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Thread: A DIY 123mm f/8 Cooke split triplet for 4x5

  1. #31

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    Re: A DIY 123mm f/8 Cooke split triplet for 4x5

    Quote Originally Posted by Dan Fromm View Post
    Matt, if you're not acquainted with dioptrique.info, take a look at it. It is in French, has prescriptions for > 1,000 lenses, many taken from patents. Eric Beltrando, its owner, is one of my friends. He was a friend of CEDIS-Boyer's owner and reoptimized Boyer prescriptions for properties of newly-arrived batches of glass. He wrote the program that produced the performance curves etc. on his site. I mention Eric and dioptrique here because he insists that Dagors (f/6.8 and f/7.7) have much less coverage than the 85 degrees Goerz claimed. He says the same about f/9 w/a Dagors, see http://www.dioptrique.info/OBJECTIFS11/00533/00533.HTM. He calculated that the f/18 Protar V has much more coverage. See http://www.dioptrique.info/OBJECTIFS1/00034/00034.HTM

    I hope that I'm mistaken, but I doubt you'll be able to assemble anything like these lenses using COTS lenses.
    My circa 1933 Carl Zeiss Jena catalogue doesn't give coverage angles for their various lenses but does give the "Diameter of circle covered at small stops"; 10 1/2 and 15 1/2 inches respectively for the 18 cm f/6.8 and f/9 Dagors (this catalogue is for the U.S. market). Doing the arithmetic and trigonometry this gives coverage angles of 70 and 95 degrees. So for the f/6.8 Dagor they are showing a bit less than what Goerz American claimed. As for the Wide Angle Dagor, Goerz American claimed 100 degrees at f/45 until at least the early 1950's; later they dialed this back to 90 degrees.

    This Zeiss Jena catalogue shows the 18 cm Series V (f/18) Protar covered a 16 inch circle "at small stops".

    David
    Last edited by David Lindquist; 24-May-2021 at 20:11.

  2. #32
    Nodda Duma's Avatar
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    Re: A DIY 123mm f/8 Cooke split triplet for 4x5

    Quote Originally Posted by Dan Fromm View Post
    If we had ham we could have ham and eggs if we had eggs.
    I’m going to use that in a meeting in the near future
    Newly made large format dry plates available! Look:
    https://www.pictoriographica.com

  3. #33

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    Re: A DIY 123mm f/8 Cooke split triplet for 4x5

    Marketing value of advertised and want to believe image circle of any given view camera lens. This ideology and desire persist to this day without the much needed balance of what lenses-optics the camera is capable of dealing with and actual image goal requirements.

    During the mid 1980's first wide angle lens acquired for 4x5 was a 4-3/8" golden wide angle dagor. Worked mostly good for 4x5 if stopped down smaller than f22. This "Golden" wide angle dagor was advertised as good coverage or image circle large enough for 5x7 with camera movements. Few short years later, 5x7 happened, the same "Golden" wide angle dagor was applied to the 5x7 film format, it just barely covered 5x7 at f45 with slight darkening of the corners unless the GWDR was used direct on film center zero camera movements. Did not take long before the very real optical performance limitations of the GWDR found it a new home after being replaced by a 115mm f6.6 Grandagon. Absolute superior optical performance to the GWDR, never looked back and have continued with majority of modern wide angle lenses since.

    There is a place for vintage wide angle lenses like this, such as hiker-back packers with light weigh field folders where space and weight is paramount. Except too many place these values as the overly generalized features that is most important to all view camera users.. which is never accurate or true.

    That said, Dagors have their place and remain a top choice for specific image goals. Much about knowing what the image goals are then applying the lens and remainder of the image making system to meet these image goal needs.


    Bernice






    Quote Originally Posted by David Lindquist View Post
    My circa 1933 Carl Zeiss Jena catalogue doesn't give coverage angles for their various lenses but does give the "Diameter of circle covered at small stops"; 10 1/2 and 15 1/2 inches respectively for the 18 cm f/6.8 and f/9 Dagors (this catalogue is for the U.S. market). Doing the arithmetic and trigonometry this gives coverage angles of 70 and 95 degrees. So for the f/6.8 Dagor they are showing a bit less than what Goerz American claimed. As for the Wide Angle Dagor, Goerz American claimed 100 degrees at f/45 until at least the early 1950's; later they dialed this back to 90 degrees.

    This Zeiss Jena catalogue shows the 18 cm Series V (f/18) Protar covered a 16 inch circle "at small stops".

    David

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