| 摘要 |
PROBLEM TO BE SOLVED: To provide a lens small in size, light in weight and excellent in optical characteristic with simple fours-sheets and three-group constitution. SOLUTION: This lens consists of a 1st lens 1 which is formed of synthetic resin and has negative power, a lightness stop r3, a 2nd lens 2 which is formed of synthetic resin and has a surface of larger curvature on the image side and positive refracting power, a 3rd meniscus lens 3 which is convex to the object side and has negative refracting power, and a 4th lens 4 which has a cemented part with the 3rd lens 3 and positive refracting power in order from the object side, and the 1st lens 2 has an aspherical surface decreasing in negative refracting power toward its peripheral part as at least one surface r1; and the lens of 4-element constitution meets the requirements prescribed by (1) 1.2<|f1/f|<2.5, (2) 1.0<(D2+D3)/f<2.5, and (3) 20<ν-ν3<50, where f1 is the focal length of the 1st lens, (f) the composite focal length of the whole system, D2 the air interval between the 1st lens and lightness stop, D3 the air interval between the lightness stop and 2nd lens,ν3 the Abbe number of the 3rd lens, andν4 the Abbe number of the 4th lens.
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