Recently shot and developed two rolls of Kentmere 400 35mm b&w film, using a Minolta X-570 SLR. There are thick black bands of various sizes cutting vertically across my negatives. They seem to happen in sets of two or three, and they seem to be randomly distributed across the film. The last time I developed film from this camera was years ago, but I never experienced this problem.
What is causing these bands and how can I prevent them in the future?