PROJECTION FINITE ZOOM LENS

摘要

PROBLEM TO BE SOLVED: To provide a projection finite zoom lens for a liquid crystal projector having a high F-number, high resolution, a large image circle and a high zoom ratio by regarding 1.8-inch liquid crystal with high definition (XGA) as an object. SOLUTION: This lens is constituted by arranging a 1st group having negative refractive power, a 2nd group having positive refractive power, a 3rd group having the negative refractive power and a 4th group including a prism and having the positive refractive power in order from a screen side. The focal distance of an entire system is changed by non-linearly moving the 1st, the 2nd and the 3rd groups. Assuming that the focal distance at a wide angle end is fw , and the focal distances of the 1st, the 2nd, the 3rd and the 4th groups are f1 , f2 , f3 and f4 , they satisfy conditions: 2.8<|f1 /fw|<3.2, 1.4