JPH08220309A - Fresnel lens - Google Patents

Abstract

PURPOSE: To prevent the diffusion of projected radiation light to a direction different from an exit direction and to concentrate the light only in the projection direction even if diagonal projection is executed by coating rise faces with light shielding films. CONSTITUTION: This Fresnel lens composed by repetition of Fresnel faces 1 which condense the radially projected light and the rise faces 2 which prevent an excessive increase in the thickness of the lens and connect the adjacent Fresnel faces. The Fresnel faces 1 and rise faces 2 are concentrically worked around the lens. The rise faces 2 are coated with the light shielding films 6. The incident projected light 10 on the left side Fresnel faces 1 is refracted as exit light 11 when the Fresnel lens is subjected to diagonal irradiation. The other incident light 12 heads toward the rise faces 2 but is shielded by the light shielding films 6 and is prevented from entering the inside of the lens. The incident projected light 13 on the right side Fresnel faces 1 is refracted as exit light 14. The other incident light 15 heads toward the rise faces 2 but is shielded by the light shielding films 6 and is prevented from entering the inside of the lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Fresnel lens used for a screen that displays a radial projection image.

[0002]

2. Description of the Related Art In recent years, in projection type display devices, an image is displayed on an image display body such as a cathode ray tube or a liquid crystal panel, and the display is projected as a radial projection light on a screen through a projection lens. At this time, the projection type display device projects a projected image from the front or the rear of the screen, and a reflection type screen or a projection type diffusion screen is used for the screen depending on the difference between the front side and the rear side.

Since the projection image light is radial projection light, a large lens for condensing is provided on the latter screen used when projecting from the rear of the screen so that a screen observer can observe an image of uniform brightness over the entire screen. Was used. As this large-sized lens, a Fresnel lens which is lightweight and has high mass productivity is mainly used. When the radial projection image light is projected from the projection type display device to the screen including the Fresnel lens, the projection image light is converged by the lens because it is projected from the vicinity of the focal length on the central axis of the lens, and the observer sees it. We were able to observe an image of uniform brightness over the entire screen.

FIG. 3 shows a conventional Fresnel lens. As shown in the figure, the Fresnel lens is configured by repeating a Fresnel surface 1 having a function of condensing the radial projection light and a rise surface 2 connecting the adjacent Fresnel surfaces 1 to prevent the lens from becoming too thick. Has been done. The Fresnel surface 1 and the rise surface 2 are processed concentrically with respect to the lens center axis 4. The lens surface having the Fresnel surface 1 and the rise surface 2 is installed on the side opposite to the projection light source 9.

The Fresnel angle x of the Fresnel surface 1, that is, the inclination angle with respect to the plane perpendicular to the lens center axis, is set so as to gradually increase from the lens center toward the periphery in accordance with the focal length of the lens. A focusing function of refracting the radial projection light from the point 100 separated by the focal length on the axis 4 and emitting it in a direction parallel to the lens center axis 4 is realized. The rise angle η of the rise surface 2, that is, the inclination angle with respect to the lens center axis 4, is set so that the radial projection light from the point 100 separated by the focal length on the lens center axis 4 does not enter the rise surface 2. It is set larger toward the surroundings.

Therefore, when the radial projection light is projected onto the Fresnel lens from the point 100, which is on the lens center axis 4 which is perpendicular to the lens surface and which is separated by the focal length of the lens as described above, it is almost incident on the rise surface 2. Without passing, the light passes through the Fresnel surface 1 and becomes parallel light. Further, depending on the degree of the Fresnel angle x of the Fresnel surface, the light can be focused in the direction of the observer.

[0007]

However, projection from a position other than on the lens center axis 4 of the Fresnel lens,
When so-called oblique projection is performed, oblique projection light is generated on the rise surface 2
There is a problem that the light is incident on and refracted, and is totally reflected by the rise surface 2 and is emitted as leakage light in a direction other than the projection direction.

