JP2015031912A - Projection optical system and image projection apparatus - Google Patents

Abstract

A projection optical system and an image projection apparatus capable of projecting onto a curved screen with good projection performance at a short projection distance are provided. A projection optical system (300) is provided with a first optical system (301) having refraction action and a second optical system (302) having reflection action in order from the side of an image display device (500). At least two free-form curved lenses 12 and 13 are provided on the second optical system 302 side, and the second optical system 302 is provided with a free-form curved mirror 14 having a concave reflecting surface on the first optical system 301 side. The system 301 forms an intermediate image conjugate with the image displayed on the image display element 500 between the first optical system 301 and the second optical system 302, and the second optical system 302 The intermediate image is magnified and projected onto a curved screen 400 having a concave curved surface on the optical system 302 side. [Selection drawing] Fig. 5

Description

  The present invention relates to a projection optical system and an image projection apparatus.

Some projection optical systems that project an image at a short projection distance include a refractive lens and a reflection mirror. Advantages of a short projection distance include a reduction in the installation space of the image projection apparatus, projection light can be hard to enter the viewer's eyes, and the shadow of the presenter is not reflected in the projection image. It is done.
Patent Documents 1 to 3 disclose a projection optical system that projects an image at a short projection distance. Specifically, Patent Document 1 discloses an image projection apparatus including a lens group including a plurality of lenses, first and second lenses that are free-form surface lenses, and a free-form surface mirror in order from the image display element side. Is disclosed.
Patent Document 2 discloses a projection optical system and an image projection apparatus that include a rotationally symmetric lens group, a free-form surface lens group, and a free-form surface mirror in this order from the image display element side.
Patent Document 3 discloses an image projection apparatus including a projection optical system, a correction optical system, and a curved screen decentered with respect to the projection optical system. Patent Document 3 discloses that the correction optical system includes a reflecting surface formed of an extended rotation free-form surface.

JP 2011-253024 A JP 2013-044993 A JP 2012-008358 A

  However, since the image projection apparatuses described in Patent Document 1 and Patent Document 2 are intended to project an image onto a flat screen, when the image is projected onto a curved screen, the projection performance is extremely deteriorated. There is a problem. In addition, since the reflection mirrors included in the image projection apparatuses described in Patent Documents 1 to 3 are all convex mirrors, the reflection mirror is disposed on the screen side that is offset with respect to the projection optical system. Therefore, there is a problem that the reflection mirror protrudes to the upper part of the image projection apparatus, which obstructs visual recognition.

  The projection optical system according to the first embodiment includes, in order from the image display element side, a first optical system having a refractive action and a second optical system having a reflective action. The first optical system includes at least two free-form surface lenses on the second optical system side. The second optical system includes a free-form surface mirror having a concave reflecting surface on the first optical system side. The first optical system forms an intermediate image conjugate with the image displayed on the image display element between the first optical system and the second optical system. The second optical system projects the intermediate image on a curved screen having a concave curved surface on the second optical system side.

  The image projection apparatus according to the second embodiment includes the projection optical system according to the first embodiment.

  According to the present invention, it is possible to provide a projection optical system and an image projection apparatus that can project onto a curved screen with a good projection performance at a short projection distance.

It is a figure which shows the image projection apparatus which concerns on Embodiment 1 of this invention. It is a figure which shows the image projection apparatus which concerns on Embodiment 1 of this invention. It is a perspective view which shows the projection optical system and curved surface screen which concern on Embodiment 1 of this invention. It is side surface sectional drawing which shows the projection optical system and curved screen which concern on Embodiment 1 of this invention. It is an upper surface sectional view showing the projection optical system and the curved screen according to the first embodiment of the present invention. It is side surface sectional drawing which shows the projection optical system which concerns on Embodiment 1 of this invention. It is a table | surface which shows the lens data of the projection optical system which concerns on Embodiment 1 of this invention. It is a table | surface which shows the surface shape data of the 11th lens which concerns on Embodiment 1 of this invention. It is a table | surface which shows the surface shape data of the 12th lens based on Embodiment 1 of this invention, a 13th lens, and a free-form surface mirror. It is a perspective view explaining the sag amount of the 13th lens which concerns on Embodiment 1 of this invention. It is a figure which shows the distortion aberration of the projection optical system which concerns on Embodiment 1 of this invention. It is a figure explaining the coordinate on the curved-surface screen which concerns on Embodiment 1 of this invention. It is a figure which shows the spot diagram of the projection optical system which concerns on Embodiment 1 of this invention. It is side surface sectional drawing which shows the projection optical system and curved surface screen which concern on Embodiment 2 of this invention. It is upper surface sectional drawing which shows the projection optical system and curved surface screen which concern on Embodiment 2 of this invention. It is side surface sectional drawing which shows the projection optical system which concerns on Embodiment 2 of this invention. It is a table | surface which shows the lens data of the projection optical system which concerns on Embodiment 2 of this invention. It is a table | surface which shows the surface shape data of the 11th lens which concerns on Embodiment 2 of this invention. It is a table | surface which shows the surface shape data of the 12th lens based on Embodiment 2 of this invention, a 13th lens, and a free-form surface mirror. It is a figure which shows the distortion aberration of the projection optical system which concerns on Embodiment 2 of this invention. It is a figure explaining the coordinate on the curved-surface screen which concerns on Embodiment 2 of this invention. It is a figure which shows the spot diagram of the projection optical system which concerns on Embodiment 2 of this invention. It is a figure which shows the distortion aberration at the time of projecting an image on a curved-surface screen using the conventional projection optical system.

