SCT tube currents, trying something different.

We all know that SCTs are slow to cool down, and until they do, they
don't provide optimal images, visually or photographically.
Problem is, when they DO finally cool down, they keep on cooling down
through radiation, and sometimes get below dew point and start dewing
up. So we use a dew shield to retard the formation of dew on the
corrector. And if things are bad enough, we use an electric dew heater
to keep the corrector warm enough so that it never drops below dewpoint.

Some of you live along the Gulf Coast and know that you can fill a
swimming pool (or at least make up for evaporation) by setting up a
drain line from a C-14 and sending its drippings to the pool.

So I'm thinking about this, and I see the problem as one of heat
transfer. And I see us wanting to take heat out of the scope, and later,
put some back into the scope (or at least certain parts of the scope).

Take heat out and put heat back in. That bugs me. So I'm thinking some
more and I'm wondering if the problem could be solved by retarding heat
transfer...keeping the scope warm. This couldn't work on a Newt, of
course, because they are open tubes (and they have major dewshields
built in). But what if you were to wrap your SCT in a thermal blanket
that cut heat emissions? The aluminum tube wouldn't radiate heat as
fast, setting up tube currents. Wrap the mirror cell and corrector
flange too. And slap a big old thermal blanket covered dewshield over
the end of it. What would happen then?

I think most of the problem lies in those aluminum tubes. They radiate
heat so quickly that they set up tube currents because they're colder
than the air trapped inside the tube. Of course, you can blow cold air
into the tube (but if you live someplace humid, you're going to be
blowing water into the tube, too). So I have to test this hypothesis,
and I intend to. I've wrapped a C8 in aluminized bubble wrap. Looks
like a darned heating duct with an eyepiece jammed in the end.
Kind of like this: http://www.bogusnet.net/gallery/thermal/PC050480
Trouble is, it clouded over as soon as I did this, so I can't do a
star-test avi movie.
But it can't stay cloudy forever. This ain't England.
Anyway, somebody has to try crazy ideas out to see if they're actually
crazy, right?

Clear Skies,
Uncle Bob

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