Re: [ATM] how good is this mirror?

["Bob May" <bobmay@nethere.com>]

`Jus5 for reference, an 8" pyrex blank (full thickness) is $40
plus shipping from one supplier.  A thin blank, of courese, would
be cheaper, probably about $30 as much of the cost is in the
weight of the glass.
That means that if you paid about $30 for it, you basically paid
retail for the glass and got a free surface ready to finish to
boot.
Put the mirror in a telescope and see how bad a 1/4 wave surface
accuracy really is and then start figuring the glass to get a
much better surface.  The coating will come off with just a few
passes of the lap and will probably show quite vividly whare the
high spots are on the surface.  Don't forget that the glass
surface itself reflects about 4% of the light so you can use it
in the scope as you proceed and see the difference in the quality
of the image and how much better a star is focused to the focal
plane.
Bob May
bobmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
Addresses have been munged up to keep spammers from bothering me.
replace the obvious words with the proper character.
Thank you for your understanding!

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