Embodiments to which the present invention can be applied will be described below. In addition, this invention is not limited to the following embodiment.
Embodiment 1 FIG.
FIG. 1 shows an image projection apparatus according to Embodiment 1 of the present invention. The image projection apparatus shown in FIG. 1 is a single-plate DLP projector 100 that uses a DMD (Digital Micro-Mirror Device) (registered trademark) panel as an image display element. For convenience of explanation, only the optical elements of the image projection apparatus are shown in FIG. 1, and other elements are omitted. As shown in FIG. 1, a single-plate DLP projector 100 includes a DMD panel 101 (image display element), a TIR prism 102, a projection optical system 103, and the like. A light beam emitted from a light source (not shown) is refracted and reflected by the TIR prism 102 and enters the DMD panel 101. The light beam emitted from the DMD panel 101 passes through the TIR prism 102 and enters the projection optical system 103. The projection optical system 103 projects the incident light beam onto a curved screen (not shown). In the single-plate DLP projector 100, the light emitted from the light source is incident on the prism 102 as R (Red), G (Green), and B (Blue) light beams alternately in a time division manner.

  FIG. 2 shows another example of the image projection apparatus according to Embodiment 1 of the present invention. The image projection apparatus shown in FIG. 2 is a three-plate liquid crystal projector 200 using a liquid crystal panel as an image element. For convenience of explanation, only optical elements of the image projection apparatus are shown in FIG. 2 and other elements are omitted. As shown in FIG. 2, the three-plate liquid crystal projector 200 includes two dichroic mirrors 201, three reflection mirrors 202, a liquid crystal panel 203 for R light, a liquid crystal panel 204 for G light, a liquid crystal panel 205 for B light, a dichroic. A prism 206, a projection optical system 207, and the like are provided. Light rays emitted from a light source (not shown) are reflected by the dichroic mirror 201 and the reflection mirror 202 and enter the R light liquid crystal panel 203, the G light liquid crystal panel 204, and the B light liquid crystal panel 205, respectively. . Light beams emitted from the R light liquid crystal panel 203, the G light liquid crystal panel 204, and the B light liquid crystal panel 205 are transmitted through and reflected by the dichroic prism 206 and enter the projection optical system 207. The projection optical system 207 projects the incident light beam onto a curved screen (not shown).

  The image projection apparatus according to the present invention may be any of the single-plate DLP projector 100 and the three-plate liquid crystal projector 200 described above. That is, the projection optical system according to the present invention may be any of the above-described projection optical system 103 and projection optical system 207. Therefore, hereinafter, for the sake of explanation, the projection optical system 103 and the projection optical system 207 will be simply referred to as the projection optical system 300.

