Mamiya M645 finder prism damage caused by degrading foam

Discussion in 'Medium Format Cameras and Accessories' started by cinejerk, Mar 29, 2012.

  1. cinejerk

    cinejerk Member

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    I sure wish I had found out about the prism foam damage issue before I bought my camera. :sad:
    I did find some info buried in a thread about the Mamiya M645 foam damage issue but it took a
    lot of searching.
    Maybe this thread will alert prospective purchasers as to what questions to ask the sellers.
    I don't know if anyone has found a reasonable place to re-coat the prisms. I did find someone
    who coats telescope mirrors but at $50 it probably isn't going to happen.
     
  2. cinejerk

    cinejerk Member

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    I guess these things are just too old to care about. :D
     
  3. benjiboy

    benjiboy Subscriber

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    I would just buy another prism finder.
     
  4. cinejerk

    cinejerk Member

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    That's exactly what I'm going to have to do Ben.

    Repairing them is not very cost effective.

    These aren't being made anymore and from what I hear they could all have this problem.

    Like a ticking time bomb !! :D
     
  5. wblynch

    wblynch Member

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    Think of the future when they are not easily purchased. We will have to repair them. I would hope people don't chuck them in the bin today. Pretty soon they will be precious and then "worth it" to get them fixed.
     
  6. ic-racer

    ic-racer Member

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    I'm curious about this (I don't have a M645 prism to check). I have not seen the goop from a bad SLR mirror-bump foam cause a problem with the mirrored surface. The goop has always come off with solvent, leaving the silvered front mirror OK.
     
  7. John Koehrer

    John Koehrer Subscriber

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    On the prisms I've seen the reflecting surface looks like it's given a protective(?) coat of lacquer or enamel. THat may be the weakness.
     
  8. cinejerk

    cinejerk Member

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    The guy I talked to who does telescope mirror's said that when he does a prism like that he does paint the back with lacquer.
    Maybe you've got something there. It doesn't seem the foam residue would attack straight aluminum.
    But it doesn't seem it would penetrate lacquer either.
    I don't know.
     
  9. MattKing

    MattKing Subscriber

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    I always understood that the problem with the prisms was predominantly one of element separation, not damage from degrading foam?
     
  10. chriscrawfordphoto

    chriscrawfordphoto Member

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    Some Olympus 35mm SLRs had the same issue, degrading foam released chemicals that ate into the prism. Which 645 prisms are we talking about? I have a 645 Super with non-metered prism. Is this something I need to watch for on mine, or was it only older 645 models whose prisms had this?
     
  11. wblynch

    wblynch Member

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    Good point. There are several different ones even for the M645. I have two of the metered prisms and they show no signs of foam degradation.
     
  12. cinejerk

    cinejerk Member

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    Yes they have separation problems too. The problem I'm talking about is from foam degradation under the hold down clamp. It shows up as a rectangle in the viewing area. I'm not sure if the newer prisms have that problem or not.
    That's the main problem. There doesn't seem to be a whole lot of information around.
    Here is an example of the problem.

    http://www.pbase.com/pganzel/image/71821169
     
  13. ic-racer

    ic-racer Member

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    Thank you for the picture. Clearly a problem there.
     
  14. cinejerk

    cinejerk Member

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    I finally got a response from the guy that was repairing the prism in the above link. He said when he got the silvering cleaned off he cut a front surface mirror and just taped it on.
    I wonder how that compared optically to the original. I suppose that doesn't matter all that much because it doesn't show up in your final image. Unless it impedes your ability to focus in the first place. :pouty: