Originally posted by robgo2 I'm not sure about this point. It is often stated that one of the advantages of FF over APS-C is its ability to achieve shallower DOF. I have always assumed that this took FOV into account, but I may be wrong.
It does, in a way. There are quite a few lengthy discussions of the topic in other threads, but the gist of it is, if you keep the same f-stop, then indeed, the FF camera has less DOF. So 77 @ f/1.8 on FF has less DOF than 50mm @ f/1.8 on APS-C. You get "equivalent" DOF by matching the physical aperture size rather than the f-stop (which is a ratio of aperture size to focal length).
Anyhow, my point mainly had to do with the fallacy that a lens has some inherent "perspective" that creates some specific amount of "distortion" that is a function of focal length. Those qualities are actually a function of subject distance, which in turn is a function of angle of view. So for two camera/lenses combos that produce the same angle of view, perspective/distortion is precisely the same even if the focal lengths involved are different. The post to which I had been responding appeared to be implying otherwise. But it is true you need different f-stop values (but the same physical aperture size) to match DOF.