JP4016008B2 - Imaging optics - Google Patents

Description

  The present invention relates to an imaging optical system for reading an image from an oblique direction and projecting the image.

Means for realizing an imaging optical system related to image capture or image projection from an oblique direction (hereinafter collectively referred to simply as an oblique incidence imaging optical system) are roughly classified into the following two methods. The That is,
(1) Decenter method (2) Tilt method.

  FIG. 24 shows the basic principle of the decentering method. In this method, the object plane 4 and the image plane 2 having a conjugate relationship with each other are basically parallel, and the optical axis 3A of the imaging optical system 30 is orthogonal to both planes. In order to realize the oblique incidence imaging optical system, for example, the image detection region 201 placed on the image plane 2 is moved downward from the optical axis 3A. By this operation, the corresponding imaging region 401 on the object plane 4 is displaced upward in the figure, and as a result, an oblique incidence imaging optical system can be realized without using a special optical system. The advantage of this scheme is that no extra distortion occurs. The disadvantage is that it is displaced from the optical axis 3A, so that the image circle of the imaging optical system 30 must be made sufficiently large in advance, so that aberration correction becomes difficult and the imaging optical system 30 tends to be enlarged. It is.

  The basic principle of the tilt method, which is another method, is shown in FIG. A significant difference from the decentering method is that the optical axis 3A of the imaging optical system 30 is oblique to the object plane 4. At the same time, the image plane 2 also crosses the optical axis 3A. Further, the image plane 2, the object plane 4, and the main plane 3H of the imaging optical system 30 intersect at the intersection line A on the respective extension lines, and satisfy the so-called Scheinmpflug principle which is a tilt type imaging condition. . The advantage of this method is that the imaging optical system 30 is not so large and the resolving power is relatively good. The disadvantage is that a large distortion is newly generated. A typical example of the distortion generated at this time is shown in FIG. This can be easily understood by considering the relationship of magnification with respect to the image formation in FIG.

  The oblique incidence imaging optical system is classified into one of the above two methods or a composite type thereof. The imaging optical system must satisfy predetermined specifications required for the optical system, such as size, resolution, and distortion. Also in the prior art, while following either of the above methods, various efforts have been made to solve the problems that they have, and efforts have been made to provide an optical system that meets the purpose. Let's look at some examples.

  FIG. 27 is a sectional view relating to a projection lens of a projector disclosed in Japanese Patent Application Laid-Open No. 05-273460. The oblique incidence imaging optical system is realized by moving the projection lens 30 composed of a refractive optical element and the image forming element 2 in a direction perpendicular to the optical axis 3A. At this time, in order to avoid moving to the condenser lens 301 in the vicinity of the image forming element 2, the optical axis of the projection lens is tilted simultaneously with the movement of the projection lens 30. This is basically classified as the decenter method, and it is considered that eccentricity is used as the degree of freedom of correction. In this specific example, projection with a maximum field angle 2ω of about 51 ° is realized.

  FIG. 28 is a sectional view of US Pat. No. 5,871,266, which was devised as a projector device by the present applicant. The illumination unit 1 including the light source 1, the image forming unit 2 including the image element such as liquid crystal, and the imaging unit 3 are used as the basic configuration, and the illumination unit 1 and the imaging unit 3 are comprehensively optimized so that the oblique incidence is achieved. An imaging optical system is to be realized. In the specific configuration example, an embodiment in which the imaging unit 3 is configured by only a small number of reflecting mirrors is also disclosed. The luminous flux from the illumination unit 1 is separated into three primary colors by the dichroic mirrors 2a and 2b, and illuminates the three reflective image forming elements 2g, 2h, and 2i. The light beams reflected by the image forming elements are combined again by the dichroic mirrors 2 a and 2 b and travel toward the imaging unit 3. The image forming unit 3 is composed of three reflecting mirrors, 3a, 3b, and 3d, and forms an image on a screen 4 (not shown) by sequentially reflecting the light beams from the image forming elements 2g, 2h, and 2i. . In this specification, the significance of the oblique incidence imaging optical system in the projection apparatus is discussed in detail. Further, as an application example to a thin rear projection device, a device having a maximum angle of view 2ω exceeding 100 degrees is disclosed. This method is also basically classified as a decentering method.

  Despite the possibility of realizing such an innovative projection apparatus, the method of US Pat. No. 5,871,266 has several drawbacks. One of them is that when a reflecting mirror is used in the imaging system, higher surface accuracy is required compared to a refractive optical element. This can be easily understood by thinking of how the light beam contributing to imaging is reflected by the reflecting mirror. For example, consider a fixed spot region that is formed on a reflection surface by an arbitrary light beam that is emitted from an image element and forms an image at a point on the screen. For example, if there is a shape error of λ / 4 in this region (λ is 0.55 μm, for example), a wavefront aberration of about λ / 2 occurs due to reflection. This causes a reduction in resolution that cannot be ignored for the imaging system. In other words, in the case of a reflective optical system, it can be said that the reflection surface itself is very vulnerable to undulation errors.

  Another drawback is the angle taken from the image element. In order to realize an oblique incidence imaging optical system with a simple configuration, a divergent light beam having an angular width of 8 degrees or less is used as described in the claims. In the case of this patent, the overall efficiency including the illumination system is improved to improve the luminous efficiency, but there are various restrictions such as the size of the available light source, the size of the device, and the cost requirements. When the conditions are considered, the application range is narrowed.

  Japanese Patent Application Laid-Open No. 10-206791 also relates to a projection system of a projector, and is classified into a decentering method as in the previous examples. In the present invention, in order to increase the degree of design freedom, a decentered optical element and a free-form surface are employed in the imaging system 30 of FIG. 29, and a projection system exceeding the maximum field angle 2ω = 68 degrees is realized. Then, it is used as an imaging system for performing oblique projection as shown in FIG. In this case, the two conjugate planes 2 and 4 are substantially parallel. However, in spite of the adoption of such a decentered optical element, the angle of view itself has not increased, and on the other hand, the difficulty in manufacturing and assembling parts increases.

  In the above, some known examples classified mainly into the decenter method have been described. Next, let's look at a known example based mainly on the tilt method.

  U.S. Pat. No. 5,274,406 in FIG. 31 also relates to an application to a projection apparatus, particularly a rear projection display apparatus. This example is a free-form surface having a symmetric projection lens 30 composed of refractive optical elements shown in FIG. 32 and a fine Fresnel-like staircase structure provided in the vicinity of the image plane shown in FIG. And a mirror 301. In this example, in order to reduce the depth of the rear projection device, a tilt method in which the optical axis of the projection lens 30 is inclined with respect to the screen 4 and the image forming element 2 is adopted. In addition, distortion caused by tilting the optical axis is corrected by using the free-form surface mirror shown in FIG. 33 (a), and at the same time, the imaging conditions newly generated by using such a mirror are not matched. The problem is dealt with by making the mirror Fresnel.

  With such a device, a 36-inch diagonal rear projection display device is realized with a thickness of 28 cm. In the rear projection device, the diagonal length of the display unit is expressed as “inch”, and the numerical value obtained by replacing it with “cm” is one target numerical value. In this example, however, the thinning beyond the target is realized. . Although the apparatus can be thinned by the above method, the distance along the arbitrary light beam from the projection lens 30 to the Fresnel mirror 301 is D1, and the distance along the same light beam from the Fresnel mirror to the screen is D2. , D1> D2, and the Fresnel mirror inevitably increases in size. As a result, the manufacture of free-form surfaces and Fresnel mirrors is a very difficult task. In addition, since the Fresnel structure introduced to prevent a decrease in resolution has a finite step structure, the step itself becomes a factor that deteriorates the resolution.

  JP-A-6-265814 and JP-A-7-151994 in FIG. 34 are other examples which belong to the tilt system. In these examples, distortion is corrected by using a tilt method in multiple stages. For example, FIG. 35 shows a schematic diagram in the case of two stages. The light beam from the image element placed at 2 forms an intermediate image at 4 by the first imaging system 3. The intermediate image is re-imaged on the screen 4 'by the second imaging system 3'. With respect to such a configuration, by imposing constant conditions on the installation angle, magnification, focal length, and the like of each optical system, it is possible to eliminate distortion in principle and to ensure resolving power. In the case of this method, the optical axis of each imaging system 3 and 3 'intersects the common intermediate image 4 with a predetermined angle, so that the actual light beam must be transmitted from 3 to 3' without being lost. There is. Normally, this is realized by placing a pupil coupling element such as an eccentric Fresnel lens as shown in FIG. 36 at a position where an intermediate image is formed. For example, the image element has a minimum pixel structure such as a liquid crystal panel. If it has, it interferes with the periodic structure of Fresnel and causes moire. In this known example, such a pupil coupling element is shifted from the intermediate image to avoid this problem.

  As a disadvantage of this system, the optical axis of each optical system 3, 3 ′ and the intermediate image 4 or the image element 2 are largely inclined, and it is often difficult to satisfy the mechanical requirements. Although the details are not mentioned here, the pupil coupling element in FIG. 36 is one of the problems that are problematic until the end.

