ND filter, light-reducing device, and imaging device

Abstract

The present invention provides an ND filter and a light-reducing device that suppress the increase in device size associated with an increase in the number of filter elements. [Solution] An ND filter 50F comprising two overlapping cells 10, 20, each cell 10, 20 comprising a liquid crystal layer 13, 23 containing a liquid crystal compound and a dichroic dye, and configured to change the liquid crystal layer 13, 23 from twisted orientation to vertical orientation by an electric field formed in the liquid crystal layer 13, 23. Viewed from a viewpoint opposite to the surface of the ND filter 50F, the two liquid crystal layers 13, 23 are arranged so that the orientation axes of their opposing surfaces intersect, and the orientation axis of the midplane in the two liquid crystal layers 12, 23 is antiparallel with a tilt angle opposite to the plane along the liquid crystal layers 13, 23.

Description

Technical Field

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

Background Art

[0002] An ND filter (Neutral Density filter) that attenuates incident light in the visible light wavelength band is required to reduce the intensity of incident light to 1 / 4 or 1 / 64 of its original level. An ND filter that can change the 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, see Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the 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 switches filter elements causes an increase in device size as the number of filter elements provided in the dimming device 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 a twisted orientation to a vertical orientation by an electric field formed in the liquid crystal layer, and, 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 opposing planes, and the orientation axis direction of the midplanes in the two liquid crystal layers is antiparallel with a tilt angle opposite to the plane along the liquid crystal layer.

[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 a twisted orientation to a 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 the orientation axes of the opposing surfaces intersect, and the orientation axis of the midplane in the two liquid crystal layers is antiparallel with a tilt angle opposite to the plane along the liquid crystal layer.

[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 comprising a liquid crystal layer containing a liquid crystal compound and a dichroic dye, and is configured to change the liquid crystal layer from a twisted orientation to a vertical orientation by an electric field formed in the liquid crystal layer, and when viewed from a viewpoint opposite to the surface of the ND filter, the two liquid crystal layers are arranged so that the orientation axes of the opposing surfaces intersect, and the orientation axis of the midplanes in the two liquid crystal layers is antiparallel with a tilt angle opposite to the plane along the liquid crystal layer. [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 orientation axis direction of the liquid crystal layer. [Figure 3] Figure 3 is a diagram showing the twist angle in the liquid crystal layer. [Figure 4] Figure 4 is a diagram showing the orientation axis angles in two cells. [Figure 5] Figure 5 is a diagram showing the relationship between the tilt angles of two cells. [Figure 6] Figure 6 is a table showing the detailed configuration of test examples 1-1 to 1-5. [Figure 7] Figure 7 shows the transmitted image in the absence of an electric field using an ND filter in Test Example 1-1. [Figure 8] Figure 8 shows the transmitted images in the absence of an electric field using the ND filter in Test Examples 1-4. [Figure 9] Figure 9 shows the transmitted images in the absence of an electric field using ND filters in Test Examples 1-5. [Figure 10] Figure 10 is a graph showing the field of view dependence of the ND filter in Test Example 1-1. [Figure 11] Figure 11 is a graph showing the field of view dependence of the ND filters in test examples 1-5. [Figure 12] Figure 12 is a diagram showing the configuration of the dimming device. [Figure 13] Figure 13 is a table showing the detailed configuration of test examples 2-1 to 2-4. [Figure 14] Figure 14 is a graph showing the transmittance when light is blocked for test examples 2-1 to 2-4. [Figure 15] Figure 15 is a graph showing the transmittance when the material is clear for test examples 2-1 to 2-4. [Figure 16]Figure 16 is a graph showing the relationship between the alignment order parameter of each color dichroic dye and the cell gap in Test Examples 2-1 to 2-4. [Figure 17] Figure 17 is a graph showing the relationship between the alignment order parameter of each color dichroic dye and the dye concentration in Test Examples 2-1 to 2-4. [Figure 18] Figure 18 is a table showing the detailed configuration of Test Examples 2-1 to 2-5. [Figure 19] Figure 19 is a graph showing the relationship between the transmittance during light shielding and the twist pitch in Test Examples 2-1 to 2-5. [Figure 20] Figure 20 is a graph showing the relationship between the transmittance in a transparent state and the twist pitch in Test Examples 2-1 to 2-5. [Mode for Carrying Out the Invention]

[0010] (First Embodiment) A first embodiment of the ND filter, the dimming device, and the imaging device will be described. [Layer Configuration of ND Filter 50F] As shown in Figure 1, the ND filter 50F includes a first cell 10 and a second cell 20. The first cell 10 and the second cell 20 are fixed to each other 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 includes 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 of the support layers 11A and 12A is an example of a transparent support layer. Each of the electrode layers 11B and 12B is an example of a transparent electrode layer. The first upper base material 11 is composed of the first upper support layer 11A, the first upper electrode layer 11B, and the first upper alignment layer 11C. The first lower base material 12 is composed of the first lower support layer 12A, the first lower electrode layer 12B, and the first lower alignment layer 12C.

