(multi-coated)

OM-2000 with mirror and aperture prefire
Vignetting = C @ f/3.5, B- @ f/5.6, B+ @ f/8, A- @ f/11 and 16
Distortion = none!
Aperture Center Corner
f/3.5    B      C
f/5.6    B+     B+
f/8      B+     B
f/11     B+     B
f/16     B+     B
Notes: Hot spotting at f/3.5 due to strong vignetting. Moderate contrast in this 8 condition sample.

OM-1 with mirror lockup
Aperture Center Corner
f/3.5    C      C
f/5.6    B      B+
f/8      B      A-
f/11     A-     A+
f/16     B      A
Notes: Vignetting characteristic of wide angle lenses, improving with stopping down; moderately high contrast images; remarkable lack of distortion; lens design emphasizes outer zones at expense of center image zone (which gives a sharper overall impression of an image); overall optimum aperture at f/11. A 10- condition sample.