ND filter, light-reducing device, and imaging device

Abstract

The present invention provides an ND filter, a light-reducing device, and an imaging device that suppress the increase in device size associated with an increase in the number of filter elements. [Solution] The ND filter 50F comprises two overlapping cells 10 and 20. Each cell 10 and 20 includes a liquid crystal layer 13 and 23 containing a liquid crystal compound and a dichroic dye, and is configured to change the orientation of the liquid crystal layer 13 and 23 from horizontal or twisted orientation to vertical orientation by an electric field formed on the liquid crystal layer 13 and 23. In each cell 10 and 20, the product of the thickness of the liquid crystal layer 13 and 23 and the concentration of the dichroic dye in the liquid crystal layer 13 and 23 is the cell concentration, the sum of the cell concentrations in the two cells 10 and 20 is 220 μm·% or less, the cell concentration in each cell 10 and 20 is 20 μm·% or more, and the thickness of each liquid crystal layer 13 and 23 is 10 μm or less.

Description

Technical Field

[0001] The present disclosure relates to an ND filter, a dimming device, and an imaging apparatus. Background Art

[0002] A Neutral Density (ND) filter that attenuates incident light in the visible light wavelength band is required to reduce the intensity of the incident light to a quarter or a sixty-fourth of its original level. An ND filter with a variable attenuation ratio includes a plurality of filter elements having mutually different attenuation ratios, and arranges a filter element selected from the plurality of filter elements on the optical axis (for example, refer to Patent Documents 1 to 3). Prior Art Documents Patent Documents

[0003] Patent Document 1 Japanese Unexamined Patent Application Publication No. 2022-36766 Patent Document 2 Japanese Unexamined Patent Application Publication No. 2021-101230 Patent Document 3 Japanese Unexamined Patent Application Publication No. 2021-76783 Summary of Invention Problems to be Solved by the Invention

[0004] On the other hand, a mechanism for selecting a desired filter element from a plurality of filter elements increases the space occupied by the device as the number of filter elements increases, or increases the weight of the device by the weight of the drive source. For this reason, a dimming device that is provided with an ND filter having a plurality of filter elements and configured to switch the filter elements leads to an increase in the size of the device as the number of filter elements increases. Means for Solving the Problems

[0005] An ND filter for solving the above problems is an ND filter having two overlapping filter elements, each filter element comprising a liquid crystal layer containing a liquid crystal compound and a dichroic dye, configured to change the liquid crystal layer from horizontal or twisted orientation to vertical orientation by an electric field formed in the liquid crystal layer, and when viewed from a viewpoint facing the surface of the ND filter, the two liquid crystal layers are arranged so that their orientation axes intersect on the opposing planes, the angle formed by the orientation axes of the two liquid crystal layers on the opposing planes is 80° or more and 100° or less, in each filter element the product of the thickness of the liquid crystal layer and the concentration of the dichroic dye in the liquid crystal layer is the cell concentration, the sum of the cell concentrations in the two filter elements is 220 μm·% or less, the cell concentration in each filter element is 20 μm·% or more, and the thickness of each liquid crystal layer is 10 μm or less.

[0006] A dimming device for solving the above problems comprises an ND filter having two overlapping filter elements and a drive unit for driving the ND filter, wherein each filter element has a liquid crystal layer containing a liquid crystal compound and a dichroic dye, and is configured to change the liquid crystal layer from horizontal or twisted orientation to vertical orientation by an electric field formed in the liquid crystal layer, and when viewed from a viewpoint facing the surface of the ND filter, the two liquid crystal layers are arranged so that their orientation axes intersect on the opposing planes, the angle formed by the orientation axes of the two liquid crystal layers on the opposing planes is 80° or more and 100° or less, in each filter element the product of the thickness of the liquid crystal layer and the concentration of the dichroic dye in the liquid crystal layer is the cell concentration, the sum of the cell concentrations in the two filter elements is 220 μm·% or less, the cell concentration in each filter element is 20 μm·% or more, and the thickness of each liquid crystal layer is 10 μm or less.

[0007] An imaging device for solving the above problems comprises a lens unit, an image sensor, and an ND filter disposed between the lens unit and the image sensor, wherein the ND filter comprises two overlapping filter elements, each filter element comprises a liquid crystal layer containing a liquid crystal compound and a dichroic dye, and is configured to change the liquid crystal layer from horizontal or twisted orientation to vertical orientation by an electric field formed in the liquid crystal layer, and when viewed from a viewpoint facing the surface of the ND filter, the two liquid crystal layers are arranged so that their orientation axes intersect on the opposing surfaces, the angle formed by the orientation axes of the two liquid crystal layers on the opposing surfaces is 80° or more and 100° or less, in each filter element the product of the thickness of the liquid crystal layer and the concentration of the dichroic dye in the liquid crystal layer is the cell concentration, the sum of the cell concentrations in the two filter elements is 220 μm·% or less, the cell concentration in each filter element is 20 μm·% or more, and the thickness of each liquid crystal layer is 10 μm or less. [Effects of the Invention]

[0008] The ND filter, light-reducing device, and imaging device of this disclosure can suppress the increase in device size that occurs with an increase in the number of filter elements. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a cross-sectional view showing the layer structure of an ND filter. [Figure 2] Figure 2 is an exploded perspective view showing the alignment axis direction of the liquid crystal layer in horizontal orientation. [Figure 3] Figure 3 is an exploded perspective view showing the orientation axis direction of the liquid crystal layer in twisted orientation. [Figure 4] Figure 4 is a graph showing the relationship between the sum of cell concentrations and absorbance. [Figure 5] Figure 5 is a graph showing the relationship between cell concentration and rise time. [Figure 6] Figure 6 is a graph showing the relationship between cell concentration and rise time. [Figure 7] Figure 7 is a graph showing the relationship between cell concentration and fall time. [Figure 8] Figure 8 is a graph showing the relationship between cell concentration and the fall time response. [Figure 9] Figure 9 shows the configuration of the dimming device. [Modes for carrying out the invention]

[0010] An embodiment of an ND filter and a light-reducing device will be described with reference to the drawings. [Layer structure of ND filter 50F] As shown in Figure 1, the ND filter 50F comprises a first cell 10 and a second cell 20. The first cell 10 and the second cell 20 are bonded together by an optically transparent adhesive layer 30. The first cell 10 and the second cell 20 are separate filter elements.

[0011] The first cell 10 comprises a first upper support layer 11A, a first upper electrode layer 11B, a first upper alignment layer 11C, a first lower support layer 12A, a first lower electrode layer 12B, a first lower alignment layer 12C, and a first liquid crystal layer 13. Each support layer 11A, 12A is an example of a transparent support layer. Each electrode layer 11B, 12B is an example of a transparent electrode layer.

