From: "Jerry" 
To: "'Amul Munshi'" , 
Reply-To: "Jerry" 





        Plugging your numbers into a program based on Texereau's graphical
method in his book, I get your mirror at about 1/13 wave.

        That is not bad.  If you wished to make it better you would need to
reduce the amount of correction from zone 1 to zone 2 and increase
correction from zone 2 to zone 3. It is easy to do that with TOT accented
pressure on zone 2. It would be a VERY SHORT "one time around"
session, maybe 3 minutes. If you have not used accented pressure before you
might have trouble and may make it worse. I am not recommending you try to
make it better and I am not recommending that you don't try. An experienced
worker would find the shape you have very easy to make much better quickly.
But without the experience you have a better chance of making it worse.

        For a first mirror 1/13 wave is good. And if you have that after
only one parabolizing session it has been "too easy" for you. If
after measuring a few more times you have verified your numbers, I think
the conventional wisdom would be to call that one done and put it in a
telescope.

        Advice for the future mirror. If you are that close to a parabola
after only one parabolizing session, that session was too long. There will
be differing opinions on this, and it depends on mirror size and f ratio,
but I would say that the first session you would expect to see about 5 to
10 percent correction. So lets say about 1/10 as long as you worked. There
are variables in there for different working conditions and the worker. But
the idea would be to get a start off in the direction of a parabola and
test to see how uniformly it is parabolizing, see if you are developing
zones, and make adjustments to the stroke. As you get close to the
parabola, somewhere around 85 to 90 percent correction, do shorter sessions
and test more. The first parabolizing session I would usually only do three
or four times around the barrel as I am only interested in gauging the
smoothness and speed of correction. I might do several times around in a
session after I have a feel for how fast the lap is working.

Jerry


-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net] On Behalf Of Amul
Munshi
Sent: Tuesday, July 01, 2003 11:16 PM To: atm{at}shore.net
Subject: RE: ATM First Foucault Readings

 After my first parabolizing session, I did a set of zonal measurements
 (inches):

 0.000    0.064 0.08    0.106
 0.000    0.046 0.07    0.101
 0.000    0.051 0.07    0.106
 0.000    0.048 0.063    0.102

 Clear Aper: 7.875 inch
 ROC : 111.25 inch
 Secondary 1.5inch diameter

Hi Everyone

Sorry I forgot to post the zone radii

Inner Radius of zone 1 : 0.75  (to mask the central hole) Outer Radius of
Zone 1 : 2.0730
Outer Radius of Zone 2 : 2.8340
Outer Radius of Zone 3 : 3.4310
Outer Radius of Zone 4 : 3.9380

Source if fixed


 BTW I'm not so sure about the readings on the edge zone, will take new
readings again tomorrow and post again


 Aditya Munshi

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