| 摘要 |
PURPOSE:To provide a condenser lens which is as large as -0.2--0.3 in working power, has 0.45-0.50 numerical aperture on the optical disc side, has a relatively large working distance and a relatively large effective field angle as large as + or -2 deg. and the aberration of which is thoroughly corrected for the minor change in the object image distance by forming the lens system constituted of the four groups and four elements satisfying the specifice conditions. CONSTITUTION:A condenser lens is constituted, successively from a light source side, of the 1st lens 11, the 2nd lens 12, the 3rd lens 13 and the 4th lens 14 and satisfies the conditions (1)-(5). (1) 1.4f<f1<1.7f, (2) r1>¦r2¦, (3) 2.7f<f2<3.6f, (4) 1.0<f3/f4<1.3, (5) d2<0.1f, where K is the combined focal length over the entire part of the lens system, f1, f2, f3, f4 are respectively the focal lengths of the 1st lens 11, the 2nd lens 12, the 3rd lens 13 and the 4th lens 14. r1, r2 are respectively the radii of curvature of the faces of the lens 11 on the light source side and the image side and d2 is the air space between the lens 11 and the lens 12. |
