Why is so much nonsense talked about telephoto compression?

If both pictures (15mm and 800mm) were taken from the same distance, and you crop in the 15mm image enough (supposedly having infinite resolution in the image), you would achieve the same image as the one taken with 800mm.

Except maybe for the depth of field, that I still have to think about, I'm still not versed on this topic of depth of field - aperture equivalence between focal lengths. I know what f/XX means, I know what it does on the depth of field, but have still to think about it thoroughly to be sure.

Now on the 'telephoto compression', I always understood it as the capability of a telephoto lens to show foreground, subject and background somehow 'closer' to each other than it is, simply by using a very narrow angular cropping through reality. And a good amount of depth of field if one does want foreground and background in focus, to achieve fully this 'compression' effect. With shallow depth of field, this 'compression' is less visible, and the subject is simply isolated by foreground and background blur.

I do not venture on the topic of 'proper distance to look at a print' and effect it can produce, nor if there are rules to respect there.

Greg

"Why is so much nonsense talked about telephoto compression?"

It could have something to do with people posting it up in forums!

If I see an explanation that doesn't make sense, then I describe it as nonsense. Are you seriously suggesting that I should not use the word "nonsense"?

Why? What is objectionable about that word?

In terms of DoF you should think in terms of reproduction ratio. If you fill the frame with a house fly you get only a slice in focus @ f/22, while if you build an artificial house fly the size of an actual house and fill the frame with it, you'll get it front to back in focus @ f/4.

So in the above portrait examples the DoF with the 800mm lens is very thin because the head fills the frame. While if you shot the 15mm portrait from the same location the DoF would be infinite because the reproduction of the head on the sensor would be microscopic.

You don't know why you posted this?

I avoid this style. It makes everybody angry instead of wanting to hear your opinions on the matter, taking the discussion to a personal level. Moreover, it might not be as nonsensical as you think, just a different view, or a different understanding of the matter. E.g., if you say that compression is generated by the viewing distance to the final photo, you have a very different meaning of the term "compression" than I have. I still would not call your words nonsense.

I agree about avoiding terms like "nonsense" when talking about other people's opinions. However, what I was talking about was not opinions, but science. A scientific statement is a matter of facts and logic, not opinion. It is either right or wrong. Let me correct that: it is either possibly right or wrong. General scientific statements (theories) can never be proved right, although they can be proved wrong.

If you think something is wrong, then it is best to say so, rather than put it in euphemistic terms.

I used the term "nonsense" to describe a theory that I think is logically wrong. I think most people who talk about telephoto compression get their facts right (more or less). What they get wrong is the logic used in constructing an explanation. It doesn't make sense, hence the term "nonsense".

There was no personal criticism in my OP. It was criticism of the common explanations of telephoto compression.

I mean the compression that is seen when looking through a telescope, which is exactly the same as the compression seen when you view an image from a shorter distance.

For example, if you view an image from 4 metres away and then move in to only 0.4 metres away, what you see is exactly the same as standing 4m away and using a 10x telescope to view the image. Try it and see for yourself. You need to start with a telephoto image (say 500mm lens) and print it at about 8x12 inches or thereabouts. From 4m away you'll see it with approximately normal perspective, while from 0.4m it will look just like looking through a 10x telescope.

Yup.

I'd like Tom to confirm whether this is the effect he is referring to, what he calls "nonsense" or whether he is talking about something else.

What will look the same? The ratio of the size of the foreground to the background? Are you saying that moving further away from a print will suddenly change the relative sizes of subjects in the print? That makes no sense to me, I don't believe that is what you mean at all. So what do you mean? I guess there is no chance of getting everyone on the same page until we can standardise the language we are using and everyone is talking about the same thing.

I think the problem with the word "nonsense" is that, although it is a perfectly fine word in itself, it has attracted a pejorative undertone - people most commonly use it as a euphemism for "you are incorrect because you are an idiot". These days it's an emotion-laden aggressive word. Best avoided.

Better to say something gentle like "that's not quite right", then you have created a mood in which other people are prepared to listen. Language is primarily used to influence the emotions of your audience, rather than for precise descriptions. Although engineers may regret that fact, it is nonetheless true. One of the reasons why people lie so frequently and effectively.

