The Ansel Adams Fallacy: "True perspective depends only on the camera-to-subject distance"

It's also irrational to claim that changing the viewing position of the image changes the lighting angle in the scene. These are separate effects. Perspective is ONLY changed by changing camera position. Human perception of the image in relation to how the image is projected/displayed is a separate topic only peripherally related. Neither one controls the other.

But I didn't say that, here's what I did say in the reply above:

dprevived.com/t/the-ansel-adams-fallacy-true-perspective-depends-only-on-the-camera-to-subject-distance/5326/post/71998/

I've already tried to show you where observation fails to support your theories but you seem so entrenched in your position that you seem also to be unable to see. You just assume I haven't checked or that I must be wrong. I don't need to ask if you have experimented as I know you have, but the trouble is you seem literally quite blind to anything that contradicts. And even though you accept that human perception differs form pure geometry you don't seem to apply that to your own vision. You still talk about reality being what you see and assume that you are looking at pure geometry.

You're wrong about the effect viewing distance has on perspective, your conclusions are not supported by observation. Basically all that happens is when you view images at the wrong distance you see a distortion that is similar to the truth of the pure geometry or perspective defined by camera position. As you change position towards the centre of perspective that distortion disappears. It doesn't reverse. "Wide angle distortion" and "telephoto compression" work in opposite directions and they are both defined by subject distance alone, this is not reversed by the distance you view the image.

Ansel Adams is not wrong, it's mathematically correct and it's a good way to visualise it. The full scientific explanation also involves human perception and so takes a perceptual leap that you are unwilling to entertain as even just a remote possibility.

Changing the viewing position changes the angle of view, but who said anything about lighting?

There is a very well-established theory of perspective that explains mathematically what happens when we make a 2D photograph of a 3D scene from a given camera position. That theory also explains mathematically what we see when we look at that photograph from a given viewing position in comparison to what we saw when looking at the original scene. Any good mathematician has no problem understanding both of these.

As I understand it, you fully accept the first part (taking the photograph), but you do not accept the second part (viewing the photograph). Is that correct?

The "perceptual leap" that you refer to is simply an excuse to avoid a proper scientific explanation. Either you can explain clearly and logically what you mean or your theory is effectively nonsense.

So, please explain what you think observation would show in the following situation.

You take a photograph of two people, both of height 1.8m. One is standing 10m from the camera and the other is standing 20m from the camera.

The photo is viewed from (1) the centre of perspective, and (2) the point halfway between the centre of perspective and the centre of the image.

How would you describe what is seen in each of those two cases? What is the difference between the two?

Please answer the question and do not use evasive tactics.

Although the question is not addressed to me, I would say:

Case (1) the person at 10m subtends twice the angle of the person at 20m.

Case (2) the person at 10m subtends twice the angle of the person at 20m.

Ergo, no difference, 😉

If you assume that the absolute size of the image makes no difference then it is easy to prove that the viewing distance makes no difference.

But why do you assume that the absolute size is unimportant? I think this is probably the key to the whole of this discussion. I think Ansel Adams assumed that an image always looks exactly the same whether you look at it as a 4" x 5" print or as a 4' x 5' print.

If you view a 4" x 5" print alongside a 4' x 5' print of the same image, they will look like two prints of the same image. However, it is also obvious that one is much larger than the other. Why assume that the absolute size has no effect on how we "see" the two prints?

Leon Battista Alberti (1404 - 1472) wrote:

In other words, he thought that viewing distance does matter.

It puzzles me that so many photographers today are willing to assume that viewing distance does not matter and think that it is obvious that it doesn't matter.

It is obvious to me that it doesn't matter if you are purely seeing the photo as a 2D object. However, if you are viewing the photo in a situation where it is possible that you could imagine that you were looking at a real scene, then I think it is obvious that the angular size with which you see objects in the scene does matter and affects your perception of depth in the scene.

Suppose you are looking through a keyhole into a room containing two people. How do you judge depth in that situation? The keyhole is very small and prevents you from using binocular vision to judge depth. It also prevents you from moving your head from side to side to use parallax to help judge distance. Yet most people can easily tell if both people are standing close to the keyhole or if they are standing some distance away. How?

Yes.

LOL 😂😂😂

You sure about that?

Let's try again. But I have no illusions that you will read this with an open mind, people can get so rooted in their own opinions that they can't see far enough beyond them even to see actual words right in front of them. Such is the nature of human vision 😀

Didn't you state in the OP?

And also you clearly said a short while ago:

Now call me old fashioned and a stickler for maths, but your statement from the OP clearly suggests that you are at a null point where you see neither "telephoto compression" nor "wide angle distortion". And your statement above clearly links the centre of perspective to a reality that is governed by pure geometry and that reality directly to what you see.

