Optical system, image projection device, and imaging apparatus

Abstract

To provide an optical system that allows projection or imaging with a short focus on a large screen by using a small-sized prism.SOLUTION: An optical system according to the present disclosure comprises a first sub optical system and a second sub optical system in order from a reduction side toward an enlargement side. The second sub optical system includes a prism having a first transmission surface, a first reflection surface, a second reflection surface, and a second transmission surface in order from the reduction side. The first reflection surface has a shape in which a concave surface is directed in a direction in which an incident light beam is reflected. The second reflection surface is located between the first reflection surface and a first optical surface located on the most enlargement side of the first sub optical system, in a first direction from the reduction side to the enlargement side in the first sub optical system. When a surface including a position where a principal ray passing through the center of a direction of a predetermined side in a rectangular area of reduction conjugate points is reflected on the first reflection surface, as a Y cross section, a curvature shape of the first reflection surface is set so that, when seen from a direction perpendicular to the Y cross section, parts of the plurality of principal rays passing through the reduction conjugate points intersect on an optical path between the first reflection surface and the second transmission surface.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Patent Document 1 discloses a variable magnification optical system that employs an off-axial optical element arranged in a decentered position, thereby bending the optical path in the variable magnification optical system into a desired shape and shortening the overall length of the variable magnification optical system.

[0003] Patent Document 2 discloses an imaging optical system including multiple decentered prisms. In detail, two decentered prisms, each having a rotationally asymmetric reflecting surface, are arranged on either side of an aperture, and the medium of decentered prism 10 in front of the aperture and the medium of decentered prism 20 behind the aperture have different optical properties. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-20196 [Patent Document 2] JP 2003-84200 A [Patent Document 3] Patent No. 6390882 Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure provides an optical system that enables short-focus, large-screen projection or imaging using a small prism, and also provides an image projection device and an imaging device that use such an imaging optical system. [Means for solving the problem]

[0006] One aspect of the present disclosure is an optical system comprising, in order from the reduction side to the enlargement side, a first sub-optical system and a second sub-optical system, the second sub-optical system comprises, in order from the reduction side, a prism having a first transmitting surface, a first reflecting surface, a second reflecting surface, and a second transmitting surface, the first reflecting surface having a concave shape facing in a direction in which an incident light ray is reflected, and the second reflecting surface is located between a first optical surface of the first sub-optical system that is located closest to the enlargement side and the first reflecting surface in a first direction from the reduction side to the enlargement side of the first sub-optical system, the Y cross section being a surface that includes a position where a chief ray passing through the center of a direction of a predetermined side of a rectangular area of ​​a reduction conjugate point is reflected by the first reflecting surface, and the curvature shape of the first reflecting surface is set so that, when viewed from a direction perpendicular to the Y cross section, some of the chief rays passing through the reduction conjugate point intersect on the optical path between the first reflecting surface and the second transmitting surface.

[0007] 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.

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

[0009] In the optical system according to the present disclosure, multiple chief rays intersect on the optical path between the first reflecting surface and the second transmitting surface of the prism in both the Y cross section and the X cross section, which enables short-focus and large-screen projection or imaging using a small prism. [Brief description of the drawings]

[0010] [Figure 1] Layout diagram showing the optical system according to the first embodiment [Diagram 2] 2A is a Y-sectional view showing an optical path along which a principal ray passes in the optical system according to the first embodiment. FIG. 2B is an X-sectional view of the optical system as viewed from above. [Diagram 3]FIG. 1 is an explanatory diagram showing a usage mode of an image projection device using the optical system according to the first embodiment; [Figure 4] Graph showing the relative positional relationship between the reflecting surface and the Y-direction intermediate image and the X-direction intermediate image in the optical system 1 according to Example 1. [Diagram 5] Layout diagram showing the optical system according to Example 2 [Figure 6] 6A is a Y-sectional view showing an optical path along which a principal ray passes in the optical system according to the second embodiment; FIG. 6B is an X-sectional view showing the optical system as viewed from above; [Figure 7] FIG. 11 is an explanatory diagram showing a usage state of an image projection device using the optical system according to the second embodiment. [Figure 8] Graph showing the relative positional relationship between the reflecting surface and the Y-direction intermediate image and the X-direction intermediate image in the optical system according to Example 2. [Figure 9] Layout diagram showing an optical system according to Example 3 [Figure 10] 10A is a Y-sectional view showing an optical path along which a principal ray passes in the optical system according to Example 3. FIG. 10B is an X-sectional view of the optical system as viewed from above. [Figure 11] FIG. 11 is an explanatory diagram showing a usage mode of an image projection device using the optical system according to the third embodiment. [Figure 12] Graph showing the relative positional relationship between the reflecting surface and the Y-direction intermediate image and the X-direction intermediate image in the optical system according to Example 3. [Figure 13] Layout diagram showing the optical system according to Example 4 [Figure 14] 14A is a Y-sectional view showing an optical path along which a principal ray passes in the optical system according to Example 4. FIG. 14B is an X-sectional view showing the optical system as viewed from above. [Figure 15] FIG. 11 is an explanatory diagram showing a usage mode of an image projection device using the optical system according to the fourth embodiment. [Figure 16] Graph showing the relative positional relationship between the reflecting surface and the Y-direction intermediate image and the X-direction intermediate image in the optical system according to Example 4. [Figure 17] FIG. 1 is a diagram illustrating a three-dimensional shape of a prism PM according to a first embodiment; [Figure 18] FIG. 13 is an explanatory diagram showing an example of an image region at a contracted conjugate point; [Figure 19] 1 is an explanatory diagram showing the definitions of the imaging magnification at an intermediate imaging position and the imaging magnification at a magnification conjugate point; [Figure 20] 4A to 4C are cross-sectional views in the Y direction showing various examples of stepped structures of the prism. [Figure 21] FIG. 1 is a block diagram illustrating an example of an image projection device according to the present disclosure. [Figure 22] FIG. 1 is a block diagram illustrating an example of an imaging device according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of already well-known matters or duplicate explanation of substantially the same configuration may be omitted. This is to avoid the following explanation becoming unnecessarily redundant and to facilitate understanding by those skilled in the art.

[0012] The applicant provides the accompanying drawings and the following description so that those skilled in the art can fully understand the present disclosure, and does not intend for them to limit the subject matter described in the claims.

[0013] Below, each embodiment of the optical system according to the present disclosure will be described. In each embodiment, the optical system is used in a projector (one example of an image projection device) that projects image light of an original image SA, which is obtained by spatially modulating incident light by an image forming element such as a liquid crystal or a DMD (digital micromirror device) based on an image signal, onto a screen. That is, the optical system according to the present disclosure can be used to enlarge and project an original image S on an image forming element arranged on the reduction side by arranging a screen (not shown) on an extension line of the enlargement side. However, the projection surface is not limited to a screen. The projection surface also includes walls, ceilings, floors, and windows inside a house, a store, or a vehicle or aircraft used for transportation.

