Projector

Abstract

To provide a projector with which it is possible to suppress the peripheral part of a projection image formed by an optical modulator element from becoming dark, even when a Fresnel lens is located on the incidence side of the optical modulator element.SOLUTION: The projector comprises: a light source; a Fresnel lens group that parallelizes the beam emitted from the light source; an incidence-side polarizing plate that passes the beam emitted from the Fresnel lens group through; an optical modulator element that modulates the beam having passed through the incidence-side polarizing plate and forms a projection image; an emission-side polarizing plate that passes the beam modulated by the optical modulator element through; and a projection lens that projects the beam having passed through the emission-side polarizing plate. The Fresnel lens group includes a plurality of Fresnel lens. The first Fresnel lens which are closest to the light source among the Fresnel lens group has positive power. The incidence plane of the first Fresnel lens does not have a Fresnel surface. The mission plane of the first Fresnel lens has a Fresnel surface.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a projector. [Background technology]

[0002] A projector that uses a Fresnel lens to collimate light from a light source is described in Patent Document 1. The projector in this document includes a light source, a Fresnel lens into which light from the light source is incident, an entrance polarizing plate through which the light emitted from the Fresnel lens passes, a liquid crystal panel that forms a projected image by modulating the light emitted from the entrance polarizing plate, an exit polarizing plate through which the light emitted from the liquid crystal panel passes, and a projection lens that expands the light emitted from the exit polarizing plate. The Fresnel lens collimates light from the light source. The entrance polarizing plate does not transmit the polarized component of the light emitted from the Fresnel lens that is aligned with the absorption axis of the entrance polarizing plate. The liquid crystal panel modulates the polarized component that has passed through the entrance polarizing plate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] China Utility Model No. 201622432 Summary of the Invention [Problem to be solved by the invention]

[0004] Here, the light distribution of the light rays incident on the Fresnel lens, which is a shape obtained by dividing the curved surface of the lens into concentric circles, is circular. However, the light distribution of the light rays emitted from the Fresnel lens is elliptical because the transmittance of the light rays varies depending on the polarization direction and incident angle of the light rays incident on the Fresnel lens. For this reason, the elliptical light rays transmitted by the incident side polarizing plate hit the liquid crystal panel, causing a problem that the peripheral parts of the projected image formed on the liquid crystal panel become dark. [Means for solving the problem]

[0005] In order to solve the above problems, the projector of the present invention includes a light source, a Fresnel lens group that collimates light rays emitted from the light source, an entrance side polarizing plate that transmits the light rays emitted from the Fresnel lens group, a light modulation element that modulates the light rays transmitted through the entrance side polarizing plate to form a projected image, an exit side polarizing plate that transmits the light rays modulated by the light modulation element, and a projection lens that projects the light rays transmitted through the exit side polarizing plate, wherein the Fresnel lens group includes a first Fresnel lens having positive power that is arranged closest to the light source in the Fresnel lens group, and a second Fresnel lens having positive power that is arranged closer to the light modulation element than the first Fresnel lens, and the entrance surface of the first Fresnel lens does not have a Fresnel surface, and the exit surface of the first Fresnel lens has a Fresnel surface. [Brief description of the drawings]

[0006] [Figure 1] 1 is a schematic diagram of a main part of a projector according to a first embodiment. [Diagram 2] FIG. 13 is a diagram showing the relationship between the angle of incidence and the transmittance. [Diagram 3] 1 is a diagram illustrating the shape of the light distribution of polarized components along the X-axis direction of a light beam emitted from a Fresnel lens. [Figure 4] 1 is a diagram illustrating the shape of the light distribution of the polarized components along the Y-axis direction of a light beam emitted from a Fresnel lens. [Diagram 5] FIG. 1 is a schematic diagram of a main part of a projector of a comparative example. [Figure 6] FIG. 11 is a schematic diagram of a main part of a projector according to a second embodiment. [Figure 7] FIG. 11 is a schematic diagram of a main part of a projector according to a third embodiment. [Figure 8] FIG. 11 is a schematic diagram of a main part of a projector according to a fourth embodiment. [Figure 9] FIG. 13 is a schematic diagram of a main part of a projector according to a fifth embodiment. [Figure 10] FIG. 13 is a schematic diagram of a main part of a projector according to a sixth embodiment. [Figure 11] FIG. 13 is a schematic diagram of a main part of a projector according to a seventh embodiment. [Figure 12] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a projector according to an embodiment of the invention will be described with reference to the drawings.

[0008] [Embodiment 1] Fig. 1 is a schematic diagram of a main part of a projector according to embodiment 1. As shown in Fig. 1, the projector 1 includes an image forming unit 2 that generates a projection image to be projected onto a screen S, a projection lens 3 that enlarges the projection image and projects the enlarged image onto the screen S, and a control unit 4 that controls the operation of the image forming unit 2.

[0009] The image forming unit 2 includes a light source 10, a pickup lens 11, a Fresnel lens group 20, an incident side polarizing plate 12, an optical modulation element 13, and an exit side polarizing plate 14. The light source 10, the pickup lens 11, the Fresnel lens group 20, the incident side polarizing plate 12, the optical modulation element 13, and the exit side polarizing plate 14 are arranged along an optical axis N. The light source 10 is, for example, an ultra-high pressure mercury lamp, a solid light source, or the like. In this embodiment, the light source 10 is an LED that emits randomly polarized white light. The pickup lens 11 guides the light beam emitted from the light source 10 to the Fresnel lens group 20. Here, in the following description, for convenience, three mutually orthogonal axes are referred to as the X-axis, the Y-axis, and the Z-axis. The direction along the optical axis N of the Fresnel lens group 20, in which the light beam from the light source 10 enters the Fresnel lens group 20 and is emitted, is referred to as the +Z direction. In the present invention, the polarized light component along the X-axis direction is sometimes called X-polarized light, and the polarized light component along the Y-axis direction is sometimes called Y-polarized light.

[0010] The Fresnel lens group 20 collimates the light beam emitted from the light source 10. The incident-side polarizing plate 12 is disposed between the Fresnel lens group 20 and the light modulation element 13. The incident-side polarizing plate 12 transmits a light beam having a polarization component that intersects with the absorption axis of the incident-side polarizing plate 12 among the polarization components contained in the light beam emitted from the Fresnel lens group 20. In this embodiment, the incident-side polarizing plate 12 transmits a light beam having a polarization component that is aligned along the X-axis direction among the polarization components contained in the light beam emitted from the Fresnel lens group 20.

[0011] The light modulation element 13 forms a projection image by modulating the light beam having a polarized component along the X-axis direction that has passed through the incident-side polarizing plate 12. The light modulation element 13 is a liquid crystal panel 130. In this embodiment, the liquid crystal panel 130 is made of a single panel having pixels made up of a plurality of sub-pixels that modulate three different colors of light, and forms a color projection image. In other words, the projector 1 in this embodiment is a single-panel type projector.

[0012] The exit-side polarizing plate 14 transmits either the polarized component along the X-axis direction or the polarized component along the Y-axis direction among the polarized components contained in the light emitted from the liquid crystal panel 130. In this embodiment, the exit-side polarizing plate 14 transmits the polarized component along the Y-axis direction among the polarized components contained in the light emitted from the liquid crystal panel 130.

[0013] The projection lens 3 projects the light transmitted through the exit-side polarizing plate 14 onto a screen S. The projection lens 3 includes a plurality of lenses. The control unit 4 operates the liquid crystal panel 130 based on an external image signal such as a video signal.

