FOCUS DETECTION DEVICE WITH WAVEFRONT ABERRATION CORRECTION

A focus detection device includes a focus adjustable objective lens for forming an image of an object, first and second image forming lenses for forming first and second images of the image of the object, and first and second image sensors for sensing the first and second images so as to generate first and second signals representative of light intensity distributions of the first and second images. A first calculating member calculates a distance between the first and second images in accordance with the first and second signals, a second calculating member for calculating an amount of deviation of the image relative to a focal plane in accordance with the distance calculated by the first calculating member. A main portion determining member determines a location of a main portion of the first image in accordance with the first signal and a correction member corrects one of the calculation results obtained by the first and second calculating members when the determination of the main portion determining member indicates that the main portion is located outside a central portion of the first image, thus lessening error due to wave front aberration.