Patent ID: 8120697

Claim:
An imaging device equipped with an optical system including a focus lens arranged to adjust an in-focus state, the imaging device comprising: an imaging assembly configured to convert an optical image formed by the optical system into a video signal; an in-focus evaluation value extraction module configured to adjust the video signal with a preset gain and to detect an in-focus evaluation value by extracting, from the adjusted video signal, at least an intensity of a signal in a certain band including a high-frequency component included in the optical image formed by the optical system; a maximum value holding module configured to start a positional shift of the focus lens included in the optical system in a direction of increasing the in-focus evaluation value and to keep a maximum value of the in-focus evaluation value detected in the direction of the positional shift; a criterion threshold setting module configured to set a criterion threshold value to an adjusted value of decreasing the maximum value by a rate determined corresponding to a moving speed of the focus lens on each occasion of detecting the in-focus evaluation value; and an in-focus position determination module configured to compare each detected in-focus evaluation value with the set criterion threshold value and, when the detected in-focus evaluation value is less than the set criterion threshold value, determine a position of the focus lens giving the maximum value of the in-focus evaluation value as an in-focus position.