[0014] In addition, the optical system according to the present disclosure can also be used to collect light emitted from an object located on the extension of the magnification side and form an optical image of the object on the imaging surface of an imaging element arranged on the reduction side.

[0015] (Embodiment 1) The optical system according to the first embodiment of the present disclosure will be described below with reference to FIGS.

[0016] Example 1 Fig. 1 is a layout diagram showing an optical system 1 according to a first embodiment. The optical system 1 includes a first sub-optical system including an aperture stop ST and a second sub-optical system including a prism PM. In Fig. 1, a reduction conjugate point which is an imaging position on the reduction side is located on the left side, and a magnification conjugate point which is an imaging position on the magnification side is located on the right side. The second sub-optical system is provided on the magnification side of the first sub-optical system.

[0017] FIG. 18 is an explanatory diagram showing an example of an image area at a reduction conjugate point. The image area at the reduction conjugate point is defined as a rectangular area having a longitudinal direction (X direction) and a lateral direction (Y direction), and has an optically conjugate imaging relationship with the image area at the expansion conjugate point. A light ray travels along the normal direction (Z direction) of this rectangular area. This rectangular area has an aspect ratio of, for example, 3:2, 4:3, 16:9, 256:135, etc., and corresponds to the image display area of ​​an image forming element in the case of an image projection device, and corresponds to the imaging area of ​​an imaging element in the case of an imaging device.

[0018] Furthermore, an intermediate imaging position that is conjugate to each of the reduction conjugate point and the enlargement conjugate point is located inside the optical system 1. This intermediate imaging position is shown as a Y-direction intermediate image IMy in Fig. 1, but an X-direction intermediate image IMx is not shown and will be described later with reference to Fig. 4.

[0019] The first sub-optical system includes, in order from the reduction side to the enlargement side, an optical element PA and lens elements L1 to L14. The optical element PA represents an optical element such as a TIR (total internal reflection) prism, a prism for color separation and color synthesis, an optical filter, a parallel plate glass, a quartz low-pass filter, and an infrared cut filter. The original image SA is placed on the reduction-side end surface of the optical element PA (surface 1). Note that for the surface numbers, refer to the numerical examples described later.

[0020] The optical element PA has two parallel, flat transmitting surfaces (surfaces 2, 3). Lens element L1 has a positive meniscus shape with a convex surface facing the reduction side (surfaces 4, 5). Lens element L2 has a negative meniscus shape with a convex surface facing the reduction side (surfaces 6, 7). Lens element L3 has a biconvex shape (surfaces 7, 8). Lens element L4 has a negative meniscus shape with a convex surface facing the enlargement side (surfaces 8, 9). Lens elements L2 to L4 are bonded together to form a compound lens. Lens element L5 has a biconcave shape (surfaces 10, 11). Lens element L6 has a biconvex shape (surfaces 11, 12). Lens elements L5 and L6 are bonded together to form a compound lens.

[0021] Lens element L7 has a biconvex shape (surfaces 14, 15). Lens element L8 has a negative meniscus shape with a convex surface facing the enlargement side (surfaces 16, 17). Lens element L9 has a positive meniscus shape with a convex surface facing the enlargement side (surfaces 17, 18). Lens elements L8 and L9 are bonded together to form a compound lens. Lens element L10 has a biconvex shape (surfaces 19, 20). Lens element L11 has a biconvex shape (surfaces 21, 22). Lens element L12 has a biconcave shape (surfaces 22, 23). Lens elements L11 and L12 are bonded together to form a compound lens. Lens element L13 has a negative meniscus shape with a convex surface facing the reduction side (surfaces 24, 25). Lens element L14 has a positive meniscus shape with a convex surface facing the enlargement side (surfaces 26, 27).

[0022] Figure 17 shows a schematic diagram of the three-dimensional shape of the prism PM of Example 1, where Figure 17(a) is a rear view, Figure 17(b) is a front view, Figure 17(c) is a top view, Figure 17(d) is a bottom view, and Figure 17(e) is a side view.

[0023] The second sub-optical system includes a prism PM formed of a transparent medium, such as glass or synthetic resin. The prism PM has a transmitting surface A located on the reduction side, a transmitting surface B located on the enlargement side, and two reflecting surfaces R1 and R2 located on the optical path between the transmitting surface A and the transmitting surface B. The transmitting surface A has a free-form shape with a concave surface facing the reduction side (surface 28). The reflecting surface R1 has a free-form shape with a concave surface facing in the direction in which the light ray incident on the reflecting surface R1 is reflected (surface 29). The reflecting surface R2 has a planar shape (surface 30). The transmitting surface B has a free-form shape with a convex surface facing the enlargement side (surface 31).

[0024] The aperture stop ST defines the range through which the light beam passes through the optical system 1, and is positioned between the reduction conjugate point and the intermediate image position described above. As an example, the aperture stop ST is located between the lens elements L6 and L7 (surface 13).

[0025] The intermediate images formed at the intermediate imaging position, that is, a part or the whole of the Y-direction intermediate image IMy and the X-direction intermediate image IMx, are positioned inside the medium of the prism PM. Furthermore, when the long direction of the rectangular area of ​​the reduction conjugate point is defined as the X direction, the short direction as the Y direction, and the normal direction as the Z direction, a plane including the position where the principal ray passing through the center in the X direction is reflected by reflecting surface R1 is defined as the Y cross section, and a cross section perpendicular to the Y cross section is defined as the X cross section, the light beam passing through the first sub-optical system has different intermediate image formation positions in the Y cross section and the X cross section, i.e., the Y direction intermediate image IMy and the X direction intermediate image IMx are formed at different positions. This makes it possible to reduce the impact of disturbances such as dust and dirt on image quality.

[0026] Fig. 2(a) is a Y-sectional view showing the optical path through which the chief ray passes in the optical system 1 according to the first embodiment, and Fig. 2(b) is an X-sectional view when viewed from above the optical system 1. Note that Fig. 2(b) omits the intermediate portion of the optical system 1 and diagrammatically shows only the optical path inside the prism PM.

[0027] 2(a), for the sake of clarity, a chief ray that passes through the center of the original image SA in the X direction and passes through the bottom in the Y direction (normalized height Y = 0.0 at the reduction conjugate point), and a chief ray that passes through the center of the original image SA in the X direction and passes through the top in the Y direction (normalized height Y = 1.0 at the reduction conjugate point) are shown. Both chief rays pass through the first sub-optical system, enter the inside of the prism PM through the transmitting surface A, and are then reflected by the reflecting surface R1, and intersect with each other in the region CRy indicated by the dashed circle just before reaching the reflecting surface R2.

