Optical system, stereo optical system, stereo imaging device, imaging device, and image projection device

Abstract

An optical system 10 has a reduction-side reduction conjugate point and an enlargement-side enlargement conjugate point optically conjugate to each other, and comprises a prism having a first transmission surface T1 positioned on the enlargement side, a second transmission surface T2 positioned on the reduction side, and at least three reflection surfaces M1-M4 positioned on an optical path between the first transmission surface T1 and the second transmission surface T2. The at least three reflection surfaces include, in order in the direction from the enlargement side toward the reduction side: the first reflection surface M1 and the second reflection surface M2; and the most-reduction-side reflection surface M4, which is positioned the farthest on the reduction side. An intermediate imaging position having a conjugate relationship with each of the reduction conjugate point CP and the enlargement conjugate point is positioned inside the prism. The first reflection surface M1 is provided within a region to which a plurality of principal rays traveling through the prism are focused.

Description

Optical system, stereo optical system, stereo imaging device, imaging device, and image projection device

[0001] The present disclosure relates to an optical system using a prism, a stereo optical system and a stereo imaging device using such an optical system, and an imaging device and an image projection device using such an optical system.

[0002] Japanese Patent Application Laid-Open No. 2003-122222 discloses an imaging optical system including a prism in which an entrance surface, a reflecting surface, and an exit surface are integrated.

[0003] Japanese Patent Application Laid-Open No. 2000-231060

[0004] The present disclosure provides an optical system that can be manufactured with a small number of parts, is compact and low-profile, and easily achieves a wide angle. The present disclosure also provides a stereo optical system and a stereo imaging device using such an optical system. The present disclosure also provides an imaging device and an image projection device using such an optical system.

[0005] One aspect of the present disclosure is an optical system having a reduction conjugate point on the reduction side and an expansion conjugate point on the magnification side that are optically conjugate to each other, comprising a prism having a first transmitting surface located on the magnification side, a second transmitting surface located on the reduction side, and at least three reflecting surfaces located on the optical path between the first transmitting surface and the second transmitting surface, wherein the prism has a meridional surface through which light rays reflected at the at least three reflecting surfaces pass, and the at least three reflecting surfaces include, in order from the magnification side to the reduction side, a first reflecting surface and a second reflecting surface, and a most reduction-side reflecting surface located on the most reduction side, and an intermediate imaging position that is conjugate to the reduction conjugate point and the magnification conjugate point, respectively, is positioned inside the prism, and the first reflecting surface is provided in a region where multiple chief rays traveling inside the prism converge.

[0006] A stereo optical system according to another aspect of the present disclosure includes a plurality of the optical systems described above, and the second transmitting surfaces of the plurality of optical systems are arranged adjacent to each other.

[0007] A stereo imaging device according to another aspect of the present disclosure includes the stereo optical system described above; and an imaging element having a single imaging surface corresponding to the plurality of second transmitting surfaces, receiving each optical image formed by the plurality of optical systems at a split surface obtained by dividing the imaging surface, and converting the received optical image into an electrical image signal.

[0008] An imaging device according to another aspect of the present disclosure includes the optical system described above and an imaging element that receives an optical image formed by the optical system and converts the optical image into an electrical image signal.

[0009] An image projection device according to another aspect of the present disclosure includes the above optical system and an image forming element that generates an image to be projected onto a screen via the optical system.

[0010] The optical system according to the present disclosure can be manufactured using a small number of parts, can be made smaller and thinner, and can easily achieve a wider angle.

[0011] Fig. 1(A) is an overall schematic diagram showing an example of a stereo optical system according to the present disclosure. Fig. 1(B) is an overall schematic diagram showing an example of a stereo imaging device according to the present disclosure. Fig. 1(B) is a plan view showing an example of a stereo optical system. Fig. 1(B) is a layout diagram showing an optical system according to Example 1. Fig. 1(B) is a lateral aberration diagram of the optical system according to Example 1. Fig. 1(B) is a layout diagram showing an optical system according to Example 2. Fig. 1(B) is a lateral aberration diagram of the optical system according to Example 3. Fig. 9(A) is a schematic perspective view showing several light beams passing through a prism in the optical system according to Example 1. Fig. 9(B) is a schematic perspective view showing the three-dimensional shapes of each transmitting surface and each reflecting surface of the prism. Fig. 10(A) is a plan view showing a first reflecting surface and a surrounding area. Fig. 10(B) is a cross-sectional view thereof. Fig. 10(B) is an explanatory diagram showing the definitions of angles αt1, αm2, and αt2. Fig. 10(B) is a block diagram showing an example of an image projection device according to the present disclosure. Fig. 10(B) is a block diagram showing an example of an imaging device according to the present disclosure.

[0012] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of well-known matters or redundant explanation of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy in the following explanation and to facilitate understanding by those skilled in the art.

[0013] The applicant provides the accompanying drawings and the following description to enable those skilled in the art to fully understand the present disclosure, and does not intend for them to limit the subject matter described in the claims.

[0014] Examples of the optical system according to the present disclosure are described below. The optical system according to the present disclosure can be used in an imaging device that collects light emitted from an object located on an extension of the magnification side and forms an optical image of the object on the imaging surface of an imaging element located on the reduction side.

[0015] In particular, the optical system according to the present disclosure can be used in a stereo optical system and a stereo imaging device for capturing a stereogram that allows an image to be perceived as three-dimensional by utilizing binocular parallax.

[0016] Furthermore, the optical system according to the present disclosure can be used to enlarge and project an original image on an image forming element (e.g., LCD or DMD) located on the reduction side by placing a screen (not shown) on the extension of the enlargement side. However, the projection surface is not limited to a screen. Projection surfaces also include walls, ceilings, floors, and windows inside homes, stores, and vehicles and airplanes used for transportation.

