FreeLists / az-observing / [AZ-Observing] Re: Image Question

[Andrew Cooper <acooper@xxxxxxxxx>]

Silicon dioxide (SiO2) and quartz are the same thing.  My first mirror
(6" f/5) I had coated with a silicon dioxide overcoat.  Despite being
almost 20 years old and having spent much of that time in a climate much
more humid than here it shows no visible degredation.  Maybe there is
some loss of reflectivity proper measurements would show but I can't see it.

I hope my 18" overcoated with titanium dioxide does as well.

Andrew


"Stanley A. Gorodenski" wrote:
> 
> My mirror has a silicon dioxide coating. That was supposed to be a good
> coating although I do not know if it was rated by years of service. I
> believe, though, that silicon dioxide affects sensitivity in certain
> wavelengths of the UBV system and that is where a quartz (?) coating is best
> for some photometry.
> Stan
> 
> Tom Polakis wrote:
> 
> > Is this true even here in Aridzona?  Other than a lot of dust, what
> > attacks coatings in this climate?  Shouldn't mirror coating last for
> > decades in the desert, or am I misinformed again?
> 
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-- 

Andrew Cooper
Tucson, AZ
mailto:acooper@xxxxxxxxx
http://www.whitethornhouse.com
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