is measured in mm. What you call 'equivalent focal length' refers to the field of view (FOV), and that's the proper word for it. And the FOV depends on the pair: focal length + format size (this including any pp cropping).
A 50mm is always a 50mm, no matter in which sensor size you put it. It's a 50mm on a FF camera, and it's a 50mm on an APS-C camera, but will provide a different FOV on both. A 50mm will provide on a FF body the same FOV as a 33mm on an APS-C camera, and a 50mm will provide on an APS-C camera the same FOV as a 75mm on a FF camera. As simple as this.
Regards
What you call 'equivalent focal length' refers to the field of view (FOV), and that's the proper word for it.
I see! So you consider the term 'equivalent focal length' improper. You think people might get confused by it? Or perhaps you think it's just poor English and logically incorrect.
I see! So you consider the term 'equivalent focal length' improper. You think people might get confused by it? Or perhaps you think it's just poor English and logically incorrect.
Of course your angle of view has changed. Any change in position, up or down, to one side or another, forwards or backwards, is a change in perspective and angle of view.
If it's a small change in position, the change in perspective and angle of view will probably be small. If it's a large change in position, the change in perspective will probably be large.
Changes in position, even though minor, can cause objects that were previously obscured to become visible, and objects that were previously visible to become obscured, because the angle of view has changed.
Changes in FoV can cause huge numbers of objects that were previously obscured to become visible.
Perhaps I should clarify what I mean by angle of view. I'm making a distinction between 'angle of view' and 'field of view'. The FoV of the lens/camera doesn't change as you change position, obviously. How can it? That's a property of the lens/camera system. What changes is the visual angle from the eye to the various objects within the field.
I'll just add that the wide-angle shots in Erik's presentation show a building which is clearly more distant than in the cropped versions.
"Apparently more distant", NOT "clearly more distant", because in fact the building is exactly the same distance from the camera in all shots. When you look at things through binoculars they are apparently closer because the binoculars create a more magnified image compared to your eyes alone. However I would say that it is clear that the building is apparently more distant in the wide angle image. ;)yes, and ray doesn't get it that just because you can see more of the scene in a wide angle shot the perspective hasn't change. While in a very loose sense the actual definition of the word perspective might apply, regarding the accepted use of the term in photography the perspective hasn't changed - photographers don't use the term perspective to describe a property of the actual image/print but more as a property important to understand and take advantage of when capturing images. (granted many don't understand this point, so some of the confusion as often we see photographers recommending to switch to a telephoto or wide angle to change the perspective. Implied in that comment is also repositioning yourself to change the size relationships of the object in the scene, but most don't elaborate on that point). Once you have taken a shot, you cannot change it's perspective by simply cropping it different ... which is more about FoV. As I've mentioned before, ray is trying to merge at least 3 concepts perspective, distortion, and FoV as we use them in photography (and are very useful being separate) into a single concept he calls perspective.
It is improper, inaccurate and injustified*. For someone who knows about photography it is easy to understand 'this has an equivalent focal length of 85mm', meaning that when you put a 50mm on an APS-C sensor you get the same FOV as an 85mm would provide on a FF body. But I am tired of reading misleaded new users in the forums thinking the focal length of their lens is going to change according to the camera they set it.
* The days in which the 35mm format was a universal reference passed away. Today 99% of digital cameras in the world are not FF and there are many more APS-C sized cameras than FF for instance.
I've never met anyone who thinks a lens will change its actual physical and material properties when attached to a different camera body, but I guess someone who believes in magic might think that.
If this poor guy hadn't been bombed one thousand times by people like you with things such as "M4/3 cameras provide an equivalent focal length that is twice the real focal length", he would have known that he had to set the one and only focal length of the attached lens, i.e. 50mm, never 100mm.
Regards
But would he have known what minimum shutter speed to use in the absence of any image stabiliser at all, based on the frequently mentioned adage that a shutter speed of 1/FL provides reasonably sharp results, if you hold the camera steady?
Without the concept of 'focal length equivalence', that poor guy using a 4/3rds camera without built-in image stabiliser, might have discovered he'd taken a number of irreplaceable shots that were less than adequately sharp as a result of using 1/50th sec exposure with a 50mm lens instead of the 1/100th sec exposure that focal length equivalence implies.
I have no problem in the theory or of my understanding of the term 'equivalent FoV'. I just think it's more practical to use 'equivalent focal length' because all lenses are specified with a focal length reference and not an FoV reference. Not only that, I think it would be true to say that all reviews of P&S cameras, and even the manufacturers' websites, mention the 35mm format focal length equivalence of the P&S fixed lens.
