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Comment by WaitWaitWha | Hacker News Reader

For a second I thought the entire lens, including the glass was printed on 3D.

Sadly . . .

> The only parts of the lens that can’t be 3D printed are the glass optics

Yup that's the only reason I opened the article to read. While obviously the most important thing in a lens is the optical element(s) it's a bit disappointment.

I think the title should read "print a housing for $15 glass to make a 164mm lens" or something like that to indicate that it's not the actual lens elements that they're printing, but of course it wouldn't be clickbait and many people including me wouldn't have clicked on it.

Prusa did a whole article about 3D printing optics some time ago[0]. I've also had good luck coating transparent filaments with epoxy resin to get clear parts.

[0]https://blog.prusa3d.com/3d-printed-lens-and-other-transpare...

> I've also had good luck coating transparent filaments with epoxy resin to get clear parts.

That might work if you only care about "clear", but unless you exactly match the optical properties of the resin and (printed) filament, it will be pretty useless as an optical device.

True, also the evenness of the surface is a little off without grinding which also limits the usefulness for optics. I just used it a few times when I needed an odd cylinder size that needed to be see through.

Was also a video[1] over on the Breaking Taps channel about casting clear epoxy resin to make your own lenses. Results were not perfect but good enough for some uses. Of course, that requires some actual lens elements to make the molds from, but it's something.

[1]: https://www.youtube.com/watch?v=mfAGivG9Koc

That's definitely an idea worth trying, though it was mentioned elsewhere on this post that you can 3D print and polish your masters for casting rather than relying on having the lens already.

https://news.ycombinator.com/item?id=32588947

I already expected that to be the case, so I had realistic hopes. The tech for 3d printing good lenses is still within the realm of futuristic companies/researchers: https://www.luxexcel.com/the-luxexcel-technology/

There are companies doing that, the 3D printers are however highly specialized and expensive.

I do it using a $400 Prusa Mini and epoxy resin: https://alexbock.github.io/blog/3d-lenses/index.html

It's surprisingly easy to 3D print the shape of a lens and polish by hand. I made a working telescope this way with a 3D-printed body and two cast epoxy lenses. As an added bonus, you can easily make aspherical lenses this way.

If you coat the surface with silver you can also make mirrors, but the polishing requirements for this are a lot more difficult. My attempts at a 3D-printed telescope mirror have very bad image quality compared to the excellent results from the lenses.

I'd love to see an article and sample images on the telescope.

Would be a much interesting article than the one at the link (not your link, the original HN clickbaity link)

you may be able to 3d print a mirror telescope-style "lens". But you'd probably need to somehow "polish" down the plastic and coat it. Maybe a bit of acetone and then depositing silver on it?

I made several attempts at acetone vapor smoothing on mirrors printed in ABS and ASA and the surfaces always came out very well polished at the micrometer scale but unacceptably warped, wrinkled, or patterned at the millimeter scale. The best finish I've gotten on a 3D-printed mirror was from sanding and polishing with a cotton ball soaked in cerium oxide slurry while the mirror blank spins on a pottery wheel.

Chemically depositing silver with the old-fashioned immersion setup is also very tricky as the reaction is quite temperamental. I recommend the two-part spray process if you want to try silvering a telescope mirror.

Oh very cool that you tried it. Shame it didn't work out, but I guess that all kinda makes sense.

just out of curiosity what's the "two-part spray process"?

I originally heard about it from this page written by a group who silvered a 28-inch mirror this way: https://sites.google.com/site/spraysilveringtelescopemirrors...

It's still ultimately a silver nitrate reduction reaction, but it's extremely consistent. I tried reproducing the classic silver nitrate/glucose/sodium hydroxide/ammonia silvering baths astronomers used before the modern switch to aluminum vacuum coatings, and my success rate was only about one in five attempts. It's much more difficult to execute than the typical silver nitrate demonstrations where someone silvers the inside of a glass flask because you need the silver to produce a perfectly even layer on the outside surface of the glass for a telescope. The spray reaction has worked for me every time.

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