Secondary mirror condensation

[maw lod qan]

Recently in the early mornings my secondary on my 8" dob has fogged, stopping any viewing.

Would a extension tube like I've seen on SC's help stop this or am I going to have to go the wrap route.

[Ricochet]

A dew shield will help. I used to have one for mine but I haven't used it since I fitted a cooling fan to the rear of the primary cell. The small air current flowing up the tube seems to be enough to keep the dew at bay. 

If conditions where you are are worse then a secondary dew heater will be the way to go. 

[maw lod qan]

Thanks!

This happening has surprised me. Dealt with it using DIY dew zappers on my cameras and even the finder scope. If I have to, I'll go that route too.

[NGC 1502]

 

A cooling fan blowing gently on the back of the primary helps to keep dew at bay on both mirrors.

Dewing of the secondary is common with a Newtonian.  I’ve heard some say that the primary on a solid tube Newtonian  never dews up, but in extremely damp conditions it most certainly can, and the fan helps to prevent this.

Ed.

[Louis D]

I've never had this issue with my solid tube Dob in Texas even in the depths of our sticky summers, though I don't live on the coast where they take humidity up another notch or two.

If the dew point is that high, you'll probably have condensation on everything.  As such, make sure to leave everything out to dry when you bring it inside an air conditioned space to prevent fungal growth.  I also don't recommend storing anything astro related outdoors unless it's gently heated to prevent condensation formation.

[NGC 1502]

3 hours ago, Louis D said:

If the dew point is that high, you'll probably have condensation on everything.  As such, make sure to leave everything out to dry when you bring it inside an air conditioned space to prevent fungal growth.

 

Yes indeed, if the night is very damp the telescope will be dripping wet.  If you have paper star charts don’t leave them uncovered while you’re at the eyepiece.  Eyepieces not in the focuser should be protected in a closed case or capped and in a pocket.   Those eyepiece racks on the side of a scope are a good way to have a whole row of eyepieces dewed up and useless.

Fully agreed about thoroughly drying out to prevent problems later.  If air conditioning is not available do the best you can with a well ventilated space and all caps and covers removed.

Ed.

[Louis D]

2 hours ago, NGC 1502 said:

If air conditioning is not available do the best you can with a well ventilated space and all caps and covers removed.

Central Florida like coastal Texas is pretty much entirely air conditioned.  Population growth in Florida and coastal Texas didn't really explode until after the widespread adoption of A/C.

[maw lod qan]

Scopes in an obsy. If I get dew, I leave the roof back for the sun to dry things off, before rolling it back.

We've been having a few late cold snaps, these cooler mornings what's giving me fits.

[Louis D]

5 hours ago, maw lod qan said:

Scopes in an obsy. If I get dew, I leave the roof back for the sun to dry things off, before rolling it back.

We've been having a few late cold snaps, these cooler mornings what's giving me fits.

You might try circulating air through the entire observatory as well as the tube.