STEP-BY-STEP GUIDE

STEP 1

You can speed up the cooling of a Newtonian mirror by fitting a DC fan to the rear cell so that it blows onto the rear face of the mirror. If possible, mount the fan on soft rubber washers or string it between elastic bands to isolate its vibrations.

STEP 2

A low-tech alternative to fitting an internal fan is to place a free-standing fan nearby, blowing on the mirror end. This will help to get it closer to ambient temperature, at least until you start your observing session.

STEP 3

Allow plenty of time for the scope to acclimatise to the outside temperature before use. To help speed things up, store your telescope in an unheated place, like a shed or garage, when not in use. If it is stored in a warm place, it will need longer to cool.

STEP 4

Fit the scope with a layer of aluminised radiator foil to reduce inverse tube currents caused by the chilling effect of the cold night sky, especially during still and transparent nights. This will ensure the exposed parts of the tube stay closer to ambient temperature.

STEP 5

Another way of reducing inverse tube currents is to wrap Mylar space blanket around the body of your scope. Like the more permanent insulated foil, this reduces the radiative chilling of the telescope by the night sky.

STEP 6

Rack the eyepiece far inside focus to expand the image of a bright star to one-third of the field diameter. Tube currents will be seen as swirling patterns of bright and dark, trapped within the circular disc. Experiment using your hand at the front end to see the currents.