Viewfinder optical system, viewfinder device, and imaging device

Abstract

A viewfinder optical system is provided with a display element and an eyepiece optical system disposed closer to the viewpoint side than the display element. One or more diffractive elements are disposed in the viewfinder optical system. At least one of the diffraction elements is a first diffraction element including a liquid crystal diffraction element. When the distance on the optical axis from the display surface of the display element to the surface closest to the viewpoint side of the viewfinder optical system is set as TL and the distance on the optical axis from the display surface of the display element to the optical surface of the first diffraction element is set as X1, the viewfinder optical system satisfies the conditional expression represented by 0.05 < = X1 / TL < = 1.

Description

Technical Field

[0001] The invention relates to a viewfinder optical system, a viewfinder device and a camera device. Background Art

[0002] In the past, as an observation optical system or a viewfinder optical system, optical systems described in Japanese Patent Laid-Open No. 2020-154190 and Japanese Patent Laid-Open No. 2019-144550 are known. Japanese Patent Laid-Open No. 2020-154190 describes an observation optical system having a lens including a diffractive optical surface. Japanese Patent Laid-Open No. 2019-144550 describes a viewfinder optical system including a diffractive optical element. Summary of the invention

[0003] Technical issues to be solved by the invention

[0004] In recent years, there is a demand for a viewfinder optical system that is small and capable of good observation. However, the diffraction optical surface described in Japanese Patent Gazette No. 2020-154190 is a diffraction optical surface having a physical step difference shape (hereinafter referred to as a relief-type diffraction optical surface). Since it is in contact with the air, the light scattered by the step difference may become a light spot and reduce the resolution. The diffraction optical element described in Japanese Patent Gazette No. 2019-144550 has a so-called close-fitting multilayer structure in which two layers of diffraction optical surfaces having a relief-type diffraction optical surface are closely fitted to each other. Compared with the structure in which the diffraction optical surface is in contact with the air, the close-fitting multilayer diffraction optical element can reduce the generation of light spots, but requires a high level of technology and may result in high costs.

[0005] An object of the present invention is to provide a finder optical system, a finder device, and an imaging device that are compact and do not cause high costs, and that enable good observation.

[0006] Means for solving technical problems

[0007] One embodiment of the present invention is a viewfinder optical system, comprising: a display element; and an eyepiece optical system, which is arranged on a viewpoint side relative to the display element, wherein one or more diffraction elements are arranged in the viewfinder optical system, and at least one of the diffraction elements is a first diffraction element including a liquid crystal diffraction element, and when a distance on the optical axis from a display surface of the display element to a surface of the viewfinder optical system closest to the viewpoint is set to TL, and a distance on the optical axis from the display surface to an optical surface of the first diffraction element is set to X1,

[0008] The viewfinder optical system satisfies the conditional equation (1) represented by the following equation,

[0009] 0.05≤X1 / TL≤1 (1).

[0010] When the half value of the longest diameter of the display area in the display element is set to H and the focal length of the viewfinder optical system is set to f, the viewfinder optical system of the above-mentioned embodiment preferably satisfies the conditional expression (2) represented by the following expression,

[0011] 0.3<H / f<0.7 (2).

[0012] When the distance on the optical axis from the surface of the viewfinder optical system closest to the viewpoint to the viewpoint is dEP, and the focal length of the viewfinder optical system is f,

[0013] The viewfinder optical system of the above aspect preferably satisfies the conditional expression (3) represented by the following expression:

[0014] 0<f / dEP<0.95 (3).

[0015] The eyepiece optical system preferably includes two or more positive lenses and one or more negative lenses.

[0016] The eyepiece optical system preferably includes two or more aspherical lenses and one or more spherical lenses.

[0017] The diffraction element is preferably provided on a surface of the optical element, and the Abbe number of the optical element based on the d-line is 35 or more.

[0018] The diffraction element is preferably provided on a surface of the optical element, and the d-line transmittance of the optical element is preferably 98% or more.

[0019] When the distance on the optical axis from the display surface to the optical element in the finder optical system is X, the d-line transmittance of the partial optical system composed of all the optical elements arranged in the range of 0.05≤X / TL≤1 is preferably 92% or more.

[0020] The diffraction element is preferably provided on a surface of the optical element, and lenses having optical power are arranged on both the object side and the image side of the optical element.

[0021] The diffraction element is arranged on the surface of the optical element, and a lens having optical focal length and adjacent to the optical element is arranged on at least one of the object side and the image side of the optical element. The minimum distance in the optical axis direction between the optical surface of the diffraction element arranged on the surface of the optical element and the optical surface of the lens is preferably less than 1.8 mm.

[0022] The thickness of the region having a diffraction effect of the diffraction element in the optical axis direction is preferably 10 μm or less.

[0023] At least one of the diffraction elements is a second diffraction element including a liquid crystal diffraction element, no element having optical power is arranged between the display surface and the second diffraction element, and when the distance on the optical axis from the display surface to the optical surface of the second diffraction element is set to X2,

[0024] The viewfinder optical system preferably satisfies the conditional equation (4) represented by the following equation,

[0025] 0≤X2 / TL<0.05 (4).

[0026] In this case, it is preferable that the sign of the phase difference function of the first diffraction element is different from the sign of the phase difference function of the second diffraction element.

[0027] The diffraction element preferably has a periodic structure in a direction perpendicular to the optical axis and has a concentric structure centered on the optical axis. In this case, the period of the periodic structure preferably gradually shortens from the optical axis toward the periphery. Furthermore, the period of the periodic structure of the most peripheral portion of the diffraction element is preferably greater than 0.5 μm.

[0028] The number of lenses having optical power included in the viewfinder optical system may be four or five.

[0029] Another aspect of the present invention is a finder device including the finder optical system of the above aspect and in which output light from a display element is polarized light.

[0030] Still another aspect of the present invention is an imaging device including the finder optical system of the above aspect, wherein output light from a display element is polarized light.

[0031] In this specification, "lens with positive optical power" and "positive lens" have the same meaning. "Lens with negative optical power" and "negative lens" have the same meaning. "Single lens" refers to a single lens that is not bonded. However, a composite aspheric lens (a lens that is composed of a spherical lens and a non-spherical film formed on the spherical lens, and functions as a single aspheric lens as a whole) is not considered to be a cemented lens, but is treated as a single lens. Unless otherwise specified, the sign of the optical power associated with a lens including an aspheric surface uses the sign of the optical power of the paraxial region.

[0032] The "focal length" used in the conditional expression is the paraxial focal length. The value used in the conditional expression is the value when the d-line is used as the reference. Regarding the "distance on the optical axis" used in the conditional expression, unless otherwise specified, it is the geometric distance on the optical axis. In a system capable of adjusting the diopter, the value used in the conditional expression is set to the value in the state of -1 diopter. The "d-line", "C-line" and "F-line" described in this specification are bright lines, and the wavelength of the d-line is considered to be 587.56nm, the wavelength of the C-line is considered to be 656.27nm, and the wavelength of the F-line is considered to be 486.13nm. In this specification, "mm" means millimeter, "nm" means nanometer, and "μm" means micrometer.

[0033] Effects of the Invention

[0034] According to the present invention, it is possible to provide a finder optical system, a finder device, and an imaging device that are compact and do not increase the cost, and that enable good observation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The finder optical system corresponds to Example 1 and is a cross-sectional view showing the structure of the finder optical system and light beams according to one embodiment.

[0036] Figure 2 1 and 10 are diagrams showing various aberrations of the viewfinder optical system of Example 1.

[0037] Figure 3 It is a cross-sectional view showing the structure of the finder optical system and light beams of Example 2.

[0038] Figure 4 1 and 10 are diagrams showing various aberrations of the viewfinder optical system of Example 2.

[0039] Figure 5 It is a cross-sectional view showing the structure of the viewfinder optical system and light beams of Example 3.

[0040] Figure 6 1 and 10 are diagrams showing various aberrations of the viewfinder optical system of Example 3.

[0041] Figure 7 It is a cross-sectional view showing the structure of the viewfinder optical system and light beams of Example 4.

[0042] Figure 8 1 and 10 are diagrams showing various aberrations of the viewfinder optical system of Example 4.

[0043] Fig. 9 It is a cross-sectional view showing the structure of the viewfinder optical system and light beams of Example 5.

[0044] Fig.10 1 and 10 are diagrams showing various aberrations of the viewfinder optical system of Example 5.

[0045] Fig.11 It is a cross-sectional view showing the structure of the viewfinder optical system and light beams of Example 6.

[0046] Fig.12 1 and 10 are diagrams showing various aberrations of the viewfinder optical system of Example 6.

[0047] Fig.13 It is a cross-sectional view showing the structure of the viewfinder optical system and light beams of Example 7.

[0048] Fig.14 1 and 10 are diagrams showing various aberrations of the viewfinder optical system of Example 7.

[0049] Fig.15 It is a cross-sectional view showing the structure of the viewfinder optical system and light beams of Example 8.

[0050] Fig.16 These are diagrams showing various aberrations of the viewfinder optical system of Example 8.

[0051] Fig.17 This is a diagram schematically showing the structure of an example of a liquid crystal diffraction element.

[0052] Fig.18 yes Fig.17 A plan view schematically showing the optically anisotropic layer of the liquid crystal diffraction element shown.

[0053] Fig.19 Yes means Fig.17 A conceptual diagram showing the effect of the optically anisotropic layer of the liquid crystal diffraction element.

[0054] Fig. 20 Yes means Fig.17 A conceptual diagram showing the effect of the optically anisotropic layer of the liquid crystal diffraction element.

[0055] Fig.21 This is a schematic structural diagram of an example of an exposure device for exposing an alignment film.

[0056] Fig. 22 This is a diagram schematically showing the structure of another example of a liquid crystal diffraction element.

[0057] Fig.23 Yes means Fig. 22 A conceptual diagram showing the effect of the optically anisotropic layer of the liquid crystal diffraction element.

[0058] Fig.24 It is a schematic plan view of a liquid crystal diffraction element according to one embodiment.

[0059] Fig.25 This is a schematic structural diagram of a viewfinder device and an imaging device according to an embodiment. DETAILED DESCRIPTION

[0060] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0061] In this specification, the numerical range expressed by "to" means a range including the numerical values ​​recorded before and after "to" as the lower limit and the upper limit. In addition, in this specification, "orthogonal" and "parallel" with respect to angles include the error range generally allowed in the technical field.

[0062] Figure 1 2 shows a structure of a finder optical system 5 and a cross-sectional view of a light beam according to an embodiment of the present invention. Figure 1 The example shown corresponds to Embodiment 1 described later. Figure 1 In FIG. 1 , as light beams, an on-axis light beam and an off-axis light beam corresponding to the maximum diagonal viewing angle are shown. Figure 1 , the left side is set as the display element side and the right side is set as the viewpoint side. Figure 1 The viewpoint EP does not indicate the shape but the position in the direction of the optical axis.

[0063] The viewfinder optical system 5 includes a display element 1 and an eyepiece optical system 3 disposed on the viewpoint side of the display element 1. The display element 1 is an element that displays an image. The display element 1 includes a display surface 1a that displays an image and a cover member 1b that is a parallel plate-shaped optical element having no optical power. Figure 1 In the example of FIG. 1 , the display surface 1a is located on the display element side of the cover member 1b. The display element 1 can be configured as an image display panel composed of a liquid crystal display element or an organic EL (organic electroluminescence) display element. The display element 1 and the eyepiece optical system 3 are arranged with a predetermined air gap therebetween.

[0064] When the distance between the display element 1 and the eyepiece optical system 3 changes when adjusting the diopter, it is easy to ensure the diopter adjustment distance by providing the air space.

[0065] The display element 1 is an example of an observation object. The eyepiece optical system 3 is used to observe an image displayed on the display surface 1 a of the display element 1. That is, the finder optical system 5 is configured to observe the image displayed on the display element 1 via the eyepiece optical system 3.

[0066] As an example, Figure 1The eyepiece optical system 3 includes, from the display element side to the viewpoint side, a lens G1 with positive power, a lens G2 with negative power, a lens G3 with positive power, a lens G4 with positive power, a lens G5 with negative power, and a cover member C1. The cover member C1 is a parallel plate-shaped optical element having no power.

[0067] The eyepiece optical system 3 preferably includes two or more positive lenses and one or more negative lenses. In this case, it is advantageous to correct chromatic aberration while achieving miniaturization.

[0068] The eyepiece optical system 3 preferably includes more than two aspheric lenses. In this case, it is conducive to good aberration correction. The eyepiece optical system 3 can be configured to include more than two aspheric lenses and more than one spherical lens. In this case, it is conducive to achieving low cost while performing good aberration correction.

