JP2010072128A - Rear projector - Google Patents

Abstract

In a rear projector, it is possible to reduce the thickness and the size of a collar.
A rear projector includes a projection optical system that projects light from a spatial light modulation element LC onto a back surface of a screen SC. The projection optical system includes a first optical system C that receives light from the spatial light modulation element LC and is disposed in a region on one end side in the direction along the screen in the first cross section. A first reflection surface MU that reflects light from the system, and a second optical system R on which light from the first reflection surface is incident, and a region on the other end side in the direction along the screen The second reflecting surface MR is disposed so as to be inclined with respect to the normal line of the screen and allows the light from the second optical system to enter the screen obliquely.
5 ° ≦ θ _S ≦ 25 °, 0.2 ≦ L ₁ / L ₂ ≦ 0.9, 0.8 ≦ L _P / S _Y ≦ 1.2, 0.45 ≦ L _R / S _Y ≦ 0.6 satisfies the _{-0.8L P / L R ≦ 1-2sinθ R} / tanθ S ≦ 0.5L P / L R.
[Selection] Figure 1

Description

  The present invention relates to a rear projector that projects an image obliquely from the back side of a screen disposed on the front surface of a housing.

  The rear projector as described above projects light (image light) modulated by a spatial light modulation element such as a liquid crystal panel or a digital micromirror device (DMD) obliquely onto the back of the screen via a projection optical system. The image is displayed so that it can be viewed from the front side.

  As such a projection optical system for oblique projection, as disclosed in Patent Document 1, an off-axial optical system (non-coaxial optical system) in which the optical path of the reference axis light beam is bent by a rotationally asymmetric reflecting surface. There is something configured as.

  A rear projector is required to have a thin apparatus while having a large screen. In the rear projector disclosed in Patent Document 2, a planar reflecting surface for bending is disposed between an imaging optical system composed of a plurality of lenses and a curved reflecting surface, and the imaging optical system is parallel to the screen. By arranging in the direction, the projection optical system, that is, the apparatus is thinned.

  Further, in the rear projector, there is a demand for downsizing a portion below the screen (hereinafter referred to as a collar).

  In the rear projector disclosed in Patent Document 3, a projection optical system is arranged in a lower space on the back side of the screen inside the apparatus. Then, the light beam emitted from the projection optical system is reflected by a plane reflecting surface arranged in the upper space on the back side of the screen inside the apparatus, and is projected from the tilt on the back side of the screen. According to such a configuration, the light beam can be incident at a steep incident angle from the plane reflecting surface toward the back surface of the screen. That is, it is possible to create a region through which the light beam does not pass in the lower space and arrange the projection optical system in this region. Thereby, thickness reduction of an apparatus and reduction of the height of a collar part are simultaneously realizable.

  As with the rear projector of Patent Document 3, as a rear projector that arranges a part of the projection optical system in the lower space inside the apparatus, arranges a plane reflecting surface in the upper space, and obliquely projects on the back of the screen, Documents 4-7 are also disclosed.

  In the rear projector disclosed in Patent Document 4, the planar reflecting surface is arranged perpendicular to the screen in the upper space. In the rear projector disclosed in Patent Document 5, image light is obliquely projected onto a screen while folding an optical path using a plane reflection surface arranged in an upper space and a plane reflection surface arranged on the back surface of a housing.

  In the rear projector disclosed in Patent Document 6, a refractive element for compensating aberration correction is arranged in an optical path formed by four curved reflecting surfaces, and the screen is passed through a plane reflecting surface arranged in an upper space. Projects image light at an angle.

In the rear projector disclosed in Patent Document 7, as in the rear projector of Patent Document 2, a planar reflecting surface for bending is provided between the first imaging system as a refractive system and the concave aspheric reflecting surface. To reduce the thickness of the device. Then, the image light is guided to the plane reflecting surface disposed in the upper space via the aspheric reflecting surface and obliquely projected onto the screen.
JP 2001-255462 A JP 2001-264632 A JP 2005-84576 A Japanese Patent No. 3813973 JP 2001-222063 A JP 2006-178406 A JP 2006-235516 A

  In the rear projectors disclosed in Patent Documents 3, 5, and 6, when the incident angle of the image light to the screen is made steeper, the planar reflecting surface arranged in the upper space is in the depth direction (normal direction of the screen). Since the thickness can be reduced, the apparatus can be thinned. However, in the rear projectors disclosed in these Patent Documents 3, 5, and 6, a part of the projection optical system disposed in the lower space of the apparatus is thick in the depth direction, so that the upper part of the apparatus can be thinned. However, it is difficult to reduce the thickness of the lower part of the apparatus.

  Incidentally, in the rear projectors disclosed in Patent Documents 3, 5, and 6, when the path of the light beam passing through the center of the spatial light modulator and the center of the stop is used as a reference axis, the angle formed by the reference axis and the screen ( Hereinafter, the screen incident angle) is about 25 to 30 degrees.

  In addition, the rear projector disclosed in Patent Document 5 uses the back plane reflecting surface in addition to the top plane reflecting surface, so that the device is thinned for the projection optical path length. The upper part of the screen is larger than the upper end of the screen.

  In the rear projector disclosed in Patent Document 4, since the upper planar reflection surface is arranged perpendicular to the screen, the reference axis emitted from a part of the projection optical system to the upper planar reflection surface is used. The tilt is determined by the screen incident angle. For this reason, the position of the projection optical system is in the rear direction of the apparatus, and the apparatus is thicker than the depth of the upper planar reflecting surface.

  In the rear projector disclosed in Patent Document 7, although the projection optical system is thinned using the bending plane reflection surface, the gap between the bending plane reflection surface and the concave reflection surface is large. The projection optical system is not substantially thinned. In addition, there is an exit pupil (intersection of principal rays incident on the upper and lower ends of the screen) between the concave reflecting surface and the upper planar reflecting surface, but the exit pupil is located near the middle of the two reflecting surfaces, The two reflecting surfaces are almost equal in size, which hinders the thinning of the projection optical system. For this reason, although the screen incident angle is set to about 17 degrees and the upper planar reflection surface can be thinned in the depth direction, the overall apparatus cannot be thinned.

  When the screen incident angle becomes small, it becomes necessary to use a reflective Fresnel screen as disclosed in Patent Document 4. However, in order to emit light in a direction perpendicular to the screen on the observer side, it is necessary to reduce the apex angle of the Fresnel surface as the screen incident angle decreases, which makes processing difficult.

  The present invention provides a rear projector capable of realizing a thinner device and a smaller buttocks.

  A rear projector according to one aspect of the present invention has a screen on the front surface of a housing, and projects a spatial light modulation element that modulates light inside the housing and light from the spatial light modulation device to the back surface of the screen. A projection optical system.

