A question on dew sheilds...

[FarSide]

I'm on the verge of procuring myself a dew sheld but there is a problem. After doing some research i've read that dew sheilds only really effect the top portion of a newtonian reflector while the reflector tube itself protects the primary mirror. Are dew sheilds worth it? Obviously they will help with stray light, but are they really worth buying for the mirrors themselves? I'm getting conflicting arguments from most places.

Ta very much.

[Merlin66]

I used many closed tube newtonians for many years without dew shields.

IMHO they are more critical for refractors and SCT/Mak's where the objective is open to the sky and the first place that dew would form.

I would never think of even trying to use either my C9.25 or the C11 without a dew-shield.

[FarSide]

Thank you, Merlin. I thought as much. I was more worried really about the secondary mirror being effected because the primary seems to be protected by the tube itself. Thanks for your advise.

[AstroMadBloke]

They most definatly worth it Farside. I used one on my Newtonian. On cold damp nights it wont take very long for your mirror to dew over a shield wont stop it totaly but it will give you a longer viewing period. I made my own out of a camping map and duck tape for my reflector, thing it cost me about £5 so they don't have to brake the bank if you want to try one out on your Newt.

Pete

[FarSide]

Actually, for some reason i don't get much dew on my main scope, Pete. I get a heck of a lot of dew on the outside of the tube, and on my piggyback st80, but my 10" seems to be far more resilient. Thank you for the suggestion of a camping mat. I may give that a go.

[Rapallokid]

I also bought a roll matt from camping shop, cut and taped it and it works really well. It is on a 12" Dob and makes the scope really top heavy, so i had to use a counter balance to level things out.

[NGC 1502]

This thread may help http://stargazerslounge.com/topic/157999-dew-shields-andor-heaters/

Regards, Ed.

[Shibby]

I've had nights where my secondary dews up within half an hour, which is frustrating because you don't notice at first! Also, you'll find that the higher altitude you are pointing, the sooner dew will collect. I now make a habit of putting the (door-mat) shield on every time.