Projection optical system, projection-type image display device, imaging device, and method of manufacturing optical element

The present application is based on, and claims priority from JP Application Serial Number 2019-037326, filed Mar. 1, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety.

1. Technical Field

The present disclosure relates to a projection optical system provided with a reflecting surface having a concave shape at a magnification side of an intermediate image, a projection-type image display device provided with the projection optical system, an imaging device provided with the projection optical system, and a method of manufacturing an optical element provided with a reflecting surface having a concave shape.

2. Related Art

In JP-A-2010-20344 (Document 1), there is described a projection-type image display device for projecting a projection image formed by an image formation section with a projection optical system in an enlarged manner. The projection optical system in Document 1 is constituted by a first optical system and a second optical system disposed in sequence from a demagnification side toward a magnification side. The first optical system is provided with a refracting optical system. The second optical system is formed of a reflecting mirror provided with a reflecting surface having a concave shape. The image formation section is provided with a light source and a light valve. The image formation section forms the projection image on a demagnification-side imaging surface of the projection optical system. The projection optical system forms an intermediate image between the first optical system and the reflecting surface, and then projects a final image on a screen disposed on a magnification-side imaging surface.

In the projection optical system in Document 1, when decreasing the projection distance, the intermediate image located on the demagnification side of the reflecting surface is tilted toward a direction along an optical axis of the first optical system. Here, the intermediate image enlarges as the intermediate image is tilted. When the intermediate image enlarges, there arises the necessity of enlarging the reflecting surface located at the magnification side of the intermediate image. Therefore, in the projection optical system provided only with a reflecting mirror having a concave shape at the magnification side of the intermediate image, there is a problem that the reflecting mirror is apt to grow in size when shortening the projection distance.

An aspect of the present disclosure is directed to a projection optical system including a first optical system, and a second optical system, wherein the first optical system and the second optical system are disposed in sequence from a demagnification side toward a magnification side, an intermediate image is formed between a demagnification-side imaging surface and a magnification-side imaging surface, the second optical system is an optical element having a first transmission surface, a reflecting surface, and a second transmission surface in sequence from the demagnification side toward the magnification side, the first transmission surface and the reflecting surface are located at one side of a optical axis, the second transmission surface is located at the other side of the optical axis, the reflecting surface has a concavely curved surface shape, the second transmission surface has a convexly curved surface shape protruding toward the magnification side, the optical element has a first member portion and a second member portion different in refractive index on an optical path of a ray passing through the optical element, and the first member portion is disposed so as to adhere to an outer peripheral surface of the second member portion.

Another aspect of the present disclosure is directed to a method of manufacturing an optical element, the optical element having a first transmission surface, a reflecting surface, and a second transmission surface in sequence from a demagnification side toward a magnification side, the first transmission surface and the reflecting surface being located at one side of a optical axis, the second transmission surface being located at the other side of the optical axis, the reflecting surface having a concave shape, and the second transmission surface having a convexly curved surface shape protruding toward the magnification side, the method including the steps of disposing a first transfer surface on which a surface shape of the reflecting surface is transferred as an internal surface of a metal mold, arranging a second member out of a first member and the second member different in refractive index inside the metal mold, injecting the first member between the second member and the first transfer surface inside the metal mold to make the first member cure, and applying a reflection coating to the first member to form the reflecting surface.

FIG. 1 is a schematic configuration diagram of a projection-type image display device equipped with a projection optical system.

FIG. 2 is a ray chart schematically showing the whole of the projection optical system.

FIG. 3 is a ray chart of a projection optical system in a practical example.

FIG. 4 is a ray chart of a second optical system.

FIG. 5 is an explanatory diagram of a material of an optical element constituting the second optical system.

FIG. 6 is an explanatory diagram of the magnifying power when providing only a reflecting surface on a magnification side of an intermediate image.

FIG. 7 is an explanatory diagram of the magnifying power when providing the reflecting surface and a second transmission surface at the magnification side of the intermediate image.

FIG. 8 is an explanatory diagram of a divergence angle of a light beam reaching an upper part of a screen.

FIG. 9 is an explanatory diagram of a divergence angle of a light beam reaching a lower part of the screen.

FIG. 10 is a diagram showing MTF at the magnification side of the projection optical system in the practical example.

FIG. 11 is a flowchart of a method of manufacturing an optical element.

FIG. 12 is an explanatory diagram of the method of manufacturing the optical element.

A projection optical system according to the present embodiment of the present disclosure and a projection-type image display device equipped with the projection optical system will hereinafter be described in detail with reference to the drawings.

