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Olympus OM-1 warning: Check for foam around prism, and remove it if found

L Gebhardt

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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/tutorials/FoamRemoval/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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
Lots of OM 1s have never needed a service. Not everyone spends time on camera fora.
 
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?
 
I'm not sure what's next since the rubber bung trick opened both of mine. Probably getting a lens wrench with points and use the two holes in the cap. I imagine with lots of downwards pressure you might be able to open it without damage. If you do damage it, it will only be cosmetic.
 
wood Dowl, discarded walking up glove pair of mole grips, have three wheatabix for breakfast.
 
I have had OM-1 and OM-2 cameras where the advance lever cap screw got sort of "glued" to the plastic piece under it. Probably from heat and age. No matter how hard or what method I tried, the screw was not going to come off with friction.

I don't have a proper tool so I used a pair of jewelers needle nosed pliers into the holes, with a lot of force and caution and prayers to finally get those caps off.

I found that putting adhesive remover, like Goo-Gone allowed the decorative cap to come free from the screw. I am planning to stick toothpicks in the holes and spray paint those covers with black enamel. Then I can glue them back onto the screw.

Real life ain't always as easy as it shows in books, or on the web.
 
The OM-2 also uses the foam by the prism and will go bad and eat the prism coating. Mine had to be replaced.

Dave
 
It took a pair of washing-up gloves wrapped around some pliers. Whoever had had the thing off the last time had glued it back on.
 
I just want to support this advice for every OM-1 and OM-2 owner out there - get the foam removed. Just look at my collection of damaged prisms from cameras I've repaired...


If you don't have a spare prism, after removing the foam goo and polishing the prism, it can still be used! It may look nasty but you won't be able to tell the difference when looking through the viewfinder. All you can see is a thin hair line where the silvering ends, but only when looking in the viewfinder from distance, not when looking at the focus screen because your eye can't focus at the line!
 
The next step would be trying to re-coat it oneself.
 
AgX said:
The next step would be trying to re-coat it oneself.
Click to expand...

Not necessary total internal reflection is sufficient.
Chip off any damaged paint, plastic Biro top tool, wipe off debris with Zippo rag, replace.
You normally won't detect any difference.
 
Guys,
Is it really critical to remove this foam regardless its effect is barely tangible?
I see in mine some minor discrepancies outside of the actual focusing area in the viewfinder and unless it would extend I do not really see a reason to run for CLA. However your thoughts are welcomed.
Cheers
 
Over time it will extend the corrosion into the center viewing area. Get the foam out now.
 

Sover says F2 De-1 has foam and he is not often wong...

http://soverf2repair.webs.com/DE1.htm
 

It certainly degrades the experience of using the camera. That, to me at least, makes preventing the issue before it starts a good idea.
 
sagai said:
Guys,
Is it really critical to remove this foam regardless its effect is barely tangible?Cheers
Click to expand...

Sagai,
I concur with all previous posters here. Please do yourself a favor, take L. Gebhardt's advice and get rid of the foam asap. The tutorial he points you to (http://olympus.dementix.org/Hardware/tutorials/FoamRemoval/index.html) is excellent, and cleaning the prism (as well as the adjacent areas!) really is not a very difficult operation.
Left alone, the rotting prism foam is apt to disperse little nuggets of awfully tarry stuff that will wander off into the camera body and lodge themselves in vital places that are much less accessible than where the prism sits. I have seen this several times when cleaning OM-1 bodies.
Good luck!
Michael
 
Thanks Folks!
I have a good amount of encouragement now to go for it.
 
Thanks for the info. My uncle found out about my recent film camera addiction and brought me his old OM-1. He told me there was some kind of corrosion on the mirror and when I looked through the viewfinder I saw all this black stuff around the bottom of the prism (the mirror also had stuff on it, but what I saw was definitely not the mirror). I ended up buying another OM-1 for parts to take the mirror and prism out of. This gives me a much better understanding of what I'm dealing with.
 
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