Focus detector

A two dimensional focus detector, comprising:

• an imaging lens;
• light path selecting means for permitting light from an object to alternately pass through first and second regions of said imaging lens and to alternately pass through third and fourth regions of said imaging lens, each of said regions being different from one another, said first and second regions lying along a first direction which is perpendicular to a second direction along which said third and fourth regions lie;
• photoelectric transducer means having first and second light receiving monolayers lying in said first and second directions, respectively, said transducer means being disposed in a predetermined imaging plane of said imaging lens for receiving the light passing through said first and second and said third and fourth regions, respectively;
• first and second sets of circuit means for forming first and second signals from respective outputs of said transducer means, said first and second signals representing the center of gravity of the light intensity distribution impinging upon said first and second monolayers, respectively, each one of said center of gravity signals having first and second polarities, associated respectively with the condition when said light is focused in front and in the rear of said light receiving monolayers;
• first and second sets of light path indication means for producing first and second light path signals, each said light path signal having a first predetermined level when said light passes, respectively, through said first and third regions and a second predetermined level when said light passes, respectively, through said second and fourth regions;
• first and second sets of discriminator means responsive, respectively, to said first and second light path signals and to said first and second center of gravity signals for producing, respectively, first and second focusing sense signals having a first level to indicate a front focus condition and a second predetermined level to indicate a rear focus condition, said first and second focusing sense signals being produced by correlating said polarities of said center of gravity signals with said first and second levels of said light path signals;
• and
• focusing correction means responsive to said first and second focusing sense signals and to said first and second center of gravity signals for detecting whether said front or rear focus conditions exists when the light path is changed between said first and second, and between said third and fourth regions, respectively, and for producing a control signal based on the change in magnitude of said first and second center of gravity signals for controlling said imaging lens to produce an in focus condition.