dew on the primary

I took my new 10" dob out to a nice mountain hilltop last night and saw wonderful things. It was chilly -- upper 30s -- and very damp. When I quit, the tube was wet, the telrad was wet. As always, I put the scope in an Orion carry bag and put it up in the basement when I got back home a half mile away. I got it out and set it up again tonight in the same place, but this time the primary mirror was half covered with dewdrops. The dew went away after the scope cooled down.

Questions:
1. The dew left spots on the mirror, I assume where dust used to be. I don't want to clean it every time I use it and ruin the mirror. So how bad is that? The scope seemed fine after the dew went away. I enjoyed an hour of Orion's nebula at 133x and the moon at 300x.

2. What am I doing wrong? Is it the bag? I was pleased with the bag because after several such trips in the back of the pickup, the collimation is still fine. I'm thinking the scope is dripping water on itself right now inside the bag, though. I left it outside tonight hoping the cold mountain air would keep it from condensing.

Thanks for any advice.

Under dark, wet skies.
Bob

Hello:
I don't think you're doing anything wrong. I regularly get a LOT of dew on my scope and the mirrors when I bring it home. I observe from a high (9,300ft), dry, and cold (40F) site. I live in a low (600ft), warm(70F), and wet place. Thus, when my cold telescope meets the warm, moist air of our house, it's dew city! First, I wipe everything down with a cloth to prevent corrosion. I then use a blowdrier to slowly warm the mirror to get the dew off of the mirror by just blowing the drier into the front of the scope. Given that the mirror is over 2" thick, this can take a while. Once it looks like the dew is gone, I often have to blowdry it again 15 minutes. Blowdrying only warms the mirror face, whereas the whole hunk of glass is cold. I figure that condensed water plus dust in a moist environment is a recipie for mold, which I do not want on my mirror. I will also soon dehumidify the room where the scope lives.
So, I think the dew was on your mirror from the minute you brought it into your house. A wet telescope in a wet bag isn't doing itself any favors either. I would recommend towling the scope off if it's wet when you get home, and looking at the mirror before you put it away at home to see if there's dew on it. If so, then take a few minutes to blowdry it off. A few dirty spots on the mirror isn't a big deal. Most amateurs would probably be shocked to see how dirty observatory scope mirrors can get. If there's a lot of dust, it can affect the contrast of your scope, but in general it's better to just leave your mirror alone until it really starts to bug you.

Cheers
Mike Connelley