July 31, 2010 6:00 AM PDT

DIY Weekend: Building a window to the stars

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Douglas Smith's Dobsonian telescope draws a crowd on Northern California's Mount Tamalpais.

(Credit: Patty Nason/Gavaphoto)

Want an eye-popping view of the heavens but don't own a high-powered telescope or live near an observatory? Try building your own reflecting telescope. San Francisco-based designer Douglas Smith did just that after taking a course, and ended up creating a 10-foot monster with great optics and portability.

Smith took a class at the Randall Museum led by amateur astronomer John Dobson, long known for popularizing low-cost reflectors made of plywood and plastic. So-called Dobsonian telescopes are Newtonian reflecting telescopes consisting of a primary light-gathering mirror at the bottom and a secondary mirror near the top that reflects light into the viewfinder.

The unique feature of Smith's f/7.1 telescope is that the secondary mirror and viewfinder--a group called the Upper Tube Assembly--normally rests on long aluminum truss tubes. But when the instrument is being transported, Smith detaches the UTA so it nests inside the lower part of the scope, the plywood mirror box. Weighing about 160 pounds, the entire package rolls on wheels and can fit into a compact pickup truck.

Douglas Smith and his FirstLight telescope.

(Credit: Patty Nason/Gavaphoto)

It took Smith about four years working off and on and roughly $2,000 to build the telescope, which he dubbed FirstLight (similar commercial telescopes might cost around $2,000 and up). He used AutoCAD software to design it and Excel to confirm the critical balance point calculations, while friends helped with automated cutting of the plywood with a ShopBot machine.

The priciest components were the focuser, the truss tubes and connectors, and the plywood. Smith saved money by making his own 16.5-inch mirror, originally a flat, 1-inch-thick porthole glass.

"Grinding and polishing your own glass saves a lot of money, but the process is also time-consuming and one has to have a lot of patience," Smith said. "I spent a lot of time correcting mistakes in the learning process. I'm glad I did it, but it was challenging."

Other features of the scope include a Plexiglass laser finder board, which has a green laser that Smith points at stars to get them into view, and red LED-illuminated degree indicators on the sides and the base. Smith plans to add motors that will allow the telescope to automatically compensate for the Earth's movement. With that improvement, he can take quality photos of heavenly objects.

Other astronomy enthusiasts are already impressed with FirstLight. Smith has shown it off at Maker Faire in the spring and at Mount Tamalpais in Northern California for stargazing events. Participants appreciate the fact that since it's relatively heavy, FirstLight doesn't sway in the wind like smaller scopes. But what about the optics?

"It's great to hear people say things in astonishment after seeing the detail on the moon, or the rings of Saturn or Jupiter's moons," Smith said. "Some are a little intimidated by having to climb the ladder to view when it's pointing high up, but most are OK with that. I like to say that you climb the ladder to get a little closer to the stars."

Gazing at a DIY Dobsonian telescope (photos)

To share your DIY project, simply e-mail a description of 350 words or less, including all the geeky ins and outs of your invention, plus relevant links and photos, to crave at cnet dot com. Please put DIY Weekend in the subject line.

Crave freelancer Tim Hornyak is the author of "Loving the Machine: The Art and Science of Japanese Robots." He has been writing about Japanese culture and technology for a decade. E-mail Tim.