[rollei_list] Re: AW: Rollei 35 mm SLR Flange focal distance
- From: CarlosMFreaza <cmfreaza@xxxxxxxxx>
- To: "rollei_list@xxxxxxxxxxxxx" <rollei_list@xxxxxxxxxxxxx>
- Date: Wed, 10 Sep 2014 20:35:37 -0300
Hi Emmanuel:
I found the data in the Rollei Technical Report,
thank you for your clarification about it.
Carlos
2014-09-10 7:28 GMT-03:00 Bigler Emmanuel <bigler@xxxxxxxx>:
> 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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