Final Polishing

It's been a long time since my last update on my telescope project, so here it comes.

Jan 09

  • I tried a very crude focault test, and thought that mirror was ready for aluminizing.
  • Luckily, the guy who was supposed to do the aluminizing advised me to show the mirror to some professional first.
  • Went to Kolhapur and met Atul Sane, a professional telescope mirror, who had a brief look at the mirror and immediately flung all my dreams of getting an aluminised mirror out of the window. The polish on the mirror was only superficial; there were numerous tiny pits visible on the surface.
  • He showed me techniques to see these pits. He also showed me some of his finished mirrors for comparison. Boy, some of them were like Swarovski crystals! He also showed me his Focault and Ronchi test rig, and that gave me an idea of how faint the test image looks like.
  • I also learnt that my pitch lap was a bit on the soft side. So, I had to calibrate my techniques accordingly.

Feb 09

Was too busy with other stuff. No time to work on the mirror.

March 09

  • Renewed my polishing efforts. This time I used a 4kg weight for cold-pressing.
  • The pits started decreasing in number, now that I knew what to look for.
  • Did some star testing with the mirror. The mirror seems to have slight astigmatism. But, I am not sure; it could be just an artifact of imperfect collimation. Either way, it is not a significant artifact.
  • Built a Focault tester. This time I built a proper mirror holder! Here's a tip for ATMers; build some kind of mirror holder when F testing; it makes a huge difference! It need not be very sophisticated.. use some ingenuity. As long as the mirror is well rested (more than one point contact), it should be fine. Here's my mirror holder:
  • Mirror shows a very slight hill at the center in the F test. I am not too worried though; more polishing should take care of it and the secondary mirror will anyway mask that area.

All in all… a slow and steady "march" of progress. I just hope I can enjoy the telescope before the monsoons set in.