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.