Patent ID: 7884877

Claim:
An imaging device that converts an optical image, which is captured via an optical system having a focusing function, into a video signal by means of an imaging system, the imaging device comprising: a high frequency component extractor that adjusts the video signal with a preset gain controlled according to an imaging condition and detects intensity of a specific signal in a certain frequency band, which includes at least a high frequency component and is generated in a focus state of the optical image captured via the optical system, from the adjusted video signal; a setting module that sets a variation range of changing a state of the optical system, based on at least information on a magnification change of the optical image caused by a change of the state of the optical system, where the variation range is used for detection of a state changing direction of the optical system or a focusing direction for focusing the optical image; wherein the setting module measures a rate of the magnification change that occurs with a position shift of a focus lens for focus adjustment, at least in accordance with a magnification of a zoom lens, stores the information on the relation among the variation range of changing the state of the optical system, the magnification change, and the magnification of the zoom lens, and sets the variation range based on the stored information on the relation; a signal intensity variation detector that detects a variation in intensity of the specific signal in the set variation range a specified number of times while changing the state of the optical system in the set variation range; a focusing direction detector that detects the focusing direction, based on the detected variation in intensity of the specific signal; and an optical system controller that detects the intensity of the specific signal while changing the state of the optical system in the detected focusing direction, specifies a certain state of the optical system giving a peak intensity of the specific signal as the focus state of the optical system, and controls the optical system to the specified focus state.