3, 4A, and 4B show the projection optical system 300 and the curved screen 400 according to Embodiment 1 of the present invention. In FIG. 3, FIG. 4A, and FIG. 4B, only the chief ray which permeate | transmits the projection optical system 300 is shown.
FIG. 3 is a perspective view showing the projection optical system 300 and the curved screen 400. In FIG. 3, the X-axis direction is the width direction of the curved screen 400, the Y-axis is the height direction of the curved screen 400, and the Z-axis direction is the depth direction of the curved screen 400. Further, the Z-axis direction coincides with the direction of the optical axis of the projection optical system 300.
4A is a side sectional view showing the projection optical system 300 and the curved screen 400. FIG. In other words, FIG. 4A is a cross-sectional view of the projection optical system 300 and the curved screen 400 as seen from the X-axis direction.
FIG. 4B is a top sectional view showing the projection optical system 300 and the curved screen 400. In other words, FIG. 4B is a cross-sectional view of the projection optical system 300 and the curved screen 400 as seen from the Y-axis direction.
As shown in FIGS. 3, 4A, and 4B, the curved screen 400 has a curvature only in the width direction (X-axis direction) of the curved screen 400. In other words, the curvature of the curved screen 400 is not zero only in the width direction (X-axis direction) of the curved screen 400.

FIG. 5 shows a projection optical system 300 according to Embodiment 1 of the present invention. In FIG. 5, only the chief rays that pass through the projection optical system 300 are shown. FIG. 5 is a cross-sectional view of the projection optical system 300 as viewed from the X-axis direction. In FIG. 5, the image display element 500 may be any of the above-described DMD panel 101, liquid crystal panel 203 for R light, liquid crystal panel 204 for G light, and liquid crystal panel 205 for B light. Similarly, the prism 600 may be any of the TIR prism 102 and the dichroic prism 206 described above.
As shown in FIG. 5, the projection optical system 300 includes, in order from the image display element 500 side, a first optical system 301 having a refractive action and a second optical system 302 having a reflecting action.

The first optical system 301 includes 13 refractive lenses 1 to 13. Specifically, the first optical system 301 includes a first lens 1, a second lens 2, a third lens 3,..., A twelfth lens 12, and a thirteenth lens 13 in order from the image display element 500 side. . The first lens 10 to the tenth lens 10 are spherical lenses having a refractive action. The eleventh lens 11 is an axisymmetric aspheric lens having a refractive action. The twelfth lens 12 and the thirteenth lens 13 are free-form surface lenses. That is, the first optical system 301 includes at least two free-form surface lenses 12 and 13 on the second optical system 302 side.
The second optical system 302 includes the free-form surface mirror 14 having a concave reflecting surface on the first optical system 301 side.
Further, the first optical system 301 includes a diaphragm 15 between the sixth lens 6 and the seventh lens 7.
The free-form surface means an aspheric surface formed in a non-rotational symmetry with respect to the optical axis of the first optical system 301.

  The first optical system 301 forms an intermediate image conjugate with the image displayed on the image display element 500 between the first optical system 301 and the second optical system 302. In FIG. 5, the intermediate image is indicated by a broken line. Further, the second optical system 302 enlarges and projects the intermediate image onto the curved screen 400 having a concave curved shape on the second optical system 302 side.

The projection optical system 300 according to Embodiment 1 of the present invention has an F number (F value) of 2.0 and a maximum object height of 11.5 mm. Further, the curvature radius Rx in the X-axis direction of the curved screen 400 is 6000 mm, and the curvature radius Ry in the Y-axis direction is infinite. The projection distance is 420 mm. In other words, the distance between the free-form curved mirror 14 and the curved screen 400 in the Z-axis direction is 420 mm. The maximum object height is a distance from the center to the corner end of the image display element with the optical axis of the optical system as the center.
FIG. 6 is a table showing lens data of the projection optical system 300 according to Embodiment 1 of the present invention. In the table of FIG. 6, the surface number of the object surface (the surface on which the image of the image display element 500 is displayed) is set to 0. The surface number of the image surface (the surface on which the projected image of the curved screen 400 is displayed) is 32. The surface number of the diaphragm 15 is 16. In the table of FIG. 6, “CG” means the cover glass of the image display element 500, and “P1” means the prism 600. In the table of FIG. 6, “L1” to “L13” mean the first lens 13 to the thirteenth lens 13, respectively. In the table of FIG. 6, “M1” means the free-form surface mirror 14. In the table of FIG. 6, “* 1” means that the surface shape of the eleventh lens 11 is defined by the following expression (1), and “* 2” indicates the twelfth lens 12 and the thirteenth lens. This means that the surface shapes of the lens 13 and the free-form surface mirror 14 are defined by the following equation (2).

In equation (1), Z is the sag amount, c is the curvature, k is the conic constant, AR1, AR2,..., AR30 are the first order, second order,. This is the height of the first optical system 301 from the optical axis.
In equation (2), Z is the sag amount, c is the curvature, k is the conic constant, r is the height from the optical axis of the first optical system 301, and C _j is the coefficient of the xy polynomial. Further, a relationship represented by the following expression (3) is established between m, n, and j in the expression (2).