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

[0014] The second cell 20 comprises 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 support layer 21A, 22A is an example of a transparent support layer. Each electrode layer 21B, 22B is an example of a transparent electrode layer. The second upper substrate 21 is composed of the second upper support layer 21A, the second upper electrode layer 21B, and the second upper alignment layer 21C. The second lower substrate 22 is composed of the second lower support layer 22A, the second lower electrode layer 22B, and the second lower alignment layer 22C.

[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 orientation layer 21C and the second upper support layer 21A, and is in contact with the second upper orientation layer 21C and the second upper support layer 21A. The second lower electrode layer 22B is located between the second lower orientation layer 22C and the second lower support layer 22A, and is in contact with the second lower orientation 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 an 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 are facing each other with the first lower substrate 12, the optically transparent adhesive layer 30, and the second upper substrate 21 in between.

[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. An example of an organic polymer compound is one selected from the group consisting of polyester, polyacrylate, polycarbonate, and polyolefin. An example of an inorganic polymer compound is one selected from the group consisting of silicon oxide, silicon oxide-nitride, and silicon nitride. An example of the thickness of each support layer 11A, 12A, 21A, and 22A is independently 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. The 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). An example of the thickness of each electrode layer 11B, 12B, 21B, and 22B is independently between 5 nm and 200 nm. Each electrode layer 11B, 12B, 21B, and 22B is connected to the drive unit 53 (see Figure 12) 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 intersect their rubbing directions with each other so as to form a twist angle θTB (see Figure 3) in the first liquid crystal layer 13. 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 intersect their rubbing directions with each other so as to form a twist angle θTB in the second liquid crystal layer 23. The twist angle θTB of the first liquid crystal layer 13 may be equal to the twist angle θTB of the second liquid crystal layer 23, or it may be different from the twist angle θTB of the second liquid crystal layer 23.

[0021] Each orientation layer 11C, 12C, 21C, and 22C is independently visible as either colorless and transparent or colored and transparent. An example of the thickness of each orientation layer 11C, 12C, 21C, and 22C is independently 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. An example of an organic polymer compound is one selected from the group consisting of polyimide, polyamide, and polyvinyl alcohol. An example of an inorganic oxide is one selected from the group consisting of silicon oxide, zirconium oxide, and silicone.

[0022] Each liquid crystal layer 13, 23 includes a liquid crystal composition, a dichroic dye, and a spacer. The thickness of each liquid crystal layer 13, 23 may be independently 2 μm or more and 20 μm or less. The liquid crystal composition of each liquid crystal layer 13, 23 may contain a liquid crystal compound having positive dielectric anisotropy, a liquid crystal compound having negative dielectric anisotropy, or a liquid crystal compound having substantially no dielectric anisotropy.

[0023] The liquid crystal composition contained in each liquid crystal layer 13, 23 may be a single liquid crystal compound or a combination of two or more liquid crystal compounds. 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] For example, the liquid crystal molecules constituting the liquid crystal compound contained in each liquid crystal layer 13, 23 may have positive dielectric anisotropy. Positive dielectric anisotropy means that the dielectric constant is higher 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.

[0025] Furthermore, each liquid crystal layer 13, 23 may independently have a multidomain. The multidomain comprises a domain of a liquid crystal compound having positive dielectric anisotropy and a domain of a liquid crystal compound having negative dielectric anisotropy. Negative dielectric anisotropy means that the dielectric constant is higher 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.

[0026] Liquid crystal molecules with positive dielectric anisotropy are twisted nematic liquid crystal molecules. A twisted nematic liquid crystal molecule may be at least one selected from the group consisting of biphenyl, fluorophenyl, terphenyl, pyrimidine, phenylpyrimidine, phenylpyrazine, cyclohexanecarboxylic acid ester, phenylcyclohexane, biphenylcyclohexane, and dicyanobenzene.

[0027] 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 terphenyl 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 groups and hexyloxybiphenyl groups. When it is required to increase the solubility of dichroic dyes, the twisted nematic liquid crystal molecule preferably has a cyano group.

[0028] 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.

[0029] The dichroic dye is oriented in a so-called guest-host configuration, where liquid crystal molecules are set as the host. The dichroic dye appears black when its long axis is approximately perpendicular to the direction of incident light. The dichroic dye may be a black-based dichroic dye, a mixture of cyan-based, magenta-based, and yellow-based dichroic dyes, or a combination thereof.

[0030] 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-based dichroic dyes, each having a different dichroism ratio.

[0031] 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 improved dichroism ratio are required, the dichroic dye is preferably an anthraquinone compound. The concentration of the dichroic dye in each liquid crystal layer 13,23 may be 0.5% by mass or more and 20% by mass or 2.5% by mass or more and 15% by mass, based on the mass of the liquid crystal layer 13,23.

[0032] 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.

[0033] The spacers are dispersed throughout each liquid crystal layer 13, 23. The particle size of the spacers determines the thickness of each liquid crystal layer 13, 23 in which the spacers are dispersed. An example of the thickness of each liquid crystal layer 13, 23 is 2 μm or more and 20 μm or less. 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.

