Retrofocus Objective Lens System with four lenses and Imaging Apparatus

摘要

An imaging lens system includes three lens groups having four lenses including a first lens (L1), a second lens (L2), a third lens (L3), and a fourth lens (L4) arranged in order from an object side, and an aperture stop (S) arranged between the first lens (L1) and the second lens (L2). The second lens (L2) and the third lens (L3) are joined each other. The first lens (L1) is a negative meniscus lens having, a convex surface at an object side, The second lens (L2) is a positive lens having a convex surface having a large curvature at an image side. The third lens (L3) is a negative lens having a concave surface having a large curvature at an object side. The fourth lens (L4) is a positive lens having a convex surface having a large curvature at an image side. The following conditions are satisfied: 1.4 f �¢ 1 / F 2.2 0.4 f �¢ 1 / f �¢ 23 1.6 where F is a focal length of the entire imaging lens system, f1 is a focal length of the first lens (L1), and f23 is a combined focal length of the second lens (L2) and the third lens (L3) which are joined each other. The following condition is satisfied: 1.80 N �¢ 1 where N1 is a refractive index of material of the first lens (L)1 for a d line.