JP2014106453A - Projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thinned projector, while enabling an excellent image to be projected and displayed from an oblique direction with respect to a normal line direction of a projection surface.SOLUTION: A projector 100 comprises: a light source 10; a liquid crystal light valve 40 that modulates light emitted from the liquid source 10; an optical path length control element 50 to which light emitted from the liquid crystal light valve 40 is incident; a projection lens 60 to which light emitted from the optical path length control element 50 is incident; and a declination prism 70 to which light emitted from the projection lens 60 is incident. When a central axis of the light incident to the declination prism 70 is defined as a first central axis ax1, and a central axis of light to be emitted from the declination prism 70 is defined as a second central axis ax2, the second central axis ax2 is tilted with respect to the first central axis ax1, and an optical path length of the optical path length control element is made gradually longer toward an oblique side of the second central axis ax2 with respect to the first central axis ax1 in a plane including the first central axis ax1 and the second central axis ax2.

Description

  The present invention relates to a projector.

  Conventionally, a projector that projects and displays an image on a projection surface such as a screen is known (see, for example, Patent Document 1). Patent Document 1 describes an example in which a rear projection television uses a projector built in a housing and displays an image on the back side of the screen from a direction inclined with respect to the normal direction of the screen. In the following description, the “display format in which an image is projected and displayed from a direction inclined with respect to the normal direction of the projection surface” may be referred to as “oblique projection”.

JP 2007-47767 A

  The oblique projection is performed in a normal specification mode even in a projector that displays an image from the front of the screen. For example, a projector installed on a desk displays an image by oblique projection on a wall screen.

  In the case of realizing oblique projection in a projector that displays an image from the front of the screen, conventionally, a projection optical system with a large aperture ratio is used, and the principal axis of the light bundle of image light is transmitted obliquely through the inside of the projection optical system ( (1st structure) and the structure (2nd structure) which incline the built-in projection optical system itself to a projection direction (diagonal direction) were employ | adopted.

  However, in projectors employing these configurations, it has been difficult to reduce the thickness of the device due to the configuration employed. That is, in the first configuration, the diameter of the projection optical system is increased, and in the second configuration, the projection optical system is disposed in the casing by tilting the projection optical system in the casing. The necessary space for the device becomes larger and the device becomes thicker and larger.

  The present invention has been made in view of such circumstances, and provides a thin projector while being able to project and display a good image from a direction inclined with respect to the normal direction of the projection surface. For the purpose.

  In order to solve the above problems, an embodiment of the present invention includes a light source, a light modulation element that modulates light emitted from the light source, and an optical path length control element on which the light emitted from the light modulation element is incident. And a projection optical system into which the light emitted from the optical path length control element is incident, and a declination prism into which the light emerged from the projection optical system is incident, and is incident on the declination prism When the central axis of light is the first central axis and the central axis of the light emitted from the declination prism is the second central axis, the second central axis is relative to the first central axis. The optical path length of the optical path length control element is such that the second central axis with respect to the first central axis is within a plane including the first central axis and the second central axis. Providing projectors that gradually become longer toward the inclined side

  When a light transmissive member is arranged in the optical path of the image light, the optical path length of the image light is extended in correspondence with the optical path length of the member. Therefore, when the optical path length control element is arranged on the incident side of the projection optical system as in the configuration of the present invention, the optical path length of the image light incident on the projection optical system is extended. That is, the optical path length between the light modulation element and the projection optical system is extended on the incident side of the projection optical system.

  At this time, if the central axis of the light incident on the declination prism is the first central axis and the central axis of the light emitted from the declination prism is the second central axis, the second central axis is the first central axis. The optical path length of the optical path length control element is inclined with respect to the first central axis in a plane including the first central axis and the second central axis. The length gradually increases toward the inclined side. Since the optical path length of the image light incident on the optical path length control element is extended according to the optical path length of the optical path length control element, the optical path length extended between the light modulation element and the projection optical system is the second Gradually becomes longer toward the inclined side of the central axis. Then, on the incident side of the projection optical system, an optically similar state to the state in which the light modulation element arranged at the position of the object plane of the projection optical system is tilted is formed, and an image of the light modulation element is formed. The position (image plane of the projection optical system) to be changed changes according to the optical path length extended by the optical path length control element. As a result, in the projector of the present invention, the inclination of the image plane can be corrected.