[0069] One or more diffraction elements are arranged in the viewfinder optical system 5. The diffraction element mentioned here is a kind of optical element, which is the same as the so-called diffraction optical element, but is referred to as a diffraction element in this specification. The diffraction element has a negative dispersion value and a large abnormal dispersion, so a large chromatic aberration correction effect can be obtained. By using a diffraction element, the burden of aberration correction of other lenses can be reduced, so it is beneficial to take into account both miniaturization and high performance.

[0070] At least one of the diffraction elements is configured as a first diffraction element DOE1 including a liquid crystal diffraction element. Figure 1 In the example of , the first diffraction element DOE1 is provided on the surface of the display element side of the lens G4. In order to simplify the structure, the first diffraction element DOE1 can be configured to include a liquid crystal diffraction element. The liquid crystal diffraction element is configured to include an optical anisotropic layer, the optical anisotropic layer is formed using a liquid crystal composition containing a liquid crystal compound, and has a liquid crystal orientation pattern in which the direction of the optical axis of the liquid crystal compound continuously rotates and changes along at least one direction in the plane.

[0071] The detailed structure of the liquid crystal diffraction element will be described later.

[0072] The optical surface of the liquid crystal diffraction element can be set to a surface shape without a physical step difference shape, and can be configured as a plane or a curved surface. Therefore, similarly, the optical surface of the first diffraction element DOE1 can also be configured as a plane or a curved surface without a physical step difference shape. In the relief-type diffraction optical surface with a physical step difference shape, the light scattered due to the step difference may become a light spot and reduce the resolution, but the optical surface of the liquid crystal diffraction element can eliminate this concern. In addition, the close-fitting multi-layer diffraction optical element requires technically high and expensive processing, but this processing is not required in the liquid crystal diffraction element. In addition, the liquid crystal diffraction element also has the advantage of being able to perform control that matches the polarization state of light.

[0073] The first diffraction element DOE1 is configured to satisfy the following conditional expression (1). Here, TL is the distance on the optical axis from the display surface 1a of the display element 1 to the surface closest to the viewpoint side of the viewfinder optical system 5. X1 is the distance on the optical axis from the display surface 1a of the display element 1 to the optical surface of the first diffraction element DOE1. In this specification, the optical surface of the diffraction element related to the conditional expression is the surface on the display element side and the viewpoint side of the diffraction element that is in contact with the air. As an example, in Figure 1 The distance TL and the distance X1 are shown in . By arranging the first diffraction element DOE1 within the range satisfying the conditional expression (1), it is possible to obtain a good chromatic aberration correction effect.

[0074] 0.05≤X1 / TL≤1 (1)

[0075] The viewfinder optical system 5 preferably satisfies the following conditional expression (2). Here, H is the half value of the longest diameter of the display area in the display element 1. f is the focal length of the viewfinder optical system 5. As an example, Figure 1 The half value H of the longest diameter of the display area is shown in FIG. By making the corresponding value of conditional expression (2) not less than the lower limit, it is advantageous to increase the magnification of the viewfinder. By making the corresponding value of conditional expression (2) not more than the upper limit, it is advantageous to miniaturize the viewfinder. In order to obtain better characteristics, the viewfinder optical system 5 preferably satisfies the following conditional expression (2-1), and further preferably satisfies the following conditional expression (2-2).

[0076] 0.3<H / f<0.7 (2)

[0077] 0.35<H / f<0.6 (2-1)

[0078] 0.4<H / f<0.5 (2-2)

[0079] In addition, the display area is the area where the image is actually displayed on the display surface 1a. For example, if the display element 1 has a display surface 1a with an aspect ratio of 4:3 and a plurality of pixels are arranged thereon, and an image with an aspect ratio of 3:2 is displayed on a part of the display surface 1a, the display area refers to the area where the image with an aspect ratio of 3:2 is displayed. Therefore, the diameter of the display element 1 and the longest diameter of the display area are not necessarily the same.

[0080] In this specification, "the longest diameter of the display area in the display element 1" related to H refers to a value of twice the distance between the point farthest from the optical axis Zk in the radial direction and the optical axis Zk in the display area whose center of gravity coincides with the optical axis Zk. For example, when the display area is a rectangle, the length of half the diagonal line of the display area can be set to H. Also, for example, when the display area is a perfect circle, the radius of the display area can be set to H, and when the display area is an ellipse, half of the longest diameter (long diameter) among the diameters of the display area can be set to H.

[0081] The finder optical system 5 preferably satisfies the following conditional expression (3): Here, dEP represents the distance on the optical axis from the surface of the finder optical system 5 closest to the viewpoint to the viewpoint EP.

[0082] As an example, in Figure 1 The distance dEP is shown in . When the viewpoint EP is not a single position but a range, dEP is set to be the distance on the optical axis from the surface of the viewfinder optical system 5 closest to the viewpoint to the point on the optical axis closest to the viewpoint within the range. f is the focal length of the viewfinder optical system 5. Regarding the lower limit of the conditional expression (3), since f>0 and dEP>0, it becomes f / dEP>0. By making the corresponding value of the conditional expression (3) not exceed the upper limit, it is beneficial to ensure a high viewfinder magnification and a long good viewing distance. In order to obtain better characteristics, the viewfinder optical system 5 preferably satisfies the following conditional expression (3-1), and further preferably satisfies the following conditional expression (3-2).

[0083] 0<f / dEP<0.95 (3)

[0084] 0<f / dEP<0.9 (3-1)

[0085] 0<f / dEP<0.85 (3-2)

[0086] in addition, Figure 1 The viewfinder optical system 5 of the present invention includes only one diffraction element, but the viewfinder optical system 5 of the present invention may also be configured to include a plurality of diffraction elements. For example, the viewfinder optical system 5 may be configured to include two or more first diffraction elements DEO1, in which case, it is advantageous for high performance.

[0087] In the case where the viewfinder optical system 5 of the present invention includes a plurality of diffraction elements, as described later, Fig.15 In the example shown, at least one of the plurality of diffraction elements can be configured as a second diffraction element DOE2 including a liquid crystal diffraction element. Furthermore, in order to simplify the structure, the second diffraction element DOE2 can be configured to include a liquid crystal diffraction element. As described above, the liquid crystal diffraction element has many advantages. Similar to the first diffraction element DOE1, the optical surface of the second diffraction element DOE2 can also be configured as a plane or a curved surface without a physical step difference shape.

[0088] The second diffraction element DOE2 is configured to satisfy the following conditional expression (4). Here, TL is the distance on the optical axis from the display surface 1a of the display element 1 to the surface closest to the viewpoint of the viewfinder optical system 5. X2 is the distance on the optical axis from the display surface 1a of the display element 1 to the optical surface of the second diffraction element DOE2. For example, Fig.15 In the example of , the distance on the optical axis from the display surface 1a of the display element 1 to the surface of the second diffraction element DOE2 on the viewpoint side corresponds to X2.

[0089] 0≤X2 / TL<0.05 (4)

[0090] By configuring the second diffraction element DOE2 within the range satisfying conditional formula (4), it is possible to effectively guide the light emitted from the peripheral portion of the display surface 1a away from the optical axis Zk to the viewpoint EP for observation. Thus, more peripheral light can be ensured, so a brighter image in the peripheral portion can be observed. In particular, in the viewfinder optical system 5 with a high viewfinder magnification and a long viewing distance, the light emitted from the peripheral portion of the display surface 1a tends to be shielded more, so it is effective to configure the second diffraction element DOE2 within the range satisfying conditional formula (4).

[0091] As described above, in order to guide the light emitted from the peripheral portion of the display surface 1a through the second diffraction element DOE2, it is preferably configured so that no element having optical power is arranged between the second diffraction element DOE2 and the display surface 1a of the display element 1. However, an element having no optical power, such as a parallel plate or a polarizing plate, may be arranged between the second diffraction element DOE2 and the display surface 1a of the display element 1.

[0092] When the viewfinder optical system 5 includes the second diffraction element DOE2, the sign of the phase difference function of the first diffraction element DOE1 is preferably different from the sign of the phase difference function of the second diffraction element DOE2. In this case, the first diffraction element DOE1 and the second diffraction element DOE2 can be configured in a manner that acts in a direction that cancels out the aberrations generated in the first diffraction element DOE1 and the second diffraction element DOE2, thereby facilitating the acquisition of higher optical performance in addition to the above-mentioned effects of each diffraction element.

[0093] In particular, in the entire effective diameter area of ​​the first diffraction element DOE1 and the entire effective diameter area of ​​the second diffraction element DOE2, it is preferred that the sign of the phase difference function of the first diffraction element DOE1 and the sign of the phase difference function of the second diffraction element DOE2 are different.

[0094] The diffraction element included in the viewfinder optical system 5 is preferably arranged on the surface of the optical element. As the optical element provided with the diffraction element, for example, a lens, a cover member, an optical filter, and a prism can be cited. The surface shape of the optical element provided with the diffraction element is preferably a plane or a curved surface. The "curved surface" mentioned here includes a spherical surface and an aspherical surface.

[0095] Usually, the thickness of the diffraction element in the optical axis direction is thin. In addition, it is also easy to set the diffraction element on the surface of the thin parallel flat plate-shaped optical element. As a result, compared with a general lens, the restrictions on the configuration of the diffraction element become loose, and in the system using the diffraction element, the degree of freedom of design becomes higher, which is conducive to miniaturization and high performance. In particular, when the main part of the diffraction element is a liquid crystal diffraction element, there is no concern related to the above-mentioned spot, so other optical elements can be configured near the diffraction element, which is conducive to further miniaturization.

[0096] It can be configured that, in an optical element provided with a diffractive element, a lens having optical power is disposed adjacent to the optical element on at least one of the object side and the image side of at least one optical element. In this structure, the minimum interval Dmin in the optical axis direction of the optical surface of the diffractive element disposed on the surface of the optical element and the optical surface of the lens disposed adjacent to the optical element can be set to a very small value, for example, it can also be set to less than 1.8mm. In order to achieve miniaturization, the above-mentioned minimum interval Dmin is preferably less than 0.5mm. In addition, the above-mentioned minimum interval Dmin is not necessarily limited to the interval on the optical axis, as long as it is the interval of the surface within the effective diameter of each element, for example, it can be the interval of the peripheral portion away from the optical axis Zk. That is, not only on the optical axis, but also in the peripheral portion away from the optical axis, a lens can be disposed in the very near vicinity of the optical element provided with a diffractive element.

[0097] Furthermore, in the optical element provided with the diffraction element, a lens having optical power may be arranged on both the object side and the image side of at least one optical element. Figure 1 In the example of FIG. 1 , lens G3 and lens G5 are respectively arranged on the object side and image side of lens G4, an optical element provided with the first diffraction element DOE1. In the viewfinder optical system 5, in the optical element located at the position where lenses having optical power are arranged on both the object side and the image side, as shown in FIG. Figure 1 As shown, the on-axis beam and the off-axis beam are separated and the beams are expanded. By configuring the diffraction element at this position, aberration correction can be performed effectively, which is conducive to high performance.

[0098] In the case where the diffraction element is provided on the surface of the optical element, the Abbe number vd_op of the d-line reference of the optical element on which the diffraction element is provided is preferably greater than 35 and less than 100. In this case, since ordinary materials that are not special can be used, high costs can be prevented, and since materials with high transmittance can be selected, it is beneficial to observe a brighter image. In addition, in the case where the diffraction element is provided on the bonding surface of the bonding lens, the Abbe number of the d-line reference of the lenses on both sides of the bonding surface is preferably greater than 35 and less than 100.

[0099] When the diffraction element is disposed on the surface of the optical element, the transmittance Td_op of the d-line of the optical element on which the diffraction element is disposed is preferably 98% or more. In this case, it is beneficial to observe a brighter image. In addition, when the diffraction element is disposed on the bonding surface of a bonding lens, the transmittance of the d-line of the bonding lens is preferably 98% or more.

[0100] When the distance on the optical axis from the display surface 1a of the display element 1 to the optical element in the finder optical system 5 is X, the d-line transmittance Td_part of the partial optical system composed of all the optical elements arranged in the range of 0.05≤X / TL≤1 is preferably 92% or more.

[0101] In this case, it is beneficial to observe a brighter image.

[0102] As a measurement method of the said transmittance|permeability, the method of measuring using the spectrophotometer V-650 manufactured by JASCO Corporation is mentioned, for example.

