Finder optical system, finder device, and imaging device

Abstract

This finder optical system comprises a display element and an eyepiece optical system disposed closer to the eye point side than the display element. One or more diffraction elements are disposed within the finder optical system. At least one of the diffraction elements is a first diffraction element including a liquid crystal diffraction element. The finder optical system satisfies a conditional expression represented by 0.05 ≤ X1 / TL ≤ 1 where TL is the distance on the optical axis from a display surface of the display element to a surface closest to the eye point side of the finder optical system, and X1 is the distance on the optical axis from the display surface of the display element to an optical surface of the first diffraction element.

Description

Finder optical system, finder device, and imaging device

[0001] The present disclosure relates to a viewfinder optical system, a viewfinder device, and an imaging device.

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

[0003] In recent years, there has been a demand for finder optical systems that are compact yet enable good observation. However, the diffractive optical surface described in JP 2020-154190 A is a diffractive optical surface having a physical step shape (hereinafter referred to as a relief-type diffractive optical surface), and since it is in contact with air, there is a risk that light scattered by these steps will become flare and reduce resolving power. The diffractive optical element described in JP 2019-144550 A has a so-called contact multi-layer structure in which two layers of diffractive optical surfaces having a relief-type diffractive optical surface are closely attached to each other. Contact multi-layer diffractive optical elements can reduce the occurrence of flare compared to structures in which the diffractive optical surface is in contact with air, but there is a risk that advanced technology will be required and the cost will be high.

[0004] An object of the present disclosure is to provide a finder optical system, a finder device, and an imaging device that are small and allow good observation without increasing costs.

[0005] One aspect of the present disclosure is a viewfinder optical system comprising a display element and an eyepiece optical system arranged closer to the eyepoint than the display element, wherein one or more diffractive elements are arranged within the viewfinder optical system, at least one of the diffractive elements being a first diffractive element including a liquid crystal diffractive element, and wherein, where TL is 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 eyepoint, and X1 is the distance on the optical axis from the display surface to the optical surface of the first diffractive element, the viewfinder optical system satisfies conditional expression (1) expressed as 0.05≦X1 / TL≦1 (1).

[0006] When the half value of the longest diameter of the display area of ​​the display element is H and the focal length of the viewfinder optical system is f, it is preferable that the viewfinder optical system of the above aspect satisfies conditional expression (2) expressed as 0.3<H / f<0.7 (2).

[0007] When the distance on the optical axis from the surface of the finder optical system closest to the eyepoint to the eyepoint is dEP and the focal length of the finder optical system is f, it is preferable that the finder optical system of the above aspect satisfies conditional expression (3) expressed as 0<f / dEP<0.95 (3).

[0008] The eyepiece optical system preferably includes two or more positive lenses and one or more negative lenses.

[0009] The eyepiece optical system preferably includes two or more aspherical lenses and one or more spherical lenses.

[0010] The diffraction element is provided on the surface of the optical element, and the Abbe number of the optical element based on the d-line is preferably 35 or more.

[0011] The diffraction element is provided on the surface of the optical element, and the transmittance of the optical element for the d-line is preferably 98% or more.

[0012] When the distance on the optical axis from the display surface to the optical elements in the viewfinder optical system is X, it is preferable that the transmittance of the d-line of a partial optical system consisting of all optical elements arranged within the range of 0.05≦X / TL≦1 is 92% or more.

[0013] The diffractive element may be provided on a surface of the optical element, and lenses having refractive power may be arranged on both the object side and the image side of the optical element.

[0014] It is preferable that the diffractive element is provided on the surface of the optical element, a lens having refractive power is disposed adjacent to the optical element on at least one of the object side and image side of the optical element, and the minimum distance in the optical axis direction between the optical surface of the diffractive element provided on the surface of the optical element and the optical surface of the lens is 1.8 mm or less.

[0015] It is preferable that the thickness of the region of the diffraction element having a diffractive effect in the optical axis direction is 10 μm or less.

[0016] At least one of the diffraction elements is a second diffraction element including a liquid crystal diffraction element, and no element having refractive power is disposed between the display surface and the second diffraction element. When the distance on the optical axis from the display surface to the optical surface of the second diffraction element is X2, it is preferable that the following conditional expression (4) is satisfied: 0≦X2 / TL<0.05 (4). 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.

[0017] The diffraction element preferably has a periodic structure in a direction perpendicular to the optical axis and a concentric structure centered on the optical axis. In this case, the period of the periodic structure preferably becomes gradually shorter from the optical axis toward the periphery. Furthermore, the period of the periodic structure in the outermost periphery of the diffraction element is preferably 0.5 μm or more.

[0018] The finder optical system may be configured to include four or five lenses having refractive power.

[0019] Another aspect of the present disclosure is a viewfinder device including the viewfinder optical system of the above aspect, in which output light from the display element is polarized light.

[0020] Yet another aspect of the present disclosure is an imaging device including the viewfinder optical system of the above aspect, in which the output light from the display element is polarized light.

[0021] In this specification, "lens having positive refractive power" and "positive lens" are synonymous. "lens having negative refractive power" and "negative lens" are synonymous. "Single lens" means a single lens that is not cemented. However, a compound aspherical lens (a lens in which a spherical lens and an aspherical film formed on the spherical lens are integrally configured and function as a single aspherical lens as a whole) is not considered a cemented lens, but is treated as a single lens. Unless otherwise specified, the symbols for refractive power of lenses including aspherical surfaces are those in the paraxial region.

[0022] The "focal length" used in the conditional expressions is the paraxial focal length. The values ​​used in the conditional expressions are values ​​based on the d-line. The "distance on the optical axis" used in the conditional expressions is the geometric distance on the optical axis, unless otherwise specified. In systems that allow diopter adjustment, the values ​​used in the conditional expressions are values ​​in the -1 diopter state. The "d-line," "C-line," and "F-line" described in this specification are emission lines, and the wavelength of the d-line is treated as 587.56 nm, the wavelength of the C-line as 656.27 nm, and the wavelength of the F-line as 486.13 nm. In this specification, "mm" means millimeter, "nm" means nanometer, and "μm" means micrometer.

[0023] According to the present disclosure, it is possible to provide a finder optical system, a finder device, and an imaging device that are small and allow good observation without increasing costs.

[0024] FIG. 1 is a cross-sectional view showing the configuration and light beam of a finder optical system according to an embodiment, corresponding to the finder optical system of Example 1. FIG. 2 is a cross-sectional view showing the configuration and light beam of a finder optical system of Example 2. FIG. 3 is a cross-sectional view showing the configuration and light beam of a finder optical system of Example 3. FIG. 4 is a cross-sectional view showing the configuration and light beam of a finder optical system of Example 3. FIG. 5 is a cross-sectional view showing the configuration and light beam of a finder optical system of Example 4. FIG. 6 is a cross-sectional view showing the configuration and light beam of a finder optical system of Example 5. FIG. 7 is a cross-sectional view showing the configuration and light beam of a finder optical system of Example 6. FIG. 8 is a cross-sectional view showing the configuration and light beam of a finder optical system of Example 7. FIG. 9 is a cross-sectional view showing the configuration and light beam of a finder optical system of Example 8. FIG. 10 is a cross-sectional view showing the configuration and light beam of a finder optical system of Example 8. FIG. 11 is a cross-sectional view showing the configuration of an example of a liquid crystal diffraction element. 22. It is a schematic plan view of the optically anisotropic layer of the liquid crystal diffraction element shown in FIG. 17. It is a conceptual diagram showing the function ... schematic configuration diagram of an example of an exposure device that exposes an alignment film. It is a diagram that shows the configuration of another example of a liquid crystal diffraction element. It is a conceptual diagram showing the function of the optically anisotropic layer of the liquid crystal diffraction element shown in FIG. 22. It is a schematic plan view of a liquid crystal diffraction element according to an embodiment. It is a schematic configuration diagram of a finder device and an imaging device according to an embodiment.

[0025] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0026] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. Furthermore, in this specification, "perpendicular" and "parallel" regarding angles include the error range generally accepted in the technical field.

[0027] FIG. 1 shows a cross-sectional view of the configuration of a viewfinder optical system 5 according to an embodiment of the present disclosure and light beams. The example shown in FIG. 1 corresponds to Example 1, which will be described later. In FIG. 1, the light beams are shown as an on-axis light beam and an off-axis light beam corresponding to the maximum diagonal field of view. In FIG. 1, the left side is shown as the display element side and the right side is shown as the eyepoint side. The eyepoint EP in FIG. 1 does not indicate the shape but rather the position in the optical axis direction.

[0028] The viewfinder optical system 5 includes a display element 1 and an eyepiece optical system 3 located closer to the eyepoint than the display element 1. The display element 1 displays an image. The display element 1 includes a display surface 1a on which the image is displayed and a cover member 1b, which is a parallel plate-like optical element with no refractive power. In the example shown in 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 made of, for example, a liquid crystal display element or an organic electroluminescence (EL) display element. The display element 1 and the eyepiece optical system 3 are separated by a predetermined air gap. If the distance between the display element 1 and the eyepiece optical system 3 is configured to change during diopter adjustment, providing this air gap makes it easy to ensure the distance required for diopter adjustment.

[0029] 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 1a of the display element 1. In other words, the viewfinder optical system 5 is configured to allow the image displayed on the display element 1 to be observed via the eyepiece optical system 3.

[0030] 1 includes, in order from the display element side to the eyepoint side, a lens G1 having a positive refractive power, a lens G2 having a negative refractive power, a lens G3 having a positive refractive power, a lens G4 having a positive refractive power, a lens G5 having a negative refractive power, and a cover member C1. The cover member C1 is a parallel-plate-shaped optical element that has no refractive power.

[0031] The eyepiece optical system 3 preferably includes two or more positive lenses and one or more negative lenses, which is advantageous for correcting chromatic aberration while achieving compactness.

[0032] The eyepiece optical system 3 preferably includes two or more aspherical lenses. This is advantageous for achieving good aberration correction. The eyepiece optical system 3 may also be configured to include two or more aspherical lenses and one or more spherical lenses. This is advantageous for achieving good aberration correction while reducing costs.

