(multi-coated)

@ 35mm setting

OM-1 with mirror lockup
Vignetting = C+ @ f/4, B+ @ f/5.6, A @ f/8
Distortion = pronounced barrel
Aperture Center Corner
f/4      B      B-
f/5.6    B+     B
f/8      B      B+
f/11     A-     B+
f/16     A-     B
f/22     B      B
Notes: Moderate contrast.

OM-2S with mirror and diaphragm prefire, different lens sample than above OM-1 test
Vignetting = B+ @ f/4, A- @ f/5.6 & f/8, A thereafter
Distortion = pronounced barrel
Aperture Center Corner
f/4      B      C+
f/5.6    B      B-
f/8      B+     B
f/11     A-     A-
f/16     B      B
f/22     B      B
Notes: Moderate contrast images at f/f to f/5.6 and f/22; moderately high contrast images at f/8 to f/16.

@ 50mm setting

OM-1 with mirror lockup
Vignetting = B @ f/4, A @ f/5.6
Distortion = none
Aperture Center Corner
f/4      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.

OM-2S with mirror and diaphragm prefire, different lens sample than above OM-1 test
Vignetting = A- @ f/4, A thereafter
Distortion = none
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-
Notes: Moderately high contrast images at f/4 and f/16 to f/22; moderately high contrast images at f/5.6 to f/11.

@ 70mm setting

OM-1 with mirror lockup
Vignetting = B- @ f/4, A- @ f/5.6
Distortion = slight pincushion
Aperture Center Corner
f/4      C      C
f/5.6    B-     B-
f/8      B+     B+
f/11     B      B
f/16     B      B
f/22     B      B
Notes: Moderately high contrast.