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Subject: Re: (telrad) [M]: solar astronomy
From: Mark Taylor
Reply To: mapug@shore.net
Date: Tue Dec 31 15:05:23 1996

Telrad's do in fact have a single magnifying/focussing lens, which I
presume is used to focus the projected reticle image onto the slanted
glass surface. From memory, it's something like this...

\ "\" is the glass
--=\---------- "=" is the lens
| \ + <-- | "\" is a mirror
|------------- "+" is the reticle
"<-" is the LED

I don't see how the sun would cook the reticle when shining from the
right (as pictured above) - which is exactly how it would be oriented
if the Telrad was left mounted while pointing your scope at the sun.

However, if the sunlight were coming from above or behind the unit (as
it might during setup, aiming, or off-the-scope handling) it would
then shine through the lens and focus on the reticle. Ouch!

This is just my best SWAG on this topic, having owned mine
for <1 week now, and having not even had the chance to
mount or use it yet :-( [rain, rain, go away...]

Did I get the picture right???

Mark

><<How can the Telrad be destroyed? Are there
>optical elements that focus the
>light energy? I'm not aware of any since this
>device has no magnification.
>Seems like it will not suffer any more effects
>than your skin under the sun.
>
>Am I missing something.>>
>
>Yeah, me, too.
>
>It's a very simpel device. How could radition from
>the sun possibly harm a Telrad? I thought this was
>basically a light emitting device (maybe even a
>diode) with a mask over it to project the circles
>on the mirror and then on the glass. There no
>focusing, no lenses, what's up?
>Mike Stute
>http://users.why.net/mstute
>
-------------------------------------------
Mark C. Taylor mctaylor@mindspring.com