JP2008175984A - Refractive Fresnel lens and rear projection display - Google Patents

Abstract

Provided is a refractive Fresnel lens in which a rise angle is set so as to suppress stray light from being emitted toward the front of the viewer.
A rise angle is set to approximately 17.5 ° or less in at least a part of a region having a Fresnel angle of 60 ° to 65 ° of a refractive type Fresnel lens.
[Selection] Figure 6

Description

  The present invention relates to a Fresnel lens suitable for use in a screen of a large-screen and thin rear projection display device. The present invention also relates to a rear projection display device using such a refractive Fresnel lens as a screen.

  As a kind of image display device, a rear projection display device (rear projection display) is widely used. A rear projection type display device enlarges image light emitted from a video light source such as a CRT, LCD element or DLP (Digital Light Processing) element and projects it from the rear side to a transmissive screen, and displays an image from the front side of the transmissive screen. It is what I watched.

  In general, a transmissive screen of a rear projection display device uses a Fresnel lens for converging video light to be magnified and a lenticular lens for widening the viewing angle. Of these, the Fresnel lens is an optical element in which a three-dimensional lens is concentrically divided into a plurality of annular lenses, and these annular lenses are arranged in a plane. There are two types of Fresnel lenses: a refraction type (one that converges light using refraction) and a reflection type (one that converges light using reflection).

  In recent years, there has been an increasing demand for rear projection display devices with larger screens and thinner screens. In order to satisfy this requirement, an eccentric optical system whose optical axis does not coincide with the center of the screen (the center of the screen surface of the transmissive screen) is used for the optical system in the rear projection display device. Along with that, the Fresnel lens used for the transmissive screen has a structure using only one side part (semicircular part) as seen from the center of the ring, rather than using the whole annular lens. In addition, the image height is high.

  In a refractive type Fresnel lens, a part of light is reflected by a lens that emits image light to the observer side to become stray light, and the stray light is reflected by the substrate surface and emitted to the observer side. A double image (ghost) is generated. For example, paragraph 0013 of Patent Document 1 below describes the principle of stray light generation in a refractive Fresnel lens having a low image height (using the entire annular lens).

  In the case of a refractive Fresnel lens having a high image height (using only a semicircular portion), the Fresnel angle increases as the image height increases, and stray light is observed in the region where the Fresnel angle is 60 ° to 65 °. Since the light is emitted toward the front side (at an emission angle of about 0 °), a double image is particularly easily recognized. FIG. 1 is a diagram showing how stray light is generated in the region where the Fresnel angle is 60 ° to 65 °. After a part of light is reflected by the Fresnel surface of one lens 52a of the refractive Fresnel lens 50 and becomes stray light, the stray light passes through a total of three lenses, the lens 52a and the adjacent lenses 52b and 52c. The light is reflected again by the base material surface 51 of the Fresnel lens 50 and emitted toward the front side toward the viewer.

  On the other hand, the rise angle of a conventional refractive Fresnel lens (as shown in FIG. 2, the angle formed between the rise surface opposite to the Fresnel surface that emits light and the normal of the Fresnel lens) is the principal ray of the rise surface. Is set to an angle equal to the lens internal angle so that the light does not fall on (no vignetting), or is set to an angle that is 0 ° to 5 ° smaller than the lens internal angle in consideration of the mass production margin of the lens shape. It was. FIG. 3 shows how the conventional rise angle is set. The correspondence between the Fresnel angle and the rise angle when the rise angle is set equal to the lens internal angle is indicated by a broken line a, and the rise angle is the lens internal angle. The solid line b shows the correspondence between the Fresnel angle and the rise angle when the angle is set smaller than 0 ° to 5 °.

  Conventionally, a technique for intentionally setting the rise angle of a refractive Fresnel lens has also been proposed for the purpose of eliminating coloring that occurs on the screen due to a decrease in white uniformity (Patent Document 2).

JP 11-149123 A Japanese Patent No. 3310460

  However, a technique that focuses on the relationship between the rise angle of the refractive Fresnel lens and stray light emitted toward the front of the viewer as shown in FIG. 1 has not been proposed.

  In view of the above-described points, the present invention provides a refractive Fresnel lens in which a rise angle is set so as to suppress stray light from being emitted toward the front toward the viewer, and such a refractive Fresnel lens as a transmission screen. It is an object of the present invention to provide a used rear projection display device.