That is, as shown in FIG. 4A, a part of the radial projection light is incident on the rise surface 2, is totally reflected by the rise surface 2, and is emitted in a direction 101 opposite to the projection direction. Further, the light transmitted through the rise surface 2 enters the lens again and is emitted from the adjacent Fresnel surface in the direction 102 which is greatly different from the projection direction.

Also in the example in which the lens surface having the Fresnel surface 1 and the rise surface 2 is installed on the projection light source side, as shown in FIG. 4B, a part of the radial projection light is incident on the rise surface 2. The light totally reflected by the rise surface 2 and emitted in the direction 101 opposite to the projection direction, and the light transmitted through the rise surface 2 was the total reflection light 103. These lights became an image duplication, and were observed as unnecessary images with misaligned positions other than normal images.

The present invention has been made in view of the above-mentioned prior art, and when irradiating from a position other than on the central axis of the lens perpendicular to the lens surface, that is, when oblique projection is performed, the projected radiant light is emitted. It is an object of the present invention to provide a Fresnel lens that prevents the direction from being different from the projection direction and realizes a function of concentrating projected radiation light only in the projection direction.

[0011]

The structure of the present invention which achieves such an object is characterized in that, in a Fresnel lens used for a screen displaying a projected image, the rise surface is covered with a light shielding film. Further, the rise angle is set to be equal to or larger than the projection angle of the oblique projection light, and the lens surface having the rise surface is set on the projection light source side.

[0012]

In the present invention, since the rise surface is covered with the light-shielding film, the projection light is shielded by the light-shielding film on the rise surface and is not transmitted or reflected by the rise surface (see FIG. 1A). Further, when performing so-called oblique projection, the light shielding film on the rise surface prevents the projection light from entering the rise surface on the side far from the projection light source with the lens center axis as a boundary (FIG. 1).
(B)).

Further, on the side close to the projection light source with the lens center axis as a boundary, when the rise angle is equal to the projection angle, the projection light is geometrically not incident on the rise surface, and the rise angle is slightly larger than the projection angle. Occasionally, the light shielding film prevents the projection light from entering the rise film (see FIG. 1C).
Therefore, in the Fresnel lens of the present invention, the oblique projection light does not pass through the rise surface and is incident on the Fresnel surface without being totally reflected by the rise surface, preventing emission in an abnormal direction other than the projection direction. Moreover, leakage light does not occur.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 shows an embodiment of the present invention. In this embodiment, the lens surface 8 having the Fresnel surface 1 and the rise surface 2 is installed on the projection light source 9 side.

That is, as shown in FIG. 1A, the Fresnel lens has a Fresnel surface 1 for condensing the radial projection light and a rise surface 2 for preventing the lens from becoming too thick and connecting adjacent Fresnel surfaces. It is composed by repeating.
The Fresnel surface 1 and the rise surface 2 are processed concentrically at the center of the lens. The rise surface 2 is covered with a light shielding film 6.

The Fresnel angle x of the Fresnel surface 1 is set so as to gradually increase from the lens center toward the periphery in correspondence with the lens focal length, so that the radial distance from the point on the lens center axis 4 which is separated by the focal length. A focusing function of refracting the projected light and emitting it in a direction parallel to the lens center axis 4 is realized. The rise angle η of the rise surface 2 is set equal to or slightly larger than the projection angle α of the radial projection light at the time of oblique projection. This is because as the rise angle η increases, the ratio occupied by the rise surface 2 increases and the amount of projection light cut by the light shielding film 6 increases.

FIG. 1B shows the locus of radial projection light when oblique projection is performed using the Fresnel lens of this embodiment.
It is shown in (c). The projection light source 9 is located on the right side of the lens center axis 4 of the Fresnel lens in FIG. FIG.
As shown in (b), when the projection lights 10 and 12 are directed to the left side of the Fresnel lens, a part of the projection light 10 enters the Fresnel surface 1 and is refracted to become an exit light 11, while the other part of Although the projected light 12 is directed to the rise surface 2, it is blocked by the light shielding film 6 and does not enter the lens.

