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Re: [ATM] ATM Digest, Vol 41, Issue 2
David,
You may want to check out Mike Lockwood's page on figuring with full-size laps here:
http://tinyurl.com/3872nh
He addresses specifically the issue with undercorrected outer zones and how to address when using full-size laps. His techniques are pretty basic, well explained, and best of all... they work! I've had good success using his techniques. His idea of correcting the outer zones first works well because as you've discovered, correcting the inner zones is relatively easy.
Curt Diggs
Message: 1
Date: Tue, 01 May 2007 19:30:59 -0700
From: David Steinhauer
Subject: [ATM] Reducing the outer zone in figuring
To: atm@atmlist.net
Message-ID: <4637F7E3.3070805@verizon.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
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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End of ATM Digest, Vol 41, Issue 2
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