[0034] [Alignment axis direction of liquid crystal layers 13 and 23] A single plane along the two liquid crystal layers 13 and 23 is the reference plane. The orientation axis direction of the reference plane is the average of the directions along the long axes of the liquid crystal molecules located on the reference plane when there is no electric field. The orientation axis direction of each plane is defined by using each plane along each liquid crystal layer 13 and 23 as the reference plane. Each liquid crystal layer 13 and 23 gradually changes its orientation axis direction from the upper orientation layers 11C and 21C toward the lower orientation layers 12C and 22C.

[0035] In Figure 2, the orientation axis direction of specific surfaces in the liquid crystal layers 13 and 23 is represented by arrows indicating the component of the orientation axis direction along that surface. As shown by the solid line in Figure 2, the orientation axis direction of the surface 13T in contact with the first upper alignment layer 11C in the first liquid crystal layer 13 is the first upper axis direction DT1. The orientation axis direction of the surface 13B in contact with the first lower alignment layer 12C in the first liquid crystal layer 13 is the first lower axis direction DB1. The surface 13M located in the center of the first liquid crystal layer 13 in the thickness direction is the midplane, and the orientation axis direction of the midplane in the first liquid crystal layer 13 is the first central axis direction DM1.

[0036] 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 toward 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.

[0037] As shown by the dashed line in Figure 2, the orientation axis direction of the surface 23T in contact with the second upper alignment layer 21C in the second liquid crystal layer 23 is the second upper axis direction DT2. The orientation axis direction of the surface 23B in contact with the second lower alignment layer 22C in the second liquid crystal layer 23 is the second lower axis direction DB2. The surface 23M located in the center of the thickness direction of the second liquid crystal layer 23 is the midplane, and the orientation axis direction of the midplane in the second liquid crystal layer 23 is the second central axis direction DM2.

[0038] Each alignment layer 21C, 22C rotates the orientation axis of the second liquid crystal layer 23 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.

[0039] [Twisted corner] The reference direction is one direction along the reference plane, and this reference direction is common to the two cells 10 and 20. The angle formed between the component in the orientation axis direction within the reference plane and the reference direction is the azimuth angle of the reference plane in the liquid crystal layers 13 and 23.

[0040] As shown in Figure 3, the twist angle θTB of the first liquid crystal layer 13 is the difference between the azimuthal angle of the surface in contact with the first upper alignment layer 11C within the first liquid crystal layer 13 and the azimuthal angle of the surface in contact with the first lower alignment layer 12C within the first liquid crystal layer 13. That is, the twist angle θTB of the first liquid crystal layer 13 is the angle formed by a straight line extending in the first upper axis direction DT1 and a straight line extending in the first lower axis direction DB1, as viewed from a viewpoint facing the first upper support layer 11A. 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 θTB of the first liquid crystal layer 13 is a predetermined angle. The twist angle θTB 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°.

[0041] The twist angle θTB of the second liquid crystal layer 23 is the difference between the azimuthal angle of the surface in contact with the second upper alignment layer 21C within the second liquid crystal layer 23 and the azimuthal angle of the surface in contact with the second lower alignment layer 22C within the second liquid crystal layer 23. That is, the twist angle θTB 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 facing the second upper support layer 21A. 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 θTB of the second liquid crystal layer 23 is a predetermined angle. The twist angle θTB 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°.

[0042] [Orientation axis angle θ12] As shown in Figure 4, the ND filter 50F has an orientation axis angle θ12 at the boundary between two cells 10 and 20. The orientation axis angle θ12 is the angle formed by a straight line extending in the first lower axis direction DB1 and a straight line extending in the second upper axis direction DT2, as viewed from a viewpoint facing the first upper support layer 11A. The two cells 10 and 20 are fixed to each other by the optically transparent adhesive layer 30 such that the orientation axis angle θ12 is a predetermined angle greater than 0° and less than 180°.

[0043] The orientation axis angle θ12 may be between 80° and 100°, between 85° and 95°, or 90°. When the orientation axis angle θ12 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, 20 is shielded from light, the first cell 10 can easily shield the transmitted light from the second cell 20.

[0044] [Tilt angle, offset angle] As shown in Figure 5, each alignment layer 11C, 12C, 21C, and 22C imparts a tilt angle greater than 0° to the liquid crystal molecules. The tilt angle of the liquid crystal molecules is the angle in the liquid crystal molecule when there is no electric field, and is the angle formed between the long axis of the liquid crystal molecule and the reference plane. The average of the tilt angles of the liquid crystal molecules constituting the liquid crystal layers 13 and 23 is the average tilt angle, and the average tilt angle obtained by measurement can be used as the tilt angle of the midplane. The tilt angle of each midplane may be between 0.5° and 12°, or between 1° and 8°.

[0045] The ND filter 50F has a cell misalignment angle. The cell misalignment angle is the angle formed by the components along the two upper axial directions DT1 and DT2 reference planes. The ND filter 50F has a midplane misalignment angle. The midplane misalignment angle is the angle formed by the components of the two central axis directions DM1 and DM2 along the reference planes.