  In JP-A-07-13157, as shown in FIG. 37, a parallel light beam from a light source 1a is guided to an image element 2, and the reflected light is condensed on a pupil of a projection lens 3b by a first parabolic mirror 3a. Further, the light beam that has passed through the projection lens 3 b is reflected by the second parabolic mirror 3 c and forms an enlarged image on the screen 4. This method is basically a tilt method, but a thin parabolic mirror 3a is added for coupling with the illumination light beam, and a second parabolic mirror 3c is added to make the light beam incident on the screen as a constant angle light beam. A projector is to be obtained. Although the concrete configuration example is not described in the specification and its feasibility is unknown, it may be possible to draw a fundamental picture, but such a configuration satisfies the actual optical specifications. I think I can't.

  Japanese Patent Application Laid-Open No. 09-179064 shown in FIG. 38 is also classified as a tilt system. Like US Pat. No. 5,871,266 and Japanese Patent Application Laid-Open No. 07-13157, an imaging system 30 including a refractive optical element and a concave reflecting mirror 31 are provided. It has a combined configuration. The light beam from the image element 2 passes through the optical system 30 composed of the refractive optical elements 3a to 3g in FIG. 39, is further reflected by the concave reflecting mirror 31, and enters the screen 4 as a light beam having the same inclination. . This method uses the characteristics of an afocal system to correct tilt distortion.

  As shown in FIG. 40, when an afocal system is configured by two optical systems 30 and 31, and the distance between the two optical elements is set to be the sum of the focal lengths, as is well known, The magnification is always constant regardless of the position. Such an optical system is constituted by an optical system 30 having a positive focal length made of a refractive optical element and a concave mirror 31 having the same positive focal length so as to be incident on the screen 4 at a certain angle. , Distortion can be corrected.

  In the case of this conventional example, there is also described an embodiment in which the light is incident at an acute angle of, for example, 70 degrees with respect to the normal line of the screen 4 corresponding to the object plane. Furthermore, in order to reduce distortion and improve resolution, a decentered optical element and a free-form surface are used to ensure the degree of freedom. A disadvantage of this method is that the distance between the two optical systems 30 and 31 is inevitably long because an afocal system is constituted by two optical systems and further an enlargement system. That is, when the distance along the light beam from the projection lens 30 to the concave mirror 31 is D1, and the distance along the same light beam from the concave mirror 31 to the screen 4 is D2, D1> D2 for most of the light beam. Becomes larger. This causes a problem in mass productivity.

  The above known examples are mainly related to the projection apparatus, but as another application of the oblique incidence imaging optical system, an example of a head mounted display (HMD) apparatus will be considered.

The important design items for this application are:
・ Wide viewing angle (large enlarged image)
・ The equipment is small and light. In terms of the viewing angle, the size of the pupil is almost determined, so if the required viewing angle is determined, the required size of the image element is almost determined in relation to the angle of capture from the image element. FIG. 41 shows the standard method. The light beam from the image element 2 once forms the intermediate image 4 by the relay optical system 30, expands it with the concave mirror 31, and observes it with the eye placed on 303. The concave mirror 31 also plays a role of collecting chief rays in the pupil. In this example, since it is basically a coaxial system, the optical system is easy to design. However, if the space between the eye and the concave mirror 31 is necessary and the space for storing the relay unit 30 is also combined, the distance becomes considerably large.

  FIG. 42 shows an HMD optical system described in JP-A-5-303055. The light beam from the image element 2 forms an enlarged image through the relay system 30 and the concave mirror 31 constituting the imaging optical system, and is observed with the eye placed on the 301. This is basically the same as the above configuration, but an eccentric system is adopted in order to reduce the thickness of the apparatus by omitting the beam splitter. This is a grazing incidence imaging optical system classified as a tilt system.

  Japanese Patent Laid-Open No. 7-191274 develops Japanese Patent Laid-Open No. 5-303055, and as shown in FIGS. 43 and 44, a single concave mirror is composed of a plurality of convex mirrors and concave mirrors, so that the correction of aberrations is made more reliable. It is what. By adding a convex mirror, the degree of freedom of image height aberration correction is increased and the range of design is expanded. Also in this case, the reflecting mirror closest to the eye is a concave mirror. In addition, in the embodiment, an example is also disclosed in which the relay system 30 is also configured by a reflecting mirror and is configured by a reflection optical system. This is similar in that it can be configured with only a reflecting mirror, like the projection optical system of US Pat. No. 5,871,266 described in the section of the projection apparatus.

  Japanese Patent Laid-Open No. 10-239631 shown in FIG. 45 is an example in which a combination of reflecting surfaces of Japanese Patent Laid-Open No. 7-191274 is spatially folded to make it compact. Although it is small, aberration correction is effectively performed using the two refracting surfaces 301 and 304 and the two reflecting surfaces 302 and 303. Furthermore, in order to secure a degree of freedom, a free-form surface is used for each optical surface. This is an epoch-making method in applications where two image elements for both eyes can be used and a relatively large Fno is allowed, such as HMD.

  As mentioned above, we have seen the conventional examples of the two application fields of the oblique incidence imaging optical system, but the oblique incidence imaging optical system has come to be used in various other applications. The application of has also been spreading. For example, in the field of HMD, a new oblique incidence imaging optical system that satisfies the current requirements as proposed in the above Japanese Patent Laid-Open No. 10-239631 has been proposed. Is insufficient. As disclosed in Japanese Patent Application Laid-Open No. 7-191274, it may be possible to compensate for the lack of freedom by increasing the number of reflecting surfaces. However, increasing the number of reflecting surfaces requires high surface accuracy and rebounds on cost. come. There is a need for further technological development in this area.

  On the other hand, in the case of application to a projection device or an imaging system, different from the case of observing with an eye, more severe performance is required. In particular, image elements such as liquid crystals and image sensors such as CCDs have been miniaturized, and at the same time, the size of one pixel is in the single digit range of μm. As a result, the optical system is required to have high brightness as well as high resolution. On the other hand, downsizing of the element is also an advantageous condition for downsizing of the optical system. In this application field, as disclosed in US Pat. No. 5,871,266, if projection can be performed with an angle of view exceeding a half angle of view of 70 °, a display having a depth of 1/3 or less than that of the prior art can be realized. In addition to the application to the videophone system shown in Japanese Patent Application Laid-Open No. Hei 6-13311 in FIG. 46, not only a projection device, but also a thin image reading device such as a scanner and a three-dimensional image reading device, a camera, etc. It can be applied to various input / output devices.

  What is required as a technical problem is to increase the means for realizing the oblique incidence imaging optical system as much as possible. Unfortunately, as we have seen in the prior art, these optical systems have some problems such as brightness, resolving power, size, productivity, and cost, and an oblique incidence imaging optical system suitable for a wide range of applications. Currently there are few.

  The present invention provides a new means for realizing an oblique-incidence imaging optical system, and is intended to be applied to various applications. It also provides means for realizing a bright oblique-incidence imaging optical system in which distortion can be controlled while the half angle of view exceeds 70 °, which was practically difficult with the prior art.

  According to the present invention, in the imaging optical system, on one conjugate plane A having a conjugate relationship, a light beam at a point in a predetermined range contributing to imaging has an opening angle of 10 ° or more. Is the first condition. As a next condition, the basic configuration of the optical system is composed of a plurality of optical elements and has a first optical system having a light beam converging action at least in the vicinity of the reference axis, and a light beam diverging action at least in the vicinity of the reference axis. And a second optical system. The light beam emitted from the conjugate plane A converges on the other conjugate plane B through the two optical systems in sequence.

  For each light beam passing through these optical systems, the optical system is configured to satisfy certain conditions. That is, let the distance along the reference axis of the first optical system from the first optical system to the second optical system be S1, and the distance S2 along the reference axis of the second optical system from the second optical system to the conjugate plane B. Next, with respect to an arbitrary light beam after exiting the first optical system, the distance to the convergence point at which the distance along the reference axis of the first optical system is the longest in all cross sections including the principal ray of the light beam is determined. L1, the distance to the convergence point where the distance along the reference axis of the first optical system is the shortest in the light beam cross section different from this light beam cross section is L2. In the distance L1 sequentially calculated for each light beam as described above, the value of L1 for the light beam emitted from the nearest vicinity of the reference axis of the first optical system is set to L11, and the reference value of the first optical system is also set to L2. The value of L2 relating to the light beam exiting from the nearest axis is L21, and the value of the light beam exiting farthest from the reference axis of the first optical system among L1 is L1n, and the reference value of the first optical system is also L2 Let L2n be a value related to the light beam that is emitted farthest from the axis. The following conditions hold for these distances.

S1 ≦ L11 ≦ S1 + S2
S1 ≦ L21 ≦ S1 + S2
L11 / L1n <0.25
0 <L21 / L2n <1.5
Further, regarding an arbitrary light beam that is emitted from a predetermined range on the conjugate surface A and is condensed on the conjugate surface B, the distance along the light beam from the first optical system to the second optical system is determined from D1 and the second optical system. When the distance along the same light beam to the conjugate plane B is D2,
D1 <D2
Satisfied.

The imaging optical system further includes a distance S1 along the reference axis of the first optical system from the first optical system to the second optical system, and a reference axis of the second optical system from the second optical system to the conjugate plane B. The distance S2, the distance L11 related to the light beam emitted from the vicinity of the reference axis of the first optical system in the distance L1 to the longest convergence point in each light beam section, and the first optical element in the distance L2 to the shortest convergence point Regarding the distance L2n relating to the light beam emitted most distant from the reference axis of the system, and the difference ΔSL between the maximum value and the minimum value of the ratio S1 / L1 between S1 and L1 relating to each light beam, the following conditions
S1 / L11> 0.6
(S1 + S2) / L2n <1
ΔSL> 0.6
It is better to satisfy at least one of the conditions.

