In Figure 1 is an 8" refractor made by H. P. Garrison, R.F.D. 1, Oceanside, Calif., working from the very detailed instructions by Haviland in "ATMA", the companion volume to "Amateur Telescope Making".

"The objective lens," Garrison writes, "was made from a pair of Chance Brothers hard crown and dense flint, ground to a focal length of 134", or f/16.75. I spent much time regrinding and polishing five times, but I did not mind that because I was learning all the time. Now I have a lens that will stand 75 diameters' magnification to the aperture inch when the seeing is good, and I feel I am very well repaid for the extra work.

"The mounting is made from Chevrolet truck parts, steel pipe, and boiler plate, and the axes are mounted on ball bearings. The tube is of 20-gage galvanized iron 8-1/2" in diameter.

"The mounting works very smoothly but, in the wind, as shown in the illustration, taken before a 14' by 14' roofless observatory with 6' walls was erected, it was very shaky.

"The cell, Figure 2, is made of aluminum cast in one piece, and is held in place by means of brass clips. This permits removal of the lens without disturbing the adjustment."

FRAMED attractively in the twigs of a neighboring tree, as shown in Figure 3 stands the huge, 137' dome for the 200" telescope, atop Mt. Palomar, California, with the great mounting inside practically ready to receive the big mirror next year. This artistic photograph was taken by Ted Watterson, official photographer at Mt. Palomar.

Figure 4 is a 1/340-scale replica of the same great dome, cast in brass and aluminum by Fred Ferson, 404 Reynoir St., Biloxi, Miss., author of the chapter on molding and casting in "ATMA". The patterns were made by Russell W. Porter and presented to Ferson, a friend. Ferson then poured the castings, machined them, and finished them to a degree of neatness that makes of this replica a most attractive desk, or other, ornament-suitable also for adaptation as a cigaret humidor, ash receiver, or other utility. Ferson hopes to install in some of these replicas a model of the 200" telescope itself, if there is enough demand.

The base is 8-1/2" in diameter, is made of brass, weighs about six pounds and is lettered "Two-hundred Inch Telescope Observatory A.D. 1940." This brass base includes an integral standing collar part reaching upward as far as the bead seen above the entrance doorway. The upper portion is cast in aluminum, contrasting attractively in hue with the brass base, and consists of a hollow spherical dome 5-5/8" in diameter, to which an accurate replica of the shutters is attached fixedly. This upper portion may be rotated, as on the original, also lifted off to get at the interior, which is machine-finished.

Sharp-eyed comparisons will reveal that the entrance door in Figure 2 differs from that in Figure 3, the original. These, however, are different doors and on different sides, the door in the replica being the huge one for the introduction of the big mirror and the other merely for the introduction of the astronomers.

In Figure 5 are two lesser items cast by casting-enthusiast Ferson The larger is a 34-ounce brass plaque, 5" by 3/8", made from a pattern by Porter who, when visiting at Ferson's home, poured plaster of Paris into a metal ring and with his jack knife quickly whittled in bas relief in the soft plaster the cartoon of the "Mirror Maker" sweating and straining at his work of preliminary polishing. The smaller piece (32 ounces) is a brass "Telescope Nut" peering into an eyepiece from an awkward seated position, and was cast by Ferson from a pine pattern whittled out by Porter. The two photographs on page 337 of "ATMA" show Ferson with Porter smiling at the camera.

STELLAFANE'S annual convention or informal get together of amateur telescope makers and astronomers will be held atop Mt. Porter, near Springfield, southeastern Vermont, on Saturday, July 22. All having interest in astronomy or telescopes may come freely and bring families, friends. They will find about 200 others similarly afflicted (that is, telescopitis, families) siting on grass or hard outcrops of Vermont Jurassic schists ready to swap chin music about telescoptics from noon to six. Then comes supper en masse in a big circus tent (about a dollar). At dusk, reports and speeches by amateurs from hither and yon begin and wear on till all are unconscious: following which those who revive may stay all night, using Stellafane's telescopes and those brought by visitors-bring yours. Good parking. Places to camp. Bubbling spring. Scenery. Air. Not a mosquito.

