[pmrid (Peter)]

One for the observatory-owners I suppose. With my permanentkly mounted scopes, over a surprisingly short time, I am seeing quite a buildup of a dusty film on the primary and secondary on my Newt and on the objective on my refractor. Over winter we've had quite a bit of fog but I tried to counter that by running an oil-heater in the obs between 10 pm and dawn every night. But seemingly, to no avail.
How do others protect theor optical surfaces from the dreaded dust and other films and so forth? Keeing dust caps on obviously, but that doesn't seem to have made much difference to my scopes at least.
ANy thoughts?
Peter