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When is a Mirror dirty enough to need cleaning?
Looking down the tube at my primary mirror (with a torch) I can see dust on the surface of the mirror, not much but its there and without the torch its very hard to see at all. Also there seems to be a light haze on the surface when the torch is shined across it at an angle, and I seem to recall in my reading that others had reported this as well (one attributing it to cooking). The scope (12" Dob) is not kept in the house so cooking is out, and I was leaning towards plastic outgassing (like the haze that builds up on the inside of car windscreens). No smokers at my place so it's not that sort of haze. There plastic tube cap and the shower cap that I keep on the back end when its not being used might be the source of the haze, or maybe the EVA light shield that I made from a camper mat.
The scope is only three months old but it gets used a fair bit (like two to three nights per week weather permitting). I always have the fan running when I am using it to keep the dew away (needed this winter).
BTW my primary mirror in my Celestron 130 is still pristine, but the Dob gets used more these days.
Is this something to be worried about? How dirty is dirty? I read about people saying never clean it, others say clean it once a year, etc. What's the consensus?
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