JP5754522B2 - Image projection device - Google Patents

Description

  One aspect of the present invention relates to an image projection apparatus.

  In recent years, a display device (hereinafter referred to as a light valve) using a transmission type, reflection type dot matrix liquid crystal, DMD (Digital Micro-mirror Device) or the like is used to enlarge and project an image displayed on the light valve onto a screen. Attention has been focused on an enlarged projection method that shows a large screen. According to such a magnified projection method, it is possible to obtain a powerful large screen without being restricted by the size of the screen. Therefore, the image magnified projection device (projector) can be used more widely in offices, schools, and homes. Is being used. The image display device includes a front projection type that observes reflected light by enlarging and projecting the image on the light valve onto a projection screen such as a reflective screen provided away from the device, and a transmissive screen in the device. There is a rear projection type in which an image on the light valve is enlarged and projected from the back side of the screen, and the image is observed from the screen surface side.

  However, assuming a situation where the projector is actually used, the installation location of the projector becomes a problem. For example, in the case of a front type projector that projects an image forward in an office, when using it in a relatively small meeting room with a small number of people, the projection screen size, projection distance, connection with a PC, a desk that is easy to discuss Due to the layout and other factors, there were not a few restrictions on the installation location of the projector, and there were problems with poor usability. In addition, especially when projecting presentation materials on a projector and explaining it, the presenter may be forced to stand between the projector and the screen, but the shadow of the presenter is reflected on the screen at that time. As a result, there is a problem that a part of the projection screen cannot be seen by the listener.

  Recently, various devices have been devised to reduce the projection distance on a large screen. For example, in order to obtain a screen size of 50 to 60 inches diagonally, the conventional technology requires at least about 1 m with the front type. A projection distance is necessary, and at this distance, the shadow of the presenter often appears on the screen and becomes a problem.

  In addition, rear-type display devices and rear projectors have been provided in which a projector is housed in a cabinet and rear-projected onto a screen provided in the front of the cabinet so that an enlarged image can be viewed from the front of the cabinet. However, there is a limit to the miniaturization of the device itself even if it is bent several times with a plane mirror etc. in the housing, in order to achieve space saving in the depth direction. There is an increasing demand to reduce the projection distance.

  In order to solve the above problem, an invention in which the projection distance of the optical system is shortened is described in, for example, Japanese Patent Application Laid-Open No. 2004-258620 (Patent Document 1).

  In the invention described in Japanese Patent Application Laid-Open No. 2004-258620, an optical image in which an intermediate image is formed by a first optical system having a positive power, and the intermediate image is enlarged and projected on a free curved surface reflecting surface having a positive power. It is a system. In any embodiment, the shape of the free-form surface mirror is as follows: “A rotationally asymmetric reflection surface is a curved surface expressed as a function of two-dimensional coordinates, and at least one of the two-dimensional coordinates in the region of the curved surface irradiated with light. The partial differential coefficient of the function with respect to the coordinates in one direction is a positive or negative value ”and has a smooth shape with no inflection point. Since the first optical system consisting of a refractive optical system is a decentered optical system including a lens that is shifted decentered and tilted decentered, it is very difficult to assemble because the optical axis reference centering cannot be performed when assembling the lens during manufacturing. It is difficult to manufacture. Further, in Example 6, the first optical system is obtained by adding a free-form surface lens to an axially symmetric lens system that is not decentered. In addition, it is difficult to assemble the optical system.

  In another example, there is an invention described in Japanese Patent Application Laid-Open No. 2006-292901 (Patent Document 2).

In the invention described in Japanese Patent Laid-Open No. 2006-292901, an optical system in which the projection distance is shortened by using a free-form surface mirror for the lens system and the second optical system is achieved. An inflection point is observed (there is a point where ∂ ² f (x, 0) / ∂x ² = 0 at y = 0). Therefore, there are positions where the power of the surface reverses positive and negative, and in order to compensate for this, there are many optical elements that are highly difficult to manufacture in the lens system of the first optical system that controls the light beam incident on the free-form surface mirror. It was necessary to arrange a free-form lens. For this reason, a free-form surface lens that includes a core and has a high degree of manufacturing difficulty makes the optical system expensive and difficult to assemble.

  On the other hand, the inventor of the present invention is capable of enlarging and projecting an image on an object surface at a short projection distance, and has a simple optical system, so that the apparatus cost is low, and the new projection optics achieves ease of assembly. And an image display device using this projection optical system have been conceived.

One object of the present invention is to provide an image projection apparatus including a projection optical system that can be more easily manufactured .

A first aspect of the present invention includes a light source, an image forming element, a rotationally symmetric optical system and a rotationally asymmetric optical system, and projects an image formed on the image forming element using light from the light source. In the image projection apparatus including a projection optical system that projects onto a surface, the rotationally asymmetric optical system includes at least one optical element having a rotationally asymmetric reflective surface, and the rotationally asymmetric reflective surface includes two-dimensional coordinates. And the partial differential coefficient of the function with respect to the coordinates in at least one direction in the two-dimensional coordinates is a positive or negative value in the curved surface region irradiated with the light. with some, the curved surface is in the region, closer to the rotationally symmetric optical system of the optical axis in one direction, a large valley shape formed in a direction perpendicular to the one direction, 且, Farther from the optical axis in a direction perpendicular to the direction of the one direction and the optical axis, with those that is configured to a large curvature in a plane containing the direction of the one direction and the optical axis, the rotating An optical element having power constituting a symmetric optical system is composed of a plurality of lenses, and a rotational symmetry axis of the rotationally symmetric optical system does not intersect the image formed on the image forming element. The image projection apparatus.

According to one aspect of the present invention, it is possible to provide an image projection apparatus including a projection optical system that can be more easily manufactured .

