Originally Posted by davidnewtonguitars
I use Kodak photo-flo and 2 well wetted and squeezed out sponges to wipe the film before hanging to dry. I've done this since I have developed film with no effects.
I think this is a "bad spot" on the emulsion, as I can not detect any actual scratches on the film. If it were a bad curtain, I think it would be on every frame, and worse on a well lit scene, and it is the opposite, worse on a poorly lit interior.
Italics mine: PF
I thought so too along those lines, as I got some frames at the first part of the roll that seemed to be okay. It got worse as the roll went on, which might suggest the curtain was getting worse with use.
On my camera, I inspected the curtains, and it appears one of them has been recently replaced with the other one being all cracked up. I've been told the striation will appear mostly when using the faster shutter speeds, so maybe you were changing shutter speed, instead of aperture like I do. The same issue happened with some BW400CN I next ran in the camera (and used a different lab for the developing), only it was worse which kind of backs up my theory of the curtains getting worse with use.
It also had a front side light leak which meant whomever changed the one curtain didn't do a very good job of it.