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Hi Peter,
Agree with Josh about the flat frame. The vignetting pattern in a flat is due to the baffles and the lens cell aperture relative to the sensor location in the tube. The focal plane tilt is related to the orthogonality of the various adapters. Two different types of surfaces doing completely uncorrelated things, which leads to uncorrelated measurements. They only happen to look correlated when everything is setup perfectly!
Your rotation test was good. The wandering you see is likely the gear play that must be present in any moving system. I see about 5mm of radial runout in your movie (call it 6 mm to make the math easier), so that gives 6 mm / 6 m = 1 mrad of runout, which is 206". That should be OK at f/7 with an APS chip.
What is the distance from the rotator to the sensor? That number in millimeters times 1 mrad runout will equal the radius of the orbit on the CCD in microns. I'll guess for now ~40 mm. So the orbit on the CCD could be 40 um or about 7 pixels (KAF16200?). Much smaller than your picture previously IIRC. So not a worry at the moment.
So you can try to mount the rotator with the laser in it to point at the center of the primary lens with paper cover as you described previously. That sorta helps, I'm just not sure how precise it will be. When shimming you will be at the few mrads level in resolution, that corresponds to less than 2mm offset of your laser dot on your objective.
BTW where is the flattener in all this, before or after the rotator? You could post a pic of the optical train if you like, that might help in the conversation.
Regards,
EB
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