| 摘要 |
PROBLEM TO BE SOLVED: To provide a small-sized, high performance sure-wide angle lens system for a digital camera that has an F number of about 2.8 and a half view angle of≥40°. SOLUTION: The super-wide angle lens system comprises, in order from the object side, a front group having a negative focal distance and a rear group having a positive focal distance. In the super-wide angle lens system, the front group includes, in order from the object side, a first positive lens, a second negative lens, a third negative lens, and a fourth negative lens, and satisfies the following conditional equations (1) and (2): (1) 0>f/f<SB>1-2</SB><0.1 and (2) 0<SF1<3.0, wherein f is the focal distance of the entire system, f<SB>1-2</SB>is the focal distance of the image-side face of the first positive lens and f<SB>1-2</SB>= r<SB>2</SB>/(1-n<SB>1</SB>), wherein r<SB>2</SB>is the curvature radius of the image-side face of the first positive lens and n<SB>1</SB>is the refractive index of the first positive lens, and SF1 is the shaping factor of the first positive lens and SF1 = (r<SB>1</SB>+r<SB>2</SB>)/(r<SB>1</SB>-r<SB>2</SB>), wherein r<SB>1</SB>is the curvature radius of the object-side face of the first positive lens. COPYRIGHT: (C)2007,JPO&INPIT
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