Could you Build your own Telescope? The Man that Brought Astronomy to the General Public
“Precision telescopic equipment? I can’t make that!” Indeed?
Galileo Galilei did it in 1608 C.E. before we had electric motors, precision glass forges, or even half-decent tools. Grinding lenses by hand, however, is a job for a dedicated, experienced enthusiast that wants to own their telescope.
If that is the route you want to take, then I now direct you to John Dobson, himself, who lived for almost 99 years, from 1915 to 2014, and became enamored with the stars and sky. He was a graduate with a Master’s Degree in Chemistry, but astronomy lured him into its arms from his teenage years. For the General Public, he became the Master of homebuilt telescopes.
His 90-minute YouTube presentation covers all aspects of building a Dobsonian Light Bucket telescope, the most popular variety for DIYers. And, yes, it bears that name around the world because of John Dobson’s incalculable contributions to everyday, pedestrian astronomy.
He entered the mainstream of astronomical consciousness in the late 1960s but had been designing and building them as a monk in the Vedanta Society monastery in San Francisco for 23 years before 1967. His task for the Vedanta was to reconcile astronomy with the Vedanta teachings, so he built telescopes, rolling them about, outside the Monastery, and arousing interest in passersby.
After nearly a quarter of a century, he left the order because they wanted him to stop making telescopes. It was his passion, so he moved on. People still loved encountering him and his telescopes in public, and he wanted to share the skies with everyone.
His pet peeve was the cost of decently powerful observing instruments for amateurs. Everybody should be able to get access to something suitable without paying an arm and a leg for it, he thought.
Of course, Dobson freely admitted he hadn’t been the first. What he did do was collect all the assorted techniques and knowledge into one place. He became the foremost popularizer of that particular pursuit.
Precision-ground astronomical lenses or mirrors were mind-numbingly expensive because they required a level of accuracy in the curve of 0.000005”, or 0.127 μm, over its entire width. A refractor-based project, requiring many perfect surfaces, made the task extremely complicated, so a mirrored reflector was the route to go, to keep it simple. Getting one perfect surface was comparatively easy. A refractor has a minimum of two lenses: an objective and an eyepiece. Each of those has two surfaces to grind, making the project at least four times harder.
He toted around a 9" reflector for a long time (he named it "Tumbleweed" because it traveled to so many random locations). He also made innumerable 12”, 16”, and even 24” versions in his career. He also happily conducted classes to teach hobbyists how to make their own unique mirrors.
Before the invention of modern super-materials, telescope lenses and mirrors had to be heavy and thick to resist changes in shape due to gravity. This is still a familiar technique used today when making your lenses. The best source for large pieces of glass to grind into mirrors was old shipyards. Porthole glass on sea vessels was one to two inches thick—ideal for making mirrors—even if it wasn’t optically clear enough for a lens. And it could be free if you sourced it on your own.
The great advantage, even in a city polluted by light, was that the Dobsonian Reflector (aka Light Bucket) telescope could bring magnificent views, even in just a shadowed part of a public park.
Now, Let’s Be Honest…
You could buy an inexpensive hobbyist telescope and thoroughly enjoy the experience of scanning the night skies. That is the route that most people take because we have modern mechanization that makes lens manufacturing a fast, easy, painless process.
Building a telescope is a personal journey. It is a way to become intimate with your hobby, a way of understanding every single aspect of it, and why something occurs (or fails to happen) as you’re enjoying it. It is certainly not a requirement.
If you want to grind your own mirror, John Dobson’s instructions in the abovementioned video are comprehensive and clear. If you're going to do the bulk of the assembly yourself, to exercise control over the process, to enhance understanding, or simply to save money, then there are parts-sources online, or which can be recommended to you by members of your local astronomy group.
Dobson’s solution for economy was to use Altazimuth mounts exclusively because they could be entirely constructed of plywood. The design required that they move up & down and left & right. An Equatorial mount is considered superior, especially for automation, but that was never the purpose.
His technique allowed the use of all sorts of readily-available weight-bearing surfaces for the azimuth (horizontal motion). He used discarded 33 RPM phonograph records or old 16” hard drive disks, and little strips of nylon. Those allowed the bearing plate on the bottom to spin easily for 360º.
