"The polar and declination axes are of 1 5/8-inch cold-rolled steel tubing turned true, and ground into the four bearings. These were cut from scrap bronze, bored to fit the tubing. Turning friction can be adjusted by tightening the capscrews on the split side of the bearings. Thrust is taken up by steel collars on the axes. An adjustment atop the hollow tripod allows an azimuth change to be made without moving the legs around.

"The legs are 2 l/2-inch bar channel, bolted to the base. They have leveling screws at the bottom. This seemed to be the most logical way of supporting the instrument, since it is used in the city, standing on concrete walks "Motions in right ascension and declination are made by two slow-motion thumbscrews. The worm and worm-gear ratio is about 20 to 1. Worms and worm gears also were made by Mr. Marshall. The thin, split extensions of the hubs of the worm gears are tapered and threaded on the outside. The worm gears are locked in position on the axes by turning up the threaded collars on these extensions. Quick adjustment through large arcs can be made when the collars are turned back. The axes then turn freely in the bores of the worm gears.

"The telescope is further glorified with two circles graduated in degrees. The finder was made from a piece of brass tubing. Its optical system is from the lenses of an old box camera. It serves the purpose well, in spite of the chromatic aberration.

"The total cost of material, including the prism and aluminizing the mirror, was $5.75. The man-hours that went into this telescope are astronomical."

If you are flirting with the idea of building a telescope, and have been reading this department of the magazine for months or years, as we know many do before actually making the pick-up, do not be frightened off by the large size of some of the instruments described here from time to time, since these are not first telescopes. Most amateurs start with a 6" size, make an 8", perhaps a 10" or a 12 1/2", and by that time have gained enough experience to tackle something larger, if they wish to go that far. Unusual–probably unique–is the 16" reflector of Springfield type (Figure 2) described below, made by a user of the handbook, "Amateur Telescope Making," C. W. Hough Box 145, Route 1, Pasadena, California. Actually this is three telescopes on one mounting, the "other two" being 3" refractors mounted beneath the tube of the main reflector. By moving a simple slide the same eyepiece may instantly be applied to any one of the three. Hough writes:

"The 16" mirror for the reflecting telescope was ground and polished by hand on an HCF lap. Its short focus–48", or f/3–required the removal of about 1/3" of glass at the center of the curve. [When asked why he chose this great focal ratio, instead of the more usual f/8, Hough replied that he was attracted by the difficulties promised in "ATM" in hand-working a mirror larger than 12" in diameter, and in figuring one of great focal ratio; he also wanted large light-gathering power.-Ed.]

"The equatorial mounting was made from an old Dodge rear axle and drive shaft. On the upper end of that axle is mounted a wheel hub and brake drum, and to this unit is bolted a forged yoke which supports a 200-pound lead counterweight.

"Sliding around the outside of the drum is a setting circle, which may be clamped wherever desired for settings in right ascension.

"On the brake drum on the end of the sloping polar axis shaft and bolted to it at right angles, is the end of the propeller shaft housing from the same old Dodge car. This unit consists of the housing, ball-bearing cage, and drive shaft. This drive shaft was bored out and serves as the light-channel from the diagonal to the prism beneath the eyepiece.

"The second wheel hub is mounted on this drive shaft, and on the hub part is mounted a second brake drum through a plate friction clutch. This is driven in slow motion by a worm and right and left hand-wheels. A similar friction clutch is built inside the first or polar axis brake drum, and like the other, is turned in slow motion by double hand-wheels, or else may be driven by an electric motor back-geared to the hand-wheel shaft (Figure 3). The declination circle is screwed to the flat face of the second brake drum and is dimly lighted by a 6-volt lamp, the hour circle being similarly lighted.

"The main tube is 17" in diameter and 100" long, hence the telescope's pet name, 'The "100-inch-Long". The tube's four internal stiffening rings were made by spinning a 19" diameter steel plate, turning the edge at right angles and cutting out the center.

"Between the tube and brake drum is a short stub, or T, of metal tubing welded to the tube, and through holes in this stub piece two 3" refracting telescopes, pointing in opposite directions, one an f/12, the other an f/18, are inserted, their outer ends bolted to the big tube.

