55mm f/1.2 Zuiko (single-coated, non-radioactive version with all black filter rim)

OM-4T with mirror and aperture prefire
Vignetting = C- @ f/1.2, B- @ f/2, A- @ f/2.8, A thereafter
Distortion = slight barrel
Aperture  Center    Corner
f/1.2     C-        C+
f/2       B         C+
f/2.8     B+        B
f/4       B         B
f/5.6     B+        B
f/8       B+        B+
f/11      B+        B+
f/16      B+        B
Notes: Moderately low contrast images at f/1.2; moderate contrast images at f/16; moderately high contrast at f/2 to f/4 and f/11; high contrast images at f/5.6 to f/8. No color cast, nor discoloring with age. Paired comparison to the radioactive, silver snout version above, with all grade differences significant to the 1/3rd grade level.