"The main reflector is a 12", f/8 affair. and provision is made for photographing both at primary focus and with a magnifying eyepiece. For photographing star fields we have fitted a camera on the other side of the polar axis, for which we made our own 4", f/6 lens. When the Schmidt we are making is ready we will probably mount it in place of this camera. When photographing with the star field camera we use the 12" reflector as a following telescope, and when photographing with the reflector we use the 4" refractor shown on the photographic attachment.

"Our telescope mount is driven by a synchronous motor which in turn is driven from an oscillator. An oscillating valve drives two power valves in push-pull and the output, five watts, is ample to drive the telescope with plenty of reserve power. An H. F. pentode valve oscillating as a Dow oscillator has part of its capacity on the tuned circuit connected to a switch, so that the addition or reduction of capacity varies the frequency of the oscillator and hence the frequency of the supply to the motor.

"I have been carrying on some very intensive investigations into stable oscillators and I have utilized the results of this work when designing my own oscillator for the telescope drive. This oscillator, going off at 50 cycles, will remain constant in frequency to about 0.05 percent during an evening's run of several hours. This actual drift is negligible compared with errors due to refraction in the atmosphere and, as the speed of the motor is hand controlled, the small but steady drifts can be taken care of. The variation in capacity is by means of a two-flick switch held in the hand at the end of a flexible shielded lead, and being small and worked with a flick of a finger, it is really very nice to handle. We have had this control in operation for about 15 months and have never had the slightest bit of trouble with it."

The two Coxes wish to get in touch with American amateurs. They are making a variety of things, including a Schmidt camera, an aluminizing outfit, and an automatic guiding rig. They have just finished an observatory for the telescope shown in Figure 1 and, with a diameter of 10', this has a slot that can be opened to 66" because of the spread of their camera and telescope.

IN Figure 2 is another Briton's telescope, the maker of the optics in it being Horace E. Dall, 166 Stockingstone Road, Luton. Bedfordshire, England. Dall is the author of two chapters in ATMA and his vocation is research and design for a firm that manufactures industrial measuring and controlling instruments, particularly for water, steam, gas, air, oil, and other fluid flow. Someone nicknamed the 'scope the "jack-knife" telescope and it apparently stuck. Dall writes:

"It's not everybody's luck to possess a first-class astronomical object glass of large aperture, but possession of the O.G. is only part of the battle. The usual focal length is anything from 13 to 17 diameters and the rigid mounting of such a long telescope on a stand tall enough to give comfortable vision at the eye end is no light job.

"Captain M. A. Ainslie, of Bournemouth, England, possessed an 8-1/2" object glass of 10' focus, and having decided that the ordinary long tube mounting was too cumbersome to consider, schemed out a system of folding which better than halves the length and gives far more comfortable vision-even than a standard refractor fitted with star diagonal.

"Only one additional reflection is needed, in comparison with the latter, and the final image has the advantage of normal astronomical inversion, while the eye tube can be swung round to suit any chosen angle of view either for comfort or orientation of image (see end elevation). It will be seen that the center of gravity of the system comes fairly near to the eyepiece mount. This adds further to the comfort by reducing the range of movement of the eyepiece.

"The illustration shows the details of the sturdy portable form of equatorial mounting adopted-with slow motion and circles. A long dew cap is fitted to the O.G. and the whole tube is of wood and covered with zinc for working in the open. Mr. Perry (Figure 2, left) of Luton built the entire stand and tube, while the optical items and most of the instrument work were by my self. The instrument is now in regular use (mostly on planetary work) by Captain Ainslie (at right in Figure 2), who is one of England's most prominent amateur astronomers. He also possesses a reflector of larger aperture (9") made by himself many years ago, and the use of the two instruments side by side entirely confirms the well-recognized fact that a refractor (folded or not) gives much steadier images than a reflector though on comparatively rare occasions the latter shows to advantage."

THIRD of these three overseas items is a communication from W. H. Haase Kramatlaan 22, Batavia-Centrum, Netherlands East Indies, who says that, 30 years ago in Holland, he made a simple telescope and that he now has a medium-sized refractor. His comments are:

"In ATM, as a fit instrument for amateurs you put the Newtonian reflector well to the front; the Cassegranian and Gregorian come respectively second and third. As to the Herschelian, your remark on page 449 that it is favored by few and you give the reasons why. Anybody having practical experience with the instruments will agree with the order of use as given by you. Yet there exists or has existed a fifth possibility, a handy combination of the Herschelian and the Cassegranian, which is not mentioned in ATM. I enclose a sketch of the principle (Figure 3).