  In order to solve the above-mentioned problem, the first refractive Fresnel lens according to the present invention has a lens shape having a rise angle of approximately 17.5 ° or less in at least a part of a region having a Fresnel angle of 60 ° to 65 °. It is characterized by.

  In this refractive Fresnel lens, as will be described later, stray light reflected by the Fresnel surface of one lens in a region having a Fresnel angle of 60 ° to 65 ° passes through a total of three lenses including the lens, It is divided into rays that pass through a total of four lenses including that lens. Thereby, the stray light reflected on the substrate surface and emitted to the observer side is divided into two directions of stray light directed to the front and stray light directed to other than the front, and therefore, in a region having a Fresnel angle of 60 ° to 65 °. , Stray light emitted toward the front of the viewer is reduced. Therefore, it is possible to suppress stray light from being emitted toward the front side toward the viewer.

  Next, the second refractive Fresnel lens according to the present invention is characterized in that the rise angle is switched so as to discontinuously decrease within the region of the Fresnel angle of 60 ° to 65 °. To do.

  In this refracting type Fresnel lens, as will be described later, the stray light emission angle is discontinuous in the region of the Fresnel angle of 60 ° to 65 ° so as to jump the angle range emitted toward the front to the observer side. Switch to. Therefore, it is possible to suppress stray light from being emitted toward the front side toward the viewer.

  Next, the third refractive Fresnel lens according to the present invention is characterized in that the rise angle gradually decreases as the Fresnel angle increases in the region of the Fresnel angle of 60 ° to 65 °.

  In this refracting Fresnel lens, as will be described later, the region where stray light is emitted toward the front of the viewer becomes narrower among regions having a Fresnel angle of 60 ° to 65 °. Therefore, it is possible to suppress stray light from being emitted toward the front side toward the viewer.

Next, a first rear projection type display device according to the present invention is provided.
An image light source,
A transmissive screen using a refractive Fresnel lens;
In a rear projection type display device having an optical system for projecting image light from the image light source to the transmission screen from the back side,
The refractive Fresnel lens has a lens shape having a rise angle of approximately 17.5 ° or less in at least a part of a region having a Fresnel angle of 60 ° to 65 °.

Moreover, the second rear projection display device according to the present invention includes:
An image light source,
A transmissive screen using a refractive Fresnel lens;
In a rear projection type display device having an optical system for projecting image light from the image light source to the transmission screen from the back side,
The refractive Fresnel lens is characterized in that the rise angle is switched so as to decrease discontinuously within a region of a Fresnel angle of 60 ° to 65 °.

The third rear projection display device according to the present invention is
An image light source,
A transmissive screen using a refractive Fresnel lens;
In a rear projection type display device having an optical system for projecting image light from the image light source to the transmission screen from the back side,
The refractive type Fresnel lens is characterized in that the rise angle gradually decreases as the Fresnel angle increases within a range of the Fresnel angle of 60 ° to 65 °.

  Each of these rear projection display devices uses the above-described refractive Fresnel lens according to the present invention for a transmission screen, and emission of stray light from the refractive Fresnel lens toward the front is suppressed. Therefore, it is possible to suppress the generation of a double image caused by this stray light.

  According to the refractive type Fresnel lens according to the present invention, it is possible to suppress the stray light from being emitted toward the front side toward the observer side. Further, according to the rear projection type display device according to the present invention, the stray light emitted from the refractive Fresnel lens used in the transmission screen toward the front side is suppressed from being emitted to the front side, so that this stray light causes 2 The effect that generation | occurrence | production of a multiple image can be suppressed is acquired.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 4 is a diagram showing an outline of an optical system of a rear projection display device to which the present invention is applied. An optical engine 2 and mirrors 3 and 4 are provided inside the rear projection display device 1. In addition, a transmissive screen 5 is disposed on the front surface (the right surface in the drawing) of the rear projection display device 1.

  In the optical engine 2, although not shown, an image light source (a light source lamp and a light modulation element such as an LCD panel that modulates light from the lamp in accordance with image data) and an image light source And a projection lens for projecting image light. The image light projected from the projection lens in the optical engine 2 is sequentially reflected and magnified by the mirrors 3 and 4, projected from the back onto the transmissive screen 5, and forward of the rear projection display device 1 from the transmissive screen 5. Is emitted.

