Amateur Telescope Making Main Page
stellafane.org254 points by Tomte 10 days ago
254 points by Tomte 10 days ago
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.
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.
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?
I made my first 10" telescope - rough and fine ground, polished, figured, and built the telescope and mount at 10 under the instruction famous (later) John Dobson in San Francisco. It's not hype to say he was one of the most significant figures in popularizing astronomy in modern history.
https://en.wikipedia.org/wiki/John_Dobson_(amateur_astronome...
I later went on to make a 16" and then "fell off the wagon" and bought refractors, equatorial mounts and cameras. But I never could have gotten started without him.
Thank you for posting that. I own a Dobsonian telescope, but never wondered about the figure behind its name.
People don't talk about it now but when he first started the "established" telescope making folks spoke derisively of him, his techniques, and his telescopes.
Why?
To start with "we" - he and his students - made the mirrors out of old portlights (the glass in portholes), so it was "assumed" they would flex (since they were thinner than store-bought mirror blanks) and would be subject to thermal issues.
Then of course was the fact the telescope tube was made out of a heavy cardboard concrete form called a "Sonotube", which you'd waterproof and paint - paint color and pattern choice being one of the most creative parts of the project. The "diagonal" - the mirror which directed the light path 90-degrees out to the eyepiece - was mounted on a 1"-2" dowel with 3 slots cut into it and held in place by wood shingles.
The mirror mount itself was a 3/4" piece of plywood with 3 bolts in it, which you'd use to collimate the mirror once it was mounted in the tube.
And then the mount. Not only was it "alt-azimuth", it was made of plywood. You built a box around the tube, and two circles on the box fit into 1/2 circles in the mount.
There are more details on the Stellafane page - https://stellafane.org/tm/dob/index.html - but those are even fancier than the ones we made!
But Dobson's ultimate heresy was his approach to figuring the mirror:
Instead of using a "Foucault Tester" to measure and figure the mirror, he'd mount the polished mirror in the telescope and point it at a point source of light - usually the sun's reflection off a ceramic power line insulator.
By moving the image in and out of focus and looking for bright rings in the image, you could tell the shape of the mirror and whether is had hills or valleys in the figure. The end result was a parabola accurate to 1/2 or 1/4 wave (he said he could get it to 1/10th wave, and I have no reason to doubt it).
To the folks used to using much fancier foucault or even more advanced testing methods on much more expensive mirror blanks this was impossible and widely derided and, frankly, made fun of. People weren't very nice.
But when they took the mirrors and tested them with their foucault and diffraction testers they got a big surprise - the curves _were_ accurate and of high quality. And, _big_ - people regularly made 16" telescopes this way, and the San Francisco Sidewalk Astronomers had a portable 24" for goodness sake.
(I think people kind of forgot he used to be a physicist, and probably knew a thing or two about light).
The other big beef was the alt-azimuth mount. Not only did it not have setting circles to find things in the sky by RA and Dec, it wouldn't automatically track, so it could never be used to take pictures (you can get Dobsonians which will do that today natch now that we have computer controlled stepping motors).
But the point was _none of that mattered_: He wanted to make telescopes for people to look through, not take pictures with. So if he could build a telescope he could wheel out into Golden Gate park, set up in 15 minutes, and have 100 people see stars, planets and nebulae, that was The Win.
And teaching regular people - including kids - of both genders - how to make their own telescope, well that was almost as good. A big part of that was it was _affordable_, which meant many, many more people could make telescopes than otherwise. In Dot-Com vernacular, he grew the TAM (Total Addressable - or would that be Astronomical - Market), well, astronomically.
(Bada-Bing, I'm here all week folks).
But seriously, I can tell you from experience, no astrophotograph you take will ever, ever, compare to seeing Saturn, or M31, or any one of many other things with your own eye, and in a telescope you built.
Sorry for the long screed - got started and stirred up some memories there.
No worries, he got me too. No I do not subscribe to everything he thought on a cosmological level but the importance of vintage photons direct to brain for everyone resonated.
Bringing telescopes out of the rarefied world of astronomers where they were "precious" to professional and amateur alike is what I see as his greatest legacy.
I build "public friendly" scopes as a result. If anyone is thinking of a new mount for a Newtonian may I suggest looking up "Sudiball" mount as they allow you to accommodate a wider range of eyepiece heights for a given target. (so parents are less likely to put their kids in a half-nelson screeching "DON'T TOUCH DON'T TOUCH" as they poke them in the ear with your scope)
Slightly OT: there is a total lunar eclipse today/tomorrow for many around the world.