[0012] The first liquid crystal layer 13 is located between the first upper alignment layer 11C and the first lower alignment layer 12C. The first liquid crystal layer 13 is in contact with the first upper alignment layer 11C and the first lower alignment layer 12C. The first upper alignment layer 11C is located between the first liquid crystal layer 13 and the first upper electrode layer 11B and is in contact with the first liquid crystal layer 13 and the first upper electrode layer 11B. The first lower alignment layer 12C is located between the first liquid crystal layer 13 and the first lower electrode layer 12B and is in contact with the first liquid crystal layer 13 and the first lower electrode layer 12B.

[0013] The first upper electrode layer 11B is located between the first upper alignment layer 11C and the first upper support layer 11A, and is in contact with the first upper alignment layer 11C and the first upper support layer 11A. The first lower electrode layer 12B is located between the first lower alignment layer 12C and the first lower support layer 12A, and is in contact with the first lower alignment layer 12C and the first lower support layer 12A.

[0014] The second cell 20 includes a second upper support layer 21A, a second upper electrode layer 21B, a second upper alignment layer 21C, a second lower support layer 22A, a second lower electrode layer 22B, a second lower alignment layer 22C, and a second liquid crystal layer 23. Each of the support layers 21A and 22A is an example of a transparent support layer. Each of the electrode layers 21B and 22B is an example of a transparent electrode layer.

[0015] The second liquid crystal layer 23 is located between the second upper alignment layer 21C and the second lower alignment layer 22C. The second liquid crystal layer 23 is in contact with the second upper alignment layer 21C and the second lower alignment layer 22C. The second upper alignment layer 21C is located between the second liquid crystal layer 23 and the second upper electrode layer 21B, and is in contact with the second liquid crystal layer 23 and the second upper electrode layer 21B. The second lower alignment layer 22C is located between the second liquid crystal layer 23 and the second lower electrode layer 22B, and is in contact with the second liquid crystal layer 23 and the second lower electrode layer 22B.

[0016] The second upper electrode layer 21B is located between the second upper alignment layer 21C and the second upper support layer 21A, and is in contact with the second upper alignment layer 21C and the second upper support layer 21A. The second lower electrode layer 22B is located between the second lower alignment layer 22C and the second lower support layer 22A, and is in contact with the second lower alignment layer 22C and the second lower support layer 22A.

[0017] The first lower support layer 12A of the first cell 10 is fixed to the second upper support layer 21A of the second cell 20 by the optically transparent adhesive layer 30. The surface of the first liquid crystal layer 13 that is in contact with the first lower alignment layer 12C and the surface of the second liquid crystal layer 23 that is in contact with the second upper alignment layer 21C face each other with the first lower support layer 12A, the optically transparent adhesive layer 30, and the second upper support layer 21A interposed therebetween.

[0018] Each support layer 11A, 12A, 21A, and 22A is visible as colorless and transparent. The materials constituting each support layer 11A, 12A, 21A, and 22A are independently either organic polymer compounds or inorganic polymer compounds. Examples of organic polymer compounds are selected from the group consisting of polyester, polyacrylate, polycarbonate, and polyolefin. Examples of inorganic polymer compounds are selected from the group consisting of silicon oxide, silicon oxide-nitride, and silicon nitride. The thickness of each support layer 11A, 12A, 21A, and 22A is independently, for example, between 20 μm and 500 μm.

[0019] Each electrode layer 11B, 12B, 21B, and 22B is visible as colorless and transparent. The materials constituting each electrode layer 11B, 12B, 21B, and 22B are independently a conductive inorganic oxide, a metal, or a conductive organic polymer compound. An example of a conductive inorganic oxide is one selected from the group consisting of indium tin oxide, fluorine-doped tin oxide, tin oxide, and zinc oxide. An example of a metal is gold or silver nanowire. An example of a conductive organic polymer compound is one selected from the group consisting of carbon nanotubes and poly(3,4-ethylenedioxythiophene). The thickness of each electrode layer 11B, 12B, 21B, and 22B is independently, for example, between 5 nm and 200 nm. Each electrode layer 11B, 12B, 21B, and 22B is connected to the drive unit 53 (see Figure 9) through wiring.

[0020] Each alignment layer 11C, 12C, 21C, and 22C is a horizontal alignment film that independently regulates the orientation axis direction of the liquid crystal molecules. A pair of alignment layers 11C and 12C determines the orientation axis direction of the liquid crystal molecules in the first liquid crystal layer 13. A pair of alignment layers 11C and 12C align or intersect their rubbing directions with each other so that the liquid crystal molecules in the first liquid crystal layer 13 have the orientation described later. A pair of alignment layers 21C and 22C determine the orientation axis direction of the liquid crystal molecules in the second liquid crystal layer 23. A pair of alignment layers 21C and 22C align or intersect their rubbing directions with each other so that the liquid crystal molecules in the second liquid crystal layer 23 have the orientation described later.

[0021] Each orientation layer 11C, 12C, 21C, and 22C is independently visible as either colorless and transparent or colored and transparent. The thickness of each orientation layer 11C, 12C, 21C, and 22C is independently, for example, between 20 nm and 500 nm. The materials constituting each orientation layer 11C, 12C, 21C, and 22C are independently either organic polymer compounds or inorganic oxides. Examples of organic polymer compounds are selected from the group consisting of polyimide, polyamide, and polyvinyl alcohol. Examples of inorganic oxides are selected from the group consisting of silicon oxide, zirconium oxide, and silicone.

[0022] Each liquid crystal layer 13, 23 comprises a liquid crystal composition, a dichroic dye, and a spacer. The liquid crystal compounds constituting the liquid crystal composition of each liquid crystal layer 13, 23 may independently have positive dielectric anisotropy. Liquid crystal compounds with positive dielectric anisotropy have a higher dielectric constant in the direction along the long axis of the liquid crystal molecule than in the direction along the short axis of the liquid crystal molecule.

[0023] The liquid crystal composition contained in each liquid crystal layer 13, 23 may be a single liquid crystal compound having positive dielectric anisotropy, or a combination of two or more liquid crystal compounds having positive dielectric anisotropy. The blending ratio of the combination of two or more liquid crystal compounds is adjusted as appropriate according to requirements such as dielectric anisotropy, flexibility, stability, and responsiveness.

[0024] Each liquid crystal layer 13, 23 may independently have a multi-domain. The multi-domain comprises a domain of a liquid crystal compound having positive dielectric anisotropy and a domain of a liquid crystal compound having negative dielectric anisotropy. A liquid crystal compound with negative dielectric anisotropy has a higher dielectric constant in the direction along the short axis of the liquid crystal molecule than in the direction along the long axis of the liquid crystal molecule.