Projection-Type Image Display Device

FIG. 1 is a schematic configuration diagram of a projection-type image display device equipped with the projection optical system according to the present disclosure. As shown in FIG. 1 , the projection-type image display device 1 is provided with an image formation section 2 for generating image light to be projected on a screen S, a projection optical system 3 for projecting the image light in an enlarged manner, and a control section 4 for controlling an operation of the image formation section 2 .

Image Light Generation Optical System and Control Section

The image formation section 2 is provided with a light source 10 , a first integrator lens 11 , a second integrator lens 12 , a polarization conversion element 13 , and a superimposing lens 14 . The light source 10 is formed of, for example, a super-high pressure mercury lamp or a solid-state light source. The first integrator lens 11 and the second integrator lens 12 each have a plurality of lens elements arranged in an array. The first integrator lens 11 divides a light beam from the light source 10 into a plurality of light beams. Each of the lens elements of the first integrator lens 11 converges the light beam from the light source 10 in the vicinity of the corresponding one of the lens elements of the second integrator lens 12 .

The polarization conversion element 13 converts the light from the second integrator lens 12 into predetermined linearly polarized light. The superimposing lens 14 superimposes the images of the respective lens elements of the first integrator lens 11 on the display area of each of a liquid crystal panel 18 R, a liquid crystal panel 18 G, and a liquid crystal panel 18 B described later via the second integrator lens 12 .

Further, the image formation section 2 is provided with a first dichroic mirror 15 , a reflecting mirror 16 and a field lens 17 R, and the liquid crystal panel 18 R. The first dichroic mirror 15 reflects R light as a part of the light beam having entered the first dichroic mirror 15 from the superimposing lens 14 , and transmits G light and B light each of which is a part of the light beam having entered the first dichroic mirror 15 from the superimposing lens 14 . The R light having been reflected by the first dichroic mirror 15 enters the liquid crystal panel 18 R via the reflecting mirror 16 and the field lens 17 R. The liquid crystal panel 18 R modulates the R light in accordance with an image signal to thereby form a red projection image.

Further, the image formation section 2 is provided with a second dichroic mirror 21 , a field lens 17 G, and the liquid crystal panel 18 G. The second dichroic mirror 21 reflects the G light as a part of the light beam from the first dichroic mirror 15 , and transmits the B light as a part of the light beam from the first dichroic mirror 15 . The G light having been reflected by the second dichroic mirror 21 enters the liquid crystal panel 18 G via the field lens 17 G. The liquid crystal panel 18 G is an image display element. The liquid crystal panel 18 G modulates the G light in accordance with the image signal to thereby form a green projection image.

Further, the image formation section 2 is provided with a relay lens 22 , a reflecting mirror 23 , a relay lens 24 , a reflecting mirror 25 and a field lens 17 B, and the liquid crystal panel 18 B. The B light having been transmitted through the second dichroic mirror 21 enters the liquid crystal panel 18 B via the relay lens 22 , the reflecting mirror 23 , the relay lens 24 , the reflecting mirror 25 , and the field lens 17 B. The liquid crystal panel 18 B is the image display element. The liquid crystal panel 18 B modulates the B light in accordance with the image signal to thereby form a blue projection image.

The liquid crystal panel 18 R, the liquid crystal panel 18 G, and the liquid crystal panel 18 B surround a cross dichroic prism 19 from three directions. The cross dichroic prism 19 is a light combining prism, and combines the light modulated by the respective liquid crystal panels 18 R, 18 G and 18 B with each other to generate the image light.

The projection optical system 3 projects the image light (the projection images formed by the respective liquid crystal panels 18 R, 18 G, and 18 B) combined by the cross dichroic prism 19 on the screen S in an enlarged manner.

The control section 4 is provided with an image processing section 6 to which an external image signal such as a video signal is input, and a display drive section 7 for driving the liquid crystal panel 18 R, the liquid crystal panel 18 G, and the liquid crystal panel 18 B based on the image signals output from the image processing section 6 .

The image processing section 6 converts the image signal input from external equipment into the image signals including the tones and so on of the respective colors. The display drive section 7 makes the liquid crystal panel 18 R, the liquid crystal panel 18 G, and the liquid crystal panel 18 B operate based on the projection image signals of the respective colors output from the image processing section 6 . Thus, the image processing section 6 displays the projection images corresponding to the image signals on the liquid crystal panel 18 R, the liquid crystal panel 18 G, and the liquid crystal panel 18 B, respectively.

