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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