(single-coated, rare earth radioactive version with silver filter rim)

OM-1 with mirror lockup
Vignetting = NA
Distortion = slight barrel

Aperture Center Corner
f/1.2    C+     B-
f/2      B      B-
f/2.8    B-     B
f/4      B+     B+
f/5.6    B+     A-
f/8      A-     A
f/11     A-     A-
f/16     A-     A-

Notes: Moderate contrast with high resolution, except very low contrast at f/1.2.

OM-4T with mirror and aperture prefire, different lens than above

Vignetting = C- @ f/1.2, C+ @ f/2, A- @ f/2.8, A thereafter
Distortion = slight barrel

Aperture Center Corner
f/1.2    C-     C+
f/2      B-     B-
f/2.8    B      B
f/4      B      B+
f/5.6    B+     B+
f/8      A-     A-
f/11     A-     B+
f/16     B+     B+

Notes: Moderate contrast images at f/1.2; moderately high contrast at f/2; high contrast images at f/2.8 to f/4; very high contrast images at f/5.6 to f/16. Paired comparison with the non-radioactive, black snout version below, with all grade differences significant to the 1/3rd grade level. Comments: This lens utilized one or more radioactive rare earth elements (lanthium or thorium floride), which are high refractive index (and extra low dispersion?) elements but with the undesirable side effect of yellowing with age. The yellowing is attributable to the effects of radioactive decay. This design has particularily strong radioactivity, which registers on a Gieger counter through the mirror and the shutter when metered at the film plane (gamma radiation?). It does not fog fast (ISO 800) film in tests of up to 3-4 minutes exposure time.