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  1. #1
    L Gebhardt's Avatar
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    Olympus OM-1 warning: Check for foam around prism, and remove it if found

    So I pulled out my OM-1 and noticed some strange looking goo in the bottom of the viewfinder. I determined it wasn't on the focus screen, but rather on the prism. A bit of searching found that this is a common problem. Olympus installed some foam in most of the OM1s as a light shield. It's apparently not really needed, and for a while the factory left it out. Then they went back to using it for the OM-1N. The problem is the foam deteriorates and turns into a tarry prism eating mess. And unfortunately once the foam eats the paint and silver off the prism there's not an easy way to repair the prism.

    I luckily had a spare OM-1 that had some other issues, but a clean prism. I followed the instructions at http://olympus.dementix.org/Hardware...val/index.html and was able to swap the prisms.

    If you have an OM-1 it would be in your best interest to open the camera up and see if there is foam installed over the prism. If there is foam you should remove it before it kills your prism. It took me about 40 minutes to follow the directions to open the cameras and swap the prisms. It should be even quicker if you just need to remove the foam.

  2. #2

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    That's a problem with most Japanese cameras. The foam that's used as light seals and in other areas either turns to a crumbly mess (if you're lucky) and gets all over the focusing screen or turns to goo. If it ends up in the shutter, then it's a real mess.

  3. #3

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    As elekm points out, that's a common problem. Periodically, I have my Minolta SRTs cleaned, lubricated, and adjusted. The guy who does it for me replaces the foam as a normal part of a CLA.

  4. #4
    L Gebhardt's Avatar
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    Just to be clear, this isn't the foam damper that the mirror bumps into, but rather foam hidden under the top plate. Is that normally replaced in a CLA? Do Nikon cameras have foam buried there that eats prisms? If so I need to get some of them replaced.

  5. #5

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    An OM10 prisms will swap into a OM1 usually and a parts OM10 is cheaper and easier to find, the OM10 prism may not be multicoated.

  6. #6

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    This is a well known problem with the OM-1. Olympus used the foam to prevent light leaks around the viewfinder, but stopped using it in later models. There is no light leak problem with it removed.

    There is really no need to replace the prism as the damaged section will normally be confined to the very bottom of the viewfinder. Also, the prism doesn't need the silvering to reflect light - what you actually see is the edge of the damaged silvering. Just remove all the nasty foam gook, then remove the prism. Polish the damaged area to feather the silvering smoothly around the damaged area (Use Simichrome or toothpaste). The damage will no longer be visible in the viewfinder.

    I've done both the replacement and the repair method and have found the repair the best route to go. You don't have the expense or extra time involved in trying to find a replacement prism.

  7. #7
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    Tim, that's good to know that you can repair the prisms. Everything else I've read has said they are shot once the silvering is gone. I guess they rely on a large enough angle to have total internal reflections if the silver can be removed. If so, I wonder why they needed to silver them, and why the pitting is visible. Either way I'll try to polish mine just to see how it works.

  8. #8

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    Wow, suprised folks are still finding this out. I probably knew about this 20 years ago but have been using OM-1's for 40 years. Yeah, just clean off the old foam and don't brother to replace the prism foam, it's not necessary.

  9. #9

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    Lots of OM 1s have never needed a service. Not everyone spends time on camera fora.

  10. #10

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    I've got two OM-1's that have the foam issue. The rubber bung tricked worked on one to get the wind-on lever cover off, but the other one really, really doesn't want to come off, what do I do then?

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