The stars have all gone dim!

[Black Knight]

This is probably a really noob question, but I've had my reflector outside now for around an hour getting setup for this evening. Initially, the view through the eyepiece was fine, although it has deteriorated now to the point where I can hardly see even Vega. The stars have all gone dim! I've tried different eyepieces, no luck.

What's happening! How do I get the stars back? Do I need a dew heater on the OTA, and if so where would I put it?

BTW, it is very cold outside probably around freezing.

[brantuk]

I would say you need to turn the moon off lol. Unfortunately it is bright and washes out a lot of dso's. It's gone cloudy over here too.

A real dark observing site on a clear moonless night makes an amazing difference, so if you're in a light polluted area (eg city lights reflected off the atmosphere) then it won't help. You could also be dewing up so a dew band and controller or a hair dryer on gentle heat might help. Also keep ep's in the warmth of your pocket.

[Brett]

Probably a long shot but did you leave the moon filter on On a serious note do the mirrors look clear and how do the stars look without the scope, it might be atmospheric.

Brett

[Ben Ritchie]

Dew?

[Black Knight]

Dew?

Well that's what I am wondering. Do reflectors get affected by dew? There is a very light film of dew on the outside of the OTA.

[Ben Ritchie]

It depends, the primary is usually ok but the secondary mirror can dew up

[Astro_Baby]

Yes reflectors get dew and the 200 like most modern regelectors wil dew up readily because the secondary is so close to the end of the tube.

Take a look down the focus tube and have a look - you will soon spot dew. If dew is the problem the best solution is a dewshield which you can either buy or make.

A dewshield will keep the dew away under all but the very worst conditions and it will also stop stry light going down the tube.

You can also get a secondary heater which wraps around the secondary mirror but I have found when a dewshield cant keep the dew off its usually because dew is so bad EVRYTHING including the primaryt and the eyepieces are dewing badly.

I also have a 12v hairdryer which can be used to blow the dew off but its seldom used because if the dew is that bad your on a losing battle.

[Black Knight]

OK thanks. Dewshield it is then

[brianb]

The stars have all gone dim!

Thickening high cloud layer? There's certainly one here - the moon looks like it's shining through about 3 layers of ground glass ....

[Black Knight]

There's certainly a thickening cloud layer here now, although it was clear earlier. I thought it was supposed to be clearish tonight?