FIG. 1 is a diagram showing the configuration of the projection optical system of Example 1 according to the embodiment of the present invention. FIG. 2 is a diagram illustrating a 24-plane local coordinate system, a reference XY plane, and a free-form curved reflecting mirror within an effective diameter of the projection optical system according to the first embodiment. FIG. 3 is a diagram showing a free-form curved reflecting mirror within the effective diameter when x ₀ = 0, 10, 20, 30, 40, 50, 60 in the projection optical system of Example 1 when x ₀ = 0, 10, 20, 30, 40, 50, 60. FIG. 4 shows a second-order differential curve 自由 of the free-form curved reflecting mirror within the effective diameter when x ₀ = 0, 10, 20, 30, 40, 50, 60 in the projection optical system of Example 1 and x ₀ = 0, 10, 20, 30, 40, 50, 60. It is a figure which shows ² f (x0, y) / (y) ² . 5 is parallel to the XZ plane in the projection optical system of Example 1, and y ₀ = 40, 30, 20, 10, ₀ , −10, −20, −30, −40, −50, −60, and −70. It is a figure which shows the free-form surface reflective mirror in an effective diameter when it is set to. 6 is parallel to the XZ plane in the projection optical system of Example 1, and y ₀ = 40, 30, 20, 10, ₀ , −10, −20, −30, −40, −50, −60, and −70. Is a diagram showing a second derivative curve ∂ ² f (x, y0) / ∂x ² of the free-form curved reflecting mirror within the effective diameter. FIG. 7 is a diagram illustrating an arrangement of objects on the object plane in the first embodiment. FIG. 8 is a spot diagram for the projection optical system of the first embodiment. FIG. 9 is a diagram illustrating the position of each spot on the image plane of the projection optical system according to the first embodiment. FIG. 10 is a diagram showing the configuration of the projection optical system of Example 2 according to the embodiment of the present invention. FIG. 11 is a diagram illustrating a free-form surface reflecting mirror within the effective diameter when x ₀ = 0, 10, 20, 30, 40, 50 in the projection optical system of Example 2 when x ₀ = 0, 10, 20, 30, 40, 50. FIG. 12 shows the second-order differential curve ∂ ² f of the free-form curved reflecting mirror within the effective diameter when x ₀ = 0, 10, 20, 30, 40, 50 parallel to the YZ plane in the projection optical system of Example 2. it is a diagram showing the ^{(x0, y) / ∂y 2} . FIG. 13 shows a free-form curved reflecting mirror within an effective diameter when y ₀ = 60, 50, 40, 30, 20, 10, ₀ , −10 in the projection optical system of Example 2 when y ₀ = 60, 50, 40, 30, 20, 10, ₀ , −10. FIG. FIG. 14 shows two free-form curved reflecting mirrors within the effective diameter when y ₀ = 60, 50, 40, 30, 20, 10, ₀ , −10 in the projection optical system of Example 2 when y ₀ = 60, 50, 40, 30, 20, 10, ₀ , −10. FIG. 6 is a diagram illustrating a ^second derivative curve ∂ ² f (x, y0) / ∂x ² . FIG. 15 is a diagram illustrating an arrangement of objects on the object plane in the second embodiment. FIG. 16 is a spot diagram for the projection optical system according to the second embodiment. FIG. 17 is a diagram illustrating the position of each spot on the image plane of the projection optical system according to the second embodiment. FIG. 18 is a diagram illustrating an example of one image projection apparatus including the projection optical system of the example according to the embodiment of the present invention. FIG. 19 is a diagram illustrating an example of another image projection apparatus including the projection optical system of the example according to the embodiment of the present invention. FIG. 20 is a diagram for explaining Petzval sum.

  (Projection optical system and image projection apparatus)

  Embodiments described herein relate generally to a projection optical system and an image projection apparatus.

  A first object of an embodiment of the present invention is to provide a projection optical system that can be more easily manufactured.

  A second object of the embodiment of the present invention is to provide an image projection apparatus including a projection optical system that can be more easily manufactured.

  A first aspect of an embodiment of the present invention is a projection optical system that includes a rotationally symmetric optical system and a rotationally asymmetric optical system and projects light from an object onto a projection surface. It is composed of at least one optical element having a rotationally asymmetric reflective surface, and the rotationally asymmetric reflective surface is a curved surface expressed as a function of two-dimensional coordinates, and the region of the curved surface irradiated with the light In the projection optical system, the partial differential coefficient of the function with respect to the coordinate in at least one direction in the two-dimensional coordinate is a positive or negative value.

  According to a second aspect of the embodiment of the present invention, in the image projection apparatus that projects an image onto a non-projection surface, the image projection apparatus includes the projection optical system according to the first aspect of the embodiment of the present invention. It is.

  According to the first aspect of the embodiment of the present invention, it is possible to provide a projection optical system that can be more easily manufactured.

  According to the 2nd aspect of embodiment of this invention, it becomes possible to provide the image projection apparatus containing the projection optical system which can be manufactured more easily.

  Next, an embodiment (embodiment) of the present invention will be described with reference to the drawings.

  A first embodiment of the present invention is a projection optical system that includes a rotationally symmetric optical system and a rotationally asymmetric optical system and projects light from an object onto a projection surface, and the rotationally asymmetric optical system includes: A projection optical system comprising at least one optical element having a rotationally asymmetric reflecting surface.

  According to the first embodiment of the present invention, it is possible to provide a projection optical system that can be manufactured more easily.

  In the projection optical system according to the first embodiment of the present invention, it is preferable that the rotationally asymmetric reflecting surface is a curved surface expressed as a function of two-dimensional coordinates, and the curved surface irradiated with the light. In the region, the partial differential coefficient of the function with respect to the coordinate in at least one direction in the two-dimensional coordinate is a positive or negative value.

  In the projection optical system according to the first embodiment of the present invention, preferably, the coordinates in at least one direction in the two-dimensional coordinates are the coordinates in the first direction in the two-dimensional coordinates and the coordinates in the two-dimensional coordinates. Consists of coordinates in a second direction orthogonal to one direction.

For example, the projection optical system according to the first embodiment of the present invention is a projection optical system that projects an object on an image plane by enlarging or reducing an object, and includes at least a first optical system composed of an axially symmetric optical system, An optical system comprising a second optical system including one free-form curved reflecting surface, wherein the free-form curved form is expressed as Z = f (x, y), where Z is the sag amount from the reference XY plane. Further, a second-order differential expression ∂ ² f (x, y ₀ ) / ∂x ² or ∂ of a curve formed when a surface within the effective diameter of the reflecting surface is cut by an arbitrary cross section parallel to the XZ plane or the YZ plane ^The projection optical system may be characterized in that ² f (x ₀ , y) / ∂y ² satisfies the following expression.

