| 摘要 |
PROBLEM TO BE SOLVED: To obtain a zoom lens and a projection optical system using the same capable of projecting picture information displayed on a liquid crystal display element onto a screen surface while maintaining high optical performance. SOLUTION: This zoom lens is provided with a 1st lens group having negative refractive power, a 2nd lens group having positive refractive power, a 3rd lens group having negative refractive power, a 4th lens group having positive refractive power and a 5th lens group having positive refractive power in order from a 1st conjugate point side when a conjugate point having a longer distance is set as the 1st conjugate point. In the case of varying power from a zoom position at a wide-angle end to a zoom position at a telephoto end, two or more lens groups are moved, the 1st and the 5th lens groups are fixed in the midst of varying the power. When a conjugate point having a shorter distance is set as a 2nd conjugate point and the shortest distance as an absolute value in the midst of varying the power out of a distance from a lens surface on the 2nd conjugate point side to an exit pupil position is defined as (tk) and the focal distance at the wide-angle end of the entire system is defined as (fw), the zoom lens satisfies|tk|/fw>1.5.
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