Cooling down time cold nights

[timetraveler3]

Hi,

My scope is a 114mm Celestron reflector. My question is when I go outside now that it is cold, I leave it out there for about twenty minutes for the scope to cool down. Should I leave the cap on the tube on or of during this time  or doesn't it matter? Will more condensation form either way?

[Charic]

timetraveler3........It should cool quicker with the cap off.

[Eastridge]

I have always understood cap should be taken off to improve airflow

[Mr Q]

  Both replies are correct. And to quicken up the process, position the scope tube parallel to the ground so the warm air in the tube escapes (rises to the top edge) out the ends while cooler air is sucked in at the bottom tube edge. If a gentle wind is present, all the better since the flow of air across the tube ends hastens the air circulation inside the tube. In this case, position the tube at a right angle to the air (wind) flow.

  But why wait for the scope to cool down! Before it does, you can use it to observe extended objects (nebulae, etc.) that do not require so much viewing detail. Then when the scope is cooled down, you can then go for objects requiring more resolution in detail (planets, close double stars, etc.). Using this method allows you to observe as soon as the scope is set up instead of waiting around a half hour or more for the scope to cool down.

[Moonshane]

exactly what Mr Q said. I have a 114mm scope and it's great at low power straight away. even with my 16" lump I observe at low power pretty much straight away. the views get better of course with longer cooling but I have learned my lesson from the number of times I have put my scope out under clear skies, left it to cool, come back out to cloudy skies, put the scope away again......

[Naemeth]

Why wait? I start observing straight away with my 10" (low power only until it's cooled down somewhat), it's only really with higher power observing that thermal currents become noticeable.