Don't panic, you have a relatively straightforward mechanical axis misalignment that should be easily fixable.
Short answer, ditch the corrector shims, align the corrector with secondary MIRROR, not the secondary housing, to the baffle tube with the Cheshire, and see if that gets you aligned.
Do all preliminary collimation in daytime using Casady, link below. This preliminary collimation can be very tough at night IMHO, while final tuning is not too bad at night. So I ALWAYS start with a Casady daytime (pre)collimation.
That said, I use artificial stars in daytime, too, for near-final collimation, finishing at night. A small ball bearing at 50+ meters works, as does the Hubble 5 star light http://hubbleoptics....cial-stars.html
Your issue should be curable. My misassembled M8 was far far worse, and now is only .5mm out, with the secondary 6-7mm off-center in the cell but almost in line with the primary and baffle tube. And that is an extreme example. It WORKS now where it was trash before.
Your scope sounds as if it has been apart in the past, but the possibility of factory misassembly exists, as mentioned by Starman. Worst case,on a Celestron you may be able to loosen the rear cell and shift it to center the baffle tube at it's end, but that is only a last resort. I would avoid it!
Although it sounds silly, which 3 o'clock?
All the markings go to the 3 o'clock viewed from the corrector end, that is, the e o'clock on the side opposite the focuser knob.
If it were a Meade with no hand figuring, where spin alignment appears to only use eccentric positioning of the secondary to get the secondary mechanically centered with the baffle tube axis, I would devote all efforts to the secondary-baffle tube mechanical alignment. With yours, start with checking that you used the correct reference point
If you used the wrong reference point, fix it and you very possibly will be done, check with Cheshire.
Prep your knowledge base and reread my long posts.
to see how to do a daytime setup. It works amazingly well.
Read the Wilmslow C14 pages http://www.wilmslowa..._alignment.html
for a inexpensive final mechanical-optical test setup. But you are not ready to implement it until you use the Cheshire to get most of it done. It also lays out the possible issues.
DON'T mess with the primary! Do everything else, but if you damage the primary it's game over.
Reread the Casady tabletop method, it DOES work at getting a near perfect initial collimation. AFTER you get your axis alignments fixed.
Keep using it along with the Cheshire to gauge progress.
If your sky or artificial star in focus, collimation still has the Casady reflected 'circles' nonconcentric in a post-collimation check, some minor mechanical alignment issues might remain. If slight, don't go nuts trying to cure them.
Time to adjust!
Remove the factory corrector shims as you are obviously out of the baffle tube defined mechanical (and hopefully primary-optical center). Celestron, with Fastar on, went to a true perforation/corrector centering, unshimmed on rubber, or, now, grub screw located at the edges. Cork spacers worked well only on baffle tubes correctly centered. That's one reason for soft images, as well as lost spin alignments, and simple misassembly.
You may need to glue or otherwise secure the semicircular paper corrector cushions to the front cell lip, only, if the factory glue failed and they keep falling into the tube. You will be shifting the c. plate a few times.
Ideally I center the corrector perforation separately from the secondary, but you may find this hard to do, and it may require a means of visualizing the geometric center of the secondary. Therefore it is likely most practical to do the centering with only the sec. housing assembled to the corrector.
Use the Cheshire or (much more accurate, but none currently in production, why?) a concontric circle holographjc projection laser collimator to make your centering adjustments.
You have two freedoms of movement in the corrector secondary assembly; the corrector within the cell (5+mm), and the secondary housing within the corrector (about 1mm). Use them to get the secondary mirror centered, the goal. With the Cheshire method, I'd adjust them while the corrector and secondary are assembled. That's what I cover below.
If working alone, you may be forced to use a diagonal to work with the tube near vertical let gravity hold the corrector in place as you work,not ideal but...
Or adjust the retainer screws to let a slight amount of friction let you shift the plate but still hold it in place. Tricky though.
The cheshire method kind of forces these choices on you.
I compared my laser method to the Cheshire, and the laser was easier to get perfect, but the Chesire did work. Absolute concentricity is hard to judge though.
Shift the corrector-secondary together until you have the two thin bright outer circular lines in your photo concentric to the bright secondary circle. And the baffle tube.
As to the pattern in the very centermost reflection in your photo, I could not figure how to use it (doing so messed things up) so ignore it. Reexamining your photo it appears to simply be an image of the camera used, of no use to us in alignment.
You will have to remove the corrector shims and shift the plate. You may also have to shift the secondary housing within the corrector perforation; optical pros here seem to indicate this will not create a new problem. Don't worry about shim removal! You can add custom thickness ones if desired at the end.
My C11 is mechanically assembled fine so I shimmed the secondary holder concentric to the plate with UHMW tape, Teflon plumbing tape should also work, but in my M8, the corrector and the secondary housing, both, are shimmed totally to one edge of the hole. I shifted the corrector plate to center the perforation and secondary, and confirmed the alignments with projection and Casady reflections.
Yours does not look as mechanically close to alignment, but start with a centered in perforation housing, and shift it if needed as you work.
The secondary housing can shift in the perforation, as you have found, so either shim it within the perforation once done, or use a thin rubber/sorbothane gasket to help keep it in place. They are sold pre-cut for C11 and C8s, see https://starizona.co...n-kit-c8-gasket
I am sure you can make one if thin material is available, e.g. Amazon. It also reduces the possibility of secondary tightening induced pinching.
If the movement freedoms of the corrector and secondary housing are not enough, you can see if rotation of the corrector and/or secondary can finish the job. The secondaries are apparently often slightly eccentric to the housing and pick.
I assume the misalignment will be accomplished simply by shifting, and then 'locking down' the corrector and secondary.
The method mentioned by Starman can be utilized with a regular laser collimator with a 45 degree target and a side hole to view the return hit, such as made popular with barlowed laser Newtonian collimation, and are available on EB and elsewhere, BUT the geometry of the secondary collimation adjusters, pivot point, aluminum puck and the scope might require this be left as a final, iterative tuning. Any turning of collimation screws affects the return point even with a centered secondary because the pivot is not at the center of curvature and tilts the return, I believe.
If you can safely (without scratching the secondary) find a way to get the secondary level and parallel to the housing and corrector, it might allow the laser to be used as a primary centering method.
I think it is safest to leave the laser return method to the very end, and I personally found it was not useful in final tuning as the holograph method was reliable. I did get a return within 1-2mm of the laser return target center when done. This was, I thought, an impressive confirmation of the centering method used above, as was attaining a textbook star collimation pattern.
As I have mentioned, I have used the C Edge white paper and the Wilmslow C14 sites, and CN posts, as other resources and hands-on experimentation in figuring out the seemingly simple (but actually complex) issues in SCT alignment, pre-collimation.
I applied this to my 'crooked' M8, and my totally 'spun' out of factory alignment C11. Over my AZ trip last week the C11 is now spot-on, with star and Casady alignments matching, and my M8 is as close as possible to being opto-mechanically aligned without bending the baffle tube a bit (apparently possible) or regluging the secondary an extra 1mm further off center, obviously safer. Both now give great images, although the Meade needs a secondary recoat.
The Meade was the best $75 learning tool I've bought in a long time, and my kids got a great scope out of it.
Good luck, keep calm, and be nondestructive in all attempts.
Edited by markb, 26 November 2019 - 12:35 PM.