[0014] (Fresnel lenses) The Fresnel lens group 20 has a plurality of Fresnel lenses. In this embodiment, the Fresnel lens group 20 has a first Fresnel lens 21 arranged closest to the light source 10, and a second Fresnel lens 22 arranged closer to the liquid crystal panel 130 than the first Fresnel lens 21. Here, the Fresnel lens in this embodiment is a Fresnel lens having a shape in which the curved surface of the lens is divided into concentric circles.

[0015] The first Fresnel lens 21 is made of resin. The first Fresnel lens 21 has a positive power. The incident surface 211 of the first Fresnel lens 21 has a flat surface 213. That is, the incident surface 211 of the first Fresnel lens 21 does not have a Fresnel surface. The exit surface 212 of the first Fresnel lens 21 has a Fresnel surface 224.

[0016] The second Fresnel lens 22 is made of resin. The second Fresnel lens 22 has a positive power. The incident surface 221 of the second Fresnel lens 22 has a flat surface 223. That is, the incident surface 221 of the second Fresnel lens 22 does not have a Fresnel surface. The exit surface 222 of the second Fresnel lens 22 has a Fresnel surface 224.

[0017] (Characteristics of Fresnel lenses) The characteristics of the Fresnel lens will be described. Fig. 2 is a diagram showing the relationship between the angle of incidence and the transmittance. Fig. 3 is a diagram explaining the shape of the light distribution of the polarized component along the X-axis direction of the light beam emitted when a light beam with a polarized component along the X-axis direction is incident on a Fresnel lens. Fig. 4 is a diagram explaining the shape of the light distribution of the polarized component along the Y-axis direction of the light beam emitted when a light beam with a polarized component along the Y-axis direction is incident on a Fresnel lens.

[0018] As shown in Figure 2, compared to the amount of P-polarized light that passes through an optical material, the amount of S-polarized light that passes through an optical material decreases significantly as the angle of incidence of the light increases. For this reason, up to Brewster's angle, the difference between the amount of P-polarized light and the amount of S-polarized light increases as the angle of incidence of the light increases. Note that while Figure 2 shows the relationship between the angle of incidence and transmittance in quartz glass, regardless of the optical material, up to Brewster's angle, the difference between the amount of P-polarized light and the amount of S-polarized light increases as the angle of incidence of the light increases.

[0019] Here, in FIG. 3, the light beam in the Fresnel lens has the following characteristics. The light beam passing through the concentric Fresnel lens is aligned along the P-polarized direction on the XY plane at the outer periphery of the Fresnel lens in the X-axis direction intersecting with the optical axis N of the Fresnel lens. The light beam passing through the concentric Fresnel lens is aligned along the S-polarized direction on the XY plane at the outer periphery of the Fresnel lens in the Y-axis direction intersecting with the optical axis N of the Fresnel lens. Therefore, in the case of X-polarized light, as the incidence angle of the light beam increases, the difference between the amount of P-polarized light passing through the outer periphery of the Fresnel lens in the X-axis direction intersecting with the optical axis N of the Fresnel lens and the amount of S-polarized light passing through the outer periphery of the Fresnel lens in the Y-axis direction intersecting with the optical axis N of the Fresnel lens increases. As a result, when the positive power of the Fresnel lens increases, the incidence angle of the light beam passing through the outer periphery of the Fresnel lens increases, so that the light beam distribution of the polarized component along the X-axis direction of the light beam emitted from the Fresnel lens changes from a circular shape G to an elliptical shape D, as shown in FIG. 3.

[0020] In FIG. 4, the light beam in the Fresnel lens has the following behavior. The light beam passing through the concentric Fresnel lens is aligned along the P-polarized direction on the XY plane at the outer periphery of the Fresnel lens in the Y-axis direction intersecting with the optical axis N of the Fresnel lens. The light beam passing through the concentric Fresnel lens is aligned along the S-polarized direction on the XY plane at the outer periphery of the Fresnel lens in the X-axis direction intersecting with the optical axis N of the Fresnel lens. For this reason, in the case of Y-polarized light, as the angle of incidence of the light beam increases, the difference between the amount of P-polarized light passing through the outer periphery of the Fresnel lens in the Y-axis direction intersecting with the optical axis N of the Fresnel lens and the amount of S-polarized light passing through the outer periphery of the Fresnel lens in the X-axis direction intersecting with the optical axis N of the Fresnel lens increases. As a result, the Fresnel lens As the positive power of the Fresnel lens increases, the angle of incidence of the light rays passing through the outer periphery of the Fresnel lens increases. As a result, as shown in Figure 4, the light distribution of the polarized component along the Y-axis direction of the light rays emitted from the Fresnel lens changes from a circular shape G to an elliptical shape D.

[0021] (Fresnel lens evaluation formula) Based on the characteristics of the Fresnel lens, the light distribution of the light emitted from the Fresnel lens can be evaluated by the following evaluation formula.

[0022] E=1 / (4Imax)×(|Iap-Ias|+|Ibp-Ibs|+|Icp-Ics|+|Idp-Ids|) ···(1)

[0023] The evaluation value E calculated by the above evaluation formula (1) is a value indicating how much the circular light distribution of light incident on a Fresnel lens changes shape on an evaluation surface set at a certain position from the light source when the light exits the Fresnel lens. In evaluation formula (1), the smaller the difference in the amount of light between X-polarized light and Y-polarized light transmitted through the Fresnel lens, the smaller the evaluation value E. In other words, the smaller the evaluation value E, the closer the light distribution exiting the Fresnel lens is to a circular shape, and the larger the evaluation value E, the more the light distribution exiting the Fresnel lens changes to an elliptical shape.

[0024] In the above evaluation formula (1), Imax indicates the illuminance value of each polarization at the center position cl in FIG. 3 and FIG. 4, and the illuminance values ​​of the polarization component along the X-axis direction (X-polarized light) and the polarization component along the Y-axis direction (Y-polarized light) are the same value. Iap indicates the illuminance value of X-polarized light at the boundary position ap in the short axis direction (+Y-axis direction) in FIG. 3. Ibp indicates the illuminance value of X-polarized light at the boundary position bp in the short axis direction (-Y-axis direction) in FIG. 3. Icp indicates the illuminance value of X-polarized light at the boundary position cp in the long axis direction (-X-axis direction) in FIG. 3. Idp (+X-axis direction) indicates the illuminance value of X-polarized light at the boundary position dp in the long axis direction in FIG. 3. Ias indicates the illuminance value of Y-polarized light at the boundary position as in the long axis direction (+Y-axis direction) in FIG. 4. Ibs indicates the illuminance value of Y-polarized light at the boundary position bs in the long axis direction (-Y-axis direction) in FIG. 4. Ics indicates the illuminance value of Y-polarized light at boundary position cs in the short axis direction (-X axis direction) in Fig. 4. Ids indicates the illuminance value of Y-polarized light at boundary position ds in the short axis direction (+X axis direction) in Fig. 4. Note that the distances from boundary position ap, boundary position bp, boundary position as and boundary position bs to central position cl are all the same. Also, the distances from boundary position cp, boundary position dp, boundary position cs and boundary position ds to central position cl are all the same.

[0025] (Comparison between the first embodiment and the comparative example) The light distribution of the light beam emitted from the Fresnel lens group 20 in the projector 1 of the embodiment 1 was compared with the light distribution of the light beam emitted from the Fresnel lens in the projector of the comparative example, using the above evaluation formula (1). Each illuminance value used in the evaluation formula (1) was calculated using simulation software. This time, LightTools by Synopsys, Inc. was used as the simulation software.

