Resolving power and distortion of typical airplane-camera lenses

Tabulations are given of the resolving power and distortion of a number of airplane-camera lenses of the type most commonly used in recent air-mapping projects. Since the image plane of best average definition does not necessarily coincide with the image plane yielding best definition on the axis of the lens, the method of selecting the image plane of best average definition and its use in connection with the determination of the equivalent focal length are described. The manner of the variation of the resolving power across the field is characteristic of the type of lens.