OF THE THOUSANDS of telescopes that have been built by amateurs in the past quarter-of a century, no two have been exact]y alike. Each instrument, designed by its owner from the basic principles described in Amateur Telescope Making, strongly embodies the builder's creativeness and individuality The resulting variety has been of endless interest.

Of course the amateur telescope maker cannot always choose his ideal telescope. He must take into account the facilities available to him. The two telescopes described below represent extremes in this respect. The builder of the first had access to practically every shop facility he could desire. The second had only a few simple tools. Each did the best he could with what he had.

"The polar axis is driven through a 4,000-to-1 double worm-gear reduction from a reversible two-speed electric motor through a shaft with universal joints. The motor is in a watertight box on the side of the pier.

"The head of the declination axis is terminated in a nose thread of the lathe-spindle type having six turns per inch. The saddle that carries the tube is bolted to a standard lathe chuck plate, which screws on the end of the declination axis. The tube can be unscrewed from the telescope mounting in 30 seconds, yet it is very rigid when in place.

"The hand-made sheet-iron tube, rolled and welded by a tinsmith, was a source of endless trouble. It was not quite round, and threw the turret ring at its top out of round when forced into place. If commercial tube selected for roundness cannot be purchased, a finishing cut should be taken in the turret ring after the tube has been forced into place. This can be done on a lathe if the D tube can be lined up on the carriage, with the tool in a holder, mounted on a face plate.

"The eyepiece revolves on an aluminum rotating turret that affords comfortable viewing angles however the tube is pointed. Since its outer end rotates on a diameter of about 24 inches, the observer can avoid climbing a ladder by looking up into the eyepiece for stars near the zenith and down into it when they are near the horizon.

"The rotating aluminum turret was designed to obtain ruggedness with light weight. It turns on an aluminum ring which is carefully machined to a shoulder and attached to the tube with flat screws. The turret is machined with a corresponding close-fitting groove. It drops over the shoulder and is held in place by a clamp ring attached with flat screws. Once these screws have been tightened to give a little friction drag they may be forgotten.

"Below the eyepiece is the right-angle finder eyepiece, which swivels in trunnions for convenience and has a lighted reticle.

"No adjustment is provided for the diagonal. The saw-steel knife-edge supports are silver-soldered into slits cut into the corners of a square piece of brass. They were checked for equal length and silver-soldered into four slotted T-shaped blocks, two screws holding each to the turret ring. The diameter of the diagonal support system was purposely made slightly smaller than the inside diameter of the turret ring, so that the screws would stretch the assembly under considerable tension before the blocks bottomed. This tension makes the support very stiff.

"The entire system supported by the turret ring was then set up in the lathe face plate and the central alignment hole in the central brass support block was faced off and accurately bored concentric with the turret-rotating surface.

"The diagonal was aligned on the bench with a bronze mating block held in place by four machine screws. The prism is held in an aluminum box and located by accurate 45-degree shoulders on the sides.

"The diagonal mounting block that supports the aluminum block is bolted into place-without any adjustment. The turret face and center hole of the diagonal support were bored at a single setting of the job on the lathe. The prism holder has a locating pin to line it up with the hole in the mounting block. This arrangement has been very successful; the eyepiece may even be horsed around without losing sight of a star.

"The mirror is mounted in a threaded cell, a heavy-walled aluminum casting, which is ventilated through a 4-inch hole in the back. It was simple to make and is easy to unscrew, but could be improved. It screws by a thread of about 9-inch pitch diameter and 10 threads per inch to an aluminum ring that is permanently attached to the tube.

"The mirror rests on four setscrews tipped with Lucite plugs, with its sides against four similar screws around the periphery, permitting collimation and centering.

"The mirror cell has never given trouble. The threads must be lubricated to prevent sticking. If the cell is screwed up too tight the star will not remain exactly on the cross-hairs of the finder; this indicates that a spring-loaded backing plate would improve the situation. A good cell is a delicate piece of design.

"Calculations indicate that there is too much glass in a prism big enough for an instrument of this size, and an aluminized flat is being substituted to improve photographic performance."

Close study of the Schlesman telescope increases one's realization of its sound design, simplicity and ruggedness. Note that almost no provisions were made for adjustment after assembly, even in the diagonal unit, which often incorporates several such provisions. This is the- hallmark of precise machine work; the parts are expected to go together correctly the first time.

The ruggedness of the axes is shown by the insert drawing of the polar-axis detail. The taper between the two bearings is from 2 1/2 inches to 1 3/4 inches, as stated above; but farther up, above the right ascension circle, the axis is a full 4 inches in diameter. The drawing truthfully represents this part as cut away to nearly half-diameter, but the whole truth is that it is a section through two recesses, each .7-inch deep, for the six studs and nuts, between these recesses the shaft has a full 4-inch diameter.

Now we turn to the second of our two telescopes, this one built with a minimum of shop facilities. Alika K. Herring of Middletown, Ohio, built the mounting shown Figure 2 for a 12 1/2-inch f/6 telescope. He writes that the entire job, of necessity, was planned to reduce the need for machine tools to a minimum. I had to beg or borrow the use of a drill press and reduce the number of trips to it by careful planning. Lathe work was required for two very minor operations that any machine shop would perform for a small fee. The total cost of the telescope was less than $60, most of which went into the materials for the optics. The mounting itself cost about $5, mostly for pipe fittings, strap iron and bolts. The wood cost me nothing."

The declination axis is babbitted into a 3-inch pipe T for its bearing. "Before inserting the pipe I wrapped the shaft with a collar of sheet metal the length of the T to provide a steel-to-steel bearing surface, since babbitt metal would eventually wear. Then I stuck the shaft through the T, lined it up meticulously, banked the ends of the T with sand and poured in the babbitt. After it cooled I drove the T off the shaft, cleaned up the ends, smeared a little fine Carborundum mixed With lubricating oil inside, reinserted the shaft and worked it around until it was a smooth-sliding fit in the T."

The concrete counterweights were cast around the axes in paint pails used as forms. While the counterweight on the polar axis could be dispensed with if the footer were lengthened, its use makes a much better balanced telescope by adding mass and therefore steadiness, It also simplifies the lower bearing.

"It would be difficult," Herring states "to devise a simpler telescope that would fulfill all requirements and still be stable. I recommend it to others who have no machine tools and a weak budget." Herring, who comes from Hawaii, asks whether he is not the first Polynesian to make a telescope.

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