| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide an imaging optical system that is small, has a large diameter with an F-number smaller than 2.4, and secures high image quality despite an angle of view that is as wide as 76°or greater. <P>SOLUTION: The imaging optical system includes, in order from an object side, a first lens group G1 of negative refractive power, an aperture diaphragm FA, and a second lens group G2 of positive refractive power. The first lens group G1 includes, in order from the object side, a front first lens group 1F of negative refractive power and a rear first lens group 1R of positive refractive power. A fixed diaphragm FB is additionally disposed between the first lens group G1 and the aperture diaphragm FA. If a distance on an axis from the lens face 6 closest to the image side in the first lens group G1 to the fixed diaphragm FB is represented by Dc and a distance on an axis from the lens face 6 closest to the image side in the first lens group G1 to the aperture diaphragm FA is represented by Ds, the imaging optical system L1 satisfies a conditional expression (1): 0.4<Dc/Ds<0.8. <P>COPYRIGHT: (C)2010,JPO&INPIT</p> |
