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Amateur Telescope Making Main Page

Amateur Telescope Making Main Page

53 comments

·March 13, 2025

chantepierre

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 :)

SAI_Peregrinus

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

bhickey

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.

carefish

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

chantepierre

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

bhickey

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.

itishappy

Fascinating! How are you fabricating the diffractive elements?

alberth

Slightly OT: there is a total lunar eclipse today/tomorrow for many around the world.

https://svs.gsfc.nasa.gov/5473

Joe_Cool

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.

m463

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...)

nickvec

JFYI, there's a total lunar eclipse occurring tonight that will be viewable across the continental United States. Don't miss the blood moon!

lifeisstillgood

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

helij

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.

chantepierre

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.

tejtm

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

relwin

Ed Ting has a good beginner's guide: https://youtu.be/NvslqVTNEWs?si=VG5YIDzELf9iSOx0

namero999

A Maksutov 127 is an excellent lunar and planetary scope, light with great portability.

michaelwilson

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.

exitb

Thank you for posting that. I own a Dobsonian telescope, but never wondered about the figure behind its name.

michaelwilson

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.

tejtm

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)

noelwelsh

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.

nvalis

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.

[0] https://www.youtube.com/watch?v=snz7JJlSZvw

megadata

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.

vibrolax

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.

gooseus

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

gabeio

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.

chasd00

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.

nextts

Like the 90s style photos. Colour profile were different on those old cameras right? Adds some character.

Hokulea

The website layout is kinda 90s too ;)

Impressive stuff though, coming from a former professional astronomer who never built a telescope from scratch.