[0028] 2(b), for the sake of clarity, a chief ray passing through the left end of the original image SA in the X direction and a chief ray passing through the right end of the original image SA in the X direction are shown. Both chief rays pass through the first sub-optical system, enter the inside of the prism PM through the transmitting surface A, and are subsequently reflected by the reflecting surface R1. Just before reaching the reflecting surface R2, they intersect with each other in a region CRx indicated by a dashed circle.

[0029] In the present disclosure, as shown in Fig. 2(a), when viewed from a direction perpendicular to the Y cross section, some of the multiple chief rays passing through the reduction conjugate point intersect on the optical path between the reflecting surface R1 and the transmitting surface B, and as shown in Fig. 2(b), when viewed from a direction perpendicular to the X cross section, the curvature shape of the free-form surface of the reflecting surface R1 is set so that some of the multiple chief rays passing through the reduction conjugate point intersect on the optical path between the reflecting surface R1 and the transmitting surface B. With this configuration, it is possible to use a small prism to make the second sub-optical system compact, and to perform short-focus, large-screen projection or imaging.

[0030] 3 is an explanatory diagram showing a usage state of an image projection device using the optical system 1 according to the first embodiment. The image projection device including the optical system 1 is placed horizontally on a support stand such as a table or on a floor. A screen SC is installed vertically above the support stand at a relatively short horizontal distance, for example, 0.5 m. Light generated by the optical system 1 is projected diagonally forward and upward, realizing a short-focus and large-screen projection.

[0031] FIG. 4 is a graph showing the relative positional relationship between the reflecting surface R1 and the Y-direction intermediate image IMy and the X-direction intermediate image IMx in the optical system 1 according to the first embodiment, as viewed from a direction perpendicular to the Y cross section. The horizontal axis is the relative position (unit: mm) in the Z direction based on IMx formed by the light ray at the bottom in the Y direction passing through the center in the X direction of the original image SA, and the vertical axis is the relative position (unit: mm) in the Y direction based on IMx formed by the light ray at the bottom in the Y direction passing through the center in the X direction of the original image SA. The diamond mark indicates the X-direction intermediate image IMx, the square mark indicates the Y-direction intermediate image IMy, and the triangular mark indicates the curved shape of the reflecting surface R1. The X-direction intermediate image IMx is a state in which the light beam passing through the optical system 1 is focused only in the X direction and is not focused in the Y direction. The Y-direction intermediate image IMy is a state in which the light beam passing through the optical system 1 is focused only in the Y direction and is not focused in the X direction.

[0032] Looking at the graph, the Y-direction intermediate images IMy are distributed obliquely with respect to the Z direction from near the coordinates (-2.5,0) to near the coordinates (-19.5,-14.5). The X-direction intermediate images IMx are distributed obliquely with respect to the Z direction from near the coordinates (0,0) to near the coordinates (-13,-15) with a concave surface facing the reduced optical path. The reflecting surface R1 is distributed obliquely with respect to the Z direction from near the coordinates (9,0) to near the coordinates (0.5,-17) with a concave surface facing the reduced optical path.

[0033] In the present disclosure, the reflecting surface R1 may have a shape in which the concave surface faces the reduced optical path side along the intermediate image position in the X direction parallel to the X cross section of the light ray passing through the center of the longitudinal direction of the rectangular area, thereby suppressing image distortion on the screen SC.

[0034] Example 2 5 is a layout diagram showing an optical system 1 according to Example 2. This optical system 1 has a similar configuration to Example 1, but the first sub-optical system includes lens elements L1 to L13, and the second sub-optical system including a prism PM projects an image obliquely downward and forward in the case of an image projector. Below, descriptions that overlap with Example 1 will be omitted.

[0035] Lens element L1 has a positive meniscus shape with a convex surface facing the reduction side (surfaces 4, 5). Lens element L2 has a negative meniscus shape with a convex surface facing the reduction side (surfaces 6, 7). Lens element L3 has a biconvex shape (surfaces 7, 8). Lens element L4 has a negative meniscus shape with a convex surface facing the enlargement side (surfaces 8, 9). Lens elements L2 to L4 are bonded together to form a compound lens. Lens element L5 has a biconcave shape (surfaces 10, 11). Lens element L6 has a biconvex shape (surfaces 11, 12). Lens elements L5 and L6 are bonded together to form a compound lens.

[0036] Lens element L7 has a biconvex shape (surfaces 14, 15). Lens element L8 has a negative meniscus shape with the convex surface facing the enlargement side (surfaces 16, 17). Lens element L9 has a biconvex shape (surfaces 18, 19). Lens element L10 has a biconvex shape (surfaces 20, 21). Lens element L11 has a biconcave shape (surfaces 21, 22). Lens elements L10 and L11 are bonded together to form a compound lens. Lens element L12 has a negative meniscus shape with the convex surface facing the reduction side (surfaces 23, 24). Lens element L13 has a biconvex shape (surfaces 25, 26).

[0037] The prism PM has a transmitting surface A located on the reduction side, a transmitting surface B located on the enlargement side, and two reflecting surfaces R1 and R2 located on the optical path between transmitting surface A and transmitting surface B. Transmitting surface A has a free-form shape with a concave surface facing the reduction side (surface 27). Reflecting surface R1 has a free-form shape with a concave surface facing in the direction in which a light ray incident on reflecting surface R1 is reflected (surface 28). Reflecting surface R2 has a planar shape (surface 29). Transmitting surface B has a free-form shape with a convex surface facing the enlargement side (surface 30).

[0038] FIG. 6(a) is a Y cross-sectional view showing the optical path along which the chief ray passes in the optical system 1 according to the second embodiment, and FIG. 6(b) is an X cross-sectional view of the optical system 1 as viewed from above.

[0039] 6(a), for the sake of clarity, a chief ray that passes through the center of the original image SA in the X direction and passes through the bottom in the Y direction (normalized height Y = 0.0 at the reduction conjugate point), and a chief ray that passes through the center of the original image SA in the X direction and passes through the top in the Y direction (normalized height Y = 1.0 at the reduction conjugate point) are shown. Both chief rays pass through the first sub-optical system, enter the inside of the prism PM through the transmitting surface A, and are then reflected by the reflecting surface R1, and intersect with each other in the region CRy indicated by the dashed circle just before reaching the reflecting surface R2.

[0040] 6(b), for the sake of clarity, a chief ray passing through the left end of the original image SA in the X direction and a chief ray passing through the right end of the original image SA in the X direction are shown. Both chief rays pass through the first sub-optical system, enter the inside of the prism PM through the transmitting surface A, and are subsequently reflected by the reflecting surface R1. Just before reaching the reflecting surface R2, they intersect with each other in a region CRx indicated by a dashed circle.