There are two effects present in those photographs:

1. The camera positions are different so the camera perspective is different in the two photos.

2. Two different focal lengths are used, so the viewing perspective differs also (if the images are viewed normally).

The first effect dominates in causing the facial distortion. The second effect is not really noticeable as the background is blurred so much in the second image. If the background was sharp, then the telephoto compression would be noticeable: the background would appear much closer to the camera (and hence closer to the subject as well).

The facial distortion is not caused by telephoto compression (effect 2), but by a change in camera perspective (effect 1).

While I will stop short of using the term "nonsense", I will say that from what I have read here there is still a great deal of misunderstanding about this topic.
Watch the first part of this video to see "Compression" debunked. This is the best example of how distance from subject and background works. I might add this Photography Channel is amongst the very best I have seen anywhere.

Essential Skills

That video repeats the very nonsense I was talking about!

It is an excellent example of thoroughly muddled thinking.

Using a long focal length causes compression provided you view your images in the same way (i.e. from the same viewing distance relative to the size of the image).

Using a long focal length has the same effect as looking at the scene through a telescope or binoculars. You see a compressed view of the scene.

It is all to do with our perception of depth in a two-dimensional image.

Have you ever used a pair of binoculars (or a telescope)? When looking through the binoculars, everything looks closer. Distances from the viewer all appear to be compressed. It is, of course, just an optical illusion. Nothing has actually moved. Looking through the binoculars creates the illusion that everything is closer to the viewer.

You get exactly the same effect when using a long focal length lens. It creates the illusion that everything is closer to the camera.

Read my posts in this thread for further explanation.

Let me analyse the argument that is so often presented when talking about telephoto compression and show where the error occurs.

The first step is often to say that a shot taken with a 500mm lens is exactly the same as a small crop from the centre of a shot taken with a 50mm lens (assuming the camera position is the same for both shots). I agree.

The second step is to conclude from this that the perspective seen by the camera is exactly the same for those two shots. It doesn't matter what focal length is used. That is also correct.

The third step is to conclude that the perspective seen by the viewer is exactly the same when viewing the two shots. This is where the error occurs. The perspective seen by the viewer depends on the distance between the viewer's eye and the image, relative to the size of the image.

A number of people here have told me that that is nonsense. They say that it is obvious that it's the same image whether you view it from one foot away or ten feet away and so the perspective must be the same. I agree that it is the same image and the camera's perspective has not changed.

However, the viewer's perspective changes with viewing distance.

Try this little experiment. Take any telephoto image that shows good compression, e.g. the background looks much closer to the subject than was the case in real life. Display (or print) it at about 36x24cm in size. If it was taken with a 500mm lens, stand 500cm away from the image to view it (or 600cm away if taken with a 600mm lens, etc.).

You will then see it with exactly the same perspective as if you viewed the original scene from the camera position. The image in your eye will be exactly the same size and shape as if viewing the original scene from the camera position. The image will look perfectly normal and not show any telephoto compression, or any other perspective distortion.

If you stand 500cm away and use 10x binoculars to view the image, you will see an enlarged perspective that shows telephoto compression. What you see through the binoculars will be exactly the same as if you viewed the original scene through 10x binoculars.

If, instead of using binoculars, you step closer and view the image from 50cm away you will see exactly the same perspective as when using the binoculars. That is a more normal viewing distance for a 36x24cm image. At this viewing distance the image shows telephoto compression in the same way that 10x binoculars show telephoto compression.

Try the experiment for yourself.

Telephoto compression, ISO sensitivity, both incorrect abstractions of somewhat complex topics. Heck, I've seen the second one in camera manuals...

I think both terms speak to what the viewers of images are seeing, the result of various photographer decisions. And then, talking to folk who just want to make images, understanding the underlying mechanism only to the extent that they need to do that. I don't like such, but I get it...

Yes indeed, but I find it quite worrying that seductively slick and simple explanations have gained so much traction despite being incorrect, while the correct explanations have been largely ignored and forgotten about.

I'm not sure what can be done to remedy this situation, other than taking every opportunity to give the correct explanation, even though it is less simple and takes a lot more effort to understand.

Pure epistemological idealism...

It is called snowflakism... pedantic Karens/Kevins that get their knickers in a twist about anything.