| 摘要 |
PROBLEM TO BE SOLVED: To obtain a zoom lens which is formed as a five-group type making the positive second group, positive third group and weak fourth group movable at varying the power, is appropriate for a projection type display device using a liquid crystal, is satisfactorily corrected in various aberrations, is bright and is wide in angle, is formed to an appropriate back focus length, and can contribute to making the entire system of the lens including the back focus shorter. SOLUTION: The zoom lens is arranged, successively from the expansion side, with a negative G<SB>1</SB>group which is fixed and performs focusing at varying the power, a positive G<SB>2</SB>group which moves by having a relation with each other for the purpose of continuous variable power and correction for moving an image field, a positive G<SB>3</SB>group, a G<SB>4</SB>group having a weak refractive power and a positive G<SB>5</SB>group which is fixed at varying the power. The G<SB>4</SB>group is comprised, successively from the expansion side, of a negative meniscus lens L<SB>11</SB>directing its convex face toward the expansion side, a cemented lens of a negative lens L<SB>12</SB>and a positive lens L<SB>13</SB>, and a positive lens L<SB>14</SB>. The G<SB>5</SB>group is comprised of a piece of the convex lens L<SB>15</SB>. Also, zoom lens satisfies (1) F<SB>n</SB><2.0, (2) F<SB>n</SB><LL/Bf<5.25, (3) f<SB>2</SB>/f<SB>3</SB><1.0, (4) 0.8<f<SB>23</SB>/fw<<SB>1.4</SB>, (5) 4.5<¾f<SB>4</SB>/f<SB>w</SB>¾, and (6) 1.6<f<SB>5</SB>/f<SB>w</SB><2.8. COPYRIGHT: (C)2006,JPO&NCIPI
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