[0046] The midplanes of each liquid crystal layer 13, 23 have tilt angles opposite to each other with respect to a single reference plane. Each liquid crystal layer 13, 23 has an average tilt angle opposite to each other with respect to a single reference plane. For example, the first liquid crystal layer 13 forms an average tilt angle above a single reference plane, while the second liquid crystal layer 23 forms an average tilt angle below that reference plane. The ND filter 50F achieves a single spray orientation using the two liquid crystal layers 13, 23.

[0047] The average tilt angle is obtained by the so-called crystal rotation method, which involves observing the transmission intensity in the absence of an electric field using a polarizing microscope while rotating a 50F ND filter, sandwiched between polarizing plates under crossed nicol conditions, by a fixed angle at a time.

[0048] The two central axis directions DM1 and DM2 are antiparallel with respect to a single reference plane. Being antiparallel with respect to a single reference plane means that the two central axis directions DM1 and DM2 have components that are opposite to each other within that reference plane, and that have components that are the same in direction in the direction normal to that reference plane. In this case, the components that are opposite to each other, i.e., the component along the reference plane in the first central axis direction DM1 and the component along the reference plane in the second central axis direction DM2, do not have to be strictly opposite directions, but it is sufficient that the angle formed by the lines along these components is between -10° and 10°. Furthermore, the angle formed by the line along the first central axis direction DM1 and the line along the second central axis direction DM2 may be between 5° and 10°.

[0049] An ND filter 50F having such antiparallel configuration reduces the dependence of the transmittance of the ND filter 50F on the viewing angle. For example, incident light L2A and L2B are incident on the second lower support layer 22A of the second cell 20 at mutually different incident angles. In this case, the first cell 10 and the second cell 20 have components in the orientation axis direction of the midplane which are in opposite directions, causing differences in the dependence of absorbance on the incident direction. As a result, the viewing angle dependence of the transmitted light from the first cell 10 acts on the emitted light L1A and L1B in such a way that it reduces the viewing angle dependence of the transmitted light from the second cell 20. Thus, the orientation axis direction of the antiparallel-arranged midplane reduces the viewing angle dependence of the transmittance of the ND filter 50F.

[0050] [Example Test] As shown in Figure 6, ND filters 50F were formed in each liquid crystal layer 13, 23 for Test Examples 1-1 to 1-5, each having the following configuration. The ND filters 50F in Test Examples 1-1 to 1-3 have antiparallel arrangements in two central axis directions DM1 and DM2 (antiparallel configuration AP). The ND filters 50F in Test Examples 1-4 and 1-5 have two mutually orthogonal central axis directions DM1 and DM2 (cross configuration CP). The dichroic dye concentration is the ratio of the weight of the dichroic dye contained in each liquid crystal layer 13, 23 to the weight of each liquid crystal layer 13, 23. • Thickness of each liquid crystal layer 13, 23: 10 μm • Concentration of dichroic pigment: 7.5% by weight

[0051] The ND filter 50F in Test Example 1-1 is equipped with orientation layers 11C, 12C, 21C, and 22C such that the first cell 10 has a twist angle θTB of 90° (clockwise rotation), and the second cell 20 also has a twist angle θTB of 90° (clockwise rotation). Furthermore, the ND filter 50F in Test Example 1-1 is arranged such that the orientation axis angle θ12 is 90°, and the cell misalignment angle and the midplane misalignment angle are both 180°.

[0052] The ND filter 50F in Test Example 1-2 is equipped with orientation layers 11C, 12C, 21C, and 22C such that the first cell 10 has a twist angle θTB of -90° (counterclockwise rotation), and the second cell 20 also has a twist angle θTB of -90° (counterclockwise rotation). Furthermore, the ND filter 50F in Test Example 1-2 is arranged such that the orientation axis angle θ12 is 90°, and the cell misalignment angle and the midplane misalignment angle are both 180°.

[0053] The ND filter 50F in Test Example 1-3 has a twist angle θTB of 100° (clockwise rotation) for the first cell 10 and a twist angle θTB of 80° (clockwise rotation) for the second cell 20. Furthermore, the ND filter 50F in Test Example 1-3 has an orientation axis angle θ12 of 90°, and the cells 10 and 20 are arranged such that the cell misalignment angle and the midplane misalignment angle are both 180°.

[0054] The ND filter 50F in Test Example 1-4 has a twist angle θTB of 90° (clockwise rotation) for the first cell 10 and a twist angle θTB of 90° (clockwise rotation) for the second cell 20. Furthermore, the ND filter 50F in Test Example 1-4 has an orientation axis angle θ12 of 0°, and the cells 10 and 20 are arranged such that the cell misalignment angle and the midplane misalignment angle are both 90°.

[0055] The ND filter 50F in Test Example 1-5 has a twist angle θTB of 0° for the first cell 10 and a twist angle θTB of 0° for the second cell 20. Furthermore, the ND filter 50F in Test Example 1-5 has an orientation axis angle θ12 of 90°, and the cells 10 and 20 are arranged such that the cell misalignment angle and the midplane misalignment angle are both 90°.

