About my telescopes

Here are some images of some of my telescope projects. Click small images to view full-scale.

My 160 mm f/5.7 Dob	My 13.1" f/4.5 Dob	My equatorial platform
The finder of my 13.1"	Collimating the main mirror	The platform with the moving part removed
The 13.1" with cage free	The mirror cell	The platform, motor and tangent drive

The small Dob has a 160 mm mirror (18 mm thick) of very nice quality - I believe British made. I led a group of builders at a local club about 5 years ago, we made five 10" and three 6" Dobs together, this is one. You may notice the folding down tube extension, and the home-made Barlow with an extension tube. The mirror cell is new, for rapid cooling - the details are not shown, but I can attach a vacuum-cleaner and cool the mirror to about 1 deg C from ambient in 10 minutes.

The big Dob is built around a Coulter 13.1" mirror that I bought in 1993. The mechanical assembly has been rebuilt more times than I can remember... But some parts and ideas have survived from the beginning, such as the 3-vane "hacksaw" diagonal. The mirror cell is similar to my brothers' (see the updating page), with 6 point floating support and a double sling for exact positioning. Collimating is done from the top side, while watching the result in the combination sight tube - one image shows the plastic tube with a wrench, tied to one of the truss members when not in use - they are T profiles (except the top ones are square tubes, for no particular reason). The truss can be disassembled, but normally I carry the whole tube assembled in the back seat of my car, ready to set up in seconds. The finder is made from a Russian 10x50 binoc half, with an Amici prism (turned backwards) added (the hooks are for rough aiming!). The mounting is very primitive but rigid - I just clamp the whole assembly to the truss tubes, aim and tighten one knob. The other knob is threaded into the metal lens housing. The diagonal cage is surrounded with a foam camping mattress, held together with Velcro pieces hot-glued. The focuser is taken from a camera objective.

The platform is very lightweight but can take either of the Dobs - the inner Teflon pieces are for the small one (I have a LP record as bearing surface). It is a tangent arm drive, with a 5.25" floppy drive stepper driven from a full-stepping IC SAA1027. The motor shaft drives a radio dial with a rubber edge (from a bicycle handle) to get gearing down. It is unfortunately a bit vibration prone - I hope I can make a microstepping driver some time. The "sector" was taken from a discarded 80 cm dia coffee table. The "south" bearing is a piece of Teflon gliding against a piece of laminate at the end of the wooden bar (not well shown). At the end of travel, the switch under the sector is tripped, automatically reversing the direction and increasing the speed for rewind. It can be run on 8 "D" cells or a 12v gel battery.

Nils Olof, 2001 Feb 2