pq-homemadeobs

TALKS  GIVEN  BY  PAUL  TO  BRISTOL  ASTRONOMICAL  SOCIETY

FROM  THE  LATE  1970’S  TO  2005

 

HOME  MADE  TELESCOPES

10th November, 1978


 

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           [Several telescopes were set up, and catalogues with lists of suppliers, laid out].

 

   Firstly I’ll talk about my experiences in telescope building, including the pitfalls. Then, by referring to all this hardware, supplies and shops exhibited here, I’ll describe how anyone, irrespective of budgets, can build instruments that will do at least half the projects the Society runs during the year. Anyone interested is recommended to note the names and addresses, and look at the catalogues of the more distant, out of Bristol suppliers. I’ll mention what instruments can be got, and at what price, with slide illustrations.

   About 20 years ago I had a very small telescope, but discovered Patrick Moore, after which, in all senses, things began to look up. There was no money for a real telescope, and I had no knowledge of suppliers, but read Moore’s books and newspaper articles on the artificial satellite era. Then I heard about a supplier, Charles Frank, who had a 6 inch reflector, equatorial mount etc., for £84, a sum of money as far as the Moon, but they also had a cheap 1.5 inch single element refractor as a kit. At 16 shillings this 30 mag. was the best I’d known, and showed Moon craters well with only moderate colour fringes.

   I continued to read Moore, although he depressingly insisted a refractor has to have at least a 3 inch objective for it to be of any astronomical use. As he set such store by a large objective, I obtained a piece of  plate glass, got a glazier to cut it into squares, and started to grind an objective.

   First, two squares of the plate glass, each of about 7 inches side, had to be made circular, and this was done using pliers. Then the glass was ground for what was intended to be a mirror, but since I did not know, and had no means of knowing where to get it aluminised I decided to use it as a lens once it was polished. The grinding and polishing took a year or more. Here it is, finished about 1970. It is a 200 inch lens, so it has something in common with Mount Palomar, only this is 200 inch focus!

   The lens was finished but not the job. The eyepiece was taken from a broken pair of binoculars. The tube and mounting was so difficult that it was abandoned. 200inches is 16.5 feet. I made a tube of rolled linoleum but this was not strong enough, and if supported in the middle it would bend at that point. By having two mirrors to give an optical system I was able to shorten the tube to 5 or 6 feet. But no good. The two mirrors were ordinary ones, and between them they distorted the image so badly, like viewing from the bottom of a swimming bath, that the telescope was hopeless. Eventually I had a lens in a short 6 inch tube which I put on a tripod and looked at it through an eyepiece squatting about 16 feet away. Mag. X 50, alright, Mag. X 100, less good, and Mag. X 200, very poor, though coloured fringes were there in abundance. A colourful show indeed, with a telescope awkward to use and impossible for objects near zenith.

 

   About three years ago I met someone who had made a telescope and he recommended H W English & Co. for much of the optics. I bought a 1.75 inch objective for about £4.50, standard eyepieces, tubing wire and plastic padding from ironmongers and made the 1.75 inch achromatic telescope you see here. The mount is  very simple, a cheap C-clamp with a bolt through it and a wooden upright. This instrument gives good lunar views, will show Saturn’s rings, Venus’s crescent, and during good conditions, Jupiter’s belts. The stand will also take binocular holders, as shown.

   A couple of years back I was given a glass porthole, 9.5 inches by 0.66 inches. Ah1 I thought, now I will make a 9.5 inch reflector. A year of grinding and everlasting polishing would, with silvering , give a first class mirror. Even un-silvered it gave acceptable views of the Moon. So it went off to Optical Instruments (Balham) Ltd. They silvered it but pointed out that it was very grey and scratched, and made of ordinary glass.

   The telescope itself was open dowel framework in two sections, one fitting into the other, to make it more transportable. But it was far from perfect. The primitive tripod was small and unsteady, the telescope, 7 feet by 13 inches when set up, was terribly cumbersome, and while X 50 was very good, X 100 and above was indifferent to poor. In fact, for planet work, it was no better than the 1.75 inch refractor. I sold the mirror, and the rest of the woodwork was dismantled to make space.

