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Completed in 2014 after 5 years of work, this is my new and rational approach to the instructions for collimating a Newtonian. A desperate search for support followed. It produced Arthur P. Norton BA on p.50 in the 11th to 15th editions of his Star Atlas. He proposed a change to how the secondary mirror was mounted in which the number of adjusters, 7 right on the limit of the human brain anyway to make the correct choice first time could be reduced to 5.
The metal work was performed by Royce, Hoffman and Ed Jones 50 years later at around the millennium but has not been taken up commercially. They either did without the secondary mirror's two lateral adjusters as per Norton or turned them into strict slaves of the central bolt. I accomplish the same with words alone.
Here then are the first 3 stages. C means for Schmidt–Cassegrain optics also. Please use them indoors straight away with a translucent 35mm film canister eyepiece, they are still available.
Stage . Screw both mirrors fully out then back again dead equally to 2 turns off C. Sense the secondary mirror's adjuster bolts' contact and firm them lightly to begin from mechanically square. Then with dead equal turns on the adjusters experiment with centre bolt turns for the best shape that can be achieved without overlap and seeing the primary mirror's retaining clips. Do not fall for trying to make everything look perfect by intuitive suck-it-and-see with any of the adjusters. New Allen keys may be fiddly but they are the most accurate.
Stage . Against a white background or by fitting one of my Cave Collimator caps, align the peep-hole so that a cursor line inscribed on it lines up with the focus tube axis. Then, if the doughnut is to one side, rotate the mirror gingerly to bring it over the focus tube axis. Minimal loosening is key, whichever one you can turn first.
Stage . Tilt the primary mirror to centre the doughnut. Star testing will now tell you it's all done or shows you fine aberrations to correct for achieving the best results C. The Schmidt–Cassegrain secondary can also be done from the front in bright daylight because the aim is to make all the perimeters concentric. Either way, the adjuster to turn is linear with the distortion direction.
Should fine adjustment to the primary mirror on a slightly defocused star of about the 3rd magnitude still not produce reliable symmetry, something inside is loose, you were interrupted or you have a very fast Newtonian that requires stages 5 to 7 of the book. You can buy it from this site and reap the benefits; the 17pp version has diagrams, setting up an EQ mount for observing, telescope optician checked cleaning of mirrors and lenses, dew covers, and the precise scientific one use for the laser collimator. The 65pp extended version tells the full story plus eyepiece matching and upgrading, a bibliography, two narratives, acknowledgements, adjusting a laser collimator, making the Cave Collimator and contains some one-shot images, all this work has given me time for!
"'The Cave Collimator was excellent for my Maksutov–Newtonian telescope and very good for my Rumak–Cassegrain."
– Professor Ian Morison, Jodrell Bank