Re: WO/Apogee SCT Crayford focuser differences?
From: Ted Kord (tedkord_at_excite.com)
Date: 07/30/04
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Date: 30 Jul 2004 13:18:06 -0700
"Dennis Woos" <dpwoos@gmavt.net> wrote in message news:<10gknefcog7ui46@corp.supernews.com>...
> > FWIW, I decided against the rear port crayford because of the recent
> > discussions on the sweet spot for SA in an SCT. I'm pretty sure that the
> > focuser on the back end is going to require that the mirror be pushed too
> > far forward for sharpest images, unless one also buys a SAFIX.
>
> One of the biggest advantages of an SCT is the flexibility in positioning
> the focal plane. Now I am reading that this is (largely?) negated by the
> optical design. True, false, overreaction? What gives?
>
> Dennis
It is true that SA varies by the positioning of the primary versus the
secondary in a SCT. How bad it affects performance, I suppose depends
on the overall quality of the optics to begin with. If SA is 1/4 wave
at the sweet spot, then it's only going to be worse at other focus points.
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