JP5067133B2 - Absorption type ND filter - Google Patents

Absorption type ND filter Download PDF

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JP5067133B2
JP5067133B2 JP2007293956A JP2007293956A JP5067133B2 JP 5067133 B2 JP5067133 B2 JP 5067133B2 JP 2007293956 A JP2007293956 A JP 2007293956A JP 2007293956 A JP2007293956 A JP 2007293956A JP 5067133 B2 JP5067133 B2 JP 5067133B2
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nd filter
absorption
substrate
film
light
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JP2009122216A (en
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秀晴 大上
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住友金属鉱山株式会社
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  The present invention relates to an absorptive ND filter that attenuates transmitted light in the visible wavelength range, and more particularly to an improvement of an absorptive ND filter having a small incident angle dependency of spectral reflection characteristics.

  An ND filter (Neutral Density Filter) that attenuates transmitted light in the visible wavelength range has recently been widely used. This type of ND filter includes a reflective ND filter that reflects and attenuates incident light. An absorption ND filter that absorbs and attenuates incident light is known. When an ND filter is incorporated in a lens optical system in which reflected light is a problem, an absorption ND filter is generally used. In this absorption ND filter, an absorbing substance is mixed in the substrate itself (colored glass ND filter) or There are a type in which an absorbing material is applied and a type in which the thin film formed on the surface of the substrate has no absorption and has absorption. In the latter case, an absorption-type multilayer ND filter is also known in which the thin film is formed of a multilayer film to prevent reflection on the surface of the thin film, and has an antireflection effect as well as a function of attenuating transmitted light. This is because, even in an ND filter for attenuating incident light, if there is a reflection on the surface, the reflected light causes undesirably causing flare or image blur.

By the way, the absorption multilayer ND filter used for a small and thin digital camera has a small installation space, so that it is necessary to make the substrate itself thin, and a resin film is an optimal substrate. As an absorption multilayer ND filter in which the thin film is a multilayer film, Patent Document 1 discloses that a substrate such as a resin film, an oxide dielectric film layer such as SiO 2 and a metal absorption film layer such as Ni. A structure provided with an absorptive multilayer film is shown.

  Recently, as a method for preventing light reflection from the transparent optical component, a method of providing an antireflection structure composed of conical projections (see FIG. 1A) arranged in a matrix on the surface of the optical component has also been proposed. (See Patent Document 2). In the case of an antireflection structure for the visible wavelength region, the cone-shaped projection groups are arranged in a matrix at a submicron pitch, and in such an antireflection structure having a pitch smaller than the wavelength of incident light. 1B can be considered as a substance whose refractive index continuously changes from the medium (air) to the substrate as shown in FIG. 1B, and has a function of preventing reflection.

  Further, Patent Document 2 discloses a step of forming a nucleus having a catalytic function on the surface of a master material, a step of growing a crystal on the formed nucleus to form an acicular crystal, and an acicular crystal formed. Also disclosed is a method for forming an antireflection structure, which includes the steps of forming an electroforming mold using the master material that has been formed, and forming a conical protrusion group on a molding material using the obtained electroforming mold. ing.

And in patent document 2, even if it is the molding material which has a large area and a curved surface shape, it is supposed that a highly accurate antireflection structure can be formed in the surface.
JP 2006-178395 A JP 2006-130841 A

  By the way, in the above-mentioned absorption-type multilayer ND filter having a function of attenuating transmitted light and an antireflection function, since the reflectance has an angle dependency, the incident angle of incident light deviates from the designed incident angle. , The reflectivity changes.

  For this reason, when an absorption type multilayer ND filter designed for vertical incidence is used under the condition of incidence of 40 degrees, the spectral reflection characteristics are different. That is, when an absorption-type multilayer ND filter designed for vertical incidence is incorporated in a condensing optical system, the incident angle is different between the light beam on the optical axis and the light beam in the peripheral portion, so that the spectral reflection characteristics are different. As a result, the reflectance generally increases.

  As an example, FIG. 2 shows the incident angle dependence of the spectral reflectance of an absorption multilayer ND filter designed for normal incidence. From the graph of FIG. 2, it can be confirmed that the spectral reflection characteristics differ depending on the incident angle of the incident light.

  If the spectral reflection characteristics differ depending on the incident angle, the hue of the image may be hindered. In particular, digital cameras, camera-equipped mobile phones, and the like have become thinner in recent years, and the length of the lens barrel has been shortened corresponding to the thinness, and accordingly, the incident angle of the light beam to the ND filter tends to increase. The above problem is becoming more prominent.

