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    Re: sun filters
    From: Frank Reed
    Date: 2008 Jan 27, 22:08 -0500

    You wrote:
    "Does anyone know if the filters on sextants are really safe to view the sun
    through? If modern sextants are safe and filter out harmfull _UV_ radiation
    is the same true for older sextants?"
    
    This has come up several times in the past few years. The short answer seems
    to be that none of us really know for sure, and also none of us are blind
    (yet) so you can count that as empirical evidence that the instruments are
    safe. In my opinion, if you're concerned, it would probably be prudent to
    get any sextant you plan to use extensively tested for UV transmission. This
    shouldn't be expensive, and better safe than sorry, right? Consider also
    that a sextant is usually used with a telescope. So in addition to the
    shades themselves, you're usually looking through more than a centimeter of
    glass (unless the optics are plastic), and glass does block dangerous UV
    very effectively.
    
     -FER
    Speaking of glass blocking dangerous wavelengths, I'm reminded of Richard
    Feynman deciding to watch the Trinity Test (first atomic bomb). He was
    sitting in a truck and he decided to watch WITHOUT protective dark glasses
    since the glass of the windshield would stop any harmful UV light! He
    figured that he was probably the only person who saw the first atomic blast
    at its full brightness.
    
    
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