Focus detecting device

摘要

In the device disclosed, an image formed by an optical system is scanned by an image sensor composed of independently arranged photoelectric transducing elements to produce an image scanning signal. A detecting circuit detects the variation of the brightness between the adjacent image elements as a measure of the sharpness of the image and the focus of the optical system. The focus detection accuracy is improved by non-linear transformation of the brightness variation signal with a non-linear transformation circuit that weighs the brightness variation signal on the basis of the signal level.