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Hello Peter,
Ok maybe too much going on here. Can you put the camera on the telescope without the rotator? The goal would be to get an acceptable CCDI map (i.e. symmetric), then use this as your baseline or target configuration (maybe sorta like the 270deg CCDI image you showed?). Since you cannot collimate just shim the camera until you are content. I think you will be less frustrated with this difficult process if you have a known target to aim at.
Side note -----
the TEC180 apparently has a field curvature of 450mm (from the Baader website). This implies a built-in defocus that varies with the distance from the optical axis (center of your CCD is close enough). I worked out the formula:
defocus = fcr * ( 1 - cos(distance/fcr) )
where fcr = 450 mm in this case.
Unfortunately using CCDI doesnt tell you the defocus amount, but by taking two pics with a focus change of (defocus) between them, see if the star in the corners snap-in versus the stars in the center.
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Can you do the measurement I outlined in b) in the previous post? (radius of orbit divided by distance from laser to screen) I think you actually have already done it but did not mention the numerical result in your first post. This angle would be a minimum amount in the shimming exercise of the camera on the rotator. The rotator to camera adapter will potentially add to this. This will maybe put you at ease knowing the rotator is at least X good.
Next put the rotator back in and don't worry about is being mounted crooked on the scope (within reason) just shim the camera wrt the rotator so you get the SAME pattern at 0 and 180, then 90 and 270, NOT the perfect symmetric pattern, the same ugly pattern at opposite angles, now the sensor is orthogonal to the rotator axis, maybe not centered but you can't fix that here so don't sweat it. The problem I see here however is the slight wobble in the image can confuse the CCDI fitting parameters and lead you astray, not sure what to do about this except don't use CCDI or be very carefully interpreting its output?
Lastly shim the rotator to make the CCDI pattern nice and symmetric (within the wobble envelope so to speak).
Yes it is annoying to have a few arcmin of pointing error just from flipping the mount and derotating when the model is good to arc-sec...(in my case 1-2' of rotate offset for 13" RMS pointing). Basically the mount models are missing a term to account for rotator motion, AFAIK there is nothing we can do about it. But since I am using ACP it just resyncs or offset slews and continues on, no problem.
Regards,
EB
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