Projection Optical System

Then, the projection optical system 3 will be described. A practical example will hereinafter be described as a configuration example of the projection optical system 3 to be installed in the projection-type image display device 1 .

Practical Example

FIG. 2 is a ray chart schematically showing the whole of the projection optical system 3 according to the present disclosure. FIG. 2 schematically shows eleven light beams F 1 through F 11 which reach the screen S from the projection optical system 3 . The light beam F 1 is a light beam which reaches the position where the image height is the lowest. The light beam F 11 is a light beam which reaches the position where the image height is the highest. The light beams F 2 through F 10 are light beams which reach respective height positions between the light beam F 1 and the light beam F 11 . FIG. 3 is a ray chart of the projection optical system of the practical example. FIG. 4 is a ray chart of a second optical system. FIG. 5 is an explanatory diagram of a material of an optical element constituting the second optical system.

As shown in FIG. 2 , the projection optical system 3 A according to the present example is constituted by a first optical system 31 and a second optical system 32 disposed in sequence from a demagnification side toward a magnification side. As shown in FIG. 3 and FIG. 4 , the projection optical system 3 A forms an intermediate image 33 between a demagnification-side imaging surface and a magnification-side imaging surface. In the present example, the intermediate image 33 is formed inside the second optical system 32 . It should be noted that the intermediate image 33 is not required to be inside the second optical system 32 .

The first optical system 31 is a refracting optical system provided with a plurality of lenses. In the present example, the first optical system 31 is provided with fifteen lenses. The second optical system 32 is formed of a single optical element 35 A. The intermediate image 33 is formed inside the optical element 35 A.

In the demagnification-side imaging surface, there are disposed the liquid crystal panel 18 R, the liquid crystal panel 18 G, and the liquid crystal panel 18 B of the image formation section 2 . In FIG. 2 and FIG. 3 , there is shown the liquid crystal panel 18 G as one of the three liquid crystal panels 18 R, 18 G, and 18 B. The liquid crystal panel 18 R, the liquid crystal panel 18 G, and the liquid crystal panel 18 B each form the projection image at one side in an optical axis N of the first optical system 31 in the demagnification-side imaging surface. On the magnification-side imaging surface, there is disposed the screen S.

As shown in FIG. 3 , the first optical system 31 has the cross dichroic prism 19 , and the fifteen lenses L 1 through L 15 . The first lens L 1 through the fifteenth lens L 15 are arranged in this order from the demagnification side toward the magnification side. In the present example, the second lens L 2 and the third lens L 3 are bonded to each other to form a first cemented lens L 21 . The fourth lens L 4 and the fifth lens L 5 are bonded to each other to form a second cemented lens L 22 . The eleventh lens L 11 and the twelfth lens L 12 are bonded to each other to form a third cemented lens L 23 . The thirteenth lens L 13 and the fourteenth lens L 14 are bonded to each other to form a fourth cemented lens L 24 . An aperture O 1 is disposed between the seventh lens L 7 and the eighth lens L 8 . The surface at the magnification side of the fifteenth lens L 15 is an aspherical surface. It should be noted that the first optical system 31 is not provided with the cross dichroic prism 19 in some cases.

As shown in FIG. 4 , the optical element 35 A has a first transmission surface 41 , a reflecting surface 42 , and a second transmission surface 43 in sequence from the demagnification side toward the magnification side. In the following description, three axes perpendicular to each other are defined as an X axis, a Y axis, and a Z axis for the sake of convenience. Further, a direction in which the first transmission surface 41 and the reflecting surface 42 are arranged is defined as a Z-axis direction, one side of the Y axis is defined as an upper side Y 1 , the other side of the Y axis is defined as a lower side Y 2 , and a plane perpendicular to the X axis and including the Y axis and the Z axis is defined as a Y-Z plane. Therefore, each of FIG. 1 through FIG. 5 shows when viewed from a direction parallel to the X axis. As shown in FIG. 2 , the optical axis N of the first optical system 31 extends in the Z-axis direction. The image formation section 2 forms the projection image at the upper side Y 1 in the optical axis N of the first optical system 31 .

The intermediate image 33 is formed at the lower side Y 2 in the optical axis N of the first optical system 31 . The screen S is located at the upper side Y 1 in the optical axis N of the first optical system 31 . The lateral direction of the screen S corresponds to the X-axis direction. The intermediate image 33 is an image vertically flipped with respect to the projection image to be formed on the screen S. Further, the intermediate image 33 is an image distorted so that a rectangular final image is projected on the screen S as the magnification-side imaging surface. More specifically, the intermediate image 33 has a shape with which the keystone distortion of the final image to be formed on the screen S becomes small. In other words, the intermediate image 33 is distorted opposite with respect to the keystone distortion of the final image. Therefore, in the intermediate image 33 , the side having the highest image height in the screen S is the shortest.

