Question: FF DoF vs APS-C

Started Oct 11, 2012 | Discussions thread
Winder Senior Member • Posts: 1,460
Re: Question: FF DoF vs APS-C

rogerstpierre wrote:

Can anyone explain this to me, as I don't understand: It is widely accepted that APS-C has more DoF than FF because of the sensor size difference, hence leading to the hole argument of FF DoF advantage.

But in the case of a Pentax APS-C camera, where it is using the same FF lens, with the same registration distance, the same focal plane, the same image circle, i.e. all parameters are equal, except that the APS-C sensor is the equivalent of masking the edges around a FF sensor, why would the image projected and recorded on the APS-C sensor by any different than the corresponding area on a FF sensor ?  Makes no sense. I can understand that if you compare an image taken with a 55mm on FF to the same image taken with a 30mm lens on APS-C (i.e. same field of view) that the DoF are different as the FL is different, but both images taken with the same 55mm lens should have the exact same DoF no ?  Am I missing something or is this whole argument about FF DoF advantage just a case of twisted logic ?  i.e. there is no difference in DoF between FF and APS-C.  All that changes, is the distance required between camera and subject to achieve the same result !

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The image taken on APS-C has to be enlarged more to equal the output of the FF (everything else equal).

If you are shooting to equalize field of view between APS-C and FF they you have to step back from the subject with the APS-C and moving father from the subject increases the DoF.

If you keep subject distance the same you will get a smaller FoV than a FF and because of the enlargement of the final output (for equal size) the the APS-C actually has less DoF.

The "advantage" only exists in certain situations and is pretty nominal.  I prefer FF for use with wide angle glass and APS-C for longer glass.  I prefer FF for large prints, but APS-C with really good glass can make excellent prints at a decent size.

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Contax 645, Canon 5D (sold), Olympus E-3 (sold), Playing with a K-7 and K-5

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