>As I recall, reciprocity failure is: as film receives more and more
>exposure, it becomes LESS sensitive so it needs more exposure.
>
>John
Reciprocity-law failure is a phenomenon which occurs under low light
conditions with film. The film becomes less sensitive at the extremes of
its chemically designed light range, either with very long exposures in low
light or with extremely short exposures. Color balance is frequently
affected as well because the film layers do not usually have the same
failure threshold. It has been suggested that the phenomenon may be caused
by the fact that chemical reactions require a certain threshhold of energy
to be added in order to occur. Since film exposure is a chemical reaction
which occurs when photons are added, intensity of photon bombardment of the
film molecules in low light or the duration of the bombardment in short
duration flash get to be significant. It is sort of like holding your hand
above a flame. Your hand can absorb a lot of energy over a long time
without burning it. You can even plunge your hand into the intensity of the
flame for an instant without burning it, but if you put your hand close to
the flame for a short while you will get a very good exposure. :-)
Winsor
Winsor Crosby
Long Beach, California
mailto:wincros@xxxxxxxxxxx
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