US 4,392,726 AGranted

Automatic focus control system for video camera with improved position detecting apparatus

AssigneeOlympus Optical Co., Ltd.

InventorKenji Kimura

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Abstract

An automatic focus control system for a video camera includes a first circuit which provides a detection signal having higher frequency components of a video signal provided by the video camera. The level of the detection signal varies according to a relative distance between the lens system of the video camera and the light receiving plane of the image pickup device of the video camera. The focus control system also includes a second circuit which detects an extreme value of the amplitude of the detection signal, and fixes the relative distance between the lens system and the light receiving plane of the image pickup device by stopping the actuation of the focusing mechanism of the video camera.

Claims17

Dependent claims

A focus control apparatus adapted to a camera including a lens system, image pickup means for providing a video signal disposed on the optical axis of the lens system, and moving means for varying a relative distance between a light receiving surface of the image pickup means and the lens system so that an object is focussed onto the light receiving surface, said relative distance being varied in a first direction or a second direction which is opposite to said first direction, comprising:

first means coupled to said image pickup means including means for providing a detection signal which includes higher frequency components of the video signal provided by said image pickup means;
and means for varying the level of said detection signal according to said relative distance between said light receiving surface and said lens system;
second means coupled to said first means and to said moving means for fixing said relative distance when said detection signal substantially takes an extreme value;
and
third means coupled to said second means and to said moving means for causing a predetermined amount of the relative distance variation in said second direction when the relative distance variation is effected in said first direction and when the relative distance variation in said first direction exceeds by said predetermined amount a point at which said detection signal takes said extreme value;
said third means including activating means coupled to said moving means for actuating said moving means during a given predetermined period of time which corresponds to said predetermined amount of said relative distance variation in said second direction.

3 more elements

A focus control apparatus adapted to a camera including a lens system, photographing means for providing a photo signal and focusing means for varying a relative distance between a light receiving plane of the photographing means and the lens system so that an object is focused onto the light receiving plane, said relative distance being varied in a forward direction or a reverse direction which is opposite to said forward direction, comprising:

first means coupled to said photographing means and including means for sampling and holding the level of said photo signal to provide a detection signal having a staircase-like waveform which contains higher frequency components of the photo signal obtained from said photographing means;
and means for varying the level of said detection signal according to said relative distance between said light receiving surface and said lens system;
second means coupled to said first means and to said focusing means for detecting a level change portion of said staircase-like detection signal and for fixing said relative distance when the level change portion of said detection signal substantially corresponds to an extreme value of the level of said photo signal;
and
third means coupled to said second means and to said focusing means for causing a given amount of the relative distance variation in a forward direction when the relative distance variation is effected in a reverse direction opposite to the forward direction and when the relative distance variation in the reverse direction exceeds by said given amount a point at which said detection signal takes said extreme value;
said third means including actuating means coupled to said moving means for actuating said moving means during a given predetermined period of time which corresponds to said given amount of relative distance variation in said forward direction.

3 more elements

Dependencies are inferred from the claim text.