Patent ID: 8614755

Claim:
An optical device comprising: an image pickup element which has a plurality of imaging pixels configured to perform a photoelectric conversion of an object image formed by a light beam emitted from an image pickup optical system and a plurality of focus detection pixels configured to perform a photoelectric conversion of two images formed by two divided light beams of the light beam emitted from the image pickup optical system; a focus detector configured to obtain, from the plurality of focus detection pixels, first and second pairs of image signals having optical base lengths different from each other; a selector configured to select one of the first and second pairs of image signals based on at least one correlation amount of the first and second pairs of image signals; and a calculator configured to calculate a defocus amount based on the selected pair of image signals, wherein a corresponding micro lens is arranged for each pixel of the plurality of imaging pixels and the plurality of focus detection pixels, wherein the plurality of focus detection pixels include first, second and third focus detection pixels, each of which has a different opening center position, wherein the focus detector obtains the first pair of image signals from the first and second focus detection pixels and obtains the second pair of image signals from the first and third focus detection pixels, wherein the optical base length of the second pair of image signals is shorter than the optical base length of the first pair of image signals, and wherein a distance between the first and third focus detection pixels is greater than a distance between the first and second focus detection pixels.