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Help please anyone. Last time I used my 8” Dob I noticed little rain spots and a damp film on the mirror when I brought it inside. I put the scope under the heat pump and the spots cleared away, but it still looks like a a slight film on the mirror.
I use the fan on the scope when I am observing, so it doesn’t fog up and have left the fan running after I bring it inside for a while in case there is any dampness.
My question is: It appears that I still have a slight film on the mirror, how do I remove it?
All hints, tips regarding mirror cleaning re spots, film etc. would be most appreciated.
Cheers and Thank You
Karen
Best not to do anything 🙂
My dob has spiders webs in it! I have cleaned it once in the 6 years I have owned it, and it made very little difference despite having a heavy coating of pine pollen all over it.
Even the slightest dust will show up and look awful when a light is shone down the tube, but the actual amount of light reflected off dust is tiny compared to the a full reflection of the torch, and light reflected by the dust is not focused on the eyepiece.
I’ve got an old mirror with a badly degraded reflective coating, blotchy with dark spots all over it. Beautiful views!
Cleaning a mirror damages the surface on the microscopic level where it matters. A dirty mirror is still perfect at the microscopic level, until it is cleaned. Dust is very small, it covers up only a very tiny fraction of the mirror surface, even when it looks bad!
The professionals generally don’t clean mirrors. If it gets really bad, they replace the reflective coating, rather than look through a clean, but damaged coating. It often gets quite bad before they do anything. Us amateurs may have to resort to cleaning, but it’s a last resort.
The book “Astronomy hacks” says about cleaning mirrors: “if you still think it really needs cleaning, don’t.”
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