[0056] Figures 7 to 9 show the transmitted white light images of the ND filter 50F in the absence of an electric field (light shielding) for test examples 1-1, 1-4, and 1-5. It was found that the transmitted images using the ND filter 50F in test examples 1-2 and 1-3 were almost identical to the transmitted image using the ND filter 50F in test example 1-1.

[0057] [Damping coefficient] As shown in Figure 7, the ND filter 50F in Test Example 1-1 exhibited a high overall black level when light was blocked. The ND filter 50F in Test Example 1-1 showed a total light transmittance of 1.05% when light was blocked, indicating a higher attenuation coefficient than ND64. Furthermore, the ND filter 50F in Test Example 1-1 showed a total light transmittance of 25.1% when 5V was applied (transparent) and a total light transmittance of 32.4% when 10V was applied (transparent).

[0058] This confirmed that the ND filter 50F in Test Example 1-1 has an attenuation coefficient that spans a wide range from ND4 to ND64. Furthermore, the ND filters 50F in Test Examples 1-2 and 1-3 were also found to have an attenuation coefficient that spans a wide range from ND4 to ND64, similar to the ND filter 50F in Test Example 1-1.

[0059] As shown in Figure 8, the ND filter 50F in Test Example 1-2 exhibited a low overall black level when light was blocked. The ND filter 50F in Test Example 1-2 showed a total light transmittance of over 1.56% when light was blocked, i.e., it had a lower attenuation coefficient than ND64.

[0060] As shown in Figure 9, the ND filter 50F in Test Example 1-5 exhibited a high overall black level when light was blocked. The ND filter 50F in Test Example 1-5 showed a total light transmittance of less than 1.56% when light was blocked, indicating a higher attenuation coefficient than ND64.

[0061] [Viewing angle] Figures 10 and 11 show the transmittance dependence of the ND filter 50F at each measurement azimuth angle for Test Examples 1-1 and 1-5, obtained using the measurement conditions described below. It was found that the transmittance dependence of the ND filter 50F in Test Examples 1-2 and 1-3 was almost the same as that of the ND filter 50F in Test Example 1-1. • Measuring device: Motorized 6-axis goniometer for display measurement (DMS803 / manufactured by Instrument Systems GmbH) ·Tilt angle (elevation angle): 0° or more and 30° or less • Rotation angle (measured azimuth angle): 0° or more and less than 360°

[0062] As shown in Figure 10, the transmittance of the ND filter 50F in Test Example 1-1 shows a greater dependence on the rotation angle (viewing angle) as the elevation angle increases from 0° to 30°. However, it was also observed that the viewing angle dependence was sufficiently low across the entire range of elevation angles from 0° to 30°.

[0063] As shown in Figure 11, the transmittance of the ND filter 50F in Test Examples 1-5 also shows increased dependence on the viewing angle as the elevation angle increases from 0° to 30°. However, a large dependence on the viewing angle was observed at elevation angles between 20° and 30°.

[0064] [Dimming device] As shown in Figure 12, 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 light reduction devices.

[0065] 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. 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.

[0066] 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 based on the input of a voltage signal. The filter drive unit 53F is equipped with a switching mechanism that rotates or slides 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.

[0067] The input and output of the voltage signal change the orientation state of each liquid crystal layer 13, 23 between 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.

[0068] When the filter drive unit 53F stops inputting voltage signals to the two liquid crystal layers 13 and 23, the two liquid crystal layers 13 and 23 form a twisted orientation according to the orientation restricting force of each alignment layer 11C, 12C, 21C, and 22C. The ND filter 50F, with the liquid crystal layers 13 and 23 having a twisted orientation, blocks the transmitted light from the lens unit 50L through the absorption of dichroic dyes in each cell 10 and 20, and the intersection of the orientation axis direction at the boundary between cells 10 and 20, thereby reducing the light transmitted to the image sensor 50D.

[0069] When the filter drive unit 53F inputs a voltage signal to the two liquid crystal layers 13 and 23, the two liquid crystal layers 13 and 23 form a vertical alignment against the alignment restricting force. The two liquid crystal layers 13 and 23, having a vertical alignment, transmit light from the lens unit 50L, thereby transmitting light to the image sensor 50D.

[0070] When the filter drive unit 53F inputs a voltage signal to the liquid crystal layer 13 and stops inputting a voltage signal to the liquid crystal layer 23, the liquid crystal layer 13 has a vertical orientation and the liquid crystal layer 23 has a twisted orientation. The liquid crystal layer 23 having a twisted orientation blocks a portion of the transmitted light from the lens unit 50L due to the absorption of the dichroic dye. The liquid crystal layer 13 having a vertical orientation transmits the transmitted light from the second cell 20 toward the image sensor 50D.

[0071] [effect] According to the first embodiment described above, 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.

[0072] (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.

[0073] (3) 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.

[0074] (4) Because the orientation axis angle θ12 at the boundary between the two cells 10 and 20 is greater than 0°, when each cell 10 and 20 is shielded, the first cell 10 easily shields the transmitted light from the second cell 20. Furthermore, because the two central axis directions DM1 and DM2 are antiparallel, the change in the transmittance of the ND filter 50F with respect to the viewing angle is suppressed.