  The optical system (projection lens and mirrors 3 and 4 in the optical engine 2) inside the rear projection display device 1 is an eccentric optical system whose optical axis does not coincide with the screen center (the center of the screen surface of the transmission screen). is there.

  FIG. 5 is a diagram showing an outline of the structure of the transmissive screen 5. 5A shows the cross-sectional structure of the transmissive screen 5. The transmissive screen 5 has a refractive Fresnel lens 10 on the light source side (the mirror 4 side in FIG. 4), and vice versa. On the side (observer side), a lenticular lens 20 is provided for widening the viewing angle in the horizontal direction.

  FIG. 5B is a view of the refractive Fresnel lens 10 as viewed from the observer side. The refraction type Fresnel lens 10 does not use the entire annular lens obtained by concentrically dividing a three-dimensional lens, but uses only one side portion (semicircular portion) when viewed from the center of the annular shape. It has become.

  Next, setting of the rise angle in the refractive Fresnel lens 10 will be described. FIG. 6 is a diagram showing a setting example of the rise angle of the refractive Fresnel lens 10 corresponding to the first refractive Fresnel lens according to the present invention. 6, the setting of the conventional rise angle shown in FIG. 3 is indicated by broken lines a and b as in FIG. 3, and the setting of the rise angle in the refractive Fresnel lens 10 (Fresnel angle and rise). (Corresponding relationship with the corner) is indicated by a solid line c.

  In the conventional case, as shown by the broken line a and the solid line b, the rise angle is 22.5 ° or more in the region where the Fresnel angle is 60 ° to 65 °. On the other hand, in the refractive type Fresnel lens 10, the rise angle is within the range of 10 ° to 15 ° in the entire region of the Fresnel angle 60 ° to 65 °.

  FIG. 7 shows the lens shape and ray path (FIG. 7B) in the region of the Fresnel angle 60 ° to 65 ° of the refractive Fresnel lens 10 in which the rise angle is set as shown in FIG. It is a figure shown in contrast with the lens shape and light beam path (FIG. 7A) of a conventional refractive Fresnel lens.

  In the conventional case, as shown in FIG. 7A, all the stray light reflected by the Fresnel surface of one lens 52a in the region of Fresnel angle 60 ° to 65 ° is a total of three lenses including the lens 52a. Pass 52a-52c. As a result, as shown in FIG. 1, the stray light is reflected by the base material surface 51 and then emitted toward the front side toward the viewer.

  On the other hand, in the refractive type Fresnel lens 10, as shown in FIG. 7B, the stray light reflected by the Fresnel surface of one lens 12a in the region of the Fresnel angle 60 ° to 65 ° includes the lens 12a. The light beam is divided into a light beam that passes through the three lenses 12a to 12c and a light beam that passes through a total of four lenses 12a to 12d including the lens 12a. FIG. 8 is a diagram showing how the stray light is divided (FIG. 8B) in comparison with the conventional case (FIG. 8A). Among these, the stray light that passes through the four lenses 12a to 12d is emitted in an oblique direction toward the viewer.

  As described above, the stray light reflected by the base material surface 11 and emitted to the viewer side is divided into two directions of stray light directed to the front and stray light directed to other than the front, so that the Fresnel angle is 60 ° to 65 °. In the region, stray light emitted toward the front side toward the observer side is reduced. Therefore, stray light is suppressed from being emitted toward the front side of the observer in a region having a Fresnel angle of 60 ° to 65 °.

  As a result, in the rear projection display device 1 using the refractive Fresnel lens 10 whose rise angle is set as shown in FIG. 6 for the transmissive screen 5, the refractive Fresnel lens 10 has a Fresnel angle of 60 ° to 65 °. Since stray light emitted toward the front side toward the observer side is reduced, the generation of a double image caused by this stray light is suppressed.

  The inventor changed the rise angle in the range of about 5 ° to 25 ° under the condition of the Fresnel angle: 64 ° and the incident angle of the image light on the transmission screen: 48 °. The ratio of stray light splitting was measured. FIG. 9A is a graph showing the measurement results, and the numerical values on the vertical axis represent the total stray light reflected by the Fresnel surface of one lens as shown in FIG. This is the ratio of stray light that passes through a total of three lenses including the lens (that is, stray light emitted toward the front side toward the viewer).