Further, in the following description, a virtual axis M extending in the Z-axis direction is set on the Y-Z plane. The virtual axis M is a design basis axis of the optical element 35 A. The virtual axis M is perpendicular to the screen S as the magnification-side imaging surface.

The first transmission surface 41 and the reflecting surface 42 are located on the lower side Y 2 of the virtual axis M. The second transmission surface 43 is located at the upper side Y 1 of the virtual axis M. The reflecting surface 42 is provided with a concavely curved surface shape when viewed from the first transmission surface 41 or the second transmission surface 43 . Therefore, the reflecting surface 42 has positive power. The reflecting surface 42 is disposed by applying a reflection coat on the optical element 35 A from the outside. The second transmission surface 43 is provided with a convexly curved surface shape protruding toward the magnification side. Therefore, the second transmission surface 43 has positive power. Here, the first transmission surface 41 , the reflecting surface 42 , and the second transmission surface 43 constitute a coaxial optical system having a plane rotationally symmetric with respect to the virtual axis M. Therefore, the virtual axis M is the design basis axis of the optical element 35 A. In the present example, the virtual axis M coincides with the optical axis N of the first optical system 31 .

In the optical element 35 A, each of an upper half and a lower half is configured to be rotationally symmetric about the virtual axis M. In other words, the first transmission surface 41 , the reflecting surface 42 , and the second transmission surface 43 are provided with shapes obtained by rotating cross-sectional shapes in the Y-Z plane shown in FIG. 3 around the virtual axis M in an angular range of 90° toward each of one side and the other side in the X-axis direction. In the present example, the first transmission surface 41 , the reflecting surface 42 , and the second transmission surface 43 are each provided with an aspherical surface shape.

In the optical element 35 A of the second optical system 32 , there can be defined an imaginary line P connecting an upper intersection point 53 and a lower intersection point 54 to each other, wherein an upper peripheral ray 51 a of an upper end light beam 51 passing through an upper end in the Y-axis direction of an effective ray range 50 of the second transmission surface 43 and an upper peripheral ray 52 a of a lower end light beam 52 passing through a lower end in the Y-axis direction of the effective ray range 50 cross each other on the Y-Z plane at the upper intersection point 53 , and a lower peripheral ray 51 b of the upper end light beam 51 and a lower peripheral ray 52 b of the lower end light beam 52 cross each other on the Y-Z plane at the lower intersection point 54 . The imaginary line P is tilted with respect to an imaginary vertical line V perpendicular to the virtual axis M on the Y-Z plane. Further, the tilt angle θ at which the imaginary line P is tilted with respect to the imaginary vertical line V is equal to or larger than 90°. In other words, the tilt angle θ of the upper intersection point 53 side of the imaginary line P rotating clockwise pivoted on the intersection point between the imaginary vertical line V and the imaginary line P is equal to or larger than 90°. Here, the imaginary line P can also be called a pupil on the Y-Z plane. The ray having entered the optical element is converged on the imaginary line P or in the vicinity of the imaginary line P. The ray having entered the optical element becomes the smallest in flux diameter in an area A in the vicinity of the imaginary line P.

Here, as shown in FIG. 5 , the optical element 35 A is provided with a first member portion 65 and a second member portion 66 different in refractive index from the first member portion 65 on an optical path of the ray having entered the optical element 35 A. The first member portion 65 is provided with a first first-member portion 65 ( 1 ) provided with the first transmission surface 41 , a second first-member portion 65 ( 2 ) provided with the reflecting surface 42 , and a third first-member portion 65 ( 3 ) provided with the second transmission surface 43 . The second member portion is located between the first first-member portion 65 ( 1 ) and the second first-member portion 65 ( 2 ) in the Z-axis direction. Further, the second member portion is located between the second first-member portion 65 ( 2 ) and the third first-member portion 65 ( 3 ) in the Z-axis direction. In the present example, the first member portion 65 is made of resin. The second member portion 66 is made of glass. As shown in FIG. 4 , the flux diameter of the ray having entered the optical element 35 A becomes the smallest in the second member portion 66 . In other words, the area A where the flux diameter of the ray having entered the optical element 35 A becomes the smallest is located inside the second member portion 66 .

