| 摘要 |
PURPOSE:To improve image-forming performance up to the outermost circumference of a picture plane by using the 1st - the 4th lens groups which have a positive, a negative, a positive, and a negative refracting power successively from an object side as elements of an F2.8, 56-60 deg. angle-of-view lens which suits to a camera of 8.3X10.6mm. picture size, and specifying aspherical surfaces of the 3rd or 4th lens group and satisfying specific requirements. CONSTITUTION:The 1st lens group L1 consists of a positive lens having a convex surface of large curvature facing the object side, the 2nd lens group L1 consists of a biconcave lens; and the 3rd lens group L3 consists of a biconvex lens, and the 4th lens group L4 consists of a negative surface having a convex surface on the image side. Then, at least either of surfaces of the 3rd and the 4th lens groups L3 and L4 which form an air gap is made aspherical so that deviation from paraxial curvature increases toward the outside of the groups radially from the optical axis, and the other surface is made spherical. Further, inequalities (1) and (2) hold. |