[0033] One or more diffractive elements are disposed within the viewfinder optical system 5. The diffractive element referred to here is a type of optical element and is the same as a so-called diffractive optical element, but is referred to as a diffractive element in this specification. Diffractive elements have a negative dispersion value and large anomalous dispersion, and therefore provide a significant chromatic aberration correction effect. The use of a diffractive element can reduce the burden of aberration correction on other lenses, which is advantageous for achieving both compactness and high performance.

[0034] At least one of the diffraction elements is configured to be a first diffraction element DOE1 including a liquid crystal diffraction element. As an example, in the example of FIG. 1, the first diffraction element DOE1 is provided on the surface of lens G4 facing the display element. To simplify the configuration, the first diffraction element DOE1 may be configured to be a liquid crystal diffraction element. The liquid crystal diffraction element includes an optically anisotropic layer formed using a composition containing a liquid crystal compound and having a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound is continuously rotated along at least one direction in the plane. The detailed configuration of the liquid crystal diffraction element will be described later.

[0035] The optical surface of the liquid crystal diffraction element can be a surface shape without any physical steps and can be configured as a flat or curved surface. Similarly, the optical surface of the first diffraction element DOE1 can also be configured as a flat or curved surface without any physical steps. While a relief-type diffractive optical surface with a physical step shape may cause light scattered by the steps to flare, reducing resolution, the optical surface of the liquid crystal diffraction element can eliminate such concerns. Furthermore, while a contact multilayer diffractive optical element requires technically advanced and expensive processing, a liquid crystal diffraction element does not require such processing. Furthermore, a liquid crystal diffraction element has the advantage of being able to control the polarization state of light.

[0036] The first diffractive element DOE1 is positioned so as 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 of the viewfinder optical system 5 closest to the eyepoint. 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 diffractive element DOE1. In this specification, the optical surface of the diffractive element related to the conditional expression is the surface of the diffractive element that is in contact with air, either the surface on the display element side or the surface on the eyepoint side. As an example, the distance TL and the distance X1 are shown in FIG. 1. By positioning the first diffractive element DOE1 within a range that satisfies the conditional expression (1), it is possible to obtain a good effect in correcting chromatic aberration. 0.05≦X1 / TL≦1 (1)

[0037] It is preferable that the finder optical system 5 satisfies the following conditional formula (2). Here, H is half the maximum diameter of the display area on the display element 1. f is the focal length of the finder optical system 5. As an example, FIG. 1 shows half the maximum diameter H of the display area. Ensuring that the corresponding value of conditional formula (2) is not equal to or less than the lower limit is advantageous for increasing the finder magnification. Ensuring that the corresponding value of conditional formula (2) is not equal to or greater than the upper limit is advantageous for miniaturization. In order to obtain better characteristics, it is more preferable that the finder optical system 5 satisfies the following conditional formula (2-1), and it is even more preferable that it satisfies the following conditional formula (2-2). 0.3<H / f<0.7 (2) 0.35<H / f<0.6 (2-1) 0.4<H / f<0.5 (2-2)

[0038] The display area is the area on the display surface 1a where an image is actually displayed. For example, if the display element 1 has a display surface 1a with an aspect ratio of 4:3 on which a plurality of pixels are arranged and an image with an aspect ratio of 3:2 is displayed on a portion 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 do not necessarily coincide.

[0039] In this specification, the "longest diameter of the display region of the display element 1" in relation to H means twice the value of the distance between the optical axis Zk and the point farthest from the optical axis Zk in the radial direction in a display region whose center of gravity coincides with the optical axis Zk. For example, if the display region is rectangular, H can be half the length of the diagonal of the display region. Furthermore, for example, if the display region is circular, H can be the radius of the display region, and if the display region is elliptical, H can be half the longest diameter (major diameter) of the diameters of the display region.

[0040] It is preferable that the finder optical system 5 satisfy the following conditional expression (3). Here, dEP is the distance on the optical axis from the surface of the finder optical system 5 closest to the eyepoint to the eyepoint EP. An example of the distance dEP is shown in FIG. 1. If the eyepoint EP is not a single position but a range, dEP is the distance on the optical axis from the surface of the finder optical system 5 closest to the eyepoint to the point on the optical axis closest to the eyepoint within that range. f is the focal length of the finder optical system 5. Since f > 0 and dEP > 0, the lower limit of conditional expression (3) is f / dEP > 0. Ensuring that the corresponding value of conditional expression (3) is not greater than or equal to the upper limit is advantageous in ensuring a high finder magnification and a long eye relief. In order to obtain better characteristics, it is more preferable that the finder optical system 5 satisfy the following conditional expression (3-1), and even more preferable that it satisfy the following conditional expression (3-2). 0<f / dEP<0.95 (3) 0<f / dEP<0.9 (3-1) 0<f / dEP<0.85 (3-2)

[0041] 1 includes only one diffractive element, the finder optical system 5 of the present disclosure may be configured to include multiple diffractive elements. For example, the finder optical system 5 may be configured to include two, three, or more first diffractive elements DOE1, which is advantageous for improving performance.

[0042] When the viewfinder optical system 5 of the present disclosure includes multiple diffractive elements, at least one of the multiple diffractive elements may be configured as a second diffractive element DOE2 including a liquid crystal diffractive element, as in the example shown in FIG. 15 (described later). Furthermore, for simplified configuration, the second diffractive element DOE2 may be configured as a liquid crystal diffractive element. As described above, liquid crystal diffractive elements have many advantages. Like the first diffractive element DOE1, the optical surface of the second diffractive element DOE2 can be configured as a flat or curved surface without any physical steps.

[0043] The second diffractive element DOE2 is disposed so as to satisfy the following conditional expression (4): TL is the distance on the optical axis from the display surface 1a of the display element 1 to the surface of the viewfinder optical system 5 closest to the eyepoint; and 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 diffractive element DOE2. For example, in the example of FIG. 15, X2 corresponds to the distance on the optical axis from the display surface 1a of the display element 1 to the surface of the second diffractive element DOE2 closest to the eyepoint. 0≦X2 / TL<0.05 (4)

[0044] By locating the second diffractive element DOE2 within a range that satisfies conditional expression (4), it is possible to efficiently guide light rays emerging from the peripheral portion of the display surface 1a, which is distant from the optical axis Zk, to the eyepoint EP for use in observation. This ensures a greater amount of peripheral light, allowing images to be observed with brighter peripheral portions. In particular, in a finder optical system 5 with a high finder magnification and a long eye relief, there is a tendency for many light rays emerging from the peripheral portion of the display surface 1a to be blocked, so locating the second diffractive element DOE2 within a range that satisfies conditional expression (4) is effective.

[0045] In order to guide the light rays emerging from the peripheral portion of the display surface 1a by the second diffraction element DOE2 as described above, it is preferable that no element having refractive power is disposed between the second diffraction element DOE2 and the display surface 1a of the display element 1. However, an element having no refractive power, such as a parallel plate or a polarizing plate, may be disposed between the second diffraction element DOE2 and the display surface 1a of the display element 1.

[0046] When the finder optical system 5 includes the second diffractive element DOE2, it is preferable that the sign of the phase difference function of the first diffractive element DOE1 is different from the sign of the phase difference function of the second diffractive element DOE2. In this case, the first diffractive element DOE1 and the second diffractive element DOE2 can be configured so that the aberrations generated by the first diffractive element DOE1 and the second diffractive element DOE2 cancel each other out, which is advantageous in achieving even higher optical performance in addition to the above-mentioned effects of each diffractive element. In particular, it is preferable that the sign of the phase difference function of the first diffractive element DOE1 is different from the sign of the phase difference function of the second diffractive element DOE2 over the entire effective diameter of the first diffractive element DOE1 and the entire effective diameter of the second diffractive element DOE2.

[0047] The diffractive element included in the viewfinder optical system 5 is preferably provided on the surface of an optical element. Examples of optical elements on which the diffractive element is provided include lenses, cover members, filters, and prisms. The surface shape of the optical element on which the diffractive element is provided is preferably flat or curved. The term "curved surface" as used herein includes spherical and aspherical surfaces.

[0048] Generally, a diffraction element has a thin thickness in the optical axis direction. It is also easy to provide a diffraction element on the surface of a thin, parallel-plate-shaped optical element. For these reasons, restrictions on the placement of a diffraction element are less restrictive than for a general lens, and systems using a diffraction element have a higher degree of design freedom, which is advantageous for miniaturization and high performance. In particular, when the main part of the diffraction element is a liquid crystal diffraction element, there is no concern about the above-mentioned flare, and other optical elements can be placed near the diffraction element, which is even more advantageous for miniaturization.

[0049] Among the optical elements provided with a diffractive element, at least one optical element may be configured such that a lens having refractive power is disposed adjacent to the optical element on at least one of the object side and image side. In such a configuration, the minimum distance Dmin in the optical axis direction between the optical surface of the diffractive element provided on the surface of the optical element and the optical surface of the lens disposed adjacent to the optical element can be made very small, for example, 1.8 mm or less. In order to achieve compactness, the minimum distance Dmin is preferably 0.5 mm or less. Note that the minimum distance Dmin does not necessarily have to be the distance on the optical axis, but may be the distance between the surfaces within the effective diameter of each element, for example, the distance in the peripheral portion away from the optical axis Zk. In other words, it is possible to arrange lenses in close proximity to the optical element provided with a diffractive element not only on the optical axis but also in the peripheral portion away from the optical axis.

[0050] Furthermore, at least one of the optical elements having a diffractive element may have a lens having refractive power disposed on both the object side and the image side. In the example shown in FIG. 1, lenses G3 and G5 are disposed on the object side and the image side, respectively, of lens G4, which is the optical element having the first diffractive element DOE1. In the viewfinder optical system 5, in the optical element at the position where lenses having refractive power are disposed on both the object side and the image side, as shown in FIG. 1, the on-axis light beam and the off-axis light beam are separated and the light beam is diverged. By disposing a diffractive element in such a position, aberrations can be effectively corrected, which is advantageous for improving performance.

