Hi

just made this dew sheild earlier and was wondering has
anyone else here tried anything similiar?
If so how well does it work? is this enough to keep dew away
for an extra hour or two? will I need a dew heater aswell.
I was out observing lastnight and I barely got an hour and
my telescope was all fogged up, so im getting pritty fustrated.

Any advice greately appreciated.

Cheers
Derek.

Hi Derek,

First of all, what is the material you made the dew shield from? A 'classic' dew shield is just an extension onto the end of the tube, more for SCT's and refractors. However, further repelling of dew can be obtained for all scopes by using that foam stuff that can typically be found in camping shops as sleeping bag underlay. It has to power to absorb moisture from the air but becomes useless on much larger aperture instruments (after a certain size, an observatory isd the best defense).

Ultimately, a dew heater is the best way to go.

Seanie.

Hi Seanie

All its made from is 3mm thick poster paper, and I put lots of layers
of duck tape inside and outside to keep that dry.
a long shot eh!

cheers

barr wrote:

Hi Seanie

All its made from is 3mm thick poster paper, and I put lots of layers
of duck tape inside and outside to keep that dry.
a long shot eh!

cheers

Long Shot? You won't see where that lands! Your cardboard idea is a good one, but on an intense night it will just get damp and flop on itself becoming a nuisance. Off the top of my sleepy head I can't think right now what else in the home you could use...

Well Seanie your idea of the foam stuff does sound like a
better one, so I hope tomorow night is clear and ill give this
one a try and see what happens:)
O ya are the ones that can be bought from celestron and meade
any better or would theese home made ones give the the same results.

Thanks Seanie.

Derek

I use a sheet of camping bed foam and it works perfectly.
Costs less than 10euro.

Michael.

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

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

Good to see it worked well for you Derek.
Well done on getting your scope out and doing some outreach.

Michael.

Great stuff Derek. Meant to ask you on Saturday night if it worked. Was good to see a lot people turn up.

Pat.

Nephin wrote:

Great stuff Derek. Meant to ask you on Saturday night if it worked. Was good to see a lot people turn up.

Pat.

Hi Pat,

Ya it was a great turnout, id like to do something like that again very enjoyable,

was just thinking ther if this type of thing came about again id av to get sum type

of lights or glow sticks on ends of the tripod so people can see exactly wher tripod ends

are, and not be walking into them and putting of my "already dodgy" polar alignment:ohmy:

anyway its good craic


cheers Derek.

Spot on Derek, well done!

Seanie.