[raymo]

O.K., back to basics. Process of elimination; Eliminate the whole imaging
train. Pop a high power EP into the focuser, find a reasonably bright star,
and move it around the the field of view, defocussed a little if necessary, and if it starts out round and remains round, and the amount of coma is the same in all directions, then the focuser is perpendicular to the tube. If the star is elongated, you will know where you have to shim the focuser by the direction of elongation. When the focuser is deemed to be fine, add some weight to the procedure by using your camera [without the coma corrector], and with the R.A. drive running take some snaps, say 10 secs, and if the stars are round, then the focuser's draw tube is not sagging enough to cause a problem. If the stars are not round, then either the draw tube is sagging, or the camera is not perpendicular to the focuser.[as can happen with a worn or very cheap T ring when using a DSLR]. If the
stars are round, put the coma corrector back in place and snap again; if
they are now elongated again, you know the coma corrector is not perpendicular to the light path.
The chromatic effects are coming from the optics used to magnify the star, not the scope. My 24mm Koenig was unusable for projection
use because of its awful CA.
raymo