Use of Crossed Cylinder Lens in Photographic Lens Evaluation

Two methods are described for testing cameras and camera lenses by utilizing the properties of the crossed cylinder lens, an ophthalmic test device. In the first, the cylinder lens is used in conjunction with a rectangular grid to defocus the star image formed by a collimator. This test permits quantitative determination of axial chromatic aberration, spherical aberration and its variations with wavelength, and coma of the lens. In the second, a segment of the cylinder lens is used as a supplementary lens attachment to the camera, which photographs a polar coordinate chart. Analysis of the photograph permits determination of the sagittal and tangential field curvatures, and also indicates errors in focal adjustment and misalignment of film plane with respect to the lens axis. Since these tests require cylinder lenses of smaller dioptric power and quality superior to that available from the ophthalmic lens industry, methods for the construction and synthesis of large-aperture, weak, cross cylinder lenses and segments thereof are given. Experimental details of the lens testing procedures, together with examples of photographic determination of the various camera and lens defects, are presented. A sensitive test for lateral chromatic aberration is included in an appendix.