In-focus sensing device for sensing an in-focus condition using a ratio of frequency components at different positions

An in-focus state sensing device for a camera, comprising:

• an optical system for forming a subject image, the optical system having a focal surface;
• two optoelectric transducers, respectively arranged at two adjacent positions which are conjugated with the focal surface of the optical system, for converting the subject image formed by the optical system into respective optoelectric conversion signals;
• frequency component ratio sensing means for extracting frequency components in an equal band from the two optoelectric conversion signals from the two optoelectric transducers, respectively, for obtaining a ratio of the two extracted frequency components based on the extracted two frequency components, and for producing a ratio output signal corresponding to the obtained ratio;
• defocus amount sensing means for obtaining a defocus amount based on the ratio output signal of the frequency component ratio sensing means, and for producing an output corresponding to the obtained defocus amount;
• driving means for driving the optical system based on the output of the defocus amount sensing means;
• and
• judging means for judging whether or not the optical system is in the vicinity of the in-focus position based on the ratio output signal;
• switching means for changing the band of the frequency components extracted by the frequency component ratio sensing means, responsive to a judging result obtained by the judging means based on the ratio output signal, as a function of whether the optical system is in the vicinity of or away from an in-focus position.

An in-focus state sensing device for a camera, comprising:

• an imaging lens;
• sensor means for receiving a subject image through the imaging lens at adjacent two positions which are conjugated with a focal surface, and for producing two respective optoelectric conversion analog signals;
• analog-to-digital conversion means for converting the optoelectric conversion analog signals from the sensor means into respective digital output signals;
• Discrete Fourier Transform means for receiving the digital output signals from the analog-to-digital conversion means, and for computing two specific frequency components of the optoelectric conversion analog signals at the two positions by Fourier transform, respectively, and for outputting the two computed specific frequency components;
• memory means for storing the two specific frequency components computed by the Discrete Fourier Transform means;
• control means for computing a ratio of the two specific frequency components which are computed by the Discrete Fourier Transform means and stored in the memory means, for obtaining a defocus amount based on the computed ratio, for judging whether or not the imaging lens is in a vicinity of an in-focus position based on the defocus amount which in turn was obtained based on the computed ratio, and, responsive to said judging, for changing the frequency to be sensed by the Discrete Fourier Transform means so that when the imaging lens is in a vicinity of an in-focus position, specific high-frequency components are sensed by the Discrete Fourier Transform means, and when the imaging lens is away from the vicinity of the in-focus position, specific low-frequency components are sensed by the Discrete Fourier Transform means;
• and
• lens-driving means for driving the imaging lens based on the defocus amount obtained by the control means.

An in-focus state sensing device for a camera, comprising:

• a pair of optoelectric transducers, each arranged at a respective position near a focal conjugate surface of an imaging optical system, and for respectively optoelectrically converting an optical distribution of a subject at said positions, and for producing respective converted signals;
• frequency component extracting means for extracting specific frequency components from the respective converted signals from the pair of optoelectric transducers, and for outputting the respective specific frequency components so as to respectively correspond to the two positions;
• frequency component ratio sensing means for obtaining a ratio of the specific frequency components which correspond to the two respective positions, extracted at the frequency component extracting means, and for producing a ratio output signal;
• converting means for converting the frequency component ratio represented by the ratio output signal from the frequency component ratio sensing means into a defocus amount for the imaging optical system;
• and
• lens driving means for driving the imaging lens based on the defocus amount from the converting means;
• and
• wherein the frequency component extracting means uses as the specific frequency a first frequency component able to cover a wide defocus range in an initial stage of an in-focus state sensing operation and judges, based on the defocus amount, whether or not the imaging optical system is in the vicinity of the in-focus position, and when it is judged that the imaging optical system has reached the vicinity of the in-focus position, the frequency component extracting means uses as the specific frequency a second frequency component with a higher sensing accuracy.

An in-focus state sensing device for a camera, comprising:

• first and second optoelectric transducers for optoelectrically converting two optical distributions of a subject with different focal states, near a focal conjugate surface of an imaging lens, and for respectively producing first and second optoelectric conversion signals;
• frequency component extracting means for extracting specific frequency components from the first and second optoelectric conversion signals, respectively;
• frequency component ratio sensing means for obtaining a ratio of the frequency components using the respective frequency components extracted by the frequency component extracting means, and for producing a frequency component ratio output signal;
• converting means for converting the frequency component ratio represented by the ratio output signal from the frequency component ratio sensing means into a defocus amount for the imaging lens;
• and
• lens driving means for driving the imaging lens based on the defocus amount from the converting means;
• and
• wherein the frequency component extracting means includes means for selecting from more than one frequency to be sensed a frequency able to cover a wide defocus range in an initial stage of an in-focus state sensing operation, and after having reached the vicinity of the in-focus position, as judged based on the defocus amount, changing the frequencies to be sensed based on the frequency component ratio output signal from the frequency component ratio sensing means.

A method of sensing an in-focus condition in a camera, comprising the steps of:

• optoelectrically converting a subject image at two adjacent positions which are conjugated with a focal surface, respectively, and for producing respective optoelectric conversion signals;
• obtaining specific frequency components of the optoelectric conversion signals;
• obtaining a ratio of the obtained specific frequency components of the optoelectric conversion signals;
• judging whether or not the obtained ratio is within a specific range;
• obtaining specific frequency components of higher frequencies when the obtained ratio is judged to be within a specified range, and for obtaining a frequency component ratio of the obtained higher frequencies;
• and
• judging that the camera is in an in-focus condition when the frequency component ratio of higher frequencies is within a specified range.

An in-focus condition sensing device for a camera, comprising:

• an imaging lens;
• frequency component ratio sensing means for optoelectrically converting a subject image passing through the imaging lens in two places to produce respective converted signals, for sensing specific frequency components of the respective converted signals, and for obtaining a ratio of the sensed specific frequency components of the converted signals;
• defocus amount computing means for computing a defocus amount by an equation using the specific frequency component ratio obtained by the frequency component ratio sensing means, and wherein the contents of the equation when the specific frequency component ratio is in a specified range differ from those when the specific frequency component ratio is out of the specified range;
• and
• driving means for driving the imaging lens based on the defocus amount computed by the defocus amount computing means.

An in-focus state sensing device for a camera, comprising:

• an optical system for directing luminous fluxes from a subject;
• optoelectric transducer means for converting the luminous fluxes passing through the optical system at a plurality of positions with different optical path lengths, into respective electric signals responsive to an optical distribution of the luminous fluxes, in accordance with the respective positions;
• frequency extracting means for extracting specific frequency components, based on the electric signals which are output from the optoelectric transducer means and which correspond to the positions, respectively;
• frequency component ratio sensing means for obtaining a ratio of two frequency components which are output from the frequency extracting means and which have different associated path lengths, and for producing a ratio output signal;
• defocus amount computing means for obtaining a defocus amount for the optical system based on the ratio represented by the ratio output signal from the frequency component ratio sensing means;
• driving means for driving the optical system based on the defocus amount from the defocus amount computing means;
• judging means for judging whether or not the optical system is in the vicinity of the in-focus position based on a first frequency which is set as a specific frequency at the frequency extracting means;
• and
• frequency switching means for setting a second frequency as the specific frequency when the judging means, based on the ratio output signal and the first frequency, judges that the optical system has reached the vicinity of the in-focus position.