To tip up and down (altitude) simply requires a U-shaped plywood frame to match the round plywood disks on either side of the box which holds the telescope tube itself. Again, with nylon strips attached to both pieces, the motion is smooth and easy, but the friction was also sufficient to keep it in place once you let go.
Note the tube itself in this example. Do you recognize it? That’s right—it is a commercial product for pouring concrete columns, seen on construction sites all over the world. Sonotube® is terrific for making telescopes because it is inexpensive, waterproof, sturdy, durable, lightweight, and comes in 2-inch increments, from 6”, all the way up to 36” in diameter. That means you are free to make your mirror any size you desire, within the realm of practicality.
The design makes it easy to transport because the tube sits in the base, perfectly balanced when it use, but comes apart easily into two durable pieces for transportation.
Fair Warning: A borosilicate glass blank, touted for years as the best glass for making mirrors is expensive. New techniques have made them unnecessary for the hobbyist, fortunately, since a 16” x 3” blank would cost $1,400 or more. Even a 12” x 2” blank could cost $1,200—putting it out of reach for many people.
Nowadays, we use plate glass blanks which, due to modern manufacturing methods, are completely free of internal stresses. A 12” x ¾” blank can be had for <$70 (plus shipping). Look at this image from the friendly folks at telescopemirrorblanks.com. The blank is sitting on top of a cheap plastic protractor, and being viewed with polarized light. As you can see, the plastic is full of internal strains, but the plate-glass blank is absolutely perfect—and that is what will give you a perfect mirror.
The advantages of plate glass are manifold. First of all, it is a much softer glass, meaning that grinding goes much more quickly. And, as you can see, it is just a fraction of the thickness. This means there is less strain from gravity operating to distort the mirror.
Equally important, the glass adapts to the external air temperature much faster, so your mirror spends less time “being warped” when you first bring it from indoors to outdoors. On top of that, rapid outdoor temperature changes can persist with a thick mirror but pass quickly with the new thinner types.
So, if you already own a telescope, get outside this winter when the air is steady and calm (unlike summer’s tumultuous atmosphere). This is dozens and dozens of images of Neptune, composited in software. Go ahead and try to get a better photo. Or you can ignore this challenge, and just limit yourself to staring at Uranus…
Complete telescope kits, including the structural tubes, blanks, final optics (eyepieces and lenses), including all of the required carbides, oxides, and final polishes, can be purchased, ready for you begin, and I wouldn't discourage you from trying. However, here is the critical part before you begin:
Join a local astronomy club; meet the people involved; get some hands-on practical advice. Making a mirror is not a weekend project. Even before you buy a telescope, get into observing with your new friends at the club; see if the interest persists, or even grows.
You see, some people get scared when they see how big the Universe is, or how comparatively small we are. For example this video shows just the nearest 400,000 galaxies to Earth. In fact it represents just 1/250000th of the Universe as we currently understand it. Each pool of light you see is a real galaxy, about 100,000 lightyears across. Stars are so small on this scale that you can’t even see them individually.
Something to think about
In the grand scheme of things, all the corrupt politicians or villains of history are meaningless. Idi Amin, Genghis Kahn, Adolph Hitler, and their ilk all performed their horrors on a speck of rock called Earth that is only 0.0003% of the entire solar system. That Solar System is only one of 300,000,000,000 such systems in our Milky Way galaxy. And our galaxy is just one amongst 2,000,000,000,000 in the Observable Universe.
Stuff beyond the Observable Universe is so far away that light hasn’t had time to travel here, so we can never see it. More importantly, the Universe is expanding at the far edges faster than the speed of light; galaxies are moving beyond the point where we can see them, vanishing in the distance, and we can therefore never know how massive the Universe is because… physics!
The thing is, yes, the Universe is vast and immense. Its size is literally beyond our comprehension except in the most abstract way. For example, we can estimate that there are 7.5 x 1016 grains of sand on our whole planet (beaches and deserts) and that there are 16 x 1021 stars in the Observable Universe. That is five orders of magnitude more stars. So if you picked up 10 grains of sand, you would have to move the decimal place five spots to the right to see the size change. Those 10 grains would become 1,000,000 grains of sand, or about 125 ml (half a cup).
It’s not only bigger than we imagine—it’s bigger than we can imagine—but that is the beauty of it. If you're given to philosophy, consider this: Intelligence might not be random—it may be a deliberate, necessary act by the Universe to understand why it exists. Intelligence is essential… and so are you.