[0103] The thickness of the diffraction element in the optical axis direction of the region with diffraction is preferably less than 10 μm. In this case, it is beneficial to have a higher transmittance, so it is beneficial to observe a brighter image. The thickness of the diffraction element in the optical axis direction of the region with diffraction can be measured using a scanning electron microscope (SEM).

[0104] All lenses having optical power included in the eyepiece optical system 3 may be configured as uncemented single lenses. In this case, the degree of freedom in design can be increased, which is advantageous for correction of various aberrations.

[0105] The number of lenses having optical power included in the finder optical system 5 is preferably 4 or 5. In this case, it is advantageous to correct overall aberrations well and to reduce the number of lenses and achieve a compact structure.

[0106] in addition, Figure 1 The example shown is an example, and various modifications can be made without departing from the technical spirit of the present invention. The number of lenses with optical power and the number of cover parts included in the eyepiece optical system of the present invention can be set to Figure 1 of different numbers of examples. For example, Figure 1 The lenses with optical power included in the eyepiece optical system 3 are 3 positive lenses and 2 negative lenses, but in the technology of the present invention, the lenses with optical power included in the eyepiece optical system can be configured as 3 positive lenses and 1 negative lens. In addition, the shape of the lens included in the eyepiece optical system can also be set to be different from Figure 1 Examples of different shapes.

[0107] Including the structure related to the conditional expression, the above-mentioned preferred structure and possible structure can be arbitrarily combined, and it is preferred to selectively adopt them appropriately according to the required specifications. In addition, it is preferred that the conditional expression satisfied by the viewfinder optical system 5 of the present invention is not limited to the conditional expression recorded in the form of the expression, and includes all conditional expressions obtained by arbitrarily combining the lower limit and the upper limit from the preferred, more preferred and further preferred conditional expressions.

[0108] As an example, a preferred mode of the viewfinder optical system 5 of the present invention comprises a display element 1 and an eyepiece optical system 3 arranged on the viewpoint side closer to the display element 1, and one or more diffraction elements are arranged in the viewfinder optical system 5, at least one of the diffraction elements is a first diffraction element DOE1 including a liquid crystal diffraction element, satisfying the above-mentioned conditional formula (1).

[0109] Next, an embodiment of the viewfinder optical system 5 of the present invention will be described with reference to the accompanying drawings. In addition, in order to avoid complicating the description and drawings due to the increase in the number of digits of the reference symbols, the reference symbols marked on the components of the cross-sectional views of each embodiment are used independently in each embodiment. Therefore, even if the same reference symbols are marked in the drawings of different embodiments, they are not necessarily the same structure.

[0110] [Example 1]

[0111] The structure of the viewfinder optical system 5 of Example 1 is shown in FIG. Figure 1 The diagram method and structure are as described above, so some repeated descriptions are omitted here.

[0112] The finder optical system 5 of Example 1 includes a display element 1 and an eyepiece optical system 3 in order from the display element side to the viewpoint side. The eyepiece optical system 3 includes five lenses, namely, lens G1 to lens G5, and a cover member C1 in order from the display element side to the viewpoint side. A first diffraction element DOE1 is provided on the surface of lens G4 on the display element side.

[0113] Regarding the finder optical system 5 of Example 1, basic lens data is shown in Table 1, specifications are shown in Table 2, aspheric surface coefficients are shown in Table 3, and phase difference coefficients are shown in Table 4.

[0114] Table 1 is as follows. In the Sn column, the surface numbers of the surfaces when the surface of the display element 1 equipped with the display surface 1a is set as the first surface and the numbers are increased one by one toward the viewpoint side. In the R column, the radius of curvature of each surface is shown. In the D column, the surface interval on the optical axis between each surface and the surface adjacent to the viewpoint side is shown. In the Nd column, the refractive index of each component relative to the d-line is shown. In the vd column, the Abbe number of each component based on the d-line is shown.

[0115] In Table 1, the viewpoint EP is also recorded, and the surface number and the term (EP) are recorded in the Sn column of the surface equivalent to the viewpoint EP. In Table 1, the sign of the curvature radius of the surface that makes the convex shape toward the display element side is set to positive, and the sign of the curvature radius of the surface that makes the convex shape toward the viewpoint side is set to negative. The surface number of the aspheric surface is marked with an * mark, and the column of the curvature radius of the aspheric surface records the numerical value of the curvature radius of the paraxial axis. In addition, in Table 1, the surface number of the surface corresponding to the diffraction element is marked with a ** mark.

[0116] Table 2 shows the focal length f of the finder optical system 5 , the diagonal viewing angle at the full viewing angle, and the half-value H of the longest diameter of the display area. The diagonal viewing angle refers to the viewing field in the diagonal direction of the rectangular field of view.

[0117] In Table 3, the Sn row shows the surface number of the aspherical surface, and the KA and Am rows show the numerical values ​​of the aspherical coefficients of each aspherical surface. m is an integer greater than 3, for example, in the aspherical surface of Example 1, m=3, 4, 5, ... 16. The "E±n" (n: integer) numerical values ​​of the aspherical coefficients in Table 3 mean "×10 ±n KA and Am are aspherical coefficients in the aspherical formula represented by the following formula.

[0118] Zd=C×h 2 / {1+(1-KA×C 2 ×h 2 ) 1 / 2}+∑Am×h m

[0119] in,

[0120] Zd: Aspheric surface depth (the length of the perpendicular line from a point on the aspheric surface at height h to a plane tangent to the aspheric surface vertex and perpendicular to the optical axis Zk)

[0121] h: Height (distance from the optical axis Zk to the aspherical surface)

[0122] C: The reciprocal of the paraxial radius of curvature

[0123] KA, Am: Aspheric coefficients

[0124] The aspherical ∑ means the sum related to m.

[0125] In Table 4, the Sn row shows the surface number of the surface corresponding to the diffraction element, and the Pj (j=2, 4, 6) row shows the phase difference coefficient value of each diffraction element. The phase difference coefficient value "E±n" (n: integer) in Table 4 means "×10 ±n ”. Pj is the phase difference coefficient in the phase difference function PH(h) expressed by the following formula.

[0126] PH(h)=∑Pj×h j

[0127] in,

[0128] Pj: Phase difference coefficient

[0129] h: Height (the distance from the optical axis Zk to the surface corresponding to the diffraction element)

[0130] The Σ of the phase difference function PH(h) represents the sum associated with j.

[0131] In the data of each table, degrees are used as the unit of angle and mm (millimeter) is used as the unit of length. However, since the optical system can be used regardless of the enlargement ratio or the reduction ratio, other appropriate units can also be used.

[0132] In addition, in each of the tables shown below, numerical values ​​rounded to a predetermined number of digits are described.

[0133] [Table 1]

[0134] Example 1

[0135] Sn R D Nd vd 1 ∞ 0.5000 1.51900 64.90 2 ∞ 3.8000 *3 -990.6320 5.9827 1.85135 40.10 *4 -10.1885 1.8394 *5 -14.7692 1.7972 1.63351 23.63 *6 17.8085 0.6430 7 -300.9022 6.8788 1.83481 42.74 8 -16.6167 0.3011 **9 70.1360 4.8856 1.85150 40.78 10 -31.6736 0.3000 *11 -24.4646 1.1625 1.63351 23.63 *12 -52.2275 1.7803 13 ∞ 0.8000 1.49023 57.50 14 ∞ 20.0000 15(EP) ∞

[0136] [Table 2]

[0137] Example 1

[0138] f 14.45 Diagonal viewing angle 46.76° H 6.35

[0139] [Table 3]

[0140] Example 1

[0141]

[0142] [Table 4]

[0143] Example 1

[0144] Sn 9 P2 -8.8865E+00 P4 -1.5920E-03 P6 -9.6550E-06

[0145] exist Figure 2 2 and 3 show various aberration diagrams of the finder optical system 5 according to Example 1. Figure 2 In the figure, spherical aberration, astigmatism, distortion aberration and lateral chromatic aberration are shown from the left. In the spherical aberration diagram, aberrations on the d-line, C-line and F-line are shown with solid lines, long dashed lines and short dashed lines, respectively. In the astigmatism diagram, aberrations on the d-line in the sagittal direction are shown with solid lines, and aberrations on the d-line in the tangential direction are shown with short dashed lines. In the distortion aberration diagram, aberrations on the d-line are shown with solid lines. In the lateral chromatic aberration diagram, aberrations on the C-line and F-line are shown with long dashed lines and short dashed lines, respectively. The unit "dpt" of the horizontal axis of the spherical aberration diagram and the astigmatism diagram represents the diopter.

[0146] The unit "min" on the horizontal axis of the magnification chromatic aberration diagram indicates the minute of the angle. In the spherical aberration diagram, the diameter of the viewpoint EP when the unit is set to mm (millimeter) is shown after "Φ=". In the other aberration diagrams, the value of the diagonal viewing angle at the half viewing angle is shown after "ω=".

[0147] Unless otherwise specified, the symbols, meanings and recording methods related to the above-mentioned Example 1 are the same as those of the following Examples, so repeated descriptions are omitted below.

[0148] [Example 2]

[0149] The structure and light beams of the viewfinder optical system 5 of Example 2 are shown in FIG. Figure 3 The viewfinder optical system 5 of Example 2 includes a display element 1 and an eyepiece optical system 3 in order from the display element side to the viewpoint side. The eyepiece optical system 3 includes a lens G1 with positive focal power, a lens G2 with negative focal power, a lens G3 with positive focal power, a lens G4 with positive focal power, a lens G5 with negative focal power, and a cover member C1 in order from the display element side to the viewpoint side. The cover member C1 is a parallel plate-shaped optical element having no focal power. A first diffraction element DOE1 is provided on the surface of the cover member C1 on the display element side.

[0150] Regarding the viewfinder optical system 5 of Example 2, basic lens data is shown in Table 5, specifications are shown in Table 6, aspheric coefficients are shown in Table 7, phase difference coefficients are shown in Table 8, and various aberration diagrams are shown in Table 9. Figure 4 .

[0151] [Table 5]

[0152] Example 2

[0153] Sn R D Nd vd 1 ∞ 0.5000 1.51900 64.90 2 ∞ 3.3294 *3 -126.9268 3.6755 1.85135 40.10 *4 -9.2552 1.6551 *5 -9.8701 1.8796 1.63351 23.63 *6 17.6814 0.7564 7 -436.0085 6.6939 1.80420 46.50 8 -15.8219 0.3000 9 62.4146 5.0360 1.88300 40.80 10 -31.3085 0.4744 *11 -27.6583 1.1625 1.63351 23.63 *12 -39.1784 1.5000 **13 ∞ 0.8000 1.49023 57.50 14 ∞ 22.0000 15(EP) ∞

[0154] [Table 6]

[0155] Example 2

[0156] f 14.47 Diagonal viewing angle 46.76° H 6.35

[0157] [Table 7]

[0158] Example 2

[0159]

[0160] [Table 8]

[0161] Example 2

[0162] Sn 13 P2 -1.5561E+01 P4 1.0588E-01 P6 -9.3460E-04

[0163] [Example 3]

[0164] The structure and light beams of the viewfinder optical system 5 of Example 3 are shown in FIG. Figure 5 The viewfinder optical system 5 of Example 3 includes a display element 1 and an eyepiece optical system 3 in order from the display element side to the viewpoint side. The eyepiece optical system 3 includes a lens G1 with positive refractive power, a lens G2 with negative refractive power, a lens G3 with positive refractive power, a lens G4 with positive refractive power, and a cover member C1 in order from the display element side to the viewpoint side. The cover member C1 is a parallel plate-shaped optical element having no refractive power.

[0165] A first diffraction element DOE1 is provided on the surface of the cover member C1 on the display element side.

[0166] Regarding the viewfinder optical system 5 of Example 3, basic lens data is shown in Table 9, specifications are shown in Table 10, aspheric coefficients are shown in Table 11, phase difference coefficients are shown in Table 12, and various aberration diagrams are shown in Table 13. Figure 6 .