  A path followed by a central principal ray passing through the center of the spatial light modulation element and the center of the stop included in the projection optical system is used as a reference axis, and the final reference axis part incident on the screen and the normal line of the reference axis are included. The cross section is the first cross section. At this time, the projection optical system has at least one light incident from a spatial light modulation element disposed in an area on one end side in the direction along the screen in the first cross section in the housing. A first optical system configured by a lens, a first reflective surface that reflects light from the first optical system, and at least one curved reflective surface, and light from the first reflective surface is And an incident second optical system. Further, the projection optical system is disposed in a region on the other end side in the direction along the screen in the first cross section in the inside of the housing, and is inclined with respect to the normal line of the screen, A second reflecting surface that allows light to enter the screen obliquely is provided. And it is characterized by satisfying the following conditions.

5 ° ≦ θ _S ≦ 25 °
0.2 ≦ L ₁ / L ₂ ≦ 0.9
0.8 ≦ L _P / S _Y ≦ 1.2
0.45 ≦ L _R / S _Y ≦ 0.6
−0.8 L _P / L _R ≦ 1-2 sin θ _R / tan θ _S ≦ 0.5 L _P / _LR

However, in the first cross section, θ _S is the absolute value of the angle formed between the screen and the final reference axis portion incident on the screen from the second reflecting surface, and θ _R is the second reflecting surface with respect to the normal line of the screen. Is an absolute value of the inclination angle, and L ₁ is a curved surface reflection disposed at a position farthest from the screen among at least one curved surface reflection surface in the second optical system from the intersection of the first reflection surface and the reference axis. The distance along the screen normal to the intersection of the surface and the reference axis. L ₂ is the length of the second reflecting surface along the normal of the screen, and L _P is the second reflecting surface along the reference axis among at least one curved reflecting surface in the second optical system. Is the distance along the reference axis from the final curved reflecting surface close to the second reflecting surface. _LR is the distance along the final reference axis portion from the second reflecting surface to the screen, and _SY is the length of the screen.

  According to the present invention, the arrangement of each surface constituting the projection optical system, the projection distance, the installation angle of the second reflecting surface, the screen incident angle, and the like can be appropriately set. Downsizing can be realized.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  First, prior to description of specific embodiments, a configuration common to each embodiment will be described with reference to FIGS. 18 and 19.

  A rear projector according to an embodiment of the present invention has a housing B, and a screen SC as a projection surface is disposed on the front surface of the housing B.

  Further, inside the housing B, a spatial light modulation element (not shown in FIGS. 18 and 19) that modulates light, and a projection optical system P that projects light from the spatial light modulation element onto the back surface of the screen SC. , MR are arranged.

  Here, in the embodiment, a path followed by the central principal ray or the reference axis ray passing through the center of the spatial light modulator and the center of the stop included in the projection optical system is set as the reference axis. A section including the final reference axis portion incident (arrived) on the screen SC (from a second reflecting surface described later) and the normal line of the screen SC is defined as the first section. In the following description, the normal line of the screen SC is referred to as a screen normal line, and the direction in which the screen normal extends (back direction) is referred to as a screen normal line direction.

  The projection optical system includes a lower projection optical system P and a second reflecting surface MR. The lower projection optical system P includes a first optical system C and a first reflecting surface MU disposed in one end side region in the direction along the screen SC in the first cross section in the housing B. And a second optical system R. The first optical system C includes at least one lens, and light from the spatial light modulation element is incident on the first optical system C. The first reflecting surface MU reflects the light from the first optical system C. The second optical system R is composed of at least one curved reflecting surface, and light from the first reflecting surface MU is incident on the second optical system R.

  Further, the second reflecting surface MR is disposed in a region on the other end side in the direction along the screen SC in the first cross section in the inside of the housing B so as to be inclined with respect to the screen normal line. Light from the optical system R is obliquely incident on the screen SC.

  And the rear projector of an Example satisfies all the following conditions.

5 ° ≦ θ _S ≦ 25 ° (1)
0.2 ≦ L ₁ / L ₂ ≦ 0.9 (2)
0.8 ≦ L _P / S _Y ≦ 1.2 (3)
0.45 ≦ L _R / S _Y ≦ 0.6 (4)
−0.8 L _P / L _R ≦ 1-2 sin θ _R / tan θ _S ≦ 0.5 L _P / L _R (5)
In the conditions (1) to (5), θ _S , θ _R , L ₁ , L ₂ , L _P , L _R , and _SY are all values in the first cross section. θ _S is an absolute value of an angle formed by the final reference axis portion incident on the screen SC from the second reflecting surface R and the screen SC, and is referred to as a screen incident angle in the following description. theta _R is the absolute value of the slope angle of the second reflecting surface R relative to the screen normal.

L ₁ is a curved reflecting surface arranged at a position (the backmost side) farthest from the screen SC among at least one curved reflecting surface in the second optical system R from the intersection of the first reflecting surface MU and the reference axis. The distance along the screen normal to the point of intersection with the reference axis. L ₂ is a length along the screen normal of the second reflecting surface MR.

In addition, L _P has a reference axis from the last curved reflection surface closest to the second reflection surface MR along the reference axis to the second reflection surface MR among the at least one curved reflection surface in the second optical system R. The distance along. _LR is a distance along the final reference axis portion from the second reflecting surface MR to the screen SC, and _SY is the length of the screen SC.

  Definitions of terms used in the embodiment of the present invention will be described with reference to FIG. The light (image light or projection light) from the lower projection optical system P is a second reflecting surface (planar reflecting surface) disposed on the other end side (upper side) in the direction along the screen SC inside the housing B. : Hereinafter referred to as a second plane reflecting surface) and is reflected by the MR and enters the back surface of the screen SC. In the embodiment, the direction indicated by the arrow a is the screen side, and the direction indicated by the arrow b is the back side. The direction indicated by the arrow c is the upper end side, and the direction indicated by the arrow d is the lower end side.

  The back surface of the housing B may not be parallel to the screen SC, and may be inclined or curved as long as the apparatus does not become thick. Further, the upper surface of the casing B may extend perpendicularly to the screen SC, or may be inclined so as to be lowered toward the back side as shown in the figure.

  The bottom surface of the housing B is preferably horizontal from the viewpoint of installation stability. However, the housing B may be stabilized by attaching legs even if it is not horizontal.

  A screen SC is disposed on the front surface of the housing B, and is fixed to the housing B by an unillustrated outer frame. The thickness or depth of the casing B (that is, a device called a rear projector) is a length D. In addition, the height of the lower buttock of the screen SC is H. The height H of the buttocks is the length from the lower end of the screen SC to the bottom surface of the housing B on the front surface of the housing B as viewed from the observer.

