G'day Robin,
I've got a f/4.7 10", MPCC, and the Cat's Eye kit as well. I'm getting similar not-quite-right stars and am trying to pin down the cause of that as well. They look
very similar to what you're showing in those shots.
Pretty sure it's not the collimation, as the Cat's Eye kit indicates it's all good, and I've had Peter (peter_4059) check it a couple of times to reassure myself I'm on the right track. He has a very similar scope to mine and his stars a something to aspire to.
Am convinced now it's a combination of the spacing between the MPCC and the camera, and a bit of the MPCC not sitting perfectly square in the focuser.
For the spacing, I had calculated the theoretical distance that should be between the camera and MPCC and it rounded off to 20mm. But given tolerances it could be plus or minus a couple of mm from there. Have ordered a set of rings that should allow me to now get spacings from 17mm to 23mm in mm increments so I can fine tune it.
For the squareness of the MPCC in focuser, still playing with ideas but either filling in that indent around the MPCC barrel so it doesn't cause a problem with my focuser compression ring, or also thinking of putting a ring on the focuser side of the MPCC's flange stop. My thread on this
here.
The spacing rings should turn up in the next day or 2 and I'll be doing some testing (fingers crossed) this week. Will let you know how I go.