[0026] Here, FIG. 5 is a schematic diagram of a main part of a projector 100 of a comparative example. The projector 100 of the comparative example differs from the projector 1 of the first embodiment in that it has one Fresnel lens 60. Therefore, in the comparative example, the same components as those of the first embodiment are given the same reference numerals and descriptions thereof may be omitted. The Fresnel lens 60 has a positive power. As shown in FIG. 5, an entrance surface 601 of the Fresnel lens 60 has a flat surface 603. An exit surface 602 of the Fresnel lens 60 has a Fresnel surface 604.

[0027] The procedure for comparing the first embodiment with the comparative example is as follows: The illuminance values ​​corresponding to each position of the light distribution of the light beam emitted from the second Fresnel lens 22 of 20 and the illuminance values ​​corresponding to each position of the light distribution of the light beam emitted from the Fresnel lens 60 of the comparative example were determined using LightTools, and then each evaluation value E was calculated using evaluation formula (1), and each evaluation value E was compared.

[0028] The lens data of each Fresnel lens in the first embodiment set by LightTools is as follows: D is the on-axis surface distance.

[0029] 1 of 1 D Material Light source 150mm First Fresnel lens First lens surface 3mm PMMA Second lens surface 2mm 2nd Fresnel lens 3rd lens surface 3mm PMMA Fourth lens surface: 12mm Evaluation Evaluation - -

[0030] 2 of embodiment 1 D Material Light source 150mm First Fresnel lens First lens surface 3mm PMMA Second lens surface 2mm 2nd Fresnel lens 3rd lens surface 3mm PMMA Fourth lens surface: 12mm Evaluation Evaluation - -

[0031] 3 of embodiment 1 D Material Light source 150mm First Fresnel lens First lens surface 3mm PMMA Second lens surface 2mm 2nd Fresnel lens 3rd lens surface 3mm PMMA Fourth lens surface: 12mm Evaluation Evaluation - -

[0032] The data of the focal length of each Fresnel lens in the first embodiment set by LightTools is as follows: f1 is the focal length of the first Fresnel lens 21. f2 is the focal length of the second Fresnel lens 22. f is the combined focal length of the first Fresnel lens 21 and the second Fresnel lens 22.

[0033] 1 of embodiment 1 2 of embodiment 1 3 of embodiment 1 f1 230mm 297mm 420mm f2 420mm 297mm 230mm f 150mm 150mm 150mm

[0034] The lens data for the Fresnel lens of the comparative example set in LightTools is as follows: D is the on-axis surface spacing.

[0035] Comparative Example D Material Light source 150mm Fresnel lens 1st lens surface 3mm PMMA Second lens surface: 17mm Evaluation Evaluation - -

[0036] The data of the focal length of the Fresnel lens of the comparative example set in LightTools is as follows: f0 is the focal length of the Fresnel lens 60;

[0037] Comparative Example f0 150mm

[0038] Other parameters set by LightTools in the first embodiment, items 1 to 3, and the comparative example are as follows:

[0039] Facet Specification: Polynomial Material: PMMA Shape: Circular Diameter: 150.0000 Thickness: 3.0000 Type: Equi-Depth Maximum Depth: 0.0600 Maximum Width: 0.5000 Conic Constant: -1.0000

[0040] The illuminance values ​​corresponding to each position of the light distribution of the light beam emitted from the second Fresnel lens 22 of the Fresnel lens group 20 of the first to third embodiments and the Fresnel lens 60 of the comparative example on the evaluation surface set by LightTools are as follows. Note that the positions of the evaluation surfaces of the first to third embodiments and the comparative example are the same.

[0041] Imax Iap Ibp Icp Idp 1 of embodiment 1 2.41306 1.68720 1.66422 1.75556 1.76837 2 of embodiment 1 2.39815 1.70390 1.63370 1.75054 1.72988 3 of embodiment 1 2.37298 1.69014 1.67326 1.76322 1.78062 Conventional example 2.65764 1.89133 1.87011 2.04134 2.04515

[0042] Ias Ibs Ics Ids 1 of embodiment 1 1.75609 1.73488 1.68813 1.69304 2 of embodiment 1 1.76979 1.69894 1.68535 1.66545 3 of embodiment 1 1.77052 1.75384 1.68317 1.69978 Conventional example 2.02164 2.00043 1.90976 1.91331

[0043] The evaluation value E of the Fresnel lenses 1 to 3 of the first embodiment and the comparative example is as follows.

[0044] E 1 of embodiment 1 0.02925 2 of embodiment 1 0.02718 3 of embodiment 1 0.03391 Conventional example 0.04930

[0045] As shown above, the evaluation value E of the first to third embodiments is smaller than the evaluation value E of the comparative example. As a result, when the focal length f of the Fresnel lens group 20 of the first to third embodiments is the same as the focal length f0 of the Fresnel lens 60 of the comparative example, the lens power per Fresnel lens of the first to third embodiments is smaller than the lens power of the Fresnel lens 60 of the comparative example, so it can be seen that the light distribution of the light beam emitted from the second Fresnel lens 22 of the Fresnel lens group 20 of the first to third embodiments is smaller in shape change than the light distribution of the light beam emitted from the Fresnel lens 60 of the comparative example. That is, the light distribution of the light beam emitted from the second Fresnel lens 22 of the Fresnel lens group 20 of the first to third embodiments is closer to a circular shape than the light distribution of the light beam emitted from the Fresnel lens 60 of the comparative example.

[0046] Among the embodiments 1-3, the light distribution of the light emitted from the second Fresnel lens 22 of the Fresnel lens group 20 in the embodiment 1-2 is closest to a circle. That is, when the focal length of the first Fresnel lens 21 and the focal length of the second Fresnel lens 22 are the same, the light distribution of the light emitted from the Fresnel lens group 20 is closest to a circle.

[0047] (Action and effect) The projector 1 of this embodiment includes a light source 10, a Fresnel lens group 20 that collimates the light beam emitted from the light source 10, an incident side polarizing plate 12 that transmits the light beam emitted from the Fresnel lens group 20, a liquid crystal panel 130 that modulates the light beam transmitted through the incident side polarizing plate 12 to form a projection image, an exit side polarizing plate 14 that transmits the light beam modulated by the liquid crystal panel 130, and a projection lens 3 that projects the light beam transmitted through the exit side polarizing plate 14. The Fresnel lens group 20 includes a plurality of Fresnel lenses. A first Fresnel lens 21 that is disposed closest to the light source 10 among the Fresnel lens group 20 has a positive power. An incident surface 211 of the first Fresnel lens 21 does not include a Fresnel surface. An exit surface 212 of the first Fresnel lens 21 includes a Fresnel surface 214. The Fresnel lens group 20 includes a second Fresnel lens 22 disposed closer to the liquid crystal panel 130 than the first Fresnel lens 21. The second Fresnel lens 22 has a positive power. An entrance surface 221 of the second Fresnel lens 22 does not have a Fresnel surface. An exit surface 222 of the second Fresnel lens 22 has a Fresnel surface 224.

[0048] According to this embodiment, since the Fresnel lens group 20 has two Fresnel lenses, the lens power per lens can be reduced compared to the case of a single Fresnel lens. This can reduce the change in shape of the light distribution of the light beam emitted from the second Fresnel lens 22. As a result, the light distribution of the light beam emitted from the Fresnel lens group 20 is close to a circular shape, so that it is possible to prevent the peripheral part of the projected image formed by the liquid crystal panel 130 from becoming dark. Therefore, the projector 1 can project an enlarged image with uniform brightness.

