Patent ID: 7394048

Claim:
A focusing device comprising: first and second sensors which convert an optical image of a subject, formed on a plane of incidence, into an image signal and output the image signal; a first imaging optical system which forms the optical image on the first sensor; a second imaging optical system which splits the optical image from the first imaging optical system in the direction of the second sensor and further splits the optical image into two so that a front focus image in which the point that is in focus is in front of the optical image on the first sensor and a back focus image in which the point that is in focus is behind the optical image on the first sensor are formed on the second sensor; a focus detecting circuit which detects an optimum focus position of the optical image on the first sensor by calculating a focus evaluation value from a high-frequency component of a front sensor image in a front focus position obtained from the second sensor and a focus evaluation value from a high-frequency component of a back sensor image in a back focus position obtained from the second sensor and by comparing the focus evaluation values; and a focus control circuit which controls the focusing of the first imaging optical system on the basis of the focus position detected by the focus detecting circuit.