(multi-coated)

With comparative SQF values from Popular Photography, published April 1998);OM-1 with mirror lockup

@ 35mm setting
Vignetting = B- @ f/3.5, A- @ f/5.6
Distortion = very pronounced barrel
Aperture Center Corner Popular Photography SQF
f/3.5    C+     B-     F
f/5.6    B-     B-     B+
f/8      B      B      A
f/11     B      B      A
f/16     B      B-     B+
f/22     B      C+     B

@ 50mm setting
Vignetting = B+ @ f/4, A- @ f/5.6, A @ f/8
Distortion = slight barrel
Aperture Center Corner Popular Photography SQF
f/4.0    C      B      C+
f/5.6    B+     B      B
f/8      B      B+     A
f/11     B+     B      A
f/16     B      B      B+
f/22     B-     B-     B
Notes: Contrasty images.

@ 70mm setting
Vignetting = A-
Distortion = none
Aperture Center Corner Popular Photography SQF
f/4.8    C-     C-     D
f/5.6    B-     B-     B
f/8      B+     B-     B+
f/11     B+     B      B+
f/16     B      B      B
f/22     B      C+     C+
Notes: Contrasty at expense of resolution at all focal lengths. Slightly larger and easier to handle than the earlier f/3.5~4.5 lens, but not as good performing. Made by Cosina.