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Subject: Re: Film camera question



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.

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