Dew Prevention for Guidescope

[Steve789]

Do I need it? I have never experienced dew bad enough to prevent me from finding a guide star but I'm wondering if an accumulation of dew on my guide scope might be the cause of slight guiding errors? In other words can it change the light path enough to affect the guiding over the course of a session?

[StuartJPP]

My answer would be yes it would affect performance...to what degree depends on how bad it gets...a slightly defocussed star isn't a major problem for guiding and is sometimes better but it depends on how opaque the front element becomes. I'd prefer to keep the optics clear and defocus myself manually rather than relying on nature to take its course.

First step in prevention is a dew shield and if that isn't enough, a dew heater.

[Ouroboros]

Yes, it can be a problem.  I've lost guiding a few times due to dew. A dew shield made out of sleeping mat foam works well. I always have a hair drier to hand when it really gets bad.  Warm air wafted gently over the guidescope's objective lens from a hair dryer on gentle blow and some distance away works a treat. 

[Shelster1973]

I am with the others and say a definitive yes, a dew shield is needed for a guidescope.

I made mine out of a black bin bag filler.  Is nice and easy to shape round and also is stiff enough not to floop about.  Made it approx 2/3rd the lenght of the scope body so as to project well forward of the objective.  The lenght does not effect the performance of the guidescope either.  Also used the same to make the dew shield for my main scope.  There is a thread on it in the DIY section so you can see the finished results....

[PeterCPC]

Yep, I use a dew heater on mine.

Peter

[Steve789]

Thanks for the replies. This is something I've been wondering about for a while. I use a small 50mm guidescope that has a dew shield built in but still gets dewed up. I'll look into getting a dew heater and controller.

[wxsatuser]

Dew bands on 60mm guidescope and 105mm Sigma macro lense.

[Owmuchonomy]

Oh yes. I have exactly the same guider as Mike and it dews up quite easily.  I use a Kendrick 3" dew band.

[StuartJPP]

7 minutes ago, wxsatuser said:

Dew bands on 60mm guidescope and 105mm Sigma macro lense.

Yep, looks similar to my heater...I made mine out of 8x resistors embedded between two pieces of wide elastic fabric sewn together by hand....works well...mine only needs about 1W or less.