JP5871039B2 - Projection optical system and image projection apparatus - Google Patents

Description

  The present invention relates to a projection optical system that enlarges and projects an image on a projection surface, and an image projection apparatus that includes the projection optical system.

  Liquid crystal projectors that are widely known as image projection apparatuses have recently been improved in the resolution, the price, and the like due to the higher resolution of the liquid crystal panel, the higher efficiency of the light source lamp. In addition, small and light image projection apparatuses using DMD (DigitAl Micro-mirror Device) or the like have become widespread, and image projection apparatuses are being widely used not only in offices and schools but also at home. In particular, front type projectors have improved portability and are used for small conferences of several people.

  In such an image projection apparatus, various techniques relating to focus adjustment for focusing on the screen are disclosed. For example, Patent Document 1 discloses a technique for performing focus adjustment by moving each of a plurality of lens groups constituting a projection optical system. Patent Document 2 discloses a technique for performing focus adjustment by individually moving a focus lens group and an aspherical mirror in a lens system constituting a projection optical system.

  However, the technique disclosed in Patent Document 1 does not disclose the direction in which each of the plurality of lens groups is moved, and there is a possibility that distortion generated during focus adjustment cannot be corrected. Further, in the technique of Patent Document 2, the aspherical mirror is moved, but it is not desirable to move the aspherical mirror whose main function is distortion correction in terms of increasing positional errors with other components, Similar to the case of Patent Document 1, there is a possibility that the distortion generated during focus adjustment cannot be corrected.

  The present invention has been made in view of the above, and an object of the present invention is to provide a projection optical system capable of correcting distortion generated during focus adjustment, and an image projection apparatus having the projection optical system.

The present projection optical system is a projection optical system that enlarges and projects an image formed on an image forming element onto a projection surface, and a plurality of lens groups emit light on an optical path from the image formation element to the projection surface. A coaxial optical system sharing an axis and a concave mirror are arranged in this order, the coaxial optical system includes an aperture stop, and the plurality of lens groups are arranged in the optical axis direction when adjusting a focal point. A plurality of independently moving focus groups, wherein the concave mirror is fixed when adjusting the focal point, and one of the plurality of focus groups has a negative refractive power and a negative refractive power; When the focus group closest to the concave mirror is the first focus group, the aperture stop is disposed closer to the image forming element than the first focus group, and the other focus groups are If having a refractive power are the open To move in the same direction of the optical axis direction as the first focus group with respect to the diaphragm, opposite the direction of the first focusing unit and the optical axis direction with respect to the aperture stop if having a negative refractive power As a requirement.

  According to the disclosed technology, it is possible to provide a projection optical system capable of correcting distortion generated during focus adjustment, and an image projection apparatus including the projection optical system.

It is a schematic diagram which illustrates the image projection apparatus which concerns on 1st Embodiment. It is an optical path diagram which illustrates the projection optical system which concerns on 1st Embodiment. It is FIG. (1) for demonstrating a concave surface mirror. It is FIG. (2) for demonstrating a concave surface mirror. It is FIG. (3) for demonstrating a concave-surface mirror. It is FIG. (1) for demonstrating distortion of the image projected on the to-be-projected surface. It is FIG. (2) for demonstrating distortion of the image projected on the to-be-projected surface. It is FIG. (3) for demonstrating distortion of the image projected on the to-be-projected surface. It is FIG. (4) for demonstrating distortion of the image projected on the to-be-projected surface. It is FIG. (5) for demonstrating distortion of the image projected on the to-be-projected surface. It is FIG. (6) for demonstrating distortion of the image projected on the to-be-projected surface. It is FIG. (1) for demonstrating the focus adjustment which concerns on 1st Embodiment. FIG. 6 is a diagram (No. 2) for describing focus adjustment according to the first embodiment; FIG. 6 is a diagram (No. 3) for explaining the focus adjustment according to the first embodiment; It is FIG. (1) for demonstrating the focus adjustment which concerns on 2nd Embodiment. It is FIG. (2) for demonstrating the focus adjustment which concerns on 2nd Embodiment. It is FIG. (3) for demonstrating the focus adjustment which concerns on 2nd Embodiment. It is FIG. (1) for demonstrating the focus adjustment which concerns on 3rd Embodiment. It is FIG. (2) for demonstrating the focus adjustment which concerns on 3rd Embodiment. It is FIG. (3) for demonstrating the focus adjustment which concerns on 3rd Embodiment. It is a figure for demonstrating the focus adjustment which concerns on the modification of 1st Embodiment.

  Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted. In each embodiment, the major axis direction (lateral direction) of the screen is X, the minor axis direction (vertical direction) is Y, and the normal direction is Z.

<First Embodiment>
FIG. 1 is a schematic view illustrating an image projection apparatus according to the first embodiment. 1 generally illuminates the image forming element 17 with light emitted from the light source 11, and projects an enlarged image of the image forming element 17 onto the screen 90 by the projection optical system 18. It is. As the light source 11, a halogen lamp, a xenon lamp, a metal halide lamp, an ultrahigh pressure mercury lamp, an LED, or the like can be used. As the image forming element 17, for example, a DMD, a liquid crystal panel, or the like can be used.

  The image projection apparatus 10 will be described more specifically. The light emitted from the light source 11 is condensed at the entrance of the integrator rod 13 by the reflector 12. The integrator rod 13 is, for example, a light pipe formed by combining four mirrors into a tunnel shape. The light condensed at the entrance of the integrator rod 13 is repeatedly reflected by the mirror surface in the integrator rod 13, and the unevenness in the amount of light becomes uniform at the exit of the integrator rod 13. The exit of the integrator rod 13 is regarded as a surface light source that emits illumination light with uniform light amount unevenness, and a light source image of this surface light source is transmitted through, for example, the illumination lens 14, the first mirror 15, and the second mirror 16. And formed on the image forming element 17. Since the image forming element 17 is illuminated with a uniform illuminance distribution, the image projected on the screen 90, which is an enlarged image thereof, also has a uniform illuminance distribution.

  When the image forming element 17 is a DMD, it includes a large number of micromirrors, and the angle of the micromirrors can be changed, for example, from −12 ° to + 12 °. For example, when the angle of the minute mirror is −12 °, the reflected light of the illumination light from the minute mirror enters the projection optical system 18, and when the angle of the minute mirror is + 12 °, the reflected light of the illumination light enters the projection optical system 18. If the angle of the illumination light directed to the DMD is set so that the tilt angle of each micromirror of the DMD is controlled, a digital image can be formed on the screen 90.

  Note that a plurality of image forming elements 17 such as red, green, and blue are used, and the illumination light transmitted through the color filter is applied to each of the image forming elements 17 so that the light synthesized by the color synthesizing unit is incident on the projection optical system 18. Thus, a color image can be projected on the screen 90.

  FIG. 2 is an optical path diagram illustrating the projection optical system according to this embodiment. Referring to FIG. 2, the projection optical system 18 includes a coaxial optical system 19 composed of a lens group, and a concave mirror 20 that is a non-coaxial optical system that does not share an optical axis with the coaxial optical system 19. . The projection optical system 18 may have a plurality of concave mirrors. A indicates the optical axis of the coaxial optical system 19. In the projection optical system 18, the coaxial optical system 19 once forms the intermediate image 17 a of the image forming element 17, and the intermediate image 17 a is greatly bounced up by the concave mirror 20 and projected onto the screen 90. A specific configuration of the coaxial optical system 19 will be described later.

  The concave mirror 20 will be described in more detail. In order to project an image at a close distance to the screen 90, it is usually necessary to create an image above an image projection apparatus such as a projector for easy viewing of the screen. For example, as shown in FIG. As described above, the center of the image forming element 17 is decentered without being placed on the optical axis A of the coaxial optical system 19. The image quality is maintained by widening the performance guarantee range of the coaxial optical system 19 (that is, by using a wide-angle lens). However, since there is a limit to the wide-angle lens of the coaxial optical system 19, in order to project an image from the vicinity of the screen 90 using such a coaxial optical system 19, it is necessary to increase the optical path using a mirror. There is. Although the rear projection television system shown in FIG. 3 is used, it is difficult to attach a mirror to a portable image projection device used in a normal conference room. Mirrors are required, which is expensive and space consuming. Therefore, the method as shown in FIG. 3 is not preferable.

