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Four thirds, telephoto lenses and perspective compression. (question)

Jonathon Delacour

Subscriber Member
This fascinating collision of fact and opinion illustrates a phenomenon that is explained in a famous research paper (link to PDF) by Justin Kruger and David Dunning titled Unskilled and Unaware of It: How Difficulties in Recognizing One's Own Incompetence Lead to Inflated Self-Assessments.
People tend to hold overly favorable views of their abilities in many social and intellectual domains. The authors suggest that this overestimation occurs, in part, because people who are unskilled in these domains suffer a dual burden: Not only do these people reach erroneous conclusions and make unfortunate choices, but their incompetence robs them of the metacognitive ability to realize it. Across 4 studies, the authors found that participants scoring in the bottom quartile on tests of humor, grammar, and logic grossly overestimated their test performance and ability. Although their test scores put them in the 12th percentile, they estimated themselves to be in the 62nd. Several analyses linked this miscalibration to deficits in metacognitive skill, or the capacity to distinguish accuracy from error. Paradoxically, improving the skills of participants, and thus increasing their metacognitive competence, helped them recognize the limitations of their abilities.
The corollary to unskilled individuals overestimating their ability ("the less I know, the more I think I know") is that skilled individuals consistently underestimate their ability ("the more I know, the more I realize how much I still have to learn").
 
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Abbazz

Guest
Patently and totally incorrect. It's funny how the internet is full of opinions without supporting evidence, haphazardly stated as "facts".
Funny guy, huh?

Of course, and as stated clearly in Robert Campbell's very informative post, focal length has nothing to do with perspective. It's camera distance to the subject that governs perspective. If you don't believe it, I guess you could use some time with a few good technical books on the subject.

Cheers!

Abbazz
 

brianc1959

New member
Brian, Very happy to see you here! :)

[For those who do not know: Dr.Brian Caldwell is a professional lens designer.]
Hi Vivek:
Thanks - and good to see you here as well. I originally found this site because I was (and am) interested in medium format digital backs, but I've recently become a big fan of micro fourthirds and this seems to be the best forum around.

Brian
 

brianc1959

New member
Hello Brian



not knowing enough to know why (but keen to be pointed at readings) are we talking about being out by much or just a little?
Out by enough to make the wrong conclusion. Wide angle lenses tend to have their entrance pupil near the front element, whereas the entrance pupil shifts back toward the image plane in telephoto lenses. So, you would have to move camera and lens closer to the object when taking the tele shot in order to have the telephoto entrance pupil coincide with the position of the wide angle entrance pupil.

The effect of making an error is greater when photographing closeup subjects because the error of entrance pupil placement in the two setups is a sizeable fraction of the object-image distance. If the poster had done the experiment outdoors with a more distant subject the error would have been much smaller and he probably wouldn't have jumped to the wrong conclusion.

Note: The entrance pupil of a lens is often mistakenly called the nodal point by people doing stitched panoramas. Its easy to find using the parallax method if you've got a pano head on a tripod.
 

brianc1959

New member
Hello Brian



not knowing enough to know why (but keen to be pointed at readings) are we talking about being out by much or just a little?
Out by enough to make the wrong conclusion. Wide angle lenses tend to have their entrance pupil near the front element, whereas the entrance pupil shifts back toward the image plane in telephoto lenses. So, you would have to move camera and lens closer to the object when taking the tele shot in order to have the telephoto entrance pupil coincide with the position of the wide angle entrance pupil.

The effect of making an error is greater when photographing closeup subjects because the error of entrance pupil placement in the two setups is a sizeable fraction of the object-image distance. If the poster had done the experiment outdoors with a more distant subject the error would have been much smaller and he probably wouldn't have jumped to the wrong conclusion.

Note: The entrance pupil of a lens is often mistakenly called the nodal point by people doing stitched panoramas. Its easy to find using the parallax method if you've got a pano head on a tripod.
 

JBurnett

Well-known member
Of course, and as stated clearly in Robert Campbell's very informative post, focal length has nothing to do with perspective. It's camera distance to the subject that governs perspective.
Yes, BUT... it's focal length that determines the camera to subject distance, and therefore it's focal length that I choose in order to obtain a particular perspective.

