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Thread: How hard/easy to mount lens in a 'new' Copal shutter

  1. #31

    Join Date
    Dec 2005
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    Los Angeles, CA
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    Re: How hard/easy to mount lens in a 'new' Copal shutter

    Quote Originally Posted by Sal Santamaura View Post
    Bob provided a complete answer in his post (#2). Everything after that has served only to confuse the matter.

    First, although supplies are dwindling, new Copal shutters are still available. Second, shims are used to fine tune cell spacing so that optical variations can be compensated, not because of shutter manufacturing tolerances. Those optical variations are more than an order of magnitude greater than Copal's thickness tolerance.

    Using Rodenstock as an example, shims ranged from 0.5 to 1.5mm. Copal shutters carry a thickness tolerance of ±0.025mm.
    So who does this fine tuning, Sal... the yenta that’s mating a lens to a shutter? Based on some optical measurements?

  2. #32

    Join Date
    Jul 2016
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    Re: How hard/easy to mount lens in a 'new' Copal shutter

    Quote Originally Posted by BrianShaw View Post
    that’s mating a lens to a shutter? Based on some optical measurements?
    The lens is not mated to a shutter, all modern shutters are equal, what is mated is a front cell to a rear cell, for each pair of cells there is an optimal lens spacing, not because the threads of the cells are not done equal, but because glasses are not all equal, refraction index of a batch may vary slightly (say an 1 per 1000), thermal issues during manufacturing, etc who knows... but optical design may allow a better compensation of aberrations (front+rear) by shimming.

    So if replacing a shutter we can use a caliper to check that the new one is same thickness, but the important thing it will be reusing the shimming that mates the front cell to the rear one for best performance.

  3. #33

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    Dec 2001
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    NJ
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    6,753

    Re: How hard/easy to mount lens in a 'new' Copal shutter

    Papi, Boyer recomputed lenses for each batch of glass. My friend Eric Beltrando sometimes did that work for his friend M. Kiritsis, Boyer's last owner.

  4. #34

    Join Date
    Jul 2016
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    1,929

    Re: How hard/easy to mount lens in a 'new' Copal shutter

    Quote Originally Posted by Dan Fromm View Post
    Papi, Boyer recomputed lenses for each batch of glass. My friend Eric Beltrando sometimes did that work for his friend M. Kiritsis, Boyer's last owner.
    Just an speculation... if a design may make spherical and chromatic aberrations more or less proportional in the front cell depending on glass, and the same in the rear cell but with aberrations compensating in the other sense... then inter-cell spacing would adjust how big the aberrations are when rays arriving to the rear cell, in order to get an optimal cancellation.

    What I say is that if a design is sound enough perhaps shimming could compensate glass variability without recomputing the lens and messing in serial production. Perhaps in most modern computerized designs a priority was alowing a clean compensation of glass variability by a simple shimming... I repeat , just speculating... just realizing the value of that possibility...

  5. #35

    Join Date
    Nov 1999
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    San Clemente, California
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    3,207

    Re: How hard/easy to mount lens in a 'new' Copal shutter

    Quote Originally Posted by BrianShaw View Post
    So who does this fine tuning...
    As Bob has posted endlessly over the years, the factory does it using elaborate optical measuring equipment. That's why it's important to transfer the original shims when moving cells into a replacement shutter. An independent optical facility could perform similar optimization if 'loose' cells need placement in a shutter or if re-shuttering cells where it's not known whether original shims existed or have been changed.

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