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Collimating a Newtonian - a link sent to us

Posted by Mid-Cheshire Astronomical Group on February 4, 2018 at 6:10 PM

A transcript here.


or, Making you mighty in collimation by myself, Peter Clark, a retired Master Mariner and amateur astronomer, living near South Cave in rural East Yorkshire, England. 'With California like skies, says renowned artist David Hockney.


It is in fact the script for the You Tube movie accessed via 'Collimating a Newtonian NHBS' then clicking on the arrow.

It began in 2006 as a stumble when the black plastic front cap of my 8” Wise-Newtonian cracked, so I made a new one in translucent fibre glass. Three years later when starting yet another session of indoor collimation I forgot to take it off.


'Eureka' was the response to the clear uninterrupted view through a peephole eyepiece without moving the telescope, such that the indoor stages could now be performed more easily. Take a look with a Cave Collimator off then with it on. Without moving the telescope, any distractions are dispersed as shown on the book's front cover. I became successful enough at f 4.4, but not with the f 3 spherical primary mirror of the 8”. This was because by being wrong, no instructions for Newtonian secondary mirrors could scale up to f 3.


It took 5 years from 2009 to produce the correct methods. These have proved to work perfectly and with full relevance to slower ones. Then hunting for support or else produced four suspects with the wherewithal to escape from what everyone including myself had all been sucked into. What a relief! In order to prevent intuitive and unscientific adjustments these like minds had removed two of the secondary mirror's adjusters or changed their use:-


Norton's Star Atlas 11th-16th editions, p.50, says, 'Rather than having 3 adjuster bolts, a better arrangement for the mounting of the secondary mirror is a single angle adjusting screw and a central bolt for rotating and clamping it.' Arthur P. Norton B.A. was far too polite about it and died in 1955.

Conradhoffman.com/secondary greatly improved 'The dastardly thing' in c. 2000, by his design that retains three bolts, two of which are strict followers of the central bolt.


In 2007 R.F.(Bob) Royce, in his Ultimate Newtonian web pages, 'How many times have you struggled with conventional 3 bolts holder and endured much frustration and bad language...the basic adjustment design process is INCORRECT and ILLOGICAL and does not follow right angle relationships.' The instructions in my book do exactly that.


Oct. 2010. Sky & Telescope page 70 shows Ed Jones's Tracking Travelscope, using Norton's arrangement of the secondary mirror.

From 2012 my instructions began to compliment their metalwork and start being CORRECT by starting from mechanically square, the two maverick adjusters having become strict followers of the central bolt.

The book's 3rd edition of 3.2014 has 'Rotation is superior to slewing' with these bolts, and by experience to 2009 the laser collimator had become regarded as the most unwelcome of tools.

Then in 2015 a 4th edition was suddenly needed. The Laser Collimator had become the answer to me losing the black art of sometimes getting the secondary's vertical tilt angle spot on, angels in bed saying, 'Ignore the maker's advice and try it for this purpose only.'

So Newtonian secondary mirrors need just a central bolt for travel along the main axis to position it under the focusing tube and rotate it into alignment with the eyepiece and primary mirror. Also an off centre bolt for setting the vertical angle and clamping everything. The usual two lateral bolts fitted allow unscientific fiddling. It is bad enough having one increasingly black art adjustment because of the 90° reflection angle as the f ratio reduces, without having three hit or miss bolts to be played with just because they are there. Nothing more complicated than a one port laser collimator for the secondary's vertical tilt only is well worth having.

And now to make you mighty in collimation with instructions that scale up to the task in just 4 or 6 pages. They will get it done without you being whipped by ghosts into the usual maybes and sometimes of the just about adequate and sadly wrong universal methods I have been blessed with the time to sort out that manufacturers just do not have.

Categories: Techniques

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