I would appreciate any general comments on the use of a 2X teleconverter and how it affects the optical qualities of a lens. Also, how would the Hexanon brand compare to an after-market brand such as Vivitar? I see there is a Konica mount 3X teleconverter from Kenco - again, any comments?

-- Anonymous, October 09, 2000

Answers

Teleconvertors

Teleconvertors increase the focal lenght of a lens by whatever the "multiplier" is - so a 50 mm lens with a 2x converter has a 100 mm focal length, with a 3x would be 150, etc. Teleconvertors do NOT change the maximum aperature of a lens, so use of a teleconvertor makes the lens "slower" - a 50 mm lens at f 2.0 would be f 4 with a 2x, etc. Teleconvertors often allow closer focus.

Teleconvertors generally degrade image quality. Essentially a convertor moves the lens further away from the focal plane and then has to "refocus" the image. The problem often comes in getting edge sharpness - At small aperatures, the loss of sharpness may not be apparent, but at large aperature, it may be woefully obvious. I think it makes a BIG difference which teleconvertor you use and with which lens. Wider angle lenses tend to do poorly with teleconvertors - for example, a 28 mm with a 2x usually has noticeably poorer image quality than a 50mm lens. Off brand convertors do not do well in my experience.

Vivitar made some "matched multipliers" for the Series One lenses - they were specifically designed to work with a certain lens (example the 70-150 Series One zoom came with a 2x to make it a 140-300). These had quite high resolution - the 70-150 actually had better macro capacity with the multiplier - I believe a flatter field of focus.

My best recoomendation - If you get one of the Vivitar Series One with the "matched multipliers" that is probably the best. Else I would recommend the Konica. Thanks!

-- Anonymous, October 25, 2000