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Thread: Changing shutters?

  1. #21

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    Re: Changing shutters?

    Quote Originally Posted by Dan Fromm View Post
    But for post-WWII lenses mounted in post-WWII lenses that conform to the Compur/Prontor/Copal/Seiko #0, #1, and #3 standards, moving a pair of cells from one shutter to another seems fairly safe.
    I agree.

    There certainly was a problem of inconsistent dimensions among manufacturers of older shutters. I didn't know when that was standardized.

    I've done an awful lot of shutter repairs, most being for complete lenses, and I only recall finding shims in one lens.

    Modern machining methods can produce parts (and complete shutters) to very tight dimensional tolerances.

    In the days before CNC machine processes, making parts to tight tolerances cost a lot more than using lax tolerances.
    In that situation it was much cheaper to make the shutter slightly short and use shims to achieve the correct dimension.
    This also provided correction for dimensional errors in the cells themselves, if the lens was set up on an optical bench.

    - Leigh

  2. #22

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    Re: Changing shutters?

    Ed... Any chance you can do a comparison of the two lenses regarding *gasp* bokeh? Then swap the cells and duplicate the test? I'd really like to see the difference between the round vs. penta iris shape. Ill bet others are interested too. BTW, I'll be doing similar comparisons one of these days.

  3. #23

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    Re: Changing shutters?

    Quote Originally Posted by Dan Fromm View Post
    <snip>On a related point, I've removed a moderate number of cells from shutters and barrels for cleaning, have never found a shim between cell and shutter. Has anyone here done the same and found a shim?
    Yes, I bought a new 150mm Sironar (or Sironar-N, can't remember) about 36-37 years ago and it was shimmed front and rear with different thickness brass shims. The 210mm and 300mm I bought at the same time had no shims. These were Copal shutters but I can't remember if they were all black or silver-rimmed.

  4. #24

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    Re: Changing shutters?

    I've only found shims on MF folding rangefinders, never on a LF lens... yet.

  5. #25

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    Re: Changing shutters?

    Quote Originally Posted by Dan Fromm View Post
    Have you measured? I have. Pukka Copal and Compur #1s are 20 mm. The #1 Copals engraved Polaroid Copal are 22 mm. Which drawings did you consult?
    What's a Pukka? Sounds like something you'd apologize for if you did it in public.

    You're talking about the cell spacing, which is 20mm 0,025mm per the Copal spec.

    Different reference surface.

    As stated in post #4, the 22mm dimension that I gave is from the front face of the shutter,
    not from the cell seating plane, as shown in this drawing (dimension at the very bottom):



    - Leigh
    Last edited by Leigh; 4-Jun-2012 at 10:53.

  6. #26

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    Re: Changing shutters?

    Quote Originally Posted by Dan Fromm View Post
    On a related point, I've removed a moderate number of cells from shutters and barrels for cleaning, have never found a shim between cell and shutter. Has anyone here done the same and found a shim?
    It seems to be very rare in modern taking lenses (like a Apo-Symmar) - the makers now seem to adjust the cells for maximum performance when there is no shim between cells and shutters. And modern shutters are generally dead accurate to standard unless explicitly made in another flange depth.

    I've often seen shims on process lenses, as these weren't only optimized for peak performance, but had additionally to be also adjusted to match the nominal focal length precisely, as the all-important magnification scales on process cameras depended on that accuracy - being able to play with inter-cell spacing seems to be helpful there.

    But on old (pre seventies) lenses and shutters, shims are common - the pre CNC way of eliminating tolerances was to cut everything to be slightly undersized and bridge the resultant gap with shims.

  7. #27

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    Re: Changing shutters?

    Quote Originally Posted by Leigh View Post
    The diameter of the entrance pupil is the physical diameter of the opening through the diaphragm blades multiplied by a constant that's a function of the lens design. Each of your lens types will have a different constant.
    In real life, there aren't that many fundamentally different lens designs across modern LF lenses. Indeed you often have no choice among design types if the focal length, maximum aperture and shutter size are to be the same. And within a design type, that constant does not vary that much, usually by much less than a third stop - things only start to get difficult once you switch design types...

  8. #28

    Re: Changing shutters?

    All well and good but on Friday I mounted a brand new Rodenstock 45mm Apo Sironar Digital lens in Copal 0 into a Linhof recessed board and sure enough, between the front group and the shutter there were two shims.

    On Wed. of last week I mounted a 35mm 4.0 Rodenstock HR Digaron-S lens in Copal 0 onto another recessed board and it also had shims.

    2 out of 2 isn't so rare! And these are some of the newest lenses for large format cameras.

  9. #29
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    Re: Changing shutters?

    My 90mm f6.8 Grandagon hasb a couple of shims between the front cell & shutter, I've only come across one other lens with a shim.

    Somewhere Dean Jone (razzledog) mentions he found inconsistent Compur shutters used with early 90mm f6.8 Angulons, some were out of tolerance and the cell spacing was too wide. He found that remaching the shutter housing to the correct tolerances improved the sharpness of what had been previously poor Angulons. Not someting to do at home though

    Ian

  10. #30

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    Re: Changing shutters?

    Quote Originally Posted by Old-N-Feeble View Post
    Ed... Any chance you can do a comparison of the two lenses regarding *gasp* bokeh? Then swap the cells and duplicate the test? I'd really like to see the difference between the round vs. penta iris shape. Ill bet others are interested too. BTW, I'll be doing similar comparisons one of these days.
    Yes, I can do that although I will do it using my 6x9 back.

    I am surprised this thread has had the legs it has and I have been very interested in all the replies, many thanks to you all.

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