For base work one of the modern automatic print-drying machines used in commercial photography would be desirable. Glossy surfaces are given prints by the usual ferrotype plate method. But this is too time-consuming for war practice, and besides has but doubtful advantage where papers of the glossy type are chosen.
VI
PRACTICAL PROBLEMS AND DATA
CHAPTER XXV
SPOTTING
“Spotting,” as distinct from mapping or from the photography of continuous strips, is the photography of a definite individual objective. In military work spotting or “pin pointing” includes the photography of particular trenches or pivotal points in a trench system before an attack (Fig. [123]), of roads or bridges along which an advance must pass (Fig. [124]), of batteries or big guns which are the subject of artillery fire (Fig. [125]), both before and after their bombardment (Fig. [126]), of gun puffs or exploding bombs (Fig. [131]).
The technique of spotting consists largely in getting properly over the target and then securing the exposure at just the right moment. This is chiefly a question of proper piloting; but the aid which can be offered to the pilot by camera auxiliaries designed particularly for spotting needs is very large.
Discussion of the task of the pilot who must steer a photographic plane accurately over a previously selected point of interest cannot be undertaken without raising the question of who should take the picture, pilot or observer? In the English service the most general practice was for the pilot to be charged with the responsibility both of covering the objective and of exposing. If a propeller drive was used on the camera, this left to the observer only the task of changing magazines. If the camera was hand operated the plates were changed either by the observer, or else, as was frequently the case, distance operating devices were attached, so that the pilot even then did everything except change the magazines, and the observer was kept free to watch the sky for enemy aircraft. A very desirable adjunct to the camera when plates are shifted automatically or by the observer is a distance indicator, to show the pilot when the shutter is set. Electrical indicators for this purpose have been devised.
Fig. 123.—Low view of trenches on the Yser, showing concrete structures undamaged by bombardment.
Fig. 124.—The Piave River. To left, destroyed bridge, to right, pontoon bridge under construction.
Italian aerial photographic service.