[0017] (Embodiment 1) Fig. 1(A) is an overall schematic diagram showing an example of a stereo optical system according to the present disclosure, and Fig. 1(B) is an overall schematic diagram showing an example of a stereo imaging device according to the present disclosure. Fig. 2 is a plan view showing an example of the stereo optical system. The stereo imaging device 1 includes a stereo optical system 10S including a free-form surface prism and an imaging element 20, and generally has two imaging windows 2L and 2R separated by a distance equal to a base line length that generates binocular parallax.

[0018] The stereo optical system 10S is constructed by integrating two prisms, 10L and 10R, one on each side. The prisms can be integrated by a) gluing two separately manufactured prisms together, or b) molding them together using a mold or the like.

[0019] As an example, the left prism 10L is provided with a first transmitting surface T1L, a first reflecting surface M1L, a second reflecting surface M2L, a third reflecting surface M3L, a fourth reflecting surface M4L, and a second transmitting surface T2L. The right prism 10R is provided with a first transmitting surface T1R, a first reflecting surface M1R, a second reflecting surface M2R, a third reflecting surface M3R, a fourth reflecting surface M4R, and a second transmitting surface T2R. The two second transmitting surfaces T2L and T2R are arranged adjacent to each other, and a single image sensor 20 is provided behind the two second transmitting surfaces T2L and T2R. The single image sensor 20 has a single imaging surface corresponding to the second transmitting surfaces T2L and T2R and receives optical images from the two second transmitting surfaces T2L and T2R at split surfaces that divide the imaging surface. Note that instead of a single image sensor 20, multiple image sensors each having a single imaging surface may be provided.

[0020] Light emitted from the object enters the imaging windows 2L and 2R, passes through the first transmitting surfaces T1L and T1R, is reflected inside the prism, exits from the second transmitting surfaces T2L and T2R, passes through the cover glass CG, and is imaged on the imaging surface of the image sensor 20. This imaging surface corresponds to the reduction conjugate point on the reduction side, and the object corresponds to the magnification conjugate point on the magnification side.

[0021] By integrating the two prisms 10L and 10R, it is possible to reduce the change in the glare angle due to errors when mounting the two optical systems.

[0022] Second Embodiment An optical system according to a second embodiment of the present disclosure will be described below with reference to FIGS.

[0023] 3 is a layout diagram showing an optical system 10 according to Example 1. The optical system 10 corresponds to the prisms 10L and 10R shown in Fig. 2, and has a magnification-side conjugate point (not shown, surface number S1) located on the left side of the drawing, and a reduction-side conjugate point CP (surface number S21) located on the right side of the drawing (for surface numbers S1, S21, etc., see the numerical examples described later).

[0024] The image area on the conjugate plane containing the reduction conjugate point CP is defined as a reduction-side rectangular area having a longitudinal direction (X direction) and a transverse direction (Y direction). The image area on the conjugate plane containing the magnification conjugate point is also defined as an enlargement-side rectangular area having a longitudinal direction and a transverse direction. These reduction-side rectangular area and enlargement-side rectangular area have an optically conjugate imaging relationship. The chief ray travels along an optical axis parallel to the normal direction of this reduction-side rectangular area. This reduction-side rectangular area has an aspect ratio of, for example, 3:2, 4:3, 16:9, 16:10, or 256:135. In the case of an imaging device, this area corresponds to the imaging area of ​​the imaging element. In the case of an image projection device, this area corresponds to the image display area of ​​the image forming element.

[0025] Within the optical system 10, an intermediate image position is located that is conjugate to the reduction conjugate point CP and the magnification conjugate point. This intermediate image position appears as a Y-direction intermediate image IMy in the meridional plane (YZ plane) and as an X-direction intermediate image IMx in the sagittal plane (XY plane). In Figures 3, 5, and 7, only the Y-direction intermediate image IMy in the meridional plane is shown, and the X-direction intermediate image IMx in the sagittal plane is not shown. Furthermore, when the reflecting surface is curved, the reflection position of the light beam located within the meridional plane and the reflection position of the light beam located outside the meridional plane are shifted.

[0026] The optical system 10 includes a prism made of a transparent medium, such as glass or synthetic resin, and a cover glass CG disposed in front of the image sensor 20. The cover glass CG is a flat plate with zero optical power and may be omitted. The prism has a first transmitting surface T1 located on the magnification side, a second transmitting surface T2 located on the reduction side, and four reflecting surfaces: a first reflecting surface M1, a second reflecting surface M2, a third reflecting surface M3, and a fourth reflecting surface M4 located on the optical path between the first transmitting surface T1 and the second transmitting surface T2. The first transmitting surface T1 (surface number S1) has a free-form surface shape with a convex surface facing the magnification side. The first reflecting surface M1 (surface number S4) has a substantially planar free-form surface shape with zero optical power. The second reflecting surface M2 (surface number S8) has a free-form surface shape with a concave surface facing the direction in which light rays incident on the second reflecting surface M2 are reflected. The third reflecting surface M3 (surface number S12) has a free-form surface shape with a concave surface facing in the direction in which light rays incident on the third reflecting surface M3 are reflected. The fourth reflecting surface M4 (surface number S16) has a free-form surface shape with a concave surface facing in the direction in which light rays incident on the fourth reflecting surface M4 are reflected. The second transmitting surface T2 (surface number S18) has a free-form surface shape with a convex surface facing the reduction side. In this embodiment, the fourth reflecting surface M4 corresponds to the most reduction-side reflecting surface.

