| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a zoom lens for achieving a back focus amount of 2.4 or more while achieving a zoom magnification of 1.5 or more. <P>SOLUTION: This zoom lens 1 includes, sequentially from the enlargement side, a first lens group 11 of negative optical power as a whole and second to fourth lens groups 12-14 of positive optical power as a whole. During magnification change, the second and third lens groups 12 and 13 move along the optical axis AX, the first lens group 11 includes positive lens 111 and three negative lenses 112, 113 and 114 that are convex on the most enlargement side, and the second lens group 12 is formed of a positive single lens 121. The third lens group 13 has a negative lens 131, positive lens 132, and positive lens 133 sequentially from the most enlargement side, moves during the magnification change, and establishes 7<f3/fw<9 and 2.4<bf/fw<3.5. Here, f3 is focal distance of the third lens group 13, fw is focal distance of the whole lens at a wide angle end, and bf is back focus length of air conversion. <P>COPYRIGHT: (C)2011,JPO&INPIT |