[0167] [Table 9]

[0168] Example 3

[0169] Sn R D Nd vd 1 ∞ 0.5000 1.51900 64.90 2 ∞ 4.1600 *3 -498.7025 4.9841 1.85135 40.10 *4 -9.6281 1.5139 *5 -10.4986 1.4564 1.63351 23.63 *6 20.2260 1.0485 7 -204.3388 6.2115 1.80420 46.50 8 -14.1852 0.3000 9 -244.9143 2.8305 1.81600 46.62 10 -31.4516 1.5000 **11 ∞ 0.8000 1.49023 57.50 12 ∞ 18.0000 13 (EP) ∞

[0170] [Table 10]

[0171] Example 3

[0172] f 14.57 Diagonal viewing angle 46.76° H 6.35

[0173] [Table 11]

[0174] Example 3

[0175] Sn 3 4 5 6 KA 1.0000000E+00 1.0000000E+00 1.0000000E+00 1.0000000E+00 A3 0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00 A4 -5.9399148E-04 -6.6567358E-04 -9.4138410E-04 -2.7859338E-04 A5 -2.8124923E-04 5.7132628E-05 1.8590678E-04 -1.1640688E-05 A6 7.9580182E-05 3.8010429E-05 3.2589632E-05 2.1689886E-06 A7 7.9109437E-06 -1.3015492E-06 -2.7025337E-06 1.0398784E-07 A8 -3.1803839E-06 -1.0338175E-06 -1.5632164E-06 -1.2000773E-08 A9 -1.2539625E-07 1.3927962E-09 -2.8480377E-08 -4.3427104E-10 A10 6.2726166E-08 1.7902590E-08 4.4876560E-08 4.4752133E-11 A11 1.0733741E-09 6.6255245E-11 9.5143737E-10 9.4929632E-13 A12 -6.6313895E-10 -1.6949801E-10 -6.6375324E-10 -9.1276391E-14 A13 -4.3584734E-12 -3.2045932E-14 -8.1386213E-12 -1.0525015E-15 A14 3.5834063E-12 7.8687496E-13 4.6352901E-12 8.0832033E-17 A15 6.2626926E-15 -1.5256601E-15 2.3519619E-14 4.6218898E-19 A16 -7.7739216E-15 -1.3801180E-15 -1.2049946E-14 -1.5136413E-20

[0176] [Table 12]

[0177] Example 3

[0178] Sn 11 P2 -1.1291E+01 P4 1.8212E-02 P6 -5.3489E-05

[0179] [Example 4]

[0180] The structure and light beams of the viewfinder optical system 5 of Example 4 are shown in FIG. Figure 7 . The viewfinder optical system 5 of Example 4 includes a display element 1 and an eyepiece optical system 3 in order from the display element side to the viewpoint side. The eyepiece optical system 3 includes a cover member C1, a lens G1 with positive focal power, a lens G2 with negative focal power, a lens G3 with positive focal power, a lens G4 with negative focal power, a lens G5 with positive focal power, and a cover member C2 in order from the display element side to the viewpoint side. The cover member C1 and the cover member C2 are parallel plate-shaped optical elements having no focal power. A first diffraction element DOE1 is provided on the surface of the cover member C1 on the display element side.

[0181] Regarding the viewfinder optical system 5 of Example 4, basic lens data is shown in Table 13, specifications are shown in Table 14, phase difference coefficients are shown in Table 15, and various aberration diagrams are shown in Table 16. Figure 8 middle.

[0182] [Table 13]

[0183] Example 4

[0184] Sn R D Nd vd 1 ∞ 0.5000 1.51900 64.90 2 ∞ 2.3000 **3 ∞ 0.5000 1.51900 64.90 4 ∞ 1.5002 5 1832.6599 6.2712 2.00100 29.13 6 -17.4617 2.2258 7 -10.3093 1.6692 1.63351 23.63 8 32.1562 0.2680 9 36.4438 7.0000 1.91082 35.25 10 -19.5459 0.2000 11 53.3806 1.0000 1.63351 23.63 12 20.8509 1.1526 13 38.4982 3.5854 1.80420 46.50 14 -41.0527 1.5000 15 ∞ 0.8000 1.49023 57.50 16 ∞ 17.0000 17 (EP) ∞

[0185] [Table 14]

[0186] Example 4

[0187] f 14.89 Diagonal viewing angle 46.74° H 6.35

[0188] [Table 15]

[0189] Example 4

[0190] Sn 3 P2 -1.3795E+02 P4 1.6385E+00 P6 -1.3118E-02

[0191] [Example 5]

[0192] The structure and light beams of the viewfinder optical system 5 of Example 5 are shown in FIG. Fig. 9 . The viewfinder optical system 5 of Example 5 includes a display element 1 and an eyepiece optical system 3 in order from the display element side to the viewpoint side. The eyepiece optical system 3 includes a lens G1 with positive focal power, a lens G2 with negative focal power, a cover member C1, a lens G3 with positive focal power, a lens G4 with positive focal power, a lens G5 with negative focal power, and a cover member C2 in order from the display element side to the viewpoint side. The cover member C1 and the cover member C2 are parallel plate-shaped optical elements having no focal power. A first diffraction element DOE1 is provided on the surface of the cover member C1 on the display element side.

[0193] Regarding the viewfinder optical system 5 of Example 5, basic lens data is shown in Table 16, specifications are shown in Table 17, aspheric coefficients are shown in Table 18, phase difference coefficients are shown in Table 19, and various aberration diagrams are shown in Table 10. Fig.10 .

[0194] [Table 16]

[0195] Example 5

[0196] Sn R D Nd vd 1 ∞ 0.5000 1.51900 64.90 2 ∞ 3.5236 *3 26.6998 4.1921 1.85135 40.10 *4 -10.8697 1.5098 *5 -9.4129 2.0444 1.63351 23.63 *6 19.4343 1.3222 **7 ∞ 0.5000 1.51900 64.90 8 ∞ 0.5646 9 -873.0604 6.9901 1.83481 42.72 10 -17.2368 0.3935 11 48.5358 4.5813 1.88300 40.80 12 -36.3361 0.8508 *13 -30.6173 1.0563 1.63351 23.63 *14 -131.5374 1.7979 15 ∞ 0.8000 1.49023 57.50 16 ∞ 20.0000 17 (EP) ∞

[0197] [Table 17]

[0198] Example 5

[0199] f 14.50 Diagonal viewing angle 46.74° H 6.35

[0200] [Table 18]

[0201] Example 5

[0202]

[0203] [Table 19]

[0204] Example 5

[0205] Sn 7 P2 -1.7398E+01 P4 7.7702E-02 P6 -2.5648E-04

[0206] [Example 6]

[0207] The structure and light beams of the viewfinder optical system 5 of Example 6 are shown in FIG. Fig.11 The viewfinder optical system 5 of Example 6 includes a display element 1 and an eyepiece optical system 3 in order from the display element side to the viewpoint side. The eyepiece optical system 3 includes a cover member C1, a lens G1 having positive power, a lens G2 having negative power, a lens G3 having positive power, a lens G4 having positive power, a lens G5 having negative power, and a cover member C2 in order from the display element side to the viewpoint side.

[0208] The cover member C1 and the cover member C2 are parallel plate-shaped optical elements having no optical power. The viewfinder optical system 5 of Example 6 includes two first diffraction elements DOE1. The first diffraction elements DOE1 are provided on the display element side surface of the cover member C1 and the display element side surface of the cover member C2, respectively.

[0209] Regarding the viewfinder optical system 5 of Example 6, basic lens data is shown in Table 20, specifications are shown in Table 21, aspheric coefficients are shown in Table 22, phase difference coefficients are shown in Table 23, and various aberration diagrams are shown in Table 24. Fig.12 middle.

[0210] [Table 20]

[0211] Example 6

[0212] Sn R D Nd vd 1 ∞ 0.5000 1.51900 64.90 2 ∞ 2.3000 **3 ∞ 0.5000 1.51900 64.90 4 ∞ 1.6051 *5 34.7659 4.1764 1.85135 40.10 *6 -10.8415 1.6085 *7 -9.6977 1.9528 1.63351 23.63 *8 20.1585 1.2854 9 -209.9199 6.0381 1.83481 42.72 10 -16.8866 0.4132 11 58.0113 4.3365 1.90043 37.37 12 -33.1127 0.3000 *13 -35.7957 1.0645 1.63351 23.63 *14 -98.6523 1.5000 **15 ∞ 0.8000 1.49023 57.50 16 ∞ 19.0000 17 (EP) ∞

[0213] [Table 21]

[0214] Example 6

[0215] f 13.78 Diagonal viewing angle 46.74° H 6.35

[0216] [Table 22]

[0217] Example 6

[0218]

[0219] [Table 23]

[0220] Example 6

[0221] Sn 3 15 P2 -7.2415E+01 -7.5911E+00 P4 1.0934E+00 6.3242E-02 P6 -1.0466E-02 -5.8068E-04

[0222] [Example 7]

[0223] The structure and light beams of the viewfinder optical system 5 of Example 7 are shown in FIG. Fig.13 The viewfinder optical system 5 of Example 7 includes a display element 1 and an eyepiece optical system 3 in order from the display element side to the viewpoint side. The eyepiece optical system 3 includes a lens G1 with positive refractive power, a lens G2 with negative refractive power, a lens G3 with positive refractive power, a lens G4 with positive refractive power, a lens G5 with negative refractive power, and a cover member C1 in order from the display element side to the viewpoint side.

[0224] The cover member C1 is a parallel plate-shaped optical element having no optical power. The viewfinder optical system 5 of Example 7 includes a first diffraction element DOE1 and a second diffraction element DOE2. The first diffraction element DOE1 is provided on the surface of the cover member C1 on the display element side. The second diffraction element DOE2 is provided on the surface of the cover member 1b on the display element side included in the display element 1. That is, in the viewfinder optical system 5 of Example 7, the display surface 1a of the display element 1 and the second diffraction element DOE2 are located at the same position in the optical axis direction.

[0225] Regarding the viewfinder optical system 5 of Example 7, basic lens data is shown in Table 24, specifications are shown in Table 25, aspheric coefficients are shown in Table 26, phase difference coefficients are shown in Table 27, and various aberration diagrams are shown in Table 28. Fig.14 middle.

[0226] [Table 24]

[0227] Example 7

[0228] Sn R D Nd vd **1 ∞ 0.5000 1.51900 64.90 2 ∞ 3.3269 *3 -451.8028 4.3768 1.85135 40.10 *4 -9.3270 1.1725 *5 -10.2753 1.9211 1.63351 23.63 *6 17.8022 0.7577 7 -337.4437 6.9426 1.77250 49.60 8 -15.9370 0.3000 9 61.4077 5.5436 1.87070 40.73 10 -30.9223 0.4824 *11 -26.8635 1.1625 1.63351 23.63 *12 -40.4102 1.6000 **13 ∞ 0.8000 1.49023 57.50 14 ∞ 22.2000 15(EP) ∞

[0229] [Table 25]

[0230] Example 7

[0231] f 14.55 Diagonal viewing angle 46.74° H 6.35

[0232] [Table 26]

[0233] Example 7

[0234]

[0235] [Table 27]

[0236] Example 7

[0237] Sn 1 13 P2 1.8321E+02 -1.2455E+01 P4 -2.8747E+00 8.3989E-02 P6 3.0351E-02 -8.6054E-04

[0238] [Example 8]

[0239] The structure and light beams of the viewfinder optical system 5 of Example 8 are shown in FIG. Fig.15 The viewfinder optical system 5 of Example 8 includes a display element 1 and an eyepiece optical system 3 in order from the display element side to the viewpoint side. The eyepiece optical system 3 includes a lens G1 with positive refractive power, a lens G2 with negative refractive power, a lens G3 with positive refractive power, a lens G4 with positive refractive power, a lens G5 with negative refractive power, and a cover member C1 in order from the display element side to the viewpoint side.

[0240] The cover member C1 is a parallel plate-shaped optical element having no optical power. The viewfinder optical system 5 of Example 8 includes a first diffraction element DOE1 and a second diffraction element DOE2. The first diffraction element DOE1 is provided on the surface of the cover member C1 on the display element side. The second diffraction element DOE2 is provided on the surface of the cover member 1b included in the display element 1 on the viewpoint side.

[0241] Regarding the viewfinder optical system 5 of Example 8, basic lens data is shown in Table 28, specifications are shown in Table 29, aspheric coefficients are shown in Table 30, phase difference coefficients are shown in Table 31, and various aberration diagrams are shown in Table 32. Fig.16 middle.