[0027] FIG. 9A is a schematic perspective view showing several light beams passing through a prism of the optical system 10 according to Example 1. FIG. 9B is a schematic perspective view showing the three-dimensional shapes of each transmitting surface and each reflecting surface of the prism. In the case of an imaging device, light emitted from the magnification-side rectangular region passes through the first transmitting surface T1, is reflected in order by the first to fourth reflecting surfaces M1 to M4, passes through the second transmitting surface T2, passes through the cover glass CG, and is collected at the imaging element 20. In this case, the first reflecting surface M1 is provided in a region where multiple chief rays traveling inside the prism converge, and can function as an aperture stop AS that excludes light traveling in the region surrounding the first reflecting surface M1 and uses only the light reflected by the first reflecting surface M1.

[0028] 4 is a diagram of lateral aberration of the optical system 10 according to Example 1. Each graph corresponds to the normalized coordinates (X, Y) of the first rectangular region at the reduction conjugate point, where (X, Y) = (0, 0), (0, 1), (0, -1), (1, 0), (1, 1), and (1, -1), respectively. The three wavelengths used in the calculation are 656.2725 nm, 587.5618 nm, and 486.1327 nm. These graphs show that a clear light spot is obtained in the reduction-side rectangular region (e.g., the imaging plane), demonstrating excellent optical performance.

[0029] (Example 2) Fig. 5 is a layout diagram showing an optical system 10 according to Example 2. The optical system 10 corresponds to the prisms 10L and 10R shown in Fig. 2, respectively, and has a magnification-side magnification conjugate point (not shown, surface number S1) located in the upper right corner of the drawing, and a reduction-side reduction conjugate point CP (surface number S21) located in the lower right corner of the drawing (for surface numbers S1, S21, etc., see the numerical examples described below). This optical system 10 has a configuration similar to that of Example 1, and therefore, hereinafter, descriptions that overlap with Example 1 may be omitted.

[0030] An intermediate image position that is conjugate to the reduction conjugate point CP and the enlargement conjugate point is located inside the optical system 10. This intermediate image position appears as a Y-direction intermediate image IMy on the meridional plane (YZ plane) and as an X-direction intermediate image IMx on the sagittal plane (XY plane).

[0031] The optical system 10 includes a prism made of a transparent medium and a cover glass CG. The prism has a first transmitting surface T1 located on the magnification side, a second transmitting surface T2 located on the reduction side, and three reflecting surfaces: a first reflecting surface M1, a second reflecting surface M2, and a third reflecting surface M3 located on the optical path between the first transmitting surface T1 and the second transmitting surface T2. The first transmitting surface T1 (surface number S1) has a free-form surface shape with a convex surface facing the magnification side. The first reflecting surface M1 (surface number S4) has a substantially planar free-form surface shape with zero optical power. The second reflecting surface M2 (surface number S8) has a free-form surface shape with a concave surface facing in the direction in which light rays incident on the second reflecting surface M2 are reflected. The third reflecting surface M3 (surface number S12) has a free-form surface shape with a concave surface facing in the direction in which light rays incident on the third reflecting surface M3 are reflected. The second transmitting surface T2 (surface number S14) has a free-form curved surface with a convex surface facing the reduction side. In this embodiment, the third reflecting surface M3 corresponds to the most reduction-side reflecting surface.

[0032] In the case of an imaging device, light emitted from the enlargement-side rectangular region passes through the first transmitting surface T1, is reflected in order by the first to third reflecting surfaces M1 to M3, passes through the second transmitting surface T2, passes through the cover glass CG, and is collected at the imaging element 20. In this case, the first reflecting surface M1 is provided in a region where a plurality of chief rays traveling inside the prism converge, and can function as a stop AS that excludes light traveling into the region surrounding the first reflecting surface M1 and uses only the light reflected by the first reflecting surface M1.

[0033] 6 is a lateral aberration diagram of the optical system 10 according to Example 2. The normalized coordinates and wavelengths in each graph are the same as those in Example 1. These graphs show that a clear light spot is obtained in the reduced-side rectangular region (e.g., the imaging surface), demonstrating excellent optical performance.

[0034] Example 3 Fig. 7 is a layout diagram showing an optical system 10 according to Example 3. The optical system 10 corresponds to the prisms 10L and 10R shown in Fig. 2, respectively, and has a magnification-side conjugate point (not shown, surface number S1) located on the left side of the drawing, and a reduction-side conjugate point CP (surface number S21) located on the right side of the drawing (for surface numbers S1, S21, etc., see the numerical examples described below). This optical system 10 has a configuration similar to that of Example 1, and therefore, hereinafter, descriptions that overlap with Example 1 may be omitted.

[0035] An intermediate image position that is conjugate to the reduction conjugate point CP and the enlargement conjugate point is located inside the optical system 10. This intermediate image position appears as a Y-direction intermediate image IMy on the meridional plane (YZ plane) and as an X-direction intermediate image IMx on the sagittal plane (XY plane).

