MULTIFOCUS OPTICAL SYSTEM AND OPTICAL DEVICE USING THE SAME

摘要

PROBLEM TO BE SOLVED: To reduce the production cost and the inspection cost and to change a defective product to a non-defective product by part exchange even when a product is judged as defective at the time of inspection while securing the excellent recording and reproduction of a signal with respect to plural types of optical disks having different thicknesses by constituting an objective optical system of a multifocus optical system by arranging a plate member having a ring zone refracting one part of incident luminous flux and a positive lens. SOLUTION: The 1st luminous flux 10A (dotted line) emitted from a groove part 15A and the 2nd luminous flux 10B (solid line) emitted from other plate areas 15B and 15C are converged with the same refractive power in a positive lens 5B. However, the incident angles thereof on the positive lens 5B are different from each other, so that the converging positions of both of them are different from each other and the luminous flux from the groove part 15A is condensed on the signal recording surface 6A of an optical disk such as a CD which is geometrically thick and the 2nd luminous flux 10B from the areas 15B and 15C is condensed on the signal recording surface 6B of an optical disk such as a DVD which is geometrically thin.