But pure geometry dictates that when I view an image of a distant object I should see foreshortened or "telephoto compression" at the centre of perspective because that is the pure geometrical reality of the perspective from that point.

The problem is, and always has been, that you think your vision is absolute and so just automatically relate what you see to pure geometry without even thinking. So let's cancel that assumption and look at what we see and the world as described by pure geometry side by side and see if they do line up.

When I view an image of a distant object from inside the centre of perspective I see the perspective as being roughly what pure geometry predicts, foreshortened. As I move away the perspective looks normal and then just stabilises. If I view an image of a close object from outside the centre of perspective I see the perspective as being roughly what pure geometry predicts until I reach a point where it look normal then I reach a point where my nose is against the print. It never looks foreshortened and my understanding of distant objects stays remarkably constant.

So if we view images of distant objects from too close, or images of near objects from too far, then we see something similar to the correct perspective as described by pure geometry. As we move towards the centre of perspective the perspective we see resembles what we see in the real 3D world.

That is it, that is the entirety of what observation shows us. This never reverses with viewing position so close objects never display "telephoto compression" and vice-versa.

The statement below is scientific fact, demonstrated and confirmed countless times, even the Renaissance painters understood this:

Eye and Brain - R L Gregory:

"When an artist employs strict geometrical perspective he does not draw what he sees-he represents his retinal image. As we know these are very different; for what is seen is affected by constancy scaling. A photograph, on the other hand, represents the retinal image but not how the scene appears... ...The camera gives true geometrical perspective; but because we do not see the world as it is projected on the retina, or in the camera, the photograph looks wrong."

Now your theories, assumptions and predictions directly contradict this. My observations in bold above don't.

The world of pure geometry describes a world where perspective is the distortion in the shape of objects caused by a single viewpoint, and that pure geometry must predict a world where perspective is in constant motion relative to viewpoint.

I think that they have also figured out that this isn't quite how the world appears to us. And I've already described in a previous post the effect of constancy scaling, and just how that would work if you applied something calibrated to cancel that motion to an object that displays a static perspective like a photo. Guess what? Yes, it also fits perfectly with the observations in bold above.

Really? I've already been through how you can't relate human vision directly to pure geometry, how constancy scaling prevents this, how we only ever see the front elevation and have no knowledge of the side elevation, etc... etc...

And what do you do? Try to force me to describe human vision in terms of pure maths and only in pure maths or be labelled evasive and dismissed by youself.

I don't fall for tricks like that, and I don't find them to be very objective or scientific.

How about a diagram, and some maths to back it up?

First of all, it wasn't a trick. I simply asked you to explain "what you think observation would show in the following situation." I didn't force you to describe it in terms of pure maths or anything else. I was curious about how you would describe it. It seems that you don't want to describe it at all, except in very vague generalisations, e.g.

Nothing precise there, no mathematical formulas, almost nothing of any practical value to anyone.

I like to give people the benefit of the doubt and give them every opportunity to explain themselves more fully and in more detail if I cannot understand what they say. You have been given every opportunity, but you simply repeat the same vague statements time and again and refuse to go into any more detail, yet you have the temerity to criticise the theory of perspective that has been understood for centuries and claim that it is not possible to explain what we see in a photograph in terms of mathematics.

You claim that you agree with the statements about perspective in the Manual of Photography, but you then proceed to describe perspective in your own fanciful ways that contradict the traditional understanding of perspective.

I guess that you will continue to talk the same old nonsense and continue to claim that what you say is sound science and that I (or anyone else disagreeing with you) am the one talking nonsense. The Donald Trump technique?

[deleted]

[deleted]

@TomAxford Your theories on perspective contradict the traditional view of perspective, they contradict the maths of image geometry, they contradict what is clear by simple observation and they contradict current scientific theory.

You don't even seem to understand the maths of pure geometry to the point that you can't see the world it predicts, or how it differs from the world we see through human eyes. It's not hard to do this, any halfway competent mathematical can do it.

Instead you take an effect where we see distortion in the fixed perspective of a 2D image when we view it through human eyes and insist that it can be explained through pure geometry alone, even though pure geometry predicts something quite different.

You haven't even worked it out that "telephoto compression" and "wide angle distortion" are the true geometries of the respective images. Instead you take the one point when you view an image and don't see that perspective and use that as the point that you see perspective as described by pure geometry.

I've been trying all through this to prompt you to question your base assumptions and question that you are not looking at this whole thing back to front. But no, TomAxford alone has absolute vision and so what he sees is the absolute truth and this relates directly to pure geometry.

Even though that viewpoint even contradicts pure geometry, and everything else noted above.