For any coordinate x and y within the effective diameter,
∂ ² f (x, y ₀ ) / ∂x ² ≠ 0 or ∂ ² f (x ₀ , y) / ∂y ² ≠ 0
(However, x ₀ and y ₀ are constants indicating coordinates within the effective diameter.) (1)
In this example, since there is no inflection point in the free-form curved reflecting mirror, there is no place where the positive / negative power is reversed in the plane. The first optical system can be configured with an axisymmetric optical system that is easy to assemble and easy to manufacture while achieving good resolution performance on the image plane. Become.

  That is, such a projection optical system controls the power in the X and Y directions independently by being asymmetric with respect to the first optical system, which is an axially symmetric optical system that achieves ease of assembly during manufacture. A second optical system including a free-form surface mirror that can achieve good resolution on the image surface because the free-form surface shape has no inflection point, and therefore the surface power does not reverse positive or negative It is possible to enlarge and project an image on the object surface with a short projection distance, and to provide an optical system that achieves easy assembly with a low device cost due to a simple optical system. Is possible.

  The projection optical system may be a projection optical system in which a reflection surface having the power of the second optical system is only the reflection surface having the free-form surface.

  In the case of this example, it may be easy to assemble a mirror optical system that is severe with respect to positional deviation such as decentering accuracy.

  In the projection optical system according to the first embodiment of the present invention, preferably, an image conjugate with the object is formed between the rotationally symmetric optical system and the rotationally asymmetric optical system.

  For example, the projection optical system described above may be a projection optical system having an intermediate image in which a light beam emitted from an object is substantially converged between a first optical system and a second optical system.

  In the case of this example, once the intermediate image is formed, the entire optical system magnification can be divided before and after the intermediate image, so that the design can proceed independently and the design can be facilitated.

  In the projection optical system according to the first embodiment of the present invention, preferably, the rotational symmetry axis of the rotationally symmetric optical system does not intersect the object.

  For example, in the above projection optical system, the object to be projected may be a projection optical system that does not run on the optical axis of the first optical system.

  In this example, when the light beam emitted from the first optical system enters the free-form surface reflecting mirror, it easily enters the free-form surface reflecting mirror at a position shifted with respect to the optical axis and is reflected by the free-form surface reflecting mirror. In some cases, the incident light beam easily forms an image on the image plane without hitting the first optical system (the first optical system rarely emits light from the free-form surface mirror to the screen).

  In the projection optical system according to the first embodiment of the present invention, it is preferable that the optical element having power constituting the rotationally symmetric optical system includes at least one lens.

  For example, in the above-described projection optical system, the projection optical system in which the element having the power constituting the first optical system is only a lens may be used.

  In the case of this example, a mirror system having higher decentration sensitivity with respect to the refractive system is not employed in the first optical system, so that assembly adjustment may be easy.

  In the projection optical system according to the first embodiment of the present invention, preferably, the rotationally symmetric optical system includes at least one optical element having a rotationally symmetric aspherical surface.

  For example, in the above-described projection optical system, the projection optical system may have a surface having an axisymmetric aspheric shape in the first optical system.

  In the case of this example, by adopting an axisymmetric lens, the degree of freedom in design is improved, the light beam convergence is good, the resolution performance is improved, and the same function can be followed with a small number of sheets. is there.

  In the projection optical system according to the first embodiment of the present invention, preferably, the optical element having power closest to the rotationally asymmetric optical system in the rotationally symmetric optical system includes at least the rotationally symmetric aspherical surface. One of the optical elements.

  For example, in the projection optical system described above, at least one of the surfaces having an axisymmetric aspheric shape in the first optical system is disposed on a surface located closest to the image plane of the first optical system. It may be a projection optical system.

  In the case of this example, the light beam incident on the lens located closest to the image plane side is separated into the most part of the first optical system and enters the lens, so that each light beam can be controlled independently. In particular, it is easy to control distortion and curvature of field, and the imaging performance on the image plane may be improved.

  In the projection optical system according to the first embodiment of the present invention, preferably, the rotationally symmetric optical system includes a folding mirror that folds the rotationally symmetric axis of the rotationally symmetric optical system.

  For example, in the projection optical system described above, a projection optical system in which a reflection mirror for turning back the optical path is disposed in the first optical system.

  In the case of this example, by arranging the folding mirror in the first optical system and folding the optical path, the optical path from the object to the folding mirror can be folded back into a space where the space is vacant. Can occupy a small area, and the housing size can be compact.

  In the projection optical system according to the first embodiment of the present invention, preferably, the rotationally asymmetric optical system is an optical system that converges the light.

  For example, in the projection optical system described above, the second optical system may be a projection optical system having a positive power.

  In this example, the light flux from the intermediate image to the second optical system diverges, but it may be able to be condensed again by a reflecting surface having positive power. When the number of reflecting surfaces is 2 or more, the combined power of the reflecting surfaces may be positive, and there may be a reflecting surface with a negative power. At this time, the power of one or more reflecting surfaces is positive. The reflecting surface having a positive power is a concave mirror.

  The projection optical system according to the first embodiment of the present invention is preferably a substantially telecentric optical system on the object side.

  For example, in the above-described projection optical system, a projection optical system in which the object side is a substantially telecentric optical system may be used.

  In the case of this example, since the principal ray of the light beam emitted from the uniformly illuminated image forming element can be taken into the first optical system at the same angle, the brightness of the magnified image on the image plane can be made almost uniform. . In addition, when a film having an incident angle characteristic is disposed between the image forming element and the first optical system, there is no spread of the incident angle on the film due to a change in the angle of the principal ray emitted from the image forming element, and each light flux Therefore, the incident angle range for achieving the film performance can be narrowed, and the cost can be easily reduced.

  The projection optical system according to the first embodiment of the present invention preferably reflects the light from the first optical system that forms a second image conjugate with the first image, and the second image. A projection optical system including a reflective optical element that includes a second optical system that projects a third image conjugate with the second image onto a projection surface, wherein the first optical system includes: A projection optical system having a Petzval sum with a sign opposite to the sign of the Petzval sum of the second optical system.

  In this case, it is possible to provide a projection optical system with reduced field curvature. Thereby, the curvature of field on the screen surface, which is the image plane, can be reduced, and the resolution performance can be improved.

  In the projection optical system according to the first embodiment of the present invention, preferably, the Petzval sum of the first optical system is negative.

