Tamron SP 24-48mm f/3.5~3.8 (multi-coated)
OM-2S with mirror and diaphragm prefire

@ 24mm setting
Vignetting = B @ f/3.6, B+ @ f/5.6, A- @ f/8, A thereafter
Distortion = pronounced waveforming with pronounced barrel tendancy
Aperture Center Corner
f/3.6    *      *
f/5.6    *      *
f/8      A      A-
f/11     B+     B
f/16     B+     B+
f/22     B      B-
f/32     C+     C+
Notes: * = data not available. Exhibited obvious distortion, perhaps unacceptable to many users. Moderately high contrast images at f/8 and f/16 to f/22; high contrast images at f/11; moderate contrast images at f/32.

@ 36mm setting
Vignetting = A- @ f/3.65, A thereafter
Distortion = none
Aperture Center Corner
f/3.65   B      B-
f/5.6    B+     B
f/8      A-     A-
f/11     A-     A-
f/16     B      B
f/22     B-     B-
f/32     C      C
Notes: Moderate contrast images at f/3.65 and f/22 to f/32; moderately high contrast images at f/5.6 and f/16; high contrast images at f/8 to f/11.

@ 48mm setting
Vignetting = A- at f/3.8, A thereafter
Distortion = none? (perhaps slight waveforming)
Aperture Center Corner
f/3.8    B      B-
f/5.6    B+     B
f/8      B+     A-
f/11     B+     A-
f/16     B      B
f/22     B      B
f/32     C+     B-
Notes: Moderately high contrast images at f/3.8 and f/22; high contrast images at f/5.6 to f/16; f/32 contrast not determined.