| 摘要 |
PURPOSE:To obtain an objective lens for an optical disk that has long acting distance and nicely corrected aberrations by satisfying specified conditions in a lens system of five-group five-element constitution made of a negative meniscus lens, a positive lens, a negative meniscus lens, a positive lens and a positive meniscus lens. CONSTITUTION:In a lens system of five-group five element constitution made of a negative meniscus lens, a positive lens, a negative meniscus lens, a positive lens, and a positive meniscus lens in the order from the object side, conditions given in expressions I -IV are satisified. In the expressions, F is composite focal length of the whole system, F1.2.3 is composite focal length of the third group lens, F4, F5 are focal lengths of the fourth group lens and fifth group lens respectively, and r1, r5 are radius of curvature of faces of light source side of the first group lens and third group lens respectively. Specified acting distance is obtained by the expression I , and together with the expression II- expression IV, aberrations are corrected nicely. Thus, an objective lens for an optical disk of long acting distance in which aberrations are nicely corrected can be obtained. |
