| 摘要 |
PROBLEM TO BE SOLVED: To provide a large-aperture lens system in which the number of lenses is reduced and coma flare, astigmatism, and axial spherical aberration are excellently corrected to achieve excellent optical performance and which is bright by an F-number (aperture ratio) of about 1.8.SOLUTION: The large-aperture lens system comprises, in order form an object side, a front group having positive refractive power, an aperture diaphragm, and a rear group having positive refractive power. The front group comprises, in order from the object side, a positive first lens, a positive second lens, and a negative third lens, and the rear group comprises, in order from the object side, a negative fourth lens, a positive fifth lens, and a positive sixth lens. The large-aperture lens system satisfies the following conditional expressions (1) and (2): 1.03<L2f/f<1.83 (1), 0.3<(r5-r4)/(r5+r4)<0.8 (2), where L2f is the focal length of the second lens, f is the focal length of the entire system, r4 is the curvature radius of the surface on the image side of the second lens, and r5 is the curvature radius of the surface on the object side of the third lens. |
