I'm writing this in the hope that it may help someone else with the same frustrating issue .
To cut a long story short , I was having ongoing focusing issues with my 12 inch LX200 . After years of trying to figure it out I used a Farpoint laser collimator to find the true centre of the primary optical axis . Upon doing this I found that my SCT was unable to be properly collimated due to the limited movement of the corrector plate and poor manufacturing .
About 4 or 5 years ago I bought a Meade 12 inch LX200 ACF .
The moment I looked through the scope for the first time I was disappointed . I couldn't seem to get it in proper focus .
It was suggested that I probably needed a good focuser . After installing the moonlite focuser the same thing happened . Couldn't get it into focus .
After trawling through the astronomy forums I found the possible problem . Collimation .
I bought a Hotech laser collimator .
During the collimation process I reached a point where I had to centre the secondary mirror to the primary optical axis . I noticed an immediate problem . I could get it close but not perfect . I couldn't push the corrector plate and secondary mirror far enough in one direction to properly centre the mirror . I assumed this was inexperience and didn't think much of it .
After years of collimating and recollimating with no success , I looked around for advice and found that a field flattener/ reducer might help and bought a Celestron F.63 x flattener/corrector . It didn't work and apparently was never going to work . I gave up on the LX200 and bought a proper astrophotography scope .
Faced with the prospect of having to sell the scope I tried one last time to see what was wrong .
This time I used a Farpoint laser collimator . A single centered laser with one straight beam of light . I unscrewed the adjustment screws on the focuser so the focuser was flush with the primary optical axis barrel . I then bought a piece of corflute and faced the telescope face down on the corflute and traced the telescope diameter and cut it out of the corflute . I then removed the corrector plate and secondary mirror and replaced it with the corflute and turned on the laser . The laser produced a red dot on the corflute which showed the true centre of the primary optical axis .
I burnt a quarter inch hole in the corflute with a soldering iron and covered it with a red circle sticker . I then burnt a 5 mm hole in the sticker .
The exterior plastic adjustment plate of the secondary mirror has been manufactured in a way that you can see the centre point so I poked a small hole in another red sticker and placed it over the centre point of the plate .
Removing the laser , I then sat the telescope on the floor so it was sitting on the focuser with the front of the telescope facing up . I inserted the corrector plate and looked through the corflute to find the centre of the corrector plate . It was around 6mm out and couldn't be adjusted any further . This was the problem I'd been looking for .
This would also mean that the scope was never properly collimated at the factory and never could be without machining of the exterior ring which was preventing the corrector plate from adjusting any further .
I had some special drill bits for grinding metal and ground down the exterior ring . After about 2 hours the secondary mirror was finally centered . I cleaned all the glass and tightened the corrector plate into position . I finished off the collimation procedure with the hotech collimator , found the secondary mirror was now centered and adjusted the secondary mirror to point to the centre of the primary optical axis .
I also bought a Lepus 0.62X Telecompressor to improve the clarity .
I have yet to use the scope due to the terrible weather but will post here when I do .
https://www.californiaskys.com/blog/...-ct-collimator
https://miltonhill.us/Tele/Meade%20L...ube/index.html
https://brazosvalleyastronomyclub.or...pe-repair.html