Telescope Building with John Dobson
February 9, 2018 2:24 PM   Subscribe

 
My grandfather built a 12-inch dobsonian telescope when I was a kid, although he bought the mirror from Orion Telescopes in Santa Cruz instead of spending 24 hours grinding one. It was a big step up from his Astroscan. He lived in a small town in the Sierra Nevada that was great for stargazing and if there was something particularly great that he wanted to show us we would pile into the car and head farther up the mountains, away from lights. I've been wanting to build one of these for a few years now, but will probably go with a 6-inch model if I attempt to grind the mirror by hand.
posted by ActingTheGoat at 3:52 PM on February 9 [3 favorites]


Oh man. Just watching the first few minutes of the video reminds me that my neighbor growing up built several similar telescopes over the course of my childhood. I remember looking through a couple of them over the years.

He must have been 70+ when we moved to the neighborhood in 1992, was a retired engineer with a pretty solid machine shop in his basement, and passed away a few years ago at something like 97. He loved having the neighborhood kids coming to him for what amounted to engineering questions; he built a Very Serious suspension bridge model with my brother that my folks still have.
posted by Making You Bored For Science at 4:15 PM on February 9 [2 favorites]


This is wonderful. Thanks for sharing.
posted by _Synesthesia_ at 4:58 PM on February 9 [1 favorite]


I'm perplexed how he seems to be polishing a flat piece of glass into a curve with another flat piece of glass and also have it have a uniform shape.
posted by runcibleshaw at 5:04 PM on February 9


Ok, I laughed out loud when he took out what he was using for the main bearing. (48:25)
posted by ckape at 5:14 PM on February 9 [3 favorites]


I'm perplexed how he seems to be polishing a flat piece of glass into a curve with another flat piece of glass and also have it have a uniform shape.

Pressure, when properly applied, can do amazing things.
posted by Big Al 8000 at 5:15 PM on February 9 [1 favorite]


I built one of these mirrors in the 90s in Mexico. Finished the grinding and polishing, could not afford the rest.

In the mid 2000s I went to this children's museum in San Francisco and talked with this old man who had a telescope building workshop.

I just made the connection.

Btw, Dobsonian mounts are great because of how cheap and simple they are, but nothing beats modern computer controlled mounts. Just look something up in the phone and the telescope will magically find it and follow it for hours.
posted by Index Librorum Prohibitorum at 6:02 PM on February 9 [2 favorites]


I think this is the VHS that was being sold to give him some income in his final years. He'd fallen through the cracks a bit, in that between being born in China, being a student, living a monastic life and spending so much time volunteering, he hadn't banked enough working years to be eligible for social security.
posted by bonobothegreat at 7:12 PM on February 9 [1 favorite]


Pardon the language, but there are days I fucking love Metafilter. Thanks for posting. Bought a telescope inspired by this guy. Cool.
posted by grimjeer at 7:36 PM on February 9


Great post. Didn't know about this guy myself, but yeah, telescope sensei!
posted by Rich Smorgasbord at 7:57 PM on February 9


Met John a few times over the years at Stellafane, and heard several of his talks there. He was such a generous man...
posted by grahams at 8:04 PM on February 9


I learned about John Dobson shortly after he died, and was sad to have missed him. I've watched the video from this post through a couple of times since; it's very relaxing. There's a sweet video with people's memories of him here. It's one of the most Californian things I've ever seen.

I've thought hard about building my own Dobsonian, and I still might, but knowing myself too well I bought a OneSky from Astronomers Without Borders instead. It's a small, 5 inch, Dobs, and half the money for it goes to supporting science education in developing countries. It's pretty too. I've grown quite attached to it.
posted by rhamphorhynchus at 8:34 PM on February 9 [1 favorite]


I just watched that all the way through instead of getting stuff done, though I guess I got something done anyway.

The attitude he espouses, that there is nothing you can do wrong which is permanent, is the same one which gets you through building anything at all, or restoring a car, or whatever. It's basically the "sunk cost fallacy" applied to materials, in some ways.
posted by maxwelton at 8:45 PM on February 9 [1 favorite]


John Dobson generously gave my son a ship's porthole to make an 8-inch mirror, and we visited his home for instructions on how to make the mirror and the Dobsonian 'scope. He was a very kind, simple man, who we'd just met on the street when he was showing people Saturn's rings.

We shaped the mirror (fascinating to do .. quite magical how the parabolic shape almost automatically emerges from semi-randomly pushing one piece of glass on another) and built most of the telescope & mount, but got stuck at final figuring of the mirror. Unfortunately the porthole was toughened glass, so its internal stresses changed its shape each time we tried removing a tiny fraction-of-a-wavelength bit of glass. We carried it around through several house-moves but never got it good enough to silver, and didn't have the heart to start over.
posted by anadem at 10:42 PM on February 9 [5 favorites]


Those hands sure tell a tale.
posted by calamari kid at 12:53 AM on February 10 [1 favorite]


Best. Of. Web.