  Furthermore, the area e inside the housing B is referred to as the upper part, and the area f is referred to as the lower part. The “region on one end side in the direction along the screen” indicates one region of the upper portion e and the lower portion f, and the “region on the other end side in the direction along the screen” indicates the upper portion e and the lower portion f. The other area is shown. In the embodiment, the “region on one end” is a lower portion f, and the “region on the other end” is an upper portion e. However, the “region on one end” may be the upper portion, and the “region on the other end” may be the lower portion.

  In the screen SC, “one end” means one of the upper end and the lower end, and “the other end” means the other of the upper end and the lower end. In the embodiment, “one end” is the lower end and “other end” is the upper end, but “one end” may be the upper end and “other end” may be the lower end.

  As the screen SC, a screen formed with a Fresnel lens that bends the light beam toward the viewer, as disclosed in Patent Document 4, may be used. Further, a reinforcing plate for increasing the strength, a Fresnel lens for expanding the viewing angle, a lenticular lens or a diffusing material, and a light shielding layer such as a black matrix for improving the contrast of the projected image may be stacked.

Point of incidence of light on the screen SC to define the distance L _R from the screen incident angle theta _S and the second planar reflective surface MR to screen SC, and that the reference axis ray is first incident on the screen SC .

  Next, a more detailed configuration of the rear projector of the embodiment and the above conditions (1) to (5) will be described with reference to FIG.

  A lower projection optical system P is disposed in the lower part f. The lower projection optical system P includes a first optical system C configured by at least one lens, and a second optical system R configured by at least one curved reflecting surface having an aspherical shape. The lower projection optical system P is disposed between the first optical system C and the second optical system R, and bends light (reference axis) from the first optical system C by 90 degrees to form the second optical system. A first reflecting surface (planar reflecting surface: hereinafter referred to as a first planar reflecting surface) MU that leads to the system R is included.

  The light from the lower projection optical system P is reflected by the second plane reflecting surface MR disposed on the upper portion e, and enters the screen SC obliquely. In FIG. 18, the reference axis is indicated by a one-dot chain line, and between the second plane reflecting surface MR and the screen SC, two principal rays having an angle of view formed on the upper end and the lower end of the screen SC are indicated by solid lines. ing.

  The first optical system C is arranged such that a reference axis portion in the first optical system extends in a direction perpendicular to the first cross section, that is, parallel to the normal line of the first cross section. ing. In this case, the reference axis portion in the first optical system is parallel to the screen SC. However, you may arrange | position so that the reference-axis part in a 1st optical system may incline with respect to the normal line of a 1st cross section. In this case, the first planar reflecting surface MU may be arranged with an appropriate shift from 45 degrees with respect to the reference axis.

  In FIG. 19, the second optical system R is shown as one concave reflecting surface, but the number and shape of the curved reflecting surfaces are not limited thereto. That is, the second optical system R may be composed of a plurality of curved reflecting surfaces, or may be composed of at least one convex reflecting surface. Of the at least one curved reflecting surface constituting the second optical system R, the curved reflecting surface closest to the second planar reflecting surface MR along the reference axis is referred to as a final curved reflecting surface.

In FIG. 18, θ _P is an absolute value of an angle formed by a reference axis portion incident on the final curved reflection surface of the reference axis and a reference axis portion emitted from the final curved reflection surface in the first cross section.

As described above, in the embodiment, all of θ _S , θ _R , and θ _P are shown as absolute values.

In the condition (1), when the screen incident angle θ _S exceeds the upper limit value, it becomes difficult to process the Fresnel surface for bending the light beam from the back surface (back surface) of the screen SC to the viewer side. In addition, the image misalignment due to the deflection of the screen SC increases, which increases the distortion. If the screen incident angle θ _S is lower than the lower limit value, the depth L _{2 of} the second planar reflecting surface MR increases, and the apparatus cannot be thinned.

  Here, the thinning of the apparatus refers to the intersection of the optical surface on the back side and the optical path (reference axis) in the screen normal direction from the screen SC with respect to the length of the image display area on the screen SC in the first cross section. The distance ratio (thinness ratio) is limited to 30% or less. The depth of the device is comprehensively determined by the screen, the holding member of the optical surface, and other components of the device, but in the embodiment, in order to reduce the thickness of the device particularly by the configuration of the optical system, Define thinning as follows.

In the condition (2), when L ₁ / L ₂ exceeds the upper limit value, the thickness of the lower part where the lower projection optical system P is arranged increases as compared with the upper part, and the screen incident angle θ _S is reduced. Despite this, it is impossible to reduce the thickness of the entire device. When L ₁ / L ₂ is below the lower limit value, the optical path between the first planar reflecting surface MU and the curved reflecting surface of the second optical system R interferes.

In the condition (3), when L _P is substantially equal to S _Y , that is, when L _P / S _{Y is} approximately 1, the final curved reflecting surface in the lower projection optical system P is disposed near the lower end of the screen SC. . When the value of L _P / S _Y exceeds the upper limit value of the condition (3), the lower projection optical system P is at a position lower than the lower end of the screen SC, so that the height H of the collar portion increases. When the value of L _P / S _Y is lower than the lower limit value, the lower projection optical system P approaches the second flat reflecting surface MR, and interferes with the optical path of the light ray incident on the lower end of the screen SC from the second flat reflecting surface MR. It becomes easy to do. If the lower projection optical system P is moved to the back side in order to avoid such interference, the apparatus cannot be thinned.

In the condition (4), when L _R / S _Y is 0, the reference axis portion between the lower projection optical system P and the second plane reflecting surface MR is substantially parallel to the screen SC. When L R _/ S _Y exceeds the upper limit of the condition (4), with respect to the spacing from the intersection of the second planar reflective surface MR and the reference axis to the screen SC, the intersection of the final curved reflecting surface and the reference axis Is set to the back side by 1.5 times or more. For this reason, it is difficult to reduce the thickness of the apparatus. If L _R / S _Y is below the lower limit, the final curved reflecting surface and the optical path of the light beam incident on the lower end of the screen SC from the second flat reflecting surface MR are likely to interfere with each other. Incidentally, L _R in condition (4) is substantially determined by the position of the screen incident angle theta _S and the second planar reflective surface MR.

Thus, _{L P} and _L ranges of _R are each condition (3), is limited by (4). Thus, in effect, to the screen angle of incidence theta _S, by setting the inclination angle theta _R of the second planar reflective surface MR within the upper limit value and the lower limit of the condition (5), a thin An arrangement of optical surfaces suitable for realizing a rear projector having a low height H of the collar portion can be determined.

