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Thread: "Re-scaling" a Copal 3 shutter - how to ?

  1. #1

    Join Date
    Oct 2003
    White Lake, Ontario.

    "Re-scaling" a Copal 3 shutter - how to ?

    I have a 240 Sironar in a Copal 3 shutter that I want swapped with my (barrel) 355 G-Claron. Of course, the f-stop scale will be wrong for the 355 so my question is: What is the best way to scale the shutter properly to match the new lens?


  2. #2

    Join Date
    Dec 2000
    Tonopah, Nevada, USA

    "Re-scaling" a Copal 3 shutter - how to ?

    Your current scale will be 1 stop off. For instance if your aperture were to measure roughly 22mm dia. you would find that 11X22 = 240 so it is at f11 How many of the 22's to = 360? 16
    He is no fool who gives what he cannot gain that which he cannot lose. Jim Elliot, 1949

  3. #3
    Michael Jones's Avatar
    Join Date
    Nov 1998
    Nashville, Tennessee

    "Re-scaling" a Copal 3 shutter - how to ?


    Aside from having S K Grimes engrave a new scale, you can call Schneider and order the real McCoy that screws onto that shutter. Good luck.

    “You can’t have everything. Where would you put it?”

  4. #4
    Ted Harris's Avatar
    Join Date
    Aug 2000
    New Hampshire

    "Re-scaling" a Copal 3 shutter - how to ?

    AFAIK you can also get the correct scale to screw on from Badger or Midwest. As I recall they cost around $15.00.

  5. #5

    "Re-scaling" a Copal 3 shutter - how to ?

    I contacted schneider about a scale for my 240 G-claron, as it is one stop off. I was quoted $90.00.

  6. #6

    Join Date
    Jan 2002
    Besançon, France

    "Re-scaling" a Copal 3 shutter - how to ?

    I assume that a recent Copal 3 shutter has "linear" diaphragm scales.
    So you just need to move the existing f-number scale (or a copy of it) by a certain fixed amount, probably about one f-stop.
    You can check that the aperture is properly set by applying the definition of the f-number : focal length divided by diameter of entrance pupil.
    Place a small flashlight in the focal plane and illuminate the lens backward, place a piece of (translucent) paper in front, close to the entrance lens element, you'll be able to measure the diameter of the entrance pupil easily, it is the diameter of the illuminated circle you can see through the paper.
    e.g. a 355mm lens stopped down to f/16 requires an entrance pupil diameter of 355/16 = 22 mm.
    This simple test will allow you to check that you are OK. The tolerance is reasonable, say, 1/3 f-stop off is not a big deal.

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