ATM Comments About Figure32.exe

[Aplanatic@aol.com]

Dear Fellow Grinders:

I have received a number of excellent comments, questions and suggestions 
regarding my Foucault analysis program, Figure 3.2.  Here are some of the 
items that have come up:

Surface Error Wave Rating

The program displays the mirror's *surface error*, NOT the wavefront error.  
These two measures of the mirror accuracy will, of course, differ by a factor 
of two.  I probably should change the program to display the wavefront error, 
as this seems to be the most accepted measure of the mirror's accuracy.

In calculating the surface error, the program uses a wavelength of 550 nm.

Numerical Refocus

This allows the user to try different focal locations in evaluating the 
mirror for surface error, transverse error and diffraction characteristics.  
The program finds the focal location that minimizes the weighted RMS error 
and sets the numerical refocus value to this.  This focal location may not 
minimize the P-V surface error or the transverse error, so, the user has the 
capability to vary the focal location to see if a better focal position is 
possible.

Also, the numerical refocus function is quite useful in developing a figuring 
strategy.  For instance, one might like to avoid polishing the edge of a 
mirror in favor of removing glass elsewhere.  In many instances, by varying 
the numerical refocus, one can find a focal position where the edge can be 
left alone.  Of course, in doing so, more glass than absolutely necessary 
will need to be removed.  

Zone Centers

Based on the inner and outer mask radii, the program calculates the zone 
center for the user.  I this program, the zone center is defined to be the 
point where there are equal maks areas inside and outside of it.  Since the 
eye tends to average the brightness of the entire zone when null testing, 
this seems to me to be the best estimate of the zone center.  Others may 
disagree.

Encircled Energy Ratio

The encircled energy ratio is calculated based on the integral of the light 
intensity from the center of the diffraction spot to an angular radius of 
lambda/D, where lambda is 550 nm and D is the diameter of the mirror.


Once again, thanks for the comments and questions.  If you would like to try 
the program:

Download the WINZIPed file from:

http://members.aol.com/aplanatic/fig.ZIP

Unzip the file into a new directory.  

At the DOS prompt type figure32 to begin execution.


Dave Rowe.