Projection optical system and projection type video display device

Abstract

To provide a projection optical system and a projection type video display device capable of inhibiting reduction in image quality caused by reflection of a lens surface.SOLUTION: The projection optical system according to the disclosure comprises a plurality of lenses, and projects, in a front direction, projection light emitted from a video display element along an optical axis, and displays an image formed on a display surface of the video display element onto a projection object. Light passing in a rearward direction through the projection optical system is generated by the projection light reflected on lens surfaces of the plurality of lenses. When beam tracking with paraxial beam tracking is performed on a marginal beam of on-axis luminous flux passing through the projection optical system, X denotes a distance between a condensing surface on which a first beam obtained by a marginal beam propagating in a rearward direction reflected on the display surface is reflected and condensed on each lens surface and the display surface, and f denotes a focal distance of the entire system of the projection optical system. The following condition (1) is satisfied for all lens surfaces of the projection optical system. |X|>f / 2...(1).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a projection optical system that projects and displays an image, and a projection-type image display device that includes the projection optical system. [Background technology]

[0002] Conventionally, a projection type image display device projects an image onto a projection target such as a screen or a building. In addition, the image projected onto the projection target may be photographed in order to check the positional relationship (distortion) between the projection target and the projected image. In the projection optical system of a projection type image display device, a degradation in image quality may occur due to reflection on the lens surface.

[0003] Patent Document 1 discloses an imaging optical system in which a filter is disposed in a telecentric system, and in which there is little flare that occurs when light is reflected on an imaging surface by the filter. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 1991-078716 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide a projection optical system and a projection-type image display device that can suppress degradation of image quality caused by reflection on lens surfaces. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, an image adjustment method according to an embodiment of the present disclosure provides a projection optical system that includes a plurality of lenses, projects projection light emitted from an image display element along an optical axis in a forward direction, and displays an image formed on a display surface of the image display element on a projection target, in which the projection light is reflected by lens surfaces of the plurality of lenses, thereby generating light that passes through the projection optical system in a backward direction, and in ray tracing by paraxial ray tracing for marginal rays of an on-axis light beam that passes through the projection optical system, when the distance between the focusing surface where the marginal rays propagating backward are reflected by the display surface and a first ray is reflected by each lens surface and focused is X, and the focal length of the entire projection optical system is f, the following condition (1) is satisfied at all lens surfaces in the projection optical system: |X|>f / 2 (1). Effect of the Invention

[0007] According to the present disclosure, it is possible to provide a projection optical system and a projection-type image display device that can suppress degradation of image quality caused by reflection on lens surfaces. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram showing a projection-type image display device according to a first embodiment of the present disclosure. [Diagram 2] A conceptual diagram showing an example of a propagation optical system of the projection type image display device of FIG. 1. [Diagram 3] FIG. 2 is a conceptual diagram showing another example of a propagation optical system of the projection type image display device of FIG. 1. [Figure 4] FIG. 1 is a diagram for explaining whether condition (1) is satisfied in the projection optical system according to the first embodiment of the present disclosure. [Diagram 5] FIG. 1 is a diagram for explaining whether condition (2) is satisfied in the projection optical system according to the first embodiment of the present disclosure. [Figure 6] FIG. 1 is a diagram for explaining whether condition (3) is satisfied in the projection optical system according to the first embodiment of the present disclosure. [Figure 7] Lens arrangement diagram of the projection optical system according to the first embodiment [Figure 8] 1 is a diagram showing various aberrations of the projection optical system according to Example 1. [Figure 9] Lens arrangement diagram of a projection optical system according to Example 2 [Figure 10] 11A and 11B are aberration diagrams showing various aberrations of the projection optical system according to the second embodiment. [Figure 11] Lens arrangement diagram of a projection optical system according to Comparative Example 1 [Figure 12] 1 is a diagram showing various aberrations of a projection optical system according to Comparative Example 1. [Figure 13A] FIG. 1 is a diagram showing whether condition (1) is satisfied in the projection optical system of the first embodiment. [Figure 13B] FIG. 13 is a diagram showing whether condition (2) is satisfied in the projection optical system of the first embodiment. [Figure 13C] FIG. 13 is a diagram showing whether condition (3) is satisfied in the projection optical system of the first embodiment. [Figure 14A] FIG. 13 is a diagram showing whether condition (1) is satisfied in the projection optical system according to the second embodiment. [Figure 14B] FIG. 13 is a diagram showing whether condition (2) is satisfied in the projection optical system according to the second embodiment. [Figure 14C] FIG. 13 is a diagram showing whether condition (3) is satisfied in the projection optical system according to the second embodiment. [Figure 15A] FIG. 13 is a diagram showing whether the projection optical system of Comparative Example 1 satisfies condition (1). [Figure 15B] FIG. 13 is a diagram showing whether the projection optical system of Comparative Example 1 satisfies the condition (2). [Figure 15C] FIG. 13 is a diagram showing whether the projection optical system of Comparative Example 1 satisfies the condition (3). [Figure 16] FIG. 1 is a diagram showing light propagation in a propagation optical system using the projection optical system of the first embodiment. [Figure 17] FIG. 17 is a diagram showing an image formed in the propagation optical system of FIG. 16. [Figure 18] FIG. 1 is a diagram showing light propagation in a propagation optical system using a projection optical system of Comparative Example 1. [Figure 19] FIG. 19 is a diagram showing an image formed in the propagation optical system of FIG. 18. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] According to a first aspect of the present disclosure, there is provided a projection optical system that includes a plurality of lenses, projects projection light emitted from an image display element along an optical axis in a forward direction, and displays an image formed on a display surface of the image display element on a projection target, in which the projection light is reflected by lens surfaces of the plurality of lenses, resulting in light passing through the projection optical system in a backward direction. In this projection optical system, when a marginal ray of an on-axis light beam passing through the projection optical system is traced by paraxial ray tracing, the distance between the collection surface where the marginal ray propagating backward is reflected by each lens surface and collected is X, and the focal length of the entire projection optical system is f, the following condition (1) is satisfied at all lens surfaces in the projection optical system: |X|>f / 2...(1).

[0010] According to a second aspect of the present disclosure, there is provided a projection optical system which includes a plurality of lenses, projects projection light emitted from an image display element in a forward direction along an optical axis, and displays an image formed on a display surface of the image display element on a projection target, in which the projection light is reflected by the lens surfaces of the plurality of lenses, resulting in light passing through the projection optical system in a backward direction, and in ray tracing by paraxial ray tracing for a marginal ray of an on-axis light beam passing through the projection optical system, when the ray height on the display surface of the marginal ray propagating backward is the first ray reflected by each lens surface and the length of half the diagonal length of the display surface is D, the projection optical system satisfies the following condition (2) for all lens surfaces in the projection optical system: |(H*f / 2F)|>D····(2), where f is the focal length of the entire projection optical system, and F is the F-number of the entire projection optical system.

[0011] According to a third aspect of the present disclosure, there is provided a projection optical system which includes a plurality of lenses, projects projection light emitted from an image display element in a forward direction along an optical axis, and displays an image formed on a display surface of the image display element on a projection target, in which the projection light is reflected off the lens surfaces of the plurality of lenses, resulting in light passing through the projection optical system in a backward direction, and in ray tracing by actual ray tracing, for a marginal ray of an on-axis light beam passing through the projection optical system, when a marginal ray propagating forward from the display surface is incident on each lens surface, the angle between the normal to the incident lens surface is θ (deg) and the ray height at the incident lens surface is h (mm), the projection optical system satisfies the following condition (3) at all lens surfaces in the projection optical system: 1 / (|θ|*h)<0.04····(3).