Whatever system of nomenclature one adopts, there will always be a number of people who get confused by what is meant. However, I would be willing to place a bet that a change to FoV equivalence would cause greater confusion.
Before I was doing digital my most used camera was a Pentax 67 MF camera. I used to have four lenses, 45/4, 90/2.8, 165/2.8 and 300/4. I never thought of them as 24, 50, 85 or 180 mm equivalents.
Hi,
Before I was doing digital my most used camera was a Pentax 67 MF camera. I used to have four lenses, 45/4, 90/2.8, 165/2.8 and 300/4. I never thought of them as 24, 50, 85 or 180 mm equivalents.
Best regards
Erik
Well, I would guess you're in a minority, Erik.I don't think so.
I don't think so.
I also shot MF film and I also never worried about equivalent focal lengths.
Hi Wayne,
Same with me, 6x7cm and 6x6cm (and 4x5 inch). One just knows (after a while) intuitively which lens gives the anticipated field of view.
Cheers,
Bart
Yes, on the other hand, with the new compacts there are a lot of different sensor sizes, so it may be practical to use 35 mil film as a reference.
I don't think so.
I also shot MF film and I also never worried about equivalent focal lengths. I really don't think anyone did.
I don't people think about it that much now, except when moving to a new format and getting a handle on what lens will deliver equivalent FoV to the lenses they are used to on their previous format. Once they've got that figured out (unless you use a really small sensor) they just use the actual focal length to describe their lenses.
Same with me, 6x7cm and 6x6cm (and 4x5 inch). One just knows (after a while) intuitively which lens gives the anticipated field of view.
Because I'm familiar with looking at photographs and the properties of lenses, the relative size of things in a telephoto image (what's called "compression") gives me a clue that the things in the photograph were actually quite distant from the camera. So the spacial perception of the photograph can vary from viewer to viewer - which is anything but clear ;)
Now consider the following. It's a significant point. The extension distortion of the wide-angle shot, which makes distant objects look more distant than they actually are, is transformed into the compression distortion of the telephoto shot, which makes close objects look closer than they actually are, simply by cropping both images to the same FoV.
How come? Can't you see the absurd contradiction here? Those who claim that FoV or focal length of lens have no bearing on perspective, and that only position affects perspective, must now concede that there's no such thing as extension and compression distortion. It's all an illusion.
How can one change the extension distortion in a wide-angle shot to the compression distortion of a telephoto shot and simulataneously claim that perspective has not changed?
Does anyone really believe this is merely semantics?
Does anyone really believe this is merely semantics?
That's an excellent point which I'll address. I believe it is true that an experienced photographer may notice the slight compression distortion in a telephoto shot and realise that the subject is not in fact as close as it may seem to the uncritical eye.
The same applies to the wide-angle shot. The experienced photographer may realise that the distant objects that appear really far away are in fact not as far as they appear. There may be clues that a wide-angle lens was used which, as we all know produces 'extension distortion'.
Now consider the following. It's a significant point. The extension distortion of the wide-angle shot, which makes distant objects look more distant than they actually are, is transformed into the compression distortion of the telephoto shot, which makes close objects look closer than they actually are, simply by cropping both images to the same FoV.
How come? Can't you see the absurd contradiction here? Those who claim that FoV or focal length of lens have no bearing on perspective, and that only position affects perspective, must now concede that there's no such thing as extension and compression distortion. It's all an illusion.
How can one change the extension distortion in a wide-angle shot to the compression distortion of a telephoto shot and simulataneously claim that perspective has not changed?
Does anyone really believe this is merely semantics?
Don't be ridiculous Ray,
.....you crop the wide-angle shot to an equivalent field-of-view or angle-of-view as the telephoto shot and because the angle of incident light is then equivalent, so is the apparent distortion. if you subsequently blow up the cropped wide-angle shot to the exact scale of the telephoto shot, it will exhibit the exact same compression.
The compression and expansion are not constant over the frame. It expands because it becomes wider than what would be considered a normal lens, and it compresses when the angle is narrower for a telelens. In a telelens, as well as in the center part of the wide-angle lens, incident light rays are increasingly more parallel. Thus it will look more like a parallel projection.
Basically everyone but you.
I presume by expansion you mean extension. The extension distortion in a wide-angle shot refers to the effect or impression of extended distances. The compression distortion of a telephoto shot refers to the effect of shortened distances.
How do we make something that previously looked small (and distant) appear large and close? By removing the big things in the scene (through cropping) and magnifying the small things.
