Color Photography.—Color photography from the air by any of the screen-plate or film-pack methods is probably out of the question because of the long exposures required. The screen-plates are unsuitable also because of the relatively large size of their grain compared to the detail of the aerial photograph. Ordinary three-color photography, using three separate negatives, is always subject on the earth's surface to the difficulty that the three negatives must be exposed from the same point of view, either in succession or by means of some optical arrangement which is costly from the standpoint of light. In photographing from the air this difficulty of securing a single point of view for the three photographs is absent. Three matched cameras, side by side in the fuselage, have identical points of view as far as objects on the earth below are in question. Consequently, three-color negatives are entirely possible, and indeed will be simple to make as soon as plates of adequate color sensitiveness and speed are available. Probably the new Ilford panchromatic plate has the necessary qualities.
Night Photography.—The searching eye of photography was so omnipresent in the later stages of the Great War that extensive troop movements and other preparations had to be carried out either in photographically impossible weather or else at night. The natural reply to the utilization of the cover of night is to “turn night into day” by proper artificial illumination. At first thought it might well appear that the task of illuminating a whole landscape adequately for airplane photography is well-nigh hopeless by any artificial means. On one hand we have the very short exposures alone permissible; on the other the fact that the intensity of daylight illumination is overwhelmingly greater than those common in the most extravagant forms of artificial illumination.
Toward the close of the war, however, actual experiments made with instantaneous flashes of several million candlepower showed that if proper means were provided to insure the flash going off near the ground, and if its duration were made no longer than about 1
50 second, interpretable photographs were obtainable on the fastest plates. It appears, therefore, merely a matter of manufacturers perfecting the technique of flash production, and of inventors providing the launching and igniting devices to push this kind of photography to the practical stage. The achievement of night photography cannot fail to have an enormous effect on future tactics.
The technique of night photography may take either of two directions. On one hand we may develop flashes of the requisite intensity to give all their light in 1
100 second; on the other hand, it may prove more feasible to use flashes of longer duration and to arrange for the camera shutter (of the between-the-lens type) to be exposed synchronously with the middle of the flash. One way, frequently suggested, to use these longer flashes would be to trail the charge on a long wire, through which the ignition is effected electrically. This is not likely to be satisfactory, however, for the resistance of a wire is so great that when the plane flies at any practical height, the trailed flash, if it reaches near the ground, will be forced to a very great distance behind. Probably the best solution will involve accurate synchronizing of the fuse in the freely dropped sack of flash powder with the exposing mechanism in the camera.
CHAPTER XXXII
PICTORIAL AND TECHNICAL USES
Aside from their element of novelty, aerial photographs have undoubted qualities of beauty and utility. The “bird's-eye view” has always been a favorite for revealing to the best advantage the entire form and location of buildings and of other large objects. Heretofore such views have usually had to be drawn by an imaginative artist.
Fig. 188.—Rheims Cathedral.
Aerial oblique views possess the virtues both of pictures and of plans. They are destined to be extensively used in the study of architecture (Fig. [188]). Cathedrals, castles, town halls, particularly those still in their cramped medieval surroundings where they can never be seen in their entirety from the ground, come forth in all their beautiful or quaint proportions from the airman's point of vantage. Stereoscopic aerial views are destined to occupy a valuable position also. Stereo prints of the famous buildings of Europe, taken from the air, will give to the prospective traveler or the arm-chair tourist a many fold more accurate idea of their construction than will any number of mere surface views.
