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Thread: cloudy glass

  1. #1
    David Lyga's Avatar
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    cloudy glass

    Sometimes a lens is perfect EXCEPT one of the inner elements is cloudy (probably from past moisture which has turned into fungus). Oftentimes, fungus can be removed with careful wiping with either glass cleaner or lighter fluid. However, sometimes the cloudiness seems permanent and, thus, the entire optical use of the lens is destroyed.

    Assuming one can get at that element by dismantling the lens (no, I am not talking about two cemented elements whereby the cement is the problem) is there any cure for that haze? Maybe someone has tried alternative liquids and come up with a solution. Thank you. - David Lyga

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    ic-racer's Avatar
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    Some of the stuff that does clean off is oil. Even grease has some volatility and can condense on lens elements under the right conditions.

    Grease is composed of molecules of varying molecular weight. With heat, the lighter molecules evaporate. This does two things, it allows the evaporated components the chance to re-deposit on a nearby surface (lens elements) and also causes the remaining grease to become thicker and stiffer.
    Last edited by ic-racer; 05-28-2014 at 05:32 PM. Click to view previous post history.

  3. #3
    AgX
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    I had haze on front lenses that I only succeeded in removing by using the strongest organic solvent I had on my shelves.

    Optical glass used for outer lenses and their coatings seem very forgiving. concerning cleaning. At least that is my experience with lenses going back to the 50's.

    But we got members with much more experience.


    The only lens elements I would be utmost careful with would be those from Fluoride. But the appropriate lenses should be known to us.

    In case of doubt of having a plastic lens in front of me I'm more careful than with glass lenses.

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    Depends on what it really is. Fungus will eventually etch glass - if that's the case, it's permanent. If it a substance on the surface, however, it can be removed. Glass cleaner and lighter fluid are fine for oil-based substances, but you may need something more specialized. Fungus is easily removed by moisturizing hand cream - apply generously, wait 5-10 minutes, remove and clean as normal. Haze that's formed as a result of off-gassing (usually from unstable lubricants) can sometimes be removed with toothpaste or silver polish; I've had better luck with the latter. Obviously, you need to be careful with the latter substances, as they are slightly abrasive.
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    Hello DL--hadn't seen you in a while. 2 days ago I finished up a Nippon Kogaku 50/1.4 that was full of fungus. In the end, the lens came out clean as a whistle, but when I turned it towards a lightbulb for the purpose of inducing flare, it was evident that the fungus had either etched the coatings and/or the glass. The lens was destroyed. Took it back apart for more agressive polishing with the toothpaste trick, but to no avail. It's a crying shame.

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    When hard coating became available you could send your uncoated lens in to be coated.

    To recoat they needed to dismantle, repeat the final polish and vacuum coat.

    So it is possible to salvage an etched lens but you need a production style grinder and coating facility probably not economic for a Nikon lens.

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    There's been a lot written on this topic. Much depends on the age of the lens, and the brand -- Leica lenses of the 50s and early 60s are susceptible to this, and often there's nothing that can be done without damaging the coating of the surface that's affected. Leica interior coatings of this vintage are quite delicate. Sometimes it's in the glass itself, and can't be helped. Of course, given that they're Leica lenses, there is a lot more handwringing about the issue (you don't want to damage the lens, both from a monetary and picture taking standpoint).

    I'm not sure other lens makes have this problem -- the Japanese lenses of that vintage seem to have had harder interior surface coatings. Also, newer lenses of all makes have improved coatings (and improved glass as well) so that the problem is not as severe.

    Chances are the haze is on a lens surface that's adjacent to the aperture blades, so it's caused by offgassing from lubricants used for the aperture.

    Hard though it may be to do, often the best thing to do is just resist the temptation to clean the surface, and instead get a proper lens hood to minimize flare. But if you do intend to clean an interior surface, I would suggest proper optical glass cleaner and as little pressure as possible applied with a clean, soft cloth. A lot of opinions on what sort of cloth, but microfiber seems to work well for me if it's clean. Likewise, a tissue is OK though it can leave lint. If it really looks like fungus, use hydrogen peroxide. I would not generally use lighter fluid to clean glass surfaces, however.

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    Ian Grant's Avatar
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    Up until the late 1920s optical glasses were reasonably hard but then Schott (part owned by Zeiss) introduced new optical glasses that permitted new designs particularly for faster lenses. One used by Zeiss and Leitz was particularly soft and is prone to scratches and also atmospheric attack, Leitz used it for the Summar and it was also used in some Tessars and Novars. You can have what look like mint lenses, no cleaning marks or scratches, that are low contrast, sometimes unusable. Zeiss changed the glass in Tessars again towards the end of the 1930's when the first T coating was introduced.

    Post WWII lenses varied considerably, the LF Zeiss lenses (CZJ) were much better so were the Zeiss (West Gernany) lenses, but some of the faster 35mm lenses still used softer glass not as soft as the preWWII glass but still prone to easily being scratched during careless cleaning.

    What causes the atmospheric damage I'm not sure probably sulphur compounds from pollution but I acquired an EXA Ia recently with the legendary Meyer Domiplan and barely forms an image, through a loupe the surface of the front element looks like ground glass, yet the lens barrel and mount and rest of the elements all look mint. I have a second Domiplan with worn paintwork on the barrel but reasonable optics so need to get the lens cells swapped

    With early coated lenses where fluorides were used in the coating fungus on a lens element absorbs the fluoride and weak Hydrofluoric acid can be formed etching into the glass surface.

    Ian

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    There are also haze issues when 2 cemented elements develop a haze in the join (within the adhesive). That requires separating and re-adhering them.

    also, some glass can "precipitate" for lack of a better term. e.g. chemicals leach out of the glass to the surface and form an unremovable haze.

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    AgX
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    Precipitate... as you indicated that rather would be a kind of crystallisation I guess, rather than leaching out.

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