Unusual Dual Aperture Scale On Copal #0 Shutter --- f/5.6 & f/16

Discussion in 'Large Format Cameras and Accessories' started by Old-N-Feeble, Sep 17, 2012.

  1. Old-N-Feeble

    Old-N-Feeble Subscriber

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    I've seen thousands of dual/triple aperture scales to include hundreds just on Copal #0 shutters but I've never seen one like this with max apertures of f/5.6 and f/16. This would indicate a doubling of focal length if for a convertible lens or the shutter was intended to be shared between two different sets of cells.

    Does anyone know what lens(es) this scale is for? As you can see the front scale is blank.

    DSCN6454.JPG
     
  2. Worker 11811

    Worker 11811 Member

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    I bet they are T-stops. The approximate reciprocal of F-stops which indicate the amount of light actually transmitted to the film. The slight difference between the scales accounts for light loss by the glass, aperture and other parts of the optical system.

    T-stops are often used in cinematography but they can be used in still photography, too.

    http://en.wikipedia.org/wiki/F-number#T-stop
     
  3. BradS

    BradS Member

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    Although I couldn't say which one, it looks like the scale on a early Rodenstock Sironar (which were convertible).
    does the scale not have any indication of focal length(s)?
     
    Last edited by a moderator: Sep 17, 2012
  4. BradS

    BradS Member

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    see for example, the first photo posted in eBay auction #320971419969

    That is a 100mm lens and the aperture scale is similar but, not quite the same...perhaps, the shutter you have originally came with a 135mm Sironar?


    disclaimer: not my eBay auction...and not that of anybody I know nor is the seller anybody that I have dealt with in the past. I have absolutely no connection to the seller nor any interest in the sale.
     
  5. BrianShaw

    BrianShaw Member

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    I've never heard of TStops being used on shutters except motion picture cameras. Looks like convertable lens to me.
     
  6. Old-N-Feeble

    Old-N-Feeble Subscriber

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    Ahh... this darned feeble brain of mine. Of course the FL are indicated... 150mm and 450mm.
     
  7. Old-N-Feeble

    Old-N-Feeble Subscriber

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    I just did a quick search spurred by your info. That's probably it. This shutter probably originally had an old series Sironar convertible lens mounted in it. Those converted to triple their focal length losing exactly two f/stops.

    Thanks, Brad!!

    I haven't handled many older Sironar lenses and didn't notice the scales on the photos I've seen of them. I learn something new every day... and forget ten things.
     
  8. ic-racer

    ic-racer Member

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    Rodenstock Sironar 150/450 convertible.
     
  9. PanaDP

    PanaDP Member

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    Tstops would be far, far closer together than f5.6 and T16. That would indicate a really awful, terrible, horrible lens. A realistic fstop/tstop combination is more like f5.4/T5.6 and even then, the lenses don't tell you the fstop. It's just labelled with the tstop and that's close enough to the fstop for calculations like depth of field that should be done with a geometric measure (the fstop) rather than a measured quantity of light (the tstop).
     
  10. Worker 11811

    Worker 11811 Member

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    You guys are probably right. I was only guessing.
     
  11. E. von Hoegh

    E. von Hoegh Member

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    Do you often do that, guess, based upon no knowledge or experience, an answer to a question?