[0049] Here, when the entrance surface of the Fresnel lens has a Fresnel surface, the angle of incidence of the light beam entering the entrance surface of the Fresnel lens is larger than when the entrance surface of the Fresnel lens does not have a Fresnel surface. Therefore, according to this embodiment, since the entrance surface 211 of the first Fresnel lens 21 does not have a Fresnel surface, it is possible to suppress a decrease in the amount of light beams passing through the first Fresnel lens 21 compared to when the entrance surface 211 of the first Fresnel lens 21 has a Fresnel surface. Also, since the entrance surface 221 of the second Fresnel lens 22 does not have a Fresnel surface, it is possible to suppress a decrease in the amount of light beams passing through the second Fresnel lens 22 compared to when the entrance surface 221 of the second Fresnel lens 22 has a Fresnel surface.

[0050] In this embodiment, the focal length of the first Fresnel lens 21 is the same as the focal length of the second Fresnel lens 22. This can further reduce the change in the shape of the light distribution of the light beam emitted from the second Fresnel lens 22. In addition, if the focal length of the first Fresnel lens 21 and the focal length of the second Fresnel lens 22 are the same, The lens 21 and the second Fresnel lens 22 can have the same shape. This makes it possible to reduce the production cost of the Fresnel lenses compared to a case in which the first Fresnel lens 21 and the second Fresnel lens 22 have different shapes.

[0051] In this embodiment, since the lens power per lens can be reduced, it is possible to significantly suppress the decrease in the transmittance of the polarized component along the S-polarized direction incident on the Fresnel lens when viewed on the XY plane as shown in Fig. 2. Therefore, it is possible to suppress the peripheral portion of the projected image formed by the liquid crystal panel 130 from becoming dark.

[0052] [Embodiment 2] 6 is a schematic diagram of a main part of a projector 1A of embodiment 2. In the projector 1A of embodiment 2, the orientation of the Fresnel surface of the second Fresnel lens 22 of the Fresnel lens group 20 is different from that of the projector 1 of embodiment 1. Therefore, in embodiment 2, the same components as those in embodiment 1 are denoted by the same reference numerals, and the description thereof may be omitted.

[0053] 6, the Fresnel lens group 20 has a plurality of Fresnel lenses. In this embodiment, the Fresnel lens group 20 has a first Fresnel lens 21 arranged closest to the light source 10, and a second Fresnel lens 22 arranged closer to the liquid crystal panel 130 than the first Fresnel lens 21.

[0054] The first Fresnel lens 21 is made of resin. The first Fresnel lens 21 has a positive power. The incident surface 211 of the first Fresnel lens 21 has a flat surface 213. That is, the incident surface 211 of the first Fresnel lens 21 does not have a Fresnel surface. The exit surface 212 of the first Fresnel lens 21 has a Fresnel surface 224.

[0055] The second Fresnel lens 22 is made of resin. The second Fresnel lens 22 has a positive power. The entrance surface 221 of the second Fresnel lens 22 has a Fresnel surface 224. The exit surface 222 of the second Fresnel lens 22 has a flat surface 223. In other words, the exit surface 222 of the second Fresnel lens 22 does not have a Fresnel surface.

[0056] (Comparison between the second embodiment and the comparative example) As in embodiment 1, the ray distribution of the light emitted from the Fresnel lens group 20 in the projector 1 of embodiment 2 and the ray distribution of the light emitted from the Fresnel lens 60 in the projector 100 of the comparative example were compared using the above evaluation formula (1).

[0057] The lens data of each Fresnel lens in the second embodiment set by LightTools is as follows: D is the on-axis surface distance.

[0058] 1 of embodiment 2 D Material Light source 150mm First Fresnel lens First lens surface 3mm PMMA Second lens surface 2mm 2nd Fresnel lens 3rd lens surface 3mm PMMA Fourth lens surface: 12mm Evaluation Evaluation - -

[0059] 2 of embodiment 2 D Material Light source 150mm First Fresnel lens First lens surface 3mm PMMA Second lens surface 2mm 2nd Fresnel lens 3rd lens surface 3mm PMMA Fourth lens surface: 12mm Evaluation Evaluation - -

[0060] 2 of 3 D Material Light source 150mm First Fresnel lens First lens surface 3mm PMMA Second lens surface 2mm 2nd Fresnel lens 3rd lens surface 3mm PMMA Fourth lens surface: 12mm Evaluation Evaluation - -

[0061] The data of the focal length of each Fresnel lens in the second embodiment set by LightTools is as follows: f1 is the focal length of the first Fresnel lens 21. f2 is the focal length of the second Fresnel lens 22. f is the combined focal length of the first Fresnel lens 21 and the second Fresnel lens 22.

[0062] Embodiment 2-1 Embodiment 2-2 Embodiment 2-3 f1 230mm 297mm 420mm f2 420mm 297mm 230mm f 150mm 150mm 150mm

[0063] The lens data for the Fresnel lens of the comparative example set in LightTools is as follows: D is the on-axis surface spacing.

[0064] Comparative Example D Material Light source 150mm Fresnel lens 1st lens surface 3mm PMMA Second lens surface: 17mm Evaluation Evaluation - -

[0065] The data of the focal length of the Fresnel lens of the comparative example set in LightTools is as follows: f0 is the focal length of the Fresnel lens 60;

[0066] Comparative Example f0 150mm

[0067] The other parameters set by LightTools in the second embodiment (1 to 3) and the comparative example are the same as those in the first embodiment.

[0068] The illuminance values ​​corresponding to each position of the light distribution of the light beam emitted from the second Fresnel lens 22 of the Fresnel lens group 20 of the first to third embodiments of the second embodiment and the Fresnel lens 60 of the comparative example on the evaluation surface set by LightTools are as follows. Note that the positions of the evaluation surfaces of the first to third embodiments of the second embodiment and the comparative example are the same.

[0069] Imax Iap Ibp Icp Idp 1 of embodiment 2 2.44125 1.61451 1.61877 1.71080 1.71588 2 of embodiment 2 2.43360 1.53377 1.56216 1.64476 1.68040 3 of embodiment 2 2.41587 1.51910 1.45404 1.57015 1.61005 Conventional example 2.65764 1.89133 1.87011 2.04134 2.04515

[0070] Ias Ibs Ics Ids 1 of embodiment 2 1.69512 1.70313 1.63276 1.63569 2 of embodiment 2 1.61720 1.64826 1.55991 1.59370 3 of embodiment 2 1.63691 1.56838 1.45714 1.49418 Conventional example 2.02164 2.00043 1.90976 1.91331

[0071] The evaluation value E of the Fresnel lenses 1 to 3 of the second embodiment and the comparative example is as follows.

[0072] E 1 of embodiment 2 0.03310 2 of embodiment 2 0.03504 0.04771 in embodiment 2 Conventional example 0.04930

[0073] As shown above, the evaluation value E of the first to third embodiments of the second embodiment is smaller than the evaluation value E of the comparative example. As a result, when the focal length f of the Fresnel lens group 20 of the first to third embodiments of the second embodiment is the same as the focal length f0 of the Fresnel lens 60 of the comparative example, the lens power per Fresnel lens of the first to third embodiments of the second embodiment is smaller than the lens power of the Fresnel lens 60 of the comparative example, so it can be seen that the light distribution of the light beam emitted from the second Fresnel lens 22 of the Fresnel lens group 20 of the first to third embodiments of the second embodiment has a smaller change in shape than the light distribution of the light beam emitted from the Fresnel lens 60 of the comparative example. That is, the light distribution of the light beam emitted from the second Fresnel lens 22 of the Fresnel lens group 20 of the first to third embodiments of the second embodiment is closer to a circular shape than the light distribution of the light beam emitted from the Fresnel lens 60 of the comparative example.

[0074] Among the first to third embodiments of the second embodiment, the light distribution of the light emitted from the second Fresnel lens 22 of the Fresnel lens group 20 in the third embodiment of the second embodiment is closest to a circle. That is, when the focal length of the first Fresnel lens 21 is longer than the focal length of the second Fresnel lens 22, the light distribution of the light emitted from the Fresnel lens group 20 is closest to a circle.

[0075] (Action and effect) In the projector 1A of this embodiment, the entrance surface 221 of the second Fresnel lens 22 has a Fresnel surface 224. The exit surface 222 of the second Fresnel lens 22 does not have a Fresnel surface. Therefore, even with this configuration, the projector 1A of this embodiment can obtain the same effect as the first embodiment, because the Fresnel lens group 20 has two Fresnel lenses.

[0076] Since the Fresnel surfaces of the first Fresnel lens 21 and the second Fresnel lens 22 face each other, when the first Fresnel lens 21 and the second Fresnel lens 22 are integrated into a unit using a holding member or the like, the Fresnel surfaces can be located inside the unit. This makes it possible to prevent the Fresnel surfaces from being damaged by tools or the like when assembling this unit into a projector.

[0077] In this embodiment, the focal length of the first Fresnel lens 21 is longer than the focal length of the second Fresnel lens 22. As a result, The change in the shape of the light distribution can be made smaller.

[0078] [Embodiment 3] 7 is a schematic diagram of a main part of a projector 1B of embodiment 3. The projector 1B of embodiment 3 differs from the projector 1 of embodiment 1 in that the Fresnel lens group 20 has three Fresnel lenses. Therefore, in embodiment 3, the same components as those in embodiment 1 are denoted by the same reference numerals, and the description thereof may be omitted.

[0079] As shown in FIG. 7, the Fresnel lens group 20 has a first Fresnel lens 21 arranged closest to the light source 10, a second Fresnel lens 22 arranged closer to the liquid crystal panel 130 than the first Fresnel lens 21, and a third Fresnel lens 23 arranged closer to the liquid crystal panel 130 than the second Fresnel lens 22.

[0080] The first Fresnel lens 21 is made of resin. The first Fresnel lens 21 has a positive power. The incident surface 211 of the first Fresnel lens 21 has a flat surface 213. That is, the incident surface 211 of the first Fresnel lens 21 does not have a Fresnel surface. The exit surface 212 of the first Fresnel lens 21 has a Fresnel surface 224.

[0081] The second Fresnel lens 22 is made of resin. The second Fresnel lens 22 has a positive power. The incident surface 221 of the second Fresnel lens 22 has a flat surface 223. That is, the incident surface 221 of the second Fresnel lens 22 does not have a Fresnel surface. The exit surface 222 of the second Fresnel lens 22 has a Fresnel surface 224.

[0082] The third Fresnel lens 23 is made of resin. The third Fresnel lens 23 has positive power. The incident surface 231 of the third Fresnel lens 23 has a flat surface 233. That is, the incident surface 231 of the third Fresnel lens 23 does not have a Fresnel surface. The exit surface 232 of the third Fresnel lens 23 has a Fresnel surface 234.

[0083] (Comparison between the third embodiment and the comparative example) As in embodiment 1, the ray distribution of the light emitted from the Fresnel lens group 20 in the projector 1B of embodiment 3 and the ray distribution of the light emitted from the Fresnel lens 60 in the projector 100 of the comparative example were compared using the above evaluation formula (1).

[0084] The lens data of each Fresnel lens in the third embodiment set by LightTools is as follows: D is the on-axis surface distance.

[0085] EMBODIMENT 3 D Material Light source 150mm First Fresnel lens First lens surface 3mm PMMA Second lens surface 2mm 2nd Fresnel lens 3rd lens surface 3mm PMMA 4th lens surface 2mm 3rd Fresnel lens 5th lens surface 3mm PMMA 6th lens surface 7mm Evaluation Evaluation - -

[0086] The data of the focal length of each Fresnel lens in the third embodiment set by LightTools is as follows: f1 is the focal length of the first Fresnel lens 21; f2 is the focal length of the second Fresnel lens 22; f3 is the focal length of the third Fresnel lens 23; f is the composite focal length of the first Fresnel lens 21, the second Fresnel lens 22, and the third Fresnel lens 23.

[0087] EMBODIMENT 3 f1 450mm f2 450mm f3 450mm f 150mm

[0088] The lens data for the Fresnel lens of the comparative example set in LightTools is as follows: D is the on-axis surface spacing.

[0089] Comparative Example D Material Light source 150mm Fresnel lens 1st lens surface 3mm PMMA Second lens surface: 17mm Evaluation Evaluation - -

[0090] The data of the focal length of the Fresnel lens of the comparative example set in LightTools is as follows: f0 is the focal length of the Fresnel lens 60;

[0091] Comparative Example f0 150mm

[0092] Other parameters set by LightTools in the third embodiment and the comparative example are the same as those in the first embodiment.

[0093] The illuminance values ​​corresponding to each position of the light distribution of the light beam emitted from the third Fresnel lens 23 of the Fresnel lens group 20 of the embodiment 3 and the Fresnel lens 60 of the comparative example on the evaluation surface set by LightTools are as follows. Note that the positions of the evaluation surfaces in Example 3 and the comparative example are the same.

[0094] Imax Iap Ibp Icp Idp Embodiment 3 2.14741 1.48909 1.47501 1.53156 1.53027 Conventional example 2.65764 1.89133 1.87011 2.04134 2.04515

[0095] Ias Ibs Ics Ids Embodiment 3 1.53528 1.52136 1.48549 1.48422 Conventional example 2.02164 2.00043 1.90976 1.91331

[0096] The evaluation values ​​E of the Fresnel lenses of the third embodiment and the comparative example are as follows.

[0097] E Embodiment 3 0.0215 Conventional example 0.0493

[0098] As described above, the evaluation value E of the third embodiment is smaller than the evaluation value E of the comparative example. As a result, when the focal length f of the Fresnel lens group 20 of the third embodiment and the focal length f0 of the Fresnel lens 60 of the comparative example are set to be the same, Since the power is smaller than the lens power of the Fresnel lens 60 of the comparative example, it can be seen that the light distribution of the light emitted from the second Fresnel lens 22 of the Fresnel lens group 20 of embodiment 3 has a smaller change in shape than the light distribution of the light emitted from the Fresnel lens 60 of the comparative example. In other words, the light distribution of the light emitted from the second Fresnel lens 22 of the Fresnel lens group 20 of embodiment 3 is closer to a circular shape than the light distribution of the light emitted from the Fresnel lens 60 of the comparative example.

[0099] (Action and effect) In the projector 1B of this embodiment, the Fresnel lens group 20 has a third Fresnel lens 23 arranged on the side of the second Fresnel lens 22 facing the light modulation element 13. The third Fresnel lens 23 has a positive power. Therefore, in the projector 1B of this embodiment, the Fresnel lens group 20 has three Fresnel lenses, so that the lens power per lens can be made smaller compared to the case of a single Fresnel lens. As a result, the light distribution of the light beams emitted from the Fresnel lens group 20 is closer to a circular shape, so that it is possible to further prevent the peripheral portion of the projected image formed on the liquid crystal panel 130 from becoming dark.