  FIG. 7 is a table showing surface shape data of the eleventh lens 11. As shown in FIG. 7, both lens surfaces of the eleventh lens 11 have an aspherical shape formed in rotational symmetry with respect to the optical axis of the first optical system 301. Note that aspherical coefficients not shown in the table of FIG. 7 are zero.

FIG. 8 is a table showing surface shape data of the twelfth lens 12, the thirteenth lens 13, and the free-form surface mirror. Specifically, the table of FIG. 8 shows the value of each parameter used in equation (2). As shown in FIG. 8, the R1 surface (lens surface on the image display element 500 side) and R2 surface (lens surface on the second optical system 302 side) of the twelfth lens 12, the R1 surface and R2 surface of the thirteenth lens 13, The reflecting surface of the free-form surface mirror 14 has a free-form surface shape.
In particular, the R1 and R2 surfaces of the twelfth lens 12 and the R1 and R2 surfaces of the thirteenth lens 13 are perpendicular to the X axis (the width direction of the curved screen 400) and have the optical axis of the first optical system. The shape is symmetric with respect to the plane including the plane but is perpendicular to the Y axis (the height direction of the curved screen 400) and asymmetric with respect to the plane including the optical axis of the first optical system.

Further, the R1 surface of the thirteenth lens 13 defined by the parameters shown in the equations (2), (3) and the table of FIG. 8 satisfies the following equation (4). Specifically, SL1 / SU1 is 2.05 on the R1 surface of the thirteenth lens 13.
1 <SL1 / SU1 <2.2 (4)
In the equation (4), SL1 is a sag amount at coordinates in the effective ray range through which the principal ray emitted from the corner portion closest to the optical axis of the first optical system 301 passes within the display area of the image display element 500. In the equation (4), SU1 is a sag amount at coordinates in the effective ray range through which the principal ray emitted from the corner portion farthest from the optical axis of the first optical system 301 passes within the display area of the image display element 500. is there.

  SL1 and SU1 will be described with reference to FIG. FIG. 9 is a perspective view schematically showing the thirteenth lens. In the image projection apparatus according to the first embodiment, the image display element 500 is located above the optical axis of the first optical system 301 (Y-axis plus direction side). Therefore, the principal ray emitted from the corner closest to the optical axis of the first optical system 301 in the display area of the image display element 500 reaches the upper side of the effective ray range of the thirteenth lens 13. On the other hand, the principal ray emitted from the corner portion farthest from the optical axis of the first optical system 301 within the display area of the image display element 500 reaches the lower side of the effective ray range of the thirteenth lens 13. In FIG. 9, the symmetry plane H is a plane that is perpendicular to the X axis and includes the optical axis of the first optical system 301. The sag amount of the R1 surface or the R2 surface of the thirteenth lens 13 is the optical axis direction (Z of the first optical system 301 from the position where the symmetry plane H and the R1 surface or the R2 surface of the thirteenth lens 13 intersect. Axial displacement).

Further, the R2 surface of the thirteenth lens 13 defined by the parameters shown in the equations (2), (3) and the table of FIG. 8 satisfies the following equation (5). Specifically, SL2 / SU2 is 1.51 on the R2 surface of the thirteenth lens 13.
0.6 <SL2 / SU2 <1.6 (5)
In the equation (5), SL2 is a sag amount in coordinates within the effective ray range through which the principal ray emitted from the corner portion closest to the optical axis of the first optical system 301 passes within the display area of the image display element 500. In the equation (5), SU1 is a sag amount in coordinates in the effective ray range through which the principal ray emitted from the corner portion farthest from the optical axis of the first optical system 301 passes in the display area of the image display element 500. is there.
Since the definitions of SL2 and SU2 are the same as those of SL1 and SU1, the description thereof is omitted.

  The free-form surface mirror 14 is decentered with respect to the optical axis of the first optical system 301. Specifically, it is preferable that the free-form surface mirror 14 is shifted in the Y-axis plus direction with respect to the optical axis of the first optical system 301 and tilted clockwise with respect to the X-axis. The free-form surface mirror 14 according to the first embodiment is shifted by 6.212 mm in the Y-axis plus direction with respect to the optical axis of the first optical system 301 and tilted by 3.7 ° clockwise with respect to the X-axis. Eccentric.

