A Variety of Equipment Built to Test Telescope Mirrors
Star Testing is a wonderful method to do a final check on a mirror, but requires still, dark skies - a luxury not often available. The tester shown is used with an artificial star (a light reflected in a spherical ornament) down a long hallway. The tester is basically a box with a secondary mirror holder/focuser unit that slides, so it can be adjusted to suit a variety of mirror focal lengths, and a mirror clamp that allows mirrors of different sizes to be mounted and aligned. The rest of the assembly is pretty clear from the pictures.
The tester and ornament assembly
The tester from the right, showing a 6 inch mirror being tested
Other test apparatus are very valuable. My most recent setup is a Ross Null tester. It includes a lens from Ceravolo optical plus an assembly that has both a knife edge and a Ronchi screen, illuminated with LEDs. These are shown below.
I also have a micrometer-based Foucault tester, based on an old piece of equipment that had a lead screw and scale on it.