(single-coated)

@ 75 mm setting
OM-1 with mirror lockup
Vignetting = B
Distortion = none
Aperture Center Corner
f/4      C      B+
f/5.6    C+     B+
f/8      B      A-
f/11     B+     B
f/16     A-     B+
f/22     B      B
Notes: Very high resolution at the sake of contrast.

OM-4T with mirror mirror and aperture prefire
Vignetting = B @ f/4, A- @ f/5.6, A from F/8 on
Distortion = slight barrel
Aperture Center Corner
f/4      B      B-
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 all apertures.

@ 100 mm setting

OM-1 with mirror lockup
Vignetting = none
Distortion = slight pincushion
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

OM-4T with mirror mirror and aperture prefire
Vignetting = A- @ f/4, A otherwise
Distortion = slight pincushion
Aperture Center Corner
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: Moderate contrast, except moderately high at f/8 & f/11.

@ 150 mm setting

OM-1 with mirror lockup
Vignetting = none
Distortion = pronounced pincushion
Aperture Center Corner
f/4      C      D
f/5.6    C      D
f/8      B      C-
f/11     A-     C
f/16     A-     C
f/22     B+     C-
Notes: Low contrast

OM-4T with mirror mirror and aperture prefire
Vignetting = A- @ f/4, A otherwise
Distortion = slight pincushion
Aperture Center Corner
f/4      B-     B-
f/5.6    B-     B-
f/8      B      B
f/11     B-     B-
f/16     B-     B-
f/22     C+     C+
Notes: Moderate contrast, except moderately low at f/22 and (?)moderately high at f/4. This lens sample was different than the one used for the OM-1 test above.