Hello, author here !
Other interesting builds or projects going on in the french amateur telescope maker community :
- Sunscan, by the STAROS team : a fully integrated open-source solar imaging kit : https://www.sunscan.net/fr
- Eric Royer's binocular 24" dobson : http://www.astrosurf.com/topic/124758-bino600/
- The Slim400 by Laurent Bourrasseau : https://www.cloudynights.com/forums/topic/920950-the-slim400/
- Astrowl, an electronically enhanced astronomy kit : http://www.astrosurf.com/topic/151807-projet-astrowl-de-visuel-assist%C3%A9/
- The smallest, an open-source 6" portable dobson : http://www.astrosurf.com/topic/176898-un-dobson-150-f5-facile-%C3%A0-imprimer-et-assez-compact/
- A dedicated astrophotography power supply : https://github.com/Antiath/Open-Power-Box-XXL
Of course there are many others but those are the one on the top of my head now
You wrote up "of course I refigured it" as if refiguring mirrors is something any reader would know how to do. I (and I suspect most of HN) does not; have you (or others) written on this topic?
I always love the moment in blog posts like this, where the writer with their esoteric knowledge of the project will say something like "I almost considered reflaboring the exahenge, but of course it would be a ridiculous prospect for a project of this type". And then always, inevitably, there is the followup edit; "I reflabored the exahenge."
Too rarely in life are things made better than practical consideration would dictate, just because of dedication to the craft.
Your comment brings me back to my first mirror making adventure, I was absolutely overwhelmed by the jargon and acronyms used by the mirror making community... a few years later I internalized it and use it as if it was common knowledge. I should put little explanations or details in my posts.
There was enough there for me to get the basic idea, which is fine I think. Can't really expect every niche post to have all the details necessary for a general audience and it's fun to get a glimpse into these worlds anyway.
I just love the fluent use of terms, and the whole ontology of the subject itself just seems so appealing to me. For a moment, I felt like others feel when listening to me and my colleagues discuss kernel build issues or other software challenges - befuddled, bemused, enchanted.
I guess, if/when I retire to that remote mountain hideaway, I might just get into this hobby. The idea of grinding my own mirrors to look at dew on the spiderwebs of the neighborhood is just so appealing.
Rik's monolithic Cassegrains are the perfect example of the blend of amateur and high-end professionnal work in astronomical optics, thanks for linking it ! His amateur work is incredible, like this 16" CDK : https://www.cloudynights.com/forums/topic/558284-a-400-mm-f1...
This coming year ... if the crik don't rise (as it does with some regularity).
Some of you may be able to take a picture of yourself with one of Ril ter Horst lenses as it will be launched in a 2U cubesat named OreSat1 by Oregon's Portland State University undergrads.
So cool! Thanks for sharing. It reminds me of one of those very old cameras with the bellows or accordion. I wish I could look through it myself to see what you see with it!
Nice!!
I printed a very similar (but larger) telescope back in 2018 with similar results... I didn't research my mirrors well and ended up with bad ones. Plus, it wasn't very stable at that size. I'd imagine a smaller version would be much more stable...
Thanks for sharing!!
This is the first time I've seen a build of the ABSDBS in the wild, thanks for sharing ! Sadly an 8" f/4 mirror has a very narrow range of acceptable optical quality :/. It's too bad you ended up with a bad one. Maybe refiguring it would be a great followup project though
So what are these tiny portable ones? I always assumed they were digitally augmented or virtual even - is there a minimum size for it to be a "real" telescope?
This one is a bit of a joke with my telescope making friends, but ticks all the boxes of what I consider a real telescope. You can actually buy 76mm entry-level telescopes, but they often have an unstable mount and bad optics. Starting at 150mm, you already have a lot of punch under dark skies. Visual use, live digitally enhanced, or astrophotography are 3 different hobbies.
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)
The only reason to grind a small mirror is because you want a very large mirror and need to practice first. This has long been the case, but the definition of large has gotten larger over time. Of course there is also the in between states where you buy a cheap workable mirror, and then make it higher quality. Unless you have a lot of land high on a mountain there is rarely any point in mirrors that you have to completely grind yourself - the telescope wouldn't be portable and the nearby light and atmosphere pollution means large sizes don't gain enough. (if you do live in such a place your telescope could be massive if you have the years to dedicate - can I come by and look through it one night after you build it?)
Small mirrors with a very low F-ratio are also something that you need to grind yourself. I have a 6" f/2.8 telescope and a 8" f/3.5 hyperbolic + ross telescope, and both aren't commercially available while being small mirrors !
Progress on my 16" f/3.2 is currently stalled though.. a multi-year project indeed.