One can fill a frame top to bottom with a person's face using a 17mm lens very close, or a 100mm lens from much farther away (or 8mm and 50mm in 4/3 format). Aside from an uncomfortable working distance, the perspective provided by using the 17mm lens that close is unnatural and unflattering.

Or think of product photography. Assuming the size of the product in the frame remains the same (when shot), the look of the product can be very different depending on the focal length of the lens (not to mention swings, tilts and shifts!).

I guess what I'm saying is that I think of perspective in terms of focal length rather than in terms of distance from subject. And I'll bet many others do, too. If I see a silhouette of a person against a giant ball of a setting sun I don't think "cripes, that photographer was a long way away from the subject", or "man, that must be a tiny crop from a much larger picture". I think "big telephoto".
 

madmaxmedia

New member
Yes, most people think of focal length. But I think subject distance is the better way of considering perspective, then you avoid all the ambiguities and arguments posed in this thread (I was unsure of the answer myself.)

Subject distance is the same, regardless of whether you are shooting M 4/3, full frame, small compact, or your cell phone. But focal length will vary widely depending on the camera (even though normally we all think in terms of 35mm full frame 'equivalent' so when you say 17mm, I know what you mean.)

At least for me, this whole issue about perspective cleared up completely when I realized that subject distance is what we are really talking about- that made it more inherently 'graspable' for me.

Yes, BUT... it's focal length that determines the camera to subject distance, and therefore it's focal length that I choose in order to obtain a particular perspective.

One can fill a frame top to bottom with a person's face using a 17mm lens very close, or a 100mm lens from much farther away (or 8mm and 50mm in 4/3 format). Aside from an uncomfortable working distance, the perspective provided by using the 17mm lens that close is unnatural and unflattering.

Or think of product photography. Assuming the size of the product in the frame remains the same (when shot), the look of the product can be very different depending on the focal length of the lens (not to mention swings, tilts and shifts!).

I guess what I'm saying is that I think of perspective in terms of focal length rather than in terms of distance from subject. And I'll bet many others do, too. If I see a silhouette of a person against a giant ball of a setting sun I don't think "cripes, that photographer was a long way away from the subject", or "man, that must be a tiny crop from a much larger picture". I think "big telephoto".
 

Robert Campbell

Well-known member
Yes, BUT... it's focal length that determines the camera to subject distance, and therefore it's focal length that I choose in order to obtain a particular perspective.

One can fill a frame top to bottom with a person's face using a 17mm lens very close, or a 100mm lens from much farther away (or 8mm and 50mm in 4/3 format). Aside from an uncomfortable working distance, the perspective provided by using the 17mm lens that close is unnatural and unflattering.
Yes, but: I saw a demo of this years ago. A portrait taken with a wide angle, and projected onto a large scren. One viewer was put up close to the screen, and asked for comments. He was so close to the picture that the 'distortion' that the rest of us, sitting farther away saw, wasn't apparent to him.
 

Robert Campbell

Well-known member
Brian,

Thanks for the bit about entrance pupils and perspectice -- I didn't know that. Hedgecoe's pictures are of an old gent in a field, and taken from a distance, so the entrance pupil change is pretty insignificant [I think it's Hedgecoe senior in the pix]

Note: The entrance pupil of a lens is often mistakenly called the nodal point by people doing stitched panoramas. Its easy to find using the parallax method if you've got a pano head on a tripod.
Quite; so some people refer to the 'no parallax point'.
 
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Abbazz

Guest
Yes, BUT... it's focal length that determines the camera to subject distance, and therefore it's focal length that I choose in order to obtain a particular perspective.
I work the other way round: I determine the distance to the subject considering the perspective I want to get, then I choose the lens according to the angle of view needed. An example: in order to avoid to exaggerating facial features in a portrait, I know that I have to stand at least 1.5m from the subject, so I will choose the lens according to the kind of portrait I need to achieve at a distance greater than 1.5m (on 135, it means a 135mm for a mugshot, a 85mm for half body and a 35mm for full body).

That's why people saying "zoom with your feet" make me laugh. You cannot zoom with your feet: if you change position relative to your subject, the perspective changes and you don't get the same picture as if you used a different focal length from the same standpoint.

Cheers!

Abbazz
 

pellicle

New member
Brian

Out by enough to make the wrong conclusion.
...
The effect of making an error is greater when photographing closeup subjects
...
by people doing stitched panoramas. Its easy to find using the parallax method if you've got a pano head on a tripod.
ahh hah ... that explains much ... takes me back to my optics work at uni in 1981

thanks!
 
