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Clive's attachmenent about polarising filters raiises another aspect of
dark-shades for the Sun, which appears not to have been touched on so far.

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?

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?

George.

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.


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