[peter_4059 (Peter)]

Some time ago I purchased a Kendrick primary mirror dew heater for my 10" Newt. I decided to get this after Astrofest last year when night after night I was suffering from heavy dewing of the primary that was ending my evening's imaging prematurely. At the time I tried the Newt's cooling fan and Houghy's hair dryer to no avail.

Last night I got to try the Kendrick heater properly and I'm pleased to report that it successfully kept the dew at bay and from what I can tell had little or no impact on imaging (judging by focus which I re-checked throughout the night).

I have a temperature sensor attached to the side of the primary and the heater kept the mirror about 7 degs C above ambient all night. I have recently purchased a Kendrick dew controller that has closed loop temperature control that I plan to fit to the primary allowing control of either fixed temperature, fixed delta above ambient or fixed delta above dew point. I've found the key to using this heater is to get the right amount of heat input then don't change it and the focus is then not impacted so fixed temperature is probably the way to go.

So if you are suffering from dew on the primary mirror have a look at this option.