  In this case, by making the Petzval sum of the first optical system negative, it is possible to reduce the field curvature generated by the reflecting mirror having the positive refractive power of the second optical system. Image performance may be improved.

    In the projection optical system according to the first embodiment of the present invention, the Petzval sum of the first optical system is preferably smaller than −0.0115.

  In this case, the intermediate image can be generated in a form that greatly corrects the field curvature that occurs when the intermediate image is magnified by a reflecting mirror having a positive refractive power in advance, so that the magnification can be increased. In some cases, an intermediate image that is an object can be reduced. In some cases, the reflecting mirror having the positive refractive power can be made small. In addition, resolution performance may be improved.

  In the projection optical system according to the first embodiment of the present invention, preferably, the mirror surface of the mirror having the positive refractive power is directed from the intersection of the mirror surface and the optical axis toward the periphery of the mirror surface. It is a surface with a decreasing curvature.

  In this case, the distortion of the magnified image on the screen can be corrected more favorably, and the resolution performance can be improved.

  In the projection optical system according to the first embodiment of the present invention, it is preferable that the second image is an image that is inclined and curved with respect to the optical axis.

  In this case, the field curvature of the enlarged image on the screen can be reversely corrected on the object side (intermediate image), and the resolution performance can be improved.

  The projection optical system according to the first embodiment of the present invention preferably reflects a first optical system that forms a second image conjugate with the first image, and light from the second image. A projection optical system including a reflective optical element and a second optical system that projects a third image conjugate with the second image onto a projection surface, the first optical system including a diaphragm, And at least one optical element having a positive refractive power and at least one optical element having a negative refractive power provided between the stop and the second image, the positive refractive power An optical element having the strongest positive refractive power in at least one optical element comprising: an optical element having the strongest negative refractive power in the diaphragm and at least one optical element having the negative refractive power Is a projection optical system provided between the two.

  In this case, a smaller projection optical system can be provided. In particular, since the size of the final lens diameter can be reduced, the manufacturing error is small, the resolution performance can be improved, and the cost may be reduced.

  In the projection optical system according to the first embodiment of the present invention, preferably, the optical element having the aspherical surface is an optical element having the strongest positive refractive power in the at least one optical element having the positive refractive power. Provided between the element and the second image.

  This makes it possible to independently correct the light flux at each angle of view, which may further improve the resolution of the magnified image.

  The second embodiment of the present invention is an image projection apparatus that projects an image onto a non-projection surface, and is an image projection apparatus that includes the projection optical system according to the first embodiment of the present invention.

  According to the second embodiment of the present invention, it is possible to provide an image projection apparatus including a projection optical system that can be more easily manufactured.

  For example, an image projection apparatus that mounts the above-described projection optical system and projects an enlarged image of an image forming element that displays image information arranged on the object plane on the image plane may be used.

  In the case of this example, an image display apparatus using a new projection optical system that achieves ease of assembly may be realized because the apparatus cost is low because of the simple optical system having the above-mentioned advantages.

  Further, for example, according to the image projection apparatus equipped with the above-described projection optical system, an image projection apparatus including a projection optical system with further reduced curvature of field or an image projection apparatus including a smaller projection optical system is provided. Sometimes it is possible. In addition, a projection device that employs a projection optical system that does not increase the lens size or mirror size even when the magnification ratio is high and the resolution performance is high may be realized. In some cases, it is possible to realize a projection apparatus capable of projecting at a reduced cost. Further, by employing the projection optical system according to the embodiment of the present invention for the rear projection, it may be possible to realize an apparatus capable of reducing the cost and reducing the thickness.

Example 1
FIG. 1 shows the configuration of the projection optical system of Example 1 according to the embodiment of the present invention.

  In the coordinate system in the drawings for explaining examples according to the embodiment of the present invention, the major axis direction of the screen on the image plane is X, the minor axis direction is Y, and the normal direction of the screen is Z.

  A projection optical system 10 for projecting an image formed by an image forming element 11 on an object plane onto a screen 12 on an image plane, a first optical system 13 composed of an axially symmetric optical system, and a free-form surface shape The first optical system 13 and the second optical system 14 are arranged from the image forming element 11 and are enlarged and projected as a whole. In this embodiment, the first optical system 13 is composed only of a refractive optical system such as a lens system that transmits a light beam, and the second optical system 14 is composed of a single free-form curved reflecting surface having positive power. Thus, between the first optical system 13 and the second optical system 14, the light beam from the object surface is substantially converged by the first optical system 13 to form an intermediate image 15 of the image formed by the image forming element 11. . Since the surface having the power of the second optical system 14 is only one free-form reflecting surface, it is easy to assemble a mirror optical system that is severe with respect to positional deviation such as decentering accuracy. In addition, once the intermediate image 15 is formed, the overall optical system magnification can be divided before and after the intermediate image 15, so that the design can be independently performed and the design is facilitated. Further, since the power of the second optical system 14 is positive, the diverged light emitted from the intermediate image 15 can be converged on the image plane. In addition, the embodiment of the present invention does not depend on the number of lenses, and the first optical system is a system using only lenses. For example, the first optical system 13 is designed to make the optical system compact between the lenses. A folding mirror that folds the light beam may be disposed, or a similar folding mirror may be disposed between the first optical system 13 and the second optical system 14. The folding mirror does not particularly contribute to projecting an image formed by the image forming element 11 onto the screen 12. The presence or absence of the intermediate image 15 is not limited to the embodiment of the present invention, and the embodiment of the present invention may be applied to an optical system without the intermediate image 15.

