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Thread: Making an f/stop scale?

  1. #1

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    Making an f/stop scale?

    I have a 159m Wollensak EWA lens in a non-working shutter. The f/stop lever is very stiff, but movable with effort. I've found another Wollensak shutter that is a direct screw in for the lens - it has no f/stop scale at all.

    Before spending money to send the lens and new shutter off to Grimes, I'd like to experiment with it. Could I make an f/stop scale by simply measuring the old shutter's stops with calipers, setting the new shutter's aperture to the same diameter, then making a mark on a temporary paper scale? Would it be that easy?
    Thanks,
    juan

  2. #2

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    Re: Making an f/stop scale?

    It might be better to calibrate it with a light meter. Measure a uniform light source through the lens with a light meter. Then close aperture to the point where the light meter reads 1 EV or stop less. Make a mark. Continue until the aperture is closed.

    This way, you are reading the actual light passing through the lens. That is all the film cares about.

  3. #3
    hacker extraordinaire
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    Re: Making an f/stop scale?

    I would use a digital camera or light meter to calibrate it as described above. The other method I've used is to measure the diameter of the aperture and calculate it mathematically; the problem here is accurately measuring the exit pupil of the lens, which isn't always the same as the physical aperture diameter.
    Science is what we understand well enough to explain to a computer. Art is everything else we do.
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  4. #4

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    Re: Making an f/stop scale?

    Quote Originally Posted by BetterSense View Post
    I would use a digital camera or light meter to calibrate it as described above. The other method I've used is to measure the diameter of the aperture and calculate it mathematically; the problem here is accurately measuring the exit pupil of the lens, which isn't always the same as the physical aperture diameter.
    Only if the lens has a front aperture the mechanical aperture is the optical aperture. But in the most cases the diameter of the entrance pupil divided by the focal-lenght.

    The whole procedure is described by Emmanuel Bigler here.

  5. #5

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    Re: Making an f/stop scale?

    In this case the OP has access to both shutters with the front and rear cells removed. It would seem a a simple matter to construct a scale for the new shutter that replicates the physical sizes of the aperture at the marked f-stops. Assuming that the cells really do just screw in and the spacing of both relative to the aperture is correct, then this would seem the easiest and most accurate procedure.

    Since both are Wollensak shutters it might be even easier to simply move the scale to the new shutter, but presumably the OP has already determined that that will not work.

    Good luck - Alan

  6. #6
    ic-racer's Avatar
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    Re: Making an f/stop scale?

    Quote Originally Posted by j.e.simmons View Post
    Would it be that easy?
    Yes

  7. #7

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    Re: Making an f/stop scale?

    If the cell spacing and opening size are correct on the new shutter, doing it by measuring will work fine. I've done it a number of times. If the aperture scale is printed on the shutter face, you should be able to swap them. If it's on a plate attached to the outside diameter of the shutter, same thing. Be aware that there are subtle differences in some of these shutters, though.

  8. #8
    come to the dark s(l)ide..... Carsten Wolff's Avatar
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    Re: Making an f/stop scale?

    Yes. No magic needed; i.e. what Glenn just said.
    If its the same type of shutter, it is usually dead easy just to swap the whole faceplate over, esp. so with Wollensaks.

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