| 摘要 |
A projection lens comprises 5 lenses in 5 groups including: a first-group lens that is a positive lens; a second-group lens that is a positive lens having the largest positive power (the inverse number of focal length) in the whole lens system; a third-group lens that is a positive lens; a fourth-group lens that is a positive lens; and a fifth-group lens that is a negative lens with its concave surface facing a screen side, in order from the screen side, wherein each lens of the first, third, fourth and fifth groups has at least one aspheric surface. The distance between the first-group lens and the second-group lens is relatively short, and the positive power in the fourth-group lens is relatively high. In the projection lens, an optical focal shift due to the temperature change in the fifth-group lens is hardly caused, and therefore a projection lens with minimal distortion aberration can be provided at a low cost.
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