Originally posted by interested_observer From what I have read, the trailing in the corners is due to the wide field of view at UWA - 15mm, in that the star's apparent rate of motion is greater at the lens' edge and corners than it is at the center.
That's an interesting point. Most WA lenses (neglecting the 10-17 fisheye) try to avoid the fisheye look and try to be rectilinear. That means they are going to stretch the corners a fair bit, and I never considered that this would cause star trails to appear first in the corners, long before the center. Thanks for posting this information; you learn something new every day :-).