  Therefore, in order to realize a rear projector that can display a large screen, is thinner than the conventional one, and has a lower height H of the buttock, the lower projection optical system satisfies all the above conditions (1) to (5). It is necessary to construct the system P.

  In the rear projector of the embodiment, it is preferable that at least one curved reflecting surface constituting the second optical system R has a rotationally asymmetric curvature. By making the curved reflecting surface into a rotationally asymmetric shape, it is possible to correct an asymmetrical aberration with respect to the azimuth direction, which occurs when a reflection angle is given when the curved reflecting surface is a rotationally symmetric surface.

In the rear projector of the embodiment, it is preferable that the second flat reflecting surface MR is inclined with respect to the screen normal line on the back side of the second flat reflecting surface MR. Thereby, it is possible to reduce the thickness of the apparatus while keeping the screen incident angle θ _S within the range of the condition (1).

  In the rear projector of the embodiment, it is preferable to form an intermediate image within the lower projection optical system P. When an intermediate image is formed in the lower projection optical system P, when there is one curved reflecting surface constituting the second optical system R, the shape can be concave, and the size of the curved reflecting surface increases. Can be suppressed. In addition, when there are a plurality of curved reflecting surfaces, the condensed light flux is on the divergent light side before and after the intermediate image, so that a concave surface can be arranged after the intermediate image. For this reason, an increase in the size of the curved reflecting surface can be suppressed. Further, since the aperture image can be formed at a negative magnification as the exit pupil of the lower projection optical system P, the diameter of the projected light beam can be once reduced, and the optical surface and light shielding in the lower projection optical system P can be reduced. Arrangement of members becomes easy.

  Further, as described above, the first optical system C includes at least one lens (refractive optical element). By using the first optical system C as a refractive optical system and sharing the magnification with the second optical system R, which is a reflective optical system, the number of aspherical reflecting surfaces, which is more burdensome in terms of processing accuracy and cost than a lens, is achieved. Can be reduced. That is, trapezoidal distortion correction, tilt of the image plane, asymmetrical aberration, and the like necessary for oblique projection are corrected by the second optical system R composed of a small number of aspheric reflecting surfaces, and correction of rotationally symmetric components and magnification of the aberration Can be performed by the first optical system C.

  In the rear projector of the embodiment, as described above, it is preferable that the lower projection optical system P is disposed at the lower portion and the second planar reflection surface MR is disposed at the upper portion. A stable weight balance can be obtained by disposing the lower projection optical system P, which is heavier among the lower projection optical system P and the second planar reflecting surface MR, in the lower part. Further, when dust that has entered the inside of the housing adheres to the optical surface, the contrast of the projected image decreases due to light scattering. When the second planar reflection surface MR having a large opening (reflection area) is disposed below, dust tends to accumulate on the second planar reflection surface MR due to gravity. Therefore, it is preferable to dispose the lower projection optical system P with dust-proof measures at the lower part.

  Furthermore, in order to realize a thin rear projector with a low buttocks height H, it is preferable to adopt the following configuration.

  The first optical system C includes a reference axis portion incident on the second planar reflecting surface MR from the final curved reflecting surface in the second optical system R in the direction in which the screen normal in the first section extends, and the screen SC. It is preferable to arrange | position between. In addition, a first optical system may be disposed between the extension line of the reference axis portion and the screen SC.

  In the rear projector of the embodiment, the reference axis portion on the spatial light modulation element side of the reference axis from the first plane reflection surface MU is non-parallel to the first cross section, and the first plane reflection surface It is preferable that the reference axis portion on the screen side of the MU is included in the first cross section.

  In the rear projector of the embodiment, the reference axis portion in the first optical system C among the reference axes is preferably inclined at an angle of 20 ° or less with respect to the screen.

  In the rear projector of the embodiment, the depth in the direction in which the screen normal of the lower projection optical system P extends is obtained by bending the first optical system C and the second optical system R with the first planar reflection surface MU. Is made smaller. At this time, it is desirable that the reference axis portion in the second optical system R of the reference axes is within one cross section. As a result, the second optical system R becomes an optical system that is symmetrical in the horizontal direction with respect to the screen SC. Therefore, the correction of the asymmetrical aberration is due to the deflection of the reference axis by reflection within one cross section on the curved reflecting surface. It is only necessary to correct the resulting asymmetric aberration. As a result, when the curved reflecting surface is a rotationally asymmetric aspherical surface, it can have a symmetrical shape in the horizontal direction.

  In the rear projector of the embodiment, the first cross section between the final curved reflection surface closest to the screen SC and the second planar reflection surface MR along the reference axis portion in the lower projection optical system P is used. It is preferable to have an exit pupil.

In the rear projector of the embodiment, in the first cross section, the principal ray having the field angle formed on the lower end (one end) of the screen and the principal ray having the field angle formed on the upper end (the other end) of the screen. It is preferable that the final curved reflecting surface and the second flat reflecting surface MR intersect each other. The position where the two principal rays intersect is more preferably in a region within L _P / 3 from the final curved reflecting surface.

  Furthermore, in the rear projector of the embodiment, in the first section, the length (diameter) of the final curved reflecting surface is preferably smaller than 2/3 of the length of the second planar reflecting surface MR.

  As described above, by forming an intermediate image in the lower projection optical system P, the second optical system R can form an exit pupil as an image of an aperture (aperture stop). The exit pupil has a conjugate relationship with the entrance pupil, but in the case of an off-axial optical system, the position of the pupil differs depending on the azimuth direction. Further, when a rotationally asymmetric aspherical reflecting surface is used for the second optical system R, the position of the pupil varies depending on the angle of view. For this reason, the position of the exit pupil of the entire optical system is not a single point but has a spatial distribution. However, in order to realize a thin rear projector having a low buttocks height H, the intersection of principal rays of the angle of view that forms the exit pupil position on the upper and lower ends of the screen SC in the first section, respectively. It may be defined as (intersection point).

Furthermore, when the position of this intersection is close to the second planar reflecting surface MR, the size of the final curved reflecting surface of the lower projection optical system P is increased. An increase in the size of the final curved reflecting surface leads to an increase in the overall size of the lower projection optical system P, and prevents a reduction in the thickness of the apparatus. For this reason, it is preferable to set the intersection (exit pupil) in a region within L _P / 3 from the final curved reflecting surface in the first cross section for the reason of the size of the final curved reflecting surface and aberration correction. Thus, the length of the final curved reflecting surface in the first cross section can be reduced to within 2/3 of the length of the second planar reflecting surface MR, and the apparatus can be thinned.

  In the rear projector of the embodiment, it is preferable that the second optical system R is constituted by a plurality of curved reflecting surfaces. In particular, it is better that the second optical system R is composed of four curved reflecting surfaces. Since the second optical system R has a role of correcting asymmetric aberration in oblique projection as described above, it is possible to perform better aberration correction by using a plurality of curved reflecting surfaces.

