My C5 needed collimation after I epoxied the corrector plate rim back on the tube. Collimation on these is a bit tricky and I was dreading it.
While searching this forum and the internet, I stumbled across a tool called a Duncan Mask. I cut one for my C5. It worked like a million bucks!!!!!!!!!!!!!
The dimensions on the internet are for a much larger scope, a 11 or 14 inch SCT. I don't recall. I just eyeballed it. The instructions specify a 400 power eyepiece. My experience was different. Best views of the "Y" were at 80 power with a 15mm eyepiece (FL = 1200mm).