[0075] (5) 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.

[0076] (Second Embodiment) A second embodiment of the ND filter, the light-reducing device, and the imaging device will be described below. In the following description, components similar to those in the first embodiment will be denoted by the same reference numerals, and their descriptions will be omitted. The ND filter of the second embodiment can be used in the light-reducing device and imaging device in the same way as in the first embodiment.

[0077] The ND filter 50F of the first embodiment described above has a structure in which two cells 10 and 20 are stacked, each having a liquid crystal layer 13 and 23 that forms a twisted orientation in the absence of an electric field. In this structure, the transmittance in the absence of an electric field, i.e., when light is blocked, is higher compared to the case in which a liquid crystal layer that forms a homogeneous orientation in the absence of an electric field is used. As a result, the variable range of transmittance, i.e., the range of attenuation ratio that can be achieved by the ND filter 50F, becomes narrower. In the second embodiment, the objective is to find a configuration in the ND filter 50F of the first embodiment that can further reduce the transmittance when shading.

[0078] One of the indicators representing the optical characteristics of the ND filter 50F is optical density, and ideally, the optical density of each cell 10,20 is proportional to the product of the thickness of the liquid crystal layer 13,23 and the density of the dichroic dye. Therefore, the inventors used the cell density CC, which is the product of the cell gap Gp (μm), which is the thickness of the liquid crystal layer 13,23, and the dye density Cd (%), which is the density of the dichroic dye in the liquid crystal layer 13,23, and conducted verification to find a configuration that can achieve a smaller transmittance when light is blocked at the same cell density CC. The dye density Cd is the percentage of the total mass of the dichroic dye contained in the liquid crystal layer relative to the total mass of the liquid crystal layer.

[0079] Figure 13 shows the cell gap Gp, dye concentration Cd, and cell concentration CC for the ND filter 50F used in test examples 2-1 to 2-4. In each of the ND filter 50F in test examples 2-1 to 2-4, the cell gap Gp, dye concentration Cd, and cell concentration CC are common to the first cell 10 and the second cell 20. Test examples 2-1 to 2-4 are configured to have the same cell concentration CC, but with different cell gap Gp and dye concentration Cd.

[0080] In all of the ND filter 50F test examples 2-1 to 2-4, the twist angle θTB of the first cell 10 and the second cell 20 is 90°, the alignment axis angle θ12 is 90°, the cell misalignment angle and the midplane misalignment angle are both 180°, and the two central axis directions DM1 and DM2 are antiparallel. The liquid crystal layers 13 and 23 of the ND filter 50F in each test example contain a yellow dichroic dye, a magenta dichroic dye, and a cyan dichroic dye.

[0081] Figure 14 shows the total light transmittance of the ND filter 50F for each test example when the applied voltage is 0V, i.e., when light is blocked, and Figure 15 shows the total light transmittance of the ND filter 50F for each test example when the applied voltage is 10V, i.e., when transparency is maintained.

[0082] As shown in Figure 14, under light shielding conditions, the transmittance decreases in the order of Test Examples 2-1, 2-2, 2-3, and 2-4. In other words, the larger the cell gap Gp and the smaller the dye concentration Cd, the lower the transmittance. On the other hand, as shown in Figure 15, under transparent conditions, there is not as much difference in transmittance among the test examples as there is under light shielding conditions.

[0083] Therefore, it can be said that a large cell gap Gp and a small dye concentration Cd allows for a large range of variable transmittance. In particular, compared to Test Example 2-1, where the cell gap Gp is ​​less than 10 μm, Test Examples 2-2, 2-3, and 2-4, where the cell gap Gp is ​​10 μm or more, show a significant decrease in transmittance during light shielding. For this reason, it is preferable that the cell gap Gp be 10 μm or more. In this case, it is preferable that the dye concentration Cd be 15.0% or less. The cell concentration CC may be, for example, 75 μm·% or more and 150 μm·% or less.

[0084] Next, we performed an analysis from the perspective of the degree of orientational order of dichroic pigments. Figure 16 shows the relationship between the degree of orientation order S at the maximum absorption wavelength of each color of dichroic dye in a single cell and the cell gap Gp when the applied voltage is 0V for test examples 2-1 to 2-4, and Figure 17 shows the relationship between the degree of orientation order S and the dye concentration Cd. In Figures 16 and 17, "Y" represents a yellow dichroic dye, "M" represents a magenta dichroic dye, and "C" represents a cyan dichroic dye. The degree of orientation order S was determined using the absorbance A∥ of parallel polarization and the absorbance A⊥ of perpendicular polarization by the following formula (1). S=(A∥-A⊥) / (A∥+2A⊥) ···(1)

[0085] In all three dichroic dyes—yellow, magenta, and cyan—as shown in Figure 16, a smaller cell gap Gp correlates with a lower degree of orientation order S, and as shown in Figure 17, a higher dye concentration Cd correlates with a lower degree of orientation order S. This suggests that the orientation of dichroic dyes does not easily follow the twist orientation of the liquid crystal composition, and that this can be improved by increasing the cell gap Gp and decreasing the dye concentration Cd.

