| 摘要 |
PURPOSE:To obtain a Tesaar type lens having a short overall length in a lens system consisting, successively from an object side, of a positive meniscus lens, a biconcave lens, and a combined lens of a negative meniscus lens and a biconvex lens, by satisfying prescribed conditions. CONSTITUTION:The conditions of the equations (1)-(12) are satisfied in a lens system of the 3-group constitution consisting, successively from an object side, of a positive meniscus lens, a biconcave lens and a combined lens of a negative meniscus lens and a biconvex lens. Here, d1, d3, d5, d6 are respectively the wall thicknesses of the 1st, the 2nd and the 3rd groups (both lenses), d2 is the air spacing between the 1st and the 2nd groups r2, r3, r5, r6, r7 are respectively the radii of curvature of the face on the image side of the 1st group lens, the face on the object side of the 2nd group lens and the faces of the 3rd group lenses, n1, n2 are respectively the refractive indices of the 1st and the 2nd groups, nu1 are the Abbe number of the 1st group, and (f) is the focal length of the entire system. The post-stop Tesaar type lens having a short overall length, i.e., 1.10f, and about 0.76f back focus is thus obtd. |