  Further, such an inclination of the image plane can be realized by inclining the light modulation element. However, in the projector of the present invention, since it is not necessary to incline the light modulation element, unevenness in light irradiation from the light source to the light modulation element hardly occurs, and a good image without luminance unevenness can be formed and displayed. .

  Therefore, according to the projector having such a configuration, it is possible to provide a thin projector while being able to project and display a good image from a direction inclined with respect to the normal direction of the projection surface.

In one aspect of the present invention, the distance between the light incident surface of the optical path length control element and the light exit surface of the optical path length control element gradually increases toward the inclined side. It is good also as composition which has.
According to this configuration, since the optical path length of the optical path length control element can be easily controlled by changing the shape of the optical path length control element, the design is facilitated.

In one aspect of the present invention, the optical path length control element may have a configuration in which a cross section in the plane has a rectangular shape, and a refractive index of the optical path length control element gradually increases toward the inclined side.
According to this configuration, the optical path length control element itself can be made smaller and thinner than the configuration in which the optical path length is adjusted by the thickness of the optical path length control element, which can contribute to the downsizing of the projector. .

In one aspect of the present invention, the optical path length control element has an angle formed by a light beam axis of incident light with respect to the light path length control element and a light beam axis of light emitted from the optical path length control element is the largest. It is good also as a structure arrange | positioned with the attitude | position which becomes small.
According to this configuration, the expansion of the arrangement space of the optical system can be suppressed on the downstream side of the optical path length control element, which can contribute to downsizing of the apparatus.

In one aspect of the present invention, the optical path length control element and the deflection prism may be provided so as to be retractable from the optical path of the light.
According to this configuration, the optical path length control element and the declination prism can be used properly according to whether or not oblique projection is necessary, and an appropriate apparatus configuration can be selected according to the state of image projection.

It is a schematic sectional drawing which shows the projector 100 of this embodiment. FIG. 2 is a schematic diagram illustrating functions of a projector 100. It is a figure which shows the simulation result about the luminance distribution of a projection image. It is a figure which shows the simulation result about the luminance distribution of a projection image. It is a figure which shows the simulation result about the luminance distribution of a projection image. 5 is an explanatory diagram for explaining the posture of an optical path length control element 50. FIG. It is explanatory drawing of the optical path length control element 50 and the declination prism 70. FIG. It is a schematic sectional drawing which shows the projector 200 which concerns on the modification of embodiment.

  Hereinafter, a projector according to an embodiment of the invention will be described with reference to FIGS. In all the drawings below, the dimensions and ratios of the constituent elements are appropriately changed in order to make the drawings easy to see.

  FIG. 1 is a schematic sectional view showing a projector 100 according to the present embodiment. As shown in FIG. 1, a projector 100 according to the present embodiment includes a light source 10, a pickup lens 20, a polarization conversion element 30, a liquid crystal light valve (light modulation element) 40, an optical path length control element 50, and a projection lens. (Projection optical system) 60 and a declination prism 70.

  The projector 100 emits image light in a direction intersecting with the optical axis of the projection lens 60 (a direction inclined from the central axis of the light incident on the declination prism 70) to display an image. The central axis of the light incident on the declination prism 70 is a first central axis ax1, and the central axis of the light emitted from the declination prism 70 is a second central axis ax2.

  In the following description, an xyz coordinate system is used in which a plane orthogonal to the first central axis ax1 is an xy plane, and a plane including the first central axis ax1 and the second central axis ax2 is a yz plane. Will be described as appropriate. That is, the direction parallel to the first central axis ax1 is the z direction. Although the optical axis of the projection lens 60 is not shown in FIG. 1, the optical axis of the projection lens 60 coincides with the first central axis ax1.

  The light source 10 can be a solid light source. The light source 10 is, for example, a light emitting diode, and emits white light (light source light) including red light, green light, and blue light. By using such a light source 10, the projector 100 can be reduced in size.

  The pickup lens 20 is a collimating optical system that receives light emitted from the center of the light source 10 and emits the light in a substantially parallel state. The pickup lens 20 is disposed on the central axis of the light beam emitted from the light source 10.

  The polarization conversion element 30 converts the polarization state of the light L incident from the pickup lens 20 into linearly polarized light polarized in a predetermined direction.

  The liquid crystal light valve 40 is, for example, a transmissive liquid crystal panel that employs a reflective color filter system. The liquid crystal light valve 40 is configured such that a reflective color filter, a liquid crystal element, and the like are sandwiched between a pair of glass substrates, and polarizing plates are bonded to the outer surfaces of the pair of glass substrates. In the projector 100 of this embodiment, a single plate type having only one liquid crystal light valve 40 is employed. By adopting the single plate type, the projector 100 can be downsized as compared with the three plate type using a liquid crystal light valve for each color light.

