Tamron SP 90mm f/2.5 Macro OM-1 with mirror lockup Vignetting = A- Distortion = slight pincushion Aperture Center Corner f/2.5 C- C f/4 B- B f/5.6 B B f/8 B+ B+ f/11 A- A- f/16 A- B+ f/22 B B f/32 B- B- Notes: Good detail in low contrast subject matter; at f/11 = slightly higher image rendering performance at 25% out from center of image versus a 90mm f/2 Zuiko. Tamron SP 90mm f/2.5 Macro with Tamron SP 2X teleconverter OM-1 with mirror lockup Vignetting = A Distortion = slight pincushion Aperture Center Corner f/2.5 (5) F F f/4 (8) B- C- f/5.6 (11) B C f/8 (16) B C+ f/11 (22) B B- f/16 (32) B- B- f/22 (44) C C f/32 (64) D- D- Notes: Remarkable contrast, except at f/2.5, where exceeding low; clearly diffraction limited stopped down; little quality loss in center of image at wider apertures.