From: "Bill T." 
To: atm{at}shore.net
Reply-To: "Bill T." 


>I would definitely NOT recommend trying to figure using the star test.

I agree, but my point was to trick a person feeling intimidated by Foucault
technology into at least partially parabolizing a spherical mirror, and
from there leading him on the downward spiral to full ATM techno-obsessive
addiction.

In defense of star testing, I have to say that I have seen several "at
least acceptable" mirrors made using nothing more than formula
polishing techniques augmented with only a few star tests.  If you polish
out a mirror with a a 65 to 75% lap, using short W strokes biased towards
the center, the mirror sort of stabilizes at a figure with undercorrected
but approximately paraboloidal outer zones, and a flat center.  Star tests
can be used to adjust to the general relationship between outer and inner
zones.  This is classic John Dobson technique from the mid 90's.  It works
reasonably well for non-technologically inclined people.  By these
standards, the quality of the mirror is measured not in wavefronts, but in
the soaring of the spirit when that first-quarter moon finally comes into
focus.

Bill

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