alt Hacker NewsWhen did buying a mirror on Ali overtake grinding your own? I guess when Ali became Edmund scientific ie mirror grinding hasn't been a thing since I was in shorts (the 70s)
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Mirror grinding is still a thing. Just not a thing that young people generally do. Distribution got easier and real estate got more scarce. Those of us who have garages, have filled them up.
In my understanding it's gotten considerably easier over the years with better availability of diamond and CBN abrasives, and with more electronic control of the grinding hardware. Slumping glass and bonding a thin sheet to ceramic foam reduced the costs and weight a great deal as well. Mastering these techniques make it easy to start a small business rather than to do a one-off in your garage, though.
As a sidenote: The Celestron RASA astrographs are so effective and so inexpensive of a wide-field instrument that it's a lot harder to justify the DIY activity that existed in the 2000's.
The only reason to grind a small mirror is because you want a very large mirror and need to practice first. This has long been the case, but the definition of large has gotten larger over time. Of course there is also the in between states where you buy a cheap workable mirror, and then make it higher quality. Unless you have a lot of land high on a mountain there is rarely any point in mirrors that you have to completely grind yourself - the telescope wouldn't be portable and the nearby light and atmosphere pollution means large sizes don't gain enough. (if you do live in such a place your telescope could be massive if you have the years to dedicate - can I come by and look through it one night after you build it?)
We buy pre-dug mirrors on Ali to refigure them, or dig and figure our own all the time. See Ali as a supplier of prepolished blanks :) . The l/6 I mentioned in the post are l/6 spheres, so they also need figuring.
If you just want a serviceable telescope, you haven't been able to really save any money by grinding a mirror for decades, unless you're a madman like Dobson who scrounged blanks in the form of things like porthole windows. But that's not why people do it. I haven't built a non-trivial telescope but it is not too unusual for amateur telescope makers to figure mirrors to precision that you can't easily buy, i.e. not for amateur prices. Where he talks about Ali mirrors being l/6 or better? That's really good for randomly buying something unspecified cheap on Ali. l/6 is lambda/6 which means the surface error of the mirror is less than 1/6 a wavelength of light. Utility optics are typically l/4. Really fine stuff is l/10 or l/20.