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Thread: how to work out shims

  1. #1

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    how to work out shims

    out of interest

    how is the need and thickness of shims calculated ?

    my guess is set the camera to infinity i.e. 450mm extension on 450mm lens then see if its in focus
    but how would you measure so precisely

    and how would you shim for macro ?
    my 210 macro sinaron has a shim that is 0.1mm is my vernier gauge is to be believed

    best

    robin

  2. #2

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    Re: how to work out shims

    I think you misunderstand shims, but will leave the explanation to someone else. Your macro does not have a shim because it is a macro.
    Thanks, but I'd rather just watch:
    Large format: http://flickr.com/michaeldarnton
    Mostly 35mm: http://flickr.com/mdarnton
    You want digital, color, etc?: http://www.flickr.com/photos/stradofear

  3. #3

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    Re: how to work out shims

    Are you referring to spacing rings used in mounting lenses to a barrel or shutter? If so, they are used to precisely position the lens elements at the right distance from each other and the aperture so that the lens is properly in focus. To determine what shims are needed, if any, and their size and position, one needs a sophisticated optical bench and very precise measuring equipment. It's not something that can normally be done at home...

    If you're referring to something else, then you need to elaborate a bit so we understand.

    Doremus

  4. #4
    ic-racer's Avatar
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    Re: how to work out shims

    The lens spacing with the shims will let you control flatness of field for infinity and closeup. Closing the aperture can also change focus, so you might need to expose film at working apertures, rather than try to examine the edges of the ground glass with the lens wide open to find the best lens spacing for your purposes.

  5. #5

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    Re: how to work out shims

    OP, where is this shim you mention? If it is between a cell and the shutter, it is there to compensate for a slightly off-specification cell. If it is between the back of the shutter and the lens board, it is there to provide clearance for the diaphragm's actuating lever.

  6. #6

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    Re: how to work out shims

    thanks for the replies

    the shims i’m referring to are the ones between cell and shutter
    in the case of my 210macro it’s in a Sinar DB shutter
    but it’s the same sort that’s in a copal or compur shutter

    best

    robin

  7. #7

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    Re: how to work out shims

    Quote Originally Posted by brighamr View Post
    thanks for the replies

    the shims i’m referring to are the ones between cell and shutter
    in the case of my 210macro it’s in a Sinar DB shutter
    but it’s the same sort that’s in a copal or compur shutter

    best

    robin
    But not necessarily the same thickness. That will vary from none to some depending on the specific shutter and lens.

  8. #8

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    Re: how to work out shims

    Quote Originally Posted by brighamr View Post
    thanks for the replies

    the shims i’m referring to are the ones between cell and shutter
    in the case of my 210macro it’s in a Sinar DB shutter
    but it’s the same sort that’s in a copal or compur shutter

    best

    robin
    If it came with the lens it is what's needed. The only thing you have to do is not lose it if you move the lens to another shutter.

  9. #9
    Tin Can's Avatar
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    Re: how to work out shims

    Also possible any shim has already been lost

    New user will not know


    Quote Originally Posted by Dan Fromm View Post
    If it came with the lens it is what's needed. The only thing you have to do is not lose it if you move the lens to another shutter.
    Tin Can

  10. #10

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    Re: how to work out shims

    so getting back to my actual question

    "how is the need and thickness of shims calculated" ?

    I'm quite happy with my lenses some of which have shims and some do not

    best

    robin

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