| 摘要 |
PURPOSE:To obtain a small-size attachment lens which extends the focal length about 1.5 times and reduce the brightness to the half approximately, by satisfying prescribed conditions in the lens system consisting of convex, concave, and concave meniscus lenses. CONSTITUTION:In the lens system consisting of a meniscus convex lens having a strong convex face in the image side, a meniscus concave lens having a strong concave face in the object side, and a meniscus concave lens having a strong concave face in the object side, conditions of expressions (1)-(5) are satisfied. In these expressions, fA is the resultant focal length of the lens system, and r1- r5 are radiuses of curvature of the first- the fifth faces, respectively, and n1 and n2 are refractive indexes of the first and the second lenses, respectively. Thus, a small-size attachment lens is obtained which extends the focal length about 1.5 times and reduces the brightness to the half approximately. |
