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

... 'The Camera' by Ansel Adams (Little, Brown & Company, 1980), p.106.

It is true that the perspective captured in the image depends only on the camera position (relative to the scene being captured).

However, the perspective seen by the viewer of a photograph also depends on the viewer's position (relative to the image). Photographs are usually made to be viewed and any comprehensive discussion of perspective must include the viewer's viewpoint as well as the camera's viewpoint. This has been known for a very long time and at least back to the theories of perspective developed in the fifteenth century.

Adams's misleading comments on this subject have been widely quoted and seem to have misled a whole generation of photographers. This misinformation has been copied many times on the world-wide web so that today there are hundreds of tutorials and articles available online that repeat essentially the same fallacy that telephoto compression and wide-angle distortion depend only on the camera position.

The excellent 'Manual of Photography' (originally published in 1890 as 'The Ilford Manual of Photography') contains a more accurate scientific description of perspective, including separate sections on 'Perspective on taking a photograph' and 'Perspective on viewing a photograph'. Here is a brief quotation:

... 'The Manual of Photography' by Jacobson et al. (Focal Press, 7th edition, 1978), pages 85-6.

Correct perspective simply means the perspective seen from the camera position. For correct perspective to be seen when viewing a photograph, the viewer's eye must be located at the centre of perspective of the photograph. The distance between the centre of perspective and the photograph is approximately equal to the focal length of the camera lens multiplied by the enlargement factor.

When the photograph is taken:

For a pinhole camera, the pinhole is the centre of perspective.

When the image is viewed in front of the scene itself:

In this diagram, when viewing the image from the centre of perspective, everything in the image lines up exactly with the scene beyond.

The basic mathematics of perspective is given by the equation:
object size / object distance = image size / image distance

Wide-angle perspective distortion is seen when the viewer is further away from the image than the centre of perspective. Telephoto compression is seen when the viewer is closer to the image than the centre of perspective. We are not at all sensitive to small changes in perspective when viewing photographs, so the changes need to be large before the perspective distortion becomes readily noticeable.

Some random examples of repetitions of the Ansel Adams Fallacy in various guises

Jordan Steele 2014:

Ugo Cei 2020:

Laurence Norah 2022:

Elizabeth Gray 2018:

Lee Morris 2016:

Lee Morris 2018:

Steve Berardi 2010:

Illya Ovchar 2021:

I don't think I am being in the least bit unfair.

All of the articles referenced give example images. I think is it very clear that they all expect the reader to look at their images and see perspective distortion in some of them.

I don't think any of them say how to view their images, which strongly suggests that they are completely unaware that the viewer's position relative to the image will affect the perspective seen in the image.

Also, I think all of those articles were written as tutorials to explain perspective and compression, etc. If they were talking solely about the perspective captured in the image, I would expect them to make that clear to the reader and point out that perspective distortion always depends on the way the image is viewed and not on the image itself.

I don't think any of them even mention the viewer's position or the centre of perspective.

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Yes, because I think it is important to counter misinformation whenever possible. The Ansel Adams Fallacy seems to have spread widely through the photographic community already. In my opinion, those who understand the science enough to see that misinformation is being propagated have a responsibility to try to correct it when they can.

I am sure that this misinformation is not being spread deliberately: those who do it are probably sincere and well-intentioned. However they are mistaken in their understanding and are inadvertently spreading fake science. They need to be challenged and corrected.

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Well, that certainly explains why you would prefer me not to post my criticisms of the Ansel Adams explanation of perspective distortion.

Why does it matter? We have no control over the distance our pictures will be viewed from, if we hang them on a wall, but I guess most of the time a picure will be viewed from a distance that makes this theoretical exposition irrelevant. I suspect most people will view a picture from a naturally comfortable position, that makes the "wrong" information that you have pointed out, empirically true from a practical point of view.

