Originally Posted by retinax
I'd expect stripes orthogonal to the shutter's direction of travel, not parallel. The only way I can see a shutter causing this is if there is fuzz overhanging the small opening at fast speeds, i.e. the cloth desintegrating, or leaking tons of light right next to the opening, i.e. the cloth pulling away from the metal metal thingy at the ends of either curtains.
Is it visible on the leader? In between frames?
My hunch is that parallel lines like this are likely caused while the film is moving along a light leak (or maybe even mechanically stressed) at constant speed, if not during manufacture, then likely during processing, just maybe during rewinding in camera, but seems unlikely that you could do that at such constant speed in a Barnack Leica. If they processed it in some kind of linear device, that could be it.
You're right.. I'd forgotten that the shutter runs horizontally in the III series Leica's. Gotten too used to the vertical shutter run of the digital Ms. :-)
Porosity of the shutter curtains is most likely.