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Originally Posted by Astro_Bot
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.
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Celestron do the final figuring on the secondary because it is the smallest surface to touch up. But the primary and corrector are made as a pair so they're matched before the secondary is hand figured.
From what I've read I don't believe Meade hands figure anything. They have more
generic parts. So I suspect rotating the secondary or corrector on a meade would have less effect on the system.
Quote:
Originally Posted by Astro_Bot
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.
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I guess different systems are affected differently. Do you have a Meade or Celestron?
My secondary is hand figured. Somehow the rotational position of my corrector is critical also. I don't know if the primary was hand figured to match the corrector's orientation or vice versa. There are registration marks on the primary, etched into the corrector glass and at the back of the secondary. All point to the 3'oclock position facing the scope which is opposite the focuser. There is also a mark to show which side of the corrector faces out. I read that the schmidt profile can be inside or outside the scope. It varies from one scope to the other even in the same range but it doesn't mean that it's ok to flip the glass obviously.