JP5818596B2 - Image projection device - Google Patents

Description

  The present invention relates to an image projection apparatus, and more particularly to an image projection apparatus using a reflective image display element.

  In an image projection apparatus using a reflective liquid crystal panel, it is necessary to make the optical paths of incident light to the liquid crystal panel and image light from the liquid crystal panel different. Therefore, a polarizing beam splitter that transmits P-polarized light and reflects S-polarized light is disposed on the incident surface or the exit surface side of the reflective liquid crystal panel.

  The characteristics of the polarization separation surface of the polarization beam splitter depend on the incident angle of incident light. In general, the polarization separation characteristic of the polarization beam splitter is designed to be best when the incident angle of light with respect to the normal line of the polarization separation surface is 45 °. The farther the incident angle of light with respect to the polarization separation surface is from 45 °, the farther the thickness of the thin film through which the light beam passes from the optimum value, the lower the polarization separation characteristic. As a result, when a pixel on a liquid crystal panel is driven to display black, the polarization beam splitter is not perfect, so it does not return to the light source side, and much light (leakage light) enters the projection lens. As a result, the contrast of the projected image decreases.

  Conventionally, in order to improve the contrast of a projected image, a technique is known in which a polarizing plate that blocks leakage light is arranged on the exit surface side of a polarizing beam splitter.

JP-A-3-175437

However, since the polarizing plate has a low transmittance with respect to light that should be transmitted, there is a problem that the brightness of the projected image is lowered when the polarizing plate is arranged.
Therefore, an object of the present invention is to improve contrast while suppressing a decrease in brightness.

In order to solve the above problems, an image projection apparatus of the present invention
Illumination optics,
Among the light emitted from the illumination optical system, a color separation element that guides light in a green wavelength band in a direction different from light in a blue wavelength band and light in a red wavelength band;
A polarization separation element having a polarization separation surface that separates an optical path of light in the green wavelength band from the color separation element according to a polarization direction;
A light modulation element that modulates the polarized light separated by the polarization separation surface;
An image projection apparatus having a movable means for moving a projection optical system which is modulated by the light modulation element and projects light again through the polarization separation element onto a projection surface,
The light modulation element is provided so that light emitted from the color separation element and reflected by the polarization separation surface is incident on the light modulation element,
The movable means moves from the light modulation element to the polarization separation surface within a cross section parallel to the normal line of the polarization separation surface and the optical axis of the illumination optical system. It is characterized in that it is determined so that a larger number of light beams having an incident angle larger than 45 degrees are captured than light beams having an incident angle smaller than 45 degrees.

  The image projection apparatus in which the projection optical system is integrally provided or detachably mounted also constitutes another aspect of the present invention.

  According to the present invention, it is possible to provide a high-contrast image projection apparatus while suppressing a decrease in brightness.

1 is a configuration diagram of an image projection apparatus according to a first embodiment of the present invention. Explanatory drawing of leaking light from polarizing beam splitter Diagram showing the relationship between the incident angle of light on the polarization separation surface and the characteristics of the polarization separation surface Schematic diagram of the angular distribution of leakage light on the polarization separation surface in the first embodiment of the present invention Schematic diagram of the amount of light that the projection lens can capture and its angular distribution The block diagram of the image projector of the 2nd Embodiment of this invention Schematic diagram of the angular distribution of leakage light on the polarization separation surface in the second embodiment of the present invention The block diagram of the image projector of the 3rd Embodiment of this invention Explanatory drawing of shift direction of projection lens and miniaturization of image projection device The block diagram of the image projector of the 4th Embodiment of this invention Schematic diagram of movable mechanism for projection lens shift Explanatory drawing of installation location of image projector and projection lens shift

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

Embodiment 1
FIG. 1 shows a configuration diagram of an image projection apparatus according to a first embodiment of the present invention. The Z axis in FIG. 1 is an axis parallel to the optical axis of the projection lens, and the direction toward the screen is the + Z direction. The X axis is an axis perpendicular to the Z axis and a plane including the normal line of the polarization separation plane 8, and the direction from the back to the front of the paper is the + X direction. The Y axis is an axis perpendicular to the X axis and the Z axis, and the direction from the bottom to the top of the paper is defined as the + Y direction.