  FIG. 10 shows distortion aberration when the projection optical system 300 according to the first embodiment is used to project a curved screen 400 having a width: height of 16: 9 and a size (diagonal length) of 100 inches. Indicates. Specifically, FIG. 10 shows a grid displayed on the plane when the grid (21 × 21 grid) displayed on the curved screen 400 is projected onto an infinite plane. In FIG. 10, a solid line indicates an ideal lattice, and a broken line indicates a projection of the lattice displayed on the curved screen 400. In FIG. 10, the grating displayed on the curved screen 400 by the projection optical system 300 substantially coincides with an ideal grating on a plane at infinity. In other words, the distortion of the projection optical system 300 according to the first embodiment is sufficiently reduced.

  FIG. 11A shows coordinates on the curved screen 400, and FIG. 11B shows a spot diagram at the coordinates. The spot diagram shown in FIG. 11B is an e-line spot diagram. As shown in FIG. 11B, the spot size at each coordinate is about 1 mm, and when the resolution of the image display element 500 is full HD (1920 × 1080 pixels), the size of one pixel on the curved screen 400 is 1 mm. Therefore, it can be seen that the projection optical system 300 according to the first embodiment can secure sufficient performance.

According to the image projection apparatus and the projection optical system 300 according to the first embodiment of the present invention described above, the first optical system 301 having a refractive action and the second having a reflective action in order from the image display element 500 side. An optical system 302. The first optical system 301 includes at least two free-form surface lenses 12 and 13 on the second optical system 302 side. The second optical system 302 includes the free-form surface mirror 14 having a concave reflecting surface on the first optical system 301 side. The first optical system 301 forms an intermediate image conjugate with the image displayed on the image display element 500 between the first optical system 301 and the second optical system 302. Further, the second optical system 302 enlarges and projects the intermediate image onto the curved screen 400 having a concave curved shape on the second optical system 302 side.
As a result, astigmatism and field curvature generated in the free-form surface mirror 14 can be canceled by the aberration of the intermediate image. Moreover, since the free-form surface mirror 14 has a strong refractive power, the intermediate image can be enlarged and projected at an extremely short projection distance. That is, it is possible to provide the projection optical system 300 and the image projection apparatus that can project on the curved screen 400 with good projection performance with a short projection distance.

  In addition, since the free-form surface mirror 14 has a concave reflecting surface on the first optical system 301 side, the optical components are expanded in the Y-axis minus direction (below the optical axis of the first optical system 301) in the projection optical system 300. The For this reason, the optical component does not protrude above the image projection apparatus, so that it does not interfere with visual recognition.

In the first embodiment, the R1 surface (lens surface on the image display element 500 side) and R2 surface (lens surface on the second optical system 302 side) of the twelfth lens 12, and the R1 surface and R2 surface of the thirteenth lens 13 are used. The reflecting surface of the free-form surface mirror 14 has a free-form surface shape.
As a result, it is possible to project the curved screen 400 with good focusing performance over the entire screen without distortion.

The R1 surface and R2 surface of the twelfth lens 12 and the R1 surface and R2 surface of the thirteenth lens 13 are perpendicular to the X axis (the width direction of the curved screen 400) and have the optical axis of the first optical system. The shape is symmetric with respect to the plane including the plane but is perpendicular to the Y axis (the height direction of the curved screen 400) and asymmetric with respect to the plane including the optical axis of the first optical system.
Thereby, the focusing performance and distortion performance of the entire projection screen can be improved with respect to the curved screen 400 having a curvature only in the width direction (X-axis direction) of the curved screen 400. In addition, by dispersing the aberration correction function of the free-form surface over a total of four lens surfaces of the twelfth lens 12 and the thirteenth lens 13, it is possible to effectively improve the focus performance and distortion performance and to generate on each lens surface. Aberration can be minimized, and sensitivity to manufacturing errors can be reduced.

