Tamron SP 400mm f/4 OM-1 with mirror lockup and second tripod supporting hood Vignetting = B- @ f/4, A- @ f/5.6 Distortion = none Aperture Center Corner f/4 B+ B+ f/5.6 A- B+ f/8 A B+ f/11 A+ A- f/16 A- A f/22 A- A- f/32 B B- Notes: High contrast with remarkable image quality for a super telephoto, optimum aperture appears to be f/11. Tamron SP 400mm f/4 with Olympus 1.4X Teleconverter OM-1 with mirror lockup and second tripod supporting hood Vignetting = B @ f/4, A- @ f/5.6 Distortion = moderate pincushion Aperture Center Corner f/4 (5.6) C- C f/5.6 (8) B- C+ f/8 (11) B+ B f/11 (16) A- B f/16 (22) B+ B+ f/22 (32) B B f/32 (44) B B Notes: Moderately high contrast, except atf/32 (effective f/44), where moderately low. Tamron SP 400mm f/4 with Tamron SP 1.4X Teleconverter OM-1 with mirror lockup and second tripod supporting hood Vignetting = B- @ f/4, A- @ f/5.6 Distortion = none Aperture Center Corner f/4 (5.6) B- B- f/5.6 (8) B B- f/8 (11) B- C f/11 (16) B- B- f/16 (22) C+ C+ f/22 (32) C+ C+ f/32 (44) C+ C Notes: Moderately low contrast with lack of fine details (resolution). Clearly inferior to the Olympus 1.4X teleconverter. Tamron SP 400mm f/4 with Olympus 2X Teleconverter OM-1 with mirror lockup and second tripod supporting hood Vignetting = C- @ f/4, B- @ F/5.6, B+ @ f/8 Distortion = slight pincushion Aperture Center Corner f/4 (8) C- D f/5.6 (11) C D f/8 (16) C+ C+ f/11 (22) C+ C+ f/16 (32) C+ C+ f/22 (44) C C+ f/32 (64) D D Notes: Moderate contrast but low resolution. Tamron SP 400mm f/4 with Tamron SP 2X Teleconverter OM-1 with mirror lockup and second tripod supporting hood Vignetting = B @ f/4, A- @ f/5.6 Distortion = slight pincushion Aperture Center Corner f/4 (8) C- D+ f/5.6 (11) C D+ f/8 (16) B C f/11 (22) B C+ f/16 (32) B B f/22 (44) C+ B- f/32 (64) C+ C Notes: Moderate contrast, except moderately low at f/32 (f/64 effective).