making a dew sheild.

[seanc74]

just bought new telescope celestron nexstar 130 slt. i heard about problems with dew on scope. i have not had the problem yet. they dont have dew sheild for this scope. so I figured id make one. just wondering how long should dew sheild be extending out over scope?   

[Dave In Vermont]

I believe your scope is a Newtonian reflector - yes? One doesn't typically worry about dew with these telescopes as the mirror, the primary-mirror that is, is at the bottom of a long tube. The tube itself works as a dew-shield with these scopes. The secondary-mirror, the small one directly under the focuser, could possibly be affected by dew. Though I've never heard of anyone bothering to make a dew-shield for this reason. Truss-tube models are another matter.

May I inquire where you heard about problems with dew with this scope? Usually a dew-shield is needed for refractors and SCT's and Maksutov scopes.

You've piqued my curiosity,

Dave

[Stu]

Dave, people do make dew shields for Newtonians. Two reasons, firstly as you mention to keep dew off the secondary. The other reason to do it is to stop stray light entering the focuser or tube which reduces contrast.

[Dave In Vermont]

That's cool. I was thinking of an extension for my F/4 to do such. Not for dew though, but for stray light. I note many 'Astrographs' have a longer tube to place the focuser further away from the open-end.

Dave

[Gazabone]

I recently fitted a telrad Finder to my 10" Dob. Last time out, the dew on the tel rad was awful (and the OTA itself was all but dripping itself) but there was no dew on either the primary or secondary. Having said that, I wasn't pointing the scope terribly high.

[Stu]

You can do the same with a Telrad or Rigel....

[LukeSkywatcher]

According to most people........

A dew shield should extend out from the front of a scope 2.5x the diameter of the aperture.

[Ccolvin968]

I just made one out of a foam sleeping roll that I bought for $7.50 USD. It has worked so far. My scope was dripping two nights ago, but it worked like a charm. I'll post a picture later if I get the chance.

[seanc74]

thanks everyone,like I said havn't had a problem yet figured I'd use every precaution possible.  I also wanted to keep stray light out to. as I was doing research on looking for dew sheild it came up on asrtonmy forums people were having problems with  this particular scope sounds like there conditions were pretty bad.  I went and bought a camping mat this one is going to be a progect I have to do alot of cutting just wanted to make sure I did this on one try.although I have room for error I should be able to if I screw up get about 3 trys out of this. thanks again.

[Ccolvin968]

It's not as hard as you may think. I measured twice, cut once, and then used some duct tape to secure the ends. Works like a charm. Good luck!

[triton1]

I thought it was 1.5 times the aperture,made mine from a camping mat and used a hot glue gun along the edge great for keeping out stray light and have never encountered any dew.

[LukeSkywatcher]

This is mine. Its so ugly that small children cry and animals run away when they see it. I forgot to cut a hole in it for the focuser. I now have a heated strap for my 8" SCT.

[beamer3.6m]

200p = 300mm length dew shield

130p = 180mm length dew shield

Or there abouts

[Gazabone]

Following a recent purchase of a telrad, on its first proper outing, it dewed up really badly. I opted for the telrad dew shield with mirror and love it, the mirror flips up to use the finder like a 90 deg finder. My feeble DIY skills would not have been up to producing that but the shields above will do a cracking job, wondering now if I could have spent my pennies better!

[LukeSkywatcher]

If you go too long on the dew shield.........you run the risk of it sagging down over the objective thus blocking light entering the scope. I have to say though that ive never heard of this happening unless you use really cheap thin cardboard.

[beamer3.6m]

Use a camping mate and embroidery hoops to retain its shape.

[LukeSkywatcher]

Use a camping mate and embroidery hoops to retain its shape.

Its an approved method.

[Dave In Vermont]

I'll get a bungie-cord to hold one onto the end of my F/4 Rich-Field Newt. One foam camping-mat coming up!

'ta,

Dave

[xtreemchaos]

i use a air con duct clip to hold my dew sheild on

[eyepod]

Cheap camping mats work great heres my two one for my 200p dob and the other for my 130pds all made from one £3 camping mat. I use stick on velcro pads to attach to scope.

Jason

[Chris]

Here is my method for making a dew shield for smaller scopes:

http://www.insideastronomy.com/index.php?/topic/520-diy-dew-shield-for-the-ed80/

[xtreemchaos]

and heres the one i made for my ED80.

[beamer3.6m]

That seems quite long.

Does that not interfere with the view.

[Chris]

and heres the one i made for my ED80. DSCF5098.JPG

Crikey thats a big one! Absolutely no chance of stray light with that beast

I bet you need to be super careful about fitting it concentrically, as any tilt might mask off some of your aperture.

[xtreemchaos]

 beamer & chris-better too big than too small,na it dont interfere with the view infact it aides it helps to cut out a bit of stray light by getting the scope out the window you see due to illness i dont get outside as much as i like so i do a lot of my skywatching from the window in that room. clear skys charl.