  As an example different from FIG. 3, there is a method of performing oblique projection using a concave mirror. The oblique projection is, for example, projecting at a short distance by arranging the image forming element 17 and the coaxial optical system 19 obliquely with respect to the screen 90 as shown in FIG. If this method is adopted, short-distance projection is possible, but there is a demerit that the screen is distorted in a trapezoidal shape. Therefore, the method shown in FIG. 4 is also not preferable.

  Therefore, in the present embodiment, in view of the problems of the methods of FIG. 3 and FIG. 4, the optical system is arranged as shown in FIG. This effectively corrects distortion. Here, the free-form surface mirror is, for example, a mirror whose curvature in the X direction changes along the Y axis, as shown in FIG. More specifically, when the horizontal direction of the screen 90 as the projection surface is the X direction and the vertical direction is the Y direction, the curvature of the concave mirror 20 in the X direction is closer to the optical axis A of the coaxial optical system 19. From the end of the concave mirror 20 toward the end of the concave mirror 20 farther from the optical axis A of the coaxial optical system 19 for each coordinate in the Y direction.

  In this embodiment, concave mirror 20 is fixed and does not move during focus adjustment. This is because if a large part that performs the most important function for distortion correction, such as the concave mirror 20, is moved, a positional error with respect to the coaxial optical system 19 increases, and distortion is deteriorated.

  The function of the projection optical system 18 is to form a real image of the image forming element 17 on the screen 90. The size of the image to be displayed on the screen 90 and the distance from the image projection apparatus 10 to the screen 90 vary depending on the person who uses it. In order to form a real image of the image forming element 17 on the screen 90, it is naturally necessary to focus. In the projection optical system of a normal projector (that is, a coaxial rotationally symmetric optical system), the entire projection optical system is moved to adjust the focus, or one of the lenses (or multiple lenses are a set). A focus adjustment method for moving a single lens group) is employed.

  In the case of the projection optical system 18 according to the present embodiment, the lens closest to the image forming element 17 (or a lens group in which a plurality of lenses are set) is fixed, and the other two or more lenses (or It is most desirable to adopt a focus adjustment method in which the lens group) is moved in the optical axis direction to focus. The reason is that the image distortion generated when the image is projected onto the screen 90 from a close distance is mainly corrected by the concave mirror 20 which is a non-coaxial optical system. This is because in the focus adjustment using the lens group, distortion correction is insufficient. Moreover, the brightness is not changed for each screen size when the lens group closest to the image forming element 17 is fixed.

  More specific description will be given below. In the case of oblique projection as shown in FIG. 4, the rectangular image forming element 17 has a trapezoidal shape in which the upper side is longer than the lower side on the screen 90 as in the image 90 a shown in FIG. 6. On the other hand, in the projection optical system 18 shown in FIG. 2, as shown in FIG. 7, the intermediate image 17a has a large distortion (the upper side of the screen 90 in FIG. 2, that is, the intermediate image 17a corresponding to the larger side in the Y direction). The lower side is a distortion that is longer than the upper side of the intermediate image 17a, so-called pincushion type distortion), and this is guided to the screen 90 by the concave mirror 20, so that the image 90a on the screen 90 is rectangular. Yes.

  However, as shown in FIG. 8, in order to display a screen smaller than the screen on the screen 90 of FIG. 2, the screen 90 is moved in the Z direction, and the entire extension by the coaxial optical system 19 (the coaxial optical system 19 is performed). Is moved in the Z direction), the distortion of the intermediate image 17a hardly changes. Therefore, as shown in FIG. 9, trapezoidal distortion occurs so that the upper side of the image 90 a on the screen 90 is shortened.

This phenomenon will be described in detail. 10 is a cross-sectional view of the concave mirror and screen of FIG. FIG. 11 is a cross-sectional view of the concave mirror and screen of FIG. 10 and 11, in the projection optical system 18 with a concave mirror 20, the angle of light A ₁ and the light A ₂ toward the Y direction downward toward the Y direction above the screen of the screen 90, XZ cross-section It is different. Therefore, when the screen 90 is moved to the position shown in FIG. 8, as shown in FIG. 11, the position in the X direction reaching the screen 90 is different on the screen and below the screen, so that the upper side is the same as the image 90a in FIG. A trapezoidal distortion is generated so as to be shortened.