IN February 1938, in these pages Clyde Tombaugh of Lowell Observatory, described his sun telescope: a 12" mirror, unsilvered, a right-angled prism with diagonal face turned directly toward the mirror, thus diverting some 93 percent of the light away through the other faces, and a pair of smoked glasses worn by the observer-the overall reduction in these three cutting the solar light to 1/7500 strength and thus permitting comfortable study of the solar surface. In April of the same year, D. Everett Taylor told how to make a Herschel wedge of the general kind described by Bell, in "The Telescope," for use on Sun, Moon, and Venus, this being an attachment between telescope and eyepiece designed to divert or throw away 90 percent of the light by means of a thin, wedge-shaped elliptical 8 or 10 degree, plate glass prism.

Alan Gee, "ATMA" p. 320, a cadet at the United States Military Academy, West Point, N. Y., in rummaging round the previously unused but recently rehabilitated observatory there, ran across the item shown in Figure 6, an old polarizing diagonal of considerable value, and at our invitation he describes it as follows:

"A diagonal employing the principle of polarization by reflection to cut the Sun light and heat down to a minimum without cutting the aperture (see Bell, "The Telescope,' pp. 167-8) gives beautiful colored views of the Sun. The following is a description of such a diagonal (probably made by Alvan Clark about 1880) as used on a 12" refractor f 180" focal length at full aperture.

"The construction of this diagonal is very simple. It consists essentially of three wedge (Herschel) prisms, two of which are so mounted that the incident and reflected rays to each make angles of about 57 degrees with the normal to the reflecting surfaces and thus are plane-polarized. The third wedge is intended to increase the available light range and to get a favorable observing position, and is mounted just in front of the eyepiece like an ordinary diagonal. Figure 7 shows the arrangement schematically, and Figure 8 as it appears in use. The tubes of the diagonal are of brass, soldered at the necessary angle. The two separate parts of the diagonal-the lower part A, (Figure 7) carrying one prism and attaching to the 'scope, and the upper part C carrying two prisms and the eyepiece-rotate with respect to each other about the short connecting tube B. This rotates the planes of polarization and this controls the amount of light passed on to the eyepiece and eye. "For minimum light," Gee continues, "tube C would be perpendicular to tube, D, as shown in Figure 6; for maximum light they would be parallel, as shown in Figure 7.

"The wedge prisms in this particular diagonal are mounted against soldered shoulders in separate pieces of tubing that slide into the soldered tubes forming the angle. This simplifies construction and allows removal for cleaning. "The angle the wedges must make with the incident ray is a function of the index of refraction of the glass used. The equation, tangent , where the the angle between incident ray and normal, and index of refraction, gives the exact value of the angle. For ordinary glass (1.55,approx.) the angle is 57 degrees. As all the incident rays are not parallel, anyway, this is close enough for most conditions. However, if a particularly light or dense glass is used, the exact angle should be calculated.

"Silvered surfaces or the like will not polarize by reflection, although colored glass will. Black glass can be used in place of wedge prisms if available, but should be used with the third wedge of clear glass to discard extra heat. The new polarizing materials now on the market, usually consisting of thin sheets that polarize by transmission, are not suitable for a diagonal. They pass the violet and deep red (and most of the heat) even when set for extinction, and thus are but little superior to any colored filter. Nicol prisms will work if available but are far too expensive.

"The biggest advantage of this type of diagonal lies in the fact that it cuts down the light (and heat) without cutting the aperture and without coloring the image. No colored glasses are needed. The Sun appears perfectly white and can be rigidly controlled in brilliance simply by rotating one tube with respect to the other. The difficulties of construction should not be great, the optical surfaces representing most of the work. If used on a reflector one of the wedges mounted at the required angle could well replace the main diagonal, the other being mounted before the eyepiece. The beautiful views that such a set-up gives of the 'rice grains', spots, and faculae on the Sun surely make it worth considering."

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