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Having looked at the raw files I’m wondering whether it is a collimation issue. Given that the stars look pretty good (appears to be some tilt... or is it!) I’m thinking that the FSQ is collimated but not into the centre of the mechanical axis, this may answer why the image seems to rotate around the top left corner.
It may also answer why the smaller stars remain quite still across the FOV but the larger ones are moving. If you look at the bright stars without any stretch their central PSF remains largely unchanged but as you look at the brighter flare, that’s what’s “moving”. I’m thinking that this is how the light is collimated, light further from the central optical axis has to move further across which gives it a different incidence angle. If the optical axis isn’t central to the mechanical then when it’s flipped 180° it isn’t symmetrical. Although the stars are in the same place the lights angle of incidence is different; non-symmetrical.
That’s my theory.
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