The light beam emitted from the image forming element 11 forms an intermediate image 15 by an axially symmetric first optical system 13 composed only of lenses. Thereafter, the free curved surface reflecting mirror of the second optical system 14 receives a large amount of power and is enlarged and projected onto the screen 12. At this time, since the free-form surface can generally control the power in the X direction and the Y direction independently, it can achieve good resolution performance without distortion on the screen. However, if the shape is such that the positive and negative powers are reversed within the effective diameter of the free-form reflecting mirror, the light beam incident on the reflecting mirror must be a light beam that does not anticipate the positive and negative reversal of the power of the reflecting mirror in advance. The resolution performance is not good. That is, each light beam emitted from the image forming element 11 on the object plane must be refracted by the first optical system 13 in accordance with an optical system having in-plane power that will later reverse in polarity. The first optical system 13 is complicated, for example, an eccentric optical system in which the lens is decentered, or an optical system using a free-form surface lens whose surface shape itself is not axially symmetric. The decentered optical system has difficulty in assembling the optical system, and the free-form surface lens still has difficulty in producing a free-form surface mold and its assembly. Therefore, when the sag amount from the reference XY plane is expressed as Z = f (x, y), the projection optical system 10 has a surface within the effective diameter of the reflecting surface parallel to the XZ plane or the YZ plane. secondary differential expression of the curve that can be obtained by cutting at any cross-section _{^{∂ 2 f (x, y 0}} ) / ∂x 2 or _{^{∂ 2 f (x 0, y}} ) / ∂y 2 is, any of the effective diameter The coordinates x and y are controlled so as not to be 0 (however, x ₀ and y ₀ are constants indicating the coordinates within the effective diameter), and the free-form surface shape within the effective diameter has no positive / negative reversal of power. In other words, a free-form surface reflecting mirror with no inflection point is used. As a result, the first optical system 13 can adopt an axially symmetric optical system that can be assembled by a conventional alignment method, which can reduce costs, is easy to assemble, and is free from distortion on the screen 12. The projection optical system 10 capable of projecting a projection image having resolution performance can be realized.

  Table 1 shows a numerical example 1 of the first example.

In general, a free-form surface shape is defined by assuming that the sag amount from the reference XY plane is Z in the local coordinate system, and that “X2, Y2, X2Y, Y3, X2Y2, etc.” is a coefficient of each term.
Z = f (x, y) = X2 · x ² + Y2 · y ² + X2Y · x ² y + Y3 · y ³ + X4 · x ⁴ + X2Y2 · x ² y ² + Y4 · y ⁴ + X4Y · x ⁴ y + X2Y3 · x ² y ³ + Y5 ^{· y 5 + X6 · x6 +} X4Y2 · x 4 y 2 + X2Y4 · x 2 y 4 + Y6 · y 6 + ··· (2)
It is represented by

  Also in Example 1, the coefficients of the reflecting surface 24 that employs a free-form surface are as shown in Table 2.

FIG. 2 shows a 24-plane local coordinate system, a reference XY plane, and a free-form surface reflecting mirror within an effective diameter of the projection optical system according to the first embodiment. This local coordinate system shifts eccentrically in the Y direction with respect to the optical axis and then rotates about the X axis (counterclockwise with respect to the X axis in the coordinate system of FIG. 1 is positive). The amount is shown in Table 3.

With respect to this surface shape, the second-order differential curve 自由 of the free-form surface reflecting mirror within the effective diameter when x ₀ = 0, 10, 20, 30, 40, 50, 60 is parallel to the YZ plane as shown in FIG. FIG. 4 shows ² f (x ₀ , y) / ∂y ² . Since the free-form surface of Example 1 is symmetric with respect to the YZ plane at x = 0, the odd number order term of x is not described in the above equation (2), but the embodiment of the present invention has its symmetry. However, the present invention can be applied to a free curved surface shape that is asymmetric with respect to the YZ plane. Similarly, when y ₀ = 40, 30, 20, 10, ₀ , −10, −20, −30, −40, −50, −60, and −70 parallel to the XZ plane as shown in FIG. FIG. 6 shows the second-order differential curve ∂ ² f (x, y ₀ ) / ∂x ² of the free-form surface reflecting mirror within the effective diameter of. 4 and 6, a plane parallel to an arbitrary YZ plane within an effective diameter (within x = −60 to 60, y = −70 to 40) of the free-form reflecting mirror, or parallel to an arbitrary XZ plane. The second-order differential curves ∂ ² f (x, y ₀ ) / ∂ x ² and ∂ ² f (x ₀ , y) of the surface shape (curve) sliced by a smooth surface are arbitrary coordinates x and y within the effective diameter. ∂ ² f (x, y ₀ ) / ∂ x ² <0, ∂ ² f (x ₀ , y) <0 (where x ₀ and y ₀ are constants indicating coordinates within the effective diameter). It can be seen that it is not 0. In other words, the above-described equation (1) is satisfied, and the 24-surface free-form surface reflecting mirror has a surface shape having no inflection point, and there is no place where the sign of power is reversed in the surface. Therefore, the light beam incident on the free-form surface reflecting mirror does not need to be controlled by the first optical system 13 in advance so as to receive the power of positive and negative inversion, and the first optical system 13 is easy to assemble and easy to manufacture. An optical system can be used.

  Further, the objects on the object plane are arranged so as to be shifted from the optical axis as shown in FIG.

As a result, when the light beam emitted from the first optical system 13 enters the free-form surface reflecting mirror, the light beam reflected by the free-form surface reflecting mirror is easily incident on the free-form surface reflecting mirror at a position shifted with respect to the optical axis. It is easy to form an image on the image plane without hitting the first optical system 13.

  In addition, axisymmetric aspherical surfaces are used for the surfaces 14, 15, 17, 21, and 22 of the first numerical embodiment.

As is well known, the rotationally symmetric aspherical surface has a depth Z in the optical axis direction, c a radius of paraxial curvature, r a distance in the direction perpendicular to the optical axis from the optical axis, k a conic coefficient, A, B, C,.・ If etc. are high-order aspherical coefficients,
Z = c · r ² / [1 + √ {1- (1 + k) c ² r ² }] + Ar ⁴ + Br ⁶ + Cr ⁸ (3)
The shape is specified by giving values of k, A, B, C.

  Table 5 shows the aspheric coefficient of each surface.

By using an aspherical lens, the degree of freedom in designing the surface for controlling each light beam is increased, and the imaging performance on the image surface is improved. Further, by adopting an axisymmetric aspherical surface for the lens located closest to the image plane of the first optical system 13 such as the 21 and 22 planes, the light beam incident on the lens positioned closest to the image plane is Since each light beam is separated most of the first optical system 13 and enters the lens, each light beam can be controlled independently, and in particular, it is easy to control distortion and curvature of field, and image forming performance on the image surface is improved. To do.