The second member portion 66 has a spherical shape. To the second member portion 66 , the first first-member portion 65 ( 1 ) and the third first-member portion 65 ( 3 ) adhere on one side in the Z-axis direction, and the second first-member portion 65 ( 2 ) adheres at the other side in the Z-axis direction. Therefore, a bonding surface of the first first-member portion 65 ( 1 ) and a bonding surface corresponding to the first first-member portion 65 ( 1 ) of the second member portion 66 are provided with curved surface shapes corresponding to each other. In other words, the bonding surface corresponding to the first first-member portion 65 ( 1 ) of the second member portion 66 has a convexly curved surface shape. A bonding surface corresponding to the second member portion 66 of the first first-member portion 65 ( 1 ) has a concavely curved surface shape corresponding to the convexly curved surface shape of the second member portion 66 . Further, the bonding surface corresponding to the second first-member portion 65 ( 2 ) of the second member portion 66 and the bonding surface of the second first-member portion 65 ( 2 ) have curved surface shapes corresponding to each other. In other words, the bonding surface corresponding to the second first-member portion 65 ( 2 ) of the second member portion 66 has a convexly curved surface shape, and the bonding surface of the second first-member portion 65 ( 2 ) is a concavely curved surface shape corresponding to the convexly curved surface shape of the second member portion 66 . Further, a bonding surface of the third first-member portion 65 ( 3 ) and a bonding surface corresponding to the third first-member portion 65 ( 3 ) of the second member portion 66 have curved surface shapes corresponding to each other. In other words, the bonding surface corresponding to the third first-member portion 65 ( 3 ) of the second member portion 66 has a convexly curved surface shape. A bonding surface corresponding to the second member portion 66 of the third first-member portion 65 ( 3 ) has a concavely curved surface shape corresponding to the convexly curved surface shape of the second member portion 66 .

Here, the first member portion 65 and the second member portion 66 are different in refractive index from each other. Further, the bonding surface between the second member portion 66 and the first first-member portion 65 ( 1 ), the bonding surface between the second member portion 66 and the second first-member portion 65 ( 2 ), and the bonding surface between the second member portion 66 and the third first-member portion 65 ( 3 ) each have a curved surface shape. Therefore, the optical element 35 A has the power in the bonding surface between the second member portion 66 and the first first-member portion 65 ( 1 ), the bonding surface between the second member portion 66 and the second first-member portion 65 ( 2 ), and the bonding surface between the second member portion 66 and the third first-member portion 65 ( 3 ).

Further, the first member portion 65 and the second member portion 66 are different in material from each other, and are therefore different in heat resistance from each other. In other words, the second member portion 66 made of glass is higher in transmittance of a short-wavelength ray compared to the first member portion 65 made of resin. Thus, in the second member portion 66 , rise in temperature caused by absorption of the short-wavelength ray is suppressed. Therefore, the second member portion 66 is difficult to generate heat and high in heat resistance compared to the first member portion 65 .

It should be noted that an aperture O 2 is provided to the optical element 35 A in some cases. The aperture O 2 is disposed by dividing the optical element 35 A along the imaginary line P, applying light-blocking ink to a divisional surface, and then integrally bonding the optical element 35 A thus divided. It should be noted that the aperture O 2 is only required to be formed using a member capable of blocking a part of the light beam, and is not limited to what is formed using the ink.

Lens Data

The lens data of the projection optical system 3 A is as follows. The surface numbers are provided in sequence from the demagnification side toward the magnification side. The surfaces having the surface numbers attached with “*” are aspherical surfaces. The reference symbols represent the reference symbols of the respective lenses in the first optical system 31 . In the second optical system 32 , the reference symbols represent the reference symbols of the first transmission surface 41 , the reflecting surface 42 , and the second transmission surface 43 , the first first-member portion 65 ( 1 ), the second member portion 66 , the second first-member portion 65 ( 2 ), and the third first-member portion 65 ( 3 ). Specifically, the surface number 32 corresponds to the first transmission surface 41 . The surface number 33 corresponds to the bonding surface between the first first-member portion 65 ( 1 ) and the second member portion 66 . The surface number 34 corresponds to the bonding surface between the second member portion 66 and the second first-member portion 65 ( 2 ). The surface number 35 corresponds to the reflecting surface 42 . The surface number 36 corresponds to the bonding surface between the second first-member portion 65 ( 2 ) and the second member portion 66 . The surface number 37 corresponds to the bonding surface between the second member portion 66 and the third first-member portion 65 ( 3 ). Therefore, the surface number 33 , the surface number 34 , the surface number 36 , and the surface number 37 correspond to surfaces provided with the corresponding curved surface shapes. The reference symbol r represents a curvature radius, and the unit is millimeter. The reference symbol d represents an axial surface distance, and the unit is millimeter. The reference symbol nd represents a refractive index. The reference symbol νd represents an Abbe number. The reference symbol E represents an effective diameter.

