Good-Looking Scopes

Jack Kramer

Okay, why should we care what our scopes look like? After all, no one really sees them in the dark. This was brought home with the airing of The Astronomers TV show on PBS a few years ago. One episode devoted a portion to John Dobson's efforts to bring astronomy to the public, and it showed his big scope that's swathed in heavy aluminum foil. His smaller solar telescope also looks pretty shabby. Even some older observatory instruments look the worse for wear after years of deferred TLC. A photo of the 13" refractor with which Clyde Tombaugh discovered Pluto at Lowell Observatory is an example. What a mess!

Those of you with Schmidt-Cassegrains have built-in good looks. Not you personally...your telescopes!!! Besides looking high-tech, SCTs come with fitted cases with which to carry the scopes so they arrive at the observing site and back home again unscathed. Practically every well-used Newtonian or large refractor gets its share of scratches and dents. (Their size makes them great battering rams.) Each trip through a doorway or into a vehicle leaves its mark somewhere. So this article is really intended for those of you who are building a telescope or thinking about refurbishing your present one.

The tube is the part that generally takes the brunt of the abuse. John Dobson's scopes were both made from heavy cardboard sonotube. This is intended for concrete forms, but has been one of the mainstays of telescope makers for years. It's rugged, yet fairly easy to cut. However, it's very heavy...and there's hardly any way to disguise the fact that the scope was made using spiral-wound cardboard. Several coats of epoxy paint or high-gloss spray enamel, using fine steel wool between applications, will make these tubes look pretty good. To keep the edges of sonotube from looking like the butt ends of a cardboard tube, saturate the ends in varnish or Elmer's Glue-All, smooth them with steel wool when dry, then finish. Dobson's telescopes are primarily for public star parties, so sonotube may be more practical for him. It protects the mirrors and gives something solid for people to grab onto. At public star parties, there are those who just have to hang onto the telescope when they look through the eyepiece. Coulter telescopes use sonotube to keep their prices low. For a short section of tube, Jeff Inman used a piece of small fiberboard barrel, which is lighter than Sonotube.

Other materials about on a par with sonotube for ruggedness will definitely increase the cost of the telescope. A couple of years ago, fiberglass and aluminum tubes ran about $10-$15 per foot in sizes that will accommodate a six-inch mirror. (The price may be higher now.) Both of these materials look good if left unpainted. If you're building a small refractor, the thin-wall PVC plumbing tubes work well. Most hardware stores carry the thick-wall tubes, which are extremely heavy, but the larger suppliers also carry the thinner 1/16" tubing. Roberto Garza got around this by drilling zillions of holes in the PVC tubing of his former 6" scope. PVC takes paint very well. Of course, the inside should be flat black. It's also very sturdy, and even though you may have to buy a ten foot length, it's still pretty cheap. But don't be reluctant to ask if they have any cutoff pieces. Why buy more than you need? At one time, it was a rule that you had to line the inside of your tube with cork for insulation purposes, but today the conventional wisdom seems to be that it's better to speed up the process of reaching thermal equilibrium.

The color to use on painted parts is largely a matter of personal preference. A light color is somewhat easier to see in the dark; perhaps that's why it was an unwritten law many years ago that all telescopes had to be painted white. However, a dark colored tube helps the telescope reach thermal equilibrium more quickly, since dark colors do a better job of heat dissipation. Metallic paints (copper, aluminum, etc.) don't hold up as well as high-gloss enamels. Some stained and varnished wooden parts give the scope a certain penache and hold up well. Even something as simple as exposure to the night air will eventually cause the grain of the wood to "check" slightly. A thorough sanding and refinishing every few years preserves the good looks.

Today, many telescope builders are using skeleton tubes. Usually, the design follows the Serrurier truss, which is a series of triangular tubing elements known for its rigidity. The tubing most often used is Reynolds Aluminum 1" diameter thinwall. This makes a telescope that looks high tech at a relatively low cost. Sponge rubber tubing used to insulate water pipes can be slipped over the aluminum tubes to provide a comfortable hand-hold. This design allows easy access to the optics, though stray light can be a problem. And watch out for your mirrors at a public star party - kids just have to reach out and touch!

A nicely-finished telescope isn't going to improve your chances of finding that faint galaxy or getting a sharp image of Jupiter. But be honest now. Don't you sometimes just enjoy looking at your telescope? If your reaction is "YUCK", well...

Published in the September 1996 issue of the NightTimes