Hi Robin, how significantly are the colour channels being corrected/shifted? Typically I get anywhere from 0 to +/- 1 up to 3 corrections. I'd expect the degree of correction might depend on the amount of chromatic aberation through the individual system your using. I use a pretty low quality barlow that probably contributes to some of this. Wondered if the corrector plate on a SCT might introduce some small amount compared with the no glass Dall Kirkham cassegrain I've been using? Certainly when I've tried imaging using an acro refractor the channels split apart like their own mini-rainbow.
cheers,