I have a LX90-10" ACF bought about five years ago. I have been able to collimate the OTA using Thierry Legault's collimation advice here:-
http://www.astrophoto.fr/collim.html
This amounts to a star based collimation, which requires good seeing at the time of collimation, and a scope that has settled down to ambient temperature. When done properly, the results are fairly acceptable.
I believe the collimation cannot be refined enough to compensate for incipient mirror shift. I have a crayford focuser as the main focusing device, and leave the mirror focus alone, but this must of necessity be a temporary solution. The LX200 OTA has a mirror lock which would at least allow for one less degree of freedom of the optical train, but the LX90 does not have this feature, and primary mirror shift is going to degrade collimation by significant amounts any time it occurs.
I bought a Glatter collimator with the concentric circle laser pattern, and was rather disturbed to see that it indicated the primary was **in no way** aligned with the secondary - eyepiece holder path, despite a reasonable star-tested collimation. When I moved the collimation to make the concentric circles properly aligned, the view through the scope was completely unacceptable.
Further reading convinced me that this state of affairs is endemic to modern SCTs, and true collimation is going to be a compendium of approximations rather than a path to a real goal. A bit like politics as practiced in Australia - many adjustments to get to the same rough end.
For my main purpose (occultation observing) this does not present a problem. A light curve is not significantly altered by slight mis-collimation, but the ease of setup and good pointing accuracy of the Meade SCTs is of real utility in finding dim, unremarkable stars that asteroids will pass in front of.
Views of planets and other small objects will however certainly be diminished by less than perfect collimation, and if an observer wishes to set sights on this very worthy goal, they could do much worse than take a page from Anthony Wesley's equipment setup (Mr. Wesley goes by the handle "bird" on these pages). He uses a very big (16") Newtonian and takes great care to remove air currents due to temperature fluctuations. The secondary obstruction is around 25% for a Newt, versus near 35 - 40% for a moderate SCT. This reduction in obstruction can only improve contrast. As well, collimation of a Newt is a much more confident path than the fudging of an SCT.
For myself, I cannot afford a Big Newt, and for my main purpose, the LX90-10" ACF does me well. I do feel the pain of those who would like to seem more clearly with their scope, but my suspicion is that the SCT as currently made is not able to be properly collimated to the degree that a purist would desire.
As always, your opinion may not coincide with mine, and you are welcome to hold differing views.
Regards,
Tony Barry
WSAAG