WAR-TIME PHOTOGRAPHY 99 



centimeter focus lenses and 18 x 24 centimeter plates that 

 intensive study was turned toward the possibilities of celluloid 

 film in roll form. This, from its lightness and small bulk, 

 would appear to be the ideal medium for aerial photography. 



Several interesting problems were met with in the develop- 

 ment of aerial film cameras. One was that of holding the large 

 film flat during the exposure. This was met in several different 

 ways. One method was to use a glass plate pressed against 

 the films, and since the plate was made of yellow glass, it could 

 at the same time be utilized as a color filter. Another method 

 is the use of suction through holes in the camera back, the 

 suction being produced by pump, Venturi tube, or bellows. 



Another problem of some seriousness was caused by the 

 production of static electricity from the friction of the celluloid 

 film against the camera parts. This is especially frequent at 

 high altitudes, in cold dry air. It results in tree-like discharges 

 across the face of the film, easily mistaken for trenches or 

 paths, if indeed they do not obliterate the whole picture. This 

 is a trouble which used to occur in moving picture cameras, 

 to be finally met by metal construction and by grounding the 

 apparatus the latter an expedient not permitted in the air- 

 plane. After considerable experimentation it was found that 

 this trouble could be entirely overcome by covering the suction- 

 back with coarse grained cloth impregnated with graphite, 

 whereby the fibers were turned into small electrically conduct- 

 ing paths, leading off the electric charges as soon as formed. 



The film camera embodying these features promised in time 

 to supersede the plate camera for aerial work, although it did 

 not materialize in time to be actually used in the great war. 

 The chief outstanding problem in the use of the film is pre- 

 sented by its development, washing and drying in the huge 

 rolls of 100 or 200 exposures which it was expected would be 

 needed for reconnaissance work. Special mobile photographic 

 laboratories, consisting of truck-and-trailer dark and printing 

 rooms were already part of the regular photographic section 

 outfit at the front, equipped to develop plates in a few minutes 



