=Essential Characteristics.=—In addition to the general requirements as to lens, shutter and magazine, common to all aerial cameras, the hand camera must meet the special problems introduced by holding in the hands, especially over the top of the plane's cockpit. An exceptionally good system of handles or grips must be provided whereby the camera can be pointed when pictures are taken, and held while plates are being changed and the shutter set. The weight and balance of the camera must be correct within narrow limits; the wind resistance must be as small as possible; the shutter release must be arranged so as to give no jerk or tilt to the camera in exposing. As to the method of holding the camera, a favorite at first among military men was the pistol grip, with a trigger shutter release (Fig. 37). Because of the size and weight of the camera the pistol grip alone was an inadequate means of support and additional handles on the side or bottom had to be provided for the left hand. Small (8 × 12 cm.) pistol grip cameras were used to some extent by the Germans (Fig. 42), and a number of 4 × 5 inch experimental cameras of this type were built for the American Air Service (Fig. 37). But the grasp obtained with such a design is not so good as is obtained with handles on each side or with flat straps to go over the hands. The camera balances best with the handles in the plane of the center of gravity. As to weight, no set rules are laid down, but experience has shown that a fairly heavy camera—as heavy as is convenient to handle—will hold steadier than a light one. The American 4 × 5 inch cameras described below weigh with their magazines in the neighborhood of twelve pounds. [Illustration: FIG. 37.—Pistol-grip aerial hand camera.] =Representative Types of Hand-held Cameras.=—French and German hand-held cameras are essentially smaller editions of their standard long-focus cameras, and a description of them will apply to a considerable extent to the large cameras to be discussed in a later chapter. The English and American hand-held cameras are generally quite different in type from the large ones, which are used attached to the plane. [Illustration: FIG. 38.—Diagram of French (deMaria) 26 cm. focus hand camera, using 13 × 18 cm. plates.]