Why is so much nonsense talked about telephoto compression?

I have that book by Ansel Adams and I agree that he does not appear to mention print viewing distance.

On the other hand, the Leica Manual by Willard D Morgan and Henry M Lester (2nd edition, 1936) when discussing perspective and the various Leica lenses, says:

"... we must give consideration to the size of the enlargement and the distance from which we look at it. But in general we may assume that an enlargement of 5 x 7 inches is held about 10 to 12 inches from the eye and as the size of the enlargement increases we also increase the distance from which we view it.

"Under these conditions the most favourable focal length of a lens for the negative size of the Leica camera is 50mm. A lens of this focal length will yield images of the most natural perspective."

The Manual of Photography (7th edition, 1978), first published as the Ilford Manual of Photography in 1890, has a lot to say on "Perspective on viewing a photograph".

They define correct perspective as the perspective obtained when a print "is viewed at such a distance that it subtends at the eye the same angle as was subtended by the original scene at the lens."

They go on to discuss in detail what this means and how to achieve it.

When you call simple magnification/zooming in compression, it's not really a definition.

This is just repeating the same nonsense you have said before. It has been answered many times already. Read my thread on telephoto compression. I know that it is not easy to understand, but it is worth the effort.

Also, think about depth perception and what things create the illusion of depth when we view the world (the human eye creates a two-dimensional image). The relative angular sizes of objects is an important cue, but even more important is the absolute angular size of a familiar object.

Tom, went back to the thread title and thought about a direct answer to it, from another direction...

I think people talk the "nonsense" because a photo of a telephoto "crop" of a scene doesn't look like what they normally see. The eye "lens" is effectively a very wide-angle lens, with about a130 degree field of view. We do have some sort of "selective vision" that focuses our attention to the center of the FOV we're presented with, but it's still nowhere near the selectivity of a long telephoto "crop", or "magnification". So, such a rendition to us looks "compressed", regarding objects at different distances. Simple as that.

Back in the day, on 35mm film I was taught that 50mm was a "normal" lens, approximating the human perceptive FOV. S'why I almost never used that lens; my 28mm was almost welded to my F2, because it made renditions of scenes "interesting"...

Edit: gee, too many "air-quotes" 😆

I think you may have hit upon the problem there. The older books that I have read say that 50mm is normal not because it approximates the human field of view, but because it approximates the original perspective (when the print is viewed from a distance just greater than the diagonal).

This emphasis on the human field of view seems to be an entirely modern explanation. I have never heard of any sound scientific basis for it. How does one define the human field of view, for instance? As you say, our full field of view is very wide, but our field of view for sharp vision is very narrow.

Ansel Adams also said that he disliked normal lenses and preferred the more interesting perspectives of either wide-angle or long-focus lenses. Normal lenses have undoubtedly fallen out of favour.

I got the 130 degree number from a Google search, University of Houston course material the top result. We can trust that, no? 😆

The field of sharp focus is about the size of a 50P coin I was once told. I guess our eyes work like a scanner. Human and animal vision is incredibly complex. Our brain assemble a lot of data that falls on the rods and cones.

I have also heard that our eyes have the field of view of a 28mm lens, so who knows.

Well, that may or may not be scientifically sound, but even if it is, how does it relate to a 50mm lens which has a field of view measuring 40 degrees wide, 27 degrees high and 47 degrees diagonally?

Yes, that seems to be ten times worse in the age of the internet and so much instant communication.

Bob, I'm not sure what you mean by that? I thought all digital viewfinders were 100%. After all, why would they arbitrarily crop a little off the image? What do you mean by being aware of the VF frame?

Same size implies same perspective, n'est-ce pas?

See two FlickR links to images shot from the same position by member @SandyF here:

www.dpreview.com/forums/post/67050529

They were shot from the same position by two Sigma compacts DP1 and DP2 ... 16.6mm and 24.2mm respectively and showed no unequal compression when the DP1 image was zoomed in FastStone Viewer to equalize object sizes betwixt the two. She told me to delete my example, unfortunately.

Cropping eliminates that effect of course.

In that wiki article, there's no references/proof that the absolute angular size is more important. On the contrary, it talks more about the relative angular sizes.

At least you acknowledged that the relative sizes are somewhat important, which is different from your original statement where you claimed that the compression doesn't depend on the physical distances at all:

Now about your earlier thread on telephoto compression - your examples are based on "shoot from a long distance, view at a close distance", so again the physical shooting distance directly affects the result.

But you claim that the viewing distance is everything, and I think you need a stronger evidence to support that claim.
At least I don't really see the compression effect fading away as I move an image away from my eyes. It could depend on the type of the scene and visual references in the image that help estimate the relative and actual sizes.

Also I find inconsistent your definition that the compression starts when the lens is > 43mm. How does it align with the claim that the compression depends on the viewing distance?

You are correct, both are important to our perception of depth in a 2-D image.

However, "compression" is caused by magnifying the image, which increases the absolute angular size of everything in the image, but does not change their relative sizes.

I am not saying that relative sizes are unimportant to depth perception, but simply that there is no change to the relative sizes when an image is magnified.

Take an example. Suppose I am looking at a person 100 metres away and another 200 metres away. The person seen at 100m has an angular height of about one degree, while the person 200m away has an angular height of about 0.5 degrees.

If I view the scene through 10x binoculars, the angular height of the first person becomes 10 degrees and the second person 5 degrees. My brain judges their distance away by absolute angular size and therefore thinks that the first person appears to be about 10m away and the second person about 20m away. The distance between them appears to have shrunk from 100m to 10m.

You get exactly the same effect by taking a photo with a 500mm lens and making a 5" x 7.5" print and viewing it from about 10" to 12" away.

Cropping and enlarging the crop gives exactly the same effect as using a longer focal length. Both give the same compression in our perception of depth in the image.

See also my reply to Quarkcharmed.

Now you are telling blatant lies because I never said that.

What I actually said is

dprevived.com/t/why-is-so-much-nonsense-talked-about-telephoto-compression/3111/post/42185/

Not in my images after cropping.

Your definition of "lens compression" is clearly different to what I use.

What I'm actually saying is that relative angular sizes are more important (they depend on the shooting distance).
Absolute sizes of familiar sizes of objects are also playing their part but there's other visual cues including relative sizes of objects.

Again take the same example (shot #2 that I posted above)

... and zoom in (by cropping)

I don't really see the effect of compression here. That's because the shooting distance was short enough to produce the corresponding perspective.