In addition, as shown in FIG.
When 3 and 15 are incident on the right side of the Fresnel lens, the projection angle α of the radial projection light is set to be larger than the rise angle η. Therefore, when η = α, the projection light 13 geometrically reaches the rise surface 2. When it cannot be made incident and is entirely incident on the Fresnel surface and is refracted to become the emitted light 14, on the other hand, when η> α, a part of the projected light 13 is made incident on the Fresnel surface 1 to become the emitted light 14 and at the same time as the other light. Although the projection light 15 of the part goes to the rise surface 2, it is blocked by the light shielding film 6 and cannot enter the lens.

When the radial projection light is obliquely projected, the projection angle α of the lens changes from the center of the lens toward the periphery, and accordingly the rise angle η is determined so as to satisfy the above condition. As described above, in oblique projection, the rise angle η of the lens near the projection light source with the lens center axis as a boundary
Is set to be larger than the projection angle α, and at the circumferential position at the same distance from the lens center, the same rise angle is processed. Therefore,
The light-shielding film 6 on the rise surface on the side close to the projection light source with the lens center axis as a boundary prevents the projection light from entering the lens by the rise angle or the rise angle and the light-shielding film 6 on the side closer to the oblique projection. No matter which side of the central axis of the lens is used, the light does not enter from the rise surface 2.

FIG. 2 shows the case where the Fresnel lens of this embodiment is used for front projection, in other words, when radial projection light is projected from a point separated by the focal length on the lens center axis 4. As shown in the figure, since the rise angle is set in consideration of the oblique projection, in the front projection, a part of the radial projection light 18 ₀ to 18 ₆ from the projection light source 16 travels to the rise surface 2 but rises. The remaining projection lights 17 _{0 to} 17 _{8 which} are blocked by the light-shielding film 6 on the surface 2 enter the Fresnel surface 1 having a collecting function and are emitted from the lens.

The numbers of Fresnel surfaces and rise surfaces and the number of ray trajectories of projected light shown in FIGS. 1 and 2 are merely examples and are not particularly limited. Actually, as a lens, the Fresnel surface and the rise surface are used with a fine pitch of about 0.1 mm.

[0022]

As described above in detail based on the embodiments, in the Fresnel lens of the present invention, since the rise surface is covered with the light shielding film, the projection light is shielded by the light shielding film on the rise surface, There is no transmission or reflection on the rise surface.
In particular, by setting the rise angle to be the projection angle of the oblique projection light or more and setting the lens surface including the rise surface on the projection light source side, even when so-called oblique projection is performed, the projection light source is bordered by the lens center axis. On the far side, the light-shielding film on the rise surface causes the light-shielding film on the near side to be geometrically not incident on the rise when the rise angle is equal to the projection angle, and when the rise angle is slightly larger than the projection angle. By
The projection light is prevented from entering the rise film. Therefore, in the Fresnel lens of the present invention, the oblique projection light does not pass through the rise surface and is incident on the Fresnel surface without being totally reflected by the rise surface, preventing emission in an abnormal direction other than the projection direction. Since no leak light is generated, it can be used for oblique projection light regardless of the Fresnel lens, and its application range is expanded.

[Brief description of drawings]

FIG. 1 is an explanatory diagram when performing so-called oblique projection on a Fresnel lens according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram when so-called front projection is performed on the Fresnel lens according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram of a conventional Fresnel lens.

FIG. 4 is an explanatory diagram for performing so-called oblique projection on a conventional Fresnel lens.

[Explanation of symbols]

 1 Fresnel surface 2 Rise surface 4 Lens center axis 6 Light-shielding film 8 Lens surface 9,16 Projection light source 10, 12, 13, 15, 17, Projection light 11, 14 Emission light x Fresnel angle η Rise angle α Projection angle

Claims (3)

[Claims] 1. A Fresnel lens used for a screen displaying a projected image, wherein the rise surface is covered with a light shielding film. 2. The Fresnel lens according to claim 1, wherein the rise angle is equal to or larger than a projection angle of oblique projection light. 3. The Fresnel lens according to claim 1, wherein the lens surface having the rise surface is set on the projection light source side.