. Transactions of the Society of Motion Picture Engineers (1921) . ection value. Some other uses for this system of measuring emulsion char-acter are testing of developing solutions, the action of intensifiersor reducers. The various results obtained with difTferent developers,tank solutions, temperature of development or time of develop-ment, can be shown graphically, and the instructions issued with thefilm are arrived at after careful testing in this manner. The photo-graphic value of light sources can be very effectively measured andtheir relative actinic power plotted. Apart from the dete
. Transactions of the Society of Motion Picture Engineers (1921) . ection value. Some other uses for this system of measuring emulsion char-acter are testing of developing solutions, the action of intensifiersor reducers. The various results obtained with difTferent developers,tank solutions, temperature of development or time of develop-ment, can be shown graphically, and the instructions issued with thefilm are arrived at after careful testing in this manner. The photo-graphic value of light sources can be very effectively measured andtheir relative actinic power plotted. Apart from the determination of the speed, fog 7oo and ve-locity constant of emulsions, there is another important factor whichmust be tested. This is the color sensitiveness of negative films. Tomeasure this a Hilger Dififraction-Grating Spectograph is used. Thisinstrument is designed so as to project and bring to a focus in the 149 image plane a diffraction spectrum much in the same way as theimage is brought to a focus on an ordinary camera. The instru-ment is shown in Fig. Fig. 15—Hilger Diffraction-Grating Spectrograph. The fihii or plateholder is 3^ x 4^ inches and has fitted into itan accurately engraved wave length scale. The film to be tested isexposed behind the wave length scale to the action of the spec-trum. The spectroscopic slit has in front of it a black glass wedgethat produces a gradient of exposure across the width of the spec-trum so that we obtain a negative that shows graphically the colorsensitiveness curve of the emulsion. This automatic curve plottingis due to the wedge. If an emulsion is very sensitive to a certaincolor that color will stand more damping down by the wedge, be-fore its power to impress the emulsion is lost, than will a color towhich the plate is not so sensitive, and so the maximum or peak ofthe curve represents the wavelength to which the emulsion is mostsensitive. The results obtained are shown in Fig. 16. The first
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