Why do telephoto lenses prduce........

hewhoknows

hewhoknows

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Matt
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flatter images?

My reasoining on it is that by increasing focal length i decrease the depth of field giving a flatter result. But why? Is it a matter of the shape of the glass in the lens?

Forgive me if im being a bit dim here but really would like to know the technical answer behind this question :shrug:
 
Is it not because the more you zoom in the less light is getting through the lens which in turn lowers your f stop reducing your depth of field, of course if you have a zoom lens with say for example an f stop of 2.8 all the way through the zoom this wouldn't be an issue.
 
Flatter in terms of perspective or flatter in colour?

If it's the former, it's to do with foreshortening and compressing perspective but I'm in no way qualified to tell you why - there was a thread the other day about lenses and someone posted a link to wikipedia, which although not a wholly accurate site to refer to, is at least a good starting point... :)

EDIT: this may help, although I only read the first few words :D
 
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Longer lenses tend to deliver flatter perspective becaase they are often used at greater distance. Perspective is a function of distance, not focal length. If you take the same picture from the same place, with a long and a short lens, and then enlarge the centre of the shorter lens image to the same size, and perspective will be identical.

You can also get flatter contrast with longer lenses, again because of the distance they are often used at. It's atmospheric haze.

And BTW, longer lenses don't give less depth of field per se. If you fit a longer lens, but then move back so that the subject remains the same size in the viewfinder, depth of field is the same.
 
specialman said:
Flatter in terms of perspective or flatter in colour?

:D
Click to expand...

Flatter in terms of perspective.

I've been doing a section of my course which involved taking 2 shots if the same subject; one far away with a telephoto and then walking in a straight line towards the subject to take one close up with a wide angle lens. I shot a building with one at 100mm and one at 10mm and had to explain the differences in perspective and what i thought caused it. the 100mm shot was much flatter than the 10mm shot and although I knew it would be I don't necessarily know the technical reasons why lol!!
 
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You can get a ready visual understanding for what goes on with different focal lengths and flattening of perspective by studying cinematic examples of 'dolly zoom' (AKA 'Hitchcock Zoom' or 'Vertigo Zoom' after its use by Alfred Hitchcock in Vertigo)

http://www.youtube.com/watch?v=Y48R6-iIYHs&feature=related

Most of the shots in that compilation (notably Jaws and Vertigo) show what happens when you move the camera toward a subject on a dolly while zooming out to maintain the principal subject's size in the frame (opening up the perspective as you get wider).

The last two examples, from Goodfellas and The Fellowship of The Ring, show the other way round; zooming in while moving the camera back and flattening the perspective.

You also need to be pretty smart about adjusting your focus while you're doing all this to make it work properly, not that that's really an issue with stills photography. :)

e2a: There's another dramatic pull out/zoom in one here, from Mathieu Kassovitz's La Haine, which also gives you a clear idea of the direction of travel as the zoom doesn't come into play until a few moments into the movement.

P.S. The Wiki link above is slightly broken (for me at least). Try this: Perspective distortion (photography)
 
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