  In this case, it is preferable that the reference axis portion between the final curved reflection surface and the second planar reflection surface MR intersects the reference axis portion on the spatial light modulation element side with respect to the final curved reflection surface. When the number of curved reflecting surfaces of the second optical system R is increased, it is necessary to arrange the reflecting surfaces so that there is no interference between the reflecting surfaces and between the reflecting surfaces and the optical path. As a result, the second optical system R is large. There is a possibility of becoming. Therefore, the second optical system R using a plurality of curved reflecting surfaces can be reduced in size by increasing the space utilization efficiency by intersecting the two reference axis portions (optical paths) in the second optical system R. it can.

Further, in the rear projector of the embodiment, in the first cross section, the final curved reflecting surface is the optical surface located farthest from the second planar reflecting surface MU among the plurality of optical surfaces included in the lower projection optical system P. It is preferable that

When the projection distance from the final curved reflecting surface to the screen SC is short, it is necessary to increase the power of the second optical system R. In this case, this corresponds to a wide angle of view on the exit side, which makes it difficult to correct aberrations and increases the accuracy required for the surface shape. In addition, when the exit pupil position is moved away to avoid the wide angle, the size of the final curved reflecting surface increases. For this reason, in order to increase the projection distance from the final curved reflection surface as much as possible, it is effective to dispose the final curved reflection surface at a position farther from the second planar reflection surface MR than the other optical surfaces.

More preferably, the rear projector of the embodiment satisfies at least one of the following conditions.

5 ° ≦ θ _S ≦ 20 ° (6)

−0.2 L _P / L _R ≦ 1-2 sin θ _R / tan θ _S ≦ 0.2 L _P / L _R (7)
10 ° ≦ θ _P ≦ 40 ° (8)
0 ° ≦ | θ _S −2θ _R | ≦ 7 ° (9)
Respect condition (8), when within range of the upper limit value and the lower limit value when the respective theta _P in FIGS. 20 and 21 is large if small (if exceeding the upper limit of the condition (8)) (Condition (8) ). If theta _P is large as shown in FIG. 20, the interval L _a between the first optical system C and the second optical system R is increased, there is a possibility that the thickness of the apparatus is prevented. In contrast, when theta _P is small as shown in FIG. 21, it is possible to reduce the L _a, also to ensure the required spacing from the first optical system C to the second optical system R device Can be made thinner. Further, from the viewpoint of aberration correction, it is preferable theta _P is small. The upper limit value of the condition (8) is more preferably 23 degrees.

With respect to condition (9), setting the inclination angle theta _R of the second flat reflective surface MR to outside the upper limit and the lower limit of the condition (9) to the screen angle of incidence theta _S, lower projection optical system The reference axis portion from P to the second plane reflecting surface MR is greatly inclined with respect to the screen SC. When the reference axis portion is inclined to the screen side, the lower projection optical system P and the screen SC or the light directed to the screen SC may interfere with each other. Further, when the reference axis portion is inclined to the back side, the lower projection optical system P protrudes in the back direction with respect to the depth of the second planar reflecting surface MR, and the apparatus cannot be thinned. There is a fear.

  Next, the definition of the coordinate system in the off-axial optical system in the embodiment will be described. FIG. 22 shows a coordinate system that defines the configuration data of the off-axial optical system.

  The i-th surface is defined as the i-th surface along one light ray (reference-axis light beam indicated by a one-dot chain line in FIG. 22) traveling from the reduction side to the enlargement image plane. In FIG. 22, the first surface R1 is a refracting surface, the second surface R2 is a reflecting surface tilted with respect to the first surface R1, and the third surface R3 and the fourth surface R4 are shifted and tilted with respect to the respective previous surfaces. It is a reflective surface. The fifth surface R5 is a refractive surface shifted and tilted with respect to the fourth surface R4. Each surface from the first surface R1 to the fifth surface R5 is formed on one optical element made of a medium such as glass or plastic, and is shown as a first optical element B in FIG.

  The medium of the first optical element B may be air, and the refracting surfaces that are the entrance surface and the exit surface may be deleted. In the configuration of FIG. 22, the medium from the object surface (not shown) to the first surface R1 is air, and the medium from the first surface R1 to the fifth surface R5 is a common medium. The medium from the fifth surface R5 to the sixth surface (R6) (not shown) is air.

  In the off-axial optical system, the surfaces constituting the optical system do not have a common optical axis. Therefore, an absolute coordinate system having the origin at the center of the first surface is set. Then, the center point of the first surface is set as the origin, and the path of the light beam (reference axis light beam) passing through the origin, the pupil center, and the center of the final imaging surface is defined as the reference axis of the optical system. Furthermore, the reference axis has a direction. The direction is the direction in which the reference axis ray travels during imaging.

  Note that the method of determining the reference axis of the optical system is not limited to the above, and any method that is convenient in terms of optical design, summarizing aberrations, or expressing the shape of each surface constituting the optical system may be employed. . However, in general, the path of the light beam passing through the center of the image plane and the stop, entrance pupil, exit pupil or the center of the first surface or the center of the final surface of the optical system is set as the reference axis of the optical system. To do. That is, the reference axis is set to a path through which the reference axis light beam that passes through the center point of the entrance pupil and reaches the center of the final imaging plane is refracted or reflected by the refracting surface or the reflecting surface.

  The order of the surfaces is set in the order in which the reference axis rays are refracted or reflected. The reference axis finally reaches the center of the image plane while changing its direction according to the law of refraction or reflection according to the set order of the surfaces.

  Each axis of the absolute coordinate system of the optical system is determined as follows.

  Z axis: A straight line passing through the origin and the center of the object plane. The direction from the object surface toward the first surface R1 is positive.

  Y axis: A straight line that passes through the origin and forms 90 ° counterclockwise with respect to the Z axis according to the definition of the right-handed coordinate system.

  X axis: A straight line passing through the origin and orthogonal to the Z axis and the Y axis.

  Further, in order to express the shape and tilt angle of the i-th surface constituting the optical system, there is a method of expressing the shape and tilt angle of the surface in an absolute coordinate system. However, rather than this, a local coordinate system with the origin at the point where the reference axis intersects the i-th surface is set, the shape of the surface is represented in the local coordinate system, and the angle between the reference axis and the local coordinate system is set. The shape representing the tilt angle is easier to recognize. For this reason, also in an Example, the shape of the i-th surface is represented by the following local coordinate systems.

  z-axis: surface normal passing through the origin of local coordinates.

  y-axis: A straight line that passes through the origin of local coordinates and forms 90 ° counterclockwise with respect to the z-axis according to the definition of the right-handed coordinate system.

  x-axis: a straight line passing through the origin of the local coordinates and orthogonal to the yz plane.

