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Making a Mirror

By Jeff Newsome
Published 2004-09-02 15:31:56

It took only a few nights of viewing the night skies thru a 4.25' aperture telescope to convince me that I need to see the universe with "bigger eyes"! After all , if you can see "that much" with even a small mirror, think of what must be observable with a larger mirror, I mused. The evenings of Nov., Dec., and Jan of 2003-2004 pass by with frozen feet and fingers (and the "occasional" whiskey sip!) and great views of Jupiter and Saturn, the Orion Nebula and Andromeda Galaxy, all the while nurturing the concept of moving into a bigger scope.

As I began to sift through the mountainous debris pile of astronomical gadgetry and go-to contraptions on the internet and in the backs of periodicals, I stumble across the "Dobsonian" telescope. The deceptively simple operational appearance, as well the relatively low- cost of these instruments immediately captures my attention. A Google search for "Dobsonian telescopes" brings me to the story of the remarkable John Dobson and the story of the Sidewalk Astronomers.

Sifting through the writings on his web page, both by and about him, I am captivated by not just his commitment to pushing the envelope of understanding in both the Cosmological and Astronomical world, but also by his desire, it seems, to accomplish more with less. His approach to telescopes, incorporating his deceptively simple mount, made from basic construction products, with high end optics (hopefully!), stand in marked contrast to the never ending spiral of "must have" equipment, fostered by an increasingly consumer oriented society. Don't think, just buy!.

"What an amazing individual he must have been" I think to myself, assuming that anyone of this caliber, who has had this kind of impact on such a science as astronomy, must have long since passed on, just shortly after Galileo. I mean, they just don't make 'em like that anymore, do they? But wait, they didn't have plywood back then! Lo and behold, further scrutiny of his web page reveals that , not only is John, at 89, still actively teaching Cosmology classes and lecturing all over the world, he's scheduled to teach a telescope/mirror making class in Los Angeles, my brothers hometown, in February/March of 2004.

Mirror making? Is it possible that a slothful creature such as myself, could possess the skills to produce an instrument of high optical capability? You don't know if you don't go so I quickly made the decision to explore this phenomena firsthand. Unemployment has its advantages, so scheduling, at least for me, was a non issue. It was, however, an issue for my brother who I'd be staying with as he was set to move out of his digs come early March. How to resolve this I wondered? I e-mail Donna Smith of the Sidewalk Astronomers, John's "agent" and "organizer" ("Call Donna and ask her" John would often say, "I don't know what I'm doing tomorrow!") to glean more info on the coming classes. I've decided I'll show up in town early, pay for the class, do as much as I can on my own, and hopefully hook up with John from time to time for pointers when necessary. Donna gives me the phone number for John at the Vedanta Center and suggests I call him directly to work out any details. Call him directly? I've been sifting through his writings and looking for someone who could possibly translate all of this philosophical and scientific jargon for me, and I'm supposed to call him on the phone??? What do you say to Einstein? I settle on a "hello" and explain the situation to him. I needn't have worried as John, as Donna said, is very approachable and enthusiastic, though some of the articles about him have suggested a brusque attitude, at least where mirror instruction is concerned. Let's face it. Anyone who has done instructing of any kind for any length of time experiences the "burnout" syndrome. I'll try to keep my visits brief.

Perhaps the greatest impediment in making a mirror, for me, comes not in figuring out which strokes to use during the parabolizing process, (though that will prove to be an exercise in patience development and tenacity) but in coaxing my aging (1983 ) Toyota pickup, with in excess of 200,000 miles to its credit, from my home in Driggs, Idaho down to Los Angeles, and back again. The truck leaks so much oil it has been declared a disaster area in the state of Idaho. The Exxon Valdez tanker spill in Alaska seems tame by comparison to the destruction left behind by this vehicle's passage. Nonetheless, I cast off onto the highways one beautiful February morning, in the spirit of the Wright brothers, who must have felt a similar twinge of apprehension when launching their plane at Kitty Hawk. Will this beast fly, I wonder? Three hours later in Tremonton, Utah I check under the hood to gauge the situation. Doesn't seem to be leaking. One check of the dipstick shows why. The oil is completely gone!! It is moments like this that test the metal and mental acuity of the adventurer. With a case of oil in tow, I press on, like an elk in rut, dazed but determined!

Two days after arriving in L.A., I make my way over to the Vedanta Center, where John Dobson will be giving a lecture on Cosmology, to be followed later, by the introductory Telescope Making Class. Many who have attended the morning services at the Vedanta Center stay on to listen to Johns talk. An engaging speaker with a dynamic presence, Dobson thoroughly captivates and engages this audience, leaving myself somewhat in awe of this obvious force on the planet. It is there at the lecture that I meet more Sidewalk Astronomer members, Bill Scott, Bob Alborzian, and Donna Smith. Lunch break ensues and finds several of us jammed into two cars heading to Denny's, where Dobson helps himself to the marigolds out front in the restaurant's gardens while we wait to get in. Inspired by this display, I sample some myself. Cheaper and tastier than what followed!

Back to the Vedanta Center and Bill Scott's house , where John goes over telescope basics for the un-initiated, and a discussion on focal lengths and ratios and how they figure into the mirror making process. We adjourn to the sheds out back where Bill and Bob run, just a few of us now, through the "tools" of the trade so to speak. Various glass blanks, zip log bags of different sized grinding grits, Teflon bearings for the now classic "Dobsonian" telescope mount, brass tubing for use in the focuser, and the "sono-tube" pressed cardboard concrete forms that house the primary and secondary mirrors and have become one of the trademark features of Dobsonian telescopes.

Bob Alborzian gets a couple of us started on an eight inch piece of glass, with a six inch piece of glass used as a "tool" to carve or "hog" out the middle of the glass that is to become the mirror. The smaller, one inch thick, round piece of glass stays on the bottom, 60 grit carborundum sprinkled in between the two with a little water thrown in to aid in the process and away we go, grinding the glass together, extending the stroke somewhat of the glass on top so that it's middle is worn away by the edge of the glass tool on the bottom. Called a "wet" this process is repeated several times, with both pieces of glass being rinsed when the abrasive properties of the grit wear out. Wet the glass, sprinkle on a teaspoon or so of carborundum, and grind away. Very soon, the process begins to feel a lot like work but there is something very meditative about pushing glass and you quickly begin to settle into a rhythm and pace.

After this introduction, we sift through the mirror blanks already on hand and settle on a 14. 5 inch porthole glass for my mirror project. I had originally wanted to attempt a 12" scope, but none were readily available and Bill offers me a great deal on the 14. 5" . It's badly chipped on the backside(how much this may have affected the final figure of the mirror is yet to be determined) but this only affects directly a small portion of the mirror side, so I opt to take a stab at it. (I can't recommend this for future mirror makers as the glass tended to slide around because the undercut/chipped portion allowed the glass to slide around while working on it due to the lack of contact with the nails I had used to hold it in place. This caused an unevenness in stroke, which is a contributing factor in astigmatism). For the tool , an eight inch piece of glass is available so I put that into use. (traditionally , a full sized tool or 3/4 sized tool would be used as this tool often becomes the pitch lap used in polishing . A full or 3\4 sized pitch lap not only polishes faster, but it keeps the figure of the glass more spherical , and helps minimize errors such as "turned down edge" and astigmatism. This all becomes painfully obvious to me later on! Operating in the spirit of utilizing what's available, Bill loads me up with the various grits, my two pieces of glass and I'm off to my brothers tiny garage for an education in mirror fabrication.