Quote Originally Posted by Bob Denny View Post
the derotator is turning
So I guess my question at this point is whether the flat vignetting pattern in front of the rotator (e.g. the pattern created due to the OTA) rotates with the "derotator" or holds steady with the PA over the course of a set of images with varying alt-az?

My thinking is that it would rotate with the derotator, whereas flat patterns behind the rotator, (in my case patterns due to dust on filter and sensor windows) hold steady with the PA (per Dick Berg's comment). I suppose at this point the question is more hypothetical as ideally any OTA patterns would be (de)rotationally invariant such that I wouldn't need to worry my pretty little head, or lacking (de)rotational invariance simply try to stay close to the center cause they ain't much else one can do.