Quote Originally Posted by KennyMark View Post
Stone,
Most lenses have a curved field of focus. Macro (or as is technically correct, Micro) lenses are generally designed to have a flat field of focus, in addition to having fewer optical problems (such as chromatic aberation for one possible issue) when focused closely. This is a gross generalization, so there will always be exceptions, but I know that you have experience in using the google for a better explanation than mine.
+1

True macro lenses are optimized for close work. Non-macro lenses are optimized for farther distances.

The Mamiya 140mm C lens is a true macro lens. The adjustable floating element means that it also performs quite well at farther distances.

In the 35mm world, you have to be careful. There are lenses out there that are labelled "macro" which more properly should be labeled "can work close".

Flat-field performance matters the most for flat subjects.