| 摘要 |
PROBLEM TO BE SOLVED: To provide an imaging lens which can excellently correct chromatic aberration by using a diffraction optical surface, a lens system having a minimum one-group one-lens configuration, has broadband light and a wide angle of view, and is suitable for photographing an object. SOLUTION: A concave surface R2 is formed on the object side of a plastic lens L1 having a one-lens configuration and a convex surface R4 is formed on the image point side of the plastic lens L1. The concave surface R2 and the convex surface R4 are aspherical and the diffraction optical surface R5 fulfilling a chromatic dispersion function is formed on the convex surface R4. A conditional expression (1): 0.45<L/R<0.95 and a conditional expression (2):-0.065<L'(1-n)/R'<0.035n are satisfied, wherein L is an apparent distance up to a diaphragm when viewed from the top of the convex surface when a position where a main light bream crosses an optical axis is set to a diaphragm position, L' is an apparent distance up to the diaphragm when viewed from the top of the concave surface when the position where the main light beam crosses the optical axis is set to the diaphragm position, R is the radius of curvature of the convex surface, R' is the radius of curvature of the concave surface, and n is the refractive index of a lens material. COPYRIGHT: (C)2010,JPO&INPIT |