The aspherical surface data of the surface numbers 31 , 32 , 35 , and 38 are as follows.

In the projection optical system 3 A of the present example, the optical element 35 A constituting the second optical system 32 is provided with the reflecting surface 42 shaped like a concavely curved surface, and the second transmission surface 43 shaped like a convexly curved surface protruding toward the magnification side. Therefore, the optical element 35 A is capable of refracting the light beam reflected by the reflecting surface 42 with the second transmission surface 43 . Therefore, it is easy to shorten the focal length of the projection optical system 3 A, namely to shorten the projection distance, compared to when the second optical system 32 is only provided with the reflecting surface 42 . Further, since the optical element 35 A is provided with the second transmission surface 43 shaped like a convexly curved surface protruding toward the magnification side, it is possible to prevent the reflecting surface 42 shaped like the concavely curved surface disposed at the magnification side of the intermediate image 33 from growing in size even when shortening the projection distance.

Such an advantage will be described with reference to FIG. 6 and FIG. 7 . FIG. 6 is an explanatory diagram of the magnifying power when the second optical system 32 is provided only with the reflecting surface 42 at the magnification side of the intermediate image 33 . FIG. 7 is an explanatory diagram of the magnifying power when the second optical system 32 is provided with the reflecting surface 42 and the second transmission surface 43 shaped like the convexly curved surface at the magnification side of the intermediate image 33 .

When the second optical system 32 is provided only with the reflecting surface 42 at the magnification side of the intermediate image 33 as shown in FIG. 6 , the magnifying power Q of the projection optical system 3 A is a ratio of a distance T from the reflecting surface 42 to the screen S with respect to a distance R between the intermediate image 33 and the reflecting surface 42 in the optical path of a specific ray from the intermediate image 33 to the screen S. In other words, Q=T/R is fulfilled. Therefore, the intermediate image 33 conjugated with the screen S as the magnification-side imaging surface is significantly tilted in a direction along the virtual axis M in order to match the magnifying power Q, and thus, the field curvature is made to be generated. Here, the intermediate image 33 enlarges when being tilted. Further, when the intermediate image 33 enlarges, there arises the necessity of enlarging the reflecting surface 42 located at the magnification side of the intermediate image 33 . Therefore, in the projection optical system 3 A provided only with the reflecting surface 42 shaped like a concavely curved surface at the magnification side of the intermediate image 33 , the reflecting surface 42 is apt to grow in size when shortening the projection distance. Further, when the intermediate image 33 grows in size, the distance between the first optical system 31 and the second optical system 32 is required, and the total length of the projection optical system 3 A elongates.

In contrast, in the present example, since the second optical system 32 is provided with the second transmission surface 43 shaped like a convexly curved surface at the magnification side of the reflecting surface 42 , it is possible to prevent the intermediate image 33 from growing in size. In other words, as shown in FIG. 7 , in the present example, the magnifying power Q of the projection optical system 3 A is a ratio of a distance T′ between the second transmission surface 43 and the screen S with respect to the sum of a distance R 1 between the intermediate image 33 and the reflecting surface 42 and a distance R 2 between the reflecting surface 42 and the second transmission surface 43 in the optical path of a specific ray from the intermediate image 33 to the screen S. In other words, Q=T′/(R 1 +R 2 ) is fulfilled. Thus, the intermediate image 33 conjugated with the screen S as the magnification-side imaging surface is not significantly tilted along the virtual axis M in order to match the magnifying power between the upper side and the lower side of the screen S, and the field curvature is made to decrease. Therefore, it is possible to prevent the intermediate image 33 from growing in size. Therefore, it is possible to prevent the reflecting surface 42 located at the magnification side of the intermediate image 33 from growing in size. Further, when the ray 51 on the outermost circumference can be refracted inward when passing through the first transmission surface 41 , it becomes possible to further reduce the size of the reflecting surface 42 . Further, since the second transmission surface 43 is shaped like a convexly curved surface, and has positive power, the action of converging the light beam works to make it possible to prevent the reflecting surface 42 from growing in size compared to when the second transmission surface 43 is not disposed.