  Therefore, in this embodiment, the coaxial optical system 19 of the projection optical system 18 is configured as shown in FIG. That is, the coaxial optical system 19 includes, in order from the image forming element 17 side, an aperture stop 19a, a lens group 19b, a lens group 19c, a lens group 19d, and a lens group 19e. In the present application, the term “lens group” includes a case where the lens is composed of one lens.

  In the coaxial optical system 19, the lens group 19b is a lens group having positive refractive power. The lens group 19c is a lens group having negative refractive power. The lens group 19d is a lens group having negative refractive power. The lens group 19e is a lens group having positive refractive power.

  The lens groups 19b and 19e are fixed, and the lens groups 19c and 19d are configured to reciprocate independently in the Z direction (direction of the optical axis A). That is, in the coaxial optical system 19, a plurality of lens groups (lens groups 19c and 19d) in the coaxial optical system 19 are moved by different amounts in the Z direction (the direction of the optical axis A) to perform focus adjustment. The focus method is adopted.

  The lens group 19c is a lens group that is disposed closest to the aperture stop 19a among the lens groups having negative refractive power that are configured to reciprocate. The lens group 19d is a lens group that is disposed closest to the concave mirror 20 among the lens groups having negative refractive power that are configured to reciprocate.

  The aperture stop 19a is more image-forming element 17 than the lens group 19d which is a lens group which has a negative refractive power and is arranged closest to the concave mirror 20 in a lens group having a negative refractive power which is configured to be reciprocally movable. Placed on the side. However, as shown in FIG. 12, it is preferable to dispose the aperture stop 19a near the image forming element 17 because a large pincushion distortion can be generated.

  In the state shown in FIG. 12, when the screen 90 is reduced by bringing the screen 90 closer to the concave mirror 20 as shown in FIG. 13 and the focus adjustment is performed, as shown in FIG. 14, the lens groups 19c and 19d are used. Is moved in the Z direction (direction of the optical axis A). More specifically, the lens group 19c is moved in the Z direction (the direction of the optical axis A) so as to move away from the aperture stop 19a, and the lens group 19d is moved in the Z direction (the direction of the optical axis A) so as to approach the aperture stop 19a.

  The lens group 19d has a particularly strong negative refractive power and generates a large pincushion type distortion. Since the amount of distortion of the intermediate image 17a can be reduced by moving the lens group 19d having a strong negative refractive power toward the side closer to the aperture stop 19a, a trapezoidal distortion like the image 90a shown in FIG. Can be suppressed. When the screen 90 is moved away from the concave mirror 20 to increase the screen size and focus adjustment is performed, contrary to FIG. 14, the lens group 19c is moved to the aperture stop 19a in the Z direction (optical axis). The lens group 19d may be moved in the Z direction (the direction of the optical axis A) so as to move away from the aperture stop 19a.

  As described above, the first embodiment employs a floating focus method in which a plurality of lens groups in the coaxial optical system 19 are moved by different amounts in the Z direction (the direction of the optical axis A) to adjust the focus. ing. When the screen 90 is made closer to the concave mirror 20 side to reduce the screen size and focus adjustment is performed, the lens group having a negative refractive power that is configured to be reciprocally movable is closest to the aperture stop 19a. The lens group 19c, which is a lens group having a negative refracting power, is moved in the Z direction (direction of the optical axis A) so as to be away from the aperture stop 19a, and the lens group having a negative refracting power configured to be able to reciprocate. Among them, a lens group 19d, which is a lens group having a negative refractive power and is disposed closest to the concave mirror 20, is moved in the Z direction (direction of the optical axis A) so as to approach the aperture stop 19a. As a result, the pincushion distortion of the intermediate image can be suppressed to be small, and the trapezoidal distortion of the image on the screen 90 can be suppressed.

  Also, when the screen size is increased by moving the screen 90 away from the concave mirror 20 and focus adjustment is performed, the lens group 19c is moved in the Z direction (the direction of the optical axis A) so that the lens group 19c approaches the aperture stop 19a. ) To move the lens group 19d in the Z direction (direction of the optical axis A) so as to move away from the aperture stop 19a. Thereby, it is possible to generate a pincushion type distortion of the intermediate image, and to suppress the trapezoidal distortion of the image on the screen.

