A Homemade Refracting Telescope
This three-inch refractor was built entirely from gray urethane tubing supplied by Plastruct, a company that provides plastic tubing for model makers. The mount is the popular CG-3 mount available from Celestron, Orion, and a number of other sources (see links page). The legs are alder wood from a lumberyard. The end caps were made on a vacuum-form machine. The counterweight was machined from 3-inch diameter brass rod.
This scope was designed to be as lightweight as possible to insure tracking accuracy on a small mount like the CG-3. The objective cell and internal baffles are all made from abs plastic. There is no rack and pinion focusing mechanism. To save weight, focusing is accomplished by gently turning the eyepiece tube in and out. In practise, I have found that this works quite well.
The finder mount was machined entirely from a block of gray abs plastic and designed to slide on and off with moderate friction. The 8 x 50 finder itself was made from a couple of pieces of Plastruct® tubing (see links page). The eyepiece and objective were salvaged from a pair of binoculars that had been damaged. All tension screws are nylon.
Since I had a programmable 3-axis milling machine available and a cad program that would allow me to project letters onto a surface of any shape, I decided to cut this decorative notation."Ultralight Optics" is a name that I made up to describe the main characteristic of the scope. This view also shows how the finder slides into the holder.
A lathe is an invaluable tool for a telescope maker. This solar filter uses an interior spacer to make it fit precisely over the end of the tube. This view also shows the plastic cell holding the objective lens. Good used lathes can be bought for less than $400.00, and will pay for themselves many times over when used to construct astronomical accessories.