[0036] The optical system 10 includes a prism made of a transparent medium and a cover glass CG. The prism has a first transmitting surface T1 located on the magnification side, a second transmitting surface T2 located on the reduction side, and four reflecting surfaces: a first reflecting surface M1, a second reflecting surface M2, a third reflecting surface M3, and a fourth reflecting surface M4 located on the optical path between the first transmitting surface T1 and the second transmitting surface T2. The first transmitting surface T1 (surface number S1) has a free-form surface shape with a convex surface facing the magnification side. The first reflecting surface M1 (surface number S4) has a substantially planar free-form surface shape with zero optical power. The second reflecting surface M2 (surface number S8) has a free-form surface shape with a concave surface facing in the direction in which light rays incident on the second reflecting surface M2 are reflected. The third reflecting surface M3 (surface number S12) has a free-form surface shape with a concave surface facing in the direction in which light rays incident on the third reflecting surface M3 are reflected. The fourth reflecting surface M4 (surface number S16) has a free-form shape with a concave surface facing the direction in which light rays incident on the fourth reflecting surface M4 are reflected. The second transmitting surface T2 (surface number S18) has a free-form shape with a convex surface facing the reduction side. In this embodiment, the fourth reflecting surface M4 corresponds to the most reduction-side reflecting surface.

[0037] In the case of an imaging device, light emitted from the enlargement-side rectangular region passes through the first transmitting surface T1, is reflected in order by the first to fourth reflecting surfaces M1 to M4, passes through the second transmitting surface T2, passes through the cover glass CG, and is collected at the imaging element 20. In this case, the first reflecting surface M1 is provided in a region where a plurality of chief rays traveling inside the prism converge, and can function as a stop AS that excludes light traveling into the region surrounding the first reflecting surface M1 and uses only the light reflected by the first reflecting surface M1.

[0038] 8 is a lateral aberration diagram of the optical system 10 according to Example 3. The normalized coordinates and wavelengths of each graph are the same as those in Example 1. These graphs show that a clear light spot is obtained in the reduced-side rectangular region (e.g., the imaging surface), demonstrating excellent optical performance.

[0039] In the optical systems 10 according to Examples 1 to 3, the prism integrates the first transmitting surface T1, the second transmitting surface T2, and the first to fourth reflecting surfaces M1 to M4 (Examples 1 and 3) or the first to third reflecting surfaces M1 to M3 (Example 2), thereby reducing the assembly adjustment between optical components and reducing costs. Furthermore, the optical surface of the prism having power does not have an axis of rotational symmetry, that is, it is formed as a free-form surface with different curvatures in the X-axis and Y-axis perpendicular to the surface normal. Using a free-form surface that can define different curvatures in the X-axis and Y-axis for the optical surface of the prism increases the degree of freedom in correcting distortion well, thereby enabling the optical system to be made more compact.

[0040] Next, conditions that can be satisfied by the optical system according to this embodiment will be described. Note that, although multiple conditions are specified for the optical system according to each example, it is possible to satisfy all of these multiple conditions, or to satisfy individual conditions to obtain the corresponding effects.

[0041] The optical system 10 of this embodiment is an optical system having a reduction conjugate point on the reduction side and an expansion conjugate point on the magnification side, which are optically conjugate to each other, and comprises a prism having a first transmitting surface T1 located on the magnification side, a second transmitting surface T2 located on the reduction side, and at least three reflecting surfaces M1 to M4 located on the optical path between the first transmitting surface T1 and the second transmitting surface T2, the prism having a meridional surface through which light rays reflected by the at least three reflecting surfaces M1 to M4 pass, the at least three reflecting surfaces including, in order from the magnification side to the reduction side, a first reflecting surface M1 and a second reflecting surface M2, and a most reduction-side reflecting surface M3, M4 located on the most reduction side, an intermediate imaging position which is conjugate to the reduction conjugate point CP and the magnification conjugate point, respectively, is positioned inside the prism, and the first reflecting surface M1 is provided in a region where a plurality of chief rays traveling inside the prism converge.

[0042] With this configuration, the first reflecting surface can function as a diaphragm aperture that adjusts the amount of light passing through the optical system. This allows the amount of light to be optimized at the reduction or magnification conjugate point, and prevents stray light and off-axis light from passing through. Furthermore, because the prism integrates multiple transmitting and reflecting surfaces, it can be made low-profile with fewer components, its effective diameter can be reduced, making it more compact, and it can also easily achieve a wider angle of view.

[0043] The optical system 10 according to the present embodiment may satisfy the following condition (1): -2.0<rxm1 / rym1<2.0 (1) where, rxm1: x-direction partial radius of curvature at a position where a reference ray passing through the center of the first reflecting surface M1 and the center of a conjugate plane including the reduction conjugate point CP passes through the first reflecting surface M1, rym1: y-direction partial radius of curvature at a position where a reference ray passing through the center of the first reflecting surface M1 and the center of a conjugate plane including the reduction conjugate point CP passes through the first reflecting surface M1, x-direction: direction perpendicular to the meridional plane, y-direction: direction parallel to the meridional plane and the first reflecting surface M1.

[0044] Equation (1) optimizes the relationship between the x-direction partial radius of curvature and the y-direction partial radius of curvature of the first reflecting surface. The first reflecting surface is inclined so that there is no spatial interference between an optical surface (meaning a transmitting surface or a reflecting surface, the same applies hereinafter) located on the enlargement side from the first reflecting surface and an optical surface located on the reduction side from the first reflecting surface. By satisfying equation (1), astigmatism occurring in the optical system can be suppressed. If the upper limit of equation (1) is exceeded or the lower limit is exceeded, astigmatism will worsen.

[0045] Furthermore, the optical system 10 according to this embodiment may satisfy the following condition (1a): −1.0<rxm1 / rym1<1.0 (1a)

[0046] The optical system 10 according to the present embodiment may satisfy the following condition (2): 0.0<rxt1 / ryt1<4.0 (2) where, rxt1: x-direction partial radius of curvature at a position where a reference ray passing through the center of the first reflecting surface M1 and the center of a conjugate plane including the reduction conjugate point CP passes through the first transmitting surface T1, ryt1: y-direction partial radius of curvature at a position where a reference ray passing through the center of the first reflecting surface M1 and the center of a conjugate plane including the reduction conjugate point CP passes through the first transmitting surface T1, x-direction: direction perpendicular to the meridional plane, y-direction: direction parallel to the meridional plane and the first transmitting surface T1.