[0051] When a diffractive element is provided on a surface of an optical element, the d-line Abbe number vd_op of the optical element on which the diffractive element is provided is preferably 35 or more and less than 100. In this case, it is possible to use ordinary materials that are not specialized, thereby preventing high costs, and it is also advantageous for observing brighter images because a material with high transmittance can be selected. Note that when a diffractive element is provided on the cemented surface of a cemented lens, it is preferable that the d-line Abbe numbers of the lenses on both sides of the cemented surface be 35 or more and less than 100.

[0052] When a diffractive element is provided on a surface of an optical element, the d-line transmittance Td_op of the optical element on which the diffractive element is provided is preferably 98% or more. This is advantageous for observing brighter images. Furthermore, when a diffractive element is provided on the cemented surface of a cemented lens, the d-line transmittance of the cemented lens is preferably 98% or more.

[0053] When the distance on the optical axis from the display surface 1a of the display element 1 to the optical elements in the viewfinder optical system 5 is X, it is preferable that the d-line transmittance Td_part of a partial optical system made up of all optical elements arranged within the range of 0.05≦X / TL≦1 is 92% or more. This is advantageous for observing a brighter image.

[0054] The transmittance may be measured, for example, using a spectrophotometer V-650 manufactured by JASCO Corporation.

[0055] The thickness of the diffraction element's diffractive region in the optical axis direction is preferably 10 μm or less. This is advantageous for achieving higher transmittance, which is advantageous for observing brighter images. The thickness of the diffraction element's diffractive region in the optical axis direction can be measured, for example, using a scanning electron microscope (SEM).

[0056] The eyepiece optical system 3 may be configured so that all of the lenses with refractive power are uncemented single lenses, which increases the degree of freedom in design and is advantageous for correcting various aberrations.

[0057] The number of lenses having refractive power included in the finder optical system 5 is preferably four or five, which is advantageous for achieving a compact configuration with a reduced number of lenses while still providing good correction for overall aberrations.

[0058] Note that the example shown in Figure 1 is merely an example, and various modifications are possible without departing from the spirit and scope of the technology of the present disclosure. The number of lenses with refractive power and the number of cover members included in the eyepiece optical system of the present disclosure may be different from those in the example of Figure 1. For example, the lenses with refractive power included in the eyepiece optical system 3 of Figure 1 are three positive lenses and two negative lenses, but in the technology of the present disclosure, the lenses with refractive power included in the eyepiece optical system may be three positive lenses and one negative lens. Furthermore, the shapes of the lenses included in the eyepiece optical system may also be different from those in the example of Figure 1.

[0059] The above-described preferred and possible configurations, including those related to the conditional expressions, can be combined in any desired manner, and are preferably selectively adopted as appropriate according to the required specifications. Note that the conditional expressions that the finder optical system 5 of the present disclosure preferably satisfies are not limited to those written in the form of an expression, but include all conditional expressions obtained by arbitrarily combining lower and upper limits from among the preferred, more preferred, and even more preferred conditional expressions.

[0060] As an example, a viewfinder optical system 5 according to a preferred embodiment of the present disclosure includes a display element 1 and an eyepiece optical system 3 arranged closer to the eyepoint than the display element 1, and one or more diffraction elements are arranged within the viewfinder optical system 5, at least one of which is a first diffraction element DOE1 including a liquid crystal diffraction element, and satisfies the above-mentioned conditional expression (1).

[0061] Next, examples of the finder optical system 5 of the present disclosure will be described with reference to the drawings. Note that the reference numerals assigned to the components in the cross-sectional views of each example are used independently for each example to avoid cluttering the explanation and drawings due to an increase in the number of digits in the reference numerals. Therefore, even if common reference numerals are assigned in drawings of different examples, this does not necessarily mean that the components have the same configuration.

[0062] [Example 1] The configuration of the finder optical system 5 of Example 1 is shown in Figure 1, and since the illustration method and configuration are as described above, some of the overlapping explanations will be omitted here. The finder optical system 5 of Example 1 comprises, in order from the display element side to the eyepoint side, a display element 1 and an eyepiece optical system 3. In order from the display element side to the eyepoint side, the eyepiece optical system 3 comprises five lenses, lens G1 to lens G5, and a cover member C1. A first diffractive element DOE1 is provided on the surface of lens G4 facing the display element.

[0063] For the finder optical system 5 of Example 1, basic lens data is shown in Table 1, specifications are shown in Table 2, aspherical coefficients are shown in Table 3, and phase difference coefficients are shown in Table 4.

[0064] Table 1 is described as follows. The Sn column indicates the surface number of each surface, with the surface on which the display surface 1a of the display element 1 is disposed being designated the first surface, and the numbers increase by one toward the eye point. The R column indicates the radius of curvature of each surface. The D column indicates the surface distance on the optical axis between each surface and its adjacent surface on the eye point side. The Nd column indicates the refractive index of each component with respect to the d line. The νd column indicates the Abbe number of each component based on the d line.

[0065] Table 1 also lists the eyepoint EP, and the column for Sn of the surface corresponding to the eyepoint EP lists the surface number and the term (EP). In Table 1, the sign of the radius of curvature of a surface whose convex shape faces the display element side is positive, and the sign of the radius of curvature of a surface whose convex shape faces the eyepoint side is negative. The surface numbers of aspherical surfaces are marked with an *, and the column for the radius of curvature of the aspherical surface lists the numerical value of the paraxial radius of curvature. Also in Table 1, the surface numbers of surfaces corresponding to the diffractive element are marked with an **.

[0066] Table 2 shows the focal length f of the finder optical system 5, the diagonal field of view at all angles of view, and the half value H of the maximum diameter of the display area. The diagonal field of view is the field of view in the diagonal direction in a rectangular field of view.

[0067] In Table 3, the Sn row indicates the surface number of the aspherical surface, and the KA and Am rows indicate the numerical values ​​of the aspherical coefficients for each aspherical surface. m is an integer of 3 or more, and for example, m = 3, 4, 5, ... 16 for the aspherical surfaces of Example 1. The numerical values ​​of the aspherical coefficients in Table 3, "E±n" (n: integer), are expressed as "×10 ±ｎ " KA and Am are aspherical coefficients in the aspherical formula expressed as follows: Zd = C × h ２ / {1 + (1 - KA × C ２ ×h ２ ) １ / ２} + ΣAm × h ｍ where Zd: aspherical depth (length of perpendicular line drawn from a point on the aspherical surface at height h to a plane perpendicular to the optical axis Zk where the vertex of the aspherical surface is in contact) h: height (distance from the optical axis Zk to the aspherical surface) C: reciprocal of the paraxial radius of curvature KA, Am: aspherical coefficients, and Σ in the aspherical surface formula represents the summation over m.

[0068] In Table 4, the surface numbers of the surfaces corresponding to the diffraction elements are shown in the Sn row, and the numerical values ​​of the phase difference coefficients for each diffraction element are shown in the Pj (j=2, 4, 6) row. The numerical values ​​of the phase difference coefficients in Table 4, "E±n" (n: integer), are expressed as "×10 ±ｎ " Pj is the phase difference coefficient in the phase difference function PH(h) expressed by the following formula: PH(h) = ΣPj × h ｊ where Pj is the phase difference coefficient, and h is the height (the distance from the optical axis Zk to the surface corresponding to the diffraction element), and Σ in the phase difference function PH(h) represents the summation with respect to j.

[0069] In the data in each table, the angle unit is degrees and the length unit is mm (millimeters), but since the optical system can be used with proportional magnification or reduction, other appropriate units can also be used. Also, in each table below, the values ​​are rounded to the specified decimal point.

[0070]

[0071]

[0072]

[0073]

[0074] FIG. 2 shows various aberration diagrams for the finder optical system 5 of Example 1. In FIG. 2, from left to right, spherical aberration, astigmatism, distortion, and lateral chromatic aberration are shown. In the spherical aberration diagram, aberrations at the d-line, C-line, and F-line are shown by solid lines, long-dashed lines, and short-dashed lines, respectively. In the astigmatism diagram, aberrations at the d-line in the sagittal direction are shown by solid lines, and aberrations at the d-line in the tangential direction are shown by short-dashed lines. In the distortion diagram, aberrations at the d-line are shown by solid lines. In the lateral chromatic aberration diagram, aberrations at the C-line and F-line are shown by long-dashed lines and short-dashed lines, respectively. The unit "dpt" on the horizontal axis of the spherical aberration diagram and astigmatism diagram indicates diopters. The unit "min" on the horizontal axis of the lateral chromatic aberration diagram indicates angular minutes. In the spherical aberration diagram, the diameter of the eyepoint EP in units of mm (millimeters) is shown after "φ=". In the other aberration diagrams, the value of the diagonal field of view at half angle of view is shown after "ω=".

[0075] The symbols, meanings, notation methods, and illustration methods of each data item related to the above-mentioned first embodiment are the same in the following embodiments unless otherwise specified, and therefore, redundant explanations will be omitted below.

[0076] [Example 2] The configuration and light beams of a viewfinder optical system 5 of Example 2 are shown in Figure 3. The viewfinder optical system 5 of Example 2 includes, in order from the display element side to the eyepoint side, a display element 1 and an eyepiece optical system 3. The eyepiece optical system 3 includes, in order from the display element side to the eyepoint side, a lens G1 having positive refractive power, a lens G2 having negative refractive power, a lens G3 having positive refractive power, a lens G4 having positive refractive power, a lens G5 having negative refractive power, and a cover member C1. The cover member C1 is a parallel-plate-shaped optical element with no refractive power. A first diffractive element DOE1 is provided on the surface of the cover member C1 facing the display element.

[0077] For the finder optical system 5 of Example 2, basic lens data is shown in Table 5, specifications are shown in Table 6, aspherical coefficients are shown in Table 7, phase difference coefficients are shown in Table 8, and aberration diagrams are shown in FIG.

[0078]

[0079]

[0080]

[0081]

[0082] [Example 3] The configuration and light beams of a viewfinder optical system 5 of Example 3 are shown in Figure 5. The viewfinder optical system 5 of Example 3 comprises, in order from the display element side to the eyepoint side, a display element 1 and an eyepiece optical system 3. The eyepiece optical system 3 comprises, in order from the display element side to the eyepoint side, a lens G1 having positive refractive power, a lens G2 having negative refractive power, a lens G3 having positive refractive power, a lens G4 having positive refractive power, and a cover member C1. The cover member C1 is a parallel-plate-shaped optical element with no refractive power. A first diffractive element DOE1 is provided on the surface of the cover member C1 facing the display element.