  In the following examples, specific numerical values relating to the arrangement and shape of each surface are also shown. Di is a scalar quantity representing the distance between the origins of the local coordinates of the i-th surface and the (i + 1) -th surface. Ndi and νdi are the refractive index and Abbe number of the medium between the i-th surface and the (i + 1) -th surface, respectively.

  The spherical surface has a shape represented by the following formula.

  A rotationally asymmetric aspheric surface (free curved surface) is a shape represented by the following expression.

z = C04x ² + C06y ²
+ C08x ² y + C10y ³
+ C11x ⁴ + C13x ² y ² + C15y ⁴
+ C17x ⁴ y + C19x ² y ³ + C21y ⁵
+ C22x ⁶ + C24x ⁴ y ² + C26x ² y ⁴ + C28y ⁶
+ C30x ⁶ y + C32x ⁴ y ³ + C34x ² y ⁵ + C36y ⁷
+ C37x ⁸ + C39x ⁶ y ² + C41x ⁴ y ⁴ + C43x ² y ⁶ + C45y ⁸
Since the above free-form surface formula includes only even-order terms with respect to x, the curved surface defined by this formula has a plane-symmetric shape with the yz plane as the plane of symmetry.

  1 and 8 are side sectional views of the projection optical system P, the second plane reflecting surface MR, and the screen SC in the rear projector that is Embodiment 1 of the present invention. FIG. 2 is an enlarged view of the lower projection optical system P, and FIG. 3 is a bird's eye view of the lower projection optical system P. In FIG. 3, LC indicates a spatial light modulation element provided for each of RGB colors. LV color-separates the light from the light source and the illumination optical system that illuminates the spatial light modulation element LC, and the R, G, and B lights from the RGB spatial light modulation element LC. A color separation / synthesis optical system PZ is shown.

  Although it does not specifically limit as a light source, In the present Example, the high pressure mercury lamp is used. White light from the light source enters an integrated illumination optical system including a polarization conversion element, a fly-eye lens, and a condenser lens, and then enters a color separation / synthesis optical system including a dichroic prism, a filter, a polarization beam splitter, and the like. The color separation / synthesis optical system PZ divides white light into R light, G light, and B light, and illuminates a spatial light modulation element LC provided for each color.

  As the spatial light modulator LC, a transmissive or reflective liquid crystal panel, a digital micromirror device (DMD), or the like can be used. In this embodiment, although not shown in detail, a reflective liquid crystal panel having an aspect ratio of 16: 9, a pixel count of full HD (1920 × 1080), and a diagonal size of 0.7 inch (17.78 mm) is used for RGB. Three are used.

  As the light source, an LED (light emitting diode) may be used, or a semiconductor laser or a solid-state laser may be used. What is necessary is just to comprise an illumination optical system according to the characteristic of a light source.

  The R light, G light, and B light emitted from the three spatial light modulators LC are combined by the color separation / synthesis optical system PZ to be color image light, and are incident on the first optical system C. The color image light passes through the aperture stop ST, is reflected by the first plane reflecting surface MU, and its optical path is bent by 90 degrees and guided to the second optical system R. The second optical system R is composed of four curved reflecting surfaces S1 to S4. If the angle of the first plane reflecting surface MU with respect to the incident optical axis is shifted from 45 degrees, interference between the optical unit from the light source to the first optical system C and the incident light on the screen SC or the screen SC can be avoided. it can.

  6 and 7 show a state in which the lower part of the casing B is viewed from the upper side. LP is a light source, and IU is an illumination optical system. The first planar reflection surface MU is disposed with an inclination of 45 degrees with respect to the optical axis. Optical units from the light source LP to the first optical system C are arranged in parallel to the screen SC, and interfere with light rays projected from the second planar reflecting surface MR to the lower end of the screen SC in the region g. is doing.

  On the other hand, in FIG. 7, the angle with respect to the incident optical axis of the first planar reflecting surface MU is shifted from 45 degrees so that the reflection angle becomes an acute angle smaller than 90 degrees. As a result, the reference axis portion of the optical unit from the light source LP to the first optical system C can be tilted (non-parallel) with respect to the screen SC, and interference as described above can be avoided. it can.

  The optical system LV and the first optical system C are shown in FIG. The first optical system C alone is an imaging optical system as shown in FIG.

  In the aperture stop ST, the aperture aperture diameter in the second optical system R in which the reference axis ray (central principal ray) AX is deflected, that is, the aperture aperture diameter in the Y direction is made smaller than the aperture aperture diameter in the X direction. In the system, it is desirable that the F number in the Y direction is set larger than that in the X direction in advance. Thereby, since the light beam diameter in the second optical system R can be reduced, the degree of freedom in arranging the curved reflecting surface is increased. In addition, the deflection angle of the light beam by the curved reflecting surface can be reduced, and the degree of freedom for controlling the asymmetric aberration generated by the curved reflection with the angle is improved, so that the optical design becomes easy.

  The color image light incident on the second optical system R is reflected (deflected) in this order by the curved reflecting surfaces S1, S2, S3, S4 having a rotationally asymmetric curvature. The color image light reflected by the final curved reflecting surface S4 travels to the second planar reflecting surface MR through the space between the first planar reflecting surface MU and the curved reflecting surface S3. The color image light reflected by the second plane reflecting surface MR is projected obliquely with respect to the screen SC.

  In the first cross section shown in FIG. 1, the principal ray having the angle of view that forms an image at the upper and lower ends of the screen SC is between the final curved reflecting surface S4 and the second planar reflecting surface MR of the second optical system R. The exit pupil is formed by crossing.

  In this embodiment, the aspect ratio of the display image is 16: 9, and the diagonal size is 64 inches (1625.6 mm). The screen SC only needs to have a size larger than this. Further, the screen SC may diffuse light incident obliquely on the viewer side (front side of the screen SC) with an appropriate viewing angle.

The arrangement and shape data (numerical example) of each optical surface in the rear projector of this embodiment shown in FIGS. 1 and 8 are shown below. Table 1 shows the values of θ _S , θ _R , θ _P , L _P , L _R , L ₁ , L ₂ , _SY and the thin ratio. Further, Table 2 shows values of the conditions (1) to (5), (8), and (9).

  Further, lateral aberration diagrams at 20 points on the screen SC shown in FIG. 9 are shown in FIGS. 10, 11, 12, and 13. FIG.

  In this embodiment, as shown in Table 2, since the conditions (1) to (5) are satisfied, the depths of the lower projection optical system P and the second plane reflecting surface MR are both thin, and A rear projector that can project a high-definition image with a low height is realized. Moreover, this example also satisfies the conditions (8) and (9).