[0025] Liquid crystal molecules with positive dielectric anisotropy are nematic liquid crystal molecules. Nematic liquid crystal molecules may be at least one selected from the group consisting of biphenyl, fluorophenyl, terphenyl, pyrimidine, phenylpyrimidine, phenylpyrazine, cyclohexanecarboxylic acid ester, phenylcyclohexane, biphenylcyclohexane, and dicyanobenzene systems.

[0026] The rigid portion of a liquid crystal molecule having positive dielectric anisotropy may comprise at least one selected from the group consisting of a biphenyl skeleton, a teriphenyl skeleton, a phenylpyrimidine skeleton, a phenylcyclohexane skeleton, a phenylpyrazine skeleton, and a biphenylcyclohexane skeleton. The end groups of the liquid crystal molecule may comprise at least one selected from the group consisting of alkyl groups such as methyl and hexyl groups, alkoxy groups such as methoxy and octyl groups, ester groups such as phenyl esters, cyano groups, and fluoro groups such as fluorobiphenyl groups. The side chain groups of the liquid crystal molecule may comprise at least one selected from the group consisting of cyano groups, fluoro groups such as fluorobiphenyl groups, and alkoxy groups such as methoxybiphenyl and hexyloxybiphenyl groups. When it is required to increase the solubility of the dichroic dye, it is preferable that the liquid crystal molecule has a cyano group.

[0027] Furthermore, the end groups of a liquid crystal molecule having negative dielectric anisotropy may comprise one selected from the group consisting of a nitro group, a trifluoromethyl group, an ester group, a sulfonyl group, and a pyrazine ring. The side chain groups of a liquid crystal molecule having negative dielectric anisotropy may comprise one selected from the group consisting of a nitro group, a trifluoromethyl group, an ester group, a sulfonyl group, and a pyrazine ring.

[0028] The dichroic dye is driven by a so-called guest-host configuration, in which liquid crystal molecules are set as the host. The dichroic dye exhibits black coloration through the driving of the liquid crystal molecules. The dichroic dye may be a black dye, a mixture of cyan, magenta, and yellow dyes, or a combination thereof.

[0029] The dichroic dye may be a combination of two or more dichroic dyes. The dichroism ratio of the dichroic dye is the ratio of the parallel absorbance to the perpendicular absorbance. Perpendicular absorbance is the absorption intensity of light polarized along the short axis of the liquid crystal molecule by the dichroic dye. Parallel absorbance is the absorption intensity of light polarized along the long axis of the liquid crystal molecule by the dichroic dye. If a wide viewing angle is required, the dichroic dye may contain two or more different black dyes, each with a different dichroism ratio.

[0030] The dichroic dye may be at least one selected from the group consisting of azo compounds, anthraquinone compounds, azomethine compounds, quinophthalone compounds, dioxazine compounds, tetrazine compounds, naphthoquinone compounds, perylene compounds, and merocyanine compounds. When improved lightfastness and dichroic ratio are required, the dichroic dye is preferably an anthraquinone compound.

[0031] The black dichroic dye may be at least one selected from the group consisting of polyiodine, anthraquinone black, naphthoquinone black, and perylene black. The cyan dichroic dye may be at least one selected from the group consisting of anthraquinone blue, perylene blue, and phthalocyanine blue. The magenta dichroic dye may be at least one selected from the group consisting of azo red, anthraquinone red, and perylene red. The yellow dichroic dye may be at least one selected from the group consisting of azo yellow, quinophthalone yellow, and naphthoquinone yellow.

[0032] The spacers are dispersed throughout each liquid crystal layer 13, 23. The spacers' diameter is determined by the thickness of each liquid crystal layer 13, 23 in which they are dispersed. The spacers make the thickness of each liquid crystal layer 13, 23 uniform. The spacers may be bead spacers or photospacers formed by exposure and development of photoresist. The spacers may be black transparent or colorless transparent.

[0033] [Alignment axis direction of liquid crystal layers 13 and 23] Each liquid crystal layer 13, 23 has an orientation state of either horizontal or twisted orientation in the absence of an electric field. The orientation axis direction of a specific plane in each liquid crystal layer 13, 23 is the average of the directions along the long axis of the liquid crystal molecules in the absence of an electric field on that specific plane.

[0034] Figure 2 shows the orientation axis direction when each liquid crystal layer 13, 23 has a horizontal orientation in the absence of an electric field. As shown by the solid arrows in Figure 2, the orientation axis direction of the surface 13T in contact with the first upper alignment layer 11C within the first liquid crystal layer 13 is the first upper axis direction DT1. The orientation axis direction of the surface 13M located in the center of the thickness direction of the first liquid crystal layer 13 is the first central axis direction DM1. The orientation axis direction of the surface 13B in contact with the first lower alignment layer 12C within the first liquid crystal layer 13 is the first lower axis direction DB1. The first upper axis direction DT1, the first central axis direction DM1, and the first lower axis direction DB1 coincide with each other. That is, the orientation axis directions of the liquid crystal molecules are aligned throughout the entire first liquid crystal layer 13. The orientation axis directions of the liquid crystal molecules are approximately parallel to the surfaces of the alignment layers 11C and 12C.

[0035] As shown by the dashed arrow in Figure 2, the orientation axis direction of the surface 23T in contact with the second upper alignment layer 21C within the second liquid crystal layer 23 is the second upper axis direction DT2. The orientation axis direction of the surface 23M located in the center of the second liquid crystal layer 23 in the thickness direction is the second central axis direction DM2. The orientation axis direction of the surface 23B in contact with the second lower alignment layer 22C within the second liquid crystal layer 23 is the second lower axis direction DB2. The second upper axis direction DT2, the second central axis direction DM2, and the second lower axis direction DB2 coincide with each other. That is, the orientation axis directions of the liquid crystal molecules are aligned throughout the second liquid crystal layer 23. The orientation axis directions of the liquid crystal molecules are approximately parallel to the surfaces of the alignment layers 21C and 22C.

[0036] Viewed from a viewpoint opposite the first upper support layer 11A, the angle formed by the straight line extending in the first lower axial direction DB1 and the straight line extending in the second upper axial direction DT2 is the orientation axis angle. In other words, the orientation axis angle is the angle formed by the horizontal components in the orientation axis direction of the surfaces of the liquid crystal layers 13 and 23 that face each other near the boundary between the two cells 10 and 20. The two cells 10 and 20 are fixed to each other by the optical transparent adhesive layer 30 such that the orientation axis angle is a predetermined angle greater than 0° and less than 180°.

