Telescope Building with John Dobson (2014) [video]

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

by Tomte • 9 years ago

54 14 9 years ago

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melling• 9 years ago

How is building a telescope like writing software? One of favorite sayings:

http://wiki.c2.com/?TelescopeRule

Telescope Rule

Thomson's Rule for First-Time Telescope Makers: "It is faster to make a four-inch mirror then a six-inch mirror than to make a six-inch mirror."

-- Programming Pearls, Communications of the ACM, September 1985

imroot• 9 years ago

I've been building my own dob's for the last 10 years...it's my favorite weekend activity and stress reliever, and the minute you get one done, you instantly think, "I can do an n+1 quicker than this one," then you're grinding for another year :)

Two things that I want to say that might make it easier for people who are starting out:

- Look to see if your local observatory has a mirror making room. (Volunteering at an observatory is what really started my interest in this)

- Find a local glass shop that does hot work, and ask them if they will pour your blanks for you: You'll never risk getting a glass blank crushed/chipped by UPS/FedEx and it's a LOT cheaper than buying the glass online. They will also generally be able to refer you to someplace that does cold work (which is usually $50/6 months access if it's set up as a non-profit or a museum) so you won't need to buy anything but the grit.

I was incredibly fortunate: The Toledo (Ohio) Museum of Glass rents both hot and cold shop time and I had a girlfriend at the time who was really experienced with the hot side of things (she had a MFA in Glass) and having her help me through the first few glass mirrors really helped me through the process. There were guys at the Observatory that I volunteered at (Perkins Observatory in Delaware) who had done this to give me pointers. There's a really great community that thrives on helping others online.

I could really geek out with this and talk everyone's heads off about this, but, if you have questions, feel free to shoot me an email (it's in my profile) and I'll be more than glad to help you out in any way I can.

Tomte2• 9 years ago

And most important advice: make sure you work the mirror only wet. Grinding a mirror the wrong way is a fast track to severe or even life-threatening lung illnesses.

digitalshankar• 9 years ago

More info please, i never knew this.

nerdponx• 9 years ago

My dad built a telescope for a class project in high school. They even ground the glass by hand. Even though the body is made of cardboard and electrical tape, it's still usable decades later. Really cool.

jankotek• 9 years ago

With cheap telescopes from china, it is now pointless to build your own.

mcbutterbunz• 9 years ago

Building something by hand can be more enjoyable and rewarding than just buying something off the internet.

4ad• 9 years ago

Apart from that, you will get a much better mirror than any non-professional equipment (something that costs more than your car).

rfrey• 9 years ago

Only if you think having the telescope is the point.

tzs• 9 years ago

The thing I find amazing about home made telescopes is how accurate you can make the curve of a hand ground mirror with such simple equipment. You have some intended curve you are trying to make, and you need to hit that to within something like 1/4 of the wavelength of visible light or better (call it 100 nm).

Most people would expect that seeing such small deviations would require expensive equipment that is complicated and has to be built to insane tolerances. Nope. All you need is a point-like light source, an opaque item with a sharp straight edge, and a dark room.

The point-like source can simply be a light in a can or box with a small hole for the light to escape. The sharp straight edge can be a razor blade.

With that simple equipment you can do a Foucault knife-edge test [1]. That lets you figure out what parts of the mirror are too high or too low from the intended curve, and you can use that to guide your further grinding of the mirror to bring it to the right shape.

[1] https://en.wikipedia.org/wiki/Foucault_knife-edge_test

dekhn• 9 years ago

You should also mention that the almost perfect curve can be generated automatically by just rubbing two rough surfaces (hemisphere and sphere) together.

WalterBright• 9 years ago

One of the best things my high school physics teacher did was show students how to make telescope mirrors. Every day after school there'd be two or three students there grinding away at their mirrors.

Telescope Building with John Dobson (2014) [video]

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