Posted By Timothy Iafolla
Using your suggestions from last week I successfully altered my interference fringe-type flat tester so that it now works great (using a mercury compact fluorescent bulb). I now get very clear Newton's rings when I compare one polished flat against another...works like a champ for my polished, unmirrored flats and diagonals.
One follow-up question though: how do I test a mirrored surface against the reference flat? If I place the reference on top of a face-up mirror the rings aren't visible.