Comment by chantepierre | Hacker News Reader

Comment by chantepierre | Hacker News Reader

Telescope making is much alive and there are communities of people (even young people) making their first mirrors right now. Most find their entry in the hobby via the forums (CloudyNights's ATM, Optics & DIY forum, Stargazerslounge, Astrosurf, Astrotreff.de) and amateur mirror maker Discord channels are popping up.

I also recommend anyone wanting to grind their first mirror to read about modern ways of testing in addition to all the classic books (Texereau, Sam Brown, Lecleire) about mirror making.

Bath interferometers changed the game and allow to reach λ/10 wavefront with certainty and repeatability compared to Foucault testing. They are affordable and there's a healthy community around DFTFringe, the de-facto standard interferogram analysis software at interferometry.groups.io

You can also find a Foucault + Ronchi + Bath combo tester's plans on Printables.com and a companion three-axis-table, allowing great testing ergonomics for a low cost if you have access to 3D Printing.

The best resources on how to setup a Bath Inteferometer can be found on the GAP47's website (french, but machine translatable) and GR5's YouTube channel.

Have fun :)

It's worth noting that you can also use an interferometer as a very accurate thermometer[1]. 3D printing filaments are much more sensitive to temperature variation than metals, which can be bad if you're trying to get repeatable results & don't have good temperature control.

[1] https://www.youtube.com/watch?v=vupIq4epCQA

My club, the Amateur Telescope Makers of Boston (atmob.org), holds weekly mirror grinding sessions at our clubhouse. Along with another club member I'm working on a diffracting telescope and hope to see first light this spring.

Fascinating! How are you fabricating the diffractive elements?

That's awesome, are you using lithographic processes to produce the diffractive elements ?

Yes, I'm using a photomask vendor to fabricate the objective. It's in the low hundreds of dollar to get 7um features, a bit more expensive to reach 4um and bloody murder to get 1um (~thousands).

Currently we have some tiny photon sieves, around 1.5mm aperture ~f/14. The next step is going up to 60mm @ f/6.5. The end goal, and I don't know how achievable this is, will be a very large aperture panelized scope. We've discussed making something unsteerably large, sticking it in a field and using the Earth's rotation to sweep the sky.

There's a little bit of trickery to reduce harmonics, though I'm not sure how it'll perform in practice. Please get in touch if you have experience doing diffraction simulation. After first light I plan to write everything up.

That sounds about in line with a microlithography vendor (UK) I ordered zoneplates from. 7-10µm features were accessible and going to 0.7µm was an order of magnitude higher (and went from film to chrome on glass IIRC). File size was also a factor for more complex patterns.

Do not hesitate to post results on cloudynights or your club's website, I'll refresh it from time to time ! I do not think I have enough diffraction experience to help though.

Best of luck for your endaevor.

Do you have any photomask vendors that you recommend. I am trying to do some homebrew lithography and the photomask is not coming out as crisp as I want.

I haven't used them yet, but the University of Louisville's Micro/Nano Technology Center has competitive pricing. They guarantee down to 6um and depending on the design can hit 4um. It's $375 for a 6x6 and $225 for 4x4. 1um is billed at $100/HR and was told that a 4in plate would take several days.

https://louisville.edu/micronano

After the next prototype run, I'll probably use them or MIT's Nano Fab lab.

Thanks, do you have any recommendations for other resources related to homebrew/low cost lithography?

We use Compugraphics in UK at work for DUV masks (fused quartz 6inch) , base price for 700nm CD is much better than what the sibling comment predicts (sorry but I can't disclose).

Thanks for the recommendation. Do you have any other recommendations for low cost/homebrew lithography?

Pretty cool, how did you come about to start this as a hobby?

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