Tamron 70-210mm f/4~5.6 (Adaptall 2 system)
OM-2S with mirror and diaphragm prefire

@ 70mm
Distortion: slight pincushion
Vignetting: B @ f/4, B+ @ f/5.6, A- @ f/8, A elsewise
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-
f/32     C+     B-
Notes: Moderately low contrast at f/4, f/5.6 and f/32; moderate contrast at f/8 to f/22. No other focal lengths tested.