as someone, who uses zoom telephotolenses for astro, I was wondering how Siril will behave, if I am stacking data of the same camera with somewhat different focal lengths.
Unless I use the lens fully zoomed in or out, I will probably not have the same zoom down to the last millimeter focal length every night. Will this result in problems with registering and stacking, especially in multi-night sessions?
It is supposed to work, the global star registration can rotate and scale images. Be careful to select the reference image as one for which you prefer the framing because others will be cropped to it.
In my experience, it worked great up to version 0.99.6.
All later versions may very well fail depending on your difference in focal lengths. I posted a recent thread on this very topic.
My personal workaround is to perform all duties apart from registration with the latest version (0.99.10.1), and register with 0.99.6 via a virtual desktop.