Experiences with collimating a Ritchey-Chrétien Telescope

[This is just one of many articles in the author’s Astronomy Digest.]

In September 2021 I acquired an 8 inch GSO Ritchey-Chrétien.  These are sold under a wide range of brand names but are all optically identical.  Its previous owner had produced a document on collimating one of these telescopes so I had hoped that it would have been in perfect collimation.  Sadly this was not the case as I found out when I did some first tests.  The stellar images were pretty terrible, but I was able to make a flat frame which pleasingly showed that, using the Micro 4/3  sensor camera I am using, there was virtually no vignetting. 

It is generally regarded thatRitchey-Chrétien telescopes are the trickiest tocollimate and there are many articles and YouTube videos as to how to carrythis out.  The problem is that there doesnot seem any real consensus as to how to do it and what tools are required.   Onepossible reason is the fact that there is known design flaw in the solid tubedesigns in that the focuser assembly is attached to the mirror cell.  This means that if one has to adjust theprimary mirror after having correctly adjusted the secondary – which is thefirst step – the initial secondary alignment will be upset.  I thus believe that, if the primary needs tobe adjusted, one need to take an iterative approach to achieve perfectcollimation.

I found an excellent pdf manual relating to the Orion Richey-Chrétien telescopes which describes how to collimate them.  All these Richey-Chrétien telescopes are made by Guang Sheng Optical (GSO) no matter which of the many brand names they are sold under.  Mine is a First Light Optics, Stellar Lyra, telescope.  The link is:

I essentially followed theseinstructions but carried them a bit further as will be described.

On Nov 2nd 2021 an excellent YouTube video was posted that explains exactly what I had finally found worked.

© Ian Morison