| 摘要 |
A fisheye lens system with a half angle-of-view of 90° includes a negative front lens group, a diaphragm, and a positive rear lens group. The negative front lens group includes at least three negative meniscus lens elements each of which has the convex surface facing toward the object; and the three negative meniscus lens elements satisfy the following conditions: <?in-line-formulae description="In-line Formulae" end="lead"?>0.2<SF<SUB>(i=1)<0.6</SUB> (1)<?in-line-formulae description="In-line Formulae" end="tail"?> <?in-line-formulae description="In-line Formulae" end="lead"?>0.8<SF<SUB>(i=2)</SUB>/SF<SUB>(i=1)<1.5</SUB> (2)<?in-line-formulae description="In-line Formulae" end="tail"?> <?in-line-formulae description="In-line Formulae" end="lead"?>0.8<SF<SUB>(i=3)</SUB>/SF<SUB>(i=1)<2.0</SUB> (3)<?in-line-formulae description="In-line Formulae" end="tail"?> wherein SFi designates the shaping factor of the i<SUP>th </SUP>(1<=i<=3) negative meniscus lens element (SFi=(R 1 i-R 2 i)/(R 1 i+R 2 i)); R 1 i designates the radius of curvature of the object-side surface of the i<SUP>th </SUP>(1<=i<=3) negative meniscus lens element; and R 2 i designates the radius of curvature of the image-side surface of the i<SUP>th </SUP>(1<=i<=3) negative meniscus lens element.
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