[0012] According to a fourth aspect of the present disclosure, in a projection optical system including a plurality of lenses, which projects projection light emitted from an image display element in a forward direction along an optical axis and displays an image formed on a display surface of the image display element on a projection target, the projection light is reflected by lens surfaces of the plurality of lenses, thereby generating light passing through the projection optical system in a backward direction, and in ray tracing of a marginal ray of an on-axis light flux passing through the projection optical system, at least any one of the following conditions (1) to (3) is satisfied for all lens surfaces in the projection optical system: |X|>f / 2 (1) |(H*f / 2F)|>D····(2) 1 / (|θ|*h)<0.04 (3) Where: X is the distance between the display surface and the focusing surface where the first ray, which is a marginal ray propagating backward and reflected by the display surface, is reflected by each lens surface and focused in the ray tracing by paraxial ray tracing, f is the focal length of the entire projection optical system, H is the height of the first ray reflected by each lens surface on the display surface in the paraxial ray tracing, F is the F-number of the entire projection optical system, D is half the diagonal length of the display surface, θ (deg) is the angle between the normal of the lens surface on which a marginal ray propagating forward from the display surface is incident when the marginal ray is incident on each lens surface in ray tracing by real ray tracing, h (mm) is the height of a marginal ray propagating forward from the display surface when it is incident on each lens surface in ray tracing by actual ray tracing, providing a projection optical system.

[0013] According to any one of the above aspects, it is possible to suppress degradation of image quality due to reflection on the lens surface.

[0014] According to a fifth aspect of the present disclosure, there is provided the projection optical system according to any one of the first to fourth aspects, in which the ray tracing is performed using light wavelengths contained in the projection light.

[0015] According to a sixth aspect of the present disclosure, there is provided a projection optical system as described in any one of the first to fourth aspects, in which external light propagating backward from a projection target along an optical axis passes through the projection optical system, and light of a predetermined wavelength range among the external light forms an image, and ray tracing is performed using light wavelengths included in the predetermined wavelength range.

[0016] According to a seventh aspect of the present disclosure, there is provided a projection type image display device that projects and displays an image on a projection target, comprising a light source device, a projection light generation unit that includes one or more image display elements and generates projection light modulated in response to a video signal, a light guiding optical system that guides illumination light emitted from the light source device to the projection light generation unit, and the projection optical system described in any one of the first to fourth aspects, and that performs ray tracing using the light wavelengths contained in the projection light.

[0017] According to a seventh aspect of the present disclosure, there is provided a projection type image display device that projects and displays an image on a projection object, comprising: a light source device; a projection light generation unit that includes one or more image display elements and generates projection light modulated according to a video signal; a light guiding optical system that guides illumination light emitted from the light source device to the projection light generation unit; a projection optical system described in any one of the first to fourth aspects; and an imaging optical system that allows external light propagating backward from the projection object along the optical axis to pass through the projection optical system and images light of a predetermined wavelength range from the external light, and performs ray tracing using light wavelengths included in the predetermined wavelength range.

[0018] Any of the above-described various embodiments may be appropriately combined to achieve the effects of each of the embodiments.

[0019] Hereinafter, the embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of already well-known matters or duplicate explanation of substantially the same configuration may be omitted. This is to avoid the following explanation becoming unnecessarily redundant and to facilitate understanding by those skilled in the art.

[0020] An image adjustment method and a projection-type image display device according to an embodiment of the present disclosure will be described with reference to Figures 1 to 19. The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims. In addition, in each drawing, each element is exaggerated for ease of explanation. Note that the same reference numerals are used for substantially the same components in the drawings.

[0021] <Embodiment 1> (Overall configuration of a projection type image display device) The configuration of a projection-type image display device according to the first embodiment will be described with reference to Fig. 1. Fig. 1 is a block diagram showing a projection-type image display device 10 according to the first embodiment of the present disclosure.

[0022] As shown in FIG. 1, the projection-type image display device 10 may include a light source device 30, a light guide optical system 40, a projection light generating unit 50, and a projection optical system 60. In some embodiments, the projection-type image display device 10 may further include an imaging optical system 70. The projection-type image display device 10 generates projection light Lp in the projection light generating unit 50 according to an input video signal based on light emitted from the light source device 30, and projects the projection light Lp generated by the projection optical system 60 forward to display an image on a projection target 100 such as a screen. In some embodiments, the external light Lo reflected by the projection target 100 can be taken in the projection optical system 60 backward and guided to the imaging device 70 via the projection optical system 60 to capture an image.

[0023] The light source device 30 includes a light source and an illumination optical system including various color synthesis configurations. The light source can be configured with, for example, a high-pressure mercury lamp, a xenon lamp, an LED, a semiconductor laser, etc., and the illumination optical system can include, for example, a wavelength conversion element, a light tunnel, a relay optical system, etc. Light from the light source is propagated by the illumination optical system, and illumination light Ls is emitted from the light source device 30.

[0024] The light-guiding optical system 40 guides the illumination light Ls emitted from the light source device 30 to the projection light generation unit 50. The light-guiding optical system 40 is configured by appropriately arranging various optical members such as various lenses, mirrors, rods, etc. The illumination light Ls is guided to the projection light generation unit 50 and irradiated onto the image display element 55 with a uniform illuminance distribution.

[0025] The image display element 55 can be configured, for example, by a DMD (digital mirror device). The image display element 55 has, for example, a display surface including a mirror element for each pixel, and forms an image Ms on the display surface based on an external video signal by the incident illumination light Ls. The image display element 55 also modulates the illumination light Ls in response to the video signal, generates projection light Lp, and emits it to the projection optical system 60.

[0026] The projection-type image display device 10 may be a 1-chip DLP projector having one image display element 55, or a 3-chip DLP projector having a plurality of image display elements 55. The image display element 55 is not limited to a DMD, and may be, for example, a liquid crystal element. In this case, the projection-type image display device 10 may be configured using a 3LCD system or an LCOS system.

[0027] The projection optical system 60 includes a plurality of lenses (not shown in FIG. 1, see FIGS. 2 and 3 described later), and propagates the projection light Lp from the projection light generating unit 50 forward (to the left in the figure) to project it onto the projection object 100, thereby displaying an image Mp. The configuration of the projection optical system 60 will be described in more detail later.

[0028] In this embodiment, external light Lo that is reflected by the projection object 100 and propagates backward (to the right in the figure) can be taken into the projection optical system 60. The incident external light Lo passes through the projection optical system 60 and is introduced into the imaging optical system 70. The imaging optical system 70 includes an imaging element 75, and images the external light Lo that has entered via the projection optical system 60 onto the imaging surface of the imaging element 75 as an image Mc.

[0029] Furthermore, the projection type image display device 10 may further include a control device (not shown) that controls the overall operation of the device. The control device may include, for example, a video input terminal that inputs a video signal from the outside, and various drivers. The control device is configured to control, for example, the operation of the light source device 30, the supply of the video signal to the image display element 55, and the driving of the image display element 55. A detailed description of the control device will be omitted in this specification.

[0030] In this manner, various optical elements are disposed between the image display element 55 and the projection object 100, and propagate the projection light Lp, or the projection light Lp and the external light Lo. In this specification, an optical system including various optical elements disposed between the image display element 55 and the projection object 100 and propagating the projection light Lp, or the projection light Lp and the external light Lo, is referred to as a "propagation optical system." For example, the propagation optical system 20 of the projection type image display device 10 shown in FIG. 1 includes a projection optical system 60 and an imaging optical system 70. Hereinafter, the configuration of the propagation optical system according to the projection type image display device 10 of the present disclosure will be described with reference to FIGS. 2 and 3.

