A Primary Mirror Heater

The 10" Newtonian has been prone to condensation on the primary mirror. This happens mostly in the Winter months.
Because it is stored permanently in the observatory it is subject to whatever vagaries the weather throws at it.
I have tried a de-humidifier to keep the inside of the observatory dry, but to be effective the de-humidifier would need to be on almost 100% of the time.
Last year I had the mirror re-aluminised because it was badly pitted and discoloured.

My intention now is to create an anti-condensation heater around the mirror.
  The freshly aluminised mirror in it cell.

I will use an anti-dew heating strip which will be wrapped loosely around the mirror.

The first step is to glue velcro on the three supports for the mirror.

  Velcro in place on the heater strip. The heater should not be in direct contact with the mirror. when the heater is switched off the mirror must cool to ambient temperature as quickly as possible, and a tightly wrapped heater strip would insulate it.

Small balsa wood spaces will hold the strip away from the mirror.

This will allow air to curculate between the strip and the mirror to provide effective cooling.

  The heating strip in place. A thermometer is recording the temperature between the strip and the mirror.

An Astrozap 12V heater controller is used to adjust the amount of warming.

  The heater was switched on and the temperature rose to above 33 degrees.

The heater was switched of and it took 4 hours to get down to room temperature.

A fan will be used to accelerate the cooling process.

  Mirror cell now back on the telescope tube.

Connection to the heater is by a 2.5mm DC power plug.

  To cool the mirror before use a fan is attached. It is held in place by 5 neodymium magnets - two are arrowed.


In a test the mirror was heated to about 38 degrees and then cooled.
With the fan on the mirror reached ambient temperature in 17 minutes.
With the fan off the mirror took over 100 minutes to cool down.
30 minutes of fan assisted cooling should suffice.