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Re:Answer to film puzzler



Kevin writes:

))))
>>Not true -- as the frequency would accelerate dramatically near the core of
the film, where each layer would maybe be 6" long, versus the outer edge of
the roll, where each layer would be perhaps 24" long.((

Soory Jeff - you are assuming exposure is thru the face of the film. A layer,
if exposure is thru the edge of the film is sproket to sprocket, not emulsion
to emulsion.
Kevin((((

Uh, sorry, Kevin, but I _was_ assuming that the film was fogged through the
edge.  Imagine a roll of film, viewed from the edge. Draw a line from the
edge of the film through the center of the core back to the other edge of the
film.  Let us assume that this simulates the line of Xray exposure.  (OK, the
roll could have been fogged off axis, but then the frequency would vary
pretty wildly.)

OK, if the fogging is along this line, the layers of film near the core will
be fogged every (say) 16 frames -- fogged on each side of the core, or 2
fogging incidents per layer.  

If that line continues to the edge of the roll, the fog incidence could be up
to (perhaps) 40 frames apart if there are 2 fog incidents per layer.  One per
layer (i.e. the roll only fogged from the center out to one side),  the
fogged frames would be twice as far apart.

If the roll were fogged from the edge instead, it is possible that the
intensity of the fogging could decrease towards the inner layers.  But the
same change in frequency from head to tail of the roll would occur.  

If the film were fogged before shooting, the incidence of fogging would
increase as the tail approaches.  If it were fogged after shooting, the
incidence of fogging would  decrease (i.e. more good frames between fog
incidents)  as the tail of the roll approached.

This all assumes a fairly "focused" fogging, rather than a more typical
overall fogging more typical of exposure to X rays.  But, given the fact that
the fog was repetitious and occurred at a regular rate indicates this wasn't
the case.

Personally, I wouldn't rule out lab fogging in the processor.  But I don't
believe we were ever told the length of the fogged area and  the frequency of
same.  Measuring that, through the roll, would make it a lot easier to
determine what really happened here.  If, say, the fog occurred regularly
every 6-8 feet, it sounds like processor problems instead.

But please, if I am wrong, correct me.

Jeff "I sure have beat this dead horse" Kreines