Above and Beyond: It’s All Sawdust and Mirrors
- By Phil Scott
- AirSpaceMag.com, July 01, 2010
Still life with telescope, feline, and feet. Even the National Air and Space Museum uses a Dobsonian telescope to show visitors the sun.
Phil Scott
A few years ago, I wrote in this magazine about Jeffrey Jacobs, a sidewalk astronomer who sets up his telescope on New York City streets and invites passersby to have a look at the night sky (“Moonstruck,” Soundings, Oct./Nov. 2005). New Yorkers buy lots of telescopes, which is odd, because in Manhattan you can see only the moon, the larger planets, and the brightest stars. Some say New Yorkers use their telescopes mostly to gaze into neighboring apartments.
I took a few peeks through Jacobs’ telescope myself, and later, when I moved to Florida, I decided I had to have my own, even if it let me see only the same heavenly bodies as Manhattan dwellers.
The price of high-end amateur telescopes quashed that desire, but then I learned about John Dobson, a former member of a Los Angeles Vedantan monastery who built a telescope from scratch: He ground mirrors from a ship’s glass portholes, mounted them in a cardboard tube from a construction site, and built a telescope mount from scrounged lumber, all for about $5. I called the monastery and left a message for him.
Then I consulted Google and found a site titled “How to Build a Dobsonian Telescope.” It had photos of a cannon-like object and complex-looking calculations about setting focal lengths and whatnot, and recommendations to buy what I couldn’t grind myself. It gave glowing reviews for Murnaghan Instruments of West Palm Beach, Florida. That company’s Web site listed a six-inch Dobsonian Telescope component kit—focusers, finder scope, mirrors, eyepieces, and everything else the homebuilder likely won’t discover in a dumpster—for $229.95. I called to order it, and Pat Murnaghan himself answered.
“Among people who don’t have a lot of money to spend on high-end amateur scopes,” Murnaghan said, “about the only way to get a decent, usable telescope that will let you do something beside stare at a couple of dots is either build a Dob or find a used one. With a store-bought telescope with computer-control nonsense, you have something that’s going to work for a while, then it’s going to break.”
I bought the screws and bolts that the plans said I’d need, and called Murnaghan again to ask where I could get the tube to mount the optics. He reminded me that Dobson had used a molding form for a concrete column. “The big concrete construction companies will throw you out the door,” he told me. “You can find Quik-Tube at Lowe’s.”
Next up: Plywood for the mount. I waved down Jaime, my apartment complex’s maintenance man, scooting around in a golf cart. “I need a half-sheet of plywood,” I said. “I’m building a telescope.” He motioned for me to follow him to the maintenance shed, where he pulled out an L-shape sheet. I took some quick measurements. Bingo. Jaime plugged in the power saw, and I spent the rest of the day measuring and cutting. UPS delivered a box of telescope innards that afternoon.
I studied the assembly plans, a mish-mash of verbiage probably written by a scientist. I spray-painted the inside of the tube flat-black. Then I called Murnaghan. “I’m about to cut first cardboard,” I said, playing on “first light,” what astronomers call the first view from a telescope. He gave me a quick pep talk on building a telescope, adding that I really hadn’t needed to paint the inside, despite what the plans said.
“All Dobsonians are ultimately Newtonian reflectors,” he said. “Sir Isaac did all the work. What Dobson did was bring astronomy to the masses.” Galileo’s 1609 telescope magnified light; in 1668, Isaac Newton built a telescope that gathered light instead, using a large concave “primary” mirror mounted in the far end. After the mirror collected the light, it reflected the compressed image to a smaller flat mirror in the front, which reflected the image to an eyepiece.
“If it’s a Newtonian, why is it called a Dobsonian?”
“A Dob is more of a concept than a design,” he said. “He was working with nothing. His resourcefulness and ingenuity were enough that they ended up calling his a Dobsonian telescope.”
I began building in earnest that Saturday and worked straight through Sunday afternoon, gluing and nailing the plywood pieces together, none of which lined up because in my usual careless rush, I’d cut them out-of-square. They were thinner than the directions called for, but Murnaghan said I could build the thing out of cardboard if I wanted. It needed feet to stand on, so I went dumpster-diving for a piece of 1 x 2 wood. It called for holes larger than the two drill bits I had, so I used smaller bolts than the plans called for. When I ran out of new nails, I scrounged up bent ones from a junk drawer and straightened them. The only time I proceeded with great care and precision was mounting the optics in the tube.
Once again I called Murnaghan.
“Did you find the directions in the box?”
“The ones that say ‘Do not ever look at the sun with this telescope?’ ”
“That’s the one.” One page contained the calculations for determining the distance between the screw holes for the primary and secondary mirrors, which turned out to be 41.25 inches.
My largest drill bit didn’t make a big enough hole for the eyepiece, so I enlarged it with a box cutter. Directions called for a rotating base, which swiveled on a Formica square or an album, which meant sacrificing Leo Sayer’s Endless Flight. The last part: two round bearings necessary to adjust the tube vertically. I liberated the training wheels from a Spiderman bike someone had tossed in the garbage. Once I nailed those into place, I was done. There were pencil marks and calculations written on the plywood, flat black fingerprints on the yellow Quik-Tube, and all over the floor were undersize screws and nails, sawdust, and a spilled glass of iced coffee. But I was done.
I set it up and waited until dark. Using only the eyepiece, I tried to find something to look at other than the apartment complex across the street. I spotted three stars, but the image seemed blurry, about as stunning as the first views from Hubble before the initial repair mission to fix the optics. Disappointed, I plugged paper in both ends of the tube and put it away.
The next day I asked Murnaghan if I’d gotten it right, because it was a clear night and I saw only the three stars.
“Was the background gray?”
“Yes.”
“It was probably light pollution. Take it to a dark area and try again. Focus on the moon: It should come in clean and crisp.”
It rained for the next three nights.
A couple of days later John Dobson called me back. He had returned to the monastery after he had a stroke in March 2008, although he still participates in star parties, where amateurs get together to compare telescopes. I asked him if he had that original telescope. “No,” he said. “Somebody borrowed it and set it up for ten years. They took the mirror out and left it set up in the rain, and we lost the rest of it.”
“What should I do with my telescope?” I asked.
“It’s only a little telescope,” he said. “It’s not very important what you do with it. What you need to do is get in touch with other people with telescopes when they have a star party. If you hob and nob with these people, you’ll eventually get to be a hobber and nobber yourself.”
The following evening the sky was relatively cloudless and a sliver of the moon crept up. I hauled my not-very-important telescope out to a golf course and pointed it at what was visible of the lunar surface. Like Galileo four centuries earlier, I saw its imperfect, craggy surface, the mountains, the craters, and what the ancients thought were seas. Like Murnaghan said, the view was clean and crisp.
Then I turned my new telescope on the nearest apartment building.
After suffering through a year of peace and quiet in Florida, Phil Scott returned to New York City, where he studies the moon with his telescope in Central Park.
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