Determination of the following quantities: (a) calibrated focal length; (b) location of the principal point with respect to the fiducial marks; (c) location of the point of symmetry; (d) the distortion effective in the focal plane of the camera and referred to the particular focal length; and, sometimes, (e) the resolution of the lens system, (f) the degree of flatness at the focal plane, and (g) the opening and closing cycle of the shutter as a function of time. Sometimes the locations of fiducial marks and intersections in a reseau are included in a calibration. If the camera has more than one lens system, calibration includes determining the angles between the optical axes of the individual lens systems. Setting the fiducial marks and positioning the lens system are ordinarily considered adjust-ments, although these actions are sometimes done during calibration. Unless calibration is stated specifically to be of a camera, distortion and other optical characteristics of a lens system are determined in a focal plane located at the equivalent focal length and the process is called lens calibration.