DIY Dew Heater?

The electronics aren't a problem for me. What I'm having a little trouble determining, though, is how much power is enough? I live in Vancouver where it's very humid...

I don't want to create some overpowering heater that will ruin my views so what should I be shooting for when heating a 4" MAK's objective, for example?

I intend to make variable levels of heating power, but I don't know where to start. 5W for the objective? Maybe the same for EP's?

Thanks for your ideas,

Dan

Dan,

I live in the Pacific Northwest, too, and have hooked some resistors to a 3.5" ETX. I took a wild guess and shot for 3W for the objective and on most nights this was fine, although dew would build up on really bad nights. Based on that, if I were you I'd go for about 5W on the objective, especially if you can control the heat (for that matter you might want to make it 6W).

For eyepieces 1.5W seems to be OK, but I tried going up to 2.5W and found that it didn't hurt the image at all (possibly because the heat is at the end of the optical train). The added bonus is that observing when it's freezing or below makes for a very cozy eye socket!

Doug Tanaka

Dan,

Down here in the Carolinas we get lots of dew, so I built my own dew heater system using resistors for my 8" SCT. As a starting point I'd suggest 1 watt as I've found that to be sufficient for many nights. That's considering usage of a dew shield as well as the heater. If you are not using a DS then start at 1.5w. If the wattage is too high then you can and do risk damage to your equipment/viewing. When I built mine I did a lot of looking around on the web and other sources and determined that 3w is probably max necessary for my system.

Remember that the objective of any dew heater is to raise the equipment above ambient temperature only slightly. I've heard of people bragging about 30 watt heating systems and that's just way too much unless you like cool down time to return the optics to stability.

What method are you going to use for your heater? Heat cord/resistors/other?

PT