[0100] [Embodiment 4] 8 is a schematic diagram of a main part of a projector 1C of embodiment 4. Projector 1C of embodiment 4 differs from projector 1 of embodiment 1 in that it includes a polarization conversion optical system. Therefore, in embodiment 4, the same components as those in embodiment 1 are given the same reference numerals, and descriptions thereof may be omitted.

[0101] As shown in FIG. 8, the image forming unit 2 includes a light source 10, a pickup lens 11, a Fresnel lens group 20, a first integrator lens 16, a second integrator lens 17, a polarization conversion optical system 15, an incident-side polarizing plate 12, a light modulation element 13, and an exit-side polarizing plate 14.

[0102] The first integrator lens 16 and the second integrator lens 17 are disposed on the exit side of the Fresnel lens group 20. The first integrator lens 16 and the second integrator lens 17 each have a plurality of lens elements arranged in an array. The first integrator lens 16 splits the light beam from the Fresnel lens group 20 into a plurality of beams. The second integrator lens 17 focuses the light beam from the first integrator lens 16 near the polarization conversion optical system 15.

[0103] The polarization conversion optical system 15 is disposed on the exit side of the second integrator lens 17. The polarization conversion optical system 15 converts the polarization direction of the light beam emitted from the Fresnel lens group 20. The polarization conversion optical system 15 is a polarization conversion element 150. The polarization conversion element 150 is an optical element formed of a PBS (Polarization Beam Splitter) array. Although not shown, the polarization conversion element 150 has a polarization separation layer that transmits one linearly polarized component (e.g., X-polarized light) of the polarized components contained in the light beam emitted from the Fresnel lens group 20 as is and reflects the other linearly polarized component (e.g., Y-polarized light) in a direction perpendicular to the optical axis, a reflection layer that reflects the other linearly polarized component reflected by the polarization separation layer in a direction parallel to the optical axis, and a retardation plate (e.g., 1 / 2 retardation plate) that converts the other linearly polarized component (e.g., Y-polarized light) reflected by the reflection layer into one linearly polarized component (e.g., X-polarized light). The polarization conversion element 150 of this embodiment converts Y-polarized light, which is one of the polarization components contained in the incident light beam, into X-polarized light. More specifically, the polarization conversion element 150 transmits X-polarized light, which is one of the polarization components contained in the light beam incident on the polarization conversion element 150, and converts Y-polarized light into X-polarized light, which then exits toward the incident-side polarizing plate 12.

[0104] (Action and effect) In the projector 1C of this embodiment, a Fresnel lens group 20 and an incident-side polarizing plate 12 are disposed The projector 1C of this embodiment includes a polarization conversion optical system 15 that is disposed on the projection surface 11 and that converts the polarization direction of the light beam emitted from the Fresnel lens group 20. The polarization conversion optical system 15 is a polarization conversion element 150. Therefore, compared to a configuration that does not have the polarization conversion element 150, the polarization conversion element 150 converts the Y-polarized light beam emitted from the Fresnel lens group 20 into X-polarized light beam for use, so that the projector 1C of this embodiment can increase the amount of light beam incident on the liquid crystal panel 130. The polarization conversion optical system 15 of this embodiment can be applied to the first to third embodiments.

[0105] [Embodiment 5] 9 is a schematic diagram of a main part of a projector 1D of embodiment 5. Projector 1D of embodiment 5 differs from projector 1C of embodiment 4 in that the position at which the polarization conversion optical system is arranged is different. Therefore, in embodiment 5, the same components as those in embodiment 1 are given the same reference numerals, and the description thereof may be omitted.

[0106] As shown in FIG. 9, the image forming unit 2 includes a light source 10, a pickup lens 11, a first integrator lens 16, a second integrator lens 17, a polarization conversion optical system 15, a magnifying lens 18, a Fresnel lens group 20, an incident-side polarizing plate 12, a light modulation element 13, and an exit-side polarizing plate 14.

[0107] The first integrator lens 16 and the second integrator lens 17 are disposed on the exit side of the pickup lens 11. The first integrator lens 16 and the second integrator lens 17 each have a plurality of lens elements arranged in an array. The first integrator lens 16 splits the light beam from the pickup lens 11 into a plurality of beams. The second integrator lens 17 focuses the light beam from the first integrator lens 16 near the polarization conversion optical system 15.

[0108] The polarization conversion optical system 15 is disposed on the exit side of the second integrator lens 17. The polarization conversion optical system 15 converts the polarization direction of the light beam emitted from the light source 10. The polarization conversion optical system 15 is a polarization conversion element 150. The polarization conversion element 150 in this embodiment transmits X-polarized light among the polarization components contained in the light beam incident on the polarization conversion element 150, converts Y-polarized light to X-polarized light, and emits the X-polarized light toward the incident-side polarizing plate 12. The magnifying lens 18 magnifies the light beam incident from the polarization conversion element 150, and emits it toward the incident-side polarizing plate 12.

[0109] (Action and effect) The projector 1D of this embodiment is provided with a polarization conversion optical system 15 that is disposed between the light source 10 and the Fresnel lens group 20 and converts the polarization direction of the light beam emitted from the light source 10. The polarization conversion optical system 15 is a polarization conversion element 150. Therefore, compared to a configuration that does not have the polarization conversion element 150, the polarization conversion optical system 15 converts the Y-polarized light beam emitted from the light source 10 into X-polarized light for use, so that the projector 1D of this embodiment can increase the amount of light beam incident on the liquid crystal panel 130. The polarization conversion optical system 15 of this embodiment can be applied to the first to third embodiments.

[0110] [Embodiment 6] 10 is a schematic diagram of a main part of a projector 1E of embodiment 6. Projector 1E of embodiment 6 differs from projector 1D of embodiment 5 in that the polarization conversion optical system is not a polarization conversion element. Therefore, in embodiment 6, the same components as those in embodiment 1 are given the same reference numerals, and descriptions thereof may be omitted.

[0111] As shown in FIG. 10, the image forming unit 2 includes a light source 10, a pickup lens 11, a polarization conversion optical system 15, a magnifying lens 18, a Fresnel lens group 20, an entrance side polarizing plate 12, a light modulation element 13, and an exit side polarizing plate 14.

[0112] The polarization conversion optical system 15 is disposed on the exit side of the pickup lens 11. The polarization conversion optical system 15 converts the polarization direction of the light beam emitted from the light source 10. More specifically, the polarization conversion optical system 15 converts Y-polarized light, which is included in the polarization components contained in the light beam incident on the polarization conversion optical system 15, into X-polarized light. The polarization conversion optical system 15 includes a polarization beam splitter 151, a total reflection mirror 152, and a retardation plate 153. The polarization beam splitter 151 transmits one linearly polarized component (e.g., X-polarized light) of the polarization components contained in the incident light beam as is, and reflects the other linearly polarized component (e.g., Y-polarized light) in a direction perpendicular to the optical axis N. In this embodiment, the polarization beam splitter 151 transmits P-polarized light toward the magnifying lens 18 and reflects Y-polarized light toward the total reflection mirror 152. The total reflection mirror 152 reflects the Y-polarized light reflected by the polarization beam splitter 151 in a direction parallel to the optical axis N. Retardation plate 153 (for example, a ½ retardation plate) converts the Y-polarized light reflected by total reflection mirror 152 into X-polarized light and emits it toward magnifying lens 18. Magnifying lens 18 magnifies the light beam incident from polarization conversion optical system 15 and emits it toward incident-side polarizing plate 12.

