Re: [ATM] Reducing the outer zone in figuring

[Jim Burrows <burrjaw@earthlink.net>]

At 2007-05-01 19:30 -0700, David Steinhauer wrote:

>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%

I guessed the zone radii are Couder's, and the test is moving source, 
giving the following Sixtests input file:
----------------------------------------------
David, 4223
     6
Foucault
    0.0
y, inch  X, inch
     0.75   0.0
     1.81    0.009
     2.36   0.03
     2.8    0.036
*
       -1        0
0.0
    60.0
INCH
--------------------------------------
Sixtests says the mirror's getting close:  surface RMS = 27.9 nm, 
0.665 Strehl (goal is 20 and 0.8) with high edge and center (each ca. 
70 nm high).  The best-fit parabola's R = 1523.55 mm.

If you find the deviations vs. a parabola with ROC .1 mm shorter, the 
center is 140 nm high and the deviation goes almost straight down to 
near 0 at the edge.  This is usually the easiest deviation to attack, 
much easier than going back to a sphere - the mirror is already 
undercorrected with the best fit conic constant -0.695.  You wanted 
to do MOT, and that's what Tex suggests for "Raised Center", p. 92, 
surface anomaly #10.

If this gets you still closer, post another set of Foucault readings 
along with zone radii, and say whether fixed or moving source.  If 
you're getting really close, about to say, "Good enough", take 
several readings, use the means for the Xs and input the standard 
deviation (replace the 0.0 two lines above "INCH") so Sixtests can 
say what the RMS accuracy is.

         -- Jim Burrows
         -- http://home.earthlink.net/~burrjaw
         -- mailto:burrjaw@earthlink.net
         -- Seattle N47.4723 W122.3662 (WGS84)

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