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    Re: Polarising Filters
    From: George Huxtable
    Date: 2007 Nov 27, 08:47 -0000

    Mike Daly wrote-
    | internal stops, the 'scope will take light on the area of the objective
    | lens and concentrate the light on the cornea in an area more or less the
    | same as the exit pupil of the 'scope.
    Correct so far...
    This works out to be equal to the
    | magnification of the 'scope - so if you have three times magnification,
    | you are getting three times the intensity of the radiation on the cornea
    | (less absorption in the 'scope).
    A square-law, surely. It will depend on the ratio of the two areas.
    Therefore nine times.
    That applies to the light arriving at the front surface of the eye, which
    was being discussed.
    However, as has been pointed out more than once before on this list, when
    the magnified Sun image, seen through a telescope, is painted on the retina,
    the energy falling on each unit area of the retina is no greater than it
    would be for an unmagnified Sun, seen with the naked eye. It's no brighter,
    it's just bigger.
    contact George Huxtable at george@huxtable.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    To post to this group, send email to NavList@fer3.com
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