(multi-coated)

OM-1 with mirror lockup; tripod collar
Vignetting = A
Distortion = none
Aperture  Center    Corner
f/4.5     B         C
f/5.6     B+        B
f/8       B         B-
f/11      A-        B+
f/16      A-        B+
f/22      B         B+
f/32      B         B
f/45      B-        B-
Notes: Differences to the OM-4 test below are significant at full letter grades only. Contrasty.

OM-4 with mirror and automatic diaphram prefire, plus a Bogen
Telephoto Lens Support as a replacement for the tripod collar.
Aperture  Center    Corner
f/4.5     A-        B-
f/5.6     A-        B+
f/8       A         A-
f/11      A         B+
f/16      A-        B+
f/22      B+        B
f/32      B         B-
f/45      C+        C+
Notes: Differences to the OM-1 test above are significant at full letter grades only.  Note improvement at f/8.  Significant decrease in contrast at f/32 and f/45, but very high contrast at f/4.5 through f/8.  f/8 is optimum aperture for this lens, which offers a f/4 viewing aperture.  Results would probably be the same if used with the tripod collar supplied by Olympus.