(multi-coated)

OM-1 with mirror lockup
Vignetting = A-
Distortion = none
Aperture Center Corner
f/2.8    B      B-
f/4      B-     B-
f/5.6    C+     B-
f/8      B-     B
f/11     B+     B+
f/16     B+     A-
f/22     B      B+
Notes: Moderately high contrast at expense of resolving power throughout aperture range, with impressively high contrast wide open.

135mm f/2.8 Zuiko (multi-coated) with Olympus 2X Teleconverter
OM-1 with mirror lockup
Vignetting = B
Distortion = none
Aperture    Center Corner
f/2.8 (5.6) F      F
f/4 (8)     D-     F+
f/5.6 (11)  D      D
f/8 (16)    C-     D+
f/11 (22)   C+     C+
f/16 (32)   B-     C
f/22 (44)   B-     B-
Notes: Moderately low contrast at f/22 and f/16 (effective f/44 and f/32), low contrast at f/5.6, f/4, andf/2.8 (effective f/11, f/8, and f/5.6), otherwise moderate contrast.

OM-4 with mirror and aperture prefire and Bogen Telephoto Lens Support
Vignetting = B @ f/2.8, A @ f/4
Distortion = none
Aperture    Center Corner
f/2.8 (5.6) B-     C
f/4 (8)     B+     B
f/5.6 (11)  B+     B
f/8 (16)    B+     B
f/11 (22)   B      B-
f/16 (32)   B-     B-
f/22 (44)   B-     C
Notes: Moderately low contrast at f/22 and f/16 (effective f/44 and f/32), high contrast at f/2.8 throughf/8 (effective f/5.6 through f/16), moderate contrast at f/11 (effective f/22).