Unscientific lens testing (somewhat off topic).

[David Young <youngs@IslandNet.com>]

Fellow LugNuts:

Recently I found myself in need of a 500mm mirror lens for my R5. I thought
you might be interested in the results of a little quick (yet unscientific)
testing of several models. (If your not, press DELETE now!)

I begged or borrowed a TAMRON SP 500/8 (Cdn $350 used - Japan), a VIVITAR
500/8 (Cdn $189 new - Korea), and a MTO-500/8 (Cdn $249 used - Russia).  We
shot "control" photos with a buddy's Nikon 500/8 mirror lens. (Sorry! We
were unable to borrow the Leica 500/8! We tried!)

The results were startlingly obvious, even in simple 4"x6" prints from the
local 1 hour joint.  The Tamron and MTO were very close, with a slight edge
in detail going to the MTO; but the Vivitar was, at best, blurry - even in
the small 4x6 print!  I suppose that is to be expected, for new it was just
over 1/2 the cost of the used Tamron!

I bought the MTO, despite it's bulk, because of the superior performance,
reasonable price tab and the funky wooden case it came in (complete with 4
- - 77mm filters!).

Three questions, for those who are still reading...

[1] Though engraved as a 500 f8 on the lens, the addendum sheet with it
says it's a 548mm f8.8.  Is this sort of variation normal?

[2] All three lenses, as well 500/8's by Minolta, Leica, Nikon and my
1000/11 Celestron all focus to beyond infinty.  Does anyone where know the
reason Mirror lenses do not have an infinity stop?

[3] The MTO rsults were virtually as good as the Nikkor's or Celestron's.
Yet the booklet lists resolution as "Central - 32 lines/mm" and "Peripheral
- - 20 lines/mm".  The MTO seems much better than such numbers would
indicate.  Can anybody tell me why?

Many thanks.




- ----------

David Young          |  Over the hill?
Victoria, CANADA     |  I don't remember
youngs@IslandNet.co  |  any hill ...