[0113] (Action and effect) The projector 1E of this embodiment is provided with a polarization conversion optical system 15 that is disposed between the light source 10 and the Fresnel lens group 20 and converts the polarization direction of the light beam emitted from the light source 10. The polarization conversion optical system 15 includes a polarizing beam splitter 151 that transmits the X-polarized light of the polarized components contained in the incident light beam as is and reflects the other Y-polarized light in a direction perpendicular to the optical axis N, a total reflection mirror 152 that reflects the Y-polarized light reflected by the polarizing beam splitter 151 in a direction parallel to the optical axis N, and a retardation plate that converts the Y-polarized light reflected by the retardation plate 153 into X-polarized light. Therefore, since the Y-polarized light emitted from the light source 10 is converted into X-polarized light by the polarization conversion optical system 15 and used, the projector 1E of this embodiment can increase the amount of light incident on the liquid crystal panel 130. The polarization conversion optical system 15 of this embodiment can be applied to the first to third embodiments.

[0114] [Embodiment 7] Fig. 11 is a schematic diagram of a main part of a projector 1F of embodiment 7. Fig. 12 is an exploded perspective view of an adjustment mechanism. The projector 1F of embodiment 7 differs from the projector 1 of embodiment 1 in that it includes an adjustment mechanism 70. Therefore, in embodiment 7, the same configurations as in embodiment 1 may be assigned the same reference symbols and descriptions thereof may be omitted.

[0115] 11, the image forming unit 2 includes a light source 10, a pickup lens 11, a Fresnel lens group 20, an entrance side polarizing plate 12, a light modulation element 13, an exit side polarizing plate 14, and an adjustment mechanism 70. The adjustment mechanism 70 changes the axial distance between the first Fresnel lens 21 and the second Fresnel lens 22.

[0116] As shown in FIG. 11 and FIG. 12, the adjustment mechanism 70 includes a first frame 71 that holds the first Fresnel lens 21, a second frame 72 that holds the second Fresnel lens 22, and an adjustment unit 73 that adjusts the distance between the first frame 71 and the second frame 72. The first frame 71 holds the outer peripheral portion of the first Fresnel lens 21. The first frame 71 is fixed to the main body of the projector 1F or the like. The second frame 72 holds the outer peripheral portion of the second Fresnel lens 22. The second frame 72 is fixed to the first frame 71. The adjustment unit 73 includes an adjustment screw 74 that fixes the second frame 72 to the first frame 71, and a spring 75 that is disposed between the first frame 71 and the second frame 72 and through which the adjustment screw 74 is inserted. In this embodiment, four adjustment screws 74 and four springs 75 are provided. The adjustment screw 74 is inserted through a hole provided in the second frame 72 and is screwed into a screw hole provided in the first frame 71. By rotating the adjustment screw 74, the distance between the first frame 71 and the second frame 72 is adjusted. At this time, the spring 75 is in contact with the first frame 71. A biasing force is applied between the second frame 72.

[0117] (Action and effect) The projector 1F of this embodiment includes an adjustment mechanism 70 that changes the on-axis distance between the first Fresnel lens 21 and the second Fresnel lens 22. Therefore, during manufacture, it is easy to adjust the distance between the first Fresnel lens 21 and the second Fresnel lens 22. The adjustment mechanism 70 can be applied to the first to sixth embodiments.

[0118] [Other embodiments] In the above embodiment, the projector includes the light modulation element 13 composed of one liquid crystal panel 130, but the light modulation element 13 is not limited to one liquid crystal panel 130. For example, the light modulation element 13 may be composed of three liquid crystal panels that modulate red, blue, and green light, respectively. In other words, the projector may be a three-panel type.

[0119] The adjustment mechanism 70 is not limited to the above-mentioned configuration, but may have any configuration as long as it is capable of changing the axial distance between the first Fresnel lens 21 and the second Fresnel lens 22.

[0120] It is preferable that the first Fresnel lens 21 and the second Fresnel lens 22 are disposed continuously. It is also preferable that the first Fresnel lens 21, the second Fresnel lens 22, and the third Fresnel lens 23 are disposed continuously. In this way, the Fresnel lens group 20 can be made compact.

[0121] It is preferable that the maximum value of the lens effective width of the Fresnel lens (the second Fresnel lens 22 in the case of two lenses, the third Fresnel lens 23 in the case of three lenses) arranged closest to the light modulation element 13 side in the Fresnel lens group 20 is equal to or greater than the maximum width (the diagonal in the case of a rectangle) of the effective display surface of the liquid crystal panel 130. In this way, the parallel light beams from the Fresnel lens group 20 can be made to enter the entire effective display surface of the liquid crystal panel 130 more reliably.

[0122] [Summary of this disclosure] The following is a summary of this disclosure.

[0123] (Appendix 1) A light source; a Fresnel lens group for collimating light rays emitted from the light source; an incident-side polarizing plate that transmits the light beam emitted from the Fresnel lens group; a light modulation element that modulates the light transmitted through the incident-side polarizing plate to form a projection image; an exit side polarizing plate that transmits the light beam modulated by the light modulation element; a projection lens that projects the light beam transmitted through the exit-side polarizing plate; Equipped with the Fresnel lens group includes a first Fresnel lens having positive power and arranged closest to the light source in the Fresnel lens group, and a second Fresnel lens having positive power and arranged closer to the light modulation element than the first Fresnel lens, The entrance surface of the first Fresnel lens does not have a Fresnel surface, The projector, wherein the exit surface of the first Fresnel lens has a Fresnel surface.

[0124] With this configuration, the Fresnel lens group includes a plurality of Fresnel lenses, each of which has a positive power, such as the first Fresnel lens and the second Fresnel lens. Therefore, the lens power per lens can be reduced compared to a case where only one Fresnel lens is included. This can reduce the change in shape of the light distribution of the light beams emitted from the Fresnel lens group. As a result, the light distribution of the light beams emitted from the Fresnel lens group is close to a circular shape, which can prevent the peripheral parts of the projected image formed by the light modulation element from becoming dark. Therefore, the projector can project an enlarged image with uniform brightness.

[0125] Here, when the entrance surface of the Fresnel lens has a Fresnel surface, the angle of incidence of the light beam entering the entrance surface of the Fresnel lens is larger compared to a configuration in which the entrance surface of the Fresnel lens does not have a Fresnel surface. Therefore, with this configuration, since the entrance surface of the first Fresnel lens does not have a Fresnel surface, it is possible to suppress a decrease in the amount of light beam passing through the first Fresnel lens compared to a case in which the entrance surface of the first Fresnel lens has a Fresnel surface.

[0126] (Appendix 2) The entrance surface of the second Fresnel lens does not have a Fresnel surface. The projector described in Supplementary Note 1, wherein the exit surface of the second Fresnel lens has a Fresnel surface.

[0127] As a result, since the second Fresnel lens has a positive power, the lens power can be shared between the first Fresnel lens and the second Fresnel lens. Also, since the entrance surface of the second Fresnel lens does not have a Fresnel surface, it is possible to suppress a decrease in the amount of light rays passing through the second Fresnel lens compared to a case in which the entrance surface of the second Fresnel lens has a Fresnel surface.