  As shown in this graph, when the rise angle is approximately 17.5 ° or less, the stray light passing through the three lenses is reduced to 40% or less. Therefore, stray light emitted toward the front side on the viewer side is reduced. It decreases considerably.

  In addition, the present inventor performed the sensitive evaluation by mounting on a rear projection display device and displaying a cross hatch (lattice pattern) while changing the rise angle in this way. FIG. 10 is a diagram showing the evaluation results. When the rise angle was 25 ° or 22.5 ° (conventional case indicated by the broken line a or the solid line b in FIG. 6), the result of the sensitivity evaluation was not good, but when the rise angle was 20 °, Min was improved. When the rise angle was 17.5 °, 15 °, and 10 °, the results of the sensitivity evaluation were improved.

  Thus, if the rise angle is set to approximately 17.5 ° or less, the stray light emitted toward the front of the observer is considerably reduced, and the result of the sensitivity evaluation is improved. Therefore, in the example of FIG. 6, the rise angle in the region where the Fresnel angle is 60 ° to 65 ° is within the range of 10 ° to 15 °, but the rise angle is approximately 17 in the region where the Fresnel angle is 60 ° to 65 °. You may make it 5 degrees or less.

  Further, if the rise angle is set to approximately 17.5 ° or less in at least a part of the region of the Fresnel angle 60 ° to 65 ° instead of the entire region of the Fresnel angle 60 ° to 65 °, the observer side The stray light emitted toward the front can be significantly reduced, and the result of the sensitivity evaluation can be improved.

  FIG. 9 also shows the measurement results when the rise angle is 10 ° or less. When the rise angle is 10 ° or less, the lens tip angle of the refractive Fresnel lens becomes an acute angle. When manufacturing a mold for molding, problems in the manufacturing process such as a cutting tool being chipped tend to occur. In order to avoid such a problem, it is desirable that the rise angle in the region where the Fresnel angle is 60 ° to 65 ° is approximately 17.5 ° or less and 10 ° or more.

  Next, FIG. 11 is a diagram showing a setting example of the rise angle of the refractive Fresnel lens 10 corresponding to the second refractive Fresnel lens according to the present invention. In FIG. 11, the setting state of the conventional rise angle shown in FIG. 3 is indicated by the broken line a and the solid line b as in FIG. 3, and the setting of the rise angle in the refractive type Fresnel lens 10 (Fresnel angle and rise level). Corresponding relations with corners) are indicated by two solid lines d and broken lines d ′.

  In the conventional case, as shown by the broken line a and the solid line b, the rise angle gradually increases as the Fresnel angle increases in all regions of the Fresnel lens. On the other hand, in the refractive Fresnel lens 10, the rise angle gradually increases as the Fresnel angle increases in the region where the Fresnel angle is 60 ° or less (here, it gradually increases in exactly the same manner as the solid line b). Within the region of ° to 65 °, as shown by the solid line d and the broken line d ′, the rise angle has been discontinuously switched to 15 ° or less from the state where the rise angle has increased to 22.5 °. It gradually increases with increasing Fresnel angle.

  FIG. 12 is a diagram showing the relationship between the Fresnel angle and the stray light emission angle in the refractive Fresnel lens 10 with the rise angle set as shown in FIG. 11 in comparison with the conventional case. Dashed lines d 'correspond to the solid lines b, d, and d' in FIG. 11, respectively.

  When the rise angle is set as shown by the solid line b in FIG. 11 as in the prior art, as shown in FIG. 12, the emission angle of stray light is −5 in the region where the Fresnel angle is 62.5 ° to 65 °. It is an angle of 5 to 5 degrees (that is, an angle range that is emitted toward the front of the observer substantially toward the front).

  On the other hand, in the refraction type Fresnel lens 10, as shown in FIG. 12, the emission angle of stray light is −5 ° to 5 ° (generally on the observer side) in the region of the Fresnel angle 60 ° to 65 °. The angle range (emitted toward the front) jumps discontinuously. As a result, stray light is not emitted toward the front side toward the viewer in the region where the Fresnel angle is 60 ° to 65 °.

  Thereby, in the rear projection type display device 1 using the refractive type Fresnel lens 10 whose rise angle is set as shown in FIG. 11 for the transmissive screen 5, the refractive type Fresnel lens 10 has a Fresnel angle of 60 ° to 65 °. Since the stray light is not emitted toward the front side to the observer side, the generation of a double image caused by this stray light is suppressed.

