Abstract: An optical image pick-up lens is formed from crescent-shaped first and second lenses that may be aspherical molded glass lenses or aspherical plastic lenses. A convex surface at a first side of the first lens faces toward an object, and a convex surface at a second side of the second lens faces toward a formed image. The lens enables reduced lens length and high resolution by satisfying the following relational expressions: 0.4f≦d<0.9f; 0.5f≦|R3|≦100f; and 0.01<|f2|/|f1|<0.9; where, f is an overall focal length of the lens; d is a distance from the first side of the first lens to the second side of the second lens; R3 is a radius of curvature of an object side of the second lens; f1 is a focal length of the first lens; and f2 is a focal length of the second lens.

Abstract: An optical image pick-up lens is formed from crescent-shaped first and second lenses that may be aspherical molded glass lenses or aspherical plastic lenses. A convex surface at a first side of the first lens faces toward an object, and a convex surface at a second side of the second lens faces toward a formed image. The lens enables reduced lens length and high resolution by satisfying the following relational expressions: 0.4f≦d<0.9f; 0.5f≦|R3|≦100f; and 0.01<|f2|/|f1|<0.9; where, f is an overall focal length of the lens; d is a distance from the first side of the first lens to the second side of the second lens; R3 is a radius of curvature of an object side of the second lens; f1 is a focal length of the first lens; and f2 is a focal length of the second lens.

Abstract: A method of using a single pick-up head to read and store data in discs of different thickness, especially for CD (compact disc) and DVD (digital versatile disc), the method including the step of adjusting the electronic aperture ring to change the numerical aperture, and change the distance between the disc and the object lens subject to type of the disc used.