[0047] Equation (2) optimizes the relationship between the x-direction partial radius of curvature and the y-direction partial radius of curvature of the first transmitting surface. For the reasons described above, the first reflecting surface is inclined. By satisfying equation (2), astigmatism occurring in the optical system can be suppressed. If the upper limit of equation (2) is exceeded or the lower limit is exceeded, astigmatism will worsen.

[0048] Furthermore, the optical system 10 according to this embodiment may satisfy the following condition (2a): 2.0<rxt1 / ryt1<3.0 (2a)

[0049] The optical system 10 according to the present embodiment may satisfy the following condition (3): -7.0<rxt2 / ryt2<0.0 (3) where, rxt2: x-direction partial radius of curvature at a position where a reference ray passing through the center of the first reflecting surface M1 and the center of a conjugate plane including the reduction conjugate point CP passes through the second transmitting surface T2, ryt2: y-direction partial radius of curvature at a position where a reference ray passing through the center of the first reflecting surface M1 and the center of a conjugate plane including the reduction conjugate point CP passes through the second transmitting surface T2, x-direction: direction perpendicular to the meridional plane, y-direction: direction parallel to the meridional plane and the second transmitting surface T2.

[0050] Equation (3) optimizes the relationship between the x-direction partial radius of curvature and the y-direction partial radius of curvature of the second transmitting surface. For the reasons described above, the first reflecting surface is inclined. By satisfying equation (3), astigmatism occurring in the optical system can be suppressed. If the upper limit of equation (3) is exceeded or the lower limit is exceeded, astigmatism will worsen.

[0051] Furthermore, the optical system 10 according to this embodiment may satisfy the following condition (3a): −5.0<rxt2 / ryt2<−3.0 (3a)

[0052] The optical system 10 according to the present embodiment may satisfy the following condition (4): 0.0<rxm2 / rym2<3.0 (4) where, rxm2: x-direction partial radius of curvature at a position where a reference ray passing through the center of the first reflecting surface M1 and the center of a conjugate plane including the reduction conjugate point CP passes through the second reflecting surface M2, rym2: y-direction partial radius of curvature at a position where a reference ray passing through the center of the first reflecting surface M1 and the center of a conjugate plane including the reduction conjugate point CP passes through the second reflecting surface M2, x-direction: direction perpendicular to the meridional plane, y-direction: direction parallel to the meridional plane and the second reflecting surface M2.

[0053] Equation (4) optimizes the relationship between the x-direction partial radius of curvature and the y-direction partial radius of curvature of the second reflecting surface. For the reasons described above, the first reflecting surface is inclined. By satisfying equation (4), astigmatism occurring in the optical system can be suppressed. If the upper limit of equation (4) is exceeded or the lower limit is exceeded, astigmatism will worsen.

[0054] Furthermore, the optical system 10 according to this embodiment may satisfy the following condition (4a): 0.0<rxm2 / rym2<2.0 (4a)

[0055] The optical system 10 according to the present embodiment may satisfy the following condition (5): 0.0<rxms / ryms<3.0 (5) where, rxms: x-direction partial radius of curvature at a position where a reference ray passing through the center of the first reflecting surface M1 and the center of a conjugate plane including the reduction conjugate point CP passes through the minimum reduction side reflecting surfaces M3 and M4, ryms: y-direction partial radius of curvature at a position where a reference ray passing through the center of the first reflecting surface M1 and the center of a conjugate plane including the reduction conjugate point CP passes through the minimum reduction side reflecting surfaces M3 and M4, x-direction: direction perpendicular to the meridional plane, y-direction: direction parallel to the meridional plane and the minimum reduction side reflecting surfaces M3 and M4.

[0056] Equation (5) optimizes the relationship between the x-direction partial radius of curvature and the y-direction partial radius of curvature of the most reduction-side reflecting surface. For the reasons described above, the first reflecting surface is inclined. By satisfying equation (5), astigmatism occurring in the optical system can be suppressed. If the upper limit of equation (5) is exceeded or the lower limit is exceeded, astigmatism will worsen.

[0057] Furthermore, the optical system 10 according to this embodiment may satisfy the following condition (5a): 0.0<rxms / ryms<2.0 (5a)

[0058] The optical system 10 according to this embodiment may satisfy the following condition (6): 5.0<|αt1|<30.0 (6) where, αt1: the angle formed by a normal NT1 to the first transmitting surface T1 at a position where a reference ray passing through the center of the first reflecting surface M1 and the center of a conjugate plane including the reduction conjugate point CP passes through the first transmitting surface T1, and a normal NM1 to the first reflecting surface M1 at a position where the reference ray passes through the first reflecting surface M1 (see FIG. 11 for the angle formed by each normal line).

[0059] Equation (6) optimizes the angle between the normal to the first transmitting surface and the normal to the first reflecting surface. If the lower limit of Equation (6) is exceeded, spatial interference occurs between the surfaces. If the upper limit is exceeded, it becomes difficult to manufacture the prism.

[0060] Furthermore, the optical system 10 according to this embodiment may satisfy the following condition (6a): 10.0<|αt1|<25.0 (6a)

[0061] The optical system 10 according to this embodiment may satisfy the following condition (7): |αm2|<2.0 (7) where, αm2: the angle formed by the normal to the first reflecting surface M1 at a position where a reference ray passing through the center of the first reflecting surface M1 and the center of a conjugate plane including the reduction conjugate point CP passes through the first reflecting surface M1 and the normal to the second reflecting surface M2 at a position where the reference ray passes through the second reflecting surface M2 (see FIG. 11 for the angle formed by each normal line).

