Quote:
Originally Posted by Stonius
It was around 1.2" from memory, which is not that great for that spot.
What is the relationship between seeing and dew though?
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I believe the condensation layer, which hangs just above the ground, acts as a filter of sorts, defracting incoming photons. The moisture layer maybe fairly thin, but your stuck on the ground. If you could get onto a high peak, things might be much better. For example, if you have ever seen fog settled into valleys, where it tends go hang on. Of course, this is more typical in calm windless night.
As far as the chemical hand warmers are concerned, I have used them in my pockets but they are more contact warming devices rather than radiant heaters. Heating in my observatory does work well, but you risk rising convection currents. I had thought that an observatory tent might be a workable solution, but there are not any made for large Dobs as far as I know, and you would need an internal heat source in the tent to keep the optics above dew point.