Dew shields/heaters - some advice gratefully received!

[sagramore]

Hey all.

I use a Skywatcher 130-PDS newtonian with DSLR for imaging on a NEQ6 and I piggyback a Skywatcher ST-80 refractor on it for autoguiding with a ZWO ASI120MC-S. Currently I have no dew shields or heaters and I had my first bad experience during an imaging session a few weeks ago. It wasn't particularly cold but the humidity was up and within about 30 minutes of finally having got everything aligned, focused, and shooting I was halted in my tracks by dew on both the guide scope and even the secondary mirror of the reflector.

What I would like is some advice from all of you very knowledgeable people about the most cost-efficient way of combating this kind of problem in the future. For what it's worth in this discussion I do have a reasonably beefy 12V 110Ah leisure battery in a modded box that I use to power everything when out in the field.

I have seen simple dew shields for sale (or the idea of making one hopefully wouldn't be beyond me), heated dew shields, split-ring heaters for secondary mirrors, various heater controllers, etc. and I have to admit to being a little lost because I can't tell which of these things is overkill and which is worth the money. With this coming winter being my first full one since I got all this new shiny kit I'd really like to be able to use it as much as I can!

Thanks for any help. Clear skies.

Hamish / sagramore

[Tiny Small]

Well, as for the guide scope, you can make a long dew shield out of cardboard and black tape. I'm using a 60/225 guide scope from Altair. This has a very short dew shield and fogs up in minutes. I made a dew shield about half as long as the scope, and since then, no issues what so ever. It's fee and extremely simple. If you are running from a battery, they die very quickly on winter nights, even beefy batteries like yours (sometimes only lasting around 40-50% of the time they would at room temperature) so any solution that doesn't use power is a plus. Dew shields really do work.

Lots of people also make dew shields for newts too, usually from old roll matt. I assume this is for the secondary. Might have to look into this option if I ever get a foggy secondary.