[AZ-Observing] Re: Scope Color

However, if you had a "perfect" high emissivity scope tube, it would
likely couple to the clear sky and drop the scope temp to far below
ambient.  That is why your car window can get frost on it when it never
gets below freezing...  Reminds me of what John Dobson (who has made and
looked thru LOTS of scopes and is never short of an opinion!) said about
telescope color "make it ANY color AS LONG AS IT ISN'T WHITE"!

-Dean

> Black is probably best; both because it is less distracting, but also
> for thermal reasons. If you really want to split hairs, for optimum
> performance, ie the shortest time for the 'scope to reach thermal
> equilibrium and minimize the tube currents, it doesn't matter so much
> what color it is in visible light, what you want is the paint with the
> highest emissivity you can find. Think of it this way, you want the tube
> to be as "black" as possible in the thermal infrared region
> (~10microns). This way the tube will radiate heat away as quickly as
> possible.=20
>
> OK somebody is going to say "but, white will reflect the heat", but
> presumeably you are not observing during the day. Even a white scope
> will eventually warm up over the day. What you want is to dump that
> accumulated heat as rapidly as possible.=20
>
>

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