I was figuring my first F/4 (a 15") and got stuck about halfway between a sphere and the desired prabola. I was using a modified Mom20 and a 60 percent lap. In the process, I made about 50 knife edge readings and used both Sixtests and FigureXP. It was time consuming and painful. In desperatiom, I tried a 40 percent lap (which I thought was verboten). Using both laps, I got to a Strehl of 0.938 in only a couple of hours. Oh well!
I gave the mirror to my son and immediately started working on an easier to use version of the above two programs. The result is Parab. There is nothing new and it does lack in some of the bells and whistles. Hopefully it is easier to use.
For now, consider it a beta test. I don't know if it is going to fly at all. More than once I considered giving it up. Now I need some feedback.
By the way, Jim Burrows and James Lerch are my heroes, but I am troubled because their programs are about 15 years old.
I love this comment of Jim's (who has a Phd in math): "This is numerically difficult to compute." I wish I understood the rest of his stuff. See