A 10-inch Split Ring Newtonian Reflector

My thanks to Joe Pearson for the inspiration to build the split-ring Newtonian back in 1975. If you google this design (Joe Pearson 10-inch split-ring telescope), you will find that many other builders have had success in building it. The design of the mount is similar to the original 200-inch Hale reflecting telescope on Mt. Palomar.

The scope breaks into three pieces for portability. The section in my right hand was hinged and could be folded flat. The central split ring rides on a pair of roller-skate wheels.

I built an octagonal box to get the focuser as close to the secondary mirror as possible, in order to use a small flat and minimize the secondary obstruction. This time I used a 1.5-inch flat, with no image cut-off. The curved spider vanes were an attempt to defeat the bright diffraction spikes that are caused by straight vanes. The diffraction spikes are still there but you won't see them because they are spread out over the whole field and less objectionable. The absence of glare makes some detail easier to see on bright planets. I would like to believe that using curved vanes also results in improved contrast as well, but this has been more difficult to prove.

Recently, I replaced the main bearing with a sleeve and rod turned from delrin, a plastic slicker than nylon but not as slick as teflon. A light touch of baby powder makes the perfect lubricant. The scope turns as smoothly as you could want.

In SurfCam, I drew an indexed circle with numbers, projected the circle onto a surface, and machined it with a .020" cutter, all in virtual reality. The program shows the machining on screen in 3-D. You see everything but the flying bits of dust. The file was then posted to the Arrow 500 which did the actual cutting in a sheet of white plastic .080" thick. Not exactly low-tech anymore, but then it's been 16 years since I started building this scope. There is no reason to replace a good scope when you can keep upgrading it.

The declination circles (one on each side of the scope) were drawn and cut as described above.

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