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    Re: Telescope danger to sight. Was: Venus transit ...
    From: Jared Sherman
    Date: 2004 May 12, 14:15 -0400

    George, I'm wondering if you glossed by something that deserves further
    attention.
    
    
    
    The human eye typically has a diluted pupil of 5-6mm diameter, and rarely
    more than 7mm. When contracted against bright light, that drops to something
    like 1-2mm. (I'm less familiar with the fully contracted size.)
    
    So, a human eye viewing the sun has an "onbjectve lens" with a diameter of
    2mm.
    Compared to your telescope's objective lens of 15mm.
    
    But the scope on many sextants is well wider than 15mm, easily in the 30mm.
    range. And "cheap" binoculars rapidly push past 42mm to 50mm objectives
    while common telescopes used by birders here are 77-80+ mm lens now.
    
    The comparison then is of the human eye, gathering light, IR and UV
    included, from a 2mm circle to a telescope objective gathering light from a
    50mm objective. There's an incredible amount more light being gathered, and
    even "cheap" coated optics boast a 95%+ transmission factor.
    
    Perhaps this is all that is needed to explain the warnings?
    
    
    

       
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