  On the other hand, the antireflection structure constituted by the conical protrusions has a feature that the antireflection effect is not so small even when the incident angle of incident light is increased.

  Under such a technical background, the present inventor has not described the antireflection structure of Patent Document 2 used in a lens element, a prism element, a mirror element, a lens barrel and the like, and is not described in Patent Document 2. When an application to an absorption ND filter was attempted, it was found that the above-described problem of spectral reflection characteristics due to the incident angle can be avoided. Furthermore, when the antireflection structure of Patent Document 2 is formed on both surfaces of a substrate made of a resin film, and an absorption type ND filter is formed by forming a light absorption film on at least one of the antireflection structures, It has also been found that the flare and image blur caused by it are eliminated.

  Then, the place made into the subject of this invention is providing the absorption type ND filter with small incident angle dependence of the spectral reflection characteristic discovered by this inventor.

That is, the invention according to claim 1
In an absorption ND filter that includes a substrate made of a resin film and attenuates transmitted light in the visible wavelength range,
An anti-reflection structure part composed of a group of cone-shaped projections in which a plurality of cone-shaped projections are arranged in a matrix at a submicron pitch is provided on one side of the substrate, and a single unit made of a Ni-based alloy containing Ti. The light absorption film of the layer is provided on the opposite side surface of the substrate, and the spectral reflectance is 0.5 in the range of the incident angle defined as the angle formed between the normal line and the incident light ray in the range of 0 ° to 40 °. % Or less .

The invention according to claim 2
In the absorption ND filter according to the invention of claim 1,
The single-layer light-absorbing film is made of a Ni-based alloy containing 7.5% by weight of Ti formed by a sputtering method,
The invention according to claim 3
In the absorption ND filter according to claim 1 or 2 ,
An anti-reflection structure composed of the above-mentioned cone-shaped projection group by manufacturing an electroforming mold having an inverted shape of the above-mentioned cone-shaped projection group, and molding the resin film material for a substrate by using this electro-mold by the nanoimprint method or the casting method A body part is formed.

According to the absorptive ND filter according to the present invention, the antireflection structure portion formed by the conical projection group in which a plurality of conical projections are arranged in a matrix at a submicron pitch is provided on one side of the substrate made of a resin film. Provided is an absorption type ND filter in which the reflection preventing effect is not reduced even if the incident angle of incident light is increased, and the spectral reflection characteristic is less dependent on the incident angle. Is possible.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First, in the absorption ND filter according to the present invention, an antireflection structure portion composed of a plurality of conical protrusions in which a plurality of conical protrusions are arranged in a matrix at a submicron pitch is provided on one side of a substrate made of a resin film. It is characterized by being provided.

(1) Antireflection structure part constituted by conical protrusion groups The antireflection structure part according to the present invention constituted by conical protrusion groups is formed by the method described in Patent Document 2 as described above. be able to.

  That is, a step of performing nucleation with a catalytic function on the surface of the master material, a step of growing crystals on the formed nuclei to form needle crystals, and a master material on which needle crystals are formed are used. The antireflection structure part according to the present invention can be formed by a method including the steps of forming an electroforming mold and forming the conical protrusions on the molding material using the obtained electroforming mold. it can.

  As the above-mentioned process for forming a nucleus having a catalytic function, a process for forming an island crystal of Cr as a nucleus having a catalytic function on the surface of a single crystal silicon wafer substrate which is a master disk material, or a quartz which is a master disk material Examples include a step of forming island-like crystals of Pd as nuclei having a catalytic function on the surface of a glass substrate.

  In addition, as the above-mentioned step of growing a crystal on the formed nucleus to form a needle-like crystal, any one selected from chemical vapor deposition, vapor phase epitaxy, molecular beam epitaxy, and electroless plating can be used. Exemplified is a step of growing a crystal containing at least one selected from the group consisting of carbon, silicon, silicon nitride, silicon dioxide, boron nitride, and metal on the nucleus to form a needle crystal. Is done.

