Range finder for passive type autofocussing device

摘要

A range finder for a passive type autofocussing device includes three photosensors comprising three line sensors. Differences of the luminance distribution of a scene detected by the respective photosensors are computed and the zero-cross points of the difference are detected. The zero-cross behaviors thus detected are compared to one another with the zero-cross behavior associated with one of the three line sensors being selected as a reference and the zero-cross behaviors associated with the other two line sensors being successively shifted relative to said reference until a coincidence of the zero-cross behaviors associated with the three line sensors is detected. The range to the scene is computed based on an amount that the zero-cross behaviors associated with the other two line sensors has to be shifted until coincidence is detected.