  The imaging optical system has either an imaging function for forming an enlarged image of the conjugate plane A on the conjugate plane B or an imaging function for forming a reduced image of the conjugate plane B on the conjugate plane A.

  In the imaging optical system, it is desirable that the first optical system and the second optical system each include an optical element having at least one aspherical surface or a free-form surface.

  In the imaging optical system, the first optical system can be mainly composed of a refractive optical element, and the second optical system can be mainly composed of a reflective optical element.

  In the imaging optical system, the first optical system and the second optical system can be mainly composed of reflective optical elements.

  The imaging optical system may include an optical element in which at least one of the first optical system and the second optical system is decentered with respect to the reference axis.

  In the imaging optical system, at least one of the first optical system and the second optical system can be constituted by a rotationally symmetric optical element.

  In the imaging optical system, the first optical system and the second optical system are composed of rotationally symmetric optical elements each having a common rotational symmetry axis, and the reference axis of each optical system and the common rotational symmetry axis are all coincident. You can also make it.

  The imaging optical system can also make all the light beams have an angle of 45 ° or more with respect to the normal of the conjugate plane B.

  In the above contents, first, the fact that the luminous flux has an angle width of 10 ° or more is an important condition for the oblique incidence imaging optical system to maintain a constant brightness. As a result, a bright imaging optical system can be constructed, and the application range of the oblique incidence imaging optical system can be expanded.

  Next, with respect to the distance D1 along an arbitrary light beam between the first optical system and the second optical system, and the distance D2 along the same light beam between the second optical system and the conjugate plane B, by satisfying D2> D1, It is possible to prevent the size of each optical element used in the optical system from becoming excessively large, and to solve practical problems such as the overall size of the optical system, the mass productivity of the element, and the cost.

  The fact that the first optical system has a converging action in the vicinity of its reference axis and the second optical system has a diverging action in the vicinity of its reference axis, together with several other conditions, avoids an increase in the size of the entire optical system. This is a condition for realizing an oblique incidence imaging optical system having a large angle of view with a relatively simple configuration. It is also advantageous when a long back focus is required in a projection apparatus or the like.

The distance L1 to the longest convergence point and the distance L2 to the shortest convergence point along the reference axis of the first optical system in every light beam cross section including the principal ray of the arbitrary light beam emitted from the first optical system. , When the distances from the position closest to the reference axis of the first optical system to the convergence point for the emitted light beam are L11 and L21, respectively.
S1 ≦ L11 ≦ S1 + S2
S1 ≦ L21 ≦ S1 + S2
By satisfying the above condition, the balance with the diverging action on the reference axis side of the second optical system is maintained, and in addition to the following conditions regarding the light beam away from the reference axis, a grazing incidence imaging optical system having a large angle is possible It becomes. The above two conditions mean that the convergence point of all the beam cross sections is between the second optical system and the conjugate plane B with respect to the beam closest to the reference axis of the first optical system.

  In the cross section of the light beam, when the distance along the reference axis of the first optical system is the distance L1 to the longest convergence point, the distance related to the light beam emitted from the position farthest from the reference axis of the first optical system is L1n The ratio with L11 satisfies the following relationship.

L11 / L1n <0.25
This condition is that the distance L1 to the convergence point of the light beam far from the reference axis is formed farther from the first optical system than the light beam close to the reference axis of the first optical system. This is to maintain consistency with the aberration correction condition of the optical system at a position away from the reference axis. The distances L1, L2, etc. are along the reference axis of the first optical system, but the light beam in the cross section of the light beam changes from convergence to divergence, and an imaginary convergence point is set on the incident side of the first optical system. If it has (the distance becomes negative), it is treated as a convergence point (distance) farther than ∞. As a result, the conditional expressions can be constructed without contradiction.

Another condition that the imaging optical system of the present invention should basically satisfy is L21 related to the light beam emitted from the position closest to the reference axis of the first optical system in L2, and L2n related to the light beam emitted from the farthest. Is a condition to be satisfied. That is,
0 <L21 / L2n <1.5
Satisfied.

  Before proceeding to the explanation of other conditions, we will explain the background of the basic concept of these conditions.

  In order to provide a practical oblique incidence imaging optical system, it is important that the optical system is compact and can be realized with the simplest possible configuration. As in the basic configuration of the present invention, when combining the first and second optical systems having convergence and divergence in the vicinity of the reference axis, how to reduce the size of the second optical system having the divergence, The point is whether the configuration can be simplified. Although the roles of the two optical systems cannot be completely separated, the main role of the second optical system is to distribute each light beam to a target position on the conjugate plane B. If the second optical system is made as simple as possible, many of the degrees of freedom of the second optical system are used for this purpose. Therefore, the main role of the first optical system is to maintain the balance of the entire optical system by matching the imaging conditions and angle conditions of light beams that cannot be matched by the second optical system. As described above, by satisfying the four conditions regarding the convergence position of the light beam in addition to the basic configuration conditions, the above conflicting conditions can be satisfied at the same time, and the target oblique incidence imaging optical system can be realized. Is possible.

  Return to explanation of other conditions. The following three conditions are advantageous in constructing an imaging optical system having a particularly large oblique incident angle.

S1 / L11> 0.6
(S1 + S2) / L2n <1
ΔSL> 0.6
In particular, this is an important condition for realizing a projection device that enables projection from a very close position, an extremely thin rear projection device, and the like. When realizing these devices, it is desirable to satisfy at least one of the above three conditions.

  The imaging optical system of the present invention can be used as an enlargement optical system that forms an enlarged image on the conjugate plane B with the conjugate plane A as the object plane. Although the optical system itself has the same configuration, it can be used as a reduction optical system that forms a reduced image of the conjugate plane B on the conjugate plane A by reversing the roles of the object and the image.

  The use of an optical element having at least one aspherical surface or free-form surface in the optical system widens the degree of freedom of design and at the same time satisfies the required specifications with the simplest possible configuration. It is also an indispensable condition for realizing the division of roles. It is more effective to employ these optical elements in both the first and second optical systems.

  Constructing the first optical system mainly from a plurality of refractive optical elements and the second optical system mainly from reflective optical elements avoids problems in manufacturing of the reflective system, and has a feasible oblique incidence imaging optics. It is important in providing the system. Furthermore, by configuring the second optical system with a single reflection optical element, the optical system can be simplified, which is advantageous in terms of cost.

  Although both the first optical system and the second optical system are mainly composed of a reflective optical system, there is a difficulty in mass production, but by applying the basic conditions of the present invention, it is brighter and very thin. It becomes possible to realize an oblique incidence optical system, and it can be expected as a future technology together with the manufacturing technology of the reflective optical element.

  By providing at least one component of the conjugate surface A, the first optical system, the second optical system, and the conjugate surface B, which are components of the optical system, and each optical element constituting them with a degree of freedom of decentration. Therefore, the degree of freedom in designing the entire optical system can be increased.

  Conversely, if at least one of the first optical system or the second optical system can be composed of rotationally symmetric optical elements, conventional manufacturing methods and assembly methods can be applied, greatly improving manufacturing cost and assembly. I can do it. Furthermore, it is possible to expect a greater effect by configuring the optical elements with rotationally symmetric optical elements that all have a common rotationally symmetric axis and aligning the axis with the reference axis of each optical system.

  With respect to the normal of the conjugate plane B, it is possible to solve problems in a specific application field by making all light beams incident at a certain angle or more. For example, the problem of the screen in the rear projection device and the problem of the storage space of the projection device can be solved.

  The present invention can be applied to the field of application of the oblique incidence imaging optical system, particularly to the field of forming a real image, for example, a projection device, an image reading device, a camera and the like. In particular, an oblique incidence imaging optical system having a half angle of view exceeding 60 °, which has been difficult in the past, can be realized.

  Next, an embodiment of the present invention will be described based on a specific configuration example with reference to the drawings.

  There are a wide variety of application examples of the present invention, and it is redundant to describe all these examples. Here, as a specific application example, a description will be given of a projection apparatus that forms an enlarged image of the image forming element 2 placed on the conjugate plane A on the screen 4 placed on the conjugate plane B. In addition, the projection apparatus originally needs an illumination unit, but is not essential to the present invention, and therefore, only the periphery of the imaging optical system of the present invention will be described. Accordingly, with respect to the drawings used for the description, portions other than those necessary for the description are omitted.

  From the first embodiment to the seventh embodiment, which will be described below, the first optical system and the second optical system are all configured by optical elements having a common rotational symmetry axis. In these examples, the reference axes of both optical systems are on a common straight line and coincide with the so-called optical axis. Similarly, the image forming element 2 and the screen 4 are orthogonal to the optical axis and parallel to each other. In the eighth and ninth embodiments, examples using a free-form surface that is an eccentric system or a non-rotation symmetric system will be taken up. Through these two embodiments, the effect of increasing the degree of freedom of design is confirmed.

  Each embodiment will be described sequentially.

  FIG. 1 is a sectional view of a projection apparatus according to the first embodiment of the present invention.