Okay, I get what you mean. But you previously mentioned making prints. If the wide-angle print is printed large enough so that the angle-of-view when viewed at a reasonable distance becomes equivalent to "normal", and we also look at a telephoto print where the objects of interest are the same size as the wide-angle print. Would we then still judge the objects as being at different distances or of different size?
Basically everyone but you.and we're all feeling like this about now ...
and we're all feeling like this about now ...
and we're all feeling like this about now ...
Wayne,
Some of us like to tell it as we see it, without fear of ridicule. Others prefer the herd mentality. I wonder if the problem is that some of you guys are stuck in the Aristotelian 'either/or' concept. That is, either position determines perspective, or it doesn't. I've never argued that it doesn't. I'm arguing that there are additional factors.
Yes, Ray, we know that you prefer the Humpty-Dumpty concept to the Aristotelian one. I think Wayne and Guillermo have expressed (in images) my own feeling at this point very well.
My one remaining suggestion is this: Why don't you coin a new term for your version of "perspective" which differs so greatly from the accepted meaning. How about "Rayperspective" for your version and simple "perspective" for the rest of us.
Eric
Hi Eric,
I would say the word is "Rayspective". By the way, here in the north "Per" is a very common name, so we can have Perspective, too.
Best regards
Erik
Hi Eric,Absolutely, Erik! ;D
I would say the word is "Rayspective". By the way, here in the north "Per" is a very common name, so we can have Perspective, too.
Best regards
Erik
Yes, Ray, we know that you prefer the Humpty-Dumpty concept to the Aristotelian one. I think Wayne and Guillermo have expressed (in images) my own feeling at this point very well.
My one remaining suggestion is this: Why don't you coin a new term for your version of "perspective" which differs so greatly from the accepted meaning. How about "Rayperspective" for your version and simple "perspective" for the rest of us.
Eric
Why isn't the burden on you [Ray] to make clear what you are referring to when you talk of perspective? Why is it that you [Ray] own the definition of that word?
PERSPECTIVE
“The art of drawing solid objects on a plane surface so as to give the same impression of relative position, size, or distance, as the actual objects do when viewed from a particular point.”
The art of depicting and presenting solid objects on a plane surface so as to give the same impression of relative position. size, or distance, as the actual objects do when viewed from a particular point with the naked eye or when viewed through a standard camera lens of focal length approximately equal to the diagonal of the sensor.
What frustration? If quarrelling about definitions makes your day then go right ahead.+10!
To help alleviate your frustration, I'll provide the definition again, from the most authoritative dictionary of the English language. It even provides Americanisms.
PERSPECTIVE Persepctive 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.
The difference you are seeing in the examples you are posting is simply the difference in the "correct" viewing distance--the correct viewing distance is different for each image, but you are using the same viewing distance for both and so the perspective is different. Viewing distance is simply changing apparent perspective. While you are seeing a relationship between focal length and perspective, it is an indirect relationship. Viewing distance actually gives the final perspective because you can actually get the same perspective at different distances and with different focal lengths, so those are not determining how we finally view an image--viewing distance also explains why we perceive the crop different from the whole because the whole will have the same perspective as the crop if magnified in relation to the crop. See my post above.
The difference you are seeing in the examples you are posting is simply the difference in the "correct" viewing distance--the correct viewing distance is different for each image, but you are using the same viewing distance for both and so the perspective is different. Viewing distance is simply changing apparent perspective. While you are seeing a relationship between focal length and perspective, it is an indirect relationship. Viewing distance actually gives the final perspective because you can actually get the same perspective at different distances and with different focal lengths, so those are not determining how we finally view an image--viewing distance also explains why we perceive the crop different from the whole because the whole will have the same perspective as the crop if magnified in relation to the crop. See my post above.
Having done this, it's clear to me that the choice of focal length of lens affects the sense of perspective in the resulting image, whether on print or screen. How anyone could deny that, beats me, unless he is on hallucinatory drugs.
And you are right, but it is not to do directly with focal length, but the viewing distance--I have made the same error and did research to figure it out. If I take a photograph from the same point with multiple formats and the focal length of each lens is proportional to the format diagonal (or the angle of view is the same), then the resulting perspective is the same. So is it the focal length? The angle of view? Both? Neither?
So while you are correct in stating the focal length choice will affect the apparent perspective in the image, you are incorrect to assign it to the focal length per se as the perspective will always be the same if images are viewed by the relative position equal to the taking position. The reason we see focal length choice is we view images from a standard distance, which is relative to the image size, rather than to the taking position. Once you compare images at a standard viewing distance, the change in perspective created by focal length/angle of view becomes apparent.
