David Nebenzahl wrote:
Luis Ortega spake thus:

I see a lot of developed film and contact sheets at my school and
every once in a while I see a roll of negatives or a contact sheet
that has a thin band of lighter tone (darker on the negatives) at the
bottom of most negative frames, as if all the frames got a little
overexposure only along one edge. Usually it's the bottom of the
negative frame, and the lighter band is soft edged and only about1 or
2 mm thick. The surrounding negative is normal and doesn't look fogged.

Could this be caused by the shutter curtains slowing down a little at
the end of the travel distance thus giving that part of the film a
tiny bit more light?

Probably not, since most focal-plane shutters travel horizontally across
the frame.

Most modern camera manufacturers use a verticaly traveling metal focal
plane shutter in their SLR and DSLR cameras.
It is definitely a symptom of a sticking shutter.
Don't forget that the image is _inverted_ at the film plane and the
bottom of the scene is captured at the top of the film frame.
A dark stripe on along the top of the negative (which is the bottom of
the scene) is a symptom of a sticking shutter, it starts a bit slow
(over-exposing the top edge of the film) and then runs at the correct
speed across the rest of the frame.

A few use vertical-travel curtains.

Have a good look at any AF Nikon SLR, a Canon EOS SLR, or any of the AF
Pentax SLR camera bodies, they all have a verticaly traveling metal
focal plane shutter.
Even the Voigtlander rangefinder series have a verticaly traveling metal
shutter.
The only "modern" manufacturer to use a cloth focal plane shutter is
Leica and that is only in their rangefinder cameras; Leica SLR cameras
use a verticaly traveling metal shutter.

I can't determine if these defects correspong to the direction of
travel of the camera's shutter curtain, but if it was caused by an
inconsistent shutter curtain speed it should show up along the edge
where the shutter curtain ends at.

Questions: does the dark band on the negatives extend over the frames?
In other words, is it continuous across the strip of film, or is it only
inside the frames? If continuous, it might be a light leak.

It could also indicate that the shutter is sticking slightly partway
across the film gate, and over-exposing that area of the film.