  Next, as the above-described step of forming the electroforming mold using the master material on which the needle crystal is formed, the surface of the single crystal silicon wafer substrate on which the silicon needle crystal is formed is activated with Pd, and no process is performed. After immersing in an electrolytic Ni—P plating solution to form a Ni—P plating layer on the surface of the needle-like crystal, electroplating is performed in a sulfamic acid Ni plating solution to obtain an electroforming mold. A step of obtaining an electroforming mold having an inverted shape of the needle-like crystal by releasing the crystalline silicon wafer substrate is exemplified.

  And as said process of forming a cone-shaped projection group in a forming material using the obtained electromold, at least one surface of a resin film material for a substrate by an injection molding method, a press molding method, and a thermal nanoimprint method The step of forming the conical projection group is exemplified. In addition to the thermal nanoimprint method, it can also be formed by a UV nanoimprint method or a casting method, and roll embossing that is processed by a roll-to-roll process that can be considered as a part of the thermal nanoimprint method is also possible.

(2) Resin film The material of the resin film substrate used in the absorption ND filter according to the present invention is not particularly limited, and specific examples thereof include polyethylene terephthalate (PET), polyethersulfone (PES), A single resin film selected from the resin materials of polyarylate (PAR), polycarbonate (PC), polyolefin (PO), triacetyl cellulose (TAC) and norbornene, or a resin film selected from the above resin materials and A composite with an acrylic organic film covering one side or both sides of a single body can be mentioned. In particular, as for norbornene resin materials, representative examples include ZEONOR (trade name) manufactured by ZEON Corporation, Arton (trade name) manufactured by JSR Corporation, and the like.

  However, when performing the thermal nanoimprint described above, it is necessary to determine the optimum mold pressure, mold temperature, and the like from various properties such as the viscosity of the resin film and the glass transition temperature.

(3) Light absorption film that absorbs light in the visible wavelength range The light absorption film formed on the side surface opposite to the surface on which the antireflection structure portion of the resin film substrate is formed absorbs light in the visible wavelength range. A film material having an effect of the above can be applied, and a metal film is usually used. Specifically, a Ni-based alloy to which Ti is added is used . The optical characteristics and physical characteristics can be improved by mixing the metal oxide with the saturated oxide. In order to reduce the oxidation of the metal film, for example, it is also preferable to apply an overcoat such as SiOx or SiN on the surface of the Ni-based alloy film.

  The light absorbing film can be formed by a film forming method such as a vacuum deposition method, an ion beam sputtering method, a magnetron sputtering method, or an ion plating method.

  In addition, a light absorption film composed of a metal film has characteristics such as a refractive index and an absorption coefficient depending on the additive and impurities of the film material, the residual gas during film formation, the gas released from the resin film substrate, and the film formation speed. It can be very different. Therefore, it is necessary to appropriately select these conditions and set the absorption ND filter to have desired characteristics.

In addition, when the light absorption layer is provided on one surface of the resin film substrate, plasma treatment or ion beam treatment is performed before forming the light absorption layer, and the transmittance of the resin film at a wavelength of 400 nm is 1.0% compared with that before the treatment. The flatness of the spectral transmission characteristics can be improved by performing the pre-adjustment so as to attenuate. Furthermore, since the adhesion between the light absorption film and the resin film substrate can be improved by the plasma treatment or the ion beam treatment, it is possible to prevent cracking of the light absorption film in a high temperature and high humidity environment.

(4) Absorption-type ND filter (4-1) Absorption-type ND filter in which a resin film substrate contains a substance that absorbs light in the visible wavelength range.
As one form of the absorption ND filter according to the reference example, there is an absorption ND filter in which a substance that absorbs light in a visible wavelength region is included in a substrate made of a resin film.

  And the said antireflection structure part provided in the at least single side | surface of the resin film board | substrate is comprised by the cone-shaped protrusion group of FIG. 1 (A) which has arrange | positioned the several cone-shaped protrusion in the matrix form with the submicron pitch. In this case, as shown in FIG. 1B, since the refractive index can be considered as a substance that continuously changes from the medium (air) to the substrate, it has an antireflection function.

  For this reason, when a substance that absorbs light in the visible wavelength region is included in the resin film substrate, an absorption type ND filter having an antireflection function and having a small incident angle dependency in spectral reflectance can be obtained. It becomes.

  Here, the substance that absorbs light in the visible wavelength region is not particularly limited, but metal fine particles and pigments that absorb light of a specific wavelength are preferable, and examples thereof include copper manganese oxide. In addition to metal fine particles and pigments, it is also possible to use a substance that does not have the property of absorbing only light in a specific wavelength range, such as carbon black.

