>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


Not being an optician enough to understand the astigmatism argument you make,
I have some other thoughts about this subject.

The Corrector plate has alignment marks. Shouldn't there be some on the
secondary too if its orientation was important?

Also, presuming that your secondary is centered around the centerline of the
optical path, spinning it would be no different from viewing through the
eyepiece (allowing for a star diagonal changing the path by 90 degrees) at
different position angles oriented on the back of the primary mirror cell?
Same as changing the angle of your star diagonal aspect to the OTA.

In other words, just using an eyepiece, no diagonal, and drawing a clock face
on the back end of the telescope, rotating the secondary 90 degrees would be
no different than aligning your body to the eyepiece from the 4 o'clock angle
compared to the 7 o'clock angle.

Thoughts?


Leroy Guatney
Aurora, Colorado
12" #126548
N 39 39'/W 103 56'
http://home.rmi.net/~lwlg/SCI/astronomy.html

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