Patent ID: 6471359
Filing Date: 2002-10-29
Classification: G02B

Abstract:
In a projection display apparatus including a light source, an optical illumination system, a light valve, a color separating/synthesizing system, and a projection lens, the projection lens comprising:a first lens group arranged upstream from a screen, the first lens group having a negative power and including at least one aspherical lens element and at least three spherical lens elements, the lens element of the first lens group spaced away from the screen by a maximum distance having a positive power; a second lens group arranged upstream from the first lens group, the second lens group having a positive power and including a triple cemented lens composed of three lens elements cemented together, and at least one lens element having a positive power arranged at one side of the triple cemented lens opposite to the screen; and an aperture stop arranged between the first and second lens groups, the first and second lens groups meet the following conditions: âˆ’5.410.42<5.1â€ƒâ€ƒ(2) 2.81/f<7.8â€ƒâ€ƒ(3) where, â€œf1â€  represents the effective focal length of the first lens group, â€œf2â€  represents the effective focal length of the second lens group, â€œfâ€  represents the effective focal length of the projection lens, â€œbf1â€  represents the back focal length of the projection lens, and â€œdâ€  represents the distance between the first and second lens groups.