  And any method is employ | adopted as a method of preparing the resin film board | substrate containing the substance which absorbs the light of a visible wavelength range. For example, as a method for producing a resin composition, a method in which a resin component, an absorbing material component in the visible wavelength region, and other components optionally blended are premixed, and then melt-kneaded to form a pellet. Examples of the premixing means include a Nauter mixer, a V-type blender, a Henschel mixer, a mechanochemical apparatus, and an extrusion mixer. In the preliminary mixing, granulation can be performed by an extrusion granulator, a briquetting machine, or the like as necessary. After the preliminary mixing, it is also preferable to melt and knead with a melt kneader typified by a vent type twin screw extruder and pelletize with a device such as a pelletizer. As the melt kneader, a Banbury mixer, a kneading roll, and a constant-temperature stirring vessel can be used, but a multi-screw extruder represented by a vent type twin screw extruder is preferable. By using such a multi-screw extruder, the absorbent material component is finely dispersed in the resin with a strong shearing force.

  A resin film substrate containing a substance that absorbs light in the visible wavelength region is obtained by kneading the resin composition pellets and the resin thus produced, and thermoforming them into a film.

The processing temperature, filming conditions, and the like vary somewhat depending on the type of absorbent material and resin material to be applied, but a resin film substrate can usually be produced by the following steps (A) to (C). . That is, (A) a substance (absorbing substance) that absorbs light in the visible wavelength region is added to a powder or pellet-shaped resin material, heated and dissolved at 150 to 350 ° C., and then molded to form a resin plate. (B) a step of forming the obtained resin plate into a film by an extruder, and (C) the obtained unstretched film at 30 to 120 ° C. in a uniaxial direction or biaxial at 2 to 5 times. The resin film substrate can be produced by the steps (A) to (C) of the step of producing a resin film substrate having a thickness of 10 to 200 μm by stretching in the direction.
(4-2) A light absorbing film that absorbs light in the visible wavelength region is formed on at least one of the antireflection structure portion of the resin film substrate or the opposite side surface of the substrate, and the substance that absorbs light in the visible wavelength region is the substrate. Absorptive ND filter not included
As another form of the absorption ND filter according to the reference example , an absorption ND filter in which a light absorption film of a single layer or a multilayer film that absorbs light in the visible wavelength region is formed on the antireflection structure part of the resin film substrate. Is mentioned.

  When the antireflection structure portion is constituted by the conical protrusion group of FIG. 1A in which a plurality of conical protrusions are arranged in a matrix at a submicron pitch, as shown in FIG. Further, since it can be considered as a substance whose refractive index continuously changes from the medium (air) to the substrate, it has an antireflection function.

  For this reason, when a single-layer or multilayer light-absorbing film that absorbs light in the visible wavelength region is formed on the anti-reflection structure formed by the cone-shaped projection group as shown in FIG. Thus, an absorption ND filter having a function of the above and having a small dependence on the incident angle in the spectral reflectance can be obtained. In addition, the light absorption film of the said single layer or a multilayer film may divide the performance into 2 and may be formed separately on both surfaces of the resin film board | substrate.

Moreover, as a form of the absorption ND filter according to the present invention, a single-layer light absorption film that absorbs light in the visible wavelength region on the surface of the resin film substrate opposite to the side on which the antireflection structure portion is formed. An absorptive ND filter in which is formed.

  Also in this case, an absorption type ND filter having an antireflection function and having a small incident angle dependency in the spectral reflectance can be obtained.

Further, as still another form of the absorption ND filter according to the reference example , each of the antireflection structure parts constituted by the conical protrusions is formed on both surfaces of the resin film substrate, and at least one of the antireflection structures is formed. Examples thereof include an absorption ND filter in which a light absorption film of a single layer or a multilayer film that absorbs light in a visible wavelength region is formed on a body part.

  Even in this case, an absorption type ND filter having an antireflection function and having a small incident angle dependency in spectral reflectance can be obtained, and further, an absorption type ND that can prevent not only the front surface but also the back surface reflection of the resin film substrate. A filter is obtained.

  As described above, the absorptive ND filter according to the present invention has a function of preventing reflection and has a small incident angle dependency in spectral reflectance, and is defined as, for example, an angle formed between a normal line and an incident ray. When the incident angle is in the range of 0 ° to 40 °, an absorption ND filter having a spectral reflectance of 0.5% or less is obtained. Incidentally, from the arrangement of the light receiving element located on the side opposite to the light incident side of the absorption ND filter, reflection at an incident angle of 0 ° cannot be measured originally, but it means that the reflection is limited to around 0 °. .

