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I believe QHY works to a 20 micron tolerance for orthogonality.
My FLI 16803 and Microline 16200 seem to have the same slight tilt so I use the same packer for both and I get round stars in the corners.
I think that would be the adapters or the filter wheel, MMOAG itself. I have had it that the same Proline camera gave round stars to the corners of an AP140 which you would expect to have superior machining and squareness.
No big deal, just work out the tilt and put a packer between the camera and the filter wheel on the offending corner or side. In my case its about a 0.55mm error on the top of the camera. I use a spark feeler gauge to pack it out with. That works well. Or if you want a more sophisiticated solution get the Gerd Neuman CTU tilt correcting unit. That seems to be the tilt adapter of choice.
With increasing MP counts on these CMOS cameras and faster optics on average these days, tilt is becoming increasingly obvious. Its quite common to see images with one or more corners showing tilt and distorted and bloated stars.
Greg.
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