Quote:
Originally Posted by ozark1
The dust will have little or no effect on the image. Don't worry about it beyond blowing of the worst. Paranoid people have been known to gently wash mirrors upside down with very gentle water - but it's not worth it and besides you'll never get the mirror out of that telescope (or if you do you'll never get it back and recollimated). Note, I'll take a filthy corroded collimated telescope over a clean telescope with badly aligned optics
When you lose more than 30% of the aluminium surface - that's the time for action.
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aluminium? Are you from the Snowden portion of the eastern Ozarks?
Meanwhile dust absorbs light thus reducing the reflectivity of the surface it's on. This hinders light-gathering power. It also scatters light (check out light beams in a smoke-filled room) and thus affects resolution. Clean optics are accurate optics.
Dawes Limit doesn't apply to mirrors covered with dust.
Somewhere way back Phil recommended certain techniques for cleaning first-surface mirrors. I sort of remember distilled water and a mild alkaline agent being primary ingredients.
Re a Tasco I doubt there was much attention paid to collimation in the first place.