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    Re: Polarising Filters
    From: Michael Daly
    Date: 2007 Nov 24, 01:58 -0500

    George Huxtable wrote:
    
    > I recall having read, but don't recall where, that simple local heating,
    > from the Sun image falling on the retina, is a cause of lasting damage to
    > the retina by short-term ablation. That is, it fries a hole in it. Can
    > anyone offer more information about that?
    
    This is true.  UV and blue light cause local heating and the cells in
    the retina basically boil to death.  Search for info by Ralph B. Chou on
    eclipse protection for more info - he's pretty much the leading
    authority on such radiation damage in the eye.
    
    BTW - THC enhances the damage - Ralph showed the photos of research
    results (THC doped rabbits exposed to UV) at a meeting of our astronomy
    club and it ain't pretty.
    
    > If that is indeed the case, shouldn't we be thinking about the infra-red
    > attenuation? How can we be certain that carefully crossing a pair of
    > polaroids, to minimise the light that comes through, has a corresponding
    > effect on the passage of heat? How can we be sure that an ordinary dark Sun
    > filter is correspondingly dark to infra-red? Have these matters ever been
    > addressed?
    
    IR has a lot less energy than UV.  Nonetheless, it's important for it to
    be reduced.  All filters specifically rated for solar viewing (eclipse
    filters) or for welding (#14 or higher) are safe.
    
    Mike
    
    
    
    
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