| 摘要 |
PURPOSE:To miniaturize the whole of a lens system and to extend the operating distance by using a meniscus lens, which has the concave directed to the light source and has a negative refracting power, as a first lens in the light source side to narrow the interval between the first lens and a second lens and satisfying specific relations in the whole of the lens system. CONSTITUTION:The lens system consists of the first meniscus lens which has the concave directed to the light source and has a negative refracting power, the second lens having a positive refracting power, and a third meniscus lens which has the convex directed to the light source and has a positive refracting power in order from the light source side. The lens system satisfies conditions of inequalities I-III where ri and fi are the radius of curvature of the i-th lens surface and the focal length of the i-th lens respectively and f12 and (f) are the resultant focal length of first and second lenses and the focal length of the whole of the lens system respectively. Thus, a small-sized and light-weight objective lens for optical pickup having an optical performance is obtained which has axial aberrations and out-of-axis aberrations satisfactorily corrected to keep the high aperture ratio of 0.45-0.55 NA and secures a prescribed operating distance.
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