MOTION-PICTURE PHOTOGRAPH Y 



703 



the present time the only method in extensive commercial use is the rear-projection 

 system, but of the numerous earlier techniques one, the color-separation or Pomeroy- 

 Dunning system, deserves a brief treatment for its historical importance and beca\ise 

 it is a classic illustration of photographic ingenuity. 



Figure 44 is a schematic diagram of this method. It is desired to superimpose the 

 foreground action of the two men on a previously photographed background scene. A 

 dye-image transparency is printed from the background negative, and, as indicated in 

 the figure, this "key" or "plate" is threaded through a special camera in front of and 

 in contact with an unexposed negative. The most common color for the transparency 

 is orange or yellow. The foreground action is lighted from above in the same color. 

 Obviously, then, the foreground action will photograph through the transparency and 

 form a latent image on the negative. 



A plain backdrop is suspended behind the action and strongly illuminated with 

 white light. The color of the backdrop bears a minus relation to the color of the 

 transparency and the foreground light; thus for a yellow transparency the backdrop 



Background lighi- 



Foreground 



same 



parency 



•round li'ghi of ^^>, ^ ' 



color as -trans- P^ \ ^^^^s^C 



^cy (yellow) ^^^^ l_\ V^^<:< 



Colored -Iransparency 

 (yellow) 

 Unexposed / 



negaiive ^^Y^ 



jjb — ' Camera , j 

 '■ - ^^le/ I I 



Spec/al 

 camera 



\ 



^ Colored 

 backdrop 

 (blue) 



Foreground aciion 



Fig. 44. — Composite photography by color-separation method. 



will be the complementary blue. The blue light reflected from the backdrop, entering 

 the lens of the camera, acts as a printing light for the transparency; where the trans- 

 parency is a dense yellow, no blue rays will penetrate to the negative; where the trans- 

 parency is light and 'the foreground action does not block the reflected blue of the 

 backdrop, an image of the background will be formed on the negative. Thus a com- 

 posite negative of the foreground action and the background scene will result. 



The principal disadvantage of the Pomeroy-Dunning system is that the back- 

 ground is invisible while the composite photograph is being made, which may be a 

 serious drawback whenever the foreground action must be synchronized with move- 

 ment in the background, such as moving traffic. This defect is overcome by the 

 rear-projection method of composite photography, shown in Fig. 45. Here the key 

 print is projected from a special projector to the rear side of a translucent sanded-glass 

 or cellulose screen. Sufficient light is used to permit rephotographing by a camera, 

 which is driven synchronously and phased with the projector. The camera and 

 projector motors are of the interlocked type, operating from a common source of 

 alternating current, and by reason of the phasing the projected picture is at rest while 

 the camera shutter is open. (Hence the projector requires no shutter.) The fore- 

 ground action is lighted in the usual way. The main requirement for satisfactory 

 results is a steady high-quality contrasty background negative (see Films and Film 