"The 1" diagonal prism for the 16" reflector is mounted on an adjustable unit attached to the side of the big tube.

"The mirror rests in a spun steel cell on felt pads and has the usual three adjustments, plus radial adjustments.

"Inside the T stub mentioned above is a brass slide parallel with the three telescopes,

and on it are mounted two prisms, also a 1" achromatic negative lens in the center. Handles (Figure 3) for sliding this slide project through the T, a detent holding the slide in the selected position. The prisms and slides are mounted on micrometer adjustments and the three telescopes are adjusted for identical focus and center at infinity. The 1" negative, achromatic Barlow lens mentioned above is 11" from the main diagonal, and focuses 15" farther along at the eyepiece, the cone of rays first passing through the 1/2" hole in the declination axis and being reflected by the second prism below the eyepiece. The eyepiece mounting is fixed in position.

"The telescope may be swung by hand by slight pressure, against friction of the clutches. Fine adjustments then are made by means of the handwheels. The drive motor is thrown in gear by a milled screw seen silhouetted above the lower handwheel in Figure 3. Motor speed is controlled by a variable resistance. While not synchronous, it keeps a star in the field of the 16" mirror for an hour or more without adjustment.

"I live on a hill overlooking Pasadena and Altadena, and with Mt. Wilson in the northeast, and I use the 3" f/12 as a terrestrial unit, then reverse the telescope and use the refractor and reflector interchangeably, without leaving my seat or taking my eye from the eyepiece. I believe this assembly of three different telescopes on one universal mounting, with a single, stationary eyepiece, is a new idea.

"The telescope is waterproof, the large tube having a spun cover seen hanging on the southern pier in Figure 2.

"Figure 4 shows the rear, with transformer in center, motor rheostat at right, motor holding clamp at left, polar axis clutch in center, and the worm screw rings shown in part.

"All the auxiliary equipment is mounted on the original brake band support. The foundation bolts are the 1/2" U-bolts once used for bolting the rear axle to the springs of the Dodge car. Two of these were fitted with washers and nuts and placed nuts down, one in each of the two foundation forms parallel with the axle. The other two were interlaced with the first two, with the threaded ends projecting through the form to straddle the car axle. The latter bolts were wound with clothesline, over which was wound two layers of rubber tape. Concrete was then poured and, after it was thoroughly set, the clothesline and tape were pulled out. This provided about 3/4" space for movement of the bolts for polar adjustment.

"Originally I mounted the 200-pound lead counterweight on an arm at the lower end of the polar axis shaft, but the torsion twisted the 1 1/8" shaft so much that the unit was out of balance in both east and west directions, and this is the reason for the rather heavy forged yoke which now supports the counterweight. The telescope is now perfectly balanced in all directions and extremely rigid.

"On top of the main tube, and in line with the declination axis, is an 8" by 8" manhole which gives access to the prism, and this hole normally is covered by a curved plate. My camera is attached to an identical plate which fits on the same projecting studs. This plate mounts a prism positioned in the axis of the mirror but between the mirror and main prism. Thus the two prisms do not interfere with one another. The light is turned upward, through a high-grade shutter with remote control. When making photographs, the telescope is guided by the refractor.

"I did not do any of the small optical work. Some years ago I picked up from a Third Avenue, New York, junk dealer a large assortment of lenses and eyepieces; two 3" fixed position theodolites; a 2" Throughton and Simms repeating theodolite with 12" scales, a beautiful instrument; World War I trench periscopes. The dealer had bought this for the brass! This material has been very useful. I think it carne from some of the early Coast and Geodetic Survey stations. The telescope is largely made up of junk and odds and ends."