C

ChrisJ

Guest
This may be a silly question, I'm probably over thinking it.

I know a telephoto lens compresses the perspective. The longer the telephoto the more the effect. At least on the DPreview forums people keep saying 150mm is 150mm and it's just a crop to get a 300mm angle of view. Would that mean a picture taken with the 150mm on a Olympus would have a view then a 300mm lens on something like a D700? The full frame camera compressing the perspective more then the Olympus? Ignoring DoF field differences etc.

Thanks,
Charles
There's a lot of flexing of optical muscle here, unfortunately not a lot of them have actually answerd Charles's question.

Charles you are right, a 150mm lens will behave as a 150mm lens as far as compression or any other criteria is concerned, and likewise for the 300mm lens, the 300mm lens will have more compression. The fact that the different cameras crop a different size from the projected image is neither here nor there.

Chris
 
V

Vivek

Guest
Hi Vivek:
Thanks - and good to see you here as well. I originally found this site because I was (and am) interested in medium format digital backs, but I've recently become a big fan of micro fourthirds and this seems to be the best forum around.

Brian
Hi Brian,

The forum is owned by couple of photographers and the folks its continue to attract are pretty level headed (as exemplified by this very thread).

Great set-up and great folks.

Very good to have you here. It will be a great benefit to one and all. :)
 

kwalsh

New member
There's a lot of flexing of optical muscle here, unfortunately not a lot of them have actually answerd Charles's question.
Actually, if you look at the first four posts it appears the question was answered to the OP's satisfaction back in 2008. The real mystery is why indorock revived it from the dead :)
 
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Abbazz

Guest
Actually, if you look at the first four posts it appears the question was answered to the OP's satisfaction back in 2008. The real mystery is why indorock revived it from the dead :)
...only to add incorrectly -- and rather abruptly -- that perspective depends on focal length. A 300mm lens doesn't "compress" more than a 150mm lens, whatever camera you put it on!

Cheers!

Abbazz
 

sangio

New member
Out by enough to make the wrong conclusion. Wide angle lenses tend to have their entrance pupil near the front element, whereas the entrance pupil shifts back toward the image plane in telephoto lenses. So, you would have to move camera and lens closer to the object when taking the tele shot in order to have the telephoto entrance pupil coincide with the position of the wide angle entrance pupil.

The effect of making an error is greater when photographing closeup subjects because the error of entrance pupil placement in the two setups is a sizeable fraction of the object-image distance. If the poster had done the experiment outdoors with a more distant subject the error would have been much smaller and he probably wouldn't have jumped to the wrong conclusion.

Note: The entrance pupil of a lens is often mistakenly called the nodal point by people doing stitched panoramas. Its easy to find using the parallax method if you've got a pano head on a tripod.

Because I like to make stitched panoramas, I've determined the nodal point (OK, OK the entrance pupil) for the Panasonic 14 - 45 zoom at various focal lengths. When zooming from 14 to 45 mm, the entrance pupil moves back about 10 mm.

The attached image was taken on Lago Maggiore, Italy, this past May, using the G1 and the 14 - 45 kit lens. The dimension of the stitched file is 7200 x 2600 pixels.

BTW if someone can tell me how to attach images so that they show up as regular images, not thumbnails, I'd greatly appreciate it.

regards
Santo
 

woodmancy

Subscriber Member
.........
BTW if someone can tell me how to attach images so that they show up as regular images, not thumbnails, I'd greatly appreciate it.

regards
Santo
Santo, you have to upload them to your free gallery first. Then the URL shown under your image in the gallery needs to be copied down to your post. I use the little yellow mountain icon at the top of the message box.

Keith
 
T

turbo

Guest
Patently and totally incorrect. It's funny how the internet is full of opinions without supporting evidence, haphazardly stated as "facts".


Reminds me of a 'News' item in The Onion.

"The Information Age was dealt a stunning blow Monday, when a factual
error was discovered on the Internet."
 

ggibson

Well-known member
Actually, if you look at the first four posts it appears the question was answered to the OP's satisfaction back in 2008. The real mystery is why indorock revived it from the dead :)
Bah, I can't believe I was caught by a necro. I usually check these things. :rolleyes:
 
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