[0041] 7 is an explanatory diagram showing a usage state of an image projection device using the optical system 1 according to the second embodiment. The image projection device including the optical system 1 is placed horizontally on a support stand such as a table or on a floor. A screen SC is installed horizontally forward at a relatively short vertical distance, for example, 0.3 m, from the support stand. Light generated by the optical system 1 is projected diagonally downward toward the front, achieving short-focus and large-screen projection.

[0042] FIG. 8 is a graph showing the relative positional relationship between the reflecting surface R1 and the Y-direction intermediate image IMy and the X-direction intermediate image IMx in the optical system 1 according to Example 2, as viewed from a direction perpendicular to the Y cross section.

[0043] Looking at the graph, the Y-direction intermediate images IMy are distributed obliquely with respect to the Z direction from near coordinates (-3.5,0) to near coordinates (-17,-10). The X-direction intermediate images IMx are distributed obliquely with respect to the Z direction from near coordinates (0,0) to near coordinates (-12,-10) with a concave surface facing the reduced optical path. The reflecting surface R1 is distributed obliquely with respect to the Z direction from near coordinates (5.5,0) to near coordinates (-2,-11) with a concave surface facing the reduced optical path.

[0044] In the present disclosure, the reflecting surface R1 may have a shape in which the concave surface faces the reduced optical path side along the intermediate image position in the X direction parallel to the X cross section of the light ray passing through the center of the longitudinal direction of the rectangular area, thereby suppressing image distortion on the screen SC.

[0045] Example 3 9 is a layout diagram showing an optical system 1 according to Example 3. This optical system 1 has a similar configuration to Example 1, but the first sub-optical system includes lens elements L1 to L14, and the second sub-optical system including a prism PM projects an image obliquely upward and rearward in the case of an image projector. Below, descriptions that overlap with Example 1 will be omitted.

[0046] Lens element L1 has a positive meniscus shape with a convex surface facing the reduction side (surfaces 4, 5). Lens element L2 has a negative meniscus shape with a convex surface facing the reduction side (surfaces 6, 7). Lens element L3 has a biconvex shape (surfaces 7, 8). Lens element L4 has a negative meniscus shape with a convex surface facing the enlargement side (surfaces 8, 9). Lens elements L2 to L4 are bonded together to form a compound lens. Lens element L5 has a biconcave shape (surfaces 10, 11). Lens element L6 has a biconvex shape (surfaces 11, 12). Lens elements L5 and L6 are bonded together to form a compound lens.

[0047] Lens element L7 has a biconvex shape (surfaces 14, 15). Lens element L8 has a negative meniscus shape with a convex surface facing the enlargement side (surfaces 16, 17). Lens element L9 has a positive meniscus shape with a convex surface facing the enlargement side (surfaces 17, 18). Lens elements L8 and L9 are bonded together to form a compound lens. Lens element L10 has a biconvex shape (surfaces 19, 20). Lens element L11 has a biconvex shape (surfaces 21, 22). Lens element L12 has a biconcave shape (surfaces 22, 23). Lens elements L11 and L12 are bonded together to form a compound lens. Lens element L13 has a negative meniscus shape with a convex surface facing the reduction side (surfaces 24, 25). Lens element L14 has a positive meniscus shape with a convex surface facing the enlargement side (surfaces 26, 27).

[0048] Prism PM has a transmitting surface A located on the reduction side, a transmitting surface B located on the enlargement side, and one reflecting surface R1 located on the optical path between transmitting surface A and transmitting surface B. Transmitting surface A has a free-form shape with a concave surface facing the reduction side (surface 28). Reflecting surface R1 has a free-form shape with a concave surface facing in the direction in which a light ray incident on reflecting surface R1 is reflected (surface 29). Transmitting surface B has a free-form shape with a convex surface facing the enlargement side (surface 30).

[0049] FIG. 10(a) is a Y cross-sectional view showing the optical path along which the chief ray passes in the optical system 1 according to the third embodiment, and FIG. 10(b) is an X cross-sectional view of the optical system 1 as viewed from above.

[0050] 10(a), for the sake of clarity, a chief ray that passes through the center of the original image SA in the X direction and passes through the bottom in the Y direction (normalized height Y = 0.0 at the reduction conjugate point), and a chief ray that passes through the center of the original image SA in the X direction and passes through the top in the Y direction (normalized height Y = 1.0 at the reduction conjugate point) are shown. Both chief rays pass through the first sub-optical system, enter the inside of the prism PM through the transmitting surface A, and are then reflected by the reflecting surface R1, and intersect with each other in the region CRy indicated by the dashed circle just before reaching the transmitting surface B.

[0051] 10(b), for the sake of clarity, a chief ray passing through the left end of the original image SA in the X direction and a chief ray passing through the right end of the original image SA in the X direction are shown. Both chief rays pass through the first sub-optical system, enter the inside of the prism PM through the transmitting surface A, and are subsequently reflected by the reflecting surface R1. Just before reaching the transmitting surface B, they intersect with each other in a region CRx indicated by a dashed circle.

[0052] 11 is an explanatory diagram showing a usage state of an image projection device using the optical system 1 according to the third embodiment. The image projection device including the optical system 1 is placed horizontally on a support stand such as a table or on a floor. A screen SC is installed vertically above the support stand at a relatively short horizontal distance, for example, 0.6 m, rearward. Light generated by the optical system 1 is projected diagonally upward backward, realizing a short-focus and large-screen projection.

[0053] FIG. 12 is a graph showing the relative positional relationship between the reflecting surface R1 and the Y-direction intermediate image IMy and the X-direction intermediate image IMx in the optical system 1 according to Example 3, as viewed from a direction perpendicular to the Y cross section.

[0054] Looking at the graph, the Y-direction intermediate images IMy are distributed obliquely with respect to the Z direction from near coordinates (-2,0) to near coordinates (-19,-14.5). The X-direction intermediate images IMx are distributed obliquely with respect to the Z direction from near coordinates (0,0) to near coordinates (-12.5,-15) with a concave surface facing the reduced optical path. The reflecting surface R1 is distributed obliquely with respect to the Z direction from near coordinates (9,0) to near coordinates (1,-17) with a concave surface facing the reduced optical path.

[0055] In the present disclosure, the reflecting surface R1 may have a shape in which the concave surface faces the reduced optical path side along the intermediate image position in the X direction parallel to the X cross section of the light ray passing through the center of the longitudinal direction of the rectangular area, thereby suppressing image distortion on the screen SC.

