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Thread: Basic Question on Iris Scale

  1. #1

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    Basic Question on Iris Scale

    This is a really basic question, and it seems kind of obvious to me, to the extent that I'm second guessing myself. If I'm missing something, please let me know.

    I have a lens that's f/6.3. I have a shutter that fits that has f/5.6 as the max aperture. Since f/6.3 is 1/3 stop from f/5.6, do I just add 1/3 stop to get the real aperture, at all settings? i.e. if the shutter reads f/8, it's really f/9? if the shutter reads f/16, it's really f/18?

    It seems that would be the more straightforward way to compensate than trying to fit a new iris scale, if indeed it's correct.


    [edit] Sorry, posted in wrong subforum. If a mod could move this, I'd appreciate it. Thanks.
    Last edited by alt.kafka; 30-Nov-2019 at 14:27. Reason: wrong subforum

  2. #2

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    Re: Basic Question on Iris Scale

    Why not just get new scales? On modern shutters they attach with 2 small screws. While you are at it, since someone remounted you’re Lens, you might have someone determine if it is properly spaced or if it needs shims added, or removed?

  3. #3

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    Re: Basic Question on Iris Scale

    OP, aperture scales are lens-specific. You may be able to get away with using the shutter's scale, but this isn't guaranteed.

    Here's the test:

    Open the shutter. Firing it at "T" is best.

    Open the diaphragm as far as it will go.

    Hold the lens at arm's length, front facing you with something bright behind it.

    Slowly stop the aperture down.

    The scale setting at which the diaphragm leaves begin to be visible, and become invisible when you open the diaphragm up to check, corresponds to f/6.3. From there, if the diaphragm leaves become visible when the pointer is at or above f/5.6, where they point on the scale is true f/6.3. What you have in mind to do from there will work.

  4. #4

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    Re: Basic Question on Iris Scale

    A couple of methods of making a new aperture scale are discussed here:
    https://www.largeformatphotography.i...Aperture-Scale

    Kumar

  5. #5

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    Re: Basic Question on Iris Scale

    Hmm, I see it can be at least a little more subtle than I had thought. Both of my shutters are Copal 0's, but one is a Press with no iris at all, and the other is a standard Copal 0. The lens is a Fuji, so my impression was that the Press shutter wasn't original, and would likely have replaced an original (I assume) Seiko. I did see some material about the Press shutters having different thicknesses. I don't know if it was correctly shimmed or not, but either way, I don't have much use for a shutter without an iris. I assumed my standard Copal 0 would be compatible with a Seiko. But, once again, I don't really know what I'm talking about, so I appreciate any corrections.

    I'll definitely bookmark and carefully read Kumar's link above about the aperture scale. I can see there's probably a lot of merit to just taking some emperical measurements one way or another and taping a conversion table to my lens board. I have a feeling that timing on these old mechanical devices is probably off enough to warrant an empirical approach for both shutter speed and aperture.

  6. #6

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    Re: Basic Question on Iris Scale

    Quote Originally Posted by alt.kafka View Post
    Hmm, I see it can be at least a little more subtle than I had thought. Both of my shutters are Copal 0's, but one is a Press with no iris at all, and the other is a standard Copal 0. The lens is a Fuji, so my impression was that the Press shutter wasn't original, and would likely have replaced an original (I assume) Seiko. I did see some material about the Press shutters having different thicknesses. I don't know if it was correctly shimmed or not, but either way, I don't have much use for a shutter without an iris. I assumed my standard Copal 0 would be compatible with a Seiko. But, once again, I don't really know what I'm talking about, so I appreciate any corrections.

    I'll definitely bookmark and carefully read Kumar's link above about the aperture scale. I can see there's probably a lot of merit to just taking some emperical measurements one way or another and taping a conversion table to my lens board. I have a feeling that timing on these old mechanical devices is probably off enough to warrant an empirical approach for both shutter speed and aperture.
    Again, a CLA would be best. Along with proper scales.

  7. #7
    Foamer
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    Re: Basic Question on Iris Scale

    Remember that f-stops are a RATIO, dependent on the lens' length and apertures. If there was another lens in that shutter previously you have no guarantee at all the ratio on the shutter matches the lens now in it.


    Kent in SD
    Qui sedes ad dexteram Patris,
    miserere nobis.

  8. #8

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    Re: Basic Question on Iris Scale

    Press shutters have the same tube length as comparable cock-and-shoot shutters. Their diaphragms, however, are somewhat closer to the rear of the rear tube. Some lenses whose rear cells go deep into the shutter's rear tube can be mounted on cock-and-shoot but not on comparable press shutters.

    All Copal #0 shutters have the same tube length EXCEPT Polaroid Copal Press shutters (so marked), which have longer tubes. Older Fuji lenses were delivered in Seiko, newer in Copal shutters. Even a few in Copal press, but since y'r Copal press has no diaphragm it won't have held a regular taking lens.

    Shims? Posters here carry on about cells whose position in the shutters' tube was adjusted with shims. Could be, and some posters have reported finding shims but shutters and cells were made to fairly tight tolerances. Absence of shims isn't evidence that shims were installed and misplaced.

    Oh, and by the way, in post #3 above I gave you a procedure for matching, sometimes, an aperture scale to a lens. Try it.

  9. #9

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    Re: Basic Question on Iris Scale

    1. If your lens was mounted in a shutter marked "Copal Press for Wista" it is an original shutter. These lenses were sold by Wista for their cameras, and in the case of specific lenses, which if sold with the Wista RF camera, the rangefinder was adjusted accordingly. The Wista RF rangefinder is normally adjusted for Nikkor 135, 150 and 180mm lenses, and can be adjusted for other brands.

    2. Copal #0 and Press shutters (except as noted by Dan above) are interchangeable with Seiko #0 shutters. However, Seiko #1 shutters are slightly larger than Copal #1 shutters.

    Kumar

    Kumar

  10. #10

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    Re: Basic Question on Iris Scale

    Quote Originally Posted by B.S.Kumar View Post
    1. If your lens was mounted in a shutter marked "Copal Press for Wista" it is an original shutter. These lenses were sold by Wista for their cameras, and in the case of specific lenses, which if sold with the Wista RF camera, the rangefinder was adjusted accordingly. The Wista RF rangefinder is normally adjusted for Nikkor 135, 150 and 180mm lenses, and can be adjusted for other brands.

    2. Copal #0 and Press shutters (except as noted by Dan above) are interchangeable with Seiko #0 shutters. However, Seiko #1 shutters are slightly larger than Copal #1 shutters.

    Kumar

    Kumar
    For Wista the Press has an aperture. For OEM purposes it might not have an aperture. For instance for a dedicated machine vision or duping or copying or macro or micro work under fixed lighting or lighting setups where the light output is controllable.

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