How to Get Your  Large Affordable Telescope Home
 


     They say that with a good unaided human eye it is possible to see 2,500 stars. Yes, you can, but not in this town !  We need equipment.

    I know that older members will already have telescopes, and I’m sure the limitations of these have become apparent, and given the chance most people would like to upgrade.

    Q1. Who here has not got binoculars ?

    Q2. Who has  not got a telescope ?

    Q3. Who has a telescope but would like a better one ? A bit of a catch question, as we all would like to upgrade, but at what cost ?

 

   Patrick Moore has always said buy the biggest and best astronomical telescope you can afford. ‘Cheap and nasty’ 1 inch or 2 inch ones are a waste of money and useless for astronomy, he says ( propping himself up against his 24 inch ).

   I think it is a bit harsh. Buying the best we can afford is what happens in any case, and I feel that even a trashy telescope with plastic optics is better than no telescope at all. Not all of us are as endowed as our Patrick.

 

BINOCULARS. 

These are not for detailed planet work but are excellent for Star Colours, ‘Easy’ Double Stars, Star Clusters, Orion and Andromeda Nebulae, general views of the Milky Way and the Moon. They are also good for terrestrial use, especially bird watching. For astronomy some sort of simple mount, so you can take your hands away, improves them enormously.

   If you are buying binoculars for the first time but are on a strict budget, remember that many second hand shops and car boot sales will have old but serviceable ones. Make sure they are prismatic - these have a distinctive shape and are fairly weighty. Also go for a large objective as possible, say 10 X 50’s rather than 7 X 30’s. Prismatic binoculars are like a pair of small astronomical refractors - the prisms inside turn the image the right way up. They are good light gatherers in that all the light going through them reaches the back of the eye.

   Do not get ‘Gallilean’ binoculars, field glasses or opera glasses, unless they cost less than a pound. They have a concave eyepiece, no prisms, and with a simple objective give an upright image. They are also lightweight, but despite some advantages the optical system invariably means that a lot of light misses the eye pupil altogether, especially if you push up the magnification. This is the last thing an astronomer needs ! {Toy telescopes and binoculars work like this, and never have a magnifying power of more than 5 or 6.).

   Do not bother with ‘Roof Prism’ binoculars, unless you plan to pose with them in the Royal Box at Ascot.  Very well made and of high technology, they are designed to be compact, ie. small. The objective diameter seldom exceeds 30 mm. and they are extremely expensive. 

                                                           

TELESCOPES. 

The forgoing comments also apply to small refracting telescopes. Certain types of bird watchers ‘spotter scopes’ are a single astronomical telescope with prisms to right the image, but the typical ‘entry level’ astronomical telescope is 60 mm. objective, with perhaps 3 eyepieces.

   This falls short of Patrick Moore’s minimum of 3 inches ( 76mm ) for a refractor but will give good views of the Moon, some detail of Mars, Jupiter and Saturn, and ignoring the upside down image is great for terrestrial use if mounted.

   Reflecting telescopes are the workhorses of the amateur and professional astronomer, despite the extra mirror ( ‘flat’ ) required, or silvered spot on a clear glass plate in some designs. Main mirrors of good light collecting size are far cheaper than equal sized compound lenses, and they also avoid chromatic aberration.

   If you decide to grind a large mirror you will need much time and patience, two circular blanks, grinding powder (wet), a workshop / garage, and old clothes. In the late 70’s and 80’s it seemed that everyone in the B.A.S. was acquiring or building telescopes or mirrors of ever increasing complexity. I remember one lad ( Adrian Wright ) who went to the States and came back with a 16 (or 18?) inch mirror. Everyone was truly focused on large mirrors. But beware - a large telescope coming into the house is just like a baby - a totally life changing event. The bigger it is the more demanding, and like a baby the mirror is not the culmination of the project but just the start.

   A tube has to be made or found that is big enough for not just the mirror but also its cell and cover. The cell needs screw adjustments so the mirror can be straightened in situ. The flat has to be fitted and this also needs to be adjustable to line up with the main mirror. Then a rack mount / camera mount needs to be attached.

   Then, as Patrick Moore put it so simply in one of his books, “all astronomical telescopes need mounting”. Very true, but what a can of worms that opens up for the inexperienced telescope builder.

   Tripods, ideally heavy surveyors type, are fine for smallish telescopes. The dreaded pillar and claw which often came with older telescopes is notoriously unsteady.

   Anything much bigger than a 6 inch is usually a “set in the ground” job - a concrete base or pillar -  to mount equatorially.

   There are three mounting systems

   1. The English Fork.  

   The two prongs of the rotatable fork holding the telescope point to the Pole, fifty-one and a half degrees due North. When the telescope is on the fork, and the fork is on the end of a spindle, it produces an enormous amount of overhung weight and strain on the spindle. Failand and Mount Palomar are on forks, but the base of the fork ( a triple horseshoe on Palomar ), is also on wheels, which take the strain, and cut out vibration when driven, provided it is sufficiently well engineered.

    2.   The German Mount.

      In this the telescope ( often a large refractor ) is on one side of a spindle with a matching counterweight on the opposite side. The whole apparatus is mounted on a concrete pillar. This raises the telescope higher, important for a refractor otherwise you will be rolling around on the floor to get your eye under it. It is somewhat simpler than the fork, but the height of the telescope means you need a dome to accommodate it. 

3. The Yoke Mount.

  This has two spindles and the ‘fork’ is extended into a long open-sided box, supported equatorially top and bottom. While this is very steady, and fairly simple, it also needs a lot of headroom, therefore a dome. There is also a blind spot around the Polar area of the sky because the top of the spindle blocks the telescope’s view in that direction. 

