| 摘要 |
PROBLEM TO BE SOLVED: To provide a subminiature imaging optical system suitable for a subminiature optical device. SOLUTION: The optical system includes: an aperture stop AS; a first lens L1 which has a positive refractive power and is convex at an object side; a second lens L2 which has a negative refractive power; a third lens L3 which has a positive refractive power; and a fourth lens L4 which has a negative refractive power, wherein the optical system satisfies the conditions: a total length along an optical axis direction, obtained from the distance from the aperture stop to an image face divided by the effective focal length of the whole optical system, is within a prescribed numerical range; the absolute value of the difference between Abbe numbers of the first lens and the second lens is bigger than a prescribed value; and the absolute value of the difference between the refractive indices of the first lens and the second lens is bigger than a prescribed value. COPYRIGHT: (C)2007,JPO&INPIT
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