Further, one lens surface (R1 surface) of the free-form surface lens 13 satisfies the following expression (4).
1 <SL1 / SU1 <2.2 (4)
When SL1 / SU1 is less than or equal to the lower limit of the above-described expression (4), the shape of the lens surface of the free-form surface lens 13 is asymmetric in the X-axis direction within the effective ray range with respect to the optical axis of the first optical system 301. As a result, the effect of correcting the aberration becomes too small, and it becomes difficult to ensure the focusing performance of the entire screen.
On the other hand, when SL1 / SU1 is equal to or greater than the upper limit value of the above-described expression (4), the shape of the lens surface of the free-form surface lens 13 is asymmetric in the X-axis direction within the effective ray range with respect to the optical axis of the first optical system 301. Becomes too large, the inclination angle of the lens surface increases, and the workability and processing accuracy of the free-form surface lens 13 deteriorate. Further, the workability and processing accuracy of the free-form surface lens 13 are deteriorated, so that the focusing performance of the projection optical system 300 is deteriorated.

Further, the other lens surface (R2 surface) of the free-form surface lens 13 satisfies the following expression (5).
0.6 <SL2 / SU2 <1.6 (5)
Thereby, the projection performance of the projection optical system 300 can be further improved.

  The free-form surface mirror 14 is decentered with respect to the optical axis of the first optical system 301. Thereby, the projection optical system 300 can perform image projection without distortion more effectively.

Embodiment 2. FIG.
A projection optical system 300A according to the second embodiment of the present invention will be described with reference to FIGS. 12A, 12B, 13, 14, 14, 15, 16, 17, 18A, and 18B. 12A, 12B, 13, 14, 15, 16, 17, 17, 18A, and 18B are described in FIGS. 4A, 4B, 5, 6, 7, and 8. 10, FIG. 11A, and FIG.
As shown in FIGS. 13, 14, 15, and 16, the projection optical system 300A according to the second embodiment includes a first lens 1A, a second lens 2A,. Since only the configuration of the curved mirror 14A is different from the projection optical system 300 according to the first embodiment, the same components are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 13, the projection optical system 300A includes, in order from the image display element 500 side, a first optical system 301A having a refractive action and a second optical system 302A having a reflective action.

The first optical system 301A includes 13 refractive lenses 1A to 13A. Specifically, the first optical system 301 includes a first lens 1A, a second lens 2A, a third lens 3A,..., A twelfth lens 12A, and a thirteenth lens 13A in order from the image display element 500 side. . The first lens 10A to the 10th lens 10A are spherical lenses having a refractive action. The eleventh lens 11A is an axisymmetric aspheric lens having a refractive action. The twelfth lens 12A and the thirteenth lens 13A are free-form curved lenses. That is, the first optical system 301A includes at least two free-form surface lenses 12A and 13A on the second optical system 302A side.
The second optical system 302A includes a free-form surface mirror 14A having a concave reflecting surface on the first optical system 301A side.
The first optical system 301A includes a diaphragm 15A between the sixth lens 6A and the seventh lens 7A.

  Then, the first optical system 301A forms an intermediate image conjugate with the image displayed on the image display element 500 between the first optical system 301A and the second optical system 302A. In FIG. 13, the intermediate image is indicated by a broken line. The second optical system 302A enlarges and projects the intermediate image on the curved screen 400 having a concave curved surface shape on the second optical system 302A side.

The projection optical system 300A has an F number (F value) of 2.0 and a maximum object height of 11.5 mm. Further, the curvature radius Rx in the X-axis direction of the curved screen 400 is 6000 mm, and the curvature radius Ry in the Y-axis direction is infinite. The projection distance is 420 mm. In other words, the interval in the Z-axis direction between the free curved surface mirror 14A and the curved screen 400 is 420 mm.
16, the R1 surface (lens surface on the image display element 500 side) and R2 surface (lens surface on the second optical system 302A side) of the twelfth lens 12A, the R1 surface and the R2 surface of the thirteenth lens 13A, The reflecting surface of the free curved mirror 14A has a free curved surface shape.
In particular, the R1 and R2 surfaces of the twelfth lens 12A and the R1 and R2 surfaces of the thirteenth lens 13A are perpendicular to the X axis (the width direction of the curved screen 400) and have the optical axis of the first optical system. The shape is symmetric with respect to the plane including the plane but is perpendicular to the Y axis (the height direction of the curved screen 400) and asymmetric with respect to the plane including the optical axis of the first optical system.