  The two polarizing plates included in the liquid crystal light valve 40 have a configuration in which, for example, the transmission axes are orthogonal to each other (crossed Nicol arrangement).

  The reflective color filter is composed of an R filter, a G filter, and a B filter provided for each pixel. The R filter transmits red light and reflects other color light. The G filter transmits green light and reflects other color light. The B filter transmits blue light and reflects other color light. The reflective color filter may employ a Bayer color arrangement structure, but is not limited thereto.

  The liquid crystal element is a liquid crystal element that is hermetically sealed between a color filter and a glass substrate. A polysilicon TFT is used as a switching element, and the polarization direction of incident linearly polarized light according to given image information. Modulate.

  In the liquid crystal light valve 40, the linearly polarized light emitted from the polarization conversion element 30 passes through the incident-side polarizing plate. The linearly polarized light that has passed through the polarizing plate enters the color filter, and only the color light corresponding to the filter in the incident region passes through the color filter. When the color light transmitted through the color filter passes through the liquid crystal element, the polarization direction is modulated according to the image information, and the color light whose polarization direction is modulated is emitted from the polarizing plate on the emission side. Therefore, in the liquid crystal light valve 40, the linearly polarized light emitted from the polarization conversion element 30 is modulated, and the color light modulated in accordance with the image information (hereinafter sometimes referred to as image light) is emitted.

  The optical path length control element 50 is disposed on the optical path of the image light modulated by the liquid crystal light valve 40. A material having a refractive index n having optical transparency is used as a forming material, and has a trapezoidal shape in a sectional view perpendicular to the X-axis direction. That is, in the optical path length control element 50, the surface 51 on which the image light is incident and the surface 52 on which the image light is emitted are not parallel to each other, and the surface 52 is inclined with respect to the surface 51. Specifically, in the optical path length control element 50, the distance between the surface 51 and the surface 52 is gradually increased in the + y direction.

  The projection lens 60 enlarges and projects the image light emitted from the optical path length control element 50 and forms an image on a projection surface such as a screen. That is, the liquid crystal light valve 40 is disposed on the object plane of the projection lens 60 (or a plane conjugate to the object plane), and a projection plane such as a screen is positioned on the image plane.

  The declination prism 70 has a function of refracting image light emitted from the projection lens 60 and emitting image light in a direction inclined with respect to the incident direction to the declination prism 70 on the exit side of the declination prism 70. Have. That is, the second central axis ax2 is inclined with respect to the first central axis ax1.

The projector 100 can project the image light obliquely in the y direction by having the declination prism 70. For example, by projecting image light obliquely upward from the projector 100 installed on the desk and setting the center of the display image to a height similar to the height of the observer's viewpoint, an easily visible image display is realized. be able to.
The projector 100 according to the present embodiment has the above configuration.

  FIG. 2 is a schematic diagram for explaining the function of the projector 100. FIG. 2A is an explanatory diagram of the projector 100X that does not have the optical path length control element 50, and FIG. 2B is an explanatory diagram of the projector 100 of the present embodiment. 2, the light source 10, the pickup lens 20, and the polarization conversion element 30 in FIG. 1 are omitted from illustration.

  As shown in FIG. 2A, in the projector 100X that does not have the optical path length control element 50, the image light formed by the liquid crystal light valve 40 passes through the projection lens 60 and the declination prism 70 so as to be in the y direction. The image is refracted to form a projected image. At that time, the image plane S1 of the projection lens 60 on which the projection image is formed is inclined in the −z direction on the + y side.

  In the projected image in such an image formation state, even if the focus is achieved at any position in the y direction on the xy plane, the focus is not achieved at other positions. In other words, when the projector 100 is installed on a desk for image display, if the installation plane on the desk is the xz plane, for example, a high-quality image display is performed on the projection surface on the wall parallel to the xy plane. It becomes difficult.

  On the other hand, as shown in FIG. 2B, in the projector 100 having the optical path length control element 50, it is possible to perform a good image display without focusing for the following reason.

