2013: A 42" Tuneup
Recently Tom Clark's 42" was in my shop for some work.
At the end, I took some photos of the mirror using my knife edge tester. I have included one below, just to show the smoothness that can be achieved on a large mirror. Note the cable sling support and bright diffraction ring.
The small bright streaks at about 2:00 on the mirror are reflections off of an unmachined area on the back. The lighter "streak" extending from 2:00 to 3:00 is a shiny unmachined portion on the back where the glass was thinner at the edge of the Pyrex sheet. There is a matching unmachined area on the side opposite it.
Please check back for future installements of "In the Shop".
Lockwood Custom Optics