  1 represents the optical axis of the condenser lens 5a or the optical axis of the projection lens. The one-dot chain line from the reflecting mirror 6 to the liquid crystal panel 9 is not strictly an optical axis, but is referred to as an optical axis in this specification.

  The light emitted from the light source 1 is reflected by the parabolic reflector 2, is emitted as substantially parallel light, enters the first fly-eye lens 3a, and the individual lenses constituting the first fly-eye lens 3a. It is separated into a plurality of light beams by the cell. The plurality of divided light beams pass through the second fly-eye lens 3 b and enter the polarization conversion element 4.

  The polarization conversion element 4 has a structure in which a plurality of polarization beam splitters each having a polarization separation surface are arranged, and a half-wave plate is disposed at every other exit surface of the polarization beam splitter. The non-polarized light incident on the polarization conversion element 4 is aligned with the P-polarized light and emitted. If it is desired to align with S-polarized light, a half-wave plate may be disposed on the transmission optical path of the polarization beam splitter. In that case, the position of the liquid crystal panel 9 is arranged on the side where the incident light of the polarization beam splitter 7 (polarization separation element) is reflected. P-polarized light and S-polarized light in this specification are not the polarization beam splitter of the polarization conversion element 4 but the polarization separation surface 8 of the polarization beam splitter 7 that guides the image light emitted from the liquid crystal panel 9 to the projection lens 10 side. It stipulates.

  The light aligned with the P-polarized light by the polarization conversion element 4 is reflected by the reflection mirror 6 via the condenser lenses 5 a and 5 b and enters the polarization beam splitter 7. The light incident on the polarization beam splitter 7 passes through the polarization separation surface 8 and illuminates the liquid crystal panel 9. The light source 1 to the condenser lenses 5a and 5b are used as an illumination optical system, and this illumination optical system performs Koehler illumination on the liquid crystal panel 9 (light modulation element).

  The light incident on the liquid crystal panel 9 is modulated, and the image light out of the modulated light is incident on the projection lens 10 (projection optical system) via the polarization beam splitter 7 again (reflected). Then, the image light is projected onto the screen 11 (projected surface) via the projection lens 10. On the other hand, light having a polarization component that does not become image light is transmitted through the polarization separation surface 8 and returned to the light source side. The angle formed by the surface normal of the liquid crystal panel 9 and the surface normal of the polarization separation surface at the center of the liquid crystal panel 9 is 45 °.

  FIG. 2 shows an enlarged view around the polarizing beam splitter 7 and the liquid crystal panel 9 in FIG. The broken arrow is an arrow schematically showing a light beam when black display is performed. Originally, in the case of performing black display, as shown in FIG. 2, the P-polarized light incident on the liquid crystal panel 9 is reflected without being converted in its polarization direction, and is transmitted through the polarization separation surface 8 again. Return to the light source side. Most P-polarized light is returned to the light source side as shown by the thick solid line in FIG. However, as indicated by the thin broken arrow in FIG. 2, there is light (leakage light) that is reflected toward the projection lens 10 due to the characteristics of the polarization separation surface 8 regardless of the P-polarized light. Furthermore, as represented by the thickness of the thin dashed arrow in FIG. 2, the amount of leaked light reflected with a certain spread from the same point of the liquid crystal panel 9 is the + Y direction on the exit surface of the polarization beam splitter 7. There are few, and there are many -Y directions.

