Tamron 28-70mm f/3.5~4.5 (Adaptall 2 system)
OM-2S with mirror and diaphragm prefire

@ 35mm setting
Vignetting = B+ @ f/4, A- @ f/5.6 & f/8, A thereafter
Distortion = pronounced barrel
Aperture Center Corner
f/4      B      C
f/5.6    B+     B
f/8      B      B
f/11     B+     B
f/16     B-     B
f/22     B-     B-
Notes: Moderate contrast at f/4; moderately high @ f/5.6 to f/22.

@ 70mm setting
Vignetting = B+ @ f/4.5, A- @ f/5.6, A thereafter
Distortion = slight pincushion
Aperture Center Corner
f/4.5    C+     C-
f/5.6    B      C
f/8      B+     B-
f/11     B+     B
f/16     B      B-
f/22     B      B-
Notes: Moderate contrast at f/4.5; moderately high thereafter.