Cliff PETERSON a écrit :
>
> When I talked to John at Meade he indicated that the primary, secondary and corrector were all position dependant. In looking at mine the corrector is marked. I've never had the primary out so I don't know there. As far as the secondary is concerned on mine it is held in with two pieces of plastic with threads that if over tightened or if heating is just right jump a thread and get loose, then turn. This has happened to mine and I never could find any marks that would indicate how to realign them. This causes me worry but maybe it isn't that critical and I am worried about nothing.
>
> Cliff
>

This is just one of the question I am asking myself. On a correctly
polished set of optics (optically perfect), the only position needed
mostly for spherical optics or very low power optical element (like the
Schmidt corrector) should be the position on the optical axis (both as
far as distance from the primary and offset from this optical axis, i.e.
centering on the optical axis). The only way I can see that the rotation
of the optical part on its axis could be important is that one piece is
astigmatic and you try to correct it with another astigmatic part. To
me, this is weird. That means that with some playing around the
opticians at Meade (and Celestron for that matter) are able to ship more
of the optics which are industrially fabricated, including the ones
which for a reason or another got some astigmatism during fabrication
(bad support ??? ). Any comments by somebody who knows would be
appreciated. Even in a private response (anybody from Meade out there
?).
It would mean that most (hopefully most) telescopes should not worry too
much about secondary rotation, but that for some it would be very
important to be with the right rotation. Or maybe, that for most
telescopes, orientation is crucial, and that for a happy fews, it does
not matter... ;-(
The main mirror, being glued to its support, and fixed in rotation by
the focussing mechanism cannot rotate. And I believe is thick enough
that it is not subject to astigmatism (not like a big thin dobsonian
mirror). Eventhough Meade correctors are thicker than the one on my old
C14, it is still thin enough that it should not take much to put some
astigmatism into it during the polishing stage. I found my lens to be
indexed in rotation by two different marks, and will not try to change
this orientation. Now is the question of the secondary.
If only I had a perfect telescope of the same diameter in order to
autocollimate the one I want to use ;-)...
Alain

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