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Re: Wide lenses for 12x20 @ 300mm
At 11:16 PM 04/01/2001 -0400, you wrote:
>Hello wise group of sages,
>I am looking for a good wide lens for a 12x20, and am aware of a bunch
>of options in the 360mm range, many thanks to Sandy and others on this
>group and through the archives.
>However, I am thinking about a little wider... say 300mm. I understand
>some of the Dagors will cover, but which ones? There are Goerz, Zeiss,
>and Schneider lenses... In understand the Schneider won't cover, but
>will the Zeiss and Goerz?
>This would be my first purchase of a 'classic' lens, as all my lenses
>right now are 'modern' (1980 or younger), so I am familiar with the
>performance of a modern lens, but am not quite sure what to expect in an
>older, possibly uncoated lens. Any suggestions?
>Thanks for any input...
I don't know the actual diagonal for 12 x 20 film. Most sheet film is a
little smaller than the "nominal" size. However, assuming its pretty close
it would require about a 90 degree coverage angle for a 300mm lens. This is
beyond a Dagor. Dagors will do about 87 deg at f/45. A wide angle Dagor a
little over 90 deg. The f/18 Zeiss Protar series V will cover 100 degrees
but I suspect you are going to have to use a modern lens.
As far as Dagor history, the original Dagor dates from 1892. The patent is
for an f/8 lens but the aperture was raised to f/6.8 soon after. The name
Dagor was adopted in 1904. C.P.Goerz in Germany was merged into the Zeiss
combine in 1926. Zeiss continued to make Dagors until about 1940. C.P.Goerz
American Optical Co. in the US was an independent company, at least from
1914. This company continued to make Dagors and other Goerz designs until
sold to Schneider in 1971 (by memory, not quite sure of the date) Schneider
continued to assemble some Dagors in the US but farmed out production to
Kern Optical in Switzerland. Schneider also built Apochromatic Artars until
about ten years ago.
Schneider did not continue making Dagors for long. For one thing they
were probably expensive to make and Schneider probably also thought their
f/5.6 Symmar a superior lens (there was an earlier f/6.8 Symmar, a copy of
Goerz claimed 87 degree coverage for the Dagor at f/45. It will actually
do this without vignetting but the image quality at the extremes is only
fairly good. I don't know whether the late Gold-Dot Dagor, built by Kern
actually has a smaller circle of illumination due to mechanical vignetting,
or whether its just a more honest assesment of image quality.
The Kern Dagor appears to be an actual re-design perhaps using different
glasses. The Golden Dagor, sometimes called a gold-rim Dagor was just the
old Dagor with a polished brass cell, an advertizing gimmick.
Like many older lenses the QC was not very good so quality among older
Dagors varies somewhat. Goerz had a good reputation this way so the
variation is not as great as for some other brands but each lens should be
checked out individually. Cell spacing is also important so some re-mounted
Dagors may have poor performance if the job was not done carefully.
The Series V Protar, f/18 will actually cover about 102 degrees at around
f/45. Modern WA lenses are faster, sharper, and have less fall off due to
the use of the Slusarov principle. (I'm sure I spelled that wrong).
The old Angulon also claimed 102deg coverage. It will actually illuminate
that large a circle but the image quality is not good. It is a variation of
the Dagor and its actual coverage is no better.