Over the last 18 months I have been working on a fast 8 inch scope. I thought I’d share my progress. I’ve made several mirrors between 4 and 12 inch. They were all in modest focal ratios between F5 and F10. The tolerances at at F3 are tight so the mirror was a challenge. I used a conventional Foucault tester and a ronchi screen for all the testing. When I had a good result there I tested the mirror in autocollimation.
I bought the blank here on iceinspace. It had the fast curve already ground into it. So I made a tile and plaster tool to complete grinding. Melbourne was in lockdown when I began so I used my at home time to build a new grinding / polishing machine shown below. If you are interested in the machine, I prepared a short video about it for my club last year:
https://drive.google.com/file/d/1SPF...w?usp=drivesdk