Tokina AT-X 28-85mm f/3.5~4.5
OM-4 with mirror and diaphragm prefire

@ 28mm setting
Vignetting = B+ @ f/3.5, A- @ f/5.6, A thereafter
Distortion = slight barrel
Aperture Center Corner
f/3.5    B      B-
f/5.6    A      B+
f/8      A      B+
f/11     A-     A-
f/16     A-     A-
f/22     B      B
Notes: Moderately high contrast at f/3.5, f/5.6, f/16 and f/22; high contrast at f/8 and f/11.

@ 50mm setting
Vignetting = A- @ f/4, A thereafter
Distortion = very slight waveform with no tendencies
Aperture Center Corner
f/4.0    B      B
f/5.6    B      B
f/8      B+     B+
f/11     A-     A-
f/16     A-     A
f/22     B-     B
Note: High contrast at all apertures.

@ 80mm setting
Vignetting = A- @ f/4.5, A thereafter
Distortion = slight waveform with slight pincushion tendency
Aperture Center Corner
f/4.5    B-     B-
f/5.6    B      B-
f/8      A-     B
f/11     A      B
f/16     B+     B+
f/22     B+     B
Note: Moderately high contrast at f/4.5, 5.6, f/16 and f/22; high contrast at f/8 and f/11.