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[Gyurmi]

I think everyone at this forum has been through the unhappy encounter with the sticky gunk found in the mirror housing and the back of old SLRs and also in some MF roll film holders. Here is another, less likely place, where the damn thing spreads its

[Mndean]

That one's actually pretty well known around here. It's not the only brand with the problem, but seems to be the most affected.

[Paul Ron]

The Olumpus OM1s have the same foam problems over the prisms. Shame they didn't have the forsight to see the future.

[John_s]

I found a similar problem with an old Canon FP, the foam eats away the silvering on either side of the pentaprism. If you clean it off down to the bare glass you can improve matters a little - thanks to total internal reflection?  
 
It's easy to

[Gyurmi]

That 'fix' is an interesting proposition. I must admit, I didn't dare to clean it off thinking that it would make matters worse. But, once you do that, could you perhaps use some silver paint and black paint over it? Did anyone try?

[John_s]

I tried putting silver foil over the patches, but it made no difference. Silver paint might be better. I think these pentaprisms rely on total internal reflection to reflect the light, the silvering just improves things slightly. When the silvering is