[rollei_list] Re: Planar and Xenotar
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Sat, 16 Feb 2008 21:30:08 -0800
----- Original Message -----
From: "Eric Goldstein" <egoldste@xxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Friday, February 15, 2008 6:19 AM
Subject: [rollei_list] Re: Planar and Xenotar
> lol. This of course was phrased to be as snitty as
> possible. Every
> once in a while I like to trot out the "lens wars" thread
> in memory of
> long-time list member Les Clark, who loved to have fun
> with it...
>
> However, from what I can see, the character of the 80/2.8
> Planar and
> the 75/3.5 Planar are not the same!
>
> (Flame suit at the ready)
>
> Eric Goldstein
>
> --
They may not look quite the same plus there are
evidently two forms of lens which were sold under the name
_on Rolleiflex_ cameras.
The original Planar was a symmetrical lens with six
elements designed by Paul Rudolf of Tessar fame which was an
elaboration of the symmetrical form of the Gauss lens. This
lens had good performance but was improved by H.W.Lee, of
TT&H as the Opic. Lee made the lens somewhat unsymmetrical
by shifting power from one cell to the other to improve the
performance for distant objects. Other designs of similar
type were the Schneider Xenon and Zeiss Biotar. This is a
very versitile design and a very great many high speed
lenses are based on it.
In the mid-1940's C.G. Wynne, of Wray, discovered that
he could get most of the virtues of the six-element Opic
type with one less element by combining the powers of the
two positive elements in one section. In a sense he returned
to the Gauss lens for one half of his lens. Despite the
seemingly completely non-symmetrical plan the lens actually
retains considerable symmetry and thus can be made
relatively free of coma, lateral color, and geometrical
distortion. It evidently shares with the Opic type a
relative freedom from spherical aberration. The Wynne lens
works well for speeds up to about f/2.8 but some have been
made up to f/2.
The f/2.8 Xenotar and f/2.8 Planar are versions of the
Wynne lens. They differ in the arrangement of elements. The
Xenotar has a cemented surface in the second element
consisting of a plane surface. The original Rollei Planar
has the cemented surface in the front element in a rather
highly curved surface. This probably made it more difficult
to manufacture. In addition, the spacing of the first two
elements is very close calling for great precision in the
mount, again probably increasing the difficulty and cost of
manufacture. According to the patent specifications for the
two the performance is very close although the Planar
appears to have very slightly better correction of spherical
aberration.
The VEB Zeiss Biometar is again very similar to the
above and also has very similar performance.
Schneider built only one version of the Xenotar in
f/2.8 speed. Zeiss shows a couple of other forms differing
in that they move the cemented surface to a point where it
would be easier to manufacture. The performance of these
lenses are again very similar although the original Planar
appears to be very slightly better than any of the others.
For the f3.5 version of both the Planar and Xenotar
both five and six element designes were made. I don't know
why the five element type was abandoned but it may have
proved to be more expensive to manufacture than the five
element type for the slower lens plus its greater
compactness and lighter weight would have been of less
importance. Both the Zeiss and Schneider lenses are really
classic Opic or Biotar types and share the usual virtues of
this lens. The two manufacturers used very similar designs,
both of which have plane or nearly plane cemented surfaces.
Since the six element Opic/Biotar will perform very well at
f/2 it should be outstanding at f/3.5 and have good
sharpness to the margins even wide open although, of course,
it will be improved in the margins by stopping down. One of
the advantages of both the five and six element lenses is
that the freedom from spherical aberration reduces focus
shift to a minimum. This is important for lenses which are
coupled to rangefinders or reflex finders for focusing
because any focus shift will make the focusing means
inaccurate at some stops, the range depending on where the
focusing mechanism has been adjusted for coincidence with
the lens. BTW, I think this is the real culprit for errors
often attributed to film buckling.
From the analysis available to me the performance of
all of the six element f/3.5 lenses is very close to the
f/2.8 types and all are excellent.
Note that the designs of lenses used in single lens
reflex cameras are different even though they share the same
trade names as the Rolleiflex lenses.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
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