  An image forming element 2 is placed on the conjugate plane A. The image forming element 2 in this example is a transmissive liquid crystal element having a diagonal length of 0.7 inch and an aspect ratio of 4: 3. On the left side of the image forming element 2 in FIG. 1, an illuminating unit 1 for guiding a light beam to the image forming element 2 is provided, but is omitted from the drawing for the reasons described above. The light beam emitted from the image forming element 2 passes through the first optical system 30 configured by the refractive optical element, and is reflected by the second optical system 31 configured by one reflecting mirror, and is reflected on the conjugate plane B. An enlarged image having a size of 100 inches is formed on the corresponding screen 4.

  The first optical system 30 and the second optical system 31 have reference axes 3A and 3B, respectively. With respect to a parallel light beam incident from an object point at infinity, the first optical system 30 is in the vicinity of the reference axis 3A. The second optical system 31 has a diverging action in the vicinity of the reference axis 3B. The image forming element 2 is placed below the reference axis 3A of the first optical system 30 in the drawing. A light beam 321 condensed on the lower portion of the screen 4 is a light beam emitted from a point closest to the reference axis 3 </ b> A of the first optical system 30. Similarly, a light beam 328 converged on the upper portion of the screen 4 is a light beam emitted from a point farthest from the reference axis 3A in this cross-sectional view. The distance S2 along the reference axis 3B from the second optical system 31 to the screen 4 is 2 m. The imaging optical system composed of the optical systems 30 and 31 is a front projection device that is placed on the lower side of the screen 4 and projects upward from the lower side of the observation side.

  FIG. 2 is a diagram showing how the light beam converges when the second optical system 31 does not act on the light beam after passing through the first optical system 30, and the light beams 311 to 318 in the same cross section as the cross sectional view of FIG. Is also written. The difference from FIG. 1 is that the reflecting surface constituting the second optical system 31 does not function as a reflecting surface but is transmitted as it is. The screen 4 is placed at the same distance 2 m from the reference axis 3B of the second optical system 31 as in FIG. A light beam farther from the reference axis 3B in FIG. 2 corresponds to a light beam emitted from a point away from the reference axis 3A of the first optical system. Furthermore, the convergence point of each light beam (the point where the light beam diameter becomes the smallest in each light beam cross section) is shown in the figure. The (Δ) mark indicates the convergence point within the paper surface of FIG. 2, and the (●) mark indicates the convergence point within the beam cross section orthogonal to the paper surface. The curves 31S and 31T are curves connecting the respective points. The convergence point (●) for each light beam is also the distance to the shortest convergence point along the reference axis 3A of the first optical system 30 in every light beam cross section of the light beam. Similarly, the convergence point (Δ) corresponds to the convergence point with the longest distance.

  From this figure, the convergence point (Δ) of the light beam in the paper surface that has passed through the first optical system 30 converges further from the first optical system 30 as the exit position from the first optical system moves away from the reference axis 3A. It can be seen that the convergence angle gradually decreases with the convergence point. On the other hand, there is no significant change in distance at the convergence point (●) in the cross section perpendicular to it. Here, the convergence angle is defined as the maximum opening angle at the convergence point in the focused light beam cross section. In the case of a divergent light beam having no convergence point after exiting the first optical system 30, it is defined as the maximum opening angle of the divergence and the sign is negative. Therefore, even when the convergence angle of the light beam gradually decreases and shifts to divergence, the convergence angle is expressed as being uniformly reduced.

  In an actual optical system, the screen 4 is spatially spread in the depth direction of the paper surface, and there is a light beam directed there. Since all the light fluxes are illustrated in FIG. 2, the light flux is not shown. These are listed together as numerical data together with other embodiments in the list 3 that summarizes the conditions for establishing the present invention. In the case of this example, all the convergence points are formed between the second optical system 31 and the screen 4 corresponding to the conjugate plane B with respect to an arbitrary light beam having a principal ray within the paper surface. However, as shown in Table 3, a light beam that is out of the plane of the paper, such as a light beam that is further away from the reference axis, such as a light beam that is directed diagonally to the screen 4, has a convergence point at a position beyond the screen 4.

  FIG. 3 is a sectional view of the first optical system 30. It is composed of six groups of eight refractive optical elements, and all surfaces have a rotationally symmetric shape around the reference axis 3A. Therefore, the reference axis 3A coincides with the optical axis of the so-called first optical system. In the general case including an eccentric system, such a correspondence does not hold. In this case, the choice of the reference axis is arbitrary, but the most reasonable or convenient axis may be set as the reference axis. The light beam emitted from the image forming element 2 is sequentially transmitted from the image forming apparatus 2 side through the refractive surfaces indicated by r1, r2,..., R14 and guided to the second optical system 31. In this example, the distance along the reference axis of the first optical system 30 relating to the light beam after exiting the first optical system is the distance along the reference axis 3A from the apex of the surface of r14. Since the first optical system 30 of this example is a rotationally symmetric system, the focal length in the normal sense can be defined, and f = 37.1 mm.

  Table 1 shows chief ray emission angles with respect to the light beams 311 to 318 after passing through the first optical system in FIG. In the table, the image height is a distance from the reference axis 3A of the first optical system to the emission point of the light beam of the image forming element 2. The column of the emission angle is the angle formed by each actual principal ray with respect to the reference axis 3A, and the column of the calculation angle is the calculated emission angle when θ is calculated assuming that the image height is h and h = f × tan θ holds. From this table, the actual injection angle becomes larger than the calculated angle as the distance from the reference axis 3A increases. There is almost no difference in the portion close to the reference axis 3A.

次に，図１の第２光学系を構成する反射鏡３１は，基準軸３Ｂを回転軸とする回転対称形状を有する非球面である。従って，この場合も光軸と基準軸Ｂが一致する。この反射鏡は基準軸近傍において曲率半径約４００ｍｍの凸面で，入射光束を発散させる働きを持つ。基準軸近傍に於ける焦点距離ｆ＝−２００ｍｍである。

Next, the reflecting mirror 31 constituting the second optical system in FIG. 1 is an aspherical surface having a rotationally symmetric shape with the reference axis 3B as a rotation axis. Therefore, also in this case, the optical axis and the reference axis B coincide. This reflecting mirror has a convex surface with a radius of curvature of about 400 mm in the vicinity of the reference axis and has a function of diverging an incident light beam. The focal length f in the vicinity of the reference axis is f = −200 mm.

  Further, in the present embodiment, the optical systems 30 and 31 are placed so that the respective reference axes coincide with the same straight line, and as a result, a reference axis as a common optical axis is defined. The focal length f of the entire system including the optical systems 30 and 31 in the vicinity of the optical axis is f = 14.7 mm. Table 2 shows the calculated angle obtained from the angle between the optical axis of each principal ray reflected by the second optical system 31 and the focal length of the entire system. Although there is a slight difference, the actual injection angle and the calculated injection angle are in good agreement. In the case of this embodiment, the TV distortion is 0.5% or less.

共通の光軸に沿う第１光学系３０と第２光学系３１の距離Ｓ１＝２８０ｍｍ，第２光学系３１とスクリーン４の距離Ｓ２＝２０００ｍｍである。従って，第１光学系３０と第２光学系３１間の任意の光束に沿う距離Ｄ１と，同じ光束の第２光学系３１とスクリーン４までの光束に沿う距離Ｄ２に関し，明らかにＤ２＞Ｄ１の関係が成立している。また，第１光学系３０は，画像形成素子２の任意の一点から開き角２３度（Ｆｎｏ２.５）の光束を取り込んでおり，投写系にとって十分な明るさを確保している。画像形成素子２とスクリーン４は平行に置かれ，共通の光軸３Ａ，３Ｂはそれらの法線ともなっている。

The distance S1 between the first optical system 30 and the second optical system 31 along the common optical axis is 280 mm, and the distance S2 between the second optical system 31 and the screen 4 is 2000 mm. Accordingly, regarding the distance D1 along an arbitrary light beam between the first optical system 30 and the second optical system 31, and the distance D2 along the light beam to the second optical system 31 and the screen 4 of the same light beam, clearly D2> D1. The relationship is established. Further, the first optical system 30 takes in a light beam having an opening angle of 23 degrees (Fno 2.5) from an arbitrary point of the image forming element 2, and ensures sufficient brightness for the projection system. The image forming element 2 and the screen 4 are placed in parallel, and the common optical axes 3A and 3B are their normal lines.

  The specific configuration of the first embodiment has been described above. Finally, let us look at the conditions for establishing the imaging optical system of the present invention.