(Numerical example)
Panel side NA: X0.1667 Y0.1136

surface
Xi
Yi
Zi
Di
θxi
curvature radius
Ndi
νdi


1
0
0
0
9.00
0
-304.09
496999
815459
Refractive surface C

2
0
0
9.00
1.00
0
-39.07
air

Refractive surface C

Three
0
0
10.00
10.00
0
323.26
496999
815459
Refractive surface C

Four
0
0
20.00
3.00
0
-36.41
834000
371605
Refractive surface C

Five
0
0
23.00
37.87
0
-174.88
air

Refractive surface C

6
0
0
60.87
6.50
0
-259.75
834000
371605
Refractive surface C

7
0
0
67.37
15.13
0
-80.65
air

Refractive surface C

8
0
0
82.50
127.00
0

air

Aperture ST

9
0
0
209.50
135.00
45.00
Plane
air

Flat reflective surface MU

Ten
135.00
0
209.50
140.00
18.00
Aspherical
air

Reflective surface S1

11
21.74
-82.29
209.50
150.00
13.00
Aspherical
air

Reflective surface S2

12
92.16
50.15
209.50
130.00
20.00
Aspherical
air

Reflective surface S3

13
119.19
-77.01
209.50
863.00
8.50
Aspherical
air

Reflective surface S4

14
-299.20
677.79
209.50
436.66
9.00
Plane
air

Planar reflective surface MR

15
-215.89
249.15
209.50
3.85
72.00



Screen SC


10 aspherical surfaces (reflection surface S1)

C04
7.0007E-04

C06
3.8083E-04

C08
-2.7085E-06

C10
1.8546E-07

C11
-2.0973E-08

C13
3.1529E-09

C15
5.3600E-08

C17
1.6456E-10

C19
-1.0245E-10

C21
7.8337E-12

C22
-2.5315E-12

C24
-2.8096E-11

C26
-2.3716E-11

C28
-7.2718E-11

C30
-1.5024E-13

C32
-4.4073E-14

C34
-2.3149E-13

C36
1.5775E-13

C37
1.9320E-15

C39
1.4794E-14

C41
5.3462E-15

C43
3.1291E-14

C45
5.0419E-14





11 surfaces (reflection surface S2)

C04
7.5228E-04

C06
-6.0291E-04

C08
-2.1159E-05

C10
-3.9490E-06

C11
-2.3061E-07

C13
2.6090E-08

C15
2.4452E-07

C17
2.6982E-09

C19
-2.0818E-09

C21
-1.5041E-09

C22
-5.5821E-12

C24
-1.0664E-10

C26
-1.2564E-10

C28
-2.1706E-10

C30
-2.0082E-12

C32
-2.8834E-13

C34
-4.6452E-13

C36
2.2888E-12

C37
2.4086E-14

C39
7.4776E-14

C41
1.8692E-14

C43
1.2539E-13

C45
1.2927E-13





12 surfaces (reflective surface S3)

C04
4.0892E-03

C06
1.5421E-04

C08
-3.3242E-05

C10
-5.9572E-05

C11
-5.2510E-09

C13
4.4297E-08

C15
-7.8726E-07

C17
6.9771E-10

C19
-1.5565E-09

C21
2.3227E-08

C22
-8.9881E-12

C24
-1.6138E-11

C26
9.9973E-12

C28
1.3392E-09

C30
-3.8894E-14

C32
5.6278E-13

C34
1.4991E-12

C36
-8.2264E-11

C37
2.9646E-15

C39
6.1000E-15

C41
1.9566E-14

C43
8.7015E-14

C45
-3.6167E-12





13 surfaces (reflective surface S4)

C04
-5.1563E-04

C06
-1.5492E-03

C08
1.9754E-06

C10
-2.4301E-06

C11
1.7541E-07

C13
-3.5452E-08

C15
3.6585E-08

C17
-1.2226E-09

C19
-6.2377E-10

C21
-3.6135E-10

C22
-5.8501E-11

C24
-5.4548E-13

C26
3.0524E-11

C28
-1.7003E-11

C30
2.7068E-13

C32
5.9939E-14

C34
-2.1971E-13

C36
5.5060E-13

C37
7.1861E-15

C39
4.6524E-15

C41
-1.4956E-15

C43
-1.6408E-15

C45
-4.6015E-15

  FIG. 14 shows a side sectional view of the projection optical system P, the second plane reflecting surface MR, and the screen SC in the rear projector that is Embodiment 2 of the present invention. Each symbol in the figure indicates the same component as in the first embodiment. In FIG. 14, the first optical system C and the second optical system R of the lower projection optical system P are shown in the same cross section by developing reflection on the first planar reflection surface MU. Actually, the first optical system C and the second optical system R are arranged as shown in FIG. 15 by bending the optical path at the first planar reflection surface MU.

  The color image light emitted from the first optical system C is reflected by the first planar reflecting surface MU, and its optical path is bent by 90 degrees and guided to the second optical system R. The second optical system R is reflected by one concave aspherical reflecting surface (final curved reflecting surface), reflected by the second planar reflecting surface MR, and obliquely projected onto the screen SC.

  In the first cross section shown in FIG. 14, the principal ray having the angle of view that forms an image at the upper and lower ends of the screen SC is between the concave aspherical reflecting surface and the second planar reflecting surface MR of the second optical system R. The exit pupil is formed by crossing.

In this embodiment, the arrangement and shape data of the optical surface are omitted, but the values of θ _S , θ _R , θ _P , L _P , L _R , L ₁ , L ₂ , _SY and the thin ratio in this embodiment are omitted. Is shown in Table 1. As shown in Table 2, this example also satisfies the conditions (1) to (5), (8), and (9).

  FIG. 16 shows a side sectional view of the projection optical system P, the second plane reflecting surface MR, and the screen SC in the rear projector that is Embodiment 3 of the present invention. Each symbol in the figure indicates the same component as in the first embodiment. In FIG. 16, the first optical system C and the second optical system R of the lower projection optical system P are shown in the same cross section by developing reflection on the first planar reflection surface MU. Actually, the first optical system C and the second optical system R are arranged as shown in FIG. 17 by bending the optical path at the first planar reflecting surface MU.

  The color image light emitted from the first optical system C is reflected by the first planar reflecting surface MU, and its optical path is bent by 90 degrees and guided to the second optical system R. The second optical system R is reflected by one convex aspherical reflecting surface (final curved reflecting surface), reflected by the second planar reflecting surface MR, and projected obliquely on the screen SC.

  In the first cross section shown in FIG. 17, the principal ray having the angle of view that forms an image at the upper and lower ends of the screen SC is between the concave aspherical reflecting surface of the second optical system R and the second planar reflecting surface MR. The exit pupil is formed by crossing.

