Abstract: An automatic focusing device by which the intensity distribution of an image of an object to be photographed is detected by a detecting section having an accumulation mode image sensor with a charge accumulation time in dependence upon the brightness of the object and develop a video signal corresponding to the intensity distribution. A signal processing circuit processes the video signal to determine whether the optical system of the photographing apparatus with which the focusing device is associated is focused or out of focus and when an out-of-focus condition is detected a drive direction signal is developed and applied to a drive to move the lens in a proper direction toward a focusing position.

Abstract: An automatic focusing device having a signal processing circuit for providing a focusing signal and a defocusing signal, or drive direction signal, to move the photographing lens to a focusing position the device is provided with a hunting preventing circuit in which, even if the drive direction signal is developed after it has been determined that the lens is focused on the object, the drive direction signal is made ineffective for a period of time which is shorter when the object brightness is high and longer where the brightness is low, whereby the hunting phenomenon with the lens which is liable to occur with a low brightness is positively prevented.

Abstract: An automatic focusing device in which the intensity distributions of the images of an object which are formed by light beams passing through different portions of an optical system in a photographing device are detected as video signals. A correlation output is obtained from the video signals so that the focusing condition is detected from the peak position of the correlation output. When the peak position is not one for focalization, a drive direction signal is delivered to drive the optical system towards the focusing position. A low contrast detecting circuit is provided in which is counted how many times the correlation output becomes higher than a predetermined level in one focusing condition detecting operation, and when the count value reaches a predetermined value, the drive direction signal is made ineffected, so as to prevent the occurrence of a hunting phenomenon with the optical system.

Abstract: An automatic focusing device comprises a detector for detecting distributions of the images of an object which are formed by two light beams passing through two different points in a photographing optical system and for providing corresponding video signals. The video signals are processed to obtain an output signal representative of a relative positional relation between the video signals for use in establishing the optical system moving direction and the distance of movement of the focusing position, or to determine only the direction of movement of the optical system so that the optical system is moved in the direction thus determined to the focusing position. The automatic focusing operation can be accomplished without using movable members other than the photographing lens of the optical system, or in the case of using a movable member, the focusing operation can be achieved with high accuracy by operating the movable member only once.