
Telescope Building with John Dobson (2014) [video] - Tomte
https://www.youtube.com/watch?v=snz7JJlSZvw
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imroot
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.

~~~
Tomte
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
More info please, i never knew this.

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Tomte
Seems I misremembered the "deadly" part. But still quite serious, says
[http://www.scopemaking.net/mirror/mirror.htm](http://www.scopemaking.net/mirror/mirror.htm)

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tzs
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](https://en.wikipedia.org/wiki/Foucault_knife-edge_test)

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

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

[http://wiki.c2.com/?TelescopeRule](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

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WalterBright
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.

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nerdponx
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.

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

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

~~~
4ad
Apart from that, you will get a _much_ better mirror than any non-professional
equipment (something that costs more than your car).

