Patent ID: 6639653
Filing Date: 2003-10-28
Classification: G02B

Abstract:
A double telecentric objective lens having a double telecentric optical system, wherein said double telecentric optical system comprises: a front group having a positive refracting power as a whole; and a rear group having a positive refracting power as a whole, wherein a rear focus of said front group and a front focus of said rear group coincide with each other, and a diaphragm is placed at a position where the front and rear focuses coincide, wherein said front group includes a first unit and a second unit, said first unit being formed of a cemented lens composed of a convex lens and a concave lens, and having a positive refracting power as a whole, said second unit including a convex lens or a cemented lens composed of a convex lens and a concave lens, and a concave lens, arranged in that order from an object side, and having a positive refracting power as a whole, wherein said rear group includes a third unit and a fourth unit, said third unit including a concave lens and a cemented lens composed of a convex lens and a concave lens, and having a positive refracting power as a whole, said fourth unit being formed of a cemented lens composed of a convex lens and a concave lens, and having a positive refracting power as a whole, and wherein the following conditions are satisfied:1nâˆ’n1p>0.1â€ƒâ€ƒ(1) &ngr;1pâˆ’&ngr;1n>25â€ƒâ€ƒ(2) 0.3fF2n|<0.5fFâ€ƒâ€ƒ(3) 1.4r2p/r2n)<2.7â€ƒâ€ƒ(4) n3n3pâ€ƒâ€ƒ(5) where n1p and &ngr;1p respectively represent a refractive index and an Abbe's number of said convex lens of said first unit, n1n and &ngr;1n respectively represent a refractive index and an Abbe's number of said concave lens of said first unit, r2p represents a radius of curvature of a surface of said convex lens or said cemented lens composed of said convex lens and said concave lens in said second unit that is furthermost from an object, r2n represents a radius of curvature of an object-side surface of said concave lens in said second unit, fF represents a focal length of said entire front group, n3n represents an average refractive index of said concave lenses in said third unit, n3p represents a refractive index of said convex lens in said third unit, and a refractive indices and focal length are values for the d-line (587.56 nm).