[Draco (Draco)]

Originally Posted by Rick Petrie

Hi Niv
The purpose of having a fan on a Newtonian/Dobsonian telescope is to cool or bring the mirror to ambient temperature and this will much improve the viewing through the scope. It helps to eliminate the disturbed air caused by the mirror temperature not matching the air around it. (like heat shimmer coming off a road on a hot day)
You can view with no fan attached, but much better views will be obtained with the fan on all the time while viewing as the temperature of the mirror will adjust to closely match the outside air temperature.
Well worth spending a little for batteries to power the fan.
Cheers Rick

ah ok. Thanks Rick