   Finally, the piece de resistance. A 5.25 inch refractor 5.25 inch lens by H Wideley.  Choice of altazimuth or equatorial mounting.. Rack focusing. Standard eyepieces give X 30, X 100, and X 200. Excluding lenses, the instrument costs about £20 - 25, including the mount with picador spindle. No drive ,as yet, but this will be there some day, and there is provision for it. Eye pieces around £5 - 6. The objective costs £150, and its adjustable cell £30.

 

   Now I will refer to the suppliers, and describe what is possible on various budgets, bearing in mind that our younger members are probably on low incomes.

   For less than £10 it is possible to make a telescope like the 1.75 inch seen here. Buy a 4.5 mm achromatic objective ( focal length 15 to 30 inches).   A simple convex eyepiece, say 0.5 or 1.0 inch focal length, perhaps a concave eyepiece for an upright image, but this is an inferior system. All these are available from H W English. Tubes can be had at Gardiner’s, Old Market. Stick floor tape or carpet [tape?] to the inner sliding tube to give it a snug fit. Also a simple stand.

   For £10 to £50. Similar or somewhat larger objective to the above, but a couple of standard 24.5 mm eyepieces. This budget will allow a really good tripod and picador spindle as used on the 5.25 inch. Similar tubing but notice the inner tube can be partly filled with plastic padding, suitable hollowed out to take the eyepiece, with a wire holder to stop the eyepiece falling out. On this budget one can think of building up to a 6 inch reflector if one grinds the mirror, or a 4 inch if purchased from H W English.

   £50 to £250. With this can be built a satisfactory telescope, as defined by Patrick Moore. A ready made 3 inch refractor or a home made 5.25 inch one. It will also permit the assembly of a really good reflector if the mirror is bought from H Widely. A 10 inch is about £100, an 11.75 inch £150. The carpentry would be done at home. A large picador spindle, or a 4 inch reflector (or 3 inch refractor) and mounting bought from Fullerscopes.

    £250 to £1000. Ready made 6inch and 8.5 inch reflectors from Charles Frank and Fullerscopes, complete with mounts. Also 4inch to 5inch refractors, including mounts, and the cheapest (and nastiest) 6 inch refractor with mount.

    £1000 plus. A 11.75 inch reflector from Fullerscopes is £1200. They can also supply a 6inch refractor and mount for £1100. An American 3.5 inch folded lightpath reflector is £1125, and a 7 inch version (price on application!) imported through Bretmans Ltd. Charles Frank does an excellent 14 inch “Celestion” for £4907. 89. Finally Fullerscopes will take orders for telescopes with up to 1 metre mirrors, but points out that at this level astronomy is one of the more expensive pastimes, and few amateurs would have the financial resources.

 

[There followed  demonstrations  of telescopes and pieces of equipment, some home made displayed at the meeting]

  

    Here there is the single element 7 inch lens, a 1.75 inch refractor and simple stand, and a 5.25 inch with a home made stand.  The stand is good in that it is portable and light but is slightly unsteady. An ideal stand is lighter than this and rock firm.

    The 9.5 inch mirror that I had when I gave the “Improving Your Image” talk has since been sold.

    This is a stand and telescope belonging to John Nash, who will demonstrate the answers to some questions I shall put to him.  The stand, made by Nash, is very steady but brutally heavy, and I’ll ask him to answer any questions on it that you might have.                    

   Now, he puts the 5.25inch telescope into the stand.

   Quinnell  “It would seem as if your head would have to be almost at ground level to view at high angles”.   

   Nash.  Actuates an elevating mechanism to show that this is allowed for.

   Quinnell.”Would you show how Zenith and Altoazimuth works ?”

   Nash demonstrates.

   Quinnell. How about interchanging telescopes? I’ll remove mine from its stand and transfer it to John’s, where it leaves little head room.

   Nash. Raises the shaft.

   Quinnell. Can it be used for Equatorial ?.

   Nash. Yes. Demonstrates by lifting the telescope from the stand, adds the Equatorial and replaces telescope .

   Nash then gives details of how the stand was made, the materials, the costs, and the difficulties encountered.   

 

                                                

                                              End of Session.

 

[ The talk was given some two or three years before Paul and Nash made “Galactica Quinnash”].