表３は，後述の各実施形態も含む，光束の収束位置に関する一覧表である。第１光学系と第２光学系との第１光学系の基準軸に沿う距離Ｓ１，第２光学系と共役面Ｂとの第２光学系の基準軸に沿う距離Ｓ２，第１光学系の基準軸に沿う距離が最長となる光束断面における収束点迄の距離Ｌ１，この光束断面とは異なる光束断面内において，第１光学系の基準軸に沿う距離が最短となる収束点迄の距離Ｌ２を示している。Ｌ１，Ｌ２の値は，第１光学系の基準軸の最も近傍から射出するＬ１１，Ｌ１２（表３の像高の欄が１の行）及び，第１光学系の基準軸から最も離れて射出する光束に関するＬ１ｎ，Ｌ２ｎ（像高の欄がｎの行）のみを記載している。この様な条件式計算に必要なデータに加えて，収束点Ｌ１，Ｌ２の光束断面角度として，共役面Ａから射出した直後の光束断面角度を基準に示している。反射屈折を繰り返すことで，波面形状が変化するため，この光束断面角度はあくまでも１つの目安である。

Table 3 is a list relating to the convergence position of the luminous flux, including the embodiments described later. The distance S1 along the reference axis of the first optical system between the first optical system and the second optical system, the distance S2 along the reference axis of the second optical system between the second optical system and the conjugate plane B, and the second optical system. The distance L1 to the convergence point in the light beam cross section where the distance along the reference axis is the longest, and the distance L2 to the convergence point where the distance along the reference axis of the first optical system is the shortest in the light beam cross section different from this light beam cross section Is shown. The values of L1 and L2 are L11 and L12 which are emitted from the nearest vicinity of the reference axis of the first optical system (the row of the image height in Table 3 is 1), and the light which is most distant from the reference axis of the first optical system. Only L1n and L2n (rows where the image height column is n) relating to the luminous flux to be transmitted are described. In addition to the data necessary for such conditional expression calculation, the light beam cross-sectional angle immediately after exiting from the conjugate plane A is shown as a reference as the light beam cross-sectional angle at the convergence points L1 and L2. Since the wavefront shape is changed by repeating catadioptric refraction, this light beam cross-sectional angle is only a guide.

表４は，各実施形態の条件式を確認するため，表３をもとにして算出した一覧表である。例えば，
Ｓ１≦Ｌ１１≦Ｓ１＋Ｓ２
の条件式については，上記表４のＳ１／Ｌ１１が１より小さいこと，及び（Ｓ１＋Ｓ２）／Ｌ１１が１より大きい事で確認できる。他の条件式も同様である。以上で第１の実施形態に関する基本的な説明を終えるが，第１光学系と第２光学系の基本構成を定め，光束の収束位置を制御することで，比較的簡単な構成ながら目的の斜入射結像光学系を実現することが出来る。考え方の基本は，第１光学系の役割を，第２光学系に関する光束の整合系と位置づけたことである。

Table 4 is a list calculated based on Table 3 in order to confirm the conditional expressions of the respective embodiments. For example,
S1 ≦ L11 ≦ S1 + S2
This conditional expression can be confirmed by the fact that S1 / L11 in Table 4 is smaller than 1 and (S1 + S2) / L11 is larger than 1. The same applies to other conditional expressions. This completes the basic description of the first embodiment. By defining the basic configuration of the first optical system and the second optical system and controlling the convergence position of the light beam, the target tilt can be achieved with a relatively simple configuration. An incident imaging optical system can be realized. The basic idea is that the role of the first optical system is positioned as a beam matching system for the second optical system.

  FIG. 4 shows a projection optical system according to the second embodiment of the present invention. A transmissive 1.3 inch element is used as the image forming element 2 corresponding to the conjugate plane A, and a 50 inch enlarged image is formed on the screen 4 corresponding to the conjugate plane B. The main points different from the first embodiment will be described below. First, the first optical system 30 having the reference axis 3A is composed of two refractive optical elements, and an optical element having positive power is arranged on the image forming element 2 side and negative power is arranged on the second optical system 31 side. is doing. The second optical system having the reference axis 3 </ b> B is configured by a single refractive optical element 31. Except for the point that the second optical element 31 is composed of a refractive optical element, it is basically similar to the first embodiment.

  FIG. 5 shows how the light flux converges, which corresponds to FIG. 2 of the first embodiment. The meaning of each symbol is the same as in FIG. In addition, the actual light flux includes a light flux in the depth direction of the paper, such as a light flux directed toward the diagonal of the screen 4, as in FIG.

  2 shows the same tendency as in the case of FIG. 2 except that the convergence point (Δ) of the light beam 319 farthest from the reference axis 3A is located beyond the screen 4. That is, the convergence point (Δ) in the drawing is on the curve 31T, and gradually converges to a farther distance along the reference axis 3A of the first optical system 30 as the distance from the reference axis 3A increases. In addition, the convergence angle gradually decreases. On the other hand, the convergence point (●) of the cross section perpendicular to the paper surface is on the curve 31S and is closer to the first optical system 30. Further, as can be seen from the numerical values in FIG. 5 and Table 3, the convergence point (●) has a convergence point at a distance closer to the first optical system as the distance from the reference axis 3A increases. The distance S2 along the reference axis 3B from the second optical system 31 to the screen 4 in FIG. 4 is 700 mm, and the distance S1 along the reference axis 3A between the first optical system and the second optical system is 300 mm. Further, the opening angle of the light beam taken in from the image forming element 2 by the first optical system 30 is 10 degrees (about Fno 5.6). The focal length of the first optical system is f1 = 61.3 mm, and the combined focal length of the first and second optical systems is f = 15.7 mm. Table 5 shows the emission angle of the light beam emitted from the first optical system 30 and the calculated angle obtained from the focal length.

この例でも，計算角度より，実際の角度が大きくなっている。表６に，第２光学系３１を射出後の光束の射出角度と，全系の焦点距離から計算した射出角度を示す。

In this example as well, the actual angle is larger than the calculated angle. Table 6 shows the exit angle of the light beam after exiting the second optical system 31 and the exit angle calculated from the focal length of the entire system.

第１の実施の形態とは異なり，実際の角度と，計算角度が大きく異なっている。これは，光学系の周辺に於いて，近軸的な焦点距離が意味を持たない事を示唆している。この事実にも関わらず，スクリーン４上での画像としての歪曲は，０.１６％以下に抑えられている。更に，ここで注目すべき事は，第１光学系の基準軸３Ａに関する表５の射出角度と，それに対応する第２光学系の基準軸３Ｂに関する表８の射出角度が大きく異なっていることである。これは，第２光学系の射出角度増加に果たす役割が相対的に大きいことを示している。本実施例は，ここで取り上げる実施例を通じて増加の割合が比較的小さい方の例である。それでも，射出角度の正接の比，即ち射出角のtanθの比は，光線番号３１９でも２を越えている。

Unlike the first embodiment, the actual angle and the calculated angle are greatly different. This suggests that the paraxial focal length is meaningless around the optical system. Despite this fact, the distortion of the image on the screen 4 is suppressed to 0.16% or less. Furthermore, what should be noted here is that the emission angle in Table 5 relating to the reference axis 3A of the first optical system and the emission angle in Table 8 relating to the reference axis 3B of the second optical system corresponding to each other are greatly different. is there. This indicates that the role played by the second optical system in increasing the emission angle is relatively large. The present embodiment is an example in which the rate of increase is relatively small throughout the embodiments described here. Nevertheless, the ratio of the tangent of the exit angle, that is, the ratio of the tan θ of the exit angle exceeds 2 even at the ray number 319.

  FIG. 6 is a cross-sectional view of the projection apparatus showing the third embodiment of the present invention. As the image forming element 2, a reflection type 0.9 inch element is used, and a light beam from the reflection type element is a first optical system 30 composed of a refractive optical element and a second optical system 31 composed of a single reflecting mirror. As a result, a 60-inch enlarged image is formed on the screen 4. A plane mirror 301 for folding the optical path is provided, although it does not contribute to image formation on the way. As a form of projection, as in the first and second embodiments, the projection optical system projects upward from the lower center of the screen. This example is one of typical examples when the oblique incidence imaging optical system of the present invention is used as a projection apparatus. Although it has a relatively simple configuration, it has sufficient performance as a projection system. The distance S2 from the second optical system 31 to the screen 4 is 450 mm. Further, the opening angle of the light beam taken in from the image forming element 2 by the first optical system is 14.4 degrees (Fno4). In the cross-sectional view of FIG. 6, the angle formed by the light beam 328 having the largest angle of view and the optical axis 3A is 63 degrees (the maximum angle including the light beam outside the paper is 64.7 degrees). While having such a large angle of view, there is almost no distortion at 0.03%. Of the distances D1 and D2 along the light beam from the first optical system 30 to the second optical system 31 and from the second optical system 31 to the screen 4, the light beam 321 has the smallest difference. = 298.2, D2 = 520.7, which also satisfies the condition D2> D1.

  FIG. 7 shows the position of the convergence point in each light beam cross section as in the previous examples. In this example, the rate at which the convergence point represented by the curve 31T exceeds the screen 4 further increases, and all of the light fluxes 315 and beyond have a convergence point at a position exceeding the screen 4. The light beam 318 has no convergence point and is almost parallel light (converged to infinity). In the previous two embodiments, the convergence point (Δ) always has a convergence point in the direction in which the light beam travels along the reference axis of the first optical system, but in this embodiment, as can be seen from Table 3. , L1n light flux converges at a negative distance, and the light flux becomes divergent light.

  FIG. 8 is a cross-sectional view of the first optical system 30. In this embodiment, a reflective liquid crystal is used as the image forming apparatus 2. In general, a reflective element requires a sufficient back focus as a space for guiding an illumination light beam. Also in this example, a sufficient air space is ensured between the image forming element 2 and the optical element closest to the image forming element of the first optical system 30, and the actual focal length is 8 times or more. . Incidentally, the focal length f1 of the first optical system is 35.5 mm, the focal length f2 of the second optical system is −96 mm, and the focal length of the entire system is f = 7.9 mm. Compared to the focal length of each optical system, it has a very small combined focal length.

