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Answer to Film Puzzler

Last week I wrote:

>Five lab rolls, each lab roll shows the same symptoms.
>There is a rather sever density change from beginning to end of each camera
roll, that occurs roughly twice per second.  The rate does not change from
the beginning to the end of the mag.  The density change is equal to all
three film layers and appears to pulse evenly across the frame, i.e it does
not begin on the left or right edge and wash across.  The density change is
also across the unexposed frame line, but is contained only within the
cameras aperture.
>What caused this?
>Bad film stock?
>Pre-exposure from the bag?
>The answer to me seems obvious, but I've no way to prove it.
>No prize for getting it right, except to know you were.

Rob's answer was closest to the mark:

 >I suppose the constant rate rules out preshoot radiation damage.... a
>year or so ago, I had some film that exhibited a density change such
>as you describe, but it did change frequency and became faster as I
>approached the core; the consensus from Kodak at the time was that the
>unexposed film had been zapped in transit somehow, at an airport or ?

(By the way, I suspected a shutter/sync problem in the camera).

I presented all of the clues I knew of at the time, other clues were
discovered later, e.g.  But here's what really happened and the answer is
interesting, if not scarey.

The lab souped a roll of unexposed 5279 stock from the same local batch and
found the film had been pre-fogged while still in the can.  Through manifest
records,  it seems that this stock was transported on Southwest Airlines
from Los Angeles and had been shipped in the cargo bay in close proximity to
containers of biomedical radioactive waste that apparently was improperly

Raises some real concerns if you transport your pets via the airlines,
doesn't it?  How many rem's does it take to make Spot bright?