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In the camera, several factors contribute to errors between
panels – the filters, the diaphragm settings, and the quality of the mirrors.
The filters are important because variations in filters of the same type are of
the order of magnitude of the corrections we strive to achieve. Sets should be
matched by measurement on a densitometer, CLEARLY LABELED, and
used only as sets. Stacking of two or more filters should be avoided, and
general filter effects (not local as in lighting of the sailors’ faces in
Weegee) should be left for printing. Some errors in this picture can only be
explained by assuming the use of filters of the same series but of different
values such as mixing 85’s and 85B’s. Often errors in exposure between panels,
due to the nature of the photographic process, are accompanied by shifts in color,
often plainly visible but too small to be corrected. More often they are
correctable in one are of the panel but not in others, requiring an obviously
incorrect but compromise adjustment. The converse also holds true, color errors
giving rise to brightness errors when corrections are attempted. The more
serious the initial error, the more pronounced are the deficiencies of the
final compromise correction.
The mirror surfaces can also contribute errors in intensity
and color. The aluminized and overcoated surface will normally incur a loss of
about 15% and, if properly overcoated, a negligible loss of color. Due to the
low angle of incidence near the matchline, however, a thick protective overcoat
can contribute considerable color in this most critical region. Mirrors should
be checked for color primarily in this region. The 15% general light loss is so
slight that it is usually correctable in the printer without serious color
effects, at least for normally exposed negatives, (though it would be better corrected
in the camera) but color errors are often incorrectable. Of greatest importance
is the condition of the mirror surfaces.
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