[0031] (Configuration of the propagation optical system) Fig. 2 is a conceptual diagram showing an example of the propagation optical system 20a of the projection type image display device 10 of Fig. 1, and Fig. 3 is a conceptual diagram showing another example of the propagation optical system 20b of the projection type image display device 10 of Fig. 1. The propagation optical system 20a of Fig. 2 can project the projection light Lp from the image display element 55 onto the projection object 100, and display an image on the projection surface 100a. The propagation optical system 20b of Fig. 3 can project the projection light Lp from the image display element 55 onto the projection object 100, and can also guide the external light Lo from the projection object 100 to the imaging optical system 70 via the projection optical system 60b, and form an image on the imaging surface 75a of the imaging element 75.

[0032] As shown in FIG. 2, the propagation optical system 20a is composed of a projection optical system 60a, and the projection light Lp is emitted by an image display element 55 provided in the projection light generation unit 50, propagates along a projection optical axis Oa, and enters the projection optical system 60a.

[0033] The projection optical system 60a of the propagation optical system 20a may include, for example, a back glass member 61a and a lens unit 65. In this embodiment, the back glass member 61a may include, for example, a prism element 62a including a TIR (total internal reflection) prism, a color separation prism, a color synthesis prism, etc., and an optical element 63a including various optical filters, a cover glass, etc. The lens unit 65 may include a plurality of lens elements La, Lb, Lc and an aperture A (not shown in FIG. 2). The number of the lens elements La, Lb, Lc is not limited to this, but may be, for example, 15 or more. This allows various aberrations in the projection optical system 60a to be well corrected. The aperture A is, for example, an aperture stop. The projection optical system 60a may be, for example, modularized and mounted on the projection type image display device 10. The projection light Lp incident on the projection optical system 60a passes through the back glass member 61a and the lens unit 65 in this order, and is then enlarged and projected onto the projection surface 100a of the projection subject 100. In the propagation optical system 20a, the display surface 55a of the image display element and the projection surface 100a of the projection subject are in a conjugate relationship.

[0034] When the projection light Lp passes through the lens unit 65, it is reflected by the lens surfaces of the lens elements La, Lb, and Lc, generating reflected light propagating backward (to the right in the figure). Such lens surface reflected light Ga1 may pass backward through the projection optical system 60a and reach the image display element 55. The lens surface reflected light Gb1 may be reflected again by a display surface including a mirror element in the image display element 55 or a polarizing plate in the optical element 63a, generating re-reflected light Ga2 propagating forward (to the left in the figure), and the re-reflected light Ga2 may be projected by the projection optical system 60a onto the projection object 100 to form an image different from that of the projection light Lp. This may result in a decrease in the contrast of the image by the projection light Lp displayed on the projection object 100, resulting in a decrease in image quality.

[0035] The propagation optical system 20b shown in Fig. 3 is composed of a projection optical system 60b and an imaging optical system 70. It differs from the propagation optical system 20a in Fig. 2 in that it includes the imaging optical system 70. In the propagation optical system 20b in Fig. 3, elements similar to those of the propagation optical system 20a in Fig. 2 are denoted by the same reference numerals, and description thereof will be omitted.

[0036] In the propagation optical system 20b, the projection light Lp is emitted by the image display element 55 included in the projection light generation unit 50, enters the projection optical system 60b in a forward direction (toward the left in the figure), and is enlarged and projected onto the projection surface 100a of the projection object 100. In addition, external light Lo from the projection object 100 passes through the projection optical system 60b in a backward direction (toward the right in the figure), and is then introduced into the imaging optical system 70 and forms an image on the imaging surface 75a of the imaging element 75.

[0037] The projection optical system 60b of the propagation optical system 20b is configured by, for example, a back glass member 61b and a lens unit 65. The back glass member 61b can include prism elements such as a separation prism 62b, and optical elements 63b including various optical filters, cover glass, etc. The lens unit 65 includes a plurality of lens elements La, Lb, and Lc, and an aperture A (not shown in FIG. 2). Although not shown, the back glass member 61b can include prism elements such as a TIR (total internal reflection) prism, a color separation prism, and a color synthesis prism in addition to the separation prism 62b.

[0038] The imaging optical system 70 may include, for example, a prism spacer 71 and an imaging element 75. The prism spacer 71 is an element for back focus alignment of the imaging element 75. External light Lo incident on the prism spacer 71 passes through the prism spacer 71 and is incident on the imaging element 75. The imaging element 75 may be composed of, for example, a solid-state imaging element such as a CCD image sensor or a CMOS image sensor, and converts the incident external light Lo into an electrical image signal and forms an image on an imaging surface 75a. In the propagation optical system 20b, the display surface 55a of the image display element, the projection surface 100a of the projection target, and the imaging surface 75a of the imaging element are in a conjugate relationship.

[0039] As in the above-described propagation optical system 20a, in the propagation optical system 20b, when the projection light Lp passes through the lens unit 65, it is reflected on the lens surfaces of the multiple lens elements La, Lb, and Lc, generating reflected light that propagates backward. Such lens surface reflected light Gb1 is reflected again by the separation prism 62b, generating re-reflected light Gb2 that propagates along the illustrated optical axis Ob, and the re-reflected light Gb2 enters the imaging optical system 70, allowing an image formed on the imaging surface of the imaging element 75 to be formed separately from the external light Lo. This reduces the contrast of the image due to the external light Lo displayed on the imaging surface of the imaging element 75, causing a deterioration in the image quality.

[0040] In this specification, the side of the projection subject 100 is the enlarged side of the entire projection optical systems 60a, 60b, and the projection surface 100a of the projection subject 100 is sometimes referred to as the "object surface" and the side of the projection subject 100 is sometimes referred to as the "object surface side". The side of the image display element 55 is the reduced side of the entire projection optical systems 60a, 60b, and the display surface 55a of the image display element 55 is sometimes referred to as the "image surface" and the side of the image display element 55 is sometimes referred to as the "image surface side".

[0041] Note that the configurations of the propagation optical systems 20a, 20b shown in Figs. 2 and 3 are conceptual configuration examples for explaining the propagation of the projection light Lp and the external light Lo, and the present disclosure is not limited thereto. The propagation optical system of the projection type image display device according to the present disclosure may further include other optical components. In addition, although the propagation optical systems 20a, 20b are exemplarily shown to include one image display element 55, the present disclosure is not limited thereto. The propagation optical system of the projection type image display device according to the present disclosure may have a configuration including a plurality of image display elements.

[0042] As described with reference to FIG. 2 and FIG. 3, when the projection light Lp passes through the projection optical system 60a, 60b, it is reflected by the lens surfaces of the lens elements La, Lb, and Lc included in the lens unit 65, and thus reflected light Ga1, Gb1 passing backward through the projection optical system 60a, 60b is generated. The reflected light Ga1, Gb1 may be reflected again in the projection optical system and form an image on the projection target 100 or the image sensor 75 that is different from the projection light Lp or the external light Lo. In this specification, the reflected light generated by the reflection of the projection light Lp on the lens surfaces of the lens elements in the projection optical system, for example, Ga1, Ga2 and Gb1, Gb2 shown in FIG. 2 and FIG. 3, is referred to as "ghost light", and the image formed by the ghost light is referred to as "ghost image". When a ghost image is formed on the projection target 100 or the image sensor 75, the contrast of the image or image is reduced, and the image quality of the projection type image display device is deteriorated.

[0043] Therefore, the present disclosure configures a projection optical system to suppress the formation of ghost images. This suppresses ghost light generated by light reflection on the lens surface of a lens element in the projection optical system from forming a ghost image on a projection target or an imaging element, improves the contrast of images and images, and improves the image quality of a projection-type image display device. Below, conditions satisfied by the projection optical system according to this embodiment will be described with reference to Figs. 4 to 6.

[0044] (Conditions that the projection optical system must satisfy (1)) Fig. 4 is a diagram for explaining the satisfaction of condition (1) in the projection optical system 60 according to the first embodiment of the present disclosure. Condition (1) shown in Fig. 4 is a configuration condition (1) of the projection optical system obtained by ray tracing using paraxial ray tracing for marginal rays of an axial light beam passing through the projection optical system 60 from the object surface S1 side toward the image surface S2 side. Here, the object surface S1 of the projection optical system corresponds to the surface on which the projection target object 100 is located, and the image surface S2 side corresponds to the surface on which the display surface 55a of the image display element is located.

