The ideal in the automatic-plate camera is to provide a mechanism which will not only change the plates and set the shutter, as does the semiautomatic, but make the exposures as well, at regular intervals under the control of the operator. Such a wholly automatic camera would leave the observer entirely free for other activities than photography and it is to meet this tactically desirable aim that the war-time striving for automatic cameras was due.
It is obvious that the one essential difference between the automatic and semi-automatic types lies in the self-contained exposing mechanism with its device for the timing of the exposures. There is no difficulty in arranging for the driving power to trip the shutter, but it is no easy matter to design apparatus which will space the exposures equally, and at the same time permit of a variation of the interval. It is indeed the crux of the problem of automatic camera design to provide for the easy and certain variation of the interval from the two or three seconds demanded for low stereoscopic views to the minute or more that high altitude wide angle mapping may permit. This problem is one intimately bound up with the question of means of power drive and its regulation, and will be treated in part in that connection. It is to be noted, however, that there are in general two modes of exposure interval regulation. One is by variation in the speed at which the whole camera mechanism is driven. The other is by the mere addition to a semi-automatic camera of a time controlled release which affects in no way the speed of the plate changing operation. In many respects the latter is the best way to make an automatic camera.
While the advantages of automatic cameras are great it must not be overlooked that a camera which can only be operated automatically is of limited usefulness. It is not suited for "spotting" at any definite instant, as, for illustration, at the moment of explosion of a bomb. It should, therefore, be the aim of the automatic camera designer to so build the apparatus that it can, at will, be used semi-auto-matically. In addition, to meet the contingency of any break-down in the source of power, the camera should be capable of hand operation, as in the case of the American semi-automatic deRam. In short, the automatic camera should not be a separate and different type; it should merely have an additional method of operation.
Certain desirable mechanical features of all aerial cameras have already been enumerated. Some of these may be repeated here with the addition of others peculiar to automatic cameras. As a general caution, mechanical motions depending on gravity or on springs should be avoided. Movements adversely affected by low temperatures (20 to 30 degrees below zero, Centigrade), are unsuitable. All adjustments called for in the air must be operable by distance controls whose parts are large, rugged, and not dependent on sound or delicate touch for their correct setting. The center of gravity of the camera should not change during operation (important in connection with the problem of suspension). The camera should work in the oblique as well as in the vertical position. The power required for operation must not exceed that available on the plane. Electrical apparatus, for instance, should not demand more than 100 watts.
Any devices which diminish the weight of the camera are particularly desirable in automatic plate cameras, because of the large number of exposures which such cameras encourage. For instance, if the plates could be handled without placing them in metal sheaths we should gain a substantial reduction in weight (the sheaths weigh nearly as much as the plates) as well as in the time necessary for handling.