In addition, this example shows the following additional conditions of the present invention.
S1 / L11> 0.6
(S1 + S2) / L2n <1
ΔSL> 0.6
It is also the first case that satisfies Actual values are shown in Table 4
S1 / L11 = 0.69
(S1 + S2) /L2n=0.95
ΔSL = 0.87
And all the above conditions are satisfied. When the oblique incidence angle increases as in the present embodiment, it is necessary to impose severer conditions in addition to normal conditions in order to balance the imaging characteristics. The first condition means that the farthest convergence point of the light beam emitted from the nearest reference axis of the first optical system is brought closer to the vicinity of the second optical system. The second condition means that the nearest convergence point of the light beam emitted from the position farthest from the reference axis of the first optical system converges at a position beyond the conjugate plane B. The last condition means that the distance difference between the farthest convergence point is more than a certain value with respect to the convergence point of the light beam exiting from the nearest reference axis of the second optical system and the light beam exiting farthest away. Yes. It is desirable that the components of each optical system that realizes a large oblique incident angle have a structure and a shape that satisfy at least one of such conditions. The remaining embodiments described below are examples that satisfy at least one of the above three conditions.

  FIG. 9 is a sectional view showing a fourth embodiment of the present invention. It is sectional drawing of the projection apparatus of the front projection type which projects on a screen from the observation side like the example so far. The difference from the above is that this projection apparatus is installed directly beside the screen 4 and can further move the image position to be projected. FIG. 9 is a cross-sectional view taken along a horizontal plane including the upper and lower bisectors of the screen 4. FIG. 10 shows a state where the apparatus of FIG. 9 is viewed from the observation side.

  The image forming element 2 to be used is a 0.7 inch reflective element. The light beam emitted from the image forming element 2 passes through the first optical system 30 composed of a refractive optical element and the second optical system 31 composed of a single reflecting mirror, and has a size of 60 inches on the screen 4. The image is formed. The projected image is movable in the horizontal direction. From the 60 inch image position where the horizontal end is formed by the light beam 321 and the light beam 328, the same 60 inch image formed by the light beam 321 ′ and the light beam 328 ′. It is configured so that a distance corresponding to half of the screen can be moved to a size image position. When viewed from the observer side, it appears to move from the screen 4 in FIG. 10 to 4 'indicated by a dotted line. As in this example, in a projection apparatus that can project from an oblique direction and has a short projection distance, the projection apparatus itself is unlikely to be disturbed when viewing an image. Nevertheless, this function is important in that it gives freedom to the installation location of the projector.

  FIG. 11 is a diagram showing the convergence point of the light beam emitted from the first optical system 30 in the same cross section as FIG. The light beam emitted from the first optical system 30 is reflected by the second optical system 31 and converges on the screen 4, but this figure is not affected by the second optical system 31 and is transmitted as it is. It is drawn as going to the position corresponding to. The distance S2 between the second optical system 31 and the screen equivalent surface 4 is 700 mm. A triangle represents a convergence point on the paper surface, and a black circle represents a convergence point within a beam cross section orthogonal to the paper surface. As is clear from the figure, the convergence point in the paper surface converges farther from the first optical system as the exit point of the light beam in the first optical system moves away from the reference axis 3A, and in the case of the light beam 318 ′, the convergence point is determined. It becomes divergent light that you do not have. Accordingly, the convergence angle gradually decreases from the light beam 311 and is negative for the light beam 318 ′. The convergence point (●) of the light beam in the cross section orthogonal to the paper surface is formed closer to the first optical system 30 than the convergence point (Δ) in the paper surface. The light beam 318 ′ is formed almost at the position of the screen. The opening angle of the light beam taken in from the image forming element 2 by the first optical system 30 is 14.4 degrees (Fno4), and the distortion is a maximum of 0.23%. FIG. 12 shows a cross-sectional view of the first optical system 30.

  FIG. 13 is a diagram showing a fifth embodiment of the present invention. This is a rear projection device that observes an image projected from the back of the screen from the front of the screen, as in a normal television.

  The image forming apparatus 2 corresponding to the conjugate plane A is a transmissive liquid crystal display device. A light beam emitted from the image forming apparatus 2 includes two reflecting mirrors 30a and 30b constituting the first optical system, and one sheet constituting the second optical system. The reflection mirror 31 and the plane mirror 301 are folded back to form an enlarged image on the screen 4 which is the other conjugate plane B. The size of the image forming element 2 is 1.3 inches, and the size of the image on the screen is 50 inches. By using the plane mirror 301 in this way and folding the light beam, thin rear projection becomes possible. In this projection apparatus, the thickest part is 280 mm between the plane mirror 301 and the screen 4 (where S2 = 520 mm). This is about half the conventional thickness. FIG. 14 is a view of this apparatus as viewed from the back of the screen. FIG. 15 shows how the light beam converges, and FIG. 16 shows an enlarged view of the imaging system portion. The opening angle of the light beam taken in from the image forming element 2 by the first optical system 30 is 11.5 degrees (Fno 5), and the distortion is a maximum of 0.57%.

  FIG. 17 is a sectional view showing a sixth embodiment of the present invention. This is also a rear projection device as in the fifth embodiment. FIG. 17 is a top view thereof.

  A light beam emitted from the 0.7-inch image forming apparatus 2 passes through a first optical system 30 composed of a refractive optical element, a plane mirror 301, a second optical system 31 composed of a single reflector, and a plane reflector 302. Pass through and form an image of 100 inches on the screen 4. This rear projection apparatus can also be thinned, and the distance between the plane reflecting mirror 302 and the screen 4 is 400 mm. In addition, the height from the first optical system 30 at the lower part of the projection device to the lower end of the screen 4 is low, and the overall height of the projection device is low. The opening angle of the light beam taken in from the image forming apparatus 2 by the first optical system 30 is 23.1 degrees (Fno 2.5). Further, the distortion is 0.06% or less. FIG. 18 is a front view of the entire projection apparatus, and FIG. 19 is a cross-sectional view of the first optical system 30.

  FIG. 20 is a sectional view showing a seventh embodiment of the present invention. The image forming apparatus 2 is a 0.7 inch 16: 9 horizontally long element. The light beam emitted from the image forming apparatus 2 is projected onto the screen 4 through the first optical system 30 composed of a refractive optical element and the second optical system 31 composed of a single reflecting mirror. The feature of this embodiment is that the difference between the angle of the light beam to the lower end of the screen and the angle of the light beam to the upper end of the screen is small. Specifically, the lower end side is 63 degrees, the upper end side is 77 degrees, and the angle difference is 14 degrees. The projection distance is also short, and the distance S2 from the apex of the reference axis 3B of the second optical system to the screen 4 is 167 mm. Conversely, the distance from the first optical system 30 to the second optical system 31 is longer, and S1 = 300 mm. In actual application, a plane mirror can be added and folded freely. Thus, S1> S2, but the distance along the actual light beam 321 satisfies the condition of D1 <D2. FIG. 21 is a cross-sectional view of the first optical system 30, and the opening angle of the light beam taken from the image forming element 2 is 23 ° (Fno 2.5).

  FIG. 22 is a sectional view showing an eighth embodiment of the present invention. This is an example of a rear projection apparatus similar to the fifth embodiment, in which both the first optical system and the second optical system are composed of reflecting mirrors. The difference from the fifth embodiment is that the first optical system is composed of three reflecting mirrors 30a, 30b, and 30c, and the second optical system 31 is composed of one reflecting mirror. . The light beam from the image forming apparatus 2 having a size of 0.7 inch is projected on the screen 4 as an image having a size of 40 inches. All the reflecting mirrors are composed of rotationally symmetric aspheric surfaces having rotationally symmetric axes, but all the reflecting mirrors are decentered and there is no common optical axis. In this example, as a convenient reference axis, the reference axis 3A for defining the eccentricity of each reflecting mirror is used as a common reference axis for the first optical system and the second optical system. This axis has no physical meaning and is for convenience only. The opening angle of the light beam taken in from the image forming apparatus 2 is 16.4 degrees (FNo 3.5) and has sufficient brightness. The thickness of the projection device from the plane mirror 301 to the screen 4 is 160 mm.

  FIG. 23 is a sectional view showing a ninth embodiment of the present invention. In this example, the basic configuration is almost the same as that of the eighth embodiment, but in order to make it thinner, the three reflecting mirrors constituting the first optical system 30 are made into free-form surfaces. For the same 40 inch projected image, the thickness from the plane mirror 301 to the screen 4 is only 125 mm. This is an epoch-making thickness of 25% of the diagonal. Although various defining formulas can be used for the free-form surface formation, a Zernike polynomial is adopted in this example. Further, the third mirror 30c of the first optical system 30 has a large amount of decentration, and has a rotational decentering of about 35 °. In such an optical system, the paraxial idea no longer holds. For example, the focal length f1 = -5.49 mm of the first optical system calculated from the paraxial amount, the focal length f = -1.34 mm of the entire system, and the like are apparent. However, in the vicinity of the reference axis, the basic properties that the first optical system is a converging system and the second optical system is a diverging system are of course established. The opening angle of the light beam taken from the image forming apparatus 2 is 14.4 degrees (FNo4).

  In the above, each embodiment has been described focusing on the example of the projection apparatus. What is important is that, by satisfying the basic conditions, an oblique incidence optical system can be constructed regardless of specific components of the optical system such as a refractive system and a reflective system. This leads to an increase in the selection of specific means for realizing the oblique incidence optical system in accordance with the technical level and manufacturing cost at that time.

