From: "CSC" 
To: "Atm" 
Reply-To: "CSC" 


I'd guess that the dark spots in the two line ronchi are rough spots from
thumbing and small lap work.

The last star test and ronchi here says that the edge is shorter radius.
You are null testing, and the same hooking of the lines applies here.  The
paraboloidal curvature of the lines from bench testing are departures from
a true sphere.  They're gone now and all you are seeing is the departure
from a paraboloid.  Hooking in at the extrafocal position means the edge is
shorter radius.  Maybe an effect from a groove at the 90-95% zone?

I'd say go real slow here, as you are generally undercorrected shown by the
previous star test (hollow looking disk inside of focus).  This may be an
effect of the short radius edge, which is relatively undercorrected.

Time to really analyze the foucault readings, and nail which zones) are
out. Consider all the clues you have.  Use the largest correcting lap you
can, with soft pitch, so there will be a general smoothing action for the
suspected roughness.  Go real slow.  You're dealing with a few millionths
here.

Good work. You are relying less on a single test, which makes for more
brain strain, but keeps you out of quick assumption/analysis.

Colin

-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net]On Behalf Of Jerry
B. Hillman
Sent: Sunday, June 22, 2003 10:48 PM To: Ken Hunter
Cc: atm{at}shore.net
Subject: Re: ATM TDE correction and star test



Hi Ken,
No I am not going to give up.  Now that I found a way to deal with the
edge, I will continue to work on it till it is right. The Ronchi test on a
star tonight with about 6 lines showing shows slight TDE. I moved the
focuser till only two lines showed.  Inside of focus they show a slight
outward curve.  Outside of focus they show a slight inward curve.  Also the
spaces between the lines are speckled. Numerous black spots.  Is the mirror
undercorrected?  Also, are the spots between the lines due to surface
irregularities?
I am depending on the star Ronchi to tell me things about the mirror I need
to know. I just need to know what I am seeing. Clear skies, Jerry

--- BBBS/NT v4.01 Flag-4