For anybody who can help a young lad...This question is about something I have never quite been able to grasp on my own. I understand how to properly select the optimal F-stop according to Mr. Luong, but I still don't know how to quantify the affects of diffraction. Here is an example. Let's say I photograph a scene at F22 and again at F64. I understand that the one shot at F64 is going to have a greater depth of focus that will be softer overall...even at the critical focus point, but is this going to be visible to the human eye at the original 8x10 size. If not, at what enlargement factor will the F64 shot be noticeably softer at the critical focus point than the F22 shot. Basically, what I am asking is if I shoot the same scene at F22 and F64, and I inspect just the critical focus point (not the depth of field limits), at what enlargement size will I notice a difference in sharpness when viewing the resultant prints at the normal minimal viewing distance of 25cm. By the way, I am shooting with an 8x10 and a Nikon 300mm 5.6 lens. Thank you all.