| 摘要 |
PURPOSE:To obtain a superwide-angle lens which has a 110 deg. angle of view, a 1:1.6 aperture ratio, an extremely small filter diameter, and various aberrations compensated excellently although the lens consists of seven elements in six groups. CONSTITUTION:The 1st lens 1 and the 2nd lens 2 are concave meniscus lenses having convex surfaces on an object side, and the 3rd, the 5th, and the 6th lenses are convex lenses. The 4th lens 4 is a cemented concave lens consisting of a convex lens 4a and a concave lens 4b. Then, inequalities (A)-(D) hold (where (f) is the focal length of the whole system, f1.2 is the composite focal length of the 1st and the 2nd lenses, n1 is the refraction index of the 1st lens; and nu3 is the Abbe number of the 3rd lens and r6 is the radius of curvature of the 6th surface). The condition (A) relates to coma aberration, astigmatism, and the size reduction of the whole system, and the condition (B) is for correcting the coma aberration and chromatic aberration of power with good balance in relation to the condition (A); and the condition (C) relates to the compensation of the chromatic aberration of power in relation to the condition (B), and the condition (D) is for correcting the coma aberration, astigmatism, and chromatic aberration of power with good balance. |