[0242] [Table 28]

[0243] Example 8

[0244] Sn R D Nd vd 1 ∞ 0.5000 1.51900 64.90 **2 ∞ 3.3285 *3 -351.2013 4.3859 1.85135 40.10 *4 -9.3312 1.1120 *5 -10.2891 1.9274 1.63351 23.63 *6 17.8215 0.7606 7 -323.9691 6.9593 1.77250 49.60 8 -15.9476 0.3000 9 61.3593 5.5423 1.87070 40.73 10 -30.8964 0.5261 *11 -26.8465 1.1625 1.63351 23.63 *12 -40.4660 1.6000 **13 ∞ 0.8000 1.49023 57.50 14 ∞ 22.2000 15(EP) ∞

[0245] [Table 29]

[0246] Example 8

[0247] f 14.45 Diagonal viewing angle 46.76° H 6.35

[0248] [Table 30]

[0249] Example 8

[0250]

[0251] [Table 31]

[0252] Example 8

[0253] Sn 2 13 P2 1.9964E-06 -1.2529E+01 P4 9.6154E-01 7.3074E-02 P6 1.1887E-02 -8.7394E-04

[0254] Table 32 shows the corresponding values ​​of conditional expressions (1) to (4) of the viewfinder optical system 5 of Examples 1 to 8. The values ​​shown in Table 32 are values ​​when the d-line is used as a reference. Table 33 shows the various values ​​described in the description of the above-mentioned preferred structure of the viewfinder optical system 5 of Examples 1 to 8. The "minimum spacing on the optical axis" in Table 33 is the minimum spacing on the optical axis between the optical surface of the lens arranged adjacent to the optical element on which the diffraction element is provided and the optical surface of the diffraction element. The "minimum spacing at the periphery" in Table 33 is the minimum spacing in the optical axis direction at the periphery between the optical surface of the lens arranged adjacent to the optical element on which the diffraction element is provided and the optical surface of the diffraction element.

[0255] The units of “minimum interval on the optical axis” and “minimum interval at the periphery” in Table 33 are mm.

[0256] [Table 32]

[0257]

[0258] [Table 33]

[0259]

[0260] The viewfinder optical system 5 of Examples 1 to 8 is compact, and various aberrations are well corrected to achieve high optical performance. In addition, the diagonal viewing angle of the viewfinder optical system 5 of Examples 1 to 8 is 45° or more in the full viewing angle, thereby ensuring a wide field of view. In addition, in the viewfinder optical system 5 of Examples 1 to 8, the focal length of the viewfinder optical system 5 is 15 mm or less, thereby achieving a high viewfinder magnification.

[0261] Next, refer to Figures 17 to 24 , the liquid crystal diffraction element involved in the technology of the present invention is described. Figures 17 to 24 In the drawings, the scale of the components is appropriately different from the actual scale for easy visual recognition. Fig.17 1 is a diagram schematically showing a stacked structure of the liquid crystal diffraction element 10 as an example. Fig.18 It is schematically indicated Fig.17 The plan view of the liquid crystal orientation pattern of the liquid crystal diffraction element 10 shown in FIG. The liquid crystal diffraction element 10 is in the form of a sheet. Fig.17 and Fig.18 In the orthogonal coordinate system using the x-axis, y-axis, and z-axis that are orthogonal to each other, the sheet surface of the liquid crystal diffraction element 10 is set as the xy plane, and the thickness direction is set as the direction of the z-axis.

[0262] The liquid crystal diffraction element 10 includes a support 20, an alignment film 24, and an optically anisotropic layer 26. Fig.17 In the liquid crystal diffraction element 10 , an alignment film 24 is formed on the surface of a support 20 , and an optically anisotropic layer 26 is formed on the surface of the alignment film 24 .

[0263] First, the optically anisotropic layer 26 will be described. The optically anisotropic layer 26 is formed using a composition containing a liquid crystal compound 30, and has a structure in which the liquid crystal compound 30 is stacked and aligned in the same manner as a conventional optically anisotropic layer formed using a composition containing a liquid crystal compound. Fig.17 and Fig.18 In the example, the direction of the z axis is the stacking direction of the liquid crystal compound 30 and is a direction perpendicular to the optical surface of the liquid crystal diffraction element 10 .

[0264] exist Fig.18 In the schematic plan view of the liquid crystal diffraction element 10 shown in FIG. 1 , only the liquid crystal compound 30 on the surface of the alignment film 24 is schematically shown in order to clearly show the structure of the liquid crystal diffraction element 10. Fig.18As shown, the optical anisotropic layer 26 has a liquid crystal orientation pattern in which the direction of the optical axis 30A originating from the liquid crystal compound 30 changes while continuously rotating in one direction within the surface of the optical anisotropic layer 26. Here, one direction in which the optical axis 30A is rotated and changed is consistent with the direction of the x-axis in the xy plane. In the following description of the liquid crystal diffraction element 10, one direction in which the optical axis 30A is rotated and changed is described as the x-direction. In addition, in the following description, the direction of the y-axis is also referred to as the y-direction, and the direction of the z-axis is also referred to as the z-direction.

[0265] The optical axis 30A from the liquid crystal compound 30 is an axis where the refractive index in the liquid crystal compound 30 becomes the highest, which is a so-called slow axis. Fig.17 As shown, when the liquid crystal compound 30 is a rod-shaped liquid crystal compound, the optical axis 30A is along the long axis direction of the rod shape. In the following description, the optical axis 30A derived from the liquid crystal compound 30 is also referred to as the optical axis 30A of the liquid crystal compound 30 or simply the optical axis 30A.

[0266] The orientation of the optical axis 30A changes while continuously rotating in the x direction. Specifically, the angle formed by the optical axis 30A of the liquid crystal compound 30 arranged along the x direction and the x direction gradually changes from θ to θ+180° or θ-180° along the x direction according to the position in the x direction. Here, "gradually changing angle" can change at a constant angle interval or can change continuously. Among them, the difference in the angle of the optical axis 30A of the liquid crystal compound 30 adjacent to each other in the x direction is preferably 45° or less, more preferably 15° or less, and further preferably a smaller angle.

[0267] On the other hand, in the y direction orthogonal to the x direction, the liquid crystal compounds 30 with the same optical axis 30A are arranged at equal intervals. In other words, among the liquid crystal compounds 30 forming the optically anisotropic layer 26, the angles between the optical axis 30A and the x direction are equal among the liquid crystal compounds 30 arranged in the y direction.

[0268] In the liquid crystal diffraction element 10 having such a liquid crystal orientation pattern of the liquid crystal compound 30, the length (distance) of rotating the optical axis 30A of the liquid crystal compound 30 in the x direction by 180° is also referred to as one period Λ in the liquid crystal orientation pattern, one period Λ of the liquid crystal orientation pattern, or simply one period Λ. In other words, the length of one period in the liquid crystal orientation pattern is defined by the distance from the angle between the optical axis 30A of the liquid crystal compound 30 and the x direction to θ to θ+180°. Specifically, Fig.18As shown, the distance between the centers of two liquid crystal compounds 30 in the x direction coinciding with the direction of the optical axis 30A is set to one period Λ. In the liquid crystal diffraction element 10, the liquid crystal orientation pattern of the optical anisotropic layer 26 is a pattern in which the liquid crystal orientation of one period Λ is repeated in the x direction.

[0269] As described above, in the optically anisotropic layer 26, the liquid crystal compounds 30 arranged in the y direction have the same angle between the optical axis 30A and the x direction. The region R is where the liquid crystal compounds 30 arranged in the y direction have the same angle between the optical axis 30A and the x direction.

[0270] In this case, the value of the in-plane retardation Re in each region R is preferably half the wavelength of the light (hereinafter referred to as the object light) to be diffracted by the liquid crystal diffraction element 10. That is, when the wavelength of the object light is λ, the in-plane retardation Re is preferably λ / 2. This is because the closer the value of the in-plane retardation is to the half wavelength of the object light, the higher the diffraction efficiency can be obtained in the diffraction of the object light.

[0271] The in-plane retardation Re is calculated by the product of the refractive index difference Δn associated with the refractive index anisotropy of the region R and the thickness of the optical anisotropic layer 26. The refractive index difference associated with the refractive index anisotropy of the region R is a refractive index difference defined by the difference between the refractive index in the direction of the slow axis in the plane of the region R and the refractive index in the direction perpendicular to the direction of the slow axis. That is, the refractive index difference Δn associated with the refractive index anisotropy of the region R is equal to the difference between the refractive index of the liquid crystal compound 30 in the direction of the optical axis 30A and the refractive index of the liquid crystal compound 30 in the direction perpendicular to the optical axis 30A in the plane of the region R. That is, the refractive index difference Δn depends on the liquid crystal compound 30, and the in-plane retardation Re of each region R is substantially the same.

[0272] Let the in-plane retardation at wavelength λ be Re(λ), and the refractive index difference associated with the refractive index anisotropy at wavelength λ be Δn λ When the thickness of the optical anisotropic layer 26 is d, the in-plane retardation Re(λ) of the optical anisotropic layer 26 with respect to incident light of wavelength λ nm is Re(λ)=Δn λ ×d indicates.

[0273] In this case, the in-plane retardation Re (λ) of the optically anisotropic layer 26 is preferably within the range defined by the following formula and can be appropriately set.

[0274] 0.7×(λ / 2)nm≤Δn λ ×d≤1.3×(λ / 2)nm

[0275] Re(λ) is obtained by measuring at a wavelength λ using, for example, AxoScan (manufactured by Axometrics). The slow axis direction (°) Re(λ)=R0(λ) is calculated by inputting the average refractive index and film thickness into AxoScan.

[0276] The unit of film thickness is μm. When the refractive indexes in the x-direction, y-direction, and z-direction are nx, ny, and nz, respectively, the average refractive index is represented by ((nx+ny+nz) / 3). In addition, R0(λ) is represented by a value calculated by AxoScan, which refers to Re(λ).

[0277] When the in-plane retardation value is set to λ / 2, the optical anisotropic layer 26 has a function as a normal half-wave plate. That is, when the in-plane retardation value is set to λ / 2, the optical anisotropic layer 26 has a function of imparting a phase difference of half a wavelength, that is, 180°, to two linear polarization light components orthogonal to each other included in the light incident on the optical anisotropic layer 26. In addition, it is the optical anisotropic layer 26 that functions as the half-wave plate, but the present invention also includes a mode in which a laminate integrally provided with the support 20 and the orientation film 24 functions as a half-wave plate.

[0278] When circularly polarized light is incident on the optically anisotropic layer 26 as described above, the light changes its traveling direction due to diffraction, that is, it is deflected due to diffraction, and the rotation direction of the circularly polarized light is changed. Fig.19 and Fig. 20 The optical anisotropic layer 26 is exemplified and conceptually represented in FIG. As described above, the optical anisotropic layer 26 has a structure in which the aligned liquid crystal compounds 30 are stacked. Fig.19 and Fig. 20 In the figure, for ease of understanding, the drawing is simplified, and only the liquid crystal compound 30 on the surface of the alignment film 24 in the optically anisotropic layer 26 is shown.

[0279] Fig.19 and Fig. 20 The in-plane retardation of the optically anisotropic layer 26 is set to λ / 2.

[0280] In this case, if Fig.19 As shown, when left circularly polarized light P is incident on the optical anisotropic layer 26, L That is, when the incident light L1 passes through the optical anisotropic layer 26, the incident light L1 is given a phase difference of 180°, so that the transmitted light L2 is converted into right circularly polarized light P R .

[0281] Furthermore, when the incident light L1 passes through the optical anisotropic layer 26 , the absolute phase thereof changes according to the direction of the optical axis 30A of each liquid crystal compound 30 .

[0282] At this time, since the direction of the optical axis 30A changes while rotating in the x direction, the amount of change in the absolute phase of the incident light L1 differs depending on the direction of the optical axis 30A.

[0283] In addition, since the liquid crystal orientation pattern formed in the optically anisotropic layer 26 is a periodic pattern in the x direction, Fig.19 As shown, a periodic absolute phase Q1 in the x direction corresponding to the orientation of each optical axis 30A is given to the incident light L1 that has passed through the optical anisotropic layer 26 .

[0284] As a result, an equiphase surface E1 inclined in the direction opposite to the x direction is formed.

[0285] Therefore, the transmitted light L2 is deflected so as to be inclined in a direction perpendicular to the equal phase plane E1 , and travels in a direction different from the travel direction of the incident light L1 .

[0286] Thus, the left circularly polarized light P L The incident light L1 is converted into right circularly polarized light P which is tilted by a predetermined angle in the x direction relative to the incident direction. R The transmitted light L2.

[0287] On the other hand, Fig. 20 As schematically shown in FIG. 1 , when right circularly polarized light P is incident on the optical anisotropic layer 26 having the same in-plane retardation R When the incident light L4 passes through the optical anisotropic layer 26, the incident light L4 is given a phase difference of 180° and converted into left circularly polarized light P L The transmitted light L5.

[0288] Furthermore, when the incident light L4 passes through the optical anisotropic layer 26 , the absolute phase thereof changes according to the direction of the optical axis 30A of each liquid crystal compound 30 .

[0289] At this time, since the direction of the optical axis 30A changes while rotating in the x direction, the amount of change in the absolute phase of the incident light L4 differs depending on the direction of the optical axis 30A.