[0045] In this specification, "axial light beam" refers to a light beam that is emitted from the optical axis Oa and contributes to image formation. "Marginal ray of axial light beam" refers to a light beam that passes through the outermost part (the position farthest from the optical axis) of the axial light beam. Paraxial ray tracing is a simulation technique that, based on the paraxial assumption, sequentially calculates the propagation path of light beams due to transmission, refraction, and reflection on the surface of each optical element of the optical system in a geometrical optical manner.

[0046] In the paraxial assumption, for example, when a ray of light is incident on a lens surface with a radius of curvature r, the inclination angle with respect to the optical axis is α1, the distance from the optical axis to the position where the ray reaches the lens surface is the height of the ray of light is h, and the refractive indices on the entrance side and exit side are n1 and n2, respectively, then when the ray of light exits from the lens surface, the inclination angle with respect to the optical axis α2 is calculated by the following formula (a). n2*α2=n1*α1+(n2-n1)*(h / r)···(a)

[0047] In this way, the ray height h and the incident inclination angle α1 at a certain lens surface can be used to obtain the exit inclination angle α2 after refraction at the lens surface, and the inclination angle α2 is passed on as the input incident inclination angle for the next lens surface, so that the inclination angle and ray height of the ray arriving at each successive lens surface can be calculated sequentially. Paraxial ray tracing can be performed based on known techniques, and further detailed description is omitted here.

[0048] Specifically, paraxial ray tracing is performed at the image plane focal position as shown in Fig. 4. At this time, under the paraxial assumption, a marginal ray G0 of an axial light beam from an object surface S1 with an object distance at an infinity position is parallel to the optical axis Oa, that is, the inclination angle with respect to the optical axis is α=0 degrees and the ray height is H0=1, and passes through the projection optical system 60 to be focused at a focal point M on the optical axis Oa at the image surface S2. At this time, the focal length of the entire projection optical system 60 is f.

[0049] Next, the light ray G1 reflected by the image surface S2 propagates toward the object surface S1 with an inclination angle α12, reaches the right lens surface LaR2 of the lens La, and after being refracted within the lens La, reaches the left lens surface LaR1.

[0050] Next, the lens surface LaR1 acts as a lens reflecting surface, and the reflected light ray travels toward the image surface S2, and after being refracted at the lens surface LaR2, it is emitted from the projection optical system 60, and the emitted light ray G11a is condensed on the condensing surface P1. At this time, the distance X1 between the condensing surface P1 and the image surface S2 can be calculated.

[0051] In FIG. 4, the light ray G11a emitted from the projection optical system 60 is conceptually shown to form a focal point on the optical axis Oa, but the present disclosure is not limited thereto. For example, in an actual optical system, due to the occurrence of aberration, the light reflected by the lens reflecting surface and emitted from the projection optical system may not form a focal point on the optical axis Oa. In this specification, the condensing surface refers to a surface on which the condensing spot or beam waist of the light beam reflected by the lens reflecting surface and emitted from the projection optical system 60 is located. In addition, the condensing surface P1 of the light ray G11a is shown to be on the under side (left side in the figure) of the image surface S2, but the light ray emitted from the projection optical system 60 may be condensed on the condensing surface P2 on the over side (right side in the figure) of the image surface S2, for example, as in the illustrated light ray G11b. At this time, the distance X2 between the condensing surface P2 and the image surface S2 is calculated. The absolute values ​​of the calculated distances X1 and X2 are indicated by |X|.

[0052] In this way, when paraxial ray tracing is performed sequentially for the lens surfaces of each lens La, Lb, Lc, etc. included in the projection optical system 60 in the order of object surface S1 → image surface S2 → lens reflecting surface → focusing surfaces P1, P2, the projection optical system can be configured so that the lens surfaces satisfy the following condition (1). |X|>f / 2 (1) Here, in paraxial ray tracing, X is the distance between the focusing surface where a marginal ray of the axial light beam propagates backward from the object surface S1, passes through the projection optical system 60, and is reflected at the image surface S2 where the display surface 55a of the image display element is located, and is then reflected and focused by each lens surface of the projection optical system, and the image surface S2, and f is the focal length of the entire projection optical system 60.

[0053] When the lens surfaces of the lenses constituting the projection optical system satisfy condition (1), the ghost images caused by ghost lights Ga1, Ga2 or Gb1, Gb2 generated when the projection light Lp shown in Fig. 2 or Fig. 3 is reflected by the lens surfaces of the lens elements of the projection optical system will have a focal depth that is out of the projection surface 100a of the projection target 100, which is the conjugate surface of the image display element 55, or the imaging surface 75a of the imaging element 75. This makes it possible to suppress a decrease in the contrast of the image or image captured by the ghost images, and improve the image quality of the projection type image display device.

[0054] (Conditions that the projection optical system must satisfy (2)) 5 is a diagram for explaining whether condition (2) is satisfied in the projection optical system 60 according to the first embodiment of the present disclosure. Condition (2) shown in Fig. 5 is a configuration condition (2) of the projection optical system obtained by paraxial ray tracing for a marginal ray of an on-axis light beam passing through the projection optical system 60 from the object surface S1 side toward the image surface S2 side.

[0055] Specifically, paraxial ray tracing is performed at the image plane focal position as shown in Fig. 5. At this time, under the paraxial assumption, a marginal ray G0 of an axial light beam from an object surface S1 with an object distance at an infinity position is parallel to the optical axis Oa, that is, the inclination angle with respect to the optical axis is α=0 degrees and the ray height is H0=1, and passes through the projection optical system 60 to be condensed at a focal point M on the optical axis Oa at the image surface S2. At this time, the focal length of the entire projection optical system 60 is f.

[0056] Next, the light ray G4 reflected by the image surface S2 propagates toward the object surface S1 with an inclination angle α42, enters the right lens surface LdR2 of the lens Ld, and is reflected by the lens surface LdR2 as a lens reflecting surface, resulting in the emission of light ray G42 which reaches the image surface S2, and the height H of the light ray at the image surface S2 is calculated.

[0057] In this way, when paraxial ray tracing is performed sequentially for the lens surfaces of each lens Ld, Le, Lf, etc. included in the projection optical system 60 in the order of object surface S1 → image surface S2 → lens reflecting surface → image surface S2, the projection optical system can be configured so that the lens surfaces satisfy the following condition (2). |(H*f / 2F)|>D····(2) Here, H is the ray height at which, in paraxial ray tracing, a marginal ray of the axial light beam propagating backward from the object surface S1 and passing through the projection optical system 60 is reflected by the image surface S2 and then reflected by each lens surface of the projection optical system to reach the image surface S2, f is the focal length of the entire projection optical system 60, F is the F-number of the entire projection optical system 60, and is the focal length f of the entire projection optical system 60 divided by the effective aperture 2R. D is half the diagonal length of the display surface 55a of the image display element.

[0058] In the propagation optical system 20a, 20b shown in FIG. 2 or FIG. 3, when the light beams of ghost light Ga2, Gb2 generated by the reflection of the projection light Lp on the lens surface of the lens element in the projection optical system form a partial focus in the propagation optical system, it is known that a strong ghost image is formed on the projection surface 100a or the imaging surface 75a. When the lens surface of each lens constituting the projection optical system satisfies the condition (2), the formation of a partial focus by the light beams of ghost light Ga2, Gb2 can be suppressed. This makes it possible to prevent the formation of a strong ghost image on the projection surface 100a or the imaging surface 75a, suppress the decrease in the contrast of the image or image due to the ghost image, and improve the image quality of the projection type image display device. In this specification, (H*f / 2F) on the left side of the above condition (2) is sometimes referred to as the "spot size index" and expressed as "Prt_h".

