Patent ID: 8848095

Claim:
A focus detector for detecting a defocus amount of an image pickup optical system based on a displacement amount between a pair of images formed by a pair of light beams divided from the image pickup optical system and passed through a pair of pupil areas, the focus detector comprising: a pair of lenses; a pair of phase difference detecting sensors for photoelectrically converting a pair of subject images formed by the pair of lenses into a pair of image signals; a first correlation computing unit for dividing the pair of image signals based on a reference number-of-pixels to compute an image displacement amount for each divided area; a waveform coincidence degree computing unit for computing a coincidence degree of the pair of image signals in the each divided area where the image displacement amount is computed by the first correlation computing unit; a defocus amount computing unit for computing a defocus amount based on the coincidence degree of the pair of image signals computed by the waveform coincidence degree computing unit; a second correlation computing unit for computing an image displacement amount based on the pair of image signals from the pair of phase difference detecting sensors; and a reference number-of-pixels selecting unit for selecting the reference number-of-pixels from among a number of pixels to be subject to computation of the image displacement amount with respect to a plurality of the image displacement amounts computed by the second correlation computing unit.