[0290] In addition, since the liquid crystal orientation pattern formed in the optically anisotropic layer 26 is a periodic pattern in the x direction, Fig. 20 As shown, the incident light L4 passing through the optical anisotropic layer 26 is provided with a periodic absolute phase Q2 in the x direction corresponding to the orientation of each optical axis 30A.

[0291] Here, due to Fig. 20 The incident light L4 is right circularly polarized light P R, so the periodic absolute phase Q2 in the x direction corresponding to the orientation of the optical axis 30A is Fig.19 The left circularly polarized light P L The situation of the incident light L1 is the opposite.

[0292] As a result, an equal phase surface E2 inclined in the x direction opposite to the case of the incident light L1 is formed in the incident light L4.

[0293] Therefore, the transmitted light L5 is deflected in a manner inclined toward a direction perpendicular to the equal phase plane E2, and travels in a direction different from the travel direction of the incident light L4.

[0294] Thus, right circularly polarized light P R The incident light L4 is converted into left circularly polarized light P which is tilted by a predetermined angle in the direction opposite to the x direction relative to the incident direction. L The transmitted light L5.

[0295] Here, the deflection angle (diffraction angle) of the transmitted light L2 and the transmitted light L5 can be adjusted by changing one period Λ of the liquid crystal orientation pattern formed in the optical anisotropic layer 26. Specifically, the shorter one period Λ of the liquid crystal orientation pattern is, the stronger the interference between the lights passing through the adjacent liquid crystal compounds 30 is, so the transmitted light L2 and the transmitted light L5 can be deflected more. In addition, by setting the rotation direction of the optical axis 30A of the liquid crystal compound 30 rotating along the x direction to the opposite direction, the deflection direction of the transmitted light can be set to the opposite direction.

[0296] In the above example, the liquid crystal compound 30 is a rod-shaped liquid crystal compound, but the type of liquid crystal compound contained in the optically anisotropic layer is not particularly limited, and it may be a disc-shaped liquid crystal compound. In addition, two or more rod-shaped liquid crystal compounds, two or more disc-shaped liquid crystal compounds, or a mixture of a rod-shaped liquid crystal compound and a disc-shaped liquid crystal compound may be used.

[0297] The optically anisotropic layer may further contain other components such as a leveling agent, an alignment control agent, a polymerization initiator, and an alignment aid.

[0298] As the rod-like liquid crystal compound, preferably used are azomethines, azoxyls, cyanobiphenyls, cyanophenyl esters, benzoates, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolans and alkenylcyclohexylbenzonitriles. Not only the above low molecular weight liquid crystal molecules but also high molecular weight liquid crystal molecules can be used.

[0299] As the discotic liquid crystal compound, for example, the discotic liquid crystal compounds described in Japanese Patent Application Publication No. 2007-108732 and Japanese Patent Application Publication No. 2010-244038 can be preferably used. In addition, when the discotic liquid crystal compound is used for the optically anisotropic layer, the liquid crystal compound rises in the thickness direction in the optically anisotropic layer, and the optical axis derived from the liquid crystal compound is defined as an axis perpendicular to the disc surface, the so-called fast axis.

[0300] The optical anisotropic layer is preferably broadband with respect to the wavelength of incident light, and is preferably composed of a liquid crystal material with reverse dispersion of birefringence. Furthermore, it is also preferred that the optical anisotropic layer is substantially broadband with respect to the wavelength of incident light by imparting a twist component to the liquid crystal composition and by stacking different phase difference layers. For example, in an optical anisotropic layer, a method for realizing a broadband patterned 1 / 2 wave plate by stacking two layers of liquid crystals with different twist directions is shown in Japanese Patent Publication No. 2014-089476, etc., and this method can be used.

[0301] Next, the support 20 is described. The support 20 supports the orientation film 24 and the optical anisotropic layer 26. As long as the support 20 can support the orientation film 24 and the optical anisotropic layer 26, various sheet-like objects, such as films or plate-like objects, can be used. As the support 20, a transparent support is preferred, and polyacrylic resin films such as polymethyl methacrylate, cellulose resin films such as cellulose triacetate, cycloolefin polymer films (for example, ARTON (registered trademark) manufactured by JSR Corporation, ZEONOR (registered trademark) manufactured by Zeon Corporation), polyethylene terephthalate (PET), polycarbonate, and polyvinyl chloride can be cited. The support 20 is not limited to a flexible film, and can be a non-flexible substrate such as a glass substrate. In addition, the support 20 can be a multi-layer support, and as a multi-layer support, it includes any one of the above-mentioned supports as a substrate, and other layers of supports are provided on the surface of the substrate.

[0302] The thickness of the support 20 is not limited, and can be appropriately set to a thickness that can maintain the alignment film 24 and the optical anisotropic layer 26 according to the purpose of the liquid crystal diffraction element 10 and the material of the support 20. The thickness of the support 20 is preferably 1 to 1000 μm, more preferably 3 to 250 μm, and further preferably 5 to 150 μm.

[0303] Next, the orientation film 24 is described. The orientation film 24 is a film used to orient the liquid crystal compound 30 into a predetermined liquid crystal orientation pattern when forming the optical anisotropic layer 26. As described above, the optical anisotropic layer 26 of the liquid crystal diffraction element 10 has a liquid crystal orientation pattern in which the direction of the optical axis 30A changes while continuously rotating in one direction in the plane. Therefore, the orientation film 24 forms the optical anisotropic layer 26 in a manner that can form the liquid crystal orientation pattern.

[0304] Various known alignment films are used as the alignment film 24. For example, a friction-treated film formed of an organic compound such as a polymer, an oblique vapor-deposited film of an inorganic compound, a film having microgrooves, and a film formed by accumulating an LB (Langmuir-Blodgett) film using the Langmuir-Blodgett method using an organic compound such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearate.

[0305] In the liquid crystal diffraction element 10, the alignment film 24 is preferably formed by irradiating a material having a photo-alignment property with polarized light or non-polarized light. That is, in the liquid crystal diffraction element 10, as the alignment film, the photo-alignment film 24 formed by coating a photo-alignment material on the support 20 is preferably used. The irradiation with polarized light can be performed in a vertical direction or an oblique direction relative to the photo-alignment film, and the irradiation with non-polarized light can be performed in an oblique direction relative to the photo-alignment film.

[0306] The thickness of the alignment film 24 is not limited, and may be appropriately set to a thickness that can obtain a desired alignment function according to the material forming the alignment film 24. The thickness of the alignment film 24 is preferably 0.01 to 5 μm, and more preferably 0.05 to 2 μm.

[0307] The method for forming the alignment film 24 is not limited, and various known methods can be used depending on the material for forming the alignment film 24. For example, there is a method in which the alignment film is applied on the surface of the support 20, dried, and then exposed to a laser beam to form an alignment pattern.

[0308] exist Fig.21 An example of an exposure device for exposing an alignment film to form an alignment pattern is conceptually shown in FIG. Fig.21 In the example shown, exposure of the alignment film 24 of the liquid crystal diffraction element 10 is illustrated as an example.

[0309] Fig.21The exposure device 50 shown in the figure comprises: a light source 54 having a laser 52; a beam splitter 56 for separating the laser light 70 emitted by the laser 52 into two light beams 72A and 72B; a reflector 58A and a reflector 58B respectively arranged on the optical paths of the two separated light beams 72A and 72B; and a quarter wave plate 60A and a quarter wave plate 60B. In addition, the light source 54 emits linearly polarized light P0. The quarter wave plate 60A and the quarter wave plate 60B have mutually orthogonal optical axes.

[0310] The quarter wave plate 60A converts the linear polarized light P0 (light 72A) into right-handed circularly polarized light P R , the quarter wave plate 60B converts the linear polarized light P0 (light 72B) into left-handed circularly polarized light P L .

[0311] The support 20 having the alignment film 24 before the alignment pattern is formed is arranged in the exposure section, and the two light beams 72A and 72B are made to cross and interfere with each other on the alignment film 24, and the interference light is irradiated onto the alignment film 24 for exposure. Due to the interference at this time, the polarization state of the light irradiated onto the alignment film 24 changes periodically in the form of interference fringes. Thus, in the alignment film 24, an alignment pattern in which the alignment state changes periodically can be obtained.

[0312] In the exposure device 50, the period of the alignment pattern can be adjusted by changing the cross angle β of the two light beams 72A and 72B. That is, in the exposure device 50, by adjusting the cross angle β, a period Λ in one direction of rotation of the optical axis 30A in the alignment pattern in which the optical axis 30A of the liquid crystal compound 30 rotates continuously in one direction can be adjusted.

[0313] By forming the optically anisotropic layer 26 on the alignment film 24 having the alignment pattern in which the alignment state changes periodically, it is possible to form the optically anisotropic layer 26 having the liquid crystal alignment pattern in which the optical axis 30A derived from the liquid crystal compound 30 rotates continuously in one direction. Furthermore, by rotating the optical axes of the quarter wave plate 60A and the quarter wave plate 60B by 90 degrees, the rotation direction of the optical axis 30A can be reversed.

[0314] Next, refer to Fig. 22 and Fig.23 , another example of a liquid crystal diffraction element 12 involved in the technology of the present invention is described.

[0315] Fig. 22Schematically shows the stacked structure of the liquid crystal diffraction element 12. The liquid crystal diffraction element 12 includes a support 20, an alignment film 25, and an optical anisotropic layer 27. The alignment film 25 is formed on the surface of the support 20, and the optical anisotropic layer 27 is formed on the surface of the alignment film 25. The liquid crystal diffraction element 12 is in the form of a sheet similar to the liquid crystal diffraction element 10. Fig. 22 In the orthogonal coordinate system using the x-axis, y-axis, and z-axis that are orthogonal to each other, the sheet surface of the liquid crystal diffraction element 12 is set as the xy plane, and the thickness direction is set as the z direction.

[0316] The optical anisotropic layer 27 is a layer formed using a composition containing a liquid crystal compound 30, and has a structure in which the oriented liquid crystal compounds 30 are stacked. The optical anisotropic layer has a liquid crystal orientation pattern in which the direction of the optical axis 30A originating from the liquid crystal compound 30 in the plane of the optical anisotropic layer 27 changes while continuously rotating in one direction in the plane of the optical anisotropic layer. Here, one direction in which the optical axis 30A rotates and changes in the liquid crystal diffraction element 12 is set as the x direction. Fig. 22 In the example, the z direction is the stacking direction of the liquid crystal compound 30 and is a direction perpendicular to the optical surface of the liquid crystal diffraction element 12.

[0317] The optically anisotropic layer 27 is formed so that the period Λ of the liquid crystal orientation pattern is different in different regions within the plane. Fig. 22 In the portion shown, the optically anisotropic layer 27 is formed from Fig. 22 The left side of has three regions A0, region A1 and region A2, and the period Λ of the liquid crystal orientation pattern in each region is different. Specifically, the period Λ of the liquid crystal orientation pattern in region A2 is A2 One period Λ of the liquid crystal alignment pattern in region A1 A1 The liquid crystal orientation pattern of region A1 has a period of Λ A1 One period of the liquid crystal alignment pattern in region A0 is Λ A0 Short. That is, Λ A0 >Λ A1 >Λ A2 .

[0318] Furthermore, the regions A1 and A2 have a structure (hereinafter also referred to as a twisted structure) in which the optical axis is twisted and rotated in the thickness direction (z direction) of the optical anisotropic layer 27. The twist angle in the thickness direction of the region A1 is smaller than the twist angle in the thickness direction of the region A2. The region A0 is a region without a twisted structure. That is, the twist angle in the region A0 is 0°. The twist angle is the twist angle in the entire thickness direction.

[0319] As described above, the optically anisotropic layer 27 has a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound 30 is rotated in one direction, has regions where the twist angle of rotation is different within the plane, and further has a region where the optical axis is twisted and rotated in the thickness direction of the optically anisotropic layer 27. The alignment film 25 is formed so that the optically anisotropic layer 27 has the liquid crystal orientation pattern described above.

[0320] refer to Fig.23 , the function of the optical anisotropic layer 27 having the above structure is described. In addition, in the liquid crystal diffraction element 12, basically only the optical anisotropic layer 27 exhibits an optical function. Fig.23 In order to simplify the drawing and clearly illustrate the structure and the effect, only the optically anisotropic layer 27 is shown.

