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

["Stanley A. Gorodenski" <stan_gorodenski@xxxxxxxxxxxxx>]

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?
>
> In the misinformed department, I will ask if it's not "technology"
> (Austin Powers quotes added for effect) that is improving mirrors today,
> what is it then?  I defy you to find a good mirror greater than 16 inches
> in diameter and faster than f/5 made before 1980 that was available
> commercially for a reasonable price.  Today, the shopper has many
> options.  What were an amateur astronomer's options 20 years ago?

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