Further, in the present example, the intermediate image 33 is located between the first transmission surface 41 and the reflecting surface 42 in the optical element 35 A. Therefore, it is possible to make the first optical system 31 and the optical element 35 A close to each other compared to when the intermediate image 33 is formed between the first optical system 31 and the optical element 35 A. Thus, the projection optical system 3 A can be made compact.

Further, in the present example, the first transmission surface 41 , the reflecting surface 42 , and the second transmission surface 43 of the second optical system are each an aspherical surface. Therefore, in the projection optical system 3 A according to the present example, it is possible to prevent generation of aberration.

Further, in the present example, since the first transmission surface 41 located on the demagnification side of the intermediate image 33 is the aspherical surface, it is possible to prevent the aberration from occurring in the intermediate image 33 . Further, the bonding surface between the first first-member portion 65 ( 1 ) and the second member portion 66 is located at the magnification side of the intermediate image 33 , and the bonding surface is provided with the curved surface shape. Therefore, it is easy to correct the aberration generated in the intermediate image 33 . Further, in the present example, the intermediate image 33 is not significantly tilted along the virtual axis M, but the intermediate image 33 is standing in a direction perpendicular to the virtual axis M. Therefore, it is easy to make the first transmission surface 41 and the intermediate image 33 close to each other in the Z-axis direction, and it is possible to dispose the aspherical surface at a position close to the intermediate image 33 . Therefore, it is possible to efficiently correct the aberration generated in the intermediate image 33 .

Further, in the present example, since the imaginary line P is tilted with respect to the imaginary vertical line V, it is possible to prevent an amount of the light in the upper peripheral part of the screen S from decreasing compared to when the imaginary line P is parallel to the imaginary vertical line V. In other words, when the imaginary line P is tilted with respect to the imaginary vertical line V, the divergence angle θ 0 of the light beam reaching the upper side of the screen S becomes large compared to when the imaginary line P is parallel to the imaginary vertical line V. Thus, an amount of the light reaching the upper side of the screen S increases. Here, FIG. 8 is an explanatory diagram of the divergence angle of the light beam reaching the screen S. FIG. 8 is a partial enlarged view of the part A shown in FIG. 2 . The divergence angle θ 0 of the light beam reaching the upper side of the screen S corresponds to a difference between an angle θ 1 formed by the screen S and the upper peripheral ray 51 a of the upper end light beam 51 and an angle θ 2 formed by the screen S and the lower peripheral ray 51 b of the upper end light beam 51 .

Further, when the divergence angle θ 0 of the light beam reaching the upper side of the screen S becomes large, the difference from the divergence ingle θ 0 of a light beam reaching a lower side of the screen S becomes small. Therefore, it is possible to prevent the amount of light in the upper peripheral part of the screen S from decreasing compared to that in the lower side. Here, FIG. 9 is an explanatory diagram of the divergence angle of the light beam reaching the screen S. FIG. 9 is a partial enlarged view of the part B shown in FIG. 2 . The divergence angle θ 0 of the light beam reaching the lower side of the screen S corresponds to a difference between an angle θ 1 formed by the screen S and the upper peripheral ray 52 a of the lower end light beam 52 and an angle θ 2 formed by the screen S and the lower peripheral ray 52 b of the lower end light beam 52 .

Further, in the present example, the tilt angle θ at which the imaginary line P is tilted with respect to the imaginary vertical line V is equal to or larger than 90°. Thus, the divergence angle θ 0 of the light beam reaching the lower side of the screen S becomes small. Therefore, since the difference between the divergence angle θ 0 of the light beam reaching the upper side of the screen S and the divergence angle θ 0 of the ray reaching the lower side of the screen S becomes small, it is possible to suppress the difference in amount of light between the upper side and the lower side generated in the screen S.

Then, in the present example, the ray passing through the optical element 35 A is converged inside the optical element 35 A by the reflecting surface 42 shaped like a concavely curved surface. Therefore, the light density rises inside the optical element 35 A, and a part of the optical element 35 A becomes high in temperature. In this case, there arises a problem that the part of the optical element 35 A having become high in temperature thermally expands to incur deterioration in optical performance of the projection optical system 3 A.

To cope with such a problem, the optical element 35 A is provided with the first member portion 65 made of resin and the second member portion 66 made of glass on the optical path of the ray passing through the optical element 35 A. Further, the area A where the flux diameter of the ray having entered the optical element 35 A becomes the smallest is made to be located in the second member portion 66 . Thus, the area A in which the light density becomes high inside the optical element 35 A, and which is apt to become high in temperature is formed of a material which is difficult to generate heat and high in heat resistance. Therefore, it is possible to prevent or avoid a part of the optical element 35 A having become high in temperature from thermally expanding to incur deterioration in optical performance of the projection optical system 3 A.

