David Pevear is a retired geologist and life-long maker and fixer of things. He can usually be found puttering about the house, busily maintaining or repairing something. One of his most intriguing projects is his open frame telescope.
Amateur telescope making was a popular topic in magazines such as American Scientific in the 1950s. Now in his early 70s, David sent away for plans when he was in the 7th grade. The plans folded out in a huge sheet that included several construction options. David decided build an open frame design, without an enclosing tube.
Interestingly, for much of the construction, David no longer had the plans. He just took the concept and worked with it from there. Parts for the telescope came from all over. Many parts have been replaced or upgraded over the years.
The main mirror base includes scrap wood from 7th grade shop class, three automotive valve springs, and a piece of duraluminum he scrounged from the father of a friend, who worked in a machine shop at Grumman Aerospace. An old stove pipe shields the mirror from ambient light and protects it from dust.
The main supporting frame is iron pipe and fittings. A heavy tripod made from 2×4 lumber, metal brackets, and an old gear from a farm tractor form a steady base for the telescope. It is important to avoid vibration when using the telescope, especially when using higher power eye pieces. Otherwise you can easily lose the object you are trying to view.
Connecting the tripod to the supporting frame is a ball and trailer hitch with a big wingnut to adjust the tension. David couldn’t find this unusual trailer hitch anywhere he looked in Houston, where he was living at the time, so he ordered one. Ironically, it arrived with a packing slip from a warehouse in Houston. You never know where your parts might come from.
The most challenging parts of an amateur telescope are the optics, which require a great deal of precision. Surprisingly, they can be made with fairly simple tools and materials. Polishing the main concave mirror is time-consuming, and requires testing to ensure that the correct shape has been achieved and surface imperfections removed. David had polished his mirror to within acceptable tolerances, but he was never quite happy with it. He eventually bought a professionally made mirror, when they became available for only $15.
The spotting scope is used to align the telescope for viewing. David’s uses a lens from an old projector. The tube used to be made from cardboard before he replaced it with PVC pipe.
David hadn’t used his telescope for a few years when I visited him. It had been stored in a wine cellar, and humidity had allowed mold to grow. Mold is a problem for telescope optics, because the mold can produce an acid that can etch the lenses and mirrors. I watched as David disassembled and cleaned the scope with care.
Reassembly required precise alignment of the mirrors with the eye piece. The three valve springs were adjusted to center the main mirror. Next came the secondary mirror. This was a fiddley operation. Most Newtonian telescopes use a mechanism called a ‘spider’ to align the secondary mirror with the center of the main mirror. David’s more simple set screws and metal bracket take a lot of tweaking to get just right, but achieve the same result.
The payoff for all this work came on a clear evening. David lugged the heavy telescope out to the backyard. The clear Southern California sky began to darken, and the full moon rose over the mountains to the east. We saw Venus rising to the west. David pointed out another bright dot in the sky, and said he thought it was probably Saturn.
Aiming the telescope by grasping the iron support frame with widely spaced hands, David steered the scope into position. We took a look and could clearly see the rings of Saturn, its distant light captured by the main mirror. The moon was almost too bright to view, and usually requires the use of a filter. We could see sharply defined craters and shadows against the bright white of the moon’s surface.
There is something wonderful about seeing the celestial beauty nature has to offer through something so obviously home-made. It is a reminder that science and exploration are not so very far from our reach. It is a link between understanding the universe and understanding how to make things with our own hands. In this way, we can experience kinship with the earliest scientific pioneers, and encourage a spirit of discovery in explorers young and old.