You've seen the situation at star parties when a pair of binoculars on a conventional tripod is trained on a particular object that several people want to look at. They always seem to have difficulty in getting themselves into a position where they can peer through the eyepieces without nudging it off aim.

What we needed was a stand to carry a pair of binoculars or a small telescope to accommodate such accidental nudges, and allow it to be moved about to suit various viewers' heights, without losing the object originally trained on.

The drawback of those offered for sale in the pages of S&T, is that they "pantograph" only in the vertical plane. So moving up and down is OK, but moving it side to side loses the object. To get away from the ever-present sideways nudging, I worked on a two parallelogram design, with one pin-jointed vertically, and the other horizontally.

The added torsional loads imposed by having it move sideways meant the parallelograms had to be made wider (the advertised ones appear to be no wider than half an inch) but still as light as possible. To get a reasonable pantographic movement up and down as well as side to side I decided the long sides of each parallelogram were to be 18". To cater for the torsional loads the arms needed to be about 2" wide. The parallelograms consist of cast aluminium blocks for the short sides (2" long) and steel tubes for the long sides (18" long) ie. 18” x 2” parallelograms. The castings also acting as pivoting nodes.

The long sides are pairs of 15mm Dia. steel tubes ie. 4 tubes for each parallelogram, two pairs 2" apart. The base or first node, has pin-joints that move up and down only. The middle node carries pin-joints that move up and down on the face that faces the base node, but joints that move side to side, on its outer face. The end node of course, has pins rotating side to side only. This node carries the binoculars on a pan and tilt head. Each end of each long tube (4 to a parallelogram) is epoxied into the "upright" of a 15mm copper household plumbing "T"-piece. There are 8 such assemblies. To ensure all 8 tubes were exactly the same length, critical for good performance, the assemblies were made all together in a jig on a flat table.

A long length of tubing was slipped through the "cross-bar" of the T-pieces at one end of the tubes and another length through the "cross-bar" of the T-pieces of the other end. These lengths of tubing, were positioned on V-blocks at a set distance apart. Corner to corner dimensions were checked carefully too. The whole lot was then dis-assembled, cleaned, abraded for key, the epoxy was mixed and applied, and all the pieces were put together again. Quite a pain when my wife came in to see what I was doing on her kitchen table. When the long sides had cured it was time for the final assembly. The short sides/nodes, the aluminium castings, had been machined on a jig borer in a friendly tool room to ensure the centre distance of the pairs of holes, 17mm Dia, were all the same. 16 off 15mm I/D x 17mm O/D PTFE bushes had been pressed into the holes in the castings.

8 off short lengths of the same size tubing were made up, 6 off at 4" and 2 more, 6" long. These were the "pins" of the pin-joints. The longer ones were to be used in the base node to carry the balance arms which extend the other side of the pier from the rest of the mount, and carry the balance weights, just like those in the ads. 16 off steel washers were made with bores to fit tightly on the "pins". The balance weights are short lengths of 2" Dia steel bar, bored 16mm Dia. through, and secured to the balance extensions arms with 1/4" bolts at a position where the instrument is balanced. The whole is secured, with a 1/2" bolt through the base node, to the top of one of the telescope piers outside the observatory.

The stand can carry a telescope or binoculars up to 5lb in weight and can pan across its swept area without losing the object trained on, so passing the binoculars from one to another sideways or up and down is easy. If it has a drawback it's in putting it away, it must be carried vertically, as any uncontrolled movement can nip fingers between the long sides. For which trait it is known as the Finger-Trapper.

Brian Joynes.