Lee,
But getting back to wintertime dark skies in the northern climes - I was thinking of a heater of some kind across the lens (e.g. hair dryer). But would this create "distortion" due to the warmed air in the immediate front of the lens on a sub-freezing night?
George,
You can use a hair dryer to warm up optics for visual observing, but it may not last long enough to get the exposure you need. It would likely create enough turbulence during the shot to ruin the image. Hair dryer elements can also glow if hot enough.
See my note about 9 postings before yours for "dew chaser" comments.
String enough resistors in series to draw about 2 Watts from a battery, make sure they are electrically insulated, and wrap the string of resistors around the lens barrel near the front element. Use a lens shade, and you can even wrap some closed cell foam around the outside of the resistors to hold in the heat. A couple of Watts will keep the lens just above the dewpoint without creating turbulence. Figure out how many hours you want it to run and use a lead acid, deep cycle, or power supply with sufficient amps or amp/hours for the task. Some people use gutter heating tape of the right length/resistance to generate a couple of Watts. I use one that was given to me that I can wrap around two lenses at once. You can use a cigarette lighter plug for 12V (well... 13.8V) from a car battery.
One of these
http://www.sciplus.com/singleItem.cfm?terms=2945 will also work off 12V, giving you about a Watt. (DON"T USE IT ON MAINS VOLTAGE TO WRAP YOUR CAMERA!)
Since you're a ham, I know you don't need the math spelled out for you, or that last warning. You can google for more options or ideas.
Hope this helps.
Lee
Here's a link with DIY instructions. For most camera lenses one Watt is likely sufficient, but two won't hurt unless you need to stretch battery life.
http://skytonight.com/howto/diy/3304231.html