[0059] (Conditions that the projection optical system must satisfy (3)) Fig. 6 is a diagram for explaining whether condition (3) is satisfied in the projection optical system 60 according to the first embodiment of the present disclosure. Condition (3) shown in Fig. 6 is a configuration condition (3) of the projection optical system obtained by actual ray tracing for a marginal ray of an on-axis light beam propagating from the image surface S2 side toward the object surface S1 side.

[0060] In actual ray tracing, without making the paraxial assumption, when a ray enters a lens surface, the angle of incidence with respect to the normal to the lens surface is θ1, and the refractive indices on the entrance and exit sides are n1 and n2, respectively. When the ray exits the lens surface, the exit angle θ2 with respect to the normal to the lens surface is calculated according to Snell's law, that is, by the following formula (b). n2*sinθ2=n1*sinθ1...(b)

[0061] In this way, the incidence angle θ1 of the light incident on a certain lens surface can be used to obtain the exit angle θ2 of the light exiting from the lens surface. In real ray tracing, the exit angle θ2 is taken over as the incidence angle for the next lens surface, and the incidence angle and ray height of the light reaching each successive lens surface can be calculated in sequence according to the Gaussian equation for the refractive surface, etc. Real ray tracing can be performed based on known techniques, and further detailed description is omitted here.

[0062] Specifically, actual ray tracing is performed at the image plane focal position as shown in Fig. 6. At this time, when a marginal ray of the axial light beam from the image plane S2 propagates toward the object surface S1 and is incident on the right lens surface LgR2 of the lens Lg, the incident angle θ72 of the incident ray G72i with respect to the normal line LgN2 of the lens surface LgR2 and the ray height h72 at the lens surface LgR2 are calculated.

[0063] Next, ray G72i is reflected by ray G72r and refracted at lens surface LgR2 before traveling on, successively reaching the left lens surface LgR1 of lens Lg and lens surfaces LhR2 and LhR1 of lens Lh, and the angle of incidence and ray height when incident on each lens surface can be calculated successively.

[0064] In this way, when actual ray tracing is performed on the marginal rays of the on-axis light beam from the image surface S2, the projection optical system can be configured so that the lens surfaces of each of the lenses Lg, Lh, etc. included in the projection optical system 60 satisfy the following condition (3). 1 / (|θ|*h)<0.04 (3) Here, θ (deg) is the angle between the normal to the lens surface on which a marginal ray of the axial light beam propagating forward from the image surface S2 is incident in actual ray tracing, and h (mm) is the height of the ray at that lens surface.

[0065] By satisfying the condition (3) for each lens surface of the projection optical system, when the projection light Lp passes through the projection optical system, the light reflected from the lens surface tends to deviate from the optical path traced forward when propagating backward, and the normal incidence angle when it reaches the next lens surface deviates from the original incidence angle. Therefore, the light intensity of the ghost light Ga2, Gb2 (see FIG. 2 or FIG. 3) that passes backward through the projection optical system and reaches the projection surface 100a or the imaging surface 75a by re-reflection is reduced. This makes it possible to suppress the decrease in contrast of the image or imaging due to the ghost image, and improve the image quality of the projection type image display device. In this specification, the (1 / (|θ|*h)) on the left side of the above condition (3) is sometimes called the "ghost index" and expressed as "Gin".

[0066] The reference value 0.04 of the ghost index Gin on the right side of the condition (3) is determined by the brightness of the projection-type image display device. The projection-type image display device 10 according to the present embodiment has a high brightness of, for example, 5000 lumens or more. For example, in a projection-type image display device having a brightness of 3000 to 30,000 lumens, the reference value of the ghost index Gin can be determined to be 0.04.

[0067] 6 shows the calculation of the ghost index Gin based on the incidence angle and ray height at each lens surface of the marginal ray of the axial light beam propagating from the image surface S2 side to the object surface S1 side, but the present disclosure is not limited to this. For example, the ghost index Gin can also be calculated based on the emergence angle and ray height at each lens surface of the marginal ray of the axial light beam propagating from the object surface S1 side to the image surface S2 side. In addition, the projection optical system can be configured so that the ghost index Gin calculated in this way satisfies the above condition (3).

[0068] In addition, in the ray tracing under the above conditions (1) to (3), it is desirable to use a light wavelength capable of forming a ghost image. This makes it possible to more effectively suppress the decrease in contrast of the image or image capture due to the ghost image. Specifically, for example, in the propagation optical system 20a shown in FIG. 2, ray tracing can be performed using a light wavelength contained in the projection light. For example, ray tracing can be performed using a light wavelength of 550 nm in the visible light range. In addition, in the propagation optical system 20b shown in FIG. 3, when light in a predetermined wavelength range of the external light Lo is introduced into the image capture optical system 70 to capture an image, ray tracing can be performed using a light wavelength contained in the wavelength range. For example, but not limited to this, when capturing an image using light in the visible light range, ray tracing can be performed using a light wavelength of 550 nm in the visible light range, and when capturing an image using light in the infrared range, ray tracing can be performed using a light wavelength of 800 nm in the infrared range.

[0069] The configurations of the projection optical systems according to the first and second embodiments and the first comparative example will be described with reference to FIGS.

[0070] <Examples and Comparative Examples> (Lens arrangement of the projection optical system) Fig. 7 is a lens arrangement diagram of the projection optical system 60A according to the embodiment 1. In each of the lens arrangement diagrams shown in Figs. 7, 9, and 11 below, the left side of the diagram is the enlargement side or object surface S1 side of the entire system, which corresponds to the projection surface 100a side of the projection target 100. The right side of the diagram is the reduction side or image surface S2 side of the entire system, which corresponds to the imaging surface 55a side of the image display element 55.

[0071] The projection optical system 60A in FIG. 7 includes a back glass member 61A and a lens unit 65A. The lens unit 65A according to the first embodiment is configured with the first to seventeenth lens elements La1 to La17 arranged side by side, and the first to seventeenth lens elements La1 to La17 are respectively configured with a positive lens or a negative lens. The positive lens has a biconvex shape or a positive meniscus shape, and thus has a positive power. The negative lens has a biconcave shape or a negative meniscus shape, and thus has a negative power. A diaphragm A is disposed on the reduction side of the eighth lens element La8.

[0072] The back glass member 61A includes various prisms, filters, cover glass, etc. In Fig. 7, the back glass members La21 and La22 for the image surface S2 corresponding to the display surface 55a of the image display element 55 are conceptually shown.

[0073] Fig. 8 is an aberration diagram showing various aberrations of the projection optical system 60A according to Example 1. Note that each aberration diagram shown in Fig. 8, Fig. 10, and Fig. 112 below illustrates various aberrations in the entire corresponding projection optical system in a focused state.

[0074] The aberration diagram shown in FIG. 8 includes, from the left, a spherical aberration diagram in which the spherical aberration is plotted on the horizontal axis "SA (mm)," an astigmatism diagram in which the astigmatism is plotted on the horizontal axis "AST (mm)," and a distortion diagram in which the distortion aberration is plotted on the horizontal axis "DIS (%)."

[0075] In each spherical aberration diagram, the vertical axis "F" represents the F-number. Additionally, the solid line marked "d-line" in the diagram represents the characteristics of the d-line. The dashed line marked "F-line" represents the characteristics of the F-line. The dashed line marked "C-line" represents the characteristics of the C-line. In each astigmatism diagram and distortion diagram, the vertical axis "H" represents the image height. Additionally, the solid line marked "s" in the diagram represents the characteristics of the sagittal plane. The dashed line marked "m" represents the characteristics of the meridional plane.

