Television camera having automatic focusing device for electron beam of pickup tube

摘要

A focusing current or voltage applied to a focusing coil or focusing electrode to focus an electron beam on a target of a camera tube is modulated by a modulation signal so that the focusing current or voltage varies between a maximum value and a minimum value with its average value as the center. The focusing states of the electron beam at the maximum and minimum values of the modulated focusing current or voltage are detected by a video signal from the pickup tube. Based on this detection of focusing states of the electron beam, the average value of the modulated focusing current or voltage is corrected in such a way that the focusing states of the electron beam become equal to each other which correspond to the maximum and minimum values of the modulated focusing current or voltage. The correcting operation is carried out until the focusing states of the electron beam become equal at the maximum and minimum values, and the electron beam is then focused by the focusing current or voltage corresponding to the average value in the state.