It's a nonsense question.

FACT: We do not see the world of pure geometry through human eyes. The camera sees it, and we can glimpse it in images but only if we view them from a position outside the centre of perspective. That is the correct way around. And it's pointless discussing anything until you are able to see just a little way beyond your own opinion, even if it's just the true nature of the world that pure geometry predicts.

No need to "shout", Tom.

I made no mention of the absolute size of the image. My comment referred only to the relative angular size of the two persons.

I'm very sorry, I was not intending to shout, simply trying to be unambiguous and to the point.

I agree that you referred only to the relative size, but you then deduced that there was no difference between the two cases (I assume that is what you meant by "ergo, no difference").

That deduction implied to me that you had assumed that the absolute size was unimportant. Why did you not mention the absolute angular size when it is the main thing that varies when the viewing distance changes?

No one - they are independent concepts. That's the whole point if you had actually read what I wrote.

You're doing the same thing - bringing up an unrelated point (that viewing condition can change human perception of an image) to argue something entirely separate, namely that viewing condition changes perspective, which it doesn't. Only the relative position between the camera and the scene can change perspective.

Yep, I should have said "no difference between the relative angular size of the two persons in the image in case (1) and case (2) irrespective of the absolute physical size of the viewed image" ... thereby trying to avoid misunderstanding by your good self. Pardon my lack of clarity , folks.

I did not feel that it was a factor in the context of my post.

Human vision doesn't maintain relative size and scale when viewing the real world, in terms of human vision it is unimportant.

Because that relationship is not preserved in human vision in the real 3D world it can't be (and isn't) a constant and so is not used in human vision in the way that you envision.

You continue to assume that what you see through your own eyes is absolute and directly equivalent to pure geometry and then apply pure geometry directly to to describe not only what you see, but also provide the explanation of why you see it. And a theory based on such a fundamental error of assumption will turn to mush pretty quickly. Which it does, you contradict known science, simple repeatable observation, even pure geometry and yet fail to notice. I could show you a dozen more images that demonstrate beyond any question that absolute angular size is not preserved in human vision. But it won't make any difference as you will still fail to question your assumptions and still treat the absolute angular size as proven fact. I've raised a reasonable doubt and shown you proof that confirms this doubt, real science would've looked at this objectively, (and did a long while ago).

To everybody else:

Perspective is the distortion of shape caused by a single and unique point of observation, pure geometry dictates that distortion should also be in constant motion relative to movement of the observer. Which it is. This is all obvious if you follow the maths of pure geometry.

But it is a really confusing place for us so we have developed through empirical means a way of cancelling it:

Constancy scaling.

Constancy scaling is a weird but wonderful trait of vision. What this means in practice is that constancy scaling allows us, in the world we see immediately around us and into the middle distance, to subtract that distortion that pure geometry dictates and with it the way shape and relative scale changes as we move. What it allows us is a far more accurate and stable understanding of the true shape and relationships between objects in our immediate environment. Our understanding of the shape of a book, for instance, remains constant no matter what distance or angle you view it. It may be really tempting to relate this directly to pure geometry, only constancy scaling is a proven fact, and it means that your consistent understanding of shape is because the brain is actually altering things like absolute angular size as you move.

It also means that it is impossible to apply pure geometry to human vision because human vision is actively subtracting the effects of pure geometry even as you look at your computer screen reading this. If anybody is actually reading this...

Because pure geometry is relative to distance, constancy scaling is also relative to distance, they wouldn't cancel effectively if they weren't. And so this has an odd effect when we view things out of context, like a photograph of a 3D scene where the relationships are fixed by rendering to a 2D surface and so don't move as we view at different distances.

If you view a photo of a distant object from a distance relative to the camera position (centre of perspective) then you find that constancy scaling has roughly the same effect in both the real world and the photo. But if you stand really close to the image then the brain assumes a closer distance and doesn't apply that constancy scaling, and so you begin to see the true pure geometric perspective as captured by the camera. Do the maths, work out what pure geometry dictates the image should be.

Similarly if you look at a photo of a near object from a distance behind the centre of perspective you brain assumes it is further away and so fails to subtract the distortion caused by viewing at a close distance and again you see something closer to the true pure geometric perspective as captured by the camera. Do the maths, work out what pure geometry dictates the image should be.

Of course the rub is that we learn through experience, and the whole point of constancy scaling is to give us a consistent understanding, so we even learn how to cancel the effect when viewing images. Basically even in images absolute angular size is not preserved.

It also means that mathematically and perceptually Ansel Adams is correct, distortion is primarily and fundamentally a function of camera position, wide angle distortion and telephoto compression are determined by camera position alone as they cannot be reversed by print viewing distance.