In this embodiment, the arrangement and shape data of the optical surface are omitted, but the values of θ _S , θ _R , θ _P , L _P , L _R , L ₁ , L ₂ , _SY and the thin ratio in this embodiment are omitted. Is shown in Table 1. As shown in Table 2, this example also satisfies the conditions (1) to (5), (8), and (9).

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment when the present invention is implemented.

1 is a side sectional view showing a configuration of a rear projector that is Embodiment 1 of the present invention. 2 is an enlarged view of a lower projection optical system in Embodiment 1. FIG. 2 is a bird's-eye view of a lower projection optical system in Embodiment 1. FIG. 1 is a cross-sectional view of a first optical system in Embodiment 1. FIG. FIG. 3 is a diagram showing that the first optical system in Embodiment 1 is an imaging optical system. The figure which looked at the housing | casing lower part of the comparative example of Example 1 from the top. The figure which looked at the housing lower part of Example 1 from the top. FIG. 3 is a side cross-sectional view illustrating a schematic configuration of the rear projector according to the first embodiment. FIG. 3 is a diagram illustrating evaluation positions of lateral aberration in Example 1. FIG. 3 is a lateral aberration diagram in Example 1. FIG. 3 is a lateral aberration diagram in Example 1. FIG. 3 is a lateral aberration diagram in Example 1. FIG. 3 is a lateral aberration diagram in Example 1. FIG. 6 is a side cross-sectional view (partially developed view) illustrating a schematic configuration of a rear projector that is Embodiment 2 of the present invention. FIG. 6 is a side cross-sectional view illustrating a schematic configuration of a rear projector according to a second embodiment. FIG. 6 is a side cross-sectional view (partially developed view) illustrating a schematic configuration of a rear projector that is Embodiment 3 of the present invention. FIG. 6 is a side cross-sectional view illustrating a schematic configuration of a rear projector according to a third embodiment. Theta _S in the embodiment, θ _R, θ _P, shows the _{L P, L R, L 1} , L 2, S Y. The figure for demonstrating the definition in an Example. The figure which shows the case where (theta) _P is large. The figure which shows the case where (theta) _P is small in an Example. The figure for demonstrating a coordinate system.

Explanation of symbols

B Case P Lower projection optical system C First optical system R Second optical system LC Spatial light modulation element LV Light source, illumination optical system, and color separation / synthesis optical system MU First planar reflection surface MR Second planar reflection SC screen

Claims (11)

Has a screen on the front of the housing,
Inside the housing,
A spatial light modulator for modulating light;
A projection optical system for projecting light from the spatial light modulator on the back of the screen;
A path along which a central chief ray passing through the center of the spatial light modulation element and the center of the stop included in the projection optical system follows as a reference axis, and the final reference axis portion incident on the screen of the reference axis and the normal of the screen When the cross section including the first cross section,
The projection optical system is disposed in a region on one end side in the direction along the screen in the first cross section in the inside of the housing,
A first optical system composed of at least one lens on which light from the spatial light modulation element is incident;
A first reflecting surface for reflecting light from the first optical system;
A second optical system configured by at least one curved reflecting surface and receiving light from the first reflecting surface;
And the light from the second optical system is disposed in the inside of the housing in a region on the other end side in the direction along the screen in the first cross section and inclined with respect to the normal line of the screen. Having a second reflecting surface for obliquely incident on the screen,
A rear projector that satisfies the following conditions.

5 ° ≦ θ _S ≦ 25 °
0.2 ≦ L ₁ / L ₂ ≦ 0.9
0.8 ≦ L _P / S _Y ≦ 1.2
0.45 ≦ L _R / S _Y ≦ 0.6
−0.8 L _P / L _R ≦ 1-2 sin θ _R / tan θ _S ≦ 0.5 L _P / _LR

However, in the first cross section,
θ _S is an absolute value of an angle formed by the final reference axis portion incident on the screen from the second reflecting surface and the screen,
θ _R is the absolute value of the tilt angle of the second reflecting surface with respect to the normal of the screen,
L ₁ is a curved reflecting surface arranged at a position farthest from the screen among the at least one curved reflecting surface in the second optical system from the intersection of the first reflecting surface and the reference axis, and the reference. The distance along the normal of the screen to the intersection with the axis,
L ₂ is the length along the normal of the screen of the second reflective surface;
L _P is the reference axis from the last curved reflection surface closest to the second reflection surface along the reference axis to the second reflection surface among the at least one curved reflection surface in the second optical system. The distance along
_LR is a distance along the final reference axis portion from the second reflecting surface to the screen;
_SY is the length of the screen.   The first optical system includes a reference axis portion incident on the second reflecting surface from the final curved reflecting surface in the second optical system in a direction in which a normal line of the screen in the first cross section extends. The rear projector according to claim 1, wherein the rear projector is disposed between the extension line and the screen.   The reference axis portion of the reference axis that is closer to the spatial light modulator than the first reflecting surface is non-parallel to the first cross section, and is closer to the screen than the first reflecting surface. The rear projector according to claim 1, wherein a reference axis portion is included in the first cross section.   4. The reference axis according to claim 1, wherein a reference axis portion in the first optical system among the reference axes is inclined at an angle of 20 ° or less with respect to the screen. 5. Rear projector.   In the first cross section, a principal ray having an angle of view that forms an image on one end of the screen and a principal ray having an angle of view that forms an image on the other end of the screen are reflected on the final curved reflection surface and the second reflection. The rear projector according to claim 1, wherein the rear projector intersects with a surface. 6. The rear projector according to claim 5, wherein, in the first cross section, the two principal rays intersect at a region within L _P / 3 from the final curved reflecting surface.   2. The rear projector according to claim 1, wherein, in the first cross section, a length of the final curved reflecting surface is smaller than 2/3 of a length of the second reflecting surface.   The first curved surface in the first cross section is an optical surface located farthest from the second reflecting surface among a plurality of optical surfaces included in the projection optical system. The rear projector according to any one of 1 to 7. The rear projector according to claim 1, wherein the following condition is satisfied.
5 ° ≦ θ _S ≦ 20 °
−0.2 L _P / L _R ≦ 1-2 sin θ _R / tan θ _S ≦ 0.2 L _P / _LR The rear projector according to claim 1, wherein the following condition is satisfied.
10 ° ≦ θ _P ≦ 40 °
In the first cross section, θ _P is an absolute value of an angle formed by a reference axis portion incident on the final curved reflection surface and a reference axis portion emitted from the final curved reflection surface of the reference axis. . The rear projector according to claim 1, wherein the following condition is satisfied.
0 ° ≦ | θ _S −2θ _R | ≦ 7 °