First, the optical path length of the optical path length control element 50 will be described. The product of the refractive index n and the passing distance of the optical path length control element 50 on the path through which light incident on a certain point of the optical path length control element 50 passes through the optical path length control element 50 is the optical path length control element. 50 is defined as an optical path length of the optical path length control element 50 at one point. However, the optical path length according to the definition can be approximated by the product (n × d) of the distance d between the surface 51 and the surface 52 and the refractive index n at a certain point of the optical path length control element 50. Therefore, in this specification, the product (n × d) of the distance d at one point where the optical path length control element 50 is located and the refractive index n is defined as the optical path length at the one point where the optical path length control element 50 is located.
When the transparent member is disposed in the optical path of the light, the optical path length of the light is extended according to the optical path length of the transparent member. Therefore, when the optical path length control element 50 is arranged on the incident side of the projection lens 60 as in the configuration of the projector 100, the optical path length of the image light incident on the projection lens 60 corresponds to the optical path length of the optical path length control element 50. It will be extended. That is, the optical path length between the liquid crystal light valve 40 and the projection lens 60 is extended.

  Further, in the optical path length control element 50, the surface 52 is inclined with respect to the surface 51, so that the optical path length is gradually increased in the + y direction. Therefore, the extended optical path length of the image light incident on the optical path length control element 50 differs depending on the incident position of the light with respect to the optical path length control element 50 in the y direction.

  Specifically, the optical path length of the optical path length control element 50 is an inclination of the second central axis ax2 with respect to the first central axis ax1 in a plane including the first central axis ax1 and the second central axis ax2. The length gradually increases toward the side (+ y direction). Further, the optical path length of the light that has passed through the portion of the optical path length control element 50 that has a relatively large n × d is the optical path length of the image light that is the portion of the optical path length control element 50 that has a relatively small n × d. The optical path length of the transmitted light is greatly extended. Accordingly, the extension amount of the optical path length of the image light gradually increases toward the inclined side (+ y direction) of the second central axis ax2 with respect to the first central axis ax1. As a result, on the exit side of the projection lens 60, the position at which the image of the liquid crystal light valve 40 (the object plane of the projection lens 60) is formed (the image plane of the projection lens 60) is extended by the optical path length control element 50. It will change according to the optical path length.

  That is, as shown in FIG. 2C, the projection lens 60 is optically similar to the state in which the liquid crystal light valve 40 is retracted in the −z direction (indicated by reference numeral 40X in the figure). . Further, since the optical path length of the optical path length control element 50 is gradually increased in the + y direction, the virtual liquid crystal light valve 40X has a relatively long optical path length as shown in FIG. Side) is inclined to recede further in the -z direction.

  Here, in the projection lens 60, an inverted image of the object plane is obtained on the image plane S2 shown in FIG. When the object plane moves away from the projection lens 60, the position of the image plane S2 changes so as to approach the projection lens 60.

  Therefore, the image plane S2 of the projector 100 in which the optical path length control element 50 is arranged has a relative optical path length in the optical path length control element 50 for image light compared to the image plane S1 of the projector 100X that does not have the optical path length control element 50. The −y side passing through a long region is inclined more in the −z direction than the + y side. As a result, the inclination of the image plane S2 from the xy plane can be reduced (correction of the inclination of the image plane), and a good image display with little focus shift can be achieved on the projection surface on the wall surface parallel to the xy plane. Become.

  Such an optical path length control element 50 can adjust the distance between the surface 51 and the surface 52 by changing the shape and can easily control the optical path length of the optical path length control element. Easy.

  In the description using FIG. 2, it has been described that the projector 100 uses the optical path length control element 50 to create the same state as when the liquid crystal light valve 40 is tilted. Compared to a projector configured by tilting the liquid crystal light valve, the projector 100 can display a higher quality image.

  That is, if the liquid crystal light valve is tilted, illumination unevenness may occur when parallel light is incident on the liquid crystal light valve, which may reduce the quality of the projected image. When the element 50 is used, there is no such fear.

  3 to 5 are diagrams showing simulation results for the luminance distribution of the projection image displayed by the projector. In each figure, (a) is a schematic diagram showing a model for which simulation is performed, and (b) is a figure showing a simulation result. In each figure (b), the luminance of the image obtained as a result of the simulation is shown by a black-white gradation display. In each figure (b), it is shown that it is an area | region brighter as white, and is an area | region darker as it approaches black.

  The simulation was performed using illumination design analysis software “LightTools 7.2.0” (manufactured by Synopsys).

  FIG. 3 shows a simulation result for the projector 100Y that does not have either the optical path length control element 50 or the deflection prism 70 that the projector 100 has, as shown in FIG. In the projector 100Y, as shown in FIG. 3B, a region with the same luminance is widened in the vertical direction (y direction) around the center a1 of the projected image.

