Quote:
Originally Posted by jungle11
On my dob there is a dust cap, and on the cap there is a smaller cap you can open. I was wondering, when i fan the primary tonight, can i just leave this cap open, or is it better to take the whole thing off to achieve equilibrium?
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Well, there is a good question. If the rear of your scope is quite open (you can see the mirror), then for cooling there is no great need to open the top of the tube.
However, if the rear is closed (and some people cover it purposely) and the air driven in by the fan has to come out somewhere else, I suggest you open the focusser - just take out the 1.25" plug. You'll feel enough airflow coming out.
Some argue that leaving the fan running through the night discourages dew formation on the primary - I haven't down the tests. Obviously do this only if vibration of the image isn't evident.
While, in theory, taking the dust cover off entirely should allow more exchange of air inside with air outside, the danger of opening the top of the tube is things falling onto the primary- ranging from dew formation to empty chip wrappers from a visitor looking for a bin! to other things that fall from the sky (Watch the pelicans and fruit bats!)
Therefore, if uncovered, keep the tube unit horizontal while cooling (don't point at the sun!) Then only the cat can get in and sleep there!