"This combination was constructed around 1900 by K. Fritsch of Vienna and its principal advantages are the total elimination of obstructions from the field of the primary and the fact that no perforation of the latter is needed-certainly no negligible point when compared with the dimensions of the secondaries in the tubes of the Cassegranian and the Gregorian reflectors. If the 'brachyte' (the combination is called brachiet in Dutch, so I translate literally) is used, more incoming rays are gained an the reflective power is greater than in other of the same opening, or aperture. I cite data from a Dutch book on astronomical instruments-J. Weeder, 'De sterrenhemel doorzocht met teleskoop en mikroskoop' edited by A. W. Sijthoff, Leiden, Holland. When put on the market by Fritsch the instrument was welcomed warmly on account of its shortness, lightness, relative power, and cheapness. The astigmatism which the Herschel shows on account of the inclination of the primary cannot have been a serious drawback. On the contrary, Weeder cites N. von Konkoly who found that the brachyte would make the best instrument for amateurs'. The sharpness of the images is called remarkable. In a 4" brachyte, magnifying 250 times, planets showed clear outlines. The ravines near Hyginus and Petavius on the moon, the Triesnecker system and even the all craters in Cleomedes could be very clearly defined. Body heat, a serious source trouble in the Herschelian, will practically have no effect in the brachyte."

TO get fun from telescope making it is not necessary to own an elaborate workshop. The instrument shown in Figure 4 was made by Orville Guthrie, R. F. D. 2, Mukwanago, Wis., from whatever came to hand, including part of an old bicycle pump. If the optical elements in the 'scope are good the performance may excel that of a swank appearing job having poor optics. The 'scope shown in the figure is being used for lunar photography and Guthrie labels the photograph "bringing the moon down to the farm''.

ANONYMOUSLY a writer who wishes to remain a shrinking violet sends us following description of the telescope shown in Figure 5--a 'scope whose heavy design would seem to indicate that Russell W. Porter's plea for ruggedness had taken root or else that the maker, unlike many others, was born with ideas of solidity in mechanisms.

"I send a picture of a home-made 10-1/2" telescope recently finished by a local resident, C. M. Cooprider 1613 Gulf Avenue, Wilmington, Calif., a mechanic employed by one of the nearby oil refineries. In response to my questions Mr. Cooprider tells me that the pedestal is made from a piece of 10" steel tubing with a steel plate three quarters of an inch thick and 20" in diameter welded to the bottom. Good use is made of a 6" malleable iron "T." The tube is of 20-gage galvanized iron broken every 2' to form a 12" tube 8' long and is supported in two 12'' ball bearings, in which it may be revolved to bring the eyepiece to an position desired by the observer. The electrically driven clock is placed within the tube supporting the polar axis. The mirror is mounted in an aluminum cell on a three-point suspension.

AUTOMATIC guiding again. Lawrence Braymer, Honey Hollow Farm, Lahaska, Pa., who helped Ritchey build the 40" aplanatic Ritchey-Chrètien reflector at the U. S. Naval Observatory and who has a Gerrish telescope (ATM, p. 50, No. IV) with 12-1/2" flat, sends us a note on this subject saying: "I think this is a new line of attack on guiding. I gave a lot of thought to it in 1931 but it's one of those things a fellow doesn't get to." Here is the note:

"An automatic guiding device should aim at keeping a 'perfect' cone of rays on exactly the same spot of the sensitive film so that each cone can pour out its quanta of light energy on exactly the same area. Let us expose a plate for 100 minutes. If we get a star image ten diameters larger than the focal point of the cone, we have certainly missed a bet, because the area that our cone has persuaded to turn black is then 100 times its own area and we have taken 100 minutes to secure what we could have got in one minute if our guiding were perfect. (Other factors enter here, but just for fun let's overlook them.) Now, while we are exposing our plate to induce the silver bromide molecules to turn black in spots, old man sky fog is at work on every molecule of our emulsion, and after four or five hours has put a limit to our exposure by trying to turn it black all over.