Further, since the intermediate image 33 is formed in the second member portion 66 , there is no chance for the intermediate image 33 to traverse the bonding surface between the first member portion 65 and the second member portion 66 . Therefore, it is possible to prevent the projection image from deteriorating due to the bonding surface between the first member portion 65 and the second member portion 66 .

Further, in the present example, the optical element 35 A has the power in the bonding surface between the second member portion 66 and the first first-member portion 65 ( 1 ), the bonding surface between the second member portion 66 and the second first-member portion 65 ( 2 ), and the bonding surface between the second member portion 66 and the third first-member portion 65 ( 3 ). Therefore, it is possible for the optical element 35 A to control a variety of types of aberration in these bonding surfaces to improve the resolution.

As described above, according to the projection optical system 3 A of the present example, it is possible to perform correction of the variety of types of aberration in the second optical system 32 even when the second optical system 32 is formed of a single optical element 35 A. Therefore, the degree of design freedom of the first optical system 31 can be ensured.

FIG. 10 is a diagram showing MTF on the magnification side of the projection optical system 3 A. The horizontal axis in FIG. 10 showing the MTF represents a spatial frequency. The vertical axis represents a contrast reproduction ratio. As shown in FIG. 10 , the projection optical system 3 A according to the present example has high resolution.

Further, in the present example, the second member portion 66 made of glass has a spherical shape in the optical element 35 A. Further, the second member portion 66 made of glass is not provided with an aspherical surface. Therefore, it is easy to manufacture the second member portion 66 . On the other hand, in the optical element 35 A, the first first-member portion 65 ( 1 ) provided with the first transmission surface 41 as an aspherical surface, the second first-member portion 65 ( 2 ) provided with the reflecting surface 42 as an aspherical surface, and the third first-member portion 65 ( 3 ) provided with the second transmission surface 43 as an aspherical surface are all made of resin. Therefore, it is easy to provide the aspherical surfaces to the optical element 35 A compared to when the first first-member portion 65 ( 1 ), the second first-member portion 65 ( 2 ), and the third first-member portion 65 ( 3 ) are made of glass.

Here, a method of manufacturing the optical element 35 A will be described. FIG. 11 is a flowchart of the method of manufacturing the optical element 35 A. FIG. 12 is an explanatory diagram of the method of manufacturing the optical element 35 A. When manufacturing the optical element 35 A, firstly, as a metal mold for manufacturing the optical element, there is prepared a metal mold 70 provided with a first transfer surface 71 , a second transfer surface 72 , and a third transfer surface 73 as internal surfaces, wherein the surface shape of the first transmission surface 41 is transferred as an internal surface on the first transfer surface 71 , the surface shape of the reflecting surface 42 is transferred on the second transfer surface 72 , and the surface shape of the second transmission surface 43 is transferred on the third transfer surface 73 .

Then, an optical member 75 (a second member) made of glass is disposed inside the metal mold 70 . In the present example, the optical member 75 has a spherical shape. Subsequently, resin (a first member) is injected in a space 76 between the optical member 75 and the first transfer surface 71 , a space 77 between the optical member 75 and the second transfer surface 72 , and a space 78 between the optical member 75 and the third transfer surface 73 in the metal mold 70 , and then the resin is made to cure. Here, ultraviolet curable resin can be used as the resin. Further, when making the resin cure, it is possible to irradiate the part where the resin is injected with ultraviolet light.

Subsequently, the optical member 75 to which the resin has integrally adhered is taken out from the metal mold 70 . Subsequently, a reflection coating is applied on the resin portion to which the second transfer surface 72 is transferred to form the reflecting surface 42 . Further, an antireflection coating is applied on the resin portion to which the first transfer surface 71 is transferred to form the first transmission surface 41 . Further, an antireflection coating is applied on the resin portion to which the third transfer surface 73 is transferred to form the second transmission surface 43 . Thus, the optical element 35 A is completed.

The second member portion 66 has the spherical shape in the example described above, but can have another shape.

It should be noted that it is also possible to dispose one or two of the surfaces of each of the first transmission surface 41 and the second transmission surface 43 on the outer peripheral surfaces of the second member portion 66 made of glass.

When constituting an imaging device using the projection optical system 3 , an imaging element 100 is disposed on the demagnification-side imaging surface of the projection optical system 3 as shown in FIG. 2 .