Had a heart attack today, went out into the observatory, after not being in there for a while (over three weeks) and took the cover off the scope and ARGHHHH!!!!!!!!!!!!! DEW all over the Primary, my heart dropped, not knowing how long it had been on there for I fired up the fan and ran inside to get the hair dryer, after about 5 minutes of blowing, the mirror was back to normal, although there is a huge amount of dirt left over from the water droplets, still deciding whether to leave it or take the primary out and give it a clean. Might test it out next clear night.
BTW anyone got a 40mm secondary they don't want and want to swap it for one that has lost alot of it's covering
My 12.5" primary Has a layer of dust too. I'm not keen on the idea of cleaning it. I did that with my 4.5"....It had a pretty good coat of crap, so I noted the view I was getting, took it out & cleaned it, then compared the views. No appreciative difference at all to my eye. But it's very hard to ignore the fact that it's got dust on it....It wants you to take it out & clean it straight away! I say resist the urge Astroman IMHO 
