Double telecentric objective lens

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:
• 1n−n1p>0.1 (1)
• ν1p−ν1n>25 (2)
• 0.3fF<|r2n|<0.5fF (3)
• 1.4<(r2p/r2n)<2.7 (4)
• n3n<n3p (5)
• where n1p and ν1p respectively represent a refractive index and an Abbe's number of said convex lens of said first unit, n1n and ν1n 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).