Focus detecting device for opthalmologic instruments

A focus detecting device for ophthalmologic instruments comprising target means including a target pattern comprised of a first slit having a longitudinal axis and a second and third slits disposed in parallel with and at the opposite sides of said first slit, said second and third slits being symmetrical with respect to the first slit, first deflecting means for deflecting a luminous flux through the first slit in one direction perpendicular to the longitudinal axis of the first slit and second deflecting means for deflecting luminous flux through each of the second and third slits in the opposite direction;

• a target projection system for projecting said target pattern on a patient's eye fundus to produce a target image comprising slit images of the first, second and third slits;
• an imaging system for forming an image of luminous flux from the target image on the eye fundus;
• means for photoelectrically detecting distances between the first slit image and the second slit image and between the first slit image and the third slit image to thereby detect a position wherein the target image is focused on the eye fundus.