(single-coated)

OM-1 with mirror lockup
Vignetting = A-
Distortion = slight pincushion
Aperture Center Corner
f/3.5    C+     C
f/5.6    C      C
f/8      B-     B-
f/11     B      B
f/16     B+     B+
f/22     B+     B

OM-2000 with mirror and aperture prefire
Aperture Center Corner
f/3.5    C      C-
f/5.6    B-     C+
f/8      B-     B-
f/11     B+     B
f/16     B+     B
f/22     B+     B
Notes: Same 9+ condition lens in both tests. Insignificant differences between tests likely due to light weight of this lens and minimal influence of shutter and automatic diaphram vibrations. Moderately low contrast.

135mm f/3.5 Zuiko (single-coated) with Olympus 2X-A Converter

OM-1 with mirror lockup
Vignetting = B+
Distortion = moderate pincushion
Aperture*  Center Corner
f/3.5 (7)  F      F
f/5.6 (11) F+     F+
f/8 (16)   C+     C
f/11 (22)  B-     C+
f/16 (32)  B      B-
f/22 (44)  C+     C+
Notes: Low contrast.

OM-4T with mirror and diaphragm prefire
Vignetting = A- @f/3.5 (7), A thereafter
Distortion = moderate pincushion
Aperture*  Center Corner
f/3.5 (7)  A-     C+
f/5.6 (11) A-     B-
f/8 (16)   A      B
f/11 (22)  B+     B
f/16 (32)  B      B-
f/22 (44)  B-     C+
Notes: *Effective aperture in parenthesis (). Identical lens as above test! Used a Bogen Telephoto Lens Support for additional stability, although it barely fits this lens/converter combo. Moderately high contrast in center and corner at f/3.5 (7), f/5.6 (11) and f/11 (22); high contrast in center and moderately high contrast in corner at f/16; moderately high contrast images in center and moderate contrast in corner at f/16 (32) and f/22 (44).