[0321] like Fig.23 As shown in FIG. 1 , when left-handed circularly polarized light LC0 is incident on region A0 in the plane of the optical anisotropic layer 27, it is deflected by an angle θ in the −x direction relative to the incident direction as described above. A0 Here, Fig.23 The -x direction is Fig. 22 Similarly, when the left-handed circularly polarized light LC1 is incident on the region A1 in the plane of the optical anisotropic layer 27, it is deflected in the -x direction by an angle θ relative to the incident direction. A0 Similarly, when the left-handed circularly polarized light LC2 is incident on the region A2 in the plane of the optical anisotropic layer 27, it is deflected in the -x direction by an angle θ relative to the incident direction. A2 And transmission.

[0322] As described above, the optically anisotropic layer having a liquid crystal orientation pattern with the optical axis 30A rotated in the x direction formed using a composition containing a liquid crystal compound 30 deflects circularly polarized light, but the shorter the period Λ of the liquid crystal orientation pattern, the larger the deflection angle (diffraction angle). As described above, since the size relationship of the period of each liquid crystal orientation pattern of region A0, region A1, and region A2 is Λ A0 >Λ A1 >Λ A2 Therefore, the magnitude relationship of the deflection angle of the transmitted light relative to the incident light in each of the regions A0, A1, and A2 is θ A0 <θ A1 <θ A2 .

[0323] In the diffraction of light in the optically anisotropic layer having a liquid crystal orientation pattern in which the direction of the optical axis of the liquid crystal compound 30 changes while continuously rotating in the plane, if the diffraction angle becomes larger, the diffraction efficiency decreases, that is, the intensity of the diffracted light becomes weaker. Therefore, in the case where the optically anisotropic layer is set as a structure having regions with different periods Λ of the liquid crystal orientation pattern, since the diffraction angle is different depending on the incident position of the light, the amount of diffracted light differs depending on the incident position in the plane. That is, depending on the incident position in the plane, a region where the light that has passed through the optically anisotropic layer becomes dark is generated.

[0324] In contrast, Fig. 22 and Fig.23 The optically anisotropic layer 27 shown has regions that are twisted and rotated in the thickness direction, and has regions with different twist angles in the thickness direction. Fig. 22 and Fig.23 In the example shown, the twist angle in the thickness direction of region A2 is greater than the twist angle in the thickness direction of region A1. In addition, region A0 does not have a twist structure in the thickness direction. A region having a twist structure can improve the diffraction efficiency compared to a region without a twist structure, so in the optical anisotropic layer 27, it is possible to suppress the reduction in the diffraction efficiency of the deflected light.

[0325] exist Fig.23 In the example shown, by providing a twisted structure to regions A1 and A2 having a diffraction angle greater than that of region A0, a decrease in the amount of light deflected in regions A1 and A2 can be suppressed. Furthermore, by making the twist angle of the twisted structure of region A2 having a larger diffraction angle than that of region A1 larger than that of region A1 larger than that of region A1, a decrease in the amount of light deflected in region A2 can be suppressed.

[0326] That is, in the optical anisotropic layer 27, the arrangement direction of the length of one period Λ of the liquid crystal orientation pattern is different from the arrangement direction of the magnitude of the twist angle in the thickness direction. More specifically, in the optical anisotropic layer 27, the region where one period Λ of the liquid crystal orientation pattern is shorter increases the twist angle in the thickness direction, thereby making it possible to brighten the transmitted light. Thus, even when the optical anisotropic layer 27 is configured to have regions with different one period Λ of the liquid crystal orientation pattern, the amount of transmitted light can be made uniform regardless of the incident position in the plane.

[0327] Next, refer to Fig.24 , a liquid crystal diffraction element 14 according to an embodiment of the present invention is described. Fig.24It is a plan view schematically showing a liquid crystal orientation pattern of a liquid crystal diffraction element 14 involved in one embodiment of the present invention. The liquid crystal diffraction element 14 is also in a sheet shape similar to the aforementioned liquid crystal diffraction element 12, and has an orientation film (not shown) formed on the surface of a support (not shown), and has a structure in which an optical anisotropic layer 34 is formed on the surface of the orientation film. The optical anisotropic layer 34 is formed using a composition containing a liquid crystal compound similar to the aforementioned liquid crystal diffraction element 12, and has a structure in which oriented liquid crystal compounds are stacked. Fig.24 In the example, the sheet surface is set to be parallel to the paper surface, and the stacking direction is set to be perpendicular to the paper surface. Fig.24 In the figure, for ease of understanding, the liquid crystal orientation pattern of the optically anisotropic layer 34 is shown by the optical axis 30A of the liquid crystal compound.

[0328] exist Fig.18 The optically anisotropic layer 26 and Fig. 22 In the optically anisotropic layer 27, the optical axis 30A rotates continuously only along the x direction in the plane. Fig.24 The main difference between the optical anisotropic layer 34 and these is that the liquid crystal orientation pattern is arranged radially in one direction with the direction of the optical axis 30A continuously rotating and changing. In addition, in the optical anisotropic layer 34, the regions with the same direction of the optical axis 30A are arranged in concentric circles. Fig.24 In the example, the center of the concentric circles is the center of the optical anisotropic layer 34, and the axis in the thickness direction passing through the center is set as the optical axis Zk. The optical anisotropic layer 34 has a periodic structure in a direction perpendicular to the optical axis Zk, and has a concentric structure centered on the optical axis Zk, and more specifically, has a concentric liquid crystal orientation pattern centered on the optical axis Zk.

[0329] In the optical anisotropic layer 34, the direction of the optical axis 30A continuously rotates and changes along a plurality of directions from the center of the optical anisotropic layer 34 toward the outside, for example, the direction indicated by the arrow Ar1, the direction indicated by the arrow Ar2, the direction indicated by the arrow Ar3, etc. The circularly polarized light incident on the optical anisotropic layer 34 having the liquid crystal orientation pattern changes its absolute phase in each local area where the direction of the optical axis 30A of the liquid crystal compound is different. At this time, the amount of change of each absolute phase varies depending on the direction of the optical axis 30A of the liquid crystal compound on which the circularly polarized light is incident.

[0330] The optical anisotropic layer 34 having such a concentric liquid crystal orientation pattern, that is, a liquid crystal orientation pattern in which the optical axis 30A rotates continuously and changes radially, can transmit the incident light as convergent light or divergent light according to the rotation direction of the optical axis 30A of the liquid crystal compound and the rotation direction of the incident circularly polarized light. That is, by setting the liquid crystal orientation pattern of the optical anisotropic layer 34 to a concentric shape, the liquid crystal diffraction element 14, for example, exhibits the same function as a positive lens or the same function as a negative lens.

[0331] When the function of the liquid crystal diffraction element 14 is made to be the same as that of a positive lens or the same as that of a negative lens, it is preferable that the following formula is satisfied.

[0332] Φ(r)=(π / λ)[(r 2 +fa 2 ) 1 / 2 -fa]

[0333] Here, r is the distance from the center of the concentric circle ( Fig.24 In the example of the optical axis Zk), r = (x 2 +y 2 ) 1 / 2 express.

[0334] Here, x and y represent positions in the plane, (x, y) = (0, 0) represents the center of the concentric circle, Φ(r) represents the angle of the optical axis 30A at a distance r from the center of the concentric circle, λ represents the wavelength, and fa represents the target focal length.

[0335] As described above, the shorter one period Λ in the liquid crystal orientation pattern is, the larger the angle of refraction of light in the incident direction becomes. Therefore, when the optical anisotropic layer 34 is configured to transmit the incident light as a focused beam, by gradually shortening one period Λ in the liquid crystal orientation pattern in one direction that continuously rotates from the center of the optical anisotropic layer 34 toward the optical axis 30A, it is possible to function in the same manner as a positive lens whose focusing power becomes stronger toward peripheral light from the optical axis Zk.

[0336] By setting the direction of continuous rotation of the optical axis 30A to the direction opposite to the structure in which the optical anisotropic layer 34 transmits incident light as concentrated light, the optical anisotropic layer 34 can be changed to a structure in which the incident light is transmitted as divergent light. Alternatively, by setting the rotation direction of circularly polarized light incident on the optical anisotropic layer 34 to the direction opposite to the structure in which the optical anisotropic layer 34 transmits incident light as concentrated light, the optical anisotropic layer 34 can be changed to a structure in which the incident light is transmitted as divergent light.

[0337] When the optical anisotropic layer 34 is configured to transmit incident light as divergent light, by gradually shortening a period Λ in the liquid crystal orientation pattern in an outward direction in a direction continuously rotating from the center of the optical anisotropic layer 34 toward the optical axis 30A, it is possible to function in the same manner as a negative lens in which the divergence of light becomes stronger as the optical axis Zk is directed toward the periphery.

[0338] When the period Λ of the periodic structure of the optical anisotropic layer 34 is configured to be gradually shortened from the optical axis Zk toward the periphery, it is effective to correct aberration more strongly in the peripheral portion where large chromatic aberration is likely to occur. In addition, since such a structure has good manufacturability, it is conducive to cost reduction. The period Λ of the periodic structure of the most peripheral portion of the optical anisotropic layer 34 is preferably 0.5 μm or more. In this case, it becomes a structure with good manufacturability, which is conducive to cost reduction.

[0339] When the optically anisotropic layer 34 has a structure having regions with different periods Λ of the liquid crystal orientation pattern

[0340] In order to improve the uniformity of the transmitted light, it is preferred to impart Fig. 22 In this case, it is preferable to appropriately set the twist angle in the thickness direction according to one period Λ of the liquid crystal alignment pattern in the plane and according to the desired light quantity distribution in the plane.

[0341] The liquid crystal diffraction element is described above with reference to the figures, but the liquid crystal diffraction element is not limited to the above examples, and various modifications can be made within the scope of the main purpose of the technology of the present invention. For example, the liquid crystal diffraction element in the above examples has a support and an alignment film, but the support can also be peeled off, and the liquid crystal diffraction element is composed of only the alignment film and the optical anisotropic layer, or the alignment film can be peeled off, and the liquid crystal diffraction element is composed of only the optical anisotropic layer.

[0342] In the liquid crystal diffraction element disclosed in the present invention, the alignment film is preferably provided and is not an essential component. For example, an alignment pattern can be formed on the support by a method of rubbing the support, processing the support with a laser beam, etc., so that the optical anisotropic layer can also be provided with a structure of a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound continuously rotates in at least one direction in the plane while changing.

[0343] The above-mentioned liquid crystal diffraction element 12 has the following structure: having regions with different periods Λ of the liquid crystal orientation pattern, the region with shorter period Λ of the liquid crystal orientation pattern has a larger torsion angle in the thickness direction. However, on the contrary, in the liquid crystal diffraction element of the present invention, the region with shorter period Λ of the liquid crystal orientation pattern can make the torsion angle in the thickness direction smaller. The torsion angle in the thickness direction can be appropriately set according to the period Λ of the liquid crystal orientation pattern in the plane.

[0344] Furthermore, the liquid crystal diffraction element 14 has a structure in which one period Λ of the liquid crystal orientation pattern gradually becomes shorter from the center of the optical anisotropic layer 34 toward the outside. However, in contrast, in the liquid crystal diffraction element of the present invention, one period Λ of the liquid crystal orientation pattern can be set to gradually become longer from the center of the optical anisotropic layer 34 toward the outside. In addition, for example, when it is necessary to set the light quantity distribution for the transmitted light, depending on the purpose of the liquid crystal diffraction element, it is also possible to use a structure in which one period Λ is not gradually changed in one direction of continuous rotation toward the optical axis, but a region with one period Λ different in one direction of continuous rotation of the optical axis can be partially used.

[0345] In the above example, the liquid crystal diffraction element is set to have a structure with one optical anisotropic layer, but it is not limited to this, and it can also have more than two optical anisotropic layers. In the case where the liquid crystal diffraction element has more than two optical anisotropic layers, it can have one optical anisotropic layer with a period Λ uniform over the entire surface and one optical anisotropic layer with a period Λ in different regions. In addition, in the case where the liquid crystal diffraction element has more than two optical anisotropic layers, it can further have optical anisotropic layers with different directions (directions of twist angles) twisted and rotated in the thickness direction. In this way, by further having optical anisotropic layers with different directions twisted and rotated in the thickness direction, in the region with a twist angle in the thickness direction, the transmitted light can be effectively refracted relative to the incident light of various polarization states.

[0346] The optically anisotropic layer, alignment film, and support of the present invention may be prepared by methods and materials other than those described above, and known techniques may be used. For example, techniques described in Japanese Patent No. 6985501 may be used.

[0347] Next, a device including the finder optical system 5 according to an embodiment of the present invention will be described. Fig.25 1 is a schematic diagram of a camera 100 as an imaging device according to an embodiment of the present invention. As an example, the camera 100 is a digital camera.

