For photographic work the Schmidt telescopic camera, with its oddly curved correcting lens in front, is as far ahead of a telescope camera having an ordinary paraboloidal mirror without a correcting lens, as a paraboloidal mirror is ahead of a spherical mirror for usual work-farther, in fact. Oddly enough, the Schmidt reverts to a spherical primary but it is its correcting lens that does all the business of knocking out the coma that otherwise puts tails on star images at the edge of the plate and, in fact, on all except the central eighth of a degree or so of plates taken with paraboloidal mirrors such as the 100-inch. But a Schmidt gives a good field 12 degrees or more diameter-no tails. The spherical primary is said by some writers who have never tried to make a real sphere to be easier than a paraboloid but, be that as it may, the real grief or "piece of resistence" in the Schmidt job is in the correcting plate. This is a thin piece of glass at the outer end of the tube, its curve so inconspicuous that the plate resembles an ordinary piece of thin, unaltered glass. But the extremely shallow curve is neither spherical nor paraboloidal but decreases in radius as the edge is approached, and it must be made by means of a flexible lap and a combination of patience, intuition, experience, bad language, cut and try, and occasional sheer good luck. It is not beginner's work and perhaps it is not merely fairly experienced work, but definitely is advanced work. The whole business- theory and practice-will be covered in the "A.T.M. Supplement," due in a few months -please don't ask when, for this depends on when the last cunctative contributor sends in his material. The last contributor whose long-promised "copy" comes in is to receive a prize of an invisible telescope in an intangible, imponderable carrying case.

In the meantime, here are Harold Lower's comments on some of the first photographs he and his father, Charles Lower, took with the Lower Schmidt, which embodies the famous "Soup Bowl" mirror. "The 'candid camera' shot of Dad lighting a cigaret shows what one second exposure does, by the light of a match," he writes. "This is made at a distance of 12 feet. Lens wide open. The night picture of San Diego (page 249.-Ed.) was made from Point Loma, across the Bay. Exposure 10 seconds, and over-exposed. By examining the negative with a glass one can count the windows in buildings which are more than four miles away, but it is so badly over-exposed that they don't show in the print. The two pictures of the camera with one side removed were made before the interior was blackened, so as to show the parts in position."

The crossed strings in the left hand (lower) picture were placed there for help in the very delicate, critical collimation and are not a permanent feature.

BELOW right and left are drawings of two items from Cyril G. Wates, 7718 Jasper Ave., Edmonton, Alberta, Canada. The first is a gadget to permit easy reading of setting circles in the dark. "The scale proper. Wates writes, "is a disk of 1/16" Celluloid one side of which is sprayed with black Duco. The scale divisions are cut through the Duco with a sharp knife, and the numerals scratched with a scriber. Work with a light under the Celluloid. This method gives very fine markings.

"The scale is attached to a collar which clamps to a declination axis by a set- screw, The drawing shows the common German type of mounting, but the same principle could be adapted to any mounting. The lens is a ten-cent magnifier. The mirror may be thin glass, silvered on the front and lacquered. I used a bit of chromium plated metal. The 'index' is a piece of Celluloid with a vertical line scribed and blackened. It should be as close to the scale as possible, in order to avoid parallax. Note that the Duco side of the scale must be next to the lamp, and that the base of the numerals must be toward the edge, as the mirror inverts.

"The lamp is a 3-volt flashlight globe working on one cell, to give a faint light. The socket and one side of the switch are 'grounded' on the mounting. This scale is delightful to use The divisions are seen very clearly, yet the eye is not dazzled as when using a flashlight.''

It is suggested that the light be of as low candlepower as will clearly reveal the markings, thus not unduly causing the pupil of the observer's eye to close. Mr. Wates' next item is a suggestion for a drive for an equatorial mounting. The drawing is his.

"This drive is planned for a very heavy, double yoke mounting for a 12" telescope, but could easily be adapted for other mountings, such as the common German type, by means of an extension on the polar axis.

"The actual drive consists of a screw such as is used in screw-cutting lathes, with a split nut. These screws are accurate within .0003" per inch length. The nut runs in guides (not shown), and has a thrust ball hearing at the top. The screw turns ( by means of suitable gearing) at a speed slightly in excess of 30 rev. per hour. The motor should be variable speed if possible.

Mounted on the polar axis is a pulley 72" in circumference. A suitable pulley could be picked up at any junk shop, although possibly not of the exact diameter. It would be a simple matter to alter the design and gear ratio to accommodate any pulley or screw that happened to be available.

"On the left is a heavy drive weight suspended on a suitable steel wire passing around the pulley. On the right is a steel tape attached to a yoke, which in turn is fastened to the nut. The wire and tape lie on the pulley side by side-they are not joined. Each is fastened to a stud on the face of the pulley. The pulley is a loose fit on the polar axis and can be clamped thereto by a clutch, not shown. The fine adjustment is obvious from the drawing.

"Exact speed control will be by the so called 'Chaser' system. The wheel marked 'control from clock' is not attached to the screw drive in any way, but is an entirely separate wheel driven by a pendulum clock at 30 rev. per hour sidereal time. A contact on this wheel plays between two contact on the screw drive wheel. If the latter gains the motor is slowed down, and vice versa.