  Finally, examples corresponding to the respective embodiments are shown as specific numerical examples.

  Table 7 shows a first numerical example corresponding to the first embodiment. The numbers 1 to 14 at the left end of Table 7 correspond to the symbols 1 to 14 in FIG. 3 representing the first optical system 30. Although not specifically shown, the refractive index and dispersion also correspond to the values of each surface. The number 0 corresponds to the image forming element 2, and d0 is the distance along the optical axis from the image forming element 2 to r1, which is the first surface of the first optical system.

表７の番号の欄に＊印を付してある面は，その面が非球面であることを示している。以下の第１〜第８実施例迄は，光学系設計の自由度を確保するための非球面として，次の非球面式を採用している。これ以外の定義式を採用することももちろん可能であり，選択は，通常よく使用されるという便宜的な理由に過ぎない。

A surface marked with * in the number column of Table 7 indicates that the surface is an aspherical surface. In the following first to eighth embodiments, the following aspherical formula is adopted as an aspherical surface for ensuring the degree of freedom in optical system design. It is of course possible to adopt other defining formulas, and the selection is merely a convenient reason that it is usually used frequently.

ここでＺは，各非球面の頂点を通る基準平面からの光軸方向の深さである。また，ｃは面の曲率半径Ｒの逆数，ｈは面の光軸からの距離を表している。ｋは円錐定数，Ａ₄〜Ａ₂₆は非球面補正係数である。それぞれの各係数の値は，表８に与えられる。

Here, Z is the depth in the optical axis direction from the reference plane passing through the apex of each aspheric surface. Further, c represents the reciprocal of the radius of curvature R of the surface, and h represents the distance from the optical axis of the surface. k is a conic constant, A ₄ to A ₂₆ are aspherical correction coefficient. The value of each coefficient is given in Table 8.

表７の番号１５に相当する面は，第２光学系３１を構成する反射面に関するデータである。この面も，同じ式で表される非球面である。ｄ１４は，第１光学系のｒ１４から第２光学系３１迄の光軸に沿う距離，ｄ１５は第２光学系からスクリーン４迄の光軸に沿う距離を表している。番号１６はスクリーンである。

The surface corresponding to number 15 in Table 7 is data relating to the reflecting surface constituting the second optical system 31. This surface is also an aspheric surface represented by the same equation. d14 represents the distance along the optical axis from r14 of the first optical system to the second optical system 31, and d15 represents the distance along the optical axis from the second optical system to the screen 4. Number 16 is a screen.

  Numerical examples corresponding to the second embodiment are shown in Table 9 and Table 10.

番号３，４が図４の第１光学系３０を構成する画像形成素子２側の凸レンズの面データ，番号５，６が同じく第１光学系３０のスクリーン側の凹レンズの面データに対応している。番号７，８は第２光学系３１を構成する光学素子の面データである。番号０が画像形成素子２に，番号９がスクリーン４に相当する。なお，番号１，２は色合成用プリズムに相当する。

Numbers 3 and 4 correspond to the surface data of the convex lens on the image forming element 2 side constituting the first optical system 30 in FIG. 4, and numbers 5 and 6 correspond to the surface data of the concave lens on the screen side of the first optical system 30. Yes. Numbers 7 and 8 are surface data of optical elements constituting the second optical system 31. Number 0 corresponds to the image forming element 2 and number 9 corresponds to the screen 4. Numbers 1 and 2 correspond to color combining prisms.

  Tables 11 and 12 show numerical examples corresponding to the third embodiment. Numbers 1 to 11 correspond to r1 to r11 in FIG. Further, number 0 corresponds to the image forming element 2, number 12 corresponds to the folding plane mirror, and number 13 corresponds to the aspherical mirror 31 constituting the second optical system. Number 14 corresponds to the screen.

第４の実施形態に対応する数値例を，表１３及び表１４に示す。

Numerical examples corresponding to the fourth embodiment are shown in Table 13 and Table 14.

  Numbers 1 to 13 correspond to r1 to r13 in FIG. r14 is surface data corresponding to the reflecting surface 31 constituting the second optical system. This optical system corrects aberrations over a wider range of image heights in consideration of image movement. Number 0 corresponds to an image forming element, and number 15 corresponds to a screen.

第５の実施形態に対応する数値例を，表１５及び表１６に示す。

Numerical examples corresponding to the fifth embodiment are shown in Table 15 and Table 16.

  This is a numerical example of a rear projection apparatus in which the imaging system is entirely composed of reflecting mirrors. Numbers 3 and 4 in Table 15 are surface data corresponding to the reflecting mirrors 30a and 30b in FIG. Further, number 5 in Table 15 corresponds to the surface data of the reflecting mirror 31 constituting the second optical system 31. Surface data 0 is the image forming element 2, surface data 6 is the plane reflecting mirror 301, and surface numbers 1 and 2 are color combining prisms.

第６の実施形態に対応する数値例を，表１７及び表１８に示す。番号１〜１４が，図１９の第１光学系断面図ｒ１〜ｒ１４に対応する。番号１５が９０°折り曲げ平面ミラー，番号１６が第２光学系を構成する非球面反射鏡３１，番号１７が折り返し用平面反射鏡３０１にそれぞれ対応している。番号０が画像形成装置２，番号１８がスクリーン４である。

Numerical examples corresponding to the sixth embodiment are shown in Table 17 and Table 18. Numbers 1 to 14 correspond to the first optical system cross-sectional views r1 to r14 in FIG. Reference numeral 15 corresponds to the 90 ° bent flat mirror, reference numeral 16 corresponds to the aspheric reflecting mirror 31 constituting the second optical system, and reference numeral 17 corresponds to the folding flat reflecting mirror 301. Number 0 is the image forming apparatus 2 and number 18 is the screen 4.

第７の実施形態に対応する数値例を，表１９及び表２０に示す。番号１〜１７が，図２１の第１光学系断面図ｒ１〜ｒ１７に対応する。番号１８が第２光学系を構成する非球面反射鏡３１にそれぞれ対応している。番号０が画像形成装置２，番号１９がスクリーン４である。なお，図２１には，画像形成装置２に隣接して，色分解用プリズムがあるが表では空気換算長として示している。

Tables 19 and 20 show numerical examples corresponding to the seventh embodiment. Numbers 1 to 17 correspond to the first optical system sectional views r1 to r17 in FIG. Reference numeral 18 corresponds to the aspheric reflecting mirror 31 constituting the second optical system. Number 0 is the image forming apparatus 2 and number 19 is the screen 4. In FIG. 21, there is a color separation prism adjacent to the image forming apparatus 2, but it is shown as an air conversion length in the table.

第８の実施形態に対応する数値例を，表２１，表２２及び表２３に示す。表２１の番号３，４，５が，図２２の第１光学系を構成する反射鏡３０ａ，３０ｂ，３０ｃにそれぞれ対応する面データである。また，表２１の番号６が，第２光学系３１を構成する反射鏡３１の面データに対応する。面データ０が画像形成素子２，面データ７が平面反射鏡３０１，面データ８がスクリーン４である。面番号１，２はカバー硝子である。表２３には，それぞれの反射鏡の偏心量を示している。Ｙディセンタが紙面上方向への移動，ｘ軸回転が紙面内時計回りの回転がそれぞれの偏心の正の向きである。

Numerical examples corresponding to the eighth embodiment are shown in Table 21, Table 22, and Table 23. Numbers 3, 4, and 5 in Table 21 are surface data corresponding to the reflecting mirrors 30a, 30b, and 30c constituting the first optical system in FIG. Further, number 6 in Table 21 corresponds to the surface data of the reflecting mirror 31 constituting the second optical system 31. The surface data 0 is the image forming element 2, the surface data 7 is the plane reflecting mirror 301, and the surface data 8 is the screen 4. Surface numbers 1 and 2 are cover glasses. Table 23 shows the amount of eccentricity of each reflecting mirror. The Y decenter is the upward movement of the paper, and the x-axis rotation is the clockwise rotation of the paper in the positive direction of each eccentricity.

第９の実施形態に対応する数値例を，表２４，表２５，表２６及び表２７に示す。基本的な説明は第８の実施形態の数値例と同じである。異なる点は，非球面を自由曲面に拡張するための係数表２７が追加されていることである。これは，非球面式に加えて，自由曲面を表現するために新たに付加したＺｅｒｎｉｋｅの多項式の係数を示している。この選択も，非球面の定義式の選択と同様に便宜的なもので，他の定義式を採用することも可能である。各係数に対応する多項式の形は，表２７の後に記している。

Numerical examples corresponding to the ninth embodiment are shown in Table 24, Table 25, Table 26, and Table 27. The basic description is the same as the numerical example of the eighth embodiment. The difference is that a coefficient table 27 for expanding an aspheric surface to a free-form surface is added. This indicates a coefficient of a Zernike polynomial newly added to express a free-form surface in addition to the aspherical expression. This selection is also as convenient as the selection of the aspherical definition formula, and other definition formulas can be adopted. The form of the polynomial corresponding to each coefficient is described after Table 27.