[0037] The orientation axis angle can be between 80° and 100°. Alternatively, it can be between 85° and 95°, or even 90°. When the orientation axis angle is close to 90°, the absorption axis of the dichroic dye in the first liquid crystal layer 13 and the absorption axis of the dichroic dye in the second liquid crystal layer 23 are orthogonal. Therefore, when each cell 10 and 20 is shielded from light, the first cell 10 can easily shield the transmitted light from the second cell 20.

[0038] Figure 3 shows the orientation axis directions when each liquid crystal layer 13, 23 has a twisted orientation in the absence of an electric field. Each liquid crystal layer 13, 23 gradually changes the orientation axis direction of the liquid crystal molecules from each upper orientation layer 11C, 21C toward each lower orientation layer 12C, 22C.

[0039] Specifically, as shown by the solid arrows in Figure 3, each alignment layer 11C, 12C rotates the orientation axis of the first liquid crystal layer 13 counterclockwise from the first upper alignment layer 11C toward the first lower alignment layer 12C, from the first upper axis direction DT1 to the first lower axis direction DB1, when viewed from a viewpoint opposite to the first upper support layer 11A. Alternatively, each alignment layer 11C, 12C may rotate the orientation axis of the first liquid crystal layer 13 clockwise from the first upper alignment layer 11C toward the first lower alignment layer 12C.

[0040] As shown by the dashed arrows in Figure 3, each alignment layer 21C, 22C rotates the orientation axis of the liquid crystal molecules counterclockwise from the second upper axis direction DT2 to the second lower axis direction DB2, when viewed from a viewpoint opposite to the second upper support layer 21A, from the second upper alignment layer 21C toward the second lower alignment layer 22C. Alternatively, each alignment layer 21C, 22C may rotate the orientation axis of the second liquid crystal layer 23 clockwise from the second upper alignment layer 21C toward the second lower alignment layer 22C.

[0041] Viewed from a viewpoint opposite the first upper support layer 11A, the angle formed by the straight line extending in the first upper axis direction DT1 and the straight line extending in the first lower axis direction DB1 is the twist angle of the first liquid crystal layer 13. That is, the twist angle of the first liquid crystal layer 13 is the difference between the azimuth angle of the surface in contact with the first upper alignment layer 11C within the first liquid crystal layer 13 and the azimuth angle of the surface in contact with the first lower alignment layer 12C within the first liquid crystal layer 13. The azimuth angle of a specific surface in each liquid crystal layer 13, 23 is the angle formed between the horizontal component in the direction of the alignment axis of that specific surface and the reference direction. The reference direction is the direction along the surface direction of the liquid crystal layers 13, 23 and is common to the two cells 10, 20.

[0042] Each alignment layer 11C, 12C applies an alignment restricting force to the liquid crystal molecules of the first liquid crystal layer 13 so that the twist angle of the first liquid crystal layer 13 is a predetermined angle. The twist angle of the first liquid crystal layer 13 may be 80° or more and 100° or less, 85° or more and 95° or less, or 90°.

[0043] The twist angle of the second liquid crystal layer 23 is the angle formed by a straight line extending in the second upper axis direction DT2 and a straight line extending in the second lower axis direction DB2, as viewed from a viewpoint opposite the second upper support layer 21A. In other words, the twist angle of the second liquid crystal layer 23 is the difference between the azimuth angle of the surface in contact with the second upper alignment layer 21C within the second liquid crystal layer 23 and the azimuth angle of the surface in contact with the second lower alignment layer 22C within the second liquid crystal layer 23.

[0044] Each alignment layer 21C, 22C applies an alignment restricting force to the liquid crystal molecules of the second liquid crystal layer 23 so that the twist angle of the second liquid crystal layer 23 is a predetermined angle. The twist angle of the second liquid crystal layer 23 may be 80° or more and 100° or less, 85° or more and 95° or less, or 90°. The twist angle of the second liquid crystal layer 23 may be equal to the twist angle of the first liquid crystal layer 13, or it may be different from the twist angle of the first liquid crystal layer 13.

[0045] In the case of twist orientation, as in the case of horizontal orientation, the orientation axis angle formed by the straight line extending in the first lower axial direction DB1 and the straight line extending in the second upper axial direction DT2, as viewed from a viewpoint opposite the first upper support layer 11A, should be between 80° and 100°. The orientation axis angle may also be between 85° and 95°, or 90°.

[0046] Furthermore, each alignment layer 11C, 12C, 21C, and 22C may be given a tilt angle greater than 0° to the liquid crystal molecules. The tilt angle of the liquid crystal molecules is the angle formed by the direction along the long axis of the liquid crystal molecules in the absence of an electric field, relative to the plane along the liquid crystal layers 13 and 23. The tilt angle of the liquid crystal molecules may be between 0.5° and 12°, or between 1° and 8°. The tilt angles of the liquid crystal molecules in the first liquid crystal layer 13 and the second liquid crystal layer 23 may be the same or different.

[0047] In the ND filter 50F with the above configuration, when a voltage is applied to each cell 10, 20, each liquid crystal layer 13, 23 changes its orientation from the horizontal or twisted orientation described above to a vertical orientation, depending on the magnitude of the applied voltage. That is, the long axis of the liquid crystal molecules is oriented in a direction along the thickness direction of the liquid crystal layers 13, 23. Along with the change in the orientation of the liquid crystal molecules, the dichroic dye also changes the orientation of its long axis in the same way. In this configuration, the transmittance of the ND filter 50F is at its minimum when no voltage is applied, and this state is the light-shielding state of the ND filter 50F. Then, as the applied voltage increases, the transmittance of the ND filter 50F increases. The state with maximum transmittance is the transparent state of the ND filter 50F.

[0048] Thus, different attenuation ratios can be achieved in the ND filter 50F depending on whether or not voltage is applied and the magnitude of the applied voltage. Therefore, since it is possible to reduce the mechanism required for switching the mechanical filter elements, the size of the light-reducing device equipped with an ND filter can be suppressed.

[0049] The attenuation ratio of the ND filter 50F may be, for example, 1 / 4 to 1 / 64 or 1 / 4 to 1 / 128. Alternatively, the attenuation ratio of the ND filter 50F may be 1 / 5 to 1 / 64 or 1 / 5 to 1 / 128. The transmittance of the ND filter 50F in the light-blocking state may be 1.56% or less, or 0.78% or less. The transmittance of the ND filter 50F in the transparent state may be 20% or more, or 25% or more.