  In order to greatly change the pincushion distortion, it is effective to move the lens group 19d in the Z direction (direction of the optical axis A) so as to approach the aperture stop 19a. Although a method of moving a lens group having positive refractive power in a direction far from the aperture stop 19a is also effective as distortion correction, if a lens having strong positive refractive power is arranged near the concave mirror 20, a large pincushion distortion is generated in the intermediate image. This is not preferable because it is difficult to generate the image or to increase the lateral magnification of the intermediate image.

  Further, the lens group 19d is largely moved to cause distortion (convergence), and the focus shift due to an excessive movement amount that has moved too much as the focus drive causes the lens group 19c with a small distortion generation amount to be opposite to the lens group 19d. It can be corrected by moving it. In other words, the lens group 19d can be moved greatly by arranging the lens group 19c with a small amount of distortion.

<Second Embodiment>
In the second embodiment, the coaxial optical system 29 of the projection optical system 18 is configured as shown in FIG. That is, the coaxial optical system 29 includes, in order from the image forming element 17 side, an aperture stop 29a, a lens group 29b, a lens group 29c, a lens group 29d, a lens group 29e, and a lens group 29f. In the second embodiment, the description of the same components as those of the already described embodiments is omitted.

  In the coaxial optical system 29, the lens group 29b is a lens group having positive refractive power. The lens group 29c is a lens group having negative refractive power. The lens group 29d is a lens group having a positive refractive power. The lens group 29e is a lens group having negative refractive power. The lens group 29f is a lens group having positive refractive power.

  The lens groups 29b and 29f are fixed, and the lens groups 29c, 29d, and 29e are configured to reciprocate independently in the Z direction (direction of the optical axis A). That is, in the coaxial optical system 29, the plurality of lens groups (lens groups 29c, 29d, and 29e) in the coaxial optical system 29 are moved by different amounts in the Z direction (the direction of the optical axis A) to adjust the focus. The floating focus method is used.

  The lens group 29c is a lens group that is disposed closest to the aperture stop 29a among the lens groups having negative refractive power that are configured to reciprocate. The lens group 29d is a lens group disposed closest to the aperture stop 29a among the lens groups having positive refractive power configured to be reciprocally movable. The lens group 29e is a lens group that is disposed closest to the concave mirror 20 among the lens groups having negative refractive power that are configured to reciprocate.

  The aperture stop 29a is more image-forming element 17 than the lens group 29e which is a lens group which has a negative refractive power and is disposed closest to the concave mirror 20 in a lens group which has a negative refractive power and is configured to be reciprocally movable. Placed on the side. However, as shown in FIG. 15, it is preferable to dispose the aperture stop 29a at a position close to the image forming element 17 because a large pincushion distortion can be generated.

  When the screen size is reduced by moving the screen 90 closer to the concave mirror 20 as shown in FIG. 16 and the focus is adjusted as shown in FIG. 16, the lens groups 29c and 29d are used as shown in FIG. , And 29e are moved in the Z direction (direction of the optical axis A). More specifically, the lens group 29c is moved in the Z direction (direction of the optical axis A) away from the aperture stop 29a, and the lens group 29d is moved in the Z direction (direction of optical axis A) so as to approach the aperture stop 29a. The lens group 29e is moved in the Z direction (direction of the optical axis A) so as to approach the aperture stop 29a.

  The lens group 29e has a particularly strong negative refractive power and generates a large pincushion type distortion. Since the distortion amount of the intermediate image 17a can be reduced by moving the lens group 29e having strong negative refracting power to the side closer to the aperture stop 29a, the trapezoidal distortion like the image 90a shown in FIG. Can be suppressed. When the screen 90 is enlarged by moving the screen 90 away from the concave mirror 20 and the focus adjustment is performed, contrary to FIG. 17, the lens group 29c is moved closer to the aperture stop 29a in the Z direction (optical axis). A direction), the lens group 29d is moved in the Z direction (in the direction of the optical axis A) away from the aperture stop 29a, and the lens group 29e is moved in the Z direction (in the direction of optical axis A) away from the aperture stop 29a. Move it to

