-I also have a 10 inch mirror that I could lengthen into a 35 foot radius sphere to make a tester so that I could improve the flat's figure. With such a long sphere and a decent Foucault tester (with micrometer positioning and an auxilliary telescope to see the very distant mirror), it should be possible to make a better flat. The 10 inch mirror is a crummy f/3 paraboloid and has an edge chip (which would be ground away) and it would be nice to be refabricate it into something useful. Working the flat would be fun, of course. This would give me the option of using the improved flat for a coelostat.
-I thought about coring the flat so that it would be handier for testing primaries. It is fine annealed and I'd check birefringence first so I'm not too worried about strain release, but coring always carries some risk of chipping and seizure/breakage, etc. Should I do it at all? Should I do it before or after refiguring (with the core plastered back in the hole during polishing)? I don't mind a coelostat mirror with a hole because I'd use it with a reflector (i.e. secondary shadow) anyway, but what would coring do to the flat's value? A big, good flat is valuable, but would coring reduce what I might get for it (probably in the ATM marketplace) in 20 years when I'm done with it?
-The flat is really okay as is. Maybe I shouldn't mess with it. What would you do?
Aart M. Olsen aart@uiuc.edu 217-333-7467 College of Veterinary Medicine Univ of Illinois at Urbana-Champaign