| 摘要 |
PROBLEM TO BE SOLVED: To realize a compact zoom lens for projection capable of maintaining high resolving power, having long back focus required for the arrangement of a color synthesizing optical system and having high telecentricity though it is a wide-angle lens whose half viewing angle is >=30 deg.. SOLUTION: The zoom lens for projection is constituted by successively arranging 1st to 6th negative, positive, positive, negative, positive and positive lens groups I to VI from an enlargement side to a reduction side and providing an aperture diaphragm ST between the 3rd and the 4th lens groups. In the case of consecutively varying power from a wide angle end to a telephoto end, the 1st and the 6th lens groups are fixed and the 2nd to the 5th lens groups are moved on an optical axis to the enlargement side. Then, the focal distance of an entire system at the wide angle end: fw, the focal distance of the 1st lens group: f1, back focus when a conjugate point on the enlargement side is infinity: Bf and the length of the entire system: L satisfy conditions (1) 1.0<Bf/fw (2) 0.9<|f1|fw<1.3 and (3) 3.0<L/fw<4.0.
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