Image display, Fresnel lens and screen

Abstract

In a Fresnel screen for displaying an image, comprising, a screen surface, and a reverse surface opposite to the screen surface in a thickness direction of the screen to be prevented from facing to the viewer, the Fresnel screen has first prism surfaces extending to have respective longitudinal arc-shapes juxtaposed with each other as seen in the thickness direction to deflect light beams for forming the image in at least one of directions perpendicular to each other as seen in the thickness direction, and second prism surfaces extending to have respective longitudinal shapes juxtaposed with each other as seen in the thickness direction to deflect at least a part of the light beams in at least one of the directions perpendicular to each other as seen in the thickness direction.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross sectional view showing an embodiment of a projection type image display apparatus of the invention.

FIG. 2 is an oblique projection view showing a screen of rear projection type usable for the embodiment of the projection type image display apparatus of the invention.

FIG. 3 is a view for explaining how to design an original lens surface before converting the original lens surface to prism surfaces of a Fresnel lens.

FIG. 4 is a diagram showing a relationship between a distance of a position from a center of the Fresnel lens and a light incidence angle at the position.

FIG. 5 is a diagram showing a relationship between the distance of the position from the center of the Fresnel lens and a light outgoing angle at the position.

FIG. 6 is an oblique projection view showing a screen including a center of concentric circular prism surfaces.

FIG. 7 is a schematic view showing a direction of an incidence light beam α taken into an area B in FIG. 6.

FIG. 8 is an oblique projection view showing an embodiment of a Fresnel lens sheet of the invention as seen from a light beam outgoing side.

FIG. 9 is an oblique projection view showing the embodiment of the Fresnel lens sheet of the invention as seen from a light beam incidence side.

FIG. 10 is a schematic cross sectional view showing region C of the embodiment of the Fresnel lens sheet of the invention in y-z coordinates.

FIG. 11 is a view showing a relationship between the original lens surface and the prism surface of the Fresnel lens.

FIG. 12 is an oblique projection view showing another embodiment of a Fresnel lens sheet of the invention in which a height of the prism surface on a reverse surface gradually decreases radially inward.

FIG. 13 is an oblique projection view showing another embodiment of a Fresnel lens sheet of the invention in which the prism surface on a reverse surface is prevented from being formed on a central area in a direction perpendicular to a refracting direction by the prism surface on a reverse surface.

Claims

1. A projection type image display apparatus comprising an image forming source for forming an image, a screen and a projection optical device for magnifying the image formed by the image forming source and projecting it obliquely to have a predetermined angle with respect to a normal line of the screen, wherein the screen has at least a Fresnel lens sheet including a plurality of Fresnel lenses concentrically arranged on a light emitting side of the Fresnel lens sheet,prism angles of the Fresnel lenses increase in a direction radially outward from a center of the concentric Fresnel lenses, andthe Fresnel lens sheet includes a plurality of incidence face prisms extending horizontally and juxtaposed vertically on a predetermined area of a light incidence surface of the Fresnel lens sheet, which area includes a position opposite to the center of the Fresnel lenses.

2. The projection type image display apparatus according to claim 1, wherein an original surface formed by continuously joining prism surfaces of the Fresnel lenses is aspherical.

3. The projection type image display apparatus according to claim 1, wherein a vertical width of the predetermined area including the incidence face prisms is T/15-T/4 when T is a vertical width of the screen.

4. The projection type image display apparatus according to claim 1, wherein the screen further has a dispersing sheet arranged on the light emitting side of the Fresnel lens sheet to disperse at least horizontally the light emitted from the Fresnel lens sheet.

5. A projection type image display apparatus comprising an image forming source for forming an image, a screen and a projection optical device for magnifying the image formed by the image forming source and projecting it obliquely to have a predetermined angle with respect to a normal line of the screen, wherein the screen has at least a Fresnel lens sheet including a plurality of Fresnel lenses concentrically arranged on a light emitting side of the Fresnel lens sheet,an original surface formed by continuously joining prism surfaces of the Fresnel lenses is aspherical, and the Fresnel lens sheet includes a plurality of incidence face prisms extending horizontally and juxtaposed vertically on a predetermined area of a light incidence surface of the Fresnel lens sheet, which area includes a position opposite to the center of the Fresnel lenses.

6. The projection type image display apparatus according to claim 5, wherein the projection optical device has a curved surface mirror to reflect the magnified image onto the screen, and aspherical coefficients defining the aspherical shape of the original surface are determined so that the projected image proceeding into the incidence surface of the Fresnel lens sheet after being reflected by the curved surface mirror is deflected to be emitted from the substantial whole of the screen with outgoing angles of substantial zero.

7. A screen usable for a projection type image display apparatus, comprising at least a Fresnel lens sheet including a plurality of concentric Fresnel lenses on a light emitting surface thereof, anda dispersing sheet arranged at a light emitting side of the Fresnel lens sheet to disperse at least horizontally the light emitted from the Fresnel lens sheet,wherein prism angles of the Fresnel lenses increase in a direction radially outward from a center of the concentric Fresnel lenses, andthe Fresnel lens sheet includes a plurality of incidence face prisms extending horizontally and juxtaposed vertically on a predetermined area of a light incidence surface of the Fresnel lens sheet, which area includes a position opposite to the center of the Fresnel lenses.

8. The screen according to claim 7, wherein a light flux from a center of an image forming source for forming an image proceeds into an incidence surface of the Fresnel lens sheet obliquely to a normal line of the incidence surface.

9. The screen according to claim 7, wherein an original surface formed by continuously joining prism surfaces of the Fresnel lenses is aspherical.

10. The screen according to claim 7, wherein a vertical width of a predetermined area including the incidence face prisms is T/15-T/4 when T is a vertical width of the screen.

11. The screen according to claim 7, wherein a prism height of the incidence face prisms at a central portion of the screen is lower than a prism height of the incidence face prisms at another portion thereof other than the central portion.

12. The screen according to claim 7, wherein the incidence face prisms is prevented from being arranged at a central portion of the screen on the predetermined vertical area.

13. The screen according to claim 7, wherein the center of the Fresnel lenses is arranged in the vicinity of a lower end of the screen, and the incidence face prisms extend substantially parallel to an edge of the lower end of the screen.

14. The screen according to claim 7, wherein the dispersing sheet including a plurality of lenticular lenses juxtaposed horizontally and one of micro-beads and a total internal reflection surface for reflecting at least horizontally the light emitted from the Fresnel lens sheet to be dispersed.

15. A Fresnel lens sheet usable for a screen in a projection type image display apparatus, comprising, Fresnel lenses concentrically arranged on a light emitting surface of the Fresnel lens, anda plurality of incidence face prisms arranged on a predetermined area of a light incidence surface of the Fresnel lens sheet, which area includes a position opposite to a center of the Fresnel lenses,wherein the incidence face prisms extend horizontally and are juxtaposed vertically on the predetermined area, andprism angles of the Fresnel lenses increase in a direction radially outward from the center of the concentric Fresnel lenses.

16. The Fresnel lens sheet according to claim 15, wherein an original surface formed by continuously joining prism surfaces of the Fresnel lenses is aspherical.