[0050] In the ND filter 50F of this embodiment, the optical path length is increased due to the stacking of two cells 10 and 20, resulting in high absorbance in the absence of an electric field. Furthermore, because the orientation axis angle is between 80° and 100°, the dichroic dye with a large absorption coefficient acts selectively, which also contributes to high absorbance. Therefore, light shielding is suitably possible.

[0051] [Cell concentration] The characteristics related to the thickness of the liquid crystal layers 13 and 23 and the density of the dichroic dye in the ND filter 50F of this embodiment will be described.

[0052] The product of the thickness (μm) of the first liquid crystal layer 13 and the concentration (%) of the dichroic dye in the first liquid crystal layer 13 is the first cell concentration CC1. The concentration of the dichroic dye in the first liquid crystal layer 13 is the percentage of the mass of the dichroic dye contained in the first liquid crystal layer 13 relative to the total mass of the first liquid crystal layer 13.

[0053] The second cell concentration CC2 is the product of the thickness (μm) of the second liquid crystal layer 23 and the concentration (%) of the dichroic dye in the second liquid crystal layer 23. The concentration of the dichroic dye in the second liquid crystal layer 23 is the percentage of the mass of the dichroic dye contained in the second liquid crystal layer 23 relative to the total mass of the second liquid crystal layer 23.

[0054] The sum of the first cell concentration CC1 and the second cell concentration CC2 is 220 μm·% or less. Furthermore, each of the first cell concentration CC1 and the second cell concentration CC2 is 20 μm·% or more. Furthermore, the thickness of the first liquid crystal layer 13 and the thickness of the second liquid crystal layer 23 are each 10 μm or less.

[0055] The first cell density CC1 and the second cell density CC2 may be different from each other or the same. When the first cell density CC1 and the second cell density CC2 are the same, the uniformity of the characteristics in the ND filter 50F is improved. The thickness of the first liquid crystal layer 13 and the thickness of the second liquid crystal layer 23 may be different from each other or the same. When the thickness of the first liquid crystal layer 13 and the thickness of the second liquid crystal layer 23 are the same, the uniformity of the characteristics in the ND filter 50F is improved. The density of the dichroic dye in the first liquid crystal layer 13 and the density of the dichroic dye in the second liquid crystal layer 23 may be different from each other or the same. When the density of the dichroic dye in the first liquid crystal layer 13 and the density of the dichroic dye in the second liquid crystal layer 23 are the same, the uniformity of the characteristics in the ND filter 50F is improved.

[0056] The thickness of the first liquid crystal layer 13 and the thickness of the second liquid crystal layer 23 may each be 5 μm or more. The concentration of the dichroic dye in the first liquid crystal layer 13 and the concentration of the dichroic dye in the second liquid crystal layer 23 may each be 2% by mass or more and 20% by mass or less, and 2.5% by mass or more and 15% by mass or less.

[0057] The reasons for the specified cell concentrations CC1 and CC2 mentioned above will be explained. One of the challenges in the ND filter 50F is to reduce the transmittance in the non-electric field state, that is, to increase the absorbance in the non-electric field state. In each liquid crystal layer 13,23, the absorbance A is expressed by the following equation (Equation 1), using the molar extinction coefficient ε, the concentration c of the dichroic dye, and the thickness l of the liquid crystal layer. The molar extinction coefficient ε is a material-specific value. Absorbance A=ε×c×l (Formula 1)

[0058] In other words, the absorbance increases as the concentration of the dichroic dye increases, and as the thickness of the liquid crystal layers 13 and 23 increases, resulting in a longer optical path length. In light of this relationship, it can be considered that there is a linear relationship between the sum of the first cell concentration CC1 and the second cell concentration CC2 and the absorbance of the ND filter 50F in the absence of an electric field.

[0059] Figure 4 shows the relationship between the sum of the first cell concentration CC1 and the second cell concentration CC2 and the absorbance of the ND filter 50F in the absence of an electric field, based on actual measurements. Figure 4 shows data obtained from a sample in which, in each liquid crystal layer 13 and 23, the liquid crystal composition is a biphenyl-based liquid crystal, the dichroic dye is an azo-based mixed dye, the orientation state is horizontal, the orientation axis angle is 90°, and each orientation layer 11C, 12C, 21C, and 22C is a polyimide-based orientation film subjected to orientation treatment by the rubbing method. The absorbance was calculated using the transmittance T of the measured ND filter 50F and the following formula (Equation 2). Absorbance A=-log 10 T...(Formula 2)

[0060] As shown in Figure 4, contrary to the estimation based on (Equation 1) above, it was found that in the region where the sum of cell concentrations CC1 and CC2 exceeds 220 μm·%, the relationship between the sum of cell concentrations CC1 and CC2 and absorbance becomes nonlinear.

[0061] In regions with high cell concentrations CC1 and CC2, it is thought that a decrease in the orientation order of the liquid crystal phase occurs because, when the liquid crystal layers 13 and 23 are thick, the restrictive effect of orientation decreases in regions far from the alignment layers 11C, 12C, 21C, and 22C, and when the concentration of dichroic dye is high, the proportion of non-liquid crystal material increases in the liquid crystal layers 13 and 23. This is thought to be the reason why it becomes difficult to obtain absorbance as the cell concentrations CC1 and CC2 increase, and why the relationship between the sum of cell concentrations CC1 and CC2 and absorbance becomes nonlinear. Furthermore, if a decrease in orientation order is the cause, it is suggested that this relationship between cell concentration and absorbance shows a similar trend even when the liquid crystal layers 13 and 23 are twist-oriented.

[0062] A decrease in orientation order means a decrease in the liquid crystal properties. Furthermore, in guest-host type driving, a higher degree of orientation order allows for more stable driving. Therefore, by utilizing the region where the sum of cell concentrations CC1 and CC2 has a linear relationship with absorbance, that is, the region where the sum of cell concentrations CC1 and CC2 is 220 μm·% or less, the absorbance corresponding to the sum of cell concentrations CC1 and CC2 can be accurately obtained, and stable driving of the ND filter 50F is possible, i.e., an accurate change in transmittance can be obtained. This allows for the desirable realization of low transmittance in the light-shielding state.

[0063] Improving the responsiveness of transmittance to changes in the electric field is also one of the challenges for the ND filter 50F. Figures 5 to 8 show the relationship between cell densities CC1 and CC2 and the response time of the change in transmittance in the ND filter 50F. Figure 5 shows the relationship between cell densities CC1 and CC2 and the rise time response time when the applied voltage to cells 10 and 20 is switched from 0.3V to 10V. Figure 6 shows the relationship between cell densities CC1 and CC2 and the rise time response time when the applied voltage to cells 10 and 20 is switched from 0.3V to 20V. Furthermore, Figure 7 shows the relationship between cell densities CC1 and CC2 and the fall time response time when the applied voltage to cells 10 and 20 is switched from 10V to 0.3V. Figure 8 shows the relationship between cell densities CC1 and CC2 and the fall time response time when the applied voltage to cells 10 and 20 is switched from 20V to 0.3V.

[0064] Figures 5 to 8 show data obtained from a sample in which, in each liquid crystal layer 13 and 23, the liquid crystal composition is a biphenyl-based liquid crystal, the dichroic dye is an azo-based mixed dye, the orientation state is horizontal, the orientation axis angle is 90°, and each orientation layer 11C, 12C, 21C, and 22C is a polyimide-based orientation film that has undergone orientation treatment by the rubbing method.

[0065] As shown in Figures 5 to 8, the fall time response time is overwhelmingly larger than the rise time response time, so shortening the fall time response time is important for improving responsiveness. Specifically, when using the ND filter 50F, a response time of 150ms or less is required.

[0066] As shown in Figures 5 and 6, in the rise response, the response time increases as the cell concentrations CC1 and CC2 increase. In the rise response, the orientation of the liquid crystal molecules changes in response to the change in the electric field due to the increase in applied voltage. The application of voltage does not directly affect the movement of the dichroic dye, and the dichroic dye moves in accordance with the liquid crystal composition. Therefore, it is thought that the time required for the overall orientation of the dichroic dye increases as the concentration of the dichroic dye increases. In addition, the thicker the liquid crystal layers 13 and 23, the longer the time required for the orientation of the liquid crystal compound to change. For these reasons, it is thought that the rise response time increases as the cell concentrations CC1 and CC2 increase.

[0067] On the other hand, as shown in Figures 7 and 8, in the fall-off response, a tendency was found that the response time became shorter as the cell concentrations CC1 and CC2 increased. More specifically, when the thickness of the liquid crystal layers 13 and 23 was constant, the response time became shorter as the cell concentrations CC1 and CC2 increased, that is, as the concentration of the dichroic dye increased. This tendency was more pronounced as the thickness of the liquid crystal layers 13 and 23 increased.

[0068] In the falling edge response, as the voltage is released, the orientation of the liquid crystal molecules and dichroic dye changes due to orientation relaxation, returning the orientation to the state it was in when there was no electric field. At this time, it is thought that the movement of the dichroic dye occurs faster because the elastic constant of the dichroic dye is greater than that of the liquid crystal compound. Therefore, it is thought that the response time decreases as the concentration of the dichroic dye increases. Furthermore, as the liquid crystal layers 13 and 23 become thicker, the region in which the orientation restriction effect of the orientation layers 11C, 12C, 21C, and 22C decreases increases, so the response time increases, and the influence of the dichroic dye on the response time increases as described above.

[0069] Furthermore, if the thickness of each liquid crystal layer 13,23 is 10 μm or less, and the cell densities CC1,CC2 are 20 μm·% or more, a response time of 150 ms or less can be achieved, thereby suitably improving the transmittance responsiveness of the ND filter 50F. From the viewpoint of enhancing these effects, it is preferable that the cell densities CC1,CC2 are 40 μm·% or more.

[0070] [Dimming device] The configuration of the light-reducing device equipped with the aforementioned ND filter 50F will be described below. As shown in Figure 9, the imaging device 50 comprises a lens unit 50L, an ND filter 50F, an image sensor 50D, and a drive unit 53. The lens unit 50L and the ND filter 50F may constitute a single lens barrel 51. The ND filter 50F and the drive unit 53 are examples of a light-reducing device.

[0071] The lens unit 50L is equipped with multiple lenses, including a focus lens for adjusting the focus. The ND filter 50F reduces the light passing through the lens unit 50L. The image sensor 50D captures the light transmitted through the ND filter 50F.

[0072] The drive unit 53 comprises an element drive unit 53A and a filter drive unit 53F. The element drive unit 53A drives the lens unit 50L and the image sensor 50D. The filter drive unit 53F is connected separately to each electrode layer 11B, 12B, 21B, and 22B. The filter drive unit 53F applies voltage separately between two electrode layers 11B and 12B and between two electrode layers 21B and 22B in response to a voltage signal input. The filter drive unit 53F includes a switching mechanism for rotating or sliding the ND filter 50F. The filter drive unit 53F switches the presence or absence of the ND filter 50F between the lens unit 50L and the image sensor 50D by controlling the drive of the switching mechanism.

[0073] The input and output of the voltage signal changes the orientation state of each liquid crystal layer 13, 23 between horizontal or twisted orientation and vertical orientation. The voltage signal input to each liquid crystal layer 13, 23 is made equal in phase, frequency, height, width, RMS value, transfer function, and delay time.

[0074] When the filter drive unit 53F stops inputting voltage signals to the two cells 10 and 20, each liquid crystal layer 13 and 23 forms a horizontal or twisted orientation according to the orientation restricting force of each alignment layer 11C and 12C. At this time, the ND filter 50F blocks the transmitted light from the lens unit 50L, thereby reducing the light for the image sensor 50D.

[0075] When the filter drive unit 53F inputs a voltage signal to the two cells 10 and 20, the two liquid crystal layers 13 and 23 form a vertical alignment against the alignment restricting force. The vertically aligned liquid crystal layers 13 and 23 transmit light from the lens unit 50L, weakening the light-reducing effect on the image sensor 50D. The strength of the light-reducing effect based on the change in transmittance of the ND filter 50F can be controlled by the magnitude of the voltage applied to the two liquid crystal layers 13 and 23. The filter drive unit 53F may input a voltage signal to one of the two cells 10 and 20 while stopping the input of a voltage signal to the other.

[0076] [Examples] The ND filter described above will be explained using a specific example. (Manufacturing of ND filters) We fabricated the first and second cells having the following configurations.

[0077] <Cell 1> Liquid crystal compounds: Biphenyl-based liquid crystal compounds Dichroic pigments: mixed black pigments of azo compounds and anthraquinone compounds. Orientation layer: A polyimide film that has undergone rubbing treatment. Liquid crystal alignment: horizontal alignment Dichroic dye concentration: 7.5% Liquid crystal layer thickness: 10 μm Cell 1 concentration: 75 μm·%

[0078] <Cell 2> Liquid crystal compounds: Biphenyl-based liquid crystal compounds Dichroic pigments: mixed black pigments of azo compounds and anthraquinone compounds. Orientation layer: A polyimide film that has undergone rubbing treatment. Liquid crystal alignment: horizontal alignment Dichroic dye concentration: 7.5% Liquid crystal layer thickness: 10 μm Cell 2 concentration: 75 μm·%

[0079] The ND filter of the example was obtained by bonding the first cell and the second cell via an optically transparent adhesive layer such that the orientation axis angle was 90°. In the ND filter of the example, the sum of the concentrations of the first cell and the second cell is 150 μm·%.

