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.
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." … Read more