[0062] Equation (7) optimizes the angle between the normal to the first reflecting surface and the normal to the second reflecting surface. If the upper limit of Equation (7) is exceeded, it becomes difficult to manufacture the prism.

[0063] Furthermore, the optical system 10 according to this embodiment may satisfy the following condition (7a): |αm2|<1.0 (7a)

[0064] The optical system 10 according to this embodiment may satisfy the following condition (8): 10.0<|αt2|<35.0 (8) where, αt2: the angle formed by the normal to the most reduction-side reflecting surfaces M3 and M4 at a position where a reference ray passing through the center of the first reflecting surface M1 and the center of a conjugate plane including the reduction conjugate point CP passes through the most reduction-side reflecting surfaces M3 and M4, and the angle formed by the normal to the second transmitting surface T2 at a position where the reference ray passes through the second transmitting surface T2 (see FIG. 11 for the angle formed by each normal line).

[0065] Equation (8) optimizes the angle between the normal to the most-reduced-side reflecting surface and the normal to the second transmitting surface. If the lower limit of Equation (8) is exceeded, spatial interference occurs between the surfaces. If the upper limit is exceeded, it becomes difficult to manufacture the prism.

[0066] Furthermore, the optical system 10 according to this embodiment may satisfy the following condition (8a): 15.0<|αt2|<30.0 (8a)

[0067] The optical system 10 according to this embodiment may satisfy the following condition (9): 0.40<|t1 / t2|<0.90 (9) where, t1: distance between the first transmitting surface T1 and the first reflecting surface M1, and t2: distance between the second transmitting surface T2 and the re-reduction-side reflecting surfaces M3 and M4.

[0068] Equation (9) optimizes the spacing between the transmitting and reflecting surfaces. If the lower limit of Equation (9) is exceeded, the angle of incidence of off-axis rays on the reduction side becomes large. If the upper limit is exceeded, the size of the first transmitting surface becomes too large.

[0069] Furthermore, the optical system 10 according to this embodiment may satisfy the following condition (9a): 0.50<|t1 / t2|<0.80 (9a)

[0070] In the optical system 10 according to this embodiment, the first reflecting surface M1 may have a reflectance of 80% or more, and the area surrounding the first reflecting surface M1 may have a reflectance of less than 10%.

[0071] With this configuration, ghost light traveling to the area surrounding the first reflecting surface can be eliminated, and only the light reflected by the first reflecting surface can be utilized.

[0072] In the optical system 10 according to this embodiment, the intermediate image position may be between the second reflecting surface M2 and the most reduction-side reflecting surfaces M3 and M4.

[0073] This configuration allows the prism to be made smaller.

[0074] In the optical system 10 according to this embodiment, the first reflecting surface M1 and the surrounding area do not have to be on the same plane.

[0075] With this configuration, ghost light traveling to the area surrounding the first reflecting surface can be efficiently eliminated.

[0076] In the optical system 10 according to this embodiment, the peripheral region may include a conical surface extending from the first reflecting surface M1 to the side opposite to the first transmitting surface T1.

[0077] With this configuration, ghost light traveling to the area surrounding the first reflecting surface can be efficiently eliminated.

[0078] In the optical system 10 according to this embodiment, the peripheral region may be provided with a material or shape that absorbs or scatters light.

[0079] With this configuration, ghost light traveling to the area surrounding the first reflecting surface can be efficiently eliminated.

[0080] 10A is a plan view showing the first reflecting surface and the surrounding region, and FIG. 10B is a cross-sectional view thereof. The first reflecting surface M1 is, for example, a circular mirror, and its surrounding region TP is provided with a function to eliminate ghost light. Techniques for this include, for example, a) making the surrounding region TP a shape that is not flush with the first reflecting surface M1, such as an inclined surface, to scatter light; b) making the surrounding region TP include a conical surface extending from the first reflecting surface M1 to the opposite side of the first transmitting surface T1, such as an inverted conical surface or pyramidal surface, to scatter light; or c) providing the surrounding region TP with a material or shape that absorbs or scatters light, such as blackening or a textured surface (finely uneven surface), to absorb or scatter light. These techniques may be used alone or in combination.

[0081] Numerical examples of the optical systems according to Examples 1 to 3 will be described below. In each numerical example, all lengths in the table are in "mm" and all angles of view are in "°". In addition, the radius of curvature, surface spacing, and material are shown in each numerical example.

[0082] The free-form surface shape of the prism optical surface is defined by the following equation using a local Cartesian coordinate system (x, y, z) with the vertex of the surface as the origin.

[0083]

[0084] Here, z: Sag amount of the surface parallel to the z axis r: Radial distance (=√(x ２ +y ２ )) c: curvature at the surface vertex k: conic coefficient C ｊ :monomial x ｍ y ｎ The coefficient of (x^my^n in the table) is

[0085] Numerical Example 1 For the optical system of Numerical Example 1 (corresponding to Example 1), lens data is shown in Table 1. The decentering type and α rotation amount of the prism optical surface are shown in Table 2. Free-form surface shape data of the prism optical surface is shown in Table 3.