  In the example of FIG. 11, the rise angle is discontinuously switched to 15 ° or less within the region of the Fresnel angle of 60 ° to 65 °. However, as shown in FIG. 10, if the rise angle is approximately 17.5 ° or less, the result of the sensitivity evaluation is improved. Therefore, the size of the rise angle is discontinuous in the region where the Fresnel angle is 60 ° to 65 °. It may be switched to 17.5 °. Or you may switch so that the magnitude | size of a rise angle may be decreased to the value of 17.5 degrees or more discontinuously within the area | region of Fresnel angles 60 degrees-65 degrees. Even in those cases, stray light can be skipped by an angle range in which stray light is emitted toward the viewer toward the front by an amount corresponding to the degree of discontinuous decrease in the rise angle. It can suppress that it radiate | emits toward a person's side toward the front.

  Next, FIG. 13 is a diagram showing a setting example of the rise angle of the refractive Fresnel lens 10 corresponding to the third refractive Fresnel lens according to the present invention. In FIG. 13, the setting state of the conventional rise angle shown in FIG. 3 is indicated by the broken line a and the solid line b as in FIG. 3, and the setting of the rise angle in the refractive type Fresnel lens 10 (Fresnel angle and rise level). The correspondence with the corners) is indicated by a solid line e.

  In the conventional case, as shown by the broken line a and the solid line b, the rise angle gradually increases as the Fresnel angle increases in all regions of the Fresnel lens. On the other hand, in the refractive Fresnel lens 10, the rise angle gradually increases as the Fresnel angle increases in the region where the Fresnel angle is 60 ° or less (here, it gradually increases in exactly the same manner as the solid line b). Within the range of ° to 65 °, as shown by the solid line e, the rise angle gradually decreases from 22.5 ° to 15 ° or less as the Fresnel angle increases, and then the Fresnel angle increases. It gradually increases with time.

  FIG. 14 is a diagram showing the relationship between the Fresnel angle and the stray light emission angle in the refractive Fresnel lens 10 in which the rise angle is set as shown in FIG. 13 in contrast to the conventional case. These correspond to the solid line b and solid line e in FIG.

  When the rise angle is set as shown by the solid line b in FIG. 13 as in the prior art, as shown in FIG. 14, the emission angle of stray light is −5 in the region of Fresnel angle 62.5 ° to 65 °. It is an angle of 5 to 5 degrees (that is, an angle range that is emitted toward the front of the observer substantially toward the front).

  On the other hand, in the refractive type Fresnel lens 10, as shown in FIG. 14, the emission angle of stray light is −5 ° to 5 ° (observer side) only in the region where the Fresnel angle is 62.5 ° to 63 °. The angle range is generally emitted toward the front. That is, in the region having the Fresnel angle of 60 ° to 65 °, the region where stray light is emitted toward the front side toward the viewer is narrow. Therefore, stray light is suppressed from being emitted toward the front side of the observer in a region having a Fresnel angle of 60 ° to 65 °.

  As a result, in the rear projection display device 1 using the refractive Fresnel lens 10 whose rise angle is set as shown in FIG. 13 for the transmission screen 5, the refractive Fresnel lens 10 has a Fresnel angle of 60 ° to 65 °. Of these, the area where stray light is emitted toward the front of the viewer is narrowed, so that the generation of a double image caused by this stray light is suppressed.

  In the example of FIG. 13, the rise angle is gradually reduced to 15 ° or less as the Fresnel angle increases within the region of the Fresnel angle 60 ° to 65 °. However, as shown in FIG. 10, if the rise angle is set to approximately 17.5 ° or less, the result of the sensitivity evaluation is improved. Therefore, the rise angle is increased as the Fresnel angle is increased in the region of the Fresnel angle 60 ° to 65 °. You may make it reduce gradually to about 17.5 degrees or less. Alternatively, the rise angle may be gradually reduced to a value of 17.5 ° or more as the Fresnel angle increases within the region of the Fresnel angle 60 ° to 65 °. Even in those cases, the area where stray light is emitted toward the front of the observer can be reduced by an amount corresponding to the magnitude of the decrease in the rise angle. It can suppress emitting toward.

