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?
Here is a talk (in french, but maybe the auto-subtitling would work?) I recorded that overviews the whole process (2h30 though, and lacks info on the Bath) : https://www.youtube.com/watch?v=Wt7lBLS0ueg
Wow, thanks for the link to Texerau. I had no idea a pdf was floating around and have wanted this book for some time. You video looks interesting, especially the part around Ronchi and Focault testing. I have 'Understanding Focault' but have to admit that reading it doesn't give me confidence.
One question I always think about is how much time and effort a "one-time" mirror maker should plan on making to exceed the quality of a generic 8" or 10" F/5-F/7 available from the Chinese mirror makers.
Zambuto seems to imply that whatever magic happens for his mirrors might be in very long, machine driven polishing to smooth out the final surface imperfections that cause scatter. With his retirement and with few mirror makers in the US, it seems like options for buying "high end" mirrors in the 6"- 10" size are very limited. I have been debating an 8" F/7 and would love to just purchase a relatively high quality mirror, but most of the mirror makers seem more taken with significantly larger mirrors.
I'm sure he didn't explain it because almost nobody knows what it is (or even how to interpret the interferograms he showed) and learning to figure optics takes years and entire books are written on the subject.
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.
History is made by people who reflabor the exahenge.
I build microscopes instead of telescopes (as a hobby). I can't tell you how many times I've taken a mostly working system and stripped it down to make some important change that affects most of the design to get only a tiny incremental improvement. Sometimes that improvement makes all the difference (for example, being smart when 3d printing a piece that carries something heavy so it doesn't deflect) and sometimes it's just an itch I need to scratch. Eventually, I learned to make two: a microscope that gets built and used, and then a microscope that is a prototype. Then I'm not tempted to take the daily driver and pull the engine.
Uh, OK. So a few decades ago a scientist I respect built his own scientific tool from parts (https://www.nature.com/articles/35073680) and I was really blown away by that idea, especially because most scientific tools are very expensive and have lots of proprietary components. I asked around at the time (~2001) and there wasn't a lot of knowledge on how to control stepper motors, assemble rigid frames, etc.
Although my day job is running compute infra, I have a background in biophysics and I figured I could probably do something similar to Joe Derisi, but lacked the knowledge, time, and money to do this either in the lab, or at home. So the project was mostly on the backburner. I got lucky and joined a team at Google a decade ago that did Maker stuff. At some point we set up a CNC machine to automate some wood cutting projects and I realized that the machine could be adapted to be a microscope that can scan large areas (much larger than the field of view of the objective). I took a Shapeoko and replaced the cutting tool with a microscope head (using cheap objectives, cheap lens tube, and cheap camera) and demonstrated it and got some good images and lots of technical feedback.
As I now had more time, money, and knowledge (thanks, Google!) I thought about what I could do to make scientific grade microscopes using 3d printer parts, 3d printing and inexpensive components. There are a lot of challenges, and so I've spent the past decade slowly designing and building my scope, and using it to do "interesting" things.
At the current point, what I have is: an aluminum frame structure using inexpensive extrusion, some 3d printed junction pieces, some JLCPCB-machined aluminum parts for the 2D XY stage, inexpensive off-the-shelf lenses and industrial vision camera, along with a few more adapter pieces, and an LED illuminator. It's about $1000 material, plus far more time in terms of assembly and learning process.
What I can do: the scope easily handles scanning large fields of view (50mm x 50mm) at 10X magnification and assembles the scans into coherent fullsize images (often 100,000x100,000 pixels). It can also integrate a computer vision model trained to identify animacules (specifically tardigrades) and center the sample, allowing for tracking as the tardigrade moves about in a large petri dish. This is of interest to tardigrade scientists who want to build models of tardigrade behavior and turn them into model organisms.
Right now I'm working on a sub-sub-sub-project which is to replace the LED illuminator with a new design that is capable of extremely bright pulses for extremely short durations, which allows me to acquire scans much faster. I am revelling in low-level electronic design and learning the tricks of trade, much of which is "5 minutes of soldering can save $10,000".
I had hoped to make this project into my fulltime job, but the reality is that there is not much demand for stuff like this, and if it does become your job, you typically focus on getting your leadership to give you money to buy an already existing scope designed by experts and using that to make important discoveries (I work in pharma, which does not care about tardigrades).
Eventually- I hope- I will retire and move on to the more challenging nanoscale projects- it turns out that while you can build microscopes that are accurate to microns with off-the-shelf hardware is fairly straightforward, getting to nanoscale involves understanding a lot of what was learned between the 1950s and now about ultra-high-precision, which is much more subtle and expensive.