  FIG. 3A is a graph showing changes in polarization separation characteristics with respect to changes in the incident angle of incident light on the polarization separation surface 8 in the XY cross section (X direction) of FIG. FIG. 3B is a graph showing changes in polarization separation characteristics with respect to changes in the incident angle of incident light on the polarization separation surface 8 in the YZ section (Y direction) of FIG. The horizontal axis represents wavelength (nm), and the vertical axis Rp represents the reflectance (%) of P-polarized light. A higher Rp value indicates more leakage light, and a smaller Rp value indicates a higher extinction ratio and better polarization separation plane characteristics. The solid line in the graph represents the polarization separation characteristic for light rays incident at an incident angle of 45 ° with respect to the polarization separation surface. The broken line in the graph represents the polarization separation characteristic for light rays incident at an incident angle that is approximately 5 ° smaller than 45 °. The alternate long and short dash line represents the polarization separation characteristic for light incident at an incident angle that is approximately 5 ° greater than 45 °. 3A and 3B are designed to satisfy the performance in the green wavelength range 500 to 580 (nm), which has the highest relative visibility among the spectrum of the light source used in the image projection apparatus. Yes.

  Consider a case where the incident angle of the light beam is changed by the same angle from the light beam incident at 45 ° with respect to the normal line of the polarization separation surface 8 as a reference. 3A and 3B, it can be seen that the change in the characteristics of the polarization splitting surface is greater when the incident angle is changed in the YZ section than when the incident angle is changed in the XY section. That is, the polarization separation surface has a better polarization separation characteristic for the change in the incident angle in the XY section (X direction) than the polarization separation characteristic for the change in the incident angle in the YZ section (Y direction).

  Further, attention is paid to the change in the angle of the YZ section in FIG. In the YZ cross section, when the incident angle is changed between + 5 ° and −5 °, it can be seen that the change in the characteristics is different from that in FIG. This is based on the film thickness through which incident light passes at an incident angle of 45 ° with respect to the normal to the polarization separation plane, and the film thickness through which incident light passes when the incident angle of the light beam changes by + 5 ° in the Y direction. This is because the thickness becomes thinner and becomes thicker when it changes by -5 °. Further, it can be seen that the peak position of the Rp characteristic (arrow in FIG. 3B) is shifted to the short wavelength side when the incident angle is 45 + 5 °, and to the long wavelength side when the incident angle is 45-5 °. In general, it is known that the reflectance characteristics of P-polarized light on the polarization separation surface (polarization separation film) shift to the short wavelength side when the thickness of the film through which the light passes decreases and to the long wavelength side when the thickness increases. . For this reason, when light in the green wavelength region (500 to 600 nm) is incident, the amount of leakage light is less when the incident angle is 45 + α ° than when 45-α °.

  This will be described with reference to FIG. 2 again. As shown in FIGS. 3A and 3B, in FIG. 2, the light incident at 45 ° + α on the polarization splitting surface 8 (the thin broken line in the figure) is incident at 45 ° -α. Leakage light is less than the light to be emitted (thick broken line in the figure).

  FIG. 4 is a schematic diagram showing the incident angle of light rays incident on the polarization separation plane and the distribution of leakage light in the XY section when the liquid crystal panel 9 is driven so that the projected image is displayed in all black. The coordinate axis represents the incident angle with respect to the polarization splitting surface 8, and the center represents that the angle deviation from 45 ° is 0 °. The lighter the part, the less light leaks, and the darker the part, the more light leaks.

  As shown in FIG. 4, the leakage light that causes the contrast to decrease is symmetric in the X direction, but is asymmetric in the Y direction. In particular, as the angle increases in the -Y direction, the leakage light becomes larger. Become more. Therefore, it is important to project as much light as possible in a region with as little leakage light as possible onto the projection surface, or to avoid projecting as much light as possible from the region with much leakage light onto the projection surface. Incidentally, the angle distribution of the leaked light as shown in FIG. 4 is obtained by displaying an all black image in an actual image projection apparatus and observing light rays from the image display element directly on the screen except for the projection lens. Can be confirmed.

