[rollei_list] Re: How rare is a Rollei with a Biometar?
- From: CarlosMFreaza <cmfreaza@xxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Sun, 4 Oct 2009 21:17:07 -0300
2009/10/4 Richard Knoppow
>... The reasons for switching back to a conventional six element Planar (we
> might as well call it that) type lens for the f/3.5 versions of the
> Rolleiflex can not be definitely answered without having access to the
> business records of Rollei and the companies who made the lenses. All else
> is guess work.
Richard, your technical comments are always very interesting.
About the six elements Planar 3.5/75 for the Rolleiflex TLR, the
Xenotar 3.5/75 also changed into six elements, I recall the Prochnow's
explanation for the change, it was made because the thickest elements
for both lenses five elements versions (second element for the Planar
and fourth element for the Xenotar) were difficult and expensive to
manufacture, Zeiss and Schneider divided these elements into two
thinner and cemented parts and then the lenses became six elements
"maintaining the quality" (Prochnow) regarding the five elements
version, being the six elements version "cheaper and easier to
manufacture"; there was no this economical and manufacture issue for
the 2.8/80 Planar and Xenotar and then they did not receive changes.
I think the point could be to know why two cemented elements, even
thinner, are cheaper and easier to manufacture than one element, even
thicker. I think the glass control quality and glass selection and
glass cut is more difficult if thicker and smaller the element,
sometimes the optical design allows to modify the elementskeeping
similar performance and this was the case for the Rolleiflex 3.5/75
Planar and Xenotar lenses.
Carlos
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