It doesn't matter when taking photographs. It is possible to be an excellent photographer without understanding the theory, just as it is possible to be an excellent driver without understanding how your vehicle works.

However, many photographers seem to think that other photographers are interested in the theory of perspective, witness the large number of tutorials on the subject of perspective and perspective distortion, a few of which I gave links to.

For example, the article by Jordan Steele goes to great lengths to show that it is a fallacy to claim that focal length is the cause of perspective distortion. However, his claim that it is not focal length but camera-to-subject distance that causes perspective distortion is equally a fallacy and suffers from much the same logical errors.

What I object to is the use of fake science (i.e. incorrect science) to explain what is going on. If you are trying to explain the theory of perspective, then it should be based on sound science, not on pseudoscience. Incorrect science should always be called out for what it is, whether it is in a book by Ansel Adams or in an online tutorial.

A sound theory of perspective distortion should be able to predict reliably whether or not it will occur in any particular situation. Those who believe that the Ansel Adams Fallacy is good science should be able to give a precise method for predicting how much (if any) perspective distortion will occur in any given situation. To my knowledge, that has never been done (at least, not in a way that is consistent with their original statements that it depends only on the camera position). I'm still waiting!

Meanwhile, those who understand the classical theory of perspective know that perspective distortion occurs if the viewer's viewpoint is not at the centre of perspective. If the viewpoint is closer, then telephoto compression occurs. If the viewpoint is further away, then wide-angle distortion occurs. Of course, you need to know how to work out the location of the centre of perspective. For a telephoto lens the centre of perspective is a long way from the image (relative to the size of the image), while for a wide-angle lens the centre of perspective is very close to the image (relative to the size of the image).

If the distance between the centre of perspective and the image is approximately equal to the length of the image diagonal, then that is, by definition, a normal focal length.

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There isn't one single definition of perspective as it is really a whole subject rather than a single idea. Read the introductory section of this article by Bruce MacEvoy (up to the page index).

Dictionaries usually say something roughly along the lines of "perspective is the art of creating the impression of three dimensions in a two-dimensional picture"

I agree that terms like "fake science" and "fallacy" and "myth" and "bunk" are not scientific and perhaps I should not be using them.

However, when I read many online tutorials on things like telephoto compression, I see such terms being widely used to try to discredit sound science.

I am just trying to fight back!

For example, the article by Jordan Steele begins:

It is not a myth that focal length will project a specific perspective.

However, for it to be true, a couple of (very reasonable) assumptions must be made: (i) we are assuming the focal length is being used on a specific sensor size, say FF; (ii) we are assuming that the resulting photographs are uncropped and viewed "normally" (from a distance roughly equal to the length of the diagonal). If these assumptions are satisfied, then the statement is far from a myth: it is true.

It is no reason to call something a myth and a fallacy simply because it is often stated without making explicit a couple of quite reasonable assumptions. Instead of calling it a myth and a fallacy, he should have simply pointed out that a couple of important assumptions should be made explicit.

However, that would negate the title of his article "Perspective - Correcting an Oft-repeated Myth" and be much less sexy.

Many of these articles have a reforming zeal that would be commendable if they were advancing the cause of science. But they are not. They are trying to replace a perfectly good theory of perspective, known for centuries, with a hand-waving non-theory.

I call it as a non-theory because it is incapable of predicting anything useful. I have asked some proponents of the Ansel Adams Fallacy how I can predict if a particular shot will show telephoto perspective and I have never had a satisfactory answer. On pressing for an answer, it sometimes eventually comes back as something like "use a telephoto lens and make sure the background is well separated from your subject", which is a common sense answer, but one that completely contradicts the statements "true perspective depends only on the camera-to-subject distance" and "focal length does not affect the perspective in a photograph."

There is a seductive simplicity to statements such as "focal length does not affect the perspective in a photograph" and "true perspective depends only on the camera position", but they do not by themselves constitute a theory of perspective that can be put to practical use.

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