NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Looking at the Sun through a telescope
From: George Huxtable
Date: 2006 Aug 4, 14:51 -0500
Ken Muldrew wrote-
the damage caused through a scope will likely be due to
heat rather than the photochemical injury that occurs with the naked
eye.
Therefore it isn't due to the brightness of the light, so the argument
that the
scope won't increase the brightness doesn't apply here. The heating
power
of the sun through a lens goes up approximately as the square of
magnification.
I'm not sure what Ken is getting at here, and what he is basing his
argument on.
Heat, like light, is electromagnetic radiation, but of a longer
wavelength, and the laws governing its propagation are exactly the
same. True, refracting index and transmission of the lens elements may
well differ from those for visible wavelengths, but in a way that will
reduce the transmission of heat, compared with that of light.
The heat energy dissipated per unit area of the retina will not be
increased by the telescope, compared with naked-eye viewing, just the
same as with visible light. The total energy will increase by the
square of the magnification (if it can all get in through the pupil),
but the area of the retina that it's painted on will also increase by
the square of the magnification, so the heat dissipation per unit area
will be no greater than it was without the telescope.
The only way that I can envisage heat-damage behaving in a different
way from light-damage is that one might expect heat to diffuse away,
more effectively, from a tiny spot into the surrounding area, than it
would if a larger area was being heated. That wasn't an argument
deployed by Ken, but it might have some validity, depending on the
time-scales involved.
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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To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
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From: George Huxtable
Date: 2006 Aug 4, 14:51 -0500
Ken Muldrew wrote-
the damage caused through a scope will likely be due to
heat rather than the photochemical injury that occurs with the naked
eye.
Therefore it isn't due to the brightness of the light, so the argument
that the
scope won't increase the brightness doesn't apply here. The heating
power
of the sun through a lens goes up approximately as the square of
magnification.
I'm not sure what Ken is getting at here, and what he is basing his
argument on.
Heat, like light, is electromagnetic radiation, but of a longer
wavelength, and the laws governing its propagation are exactly the
same. True, refracting index and transmission of the lens elements may
well differ from those for visible wavelengths, but in a way that will
reduce the transmission of heat, compared with that of light.
The heat energy dissipated per unit area of the retina will not be
increased by the telescope, compared with naked-eye viewing, just the
same as with visible light. The total energy will increase by the
square of the magnification (if it can all get in through the pupil),
but the area of the retina that it's painted on will also increase by
the square of the magnification, so the heat dissipation per unit area
will be no greater than it was without the telescope.
The only way that I can envisage heat-damage behaving in a different
way from light-damage is that one might expect heat to diffuse away,
more effectively, from a tiny spot into the surrounding area, than it
would if a larger area was being heated. That wasn't an argument
deployed by Ken, but it might have some validity, depending on the
time-scales involved.
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.
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
