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[ATM] Reducing the outer zone in figuring
I'm having a hard time reducing the outer zone of my 6" f/5 mirror.
I've tried the standard full-size tool parabolization strokes, from full
width W to 3/4 diameter center-over-center and everything in between.
The 3rd zone's correction grows and grows, but I can't seem to do
anything about the 4th zone.
Here are my current Foucault measurements:
zone R-R1 (inches) Ideal R-R1 Correction
---------------------------------------------------------
1 0.000
2 0.009 0.021 Z2-Z1 = 0.009 = 43%
3 0.030 0.040 Z3-Z2 = 0.021 = 111%
4 0.036 0.059 Z4-Z3 = 0.006 = 32%
The center zone is a piece of cake to reduce. It's the 4th zone that I
can't seem to correct without doing twice as much to the 3rd zone. I
know the next step is to bring it back toward a sphere, but then what next?
If at all possible, I'd like to be able to do it with the mirror on
top. I've tried reducing the edge with the tool on top (Texereau's
stroke C-II on p. 91), but I ended up with a turned down edge that took
many hours to eliminate.
One thing I haven't tried (that I just thought of) is spending more time
on zone 2, to keep zone 3's correction under control. Is this what I
should do? Still, I've had a hard time reducing zone 4.
David Steinhauer
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