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Hi Peter,
How do you know the camera and laser are centered on the rotator? On off-center chip (wrt the rotator) will make a stars rotate around the rotator axis, not the sensor 'axis'.
I went through this whole exercise on my system and it was pretty involved. In the end I had to shim the focuser and shim the camera separately (in different planes). It's not perfect but being remote I am hesitant to mess with it since I might 'fix it'! The closer you get to perfect the better the seeing has to be to see what you are doing.
So the order to iterate is
-collimate
-shim cam to rotator so that 180 deg rotation does nothing except move star around due reason above
-shim focuser to make aberrations even in corners
Repeat with finer collimation and small changes to shimming until happy or exasperated! And in your case you can skip the collimation step...
I found CCD inspector fairly useless for this task, the values would bounce around on consecutive readings when not doing anything to the alignment. What was really useful was Platesolve2 which analyzes 5 or more frames across focus and calculates the average focus hyperbola in the nine sectors of the chip, then displays the difference of the estimated best focus of the nine sectors relative to the center. Very robust measurement and somewhat immune from seeing variations. From these values I could calculate an approximate tilt plane and shim accordingly.
Remember it doesn't matter if the components are individually crooked, what matter is to get the CCD orthogonal to the rotator axis, then the camera+ rotator unit orthogonal to the optical axis. The camera not being centered on the rotator axis is annoying but not deal breaking.
HTH,
EB
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