The grinding phase went very well, and the mirror didn't stick to the pitch, but after polishing for what Zane terms "a ridiculous amount of time (probably dozens of hours) to give the mirror as perfect a polish as I could give it," a Ronchi test
revealed a severely turned-down edge.
Lutfu used plate glass for those, and was able to test their focal length and sphericity with a Ronchi test
and a Bath interferometer.
With Jerry's help, the mirrors were figured and evaluated with a Ronchi test
. By the end of day four, all 100 mirrors were finished and on their way to a nearby coating plant, where they were aluminized overnight and returned the next day.
Kelley used both the Ronchi test
and the star test to judge image quality while tensioning the mirror, stopping when the Ronchi bands were straight and the stars were pinpoints.
Performing a Ronchi test
on a mirror blank is a good way to check that you are producing a good figure.
We can use the same tester to perform a double-pass Ronchi test
, gaining a similar advantage over the standard Ronchi test
Mirror makers can look for such edge defects with the Ronchi test
and other methods, of course.