Agfa motion picture topics (Apr 1937-June 1940)

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Visibility Curve and Spectral Sensitivity Curve of Photographic Emulsions The visibility curve represents the relation between visual sensation and wave length. It is measured in brilliance units which are plotted for all wave lengths creating a visual sensation upon the retina of the eye. The shape and maximum of this curve changes and shifts to a certain extent with any change of the brightness level or intensity at which the readings of the brilliance units are made. For an average brightness level of a non-selective light source (white light), the maximum brilliance lies at 556 mu (yellow-green), decreasing rapidly towards longer and shorter wave lengths and becoming only I % of the maximum value at 430 mu (violet) and 690 mu (dark red). The spectral sensitivity curve of any photographic emulsion differs widely from the white light visibility curve, even when considering the best color corrected type, represented by Panchromatic film. The visibility curve resulting from certain selective light sources such as Mazda light, comes much closer in shape to that of the spectral sensitivity curve of the Panchromatic type, which is one of the reasons why corrective light filters are not in need when photographing indoor sets with Mazda light on Panchromatic film. Visual Sensation The total visual sensation can be composed of three factors, brilliance, hue, and saturation. Brilliance is that attribute of any color which makes it comparable to some member of the series of grays. Hue is an attribute of certain colors by which they differ characteristically from a gray of the same brilliance, and which permits them to be classed as reddish, yellowish, greenish, or bluish, etc. Saturation is that attribute of all colors possessing a hue which determines the degree of difference from a gray of the same brilliance. According to these definitions,* two groups of colors have to be distinguished, one of which represents the non-selective or neutral type and includes all grays between black and white. These colors are hueless and differ from each other only by the brilliance factor. The other group includes all selective colors, which in addition to being distinguishable by the brilliance factor, create a sensation of hue and saturation. Hue is the qualitative attribute, which distinguishes this color from a non-selective gray of equal brilliance, while saturation is the quantitative attribute expressing the magnitude of the difference between a selective color producing a sensation of hue and a hueless color. Absorption, Reflection and Transmission Any natural object is visible by virtue of the incident radiation which it transmits or reflects. Any object that transmits or reflects all wave lengths of *(See transactions of the Society of Motion Picture Engineers, volume 10, No. 27, Page 135 and following pages). Page Fourteen