How often are large reflectors cleaned?

[joema]

I've seen amateur reflecting telescopes with tremendous crud on the mirror and the image still looks pretty good.

Truss-type reflectors are totally open to atmospheric contamination, including dust, smog, insects, etc.

That makes me wonder, how often are large professional reflecting telescopes cleaned?

I assume there's a light cleaning period, a heavy cleaning period, and a recoating period.

Does anybody know what these are? Does the contamination in the intervening months/years mainly affect light grasp, not resolution or distortion?

[indie85]

spit n polish, y do you ask?

[Russ]

As infrequently as possible. It varies depending on the location and environmental conditions. As you noted, quite a bit of crud can be on the mirror and you still get a pretty good view.

With that said, it is a delicate ballancing act. Dust, smog, et. al., diminish seeing, cleaning scratches/degrades the mirror. In short, you clean it when the images get worse than you are willing to put up with. 8-[

[badprof]

When I was at the AAT many years ago, they used to clean and recoat it once per year. The mirror did not really need recoating every year, but they decided that since most of the work involved was in removing the mirror, they may as well recoat it whenever they had to clean it.

Cheers

[archman]

I know I clean my glasses everyday... I guess astronomical optics don't suffer from reduced clarity so much, or maybe you're all just "filthy beasts".