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  1. #1

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

    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.

    Click image for larger version. 

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  2. #2
    Worker 11811's Avatar
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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
    Randy S.

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    http://www.flickr.com/photos/randystankey/

  3. #3
    BradS's Avatar
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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 BradS; 09-17-2012 at 07:45 PM. Click to view previous post history.

  4. #4
    BradS's Avatar
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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. #5

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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. #6

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    Quote Originally Posted by BradS View Post
    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)?
    Ahh... this darned feeble brain of mine. Of course the FL are indicated... 150mm and 450mm.

  7. #7

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    Quote Originally Posted by BradS View Post
    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.
    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. #8
    ic-racer's Avatar
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    Rodenstock Sironar 150/450 convertible.

  9. #9

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    Quote Originally Posted by Worker 11811 View Post
    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
    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. #10
    Worker 11811's Avatar
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    Quote Originally Posted by BrianShaw View Post
    I've never heard of TStops being used on shutters except motion picture cameras. Looks like convertable lens to me.
    Quote Originally Posted by PanaDP View Post
    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).
    You guys are probably right. I was only guessing.
    Randy S.

    In girum imus nocte et consumimur igni.

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    http://www.flickr.com/photos/randystankey/

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