192 PICTURING MIRACLES 



them all. It divides the spectrum into two colors, red 

 and green. The light from a color-corrected lens 

 passes through a system of prisms that split the beam 

 in equal parts. One half passes through a green 

 filter and the other half through a red one before 

 striking the film, so two pictures are made at the 

 same instant through the same lens exactly one pic- 

 ture frame apart. The color separation can be con- 

 trolled by the strength of the red and green filter. 



The taking of the negative is comparatively sim- 

 ple, the film runs through the camera twice as fast 

 as the ordinary one, so you expose thirty-six to forty- 

 eight frames a second, which requires a motor drive 

 instead of the crank as in most cameras, and it also 

 means the lens and the shutter must be open wider 

 so as to get the correct exposure at the higher speed. 

 The camera itself is larger and very heavy. Com- 

 bined with the motor it is something of a chore to 

 move it, and with its seventy pounds of batteries and 

 tripod of almost equal weight one knows he is work- 

 ing every picture he takes. 



The film is developed one point stronger than for 

 the regular black and white work. The best method 

 is to develop tests by time and temperature and then 

 in total darkness develop the picture accordingly. 



The negative scenes are assembled, spliced in se- 



