[rollei_list] Re: Back-Focus and Retro-Focus
- From: Carlos Manuel Freaza <cmfreaza@xxxxxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Mon, 7 Jul 2008 12:49:06 -0700 (PDT)
Marc, the discussion was if the 2.8B Biometar was closer to the Planar or to
the Xenotar, and there is not doubt it's closer to the Xenotar as Todd Belcher
verified disassembling one of his 2.8B Biometar lens, it does not mean it's
identical regarding the Pentacon Six Biometar but both Biometars are very
similar regarding lens elements distribution, number of elements/groups and
general design.-
Carlos
--- El lun 7-jul-08, Marc James Small <marcsmall@xxxxxxxxxxx> escribió:
> De: Marc James Small <marcsmall@xxxxxxxxxxx>
> Asunto: [rollei_list] Back-Focus and Retro-Focus
> Para: rollei_list@xxxxxxxxxxxxx
> Fecha: lunes, 7 de julio de 2008, 4:17 pm
> At 02:57 PM 7/7/2008, Eric Goldstein wrote:
> >Not joking at all... That's what I was looking
> for, Carlos. Appreciate
> >the reference.
> >
> >So now we know either that the lens design has a long
> back-focus
> >(unlikely, as the design has not appeared in other
> similar
> >applications), or that the mirror on the camera allows
> for unusual
> >clearance. Wondering if it may be somewhat shortened
> and offer a
> >limited view with some lenses?
>
>
> Normal lenses do not need to be retrofocus on
> either a miniature-format or medium-format
> camera. Such designs were developed at Carl
> Zeiss Jena and then at Angenieux to accommodate
> wide-angle lenses. The original normal lens on
> the Praktiflex and Practica cameras was the CZJ
> 2/5.8cm Biotar but that was only while they
> figured out how to reduce the mirror size whle
> preserving image brightness -- the original lens
> selection for the Contax S, for instance, were
> all non-retrofocus lenses, a 4.5/4.5cm Tessar,
> the 2/5.8cm Biotar, and a 2.8/8cm Tessar. By the
> time of the Praktica FX cameras, the smaller
> mirror allowed the reworking of the 2/5.8cm
> Biotar into the 2/50 Pancolar, another non-retrofocus
> design.
>
> In the same way, an 80mm normal lens on a
> medium-format SLR does not need to be a
> retrofocus design and I cannot recall one which
> was so. The history of the Hasselblad 80mm
> lenses is a bit more complex than Carlos has set
> out but, in the end, neither the 2.8/8cm CZJ
> Biometar nor any version of the 2.8/60 CZ Planar
> were retrofocus designs. Of course, the various
> Distagons were retrofocus designs flowing
> directly from the work done by Sauer under
> Wandersleb at Jena in the late 1930's.
>
> I am not convinced that the designs and
> construction of the 2.8/8cm Biometar used in the
> Rolleiflex 2.8B is identical to that used in the
> normal lens of that designation used on the
> Pentacon Six/Praktisix. I recall the lens used
> on the Rolleiflex as being substantially smaller
> than that used on the Pentacon Six line,
> precisely as the five-element 2.8/80 CZ Planar
> used since the Rolleiflex 2.8C is much smaller
> than was the original five-element 2.8/80 CZ
> Planar used on the original Hasselblad 500C.
>
> Marc
>
>
> msmall@xxxxxxxxxxxx
> Cha robh bàs fir gun ghràs fir!
>
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