JPS59126523A - Fresnel lens and projection screen using it - Google Patents

Abstract

PURPOSE:To obtain a moire-free lens by employing a polygonal plane shape for fractionized unit segments of a spot convergent type Fresnel lens which has grades cut in a transparent substrate while the curved surface of the lens is fractionized in the optical-axis direction. CONSTITUTION:The Fresnel lens is fractionized in a mosaic shape so that a linear pattern cut in the Fresnel lens is not superposed upon the linear pattern of an array of unit lens of a micro lens in parallel, and plane shape of the frictionized unit segments is preferably reactangular or square. Then, the linear pattern is allowed to cross the linear pattern of the micro lens array at some angle (45 deg. in a figure) without being superposed in parallel, obtaining a high-contrast screen which eliminates moire.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Fresnel lens and a projection screen using the same.

In a transmissive screen that is composed of a combination of a microlens array screen such as a lenticular type or a fly's eye type, and a point condensing Fresnel lens as a correction lens, the commonly used Fresnel lens , because the unevenness is subdivided into annular shapes, there is a part that roughly matches the direction of the linear pattern accompanying the arrangement of unit microlenses forming the microlens array, and a high-contrast poisonous pattern appears in the vicinity. can be seen, and the image quality is significantly degraded.

In view of the above-mentioned drawbacks, the present invention subdivides the unevenness of the Fresnel lens into mosaic shapes, and desirably makes the planar shape of the subdivided unit segments rectangular or square, thereby improving the combination with a microlens array. To provide a moire-free projection screen in which the directions of linear patterns do not coincide within the screen plane, but intersect at an appropriate angle θ (θ4o0).

When a circular Fresnel lens, which is a common point-focusing correction lens, is combined with a lenticular lens or a fly's eye type microlens array, as shown schematically in Figs. Moiré occurs in the vicinity where the patterns overlap in a generally parallel manner. In such a combination, a diffusing agent is dispersed in at least one lens screen substrate, a transparent diffusing film (sheet) is laminated, or at least one surface is matted and a 7-hide Fresnel film is used. By performing a diffusion process such as roughening the annular edge of the lens, the moiré pattern can be reduced to some extent. However, in order to eliminate such moiré patterns, a considerable amount of matting is required, which prevents light from being scattered in unnecessary directions, ``from the projector to the screen's effective viewing area for eradication input.'' The ratio of the epoch output, that is, the effective transmission efficiency of the screen decreases.

According to the present invention, the Fresnel lens is formed into a mosaic shape so that the linear pattern engraved on the Fresnel lens and the linear pattern accompanying the arrangement of unit lenses of the microlens array do not overlap in parallel within the screen plane. The planar shape of the subdivided unit segment is preferably rectangular or square, for example, at a certain appropriate angle θ (in FIG. By making sure that they intersect at 45°),
High-contrast moiré can be removed.

Such a mosaic Fresnel lens has the following features, for example: You can get it. FIG. 4 illustrates the most common method.

That is, a large number of square glass rods 1 with a side length of about 0.5 mm are arranged and fixed without any gaps as shown in (a), and in this state, the end faces of the square rods are aligned with the optical axis in the direction in which they extend. Formed on the lens surface as shown in Q). After that, the fixed bundle of square rods is unbound and the vertices of each segment are aligned on the same plane as shown in (d) to form a Fresnel lens surface, and this surface is used as a matrix for electroforming etc. Operate the mold,
A mosaic type Fresnel lens sheet can be manufactured by transfer molding onto a transparent substrate such as plastic.

Incidentally, by reducing the thickness of the square glass rod used to make the matrix, the degree segments that form the Fresnel lens can be made finer, thereby making it possible to obtain a Fresnel lens sheet with less unevenness. Conversely, if you use a thick square glass bar, the unit segment will become larger, so
The resulting Fresnel lens sheet tends to be uneven. In addition, when manufacturing a matrix using this method, a glass square bar is convenient in terms of workability and surface finish accuracy, but the method is not limited to this.

Furthermore, in order to manufacture a projection screen by combining such a mosaic Fresnel lens with a microlens array,
In addition to combining separate Fresnel lens sheets into a microlens array, both lenses may be formed on both sides of a single sheet.

The present invention uses a mosaic Fresnel lens as described above, and when such a lens is combined with a microlens array, the line patterns of both lenses are made to intersect at a desired angle so that they are not even partially parallel, thereby achieving p1 moire. A projection screen without patterns can be obtained.

[Brief explanation of drawings]

FIG. 1 is a front view showing the principle of a Fresnel lens. Figure 2 is a plan view of a moiré pattern that occurs on a screen that combines a point-concentrating circular Fresnel lens and a lenticular microlens array, and Figure 3 shows a moiré pattern that occurs on a screen that combines a Fuller f-eye type microlens array. FIG. 4 is an explanatory diagram showing an example of fabricating a mosaic-type Fresnel lens, in which (a) is a perspective view of a bunch of hexagonal bars, (b) is a vertical cross-sectional view thereof, and (C) is a plan view of a moire pattern.
1 is a cross-sectional view of the lens after processing, (d) is a cross-sectional view of the Fresnel lens, and FIG. 5 is an example of a mosaic Fresnel lens. (a) is a plan view, (b) is a sectional view thereof, and FIG. 6 is a plan view of a screen in which a mosaic type Fresnel lens and a lenticular lens array are configured to intersect at an angle of 45°. In the figure, 1 is a glass square rod 7 / )' A α ni 1yo (to) N\ Sai 2) η Sai 3 Sen O i tail (α) Δ +1711 (7!-1, (Dashi (C) NIII 7) Victory

Claims (1)

[Claims] 1. In a point condensing Fresnel lens in which the curved surface of the lens is subdivided in the optical axis direction and each gradient is carved on a transparent substrate, the planar shape of each subdivided unit segment is a polygon. Fresnel lenses are characterized by: 2. The Fresnel lens according to claim 1, wherein the planar shape of the unit segment is one of a rectangle and a square. 3. In a screen composed of a combination of a microlens array screen and the Fresnel lens described in claim 1, the linear pattern accompanying the arrangement of unit lenses does not overlap in parallel with the linear pattern of the microlens array. A projection screen configured to intersect at a desired angle. 4. The projection screen according to claim 3, wherein the Fresnel lens is a point condensing linear Fresnel lens formed by two line condensing Fresnel lenses orthogonal to each other.