NEAT little gadget for mounting a diagonal in a Newtonian reflector is shown in Figure 5, which is self-explanatory ("Hua-i neng ta ch'ien yen," or, picture's meaning can express a thousand words, in case your Chinese has become rusty). Developed by Max Burgdorf, Natchitoches, Louisiana, and made by Lorane Brittain and Sherwood Burgdorf, it takes the place of the more customary spider support for diagonals and would cause a less complicated diffraction pattern than the latter. They embodied it in their 8" reflector

The trio, the first-named an ice manufacturer, the second an associate professor of music (teacher of counterpoint and composition) at the Louisiana State Normal College, experienced an amusing variation on the old theme supplied by professional looking-glass silverers (not telescope mirror silverers) in which they stubbornly silver the back of the mirror disk unless kept under duress; their silverer silvered the face, just as requested-and then smeared on a coat. Of paint to protect it!

SOCIAL item: Annual report of the Director of Mt. Wilson Observatory says the 72" spherical f/2.5 mirror for the 48" Schmidt telescope on Palomar Mountain has been figured at the Observatory optical shop; the entire work of grinding and polishing having been completed by Hendrix and Dietz in 21 weeks. Dietz, only a few years ago, was a beginner, reading the present department and starting in by making the orthodox 6" reflector, following the directions in "ATM." Now he is a professional with his name bracketed with that of D. O. Hendrix, Mt. Wilson's head optician. Home-town boy makes good.

MEDAL-the Coffin Foundation award-has been handed by the General Electric Company to A. W. Everest, Pittsfield, Massachusetts, employee, for his research in the measurement of steel when magnetized. Everest, with his usual modesty, won't tell exactly what he did but we hear he developed a thing actually called a magnetostrictoscope Not to be outdone by a mere $300,000,000 corporation, your scribe, on August second, at next summer's convention of amateur telescopticians in Vermont, will hand to the same Wally Everest a much larger medal, for his research on a close technic in working optical surfaces on glass, and for developing a thing called, with much greater economy of syllables, the "spit test" for radius of curvature.

NO SECOND edition of "ATMA" has been published or is contemplated, but whenever a printing of the existing edition, which is the first, runs out we try to correct those errors which our readers have kindly pointed out to us. In the second printing, made August 20, 1939, the following errors were corrected and owners of "ATMA" may change their copies as follows:

Page 71, Fig. 2: Cross off top lettering, which is reversed (and unessential).

Page 131, line 7: Delete from "assumed" to end of paragraph and substitute: "Plane mirrors used in the testing of paraboloids and of completed telescopes at their foci must be of high quality as regards smoothness of figure (+/-0.1 wave maximum), but uniform sphericity of the order of +/-1 to 10 waves can be tolerated, depending upon the application."

Page 201, line 4 of legend under Fig. 6, for first nine words substitute "print. The bottom cylinder is cast solid."

Page 227, near top, change 16620 to 1662.0.

Page 348, line 11, change "remaining" to "ramming."

Page 404, line 5, change 2.8 to 3.2.

Page 633, footnote, third line from bottom, delete decimal points.

Page 635, last paragraph, change each M to m.

Page 637, line 2, change M to m; line 3, delete m.

Those who purchased "ATMA" between August 20, 1939 and February 1941 (third printing) need change only the following:

Page 253, fifth line above bottom 16 to 15.

Page 266, in Fig. 5, lower, right-hand part, r₁, r₂, r₃ to r₇, r₈, r₉.

Page 404, first line below cut, half to quarter.

In addition to these errors of fact, a number of slips in diction were found and many of them corrected. What real errors have you found?

Suppliers and Organizations

The Society for Amateur Scientists
5600 Post Road, #114-341
East Greenwich, RI 02818
Phone: 1-877-527-0382 voice/fax

Internet: http://www.sas.org/

At Surplus Shed, you'll find optical components such as lenses, prisms, mirrors, beamsplitters, achromats, optical flats, lens and mirror blanks, and unique optical pieces. In addition, there are borescopes, boresights, microscopes, telescopes, aerial cameras, filters, electronic test equipment, and other optical and electronic stuff. All available at a fraction of the original cost.

SURPLUS SHED
407 U.S. Route 222
Blandon, PA 19510 USA
Phone/fax : 610-926-9226
Phone/fax toll free: 877-7SURPLUS (877-778-7758)
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Web Site: http://www.SurplusShed.com