JP2895070B2 - Fresnel lens sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a lens sheet, particularly to a Fresnel lens sheet combined with a lenticular lens sheet to constitute a transmission type projection screen.

(Prior Art) As a transmission type projection screen, a combination of a Fresnel lens and a lenticular lens is widely used. In this configuration, there are two types of methods for arranging the Fresnel lens sheet, that is, when the Fresnel lens surface is directed to the projection light source side and when the Fresnel lens surface is directed to the observation side.
The method of arranging the Fresnel lens surface toward the observation side has become mainstream because the loss of the light of the light source at the peripheral portion of the Fresnel lens can be reduced.

(Problems to be Solved by the Invention) However, in a transmission type projection screen having a configuration in which a lenticular lens sheet is combined with a Fresnel lens sheet having a Fresnel lens surface facing the observation side,
There is a problem that a moiré pattern is generated and image quality is remarkably deteriorated.

FIG. 3 is a view showing a projection system using the transmission type projection screen having the above-mentioned configuration.
Is a lenticular lens sheet, and 9 is a projection light source.
FIG. 4 is an enlarged sectional view including the optical path of the projection light transmitted through the Fresnel lens sheet 7 of FIG. The unit lens 1 constituting the Fresnel lens sheet 7 includes a lens surface 2 and a non-lens surface 3, and the lens surface 2 is strictly a part of a conical surface, but can be locally considered to be a flat surface.

In a conventional Fresnel lens sheet having such a flat lens surface, the projection light draws an optical path as shown by a solid line with an arrow, but there is an area where light is not transmitted as shown by a hatched portion 5. The area darkens. In the entire Fresnel lens, there is a concentrically darkened area for each pitch of the lens unit of the Fresnel lens, and when this darkened area is viewed through the lenticular sheet 8, it is sampled by the lenticular and appears to be a moire pattern. . This is the mechanism by which moiré occurs.

In view of the above circumstances, an object of the present invention is to provide a Fresnel lens sheet capable of obtaining a good image quality with reduced occurrence of a moire pattern when used as a transmission type projection screen in combination with a lenticular sheet.

[Configuration of the invention]

(Means for Solving the Problems) In order to solve the above problems, the invention of claim 1 combines a lenticular lens sheet and arranges a Fresnel lens having a Fresnel lens surface facing the observation side to constitute a transmission screen. In the lens sheet, the area close to the valley of the lens unit in the lens surface of each lens unit of the Fresnel lens sheet is constituted by a curved surface or a plurality of planes approximated to a curved surface, so that the lens surface is constituted only by the plane. A Fresnel lens sheet characterized in that light is diffused to a region corresponding to a region which does not transmit light generated in the case.

Note that it is not preferable that the curved surface is formed into an arc shape that does not have an angle with respect to the non-lens surface because the resolution of an image is deteriorated.

As a method of forming a part of the lens surface into a curved surface or a plurality of planes approximated to a curved surface, a mold that is cut using a cutting tool having a curved surface or a plurality of planes approximated to a curved surface is formed. After creating a mold using such a tool, the shape of the mold ridge is curved by blasting to gradually change the angle of the mold tool. A method of forming a Fresnel lens sheet using any of the molds prepared by the cutting method can be used.

(Function) The Fresnel lens sheet of the present invention configured as described above projects the lens surface of each lens unit by forming a curved surface or a plurality of planes approximated to a curved surface in a region near a valley of the lens unit. The darkened area can be reduced by bending the light beam to the darkened area without transmitting light. As a result, the strength of the moire pattern recognized by the observer can be significantly reduced.

(Example) Hereinafter, the present invention will be described more specifically with reference to examples.

FIG. 1 is an enlarged cross-sectional view including projection light of a Fresnel lens sheet which is an embodiment of the Fresnel lens sheet of the present invention and whose lens surface is curved in a region near a valley of a lens unit. By providing the curved surface portion 4 on the lens surface in this way, light emitted from the curved surface portion is diffused, and the region 5 through which light does not pass is reduced as compared with the case where the lens surface is composed of only a flat surface. Therefore, the strength of moiré can be reduced. Here, the shape of the curved surface portion 4 of the lens surface may be a shape such that the light is diffused in the darkened area 5 without transmission of the projection light.

FIG. 2 is a view showing a second embodiment of the Fresnel lens sheet according to the present invention, in which the lens surface is constituted by a plurality of planes approximated to a curved surface in a region near a valley of a lens unit. FIG. By providing an area 6 composed of a plurality of planes approximated to a curved surface in a part of the lens surface, the area 5 through which the projection light does not pass is divided into a plurality of areas, and the size of each area Becomes smaller. By making the size of each of these regions small enough to be indistinguishable by the human eye, it is possible to make the moiré caused by the region through which the projection light does not pass visible. By providing the region 6 composed of a plurality of planes approximated to a curved surface in a part of the lens surface as described above,
The same effect as when a part of the lens surface is curved can be obtained.

〔The invention's effect〕

Since the Fresnel lens sheet of the present invention is configured as described above, when the transmissive projection screen is configured and used in combination with the lenticular lens sheet, the strength of the generated moiré pattern can be effectively reduced and excellent. This has the effect that image quality can be obtained.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view showing one embodiment of the Fresnel lens sheet of the present invention, FIG. 2 is an enlarged sectional view showing a second embodiment of the present invention, and FIG. FIG. 4 is a diagram showing a projection system arranged in a side and combined with a lenticular sheet, and FIG. 4 is an enlarged sectional view showing a conventional Fresnel lens sheet. 1 ... Lens unit, 2 ... Lens surface, 3 ... Non-lens surface, 4 ... Curved surface portion, 5 ... Area through which projected light does not pass, 6
…… A region composed of a plurality of planes approximated by a curved surface,
7 ... Fresnel lens sheet, 8 ... Lenticular lens sheet, 9 ... Projection light source.

Claims (1)

(57) [Claims] 1. A Fresnel lens sheet which is combined with a lenticular lens sheet and has a Fresnel lens surface facing the observation side to form a transmission screen, wherein the Fresnel lens sheet has a lens unit in each lens unit. By forming a region near the valley from a curved surface or a plurality of planes approximated to a curved surface, light is diffused to a region corresponding to a region that does not transmit light that occurs when the lens surface is configured only with a plane. A Fresnel lens sheet characterized in that: