Hi Guys,
Let the story begin. I purchased a new Meade 12” F8 LX850 OTA and mounted it up on my EQ8, collimation was excellent. Rather than let sleeping dogs lay, I decided to check it out with my Hotech Advanced Laser Collimator, what the collimator showed was that the secondary holder was offset in the Corrector, "this worried me a tad". Having also an 8” LX200, I thought I would check that, guess what, its secondary holder is slightly offset in the corrector plate.
So I stared scouring the NET to see if this was normal, the first thing I came across was this:
Youtube meade corrector not drilled center
https://www.youtube.com/watch?v=WQyMk914nfM
The guy measured that his center hole in the corrector plate was 1.6mm offset in one direction. " I wouldn't recommend his solution"
I don’t believe that Meade are that sloppy given the technology today, it had to be done on purpose, and you don’t stay in business if you can’t produce a SCT that can compete with the main opposition ( Celestron).
I then found this an article in Cloudy night that suggests that the Secondary does not necessarily have to be centered, "hotly debated".
https://www.cloudynights.com/topic/4...ust-the-donut/
More souring and I came across this little gem:
(“ From: Jim McMillan, Date: Feb 2002
I'd like to respond to your query regarding the secondary mirror by sharing a bit of my experience with it. Like you, I was curious. So, after using my scope for a couple of years (and out of warranty), I fiddled with collimation. I think I got it fairly close, but the focus just didn't want to "snap" into place. I bought the Kendrick SCT collimation laser. What I determined by it was that the optical and mechanical alignment of the OTA wasn't exactly the same.
I also had heard that the secondary hole in the corrector was a bit bigger than the secondary holder. I reasoned that I could move it to try to get better optical/mechanical alignment. So, off came the corrector. To my surprise, I discovered that the secondary mirror was not centered in the holder. Apart it came. The secondary mirror is actually glued to an aluminum disk into which the collimation screws screw. At the center of the aluminum disk is a hole which the secondary pivots on. Still thinking I could improve my optics by getting everything centered, I pried the mirror from the aluminum disk, centered, and reglued it. I used a couple of layers of black electrician's tape around the secondary holder so that it fit snugly - and centered - into the corrector.
I put everything back together and....the astigmatism was so bad, my stars were now diamond-shaped. I could barely make out medium-sized craters on the moon. The next day, I called Meade and (sheepishly) told them what I did. Ollie explained to me that part of the process of setting the optics for each scope when it's manufactured is to align them such that they compensate for the inevitable mechanical misalignment of the OTA. In other words, the fact that my secondary was not centered - both in the corrector and in the holder - was on purpose. Ollie said I'd have to send my scope back and they'd "repair" it for the standard $500 fee - or install new optics for $550.
After many, many hours of trial and error, I was able to restore my optics back to where they were - and maybe even a bit better because I had so much practice at collimation. But, I think it was more a matter of luck than skill.
So, my suggestion regarding fiddling with the secondary is to be very careful what you do - and be very sure to mark it such that you can return it to its original position.”)
Which is a very interesting read indeed, this implies that you have to use a star or artificial star to collimate Meade’s correctly, you can’t use the Hotech, because it assumes mechanically and optically everything is centered, the above implies this is not the case, "intentionally". I might add that the corrector itself is accurately centered, well until the cork spacers finally compresses.
I would be interested hear from anyone who has some experience in this area, or thoughts on the subject.
Cheers
Peter