Patent ID: 8000591

Claim:
An automatic focusing apparatus comprising: a focus detection unit that photoelectrically converts at least a part of a photographing light beam; a defocus computing unit that calculates a defocus amount on the basis of an output of the focus detection unit; a drive unit that drives a focus lens on the basis of the defocus amount; a unit that sets a maximum accumulating time period that can be consumed for accumulation of charges in the focus detection unit; an object speed calculation unit that calculates an object speed; a measuring unit that measures focus detection time period; and a drive speed calculation unit that calculates a drive speed of the focus lens based on the object speed and the focus detection time period, wherein when an accumulation amount of charges in the focus detection unit reaches a threshold value within the maximum accumulating time period, at a time when the accumulation amount of charges in the focus detection unit reaches the threshold value, the defocus computing unit calculates a defocus amount using an output of the focus detection unit and outputs the defocus amount to the drive unit, when the accumulation amount of charges in the focus detection unit does not reach the threshold value within the maximum accumulating time period, at a time when the maximum accumulating time period lapses, the defocus computing unit calculates a defocus amount using an output of the focus detection unit and outputs the defocus amount to the drive unit, and the focus lens is driven on the basis of the drive speed.