Never heard of Dobson until now, seems like he was a blessing to his local and amateur astronomy communities.
posted by midmarch snowman at 6:39 AM on February 10


I polished a mirror to the point of shericalness in an evening class at the McLaughlin Planetarium in Toronto. The place was semi-mothballed at the time, due to Harris government cutbacks. It was officially closed up just before the final couple of classes and then I got busy at work and never re-connected with the instructor to pick the mirror up. I've only had the chance to look through a big mirror once. It was a view of a globular cluster and the beauty of it rang me like a bell.
posted by bonobothegreat at 6:46 AM on February 10 [1 favorite]


Ohhhh that brings back memories. Unfortunately the 8" Dobson I built back in high school is at my parents' house in Germany, so I don't get to use it often. I did dust it off to look at the Galilean moons with my nephews last summer though (turns out that's about the limit of a 5 and 7 year old's patience... still fun).
posted by kleinsteradikaleminderheit at 9:19 AM on February 10


I've only had the chance to look through a big mirror once. It was a view of a globular cluster and the beauty of it rang me like a bell.

Of all the profound and nearly religious experiences I've had, the first time I looked through a really big scope probably stands out as the most vividly and clearly remembered. It's such a huge, overwhelming thing to be able to look through such a simple device and throw your view across millions of light years and see something like a major nebula with your own eyes.

As for this post, I swear I thought I posted this a long time ago, like two years ago, and thankfully it popped up in my YT recs and I checked my history and searched MeFi for it.

It's a pretty unique piece of history and community science. John Dobson's crafty grass roots efforts have put more eyes from all demographics into space than basically anyone else in human history. He's like the Sheldon Brown of amateur astronomy, where Brown taught people how to wrench on their own bikes and build/fix/true their own wheels, Dobson taught people how to build whole bicycles.

It's difficult to understate how much Dobson revolutionized amateur astronomy. The big mirrors and scopes his design enabled used to cost 10-100x the cost. The next nearest designs that could compete in price per inch of objective mirror was stuff like the Astroscan, which off the top of my head used to go for something like $800-1200ish in about 1990 dollars, which is about a 4" mirror. And that's a budget scope. "Beginner" celestrons with azimuth mounts in the 4"-6" range were more like $5-10k, and that was usually before you bought a scope tripod, mount or tracking drive or even your choice of objectives. (I'm pretty sure my numbers are close, I remember drooling over telescopes, including the Astroscan. I had a Sears special cardboard tube and plastic everything with a decent 3" mirror.)

To put that in perspective, there are reports of user-built scopes from around that era, say, 1992 in the $1000 range with 12" or greater mirrors. And these scopes were portable because you could break them down and store them in roughly the same space that an Astroscan would take in a bag in the trunk.

So, in addition to this, now you didn't need to go buy some remote property away from light pollution and set up an observatory and a hardmount for a big refractor or commercially made reflector to be an amateur astronomer with a big scope. Now you could be a city-dweller in an apartment and own a big scope. You no longer needed tens of thousands of dollars for even a cheap big scope, an expensive house to permanently mount it and house it, and everything else. You no longer needed to be a well off or recognized astronomer like Patrick Moore to own, operate and simply enjoy a really big scope.

Heck, you could even set up your big scope right in the big city and still see things through the light pollution, because you have a really big scope. You don't even necessarily need a car, or the countryside at all.

Which is exactly what John Dobson did with his impromptu sidewalk stargazing parties in SF.

Actually, maybe Sheldon Brown is the John Dobson of bicycles. Or maybe John Dobson is the Fred Rogers of amateur astronomy.

He was just that good.

PS: The official term for "really big scope" that I've been avoiding is "light bucket". I love this term, it's amazing. And really big open framed Dobsonians look just like big buckets pointed at the sky catching light.
posted by loquacious at 9:56 AM on February 10 [5 favorites]


loquacious, if you want to spend 2018 making a bunch of stargazing and astrophotography posts I will not complain one bit.
posted by ActingTheGoat at 10:30 AM on February 10


"Beginner" celestrons with azimuth mounts in the 4"-6" range were more like $5-10k

For giggles, a 1965 Celestron ad reveals that they would sell you a 10" Schmidt/Cassegrain for $1870, or just under $15K in current moneys.
posted by GCU Sweet and Full of Grace at 11:42 AM on February 10


It's funny to think back about 30 years ago, before the NA market was filled with cheap, high-quality Chinese optics. I can't imagine that government austerity measures and trickle down economics would've gotten far without the explosion in access to cheap overseas goods.
posted by bonobothegreat at 7:00 PM on February 10 [1 favorite]


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