"No means of restoring the nut to the bottom of the screw is shown, but it is planned to have the motor and gears slide to the right, disengaging the worm and engaging a suitable gear direct from the motor shaft to restore the nut and weight. Contact will of course be provided so that the motor will be shut down when the nut reaches the bottom.

"Except at the equator, the piano wire will run over a pulley to the weight."

"IN all fairness to others and to the best of my belief I feel I can safely lay claim to the distinction (if any) of having the smallest observatory of any practical use. It measures exactly 60" x 17" x 25" To be precise, it is the scuttle hole to the roof of the house.''

This is our old friend Bill von Arx, broadcasting a fighting challenge to the world from his sky hole observatory at 573 Monroe St., Brooklyn, N. Y. What he writes shows the sad circumstances under which we poor metropolitan observers work (kindly start weeping here); in fact, your scribe's telescope is now in moth balls in the attic, because a gas station 200' distant has converted his yard into near daylight with three big flood lights. For two cents the company's name would be revealed: a famous ocean was named for it. In revenge, no gas is being bought there-will the company fail? But to return to Bill von Arx with his head sticking out of the sky hole.

"Being one of the many sufferers from city lights and cold wintry breezes." he says, "I mounted a small equatorial camera on the southern edge of the scuttle, as shown in the photograph. Standing on a substantial shelf 60" below the level of the roof it is quite comfortable to do all the observing 11 and photographing any avid amateur might want to do. Of course, several regions of the sky are obscured by neighboring chimneys, ventilators and vent pipes, but in the main these are not disadvantageous because the sky light in the lower altitudes is so bright that most of the stars are lost.

"Besides the equatorial camera I have a little 80-mm. triplet telescope of 22" focus and doubtful pedigree, on a mobile altazimuth mount which can be trundled to the roof level with little difficulty. It is dismounted on a pair of two by fours about 2' long, joined at right angles at their ends. Resting the legs of the mount on the combing of the scuttle-the mounting being fastened at the union of the two-it is quite easy to move this little glass in any position favorable for the observation being made. This manner of mounting has proved more than satisfactory in that it is light, easy to handle, and quite rigid even in strong winds.

"Between the roof and the ceiling below there is a space a little over a foot high which makes a very convenient place to keep odd maps, books, binoculars, eyepieces, as well as the two instruments mentioned above. A board laid across the ceiling makes a convenient desk for jotting notes. This is even more comfortable when a stool of small dimensions is squeezed up on the shelf with the observer. An extension cord from the outlet in the room below gives current for the drive clock on the equatorial, as well as for a small ruby light for reading charts, etc."

We asked Bill what his family does for heat while the sky hole is open and he tells us the family heat simply passes out, after which the seeing is better. Whether the family does the same seems uncertain, but it was a cold winter.

R. E. CLARK, Box 112, Langeloth, Pa., writes: "I have been experimenting with the following wrinkle, which I think is new, and thought you would care to pass it along to some of the fraternity who make a specialty of spoiling good glass. Instead of using glass for a tool, try the following: 4 parts clean, 60-mesh silica sand, 2 parts clean, 200-mesh silica flour, 3 parts Portland cement. Add lots of water and mix again very thoroughly. Pour into a mold the size you want your tool. Eliminate all air bubbles by stirring with the finger, smooth off the top, which will be the back of the tool, and allow to cure for 72 hours. If properly made there is little danger of scratches from detached grains of sand. Use plenty of water in mixing, so that the sand grains will segregate and form the working face."

GEORGE NIEIGHAN, 774 34 St., North Bergen, N. J., suggests this dodge: "Instead of using the glass tool I use a round metal plate-stove lid or other. If the pitch hardens before I can get the grooves properly made' I hold the plate over the gas burner and soften it up again."

NOW and then someone sends in a blueprint of a telescope, made at some cost of labor, and wishes it reproduced. A blue print cannot be reproduced at all. The tracing is reproducable but generally the draftsman forgets that when the drawing is reduced the lettering will be reduce in proportion. In general, we dislike blueprints, which smack of the standardization idea. Drawings of individual feature of telescopes are of interest, but few wish to "copy" a whole 'scope.

AND now a club of telescope enthusiasts has been organized in St. Louis, the "St. Louis Amateur Astronomical Society, " which is the astronomical section of the St. Louis Museum of Science and Industry. C. F. Hellweg, 5246 Cote Brilliante, is the secretary-treasurer.

THE drawing (above left), after a little study, shows how Nelson A. Mowry, 302 Garland St., Edgewood, Pittsburgh, Pa., converted a 39-cent Model A Univex camera into a celestial camera for attachment to a telescope. The lens and shutter were removed and a brass shutter inserted into a jig-sawed slot. Good pictures an inch in diameter were taken.

In the second drawing, made by Vance Johnson, 821 West 27th St., Cheyenne, Wyoming, this draftsman-artist-telescope-maker shows how he and "Bertha" (that his telescope-Bertha Johnson), and the other cow hand photographed the moon using Pan film and a dingbat of their own invention. The objet d'art ,right, also drawn by Johnson, reveals details of the new Cheyenne Mounting, with its slow motion drive.

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