Dew is a very big problem at the TAS dark site in Atoka County, Oklahoma. I really enjoy using the Telrad finder. Those two facts are not complementary. My Telrad use has become pretty much restricted to finding alignment objects to use in the narrow FOV crosshairs eyepiece to bring the Nexus DSC on-line well before dew sets in and for pointing toward the moon and brightest planets for a last peek when the session's over at teardown. That one usually involves looking through the fogged Telrad surfaces.
I have always had one of those plastic covers with the hinged flap on the objective end that's s'posed to be a dew shield. As you may know, it does @ 30% of what you need.
So I was interested to see the R-Sky guys had come to market with a dew heater for the Telrad. Nobody else I am aware of has had an active heater for it in years. When when they also developed a larger more powerful ep heater strip for the massive ep's on the market it was time to order.
The Telrad heater is shaped to fit around top of the reticle end of the Telrad and is retained by an elastic band with velcro on its end - very good fit and plenty secure. I was able to put it on and then install the plastic cover over it, retaining the cover with gaffers' tape (a.k.a. The Tape of the Gods).
I'd not plugged it in when setting up as I didn't know how the current draw of the robust ep heater that I did plug in would impact battery service life (hardly any as it turned out) but late in the session with everything wet with dew, I bent close to the scope and got a drop of water down the back of my t-shirt when it dripped off the Telrad. The unit was totally dewed over, wet on all surfaces and impossible to use for star hopping. Recognizing a good testing opportunity I plugged in the new heater.
After @ 20 minutes I checked back in to see what was up and found the optical path completely clear and the back of the plastic cover near the heater band FREE of moisture. My experience is that this thing works like a champ! As I use it - under the plastic dew shield - is probably optimal but by itself it would likely work fine if activated before dew set in and left running. Highly recommended 1st class product. The ep dew heater also works just fine. http://r-sky.org/en/
In the pic the plastic shield is slightly raised to show the heater band in place, the cord is wrapped around the base and the RCA connector shows.
Edited by havasman, 20 June 2016 - 02:17 PM.