[0086] Each prism optical surface has multiple surface numbers (for example, four surface numbers S4 to S7 for the first reflecting surface M1), and these refer to the surface numbers used in the coordinate conversion between global coordinates and local coordinates during numerical calculations. Also, "decenter & return" in the table refers to the coordinate conversion between global coordinates and local coordinates during numerical calculations. The lateral aberration diagrams shown in Figures 4, 6, and 8 correspond to image height coordinates (x, y) = (0.000, 0.000), (0.000, 1.9445), (0.000, -1.9445), (1.9445, 0.000), (1.9445, 1.9445), and (1.9445, -1.9445), respectively, in the reduction-side rectangular region. The same applies to the other numerical examples.

[0087]

[0088]

[0089]

[0090] Numerical Example 2 For the optical system of Numerical Example 2 (corresponding to Example 2), lens data is shown in Table 4. The decentering type and α rotation amount of the prism optical surface are shown in Table 5. Free-form surface shape data of the prism optical surface is shown in Table 6.

[0091]

[0092]

[0093]

[0094] Numerical Example 3 For the optical system of Numerical Example 3 (corresponding to Example 3), lens data is shown in Table 7. The decentering type and α rotation amount of the prism optical surface are shown in Table 8. Free-form surface shape data of the prism optical surface is shown in Table 9.

[0095]

[0096]

[0097]

[0098] Table 10 below shows the corresponding values ​​of the formulas (1) to (9) in the respective numerical examples 1 to 3.

[0099]

[0100] Table 11 below shows the values ​​of the variables in the formulas (1) to (9) in the respective numerical examples 1 to 3.

[0101]

[0102] Third Embodiment Hereinafter, a third embodiment of the present disclosure will be described with reference to Fig. 12. Fig. 12 is a block diagram showing an example of an image projection device according to the present disclosure. The image projection device 100 includes the optical system 10 disclosed in the second embodiment, an image forming element 101, a light source 102, a control unit 110, and the like.

[0103] The image forming element 101 is composed of a liquid crystal, a DMD, or the like, and generates an image to be projected onto the screen SR via the optical system 10. The light source 102 is composed of an LED (light emitting diode), a laser, or the like, and supplies light to the image forming element 101. The control unit 110 is composed of a CPU, an MPU, or the like, and controls the entire device and each component. The optical system 10 may be configured as an interchangeable lens that can be detachably attached to the image projection device 100, or as a built-in lens that is integrated into the image projection device 100.

[0104] The image projection device 100 described above is capable of short-focus and large-screen projection with a small device by using the optical system 10 according to the second embodiment.

[0105] Fourth Embodiment Hereinafter, a fourth embodiment of the present disclosure will be described with reference to Fig. 13. Fig. 13 is a block diagram showing an example of an imaging device according to the present disclosure. The imaging device 200 includes the optical system 10 disclosed in the second embodiment, an imaging element 201, a control unit 210, and the like.

[0106] The imaging element 201 is composed of a CCD (charge-coupled device) image sensor, a CMOS image sensor, or the like, and receives an optical image of the object OBJ formed by the optical system 10 and converts it into an electrical image signal. The control unit 110 is composed of a CPU, an MPU, or the like, and controls the entire device and each component. The optical system 10 may be configured as an interchangeable lens that can be detachably attached to the imaging device 200, or as a built-in lens integrated into the imaging device 200.

[0107] The imaging device 200 described above is capable of capturing images with a short focus and a large screen using a small device by using the optical system 10 according to embodiment 2. Furthermore, by using a plurality of imaging devices 200, a stereo camera, a multi-angle camera, etc. can be realized.

[0108] As described above, the embodiments have been described as disclosure of the technology in the present disclosure, and the accompanying drawings and detailed description have been provided for this purpose.

[0109] Therefore, the components shown in the accompanying drawings and detailed description may include not only essential components for solving the problem, but also components that are not essential for solving the problem in order to illustrate the above technology. Therefore, the fact that these non-essential components are shown in the accompanying drawings or detailed description should not be interpreted as immediately indicating that these non-essential components are essential.

[0110] Furthermore, since the above-described embodiments are intended to illustrate the technology of the present disclosure, various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents.

[0111] The present disclosure is applicable to image projection devices such as projectors and head-up displays, as well as imaging devices such as digital still cameras, digital video cameras, surveillance cameras in surveillance systems, web cameras, and in-vehicle cameras. In particular, the present disclosure is applicable to optical systems that require high image quality, such as projectors, digital still camera systems, and digital video camera systems.

Claims

1. An optical system having a reduction conjugate point on a reduction side and a magnification conjugate point on a magnification side, which are optically conjugate to each other, a prism having a first transmitting surface located on the enlargement side, a second transmitting surface located on the reduction side, and at least three reflecting surfaces located on an optical path between the first transmitting surface and the second transmitting surface; the prism has a meridional surface through which the light reflected by the at least three reflecting surfaces passes; the at least three reflecting surfaces include, in order from the enlargement side to the reduction side, a first reflecting surface and a second reflecting surface, and a most-reduction-side reflecting surface located on the most reduction side; an intermediate image position that is in a conjugate relationship with the reduction conjugate point and the enlargement conjugate point, respectively, is positioned inside the prism between the second reflecting surface and the most reduction-side reflecting surface; an optical system, wherein the second reflecting surface is located between the intermediate image position and the first reflecting surface, and the first reflecting surface is provided in a region where a plurality of chief rays traveling inside the prism converge.

2. 2. The optical system according to claim 1, which satisfies the following condition (1): -2.0<rxm1 / rym1<2.0...(1) Where: rxm1: x-direction partial curvature radius at a position where a reference ray passing through the center of the first reflecting surface and the center of a conjugate surface including the reduction conjugate point passes through the first reflecting surface rym1: y-direction partial radius of curvature at a position where a reference ray passing through the center of the first reflecting surface and the center of a conjugate surface including the reduction conjugate point passes through the first reflecting surface x direction: a direction perpendicular to the meridional plane y direction: a direction parallel to the meridional plane and the first reflecting surface It is.

