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    Re: Eyesight dangers using telescopes
    From: Bill Morris
    Date: 2009 Jun 30, 00:06 -0700

    Frank, you wrote:
    
    "(a model which would fit this, though not necessarily the 
    correct one, is simple cooling by conduction: the area receiving sunlight 
    increases with the square of the magnification while the boundary of that 
    area, which is the part that is exposed to cooling by conduction, increases 
    only linearly with magnification)."
    
    Beneath the retina is the choroid. Next to the retina is a network of 
    capillary blood vessels, especially dense in the region of the fovea, and 
    outside that a network of large and medium sized blood vessels, so it's not 
    just the boundary that would cool by conduction. 
    
    There are plenty of pictures of retinal damage from gazing at the sun with the 
    naked eye, but I haven't come across one yet of damage from use of a 
    telescope. Has anyone else? One would expect the area of damage to be 
    proportional to the size of the image, just as it is for naked eye damage. 
    
    I don't think anyone in this thread is arguing that the total amount of energy 
    reaching the retina isn't increased by using a telescope. My understanding 
    now is that the energy per unit area isn't increased. Have I got it right?
    
    Bill Morris
    Pukenui
    New Zealand
    
    
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