What sort of dew prevention do people employ?

[asterisk (Geoff)]

I know a lot of people make their own - I tried with limited success. Astrozap make a heated dew shield for a variety of telescopes

http://www.astrozap.com/pages/dew-heat.htm

I always put one of thes on my SCT - even "dry" nights end up "wet" very quickly.

Thousand Oaks have a good little dew controller if you don't want to make your own:

http://www.myastroshop.com.au/produc...asp?id=MAS-299

If you are prepared to wait (10-14 days), Smartastronomy in New York have good prices on heater straps which will plug into the Thousand Oaks unit:

http://yhst-1469288697390.stores.yah...ewheaters.html

[Krusty]

I ended up making my own dew heater with cheap parts from Dick Smith Electronics. I purchased a PWM kit http://www.dse.com.au/cgi-bin/dse.st...uct/View/K3070
because I was too lazy to design my own. And for $15, who could be bothered. I then purchased some nichrome resistance wire http://www.dse.com.au/cgi-bin/dse.st...uct/View/W3205
for an extra $4.

I built the kit and installed it in a pvc box so that the potentiometer adjustment could be accessed from the outside. I made up a length of wire with a dc socket on the end of it to go from the PWM controller to the telescope.

For my 5" SCT telescope, I wrapped insulation tape around the very end of the tube. I then wrapped a few lengths of resistance wire on top of the insulation tape, making sure the wire was not touching anything but the insulation tape. I then wrapped more insulation tape over top of the resistance wire to hold it in place. All in all, the resistance wire measured 22 ohms, so would draw just over 0.5A. I soldered a dc plug to the end of the resistance wire to plug into the wire coming from the controller.

I use this along with a dew shield. So far this has worked like a charm. Before
making this, my scope used to dew up every time I used it.

Wade.