Quote:
Originally Posted by Acrab
Is there any magic formula for to bring the mirror at his ideal temperature?
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The subject is more complex than I had originally thought, the ideal temperature is a moving target, and there is more than just the heat stored in the primary mirror to consider.
Go here for some more detailed thoughts on the subject:
https://sites.google.com/site/binocularnewtonian/
I suppose if I were to reduce it to a 2 second sound byte as it were, I would say that on the night where I took those thermal images, even though the primary got to within a fraction of a degree of the temperature of the air surrounding it, this wasn't even close to the ambient air temperature measured a few meters above the ground.
I might just add an addendum to this though and point out how much heat energy is typically stored in the mass of plywood that makes up the telescope structure.
Even though wood has (slightly) less than half the density of pyrex, it has almost double the specific heat, ergo; there is actually more thermal mass in the rocker box than the primary mirror itself. I suppose the huge surface area of the telescope structure allows it to dump heat (in to the air) relatively quickly... this may not actually be a good thing when you think about it. The problem of local seeing is not proportional to the temperature of the telescope itself but the quantity of thermal energy put in to the volume of air inside (and to some extent above) the telescope over time.
ie) A more accurate discussion should include Joules (or Watts) and how this translates to temperature forcing in air.
I think the last chapter on this subject has yet to be written.
best,
~c
fwiw) Some further reading:
http://www.cruxis.com/scope/mirrorcooling.htm