  Next, the angular distribution of light rays that can be captured by the projection lens 10 will be described. Attention is focused on the path from the light diverging from the liquid crystal panel 9 toward the projection lens 10 until it reaches the screen via the projection lens 10. The point corresponding to the center of the optical axis of the projection lens 10 in the liquid crystal panel 9, that is, the light that diverges from the center of the liquid crystal panel 9 takes in all the angle components defined by the F number of the projection lens 10. However, light that diverges from a point away from the center of the liquid crystal panel 9 is partially shielded by the vignetting of the projection lens 10. The vignetting means that a part of a light beam incident on the lens obliquely is partly removed depending on the size and thickness of the lens and the lens frame.

  The image projection apparatus adjusts the projection direction of the image to a desired direction by performing a so-called “projection lens shift” in which the projection lens 10 is decentered parallel to the liquid crystal panel 9. In addition, there is an image projection apparatus in which a movable mechanism (movable means) is provided in the projection lens and the projection lens is made movable from fixed to increase the degree of freedom in adjusting the image projection direction. In the configuration shown in FIG. 1 as well, the projection lens 10 is configured to be parallel decentered, that is, shiftable with respect to the liquid crystal panel 9, thereby projecting an image in an obliquely upward direction.

  FIG. 11 shows a schematic diagram of a general projection lens shift movable mechanism. The movable mechanism includes a mounting portion H of the projection lens 10, a first shift plate S1, and a second shift plate S2. An attachment portion H of the projection lens 10 is attached to the first shift plate S1, and a unit for connecting the attachment portion H and the first shift plate S1 is attached to the second shift plate S2.

  Each of the first and second shift plates is provided with a power transmission portion 113, and, for example, a screw-like groove is carved. By transmitting the power indicated by 112 to the power transmission unit 113, the power transmission unit 113 is configured to move independently in the vertical direction and the left-right direction (the direction indicated by 111 in FIG. 11). The power may be manual or electric. When the movable mechanism is moved electrically, a pulse motor or the like is generally used as a power source.

  Also in the configuration of the present embodiment, the above-described movable mechanism is provided (not shown), and the configuration is such that the degree of freedom in adjusting the image projection direction is increased.

  When a projection lens shift is performed using the above-described movable mechanism and an image is projected in an oblique direction, the angular distribution of light that can be captured by the projection lens 10 becomes asymmetric in the Y direction due to the above-described vignetting effect. . As a reference, FIG. 5 shows a schematic diagram of the amount of light that can be taken in by the projection lens 10 and the angular distribution when the light beam having a substantially uniform light amount distribution is incident on the projection lens 10. It can be seen that the + Y direction is less affected by vignetting and the amount of light that can be captured is greater than the -Y direction. Conversely, the amount of light that can be captured in the −Y direction is small due to the effect of vignetting.

  The present invention uses this action to shift the projection lens in the + Y direction compared to the -Y direction. That is, the movable mechanism of the projection lens of the present invention has a range in which the projection lens 10 can move within the cross section (YZ cross section) parallel to the normal line of the polarization separation surface 8 and the optical axis of the projection lens 10 as follows. Determine as follows. Of the light rays traveling from the liquid crystal panel 9 toward the polarization splitting surface 8, it is determined that many light rays having an incident angle larger than 45 degrees are captured as compared with light rays having an incident angle smaller than 45 degrees. As a result, an image with high contrast can be obtained without disposing a polarizing plate that cuts out leakage light between the liquid crystal panel 9 and the projection lens 10, so that a reduction in brightness can be suppressed.

  The projection direction depending on the installation location of the image projection apparatus will be described with reference to FIG. As shown in FIG. 12A, in the so-called “ceiling state” in which the image projection device is suspended from the ceiling in the room, the projection can be projected in the direction of the floor (downward in the drawing) so that the ceiling and the projection image do not interfere with each other. It is common.

  As shown in FIG. 12B, when an image projection apparatus is installed on a projection table such as a desk, it is generally projected in the direction of the ceiling (upward in the drawing) so that the projection table and the projection image do not overlap. It is.

  In the present embodiment, the shift direction of the projection lens in the “suspended state” or the “state of being placed on the projection table” is the same. That is, in the “suspended state” and the “state to be arranged on the projection base”, the casing of the image projection apparatus may be turned upside down.