  In the above example, the refractive Fresnel lens according to the present invention is used for the transmission screen of the rear projection display device. However, the refractive Fresnel lens according to the present invention is other than the transmission screen of the rear projection display device. It may also be used for other applications.

It is a figure which shows the mode of generation | occurrence | production of the stray light in a refractive type Fresnel lens with a high image height. It is a figure which shows the lens internal angle, rise angle, etc. of a refraction type | mold Fresnel lens. It is a figure which shows the setting of the rise angle in the conventional refractive type Fresnel lens. It is a figure which shows the optical system of the rear projection type display apparatus to which this invention is applied. It is a figure which shows the outline | summary of the structure of the transmissive screen of FIG. It is a figure which shows the example of a setting of the rise angle in the refractive type Fresnel lens of FIG. It is a figure which shows the light beam path | route of the refractive type Fresnel lens by the rise angle of FIG. It is a figure which shows the mode of the division | segmentation of the stray light in the refractive type Fresnel lens by the rise angle of FIG. It is a figure which shows the ratio of the stray light with respect to a rise angle. It is a figure which shows the sensitivity evaluation when it mounts in a rear projection type display apparatus. It is a figure which shows another example of a setting of the rise angle in the refractive type Fresnel lens of FIG. It is a figure which shows the emission angle of the stray light by the rise angle of FIG. It is a figure which shows another example of a setting of the rise angle in the refractive type Fresnel lens of FIG. It is a figure which shows the emission angle of the stray light by the rise angle of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Rear projection type display apparatus, 2 Optical engine, 3 Mirror, 4 Mirror, 5 Transmission type screen, 10 Refraction type Fresnel lens, 11 Base material surface of refraction type Fresnel lens, 12a-12d Individual lens of refraction type Fresnel lens, 20 Lenticular lens

Claims (10)

In refraction type Fresnel lens,
A refractive Fresnel lens having a lens shape having a rise angle of approximately 17.5 ° or less in at least a part of a region having a Fresnel angle of 60 ° to 65 °. In refraction type Fresnel lens,
A refraction type Fresnel lens, wherein the rise angle is switched so as to discontinuously decrease within a region of a Fresnel angle of 60 ° to 65 °. The refractive Fresnel lens according to claim 2,
A refractive Fresnel lens, wherein the rise angle is switched so as to be discontinuously reduced to approximately 17.5 ° or less within a region of a Fresnel angle of 60 ° to 65 °. In refraction type Fresnel lens,
A refractive Fresnel lens characterized in that a rise angle gradually decreases as the Fresnel angle increases within a region of a Fresnel angle of 60 ° to 65 °. The refractive Fresnel lens according to claim 4,
A refractive Fresnel lens characterized in that the rise angle gradually decreases to approximately 17.5 ° or less as the Fresnel angle increases within a region of the Fresnel angle of 60 ° to 65 °. An image light source,
A transmissive screen using a refractive Fresnel lens;
In a rear projection type display device having an optical system for projecting image light from the image light source to the transmission screen from the back side,
The refraction type Fresnel lens is a rear projection display device characterized by having a lens shape with a rise angle of approximately 17.5 ° or less in at least a part of a region having a Fresnel angle of 60 ° to 65 °. An image light source,
A transmissive screen using a refractive Fresnel lens;
In a rear projection type display device having an optical system for projecting image light from the image light source to the transmission screen from the back side,
The refraction type Fresnel lens is a rear projection type display device, wherein the rise angle is switched so as to discontinuously decrease within a region of a Fresnel angle of 60 ° to 65 °. The refractive Fresnel lens according to claim 7,
The refraction type Fresnel lens has a rear surface characterized in that the rise angle is discontinuously switched to approximately 17.5 ° or less within a region of Fresnel angle of 60 ° to 65 °. Projection display device. An image light source,
A transmissive screen using a refractive Fresnel lens;
In a rear projection type display device having an optical system for projecting image light from the image light source to the transmission screen from the back side,
The refraction type Fresnel lens has a rise angle that gradually decreases as the Fresnel angle increases in a region of Fresnel angle of 60 ° to 65 °. The refractive Fresnel lens according to claim 9,
The refraction type Fresnel lens is a rear projection type display device characterized in that the rise angle is gradually reduced to approximately 17.5 ° or less as the Fresnel angle increases within the Fresnel angle range of 60 ° to 65 °.

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