THE FASCINATION OF POSSESSING A TELESCOPE

Wanganui Chronicle, 11 March 1947, Page 4

THE FASCINATION OF POSSESSING A TELESCOPE

(“BY

SKY PILOT")

Many visitors to the Wanganui Observatory have really co:n ? to see by observation through the 9J inch Telescope that the sky contains far more of interest, beauty and wonder than they ever dreamed of. There have also been quite a few enquiries about making a telescope for oneself. This has many advantages and is to be commended. Some people would prefer to buy their own but this is a costly outlay especially for a Refractor Telescope. Another type of telescope is the Reflectoi’ which is much cheaper to buy and very much so to make and maybe said to be quite within the realm of possiblity of the handy man whose interest leads him to give some time to making the mirror. The Reflector is a very good type of telescope and it may be of interest to readers to note that the 100" Mt. Wilson and the 201’’ Palomar Telescopes are both Reflectors, the one having done a fail’ piece of work and the other about to reveal wo feel sure, the mysteries in far out space, yet undreamed of. Many amateurs and professionals have made their own telescopes and have had a great thrill in so doing. The late J. T. Ward made many Reflectors for local citizens and as a matter of fact a 20” Reflector of his own craftsmanship i s at Carter Observatory awaiting erection, once finally tested and when funds permit. Over 280 years ago Newton perfected the Reflecting Telescope whilst Herschel, Rosse, With and others furthered hi s work. Liebig made a substantial contribution as to the method of silvering the mirror’s surface while Foucalt made prefection of the delicate curve of the mirror mor e possible.

In these columns reference has been made to the outstanding work of Sir William Herschel. He was perhaps the greatest master of the type of telescope of which we .are speaking, the Reflector, at one time making a mirror of 4 feet diameter, a mavellous achievement surely for his time. Those wishing to make their own telescopes have the benefits of the splendid results of these men of the past. Up till th e middle of the 19th century the object glass or mirror was made of speculum metal “a 68/32 mixture of copper and tin which is exceedingly hard and has the property of taking a very high polish." The Reflecting power of such speculum metal is very poor compared with silvered glass. Fortunately, now the silvered glass has taken its place but this t°°, which requires silvering twice a year is giving place to the aluminized object glass, a really fine piece of work. The Reflector's chief part is the mirror which reflects the light received from the heavenly body. The rays of light are collected by this concave mirror and reflected on to a fiat at the other end of the telescope, which brings them to a focus ip the eyepiece on the side of the tube where they maybe examined by the human eye. The “flat” or "diagonal" must be as small as possible since it is situated in the direct line of the rays of light and is set at an angle of 45 degrees to the axis of the telescope. The mirror, flat, and the eyepiece and the tube ar e the main pieces of the tube apart from its mounting which should be equatorial. The glass used for the mirror since it is only used as a base for the reflecting film of silver, may be just common glass, although since this is a bad conductor of heat sudden changes in temperature may set up strains. Pyrex glass which is so much used for cooking utensils not affected to the same extent by variations of temperature and is therefore a better glass to use. The 201” mirror is made of this latter kind of glass. As glass is a hard substance to work Carborundum is the best abrasive substance to use fox’ mirror making, whilst rouge with pitcli as a carrier is used for polishing it. Pitch being hard and yet plastic makes it an ideal base for the accurate polishing ot glass. The beginner should not attempt to make a mirror larger than 6 inches in diameter as much greater skill is required in the making of larger sizes where so many unforeseen difficulties arise. A 6 inch mirror well figured and silvered will yield very satisfying results up to powers of 100. The method of proceeding with the “tools" fox’ making the mirror and the fine technique should be gathered from reading some book such as "Preparation of Mirrors fox- Astronomical Telescopes," by Geo. McHardie or Bell’s "Telescope,” or “Amateur Telescope Making,” by Ingalls. Care will have to be given to grinding, figuring, polishing, testing, and silvering ihe mirror, help for which all will b e found in McHardie’s splendid but cheap book. Flats are better purchased from reliable makers although good plate glass flats made by amateurs with a lathe at their disposal will act excellently. A suitable tube of metal or wood, or even skeleton should be decided upon and great car e given to the mounting which for serious work must be equatorial. Whatever type of mounting is decided upon see that it is rigid with easy motion for the telescope as a vibrating telescope is useless.

Quite a workable Reflector Tele scope is by no means out of the reach of ihe pel son who has set his mind upon it and is willing to apply himself to the task.

The telescope completed will immediately introduce the observer to the wonders of tiie sky and provide he anil his friends with many interesting hours of pleasure and delight. The Moon and th e members of the Solar System will be picked up very easily and Nebulae and clusters will easily be recognized. There ar e many amateur astronomers who have their own telescopes, the product of their own labour and made up of many queer, maybe, but useful materials resulting in an instrument which well repays all the time and effort employed in its making. McHardie’s splendid little book, the real help ol th P Amateur, should be on sale in local shops shortly.