Automatic focusing device for camera

摘要

An automatic focusing device for a camera having a lens, includes a camera lens focusing mechanism which adjusts the focus of the lens and which includes a rotatable driving ring, a coaxially mounted rotatable range ring and a spring which moves the range ring in correspondence with movement of the driving ring; a stepper motor which drives the driving ring so that the range ring adjusts the focus of the lens; a stepper motor driving circuit which controls the operation of the stepper motor; a home switch connected with the range ring and which determines the start of the focusing operation thereby; a shutter speed calculating circuit which calculates the shutter speed; a focusing arithmetic circuit which performs arithmetic operations for the focusing adjustment; an AF magnet sequence circuit which controls an electromagnet of the camera lens focusing mechanism to rotatably lock the range ring once the focusing operation has been completed; a main control circuit which includes software for controlling the shutter speed calculating circuit, the focusing arithmetic circuit and the AF magnet sequence circuit; and a forward/reverse rotation pulse delivering circuit which supplied respective pulse signals to the stepper motor driving circuit in response to the home switch, the shutter speed calculating circuit, the focusing arithmetic circuit and the AF magnet sequence circuit so as to ensure that the shutter is not operated when the camera lens focusing mechanism does not operate correctly.