At the Chabot Telescope Maker’s workshop, we make a lot of use of the Ronchi test. It’s great for figuring out gross defects and problems with your mirror. Back in the day, I wrote a simple program to generate Ronchi patterns for a given parabolic mirror. Here are six Ronchi patterns generated by my code for a 12.5″ mirror, with a radius of curvature of 126 inches (same as my mirror in progress) and a gratings with 100 lines per inch. The images are offset by -0.3, -0.1, .1, .3, and .5 inches respectively.

Not bad. But I can think of a few different things I can do with this code:

• First, it should be able to generate pictures for other conic surfaces than paraboloids. Being able to specify the conic constant would enable you to see hyperboloids and oblate spheroids.
• I never actually verified the results against reference implementations, or if I did, I don’t remember doing so.
• I should be able to specify deformations like turned edge or shortened inner zones.

When I get this working, I’ll post the code.