farlymac
PF McFarland
I think I've seen this before in a thread somewhere, but I'm thinking the cause is uneven emulsion layering.

The Time It Was by P F McFarland, on Flickr
PF

The Time It Was by P F McFarland, on Flickr
PF

PANAMA' 1970 by John Carter, on Flickr
Yeah, that's what I was referring to.Didn't you say your IIIf had a light leak (in my thread about my Leica IIIf)?
I clicked on your photostream, am I wrong or are some of the frames un-effected? You a jarring my memory. My window shot was with a Pentax Spotmatic, when I saw IIIf (in your post) I remember that was my first sign of the need of a new shutter on my IIIf
To add to what John Carter wrote, that Barnack needs its shutter curtains replaced.
Yes. Uneven exposure like that is almost without a doubt a focal plane shutter running irregularly, in need of at least a good CLA if not shutter curtain replacement.
G
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.
I replaced the shutters on my 3F`s and problem went away.
DAG had the cameras 6 months and tried every test and could find nothing wrong. I sent them to ? down south and he replaced the shutters & fine ever since. He worked for Yashica in his youth.
The problem only showed at higher speeds. 1/125 and up if I remember correctly.