Re: [ATM] Bubble Wrap mirror Cell.

[John Sherman <atmer@johnspics.com>]

Hi Marco,

> 1) Threre was written a few years back a good article in improving
> laminar airflow over the face of  the mirror in order too improve seeing
> - blowing air paralell to the surface of the mirror. This would
>    also have the effect of cooling the mirror more rapidly.

I'm sorry, but I can't agree. I believe the fastest way to cool your mirror
with a given fan is to blow on the back of the mirror. The air then goes
around to the front of the mirror and also cools the front. You cool both
sides at the same time - and if your fan is strong enough, it also blows
away the boundary layer.

Blowing air onto the front and allowing it to escape through holes in the
tube does not address the cooling of the back. It is even worse if the back
is insulated with bubble wrap or a flex cell. Why cool only one side of your
mirror?? It is a waste.

What Adler was saying is that *while* the mirror is cooling you can improve
the image in the eyepiece by blowing away the boundary layer. This is
certainly true. But it does take longer to cool the mirror, and a cooled
mirror is the route to the best image. A cooled mirror is not distorted by
having a warm back, and a cooled mirror does not have a boundary layer.

That is probably the best reason to abandon the bubble wrap idea.

But if you try it, let us know how it works!

John





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