Canon mechanical SLRs

[David Lyga]

For some arcane reason, used Canon mechanicals (Tlb, TL, TX, etc) oftentimes have a prism area that shows dark lines or other dark invasions in the viewfinder area. I suspect that this has something to do with the actual prism's outer coating.

Do any of you have a 'fix' for this problem, assuming that the top is off and access to that prism is easily attained? I have had this problem with no other camera. Internally, how could the prism be affected, as there are no holes allowing fungus, or other problems to manifest? So, it MUST be something on the other layer of the prism, probably on the top, which is coated in black. I have tried to cover the prism, or re-coat it, but the marks still show in the viewfinder. - David Lyga

 

[AgX]

See this thread with many good advise:
https://www.photrio.com/forum/threads/mirror-and-prism-degradation-in-old-slrs.95362/

-) recoat by vaporisation
-) recoat by precipitation
-) patch up with chrome spray, metallic pen or metallic foil

 

[David Lyga]

So, as far as I understand, the outer coating of the prism is, in fact, a mirror that has become 'de-silvered'. I guess I should have already known that but, apparently, that coating, for some reason unbeknownst to me, has 'lost' its silvering. Maybe others will illuminate this, as well. - David Lyga

 

[Mackinaw]

........ I have had this problem with no other camera........

You're lucky. I have prism de-silvering marks on my Olympus OM-1, Leicaflex Standard and Nikon F. Seems to be very common on the OM-1, from what I read on the camera repair group on Facebook. The easiest solution is to buy a junker camera that has no de-silvering, and swap prisms. Kanto Camera, in Japan, can probably re-silver a prism if you want, but it will be costly.

Jim B.

 

[David Lyga]

Thank you, Mackinaw, for telling us this. You know, it is ONLY after decades of use that we REALLY can see the pitfalls and attributes on these old cameras. I NEVER saw this problem on either the Spotmatic of SR-T. There really WAS a reason why those cameras dominated the business during their time! I never thought that the OM series was all that well constructed, even though the Olympus lenses are second to none. But the NIkon F? That is a surprise to me, although in 1959, when the Nikon F was born, maybe there was no perfected pentaprism at that time. - David Lyga

 

[Mackinaw]

I’ve taken apart several old classic 35mm SLR’s. Many manufacturers put a strap over the prism to secure it. Many also placed a foam pad between the prism and the strap as a spacer. It’s this foam pad that is the problem, most have deteriorated with age. Later Canon cameras placed a plastic spacer between the foam pad and prism, largely, but not entirely, eliminating the problem.

And you find de-silvered prisms on Pentax cameras too, I’ve seem some. Most manufacturers used the foam pad/strap idea to secure the prism back in the 1960’s.

Plus you are dealing with prisms that are now 50+ years old. Stuff will happen.

Jim B.