a photoelectric focus detecting member includes a semiconductor substrate of a first polarity and at least two closely transversely spaced parallel longitudinally extending photosensitive laminae of a polarity opposite to the first polarity to form corresponding photodiodes . each of the photosensitive laminae is masked to provide regularly spaced light receiving areas alternating with masked areas , the light receiving areas of successive transversely spaced photodiodes being relatively longitudinally offset to present a checkered pattern . the detecting element is positioned in the focal plane of a lens and is either stationary or oscillated . the difference in potential between the diodes or the amplitude of the ac current in a circuit including the photodiodes is a function of the condition of focus of the lens .