Please note: As of June 2005 this telescope as been dismantled and replaced with a 14'' LX200 after over 20 years of brilliant unrivalled service! However the scope has now made a comeback as an 18'' Dobsonian!! Click here for details

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The WYAS Telescope

In 1976 our society decided on a project to build an observatory and a 16" telescope. It was not just a project, more a survival plan, as we had the threat of eviction from our meeting place, an old barn near the castle in Pontefract, hanging over us at the time. Under such circumstances we convinced ourselves we could complete the task within a year. After all, how could anything go wrong?

When the tasks were handed out, mine was to design and build the telescope. I fell for this because I foolishly bragged about the 6" Newtonian I'd previously built.

I'd seen other amateur instruments and felt the traditional Newtonian to be very inconvenient above 10" dia., where the eyepiece had to be accessed by ladder or gantry, particularly in our case, where the dome was to entered through a trapdoor in the floor. No thought was given to making the dome, we could all do that when the time was right.

As we had no money (all our meagre funds being reserved for the observatory building itself) the telescope had to be built for nothing!

I was therefore forced to approach the task by designing to suit available materials, rather than looking for materials to meet a chosen design. As I was employed by a tractor manufacturer at the time, I decided on a German Equatorial mount, based on 2 tractor back axle assemblies as the axes, in the hope I could get them free. In the event I had to buy the pieces as scrap items, choosing carefully, pieces that had been scrapped for things that wouldn’t affect our intended use for them. The axle assemblies have 2' long x 3" dia hardened steel shafts flanged to 9" dia at one end (to carry the tractor rear wheel). They run in 4" dia taper roller bearings housed in 6" square x 18" long cast iron housings.

The machining was done for me by the company's apprentice school under a cunning subterfuge. As new bearings don't run as smoothly as used ones, British Timken helped out by donating a full set of new ones that had been run in for 200 hours on their test beds.

The general configuration of the telescope is as follows. The polar axis housing is bolted to a concrete wedge reinforced with granite road chippings and chicken wire mesh. It was cast for us by a friend in the construction business in a mould made by our oldest member, Ralph Emmerson, a retired cabinetmaker. More of him later on the Dome. Ralph tragically died 2 weeks before Patrick Moore officiated at the observatory's inauguration.

The wedge in turn sits on 4 spherically faced jacks (erstwhile tractor parts) to allow for some adjustment in both altitude and azimuth.

To get the wedge facing south we had to carefully lower it (it weighs about 120lb) onto the jacks with the securing bolts through the jacks and the holes in the wedge's flange, then sight it in using sunlight. This was done one day precisely at noon plus the Equation of Time, using a 4ft length of timber with a nail in it at one end to provide the shadow, which was cast onto a piece of wood nailed to the other end. Real high-tech. stuff!

3/8" Rawl-bolts hold the wedge down onto the top of the pier, which is made of sections of 2' 6” Dia., rubble and concrete filled, concrete sewage pipe (donated rejects, unused thankfully) with its own foundation slab of 4' x 4' x 2' thick concrete, buried 3' below the floor of the meeting room below the dome. The concrete for this and the meeting room floor came from "passing cement mixer lorries" that had a returned load of surplus or incorrect mix. The drivers were happy to find somewhere to shoot their unwanted load. Partly pre-arranged of course, but much cheaper that paying full price.

The pier passes through the meeting room's floor and ceiling without touching them, gasketted with sand and foam rubber respectively.

Back up to the telescope proper. The declination shaft's housing is bolted to the face of the polar shaft's flange (where the tractor wheel would fit), and on the face of the Dec. shaft's flange is bolted a deeply ribbed welded steel cradle. This carries the skeletal tube which consists of 6 off 7' long x 1¼” steel tubes (donated stock, they were intended to become Mini exhaust pipes, but were misdirected), held in 4 off 23" dia steel rings. The tubes are secured in the rings by grub screws and industrial adhesive. The 2 middle rings locate in channels in the curved end sections of the steel cradle and are retained there by 1/8" dia stainless steel wire cable (formerly sailing dingy halyards), running in a groove in the rings' outside diameter, and tightened into place by bicycle front wheel spindles and hand nuts. Slackening the cables allows the tube to be rotated to position the eyepiece for convenience. Similarly, the focusser sitting on its aluminium plate can be clamped between any two adjacent tubes.

Though they did work when first made, in practice we have never needed to use either method, as the Nasmyth optical system brings the focus conveniently opposite the Dec. axis where it can be used without aids by all but the smallest visitors, which, after all, was a major reason for choosing the system.

The tube's rings are made from 2" wide x 3/8" thick steel strip rolled into a ring, welded, turned, grooved and drilled for lightness and reamed for the 6 tubes. All produced free by the apprentices of a friendly machine shop.