  The specific movable range of the projection lens 10 of the present embodiment is that the movable range in the −Y direction is about 10% of the length in the Y direction of the liquid crystal panel, while the movable range in the + Y direction is about 50%. ing. The movable range of the shift is based on the center of the liquid crystal panel. For example, if it is 50%, it is shifted from the center of the panel by half of the short side length of the liquid crystal panel, and if it is 10%, it is shifted by 10% of the length of the liquid crystal panel. As described above, when the projection lens is shifted to 10% or more in the -Y direction and the projection direction is to be adjusted largely in the -Y direction, as described above, the projector can be installed upside down. If you can.

<< Embodiment 2 >>
FIGS. 6A and 6B are configuration diagrams of an image projection apparatus according to the second embodiment of the present invention. The difference from the first embodiment is that the illumination optical system includes means for compressing the light beam in the first cross section (XZ cross section) and the second cross section (YZ cross section) that include the optical axis of the illumination optical system and are orthogonal to each other. It is a point. 6A is a diagram of the image projection apparatus according to the second embodiment as viewed from the XZ cross section, and FIG. 6B is a diagram of the image projection apparatus according to the second embodiment as viewed from the YZ cross section.

  The light emitted from the light source 1 is collected by the elliptical reflector 2 </ b> A, enters the convex lens 12, is converged by the convex lens 12, and enters the concave cylindrical lens 13. In the cross section of FIG. 6A, incident light is emitted as substantially parallel light by the convex lens 12 and the concave cylindrical lens 13 (negative cylindrical lens). The light incident on the first fly-eye lens 3a is separated into a plurality of light beams by the individual lenses forming the first fly-eye lens. The light that has passed through the first fly-eye lens 3a is emitted as substantially parallel light by the convex lens 12 and the concave cylindrical lens 14 positioned in front of the second fly-eye lens 3b in the cross section of FIG. 6B. The light beams compressed in the XZ cross section and the YZ cross section pass through the second fly-eye lens 3 b and enter the polarization conversion element 4.

  Also in this embodiment, depending on the angle at which the light reflected from the liquid crystal panel 9 enters the polarization separation surface 8 of the polarization beam splitter 7, the polarization separation characteristic fluctuates and leakage light that lowers the contrast is generated. FIG. 7 shows a schematic diagram of the angular distribution of the leaked light on the polarization separation surface when the light beam is modulated to the polarization state corresponding to the all black image in the liquid crystal panel. The coordinate axis represents the incident angle with respect to the polarization splitting surface 8, and the center represents that the angle deviation from 45 ° is 0 °. The lighter the part, the less light leaks, and the darker the part, the more light leaks.

  Also in this embodiment, an image with high contrast can be displayed as in the first embodiment.

  In addition, another effect of the present embodiment is that the light flux is independently compressed in each of the XZ cross section (first cross section) and the YZ cross section (second cross section), and in the Y direction (in the second cross section than in the first embodiment). The compression rate of the luminous flux in the parallel direction is high. By compressing the light beam more strongly in the YZ section, it is possible to reduce the spread of the incident angle on the polarization separation surface in the Y direction where the fluctuation of the polarization separation surface characteristics is large. Thereby, compared with the case where the light beams in the X and Y directions are compressed by the same amount, the leakage light on the polarization separation surface is reduced, and the contrast of the projected image can be further improved.

  In this embodiment, a positive lens and a concave cylindrical lens are used as a function of compressing the light beam. However, for example, an eccentric fly-eye lens in which the fly-eye function and the concave cylindrical lens are integrated by gradually decentering the lens cell of the fly-eye lens in a direction away from the optical axis as it moves away from the optical axis may be used.

