[LargeFormat] Compound Shutters

[Richard Knoppow]

----- Original Message ----- 
From: "Wilkes, Don MSER:EX" <Don.Wilkes@gems9.gov.bc.ca>
To: <largeformat@f32.net>
Sent: Friday, December 05, 2003 8:46 AM
Subject: RE: [LargeFormat] Compound Shutters


Thanks, Richard!  I had a response from Mr Croell this
morning, which echoes
much of what you just said.  Here it is:

-------------------
Don,

D.R.P. stands for Deutsches Reichspatent (not republic,
unfortunately) and
was
superseded in West-Germany by the "Deutsches Bundespatent"
DBP. By the way,
you
can research German and other patents online (search
functions available in
English, too) at the German patent office:
http://www.depatisnet.de. Both
DRP and DBP patents are listed under the DE prefix (pulldown
menu top left
in the beginners search mask). I just checked your number
DRP 142293, and
there must be
a typo since it is about some mechanical construction.
However, it is from
1902
which was the year Rudolphs Tessar came out, so I assume its
off by only a
few
numbers?

As for your lens, the "Lens Collectors Vademecum" says the
following about
your
lens:

"Series IIb (1902) f6.3. 1.5-23.25in. It is suggested to use
14in. for 10x8,
6in. for 5x4. This was a most favoured lens! 70°. .... The
series numbering
suggests it replaced Anastigmat series II in the f6.3 series
in the lists.
This
f6.3 Tessar is the connoisseurs choice and usually
available.  In 1914 it
was
made in 3, 3.5, 4.75, 5.25, 6.0,6.5, 7.0,8.25, 10, 12, 14,
19.25, and
23.25inch,
and 14 in was suggested for 10x8, 6in for 5x4."

The Zeiss article there also mentions that serial number
1734xx was 1912, so
yours is before that.

Arne Croell
-------------------

It looks like I shall have to peer more closely at that
Patent number, and
make sure I have it right before rummaging around on that
German Patent
website.

So, who says you have to have the latest and greatest
computer-designed,
multi-coated hunk o' glass?  My pre-First-War little Tessar
managed to give
some shots of Yosemite last September which pleased me, and
that's all that
matters, right?

Cheers,
\donw


  According to Brian Caldwell a lens designer and author of
the LensView program, many of the old Zeiss lenses are so
close to being optimum that they can not be significantly
improved with computer optimization, even with changes in
glass. So, your mid-teens or early 1920's Tessar may be as
good as much modern stuff.
  I have two Tessars, 135mm, f/4.5, made in the late 1930's.
Both are very sharp lenses. I can see a difference between
them and a 127mm, f/4.7 Ektar. Evidently the Ektar has less
spherical aberration when wide open, the Tessars are very
slightly soft, but the effect is gone by about f/8. In
addition the Ektar, when uncoated, suffers from a ghost
image of bright objects in the field. The Tessars do not.
Other lenses which seem to close to optimum are the
Convertible Protar and the older version of the Biogon.
Evidently Zeiss had a lot of computational horsepower
available as well as some outstanding designers.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com