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Thread: Lost the shim in my lens

  1. #1
    wclavey's Avatar
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    Lost the shim in my lens

    I have a 210mm Sironar-N lens mounted in a Copal shutter. It had a shim behind the front cell; it was mounted that way when I purchased it. A few months ago, I was out shooting in the field; it started to rain; I was trying to remove a tight filter from the front of the lens and mistakenly unscrewed the lens cell from the shutter - - losing the shim in the knee-high weeds.

    While I cannot see a difference in the focus without the shim, either at infinity or up close, I am certain that the shim was there for a reason. I also tried to see if I could detect any change by examining the image with a loupe focused on ifinitiy, close to 1:1 and at the midpoint, adjusting the position of the front cell in the shutter by screwing it in and out. My thought was that perhaps I could calculate what size shim it needed by knowing how far out I had unscrewed the cell. Again, I could not see a difference, but I am certain that it is needed.

    So my questions are: who can do the necessary testing or how do I determine what size shim it might need and where would I get said shim? Is there someone who does that kind of testing?

  2. #2
    C. D. Keth's Avatar
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    Re: Lost the shim in my lens

    That lens should have a standard shim for that particular shutter. Contact the manufacturer, they should be able to tell you the thickness and where you can get one.
    -Chris

  3. #3

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    Re: Lost the shim in my lens

    I thought shims were installed at the factory to correct for variations in shutter thickness. For what it's worth, I checked my 210 Sironar-N, and the shim is 0.007-inches.

  4. #4
    C. D. Keth's Avatar
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    Re: Lost the shim in my lens

    That could be. I remember teching a group of identical lenses when I was in school and they all had identical shims. I assumed they were uniform but perhaps not.
    -Chris

  5. #5

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    Re: Lost the shim in my lens

    The shims is there to adjust the lens-faults like astigmatism and coma in the outer lens-areas, so if one checks the image in the center with a loupe, there is no difference between with shim or without. Also the thickness is different for infinity work and for 1:1.
    To adjust the space between front-cell and shutter is described here http://www.largeformatphotography.in...light=infinity

    Christopher, every lens will be checked in the factory and is eqipped with a shim in the thickness needed. But the difference between shims has to measured with a micrometer not by eye.

    Cheers
    Peter K

  6. #6
    C. D. Keth's Avatar
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    Re: Lost the shim in my lens

    Quote Originally Posted by Peter K View Post
    Christopher, every lens will be checked in the factory and is eqipped with a shim in the thickness needed. But the difference between shims has to measured with a micrometer not by eye.

    Cheers
    Peter K
    Thanks for the clarification. I didn't just eyeball the shims, though. The thickness was written on them in sharpie.
    -Chris

  7. #7

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    Re: Lost the shim in my lens

    So the lens is always equipped with a shim for more freedom to align the lens. Without shim one can only increase the distance frontlens - diaphragm. But this depends on this specific lens, the next batch from the same focal-lenght can be different.

  8. #8
    wclavey's Avatar
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    Re: Lost the shim in my lens

    Peter, thanks for the link. Now I can see why I could not tell a difference - - I was looking at an image in the center to try to detect a difference. I'll try it the way described in the link.

    So where do I get the shims? I have been to the major camera equipment and lens sales sites and none of them seem to have something like this described in their catalog. Can you buy something like this at the hardware store?

  9. #9

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    Re: Lost the shim in my lens

    The problem with a shim is it has to have a certain inner and outer diameter and the most critical parameter is the thickness. So a washer from the hardware store can be a solution. But normaly the shim has to be made with the needed dimensions.

  10. #10

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    Re: Lost the shim in my lens

    Quote Originally Posted by wclavey View Post
    Peter, thanks for the link. Now I can see why I could not tell a difference - - I was looking at an image in the center to try to detect a difference. I'll try it the way described in the link.

    So where do I get the shims? I have been to the major camera equipment and lens sales sites and none of them seem to have something like this described in their catalog. Can you buy something like this at the hardware store?
    Camera repair technicians will have shims.

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