Read any book about the technical aspects of photography, and you'll run across diffraction limiting, which is usually supposed to kick in at an F stop of 16 or 22 and be noticable by 32.
Now compare the absolute size of, say, a 20mm prime stopped down to f22 and a 100mm prime at f22. Your eyeballs tell you the 20mm aperature hole is a lot smaller than the 100 hole, but the 100 hole is farther from the film plane.
Question: Is it the absolute diameter of the aperature, or some formula taking into account diameter _and_ distance from the film that causes diffraction limiting?
In other words, does diffraction limiting affect a 20mm lens set at f22 _MORE_ than a 100mm set at f22? I asked a physicist friend about this one time, and he started talking like a politician. In other words, to put it bluntly, he bullshitted me rather than admiting he didn't know and couldn't calculate a reasoned answer.
-Lon
