Re: [Leica] Fogging

[Mikiro Mori <arbos@silva.net>]

Hi all,  A friend of mine has an early 35mm Summicron (8-element) with
fogging and had it cleaned.  The repairperson told him that the Summicrons
of this vintage commonly  suffer from corrosion of the glass and that he
often has to re-grind and re-coat fogged elements.  Also, Mr. Stephan Gandy
discusses fogging in his site:

http://www.cameraquest.com/mlenses.htm

He cites the following comment of Mr. Horst Braun, the Manager of the Leica
repair department:

"the special glasses with high  refractive index which were used, where
unfortunately prone to corrosive damage due to the glass components
absorption of moisture. Only later with  the availability of new
anti-reflective coatings was it possible to eliminate this problem. I still
do not believe, that lubricants should be the cause for fogging, because
also some internal lenses where affected which never could possibly come
into contact with lubricants. I suspect, that the reason why Nikon and Canon
did not have this problem at the time was probably due to the fact that they
used less sensitive glasses in their objectives."

The above repairperson also told my friend that the corrosion most severely
affects two elements that sandwitch the aperture blades.  If this is true,
it suggests that the lubricant on the aperture helps glass corrosion.

I am just curious what causes fogging and what can be done to recover the
original performance, because I myself am an owner of a fogged Summicron
35mm (8-element), too.  Does Sherry re-grind and re-coat some lenses?

Leicalement,

Mikiro

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At 5:41 pm +0200 9/8/99, Dan Post wrote:
>Karim-
>I found a really nice Summaron 35 LTM lens. Cosmetically, almost mint, and
>really a nice compact lens- and fairly sharp. It too had 'fogging', as do
>many, many lenses from the 50's when they used a lubricant similar to
>Nyloil- the watch and clock lubricant made from whale oil.
>Unlike petroleum greases that are composed of hyrocarbons of various
>molecular length, and different evaporation rates- and which tend to harden
>of a few years time, the whale oil lubricants were composed of molecules
>that are of a fairly consistant weight, complex esters that tended not to
>'dry' or harden, so the life of the lubricant was much longer, and more
>stable at different temperature extremes.
>They have a tendency, over time, to migrant, sublimate, and like the greasy
>film on your kitchen walls, from cooking, these oils, after 40-50 years,
>tended to get on the glass.
>My personal experience is that this oil, and sometimes edge separation is a
>bigger problem by far than 'fungus', even in the south whare I live. The
>upside is that the oil can be cleaned off, relatively cheaply, and the
>separation can be repaired (not so cheaply, but can be repaired). In fact, I
>have bargained the price down on a lens by $150 or so, knowing that for
>$75-85, Sherry could set it right!
>You will be surprised what a difference a good cleaning will make! My lenses
>usually gain at least one stop of contrast, and the sharpness improves
>noticably as well.
>Dan