Zinc Pest in Zeiss 10x50

[crgl820]

I received a pair of Zeiss 10x50s and noticed that the prisms on both sides were cracked. There was no damage on the outside or evidence of having been dropped. I opened them up (yes, I know what I am doing and have the correct tools and no, I do not do cleaning or repairs for others) to discover that the posts around the prisms were very degraded with zinc pest. The metal degradation was clearly enough to break the prisms and then break the metal into smaller chunks. I am going to get some measurements and see about reproducing these in something less reactive. Has anyone had a similar experience and/or already created replacements?

[DPI]

Your biggest problem is being able to replace the prisms. Fabricating the prism mounting might be doable depending on personal skill and workshop facilities. Or finding someone to make them for you. But Prisms, good luck.

[Sgt Bilko]

What kind of 10x50 are we talking of? I've had many relic binos but none (including ground dug finds) have suffered as badly as your's.

[crgl820]

Thanks DPI and Sgt Bilko - These will end up being for display as I agree, sourcing prisms is pretty much a lost cause. These are beautiful otherwise, which is why I was so surprised to find the damage. Maybe a trashed donor set will come my way. These are D.F. 10x50s from WWI. I found a few references after looking around some more about problems with chipped prisms, probably because of similar problems. I have about a dozen Dienstglas of various makers, etc., and have only seen one other with a little surface oxidation. Go figure.

[Wpgbinocular]

Sounds like you have one of the Zeiss Abbe Koenig (roof) prismed DF 10x50’s. A few years ago a fellow sent me the attached picture of a damaged WW I Zeiss DF 10x50 he had acquired. He wanted to know what could have caused such damage to the prisms and particularly the alloy housing. I seem to recall that externally the binocular was in reasonably good condition showing no signs of fire damage etc. I can’t explain how this could have happened other than there being a poor quality metal in the housing which you would not expect from Zeiss. Note that some WW II Huet Porro II’s made under German occupation will have the same sort of breakages in the prism cage alloy.

[DPI]

I have never seen anything as bad as that

[Sgt Bilko]

I see what you mean now - really bad. I've had Japanese WW2 binos which had crumbling ocular tubes (as though the material was deficient) but would have thought that, in this case, if the metal was deteriorating, it wouldn't have had the strength to damage the prisms. Mkes you wonder what some of these old binos have been through...

[DPI]

I have found that the old 12x60 'flak' binocular prisms are aligned by use of steel set screws, with glass shims between the prim and the setscrew. Nonetheless, the set screws rust and expand bringing pressure to bear on the glass shim and the prism material. I have always though that metal against glass in the long term was a really bad idea.

[Sgt Bilko]

metal against glass in the long term was a really bad idea.

True dat!