| 摘要 |
In a projection type image display apparatus, for enlarging an image on a image display apparatus 1 by means of a projection lens 2, thereby projecting the enlarged image onto a screen 6, obliquely, being inclined thereto, between the projection lens 2 and a rear-surface mirror 5, there are disposed free shaped surface mirrors 3 and 4, each having a free shaped surface for compensating a trapezoidal distortion due to oblique projection of the enlarged image. The surface configuration of the free shaped surface mirror is so shaped as to satisfy a following equation: <?in-line-formulae description="In-line Formulae" end="lead"?>|L1-L2|>1.4.Dv <?in-line-formulae description="In-line Formulae" end="tail"?> if assuming that a distance for a light beam of an upper end of the enlarged image to reach the screen after being reflected upon a free shaped surface is "L1", a distance for a light beam of a lower end of the enlarged image to reach the screen after being reflected upon the free shaped surface is "L2", and a distance from an upper end of an image on the screen to a lower end thereof is "Dv".
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