Display apparatus

A display apparatus comprising:

• a plurality of projecting means for projecting images, each of said projecting means having a projection optical system having a limited pupil diameter;
• and
• screen means arranged at a position where an image is substantially projected by said projecting means, said screen means having a plurality of Fresnel lens sheets each having a number of prisms formed on a surface on a side opposite to said projecting means, each of said prisms having an effective portion to emit a light flux from said projecting means in a predetermined direction and a non-effective portion which does not contribute to the emission of the light flux to said predetermined direction,
• wherein the non-effective portions of at least one of said plurality of Fresnel lens sheets, excluding said sheet arranged at a position nearest to said projecting means, is formed so as to have a substantially middle angle between the average value of the angles of principal rays when light fluxes from said plurality of projecting means progress in said sheets and the average value of emission angles of the principal rays when they are emitted from the effective portions of said prisms of said sheets.

A screen on which an image is projected, comprising:

• a first translucent sheet;
• and
• a second translucent sheet;
• wherein said first translucent sheet has a first surface and a second surface, with a first Fresnel lens comprising a plurality of prism-shaped structures formed on said second surface, and said second translucent sheet has a third surface and a fourth surface, with a second Fresnel lens comprising a plurality of prism-shaped structures formed on said fourth surface, and each of said prism-shaped structures of at least one of said first and second Fresnel lenses has a refractive surface refracting a beam indicative of the image and another surface, and an angle of said another surface with respect to an axis normal to said translucent sheets is set so as to have a substantially middle value between an angle of a principal ray with respect to the normal axis when the beam is incident on said refractive surface and an angle of said principal ray with respect to the normal axis when the beam is emitted from said refractive surface.

A screen on which an image is projected, comprising:

• a first translucent sheet;
• and
• a second translucent sheet;
• wherein a beam indicative of the image is transmitted to said second translucent sheet through said first translucent sheet, with said first translucent sheet having a first surface receiving the beam and a second surface on which a first Fresnel lens comprising a plurality of prism-shaped structures is formed, and said second translucent sheet having a third surface facing said second surface and a fourth surface receiving the beam through said third surface and having a second Fresnel lens comprising a plurality of prism-shaped structures formed thereon, and each of said prism-shaped structures of said second Fresnel lens has a refractive surface refracting the beam and another surface, and an angle of said another surface with respect to an axis normal to said translucent sheets is set so as to have a substantially middle value between an angle of a principal ray with respect to the normal axis when the beam is incident on said refractive surface and an angle of said principal ray with respect to said axis when said beam is emitted from said refractive surface.