Patent ID: 7488923

Claim:
A focus detection device, comprising: a micro lens array disposed near an estimated focal plane of an image forming optical system and formed by arraying a plurality of micro lenses; a light receiving device provided in correspondence to each of the plurality of micro lenses, which includes three or more light receiving portions disposed along a direction in which the plurality of micro lenses are arrayed; and a focus detection circuit that detects a focus adjustment state with the image forming optical system based upon a signal outputted from the light receiving device, wherein the focus detection circuit (i) calculates a single main area of a region which is formed by three or more light receiving portions onto which light flux originating from the image forming optical system is projected, (ii) determines a boundary line which divides the single main area into two sub areas, at least one of the sub areas including two or more light receiving portions adjacent to another light receiving portion of the same group, and (iii) splits all of the light receiving portions between a first group and a second group based on the boundary line, the first group being formed at one side of the boundary line, the second group being formed at another side of the boundary line.