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Hand-held cameras (even fancy photographer\'s cameras), rarely use film any more

ID: 1473687 • Letter: H

Question

Hand-held cameras (even fancy photographer's cameras), rarely use film any more, but the physics is nearly the same as an old fashioned camera: there is a lens, and a plane onto which the image focuses. (In the old days, the plane was where the film went, now there will likely be a solid state CCD array there. But we still call this the "film plane".) Suppose a 55.0mm focal length lens is used to focus an image onto the film plane. The maximum distance available in this (large!) camera between the lens and the film plane is 106mm.

How far ahead of the film plane should the lens be, if the object to be photographed is 1.2m away?

Explanation / Answer

here,

the focal length of the lens , f = 0.055 m

the object distance , do = 1.2 m

let the disatnce between the film plane and lens be di

using lens formula

1/f = 1/di + 1/do

1/0.055 = 1/1.2 + 1/di

di = 0.0576 m

thefilm plane should be 57.64 mm from the lens

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