[0086] As described above, a large cell gap Gp and a small dye concentration Cd increase the orientation order of the dichroic dye in the absence of an electric field, thereby reducing the transmittance of the ND filter 50F.

[0087] Here, the factors that contribute to these effects, or in other words, the factors that make it easier for the dichroic dye to follow the orientation of the liquid crystal composition in the absence of an electric field, are thought to be that a large cell gap Gp reduces the twist of orientation per unit thickness, and a small dye concentration Cd reduces the amount of dichroic dye per unit volume. To verify which of these factors has a stronger effect, the characteristics were evaluated using an ND filter 50F with a changed twist angle θTB.

[0088] Figure 18 shows the twist angle θTB, cell gap Gp, twist pitch Pt, dye concentration Cd, and cell concentration CC for ND filter 50F in test examples 2-1 to 2-5. The twist pitch Pt is the length in the thickness direction of the cell required for the orientation axis to rotate 360° in twist orientation. For example, when the twist angle θTB is 90°, the twist pitch Pt is four times the cell gap Gp. The larger the twist pitch Pt, the smaller the orientation twist per unit thickness.

[0089] Each of the test examples 2-1 to 2-4 has the same configuration as each of the test examples 2-1 to 2-4 used in Figures 13 to 17. In the ND filter 50F of test example 2-5, the cell gap Gp, twist pitch Pt, dye concentration Cd, and cell concentration CC are common to the first cell 10 and the second cell 20. In the ND filter 50F of test example 2-5, the twist angle θTB of the first cell 10 and the second cell 20 is 45°, and the orientation axis angle θ12 is 90°.

[0090] Figure 19 shows the relationship between the total light transmittance and twist pitch Pt of the ND filter 50F for each test example when the applied voltage is 0V, i.e., when light is blocked. Figure 20 shows the relationship between the total light transmittance and twist pitch Pt of the ND filter 50F for each test example when the applied voltage is 10V, i.e., when transparent.

[0091] As shown in Figure 18, the twist pitch Pt of Test Example 2-4, where the twist angle θTB is 90° and the cell gap Gp is ​​20 μm, and Test Example 2-5, where the twist angle θTB is 45° and the cell gap Gp is ​​10 μm, are identical at 80 μm.

[0092] As shown in Figure 19, the transmittance of Test Example 2-4 and Test Example 2-5 is approximately the same when light is blocked. As shown in Figure 20, when transparent, the transmittance of Test Example 2-5 does not differ significantly from that of Test Examples 2-1 to 2-4.

[0093] Therefore, it is suggested that the ease with which the dichroic dyes follow the orientation of the liquid crystal composition in the absence of an electric field is strongly influenced by the magnitude of the orientation twist per unit thickness. The smaller this twist, that is, the larger the twist pitch Pt, the higher the orientational order of the dichroic dyes in the absence of an electric field, and the lower the transmittance of the ND filter 50F.

[0094] In particular, compared to Test Example 2-1, where the twist pitch Pt was less than 40 μm, Test Examples 2-2 to 2-5, where the twist pitch Pt was 40 μm or more, showed a significant decrease in transmittance during light shielding. Therefore, it is preferable that the twist pitch Pt be 40 μm or more.

[0095] Furthermore, the configurations described above, in which the cell gap Gp is ​​10 μm or more and the twist pitch Pt is 40 μm or more, are suitable for an ND filter 50F that has a transmittance of 20% or more when transparent and a transmittance of 1.56% or less when shielded, as shown in Figures 14 and 15.

[0096] Even if the transmittance differs between the transparent and light-shielding states from the above configuration, the findings obtained from the verification in the second embodiment are applicable. Specifically, a large cell gap Gp and a small dye concentration Cd, along with a large twist pitch Pt, can reduce the transmittance of the ND filter 50F in the absence of an electric field.

[0097] Specifically, in an ND filter 50F with a higher transmittance configuration, where the transmittance when transparent is 20% or more, preferably 50% or more, and the transmittance when light-shielding is greater than 1.56%, in order to suitably obtain light-shielding performance within the above range of transmittance when light-shielding, it is preferable that the cell gap Gp is ​​2.0 μm or more, and the twist pitch Pt is 8 μm or more. In this case, the cell density CC may be 5 μm·% or more and 80 μm·% or less. Note that the total light transmittance when light-shielding is less than the total light transmittance when transparent.

[0098] [effect] According to the second embodiment described above, in addition to the effects (1) to (5) of the first embodiment, the following effects can be obtained.

[0099] (6) In an ND filter 50F having a transmittance of 20% or more when transparent and a transmittance of 1.56% or less when light-shielded, the transmittance when light-shielded can be reduced by having a twist pitch Pt of 40 μm or more in the twisted orientation of the liquid crystal layers 13 and 23. Furthermore, in an ND filter 50F with a higher transmittance configuration, having a transmittance of 20% or more, preferably 50% or more, when transparent and a transmittance exceeding 1.56% when light-shielded, the transmittance when light-shielded can be reduced by having a twist pitch Pt of 8 μm or more in the twisted orientation of the liquid crystal layers 13 and 23. This expands the variable range of transmittance in the ND filter 50F.

