Automatic focussing for camera - with grating and photoelectric detector with optimum design of grating for selectivity and sensitivity

摘要

The camera focusing system may be used to give an indication of correct focus, or to operate a servo-system. An image of the object is focussed on a grating located in an image plane and moved at right angles to the gating lines to supply a signal from a photoelectric detector the amplitude of which, or the phase difference of which in relation to a reference signal gives a measurement of the degree of out-of-focus in known fashion. To obtain an optimum comprise between adequate selectivity and adequate spatial frequency width the grating is given a spatial frequency curve with a bandwidth of a third to one octave. It consists preferably of five slits or five prisms.