| US 7,586,690 B2 | ||
| Projection type zoom lens and projection type display apparatus | ||
| Hiroshi Yamada, Saitama (Japan) | ||
| Assigned to Fujinon Corporation, Saitama-Shi (Japan) | ||
| Filed on Aug. 09, 2007, as Appl. No. 11/889,153. | ||
| Claims priority of application No. P2006-220428 (JP), filed on Aug. 11, 2006. | ||
| Prior Publication US 2008/0231962 A1, Sep. 25, 2008 | ||
| Int. Cl. G02B 15/14 (2006.01) | ||
| U.S. Cl. 359—680 [359/676] | 9 Claims |
| 1. A projection type zoom lens comprising:
a first lens group having a negative refractive power; and
second to sixth lens groups having positive refractive powers, wherein:
the first to sixth lens groups are arranged in order from a magnification side,
the first lens group comprises at least one negative lens which has an anomalous dispersion property and which has 70 or more
in Abbe number,
at least one positive lens is included in the third to fifth lens group, the at least one positive lens which has an anomalous
dispersion property and which has 70 or more in Abbe number,
at least one of the negative lens having the anomalous dispersion property is cemented to a positive lens adjacent to the
negative lens,
at least one of the positive lens having the anomalous dispersion property is cemented to a negative lens adjacent to the
positive lens,
during variation of magnification, the second to fifth lens groups move and the first and sixth lens groups are fixed,
during focus adjustment, the first lens group moves, and the following conditional expression (1) is satisfied:
bf/fw≧2.7 (1)
where bf denotes a back focus, and
fw denotes a focal length of the entire system at a wide-angle end.
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