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Author Topic: This puzzling business of "35mm lens equivalent"  (Read 38415 times)

Slobodan Blagojevic

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Re: This puzzling business of "35mm lens equivalent"
« Reply #100 on: January 18, 2012, 04:25:50 pm »

... Surely your charms would be better suited elsewhere.

Thank you!

Finally someone to recognize my usual curmudgeon persona as charming ;)

Paul Stalker

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Re: This puzzling business of "35mm lens equivalent"
« Reply #101 on: January 18, 2012, 07:18:49 pm »

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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mouse

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Re: This puzzling business of "35mm lens equivalent"
« Reply #102 on: January 18, 2012, 08:15:52 pm »

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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Ray

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Re: This puzzling business of "35mm lens equivalent"
« Reply #103 on: January 19, 2012, 12:36:46 am »

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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Ray

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Re: This puzzling business of "35mm lens equivalent"
« Reply #104 on: January 19, 2012, 12:46:02 am »

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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mouse

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Re: This puzzling business of "35mm lens equivalent"
« Reply #105 on: January 19, 2012, 02:53:22 am »

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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Rob C

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Re: This puzzling business of "35mm lens equivalent"
« Reply #106 on: January 19, 2012, 04:06:48 am »

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

Walter_temp

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Re: This puzzling business of "35mm lens equivalent"
« Reply #107 on: January 19, 2012, 04:10:44 am »

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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Fips

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Re: This puzzling business of "35mm lens equivalent"
« Reply #108 on: January 19, 2012, 04:37:36 am »

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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ErikKaffehr

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Re: This puzzling business of "35mm lens equivalent"
« Reply #109 on: January 19, 2012, 05:07:46 am »

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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Eric Myrvaagnes

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Re: This puzzling business of "35mm lens equivalent"
« Reply #110 on: January 19, 2012, 09:56:17 am »

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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-Eric Myrvaagnes (visit my website: http://myrvaagnes.com)

Ray

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Re: This puzzling business of "35mm lens equivalent"
« Reply #111 on: January 19, 2012, 09:58:40 am »

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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Ray

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Re: This puzzling business of "35mm lens equivalent"
« Reply #112 on: January 19, 2012, 10:11:04 am »

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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Slobodan Blagojevic

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Re: This puzzling business of "35mm lens equivalent"
« Reply #113 on: January 19, 2012, 11:57:16 am »

No, I tumbled into a life boat by accident ...

Walter, vada a bordo, cazzo!

Or, in translation: go back on board, &^%*$!!! ;D

Slobodan Blagojevic

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Re: This puzzling business of "35mm lens equivalent"
« Reply #114 on: January 19, 2012, 12:13:18 pm »

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. ;)

Rob C

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Re: This puzzling business of "35mm lens equivalent"
« Reply #115 on: January 19, 2012, 01:12:13 pm »

You mean, like in less is more, Slobodan?

Rob C

AlfSollund

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Re: This puzzling business of "35mm lens equivalent"
« Reply #116 on: January 19, 2012, 04:02:59 pm »

(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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jonathanlung

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Re: This puzzling business of "35mm lens equivalent"
« Reply #117 on: January 19, 2012, 04:30:39 pm »

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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Ray

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Re: This puzzling business of "35mm lens equivalent"
« Reply #118 on: January 19, 2012, 10:10:46 pm »

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.

Quote
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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hjulenissen

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Re: This puzzling business of "35mm lens equivalent"
« Reply #119 on: January 20, 2012, 01:37:46 am »

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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