Physics and Photography

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JazzKennyWowy
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Physics and Photography

Postby JazzKennyWowy » Wed Mar 14, 2018 3:56 pm UTC

Is it possible to figure out the distance of an in focus object was from the camera when the photo was taken? I was thinking if you knew the aperture, focal length, and the sensor size (probably matters if not full frame) which most photography websites have the option of including with photos. If the depth of field was too large you couldn't but with a shallow depth of field I bet you could get a pretty accurate measurement.

speising
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Re: Physics and Photography

Postby speising » Wed Mar 14, 2018 5:50 pm UTC

No.
Proof: you can focus on different things without changing any of the mentioned parameters.

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gmalivuk
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Re: Physics and Photography

Postby gmalivuk » Wed Mar 14, 2018 8:16 pm UTC

In particular, the problem is that the focal length is related to the actual distances by the equation 1/s1 + 1/s2 = 1/f, where s1 is the distance (from the front nodal point) to the in-focus object and s2 is the distance (from the rear nodal point) to the film or sensor.

If f = 50mm and s2 = 55mm, then s1 = 55cm. If s2 = 51mm then s1 = 255cm.
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Re: Physics and Photography

Postby doogly » Wed Mar 14, 2018 8:23 pm UTC

Is not s_2 very knowable by cameras?
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gmalivuk
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Re: Physics and Photography

Postby gmalivuk » Wed Mar 14, 2018 8:32 pm UTC

It's presumably entirely knowable by the camera, but I don't believe it's typically stored in image metadata.
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