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Reflectivity loss since 1994?

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#1 azure1961p


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Posted 17 February 2013 - 09:58 PM

My mirror coatings were new in 94. They are in good condition - no pinholes or hazes or blemishes. I always took care of it and clean it every six months to a year.

If it was 93% reflectivity when new in 94, what would it be now and is there some formula or rule to figure out an estimate?



#2 SeattleScott



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Posted 17 February 2013 - 11:05 PM

The standard coatings supposedly last 10 years before they degrade noticeably. The newer enhanced coatings with higher reflectivity (over 90%) and multiple protective layers are supposed to last 20 years. Note that these are rules of thumb and the actual results will vary based on the amount of use, how dusty it is where you observe, the humidity where the scope is stored, if you live near the sea (sea salt corrodes coatings faster), and how carefully you clean the mirror.

You probably have enhanced coatings if they were 94% so that would put you at 19 years. Maybe one more year to go before they are due!

#3 Binojunky



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Posted 19 February 2013 - 12:48 PM

No hard or fast rules on this, coatings on closed tube scopes like a S/Cass: can and do last for decades, I once cleaned a filthy mirror on a old Edmund newt, it had to be 30yrs old and the coatings that were original came up like new,DA.

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