Making your own dew shield

[beamer3.6m]

I wish to make my own dew shield for my 200mm explorer and would like to know what the proper astrozap ones are made of.

I was considering using roofing felt as it is black, non reflective, stiff and can be cut into whatever length is required.

Do people think this would be a good idea?

Also, what length are Dew shields normally, i.e. how far do they extend beyond the end of the scope in order to get decent dew reduction but not result in significant light loss.

I am hoping to maybe reduce the glare from my neighbours garage which seems to reflect the orange street lights, of which there are lots, directly down one side of my scope.

Any help much appreciated.

[Vega]

I'm not too experienced with this but wouldn't roofing felt run the risk of tiny bits falling on to your primary ? :shock:. Im sure someone will advise on the best material to use

Matt

[GazOC]

For the length 1.5 times the aperture is the general rule of thumb.

[George]

I bought a aluminised ground roll from Decathlon http://www.quechua.com/EN/m100-foam-mat-4219387/ on offer at 2.99 at Stockport branch, enough on the roll to go round my 10inch newt with enough left over to make half a dozen Hartmann masks

Gona spray it blue to match the scope but it already has a nice textured aluminium finish, just cut to-go round your tube, Velcro the full length and bingo cheapest dew shield possible

[Kai]

Camping Roll is a good cheap dewshield,Its the thing you put under sleeping bags,only a couple of quid.

[tom.yates]

8" Dew shield for sale on e bay at the mo astro engineering one

[beamer3.6m]

I have tried to make my own dew shield based upon your suggestions and here are the results.

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It longer than it actually is as the dew shield is pulled down by 5cm over the rim of the tube so I think I have a 25cm dew shield which based on the 1.5 ratio to diameter of the primary is not too bad.

I just need some clear skies to test it out.

Any comments welcome.

[George]

That should do the job, but looks a bit shiny inside....maybe a lick of matt black paint would do the trick

[iancandler]

An easy and cheap way to "flock" a flexible dewshild is to glue some black felt to the inside. you could get away with strong double sided tape to fix it or foam safe super glue (warning expensive for the good stuff from model shops)

[beamish]

I too used a silvered camping roll and flocked the inside with self adhesive flock from a craft shop, available on aroll for about a fiver- works an absolute treat.

Karlo

[beamer3.6m]

I tried this out the other night and it worked a treat.

The scope was out for about 4 hours and not one bit of dew on the mirrors in all that time, and it was really cold on Friday. The outside of the tube was like ice and the eyepiece was dewed up, but not the primary or the secondary.

I am going to declare this a success.