[0083] For the finder optical system 5 of Example 3, basic lens data is shown in Table 9, specifications are shown in Table 10, aspherical coefficients are shown in Table 11, phase difference coefficients are shown in Table 12, and aberration diagrams are shown in FIG.

[0084]

[0085]

[0086]

[0087]

[0088] [Example 4] The configuration and light beams of a viewfinder optical system 5 of Example 4 are shown in Figure 7. The viewfinder optical system 5 of Example 4 includes, in order from the display element side to the eyepoint side, a display element 1 and an eyepiece optical system 3. The eyepiece optical system 3 includes, in order from the display element side to the eyepoint side, a cover member C1, a lens G1 having positive refractive power, a lens G2 having negative refractive power, a lens G3 having positive refractive power, a lens G4 having negative refractive power, a lens G5 having positive refractive power, and a cover member C2. The cover members C1 and C2 are parallel-plate-shaped optical elements with no refractive power. A first diffractive element DOE1 is provided on the surface of the cover member C1 facing the display element.

[0089] For the finder 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 aberration diagrams are shown in FIG.

[0090]

[0091]

[0092]

[0093] [Example 5] The configuration and light beams of a viewfinder optical system 5 of Example 5 are shown in Figure 9. The viewfinder optical system 5 of Example 5 includes, in order from the display element side to the eyepoint side, a display element 1 and an eyepiece optical system 3. The eyepiece optical system 3 includes, in order from the display element side to the eyepoint side, a lens G1 having positive refractive power, a lens G2 having negative refractive power, a cover member C1, a lens G3 having positive refractive power, a lens G4 having positive refractive power, a lens G5 having negative refractive power, and a cover member C2. The cover members C1 and C2 are parallel-plate-shaped optical elements with no refractive power. A first diffractive element DOE1 is provided on the surface of the cover member C1 facing the display element.

[0094] For the finder optical system 5 of Example 5, basic lens data is shown in Table 16, specifications in Table 17, aspherical coefficients in Table 18, phase difference coefficients in Table 19, and aberration diagrams in FIG. 10.

[0095]

[0096]

[0097]

[0098]

[0099] [Example 6] The configuration and light beams of a viewfinder optical system 5 of Example 6 are shown in Figure 11. The viewfinder optical system 5 of Example 6 includes, in order from the display element side to the eyepoint side, a display element 1 and an eyepiece optical system 3. The eyepiece optical system 3 includes, in order from the display element side to the eyepoint side, a cover member C1, a lens G1 having positive refractive power, a lens G2 having negative refractive power, a lens G3 having positive refractive power, a lens G4 having positive refractive power, a lens G5 having negative refractive power, and a cover member C2. The cover members C1 and C2 are parallel-plate optical elements with no refractive power. The viewfinder optical system 5 of Example 6 includes two first diffractive elements DOE1. A first diffractive element DOE1 is provided on each of the display element side surface of the cover member C1 and the display element side surface of the cover member C2.

[0100] For the finder optical system 5 of Example 6, basic lens data is shown in Table 20, specifications are shown in Table 21, aspherical coefficients are shown in Table 22, phase difference coefficients are shown in Table 23, and each aberration diagram is shown in FIG.

[0101]

[0102]

[0103]

[0104]

[0105] [Example 7] The configuration and light beams of a finder optical system 5 of Example 7 are shown in Figure 13. The finder optical system 5 of Example 7 includes, in order from the display element side to the eyepoint side, a display element 1 and an eyepiece optical system 3. The eyepiece optical system 3 includes, in order from the display element side to the eyepoint side, a lens G1 having positive refractive power, a lens G2 having negative refractive power, a lens G3 having positive refractive power, a lens G4 having positive refractive power, a lens G5 having negative refractive power, and a cover member C1. The cover member C1 is a parallel-plate-shaped optical element with no refractive power. The finder optical system 5 of Example 7 includes a first diffractive element DOE1 and a second diffractive element DOE2. The first diffractive element DOE1 is provided on the display element side surface of the cover member C1. The second diffractive element DOE2 is provided on the display element side surface of the cover member 1b included in the display element 1. That is, in the finder optical system 5 of Example 7, the display surface 1a of the display element 1 and the second diffractive element DOE2 are located at the same position in the optical axis direction.

[0106] For the finder optical system 5 of Example 7, basic lens data is shown in Table 24, specifications are shown in Table 25, aspherical coefficients are shown in Table 26, phase difference coefficients are shown in Table 27, and each aberration diagram is shown in FIG.

[0107]

[0108]

[0109]

[0110]

[0111] Example 8 The configuration and light beams of a finder optical system 5 of Example 8 are shown in FIG. 15 . The finder optical system 5 of Example 8 includes, in order from the display element side to the eyepoint side, a display element 1 and an eyepiece optical system 3. The eyepiece optical system 3 includes, in order from the display element side to the eyepoint side, a lens G1 having positive refractive power, a lens G2 having negative refractive power, a lens G3 having positive refractive power, a lens G4 having positive refractive power, a lens G5 having negative refractive power, and a cover member C1. The cover member C1 is a parallel-plate-shaped optical element with no refractive power. The finder optical system 5 of Example 8 includes a first diffractive element DOE1 and a second diffractive element DOE2. The first diffractive element DOE1 is provided on the display element side surface of the cover member C1. The second diffractive element DOE2 is provided on the eyepoint side surface of a cover member 1b included in the display element 1.

[0112] For the finder optical system 5 of Example 8, basic lens data is shown in Table 28, specifications are shown in Table 29, aspherical coefficients are shown in Table 30, phase difference coefficients are shown in Table 31, and each aberration diagram is shown in FIG.

[0113]

[0114]

[0115]

[0116]

[0117] Table 32 shows the corresponding values ​​of conditional expressions (1) to (4) for the finder optical systems 5 of Examples 1 to 8. The values ​​shown in Table 32 are values ​​based on the d-line. Table 33 shows the values ​​mentioned in the above description of the preferred configurations of the finder optical systems 5 of Examples 1 to 8. The "minimum distance on the optical axis" in Table 33 is the minimum distance on the optical axis between the optical surface of the diffractive element and the optical surface of the lens arranged adjacent to the optical element having the diffractive element. The "minimum distance at the outermost periphery" in Table 33 is the minimum distance in the optical axis direction between the optical surface of the lens arranged adjacent to the optical element having the diffractive element and the optical surface of the diffractive element at the outermost periphery. The units of "minimum distance on the optical axis" and "minimum distance at the outermost periphery" in Table 33 are mm.

[0118]

[0119]

[0120] The finder optical systems 5 of Examples 1 to 8 are compact, yet achieve high optical performance with excellent correction of various aberrations. Furthermore, the finder optical systems 5 of Examples 1 to 8 have a diagonal field of view of 45° or more at all angles of view, ensuring a wide field of view. Furthermore, the finder optical systems 5 of Examples 1 to 8 have a focal length of 15 mm or less, making it possible to achieve a high finder magnification.

[0121] Next, the liquid crystal diffraction element according to the technology of the present disclosure will be described with reference to FIGS. 17 to 24. For ease of visualization, the scales of the components in FIGS. 17 to 24 are appropriately different from the actual scales. FIG. 17 is a diagram schematically illustrating the layered structure of a liquid crystal diffraction element 10 as an example. FIG. 18 is a plan view schematically illustrating the liquid crystal orientation pattern of the liquid crystal diffraction element 10 shown in FIG. 17. The liquid crystal diffraction element 10 is sheet-shaped. In FIGS. 17 and 18, in a Cartesian coordinate system using mutually orthogonal x-, y-, and z-axes, the sheet surface of the liquid crystal diffraction element 10 is the xy plane, and the thickness direction is the z-axis.

[0122] The liquid crystal diffraction element 10 has a support 20, an alignment film 24, and an optically anisotropic layer 26. In the liquid crystal diffraction element 10 of Fig. 17, the alignment film 24 is formed on the surface of the support 20, and the optically anisotropic layer 26 is formed on the surface of the alignment film 24.

[0123] 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 aligned liquid crystal compounds 30 are stacked, similar to optically anisotropic layers formed using compositions containing ordinary liquid crystal compounds. In the examples of Figures 17 and 18, the direction of the z-axis is the stacking direction of the liquid crystal compounds 30 and is perpendicular to the optical surface of the liquid crystal diffraction element 10.

[0124] In the schematic plan view of the liquid crystal diffraction element 10 shown in FIG. 18, only the liquid crystal compound 30 on the surface of the alignment film 24 is shown in order to clearly show the configuration of the liquid crystal diffraction element 10. As shown in FIG. 18, the optically anisotropic layer 26 has a liquid crystal orientation pattern in which the orientation of the optical axis 30A derived from the liquid crystal compound 30 changes while continuously rotating in one direction within the plane of the optically anisotropic layer 26. Here, the direction in which the optical axis 30A changes rotationally is aligned with the x-axis direction in the xy plane. In the following description of the liquid crystal diffraction element 10, the direction in which the optical axis 30A changes rotationally is referred to as the x-direction. In the following description, the y-axis direction is also referred to as the y-direction, and the z-axis direction is also referred to as the z-direction.

[0125] The optical axis 30A derived from the liquid crystal compound 30 is the axis along which the refractive index of the liquid crystal compound 30 is highest, that is, the so-called slow axis. As shown in Fig. 17 , when the liquid crystal compound 30 is a rod-shaped liquid crystal compound, the optical axis 30A is aligned with the long axis direction of the rod shape. In the following description, the optical axis 30A derived from the liquid crystal compound 30 will also be referred to as the optical axis 30A of the liquid crystal compound 30, or simply as the optical axis 30A.

