| 摘要 |
PURPOSE:To obtain an objective lens which is used most suitably when the distance between a light source and an information recording surface is short and consists of a small-number of constituting lenses and uses a minimum number of aspherical surfaces, by constituting the objective lens with the first lens which has the convex directed to the light source side and has a positive refracting power and the second lens which has the convex directed to the light source side and has a positive refracting power and arranging the first and the second lenses in order from the light source side and satisfying specific conditions. CONSTITUTION:The objective lens consists of the first lens which has the convex directed to the light source side and has a positive refracting power and the second lens which has the convex directed to the light source side and has a positive refracting power, and the first and the second lenses are arranged in order from the light source side, and the surface in the light source side of the second lens is aspherical, and conditions of formulas are satisfied. Through the first lens is a spherical lens which converts a divergent light to a convergent light, the negative spherical aberration generated by this conversion must be reduced as much as possible. A condition (1) is given for the purpose of reducing this spherical aberration. Since the objective lens consists of two lenses and is realized with a minimum number of apherical surfaces, this objective lens contributes to the reduction of the cost of an optical disc optical system.
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