What are the correct viewing distances in relation to print size for these two examples, in your opinion?
Since you placed two images at the same size next to each other, you have fixed the viewing distance--I will not change my position when looking at one or the other. Because that distance is held constant, you can see the impact the change in focal length or crop has on perspective between the images. But the reason for that is the correct viewing distances for each image is very different. If you scaled one image in relation to the other so that the correct viewing distance would equal the distance I am viewing the images, then the perspective would be the same, but the images would not be the same size.
BTW, this is not my opinion. If you look at my first post above, you will see a few citations as well as a link. This problem was solved a long time ago and there is nothing to suggest perspective works otherwise.
And to anticipate your question, as you get closer and further away from an image, the apparent perspective changes.
I really don't have anything to add.Nor do I.
Nor do I.
Nor does Ray. :D
Ah, Rob! The pain of Fame! You have my sympathy. I'm glad I'm (mostly) still anonymous.
Hello Eric,
It was snowing here in Mallorca when I drew open the curtains this morning; it became a little more pleasant after lunch, so I took myself off to have a coffee and then I decided to invest in a walk. That was a mistake: a threesome asked me to take their picture on a cellphone (belonging, I assumed, to one of them) and that instantly (and obviously) told me that they'd been admiring my own cellpix, and so I said of course, step this way, let's get a shot against that black curtain over the mountains surrounding the Bay. The mistake was in the time that took: before I could make it back to the car I was hit by all the hail that had been lurking within that curtain. Next time, I'll copy Mr Clooney and tell them they are mistaken, that in fact, I'm only me. Oh to be normal!
Rob C
Ah, Rob! The pain of Fame! You have my sympathy. I'm glad I'm (mostly) still anonymous.
Eric
How about a pair of statements:That does it.
1) Perspective is solely dependent upon the relative positions of observer and subject. (i.e. the current dictionary definition.)
2) The *perception* of perspective is *additionally affected by* field of view and print viewing distance.
How about a pair of statements:
1) Perspective is solely dependent upon the relative positions of observer and subject. (i.e. the current dictionary definition.)
2) The *perception* of perspective is *additionally affected by* field of view and print viewing distance.
Distant objects appear small. They are perceived as being small. No-one believes they actually are small, unless one is looking at a world of totally unfamiliar objects.I see distant objects that appear small. I perceive them to be small. I believe they actually are small and I'm looking at a world of totally familiar objects. Leaves 3"x1" - 40 yards distant.
Ray,
That flat image can now be cropped in various ways, printed at various sizes and those prints viewed at various distances by various observers (each of whom can bring any number of cultural assumptions to the experience.) In each case, their individual perception of the image may be different, but the *recorded image doesn't change*. The printed pixels do not shuffle about on the paper based on the distance of the viewer from the paper.
The very technically knowledgeable Bart, argues that it can all be explained by anamorphism, but he refuses to elaborate.
He simply implies that anamorphic distortion may be an intrinsic property of all lenses, not just the obvious volume anamorphic distortions that one sees at the edges of very wide-angle shots, which can be corrected by converters from DXO Labs.
Here you go again, misrepresenting what others have said. Amamorphic distortion (http://en.wikipedia.org/wiki/Anamorphosis) is NOT a lens property, it's a projection effect.
Sounds to me you are engaging in obfuscation.
What this has to do with a change of FoV containing objects which are not misshapen, beats me. I really do think you need to eloborate on this.
In each case, their individual perception of the image may be different, but the *recorded image doesn't change*. The printed pixels do not shuffle about on the paper based on the distance of the viewer from the paper.
I'll recap:
Focal length --> magnification,
sensor dimensions --> field of view,
lens entrance pupil --> perspective,
output viewing distance --> perspective distortion.
That's all there is to it. I'm sorry if the facts confuse you.
Cheers,
Bart
Focal length --> Magnification
Sensor size and focal length --> Field of view
The ratio of object distances --> ratio of image sizes --> True perspective
The difference between the "correct" viewing distance and actual viewing distance --> Apparent perspective
I think that would be more factual. It would certainly be more in line with the texts.
I'll recap:
Focal length --> magnification,
sensor dimensions --> field of view,
lens entrance pupil --> perspective,
output viewing distance --> perspective distortion.
That's all there is to it. I'm sorry if the facts confuse you.
Cheers,
Bart
It's the same thing, using a few more words to explain. True or actual Perspective is fixed for a given viewpoint (entrance pupil), and all relative sizes result from simple geometry.