[0076] Parameter data 1 corresponding to the projection optical system 60A of the first embodiment is shown. In the parameter data 1, surface data is shown in Table 1-1, various data is shown in Table 1-2, and single lens data is shown in Table 1-3. Table 1-1 contains data on the lens surfaces of each lens in the projection optical system 60A, including the radius of curvature r, surface spacing d, refractive index nd, and Abbe number vd of the lens surface. Tables 1-2 and 1-3 correspond to a light wavelength of 550 nm.

[0077] (Parameter data 1) [Table 1-1]

[0078] [Table 1-2]

[0079] [Table 1-3]

[0080] FIG. 9 is a lens arrangement diagram of the projection optical system 60B according to the second embodiment. The projection optical system 60B in FIG. 9 includes a back glass member 61B and a lens unit 65B. The lens unit 65B is different from the projection optical system 60A in FIG. 7 in the number of lenses, and is configured with the first to sixteenth lens elements Lb1 to Lb16 arranged side by side. The first to sixteenth lens elements Lb1 to Lb16 are each configured with a positive lens or a negative lens. A diaphragm A is disposed on the reduction side of the seventh lens element Lb7. The back glass member 61B includes various prisms, filters, cover glass, and the like. In FIG. 9, the back glass members Lb21 and Lb22 are conceptually shown with respect to the image surface S2 corresponding to the display surface 55a of the image display element 55.

[0081] 10 is an aberration diagram showing various aberrations of the projection optical system 60B according to the second embodiment. From the left side of the figure, the diagram includes a spherical aberration diagram in which the horizontal axis indicates the spherical aberration "SA (mm)", an astigmatism diagram in which the horizontal axis indicates the astigmatism "AST (mm)", and a distortion diagram in which the horizontal axis indicates the distortion "DIS (%)". The spherical aberration diagram, astigmatism diagram, and distortion diagram each indicate characteristics using the same symbols as in FIG. 8. Detailed explanations will be omitted.

[0082] Parameter data 2 corresponding to the projection optical system 60B of Example 2 is shown. In the parameter data 2, surface data is shown in Table 2-1, various data is shown in Table 2-2, and single lens data is shown in Table 2-3. Table 2-1 contains data on the lens surfaces of each lens in the projection optical system 60B, including the radius of curvature r, surface spacing d, refractive index nd, and Abbe number vd of the lens surface. Tables 2-2 and 2-3 correspond to a light wavelength of 550 nm.

[0083] (Parameter data 2) [Table 2-1]

[0084] [Table 2-2]

[0085] [Table 2-3]

[0086] FIG. 11 is a lens arrangement diagram of a projection optical system 60C according to Comparative Example 1. The projection optical system 60C in FIG. 11 includes a back glass member 61C and a lens unit 65C. The lens unit 65C includes first to seventeenth lens elements Lc1 to Lc17 arranged side by side, and the first to seventeenth lens elements Lc1 to Lc17 are each composed of a positive lens or a negative lens. A diaphragm A is disposed on the reduction side of the eighth lens element Lc8. The back glass member 61C includes various prisms, filters, cover glass, and the like. In FIG. 11, the back glass members Lc21 and Lc22 are conceptually shown with respect to an image surface S2 corresponding to a display surface 55a of an image display element 55.

[0087] 12 is an aberration diagram showing various aberrations of the projection optical system 60C according to Comparative Example 1. From the left side of the figure, the diagram includes a spherical aberration diagram in which the horizontal axis indicates the spherical aberration "SA (mm)", an astigmatism diagram in which the horizontal axis indicates the astigmatism "AST (mm)", and a distortion diagram in which the horizontal axis indicates the distortion "DIS (%)". The spherical aberration diagram, astigmatism diagram, and distortion diagram each indicate characteristics using the same symbols as in FIG. 8. Detailed explanations will be omitted.

[0088] Parameter data 3 corresponding to the projection optical system 60C of Comparative Example 1 is shown. In the parameter data 3, surface data is shown in Table 3-1, various data is shown in Table 3-2, and single lens data is shown in Table 3-3. Table 3-1 contains data on the lens surfaces of each lens in the projection optical system 60C, including the radius of curvature r, surface spacing d, refractive index nd, and Abbe number vd of the lens surfaces. Tables 3-2 and 3-3 correspond to a light wavelength of 550 nm.

[0089] (Parameter data 3) [Table 3-1]

[0090] [Table 3-2]

[0091] [Table 3-3]

[0092] (Satisfaction of conditions (1) to (3) in the projection optical systems of the examples and comparative examples) Figures 13A, 13B, and 13C show the results of judging whether each of conditions (1) to (3) is satisfied by ray tracing for each lens surface of the 1st to 17th lens elements La1 to La17 in lens unit 65A of projection optical system 60A in Figure 7. The symbol "◯" indicates that the corresponding condition is satisfied, and the symbol "×" indicates that the corresponding condition is not satisfied.

[0093] 13A is a diagram showing the satisfaction of condition (1) in the projection optical system 60A of Example 1. As shown in Table 1-2, the focal length of the entire projection optical system 60A of Example 1 is approximately 51.39 mm, and condition (1) is determined as |X|≧25.7 mm. Since the minimum value of |X| was 25.9 mm for the lens surfaces L1R1 to L17R2 of the lens elements La1 to La17, all the lens surfaces in the projection optical system 60A satisfied condition (1).

[0094] Next, FIG. 13B is a diagram showing the sufficiency of condition (2) in the projection optical system 60A of Example 1. In this example, the half diagonal length D of the display surface 55a (see FIG. 7) of the image display element was 8.75 mm, and the spot size index of condition (2) was determined to be |Prt_h|>8.75. As shown in Table 1-2, the focal length of the entire projection optical system 60A of Example 1 was about 51.39 mm, and the F value was 2.4787. In the lens surfaces L1R1 to L17R2 of the lens elements La1 to La17, all the other lens surfaces satisfied condition (2) except for the lens surface L8R2 of the eighth lens element. Only the lens surface L8R2 of the eighth lens element did not satisfy condition (2) because the value of |Prt_h| was 8.09.

[0095] 13C is a diagram showing whether condition (3) is satisfied in projection optical system 60A of Example 1. The ghost index in condition (3) was determined to be Gin<0.04. Since the maximum value of the ghost index Gin was 0.025 in lens surfaces L1R1 to L17R2 of lens elements La1 to La17, all lens surfaces in projection optical system 60A satisfied condition (3).

[0096] In this way, it was found that all of the lens surfaces L1R1 to L17R2 in the projection optical system 60A of the first embodiment satisfy at least one of the conditions (1) to (3).

[0097] 14A, 14B, and 14C show the results of judging whether each of the conditions (1) to (3) is satisfied by ray tracing for each lens surface of the 1st to 16th lens elements Lb1 to Lb16 in the lens unit 65B of the projection optical system 60B in Fig. 9. The symbol "◯" indicates that the corresponding condition is satisfied, and the symbol "×" indicates that the corresponding condition is not satisfied.

[0098] 14A is a diagram showing whether condition (1) is satisfied in the projection optical system 60B of Example 2. As shown in Table 2-2, the focal length of the entire projection optical system 60B of Example 2 is approximately 51.47 mm, and condition (1) is determined as |X|≧25.74. Since the minimum value of |X| was 42.7 mm for the lens surfaces L1R1 to L16R2 of the lens elements Lb1 to Lb16, all the lens surfaces in the projection optical system 60B satisfied condition (1).

[0099] Next, Fig. 14B is a diagram showing whether condition (2) is satisfied in projection optical system 60B of Example 2. In this example, half the diagonal length D of display surface 55a (see Fig. 7) of the image display element is 8.75 mm, and the spot size index of condition (2) is determined to be |Prt_h|>8.75. Since the minimum value of spot size index |Prt_h| was 9.8 for lens surfaces L1R1-L17R2 of lens elements La1-La17, all lens surfaces in projection optical system 60B satisfied condition (2).