<< Embodiment 3 >>
FIG. 8 is a block diagram of an image projection apparatus according to the third embodiment of the present invention. The difference from the first embodiment is that a dichroic mirror 15 is provided and light of different wavelength bands is incident on a plurality of liquid crystal panels. Reference numeral 15 denotes a dichroic mirror (color separation element), and reference numeral 16 denotes a wavelength selective phase plate, which is an element that acts only on light in the red wavelength band and rotates its polarization direction by 90 °. Reference numerals 17 and 18 denote a first polarizing beam splitter and a second polarizing beam splitter, respectively. 19 is a reflective liquid crystal panel for red (first image display element), 20 is a reflective liquid crystal panel for green (second image display element), and 21 is a reflective liquid crystal panel for blue (first image display element). 3 image display elements). Reference numeral 22 denotes a synthesis prism (color synthesis element) having a color synthesis surface that reflects light in the green wavelength band and transmits light in the red and blue wavelength bands. The dichroic mirror 15 and the first and second polarization beam splitters 17 and 18 include a plane including the color separation surface of the dichroic mirror 15 and a plane including the polarization separation surface of the first and second polarization beam splitters 17 and 18. Are arranged so as to be orthogonal to each other.

  The light beam emitted from the condenser lens 5 b enters the dichroic mirror 15. Of the incident light, the dichroic mirror 15 transmits only light in the green wavelength band (first color light), and reflects light in the blue band and red band (second and third color lights). The light in the green band is analyzed by the polarization beam splitter 17 (first polarization beam splitter), and illuminates the liquid crystal panel 20 for green. The light converted to S-polarized light by the green liquid crystal panel 20 reflects the polarization beam splitter 17, reflects the combining prism 22, and is projected onto the projection surface by the projection lens. The light whose polarization direction has not been converted by the liquid crystal panel 20 passes through the polarization beam splitter 17 again and is returned to the light source.

  The light in the red band and blue band reflected by the dichroic mirror 15 passes through the wavelength selective phase plate 16. The wavelength-selective phase plate 16 acts only on the red band light and rotates its polarization direction by 90 ° to make S-polarized light. The red band light converted into the S-polarized light is reflected by the polarization separation surface of the polarization beam splitter 18 (second polarization beam splitter), and enters the red liquid crystal panel 19. The red band light converted into the P-polarized light by the liquid crystal panel 19 is transmitted through the polarization beam splitter 18 and the combining prism 22 and then projected onto the projection surface by the projection lens 10. The S-polarized light in the red band that has not been converted by the liquid crystal panel 19 is reflected by the polarization separation surface of the polarization beam splitter 18 and returned to the light source side.

  The blue band light reflected by the dichroic mirror 15 passes through the wavelength selective phase plate 16, passes through the polarization beam splitter 18, and enters the blue liquid crystal panel 21. After being incident on the blue liquid crystal panel, the light converted from P-polarized light to S-polarized light is reflected by the polarization beam splitter 18, passes through the combining prism 22, and is projected onto the projection surface by the projection lens. The P-polarized light that has not been converted by the liquid crystal panel 21 passes through the polarization beam splitter 18 and is returned to the light source side.

  Here, when focusing on the leakage light in the green wavelength band that contributes most to the brightness, the extinction ratio of P-polarized light decreases with respect to the angle change in which the thickness of the polarization splitting surface through which the light passes is reduced as in the first embodiment. . Therefore, the leakage light in the −Y direction is larger than that in the + Y direction. Therefore, the present embodiment also provides the effect of improving the contrast while suppressing the decrease in brightness due to the polarizing plate, as in the first embodiment.

  In the case of an image projection apparatus that projects a color image using light of a plurality of wavelength bands as in the present embodiment, it has a plurality of light modulation elements (liquid crystal panels 19, 20, and 21) corresponding to each color light.

  Similar to the first embodiment, the movable mechanism (FIG. 11) of the projection lens 10 determines the movable range of the projection lens 10 as follows. That is, in the cross section parallel to the normal line of the polarization separation surface and the optical axis of the projection lens, the light beam traveling from the liquid crystal panel 20 to the polarization separation surface of the polarization beam splitter 17 is compared with the light beam having an incident angle smaller than 45 degrees. Thus, it is determined so that many rays having an incident angle larger than 45 degrees are captured.

