MOTION-PICTURE PHOTOGRAPHY 697 



Standard negative with heavy filtering will also produce night effects in daylight, 

 but because of the high exposures required, this method is inferior to the infrared 

 system. 



In marine photography, water reflecting blue sky may be darkened by the use of 

 yellow or even red filters, without much modification of the foreground. 



Polarizing Screens. — Polarizing screens take advantage, not of color differentiation, 

 like filters, but of the fact that light is a form of transverse oscillation, which may be 

 limited to a definite direction. Most light is heterogeneously polarized, i.e., the 

 oscillation occurs in every direction at right angles to the ray. But light passing 

 through a prism, or reflected from certain mirrorlike surfaces, tends to be plane polar- 

 ized, and by interposing a polarizing screen such light may be reduced in effect or 

 eliminated. The screen, when placed over a lens and appropriately orientated, dis- 



FiG. 42. — Developing machine. 



criminates against polarized reflections which may be masking detail or otherwise 

 interfering with the effect sought. It may also be used to change contrast. An 

 increase in exposure of four times is usually entailed in such applications. 



Laboratory Practice. — For all practical purposes a discussion of present-day 

 motion-picture laboratory methods may be confined to machine development and 

 sensitometric standardization as applied to the large-scale operations which machine 

 processing has rendered possible. A machine of this type, shown in compact form in 

 the photograph of Fig. 42, is one in which exposed film is unreeled and drawn con- 

 tinuously through the developing solution at a speed (for 35-mm. film) in the neighbor- 

 hood of 100 ft. per min. for negative and 120 ft. per min. for positive, either 

 by motor-driven sprockets or by a friction drive; then it is rinsed, fixed, and washed in 

 successive containers; and finally it is dried and spooled at the output end of the 

 mechanism. The time and degree of development may be varied by changes in the 

 length of the path traveled, by changes in the speed of travel, or both. 



