| 摘要 |
The imaging optical system has a first positive lens element convex toward the object side, a second negative lens element concave toward the image side, a third lens element having both surfaces with a region, in which the lens section is located on the object side than the intersection with the optical axis, a fourth positive lens element convex toward the image side with at least one surface having an aspherical shape and inflection points, and a fifth negative lens element concave toward the image side. The optical system satisfies the expressions: 0.5<|f1/f|<0.67, 0.3<|f4/f|<0.63 The third lens element satisfies the expressions: -0.4<f/R1-L3<0.2, -0.6<f/R2-L3<0.05 where f, f1, f4 denote focal lengths of the entire system, the first lens element, and the fourth lens element, and R1_L3, R2_L3 denote paraxial diameters of the object-side surface and the image-side surface of the third lens element. |
