8" Mirror: actually done!
Someone brought an extremely accurate “double pass autocollimator” tester to an amateur telescope maker meetup… and it showed an uniform shade of gray across the whole mirror, meaning no defects (ignore the circular reflections from the test stand). That means my mirror is an extremely smooth parabola! I’m done mirror grinding!
🎉 First mirror: complete! 🎉
That’s so cool! I thought I was slightly overparabolized based on my Foucalt testing. I guess not!
I don’t know the exact numeric accuracy of my mirror without an interferometer. The actual smoothness is “no deviations visible on a double pass autocollimation test”. A professional optician who was helping with the test estimated that as 1/20th wave or better, and I’m inclined to take their word for it.
Start to finish: 8 months. Total time spent working on this mirror, not counting setup or lap-pressing or testing time): 32.9 hours.