Was tightening my mount tonight inside (its cold here), when finished thought i would have a quick look at the mirror dust - there was a bit - didn't blow off so i got my lens cleaner - after wiping it on, it appears to have taken off the mirror coating, and left some grey patches on the mirror.
I am not so worried about it as it's only a 4", and I don't observe thru the scope that often. I cleaned after with detergent & dist. water but the grey patches are still there - am posting so others can see, iamges showing before & after included
Some of that patchy look on the surface of the mirror maybe due to mold. Sometimes mold can look like dust, and it may have been the case here. You'd expect any damage that may have been done by lens cleaner to be more streaky in appearance. But if you wiped it over with lens cleaner and a soft cloth, any of the mold growing on the surface would lift some of the surface coating with it. Or at least show where it was eating into the surface of the mirror.
the scope is old - early 70's vintage - but the mirror was re-coated about 2000
the lens cleaner was part of a lens cleaning kit from york optical (never had a problem with it)
Don't know if the mirror has been damp as I have only had it for few months
Mould is a possibility - i may get some alcohol to wipe it with
No ifs or buts, any cloth used to wipe the surface of a telescope mirror will leave fine scratches all over it. Any cleaner (including alcohol) is at risk of reacting with the mirror surface. The only thing I use to clean a mirror is warm demineralised water. It will remove dust and a lot of grime but not all marks, just leave them there.
If it's a 4" and the picture on the right shows the removed coating (the small blobs) I would not be too worried, You've still got a lot of mirror to work with.