[0056] Example 4 13 is a layout diagram showing an optical system 1 according to Example 4. This optical system 1 has a similar configuration to Example 1, but the first sub-optical system includes lens elements L1 to L3 and a prism PF, and the second sub-optical system including a prism PM projects an image obliquely upward and rearward in the case of an image projector. Below, descriptions that overlap with Example 1 will be omitted.

[0057] Lens element L1 has a biconvex shape (surfaces 2, 3). Lens element L2 has a negative meniscus shape with the convex surface facing the magnification side (surfaces 4, 5). Lens element L3 has a negative meniscus shape with the convex surface facing the magnification side (surfaces 6, 7).

[0058] Like the prism PM, the prism PF is formed of a transparent medium, such as glass or synthetic resin. The prism PF has a transmitting surface P located on the reduction side, a transmitting surface Q located on the enlargement side, and three reflecting surfaces K1, K2, and K3 located on the optical path between the transmitting surface P and the transmitting surface Q. The transmitting surface P has a free-form shape with a concave surface facing the reduction side (surface 9). The reflecting surface K1 has a free-form shape with a concave surface facing the reduction side and the enlargement side (surface 10). The reflecting surface K2 has a free-form shape with a convex surface facing the reduction side and the enlargement side (surface 11). The reflecting surface K3 has a free-form shape with a concave surface facing the reduction side and the enlargement side (surface 12). The transmitting surface Q has a free-form shape with a convex surface facing the reduction side (surface 13).

[0059] Prism PM has a transmitting surface A located on the reduction side, a transmitting surface B located on the enlargement side, and two reflecting surfaces R1 and R2 located on the optical path between transmitting surface A and transmitting surface B. Transmitting surface A has a free-form shape with a convex surface facing the reduction side (surface 14). Reflecting surface R1 has a free-form shape with concave surfaces facing both the reduction side and the enlargement side (surface 15). Reflecting surface R2 has a free-form shape with a convex surface facing in the direction in which the light ray incident on reflecting surface R1 is reflected (surface 16). Transmitting surface B has a free-form shape with a convex surface facing the enlargement side (surface 17).

[0060] The aperture stop ST defines the range through which the light beam passes through the optical system 1, and is positioned between the reduction conjugate point and the intermediate image position described above. As an example, the aperture stop ST is located between the lens element L3 and the transmission surface P of the prism PM (surface 8).

[0061] FIG. 14(a) is a Y cross-sectional view showing the optical path along which the chief ray passes in the optical system 1 according to the fourth embodiment, and FIG. 14(b) is an X cross-sectional view of the optical system 1 as viewed from above.

[0062] 14(a), for the sake of clarity, a chief ray that passes through the center of the original image SA in the X direction and passes through the bottom in the Y direction (normalized height Y = 0.0 at the reduction conjugate point), and a chief ray that passes through the center of the original image SA in the X direction and passes through the top in the Y direction (normalized height Y = 1.0 at the reduction conjugate point) are shown. Both chief rays pass through the first sub-optical system, enter the inside of the prism PM through the transmitting surface A, and are then reflected by the reflecting surface R1, and intersect with each other in the region CRy indicated by the dashed circle just before reaching the reflecting surface R2.

[0063] 14(b), for the sake of clarity, a chief ray passing through the left end of the original image SA in the X direction and a chief ray passing through the right end of the original image SA in the X direction are shown. Both chief rays pass through the first sub-optical system, enter the inside of the prism PM through the transmitting surface A, and are subsequently reflected by the reflecting surface R1. Just before reaching the reflecting surface R2, they intersect with each other in a region CRx indicated by a dashed circle.

[0064] 15 is an explanatory diagram showing a usage state of an image projection device using the optical system 1 according to the fourth embodiment. The image projection device including the optical system 1 is placed horizontally on a support stand such as a table or on a floor. A screen SC is installed vertically above and at a relatively short horizontal distance, for example, 0.2 m, rearward from the support stand. Light generated by the optical system 1 is projected diagonally rearward and upward, realizing a short-focus and large-screen projection.

[0065] FIG. 16 is a graph showing the relative positional relationship between the reflecting surface R1 and the Y-direction intermediate image IMy and the X-direction intermediate image IMx in the optical system 1 according to Example 4, as viewed from a direction perpendicular to the Y cross section.

[0066] Looking at the graph, the Y-direction intermediate images IMy are distributed obliquely with respect to the Z direction from near coordinates (-1,0) to near coordinates (12,-5.7). The X-direction intermediate images IMx are distributed obliquely with respect to the Z direction from near coordinates (0,0) to near coordinates (7.5,-6) with a concave surface facing the reduced optical path side. The reflecting surface R1 is distributed obliquely with respect to the Z direction from near coordinates (-4.5,-0.5) to near coordinates (-0.8,-6.8) with a concave surface facing the reduced optical path side.

[0067] In the present disclosure, the reflecting surface R1 may have a shape in which the concave surface faces the reduced optical path side along an intermediate image formation position in the X direction parallel to the X cross section of the light ray passing through the center of the longitudinal direction of the rectangular region. This makes it possible to suppress image distortion on the screen SC. In the optical system 1 according to the fourth embodiment, the prisms PF and PM are more effective in correcting lateral chromatic aberration when they are made of media having different refractive indices and Abbe numbers than when they are made of the same media.

[0068] Next, conditions that the optical system according to the present embodiment can satisfy will be described. Note that, although a number of conditions are specified for the optical system according to each embodiment, it is possible to obtain the corresponding effect by satisfying all of these conditions, or by satisfying each individual condition.

[0069] The optical system according to this embodiment is an optical system 1 having a reduction conjugate point on the reduction side and a magnification conjugate point on the magnification side, and having intermediate image formation positions therein that are conjugates to the reduction conjugate point and the magnification conjugate point, respectively. The reduction conjugate point has an imaging relationship in a rectangular area having a long direction and a short direction, a first sub-optical system including an aperture stop ST that defines a range through which a light beam passes through the optical system 1; a second sub-optical system that is provided on the magnification side of the first sub-optical system and includes a prism PM made of a transparent medium; The prism PM has a transmitting surface A located on the reduction side, a transmitting surface B located on the enlargement side, and at least one reflecting surface R1 located on an optical path between the transmitting surface A and the transmitting surface B, The aperture stop ST is positioned between the reduction conjugate point and the intermediate image position, A part or the whole of the intermediate images IMx and IMy formed at the intermediate imaging position is positioned inside the medium of the prism PM, the reflecting surface R1 closest to the intermediate image-forming position has a shape with a concave surface facing in a direction in which a light ray incident on the reflecting surface R1 is reflected; The transmitting surface B has a shape with a convex surface facing the magnification side, When the longitudinal direction of the rectangular area of ​​the reduction conjugate point is defined as the X direction, the lateral direction is defined as the Y direction, and the normal direction is defined as the Z direction, a plane including a position where a chief ray passing through the center in the X direction is reflected by the reflecting surface R1 is defined as a Y cross section, and a cross section perpendicular to the Y cross section is defined as an X cross section, the curvature shape of the reflecting surface R1 may be set so that when viewed from a direction perpendicular to the Y cross section, some of the chief rays passing through the reduction conjugate point intersect on the optical path between the reflecting surface R1 and the transmitting surface B, and when viewed from a direction perpendicular to the X cross section, some of the chief rays passing through the reduction conjugate point intersect on the optical path between the reflecting surface R1 and the transmitting surface B.

