(multi-coated)

@ 35mm setting

OM-1 with mirror lockup; first sample
Vignetting = C+ @ f/3.5, A @ f/5.6
Distortion = moderate barrel with slight waveforming
Aperture Center Corner
f/3.5    B+     B-
f/5.6    A-     B+
f/8      B+     B+
f/11     B      A-
f/16     B+     A-
f/22     B+     B
Notes: High contrast at all but f/22, where moderately low.

OM-4T with mirror and diaphragm prefire; second sample
Vignetting = B+ @ f/3.5, A- @ f/5.6, A @ f/8 and beyond
Distortion = pronounced barrel
Aperture Center Corner
f/3.5    B      B-
f/5.6    B+     A-
f/8      B+     A-
f/11     A-     A-
f/16     B+     A-
f/22     B      B+
Notes: Moderate contrast.

@ 50mm setting

OM-1 with mirror lockup; first sample
Vignetting = B+ @ f/4, A @ f/5.6
Distortion = none
Aperture Center Corner
f/4.0    B      B+
f/5.6    B+     A-
f/8      A-     A-
f/11     A      A-
f/16     B+     A-
f/22     B+     B
Notes: Moderately high contrast, except moderately low at f/22.

OM-4T with mirror and diaphragm prefire; second sample
Vignetting = B+ @ f/4, A @ f/5.6 and beyond
Distortion = slight pincushion
Aperture Center Corner
f/4.0    B      B
f/5.6    B+     B+
f/8      B+     A-
f/11     A-     A
f/16     B+     A-
f/22     B+     A-
Notes: Moderate contrast.

@ 70mm setting

OM-1 with mirror lockup; first sample
Vignetting = B+ @ f/4.5, A @ f/5.6
Distortion = moderate pincushion
Aperture Center Corner
f/4.5    B      B+
f/5.6    B+     B+
f/8      A-     A-
f/11     A-     A-
f/16     A      A
f/22     B+     B+
Notes: Moderate contrast. Extremely lightweight lens, but short distance from focal length ring to aperture ring and dim image slows handling.

OM-4T with mirror and diaphragm prefire; second sample
Vignetting = B+ @ f/4.5, A @ f/5.6
Distortion = pincushion
Aperture Center Corner
f/4.5    B      B
f/5.6    B      B
f/8      B+     B+
f/11     B+     A-
f/16     B+     B+
f/22     B+     B+
Notes: Moderately high contrast. Optimum aperture at all focal lengths is f/11.