  The projection magnification of this numerical example 1 is about 95 times, the brightness on the object side is F number = 2.1, and FIG. 8 shows the projection optical system of this numerical example 1 from the object points shown in FIG. FIG. 9 is a spot diagram in which the emitted light beam is condensed on the image plane, and FIG. 9 shows the position of each spot on the image plane. However, the origin of the coordinate system at each position on the image plane in FIG. 9 is the arrival position on the image plane of the light beam emitted from the center of the image forming element, that is, the point “2” in FIG. Thus, it can be seen that an image having good resolution performance and no distortion can be produced while the object is enlarged and brightly projected.

  Next, compensation for Petzval sum will be described.

  The light beam emitted from the first optical system enters the second optical system and is enlarged and projected by a reflection mirror having a positive power of the second optical system. Between the first optical system and the second optical system, the light beam is substantially converged to form an intermediate image of the image forming element.

  In general, the distortion of the image of the image forming element that is enlarged and projected onto the image plane by the positive power of the second optical system increases in proportion to the cube of the incident angle of view. Similarly, the field curvature is proportional to the square of the incident angle of view. In other words, when light rays emitted from object points arranged at equal intervals on the image forming element form an image on the image plane by the projection optical system, the resulting image is not evenly spaced, and the image points farther from the optical axis are displaced. The amount gets bigger. In the projection optical system of the present embodiment, when the curved surface of the reflecting mirror having positive power of the second optical system is a spherical surface, the projected image is a light beam having a large angle of view, that is, the image is further away from the optical axis. The distance between the points increases and the object is curved toward the object point. In order to correct distortion and field curvature in the magnification projection system as described above, the reflecting mirror with the positive power of the second optical system has a curved surface shape so that the positive power becomes looser as the distance from the optical axis increases. I am doing. Further, if the reflecting mirror having the positive power of the second optical system has the above-mentioned free-form surface shape, the degree of freedom in design is high, so that the aberration correction performance including the distortion aberration is improved. In this description, a concave reflecting surface is used. However, this is not limited as long as it is a Fresnel reflecting mirror, a hologram reflecting mirror, or a reflecting optical element having a condensing power.

  Furthermore, the fact that the positive power decreases with increasing distance from the optical axis means that the focal length increases with increasing distance from the optical axis, and is conjugate to the magnified image formed by the reflecting mirror having the positive power of the second optical system. Since the focal length of the intermediate image increases with distance from the optical axis, the optical path length with the reflecting mirror having the positive power of the second optical system is inclined and curved in a direction in which the light beam extends away from the optical axis.

  Here, the Petzval sum will be described. As shown in FIG. 20, the Petzval sum PTZ is an refracting surface with an optical system up to the k-plane, where the refractive index on the image side on a certain S-plane is ns, the refractive index on the object side is ns-1, the radius of curvature is rs. If configured

It is expressed.

  In general, Petzval sum is related to curvature of field, and in order to obtain a planar image with respect to a planar object, that is, to obtain an image surface with small curvature of field, it is required to make Petzval sum close to zero.

  When this is applied to the present embodiment, as described above, the free-form surface reflecting mirror (PTZ is a positive value) having the positive power of the second optical system so that the curvature of field is reduced on the screen. Becomes a curved surface shape such that the positive power becomes looser as it goes away from the optical axis, and the intermediate image also becomes inclined and curved toward the first optical system side as the light ray goes away from the optical axis. In order to form such an inclined and curved intermediate image, the first optical system that creates the intermediate image state is set to the minus side of the PTZ value of the entire optical system that projects a normal planar object onto the planar image. It is necessary to set a large PTZ value and intentionally tilt the image plane to the object side.

  As described above, the Petzval sum of the first optical system is configured to reduce the Petzval sum component generated in the second optical system.

In this example, the Petzval sum PTZ of the first optical system is changed to PTZ <−0.0115. (5)
By doing so, the size (area) of the reflecting mirror having positive refractive power of the second optical system can be reduced.

  This is because a reflection mirror having a positive refractive power has a large curvature of field due to the angle of view as its magnification increases, so in order to reduce it, if the image size is constant, It was necessary to enlarge the intermediate image (an object for a reflecting mirror having a positive refractive power) and to reduce the magnification of the reflecting mirror having a positive refractive power. However, by setting the Petzval sum of the first optical system to a large negative value as in conditional expression (5), the field curvature of the image and intermediate image created by the first optical system can be greatly curved toward the object side. In addition, since the curvature of field generated by the reflecting mirror having positive refractive power can be largely canceled, the magnification of the reflecting mirror having positive refractive power can be increased. As a result, the intermediate image can be made smaller, and the reflecting mirror itself having a positive refractive power can be made smaller accordingly.

  The projection optical system includes a first optical system that forms an intermediate image conjugate with the object, and a reflective optical element that reflects light from the intermediate image, and an image conjugate with the intermediate image on the projection surface. A second optical system for projecting, wherein the first optical system includes a stop, and at least one optical element having a positive refractive power provided between the stop and the intermediate image; The optical element having the strongest positive refractive power in the at least one optical element having the positive refractive power includes at least one optical element having a negative refractive power. The optical element having the strongest negative refractive power in at least one optical element having More specifically, the first optical system was divided into three parts when divided before and after the stop, and before and after the most spaced part of the lens group on the image plane side of the stop. Each lens group has a positive, positive, and negative power arrangement in order from the object plane side. The light beam emitted from the image forming element is refracted by the first group having a positive power, but the maximum field angle of the principal ray of the light beam emitted from the stop after the first optical system is the positive power of the first group. And the amount of parallel decentering of the image forming element with respect to the optical axis of the first optical system. The larger the maximum field angle, the greater the height of the light beam with respect to the optical axis of the light beam, and the subsequent lens diameter increases. However, the second lens group arranged after the aperture has positive power. Since the spread of the angle of view is suppressed, the lens diameter of the third group is prevented from expanding. In particular, since the third lens group has a negative power for widening the angle of view, the size of the lens diameter of the final lens can be suppressed.

(Example 2)
FIG. 10 shows the configuration of the projection optical system of Example 2 according to the embodiment of the present invention.

  In the present embodiment, a free-form surface reflecting mirror having a positive power and an axisymmetric aspherical mirror having a negative power are employed for the second optical system 14, and the combined power, that is, the second optical system 14 is The power is positive. Other optical system arrangements are the same as those in the first embodiment.

  Table 6 shows numerical examples of the second embodiment.

Table 7 shows the coefficients of the reflecting surface 24 that employs a free-form surface in Example 2.

