# US 4,392,726 A · Automatic focus control system for video camera with improved position detecting apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,392,726 A - Document ID: US4392726A - Status: Granted - Kind: A - Application number: 06/262,918 - Filed: 1981-05-12 - Granted: 1983-07-12 - Earliest claimed: 1980-06-13 - Assignees: Olympus Optical Co., Ltd. - Inventors: Kenji Kimura - Web page: https://patentgrep.com/patent/US4392726A ## CPC - H04N 23/673: {based on contrast or high frequency components of image signals, e.g. hill climbing method} - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION ## 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. ## Claims ### Claim 1 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. ### Claim 2 (depends on 1) A focus control apparatus of claim 1, further comprising fourth means coupled to said moving means for setting said relative distance at a terminating position of said second direction before the focus control is commenced and for switching the direction of said relative distance variation from said second direction to said first direction after the focus control is commenced. ### Claim 3 (depends on 1, 2) A focus control apparatus of claim 1 or 2, wherein said first means includes: filter means for providing a first signal corresponding to the higher frequency components of said video signal; detector means coupled to said filter means for providing a second signal having a level corresponding to the amplitude of said first signal; and sample/hold means coupled to said detector means for sampling and holding the level of said second signal with a given rate to provide said detection signal. ### Claim 4 (depends on 1, 2) A focus control apparatus of claim 1 or 2, wherein said second means includes: differentiator means coupled to said first means for providing a third signal having a positive or negative polarity and indicating a level change rate of said detection signal; discriminator means coupled to said differentiator means for discriminating said third signal from a predetermined threshold level to provide a fourth signal when the polarity of said third signal has been changed and said third signal corresponds to said predetermined threshold level; and stopper means coupled to said discriminator means and to said moving means for stopping said relative distance variation by said moving means according to said fourth signal. ### Claim 5 (depends on 3) A focus control apparatus of claim 3, wherein said second means includes: differentiator means coupled to said first means for providing a third signal having a positive or negative polarity and indicating a level change rate of said detection signal; discriminator means coupled to said differentiator means for discriminating said third signal from a predetermined threshold level to provide a fourth signal when the polarity of said third signal has been changed and said third signal corresponds to said predetermined threshold level; and stopper means coupled to said discriminator means and to said moving means for stopping said relative distance variation by said moving means according to said fourth signal. ### Claim 6 (depends on 4) A focus control apparatus of claim 4, wherein the extreme value of said detection signal is detected based on the change of the polarity of said third signal. ### Claim 7 (depends on 5) A focus control apparatus of claim 5, wherein the extreme value of said detection signal is detected based on the change of polarity of said third signal. ### Claim 8 (depends on 4) A focus control apparatus of claim 4, wherein the timing at which the direction of said relative distance variation is switched from said first direction to said second direction is determined by said discriminator means. ### Claim 9 (depends on 5) A focus control apparatus of claim 5, wherein the timing at which the direction of said relative distance variation is switched from said first direction to said second direction is determined by said discriminator means. ### Claim 10 (depends on 6) A focus control apparatus of claim 6, wherein the timing at which the direction of said relative distance variation is switched from said first direction to said second direction is determined by said discriminator means. ### Claim 11 (depends on 7) A focus control apparatus of claim 7, wherein the timing at which the direction of said relative distance variation is switched from said first direction to said second direction is determined by said discriminator means. ### Claim 12 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. ### Claim 13 (depends on 12) A focus control apparatus of claim 12, further comprising: fourth means coupled to said focusing means for setting said relative distance at a terminating position of said forward direction before the focus control is commenced and for switching the direction of said relative distance variation from said forward direction to said reverse direction after the focus control is commenced. ### Claim 14 (depends on 12, 13) A focus control apparatus of claim 12 or 13, wherein said first means includes: filter means for providing a first signal corresponding to the higher frequency components of said photo signal; detector means coupled to said filter means for providing a second signal having a level corresponding to the amplitude of said first signal; and sample/hold means coupled to said detector means for sampling and holding the level of said second signal with a given rate to provide said detection signal. ### Claim 15 (depends on 12, 13) A focus control apparatus of claim 12 or 13, wherein said second means includes: differentiator means coupled to said first means for providing a third signal having a positive or negative polarity and indicating a level change rate of said detecting signal; discriminator means coupled to said differentiator means for discriminating said third signal from a fixed threshold level to provide a fourth signal when the polarity of said third signal has been changed and said third signal corresponds to said fixed threshold level; and stopper means coupled to said discriminator means and to said moving means for stopping said relative distance variation according to said fourth signal. ### Claim 16 (depends on 1) A focus control apparatus of claim 1, wherein said second direction is a forward direction along said optical axis, and said first direction is a reverse direction along said optical axis. ### Claim 17 (depends on 1, 12) A focus control apparatus of claim 1 or 12, wherein said actuating means comprises a monostable multivibrator having a predetermined time constant.