[0070] With this configuration, for both the Y cross section and the X cross section, multiple chief rays intersect on the optical path between the reflecting surface R1 of the prism and the transmitting surface B. Therefore, by using a small prism, the second sub-optical system can be made compact, and short-focus, large-screen projection or imaging is possible.

[0071] In the optical system according to this embodiment, the reflecting surface R1 may have a shape in which a concave surface faces the reduced optical path side along an intermediate imaging position in the X direction parallel to an X cross section of a light ray passing through the center of the longitudinal direction of the rectangular area.

[0072] With this configuration, image distortion on the screen SC can be suppressed.

[0073] In the optical system according to the present embodiment, a light flux passing through the first sub-optical system may include different intermediate image positions in the Y cross section and the X cross section.

[0074] According to this configuration, the imaging magnification can be set separately in the X direction and the Y direction, increasing the degree of freedom in design.

[0075] 19 is an explanatory diagram showing the definitions of the imaging magnifications MX and MY at the intermediate imaging position and the imaging magnifications MMX and MMY at the magnification conjugate point. In the optical system 1 according to the present disclosure, the reduction conjugate point, the intermediate imaging position, and the magnification conjugate point are optically conjugate with each other.

[0076] In the Y direction, the length ΔY1 at the reduction conjugate point, the length ΔY2 at the intermediate imaging position in the Y direction, and the length ΔY3 at the enlargement conjugate point are each imaged at a predetermined magnification. In this case, the imaging magnification MY at the intermediate imaging position in the Y direction parallel to the Y cross section with respect to the reduction conjugate point, and the Y-direction imaging magnification MMY at the enlargement conjugate point with respect to the reduction conjugate point are given by the following formulas. MY = |ΔY2 / ΔY1| MMY = |ΔY3 / ΔY1|

[0077] Similarly, in the X direction, the length ΔX1 at the reduction conjugate point, the length ΔX2 at the intermediate imaging position in the X direction, and the length ΔX3 at the enlargement conjugate point are each imaged at a predetermined magnification. In this case, the imaging magnification MX at the intermediate imaging position in the X direction parallel to the X cross section for the reduction conjugate point, and the X-direction imaging magnification MMX at the enlargement conjugate point for the reduction conjugate point are given by the following formulas. MX = |ΔX2 / ΔX1| MMX = |ΔX3 / ΔX1|

[0078] The optical system according to this embodiment may satisfy the following condition (1a) or (1b). 0<|MX|<10 (1a) 0<|MY|<10 (1b) Where: MX: Imaging magnification at the intermediate imaging position in the X direction parallel to the X section relative to the reduction conjugate point MY: Imaging magnification at the intermediate imaging position in the Y direction parallel to the Y cross section relative to the reduction conjugate point It is.

[0079] According to this configuration, the intermediate imaging position can be appropriately set, and image distortion on the screen SC can be suppressed while maintaining the second sub-optical system small. Furthermore, within the above range, the difference between the X-direction imaging magnification and the Y-direction imaging magnification on the screen SC can be minimized. If the upper limit of condition (1a) or condition (1b) is exceeded, the intermediate image formed in the second sub-optical system becomes large, making it difficult to maintain the compact size. It is preferable to set the imaging magnifications MX and MY at the intermediate imaging position so that they gradually decrease from the normalized height Y=0 at the reduction conjugate point to Y=1. By doing so, the field curvature at the intermediate imaging position can be set to the underside (reduction optical path side), and the field curvature on the screen SC can be suppressed within a good range.

[0080] Furthermore, by satisfying the following condition (1c) or (1d), the above effect can be more effectively achieved. 0.5<|MX|<7.5 (1c) 0.5<|MY|<7.5 (1d)

[0081] Furthermore, by satisfying the following condition (1e) or (1f), the above-mentioned effect can be more effectively achieved. 0.6<|MX|<5.0 (1e) 0.6<|MY|<5.0 (1f)

[0082] The optical system according to this embodiment may satisfy the following condition (2). |MX|>|MY| ···(2) Where: MX: X-direction imaging magnification MY: Imaging magnification in the Y direction It is.

[0083] With this configuration, it is possible to minimize the difference between the X-direction imaging magnification and the Y-direction imaging magnification on the screen SC. If condition (2) is not satisfied, a difference between the X-direction imaging magnification and the Y-direction imaging magnification on the screen SC will occur, making it difficult to maintain appropriate optical performance.

[0084] In the optical system according to this embodiment, the intermediate image formation position in the X direction may be between the intermediate image formation position in the Y direction and the reflecting surface R1.

[0085] With this configuration, the difference between the X-direction imaging magnification and the Y-direction imaging magnification on the screen SC can be minimized.

[0086] The optical system according to this embodiment may satisfy the following condition (3). Σ(|OPLY|-|OPLX|)>0 (3) Where: OPLX: the optical path length between the intermediate image position in the X direction and the reflecting surface R1 OPLY: the optical path length between the intermediate image position in the Y direction and the reflecting surface R1 Σ(|OPLY|-|OPLX|): The sum of the differences between the absolute values ​​of the optical path lengths OPLX and OPLY for the three principal rays passing through the normalized heights Y = 0.0, 0.5, and 1.0 at the reduced conjugate point. It is.

[0087] With this configuration, it is possible to minimize the difference between the X-direction imaging magnification and the Y-direction imaging magnification on the screen SC. If the lower limit of condition (3) is not met, the Y-direction imaging magnification becomes smaller than the X-direction imaging magnification on the screen SC, making it difficult to properly reproduce the original image SA.

[0088] Furthermore, by satisfying the following condition (3a), the above effect can be more effectively achieved. Σ(|OPLY|-|OPLX|)>2.5 ···(3a)

[0089] Furthermore, by satisfying the following condition (3b), the above effect can be more effectively achieved. Σ(|OPLY|-|OPLX|)>5.0 ···(3b)

[0090] The optical system according to this embodiment may satisfy the following condition (4). |2×(MMX-MMY) / (MMX+MMY)|<0.30 ···(4) Where: MMX: X-direction imaging magnification at the magnification conjugate point versus the reduction conjugate point MMY: Y-direction imaging magnification at the magnification conjugate point relative to the reduction conjugate point It is.

