Vivitar Series 1 28-105mm f/2.8~3.8 (multi-coated)
OM-1 with mirror lockup

@ 28mm setting
Vignetting = D @ f/2.8, B- @ f/4, B @ f/5.6
Distortion = pronounced waveform
Aperture Center Corner
f/2.8    C+     B-
f/4      B      B
f/5.6    B      B
f/8      B-     B
f/11     B-     B
f/16     B-     B+
f/22     B-     B
Notes: High contrast images; difficult to determine effective aperture when shooting wide open (click stops very confusing).

@ 50mm setting
Vignetting = B-
Distortion = moderate waveform with distinct tendency towards pincushion
Aperture  Center Corner
f/2.8~3.8 C+     C
f/4       B-     B-
f/5.6     B+     B
f/8       B      B-
f/11      B      B-
f/16      B      B-
f/22      B      B

@ 105mm setting
Vignetting = B- @ f/3.8, B+ @ f/5.6
Distortion = pronounced pincushion
Aperture Center Corner
f/3.8    B      C
f/4      B      B-
f/5.6    B+     B
f/8      B      B
f/11     B-     B-
f/16     B-     B-
f/22     C      B-