Here's a sample video of tardigrade tracking- you can see the scope moving the stage to keep the "snout" centered. https://www.youtube.com/watch?v=LYaMFDjC1DQ
And another, this is an empty tardigrade shell filled with eggs that are about to hatch, https://www.youtube.com/watch?v=snUQTOCHito with the first baby exiting the old shell at around 10 minutes.
Yes, I took an existing vision model that could run at realtime on my laptop, and fine-tuned it with a few hundred manually labelled images of tardigrades.
I don't like the openflexure design at all. I mean... obviously it works for a lot of people, but I just don't want a flexure based stage. I like real 2-axis stages based on rolling bearings, basically cloning the X and Y parts of this: https://www.asiimaging.com/products/stages/xy-inverted-stage...
UC2 is another cool project: https://openuc2.com/ but I found their approach constraining.
Frankly I think you could just buy an inexpensive 3D printer that had an open firmware, and replace the extruder with an objective, a tube, and a camera, and you'd have something up and running cheaper for less time.
Well yes, but are you wiggling the giblet or are you flensing the grobbulus? Because the latter requires specialised equipment and a flensing trampoline, whereas the former requires a 1mm Allen key and possibly a hard whack on a nearby surface while nobody’s looking.
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.
If you are a really big fan of something, you'll get familiar with the lingo, but that doesn't mean you can play StarCraft well or weld or shred your guitar.
That's actually part of why FizzBuzz was so notorious: there were (apparently) plenty of people who could talk the talk about programming and software engineering, but couldn't do FizzBuzz.
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.
Its the usual Youtube thing where there's multiple videos. The one linked is the bibliography popular science utterly non-technical spin. There's a three part technical series, a fun two hours viewing, and the end of the third technical video goes has some performance shots. It performs really well for a tiny little thing, like per gram or per cubic centimeter the performance is excellent. Its a cool technology and when I saw it I immediately wondered if it would be possible to make a microscope the same way out of single solid cylinder of glass. I don't think so; but it would be cool. It would also make an interesting, although probably very expensive, binocular technology.
Catadioptric telescopes are in fact sometimes configured and sold as long (working) distance microscopes:
http://www.company7.com/questar/microscope.html
Not made out of a single piece of glass, though, which is one of the things that's so elegant about Rik ter Horst's design.
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
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)
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 :)
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...
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.
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.
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!
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.
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.
Hello, author here ! Other interesting builds or projects going on in the french amateur telescope maker community :
Of course there are many others but those are the one on the top of my head nowclickable links in case it's helpful for anyone:
- 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
Do you have an RSS feed just for the astronomy posts on your blog?
No, but that should be quite straightforward to add with Astro, I will check that.
I am not an RSS user myself, I tested it with an online reader and it should be working.Cool, thank you very much.
I just tried it, the links don't seem to be working. I get sent to https://lucassifoni.info/miniscope-tiny-telescope.mdx for example
Thank you for the links and the write-up!
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.
Very cool, thanks for sharing! Any ideas of adding 2 gimbal motors to this for GOTO? MS6010v3 or something lighter would seem like a good fit.
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?
Sure ! Here are a few links :
https://stellafane.org/stellafane-main/tm/index.html
How to make a telescope, by Jean Texerau, which was the absolute bible of this field : https://rexresearch1.com/AstronomyTelescopesLibrary/HowMakeT...
Here is a talk (in french, but maybe the auto-subtitling would work?) I recorded that overviews the whole process (2h30 though, and lacks info on the Bath) : https://www.youtube.com/watch?v=Wt7lBLS0ueg
Here is Gordon Waite's youtube channel which actually shows a lot of the moves : https://www.youtube.com/@GordonWaite/videos
Best resource on the Bath (french, but should translate well) : https://gap47.astrosurf.com/index.php/technique/optique-inst...
Wow, thanks for the link to Texerau. I had no idea a pdf was floating around and have wanted this book for some time. You video looks interesting, especially the part around Ronchi and Focault testing. I have 'Understanding Focault' but have to admit that reading it doesn't give me confidence.
One question I always think about is how much time and effort a "one-time" mirror maker should plan on making to exceed the quality of a generic 8" or 10" F/5-F/7 available from the Chinese mirror makers.
