Bostjan/Roy

I had a similar problem several years ago with my 10". Here's what I
learned...

If you call Meade about it, they want you to return the scope for
re-alignment (which is not the same as collimation). They really didn't
want to talk about either what they were going to do to get the secondary
back in position, or what I could do to do the same thing. I figured I had
turned the secondary about 15 degrees at the most, and could most likely get
it back close to where it started.

A talked to a few more people (John Piper might have been one of them), and
finally got a single detail about the process - the rotational position of
the secondary is adjusted within a 5 degree band about an "optimal" point.
I have no idea what test is used, or what the tech is looking for while
rotating the secondary - that is, I have no concrete information on what the
effect of rotating the secondary is on the image quality.

With this information in hand, I decided to do some "qualitative tests". I
removed the corrector/secondary (yes, this is really the only good way to
retighten the loose secondary housing), and removed the secondary baffle,
releasing the secondary from the corrector. A quick inspection showed
several things - 1)the hole in the corrector is significantly larger than
the secondary housing, making it difficult to recenter the assembly, and 2)
there were no alignment marks anywhere on the corrector or secondary housing
the marked the "correct" position. I did find an abrasion on the edge of
the corrector that seemed to be similar to an indentation on the rubber
gasket of the secondary. I marked both of these points on the outside of
the corrector and secondary housing (so I could use them when the scope was
reassembled. I added a few shims to keep the secondary centered in the
corrector, and put everything back together.

I spent several nights going through a
collimate/check-the-image/turn-the-secondary process. Each time I
recollimated, I checked for focus patterns on either side of focus, in focus
star images throughout the field, and for some reason, color artifacts.
That was about all I could think of that would be apparent under viewing
conditions.

The final result was that unless the secondary was off by at least 90
degrees, no significant image changes were apparent. Minor changes,
yes...but none that would say, "wow...that's perfect!" or "Geeze...I broke
it!" I also consider the proper centering of the secondary to be more
critical that minor changes in the rotation position (just a guess, really).
I finally got the allignment back where I was getting the best images.

Well, that's my experience. I'm not assuming that EVERY scope would have
the same sensitivity to these adjustments. I'm sure there are quite a few
on both sides of my single sample. After all, a sample of one is not enough
to make generalizations.

I hope this gives you something to add to your library of information.

Clear Skies and Dark Nights!

John Rostoni
http://tbare.sciastro.net


-----Original Message-----
Sent: 08/22/01 4:55 AM
Subject: Re: [M]: 16"LX200 sec.mirror rotating?!


Bostjan,

I have a 12"LX200 and recently discovered while collimating that it also
rotates.

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