[0126] The phrase "the orientation of the optical axis 30A changes while continuously rotating in the x direction" specifically means that the angle formed between the optical axis 30A of the liquid crystal compound 30 aligned along the x direction and the x direction varies depending on the position in the x direction, and the angle formed between the optical axis 30A and the x direction gradually changes along the x direction from θ to θ+180° or θ−180°. Here, "the angle gradually changes" may mean that the angle changes at regular angle intervals or that the angle changes continuously. However, the difference in angle between the optical axes 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 even more preferably a smaller angle.

[0127] On the other hand, in the y direction perpendicular to the x direction, the liquid crystal compounds 30 having 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 axes 30A and the x direction are equal among the liquid crystal compounds 30 arranged in the y direction.

[0128] In the liquid crystal diffraction element 10 having such a liquid crystal orientation pattern of the liquid crystal compound 30, the length (distance) over which the optical axis 30A of the liquid crystal compound 30 rotates 180° in the x direction is also referred to as one period Λ of 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 of the liquid crystal orientation pattern is defined as the distance from the angle between the optical axis 30A of the liquid crystal compound 30 and the x direction from θ to θ + 180°. Specifically, as shown in FIG. 18 , the distance between the centers in the x direction of two liquid crystal compounds 30 whose x direction and the direction of the optical axis 30A coincide is defined as one period Λ. In the liquid crystal diffraction element 10, the liquid crystal orientation pattern of the optically anisotropic layer 26 is a pattern in which this one period Λ of liquid crystal orientation is repeated in the x direction.

[0129] As described above, in the optically anisotropic layer 26, the liquid crystal compounds 30 aligned in the y direction have the same angle between their optical axes 30A and the x direction. A region where the liquid crystal compounds 30 aligned in the y direction and whose optical axes 30A and the x direction form the same angle is referred to as region R.

[0130] 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 target light) to be diffracted by the liquid crystal diffraction element 10. That is, when the wavelength of the target light is λ, the in-plane retardation Re is preferably λ / 2. This is because the closer the in-plane retardation value is to the half wavelength of the target light, the higher the diffraction efficiency that can be obtained in diffracting the target light.

[0131] The in-plane retardation Re is calculated by the product of the refractive index difference Δn associated with the refractive index anisotropy of region R and the thickness of the optically anisotropic layer 26. Here, the refractive index difference associated with the refractive index anisotropy of 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 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 region R is equal to the difference between the refractive index of liquid crystal compound 30 in the direction of optical axis 30A and the refractive index of liquid crystal compound 30 in the direction perpendicular to optical axis 30A in the plane of region R. In other words, the refractive index difference Δn depends on liquid crystal compound 30, and the in-plane retardation Re of each region R is approximately equal.

[0132] The in-plane retardation at a wavelength λ is Re(λ), and the refractive index difference due to the refractive index anisotropy at a wavelength λ is Δn λ and the thickness of the optically anisotropic layer 26 is d, the in-plane retardation Re(λ) of the optically anisotropic layer 26 for incident light having a wavelength of λ nm is given by Re(λ)=Δn λ 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: 0.7×(λ / 2) nm≦Δn λ ×d≦1.3×(λ / 2)nm

[0133] Re(λ) can be obtained by measuring at a wavelength λ using, for example, an AxoScan (manufactured by Axometrics). By inputting the average refractive index and film thickness into AxoScan, the slow axis direction (°) Re(λ) = R0(λ) is calculated. The film thickness is measured in μm. The average refractive index is expressed as ((nx + ny + nz) / 3), where nx, ny, and nz are the refractive indices in the x, y, and z directions, respectively. Note that R0(λ) is displayed as a numerical value calculated by AxoScan, but it means Re(λ).

[0134] When the in-plane retardation value is set to λ / 2, the optically anisotropic layer 26 functions as a general half-wave plate. That is, when the in-plane retardation value is set to λ / 2, the optically anisotropic layer 26 has the function of imparting a phase difference of half the wavelength, i.e., 180°, to two orthogonal linearly polarized components contained in light incident on the optically anisotropic layer 26. Note that while it is the optically anisotropic layer 26 that functions as a half-wave plate, the present disclosure also includes an embodiment in which a laminate integrally including the support 20 and the alignment film 24 functions as a half-wave plate.

[0135] When circularly polarized light is incident on the optically anisotropic layer 26 described above, the light's direction of travel is changed by diffraction, i.e., the light is deflected by diffraction and the rotation direction of the circularly polarized light is converted. This action is conceptually shown in Figures 19 and 20, illustrating the optically anisotropic layer 26. As described above, the optically anisotropic layer 26 has a structure in which aligned liquid crystal compounds 30 are stacked, but for ease of understanding, Figures 19 and 20 simplify the drawings and only show the liquid crystal compounds 30 on the surface of the alignment film 24 in the optically anisotropic layer 26.

[0136] 19 and 20, the in-plane retardation of the optically anisotropic layer 26 is assumed to be λ / 2. In this case, as shown in FIG. Ｌ When the incident light L1 having a phase difference of 180° is incident on the optically anisotropic layer 26, the incident light L1 is given a phase difference of 180° by passing through the optically anisotropic layer 26, and the transmitted light L2 is converted into right-handed circularly polarized light P Ｒ is converted to

[0137] Furthermore, when the incident light L1 passes through the optically anisotropic layer 26, the absolute phase changes depending on the orientation of the optic axis 30A of each liquid crystal compound 30. At this time, the orientation of the optic axis 30A changes while rotating along the x direction, so the amount of change in the absolute phase of the incident light L1 varies depending on the orientation of the optic axis 30A. Furthermore, since the liquid crystal orientation pattern formed in the optically anisotropic layer 26 is a periodic pattern in the x direction, the incident light L1 that passes through the optically anisotropic layer 26 is given an absolute phase Q1 that is periodic in the x direction corresponding to the orientation of each optic axis 30A, as shown in Figure 19. As a result, an equiphase surface E1 that is tilted in the opposite direction to the x direction is formed.

[0138] Therefore, the transmitted light L2 is deflected so as to tilt toward a direction perpendicular to the equiphase surface E1, and travels in a direction different from the traveling direction of the incident light L1. Ｌ The incident light L1 is right-handed circularly polarized light P that is tilted at a certain angle in the x direction with respect to the incident direction. Ｒ is converted into transmitted light L2.

[0139] On the other hand, as conceptually shown in FIG. 20, right-handed circularly polarized light P Ｒ When the incident light L4 is incident, the incident light L4 is given a phase difference of 180° by passing through the optically anisotropic layer 26, and is converted into left-handed circularly polarized light P Ｌ The light is converted into transmitted light L5.

[0140] Furthermore, when the incident light L4 passes through the optically anisotropic layer 26, the absolute phase changes depending on the orientation of the optic axis 30A of each liquid crystal compound 30. At this time, the orientation of the optic axis 30A changes while rotating along the x direction, so the amount of change in the absolute phase of the incident light L4 differs depending on the orientation of the optic axis 30A. Furthermore, since the liquid crystal orientation pattern formed in the optically anisotropic layer 26 is a periodic pattern in the x direction, the incident light L4 that has passed through the optically anisotropic layer 26 is given an absolute phase Q2 that is periodic in the x direction corresponding to the orientation of each optic axis 30A, as shown in FIG.

[0141] Here, the incident light L4 in FIG. 20 is right-handed circularly polarized light P ＲTherefore, the absolute phase Q2 periodic in the x direction corresponding to the direction of the optical axis 30A is Ｌ As a result, the incident light L4 forms an equiphase surface E2 that is inclined in the x direction, opposite to the case of the incident light L1.

[0142] Therefore, the transmitted light L5 is deflected so as to tilt toward a direction perpendicular to the equiphase surface E2, and travels in a direction different from the traveling direction of the incident light L4. Ｒ The incident light L4 is a left-handed circularly polarized light P that is tilted at a certain angle in the direction opposite to the x-direction with respect to the incident direction. Ｌ is converted into transmitted light L5.

[0143] Here, by changing the period Λ of the liquid crystal orientation pattern formed in the optically anisotropic layer 26, the angle of polarization (diffraction angle) of the transmitted light L2 and the transmitted light L5 can be adjusted. Specifically, the shorter the period Λ of the liquid crystal orientation pattern, the stronger the interference between the lights passing through adjacent liquid crystal compounds 30, thereby allowing the transmitted light L2 and the transmitted light L5 to be deflected more. Furthermore, by reversing the direction of rotation of the optical axis 30A of the liquid crystal compounds 30, which rotates along the x-direction, the direction of polarization of the transmitted light can be reversed.

[0144] 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 may be a discotic liquid crystal compound. Also, two or more rod-shaped liquid crystal compounds, two or more discotic liquid crystal compounds, or a mixture of a rod-shaped liquid crystal compound and a discotic liquid crystal compound may be used. 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.

[0145] As the rod-shaped liquid crystal compound, azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoates, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes, and alkenylcyclohexylbenzonitriles are preferably used. Not only the above-mentioned low-molecular-weight liquid crystal molecules, but also polymeric liquid crystal molecules can be used.

[0146] As the discotic liquid crystal compound, for example, those described in JP-A Nos. 2007-108732 and 2010-244038 can be preferably used. When a discotic liquid crystal compound is used in the optically anisotropic layer, the liquid crystal compound stands up 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, i.e., a so-called fast axis.

[0147] The optically anisotropic layer preferably has a broadband with respect to the wavelength of incident light, and is preferably constructed using a liquid crystal material with a birefringence that exhibits reverse dispersion. It is also preferable to impart a twist component to the liquid crystal composition or to laminate different retardation layers, thereby making the optically anisotropic layer substantially broadband with respect to the wavelength of incident light. For example, JP 2014-089476 A discloses a method for realizing a broadband patterned half-wave plate by laminating two layers of liquid crystal with different twist directions in an optically anisotropic layer, and this method may also be used.

