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John
Nobody mentioned waiting 15 mins for your mirror to cool being a problem, the fact is pyrex glass which is a volcanic mineral has been proven countless times as a better glass for astronomy, ultimately the combination of a good coating and pyrex glass as a base makes for this to be a moot conversation as BK7 glass just doesn't stack up.
P.S. on the evening in question the 16'' and 12'' scopes were collimated with a cat's eye laser, so we can rule that out.
GSO just don't come close to being as bright as the skywatcher tubes , unless my eyes vary from moment to moment it's been proven to me many times over in comparisons back to back.
Below is taken from a professor at Cambridge University discussing different glass for telescopes.
I'd believe him over some taiwan company any day
"The substrate is important. Cervit, Zerodur, Astrosital and Quartz are better than Pyrex. Pyrex is better than BK7. BK7 is better way than plate glass".
I rest my case, and hey 100% ?
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