Vivitar Series 1 90-180mm f/4.5 Flat Field Zoom (multi-coated)
OM-4 with mirror and diaphragm prefire

@ 90mm setting
Vignetting = slight barrel
Distortion = B+ @ f/4.5, A thereafter
Aperture Center Corner
f/4.5    B      B+
f/5.6    B+     B+
f/8      B+     B+
f/11     A      A-
f/16     A-     A-
f/22     B      B+
Notes: Moderately high contrast at f/4.5; high contrast at f/5.6 to f/16; moderate contrast at f/22.

@ 135mm setting
Vignetting = B+ @ f/4.5, A thereafter
Distortion = slight pincushion
Aperture Center Corner
f/4.5    B-     C+
f/5.6    B-     B-
f/8      B      B-
f/11     B+     B+
f/16     A-     B+
f/22     B+     B+
Notes: Moderately high contrast at f/4.5 to f/16; moderate at f/22.

@ 180mm setting
Vignetting = B @ f/4.5, A- @ f/5.6 to f/8; A thereafter
Distortion = moderate pincushion
Aperture Center Corner
f/4.5    B+     B-
f/5.6    B+     B-
f/8      B+     B
f/11     A-     B+
f/16     B+     A-
f/22     B      B+
Notes: Moderately low at f/4.5 and f/22; moderately high at f/5.6 to f/16.