3. 2. The optical system according to claim 1, which satisfies the following condition (2): 0.0<rxt1 / ryt1<4.0...(2) Where: rxt1: x-direction partial radius of curvature at a position where a reference ray passing through the center of the first reflecting surface and the center of a conjugate surface including the reduction conjugate point passes through the first transmitting surface ryt1: y-direction partial radius of curvature at a position where a reference ray passing through the center of the first reflecting surface and the center of a conjugate surface including the reduction conjugate point passes through the first transmitting surface x direction: a direction perpendicular to the meridional plane y direction: a direction parallel to the meridional plane and the first transmitting surface It is.

4. 2. The optical system according to claim 1, which satisfies the following condition (3): -7.0<rxt2 / ryt2<0.0...(3) Where: rxt2: x-direction partial curvature radius at a position where a reference ray passing through the center of the first reflecting surface and the center of a conjugate surface including the reduction conjugate point passes through the second transmitting surface ryt2: y-direction partial curvature radius at a position where a reference ray passing through the center of the first reflecting surface and the center of a conjugate surface including the reduction conjugate point passes through the second transmitting surface x direction: a direction perpendicular to the meridional plane y direction: a direction parallel to the meridional plane and the second transmitting surface It is.

5. 2. The optical system according to claim 1, which satisfies the following condition (4): 0.0<rxm2 / rym2<3.0...(4) Where: rxm2: x-direction partial curvature radius at a position where a reference ray passing through the center of the first reflecting surface and the center of a conjugate surface including the reduction conjugate point passes through the second reflecting surface rym2: y-direction partial radius of curvature at a position where a reference ray passing through the center of the first reflecting surface and the center of a conjugate surface including the reduction conjugate point passes through the second reflecting surface x direction: a direction perpendicular to the meridional plane y direction: a direction parallel to the meridional plane and the second reflecting surface It is.

6. 2. The optical system according to claim 1, which satisfies the following condition (5): 0.0<rxms / ryms<3.0...(5) Where: rxms: the x-direction partial curvature radius at the position where a reference ray passing through the center of the first reflecting surface and the center of the conjugate surface including the reduction conjugate point passes through the most reduced side reflecting surface ryms: y-direction partial curvature radius at the position where a reference ray passing through the center of the first reflecting surface and the center of a conjugate surface including the reduction conjugate point passes through the most reduction side reflecting surface x direction: a direction perpendicular to the meridional plane y direction: a direction parallel to the meridional plane and the most reduced side reflecting surface It is.

7. 2. The optical system according to claim 1, which satisfies the following condition (6): 5.0<|αt1|<30.0…(6) Where: αt1: An angle between a normal to the first transmitting surface at a position where a reference ray passing through the center of the first reflecting surface and the center of a conjugate surface including the reduction conjugate point passes through the first transmitting surface and a normal to the first reflecting surface at a position where the reference ray passes through the first reflecting surface. It is.

8. 2. The optical system according to claim 1, which satisfies the following condition (7): |αm2|<2.0…(7) Where: αm2: An angle between a normal to the first reflecting surface at a position where a reference ray passing through the center of the first reflecting surface and the center of a conjugate surface including the reduction conjugate point passes through the first reflecting surface and a normal to the second reflecting surface at a position where the reference ray passes through the second reflecting surface It is.

9. 2. The optical system according to claim 1, which satisfies the following condition (8): 10.0<|αt2|<35.0...(8) Where: αt2: An angle between a normal to the first reflecting surface at a position where a reference ray passing through the center of the first reflecting surface and the center of a conjugate surface including the reduction conjugate point passes through the first reflecting surface and a normal to the second reflecting surface at a position where the reference ray passes through the second reflecting surface. It is.

10. 2. The optical system according to claim 1, which satisfies the following condition (9): 0.40<|t1 / t2|<0.90...(9) Where: t1: distance between the first transmitting surface and the first reflecting surface t2: Distance between the second transmitting surface and the re-reduction side reflecting surface It is.

11. The optical system of claim 1 , wherein the first reflective surface has a reflectivity of 80% or more and a surrounding area of ​​the first reflective surface has a reflectivity of less than 10%.

12. The optical system of claim 11 , wherein the first reflective surface and the surrounding area are not coplanar.

13. The optical system of claim 12 , wherein the peripheral region includes a conical surface extending from the first reflective surface to a side opposite the first transmissive surface.

14. The optical system of claim 12 , wherein the surrounding area is provided with a material or shape that absorbs or scatters light.

15. The second reflecting surface has a shape with a concave surface facing in a direction in which an incident light ray is reflected, The optical system according to claim 1 , wherein the most-reduced-side reflecting surface has a shape with a concave surface facing in a direction in which an incident light ray is reflected.

16. The optical system described in claim 1, wherein the first transmitting surface has a shape with a convex surface facing the enlargement side, and the second transmitting surface has a shape with a convex surface facing the reduction side.

17. The optical system described in claim 1, wherein the multiple chief rays intersect between the minimum reduction side reflecting surface and the second transmitting surface.

18. 18. A stereo optical system comprising a plurality of optical systems according to claim 1, wherein the second transmitting surfaces of the plurality of optical systems are disposed adjacent to each other.

19. An optical system according to any one of claims 1 to 17; and an image sensor that receives an optical image formed by the optical system and converts it into an electrical image signal.

20. An optical system according to any one of claims 1 to 17; and an image forming element that generates an image to be projected onto a screen via the optical system.