[0100] (7) The large cell gap Gp of the liquid crystal layers 13 and 23 and the small dye density Cd make it possible to reduce the transmittance when light is blocked. This expands the variable range of transmittance in the ND filter 50F. In particular, in an ND filter 50F in which the transmittance when transparent is 20% or more and the transmittance when light is blocked is 1.56% or less, the transmittance when light is blocked can be suitably reduced by having a cell gap Gp of 10 μm or more. Furthermore, in an ND filter 50F with a higher transmittance configuration in which the transmittance when transparent is 20% or more, preferably 50% or more, and the transmittance when light is blocked exceeds 1.56%, the transmittance when light is blocked can be suitably reduced by having a cell gap Gp of 2.0 μm or more.

[0101] (Example of change) Each of 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.

[0102] [Layer composition] The ND filter 50F may omit either the first lower support layer 12A or the second upper support layer 21A, as well as the optically transparent adhesive layer 30. For example, the ND filter 50F may omit the first lower support layer 12A and the optically transparent adhesive layer 30, and may have the first lower electrode layer 12B on the upper surface of the second upper support layer 21A.

[0103] The ND filter 50F may have three or more cells. In this case, the cells other than the two cells 10 and 20 may have the same configuration as the first cell 10, or the same configuration as the second cell 20, or they may have different tilt angles than the two cells 10 and 20.

[0104] The first cell 10 may also 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 reduce the amount of static charge on the first cell 10. The other functional layers may also have a so-called reflection suppression function that suppresses the reflection of light incident on the ND filter 50F by the ND filter 50F. The second cell 20 may also include functional layers other than the support layers 21A, 22A, electrode layers 21B, 22B, alignment layers 21C, 22C, and liquid crystal layer 23. 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.

[0105] [Dimming device] The drive unit 53 may simultaneously input a voltage signal to the first upper electrode layer 11B and the second upper electrode layer 21B, or 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 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.

[0106] 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.

[0107] 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. The drive unit 53 may generate voltage signals with mutually different characteristics to compensate for individual differences based on the stored data.

[0108] 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. 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.

[0109] [Imaging device 50] 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.

[0110] 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.

[0111] 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]

[0112] θTB…Twist angle 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 twisted to vertical 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 the orientation axes of their opposing surfaces intersect. The orientation axis direction of the midplanes in the two liquid crystal layers is antiparallel, having a tilt angle opposite to the plane along the liquid crystal layers. An ND filter characterized by the following.

2. The twist angle of the liquid crystal layer is 80° or more and 100° or less. The ND filter according to claim 1.

3. When viewed from a viewpoint facing the surface of the ND filter, the angle formed by the orientation axis direction of the two liquid crystal layers on the mutually opposing surfaces is 80° or more and 100° or less. The ND filter according to claim 1.

4. The dichroic dye has equal concentrations in the two liquid crystal layers. The ND filter according to claim 1.

5. Each filter element comprises two transparent electrode layers sandwiching the liquid crystal layer constituting 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.

6. Each filter element comprises two transparent support layers sandwiching the liquid crystal layer constituting the filter element, with one of the transparent support layers in one filter element being 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.

7. The thickness of the liquid crystal layer is 2 μm or more and 20 μm or less. The concentration of the dichroic dye in the liquid crystal layer is 0.5% by mass or more and 20% by mass or less. The ND filter according to claim 1.

8. The light transmittance when shielded is 1.56% or less. The ND filter according to claim 1.

9. The thickness of the liquid crystal layer is 10 μm or more. The ND filter according to claim 8.

10. In the aforementioned twist orientation, the length in the thickness direction of the liquid crystal layer required for the orientation axis direction to rotate 360° is the twist pitch. The aforementioned twist pitch is 40 μm or more. The ND filter according to claim 8.

11. The light transmittance when shading is greater than 1.56%. The ND filter according to claim 1.

12. In the aforementioned twist orientation, the length in the thickness direction of the liquid crystal layer required for the orientation axis direction to rotate 360° is the twist pitch. The aforementioned twist pitch is 8 μm or more. The ND filter according to claim 11.

13. An ND filter with two overlapping filter elements, A drive unit for driving the ND filter, A dimming device comprising, 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 twisted to vertical 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 the orientation axes of their opposing surfaces intersect. The orientation axis direction of the midplanes in the two liquid crystal layers is antiparallel, having a tilt angle opposite to the plane along the liquid crystal layers. A dimming device characterized by the following features.

14. Each filter element comprises two transparent electrode layers sandwiching the liquid crystal layer constituting the filter element, and the drive unit drives the liquid crystal layer for each filter element. The dimming device according to claim 13.

15. The lens part, Image sensor and An ND filter is disposed between the lens unit and the image sensor, An imaging device comprising, 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 twisted to vertical 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 the orientation axes of their opposing surfaces intersect. The orientation axis direction of the midplanes in the two liquid crystal layers is antiparallel, having a tilt angle opposite to the plane along the liquid crystal layers. An imaging device characterized by the following features.

16. 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 15.

Images