  As described above, the second embodiment employs a floating focus method in which a plurality of lens groups in the coaxial optical system 29 move by different amounts in the Z direction (the direction of the optical axis A) to perform focus adjustment. ing. When the screen 90 is made closer to the concave mirror 20 side to reduce the screen size and focus adjustment is performed, the lens group having negative refractive power that is configured to be reciprocally movable is closest to the aperture stop 29a. The lens group 29c, which is a lens group having a negative refracting power, is moved in the Z direction (direction of the optical axis A) so as to be away from the aperture stop 29a. Among them, a lens group 29d, which is a lens group having a positive refracting power and is disposed closest to the aperture stop 29a, is moved in the Z direction (direction of the optical axis A) so as to approach the aperture stop 29a, and is configured to be able to reciprocate. Among the lens groups having negative refractive power, the lens group 29e, which is a lens group having negative refractive power and is disposed closest to the concave mirror 20, is moved in the Z direction so as to approach the aperture stop 29a. Move (in the direction of the optical axis A). This makes it possible to suppress the pincushion distortion of the intermediate image and to suppress the trapezoidal distortion of the image on the screen.

  Also, when the screen size is increased by moving the screen 90 away from the concave mirror 20 and the focus adjustment is performed, the lens group 29c is moved in the Z direction (direction of the optical axis A) so as to approach the aperture stop 29a. ), The lens group 29d is moved in the Z direction (direction of the optical axis A) away from the aperture stop 29a, and the lens group 29e is moved in the Z direction (direction of optical axis A) away from the aperture stop 29a. Thereby, it is possible to generate a pincushion type distortion of the intermediate image, and to suppress the trapezoidal distortion of the image on the screen.

  Further, the lens group 29e is largely moved to cause distortion (convergence), and the focus shift due to an excessive movement amount that has moved excessively as the focus drive causes the lens group 29c having a small distortion generation amount to be opposite to the lens group 29e. The correction is performed by moving the lens group 29d with less distortion generation in the same direction as the lens group 29e. In other words, the lens group 29e can be moved greatly by arranging the lens groups 29c and 29d with a small amount of distortion.

  In addition, when the negative refractive power of the lens group 29e is increased or the movement amount of the lens group 29e is increased to generate a very large distortion change, a large focus correction by other lens groups is required. At this time, the lens group 29c having a weak negative refracting power and the lens group 29d having a weak positive refracting power are moved in opposite directions, respectively, so that focus adjustment can be performed without generating extra distortion.

<Third Embodiment>
In the third embodiment, the coaxial optical system 39 of the projection optical system 18 is configured as shown in FIG. That is, the coaxial optical system 39 includes an aperture stop 39a, a lens group 39b, a lens group 39c, and a lens group 39d in order from the image forming element 17 side. In the third embodiment, the description of the same components as those of the already described embodiments is omitted.

  In the coaxial optical system 39, the lens group 39b is a lens group having positive refractive power. The lens group 39c is a lens group having positive refractive power. The lens group 39d is a lens group having negative refractive power.

  The lens group 39b is fixed, and the lens groups 39c and 39d are configured to reciprocate independently in the Z direction (direction of the optical axis A). That is, in the coaxial optical system 39, a plurality of lens groups (lens groups 39c and 39d) in the coaxial optical system 39 move by different amounts in the Z direction (the direction of the optical axis A) to perform focus adjustment. The focus method is adopted.

  The lens group 39c is a lens group disposed closest to the aperture stop 39a among the lens groups having positive refractive power configured to be reciprocally movable. The lens group 39d is a lens group disposed closest to the concave mirror 20 among the lens groups having negative refractive power configured to be reciprocally movable.

  The aperture stop 39a is more image-forming element 17 than the lens group 39d which is a lens group which has a negative refractive power and is arranged closest to the concave mirror 20 in a lens group having a negative refractive power which is configured to be able to reciprocate. Placed on the side. However, as shown in FIG. 18, it is preferable to dispose the aperture stop 39a near the image forming element 17 because a large pincushion distortion can be generated.

  From the state of FIG. 18, when the screen 90 is made smaller by bringing the screen 90 closer to the concave mirror 20 side as shown in FIG. 19 and the focus adjustment is performed, as shown in FIG. 20, lens groups 39c and 39d are used. Is moved in the Z direction (direction of the optical axis A) so as to approach the aperture stop 39a.