Mirror grinding is still a thing. Just not a thing that young people generally do. Distribution got easier and real estate got more scarce. Those of us who have garages, have filled them up.
In my understanding it's gotten considerably easier over the years with better availability of diamond and CBN abrasives, and with more electronic control of the grinding hardware. Slumping glass and bonding a thin sheet to ceramic foam reduced the costs and weight a great deal as well. Mastering these techniques make it easy to start a small business rather than to do a one-off in your garage, though.
As a sidenote: The Celestron RASA astrographs are so effective and so inexpensive of a wide-field instrument that it's a lot harder to justify the DIY activity that existed in the 2000's.
There is quite a vibrant community of young people grinding mirrors, it just has displaced to Discord. The "Observational astronomy" discord server has a lot of late-teenagers and young adults grinding. Our french Astro-FR server has people in their thirties grinding. But as you pointed out, garages are sparse and people seem to take shortcuts : finding bad pre-polished mirrors as blanks, slumping glass sheets to shape and continuing with fine grinding...
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.
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 :)
We buy pre-dug mirrors on Ali to refigure them, or dig and figure our own all the time. See Ali as a supplier of prepolished blanks :) . The l/6 I mentioned in the post are l/6 spheres, so they also need figuring.
Very cool project! I always wanted a telescope as a kid but kind of forgot about that desire as an adult. Didn’t know you could build your own like this.
Watch your local craigslist or facebook marketplace. With a little patience, you will probably find a good 8" or 10" dobsonian at a great price. I picked up a lovely 8" dob for less than $200. Most of the generic 8" F/6 dobsonians seem pretty decent.
Or check your local library. It may have a smaller Starblast table-top dobsonian you can check out - I did that when traveling once.
Whatever you do, do NOT buy a small cheap refractor on some flimsy mount. They are mostly awful.
There are a lot of DIY telescopes out there. I suggest you spend several days reading about what others have done (and why). Start with an easy build to prove you can - people who get something small done are much more likely to finish a larger telescope, so start small as a practice run.
- Sunscan, by the STAROS team : a fully integrated open-source solar imaging kit : https://www.sunscan.net/fr
- Eric Royer's binocular 24" dobson : http://www.astrosurf.com/topic/124758-bino600/
- The Slim400 by Laurent Bourrasseau : https://www.cloudynights.com/forums/topic/920950-the-slim400...
- Astrowl, an electronically enhanced astronomy kit : http://www.astrosurf.com/topic/151807-projet-astrowl-de-visu...
- The smallest, an open-source 6" portable dobson : http://www.astrosurf.com/topic/176898-un-dobson-150-f5-facil...
- A dedicated astrophotography power supply : https://github.com/Antiath/Open-Power-Box-XXL
I'll share them with a friend who loves astronomy and who loves to organize star-gazing events that he livens up with his Unistellar telescope.
Too rarely in life are things made better than practical consideration would dictate, just because of dedication to the craft.
Thanks for sharing the post!
"Exorcise the lattice hoard to siphon the new incarnation."
What we said:
"Purge the web cache to download the new version."
I guess, if/when I retire to that remote mountain hideaway, I might just get into this hobby. The idea of grinding my own mirrors to look at dew on the spiderwebs of the neighborhood is just so appealing.
> Optical Engineer Rik ter Horst shows us how he makes very small telescopes (at home) which are intended for use in micro-satellites.
https://www.youtube.com/watch?v=HxwhCmO90UQ
https://www.oresat.org/home
pictures would be captured by hand held groundstations
https://www.oresat.org/technologies/ground-stations
https://yesteryearforever.xyz/ABSDBS
https://en.wikipedia.org/wiki/Newton%27s_reflector
Very nice and I might look for one of these mirror kits.
Progress on my 16" f/3.2 is currently stalled though.. a multi-year project indeed.
In my understanding it's gotten considerably easier over the years with better availability of diamond and CBN abrasives, and with more electronic control of the grinding hardware. Slumping glass and bonding a thin sheet to ceramic foam reduced the costs and weight a great deal as well. Mastering these techniques make it easy to start a small business rather than to do a one-off in your garage, though.
As a sidenote: The Celestron RASA astrographs are so effective and so inexpensive of a wide-field instrument that it's a lot harder to justify the DIY activity that existed in the 2000's.
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 :)
If you want a working telescope for $small, buy a second hand one.
If you want to mess around with mirrors for hours on end then build one!
Or check your local library. It may have a smaller Starblast table-top dobsonian you can check out - I did that when traveling once.
Whatever you do, do NOT buy a small cheap refractor on some flimsy mount. They are mostly awful.