[0348] The camera 100 includes a viewfinder device 101 according to an embodiment of the present invention. The camera 100 also includes an imaging lens 102 , an imaging element 103 , a processor 104 , a display unit 105 , an operation unit 106 , and a recording unit 107 .

[0349] The viewfinder device 101 includes a viewfinder optical system 5 and a drive unit 7 according to an embodiment of the present invention. The viewfinder optical system 5 includes a display element 1 and an eyepiece optical system 3. The drive unit 7 drives the display element 1. The display element 1 outputs output light as polarized light. As an example, Fig.25 The output light of the example is circularly polarized light Pc. The output light from the display element 1 is incident on the eyepiece optical system 3. As described above, the eyepiece optical system 3 includes a liquid crystal diffraction element, and by setting the light incident on the eyepiece optical system 3 to circularly polarized light Pc, the light from the display element 1 can be effectively guided.

[0350] In addition, the output light from the display element 1 may be linearly polarized light, in which case it is preferred to dispose an element such as a quarter wave plate between the display element 1 and the eyepiece optical system 3 so that the circularly polarized light Pc is incident on the eyepiece optical system 3. When a liquid crystal display element or an organic EL (organic electroluminescence) display element that outputs circularly polarized light is used as the display element 1, the output light thereof is polarized light, and thus a structure having good affinity with the eyepiece optical system 3 including a liquid crystal diffraction element can be provided.

[0351] The imaging lens 102 forms an image of a subject. The imaging element 103 captures the image formed by the imaging lens 102. As the imaging element 103, for example, a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) can be used. The imaging element 103 outputs a captured image as a captured image to the processor 104. The processor 104 performs image processing on the captured image, and outputs the image data subjected to the image processing to the display unit 105 and the drive unit 7. The display unit 105 displays the image. The drive unit 7 causes the display element 1 to display the image.

[0352] The user 110 observes the image displayed on the display element 1 through the eyepiece optical system 3 through the viewfinder device 101 . The user 110 also operates the operation unit 106 to capture a still image or a moving image, and the image data obtained by the capturing is recorded in the recording unit 107 .

[0353] The above embodiments and examples are used to illustrate the technology of the present invention, but the technology of the present invention is not limited to the above embodiments and examples, and various deformations can be made. For example, the radius of curvature, surface spacing, refractive index, Abbe number, aspheric coefficient and phase difference coefficient of each lens are not limited to the values ​​shown in the above numerical examples, and other values ​​can be used.

[0354] Furthermore, the imaging device according to the embodiment of the present invention is not limited to the above-mentioned example, and the present invention can also be applied to a film camera, a video camera, and the like.

[0355] The following additional notes are further disclosed with respect to the above-mentioned embodiments and examples.

[0356] [Supplementary Item 1]

[0357] A viewfinder optical system comprising:

[0358] display element; and an eyepiece optical system, arranged closer to the viewpoint side than the display element,

[0359] One or more diffraction elements are arranged in the viewfinder optical system.

[0360] At least one of the diffraction elements is a first diffraction element including a liquid crystal diffraction element,

[0361] When the distance on the optical axis from the display surface of the display element to the surface of the viewfinder optical system closest to the viewpoint is TL,

[0362] When the distance on the optical axis from the display surface to the optical surface of the first diffraction element is denoted as X1,

[0363] The viewfinder optical system satisfies the conditional equation (1) represented by the following equation,

[0364] 0.05≤X1 / TL≤1 (1).

[0365] [Supplementary Item 2]

[0366] The viewfinder optical system according to supplementary item 1, wherein:

[0367] When the half value of the longest diameter of the display area in the display element is set to H, and

[0368] When the focal length of the viewfinder optical system is set to f,

[0369] The viewfinder optical system satisfies the conditional equation (2) represented by the following equation,

[0370] 0.3<H / f<0.7 (2).

[0371] [Supplementary item 3]

[0372] The viewfinder optical system according to Supplementary Item 1 or 2, wherein:

[0373] When the distance on the optical axis from the surface closest to the viewpoint side of the viewfinder optical system to the viewpoint is dEP, and

[0374] When the focal length of the viewfinder optical system is set to f,

[0375] The viewfinder optical system satisfies the conditional equation (3) represented by the following equation,

[0376] 0<f / dEP<0.95(3).

[0377] [Supplementary Item 4]

[0378] The finder optical system according to any one of Supplementary Items 1 to 3, wherein the eyepiece optical system includes two or more positive lenses and one or more negative lenses.

[0379] [Supplementary Note 5]

[0380] A viewfinder optical system according to any one of supplementary items 1 to 4, wherein:

[0381] The eyepiece optical system includes more than two aspherical lenses and more than one spherical lens.

[0382] [Supplementary Item 6]

[0383] A viewfinder optical system according to any one of supplementary items 1 to 5, wherein:

[0384] The diffraction element is arranged on the surface of the optical element,

[0385] The optical element has an Abbe number of 35 or more based on a d-line.

[0386] [Supplementary Note 7]

[0387] The viewfinder optical system according to any one of supplementary items 1 to 6, wherein the diffraction element is arranged on a surface of the optical element,

[0388] The optical element has a d-line transmittance of 98% or more.

[0389] [Supplementary Item 8]

[0390] A viewfinder optical system according to any one of supplementary items 1 to 7, wherein:

[0391] When the distance on the optical axis from the display surface to the optical element in the finder optical system is X,

[0392] The d-line transmittance of the partial optical system composed of all optical elements arranged in the following range is 92% or more,

[0393] 0.05≤X / TL≤1.

[0394] [Supplementary Item 9]

[0395] A viewfinder optical system according to any one of supplementary items 1 to 8, wherein:

[0396] The diffraction element is arranged on the surface of the optical element,

[0397] Lenses having optical power are arranged on both the object side and the image side of the optical element.

[0398] [Supplementary Item 10]

[0399] A viewfinder optical system according to any one of supplementary items 1 to 9, wherein:

[0400] The diffraction element is arranged on the surface of the optical element,

[0401] A lens having optical power is arranged adjacent to the optical element on at least one of the object side and the image side of the optical element,

[0402] The minimum distance between the optical surface of the diffraction element provided on the surface of the optical element and the optical surface of the lens in the optical axis direction is 1.8 mm or less.

[0403] [Supplementary Item 11]

[0404] A viewfinder optical system according to any one of supplementary items 1 to 10, wherein:

[0405] The thickness of the region having a diffraction effect of the diffraction element in the optical axis direction is 10 μm or less.

[0406] [Supplementary Item 12]

[0407] A viewfinder optical system according to any one of supplementary items 1 to 11, wherein:

[0408] At least one of the diffraction elements is a second diffraction element including a liquid crystal diffraction element,

[0409] No element having optical power is arranged between the display surface and the second diffraction element, and when the distance on the optical axis from the display surface to the optical surface of the second diffraction element is set to X2,

[0410] The viewfinder optical system satisfies the conditional equation (4) represented by the following equation,

[0411] 0≤X2 / TL<0.05 (4).

[0412] [Supplementary Item 13]

[0413] The viewfinder optical system according to supplementary item 12, wherein:

[0414] The sign of the phase difference function of the first diffraction element is different from the sign of the phase difference function of the second diffraction element.

[0415] [Supplementary Item 14]

[0416] A viewfinder optical system according to any one of supplementary items 1 to 13, wherein:

[0417] The diffraction element has a periodic structure in a direction perpendicular to the optical axis and has a concentric circular structure centered on the optical axis.

[0418] [Supplementary Item 15]

[0419] The viewfinder optical system according to supplementary item 14, wherein:

[0420] The period of the periodic structure gradually becomes shorter from the optical axis toward the periphery.

[0421] [Supplementary Item 16]

[0422] The viewfinder optical system according to Supplementary item 14 or 15, wherein:

[0423] The period of the periodic structure at the outermost portion of the diffraction element is greater than or equal to 0.5 μm.

[0424] [Supplementary Item 17]

[0425] A viewfinder optical system according to any one of supplementary items 1 to 16, wherein:

[0426] The number of lenses with optical power included in the viewfinder optical system is 4 or 5.

[0427] [Supplementary Item 18]

[0428] A viewfinder device comprising the viewfinder optical system according to any one of supplementary items 1 to 17,

[0429] The output light from the display element is polarized light.

[0430] [Supplementary Item 19]

[0431] A camera device comprising a viewfinder optical system according to any one of Supplementary Items 1 to 17,

[0432] The output light from the display element is polarized light.

[0433] All documents, patent applications, and technical specifications described in this specification are incorporated herein by reference in the same manner as if each document, patent application, and technical specification was specifically and individually described as being incorporated by reference.

Claims

1. A viewfinder optical system comprising: display element; and an eyepiece optical system, arranged closer to the viewpoint side than the display element, One or more diffraction elements are arranged in the viewfinder optical system. At least one of the diffraction elements is a first diffraction element including a liquid crystal diffraction element, When the distance on the optical axis from the display surface of the display element to the surface of the viewfinder optical system closest to the viewpoint is TL, When the distance on the optical axis from the display surface to the optical surface of the first diffraction element is denoted as X1, The viewfinder optical system satisfies the conditional equation (1) represented by the following equation, 0.05≤X1 / TL≤1 (1).

2. The viewfinder optical system according to claim 1, wherein: When the half value of the longest diameter of the display area in the display element is set to H, and When the focal length of the viewfinder optical system is set to f, The viewfinder optical system satisfies the conditional equation (2) represented by the following equation, 0.3 <H / f<0.7 (2)。 3. The viewfinder optical system according to claim 1, wherein: When the distance on the optical axis from the surface closest to the viewpoint side of the viewfinder optical system to the viewpoint is dEP, and When the focal length of the viewfinder optical system is set to f, The viewfinder optical system satisfies the conditional equation (3) represented by the following equation, 0 <f / dEP<0.95 (3)。 4. The viewfinder optical system according to claim 1, wherein: The eyepiece optical system includes more than two positive lenses and more than one negative lens.

5. The viewfinder optical system according to claim 1, wherein: The eyepiece optical system includes more than two aspherical lenses and more than one spherical lens.

6. The viewfinder optical system according to claim 1, wherein: The diffraction element is arranged on the surface of the optical element, The optical element has an Abbe number of 35 or more based on a d-line.

7. The viewfinder optical system according to claim 1, wherein: The diffraction element is arranged on the surface of the optical element, The optical element has a d-line transmittance of 98% or more.

8. The viewfinder optical system according to claim 1, wherein: When the distance on the optical axis from the display surface to the optical element in the finder optical system is X, The d-line transmittance of the partial optical system composed of all optical elements arranged in the following range is 92% or more, 0.05≤X / TL≤1.

9. The viewfinder optical system according to claim 1, wherein: The diffraction element is arranged on the surface of the optical element, Lenses having optical power are arranged on both the object side and the image side of the optical element.

10. The viewfinder optical system according to claim 1, wherein: The diffraction element is arranged on the surface of the optical element, A lens having optical power is arranged adjacent to the optical element on at least one of the object side and the image side of the optical element, The minimum distance between the optical surface of the diffraction element provided on the surface of the optical element and the optical surface of the lens in the optical axis direction is 1.8 mm or less.

11. The viewfinder optical system according to claim 1, wherein: The thickness of the region having diffraction effect of the diffraction element in the optical axis direction is less than 10 μm.

12. The viewfinder optical system according to claim 1, wherein: At least one of the diffraction elements is a second diffraction element including a liquid crystal diffraction element, No element having optical power is arranged between the display surface and the second diffraction element, and when the distance on the optical axis from the display surface to the optical surface of the second diffraction element is set to X2, The viewfinder optical system satisfies the conditional equation (4) represented by the following equation, 0≤X2 / TL<0.05 (4).

13. The viewfinder optical system according to claim 12, wherein: The sign of the phase difference function of the first diffraction element is different from the sign of the phase difference function of the second diffraction element.

14. The viewfinder optical system according to claim 1, wherein: The diffraction element has a periodic structure in a direction perpendicular to the optical axis and has a concentric circular structure centered on the optical axis.

15. The viewfinder optical system according to claim 14, wherein: The period of the periodic structure gradually becomes shorter from the optical axis toward the periphery.

16. The viewfinder optical system according to claim 14, wherein: The period of the periodic structure at the outermost portion of the diffraction element is greater than 0.5 μm.

17. The viewfinder optical system according to claim 1, wherein: The number of lenses with optical power included in the viewfinder optical system is 4 or 5.

18. A viewfinder device comprising the viewfinder optical system according to any one of claims 1 to 17, The output light from the display element is polarized light.

19. An imaging device comprising the viewfinder optical system according to any one of claims 1 to 17, The output light from the display element is polarized light.

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