It was realised that the design lent itself to a solar telescope particularly well.
Four telescopes were made during the winter of 1993-4.
The optics are 5" Newtonian f.11. The mirror and diagonal are unaluminised, matt ground on the rear surface and painted black to stop rear refections.
For ease of construction no optical adjustments have been built in. The mirror is glued to bubblepack on a plywood disk acting as the mirror cell. The diagonal is stuck onto a 45 deg block on a single cross member in the tube.
Collimation is done at assembly by aligning the mirror on its plywood disk correctly and then fixing the disk with screws in the tube. The diagonal is stuck to its block with "Milliput" and when collimated the milliput is left to harden. This works very well. An f.11 system is very easy to collimate by eye and very tolerant of residual errors. No changes in alignment have occurred since assembly.
For cleaning the diagonal is swivelled on its block to face the top of the tube, and the main mirror is removed on its plywood disk. A wipe with acetone cleans the glass, and the mirror will go back in an identical position. The diagonal is swivelled back into position and aligned by eye.
The mirror was made of 1/2" window glass. Four mirrors of identical focal length were made on one tool. They were polished and figured in turn on a single lap.
The two unaluminised surfaces produced an image of the sun that is very bright but cannot damage the eyes. A double polarising filter fitted to the eyepiece barrel and eyepiece tube enables adjustment of the final image brightness to comfortable levels.
The eyepiece used was salvaged from faulty or damages binoculars, and can be fitted to the telescope in a number of ways as long as it can move to adjust for focus, this only needs to be a push fit in a block of plastic of even wood drilled out to suit the eyepiece.
The mount is a standard Dobsonian design.
Mirrors Window glass cut by glazier to rough disks - £5.00 each. Diagonal Astronomical Suppliers at cost - £10.00 approx each. Tube One 6 metre length of 6" PVC ducting - Plumbing merchants at £3.00 per length of tube (£12.00 for the 6 metre length). Cell, Diagonal holder, Wood for mount, screws etc: very little cost.Total cost per finished telescope £25.00
Aluminised this would make a good first lunar and planetary telescope.