Canon FD 28mm f/2.8 S.C. breech mount
Canon F-1 with mirror and diaphragm prefire

Vignetting = B @ f/2.8, A- @ f/4, A thereafter
Distortion = barrel

Aperture Center Corner
f/2.8    A-     B
f/4      A-     B+
f/5.6    A-     A-
f/8      B+     A
f/11     A-     A-
f/16     B      B
f/22     B+     B+

Note:
high contrast at all apertures.