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  1. #1

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    Thorium in lenses at Kodak

    From today's paper in Rochester: http://www.democratandchronicle.com/...ioactive-waste

    Try http://on.rocne.ws/14GwIvp if the longer URL doesn't work.

    "For many years, Kodak was a global leader in cameras as well as film. And not a few of its cameras came with lenses that made Geiger counters chatter.
    As much as 30 percent of these lenses consisted of thorium, a naturally occurring radioactive metal. Added to glass, it improves the ability of a lens to refract light, or change its direction, so that it can be focused.
    Other companies used thoriated glass in lenses, but the process was developed by a Kodak consultant, George W. Morey, and first patented by the company in the United States in 1936. Kodak later developed a thorium lens coating to achieve the same effect.
    The use of thoriated glass ended in the 1980s."

  2. #2
    benjiboy's Avatar
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    I think the Japanese government outlawed Thorium Salts being added to optical glass because of health and safety issues with workers who ingested the dust from grinding the glass.
    Ben

  3. #3

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    Radioactive glass has been discussed several times on APUG.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  4. #4

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    Quote Originally Posted by Gerald C Koch View Post
    Radioactive glass has been discussed several times on APUG.
    Yup, but the article gives a little history information I hadn't seen earlier.

  5. #5
    Poisson Du Jour's Avatar
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    Old Pentax Takumars often had thorium in them. No news here.
    .::Gary Rowan Higgins

    A comfort zone is a wonderful place. But nothing ever grows there.
    —Anon.






  6. #6
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    Coleman lantern mantles, the kind you use for camping, were made using thorium nitrate into the 1990's and plenty are still out in the wild. I have a package of them stored safely away that send my geiger counter absolutely nuts. I'd be far more concerned about those things than some glass-bound thorium waste buried in a supposedly properly built landfill. With all the environment scrutiny Kodak has had to endure, I'd feel pretty confident that the landfill was built correctly.
    All this has happened before, and all this will happen again.

  7. #7

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    Quote Originally Posted by Poisson Du Jour View Post
    Old Pentax Takumars often had thorium in them. No news here.
    I bought an old Spotmatic a few years ago with a 55 1.8 Super-Takumar. This was before I knew anything about the radioactive glass. It looked lile every piece of glass in it was made from melted-down 81B filters. I could have put a bulb behind it an used it as a safelight. I had never see such a sight. They say you can put it out in the sun and bleach it. That summer I'd carry it out and put it on the deck rail every day, and it did lighten up some, but not entirely. The lens was essentially ruined.

  8. #8
    Poisson Du Jour's Avatar
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    Takumars with thorium elements still have a cult status among collectors. I have seen only one and the rear element was the one with thorium (200mm). I think a single x-ray will expose you to far more radiation than a creaky Takumar, so nothing to panic about, and you might even strike up an interesting conversation over a Twinings!
    .::Gary Rowan Higgins

    A comfort zone is a wonderful place. But nothing ever grows there.
    —Anon.






  9. #9

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    There are few things that evoke more irrationality in humans than radioactivity. The naturally occurring radiation from cosmic rays, UV, man-made (X-rays etc) and even compounds inside our bodies (Potassium 40, Carbon 14) will completely overshadow any dose you may receive from your Kodak Ektar or Pentax Takumar lens. The thorium is vitrified, and the decay particles will be arrested inside the glass matrix. This incidentally is why the glass eventually turns yellowish.

    There has never been proof that low doses of radiation are harmful, but it was poorly understood why. It has recently been discovered that cell repair following radiation damage happens at extraordinary efficiency up to a certain dose rate. Above that rate, the repair mechanism starts to get overloaded, and the efficiency drops to the point where permanent cell damage becomes linear with dose. Think of it as a repair shop with a single technician. If he services fewer units than his capacity, each unit can be fully repaired, but if he is overloaded, he will rush and make mistakes. The international radiation dose limits are several orders of magnitude below the linear rate, though, as is the natural radiation dose a person will receive from natural sources (other than skin exposed to UV in large doses).

  10. #10
    benjiboy's Avatar
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    It's fairly well known that the Kodak Aero Ektars were radioactive and many others http://camerapedia.wikia.com/wiki/Radioactive_lenses
    Ben

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