Patent ID: 6829088
Filing Date: 2004-12-07
Classification: G03B

Abstract:
A picture display of a rear surface projection type comprising:a projector for shooting out a light flux modulated by a picture, a transparent screen, on a rear surface of which said light flux shot out from said projector is projected, and a sawlike prismatic surface which is formed on said rear surface of said transparent screen, and provided with plural edges shaped into concentric circles centering around a central point situated outside said transparent screen, wherein an optical axis of said projector passes through said central point, and a ray of light incident on a first face looking downward and neighboring with each of said plural edges is transmitted into said transparent screen, and said ray of light transmitted through said first face is reflected by a second face looking upward and neighboring with said same edge to a front surface of said transparent screen, wherein an angle formed by said ray of light incident on said first face and said optical axis of said projector is greater than 40Â° and less than 90Â°, wherein: an angle &agr;2 formed by said first face and a line perpendicular to said optical axis of said projector is given by a following equation that tan&agr;2=[n2 sin {sinâˆ’1((n3/n2)sin &thgr;2+n1 sin &thgr;1)+2&agr;1}+n1 sin &thgr;1]/[n1 cos &thgr;1âˆ’n2 cos {sinâˆ’1((n3/n2)sin &thgr;2+n1 sin &thgr;1)+2&agr;1}], wherein a refractive index of a first medium brought into contact with said sawlike prismatic surface of said transparent screen is denoted by n1, a refractive index of a second medium forming said transparent screen is denoted by n2, a refractive index of a third medium brought into contact with a front surface of said transparent screen is denoted by n3, an angle formed by said ray of light incident on said first face and said optical axis of said projector is denoted by &thgr;1, a refraction angle of a ray of light shot out from said front surface of said transparent screen is denoted by &thgr;2, and an angle formed by said first and second faces is denoted by &agr;1.