P3D Re: 55mm lenses on 35mm SLRs (PHOTO-3D digest 3673)

[bobh@xxxxxxxxxxxxxxxxxx]

RE: Looking for 55mm lens for beamsplitter etc.
As one who has lived in photography for 60 years, it is interesting to 
know WHY there is (was) a 55mm lens!
When the SLR was introduced, the 55mm focal length was the 
shortest that would clear the moving mirror, so all cameras had 
55mm or 58mm lenses. THERE were NO wide angle lenses for this 
reason. In fact in Japan they sold many small RF or viewfinder 
cameras with 35mm or 28mm fixed lenses to be a companion to 
the SLR with no wide angle. The French firm Pierre Angineaux
developed a 'reversed telephoto' design they named "Retrofocus" 
and made a "35mm wide angle for the Exakta", this was a lens with 
the field of view of a 35mm but a long back focus that cleared the 
mirror. Such lenses became known as retrofocus regardless of 
make or trademark.  Soon lens makers used this technique to make 
50mm lens (which had been hewn in stone by Leica as the standard 
for a 35mm camera normal lens..a bit long for the diagonal of the 
negative measure of normal = 43mm). And later all kindw of wide 
angles. BUT it is still true today that any lens shorter than 55mm for 
an SLR is a 'retrofocus' design to some degree. (One exception, 
the wide angle 38mm for the Canon Pellix which had no moving 
mirror but a fixed pellicle beam splitter.)  BobH
Bob Howard (bobh@xxxxxxxxxxxxxxxxxx)
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