Re: JohB Lens Matching ( digest 1606)

[P3D Bob Howard <bobh@xxxxxxxxxxxxxxxxxxxx>]

RE: John relates a fascinating experience of going to a Canon Repair
Station who has collected a bushel of SLRs for parts, and has hobs of
lenses..which he measured with a grid (Pattern at a distance??)
He says specs say 1% tolerance on fl. And he picked two that were best
cosmetically and with in a tenth on his measurement. Says with this 1%
Spec and Kingslake saying stereo lenses ought to be within 1% you can
pick any Canon lens. 

I wonder? a)Canon (and all other SLR) 50mm lenses are retrofocus to
clear the mirror. (It was some years and only after Angeineaux
introduced the retrofocus wideangles that SLR lenses could come down
form the 55mm needed to clear the mirror to 50mm.) So the fl is a wierd
one compared to a simple Tessar or Cooke triplet design.
 b} Most 50mm lenses have 1% or more barral distortion..so matching with
a grid might be picking least distortion. Or a distrotion and focal
lenght mix.
 c) if images are truly equal superimosed..then I would say don't worry
like the kid on MAD Magazine. Also the eyes may tolerate image size
difference very well. BobH


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