I recently got a 35mm Summicron ASPH for my M9 (2012 serial number).
I am surprised and disappointed to see definite softness in the image center at the f 4 - 5.6 range. The image is fine away from center all the way into the corners. At larger apertures it seems OK and it is fine again at f8.
The MTF chart does not seem to reflect this softness at all, nor did I expect it at what is rated to be an excellent lens.
I would appreciate comments on your experience with this lens, as I suspect (hope?) that the issue is an isolated one.