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The process I use for my CDK is first to get the secondary reference marks (two concentric circles on my scope) exactly concentric with the centre of a Tak or cat's eye - easier with the Tak because it has magnification - using only the secondary adjusting screws. I also find that a Howie Glatter laser plus Tublug works well
When that has been achieved, the secondary is collimated.
Then using a defocused star field, I adjust the primary screws only to get the central stars showing exactly concentric donuts, with the extreme corner stars as concentric as possible, with any deviation from concentricity symmetrical about the centre of the fov. This is very critical.
When all that comes together the in-focus image should be optimised across the whole fov.
It is critically important for these designs that the mirror to mirror distance be right on specification. The sweet spot is very tight for the best performance to be attained.
Mark
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