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Re: [Rollei] Newbie soon-to-be Rollei TLR owner (x2)



- ----- Original Message -----
From: "alex olstein" <alexolstein  >
To: <rollei  
Cc: "zz" <alexolstein  >
Sent: Tuesday, November 26, 2002 12:15 PM
Subject: Re: [Rollei] Newbie soon-to-be Rollei TLR owner
(x2)


> Marketing reasons,  Xenotar was more for Europe, while
Planar was for
> export.  Helps keep "unofficial" gray market  products
ffrom competing with
> official products in different areas.
>
> Alex Olstein
>
>

  I don't think this was the reason.
  Rollei traditionally used Zeiss lenses. Following WW-2,
for various reasons, they began to use Schneider as an
alternative source. Schneider's post WW-2 quality seems to
have very much improved over their pre-war quality, becoming
excellent. Rollei used Xenar lenses as a second source for
Tessar type lenses. The quality difference between the
Tessar and post war Xenar is a matter of some controversey,
probably because there isn't much, both are excellent.
  The Xenotar was designed to provide better performance at
large stops than the Tessar. While many f/2.8 Tessars had
been built and used the performance of the generic design at
this speed leaves a lot to be desired. The extra element in
the Xenotar allowed better correction of rim rays, hense,
superior sharpness, especially in the corners, when wide
open. The Xenotar is essentially a Planar or Biotar type
lens with two elements combined. This results in eliminating
a cemented surface and one element. Cemented surfaces are
quite expensive to make so eliminating one is significant.
While six elements are needed for good performance at f/2
the five element design allows excellent correction at
f/2.8.
  The five element Planar followed the Xenotar, probably
because Rollei wanted to continue offering Zeiss lenses, and
as a second source.
  The two lenses are not identical in either construction or
performance, but one is not "better" than the other. The
differences are probably due to judgements made by the
designer about how to balance the residual aberrations.
This shows up as differences in the edge contrast vs:
resolution, and in other ways. The five element Xenotar is
also probably cheaper to make since the cemented surface is
plane; the Planar having a fairly steeply curved cemented
surface plus at least one quite thin element.
  While there is a never ending discussion about the
relative merits of the two lenses the fact is that both are
outstanding. Its likely that much of the difference observed
is due to variations in camera adjustments rather than the
lenses.
  There are more variations in type for the f/3.5 versions
of both lenses. There is a five element Xenotar and six
element versions of both lenses. I have no idea why the six
element design was chosen for the slower lens, the extra
element would have been more useful for the faster one.
  My experience with Xenar vs: Xenotar is that when stopped
down to "optimum" (around f/11 for the Xenar) there is not a
whole lot of difference. However, the improved performance,
especially away from the axis, is pretty obvious when used
wide open. My experience is that the Xenotar is an
outstanding lens.
 To those claiming better resolution or some other factor
for one lens over the other I ask how the quality was
measured and how many lenses were sampled. I think many
opinions are based on hearsay and not on fact.
Characterising the performance of a lens is not a simple
matter. I would also add that measurements made from film
are fraught with errors which are hard to control, although,
of course, that is how the lens is going to be used.
  My advise in buying a used Rollei, or any other used
camera for that matter, is to pay attention to the condition
of the individual camera more than to which lens it has.


- ---
Richard Knoppow
Los Angeles, CA, USA
dickburk  
>
> > Hi Jerry,
> >
> > > ...Xenotar vs. Planar...
> > > They are, and always have been, equal to each other.
> >
> > There are no visible differences in the images?  Why, if
they are equal,
> > would Rollei even bother to give you a choice then?
> >
> > Austin
> >
>

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