  Next, as a specific example of the present invention, a conical projection having a height of 600 nm and a pitch of 200 nm is formed on the surface of a PET film having a thickness of 100 μm that is transparent in the visible wavelength range by a thermal nanoimprint method (also referred to as a direct nanoimprint method). Forming a Ni-based alloy containing 7.5 wt% Ti by sputtering on the PET film surface opposite to the surface on which the antireflection structure portion is formed. An absorption ND filter according to the present invention was manufactured by forming a film of about 50 nm. Further, the spectral transmittance and the spectral reflectance at the incident angle of 10 °, the incident angle of 20 °, the incident angle of 30 °, and the incident angle of 40 ° of the obtained absorption ND filter were measured, and the spectral transmittance was shown in FIG. Fig. 5 shows the spectral reflectance.

  From the graph of FIG. 5 showing the spectral reflectance, in the absorptive ND filter according to the present invention, the reflectance is measured at any of an incident angle of 10 °, an incident angle of 20 °, an incident angle of 30 °, and an incident angle of 40 °. Is as low as 0.5% or less, and it is confirmed that the incident angle dependency is extremely small. Moreover, since it is not necessary to form a complicated multilayer film on this absorption ND filter, it is excellent in productivity. It was confirmed that

  Next, in order to compare the performance of the absorptive ND filter according to the present invention, Example 1 (an antireflection structure portion constituted by a conical projection group is formed on one side of a resin film substrate and on the opposite side of the substrate) Absorptive ND filter provided with a light absorbing film), Comparative Example 1 (absorptive ND filter provided with a light absorbing film on one surface of a resin film substrate without forming an antireflection structure part composed of conical projections) ) And Comparative Example 2 (conventional absorptive multilayer ND filter), three types of ND filters with an average transmittance of 6.3% were manufactured, and the reflection of these ND filters with an average transmittance of 6.3%. The angular dependence of rate was compared.

  This will be specifically described below.

  An absorption type ND filter was manufactured in which an antireflection structure part composed of conical projections was formed on one side of a resin film substrate and a light absorption film was provided on the opposite side of the substrate.

  That is, an antireflection structure constituted by a group of conical projections having a height of 600 nm and a pitch of 200 nm on one side of a PET film having a thickness of 100 μm that is transparent in the visible wavelength range, by a thermal nanoimprint method (also referred to as a direct nanoimprint method). A body part was formed. The mold pressure was 10 MPa and the mold temperature was 130 ° C.

  Next, a Ni-based film containing 7.5 wt% Ti by sputtering on the surface opposite to the antireflection structure portion forming surface of the PET film (resin film substrate) on which the antireflection structure portion is formed. An absorption ND filter according to Example 1 was manufactured by forming an alloy film of about 50 nm.

  FIG. 4 shows the spectral transmittance and FIG. 5 shows the spectral reflectance at the incident angles of 10 °, 20 °, 30 ° and 40 ° of the obtained absorption ND filter according to Example 1.

  Here, the spectral reflectance was measured using a self-recording spectrophotometer manufactured by JASCO Corporation. However, an incident angle of 0 ° (perpendicular incidence) could not be measured because the device arrangement was such that the irradiated light and reflected light overlapped. Further, at the time of measuring the reflectance, in order not to be affected by the back surface reflection, the back surface was rubbed with a paper file or an abrasive to perform a process of diffusing the reflection from the back surface.

  From the graph of the spectral transmittance in FIG. 4 and the graph of the spectral reflectance in FIG. 5, the reflectance is 0 at any angle of the incident angle of 10 °, the incident angle of 20 °, the incident angle of 30 °, and the incident angle of 40 °. It was confirmed that the incident angle dependency was extremely small with a low value of .5% or less.

[Comparative Example 1]
An absorption type ND filter absorption type ND filter in which a light absorption film was provided on one side of a resin film substrate was formed without forming an antireflection structure part composed of conical projections.

  That is, an absorption according to Comparative Example 1 was formed by forming a Ni-based alloy containing 7.5 wt% Ti by sputtering on one side of a PET film in which the antireflection structure portion in Example 1 was not formed. A type ND filter was produced.

