Anyone here ever built a telescope?

[Buttercup]

I don't mean the more recent "same day" kits. I mean really making a telescope, including grinding and polishing a mirror.

When I was a kid, wanted to. Had a copy of "All About Telescopes" by Sam Brown. Just now checked price for that on Bookfinder.com; ouch. A classic; expensive. My copy got lost somewhere in time.

My dad wasn't into "making stuff," and an uncle -- who made a violin -- lived too far away/didn't visit frequently enough.

Anyway, just curious for replies in this regard.

I do have a telescope (a gift from age 15). Sometimes think I'd still like to tackle such a project.

[mike alexander]

In high school, 1968. My guides were Texerau's "How to Make a Telescope" and the classic ATM collections from Scientific American with the great Russel Porter drawings. Materials came mostly from Edmund Scientific. 8" Pyrex blank, splurged on a phenolic tube, still got the materials (including secondary, spider, focusser, mirror cell, etc.) for about $100, using my high school graduation gifts. Made a knife-edge tester and actually saw shadows, although what they meant in any quantitative sense probably escaped me.

Still, it was proof that it is well-nigh impossible to completely screw up a homemade telescope. Everybody came out to ooh and ahhh at Saturn.

[Buttercup]

In high school, 1968. My guides were Texerau's "How to Make a Telescope" and the classic ATM collections from Scientific American with the great Russel Porter drawings. Materials came mostly from Edmund Scientific. 8" Pyrex blank, splurged on a phenolic tube, still got the materials (including secondary, spider, focusser, mirror cell, etc.) for about $100, using my high school graduation gifts. Made a knife-edge tester and actually saw shadows, although what they meant in any quantitative sense probably escaped me.

Still, it was proof that it is well-nigh impossible to completely screw up a homemade telescope. Everybody came out to ooh and ahhh at Saturn.

Cool. :-D

Was grinding the mirror as difficult as it seems? Because that seemed SO intimidating, based on book's instructions. I'd still like to do it. Have a telescope already, but...why not?? :-)

[RickJ]

I even ground the lenses of the eyepieces. Big failure that part but the rest was good. Back in 1953 when I started my first scope it was the only way you could afford the hobby. When I helped form an astronomy club in 1961 about 90% used home made scopes except for the eyepieces. I was the only one I'm aware of that tried making their own eyepiece. Not recommended! I thought my 6" was very poor and filed it away. I met an elderly guy (but younger than I am today) who suggested it was the eyepiece and loaned me a 4mm Ortho he never used. Even at that over magnification (the scope was f/12) the image was very sharp. I bought a set of orthos that are still my main eyepieces. In today's dollars each one cost over $600! Prices of good optics has fallen tremendously from the mid 1950's when I got going in the hobby.

Making the mirror (first one especially) is time consuming but not difficult at all. A great example of regression to the mean. Every stroke you make is "wrong" but by rotating the tool in one direction while walking around the barrel the mirror is attached to in the other, all the mistakes average out and you can end up with a mirror of far higher accuracy than most commercial mirrors. Though today there's little monetary savings by grinding your own mirror, there is great satisfaction of a job well done. Two high school kids ground the 8" mirror used for over 30 years by Hyde Memorial Observatory. They made every mistake in the book and invented a few new ones along the way but of the three main scopes, a Cave Cassegrain from the 50's and a new C14, it had the best optics.

Rick

[Buttercup]

I even ground the lenses of the eyepieces...

Wow. :-o Now that's ambitious. Thanks for sharing your story. :-)

[geonuc]

I'm in the process, you might say. A very long process that started twenty years ago.

It's a Dobsonian, 10", and so far I have the tube constructed. It's made of thin wood slats glued together over forms and then covered with fiberglass. I used canoe-making techniques.

[profloater]

at school circa 1958/59 we built a reflector and ground the glass balnks ourselves. easy but time consuming. The glass blanks 8 inch were fastened with pitch and th egring ing paste was similar to car valve grinding paste then polished with jeweller's rouge. Silvering was sent out. It worked well on a wooden frame the eyepiece and secon mirror were bought. Cannot remember how many hours we spent grinding but it was easy and we found the radius oprtically with pins etc.

[Hornblower]

I built a 6" f/8 Newtonian in 1964-65, while in high school, using Allyn Thompson's book as a guide for making the primary mirror. I was too impatient to persist in solving figuring mysteries at the time, so I ended up with a mirror that looked dreadful on the Foucault test stand, but still gave fairly decent images. I would estimate the wavefront error at best focus as about 1/3 wave, based on a reduction of Foucault measurements I got from Sky and Telescope in the mid-1970s. I have recently resurrected this scope on a homemade Dob mount, and the mirror is at a commercial shop in California being refigured.

In 1985 I built a 17.5" Dob, using Coulter optics before they folded. The image quality is creditable for such a cheap mirror in that size, and I have pushed it as high as 400x on globular clusters such as M3 and M13. The views of those clusters in a dark sky are stunning.

[mike alexander]

I should add that silvering your own mirror is also quite satisfying. A bit messy, but fun. A commercial aluminum coating is better, probably. But so what?

I don't know the availability of concentrated nitric acid nowadays. But with glucose available on the grocer's shelf you won't have to make your own invert sugar from sucrose.

Personal opinion is that nothing gives a better polish than jeweler's rouge. Cerium oxide is faster but I never liked the look of the final finish. I repolished with soapy rouge and got a much better finish.

[astropaz]

I recently got myself a 8" blank and all the grit to grind it. At the moment I'm sealing off the tool and waiting on some tile nippers before attaching the tiles to the tool and then I can make the leap forward to start grinding.
All this with the hope that once it's done I'll then go on to build a nice travel dob.

It may take a while but that's the plan anyway.