| 摘要 |
PURPOSE:To realize a superwide-angle photographic lens at a low-cost by employing two-group, two-element constitution of a concave meniscus lens with negative power as a 1st lens and a biconvex lens with positive power as a 2nd lens and making the lenses meet specific requirements. CONSTITUTION:The lens consists of two elements in two groups, i.e., the 1st concave meniscus lens 20 with the negative power and the 2nd biconvex lens with the positive power in order from the object side to the image side, and >=1 lens surface is made aspherical so as to realize high brightness and a superwide angle. Further, conditional inequalities AB and A hold for the focal length (f) of the whole system, the focal length f2 of the 2nd lens 12, and the surface gap D2 between the image-side lens surface of the 1st lens 10 and the object-side lens surface of the 2nd lens 12. The inequality determines the power distribution and the inequality B prescribed the size of the lens system and the power of each lens. |
