The tiniest yet real telescope I've built (opens in new tab)

clickable 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?

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?

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.

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.

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.

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.

Came here to link this, but you beat me to it :)

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.

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.

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?)

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.

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

Absolutely, second hand is the most direct path to getting a telescope.

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...

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.

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-...

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.

Thanks, it's heartwarming. It's my current longest living attempt at a blog

Hi, I could send you the link but as outlined in the post, this specific mirror was very out of tolerance..