Using dew heaters in a dome

[codemonkey]

For those of you who have a dome, do you find that you still need to use dew heaters, or does the dome itself act as a giant dew shield?

[AstroJunk]

The dome will indeed act as a giant dew-shield but only for a while. I find the inside of the dome will dew first followed by the scope. Of course, the scope is protected from the breeze so will naturally stay a little warmer for a little longer but I still have a dew strap on for those nights when it all gets too much!

[codemonkey]

Thanks Jonathan, I suspected as much.

[strongmanmike]

I have never seen dew on my optics in my Sirius 2.3m dome.

I have a dew heater pad behind my Newt secondary and around the inside of the OTA just in front of the primary mirror and here in Canberra, during the late spring, summer and early autumn I don't need to run the dew heaters at all but I do keep the three rear fans running all the time and they suck air out of the back of the scope. In winter, I also keep the rear fans running and generally run the tube heater and put the secondary heater on a low setting.

Canberra is of course known for it's generally dryer climate.

In warmer coastal and humid Newcastle I didn't have any protection and with the secondary and tube heaters running and the rear fans sucking, I never had dew on my optics (http://www.pbase.com/strongmanmike2002/image/134534743/original).

Mike

[Slawomir]

Some locations within the same area could be more prone to have dew forming. I never had any dew on my telescopes when shooting from a balcony in Brisbane, but now when imaging from our little courtyard I get dew quite often. The house is positioned in a low-lying area. Just my 5 cents.

[codemonkey]

Thanks Mike and Suavi for sharing your experiences. Sounds like there's no clear-cut answer and it probably depends on a number of variables.

We get pretty heavy dew here, especially in the cooler months. I was hoping to avoid running a dew heater as I don't really trust what they might be doing in terms of the possibility of temp differentials causing "scope seeing"

[Phil Hart]

I've had dew on optics in my dome in central Victoria in the winter half of the year. I'm using a refractor. When pointing high in the sky the radiative cooling can be pretty strong.

Phil

[codemonkey]

Thanks Phil. I suspect I'd run into that here as well, with my refractor. I was hoping I was wrong though.