JPS5726812A - Focus control device - Google Patents

Abstract

PURPOSE:To execute focusing precisely, by projecting a pattern which has been placed at a conjugate position to the surface of an object to be photographed on an optical axis so as to be slightly inclined against the optical axis, on the object to be photographed, and providing an image pickup means of its projected image. CONSTITUTION:A striped pattern on a negative 9 which has been placed at an image formation position of an object 1 to be photographed, so as to be slightly inclined against an optical axis 6 is projected on the object 1 to be photographed, through a light source 10. Said striped pattern is reflected on an image sensor 8 through semitransparent mirrors 5, 7, and a signal (b) is outputted from an operating circuit 18. This signal (b) is inputted through a wave detector 19 and a shaping circuit 20 to an FF 21 which is set by a synchronizing signal (a), and outputs a square wave (e). The signal (e) is compared with a reference signal Es by a comparator 23 through an averaging circuit 22. A motor 17 is controlled through a driving circuit 24 by a differential output of the comparator 23 so that an image formation point P on the object to be photographed, of the striped pattern coincides with a point on the optical axis of the object to be photographed, and when P coincides with the point S, the motor 17 is stopped, and forcusing is executed precisely.