Dual Scale Dagor

Discussion in 'Large Format Cameras and Accessories' started by Steve S, May 27, 2012.

  1. Steve S

    Steve S Member

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    I was lucky enough to be able to get to Photographica in Victoria, London this year where I bought this lens. It is marked 'C P Goerz Berlin No 132718 Doppel Anastigmat DRP No 74437 Series III No 4 f = 240mm'. A nice find particularly as it came mounted in a compound shutter and attached to a MPP lens board. What I have not seen before is the dual aperture scale:
    Scale 1 (outermost) reads 6.8, 8, 11, 16, 22, 32, 45 and 64
    Scale 2 (innermost) reads 4.6, 6, 12, 24,48,96, 192, and 384

    Scale 1 is the one we are now all familiar with and scale two is understandable as a simple arithmetic progression representing a halfing or doubling of transmitted light depending on the direction in which the aperture ring is moved. At first I thought these might be U.S. f stops as seen on many of the early Kodak cameras but the equivalent values are different to those I was able to find in my searches, for example the U.S. equivalent to f 16 is 32, not 24 as here. Then I found a reference to Goerz stops but could find no further information.
    So my question is (after a rather long-winded preamble) can anyone confirm whether these are indeed Goerz stops and if so, how are they calculated?
     

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  2. Whiteymorange

    Whiteymorange Member

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    Not sure how they are calculated, but here is an 1899 chart of comparative scales, thanks to David Stein and the largeformatphotography.info site.
     
  3. premortho

    premortho Member

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    U.S. 16 equals f16, and US numbers either halve or double from there. Example; us32 equals f22, us8 equals f11.
     
  4. Sirius Glass

    Sirius Glass Subscriber

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    Based in the reference in post #2, the second scale is Georz.