 Reto C. Derungs |
Depth of the field Is it an optical fact that the depth of field of any lens (compared at the same f-stop and focus length) is identical - or not?
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BetterPhotoJim.com - Jim Miotke  Contact Jim Miotke Jim Miotke's Gallery |
As I understand it, this is true.
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Michael Christopher |
Actually this is not true. If you decrease the focal length by 1/2, the depth of field increases by four times. Depth of field is inversely proportional to the square of the focal length. A short lens has more depth of field. A 50mm lens has 4x the depth of field a 100mm lens does.
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BetterPhotoJim.com - Jim Miotke Contact Jim Miotke Jim Miotke's Gallery |
We may both be correct but you are to be commended for catching me on my lazy answer. The true answer all depends upon the meaning of "focus length" in the question. I read it as "focal length" - and was thinking our questioner was referring to lenses of the same focal length - but he may very well be referring to the distance from the camera to the point the photog is focusing upon in the scene. Your answer, though, clearly articulates how depth of field increases as the focal length decreases. If a photographer wants maximum depth of field, a normal or wide-angle lens may be the best choice. If a photographer wants to minimize depth of field - to focus attention of the subject, for example - a 100mm or longer lens would more than likely be the best choice. Then, after selecting the most appropriate lens, the next step would be to manipulate aperture until the desired depth of field was achieved. Thanks again for your answer!
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