Sadly under the horizon for me. But it's raining anyways.
Better luck next time to anyone around here and happy eclipse to the people that can enjoy it.
You don't even need to grind your own mirror to get in on the action.
Younger I made a 6" scope from a bought mirror set, and the first time I used it I caught one of Jupiters moons occulting in realtime.
I’m almost afraid to ask on this thread but if a dad wanted to purchase a simple telescope that would be good enough to see say Jupiter, or Mars on a decent night in the UK to try and ref the kids excited, where does one start? I have dived into some sites but I think I am asking the wrong questions
If storage is an issue, a SkyWatcher Heritage 150p is a well-priced 6" collapsible Dobsonian. Mirror quality is good. For a bit more you can buy the Virtuoso version which has a motorised mount, letting you key in what you want to view, rather than pushing it into place (though some would argue this is part of the fun). It comes with everything you need, but for a better view of the planets you might want to purchase a 2x Barlow lens such as a Celestron Omni.
With visual telescopes, bigger aperture is better. Not only do they collect more light but they are able to resolve more detail. 8" or 10" Dobsonians will offer much better viewing, but at the expense of size and cost.
Also, a solid-tube 6" Dobsonian may outperform the Heritage 150p in areas with a lot of streetlights, as the collapsible design can let in a lot of stray light. I made a shroud for mine, which helps, but it isn't perfect. You can't store a 6" solid-tube Dobsonian on a shelf though.
Finally, don't underestimate a pair of 10x50 binoculars. You won't get a great view of the planets, but the skies are much more impressive through them.
If you want a purely visual experience (which I recommend), a dobsonian telescope has the best capability VS price ratio. The collapsible 150mm dobsons are already very powerful and quite compact. Avoid anything on a tripod under 500$, you'd be paying the "looks like a telescope" tax and have something deceptive.
If you have a garden 8" Dobsonian or even larger if you can handle it. If in a flat a 4" Apochromatic refractor. Mars can be so so but good views of Jupiter, Saturn and Luna can be had in the UK. Both good for double stars as well and even deep sky objects if in a low light pollution area.
Perusing Stellafane's pages is likely as good as it gets for both a broad and thorough introduction. As with many things, it is an art of trade offs.
Aperture rules until the work to set up means it sits unused.
The objects you mention are bright (and small) and can be seen in anything, including nothing, which fills department stores with small scopes known to amateur astronomers as "Hobby Killers".
So immerse yourself a bit, pick up some language and basics, then find a local club to try before you buy, clubs or generous members may have a loaners scopes so you can figure out where you want to be on the what you can see v.s how much effort you can put in scale.
cheers
A Maksutov 127 is an excellent lunar and planetary scope, light with great portability.
Ed Ting has a good beginner's guide: https://youtu.be/NvslqVTNEWs?si=VG5YIDzELf9iSOx0
JFYI, there's a total lunar eclipse occurring tonight that will be viewable across the continental United States. Don't miss the blood moon!
There is a very detailed video documentation [0] about telescope building techniques, featuring insights from John Dobson, the inventor of the Dobsonian telescope mentioned on the page.
I saw this post today: https://bsky.app/profile/martin.kleppmann.com/post/3lkax2h5v...
Real amateurs modify their whole house to fit in the telescope, apparently.
Not amateurs, but a NASA contractor managed to mess up Hubble's mirror back in the day.
Involves chipped paint and household washers.
https://hackaday.com/2020/04/29/test-equipment-shim-washers-...
Simon Winchester also covers it in great detail in his book Exactly: How Precision Engineers Created the Modern World
If you're interested in precision making and how it all came to be it's a very joyful read.
I spent 25+ years in the precision optics industry, a large portion of which was building machines and instruments for fabricating and testing aspheric lenses and mirrors. Designing, performing, and validating null tests is technically terrifying. Not only is the clock ticking, but every operation on the artifact carries a risk of destroying it, or making it unusable.
It's not life-and-death, but it's pretty satisfying nerd work.
I'm always amazed when I see a site that looks like it was built in the early 00s that is still being kept up to date with their Events and News pages.
Btw, for those very interested it looks like they have a yearly convention in VT, with registration opening May 1 — https://stellafane.org/convention/2025/index.html
I am a member of Stellafane (STMs). The convention every year is amazing. It’s so fun to be surrounded by people who are so interested in astronomy that they travel to a convention out of their own state!
The keynote speaker last year was talking about the James Webb Telescope build, absolutely fascinating. There are tons of things to do. They also have a competition which judges on various aspects of telescopes. I have really enjoyed growing up around this convention.
