Quote:
Originally Posted by Peter.M
aluminium is 5x WORSE than glass. You want the mirror to not expand
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Yep sorry, typo..
Corrected.
Another point in favour of borosillicate glass:
I have Coulter Optics 10" F/5.6 parabolic mirror, I purchased it back in 1980... it was never been re-coated, I washed it 3 times so far, and apart from small damage on Al coating (when the secondary fell on it during mishap 6 years ag0), it is like new.
I would like to see plastic mirror that old.. and performing as well as this one