Quote Originally Posted by Yashinoff View Post
F45 on 500mm is probably too large for diffraction to have much effect, the aperture would still be larger than f16 on 50mm.
Sorry. Diffraction depends solely upon the stop, it has nothing to do with focal length. The diffraction limit in LP/MM can be approximated by dividing the stop # into 1500. At f:45 the diffraction limit is about 30 LP/MM regardless of the focal length of the lens.