[rollei_list] Re: AW: Rollei 35 mm SLR Flange focal distance
- From: Bigler Emmanuel <bigler@xxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Wed, 10 Sep 2014 12:28:10 +0200
Thanks to Carlos, now we know the exact story.
Sorry for the noise, since I made a wrong interpretation of what was
supposed to be (in French) a 'tirage optique' of 44.50 mm ; in French
usually "tirage optique' is "back focal distance" measured form the last
lens vertex; in German technical sheets the lats lens vertex is denoted
by S', and the back focal distance it is denoted by S'F' or
S'A'_{infinity} but in fact G. Métrot meant : position of bayonet lens
seat measured _optically_ by reference to the ground glass and not
_mechanically_ by reference to the pressure plate. This is completely
different.
Thanks again Carlos for the explanation ! Hence 44.50 is a measurement
from the lens bayonet seat to a ground glass plane located somewhere at
the film gate, and 44.67 is with reference to the film pressure plate
(which actually is not really in contact with the film, like in the
Rollei TLR).
So Dirk-Roger, forget about the "lens vertex" (the summit of the last
lens surface, on the optical axis, the glass part which is the closest
to the focal point) which is totally irrelevant here since various
lenses of the same mounts have their last lens element located at
various places. In SLR cameras, tele lenses usually have the last lens
vertex deeply recessed inside the lens mount, whereas for other lenses
it can be very close to the bayonet seat.
For example, in C-type Hasselblad 2.8-80 planars, two small protruding
crescent-shaped pieces of metal located around the last lens element are
required to protect the glass form scratches. And the back focal
distance is shorter than the flange focal distance since the 2.8-80
plabar lens slightly enters inside the camera body.
--
Emmanuel
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