[0091] With this configuration, image distortion on the screen SC can be suppressed, and the difference between the X-direction imaging magnification and the Y-direction imaging magnification can be minimized. If the upper limit of condition (4) is exceeded, the Y-direction imaging magnification will differ from the X-direction imaging magnification on the screen SC, making it difficult to properly reproduce the original image SA. Condition (4) specifies the range within which the original image SA can be properly reproduced on the screen SC.

[0092] Furthermore, by satisfying the following condition (4a), the above effect can be more effectively achieved. |2×(MMX-MMY) / (MMX+MMY)|<0.15 ···(4a)

[0093] Furthermore, by satisfying the following condition (4b), the above effect can be more effectively achieved. |2×(MMX-MMY) / (MMX+MMY)|<0.08 ···(4b)

[0094] The optical system according to the present embodiment may satisfy the following condition (5). |θi|<50 (5) Where: θi: the angle of incidence (degrees) of the principal ray with respect to the normal of the transmitting surface B at the position where the principal ray is incident on the transmitting surface B when the principal ray passes through the transmitting surface B of the medium It is.

[0095] According to this configuration, it is possible to suppress the light reflected by the transmitting surface B when passing through the transmitting surface B, and it is possible to reduce the loss of the transmitted light, thereby suppressing the decrease in the amount of light in the projected image.

[0096] In the optical system according to the present embodiment, the transmitting surface B may have the largest effective area among the transmitting surface A, the transmitting surface B, and the at least one reflecting surface R1.

[0097] With this configuration, a uniform amount of light can be achieved in the projected image.

[0098] In the optical system according to this embodiment, the aperture stop ST may be positioned between the reduction conjugate point and the transmitting surface A.

[0099] With this configuration, the prism PM can be made smaller.

[0100] In the optical system according to this embodiment, all of a plurality of chief rays passing through the reduction conjugate point may intersect on an optical path between the reflecting surface R1 and the transmitting surface B.

[0101] According to this configuration, the second sub-optical system can be made compact by using a small prism, and projection or imaging with a short focal length and a large screen can be achieved.

[0102] In the optical system according to the present embodiment, either an entrance pupil or an exit pupil corresponding to the aperture stop may be positioned within the prism. Note that the entrance pupil is an image of the aperture stop as viewed from the reduction side. The exit pupil is an image of the aperture stop as viewed from the enlargement side.

[0103] According to this configuration, the second sub-optical system can be made compact by using a small prism, and projection or imaging with a short focal length and a large screen can be achieved.

[0104] In the optical system according to this embodiment, the intermediate image position may be positioned away from the reflecting surface R1 on the reduction side.

[0105] With this configuration, image distortion on the screen SC can be suppressed.

[0106] 20(a) to (d) are cross-sectional views in the Y direction showing various examples of the stepped structure of the prism PM. The various lens elements and prisms that make up the optical system 1 are generally attached to the inside of the lens barrel 50 using adhesives, metal fittings, etc. At that time, a highly accurate attachment structure is required to faithfully reproduce the various dimensions of the optical design.

[0107] Prism PM is provided with, for example, an end face PMa and an inside corner PMb that serve as mounting references. Meanwhile, lens barrel 50 is provided with an end face 50a and an outside corner 50b that correspond to the shapes of end face PMa and inside corner PMb. During mounting, end face PMa and end face 50a fit together, and inside corner PMb and outside corner 50b fit together, allowing prism PM to be fixed to lens barrel 50 with high precision and stability.

[0108] In the optical system according to this embodiment, a stepped structure may be formed on the outer periphery of the prism PM.

[0109] This configuration allows the prism to be attached to the external housing with high precision and stability.

[0110] The optical system according to this embodiment may be an imaging optical system.

[0111] With this configuration, the second sub-optical system can be made compact, and projection or imaging with a short focal length and a large screen is possible.

[0112] Numerical examples of the optical system according to Examples 1 to 4 will be described below. In each numerical example, all the units of length in the table are "mm", and all the units of the angle of view are "°". In each numerical example, the radius of curvature, surface spacing, Nd (refractive index for the d-line), vd (Abbe number for the d-line), N550 (refractive index at a wavelength of 550 nm), and decentering data (displacement amounts X, Y, and Z of the prism surface relative to the surface immediately preceding the optical system, and normal directions α, β, and γ of the prism surface relative to the surface immediately preceding the optical system) are shown. In addition, "variable" in the surface spacing means that it can be changed according to the image size (100" (inch), 80", 60", etc.) at the magnification conjugate point, as shown in the table below. In each numerical example, the shape of the aspheric surface is defined by the following formula. In addition, only coefficients other than the Conic coefficient k that are not 0 are shown as the aspheric coefficients.

[0113]

number

[0114] Where: z: Sag amount of the surface parallel to the z axis, r: radial distance (=√(x 2 +y 2 )) c: Curvature at the vertex of the face k: Conic coefficient, A~H: 4th to 18th order coefficients of r It is.

[0115] In addition, the free-form surface shape is expressed as a local Cartesian coordinate system (x, y, z) with the vertex of the surface as the origin. It is defined by the following formula using

[0116]

number

[0117]

number

[0118] In the following data, the i-th term of x and the j-th term of y, which are the free-form surface coefficients in the polynomial, are written as x**i*y**j. For example, "X**2*Y" indicates that the free-form surface coefficients are the quadratic term of x and the linear term of y in the polynomial.

[0119] (Numerical Example 1) For the optical system of Numerical Example 1 (corresponding to Example 1), lens data is shown in Table 1, aspheric lens shape data is shown in Table 2, and free curved surface shape data of the prism is shown in Table 3.

[0120] [Table 1]

[0121] [Table 2]

[0122] [Table 3]

[0123] (Numerical Example 2) For the optical system of Numerical Example 2 (corresponding to Example 2), lens data is shown in Table 4, aspheric lens shape data is shown in Table 5, and free curved surface shape data of the prism is shown in Table 6.

[0124] [Table 4]

[0125] [Table 5]

[0126] [Table 6]

[0127] (Numerical Example 3) For the optical system of Numerical Example 3 (corresponding to Example 3), lens data is shown in Table 7, aspheric lens shape data is shown in Table 8, and free curved surface shape data of the prism is shown in Table 9.

[0128] [Table 7]

[0129] [Table 8]

[0130] [Table 9]

[0131] (Numerical Example 4) For the optical system of Numerical Example 4 (corresponding to Example 4), lens data is shown in Table 10, and free curved surface shape data of the prism is shown in Table 11. In Example 4 only, the lens data is in absolute coordinates with respect to the first surface.

[0132] [Table 10]

[0133] [Table 11]

[0134] The following Tables 12 to 15 show the corresponding values ​​of the conditional expressions (1) to (4) in each of Numerical Examples 1 to 4, respectively.

