|
Neil,
The reference temperature probe should not be attached to any solid object. For the most accurate ambient air temperature you would house it in an insulated tunnel and draw a continuous stream of air over it using a cpu fan for example. The best location for it should be determined by experiment. After using a thermal infra red imaging camera to analyse the cooling properties of large newtonians I came to the realisation that there is even a temperature gradient from the top to the bottom of the telescope. The top cage is likely to be one or two degrees cooler than the mirror box (at any given time) and often radiates enough heat to be somewhat below ambient temperature (this is why you get condensation on dewy nights)
The best way to avoid dew and thermal plumes is simply to blow air across your optics at 2.5m/s (Ref; Wilson, ESO)
|