Camera focus detecting device

Claim 1

A focus detecting device for a lens system comprising: means for dividing the image of an object into two optically equal images of the object; means for shifting at least one of the two images of that object with respect to the other image; first and second photoelectric conversion element groups adapted to convert the variations in relative position of the two images of the object into electrical signals, each of said first and second groups including n photoelectric conversion elements, each photoelectric conversion element in said first group providing a current output i m and each photoelectric conversion element in said second group providing a current output i' m , where m=1, 2, 3, . . . n is the number in order of each photoelectric conversion element in its respective group and the outputs i i through i n and i' 1 through 1' n are proportional to the quantities of light applied to respective photoelectric conversion elements; an optical system for projecting the images of the object onto the two photoelectric conversion element groups; and a calculation circuit means for receiving outputs from said conversion elements and for calculating a first voltage from the differential comparison of the outputs of conversion elements in opposite groups which are laterally offset in a first direction with respect to one another, a second voltage from the differential comparison of the outputs of conversion elements in opposite groups which are laterally offset in a second direction, opposite to said first direction, with respect to one another, and for generating a third voltage corresponding to the difference between said first and second voltages, which third voltage differs in polarity on opposite sides of the proper focalization point of said lens system.