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Old 07/12/07, 16:49   #1 (permalink)
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Default Why lens haze?

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When reading an auction catalog, I note that the majority of classical M lenses in it were more or less hazy. This seems to be an increasing problem. What is the cause? Why is this much less of a problem with Zeiss or Nikon or Canon glass of the same age? It seems that only coated lenses are afflicted. In that case, it is probably not a progressive de-vitrification of the glass, in the mass. So, is it some kind of surface deterioration or attack? Does it destroy coatings? Can anything be done about it? If so, I reckon that somebody will soon start making some money ...

This posting will probably rectify my image as an insufferable know-all.

The old man from the Age B.C. (Before Coating)
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Old 07/12/07, 17:28   #2 (permalink)
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Default Re: Why lens haze?

IMHO it might be caused by some of the lubricants gassifying and coating the lenses (sort of like washing the inside of the windows in your house after winter...they pick up particulate matter from cooking, the fireplace, etc). Most of my lenses are from the 1960-80s, and the thin films have been readily cleanable by me or service personnel.
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Old 07/12/07, 17:52   #3 (permalink)
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Default Re: Why lens haze?

There are two "respectable" theories that I know of - the whale oil theory, and the "soft coating" theory. It's of course quite possible that they both right for different lenses...... See here:

Leica FAQ - Lens fogging - causes and cures?

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Old 07/12/07, 18:30   #4 (permalink)
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Default Re: Why lens haze?

And of course fungus; that stuff will live on the glass surface of both coated and uncoated lenses. It produces acid that etches the lens irrepairably.
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Old 07/12/07, 18:38   #5 (permalink)
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Default AW: Re: Why lens haze?

Quote:
Originally Posted by sandymc View Post
There are two "respectable" theories that I know of - the whale oil theory, and the "soft coating" theory.
I do not believe in the soft coating theory for the following reason: I have seen lenses with lens haze from both the period of (internally) soft coated lenses and from the period of (also internally) hard coated lenses. To be more specific, all Summarit 1.5/50mm lenses are safe to be assumed as internally soft coated lenses, the same goes for Hektor 4.5/135mm lenses, but all lenses above SN 2,000,000 are safe to be assumed as internally hard coated lenses, and I have seen hazy ones of those lenses, too, e.g. Summicron 35mm (8-element) and 50mm (7-element) lenses with nos. well beyond 2,000,000.

The big difference is that the latter lenses may be cleaned without taking off the internal coatings, while the former will lose their internal coatings in the cleaning process and will have to be recoated.

In my view, the lubricant evaporating theory and the microcondensation theory are both plausible and will likely both contribute to the hazing effect in varying degrees, depending on user circumstances and geographical location of the lenses.

Andy
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Old 07/12/07, 22:49   #6 (permalink)
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Default Re: Why lens haze?

But these explanations leave open the other half of Luigi's question:

Why not Zeiss? Why Leica only?

And an implied third part: When did it stop? In other words, we outsiders have theories as to why it happens. Should we assume that the insiders have discovered the reason and quit using the technique/technology that was responsible for it? If so, when?

What did Zeiss know and when did they know it?

Inquiring minds want to know!

--HC
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Old 07/12/07, 23:31   #7 (permalink)
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Default Re: Why lens haze?

This soft coating myth must end! It's the leaded glass which is soft...think crystal. Coatings began with Magnesium Fluoride. As to the haze, it has to do with natural lubricants being used in the helical. Japanese companies began using synthetic lubes before Leitz did.
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Old 08/12/07, 09:46   #8 (permalink)
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Default Re: Why lens haze?

Jaap, the phenomenon I was referring to is a whitish, even 'fog', entirely different from fungus.

One theory I have heard is that the lens surfaces were not sufficiently 'micro-clean' before the coating was applied, and that this has made the surfaces vulnerable. In that case I suspect cleaning would also destroy the coating. But if the 'gasified whale oil theory' is right, then cleaning should be possible. Until now of course a less expensive expedient was just finding a clean lens, but the supply of clean 7-element 50mm Summicrons seem to be drying up.

Are there people who are competent to do a job like this? After all, the lens has to be re-assembled again and still focus! Sounds very expensive to me.

The old man from the Age of the Pinhole
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Old 09/12/07, 03:55   #9 (permalink)
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Default Re: Why lens haze?

Greetings all.

I have had several hazy lenses (from my LTM days) cleaned by John van Stelton of Focal Point (in Colorado). Here are a few things I learned in the process.

1) getting lenses cleaned doesn't hurt the coatings. Echoing what wizard and leitz_not_leica say above, I'm not sure what a soft coating would be. In any case, the old coatings withstand cleaning just fine.

2) for some reason I don't understand, cleaning doesn't work equally well all the time. I had a coated 5cm Elmar (red dial) and an uncoated 9cm Elmar both clean up perfectly, while a 135 Hector did not respond all that well (it wasn't, to begin with, as hazy as the other two either.)

3) I would certainly recommend van Stelton. He regularly works on glass for the military, and certainly has the expertise to clean the lenses. In fact, it was Don Goldberg who first recommended van Stelton to me, back in the early 90s. Don can also do the cleaning, I believe. In fact, anyone who can expertly disassemble and reassemble a lens can clean it. The cleaning isn't rocket science, but getting the lens back together to spec. might be. So I wouldn't try it at home.

4) It's certainly true that hazing is (hopefully was) a Leitz/Leica problem. But Zeiss had more trouble with cemented elements separating. Or so I recall.

Hope this helps some.

Brent Orton
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Old 09/12/07, 07:49   #10 (permalink)
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Default Re: Why lens haze?

Thanks everybody for your replies. It sems that the case may be less hopeless than some
of us thought.

Re soft coatings: Early coatings (from the date of Smakula's first, secret Zeiss patent of 1935 and later) were done at lower temperatures and in a less 'hard' vacuum than was the case later. This meant that the coating was physically soft, and it was originally only applied to internal surfaces because they did not stand up even to cautious cleaning. Later surfaces became harder and we know that Leitz and Leica have worked hard on that aspect. Today's coatings may in many cases actually be harder than the glass under them.

The old man from the Age B.C. (Before Coating)
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