Quote:
Originally Posted by Acrab
Clive, my telescope is based in a Kriege-Berry design, like your 25" obsession. Wood, aluminum, metal primary mirror cell metal and few more. Mechanically there are few parameters to enter and I am convinced that the problem is in the boundary layer, not in local atmospheric turbulence. I would like to see the behavior of your 2" thick mirror under conditions of winter, where the temperature can fall about 6 or 8 ° C in two hours. In the U.S. the amateur astronomers of Florida boast excellent conditions for observing with large dobson precisely because thermal fluctuation are minimal and the mirror has time to acclimate within acceptable parameters
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Clive's scope hasn't a great deal in common with an Obsession - it's actually my scope in the pictures. In winter here, the temperature fall is nowhere near as severe as you describe. We may see a gradual drop from 16 degrees in the mid afternoon to around 0 before sunrise on the coldest nights. On these nights, when the rest of the atmosphere behaves, the performance of this mirror is good. On summer nights such as the one Clive used his thermal imaging camera, the mirror has equilibrated, yet the views are quite poor due to turbulence in the atmosphere. Yes I'm sure it's the atmosphere, because it knocks every other scope (from SCT to million-dollar refractor) around as well.
Next time I take the scope out, I will try an experimental cooling system I have devised that should be able to pull an additional 250KJ out of the back of the mirror in 15 minutes or so. Worth a data point or two.
cheers,
Andrew.