Re: [woodandbrass] Re: Antique brass CZJ 240mm Anastigmat-Weitwinkel lens!
----- Original Message -----
From: "Stephen Shohet" <sbshohet@...>
Sent: Friday, August 17, 2012 4:46 PM
Subject: [woodandbrass] Re: Antique brass CZJ 240mm
> Thank you, Richard for the PDF with patent pictures!
> Clearly very
> different from any bigdistant bizarre variation on a
> Goerz-type double
> meniscus. Steve
The story is that Von Hoegh approached Zeiss with the
design for what became the Dagor and was turned away. He
then went to Goerz who accepted the design and made the lens
but swindled von Hoegh out of his royalties.
The reason Zeiss declined the design was that Paul
Rudolph was already working on a similar lens. von Hoegh
shows two versions of the Dagor in his patent differing in
the order of powers of the cemented elements. The version
that was produced by Goerz has the positive elements on the
outside, the opposite arrangement was used by Zeiss for one
version of the Protar and by Watson for the Holostigmat.
This is sometimes called a "reversed Dagor" Voigtlander
used yet another arrangement for the Kollinear which has a
positive element on the outside, a second positive element
in the center, and a negative element facing the stop.
Schneider used a reversed Dagor for the well known Angulon.
Because the reversed Dagor is somewhat longer than the
normal Dagor the Angulon has oversize end elements to avoid
vignetting. The Wide Angle Dagor has equal coverage without
the extra large elements. Note that while the Angulon has
an enormous circle of illumination its actual coverage for a
reasonably sharp image is only about 95 degrees about the
same as for the W.A.Dagor. To get this coverage both lenses
must be stopped down to about f/45.
In fact the f/18 Zeiss Protar must also work at about
f/45 for its maximum coverage, again about 95 degrees. The
Schneider Angulon is slightly unsymmetrical. The purpose is
to improve the correction for distant objects.
I have what seems to be a prototype Angulon, its an
awful lens. According to a friend who is a lens designer the
original patent specifications indicate this. Some error was
made in the design. Since a lot of Angulons were built and
evidently had satisfactory performance it must have been
redesigned rather early in its production. Mine has very
serious color fringing which lenses of this type should be
pretty much free of.