The local coordinate system shifts in the Y direction with respect to the optical axis and then rotates about the X axis (counterclockwise with respect to the X axis in the coordinate system of FIG. 10 is positive). The amount is shown in Table 8.

With respect to this surface shape, the second-order differential curve ∂ ² f of the free-form curved reflecting mirror within the effective diameter when x ₀ = 0, 10, 20, 30, 40, 50 parallel to the YZ plane as shown in FIG. FIG. 12 shows (x ₀ , y) / ∂y ² . In addition, since the free-form surface of Example 2 is also symmetric with respect to the YZ plane at x = 0, the odd number order term of x is not described in the above equation (2), but the embodiment of the present invention has its symmetry. However, the present invention can be applied to a free curved surface shape that is asymmetric with respect to the YZ plane. Similarly, the second derivative curve of the free-form curved reflecting mirror within the effective diameter when y ₀ = 60, 50, 40, 30, 20, 10, ₀ , and −10 is parallel to the XZ plane as shown in FIG. FIG. 14 shows ∂ ² f (x, y ₀ ) / ∂ x ² . 12 and 14, a plane parallel to an arbitrary YZ plane within an effective diameter (within x = −50 to 50, y = −10 to 60) of the free-form surface reflecting mirror, or parallel to an arbitrary XZ plane. The second-order differential curves ∂ ² f (x, y ₀ ) / ∂ x ² and ∂ ² f (x ₀ , y) of the surface shape (curve) sliced by a smooth surface are arbitrary coordinates x and y within the effective diameter. ∂ ² f (x, y ₀ ) / ∂ x ² <0, ∂ ² f (x ₀ , y) <0 (where x ₀ and y ₀ are constants indicating coordinates within the effective diameter). It can be seen that it is not 0. In other words, the above-described equation (1) is satisfied, and the 24-surface free-form surface reflecting mirror has a surface shape having no inflection point, and there is no place where the sign of power is reversed in the surface. Therefore, the light beam incident on the free-form surface reflecting mirror does not need to be controlled by the first optical system 13 in advance so as to receive the power of positive and negative inversion, and the first optical system 13 is easy to assemble and easy to manufacture. An optical system can be used.

  Also, the objects on the object plane are arranged as shown in FIG.

In addition, axisymmetric aspheric surfaces are used for the 14, 15, 17, 21, 22, and 25 surfaces in the second numerical embodiment.

  Further, even though the 25th surface is an axisymmetric aspherical surface, an odd-order aspherical surface in which an odd-order term is added thereto is adopted.

As is well known, the rotationally symmetric odd-order aspherical surface is such that Z is the depth in the optical axis direction, c is the paraxial radius of curvature, r is the distance from the optical axis in the direction perpendicular to the optical axis, k is the cone coefficient, C3, C4, C5, If C6... Is a higher order aspheric coefficient,
Z = c · r ² / [1 + √ {1− (1 + k) c ² r ² }] + C3 ³ + C4r ⁴ + C5r ⁵ + C6r ⁶ + C7r ⁷ (4)
The shape is specified by giving values of k, C3, C4, C5, C6.

  Table 10 shows the aspheric coefficient of each surface.

By using an aspherical lens, the degree of freedom in designing the surface for controlling each light beam is increased, and the imaging performance on the image surface is improved. Further, by adopting an axisymmetric aspherical surface for the lens located closest to the image plane of the first optical system 13 such as the 21 and 22 planes, the light beam incident on the lens positioned closest to the image plane is Since each light beam is separated most of the first optical system 13 and enters the lens, each light beam can be controlled independently, and in particular, it is easy to control distortion and curvature of field, and image forming performance on the image surface is improved. To do.

  The projection magnification of the present numerical example 2 is about 105 times and the brightness on the object side is F number = 2.4. FIG. 16 shows the object points shown in FIG. 15 for the projection optical system of the present numerical example 2. FIG. 17 shows the positions of the spots on the image plane. However, the origin of the coordinate system in FIG. 17 is the arrival position on the image plane of the light beam emitted from the center of the image forming element, that is, the point “2” in FIG. Thus, it can be seen that an image having good resolution performance and no distortion can be produced while the object is enlarged and brightly projected.

  The projection optical system of the Example which concerns on embodiment of this invention is employ | adopted for a projection apparatus, and can also be set as an image projection apparatus.

  In the example of one image projection apparatus 20 including the projection optical system of the example according to the embodiment of the present invention as shown in FIG. 18, when the projection optical system 10 is applied to the projection apparatus, the image forming element 11 is used. An illumination light source 21 is used. As the illumination light source 21, a halogen lamp, a xenon lamp, a metal halide lamp, an ultrahigh pressure mercury lamp, an LED, or the like is used. Usually, an illumination optical system is mounted so that high illumination efficiency can be obtained. As a specific example of the illumination optical system, a reflector 22 (integrated with the light source 21) disposed in the vicinity of the light source or a light beam having directivity reflected by the reflector 22 is used as the first relay lens 23. And an optical system in which an illumination distribution can be obtained uniformly on the surface of the image forming element 11 by the illuminance uniformizing means 25 and the second relay lens 23 called an integrator optical system via the polarization conversion element 24. Alternatively, the color light may be projected by using the color wheel 26 to color the illumination light and controlling the image of the image forming element 11 in synchronization therewith. When a reflection type liquid crystal image forming element is used, more efficient illumination is possible by using the polarization separation means 27 of the illumination light path combined with PBS and the projection light path. When a DMD panel is mounted, optical path separation using a total reflection prism is employed. Thus, an appropriate optical system may be employed according to the type of light valve.

  In the example of another image projection apparatus 20 including the projection optical system of the example according to the embodiment of the present invention as shown in FIG. 19, the illumination light of each color separated by the color separation means 28 is used. The light beam is applied to a plurality of image forming elements 11 such as red, green, and blue, the illumination light beam is modulated by each element, and the light synthesized by the color synthesizing means 29 using a dichroic film such as a dichroic prism is projected. Needless to say, a color image can be projected onto the screen 12 by being incident on the optical system 10.

