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Re: Wide lenses for 12x20 @ 300mm
At 07:16 PM 04/02/2001 -0600, you wrote:
>At 01:33 AM 02/04/2001 -0400, you wrote:
>>I have a Carl Zeiss 300mm Dagor that easily covers 14x17 (~same diagonal as
>>12x20) at infinity. I also have a 240mm CZ Dagor that just hits the
corners
>>on 14x17.
>>
>>Kerik Kouklis
>>www.Kerik.com
>>
>
>A 19" Dagor will give more than enough coverage - up to 20x24 in fact when
>stopped down. I don't know where Richard got his information that Dagors
>will not cover 12x20, but it is not correct. I can confirm Kerik's
>comments about the 14" 7.7 Carl Zeiss Dagor as well - enough coverage for
>14x17 for sure, with some movements.
>
The question, as you quoted above, was for a 12" (300mm) lens, not a 19"
lens. The format requires a 23" image circle. The angle required of a 12"
lens to cover a 23" circle is something over 87deg, the absolute limit of
the lens. For a 19" lens its only about 60 degrees, which a Dagor will do
at f/22.
The diagonal for 14 x 17 is 22 inches, not a big difference but maybe
enough to result in some vignetting for the 12 x 20. For the 14x17 format
the iamge angle is 85 degrees.
For a 340mm lens and 14x17 the image angle is 95 deg. A Wide Angle Dagor
may do this but it would be a very unusual standard Dagor which could make
it.
The design results in a certain thickness of elements which determines
the ultimate coverage angle because of mechanical vignetting.
Goerz American's version of the W.A.Dagor was an f/8 lens, the Zeiss and
German Goerz version is an f/9 lens.
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com