RE: ATM Baffling a newt - street light tests

[Krajci Tom Det5 57 Wg <Tom.Krajci@barksdale.af.mil>]

> From: Mel Bartels [SMTP:mbartels@efn.org]
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> I use a focused high powered flashlight beam - have someone aim it all
> over the scope from all sorts of orientations while you look through the
> eyepiece with your eye severly cupped so that you can only see what's
> through the eyepiece.  If you cannot tell when the flashlight is on or
> off, then you are ok - that's my test for my super open no shroud light
> dobs.  Moon glow at a slight angle can be handled well by a focuser
> baffle and felt opposite the diagonal - works quite well for me.
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        [Tom Krajci Capt]  That's encouraging, becuase I plan to make my
sixteen inch a very open scope too - the main purpose to reduce its
vulnerability to wind.

        However, the thing that surprised me most with my streetlight test
was how much light was scattered off the main mirror.  (The veiling glare
contribution from the tube wall opposite the focuser was tiny compared to
scatter off the main mirror.)  This is a clean mirror with a two month old
coating, and a good polish.  Do others see similar light scattering off
their primary mirror when they point the scope at the full moon or a
streetlight?  Or do I have a high scatter mirror?

        I know that it's been said many times:  "Mirrors will fail the
flashlight test at night, so don't be alarmed by what you see."  So perhaps
I'm expecting too much from my mirror?

        Mel, Chuck, do you mean to say that in your demonstration, when the
flashlight beam is striking the main mirror at an oblique angle, that you
can't detect that at the eyepiece?

        Tom Krajci