Bad-weather Build: thin film dew heating strips

August 21, 2022

I have been thinking about a low-profile method for warming up the main scope and guide scope, and Polyimide film heaters seem like the perfect candidate. They're very thin, adhesive backed, and come in voltages (12v dc) and max output wattage that seem perfect for dew control. These aren't new in astrophotography. I know ZWO uses a Polyimide heating ring dew heater for the front of their cooled cameras, and I am pretty sure Deep Sky Dad uses similar film heating for the built in dew control on the motorized telescope cover and controllable flat panel available for some William Optics, Takahashi, and Askar scopes.

The build for this is relatively simple. I cut up an old stereo + video RCA cord, using the red and white male end audio jacks. I soldered the two leads from the jacks to the two leads from the heater film, covered the splice with shrink tubing, and that's it. I plugged both into the Pegasus Astro Pocket Powerbox to get a sense of where to set the PWM dial for best dew control results. It turned out to be quite a bit lower than expected.

CAUTION: The dew heating range in the Pocket Powerbox is 0 to 255, and I normally run my dew strips somewhere near maximum. You have to be careful with the Polyimide film though, because these generate a lot more heat, maybe enough to damage some scopes. After a couple tests, it seems like a range of 30 to 75 works. The next step is more testing--soon as the night skies clear up!