  In the case of an image projection apparatus that projects a color image, all the light modulation elements and the polarization separation surface that detects light modulated by the light modulation elements satisfy the movement range of the projection lens 10 defined by the movable mechanism. preferable. However, the light modulation element that modulates specific color light may satisfy the above relationship. At this time, as in the present embodiment, since the specific light modulation element is a light modulation element (liquid crystal panel 20) that modulates light in the green wavelength band, the color light having better relative visibility than other colors. In contrast, the same effect as in the first embodiment can be obtained. As a result, an image that feels higher in contrast can be displayed.

  Another effect of the third embodiment is that the image projection apparatus can be downsized in the direction in which the projection lens 10 is shifted (Y direction in FIG. 8). The lens barrel and the movable mechanism of the projection lens 10 are relatively large parts. Therefore, depending on the movable range of the projection lens 10, the housing of the image display device must be enlarged.

  In the present embodiment, in addition to the above effects, the image display device is downsized. FIG. 9 shows a conceptual diagram of the effect of miniaturization. FIG. 9A shows a configuration in which the movable range is increased in the + Y direction compared to the −Y direction as in this embodiment, and FIG. 9B shows a configuration in which the movable range is increased in the + Y direction compared to the −Y direction. Represent. In the configuration of FIG. 9B, since the movable range is increased in the −Y direction with reference to the central axis of the combining prism, it is necessary to increase the size to the lower end of the housing. On the other hand, in the configuration of FIG. 9A as in the present embodiment, the movable range is large in the + Y direction with respect to the central axis of the combining prism 22, so that the polarization beam splitter is compared with the configuration of FIG. 9B. And the housing can be downsized by half the size of the composite prism.

  That is, the image projection apparatus includes a synthesis prism 22 (color synthesis element) having a color synthesis surface that synthesizes the optical paths separated by the color separation element. Then, the image light modulated by the liquid crystal panel 20 (light modulation element) is reflected by the polarization separation surface and the color combining surface of the polarization beam splitter 17 and enters the projection lens 10. As in the first embodiment, the movable mechanism (FIG. 11) has an incident angle of 45 degrees compared to a light beam having an incident angle smaller than 45 degrees out of the light beams traveling from the liquid crystal panel 20 toward the polarization separation surface of the polarization beam splitter 17. The projection lens 10 is moved so as to capture many larger light beams. In the present embodiment, this moving direction is a direction from the combining prism 22 (color combining element) toward the polarization beam splitter 17 (polarization separation surface). Thereby, it is possible to reduce the size of the image projection apparatus in the direction in which the projection lens is shifted (Y direction in FIG. 8). Note that “parallel” in this specification is not limited to a completely “parallel” state.

<< Embodiment 4 >>
FIG. 10 is a configuration diagram of an image projection apparatus according to the fourth embodiment of the present invention. The difference from the third embodiment is the arrangement position of the green liquid crystal panel 20 with respect to the polarizing beam splitter 17 (first polarizing beam splitter). With this arrangement of the liquid crystal panel 20, the half-wave plate 30 is provided between the dichroic mirror 15 and the polarization beam splitter 17. Since other configurations are the same as those of the third embodiment, only differences from the third embodiment will be described below. The arrangement of the liquid crystal panel 20 of the present embodiment is an arrangement for illuminating the liquid crystal panel 20 with the reflected light from the polarization beam splitter 17. Since the green band illumination light transmitted through the dichroic mirror 15 is aligned with the P-polarized light by the polarization conversion element 4, it is not reflected by the polarization beam splitter 17 as it is. Therefore, in the present embodiment, the half-wave plate 30 is provided between the dichroic mirror 15 and the polarization beam splitter 17, and the polarization direction of the illumination light is converted to S-polarized light.

  As a result, the green band illumination light substantially aligned with S-polarized light is reflected and detected by the polarization beam splitter 17 to illuminate the liquid crystal panel 20. The light converted to P-polarized light by the liquid crystal panel 20 is transmitted through the polarization beam splitter 17, reflected by the combining prism 22, and projected onto the projection surface by the projection lens. The light whose polarization direction has not been converted by the liquid crystal panel 20 is reflected again by the polarization beam splitter 17 and returned to the light source side.

