Hi Les- the only time I’ve experienced this is when collimation was out or a tilt/flop in the image train. If you’re sure these are 100%, and after testing with different filters/camera/eyepiece to confirm none of these are affecting things it might be worth pulling the corrector plate off to ensure it’s centred and reference points line up. But only do this if you’ve exhausted other options and make sure you’ve read up on the correct procedure to do this first.
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