Ronchi Test
Tony Cecce, Corning, NY (CECCE_AJ@corning.com)
Mon, 01 May 1995 11:15:49 -0500 (EST)
I finally worked mirror to a fairly flat sphere under the knife edge test.
However, I still had a turned down edge. (I know how I got it and I swear
never to worry about a turned up edge again) It didn't look to be that
bad, extending maybe 1/8" into the mirror. I decided to try out a new
Ronchi grating I made with a CAD package and a HPLJ4. What a shock! The
Ronchi test was very sensitive to the TDE. In actuality it was severe
on the outer 1/8" but extended to a lesser degree almost 3/8". So, back
to polishing. I've been using MOT 1/4 centered strokes for 10 minutes
at a stretch. Using the ronchi grating I have been able to watch my
progress and see the edge improve. However, I have very faint zonal
defects under the focault test that I can't see with the ronchi. So it
seems that both tests really are useful.
I've finally worked the mirror to a small turned down edge (still quite
severe), but in my efforts to achieve optical perfection and completely
eliminate the TDE I have generated some small scratches that I found with
a bright light after my last session. I guess I'll have to keep on
polishing to experience for myself what can be polished out. Before I
proceed should I be worried about a contamiated lap? Or will I be alright
to just wash everything real well and continue on?
This has been an unbelievably fantastic learning experience. But, it
also comes with it's emotional up and downs. I guess the trick is to
decide at which UP to stop and say "good enough".
Looking for my next up,
Tony