several, not all, of my 50's, 60's and 70's leitz lenses have internal coating problems while all contemporary lenses from other manufacturers show none of these problems. presumably, similar lubes were used in the old days. could it be a property of the coatings themselves?

i suspect it might be a combination of both. in general, my lenses that are in better cosmetic condition are affected more than the more heavily used lenses - that suck in air (ventilate) with use.

does anyone have any answers from the repairers and/or leica themselves?

-- steve (leitz_not_leica@hotmail.com), May 20, 2002

Answers

FYI, i just asked Leica directly. I will keep you posted. Meanwhile, post your knowledge and/or theories.

-- steve (leitz_not_leica@hotmail.com), May 20, 2002.

Stephen Gandy has a discussion of foggin on this page.

-- Chris Chen (furcafe@NOSPAMcris.com), May 20, 2002.

i tend to regard mr. gandy in similar terms to how some regard mr. putz. mr. gandy stated that my dr would not mount on my early m6 (first batch), it works fine.

"prone to fogging", but not why, exactly.

one guy, limited samples, one opinion

but, his site is on my favorites list.

-- steve (leitz_not_leica@hotmail.com), May 20, 2002.

I've never personally bought the lube-contamination story. There's just very little chance of helicoid lube getting into the optical cell on M lenses as there might be with IF, FLE and zoom lenses. Exception being if some incompetent fool oiled the diaphragm mechanism. More likely it is an oxidation or reduction reaction that happens on the coatings, which are metallic oxides themselves. As you said, there are a limited number of substances used to lube lenses and it's doubtful only Leica used some secret type that just happens to fog lenses.

-- Jay (infinitydt@aol.com), May 20, 2002.

Do other manufactors use the same exotic glass that Leica used, and uses? Doubtfull. So it's not just the coatings. Couldn't it also be some of those rare earth elements floating around in the glass formulars?

-- Glenn Travis (leciaddict@hotmail.com), May 20, 2002.

Having recently done a complete DIY CLA on a 70's 50mm F2 Summicron I can see no way that the focusing thread grease can get into the air gap between the two element groups - what I did find was that the lens surface had a fine etching or piting which could not be removed with opticlean. I also understand that the coating is not hardened and so you can't use any rubbing action to clean it or you will destroy the coating (hence the use of opticlean) I did manage to remove a lot of other very fine dust and fogging and the lens performs much better into direct light than before so I must have removed quite a lot of muck. As it's impossible to seal these two inner surfaces from the air as you have to have a linkage for the aperture - over the years (possibly 30 years with this lens) contaminants from the air will very slowly build up.

-- Johann Fuller (johannfuller@hotmail.com), May 21, 2002.

Mostly if you buy an M lens clean and they fog up over time, and you don't leave it too long it will clean up perfectly. Gandy is right. The only lens I had that I could surely ascribe lubricant deposition to was a LS Canon 35mm f2 where the elements were so close a bead of oil like substance sat in the centre joining two elements; ultimately cleaned up perfect. If you buy second hand, do not underestimate the effects that extreme temperatures may have had in this regard.

-- James Elwing (elgur@acay.com.au), May 21, 2002.