  The lens group 39d has a particularly strong negative refractive power and generates a large pincushion type distortion. By moving this lens group having a strong negative refractive power to the side closer to the aperture stop 39a, the amount of distortion of the intermediate image 17a can be reduced, so that a trapezoidal distortion like the image 90a shown in FIG. Can be suppressed. When the screen 90 is enlarged by moving the screen 90 away from the concave mirror 20 and the focus adjustment is performed, contrary to FIG. 20, the lens groups 39c and 39d are moved away from the aperture stop 39a in the Z direction ( It may be moved in the direction of the optical axis A).

  As described above, the third embodiment employs a floating focus method in which a plurality of lens groups in the coaxial optical system 39 are moved by different amounts in the Z direction (direction of the optical axis A) to perform focus adjustment. ing. When the screen 90 is made closer to the concave mirror 20 side to reduce the screen size and focus adjustment is performed, the lens group having positive refracting power and configured to be reciprocally movable is closest to the aperture stop 39a. The lens group 39c, which is a lens group having a positive refractive power, and a negative refractive power arranged closest to the concave mirror 20 in the lens group having a negative refractive power configured to be reciprocally movable. The lens group 39d, which is a lens group, is moved in the Z direction (the direction of the optical axis A) so as to be close to the aperture stop 39a (however, the movement amount may not be the same). This makes it possible to suppress the pincushion distortion of the intermediate image and to suppress the trapezoidal distortion of the image on the screen.

  In addition, when the screen 90 is enlarged by moving the screen 90 away from the concave mirror 20 and the focus adjustment is performed, the lens groups 39c and 39d are moved in the Z direction so that both the lens groups 39c and 39d are moved away from the aperture stop 39a. (In the direction of the optical axis A) (however, the movement amount may not be the same). This makes it possible to suppress the pincushion distortion of the intermediate image and to suppress the trapezoidal distortion of the image on the screen.

  Further, the lens group 39d is largely moved to cause distortion (convergence), and the focus shift due to the excessive movement amount that has moved excessively as the focus drive causes the lens group 39c with a small distortion generation amount to be in the same direction as the lens group 39d. It can be corrected by moving it. In other words, the lens group 39d can be moved greatly by arranging the lens group 39c with a small amount of distortion.

  In addition, when the negative refracting power of the lens group 39d is increased or the movement amount of the lens group 39d is increased to generate a very large distortion change, a large focus correction by another lens group is required. At this time, the lens group 39c having a weak positive refractive power is moved in the same direction as the lens group 39d, so that focus adjustment can be performed without generating extra distortion.

<Fourth embodiment>
In the fourth embodiment, as shown in FIG. 21, a lens group 19d of the first embodiment, a glass lens 19d ₁ having a strong negative refractive power, a plastic lens 19d ₂ having a weak positive refractive power Are arranged adjacent to each other. Note that in the fourth embodiment, descriptions of the same components as those of the already described embodiments are omitted.

  A lens having a strong negative refracting power for generating a large distortion has a high sensitivity to a shape error and an assembly error, and if there is an error, the resolution is easily deteriorated and a focus shift is easily caused for each screen position. In particular, the interior of an image projection apparatus such as a projector is high in temperature, and even with a component having a small linear expansion coefficient such as glass, resolution degradation and focus change due to temperature change cannot be ignored.

  Therefore, a lens having a positive refractive power that cancels resolution deterioration (deterioration of aberration) and a focus change that occurs in a glass lens having strong negative refractive power is required.

  Further, in an image projection apparatus such as a projector, a temperature distribution is generated in the optical axis direction within a lens barrel that holds a lens (naturally, the image forming element 17 side is hot). Therefore, it is desirable that the lens having positive refractive power is placed in the vicinity of the lens having negative refractive power.

  Of course, if you place a glass lens with positive refractive power that has the same absolute value of refractive power as a glass lens with negative refractive power, you can cancel aberration changes and focus changes due to temperature changes of lenses with negative refractive power. However, when a lens having a strong positive refracting power and a lens having a negative refracting power are arranged side by side, the amount of refraction at each lens is large, and the assembly error sensitivity of the lens having the positive refracting power and the lens having the negative refracting power is high. High and undesirable.