The optical system was produced for us by Henry Wildey, a very experienced and famed mirror maker. He charged us £500 for the 3 items that constituted our Nasmyth optical train, an 18" parabolic primary, an hyperbolic secondary and a 2" minor dia flat. The primary was made parabolic in case we wished to convert to a Newtonian later (we bought a suitable secondary for that purpose some years later and made a second focusser plate. So now we have both capabilities, though we generally use the Nasmith system's convenience and safety, particularly for visitors). The increase from the planned 16" to 18" came about because Henry Wildey indicated that he just happened to have an 18” plate glass blank about his person, and would have no more difficulty in producing an 18" primary than a 16" one nor would it cost much more. The basic design was unaffected as the axes could easily handle the increased spread and weight.

The primary is 1½” thick rather than the accepted 3" (1:6 ratio). But we most certainly couldn’t have produced the telescope had we followed convention, as we were being advised to do from all quarters at the time. Convention required that zero or low-expansion glasses be used, at a thickness to diameter ratio of 1:6, so as to reduce the likelihood of the figure varying under the effect of changing temperature. The conventional wisdom was to be departed from at your peril in those days. Earlier discussions with Henry Wildey had however, supported my belief that conventional wisdom could be discarded in favour of a “quick cooling” principal. Failure would support all the “I told you so’s” and leave us without a useable instrument, and in fear of trying again, except along conventional lines, and we wouldn’t be able to afford that. My view was that rather than prevent the figure changing, let it change but get it back quickly, as the mirror's figure is lost only while it’s temperature is actually changing. When ambient is attained, the original figure is regained. A thin mirror held in a multi-point open cell in a skeletal tube allowing air to circulate freely, would pass through the temperature change between day and night much more quickly, and attain night ambient in time to be usable within a short time after opening the dome. The dome is lined with polystyrene foam and painted a sun-reflecting white to help reduce the primary's temperature amplitude.

Following this gamble, allowed us to use the very much cheaper plate glass and keep the cost within sight. Pyrex or Zerodur were priced really out of sight for us. This and the choice of a Nasmith optical system were the pivotal decisions in the design, both very un-conventional at the time, but happily both have proved successful.

The tube as mentioned, is skeletal to help the optical members get to ambient quickly. The mirror cell is an 18 point open design. All its various plates and levers were hand cut and bent to shape from 1mm steel sheet. All its pivots are "ball and socket" joints, the balls of which are valve tappet adjusting screws from tractor engines (where else) and the sockets are the female part of large brass press studs found on many denim jackets and windcheaters (perhaps this was taking "design to suit available materials" a bit far). Each leg of the mount's 3-legged main frame (made from stiffened 2" square steel GPO electrical trunking) ends in a 5/8" dia eyebolt (haybaler plunger adjusters) locknutted into the bottom tube ring for collimation. Both the spiders have 4 triangulated legs, each made from 2 pieces of 1" wide by 1/16" thick steel strip, supporting central telescoping tube arrangements that carry the secondary and tertiary, again all hand made. 4 because of the likelihood of generating 6 diffraction spikes if 3 legs were used. 2 legs would not be stiff enough. A telescoping facility was built into the secondary spider to allow it to be used for additional focussing capacity using rods and Meccano gears.

At this point my confidence gave out and I made out a shopping list. In the late 70's there were very few reliable places in England that supplied things astronomical. Though it wasn't that long ago in years, it certainly was in terms of product availability. The list consisted of a steel worm and aluminium wheel with a synchronous motor and gearbox for the Polar axis, a pair of aluminium scribed setting circles, a 10 x 50 finder and a 2" focuser, bringing the total cost, with the optical train to £755. The Dec drive was a 10” tangential drive powered by a hand screw and was made by a member’s father.

The telescope was designed and built in the late 70's and opened in 1983 (it sat in my garage 2 years waiting for the observatory to be completed), but it has not been allowed to get out of date. Succeeding Observatory Directors have improved and updated it and its controls as the years have passed by. We have been able to obtain a good set of eyepieces, a frequency controller for the polar drive, a Dec drive unit, a computerised setting circle system based on a BBC computer, and a variety of other bits and pieces to aid observing.

  Into the new millennium, and we are in the throes of another update. We have had the optical train refurbished by Jon Owen, the celebrated mirror maker in Halifax.

The old Beeb controlled digital setting circles have gone and been replaced by a PC based system from JMI run from a laptop through TheSky planetarium software.

Local householders have been adding security lights to their homes in greater numbers, reducing contrast, so we have clothed the tube with black lining cloth, not for mourning of course. And fitted a tertiary baffle lined with black velvet. The dome’s interior is also painted black. The velvet came as a handout from the place where the Queen’s wedding dress cloth came from. It, the baffle lining not the Queen’s dress, is actually off-cuts of the material used by Kodak for the mouths of their film cassettes.

The observatory and the telescope get an annual summer clean up and repaint. Finding clear nights is a problem one gets philosophical about, but that's mostly done in the adjoining bar.