[0135] [Table 12]

[0136] [Table 13]

[0137] [Table 14]

[0138] [Table 15]

[0139] Table 16 below shows the corresponding values ​​of conditional expression (5) in each of Numerical Examples 1 to 4.

[0140] [Table 16]

[0141] (Embodiment 2) Hereinafter, the second embodiment of the present disclosure will be described with reference to FIG. 21. FIG. 21 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 1 disclosed in the first embodiment, an image forming element 101, a light source 102, a control unit 110, and the like. The image forming element 101 is composed of a liquid crystal, a DMD, and the like, and generates an image to be projected onto a screen SC via the optical system 1. The light source 102 is composed of an LED (light emitting diode), a laser, and the like, and supplies light to the image forming element 101. The control unit 110 is composed of a CPU or an MPU, and the like, and controls the entire device and each component. The optical system 1 may be configured as an interchangeable lens that can be detachably attached to the image projection device 100, or may be configured as a built-in lens integrated into the image projection device 100.

[0142] The above image projection device 100, by virtue of the optical system 1 according to the first embodiment, is capable of short-focus and large-screen projection with a small device.

[0143] (Embodiment 3) Hereinafter, the third embodiment of the present disclosure will be described with reference to FIG. 22. FIG. 22 is a block diagram showing an example of an imaging device according to the present disclosure. The imaging device 200 includes the optical system 1 disclosed in the first embodiment, an imaging element 201, a control unit 210, and the like. 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 an object OBJ formed by the optical system 1 and converts it into an electrical image signal. The control unit 110 is composed of a CPU or an MPU, or the like, and controls the entire device and each component. The optical system 1 may be configured as an interchangeable lens that can be detachably attached to the imaging device 200, or may be configured as a built-in lens integrated into the imaging device 200.

[0144] The imaging device 200 described above is capable of capturing images with a short focal length and a large screen using the optical system 1 according to the first embodiment.

[0145] 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.

[0146] Therefore, among the components described in the accompanying drawings and the detailed description, not only components essential for solving the problem but also components that are not essential for solving the problem in order to illustrate the above technology may be included. Therefore, just because those non-essential components are described in the accompanying drawings or the detailed description, it should not be immediately recognized that those non-essential components are essential.

[0147] Furthermore, since the above-described embodiments are intended to illustrate the technology in the present disclosure, various modifications, substitutions, additions, omissions, and the like can be made within the scope of the claims or their equivalents. [Industrial Applicability]

[0148] The present disclosure is applicable to image projection devices such as projectors and head-up displays, and imaging devices such as digital still cameras, digital video cameras, surveillance cameras in surveillance systems, web cameras, vehicle-mounted cameras, etc. 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. [Explanation of symbols]

[0149] 1 Optical system SA Original Image PA Optical Elements L1~L14 lens elements ST aperture stop PM, PF Prism R1,R2,K1,K2,K3 Reflective surface A,B,P,Q Transparent surface SC Screen 100 Image projection device 200 Imaging device

Claims

1. An optical system including, in order from a reduction side to a magnification side, a first sub-optical system and a second sub-optical system, the second sub-optical system includes a prism having, in order from the reduction side, a first transmitting surface, a first reflecting surface, a second reflecting surface, and a second transmitting surface; the first reflecting surface has a concave shape facing a direction in which an incident light ray is reflected, the second reflecting surface is located between a first optical surface of the first sub-optical system that is located closest to the enlargement side and the first reflecting surface in a first direction from the reduction side to the enlargement side of the first sub-optical system, An optical system in which a Y cross section is a surface including a position where a chief ray passing through the center of a rectangular area of ​​a reduction conjugate point in a direction of a specified side is reflected by the first reflecting surface, and a curvature shape of the first reflecting surface is set so that, when viewed from a direction perpendicular to the Y cross section, some of the chief rays passing through the reduction conjugate point intersect on an optical path between the first reflecting surface and the second transmitting surface.

2. The optical system according to claim 1 , wherein the second reflecting surface is located between the first transmitting surface and the first reflecting surface in the first direction.

3. The optical system of claim 1 , wherein in the prism, the first transmitting surface and the second reflecting surface are located on a side on which the first sub-optical system is located in the first direction, and the first reflecting surface and the second transmitting surface are located on a side opposite to the side on which the first sub-optical system is located in the first direction.

4. The optical system according to claim 3 , wherein the first reflecting surface and the second transmitting surface have different curvatures.

5. The optical system according to claim 3 , wherein the first transmitting surface and the second reflecting surface have different curvatures.

6. The optical system according to claim 1 , wherein in the prism, the first transmitting surface and the first reflecting surface are located on one side in a direction perpendicular to the first direction, and the second reflecting surface and the second transmitting surface are located on the other side in the perpendicular direction.

7. The optical system according to claim 6 , wherein the second reflecting surface does not face the first reflecting surface in the first direction.

8. The optical system according to claim 7 , wherein the second reflecting surface faces the second transmitting surface in the first direction.

9. The optical system according to claim 8 , wherein the first reflecting surface faces the first transmitting surface in the first direction.

10. The optical system of claim 1 , wherein the second transmissive surface is disposed facing the first direction, and the second transmissive surface is disposed facing a second direction opposite the first direction.

11. The optical system of claim 1 , wherein the first transmitting surface has a different shape than the second transmitting surface, and the first transmitting surface and the second transmitting surface are disposed spaced apart from each other.

12. The optical system according to claim 1 , wherein the second reflecting surface has a shape with a convex surface facing in a direction in which a light ray incident on the first reflecting surface is reflected, and the first reflecting surface and the second reflecting surface have a non-planar curvature.

13. The optical system according to claim 1 , wherein the second transmitting surface is located on an opposite side to a side on which the first sub-optical system is located with respect to the second reflecting surface in the first direction.

14. The optical system of claim 1 , wherein the first reflecting surface is located between the first transmitting surface and a magnification conjugate point of the optical system in the first direction.

15. 2. The optical system according to claim 1, wherein a cross section perpendicular to the Y cross section is defined as an X cross section, and a curvature shape of the first reflecting surface is set so that, when viewed from a direction perpendicular to the X cross section, some of a plurality of chief rays passing through the reduction conjugate point intersect on an optical path between the first reflecting surface and the second transmitting surface.

16. The optical system according to claim 1 , wherein the direction of the predetermined side is a longitudinal direction of a rectangular area of ​​the reduced conjugate point.

17. An optical system according to any one of claims 1 to 16; and an image forming element that generates an image to be projected onto a screen via the optical system.

18. An optical system according to any one of claims 1 to 16; and an image sensor that receives an optical image formed by the optical system and converts it into an electrical image signal.

Images