  Also in the present embodiment, as in the first embodiment, the contrast is improved by suppressing the ratio of the leaked light from the polarization beam splitter 17 entering the projection lens. Therefore, when the projection lens is moved, the contrast can be improved in most of the movable range.

  Further, in the present embodiment, since the liquid crystal panel 20 and the holding portion associated therewith are not present in the direction in which the projection lens is shifted (Y direction), the degree of freedom of the movable range of the projection lens shift is increased. For example, in the first embodiment, the movable range in the + Y direction is set to about 50% of the length in the Y direction of the liquid crystal panel. However, the movable range of the projection lens is effectively utilized by using the position where the liquid crystal panel 20 in FIG. Can be set to 60% or larger in the + Y direction.

  In addition, the form from which the effect of this invention is acquired is not restricted to FIG. For example, even if the half-wave plate 30 is not provided, the liquid crystal panel 20 may not be disposed in the direction in which the projection lens is shifted as long as the S-polarized light is incident on the polarization beam splitter 17.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary. For example, the light source may be an LED light source or a laser light source that emits linearly polarized light. Further, the characteristics of the dichroic mirror 15 and the characteristics of the combining prism may be changed to transmit red band light and transmit blue band light and green band light. Further, the present invention can also be applied to an image projection apparatus in which three polarization beam splitters are arranged in each of three color liquid crystal panels using a cross dichroic prism.

7 Polarizing Beam Splitter 8 Polarizing Separation Surface 9 Reflective Liquid Crystal Display Element 10 Projection Lens 11 Screen

Claims (4)

Illumination optics,
Among the light emitted from the illumination optical system, a color separation element that guides light in a green wavelength band in a direction different from light in a blue wavelength band and light in a red wavelength band;
A polarization separation element having a polarization separation surface that separates an optical path of light in the green wavelength band from the color separation element according to a polarization direction;
A light modulation element that modulates the polarized light separated by the polarization separation surface;
An image projection apparatus having a movable means for moving a projection optical system which is modulated by the light modulation element and projects light again through the polarization separation element onto a projection surface,
The light modulation element is provided so that light emitted from the color separation element and reflected by the polarization separation surface is incident on the light modulation element,
The movable means moves from the light modulation element to the polarization separation surface within a cross section parallel to the normal line of the polarization separation surface and the optical axis of the illumination optical system. An image projection apparatus characterized in that, among the light rays, it is determined so as to capture more light rays having an incident angle larger than 45 degrees than light rays having an incident angle smaller than 45 degrees. A color synthesizing element having a color synthesizing surface that synthesizes the light from the light modulation element and the light in the blue wavelength band and the light in the red wavelength band from the color separation element ;
The projection optical system is configured so that the movable means captures a larger number of light beams having an incident angle larger than 45 degrees than a light beam having an incident angle smaller than 45 degrees among light beams traveling from the light modulation element to the polarization separation surface. direction of movement is an image projection apparatus according to claim 1, characterized in that from the color combining element is a direction toward the polarization separation element. Of the plurality of orthogonal optical axes including the optical axis of the illumination optical system, the first cross section is different from the cross section including the normal line of the polarization separation surface, and the second cross section includes the normal line of the polarization separation surface. And when
The illumination optical system has an optical system that makes the width of the light beam from the illumination optical system in the second cross section smaller than the width of the light beam from the illumination optical system in the first cross section ,
The projection optical system is configured so that the movable means captures a larger number of light beams having an incident angle larger than 45 degrees than a light beam having an incident angle smaller than 45 degrees among light beams traveling from the light modulation element to the polarization separation surface. direction of movement is an image projection apparatus according to claim 1 or 2, characterized in that a direction parallel to the second section. Image projection apparatus according to any one of claims 1 to 3 any one characterized by having the projection optical system.

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