Dew/Dew Shields/Heaters/hair Dryer and related issues

[Raph-in-the-sky]

Hey Guys,

Up until now, I beleived that dew wasn't affecting me... It sounded like a terrible plague to which I was immune ... Turns out I'm not!

Last time I went out, after about 45 min both my telrad and my 9x50 finders were covered in dew and unusable for the rest of the nigth. My main mirror was fine though (SW 250px full tube).

 

So here is my question. What should I do? 

I ve heard of dew shield (including home-made), heated dew shields, hair dryers,... What do you use and what would you advise for this issue? If someone could point me to a specific piece of kit that would be great!

Many thanks,

Raph

 

[joe aguiar]

hi raph

I have only used dewcap or dew shields and never powered dew strips.

there are some dewcaps that I think are beter then others

the best one in my book is the Kendrick dewcaps, and the reason is they are felt linned and even after 2 to 3 hours it prevented dew from going on my corrector plate. BUT even this after the 3hr mark is when it started BUT for me 3 hours is almost enough. When i took it out and felt the felt it was kind of semi-wet, so i concluded the felt absorbed the dew first into the felt before going forward towards the lens etc.

take into account at summer (when dew is the most problem) (in certain countries that's hot and humidy a lot I guess that's kinda different) it only starts getting dark by 930 BUT that's not dark enough to star viewing yet I would start my setup by 1030 or so. 

By time time 2am hits iam already tired since I wake up at 6am everyday mon to fri. anyway this is enough for me most times. The odd time I may have gone to 3am but probally not more.

anyway the Kendrick dewcap being felt linned servered me well.

I have tried like celestrons version that's just plastic inside and out without the felt lined and it dews up faster maybe 1.5 to 2 hr mark.

so to me the Kendrick is the best cause its felt lined the whole inside, so iam pretty sure if u just make it a dewcap yourself and its just plastic or cardboard it will prlong the dew for awhile before it dews your scope up.

try it see how long u get, if its not long enough like an hr to hr and a half then felt line it see how much longer u get from it.

also remember the dewcap should be 1.5X times to 2x times longer than your aperture. A lot of maker of scopes make the built in cap too short, so same is for the dewcap. So a 8" scope should have a 12" to 16 inches dewcap min. a 8' dewcap for a 8" scope is NOT long enough.

joejaguar

hope that helps

[Mick H]

I have AstroZap dew shield on my NexStar 8se, and I use a 12v hairdryer for my Telrad Finder Scope, both connected to Halfords 4-1 starter battery which was £50.

[Raph-in-the-sky]

If you wanted to do a quick DIY for a 9x50 finder and a Telrad, how would do?