In regard to soft edges and corner with scans, make sure, as noted by others, that the problem is indeed with the scanner and not your camera lenses. If you see good clear "grain" that is in relatively consistent focus throughout the image including corners, but the corners and edges of the image itself are soft, it is more than likely this is a problem with your camera lenses. Most camera lenses are maximized for best sharpness at the center, and particularly if not stopped down to a middle f-stop, will tend to show softness toward the edges (especially the short edge which is further away from the center), and the corners. Stopping down these lenses might help, but in some cases, if your lenses are the economy grade, it is just inherent in the lens design.
Zoom lenses often have sweet spots (and I suppose therefore "sore spots") where this problem is reduced or amplified. Art