I always saw those concrete form tubes at home depot, and wondered if you could make a telescope from them...
And the website seems to answer that question :)
https://stellafane.org/tm/dob/ota/tube.html
(that said, there's a LOT more to it...)
I worked at an educational robotics small business in DFW in the late 90s. My boss was super into amateur astronomy and made his own telescopes. Those guys remind me of the amateur rocketry people. Incredibly skilled and knowledgeable group of hobbyists.
Like the 90s style photos. Colour profile were different on those old cameras right? Adds some character.
The website layout is kinda 90s too ;)
Impressive stuff though, coming from a former professional astronomer who never built a telescope from scratch.
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I ground an 8" mirror in my living room using Jean Texereau's book as a guide (i.e., pre-YouTube). A plastic garbage bag on the floor handled any wet grit. I don't understand what grinding dust you experienced - the grit is always wet. It was a great experience and thrilling to see the view even before the mirror was aluminized.
I'm truly sorry for your experience. A first mirror can be a lot of process and can indeed get a bit messy. With experience (or guidance, which is even better) you can work cleanly and avoid glass dust contamination of your workspace.
A bit messy is understatement. And finishing such project without a good guidance is almost impossible. At final stage a few bad moves can destroy week of work! It is setting up newcomers for failure and burnout.
We made our own mirrors, because there was no other option a few decades ago.
But today mirrors are cheap, and they come with aluminum coating and rest of the telescope!
It's not about price, but enjoying the process, or making instruments that just are not commercially available. Amateurs are constantly pushing the limits of optical designs.
Here is a recent groundbreaking example from Rik Ter Horst, a 10" f/20 kutter with toroidal secondary : https://www.cloudynights.com/topic/935825-a-250-mm-f20-kutte...
I did not do anything that impressive but enjoy my own set of non-standard scopes :
- A 8" f/3.5 hyperbolic primary + ross corrector
- a 6" f/2.8 with permanently mounted 4-element corrector
and am working on a 16.5" f/3.3 that will have a permanent Paracorr II lens group.
The only messy moment was my first mirror when I learned to cut pitch, but grit and glass dust itself are no problem thanks to the wet process.
You are right though on the last bits of figuring, it's a psychological challenge and my first mirror took 3 attempts over 18 months.
Just because this was your experience does not mean others should not try, and frankly, your posts suggesting others not try is disgusting. You're on a forum for people with a hacking ethos. That's pretty much the "hold my beer" mindset with a facade of classiness in front of it.
Also, rather than saying such negative things like "don't do it", you could have wrapped up your negative experience into a parable for people to learn from before embarking upon their own journey. Just because you didn't prepare for the results of grinding something to a fine dust/powder doesn't mean others won't prepare for that. Especially after what could have been a much more positive outcome from your negative experience. Don't be a downer.
This would be haha funny if you were trying to stoke that "don't tell me no" as reverse psychology.
Do you have a reference on the health hazard aspect you mentioned? I'd heard fiberglass dust is very bad, but not regular glass.
Silicosis, but also fine dust is toxic when ingested. It can literally kill your cat or dog!
So don't have your pets in the workspace when it's not safe for them. What kind of lousy pet parent are you to not consider that? Also, wear the proper breathing equipment. This isn't some lame COVID anti-masking thread where wearing a mask says something about your politiks. It's working in a less than ideal environment, so take the proper precautions.
This is like telling people not to go outside because the dangers of UV radiation are too much. Deal with it. Wear protective clothing, don't hide in a cave. Some of us are brave enough and have the ability to judge risk/reward so that we left the cave, we crossed the oceans, we've left the planet. I'd hate to live in a world were nobody did anything risky because someone previously had a bad experience and stopped rather than looking at the bad result, making changes, improving the outcome the next time.
This is a bummer as I had been thinking about grinding my own for some time now. I'd like to know more about it and how I can protect myself.
The only part of the wikipedia for Silicosis that mentions glass is about manufacturing it and, even if it includes the grinding part, the reference it links to doesn't mention glass or grinding at all.
If you have more pointers or keywords about this subject, please let me know!
You're supposed to only grind wet, since the glass dust is a hazard. Grinding wet keeps it from being airborne.
Everywhere that I've read about grinding mirrors (and I've done a lot of reading) always says to grind wet. Any YouTube video you watch on the subject will also show them grinding wet.
When grinding a mirror you put water and grit on, grind until the grit is used up, wipe it off, and repeat. This is called a "wet".