JPS57101808A - Automatic focusing system - Google Patents

Abstract

PURPOSE:To perform accurate and stable focusing controlling by such constitution wherein main image pickup element and subimage pickup element are provided on an optical path of an image forming optical system, sharpness signals are detected, the optical positions of the subimage pickup elements are detected as position signals, and these signals are arithmetically controlled. CONSTITUTION:The video of an object is projected via a beam splitter 3 to a main image pickup element 4 and subimage pickup elements 7A, 7B disposed at front focus and rear focus, the outputs whereof are applied via high-pass filters 21-23, gates 24-26, and wave detectors 27-29 as sharpness signals P, Q, R to the function generator 42 of a control part 41. The outputs of the elements 4 and 7A, 7B are extracted synchronously through a gate 30. When the optical path differences of the elements 7A, 7B with respect to the beam splitter 3 are minimized by a driving mechanism 10, the position signals are inputted via a position detector 12 to a logical operating part 44, which receives the outputs of a subtractor 43 and a function generator 42 of R, Q, R signals and transmits the signal B to the driving mechanism 8 of an image pickup lens 1. Thereby, the accurate and stable focusing controlling is accomplished.