  FIG. 4 shows a simulation result for a projector 100Z in which the liquid crystal light valve 40 is tilted without using the optical path length control element 50 as shown in FIG. In the projector 100Z, as shown in FIG. 4B, the center a2 of the projected image is moved to the + y side from the center a1 of the projected image of the projector 100Y, and projection display is possible obliquely upward. I understand. However, in the projector 100Z, it can be seen that the luminance decreases toward the + y side around the center a2 of the projected image, and luminance unevenness occurs in the vertical direction (y direction).

  FIG. 5 shows a simulation result of the projector 100 according to this embodiment as shown in FIG. In the projector 100, as shown in FIG. 5B, the center a3 of the projected image is moved to the + y side from the center a1 of the projected image of the projector 100Y, and projection display is possible obliquely upward. I understand. Further, in the projector 100, the luminance unevenness recognized in FIG. 4B is eliminated around the center a3 of the projected image, and the same luminance in the vertical direction (y direction) as in FIG. 3B. It can be seen that the area of

  That is, in the projector 100 of the present embodiment, the optical path length is controlled using the optical path length control element 50, so that a good image with less luminance unevenness is displayed compared to the configuration in which the liquid crystal light valve 40 is actually tilted. be able to.

  Further, the optical path length control element 50 is arranged in such a posture that the angle formed by the ray axis of the incident light with respect to the optical path length control element 50 and the ray axis of the emitted light emitted from the optical path length control element 50 is the smallest. ing.

  FIG. 6 is an explanatory diagram for explaining the posture of the optical path length control element 50. First, as shown in FIG. 6A, it is assumed that the surface 51 of the optical path length control element 50 is parallel to the xy plane. In FIG. 6A, the light beam axis of the incident light to the optical path length control element 50 is denoted by reference symbol PL1, and the light beam axis of the emitted light is denoted by symbol PL2.

  In this case, as shown in FIG. 6A, when image light that is incident light is incident from the normal direction of the surface 51, the ray axis PL2 of the emitted light is refracted at the surface 52, and the incident light The angle θ1 is inclined with respect to the light axis PL1.

  On the other hand, as shown in FIG. 6B, a case is assumed where the + y side is inclined to the + z side so that the surface 51 intersects the xy plane. In FIG. 6B, the light beam axis of the incident light to the optical path length control element 50 is indicated by a symbol PL3, and the light beam axis of the emitted light is indicated by a symbol PL4.

  In this case, as shown in FIG. 6B, when image light as incident light is incident at an angle θ2 with respect to the normal direction of the surface 51, the image light is refracted at the surface 51 and the surface 52. . As a result, the angle formed by the ray axis PL4 of the emitted light and the ray axis PL3 of the incident light is smaller than the angle θ1 in FIG.

  In the projector 100 of the present embodiment, as in the optical path length control element 50 shown in FIG. 6B, the optical path length control is performed in such a posture that the angle formed by the light beam axis PL3 of the incident light and the light beam PL4 of the emitted light is the smallest. Element 50 is arranged. Therefore, the expansion of the arrangement space of the optical system on the downstream side of the optical path length control element 50 can be suppressed, which can contribute to the downsizing of the apparatus.

  In the projector 100, as shown in FIG. 7, the optical path length control element 50 and the deflection prism 70 are preferably provided so as to be retractable from the optical path of the image light. With this configuration, when oblique projection is necessary, the optical path length control element 50 and the declination prism 70 are arranged on the optical path, and when oblique projection is not necessary, the optical path length control element 50 and It is possible to selectively use the declination prism 70 by retracting it from the optical path. That is, the optical path length control element 50 and the declination prism 70 can be used properly according to the necessity of oblique projection, and an appropriate apparatus configuration can be selected according to the state of image projection.

  The optical path length control element 50 and the declination prism 70 are preferably moved in parallel in the x direction and retracted, because the thickness of the projector 100 can be suppressed.

  Although FIG. 7 shows that the optical path length control element 50 and the declination prism 70 are translated in the x direction, other configurations may be employed as long as they can be retracted from the optical path. For example, the optical path length control element 50 and the declination prism 70 are provided so as to be rotatable around a rotation axis parallel to the x-axis set at the lower end, rotate in the z-axis direction, and tilt by 90 °. It does not matter as a configuration for retreating from the road.

