Guess what, I spent over 1 hour for fine tuning the collimation.
I first use a low power eyepiece, defocus the star and adjust. Next, I put in a high power eyepiece, again defocus and fine tune the whole thing. Finally, I put it in focus and check the airy disc, fine tune again.
Next I put in my Lu070M, and re-adjust the whole thing.
If you got a SCT, the first light should be on collimation!
Accurate collimation is critical, while some collimated scope is not really stable since not all the collimation screws are tight. So, once you reached a good collimation, tighten each screws incrementally until it's rather firm in place, don't over-tighten, however.
This is also a good test for my DIY DEC motor, backlash is rather bad due to the poor motor mounting and there's no backlash compensation in the DIY hand controller, however, it's very useable. At high power, after adjusting the collimation screw, the star will simply move away rather significantly, sometimes even out of the field of my 1/3" CCD, but then a dual axis motor will help to bring it back effectively.