Zambuto seems to imply that whatever magic happens for his mirrors might be in very long, machine driven polishing to smooth out the final surface imperfections that cause scatter. With his retirement and with few mirror makers in the US, it seems like options for buying "high end" mirrors in the 6"- 10" size are very limited. I have been debating an 8" F/7 and would love to just purchase a relatively high quality mirror, but most of the mirror makers seem more taken with significantly larger mirrors.
Merci!
I'm sure he didn't explain it because almost nobody knows what it is (or even how to interpret the interferograms he showed) and learning to figure optics takes years and entire books are written on the subject.
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.
History is made by people who reflabor the exahenge.
I build microscopes instead of telescopes (as a hobby). I can't tell you how many times I've taken a mostly working system and stripped it down to make some important change that affects most of the design to get only a tiny incremental improvement. Sometimes that improvement makes all the difference (for example, being smart when 3d printing a piece that carries something heavy so it doesn't deflect) and sometimes it's just an itch I need to scratch. Eventually, I learned to make two: a microscope that gets built and used, and then a microscope that is a prototype. Then I'm not tempted to take the daily driver and pull the engine.
Ooh! Tell us about microscope making as a hobby!
Uh, OK. So a few decades ago a scientist I respect built his own scientific tool from parts (https://www.nature.com/articles/35073680) and I was really blown away by that idea, especially because most scientific tools are very expensive and have lots of proprietary components. I asked around at the time (~2001) and there wasn't a lot of knowledge on how to control stepper motors, assemble rigid frames, etc.
Although my day job is running compute infra, I have a background in biophysics and I figured I could probably do something similar to Joe Derisi, but lacked the knowledge, time, and money to do this either in the lab, or at home. So the project was mostly on the backburner. I got lucky and joined a team at Google a decade ago that did Maker stuff. At some point we set up a CNC machine to automate some wood cutting projects and I realized that the machine could be adapted to be a microscope that can scan large areas (much larger than the field of view of the objective). I took a Shapeoko and replaced the cutting tool with a microscope head (using cheap objectives, cheap lens tube, and cheap camera) and demonstrated it and got some good images and lots of technical feedback.
As I now had more time, money, and knowledge (thanks, Google!) I thought about what I could do to make scientific grade microscopes using 3d printer parts, 3d printing and inexpensive components. There are a lot of challenges, and so I've spent the past decade slowly designing and building my scope, and using it to do "interesting" things.
At the current point, what I have is: an aluminum frame structure using inexpensive extrusion, some 3d printed junction pieces, some JLCPCB-machined aluminum parts for the 2D XY stage, inexpensive off-the-shelf lenses and industrial vision camera, along with a few more adapter pieces, and an LED illuminator. It's about $1000 material, plus far more time in terms of assembly and learning process.
What I can do: the scope easily handles scanning large fields of view (50mm x 50mm) at 10X magnification and assembles the scans into coherent fullsize images (often 100,000x100,000 pixels). It can also integrate a computer vision model trained to identify animacules (specifically tardigrades) and center the sample, allowing for tracking as the tardigrade moves about in a large petri dish. This is of interest to tardigrade scientists who want to build models of tardigrade behavior and turn them into model organisms.
Right now I'm working on a sub-sub-sub-project which is to replace the LED illuminator with a new design that is capable of extremely bright pulses for extremely short durations, which allows me to acquire scans much faster. I am revelling in low-level electronic design and learning the tricks of trade, much of which is "5 minutes of soldering can save $10,000".
I had hoped to make this project into my fulltime job, but the reality is that there is not much demand for stuff like this, and if it does become your job, you typically focus on getting your leadership to give you money to buy an already existing scope designed by experts and using that to make important discoveries (I work in pharma, which does not care about tardigrades).
Eventually- I hope- I will retire and move on to the more challenging nanoscale projects- it turns out that while you can build microscopes that are accurate to microns with off-the-shelf hardware is fairly straightforward, getting to nanoscale involves understanding a lot of what was learned between the 1950s and now about ultra-high-precision, which is much more subtle and expensive.
Here's a sample video of tardigrade tracking- you can see the scope moving the stage to keep the "snout" centered. https://www.youtube.com/watch?v=LYaMFDjC1DQ And another, this is an empty tardigrade shell filled with eggs that are about to hatch, https://www.youtube.com/watch?v=snUQTOCHito with the first baby exiting the old shell at around 10 minutes.
Having it automatically follow tardigrades is so cool! It sounds like great fun. Did you make the ML model for tracking them?
I've wanted to make this the Openflexure Microscope (https://openflexure.org/projects/microscope/) but it is behind the backlog of all sorts of other things.
