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    Re: Eyesight dangers using telescopes
    From: Bill Morris
    Date: 2009 Jun 25, 23:52 -0700

    From a quick scan of the medical literature on solar retinopathy it seems that 
    you can get retinal burns without using a telescope or gazing at the sun 
    while under the influence of "substances". Several cases are reported of 
    people simply sunbathing at low latitudes in bright sunlight. In these people 
    the swelling and blistering of the retina was, as expected, confined to the 
    fovea. Nearly everyone recovers normal vision, but it can take months. 
    Experimentally, the temperature of the retina can rise by 20 celsius.
    I must say that when I have unexpectedly glimpsed the sun through a sextant 
    telescope, it has seemed mighty bright and I had assumed that the light 
    intensity at the retina was greater, without really thinking about it. Your 
    gentle and diplomatic explanation has convinced me otherwise. I guess that 
    having a large area of the retina brightly illuminated is reponsible for the 
    Diplomacy on this site is not always in evidence (no, not you Frank). Douglas 
    I hope will continue to be a valued contributor. Can we perhaps all resolve 
    to use  phrases such as "Are you perhaps mistaken?" as substitutes for more 
    direct and acerbic versions. I can well imagine many potential contributors 
    being put off if they hit the list while an argument, rather than polite 
    discussion, is raging.
    Bill Morris
    New Zealand
    Navigation List archive: www.fer3.com/arc
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