[0100] 14C is a diagram showing whether condition (3) is satisfied in projection optical system 60B of Example 2. The ghost index in condition (3) was determined to be Gin<0.04. Since the maximum value of the ghost index Gin was 0.020 in lens surfaces L1R1 to L16R2 of lens elements Lb1 to Lb16, all lens surfaces in projection optical system 60B satisfied condition (3).

[0101] In this way, it was found that all of the lens surfaces L1R1 to L16R2 in the projection optical system 60B of the second embodiment satisfy all of the conditions (1) to (3).

[0102] 15A, 15B, and 15C show the results of judging whether each of the conditions (1) to (3) is satisfied by ray tracing for each lens surface of the 1st to 17th lens elements Lc1 to Lc17 in lens unit 65C of projection optical system 60C in Fig. 11. The symbol "◯" indicates that the corresponding condition is satisfied, and the symbol "×" indicates that the corresponding condition is not satisfied.

[0103] Specifically, FIG. 15A is a diagram showing the sufficiency of condition (1) in the projection optical system 60C of Comparative Example 1. As shown in Table 3-2, the focal length of the entire projection optical system 60C of Comparative Example 1 was about 50.85 mm, and condition (1) was determined to be |X|≧25.42. The minimum value of |X| was 4.2 mm in the lens surfaces L1R1-L17R2 of the lens elements Lc1-Lc17. As shown in the table of FIG. 15A, it was found that in the projection optical system 60C of Comparative Example 1, the lens surface L1R2 of the first lens element Lc1, the lens surfaces L2R1 and L2R2 of the second lens element Lc2, and the lens surface L3R1 of the third lens element Lc3 do not satisfy condition (1).

[0104] Next, FIG. 15B is a diagram showing the satisfaction of condition (2) in projection optical system 60C of Comparative Example 1. In this embodiment, half the diagonal length D of display surface 55a (see FIG. 7) of the image display element is 8.75 mm, and the spot size index of condition (2) is determined to be |Prt_h|>8.75. The minimum value of the spot size index |Prt_h| was 1.0 in lens surfaces L1R1-L17R2 of lens elements Lc1-Lc17. As shown in the table of FIG. 15B, it was found that in projection optical system 60C of Comparative Example 1, lens surface L2R2 of second lens element Lc2 and lens surface L3R1 of third lens element Lc3 do not satisfy condition (2).

[0105] Next, Fig. 15C is a diagram showing whether condition (3) is satisfied in projection optical system 60C of Comparative Example 1. The ghost index of condition (3) was determined to be Gin<0.04. The maximum value of the ghost index Gin was 0.241 in lens surfaces L1R1-L17R2 of lens elements Lc1-Lc17. As shown in the table of Fig. 15C, it was found that in projection optical system 60C of Comparative Example 1, lens surface L2R2 of the second lens element Lc2 and lens surface L3R1 of the third lens element Lc3 do not satisfy condition (2).

[0106] As described above, it was found that, among the lens surfaces L1R1 to L17R2 in the projection optical system 60C of Comparative Example 1, the lens surface L2R2 of the second lens element Lc2 and the lens surface L3R1 of the third lens element Lc3 do not satisfy any of the conditions (1) to (3).

[0107] The formation of ghost images due to light reflection on the lens surfaces can be suppressed by configuring a projection optical system so that the lens surfaces of the lens elements satisfy conditions (1) to (3). This will be described below with reference to FIGS. 16 to 19.

[0108] (Suppression of ghost image formation caused by light reflection on the lens surface) Fig. 16 is a diagram showing the propagation of light in the propagation optical system 20A using the projection optical system 60A of Example 1. Fig. 17 is a diagram showing the image formation in the propagation optical system 20A of Fig. 16.

[0109] 16 includes the projection optical system 60A and the imaging optical system 70 of the first embodiment. The projection light Lp is emitted by the image display element 55, passes through the projection optical system 60A in the right direction in the figure along the optical axis Oa, and is enlarged and projected onto the projection target 100 (not shown). In addition, the external light Lo passes through the projection optical system 60A in the left direction in the figure, and is then introduced into the imaging optical system 70 and forms an image on the imaging surface of the imaging element 75.

[0110] When the projection light Lp passes through the lens unit 65A of the projection optical system 60A, it is reflected on the lens surfaces of the multiple lens elements, generating lens surface reflected light Gc1 that propagates toward the image display element 55. The lens surface reflected light Gc1 is reflected again by the separation prism 62A, causing ghost light Gc2 to enter the imaging optical system 70 along the optical axis Ob.

[0111] 13A to 13C, all of the lens surfaces L1R1 to L17R2 in the projection optical system 60A of the first embodiment satisfy at least one of the conditions (1) to (3). With the projection optical system 60A configured in this way, when the lens surface reflected light Gc1 propagates toward the image display element 55, the lens surfaces satisfy the condition (3), so that a large portion of the light is removed from the optical path, and the light intensity of the ghost light Gc2 reaching the imaging optical system 70 is reduced.

[0112] In addition, since the lens surface satisfies the condition (2), partial focusing by the ghost light Gc2 is not formed in the propagation optical system 20A. Furthermore, since the lens surface satisfies the condition (1), the focal depth of the image formed by the ghost light Gc2 incident on the imaging optical system 70 is out of the imaging plane of the imaging element 75.

[0113] 17, it is possible to eliminate the formation of a ghost image due to the ghost light Gc2 while the image Mc1 due to the external light Lo is clearly formed on the imaging surface 75a of the image sensor 75. This makes it possible to suppress the decrease in contrast of the image due to the formation of the ghost image, thereby improving the image quality of the projection type image display device.

[0114] The propagation optical system 20A in Fig. 16 shows an example of the configuration of a propagation optical system using the projection optical system 60A of the embodiment 1, but the same effect can be achieved by a propagation optical system using the projection optical system 60B of the embodiment 2. Also, in Fig. 17, improvement in the image quality on the imaging surface of the imaging element is shown as an example, but it is also possible to improve the contrast of the image on the projection surface (not shown).

[0115] Furthermore, the improvement of the image quality of the projection type image display device by the projection optical system configured to satisfy conditions (1) to (3) has been described using the propagation optical system 20A including the imaging optical system 70 as an example, but the present disclosure is not limited thereto. For example, even in the propagation optical system 20a not including the imaging optical system shown in Fig. 2, it is of course possible to improve the contrast of the image on the projection surface and improve the image quality by mounting the projection optical systems 60A and 60B in which all lens surfaces satisfy at least one of conditions (1) to (3) or all lens surfaces satisfy all of conditions (1) to (3).

[0116] Next, Fig. 18 is a diagram showing the propagation of light in a propagation optical system 20C using a projection optical system 60C of Comparative Example 1. Fig. 19 is a diagram showing image formation in the propagation optical system 20C of Fig. 18.

[0117] 18 includes the projection optical system 60C and the imaging optical system 70 of Comparative Example 1. The projection light Lp is emitted by the image display element 55, passes through the projection optical system 60C in the right direction in the figure along the optical axis Oa, and is enlarged and projected onto the projection target 100 (not shown). In addition, the external light Lo passes through the projection optical system 60C in the left direction in the figure, and is then introduced into the imaging optical system 70 and forms an image on the imaging surface of the imaging element 75.

[0118] When the projection light Lp passes through the lens unit 65C of the projection optical system 60C, it is reflected by the lens surfaces of the multiple lens elements, generating lens surface reflected light Gd1 that propagates toward the image display element 55. The lens surface reflected light Gd1 is reflected again by the separation prism 62C, causing ghost light Gd2 to enter the imaging optical system 70 along the optical axis Ob.