Yes, I took an existing vision model that could run at realtime on my laptop, and fine-tuned it with a few hundred manually labelled images of tardigrades.
I don't like the openflexure design at all. I mean... obviously it works for a lot of people, but I just don't want a flexure based stage. I like real 2-axis stages based on rolling bearings, basically cloning the X and Y parts of this: https://www.asiimaging.com/products/stages/xy-inverted-stage...
UC2 is another cool project: https://openuc2.com/ but I found their approach constraining.
Frankly I think you could just buy an inexpensive 3D printer that had an open firmware, and replace the extruder with an objective, a tube, and a camera, and you'd have something up and running cheaper for less time.
Well yes, but are you wiggling the giblet or are you flensing the grobbulus? Because the latter requires specialised equipment and a flensing trampoline, whereas the former requires a 1mm Allen key and possibly a hard whack on a nearby surface while nobody’s looking.
Flensing trampolines are out of my budget, so it's just giblet wiggling for me.
I've seen a few people flense without an f-tramp using a retro-stabilising grob clamp instead, if you've got one.
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.
A friend of mine once told me - learning a new field is all about learning the language of that field
What they hear:
"Exorcise the lattice hoard to siphon the new incarnation."
What we said:
"Purge the web cache to download the new version."
That metaphor would here be pretty accurate, though.
I think that's probably not an accident.
A friend of mine asked me why we have such precise terminology in IT; I asked her why English has so many different words for "chair".
That's a big part of it, but far from everything.
I'm not really sure - I deliberately stopped there because the concepts related to that field are a part of the language learnings.
If you are a really big fan of something, you'll get familiar with the lingo, but that doesn't mean you can play StarCraft well or weld or shred your guitar.
That's actually part of why FizzBuzz was so notorious: there were (apparently) plenty of people who could talk the talk about programming and software engineering, but couldn't do FizzBuzz.
You're right, people write code all day long and have no idea what pattern it is that they've just applied.
Having said that, they cannot communicate that that's what they want done, nor can they receive instructions to do something that way.
They really are hand in hand.
> You're right, people write code all day long and have no idea what pattern it is that they've just applied.
Thanks for agreeing with me, I guess. I was actually making the opposite point:
People who can talk about creating software, but who can't actually create any software.
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.
Thanks for sharing the post!
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.
Very nice! But you won't beat this ;)
> 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
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...
Dayyum, those shots are incredible! I've seen worse pictures from professional telescopes.
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.
https://www.oresat.org/home
pictures would be captured by hand held groundstations
https://www.oresat.org/technologies/ground-stations
This is the commercial company he's now CTO at.
https://www.tinytelescope.com
Nice video, except it could use some, you know, actual images made by the lens they talk about.
Its the usual Youtube thing where there's multiple videos. The one linked is the bibliography popular science utterly non-technical spin. There's a three part technical series, a fun two hours viewing, and the end of the third technical video goes has some performance shots. It performs really well for a tiny little thing, like per gram or per cubic centimeter the performance is excellent. Its a cool technology and when I saw it I immediately wondered if it would be possible to make a microscope the same way out of single solid cylinder of glass. I don't think so; but it would be cool. It would also make an interesting, although probably very expensive, binocular technology.
Catadioptric telescopes are in fact sometimes configured and sold as long (working) distance microscopes: http://www.company7.com/questar/microscope.html Not made out of a single piece of glass, though, which is one of the things that's so elegant about Rik ter Horst's design.
Came here to link this, but you beat me to it :)
You both beat me. :D
Roughly similar in size to the ones Newton made for the Royal Society as demonstration instruments.
https://en.wikipedia.org/wiki/Newton%27s_reflector
Very nice and I might look for one of these mirror kits.
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!!
https://yesteryearforever.xyz/ABSDBS
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
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)
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 :)
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...
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.
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.
What I got from this is:
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!
Absolutely, second hand is the most direct path to getting a telescope.
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!
This article gives great impressions of what you can see with your eyes through various sizes of telescopes : https://www.deepskywatch.com/Articles/what-can-i-see-through...
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.
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.
If you want to commit to a build, this one is thought to be user-friendly and a great first instrument : https://www.printables.com/model/1325533-smallest-telescope-...
Thank you! Will check it out!
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.
Very cool blog, not just post
Thanks, it's heartwarming. It's my current longest living attempt at a blog
Excellent. I might have a go at this myself. Was there a particular AliExpress seller that you got the mirror from?
Hi, I could send you the link but as outlined in the post, this specific mirror was very out of tolerance..
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