Further, the R1 surface of the thirteenth lens 13A defined by the parameters shown in the equations (2), (3) and the table of FIG. 16 satisfies the following equation (4). Specifically, SL1 / SU1 is 1.25 in the R1 surface of the thirteenth lens 13A.
1 <SL1 / SU1 <2.2 (4)

Further, the R2 surface of the thirteenth lens 13A defined by the parameters shown in the equations (2), (3) and the table of FIG. 16 satisfies the following equation (5). Specifically, SL2 / SU2 is 0.73 on the R2 surface of the thirteenth lens 13A.
0.6 <SL2 / SU2 <1.6 (5)

  The free-form surface mirror 14A is decentered with respect to the optical axis of the first optical system 301A. Specifically, it is preferable that the free-form surface mirror 14A is shifted in the Y-axis plus direction with respect to the optical axis of the first optical system 301A and is tilted eccentrically clockwise with respect to the X-axis. The free-form surface mirror 14A according to the second embodiment is shifted by 5.482 mm in the Y-axis plus direction with respect to the optical axis of the first optical system 301A and tilted by 4.2 ° clockwise with respect to the X-axis. Eccentric.

  FIG. 17 shows distortion aberration when projected onto a curved screen 400 having a width: height of 16: 9 and a size (diagonal length) of 100 inches using the projection optical system 300A according to the second embodiment. Indicates. In FIG. 17, the grating displayed on the curved screen 400 by the projection optical system 300A substantially coincides with an ideal grating on a plane at infinity. In other words, the distortion of the projection optical system 400 according to the second embodiment is sufficiently reduced.

  18A shows coordinates on the curved screen 400, and FIG. 18B shows a spot diagram at the coordinates. As shown in FIG. 18B, the size of the spot at each coordinate is about 1 mm. When the resolution of the image display element 500 is full HD (1920 × 1080 pixels), the size of one pixel on the curved screen 400 is 1 mm. Therefore, it can be seen that the projection optical system 300A according to the second embodiment can secure sufficient performance.

  According to the image projection apparatus and the projection optical system 300A according to the second embodiment of the present invention described above, the same effects as those of the image projection apparatus and the projection optical system 300 according to the first embodiment can be obtained.

  FIG. 19 shows a curved screen having a width: height of 16: 9 and a size (diagonal length) of 100 inches using a conventional projection optical system designed for projecting an image onto a flat screen. The distortion aberration when projected on 400 is shown. The description of FIG. 19 is the same as that of FIG. In FIG. 19, the grating (broken line) displayed on the curved screen 400 by the conventional projection optical system is greatly different from the ideal grating (solid line) on the plane at infinity. In other words, the distortion of the conventional projection optical system is quite large, which causes a problem in visual recognition.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

12, 12A 12th lens (free-form surface lens)
13, 13A 13th lens (free-form surface lens)
14, 14A Free-form curved mirror 100 Single plate type DLP projector (image projection device)
200 3-plate liquid crystal projector (image projection device)
103, 207, 300 Projection optical system 301 First optical system 302 Second optical system 400 Curved screen 500 Image display element 600 Prism

Claims (6)

In order from the image display element side, a first optical system having a refractive action and a second optical system having a reflective action are provided,
The first optical system includes at least two free-form surface lenses on the second optical system side,
The second optical system includes a free-form surface mirror having a concave reflecting surface on the first optical system side,
The first optical system forms an intermediate image conjugate with an image displayed on the image display element between the first optical system and the second optical system,
The second optical system is a projection optical system that enlarges and projects the intermediate image onto a curved screen having a concave curved surface shape on the second optical system side. 2. The projection optical system according to claim 1, wherein at least one lens surface of the free-form surface lens closest to the second optical system among the free-form surface lenses satisfies the following expression (4).
1 <SL1 / SU1 <2.2 (4)
In the equation (4), SL1 is a sag amount at coordinates in a light ray effective region through which a principal ray emitted from a corner portion closest to the optical axis of the first optical system passes in the display region of the image display element, and SU1 is , A sag amount at coordinates in the effective ray range through which the principal ray emitted from the corner portion farthest from the optical axis of the first optical system passes within the display area of the image display element.   The projection optical system according to claim 1, wherein the free-form curved mirror is decentered with respect to the optical axis of the first optical system.   The projection optical system according to any one of claims 1 to 3, wherein the curved screen has a curvature only in a width direction of the curved screen. The curved screen has a curvature only in the width direction of the curved screen,
The lens surface of the free-form curved lens is perpendicular to the width direction of the curved screen and symmetric with respect to a plane including the optical axis of the first optical system, but perpendicular to the height direction of the curved screen. The projection optical system according to claim 1, wherein the projection optical system has an asymmetric shape with respect to a plane including the optical axis of the first optical system.   An image projection apparatus provided with the projection optical system as described in any one of Claims 1 thru | or 5.

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