[0080] (Driving evaluation) The total light transmittance of the ND filter in the example was measured by applying a voltage to each of the first and second cells. A handheld spectroradiometer (MK550T, UPRtek) was used to measure the total light transmittance. As a result, when the applied voltage was 0V, the total light transmittance was 1.05%, when the applied voltage was 5V, the total light transmittance was 20.4%, and when the applied voltage was 10V, the total light transmittance was 26.1%. Therefore, it was confirmed that an attenuation ratio of 1 / 4 to 1 / 64 could be obtained.

[0081] Furthermore, the response time when the applied voltage was switched from 10V to 0V was measured, specifically the time required for the change in total light transmittance. A motorized 6-axis goniometer for display measurement (DMS803, Instrument Systems GmbH) was used to measure the response time. As a result, the response time was 121ms or less. Therefore, it was confirmed that good responsiveness could be obtained.

[0082] [effect] According to the above embodiments and examples, the following effects can be obtained. (1) Since the mutually overlapping cells 10 and 20 achieve mutually different attenuation ratios in a single ND filter 50F, the increase in device size due to the increase in filter elements can be suppressed. If the imaging device 50 is equipped with a switching mechanism that switches the presence or absence of the ND filter 50F between the lens unit 50L and the image sensor 50D, a single ND filter 50F can achieve a wide range of attenuation ratios, thus reducing the number of items that need to be switched. As a result, the increase in size of the imaging device 50 due to the increase in filter elements can be suppressed, providing a configuration suitable for imaging devices 50 mounted on unmanned aerial vehicles and small unmanned aircraft.

[0083] (2) Because the optical path length of the ND filter 50F is longer than that of each cell 10 and 20 due to the overlap of the two cells 10 and 20, the ND filter 50F can obtain a higher absorbance than each cell 10 and 20.

[0084] (3) In the two cells 10 and 20, the orientation axis angle is between 80° and 100°, so the dichroic dye with a large absorption coefficient acts selectively, resulting in high absorbance. (4) The sum of the concentration CC1 of the first cell and the concentration CC2 of the second cell is 220 μm·% or less. This allows for driving by the guest-host type within a range where good orientational order can be obtained, thus resulting in good absorbance.

[0085] (5) The thickness of the liquid crystal layers 13 and 23 is 10 μm or less, and the cell densities CC1 and CC2 are 20 μm·% or more. This ensures good transmittance response when the applied voltage is removed.

[0086] (6) If the liquid crystal layers 13 and 23 have a twisted orientation and the twist angle is between 80° and 100°, it is possible to adjust characteristics such as the viewing angle. (7) With an ND filter 50F, if the transmittance in the transparent state is 20% or more and the transmittance in the light-blocking state is 1.56% or less, it is possible to achieve an attenuation ratio from 1 / 5 to 1 / 64. Also, with an ND filter 50F, if the transmittance in the transparent state is 25% or more and the transmittance in the light-blocking state is 1.56% or less, it is possible to achieve an attenuation ratio from 1 / 4 to 1 / 64.

[0087] (8) Since one ND filter 50F has two liquid crystal layers 13 and 23, even though one ND filter 50F contains a large amount of dichroic dye, the concentration of dichroic dye in each liquid crystal layer 13 and 23 is suppressed to the extent that it can be dissolved in each liquid crystal layer 13 and 23.

[0088] (9) The thickness of one ND filter 50F is divided into two cells 10 and 20, and the two cells 10 and 20 are driven separately. As a result, the ND filter 50F can obtain high absorbance while ensuring the responsiveness required for switching absorbance.

[0089] [Example of changes] The embodiments described above can be modified as follows. Note that two or more of the following modifications can be combined to the extent that they do not create technical inconsistencies.

[0090] In the ND filter 50F, either the first lower support layer 12A or the second upper support layer 21A, and the optically transparent adhesive layer 30 may be omitted. For example, the ND filter 50F may not have the first lower support layer 12A and the optically transparent adhesive layer 30, but may have the first lower electrode layer 12B on the upper surface of the second upper support layer 21A.

[0091] The first cell 10 may include functional layers other than the support layers 11A, 12A, electrode layers 11B, 12B, alignment layers 11C, 12C, and liquid crystal layer 13. The other functional layers may be reinforcing layers to increase the mechanical strength of the first cell 10, or barrier layers to increase the chemical durability of the first cell 10. The other functional layers may also be an overcoat or undercoat on the first cell 10, and may raise the temperature of the first cell 10, such as with a transparent heater, suppress condensation on the first cell 10, or suppress the amount of static electricity charged on the first cell 10. Furthermore, the other functional layers may have a so-called reflection suppression function, which suppresses the reflection of light incident on the ND filter 50F by the ND filter 50F, either by themselves or in cooperation with other layers. The second cell 20 may also comprise other functional layers besides the support layers 21A, 22A, electrode layers 21B, 22B, alignment layers 21C, 22C, and liquid crystal layer 23. The other functional layers may be provided on at least one of the upper substrates 11, 21 of each cell 10, 20, or on at least one of the lower substrates 12, 22 of each cell 10, 20.

[0092] The drive unit 53 of the dimming device may simultaneously input a voltage signal to the first upper electrode layer 11B and the second upper electrode layer 21B, or it may simultaneously stop inputting the voltage signal. The drive unit 53 may simultaneously input a voltage signal to the first lower electrode layer 12B and the second lower electrode layer 22B, or it may simultaneously stop inputting the voltage signal. The configuration that simultaneously inputs and stops the voltage signal enhances the responsiveness of the ND filter 50F in switching the attenuation ratio.

[0093] The drive unit 53 may match the characteristics of the voltage signal input to the first cell 10 and the characteristics of the voltage signal input to the second cell 20, or it may make them different. The characteristics of the voltage signal may be at least one selected from the group consisting of the phase, frequency, height, width, RMS value, transfer function, and delay time of the voltage signal. A configuration in which each voltage signal has mutually different characteristics enables the ND filter 50F to achieve high resolution with a large number of attenuation ratios. Furthermore, a configuration in which each voltage signal has mutually different characteristics makes it easier to match the maintenance and switching of the attenuation ratio to the characteristics and driving mode of the image sensor 50D.

