| 摘要 |
PROBLEM TO BE SOLVED: To maintain excellent optical performance while keeping the thickness DL of a lens system within a prescribed range considering mass production with the entire length reduced. SOLUTION: The imaging lens is equipped with: a first lens L1 that is a positive lens, at least whose one surface is aspherical and whose object-side surface is convex; a second lens L2 that is a negative lens, whose image-side surface is concave; a third lens L3 that is a positive meniscus lens, whose concave surface faces an object side near an optical axis; and a fourth lens L4 whose both surfaces are aspherical, and it satisfies an expression (1): 0.85≤DL/f≤0.93, an expression (2): 0.19≤D5/f≤0.5, an expression (3):-0.8≤f/R3≤0, an expression (4): 1.25≤f/R1≤3.33 and an expression (5): (D1+D2):/f≤0.25. In the expressions, f denotes the focal length of the entire system, DL denotes the thickness of the lens system, D5 denotes the center thickness of the third lens L3, R1 and R3 denote the paraxial curvature radii of the object-side surfaces of the first and the second lenses L1 and L2, and D1+D2 denotes a distance on the optical axis from the top of the object-side surface of the first lens L1 to the top of the object-side surface of the second lens L2. COPYRIGHT: (C)2009,JPO&INPIT
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