Moisture On Primary Mirror

[Norfolk star gazer]

I had an early morning session with the scope today (very cold) and got in at about 7.30.

I left the dust cap off the 10" dob so that the moisture could evaporate, but 5 hours later it is still there.

Should I just leave it alone in the cold garage and see what happens (probably will want to use it tonight) or bring it in the house to warm up or take a hair dryer to it?

If the hair dryer is the best option, should I lay the scope flat on the dob mount and blow down the tube or blow the hot hair at the mirror end?

[Stu]

If you want to use it tonight, perhaps put the tube level and blow the hairdryer down towards the mirror, just on a cool or warm setting, not hot. The air circulation should help clear the dew.

[Norfolk star gazer]

If you want to use it tonight, perhaps put the tube level and blow the hairdryer down towards the mirror, just on a cool or warm setting, not hot. The air circulation should help clear the dew.

I assume just leaving it alone (if I don't use it tonight and give it a chance to thaw out - so to speak) won't harm the mirror if the moisture doesn't go? It's quite a cold garage today.

[Stu]

I assume just leaving it alone (if I don't use it tonight and give it a chance to thaw out - so to speak) won't harm the mirror if the moisture doesn't go? It's quite a cold garage today.

My preference would always be to clear the moisture relatively quickly to prevent it accelerating any deterioration in coatings. A few nights won't hurt but over a prolonged period it is less good. If not using tonight I'd be tempted to bring it into the house to clear it

[Norfolk star gazer]

Thanks. I gave it a quick blow dry on a low setting as suggested and it cleared in minutes. Just left with a slightly dirty mirror that has accumulated some dust. Nothing major like a dead fly, so nothing to affect the view too much.

When I'm feeling brave, I might give it a clean, but know that isn't easy!

[Stu]

Good stuff. Don't worry about a bit of dust, no need to clean it for a good while yet