  If the light flux from the image forming element 11 to the first surface of the first optical system 13 of the projection optical system 10 is substantially telecentric, the brightness of the magnified image of the image forming element 11 on the screen 12 can be made uniform. The angle characteristic of the dichroic film of the color synthesizing means 29 used in the case of color image projection using a plurality of elements as described above is narrow because only the divergence angle of the emitted light from the image forming element 11 has to be considered. It becomes easy to make itself. Further, in the case of the image projection apparatus 20 using the polarization separation means 27, the angle characteristic of the polarization separation film can also be narrowed (see FIG. 19). Of course, the embodiment of the present invention can be applied to an optical system that is not telecentric.

  Although the embodiments of the present invention and the examples according to the embodiments of the present invention have been specifically described above, the present invention is not limited to these embodiments and examples. The embodiments according to the embodiments and the embodiments of the present invention can be modified or changed without departing from the spirit and scope of the present invention.

  The embodiment of the present invention may be applicable to the projection optical system of an image projection apparatus such as a projection apparatus. In particular, there is a possibility that the embodiment of the present invention can be applied to a projection optical system that achieves a close range projection in a front projector. Further, there is a possibility that the embodiment of the present invention may be used for a projection optical system in a front projector and a projection optical system that achieves a reduction in thickness in a rear projection.

  [Appendix]

Appendix (1):
In a projection optical system that consists of a rotationally symmetric optical system and a rotationally asymmetric optical system and projects light from an object onto a projection surface,
The rotationally asymmetric optical system comprises at least one optical element having a rotationally asymmetric reflecting surface, and
The rotationally asymmetric reflecting surface is a curved surface expressed as a function of two-dimensional coordinates, and in the region of the curved surface irradiated with light, the function relating to the coordinates in at least one direction in the two-dimensional coordinates. A projection optical system, wherein the partial differential coefficient is a positive or negative value.

Appendix (2):
The coordinate of at least one direction in the two-dimensional coordinate is composed of a coordinate in a first direction in the two-dimensional coordinate and a coordinate in a second direction orthogonal to the first direction in the two-dimensional coordinate, The projection optical system according to appendix (1).

Appendix (3):
The projection optical system according to (1) or (2), wherein an image conjugate with the object is formed between the rotationally symmetric optical system and the rotationally asymmetric optical system.

Appendix (4):
The projection optical system according to any one of appendices (1) to (3), wherein the rotationally symmetric axis of the rotationally symmetric optical system does not intersect the object.

Appendix (5):
The projection optical system according to any one of appendices (1) to (4), wherein the optical element having power constituting the rotationally symmetric optical system includes at least one lens.

Appendix (6):
The projection optical system according to any one of appendices (1) to (5), wherein the rotationally symmetric optical system includes at least one optical element having a rotationally symmetric aspheric surface.

Appendix (7):
The optical element having the power closest to the rotationally asymmetric optical system in the rotationally symmetric optical system is one of at least one optical element having the rotationally symmetric aspherical surface. The projection optical system described in 1.

Appendix (8):
The projection optical system according to any one of appendices (1) to (7), wherein the rotationally symmetric optical system includes a folding mirror that folds a rotationally symmetric axis of the rotationally symmetric optical system.

Appendix (9):
The projection optical system according to any one of appendices (1) to (8), wherein the rotationally asymmetric optical system is an optical system that converges the light.

Appendix (10):
The projection optical system according to any one of appendices (1) to (9), wherein the projection optical system is a substantially telecentric optical system on the object side.

Appendix (11):
In an image projection apparatus that projects an image on a non-projection surface,
An image projection apparatus comprising the projection optical system according to any one of appendices (1) to (10).

  One aspect of the present invention may be applicable to an image projection apparatus.

DESCRIPTION OF SYMBOLS 10 Projection optical system 11 Image forming element 12 Screen 13 1st optical system 14 2nd optical system 15 Intermediate image 20 Image projection apparatus 21 Illumination light source 22 Reflector 23 Relay lens 24 Polarization conversion element 25 Illuminance equalization means 26 Color wheel 27 Polarization separation Means 28 Color separation means 29 Color composition means

JP 2004-258620 A JP 2006-292901 A

Claims (7)

A light source, an image forming element, and a projection optical system configured to project an image formed on the image forming element onto a projection surface using light from the light source, and comprising a rotationally symmetric optical system and a rotationally asymmetric optical system In the image projection device,
The rotationally asymmetric optical system comprises at least one optical element having a rotationally asymmetric reflecting surface, and
The rotationally asymmetric reflecting surface is a curved surface expressed as a function of a two-dimensional coordinate, and in the region of the curved surface irradiated with the light, the function related to the coordinate in at least one direction in the two-dimensional coordinate. The partial differential coefficient is positive or negative,
The curved surface has a larger valley shape formed in a direction perpendicular to the one direction and closer to the optical axis of the rotationally symmetric optical system in one direction in the region, and the one direction and the optical axis. In the direction perpendicular to the direction, the farther from the optical axis, the larger the curvature in a plane including the one direction and the direction of the optical axis, and
The optical element having power constituting the rotationally symmetric optical system includes a plurality of lenses,
An image projection apparatus according to claim 1, wherein a rotationally symmetric axis of the rotationally symmetric optical system does not intersect the image formed on the image forming element. The image projection apparatus according to claim 1,
The coordinate of at least one direction in the two-dimensional coordinate is composed of a coordinate in a first direction in the two-dimensional coordinate and a coordinate in a second direction orthogonal to the first direction in the two-dimensional coordinate, An image projection apparatus. In the image projection device according to claim 1 or 2,
An image projection apparatus, wherein an image conjugate with the image is formed between the rotationally symmetric optical system and the rotationally asymmetric optical system. In the image projection apparatus in any one of Claim 1 to 3,
The image projection apparatus, wherein the rotationally symmetric optical system includes at least one optical element having a rotationally symmetric aspheric surface. The image projection apparatus according to claim 4,
An image projection apparatus characterized in that the optical element having the closest power to the rotationally asymmetric optical system in the rotationally symmetric optical system is one of at least one optical element having the rotationally symmetric aspheric surface. . In the image projection apparatus in any one of Claim 1-5,
The image projection apparatus according to claim 1, wherein the rotationally symmetric optical system includes a folding mirror that folds a rotationally symmetric axis of the rotationally symmetric optical system. In the image projection device according to any one of claims 1 to 6,
The image projection apparatus according to claim 1, wherein the rotationally asymmetric optical system is an optical system that converges the light.