MOTION-PICTURE PHOTOGRAPHY 



665 



motion effects or to give the effect of accelerated movement in chases, etc., but in 

 either case sound cannot be synchronously recorded; hence the track must later be 

 adjusted to the picture. Silent pictures were usually photographed at 16 frames per 

 second, but markedly superior rendition of motion is secured at the present standard of 

 24 frames. 



Films and Film Characteristics. — Before proceeding with a discussion of motion- 

 picture films and their characteristics it is well to have in mind the division of the 

 visible spectrum into five color areas, as shown in Fig. 3. The numbers at the bottom 

 of the diagram represent wavelengths in millimicrons (one millimicron equals one- 

 millionth of a millimeter, or 10 Angstrom units). For a practical understanding of 

 the spectrographic aspects of the subject the reader will frequently find it necessarj^ 

 to correlate the data presented, both here and in later sections of this chapter, with the 

 color divisions of Fig. 3. 



Negative Films. — The types of negative films now used in 3.5-mm. motion-picture 

 photography are developments from older and simpler forms. Referring to the wedge 



"Ordinary" 

 blue-sensitive material 



Orthochromatic material 



Panchromatic material 



Fig. 4. — Spectral sensitivity of three types of photographic material for daylight. 



spectrograms'^ of Fig. 4, the top one represents an "ordinary" gelatin-silver bromide 

 emulsion, with sensitivity at a maximum in the blue region and extending on either 

 side into the violet and the blue-green. By the addition of sensitizing dyes it became 

 possible to extend the photographic response into the green and yellow, giving the 

 somewhat optimistically named "orthochromatic" type of emulsion shown in the 

 center spectrogram. The latter material would obviously render the various hues of a 

 scene in a more nearly correct gray scale than the "ordinary" emulsion. Ortho- 

 chromatic materials were generally used in motion-picture photography until about 

 1927, when the admixture of other dyes resulted in red sensitivity, theretofore lacking. 

 This produced what is known as "panchromatic" film, which, as shown in the bottom 

 spectrogram of Fig. 4, is sensitive throughout the visible spectrum. 



More recently the principal advances in negative film materials have been in the 

 direction of a marked increase in speed and a reduction in graininess. Since 1933 

 the speed of negative materials has been increased fully fourfold, thus tending to relieve 

 the cameraman of the fear of underexposure, giving better detail in the shadows, and 

 affording the laboratories greater development latitude. At the same time camera- 



' While wedge spectrograms do not give absolute values of spectral sensitivity, thej- are useful for 

 purposes of qualitative comparison. 



