Quote Originally Posted by neuroanatomist
So, you can't take the same picture

A technicality. Suppose then that you are using an MP-E 65 or else suppose that your subject is 35mm (then it is 1x on full frame and 0.625x on the 7D).


Quote Originally Posted by neuroanatomist
So, you can't take the same picture - the FF sensor will always show more background than APS-C in that scenario, right? And if that's the case, diffraction-limited resolution would not be the same - subject distance would be the same, and the FF sensor would out-resolve the APS-C, and have deeper DoF, too.

John, if you'll excuse my saying so- and I mean this in the nicest way possible- you're being silly. You are comparing taking pictures with different sized subjects (by subject size I mean the linear size of the focal plane).


If I take one picture that is 15mm across (in the focal plane) and another that is 25mm across, of course I can get more DOF and less diffraction with the 25mm across picture. It doesn't matter which was taken with the small sensor and which with the large.


In other words, my point is just this: there is no *inherent* advantage of a large sensor over a smaller (or vice versa as some have claimed). In other words, assuming I have the right lens and I want to take a particular picture with a given DOF and as little diffraction as possible, I can ask myself, "what is the best sized sensor?" The answer is "it does not matter."