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Originally Posted by Lester
Hi Doug,
I hope your mirror was dirty before you cleaned it. Many mirrors are cleaned too frequently, and is the major cause of scratching. I know it is everybodies choice as to when they clean their mirror, but it would be good to have a guide as to how dirty it has to be say before 2-5% reflection is lost.
Any way yours is clean now, go get em Doug.
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A mirror can look fairly dusty before you really need to clean it. You will
start to get a loss of contrast. Think of dust in the same way as a central
obstruction. If the dirt on your mirror were scrunched into a solid patch
would it be as big as your central obstruction your secondary causes?
Yes this maybe hard to judge. But in reality it is a similar effect. I think
there is a formula for working out the size of a central obstruction before
the is any noticable loss in performance.
regards,CS
Rob
PS: I clean mine every time I'm doing any serious imaging, or about every
6 months or so. I have never had a problem with scratching the surface.
But then again I have worked with lasers and optical surfaces used in those
applications, where a mirror 10mm x 10mm can cost AUS$300.00. However
there is one thing I never do that I have seen folks do and was shown in
the recent mirror cleaning article in AS&T and that is lay the mirror flat and
blast water at it, I always palce mine at an angle that way I'm not blasting
water down directly onto grit more blowing it side ways. But that just me
regards,CS
Rob