What happened to my film from my holiday...?

[Richard G]

Wouldn't exposure to light affect the film more through the sprocket holes? Your film has something going on that leaves an image of sprocket holes unaffected. It's got to be during development.

That puzzled me too. I think Farleymac has the answer. My take on the sprocket holes is that the light has come in and reflected off the celluloid face of the film, projecting a reflection on to the film at a distance so that the sprocket holes are larger on the strip of film affected. I of course don't know enough about how a C41 machine works to properly understand this. But PF's surmise on the role of the rollers in the machine must be close to the explanation for the bars of better exposure.

EDIT: Now I've seen an automated C41 machine online it looks like the films are taken through very straight and parallel, and so roller bar shadows ought to be straight, and the magnification of the sprocket holes by being at some distance from the affected film ought not to be possible. Unless of course something went wrong....