[0148] Next, the support 20 will be described. The support 20 supports the alignment film 24 and the optically anisotropic layer 26. Various sheet-like materials, such as films or plates, can be used as the support 20, as long as they can support the alignment film 24 and the optically anisotropic layer 26. Transparent supports are preferred for the support 20, and examples of such materials include polyacrylic resin films such as polymethyl methacrylate, cellulose resin films such as cellulose triacetate, cycloolefin polymer films (e.g., Arton (registered trademark) manufactured by JSR Corporation and ZEONOR (registered trademark) manufactured by Zeon Corporation), polyethylene terephthalate (PET), polycarbonate, and polyvinyl chloride. The support 20 is not limited to flexible films, and may also be a non-flexible substrate such as a glass substrate. The support 20 may also be multilayered. Examples of multilayer supports include those that include any of the above-mentioned supports as a substrate, with other layers provided on the surface of this substrate.

[0149] There is no limitation on the thickness of the support 20, and it may be set appropriately to a thickness that can support the alignment film 24 and the optically anisotropic layer 26 depending on the application of the liquid crystal diffraction element 10 and the material forming the support 20. The thickness of the support 20 is preferably 1 to 1000 μm, more preferably 3 to 250 μm, and even more preferably 5 to 150 μm.

[0150] Next, the alignment film 24 will be described. The alignment film 24 is a film for orienting the liquid crystal compound 30 into a predetermined liquid crystal alignment pattern when forming the optically anisotropic layer 26. As described above, the optically anisotropic layer 26 of the liquid crystal diffraction element 10 has a liquid crystal alignment pattern in which the direction of the optic axis 30A changes while continuously rotating along one in-plane direction. Therefore, the alignment film 24 is formed so that the optically anisotropic layer 26 can form this liquid crystal alignment pattern.

[0151] Various known alignment films can be used for the alignment film 24. Examples include a rubbed film made of an organic compound such as a polymer, an obliquely evaporated film of an inorganic compound, a film with microgrooves, and a film formed by accumulating an LB (Langmuir-Blodgett) film using the Langmuir-Blodgett method of an organic compound such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearate.

[0152] In the liquid crystal diffraction element 10, a so-called photo-alignment film, which is an alignment film formed by irradiating a photo-alignable material with polarized or non-polarized light, is preferably used as the alignment film 24. That is, in the liquid crystal diffraction element 10, a photo-alignment film formed by applying a photo-alignment material onto the support 20 is preferably used as the alignment film 24. Polarized light can be irradiated from a vertical direction or an oblique direction to the photo-alignment film, and non-polarized light can be irradiated from an oblique direction to the photo-alignment film.

[0153] There is no limitation on the thickness of the alignment film 24, and the thickness may be set appropriately to obtain the necessary alignment function depending on 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.

[0154] There is no limitation on the method for forming the alignment film 24, 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 an alignment film is applied to the surface of the support 20, dried, and then exposed to laser light to form an alignment pattern.

[0155] An example of an exposure apparatus for forming an alignment pattern by exposing an alignment film is conceptually shown in Fig. 21. Note that the example shown in Fig. 21 illustrates exposure of the alignment film 24 of the liquid crystal diffraction element 10.

[0156] The exposure device 50 shown in Figure 21 includes a light source 54 equipped with a laser 52, a beam splitter 56 that splits the laser beam 70 emitted by the laser 52 into two beams, beam 72A and beam 72B, mirrors 58A and 58B that are respectively arranged on the optical paths of the two split beams 72A and 72B, and quarter-wave plates 60A and 60B. The light source 54 emits linearly polarized light P0. The quarter-wave plates 60A and 60B have optical axes that are orthogonal to each other. The quarter-wave plate 60A converts the linearly polarized light P0 (beam 72A) into right-handed circularly polarized light P0. Ｒ The quarter-wave plate 60B converts the linearly polarized light P0 (light ray 72B) into left-handed circularly polarized light P Ｌ are converted to , respectively.

[0157] The support 20 having the alignment film 24 before the alignment pattern is formed is placed in an exposure section, and two light beams 72A and 72B are caused to intersect and interfere on the alignment film 24, and the alignment film 24 is exposed to the interference light. 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. As a result, an alignment pattern in which the alignment state changes periodically is obtained on the alignment film 24.

[0158] In the exposure device 50, the period of the alignment pattern can be adjusted by changing the crossing angle β of the two light beams 72A and 72B. That is, in the exposure device 50, by adjusting the crossing angle β, in the alignment pattern in which the optical axis 30A derived from the liquid crystal compound 30 continuously rotates along one direction, one period Λ in one direction in which the optical axis 30A rotates can be adjusted.

[0159] By forming the optically anisotropic layer 26 on the alignment film 24 having such an alignment pattern in which the alignment state changes periodically, it is possible to form the optically anisotropic layer 26 having a liquid crystal alignment pattern in which the optical axis 30A derived from the liquid crystal compound 30 continuously rotates in one direction. In addition, by rotating the optical axes of the quarter-wave plates 60A and 60B by 90°, the rotation direction of the optical axis 30A can be reversed.

[0160] Next, another example of a liquid crystal diffraction element 12 according to the technology of the present disclosure will be described with reference to Figures 22 and 23. Figure 22 is a diagram schematically showing the layered structure of the liquid crystal diffraction element 12. The liquid crystal diffraction element 12 has a support 20, an alignment film 25, and an optically anisotropic layer 27. The alignment film 25 is formed on the surface of the support 20, and the optically anisotropic layer 27 is formed on the surface of the alignment film 25. The liquid crystal diffraction element 12 is sheet-shaped, similar to the liquid crystal diffraction element 10. In Figure 22, in a Cartesian coordinate system using mutually orthogonal x-, y-, and z-axes, the sheet surface of the liquid crystal diffraction element 12 is the xy plane, and the thickness direction is the z direction.

[0161] The optically anisotropic layer 27 is formed using a composition containing a liquid crystal compound 30 and has a structure in which aligned liquid crystal compounds 30 are stacked. The optically anisotropic layer 27 has a liquid crystal alignment pattern in which the orientation of the optical axis 30A derived from the liquid crystal compound 30 changes while continuously rotating in one direction within the plane of the optically anisotropic layer 27. Here, the direction in which the optical axis 30A rotates in the liquid crystal diffraction element 12 is defined as the x direction. In the example of FIG. 22 , the z direction is the stacking direction of the liquid crystal compound 30 and is perpendicular to the optical surface of the liquid crystal diffraction element 12.

[0162] The optically anisotropic layer 27 is formed so that one period Λ of the liquid crystal alignment pattern differs in different regions within the plane. In the portion shown in Fig. 22, the optically anisotropic layer 27 has three regions A0, A1, and A2 from the left side of Fig. 22, and one period Λ of the liquid crystal alignment pattern differs in each region. Specifically, one period Λ of the liquid crystal alignment pattern in region A2 A2 is one period Λ of the liquid crystal alignment pattern in the region A1 A1 The period Λ of the liquid crystal alignment pattern in the region A1 is shorter than the period Λ. A1 is one period Λ of the liquid crystal alignment pattern in the region A0 A0 shorter, i.e., Λ A0 >Λ A1 >Λ A2 is.

[0163] Furthermore, 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 optically anisotropic layer 27. The twist angle in the thickness direction of region A1 is smaller than the twist angle in the thickness direction of region A2. Region A0 is a region that does not have a twisted structure. In other words, the twist angle of region A0 is 0°. Note that the twist angle is the twist angle in the entire thickness direction.

[0164] As described above, the optically anisotropic layer 27 has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound 30 rotates in one direction, has regions in which the twist angle of the rotation varies in-plane, and further has regions in which the optical axis rotates in a twisted manner 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 alignment pattern described above.

[0165] The function of the optically anisotropic layer 27 having the above-described structure will be described with reference to Fig. 23. In the liquid crystal diffraction element 12, the optical function is basically exerted only by the optically anisotropic layer 27. Therefore, Fig. 23 shows only the optically anisotropic layer 27 for the sake of simplicity and to clearly show the structure and effects.

[0166] As shown in FIG. 23, when left-handed circularly polarized light LC0 is incident on an area A0 in the plane of the optically anisotropic layer 27, it is polarized at an angle θ in the −x direction with respect to the incident direction, as described above. A0 23 is the opposite direction to the x direction in FIG. 22. Similarly, when left-handed circularly polarized light LC1 is incident on an area A1 in the plane of the optically anisotropic layer 27, it is deflected by an angle θ in the −x direction with respect to the incident direction. A1 Similarly, when left-handed circularly polarized light LC2 is incident on an area A2 in the plane of the optically anisotropic layer 27, it is polarized at an angle θ in the −x direction with respect to the incident direction. A2 Only the light is deflected and passes through.

[0167] As described above, an optically anisotropic layer formed using a composition containing liquid crystal compound 30 and having a liquid crystal orientation pattern in which the direction of the optical axis 30A rotates along the x-direction polarizes circularly polarized light, and the shorter the period Λ of the liquid crystal orientation pattern, the larger the angle of polarization (diffraction angle). As described above, the magnitude relationship of one period of the liquid crystal orientation pattern in each of regions A0, A1, and A2 is as follows: Λ A0 >Λ A1 >Λ A2 Therefore, the magnitude relationship between the angle of deflection of the transmitted light with respect to the incident light in each of the areas A0, A1, and A2 is θ A0 <θ A1 <θ A2 This becomes:

[0168] In the diffraction of light in an optically anisotropic layer having a liquid crystal orientation pattern in which the orientation of the optical axis of the liquid crystal compound 30 changes while continuously rotating within the plane, the diffraction efficiency decreases as the diffraction angle increases, i.e., the intensity of the diffracted light weakens. Therefore, when the optically anisotropic layer is configured to have regions where one period Λ of the liquid crystal orientation pattern varies, the diffraction angle differs depending on the position of incidence of light, resulting in a difference in the amount of diffracted light depending on the position of incidence within the plane. In other words, depending on the position of incidence within the plane, a region where the light transmitted through the optically anisotropic layer becomes dark appears.

[0169] In contrast, the optically anisotropic layer 27 shown in Figures 22 and 23 has regions that twist and rotate in the thickness direction, and has regions with different twist angles in the thickness direction. In the example shown in Figures 22 and 23, the twist angle in the thickness direction of region A2 is larger than the twist angle in the thickness direction of region A1. Furthermore, region A0 does not have a twisted structure in the thickness direction. Regions with a twisted structure can improve diffraction efficiency compared to regions without a twisted structure, so that the optically anisotropic layer 27 can suppress a decrease in the diffraction efficiency of polarized light.

