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Glen, it would be very easy to answer all those questions if they were spread out a bit.
You can use the coma, inherent in the design of the CC, to achieve good colimation by making it (the coma) symmetrical across the field, in every direction. For that you can use high power eyepiece and adjust the tilt of the mirrors until you get a round doughnut in the center of the field. A round doughnut indicates absence of coma and it is possible to achieve only on the optical axis. If the optical axis is in the center of the field, the colimation is done.
Easily said but a bit harder to do. My approach would be to use a laser to get the secondary pointing at the center of the field through retro reflection and then adjusting the primary to eliminate axial coma.
Mirror separation is a different matter. A small change in separation can move the focal surface (it is not a plane) something like 10x more, depending on secondary magnification. The focal length will not change much but spherical aberration will kick in, on either side of optimum spacing. This is also easy to see with a high power eyepiece. Just look at the size of the central obstruction in the slightly defocused star doughnut, inside and outside of focus. This is an incredibly sensitive test for spherical aberration.
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