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What does the term "background compression" mean? How would you tell you're achieving it, and how would you achieve it? Ideally, the right answer would also explain how this is related to background blurring. For example, is compression completely different, or does it sometimes give you some blurring.

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Note: I had a hard time picking a tag for this. Anyone who has a better idea on tags, step up and retag. –  jfklein13 Aug 16 '10 at 19:11

1 Answer 1

up vote 14 down vote accepted

"Background compression" is part of how we perceive perspective in a photograph. Images taken with a narrow field of view (longer focal lengths) will appear to have a shorter back-to-front distance than those with a wide field of view (shorter focal lengths).

It's important to remember that perspective, technically speaking, does not depend on the lens, only on your distance to the subject. If you take a shot with a wide-angle lens and crop down to the very centre, you would have the same background compression as if you took the shot with a telephoto lens (though likely not the same image quality, thanks to the crop and enlargement).

The perception of perspective in a photo is related to the fact that even though they capture wildly different fields of view, we view most photos at approximately the same size (in print, on screen, etc). A wide-angle shot is crammed into a smaller angle of view, and the narrow field of view of a telephoto shot is expanded. If you printed a wide-angle shot large enough (and stood close enough), it would appear perfectly natural.

It follows from this that you're always achieving background compression simply by standing where you stand; it's a much tricker question to figure out how to use it to your advantage compositionally. One example of using a lack of compression (background expansion) would be using an ultra-wide to convey a sense of wide-open space.

This isn't directly related to background blurring; it's possible to have a photo sharp through the entire frame exhibit various degrees of compression. Characteristics of the lens (aperture, focal length, etc) will determine the amount and qualities of background blur.

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In the 2nd sentence you contrast "longer focal lengths" with "wider focal lengths", where I expected either longer vs shorter, or wider vs. narrower. Or am I misunderstanding something, and longer vs. wider does make sense? –  jfklein13 Aug 16 '10 at 19:14
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@jfklein1319 - sorry, that's just me mixing terminology! I'll pick one and stick with it. (One might argue it has some technical basis, but it's definitely less than clear, which is what I think counts.) –  ex-ms Aug 16 '10 at 19:17
    
While I understand the technical basis, I agree it can be a little confusing if you don't have the technical knowledge. As such, your second paragraph kind of has the same mixture: "a wide shot and crop down...shot with a longer lens". It might be good to change that to "...shot with a narrower field of view" or something similar, to maintain the wide/narrow, long/short consistency. –  jrista Aug 16 '10 at 23:09
    
@jrista - I've changed it to try and be a little more clear; the second paragraph deals with lenses a little more explicitly, so I've opted for that description there. –  ex-ms Aug 17 '10 at 0:27
    
Looks good. :) –  jrista Aug 17 '10 at 0:42

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