[rollei_list] Re: Planar vs. Planar
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Wed, 3 Mar 2010 06:14:40 -0800
----- Original Message -----
From: "Elias_Roustom" <elroustom@xxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Wednesday, March 03, 2010 5:39 AM
Subject: [rollei_list] Planar vs. Planar
Maybe today, maybe tomorrow, my 3.5F should be in my hands
after several weeks in hospital.
What are noteworthy differences between the 2.8C Planar
and the 3.5F Planar that I should look forward to?
Elias
If you are referring to the lenses alone they are really
two different lenses with the same name. The Planar on the
2.8C is a five element lens of a type originated by
C.G.Wynne of Wray in England. Wynne found that he could
elminate one of the elements in a classical Planar by
combining powers of two of the elements. The Wynne lens
works well up to about f/2.8 although Wynne made a more
complex version for higher speeds. The Planar in the 3.5F
Rollei is a classic six element lens. Why both Zeiss and
Schneider switched from the five element to the six element
version is open to question. My own guess is that there was
some economic advantage in it although on first examination
it should have been the other way around. Cemented surfaces
require several extra steps which make them more expensive
to make. The Zeiss f/2.8 Planar is a more difficult lens to
build than the Schneider Xenotar. The Planar has the
cemented component in the front. The front element is very
thin and steeply curved so it must have been difficult to
make and the cemented surface would have called for great
care to avoid distortion of the thin glass. The Xenotar, on
the other hand, has the cemented component inside with a
nearly plane cemented surface. The computer analysis of the
two based on patent data shows the Planar to be very
slightly better corrected than the Xenotar despite the
Xenotar having the reputation for being the sharper of the
two.
The six element lens has a long history. The original
design came from Paul Rudolph of Zeiss, the inventor of the
Tessar. Rudolph based his lens on an earlier type sometimes
called a double-Gauss lens because it was a symmetrical
arrangement of the two element lens invented by Carl
Friedrich Gauss for use as a telescope objective. This lens
has excellent color correction but tends to have a large
amount of spherical aberration. Rudolph found that by making
the inner elements very thick he could cure the spherical.
He also split them using a cemented surface to obtain the
effect of an unavailable glass type for improving chromatic
correction. Rudolph's lens was called a Planar because it
had an unusually flat field. However, its symmetry caused
problems with correction of distant objects. The original
lens was developed further as an unsymmetrical lens by
Horace Lee of Taylor, Taylor, and Hobson. Lee's lens was
called the Opic and is really the prototype of all of the
six and more element lenses used in 35mm and other cameras.
The same idea was later used by Willie Merte of Zeiss in the
well known Biotar. Essentially the lens in the f/3.5 Rollei
is an Optic/Biotar type lens. These lenses can be corrected
well to about f/2 so its just idling at f/3.5. Probably the
choice of the Wynn lens for the f/2.8 came partly from its
lighter weight. That would not be so much of an issue with
the slower lens in the f/3.5 but its also a puzzle that
Rollei began with five element f/3.5 lenses and then went to
the more complex one. It should have been the other way
around because it is the faster lens which would need the
extra degrees of freedom for correction. The reason was
definitely not to filter UV out or anything of the sort. The
elements in the sixe element lens are all working and none
is a filter. beside, UV filtering, if desired, is
acomplished by the limited spectral transmission of some
optical glasses and also by the choice of cements, some of
which are excellent UV filters. In fact, its rathter more
difficult to make a lens with good UV transmission than
otherwise.
Now to cut to the chase, I doubt if there is much to
choose between the two designs, as there isn't much
difference between the Planar and Xenotar in practice. All
of these lenses are very highly corrected and capable of
very sharp reproduction with excellent color correction.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
Rollei List
- Post to rollei_list@xxxxxxxxxxxxx
- Subscribe at rollei_list-request@xxxxxxxxxxxxx with 'subscribe'
in the subject field OR by logging into www.freelists.org
- Unsubscribe at rollei_list-request@xxxxxxxxxxxxx with
'unsubscribe' in the subject field OR by logging into www.freelists.org
- Online, searchable archives are available at
//www.freelists.org/archives/rollei_list
Other related posts:
