I recently acquired an old Canon FD 70-210 macro f4 to use on an FTb. I shot a test roll on some cheap rebranded all-purpose 400 film and processed it today at Walgreens. In several shots at the 70mm focal length mode there appears a dark band on the right side of the picture. Below is the most pronounced example of this problem shooting at 70mm in macro mode. Any ideas what caused it? Thanks!