ATM Lurie-Houghton Corrector Material and questions

[Ari <Ari@birmingham-us.crosswinds.net>]

In ATMJ Issue #5, there is an article by F.T.A. Hoenderkamp about his
8" Lurie-Houghton. He has an f/4 scope, but in the closing, he states
the corrector "eliminates the spherical abberation and coma". If all
coma is eliminated, is a f/3 scope possible? Would the mirror be too
hard to grind?
        Also, could a clear non-optical glass (read: Pyrex) be used for the
correctors? What about plate glass (and dealing with the green images)?
I really don't have the money right now to blow on 2 8" dia. pieces of
BK7...I imagine those would cost about $100 each!
        One last thing...is there a set of detailed instructions anywhere that
tell how to grind the correctors?

Thanks in advance,
Ari Friedman
        There's light at the end of the Sonotube.