[ATM] Is this Sphere good enough?

[Don Bates <dbates59@yahoo.com>]

My thanks to the people who responded to my post about
the condition of my sphere prior to parabolizing. I
think what I learned from this is that since I am
about to deform the sphere anyway, why waste lots of
time correcting to a "perfect" sphere? I'll admit it
is tempting to see the Foucault disc turn dark all at
once without the slightest hint of a shadow, but so
what? At f6.6, its still a lousy telescope mirror. In
some ways, it seems like achieving a great sphere is
harder than I have been led to believe. In the 3
previous mirrors I have made, I don't recall ever
seeing what I would call a complete absence of shadow
under the Foucault. Much of the literature seems to
indicate that by doing TOT with the "normal" stroke,
one can achieve a clean sphere without really trying.
This has been counter to my experience. At some point,
the sphere does not get any better, and starts to
deviate at some point. I guess the key is to get as
close as practical, then go ahead and go for the
donut. I shall proceed to stalk the wild parabola...

Don


		
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