以下に，Ｚｅｒｎｉｋｅの付加項の中で，上記表２７のゼロでない項だけを取って，その具体的な式の形を順に列挙する。左側の数字が表２７の次数に対応している。

Below, only the non-zero terms in the above-mentioned Table 27 are taken from the Zernike additional terms, and the specific formula forms are listed in order. The numbers on the left correspond to the orders in Table 27.

以上，各実施の形態に対応する，具体的な数値データを示した。これらのデータの中で，第２光学系を全て１枚の反射鏡あるいは１枚の屈折素子で構成した例のみを取り上げたが，第２光学系は構成上比較的大きくなるため，複数の構成にする場合，製造的・コスト的に種々の問題を生じる。この理由から，本実施例では全て単一の素子から構成した例のみを取り上げた。これらを複数の枚数で構成することにより，自由度を増やせることは言うまでもない。また，第２光学系に全て回転対称素子を使用した例のみを載せたのも，同様の理由による。これを自由曲面とすることでも，設計の自由度は増加する。

The specific numerical data corresponding to each embodiment has been described above. In these data, only the example in which the second optical system is composed of one reflecting mirror or one refracting element is taken up. However, since the second optical system is relatively large in configuration, there are a plurality of configurations. In this case, various problems occur in terms of manufacturing and cost. For this reason, in this embodiment, only examples composed of a single element are taken up. It goes without saying that the degree of freedom can be increased by configuring these with a plurality of sheets. Further, only the example in which rotationally symmetric elements are used in the second optical system is used for the same reason. Making this a free-form surface also increases the degree of freedom in design.

It is sectional drawing of the projection apparatus showing 1st Embodiment of an oblique incidence imaging optical system. It is a figure showing the convergence condition after the 1st optical system injection | emission in 1st Embodiment. It is a 1st optical system sectional view in a 1st embodiment. It is sectional drawing of the projection apparatus showing 2nd Embodiment of an oblique incidence imaging optical system. It is a figure showing the convergence condition after the 1st optical system injection | emission in 2nd Embodiment. It is sectional drawing of the projection apparatus showing 3rd Embodiment of an oblique incidence imaging optical system. It is a figure showing the convergence condition after the 1st optical system injection | emission in 3rd Embodiment. It is a 1st optical system sectional view in a 3rd embodiment. It is sectional drawing of the projection apparatus showing 4th Embodiment of an oblique incidence imaging optical system. It is a front view of the projection apparatus showing 4th Embodiment of an oblique incidence imaging optical system. It is a figure showing the convergence condition after the 1st optical system injection | emission in 4th Embodiment. It is a 1st optical system sectional view in a 4th embodiment. It is sectional drawing of the rear projection apparatus showing 5th Embodiment of an oblique incidence imaging optical system. It is a front view of the rear projection apparatus showing 5th Embodiment of an oblique incidence imaging optical system. It is a figure showing the convergence condition after the 1st optical system injection | emission in 5th Embodiment. It is sectional drawing of the 1st and 2nd optical system in 5th Embodiment. It is sectional drawing of the rear projection apparatus showing 6th Embodiment of an oblique incidence imaging optical system. It is a front view of the projection-and-reverse copying apparatus showing the sixth embodiment of the oblique incidence imaging optical system. It is sectional drawing of the 1st optical system in 6th Embodiment. It is sectional drawing of the projection apparatus showing 7th Embodiment. It is sectional drawing of the 1st optical system in 7th Embodiment. It is sectional drawing of the rear projection apparatus showing 8th Embodiment. It is sectional drawing of the rear projection apparatus showing 9th Embodiment. It is a principle diagram of a decentered oblique incidence optical system. It is a principle diagram of a tilt type oblique incidence optical system. It is a conceptual diagram of the tilt type distortion. (A), (b) is sectional drawing of the projection lens of Unexamined-Japanese-Patent No. 05-273460. It is sectional drawing of the projection apparatus of US Pat. No. 5,871,266. It is sectional drawing of the projection lens of Unexamined-Japanese-Patent No. 10-206791. It is sectional drawing which shows the mode of projection of Unexamined-Japanese-Patent No. 10-206791. It is sectional drawing of the rear projection apparatus of US Pat. No. 5,274,406. It is sectional drawing of the projection lens used for U.S. Pat. No. 5,274,406. (A), (b) is a bird's-eye view of the Fresnel mirror used for U.S. Pat. No. 5,274,406. It is sectional drawing of the projection optical system of Unexamined-Japanese-Patent No. 6-265814. It is a schematic diagram for demonstrating a multistage tilt system. It is sectional drawing of the pupil coupling element used by a multistage tilt system. It is sectional drawing of the rear projection apparatus of Unexamined-Japanese-Patent No. 07-13157. It is sectional drawing of the projection apparatus of Unexamined-Japanese-Patent No. 09-179064. It is sectional drawing of the projection lens of Unexamined-Japanese-Patent No. 09-179064. It is a schematic diagram for demonstrating the principle of an afocal tilt system. It is typical structure sectional drawing of a head mounted display apparatus. It is sectional drawing of the HMD apparatus of Unexamined-Japanese-Patent No. 5-303055. It is sectional drawing of the HMD apparatus of Unexamined-Japanese-Patent No. 7-191274. It is sectional drawing of the HMD apparatus of Unexamined-Japanese-Patent No. 7-191274. It is sectional drawing of the HMD apparatus of Unexamined-Japanese-Patent No. 10-239631. It is a conceptual diagram of the video telephone apparatus of Unexamined-Japanese-Patent No. 6-133311.

Claims (12)

A plurality of light beams diverged from an image forming element on the conjugate plane A with an opening angle of 10 ° or more are incident on the conjugate plane B obliquely, and an image formed by the image forming element on the conjugate plane B is displayed. In an imaging optical system capable of forming an enlarged image,
A first optical system and a second optical system;
The first optical system does not have an optical axis common to all, but includes a plurality of optical elements each having a rotationally symmetric axis, and is emitted from the image forming element when the second optical system does not act. was then minimized in both the second light flux cross section that intersects the principal ray is parallel to the first beam cross-section and the first light beam cross-section of each of the light flux diameter of the light beams, the optical effect of Ru converges them beam Have
The second optical system has an optical function of Ru converges the light flux passing through the first optical system on the conjugate plane B,
The first optical system passes through a position closer to the light beam having the shortest optical path than the light beam having the longest optical path from the conjugate surface A to the conjugate surface B, and is orthogonal to the conjugate surface A. Having a reference axis,
The second optical system passes through a position closer to the light beam having the shortest optical path than the light beam having the longest optical path from the conjugate surface A to the conjugate surface B, and is orthogonal to the conjugate surface B. Having a reference axis,
The distance along the first reference axis from the exit point of the first optical system to the entrance point of the second optical system is S1, and the second reference from the exit point of the second optical system to the conjugate plane B The distance along the axis is S2.
The distance along the first reference axis from the first optical system to the convergence point in the first light beam cross section of each light beam that the first optical system converges each light beam is L1 and distance L1. L11 is a value related to the light beam emitted from the point closest to the first reference axis, L1n is a value related to the light beam emitted from the point farthest from the first reference axis,
The distance along the first reference axis from the first optical system to the convergence point of the second light beam cross-section of each light beam that causes the first optical system to converge the light beam is L2 and L2 When the value related to the light beam emitted from the point closest to the first reference axis is L21, and the value related to the light beam emitted from the point farthest from the first reference axis is L2n ,
S1 ≦ L11 ≦ S1 + S2
S1 ≦ L21 ≦ S1 + S2
L11 / L1n <0.25
0 <L21 / L2n <1.5
An imaging optical system that satisfies the following conditions. When the distance along the arbitrary light beam from the first optical system to the second optical system is D1, and the distance along the arbitrary light beam from the second optical system to the conjugate plane B is D2,
D1 <D2
The imaging optical system according to claim 1 , wherein the following condition is satisfied. When the difference between the maximum value and the minimum value of the ratio S1 / L1 between the distance L1 and the distance S1 is ΔSL,
S1 / L11> 0.6
(S1 + S2) / L2n <1
ΔSL> 0.6
The imaging optical system according to claim 1 , wherein at least one of the following conditions is satisfied. Said first optical system and second optical system, claim 3 substantially-similar reduced image and the image on the conjugate plane B from claim 1 having a formable imaging action on the conjugate plane A The imaging optical system described in 1. Wherein the first optical system is constituted by the refractive optical element, the imaging optical system according to any one of claims 1 to 3, wherein the second optical system is constructed by the reflective optical element. The imaging optical system according to any one of claims 1 to 3 , wherein the first optical system is configured by a reflective optical element, and the second optical system is configured by a refractive optical element. The imaging optical system according to any one of claims 1 to 3 , wherein the first optical system and the second optical system are configured by reflective optical elements. Wherein all of the light beam incident on the conjugate plane B is, imaging optical system according to any one of claims 1 to 3 having more than 45 ° inclination with respect to the normal line of the conjugate plane B. It said second optical system, the imaging optical system according to any one of claims 1 to 3, which is constituted by a single optical element. It said second optical system, the imaging optical system according to any one of claims 1 to 3, which is constituted by a single reflecting optical element. Said second optical system, according to any one of claims 1 to 3 having an optical element having a rotational symmetry axis which has the effect of converging the light flux passing through the first optical system on the conjugate plane B Imaging optical system. The imaging optical system according to any one of claims 1 to 3 , wherein all the optical elements constituting the first optical system are decentered from each other.

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