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The tiniest yet real telescope I've built

(lucassifoni.info)
166 points chantepierre | 1 comments | 12 Dec 25 07:35 UTC | HN request time: 0.2s | source
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ggm ◴[12 Dec 25 08:56 UTC] No.46242198[source]▶
When 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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buescher ◴[12 Dec 25 12:35 UTC] No.46243540[source]▶
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.
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1. chantepierre ◴[12 Dec 25 12:45 UTC] No.46243605[source]▶
I will correct the article, I've found great λ/6 or better spheres on Ali, but have yet to get a well corrected mirror. But starting from a λ/6 sphere instead of a flat glass blank saves so much time !

For this specific mirror, I was a bit disappointed, because it was specifcally advertised as parabolic, which made this project suitable, because coating costs trump all other costs for very small builds. Well it was 1.7x too much parabolic, and now I have to pay a coating :)