| 摘要 |
PURPOSE:To obtain the lens whose brightness is F2 or more and whose various aberrations are well corrected by providing a luminous flux defining member in front of the lens of the 3-group constitution formed by the specified four lenses and letting optical specifications satisfy the specified conditions. CONSTITUTION:A luminous flux defining member 10 is disposed on the subject side and the large-aperture lens of a focal length F is so constituted as to satisfy the conditions of formulas I-II by the 3-groups 4-elements of the positive single lens of a radius of curvature r1 at the front face forming the 1st group 1 of a combined focal length f1, the 2nd group 2 formed by a biconcave lens which is r2 in the radius of curvature of the rear face and is aspherical in the radius of curvature of the front face and the 3rd group 3 formed by a negative lens and a biconvex lens of a refractive index N4 and Abbe number nu4. The production of spherical aberrations is limited by the conditions of these formulas I, II, various averrations are well corrected by the conditions of formulas III-V, chromatic aberrations by the conditions of formula IV and the effect of flare by formula VII, whereby the large-aperture lens of brightness F2 or more and angle of view 45 deg. or more is provided. Here, phi2' denotes the composite refracting power of the air lens formed by the groups 2, 3 and d the axial air spacing of each group. |
