trying out a dew sheild

Use camping mat as a dew shield also on my C9.25. It slows dewing up, but eventually had to get a heater system.
Donal

You're welcome Derek! The foam shields from Celestron et all are pretty much the same as the bedding foam mentioned here already. As you can see, any camping shop will have the sheets for about a tenner. All you need to do then is roll it around your scope tube, taking note of any lips on the face surrounding the end of the cylinder, and tape it with scotch tape or automotive masking tape. Then, Bob's your uncle!

Seanie.

Actually I think on many nights the cardboard / duct tape one will work fine. An insulated camping matt one would likely work better, though.

Remember that dew doesn't fall out of the air. What happens is that all surfaces radiate heat, but those that are exposed to the sky don't get any back. So their temperature falls, and if it gets below the dew point then water will condense out of the air directly on them.

The purpose of a dew shield is to radiate heat back to the corrector. In this sense it works similar to a dew heater by keeping the corrector warmer. The longer the shield the less exposure to the sky and the more exposure to the shield, and therefore the more radiated heat which falls on the corrector.

(Note: you don't get as much dew/frost under a tree not because the dew falls on the tree instead, but because the tree radiates heat back to the grass and warms it above the dew point.)

Cheers,
-- Jeff.

Thanks every one,
Very helpfull and greately appreciated

Derek.

barr wrote:

Thanks every one,
Very helpfull and greately appreciated

Derek.

No problem, you're welcome!

Hi everyone.

just an update on this topic,

after all that i decided to make a new dew sheild this time from the foam padding,

lastnight was the first time I got back out under the stars to try it out,

I was out lastnight with some more people for earth hour and I set up at 8 and didnt call

it a night till nearly 10 and my scope didnt fog up at all, success :woohoo: :woohoo: :woohoo:

And this was just as well as lots of people turned out to get a look through our telescopes

so thanks again for all the advice

cheer Derek