|
Rotation of the field can indeed make a different image circle which renders your flats made for one rotation invalid for another one, even when using the same image train.
Dust is avoidable. Most cameras (Nikon, Canon) have a manual dust cleaning option which allows to blow dust away from the sensor with a blowing bulb. This option pops up the mirror and shutter so you have access to the sensor. Obviously, no lens or telescope should be mounted, use a bare body. Do this when holding the camera facing downward to be sure all dust falls off when blowing. Do this before each astrophoto session.
And when you use Photoshop for post processing and use a lens with a lens profile (so not a telescope prime focus), you can just select the 'Lens correction' option and then select the lens you used. This eliminates the need for flats.
Do this after stacking and before post processing.
|