Canon FD 28mm f/2 breech mount, S.S.C.
Canon EF with mirror and diaphragm prefire 

Vignetting = C @ f/2, B @ f/2.8, A- @ f/4 & f/5.6, A thereafter
Distortion = slight barrel 

Aperture  Center    Corner
f/2       C         C
f/2.8     A         B-
f/4       A         B+
f/5.6     A-        B+
f/8       B+        B+
f/11      A-        B
f/16      B+        B
f/22      B+        B

Note: 

high contrast at f/2.8 and f/22;

moderate contrast at f/2.