"Assuming a perfect guiding mechanism in one plane, a limit is set by sky fog and another limit is set by focal error. One plane guiding does not attempt to correct these, especially the focal error which is due to bad seeing. Why not develop a system which permits the rays to strike the plate only at those times when everything is perfect? Instead of trying to follow the wiggles of the cone of light by moving a heavy plate, why not build up our image at selected instants alone?--that is at those instants when everything is lined up and bad seeing has not made our star image look like a fried egg. In short, the rays are 'on the button' or no exposure; and, in the meantime, no sky fog. If we could do this we might get some very different looking plates. We might thus guide for 100 minutes yet get, say, two minutes' actual exposure on our plate. But these two-minute images would be smaller and darker than the images on the 100-minute plate we considered above; and, instead of a 100-minute sky fog, we have only two-minute sky fog. If we could succeed in getting our machine to occult when the cone of rays shifted about half of its area, we might get an overlapping effect, as shown in Figure 6 at the top left. At the top right in the same figure is shown the result of many closings-the central area receives more light. This is the result we would be shooting at.

"The lower drawing shows the general idea. Two guide stars might be used, to increase light and account for rotation of field. When the focal area is 'on the button' of the occulting disk (in this case a tiny cylinder formed by a bright wire of suitable size), the shutter is open. Any change in position of the cone apex spills light into the cell, which trips the shutter. Dr. Zworykin suggested a rotary shutter moving in one direction, like a movie camera shutter, driven by a spiral spring kept wound through a slipping clutch by a Telechron motor. The amplified photo-cell current trips a ratchet on the rotary shaft. Dr. Zworykin said in 1931 that RCA had used a similar shutter of extremely thin aluminum, and secured operating speed of 1/200 of a second. Camera shutters secure speed by only partially opening, hence are not suitable. The cell might be threshold sensitized in several ways by light leakage from a controlled source. An alternating current, for example, might be impressed by admission of light from a gaseous tube (Zworykin and Wilson, "Photocells and Their Application," 2nd ed., page 205 and following). The electron multiplier should be pertinent in connection with any such device. In operation, the observer would devote his time to readjusting the guiding head every time the shutter stopped clicking, It would stop exposing whenever the cone was not waving around over the 'button,' or when the 'button' was either inside or outside of focus.

"Many fascinating angles occur in considering such a gadget. I worried a lot over 'occulting disks', but felt better about them after trying it visually. I spattered a droplet of mercury on a microscope slide in balsam and pressed on a cover glass, getting hundreds of tiny opaque disks. I chose one the right size and occulted artificial star images from a refractor. If the eye is any judge, the effect was good. Note that little light is lost by reflecting surfaces. The idea of occulting during periods of bad seeing is due. Of course, to Ritchey, who says he has guided with both hands and tripped a flap shutter by a device held between his teeth.

"In many hours of consideration of the guiding problem I could think of no other approach which promised such rewards in the result. Since photography is all a matter of contrast, no other system seemed to it of such great effective exposure.

IN the Review of Scientific Instruments for July, 1937, Charles H. Tindal of the Warner and Swasey Observatory, Case School of Applied Science, Cleveland, Ohio, describes his pendulum-controlled telescope drive. This is a modification of the Gerrish drive described in Bell, "The Telescope," and is for the purpose of correcting the inaccuracies of commercial synchronized power. A limited number of reprints are available for loan to those who are interested.

IT looks at present as though the RFT, or Richest-Field Telescope, described by Walkden in the final chapter of ATMA, were destined for very considerable popularity. We have seen several, and know that others are being planned or made. Last August, when your scribe was at the annual unconventional convention of amateur telescope makers at Stellafane, Finagler's Comet was near the Dipper and everybody wanted a look-see at it. Through ordinary telescopes, even quite large ones, this proved disappointing, the comet being so thin and nebulous. However, two RFT's brought there by Cox of New York, when simply held in the arms like a howling baby (ATMA p. 639), revealed head, tail, and striations quite neatly, for these short-focus 'scopes are good light gatherers. Directed toward star clouds in the Galaxy, these RFT's proved easily to be all that Walkden claims in ATMA. We should like to publish, some time next winter, a flock of photographs of owners of RFT's with their RFT babes in arms-a sort of "RFT Club." Please send.

A governing factor in RFT design is the number of stars per galactic field of view, and the data given in ATMA were based on average galactic fields. But suppose we single out some especially dense regions of the Galaxy, like Cygnus, and design an RFT, or a RRFT, for that alone. This would be a "special purpose" RRFT, giving still more striking views in those regions. We hope later to publish a paper by Walkden, on the special purpose RRFT.

The Society for Amateur Scientists (SAS) is a nonprofit research and educational organization dedicated to helping people enrich their lives by following their passion to take part in scientific adventures of all kinds.