[0094] For example, the drive unit 53 may have mutually different characteristics for each voltage signal so as to compensate for individual differences in the attenuation ratio and responsiveness of each cell 10, 20. In this case, the drive unit 53 may store data related to the attenuation ratio and responsiveness of each voltage signal for each cell 10, 20. Based on the stored data, the drive unit 53 may generate voltage signals with mutually different characteristics so as to compensate for individual differences.

[0095] For example, one of the two cells 10 and 20, the one facing the lens section 50L, may degrade faster than the other cell. The drive unit 53 may give each voltage signal different characteristics to compensate for degradation related to the attenuation ratio and responsiveness of the voltage signal in each cell 10 and 20. In this case, the drive unit 53 may store data related to the cumulative time the voltage signal has been input and the elapsed time since the start of use of the ND filter 50F. The drive unit 53 may generate voltage signals with different characteristics to compensate for degradation based on the stored data.

[0096] At least one of each electrode layer 11B, 21B, 12B, 22B and the other electrode layers 11B, 21B, 12B, 22B may be connected in parallel to the drive unit 53. The imaging device 50 may omit the switching mechanism for rotating or sliding the ND filter 50F. By omitting the switching mechanism, the imaging device 50 can be made smaller by reducing the number of items to be switched, and can also be made lighter by eliminating the space occupied by the switching mechanism.

[0097] The drive unit 53 may change the characteristics of the voltage signal input to the first cell 10 and the voltage signal input to the second cell 20 to match the drive amount of the lens unit 50L. In this case, the drive unit 53 may store data indicating the characteristics of the lens unit 50L with respect to the drive amount for each of the cells 10 and 20. Based on the stored data, the drive unit 53 may generate voltage signals with mutually different characteristics to match the characteristics to the drive amount.

[0098] The drive unit 53 may change the characteristics of the voltage signal input to the first cell 10 and the characteristics of the voltage signal input to the second cell 20 to match the drive mode of the image sensor 50D. In this case, the drive unit 53 may store data indicating the characteristics of the image sensor 50D with respect to the drive mode for each of the cells 10 and 20. Based on the stored data, the drive unit 53 may generate voltage signals with mutually different characteristics to match the characteristics of the drive mode. [Explanation of Symbols]

[0099] 10…Cell 1 11A...First upper support layer 11B...First upper electrode layer 11C...first upper alignment layer 12A…First lower support layer 12B...First lower electrode layer 12C...first lower alignment layer 13…First liquid crystal layer 20…2nd cell 21A…Second upper support layer 21B...Second upper electrode layer 21C…Second upper alignment layer 22A…Second lower support layer 22B...Second lower electrode layer 22C…Second lower alignment layer 23…Second liquid crystal layer 30...Optical transparent adhesive layer 50…Imaging device 50L…Lens section 50D…Image sensor 50F...ND filter 53... Drive unit.

Claims

1. An ND filter having two filter elements that overlap each other, Each filter element comprises a liquid crystal layer containing a liquid crystal compound and a dichroic dye, and is configured to change the orientation of the liquid crystal layer from horizontal or twisted orientation to vertical orientation by an electric field formed in the liquid crystal layer. Viewed from a viewpoint opposite to the surface of the ND filter, the two liquid crystal layers are arranged so that their orientation axes intersect on the opposing surfaces, and the angle formed by the orientation axes of the two liquid crystal layers on the opposing surfaces is 80° or more and 100° or less. In each filter element, the product of the thickness of the liquid crystal layer and the concentration of the dichroic dye in the liquid crystal layer is the cell concentration. The sum of the cell concentrations in the two filter elements is 220 μm·% or less. The cell concentration in each filter element is 20 μm·% or more. The thickness of each liquid crystal layer is 10 μm or less. ND filter.

2. Each liquid crystal layer has a twisted orientation in the absence of an electric field. The twist angle of the liquid crystal layer is 80° or more and 100° or less. The ND filter according to claim 1.

3. Each filter element comprises two transparent electrode layers sandwiching the liquid crystal layer that constitutes the filter element, and each liquid crystal layer is configured to be driven independently of the filter element. The ND filter according to claim 1.

4. Each filter element comprises two transparent support layers that sandwich the liquid crystal layer constituting the filter element, and one of the transparent support layers in one filter element is fixed to one of the transparent support layers in the other filter element by an optically transparent adhesive layer. The ND filter according to claim 1.

5. The transmittance in the transparent state is 20% or more. The light transmittance in the light-blocking state is 1.56% or less. The ND filter according to claim 1.

6. An ND filter with two overlapping filter elements, A dimming device comprising a drive unit for driving the ND filter, Each filter element comprises a liquid crystal layer containing a liquid crystal compound and a dichroic dye, and is configured to change the orientation of the liquid crystal layer from horizontal or twisted orientation to vertical orientation by an electric field formed in the liquid crystal layer. Viewed from a viewpoint opposite to the surface of the ND filter, the two liquid crystal layers are arranged so that their orientation axes intersect on the opposing surfaces, and the angle formed by the orientation axes of the two liquid crystal layers on the opposing surfaces is 80° or more and 100° or less. In each filter element, the product of the thickness of the liquid crystal layer and the concentration of the dichroic dye in the liquid crystal layer is the cell concentration. The sum of the cell concentrations in the two filter elements is 220 μm·% or less. The cell concentration in each filter element is 20 μm·% or more. The thickness of each liquid crystal layer is 10 μm or less. Light-dimmer device.

7. Each filter element comprises two transparent electrode layers sandwiching the liquid crystal layer that constitutes the filter element, and the drive unit drives the liquid crystal layer for each filter element. The dimming device according to claim 6.

8. The lens part, Image sensor and An imaging device comprising an ND filter disposed between the lens portion and the image sensor, The aforementioned ND filter comprises two filter elements that overlap each other, Each filter element comprises a liquid crystal layer containing a liquid crystal compound and a dichroic dye, and is configured to change the orientation of the liquid crystal layer from horizontal or twisted orientation to vertical orientation by an electric field formed in the liquid crystal layer. Viewed from a viewpoint opposite to the surface of the ND filter, the two liquid crystal layers are arranged so that their orientation axes intersect on the opposing surfaces, and the angle formed by the orientation axes of the two liquid crystal layers on the opposing surfaces is 80° or more and 100° or less. In each filter element, the product of the thickness of the liquid crystal layer and the concentration of the dichroic dye in the liquid crystal layer is the cell concentration. The sum of the cell concentrations in the two filter elements is 220 μm·% or less. The cell concentration in each filter element is 20 μm·% or more. The thickness of each liquid crystal layer is 10 μm or less. Imaging device.

9. The system further includes a drive unit that switches the presence or absence of the ND filter between the lens unit and the image sensor. The imaging apparatus according to claim 8.

Images