[0119] As shown in the charts of Figures 15A to 15C, among the lens surfaces L1R1 to L17R2 in the projection optical system 60C of Comparative Example 1, the lens surface L2R2 of the second lens element Lc2 and the lens surface L3R1 of the third lens element Lc3 do not satisfy any of the conditions (1) to (3). With the projection optical system 60C configured in this way, as shown in Figure 18, when the lens surface reflected light Gd1 propagates toward the image display element 55, a small portion of the light is removed from the optical path, and most of the lens surface reflected light Gd1 enters the imaging optical system 70 as ghost light Gd2. In addition, after the light beam of the ghost light Gd2 forms an intermediate image Md by partial focusing in the imaging optical system 70, a ghost image is formed on the imaging surface of the imaging element 75.

[0120] 19, a strong ghost image Mg due to ghost light Gc2 was formed near an image Mc2 due to external light Lo on the imaging surface 75a of the image sensor 75. This caused a decrease in the contrast of the image, resulting in a deterioration in image quality.

[0121] Although FIG. 19 has been described taking as an example the degradation of image quality on the imaging surface of the imaging element, a degradation of image contrast was also observed on the projection surface (not shown).

[0122] As described above, the above-mentioned embodiments have been described as examples of the technology disclosed in this application. However, the technology in this disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made. In addition, it is also possible to combine the components described in each of the above-mentioned embodiments to create a new embodiment.

[0123] In addition, the accompanying drawings and detailed description are provided to explain the embodiments. Therefore, among the components described in the accompanying drawings and detailed description, not only essential components for solving the problem but also components that are not essential for solving the problem in order to illustrate the above technology may be included. Therefore, the fact that the non-essential components are described in the accompanying drawings or detailed description should not be interpreted as immediately being essential.

[0124] In addition, since the above-described embodiment is intended to illustrate the technology of the present disclosure, various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents. These modifications are also included in the technical scope of the present disclosure. [Industrial Applicability]

[0125] The present disclosure is applicable to various projection-type image display devices and projection optical systems installed in the projection-type image display devices. [Explanation of symbols]

[0126] 10 Projection type image display device 20 Propagation Optics 20a, 20b, 20A, 20C Propagation optical system 30 Light source device 40 Light guide optical system 50 Projection light generation section 60 Projection Optical System 60A, 60B, 60C Projection optical system 70 Imaging Device 55 Image display element 55a Display surface 61a, 61b Back glass member 61A, 61B, 61C Back glass components 62a, 62b Prism elements 62A, 62C Split prism 63a, 63b Optical elements 65 Lens unit 65A, 65B, 65C Lens Unit 71 Prism Spacer 75 Image sensor 75a Imaging surface 100 Projection target 100a Projection surface La1~La17 lens elements Lb1~Lb16 lens elements Lc1~Lc17 lens elements La21, La22, Lb21, Lb22, Lc21, Lc22 Back glass components Mc, Mc1, Mc2 imaging Mp video Ms Image Md Intermediate imaging Mg Ghost Statue

Claims

1. A projection optical system including a plurality of lenses, which projects projection light emitted from an image display element in a forward direction along an optical axis, and displays an image formed on a display surface of the image display element on a projection target, wherein the projection light is reflected by lens surfaces of the plurality of lenses, thereby generating light passing through the projection optical system in a backward direction, In ray tracing by paraxial ray tracing for a marginal ray of an axial light beam passing through the projection optical system, the marginal ray propagating backward is reflected by the display surface, and a first ray is reflected by each of the lens surfaces and collected. In this case, the distance between the display surface and the collecting surface is X, and the focal length of the entire projection optical system is f. All of the lens surfaces in the projection optical system satisfy the following condition (1): |X|>f / 2...(1) Projection optics.

2. A projection optical system including a plurality of lenses, which projects projection light emitted from an image display element in a forward direction along an optical axis, and displays an image formed on a display surface of the image display element on a projection target, wherein the projection light is reflected by lens surfaces of the plurality of lenses, thereby generating light passing through the projection optical system in a backward direction, In ray tracing by paraxial ray tracing for a marginal ray of an axial light flux passing through the projection optical system, the marginal ray propagating backward is reflected on the display surface, and the first ray is reflected on each of the lens surfaces. In this case, the ray height on the display surface of the first ray is H, and the half of the diagonal length of the display surface is D. All of the lens surfaces in the projection optical system satisfy the following condition (2): |(H*f / 2F)|>D...(2) Here, f is the focal length of the entire projection optical system, and F is the F-number of the entire projection optical system. Projection optics.

3. A projection optical system including a plurality of lenses, which projects projection light emitted from an image display element in a forward direction along an optical axis, and displays an image formed on a display surface of the image display element on a projection target, wherein the projection light is reflected by lens surfaces of the plurality of lenses, thereby generating light passing through the projection optical system in a backward direction, In ray tracing by actual ray tracing for a marginal ray of an on-axis light beam passing through the projection optical system, when the marginal ray propagating forward from the display surface is incident on each of the lens surfaces, the angle between the normal to the lens surface on which the marginal ray is incident is θ (deg) and the height of the ray on the lens surface on which the marginal ray is incident is h (mm): The following condition (3) is satisfied for all the lens surfaces in the projection optical system: 1 / (|θ|*h)<0.04...(3) Projection optics.

4. A projection optical system including a plurality of lenses, which projects projection light emitted from an image display element in a forward direction along an optical axis, and displays an image formed on a display surface of the image display element on a projection target, wherein the projection light is reflected by lens surfaces of the plurality of lenses, thereby generating light passing through the projection optical system in a backward direction, In ray tracing of a marginal ray of an axial light beam passing through the projection optical system, at least one of the following conditions (1) to (3) is satisfied on all the lens surfaces in the projection optical system: |X|>f / 2・・・・・・(1) |(H*f / 2F)|>D...(2) 1 / (|θ|*h)<0.04...(3) Where: X is a distance between the display surface and a focusing surface where a first ray, which is a marginal ray propagating backward and reflected by the display surface, is reflected by each of the lens surfaces and focused in the ray tracing by paraxial ray tracing, f is the focal length of the entire projection optical system, H is a ray height on the display surface of a ray of light reflected by each of the lens surfaces of the first ray in the ray tracing by paraxial ray tracing, F is the F-number of the entire projection optical system, D is half the diagonal length of the display surface, θ (deg) is an angle between the normal of the lens surface on which the marginal ray propagating forward from the display surface is incident when the marginal ray is incident on each of the lens surfaces in the ray tracing by actual ray tracing, h (mm) is the height of the marginal ray at the lens surface where the marginal ray propagating forward from the display surface is incident on each of the lens surfaces in the ray tracing by actual ray tracing; Projection optics.

5. The ray tracing is performed using optical wavelengths contained in the projection light. The projection optical system according to claim 1 .

6. External light propagating backward from the projection target along the optical axis passes through the projection optical system, and light in a predetermined wavelength range among the external light forms an image; The ray tracing is performed using optical wavelengths included in the predetermined wavelength range. The projection optical system according to claim 1 .

7. A projection type image display device that projects and displays an image on a projection target, A light source device; a projection light generating unit including one or more image display elements and configured to generate projection light modulated in response to an image signal; a light guiding optical system that guides the illumination light emitted from the light source device to the projection light generating unit; The projection optical system according to claim 1 , Equipped with performing the ray tracing using optical wavelengths contained in the projection light; Projection type image display device.

8. A projection type image display device that projects and displays an image on a projection target, A light source device; a projection light generating unit including one or more image display elements and generating projection light modulated in response to an image signal; a light guiding optical system that guides the illumination light emitted from the light source device to the projection light generating unit; The projection optical system according to claim 1 , an imaging optical system in which external light propagating backward from the projection target along the optical axis passes through the projection optical system, and an imaging optical system captures light in a predetermined wavelength range of the external light; Equipped with performing the ray tracing using light wavelengths included in the predetermined wavelength range; Projection type image display device.

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