During the course of the war airplane cameras have been classified on various bases, in different services. In the French service, where the de Maria type of camera was standardized early in the war, the usual classification was based on focal length; thus the standard cameras were spoken of as the 26, the 50 and the 120 (centimeter). A further distinction was then made according to the size of plate, this being originally 13X18 centimeters for the 26 centimeter, and 18X24 centimeters, for the larger cameras. In the English service the 4X5 inch plate was used almost exclusively, and their various types of cameras were known by serial lettersóC, E, L, etc. Both these modes of classification became inadequate with the ultimate agreement to standardize on the 18x24 centimeter size for all plates, and to carry lenses of all focal lengths in interchangeable elements.
For purposes of description and discussion, it is most convenient to classify cameras according to their method of operation and the sensitive material employed. On this basis we may distinguish among cameras using plates three kindsónon-automatic cameras, semi-automatic cameras, and automatic cameras. We may similarly discuss film cameras, but having treated the plate cameras comprehensively, it will be found that the discussion of all types of film camera can be handled most conveniently by studying the differences in construction and operation introduced by the characteristics of film as compared to plates.