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What's the problem with the shades that go over the eyepiece of the
telescope overheating and blowing up?  They were a fixture of sextants
for years and still are in some models.  Is there a history of this
occurring or is this speculation?  A piece of glass blew into the
cornea of my left eye and it was no fun.  Maybe the light from a
telescope could burn a hole in your retina, but lacerating your cornea
could be even more damaging to your eyesight.

On May 12, 2004, at 6:17 AM, Frank Reed wrote:

> Robert E asked:
>  "Why is this dangerous?  Is it because there is a possibility of the
> shades
>  slipping out of position?"
>
>  In a way, yes.
>
>  Fundamentally, it is dangerous because there is a telescope in the
> light path. This is intrinsically dangerous when you're looking at the
> Sun. If you carry this risk alone, then there's no problem. But do
> you??
>
>  Imagine yourself out on a street corner with your sextant on June
> 8th. You know what you're doing; nothing could go wrong. And you say
> to yourself, 'I know what I'm doing... nothing could go wrong..."   So
> you demo your sextant to your neighbor who happens to have heard about
> the transit of Venus today and is enthusiastic to see the show. And
> you're pleased to show the show... You swing the shades one way.. you
> swing them back... you demo the sight... You hand the sextant to your
> neighbor and before you've noticed he swings the shades out and looks
> straight through at the Sun. He jumps away quickly but it's too late.
> He's got a blindspot. He has permanent damage to his eye. And you've
> got a legal and moral nightmare.
>
>  That's a parable, of course, but the fundamental concept stands; it's
> error-correction. So what do you do? How do you avoid the potential
> for a minor error with major consequences when you're casually using a
> sextant to observe the Sun?
>
>  Frank R
>  [ ] Mystic, Connecticut
>  [X] Chicago, Illinois

   

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