[0170] 23 , by providing a twisted structure to regions A1 and A2, which have a larger diffraction angle than region A0, it is possible to suppress a decrease in the amount of light deflected in regions A1 and A2. Furthermore, by making the twist angle of the twisted structure in region A2, which has a larger diffraction angle than region A1, larger than that of region A1, it is possible to suppress a decrease in the amount of light deflected in region A2.

[0171] That is, the optically anisotropic layer 27 is configured so that the direction of the sequence of the length of one period Λ of the liquid crystal orientation pattern differs from the direction of the sequence of the magnitude of the twist angle in the thickness direction. More specifically, in the optically anisotropic layer 27, the region with a shorter period Λ of the liquid crystal orientation pattern has a larger twist angle in the thickness direction, thereby making it possible to brighten transmitted light. This makes it possible to make the amount of transmitted light uniform regardless of the incident position in the plane, even when the optically anisotropic layer 27 is configured to have regions with different periods Λ of the liquid crystal orientation pattern.

[0172] Next, a liquid crystal diffraction element 14 according to an embodiment of the present disclosure will be described with reference to FIG. 24 . FIG. 24 is a plan view schematically illustrating a liquid crystal orientation pattern of a liquid crystal diffraction element 14 according to an embodiment of the present disclosure. Like the aforementioned liquid crystal diffraction element 12, the liquid crystal diffraction element 14 is sheet-shaped, and has a configuration in which an alignment film (not shown) is formed on the surface of a support (not shown), and an optically anisotropic layer 34 is formed on the surface of the alignment film. Like the aforementioned liquid crystal diffraction element 12, the optically anisotropic layer 34 is formed using a composition containing a liquid crystal compound and has a structure in which oriented liquid crystal compounds are stacked. In FIG. 24 , the sheet surface is parallel to the paper surface, and the stacking direction is perpendicular to the paper surface. Also, in FIG. 24 , for ease of understanding, the drawing is simplified, and the liquid crystal orientation pattern of the optically anisotropic layer 34 is represented by the optical axis 30A of the liquid crystal compound.

[0173] In the optically anisotropic layer 26 of FIG. 18 and the optically anisotropic layer 27 of FIG. 22, the optic axis 30A continuously rotates in-plane only along the x-direction. In comparison with these, the optically anisotropic layer 34 of FIG. 24 differs significantly in that it has a liquid crystal alignment pattern in which one direction, in which the orientation of the optic axis 30A changes while continuously rotating, is radially arranged. Furthermore, the optically anisotropic layer 34 has concentric regions in which the orientation of the optic axis 30A is the same. In the example of FIG. 24, the center of these concentric circles is the center of the optically anisotropic layer 34, and the axis in the thickness direction passing through this center is the optical axis Zk. The optically anisotropic layer 34 has a periodic structure in a direction perpendicular to the optical axis Zk and a concentric structure centered on the optical axis Zk, more specifically, a concentric liquid crystal alignment pattern centered on the optical axis Zk.

[0174] In the optically anisotropic layer 34, the direction of the optical axis 30A extends in a number of directions from the center of the optically anisotropic layer 34 outward, for example, in the directions indicated by the arrows Ar １ The direction indicated by the arrow Ar ２ The direction indicated by the arrow Ar ３ The circularly polarized light changes while continuously rotating along the direction indicated by the arrows. The absolute phase of the circularly polarized light incident on the optically anisotropic layer 34 having this liquid crystal orientation pattern changes in each local region where the orientation of the optical axis 30A of the liquid crystal compound differs. At this time, the amount of change in each absolute phase differs depending on the orientation of the optical axis 30A of the liquid crystal compound into which the circularly polarized light is incident.

[0175] The optically anisotropic layer 34 having such a concentric liquid crystal orientation pattern, i.e., a liquid crystal orientation pattern in which the optical axis 30A changes by continuously rotating radially, can transmit incident light as converging light or diverging light depending on the rotation direction of the optical axis 30A of the liquid crystal compound and the rotation direction of the incident circularly polarized light. In other words, by making the liquid crystal orientation pattern of the optically anisotropic layer 34 concentric, the liquid crystal diffraction element 14 exhibits a function similar to that of a positive lens or a negative lens, for example.

[0176] When the liquid crystal diffraction element 14 is made to function in the same manner as a positive lens or a negative lens, it is preferable that the following formula be satisfied: Φ(r)=(π / λ)[(r 2 +fa 2 )1 / 2 −fa] where r is the distance from the center of the concentric circle (the optical axis Zk in the example of FIG. 24), and r=(x 2 +y 2 ) 1 / 2 Here, x and y represent positions within a plane, and (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.

[0177] As mentioned above, the angle of deflection of light with respect to the incident direction increases as the period Λ of the liquid crystal orientation pattern decreases. Therefore, when the optically anisotropic layer 34 is configured to transmit incident light as focused light, the period Λ of the liquid crystal orientation pattern can be gradually shortened from the center of the optically anisotropic layer 34 outward in one direction in which the optical axis 30A continuously rotates, thereby making the optically anisotropic layer 34 function like a positive lens whose focusing power increases from the optical axis Zk toward the periphery.

[0178] The optically anisotropic layer 34 can be changed from a configuration in which incident light is transmitted as converging light to a configuration in which incident light is transmitted as diverging light by reversing the direction of continuous rotation of the optic axis 30A. Alternatively, the optically anisotropic layer 34 can be changed from a configuration in which incident light is transmitted as converging light to a configuration in which incident light is transmitted as diverging light by reversing the rotation direction of circularly polarized light incident on the optically anisotropic layer 34.

[0179] When the optically anisotropic layer 34 is configured to transmit incident light as divergent light, by gradually shortening one period Λ in the liquid crystal orientation pattern from the center of the optically anisotropic layer 34 toward the outside in one direction in which the optical axis 30A continuously rotates, it can be made to function like a negative lens in which the divergence power of light increases from the optical axis Zk toward the periphery.

[0180] When the period Λ of the periodic structure of the optically anisotropic layer 34 is configured to gradually shorten from the optical axis Zk toward the periphery, it is effective because it can more effectively correct aberrations in the peripheral portion where chromatic aberrations tend to be large. Furthermore, such a configuration is easy to manufacture and is advantageous for reducing costs. It is preferable that the period Λ of the periodic structure in the outermost peripheral portion of the optically anisotropic layer 34 is 0.5 μm or more. In this case, the configuration is easy to manufacture and is advantageous for reducing costs.

[0181] When the optically anisotropic layer 34 has a configuration in which one period Λ of the liquid crystal orientation pattern is different, in order to improve the uniformity of transmitted light, it is preferable to impart a twisted structure in the thickness direction as shown in 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 in-plane liquid crystal orientation pattern and according to the desired in-plane light intensity distribution.

[0182] Although the liquid crystal diffraction element has been described above with reference to the drawings, the liquid crystal diffraction element is not limited to the above example, and various modifications are possible within the scope of the gist of the technology of the present disclosure. For example, the liquid crystal diffraction element of the above example has a support and an alignment film, but the support may be peeled off to form the liquid crystal diffraction element with only the alignment film and the optically anisotropic layer, or the alignment film may also be peeled off to form the liquid crystal diffraction element with only the optically anisotropic layer.

[0183] In the liquid crystal diffraction element of the present disclosure, the alignment film is provided as a preferred embodiment, but is not an essential component. For example, by forming an alignment pattern on the support by a method of rubbing the support, a method of processing the support with laser light, etc., it is possible to configure the optically anisotropic layer to have a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane.

[0184] The liquid crystal diffraction element 12 has regions with different periods Λ of the liquid crystal orientation pattern, and the shorter the period Λ of the liquid crystal orientation pattern, the larger the twist angle in the thickness direction. However, conversely, in the liquid crystal diffraction element of the present disclosure, the shorter the period Λ of the liquid crystal orientation pattern, the smaller the twist angle in the thickness direction may be. The twist angle in the thickness direction may be appropriately set according to the period Λ of the in-plane liquid crystal orientation pattern.

[0185] The liquid crystal diffraction element 14 has a configuration in which one period Λ of the liquid crystal orientation pattern gradually shortens from the center of the optically anisotropic layer 34 toward the outside. However, conversely, the liquid crystal diffraction element of the present disclosure may have a configuration in which one period Λ of the liquid crystal orientation pattern gradually lengthens from the center of the optically anisotropic layer 34 toward the outside. Furthermore, depending on the application of the liquid crystal diffraction element, for example, when it is desired to provide a light intensity distribution to transmitted light, it is also possible to use a configuration in which one period Λ does not gradually change toward one direction in which the optical axis continuously rotates, but has regions in which one period Λ is partially different in one direction in which the optical axis continuously rotates.

[0186] In the above example, the liquid crystal diffraction element has one optically anisotropic layer, but this is not limited thereto and may have two or more optically anisotropic layers. When the liquid crystal diffraction element has two or more optically anisotropic layers, it may have an optically anisotropic layer whose period Λ is uniform throughout and an optically anisotropic layer having regions whose period Λ is different. Furthermore, when the liquid crystal diffraction element has two or more optically anisotropic layers, it may further have optically anisotropic layers whose directions of twist and rotation in the thickness direction (directions of twist angles) are different from each other. In this way, by further having optically anisotropic layers whose directions of twist and rotation in the thickness direction are different, it is possible to efficiently refract transmitted light of various polarization states in the regions having twist angles in the thickness direction.

[0187] The methods and materials for producing the optically anisotropic layer, alignment film, and support of the present disclosure are not limited to those described above, and known techniques can be used, for example, the technique described in Japanese Patent No. 6,985,501.

[0188] Next, a device including a viewfinder optical system 5 according to an embodiment of the present disclosure will be described. Fig. 25 is a schematic configuration diagram of a camera 100, which is an imaging device according to an embodiment of the present disclosure. The camera 100 is, as an example, a digital camera.

[0189] The camera 100 includes a viewfinder device 101 according to an embodiment of the present disclosure. 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.

