Ammonia with old Leica lens coatings

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xwhatsit

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Hello Brian, or of course whoever else can help,

Just acquired a (cute!) little Elmar 90/4 in LTM. The serial dates it to 1949, and it's coated, reflecting a faint blue sheen.

It has a bit of haze, of course. A single spot of fungus behind the first element.

I want to clean it. It comes apart easily enough, but here I stopped. Normally I clean haze and fungus off very successfully with 50% ammonia and 50% hydrogen peroxide. I know, sounds a bit harsh. I think next time I'll use 1/3rd distilled water, 1/3rd ammonia and 1/3rd hydrogen peroxide.

However I hesitate to use this, as I've heard the early Leica coatings (and I'd assume 1949 is early?) are quite soft and ammonia will strip them off.

Should I be concerned? I tried straight distilled water and a bit of lighter fluid, but it didn't really clean it to my satisfaction. I'd like to try my normal mix, as it has a very high success rate, but I also don't want to strip off the coating.

How should I go about cleaning such a reportedly delicate lens?

Also got a Steinheil Culminar 135/4.5 LTM with the Elmar. Nicely made lens! Hope it performs OK.

Thanks all.
 
I bought a coated 1949 Summitar that had the beginnings of fungus on the inside of the first group. I used an ammonia based eyeglass cleaner with Kodak lens cleaning paper wrapped around a Q-Tip. It worked perfectly, removed the spots. Left the coating intact. I wiped firmly but gently- slow going.

And- I had a 1939 Zeiss Sonnar with an oil-damaged coating behind the aperture. Parts of the coating were really bad, detrimental to the performance. I used the same cleaner- firmly applied with swirling action- and removed it completely. Performance was greatly improved without the damaged coating.

So, the inner coatings are soft- go slowly and gently. Some firm wiping is required to really take the inner coating off.
 
Thanks for the information, Brian.

Typically I prepare the H₂O₂/ammonia solution and immerse the entire lens element in the stuff. I swirl it around but don't wipe the surface with anything. Nine times out of ten this is enough.

This tells me, then, that with perhaps a more dilute solution than I normally use, I can follow my normal technique here. Thanks very much.
 
Oh -- also -- this is relevant to the lens, I may as well ask here too;

I've run into this a couple of times, but the Elmar 90/4 seems particularly annoying. Once I've cleaned the elements, I don't like to touch them again. I leave them to dry, and try to carefully pick them up by the edges with some fresh rubber gloves.

However, the rear doublet of the Elmar 90/4 is this tightly-fitting push-in thing that goes in quite deep to the lens housing, and is secured with a ring. I can't see how to push the bloody thing in without touching the lens element again! Not a drop-in affair. Any tips here would be much appreciated!
 
Some hobby shops carry a "small parts handler" which is a small vacuum pump with small suction cup attachments.
The pump is like a solder sucker and the tips have a hole so the pump will create a vacuum. The part is put in place and if needed push in with the tip.
Micro tools may have something like this.

The hobby shop variety cost around 10-15 bucks.
 
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