    Having got your telescope mounted, the next project is building the observatory. A dome is best but hardest to build. A roll back or ‘run off’ roof is much easier to build , but might need to be fairly high.

    Still fancy a large telescope ?

    Don’t be put off. If you look at many of the suppliers I have listed ( on separate sheets ), and are advertised in astronomy magazines you will see large diameter but squat, folded light path American made telescopes. These come with setting circles, adjustable equatorial settings, motor drives, camera attachments, all the bells and whistles! Even 10 inch, 12 or 14 inch versions are available - and sort of portable! They are hassle free, fast , but expensive options.

    How much can you afford ? Well how badly do you want it ? I could save and save - the longer you save the bigger the telescope. But that’s no good. After all Mars is as close as it ever gets, so why not put in for another credit card and load the cost onto that ? We’ll need the telescope any way to see where the repayments are coming from !

    To be serious though, and at the risk of stating the obvious, of the several ways of getting a telescope the cheapest and most time consuming is the d.i.y. route and either making or buying the main mirror.. Making a refractor objective of any size is a specialist job if it is to be a colour corrected achromat. A single element objective is only optically satisfactory if it is of extremely long focal length - say f 30 to 50 - and then you will have a 20 foot telescope to mount and handle for a 6 inch objective.

    Less fraught, much quicker, and fairly inexpensive is a second hand telescope, as advertised in magazines. As ever, buyer beware. Firstly, you will need the time, transport and enthusiasm to visit potential sellers, and know what to look for. If there are any missing parts you should be able to get it very cheaply. Less chancy is a dealer in used optics / telescopes. To remain in business all his equipment must be serviceable and accurately described. Some phoning round might be a rewarding source of kit.

    Finally - buying new. “How much was that ? You could have taken us all to Benidorm for a month for that !”  “Ah, but I can take you over 99% of the way to Andromeda with this !”

    Ideally the buyer should visit the supplier and be able to not only see but look through the telescope at some distant object. Not all that easy in a high street with a very restricted horizon, but much better than taking it back later with some unforseen problem. Modern telescopes are of very good quality, but there is always the remote possibility of damage in transit. If you are sending away for it pay by credit card, not debit card, to cover re-imbursement if it fails to arrive.

    Sharing a ready made telescope is admirable - after all, the Society shares the use of Failand. However I would not recommend sharing the building, from scratch, of a large telescope and observatory. It is so simple in theory, so logical and hard to find reasons for not doing it. Two people, double the resources, twice the telescope in half the time. But the reality is different. Each partner wants more from it and puts pressure and responsibility on the other(s) to provide it.

    I’ve been there myself. It took years of Sundays, and the telescope was fine for observation and photographing the Moon and planets, but the drive could never achieve the steadiness needed for photos requiring minutes of exposure, as for nebulae and other deep sky objects. Slow wobbles cannot be detected visually, so when the film was processed stars always resembled flying seagulls, and other objects appeared smeared.

    A few meetings back I obtained a used 6.5 inch mirror from a member. It was optically good, and had its own cell and cover, so the next thing was to get some tubing at least 7 inches inside diameter, to accommodate cell and cover as well as the mirror.

    By way of Yellow Pages I contacted some builders merchants, but only ‘The Pipeline Centre’ at Brislington had offcuts of plastic pipe up to a foot across, and they had 7.5 inch piping. I was lucky. This kind of pipe normally costs £10 per foot. But I got a 5.5 foot length, and a ride home with it in a lorry for only £15. It was extremely heavy, so I could never have got it onto a bus.

    Because of the weight and the need to reach in to remove the mirror cover I am using only short lengths of this tube, along with steel stretches to make a skeleton tube (show drawing). A piece of  some 3 - 4 foot of this piping will be left over, which may be available to anyone here, assuming I don’t make a pillar and claw mount out of it! The steel pieces are  modern slotted shelving brackets, found in a skip 3 years ago, and I’ve been searching for a use for them ever since.   

    (series of slides).

 
   During the last week I made a list of suppliers with their addresses and phone numbers, which members can have. The first page, from the Internet, comprises 17 of the allegedly best suppliers in the UK. You will notice there is no address south west of Oxford. Is it the cloudy West country skies putting them off, or have we a reputation for meanness ?

    Next in the ‘local suppliers’ list are a couple of Bristol Shops which I visited.

    ‘Ace Optics’ at Kingswood is basically a camera and film shop, but has several telescopes in the window and more inside. If you express an interest in astronomy you may get into the anteroom. They had 12 to 15 telescopes / mounts, but you have to ask about prices. Standard Plossl 1.25 inch eyepieces £40 each, or choose 4 from a range of 7 for £140. Or, in the back room, a 3 mm eyepiece - like a stretched cricket ball, and just as heavy - £250. My favourite item was the ‘Russian Border Guard’ binoculars, 15 X 100 mm, on a heavy duty tripod, £1700 ! Well worth a visit.

    ‘London Camera Exchange’ had a smaller range of telescopes and could supply eyepieces for £20-25 if ordered. I did fall for an impulse buy. I had no eyepieces for my 6.5 inch, and could have got them there, but saw this baby telescope, complete with all the accessories and two eyepieces for £39. Buy two eyepieces this way and get a free telescope!

    Of course Patrick Moore would not be seen dead with such a small, 2 inch, item. Looking at Mars with it there was a reasonable disc but no real detail, but if I opened the window next time it might help.

     Finally there are ‘old suppliers’, a list put together from catalogues going back to the 70’s and 80’s. Some may have ceased trading or moved, but are worth trying, since a number can handle specialist work, or deal in second hand or ex military optics and accessories.

     Have a look at the 2 inch telescope, and I invite any questions.

                                                Thank You.