[0128] (Appendix 3) The projector described in Appendix 2, wherein a focal length of the first Fresnel lens is the same as a focal length of the second Fresnel lens.

[0129] This can reduce the change in shape of the light distribution of the light beam emitted from the second Fresnel lens. Also, if the focal length of the first Fresnel lens and the focal length of the second Fresnel lens are the same, the shapes of the first Fresnel lens and the second Fresnel lens can be the same. This can reduce the production cost of the Fresnel lens compared to when the shapes of the first Fresnel lens and the second Fresnel lens are different.

[0130] (Appendix 4) the entrance surface of the second Fresnel lens has a Fresnel surface, 2. The projector according to claim 1, wherein the exit surface of the second Fresnel lens does not have a Fresnel surface.

[0131] Since the Fresnel surfaces of the first Fresnel lens and the second Fresnel lens face each other, when the first Fresnel lens and the second Fresnel lens are integrated into a unit using a holding member or the like, the Fresnel surface can be located inside the unit. This makes it possible to prevent the Fresnel surface from being damaged by tools or the like when assembling this unit into a projector.

[0132] (Appendix 5) The projector described in Appendix 4, wherein a focal length of the first Fresnel lens is shorter than a focal length of the second Fresnel lens.

[0133] This makes it possible to further reduce the change in the shape of the light distribution of the light beam emitted from the second Fresnel lens.

[0134] (Appendix 6) 6. The projector according to claim 2, further comprising an adjustment mechanism for changing an axial distance between the first Fresnel lens and the second Fresnel lens.

[0135] This makes it easy to adjust the axial distance between the first Fresnel lens and the second Fresnel lens during manufacturing.

[0136] (Appendix 7) the Fresnel lens group includes a third Fresnel lens disposed closer to the light modulation element than the second Fresnel lens, 7. The projector according to claim 2, wherein the third Fresnel lens has a positive power.

[0137] As a result, since the Fresnel lens group has three Fresnel lenses, the lens power per lens can be made smaller than that of a single Fresnel lens. As a result, the light distribution of the light beams emitted from the Fresnel lens group is closer to a circular shape, so that the peripheral portion of the projected image formed by the light modulation element can be prevented from becoming darker.

[0138] (Appendix 8) The projector described in any one of appendix 1 to 7, further comprising a polarization conversion optical system disposed between the light source and the Fresnel lens group, which converts the polarization direction of the light beam emitted from the light source.

[0139] As a result, the polarization direction of the light beam emitted from the light source is converted by the polarization conversion optical system, so that the projector of this embodiment can increase the amount of light beam incident on the light modulation element compared to a configuration that does not have a polarization conversion optical system.

[0140] (Appendix 9) The projector described in any one of appendixes 1 to 7, further comprising a polarization conversion optical system disposed between the Fresnel lens group and the incident-side polarizing plate, which converts the polarization direction of the light beam emitted from the Fresnel lens group.

[0141] As a result, the polarization direction of the light beam emitted from the Fresnel lens group is converted by the polarization conversion optical system, so that the projector of this embodiment can increase the amount of light beam incident on the light modulation element compared to a configuration that does not have a polarization conversion optical system.

[0142] (Appendix 10) The projector described in Appendix 8, characterized in that the polarization conversion optical system includes a polarizing beam splitter that transmits one linearly polarized component of the polarized components contained in the incident light beam as is and reflects the other linearly polarized component in a direction perpendicular to the optical axis, a total reflection mirror that reflects the other linearly polarized component reflected by the polarizing beam splitter in a direction parallel to the optical axis, and a phase difference plate that converts the other linearly polarized component reflected by the total reflection mirror into one linearly polarized component. [Explanation of symbols]

[0143] 1, 1A, 1B, 1C, 1D, 1E, 1F... projector, 2... image forming section, 3... projection lens, 3... projection optical system, 4... control section, 10... light source, 11... pickup lens, 12... incident side polarizing plate, 13... light modulation element, 14... exit side polarizing plate, 15... polarization conversion optical system, 16... First integrator lens, 17... second integrator lens, 18... magnifying lens, 20... Fresnel lens group, 21... first Fresnel lens, 22... second Fresnel lens, 23... third Fresnel lens, 60... Fresnel lens, 70... adjustment mechanism, 71... first frame, 72... second frame, 73... adjustment section, 74... adjustment screw, 75... spring, 100... projector, 130... liquid crystal panel, 150... polarization conversion element child, 151...polarizing beam splitter, 152...total reflection mirror, 153...phase difference plate, 211...incident surface, 212...exit surface, 213...flat surface, 214...Fresnel surface, 221...incident surface, 222...exit surface, 223...flat surface, 224...Fresnel surface, 231...incident surface, 232...exit surface, 233...flat surface, 234...Fresnel surface, 601...incident surface, 602...exit surface, 603...flat surface, 604...Fresnel surface, N...optical axis, S...screen.

Claims

1. A light source; a Fresnel lens group for collimating light rays emitted from the light source; an incident-side polarizing plate that transmits the light emitted from the Fresnel lens group; a light modulation element for modulating the light transmitted through the incident-side polarizing plate to form a projection image; an exit side polarizing plate that transmits the light beam modulated by the light modulation element; a projection lens that projects the light beam transmitted through the exit-side polarizing plate; Equipped with the Fresnel lens group includes a first Fresnel lens having positive power and arranged closest to the light source in the Fresnel lens group, and a second Fresnel lens having positive power and arranged closer to the light modulation element than the first Fresnel lens, The entrance surface of the first Fresnel lens does not have a Fresnel surface, The projector according to claim 1, wherein the exit surface of the first Fresnel lens has a Fresnel surface.

2. The entrance surface of the second Fresnel lens does not have a Fresnel surface, The projector according to claim 1 , wherein the exit surface of the second Fresnel lens has a Fresnel surface.

3. 3. The projector according to claim 2, wherein a focal length of the first Fresnel lens is the same as a focal length of the second Fresnel lens.

4. The entrance surface of the second Fresnel lens has a Fresnel surface, The projector according to claim 1 , wherein the exit surface of the second Fresnel lens does not have a Fresnel surface.

5. 5. The projector according to claim 4, wherein a focal length of the first Fresnel lens is shorter than a focal length of the second Fresnel lens.

6. 6. The projector according to claim 2, further comprising an adjustment mechanism for changing an axial distance between the first Fresnel lens and the second Fresnel lens.

7. the Fresnel lens group includes a third Fresnel lens disposed closer to the light modulation element than the second Fresnel lens, 6. The projector according to claim 2, wherein the third Fresnel lens has a positive power.

8. 2. The projector according to claim 1, further comprising a polarization conversion optical system disposed between the light source and the Fresnel lens group, for converting the polarization direction of the light beam emitted from the light source.

9. 2. The projector according to claim 1, further comprising a polarization conversion optical system disposed between the Fresnel lens group and the incident-side polarizing plate, the polarization conversion optical system converting the polarization direction of the light beam emitted from the Fresnel lens group.

10. The polarization conversion optical system includes a polarizing beam splitter that transmits one linearly polarized component of the polarized components contained in the incident light beam as is and reflects the other linearly polarized component in a direction perpendicular to the optical axis, a total reflection mirror that reflects the other linearly polarized component reflected by the polarizing beam splitter in a direction parallel to the optical axis, and a total reflection mirror that reflects the other linearly polarized component reflected by the total reflection mirror in a direction parallel to the optical axis.

9. The projector according to claim 8, further comprising a retardation plate for converting one of the linearly polarized components into the other of the linearly polarized components.

Images