PURPOSE: To obtain an objective lens for fiber which is bright and free from an aberration, and also, can measure exactly a distance and thickness of a body to be measured, by allowing the objective lens constituted of seven groups and eleven pieces as a whole to satisfy specific conditions.
CONSTITUTION: The titled objective lens is constituted of seven groups and eleven pieces as a whole and also, allowed to satisfy a condition of an inequality. In this regard, f1:f2:(b): and (d) denote a composite focal distance of a first lens group at the time when the first lens group has been formed by combining a first lens, a second lens, a third lens and a fourth lens, a composite focal distance of a second lens group at the time when the second lens group has been formed by combining a fifth lens and a sixth lens, a distance between an axial apex of r17 and an object, when a radius of curvature of the opposed surface of the object side of the sixth lens is denoted as r17, when an object image is formed on the end face of a fiber, and an axial air interval between the first lens group and the second lens group, respectively. In such a way, a fiber objective lens which is bright and free from an aberration, and also, can execute easily focusing is obtained.
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