  FIG. 6 shows the spectral transmittance and FIG. 7 shows the spectral reflectance at the incident angles of 10 °, 20 °, 30 °, and 40 ° of the obtained absorption ND filter according to Comparative Example 1, respectively.

  Then, from the graph of the spectral reflectance in FIG. 7, a reflectance as high as 40 to 50% due to the surface reflection of the Ni alloy film was confirmed.

[Comparative Example 2]
An absorption-type multilayer ND filter according to a conventional example was manufactured.

  That is, a five-layer absorption multilayer film having a film structure shown in Table 1 was formed on both surfaces of a PET film having a thickness of 100 μm that was transparent in the visible wavelength range.

A magnetron sputtering method is used for film formation, a Si single crystal is used for the SiO 2 target, a Ni-based alloy containing 7.5 wt% Ti is used for the Ni-based alloy target, and oxygen is used only during the SiO 2 film formation. Introduced.

  FIG. 8 shows the spectral transmittance and FIG. 9 shows the spectral reflectance at the incident angles of 10 °, 20 °, 30 °, and 40 ° of the obtained absorption ND filter according to Comparative Example 2, respectively.

  Then, from the graph of the spectral reflectance in FIG. 9, it was confirmed that the reflectance in the visible wavelength range increased as the incident angle increased, and in particular, the reflectance increase on the long wavelength side was remarkable.

"Evaluation"
Compared with Comparative Example 1 and Comparative Example 2, it is confirmed that the absorption ND filter according to Example 1 has not only low reflectance but also extremely small incident angle dependency. It was not necessary to form a film, and it was confirmed that the productivity was excellent.

  Since the absorption type ND filter according to the present invention has a small incident angle dependency of spectral reflection characteristics, it has industrial potential for use in ND filters mounted on digital cameras and digital video cameras.

FIG. 1A is a schematic perspective view of a group of conical protrusions arranged in a matrix, and FIG. 1B is a cross-sectional view of the antireflection structure including the conical protrusion group provided on one side of the substrate and antireflection. The graph which shows the relationship between the cross-sectional structure of a structure, and a refractive index. The graph which shows the spectral reflection characteristic of the absorption type multilayer ND filter which concerns on a prior art example. Sectional view of an absorption ND filter according to a reference example in which a light absorption film is formed on an antireflection structure layer composed of conical projections provided on a resin film substrate, and the sectional structure and refraction of the absorption ND filter The graph which shows the relationship with a rate. 3 is a graph showing the spectral transmission characteristics of the absorption ND filter according to Example 1. FIG. FIG. 3 is a graph showing the spectral reflection characteristics of the absorption ND filter according to Example 1. The graph which shows the spectral transmission characteristic of the absorption type ND filter which concerns on the comparative example 1. FIG. The graph which shows the spectral reflection characteristic of the absorption ND filter which concerns on the comparative example 1. FIG. The graph which shows the spectral transmission characteristic of the absorption ND filter which concerns on the comparative example 2. FIG. The graph which shows the spectral reflection characteristic of the absorption ND filter which concerns on the comparative example 2. FIG.

Claims (3)

  1. In an absorption ND filter that includes a substrate made of a resin film and attenuates transmitted light in the visible wavelength range,
    An anti-reflection structure part composed of a group of cone-shaped projections in which a plurality of cone-shaped projections are arranged in a matrix at a submicron pitch is provided on one side of the substrate, and a single unit made of a Ni-based alloy containing Ti. The light absorption film of the layer is provided on the opposite side surface of the substrate, and the spectral reflectance is 0.5 in the range of the incident angle defined as the angle formed between the normal line and the incident light ray in the range of 0 ° to 40 °. % Absorption type ND filter characterized by being less than or equal to% .
  2. 2. The absorption ND filter according to claim 1, wherein the single-layer light absorption film is made of a Ni-based alloy containing 7.5 wt% Ti formed by a sputtering method.
  3. An anti-reflection structure composed of the above-mentioned cone-shaped projection group by manufacturing an electroforming mold having an inverted shape of the above-mentioned cone-shaped projection group, and molding the resin film material for a substrate by using this electro-mold by the nanoimprint method or the casting method The absorptive ND filter according to claim 1 or 2, wherein a body part is formed.
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US10502877B2 (en) 2015-08-19 2019-12-10 Canon Kabushiki Kaisha Optical filter and optical system, image pickup apparatus, and lens apparatus which include the same

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