Quote Originally Posted by Ara Ghajanian
What was happening to my negs was a very very subtle version of this example. The only way I noticed it was because I photographed something on a very green lawn and the grass at the bottom corners of the frame (vertical orientation) was a bit darker.
Ara, I realize that there's probably no grass in the upper corners of the frame. But is whatever is there darker in the corners too?

And what filters and lens hood did you use? If you used one of those collapsible rubber hoods, take a shot or two without it.

Dave, the cutoff isn't due to the diaphragm, its due to a field stop (shouldn't be one in a 50/1.4 Nikkor, but there is one in the 75/4 Apo Rodagon D 1:1) or some other mechanical obstruction, usually at the front of the lens or to the lens' design (the 38 Biogon with which I took my example shot). I hang a number of lenses in front of a #1 on my little Graphics, always worry that the shutter's barrel will block the peripheral rays.