I use the Photoshop acquire command to do this. Each 35mm frame is 3072x2048 pixels. Retouch dust and scratches Photomanipulation level 1. The Photo-CD color data is dependent on the scanner operator, especially for astrophotos. They are however, uniformly sharp, high resolution, and artifact-free.
All lenses falloff toward the corners, and wide angle lenses are particularly susceptible.
It seems to be less uniform and symmetric than lens vignette theory would predict. It doesn't need to be perfect, since subsequent color adjustment will be applied in a later step. I save the image with some white space around it as working area for later. Identify reference stars, obtain their galactic coordinates I make and then annotate negative proof prints, locate about 15-20 reference stars near the edges and where images will overlap. This is a bit tedious, but necessary.