Thanks for that demo. I agree that corrector centring is vital for image quality. That's some really useful evidence of the principle.
Quote:
Originally Posted by multiweb
Rotational shift of the corrector would cause the telescope to not focus at all. Even a 5 degree rotational offset will make the SCT unusable.
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I'm not sure about the rotational alignment, though. Isn't the corrector (and primary and secondary for that matter) symmetric? I've read reports that say they are, and a few others that claim the corrector and secondary are hand-touched for defects in the primary, but I find it hard to believe, in a mass-produced SCTs like Celestron and Meade, that there's hand-touched
anything given the prices.
I've fiddled with corrector centring in my SCT, and visually noticed a difference (soft images and, when examined closely, lop-sided astigmatism - at least that's what I've been calling it) but I couldn't see any difference with respect to rotational alignment rotating the corrector (with secondary) through 90 deg or secondary (alone) through 120 deg.