  According to the projector 100 configured as described above, it is possible to provide a thin projector while being able to project and display a good image from a direction inclined with respect to the normal direction of the projection surface.

  In the present embodiment, the optical path length control element 50 is used, but the present invention is not limited to this. FIG. 8 is a schematic cross-sectional view showing a projector 200 according to a modification of the present embodiment, and corresponds to FIG.

  A projector 200 illustrated in FIG. 8 includes an optical path length control element 55 instead of the optical path length control element 50 included in the projector 100 illustrated in FIG. The optical path length control element 55 has a rectangular shape in a cross section perpendicular to the X-axis direction, and the refractive index gradually increases in the + y direction from the first central axis ax1.

  Such an optical path length control element 55 has an optical path length represented by the product (n × d) of the refractive index n and the distance d, where d is the distance between the surface 56 and the surface 57. In the optical path length control element 55, since the refractive index n is gradually increased, the optical path length is gradually increased in the + y direction from the first central axis ax1. Therefore, similarly to the optical path length control element 50 described above, the extension amount of the optical path length of the image light depends on the incident position of the light with respect to the optical path length control element 55 in the y direction, and the second center with respect to the first central axis ax1. The length gradually increases toward the inclined side (+ y direction) of the axis ax2.

  Further, the optical path length control element 55 is arranged in such a posture that the angle formed by the light beam axis of the incident light with respect to the optical path length control element 55 and the light beam axis of the emitted light emitted from the optical path length control element 55 is the smallest. ing. In the optical path length control element 55, the surface 56 is parallel to the surface 57, and the surface 56 and the surface 57 are provided so as to be parallel to the xy plane.

  In such an optical path length control element 55, the optical path length control element itself can be made smaller and thinner than the configuration in which the optical path length is adjusted by the thickness as in the optical path length control element 50. It can contribute to the conversion.

  Even with the projector 200 having such a configuration, a thin projector can be provided while a good image can be projected and displayed from a direction inclined with respect to the normal direction of the projection surface.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such examples. Various shapes, combinations, and the like of the constituent members shown in the above-described examples are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

  The projector according to the above-described embodiment is easy to visually recognize by projecting image light obliquely upward from a state where the projector is installed on the desk, and setting the center of the display image to the same height as the viewpoint of the observer. Although it has been described that image display can be realized, the present invention is not limited to this. For example, by setting the declination direction by the declination prism 70 to be the x direction instead of the + y direction, a projector that projects image light obliquely in the horizontal direction and displays an image on the projection surface from a state of being installed on a desk. It is also possible.

  When a projector having such a configuration is used, an image can be displayed on the projection surface without arranging the projector between the projection surface and the observer, and the visual field is not blocked by the installed projector. An easily visible image display can be realized.

  DESCRIPTION OF SYMBOLS 10 ... Light source, 40 ... Liquid crystal light valve (light modulation element), 50, 55 ... Optical path length control element, 51, 52, 56, 57 ... Surface, 60 ... Projection lens (projection optical system), 70 ... Deflection prism, 100, 100X, 100Y, 100Z, 200 ... projector, a1, a2, a3 ... center, ax1 ... first center axis, ax2 ... second center axis, PL1, PL3 ... center axis of incident light, PL2, PL4 ... Center axis of emitted light

Claims (5)

A light source;
A light modulation element that modulates light emitted from the light source;
An optical path length control element on which the light emitted from the light modulation element is incident;
A projection optical system on which the light emitted from the optical path length control element is incident;
A declination prism on which the light emitted from the projection optical system enters, and
When the central axis of the light incident on the declination prism is a first central axis and the central axis of the light emitted from the declination prism is a second central axis, the second central axis is Inclined with respect to the first central axis;
The optical path length of the optical path length control element is gradually increased toward the inclined side of the second central axis with respect to the first central axis in a plane including the first central axis and the second central axis. A projector that is getting longer.   The projector according to claim 1, wherein a distance between a surface of the optical path length control element on which the light is incident and a surface of the optical path length control element on which the light is emitted gradually increases toward the inclined side. . The optical path length control element has a rectangular cross section in the plane,
The projector according to claim 1, wherein a refractive index of the optical path length control element is gradually increased toward the inclined side.   The optical path length control element is arranged in an attitude in which an angle formed by a light beam axis of incident light with respect to the optical path length control element and a light beam axis of light emitted from the optical path length control element is minimized. The projector according to claim 1.   5. The projector according to claim 1, wherein the optical path length control element and the declination prism are provided so as to be retractable from the optical path of the light.