[rollei_list] Re: xenotar 2.8f vs planar 2.8f
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Thu, 11 May 2006 14:48:37 -0700
----- Original Message -----
From: "Jeffery Smith" <jls@xxxxxxxxxx>
Sent: Thursday, May 11, 2006 12:02 PM
Subject: [rollei_list] Re: xenotar 2.8f vs planar 2.8f
Jerry branded me a troll about 4 years ago when I asked
the exact same question. I thought that it was a
completely legit question (then and now), but apparently
it is a "hook" question on this forum. I suspect the variations among lenses of one type are
larger than the differences between the two. I have a
program called Lens View which is a collection of lens
design data for perhaps 30,000 lenses. Incuded are the
prescriptions for the original f/2.8 Planar and for the
Xenotar. I am guessing a bit on the Xenotar because
Schneider has about three variations. I think I know which
was the production lens. LensView will generate files which
can be opened with all the standard lens design programs. I
have the free version of Oslo. The analysis of the two
lenses in this program shows little difference. The Planar
has slightly less zonal spherical aberration. I have not
check them for energy distribution (spot diagrams)which can
indicate differences in edge sharpness. The Zeiss design has
some features which probably made the lenses hard to make
and expensive, the Xenotar is better from a manufacturing
standpoint, i.e., no very small spacings, no extra thin
elements, no highly curved cemented surfaces all of which
are in the Planar.
By the way, I never bought a Rolleiflex with a Tessar
because I was reluctant to ask about the lens quality
compared to the others.
LensView does not have enough information on the glass
types to do a good analysis of color correction. Very few
published lens prescription give the complete glass
Over the years the Xenotar has gotten a reputation for
being sharper than the Planar. The computer analysis does
not show any reason for this. I suspect it may have
something to do with the edge contrast of the two types.
In general, both lenses are based on a design by
C.G.Wynne in the mid 1940's. By combining two elements of
the basic Planar/Biotar type he was able to eliminate one
element and one cemented surface. While the schematic of the
lens would make you think otherwise it is essentially a
symmetrical type with the advantages of cancellation of
coma, lateral color, and geometric distortion which come
with symmetry or partial symmetry.
For the f/3.5 version both Zeiss and Schneider reverted
to the conventional six-element Biotar type lens. It may be
that despite the extra element and additional cemented
surface, the six element lens was cheaper to build than the
five element version given a certain quality requirement.
My choice would be based on the condition of the
individual camera and lens. Lenses should be as near perfect
as possible. So called cleaning marks are not acceptable.
They are fine scratches and result in some diffusion of the
image and loss of contrast. A single large scratch does less
damage to the image.
The Tessars in Rolleiflex's are of very good quality.
Even the old ones are very good lenses. They are not as good
as the Planar/Xenotar for a couple of reasons: one is the
lack of symmetry. While non-symmetrical lenses can be made
to have little or no lateral color (the Kodak Commercial
Ektar is an example) such correction is difficult. Also, all
Tessar types have inherent oblique spherical aberration, a
fault which looks much like coma and results in directional
blur away from th optical axis. This fault, like coma, is
proportional to the stop, so is cured by stopping down. The
f/3.5 Tessar and Xenar are not sharp in the corners until
stopped down to around f/8. An f/3.5 Planar or Xenotar also
has some blur when wide open but will be sharp everywere at
about f/5.6. At small stops there is not much difference
between the Tessar and Planar other than the Planar type
probably has better color correction.
From my experience the Tessars and Xenars used in Rollei
cameras are a toss-up. The Xenar was cheaper but Schneider
lenses were in general cheaper than Zeiss. Perhaps this was
because of production efficiency, perhaps because of
differences in quality control. In practice, at least or the
lenses used in Rolleis there does not seem to be any
I am not sure this is true of other Tessars and Xenars
where I think the Tessar may have the edge.
While there seems to have been a wide gulf between lens
quality between Zeiss and Schneider pre-WW-2, post war
Schneider lenses are a different story. Mostly very well
designed and made with decent QC.
As far as older vs newer Tessars, the old ones were not
coated. For a lens with six glass-air surfaces coating makes
a difference but is not essential. For the five or six
element Planar/Xenotar, with 8 glass-air surfaces, flare
becomes significant so coating is important. Flare increases
geometrically with the number of surfaces.
Los Angeles, CA, USA
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