[0190] The viewfinder device 101 includes a viewfinder optical system 5 according to an embodiment of the present disclosure, and a drive unit 7. 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 polarized output light. As an example, the output light in the example of FIG. 25 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 converting the light incident on this eyepiece optical system 3 into circularly polarized light Pc, the light from the display element 1 can be efficiently guided.

[0191] The output light from the display element 1 may be linearly polarized light, in which case it is preferable to place an element such as a quarter-wave plate between the display element 1 and the eyepiece optical system 3 so that circularly polarized light Pc enters the eyepiece optical system 3. If 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 is polarized, and therefore the configuration can be one that is compatible with the eyepiece optical system 3 that includes a liquid crystal diffraction element.

[0192] The imaging lens 102 forms an image of a subject. The imaging element 103 captures the image formed by the imaging lens 102. For example, a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) can be used as the imaging element 103. The imaging element 103 outputs a captured image, which is an image of the captured image, to the processor 104. The processor 104 performs image processing on the captured image and outputs the image data after 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 103 to display the image.

[0193] A user 110 looks through the viewfinder device 101 and observes the image displayed on the display element 1 via the eyepiece optical system 3. The user 110 also operates the operation unit 106 to take a still image or a video, and the image data obtained by this shooting is recorded in the recording unit 107.

[0194] Although the technology of the present disclosure has been described above using embodiments and examples, the technology of the present disclosure is not limited to the above embodiments and examples and can be modified in various ways. For example, the radius of curvature, surface spacing, refractive index, Abbe number, aspherical coefficient, and phase difference coefficient of each lens are not limited to the values ​​shown in the above numerical examples and can take other values.

[0195] Furthermore, the imaging device according to the embodiment of the present disclosure is not limited to the above example, and the present disclosure can also be applied to a film camera, a video camera, and the like.

[0196] The following supplementary items are further disclosed in relation to the above-described embodiments and examples. [Supplementary Item 1] A finder optical system comprising a display element and an eyepiece optical system arranged closer to the eyepoint than the display element, wherein one or more diffractive elements are arranged within the finder optical system, at least one of the diffractive elements being a first diffractive element including a liquid crystal diffractive element, and wherein the finder optical system satisfies conditional expression (1) expressed as follows: 0.05≦X1 / TL≦1 (1) where TL is the distance on the optical axis from a display surface of the display element to the surface of the finder optical system closest to the eyepoint, and X1 is the distance on the optical axis from the display surface to the optical surface of the first diffractive element. [Supplementary Item 2] The finder optical system according to Supplementary Item 1 satisfies conditional expression (2) expressed as follows: 0.3<H / f<0.7 (2) where H is the half value of the longest diameter of the display area of ​​the display element, and f is the focal length of the finder optical system. [Supplementary Item 3] The finder optical system according to Supplementary Item 1 or Supplementary Item 2, which satisfies conditional expression (3) expressed as follows: 0<f / dEP<0.95 (3), where dEP is the distance on the optical axis from the surface of the finder optical system closest to the eyepoint to the eyepoint, and f is the focal length of the finder optical system. [Supplementary Item 4] The finder optical system according to any one of Supplementary Item 1 to Supplementary Item 3, wherein the eyepiece optical system includes two or more positive lenses and one or more negative lenses. [Supplementary Item 5] The finder optical system according to any one of Supplementary Item 1 to Supplementary Item 4, wherein the eyepiece optical system includes two or more aspherical lenses and one or more spherical lenses. [Supplementary Item 6] The finder optical system according to any one of Supplementary Item 1 to Supplementary Item 5, wherein the diffractive element is provided on a surface of an optical element, and wherein the Abbe number of the optical element based on the d-line is 35 or greater. [Supplementary Item 7] The finder optical system according to any one of Supplementary Items 1 to 6, wherein the diffraction element is provided on a surface of an optical element, and the optical element has a d-line transmittance of 98% or more.[Supplementary Item 8] The finder optical system according to any one of Supplementary Items 1 to 7, wherein a partial optical system consisting of all optical elements arranged within a range of 0.05≦X / TL≦1 has a d-line transmittance of 92% or more, where X is the distance on the optical axis from the display surface to the optical elements in the finder optical system. [Supplementary Item 9] The finder optical system according to any one of Supplementary Items 1 to 8, wherein the diffractive element is provided on a surface of an optical element, and lenses having refractive power are arranged on both the object side and the image side of the optical element. [Supplementary Item 10] The finder optical system according to any one of Supplementary Items 1 to 9, wherein the diffractive element is provided on a surface of an optical element, and a lens having refractive power is arranged adjacent to the optical element on at least one of the object side and the image side of the optical element, and the minimum distance in the optical axis direction between the optical surface of the diffractive element provided on the surface of the optical element and the optical surface of the lens is 1.8 mm or less. [Supplementary Item 11] The finder optical system according to any one of Supplementary Items 1 to 10, wherein the thickness of the region having a diffractive effect of the diffractive element in the optical axis direction is 10 μm or less. [Supplementary Item 12] The finder optical system according to any one of Supplementary Items 1 to 11, wherein at least one of the diffractive elements is a second diffractive element including a liquid crystal diffractive element, no element having refractive power is disposed between the display surface and the second diffractive element, and where X2 is the distance on the optical axis from the display surface to the optical surface of the second diffractive element, the finder optical system satisfies conditional expression (4) expressed as 0≦X2 / TL<0.05 (4). [Supplementary Item 13] The finder optical system according to Supplementary Item 12, wherein the sign of the phase difference function of the first diffractive element is different from the sign of the phase difference function of the second diffractive element. [Supplementary Item 14] The finder optical system according to any one of Supplementary Items 1 to 13, wherein the diffraction element has a periodic structure in a direction perpendicular to the optical axis and has a concentric structure centered on the optical axis. [Supplementary Item 15] The finder optical system according to Supplementary Item 14, wherein the period of the periodic structure gradually decreases from the optical axis toward the periphery. [Supplementary Item 16] The finder optical system according to Supplementary Item 14 or 15, wherein the period of the periodic structure at the outermost peripheral part of the diffraction element is 0.5 μm or more.[Supplementary Item 17] The finder optical system according to any one of Supplementary Items 1 to 16, wherein the number of lenses having refractive power included in the finder optical system is 4 or 5. [Supplementary Item 18] A finder device comprising the finder optical system according to any one of Supplementary Items 1 to 17, wherein light output from the display element is polarized. [Supplementary Item 19] An imaging device comprising the finder optical system according to any one of Supplementary Items 1 to 17, wherein light output from the display element is polarized.

[0197] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A viewfinder optical system, a display element and an eyepiece optical system disposed on an eye point side of the display element, one or more diffractive elements are disposed within the viewfinder optical system; At least one of the diffractive elements is a first diffractive element including a liquid crystal diffractive element; at least one of the diffractive elements is a second diffractive element including a liquid crystal diffractive element; no element having refractive power is disposed between the display surface of the display element and the second diffractive element; TL is the distance on the optical axis from the display surface to the surface of the finder optical system closest to the eyepoint, The distance on the optical axis from the display surface to the optical surface of the first diffractive element is X1. If the distance on the optical axis from the display surface to the optical surface of the second diffractive element is X2, 0.05≦X1 / TL≦1 (1) 0≦X2 / TL<0.05 (4) A finder optical system that satisfies conditional expressions (1) and (4) expressed by the following formula:

2. H is the half value of the maximum diameter of the display area of ​​the display element; When the focal length of the viewfinder optical system is f, 0.3<H / f<0.7 (2) 2. The finder optical system according to claim 1, which satisfies the conditional expression (2) expressed as follows:

3. The distance on the optical axis from the surface closest to the eyepoint of the viewfinder optical system to the eyepoint is dEP, When the focal length of the viewfinder optical system is f, 0<f / dEP<0.95 (3) 2. The finder optical system according to claim 1, which satisfies conditional expression (3) expressed as follows:

4. 2. The viewfinder optical system according to claim 1, wherein the eyepiece optical system includes two or more positive lenses and one or more negative lenses.

5. 2. The viewfinder optical system according to claim 1, wherein the eyepiece optical system includes two or more aspherical lenses and one or more spherical lenses.

6. The diffractive element is provided on a surface of an optical element, 2. The finder optical system according to claim 1, wherein the Abbe number of said optical element based on the d-line is 35 or more.

7. The diffractive element is provided on a surface of an optical element, 2. The finder optical system according to claim 1, wherein the optical element has a d-line transmittance of 98% or more.

8. If the distance on the optical axis from the display surface to the optical element in the viewfinder optical system is X, 0.05≦X / TL≦1 2. The finder optical system according to claim 1, wherein the transmittance of the d-line of a partial optical system made up of all optical elements arranged within the range is 92% or more.

9. The diffractive element is provided on a surface of an optical element, 2. The finder optical system according to claim 1, wherein lenses having refractive power are disposed on both the object side and the image side of said optical element.

10. The diffractive element is provided on a surface of an optical element, a lens having a refractive power is disposed adjacent to the optical element on at least one of an object side and an image side of the optical element; 2. The finder optical system according to claim 1, wherein the minimum distance in the optical axis direction between the optical surface of said diffractive element provided on the surface of said optical element and the optical surface of said lens is 1.8 mm or less.

11. 2. A finder optical system according to claim 1, wherein the thickness of the region having a diffractive effect of said diffractive element in the optical axis direction is 10 [mu]m or less.

12. 2. The finder optical system according to claim 1, wherein the sign of the phase difference function of said first diffractive element is different from the sign of the phase difference function of said second diffractive element.

13. 2. The finder 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 structure centered on the optical axis.

14. 14. The finder optical system according to claim 13, wherein the period of the periodic structure becomes gradually shorter from the optical axis toward the periphery.

15. 14. The finder optical system according to claim 13, wherein the period of the periodic structure in the outermost periphery of the diffraction element is 0.5 [mu]m or more.

16. 2. The finder optical system according to claim 1, wherein the finder optical system includes four or five lenses having refractive power.

17. A viewfinder optical system according to any one of claims 1 to 16, A viewfinder device in which the output light from said display element is polarized light.

18. A viewfinder optical system according to any one of claims 1 to 16, An imaging device in which the output light from the display element is polarized light.