| 摘要 |
PROBLEM TO BE SOLVED: To provide a wide-angle optical system for imaging a wide area and forming an adequately corrected image even for a close-up object. SOLUTION: The wide-angle optical system includes, in order from an object side: an aperture diaphragm; a first lens of positive refractive power; a second lens of negative refractive power; and a third lens. Both faces of the third lens are aspherical such that refractive power changes according to a distance from an optical axis so that the shape near the optical axis is convex on an object side and the shape near the periphery of the lens is concave on the object side. The wide-angle optical system satisfies conditional inequalities (1) and (2) given below. Inequality (1): 2.2<d<SB>2</SB>/d<SB>3</SB><7 and inequality (2):-0.04<f/f<SB>3</SB><0.04, in which d<SB>2</SB>is the thickness of the first lens on an optical axis, d<SB>3</SB>is a spatial distance between the first and second lenses on the optical axis, f is the focal distance of the entire wide-angle optical system, and f<SB>3</SB>is the focal distance of the third lens. COPYRIGHT: (C)2010,JPO&INPIT
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