Focus detecting apparatus

A focus detecting apparatus for detecting the focus of a photo-taking lens, comprising:

• a condenser lens disposed near the predetermined image plane of an object formed by said photo-taking lens;
• and
• a plurality of focus detection systems each comprising pupil dividing means disposed rearwardly of said condenser lens in the direction of the optical axis thereof and having at least one pair of openings for dividing the pupil of said photo-taking lens, at least one pair of re-imaging lenses disposed rearwardly of said pupil dividing means correspondingly to said at least one pair of openings for forming at least one pair of secondary images, and a photoelectric conversion element array having picture elements for detecting the amount of deviation of the relative position of said secondary images;
• with the area of said pair of openings in a first of said focus detection systems being different from that in a second of said focus detection systems, each said picture element in said first system having a first area, each said picture element in said second system having a second area, and each of said first area and said second area being determined in accordance with the area of the corresponding pair of openings such that said first area and said second area are different and respective output signal levels from the photoelectric conversion element arrays of said first and second systems are substantially equal.