Therefore, a glass lens 19d ₁ having a strong negative refractive power, positioned adjacent the plastic lens 19d ₂ having a weak positive refractive power. This makes it possible to reduce the assembly error sensitivity, and the linear expansion coefficient of plastic is about 10 times larger than that of glass. Therefore, aberrations and focus changes caused by temperature changes of the glass lens 19d ₁ having strong negative refractive power. the can be canceled by the plastic lens 19d _2.

As described above, the fourth embodiment has the same effects as those of the first embodiment, but further has the following effects. That is, a glass lens 19d ₁ having a strong negative refractive power, a weak by arranging adjacent the plastic lens 19d ₂ having a positive refractive power, it is possible to reduce the assembly error sensitivity, and strong negative refractive The plastic lens 19d ₂ can cancel out aberrations and focus changes caused by temperature changes in the glass lens 19d ₁ having power.

  The preferred embodiment has been described in detail above. However, the present invention is not limited to the above-described embodiment, and various modifications and replacements are made to the above-described embodiment without departing from the scope described in the claims. Can be added.

DESCRIPTION OF SYMBOLS 10 Image projector 11 Light source 12 Reflector 13 Integrator rod 14 Illumination lens 15 1st mirror 16 2nd mirror 17 Image formation element 17a Intermediate image 18 Projection optical system 19, 29, 39 Coaxial optical system 20 Concave mirror A Optical axis A ₁ , A ₂ light 90 Screen 90a Image 19a, 29a, 39a Aperture stop 19b, 19c, 19d, 19e, 29b, 29c, 29d, 29e, 29f, 39b, 39c, 39d Lens group 19d ₁ Glass lens 19d ₂ Plastic lens

JP 2009-251457 A JP 2009-229738 A

Claims (8)

A projection optical system for enlarging and projecting an image formed on an image forming element onto a projection surface,
On the optical path from the image forming element to the projection surface, a coaxial optical system in which a plurality of lens groups share an optical axis and a concave mirror are arranged in this order,
The coaxial optical system includes an aperture stop;
The plurality of lens groups includes a plurality of focus groups that move independently in the optical axis direction when adjusting the focus,
The concave mirror is fixed when adjusting the focus;
When one of the plurality of focus groups has a negative refractive power, and the focus group closest to the concave mirror among the focus groups having a negative refractive power is a first focus group,
The aperture stop is disposed closer to the image forming element than the first focus group;
Other focus groups, positive when having a refractive power is moved in the same direction of the optical axis direction as the first focusing unit with respect to the aperture stop, in the case of negative refractive power the aperture stop On the other hand , the projection optical system moves in the direction opposite to the optical axis direction with respect to the first focus group.   2. The projection optical system according to claim 1, wherein the first focus group is a lens group having the strongest negative refractive power among the lens groups having negative refractive power in the coaxial optical system.   The projection optical system according to claim 1, wherein the aperture stop is disposed closest to the image forming element of the coaxial optical system.   4. The projection optical system according to claim 1, wherein when adjusting a focus, the first focus group moves in a direction approaching the aperture stop. 5.   The concave mirror is a free-form surface mirror, and when the horizontal direction of the projection surface is the X direction and the vertical direction of the projection surface is the Y direction, the curvature of the concave mirror in the X direction is the coaxial The Y-direction coordinate increases from the end of the concave mirror closer to the optical axis of the optical system toward the end of the concave mirror farther from the optical axis of the coaxial optical system. The projection optical system according to any one of claims 1 to 4.   6. The projection optical system according to claim 1, wherein an optical axis of the coaxial optical system and a center of the image forming element are decentered in a vertical direction of the projection surface. Among the lens groups having negative refractive power, the lens group having the strongest negative refractive power is composed of a glass lens,
7. The projection optical system according to claim 1, wherein the plurality of lens groups include a plastic lens having a positive refractive power whose absolute value is smaller than the strongest negative refractive power.   The projection optical according to any one of claims 1 to 7, wherein the image forming element that forms an image according to a modulation signal is irradiated with illumination light from a light source, and the image formed on the image forming element is used. An image projection apparatus that performs enlarged projection on the projection surface by a system.

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