JP5600396B2 - Optical filter - Google Patents

Description

The present invention relates to an optical filter used in a photographing apparatus such as a camera or an optical apparatus.

  Conventionally, an optical device such as a digital camera or a video camera has been incorporated with a light amount adjusting device for adjusting the light amount. This light amount adjusting device adjusts the amount of light incident on a solid-state imaging device such as a CCD by opening and closing aperture blades, and is further reduced when the object field is bright.

  Accordingly, the aperture is made small in order to attenuate the amount of light when shooting a clear or high-luminance subject, but the light is diffracted by the aperture as it is, and the captured image is deteriorated. In addition, as the sensitivity of the CCD increases, the amount of light needs to be attenuated, and this tendency becomes remarkable.

  Therefore, as a countermeasure against this problem, an optical element such as a film-like ND (Neutral Density) filter is attached to the diaphragm blade so as to attenuate the amount of light while keeping the diaphragm aperture large.

  Specifically, an ND filter made of a member different from the diaphragm blades is attached to a part of the diaphragm blades with an adhesive or the like, so that when the subject has high brightness, the diaphragm aperture is not excessively reduced until the diameter of the diaphragm aperture becomes too small. In addition, the aperture opening is kept constant. Instead, the amount of passing light is limited by positioning the ND filter on the optical axis.

  Further, a light amount adjustment function of the ND filter having a density gradient may be used, and further light amount adjustment may be performed by moving the ND filter on the optical axis. In addition, various diaphragm devices have been proposed in which an ND filter is not attached to the diaphragm blades but has an optical function independently.

  As an optical element such as an ND filter, a type in which an organic dye or pigment that absorbs light is kneaded into a film-like material as shown in Patent Document 1 is known. In addition, as shown in Patent Document 2, ink is applied on a transparent substrate, and as shown in Patent Document 3, an inorganic hard film is formed on a transparent substrate using a vacuum deposition method.

Japanese Patent Laid-Open No. 10-96971 JP 2004-246305 A JP-A-10-133254

  In recent years, imaging devices such as digital cameras and video cameras have been miniaturized, and reflected light on the surface of optical elements such as ND filters may cause ghosts.

  In general, the basic configuration of an ND filter is a light absorption film (ND film) made of a laminated film such as a metal film, a metal oxide, or a dielectric film on one surface of a transparent substrate. Normally, as shown in FIG. 11 (a), the ND filter 1 has an ND film 3 formed on one side of the transparent substrate 2 and an antireflection film 4 formed on the other side. As shown, ND films 3 are formed on both surfaces of the transparent substrate 2. In addition, as shown in FIG. 11 (c), there is a case in which an antireflection film 4 is formed on both surfaces of a substrate 5 in which an organic dye or pigment is kneaded into a film material.

FIG. 12 shows a film configuration diagram of the ND film 3 shown in FIGS. 11A and 11B, in which a TiOx layer and an Al ₂ O ₃ layer are alternately laminated on the transparent substrate 2, and an SiO ₂ layer is formed on the outermost layer. A seven-layer structure is formed by forming a film.

  In recent years, a fine uneven periodic structure (Moth eye structure) in which unevenness is periodically formed at a pitch equal to or less than the wavelength of light has been put to practical use as a structure that can provide an antireflection effect. This is because the refractive index of the entire surface layer on which the fine uneven periodic structure is formed is determined by the volume ratio between air and the material forming the fine uneven periodic structure, so that the refractive index of the outermost surface is greatly reduced. Is possible.

  However, although the antireflection effect is larger than the above-described antireflection film, it is necessary to form a vapor deposition film or apply ink on a substrate with a fine uneven periodic structure for use as an optical filter. Have a problem. In particular, when it is necessary to relatively increase the film thickness, the fine uneven periodic structure may be buried with a deposited film or ink, and the antireflection effect may be weakened.

An object of the present invention is to provide an optical filter that solves the above-described problems and simultaneously has a good antireflection effect by a fine uneven periodic structure and a light attenuation effect that attenuates a predetermined wavelength.

In order to achieve the above object, an optical filter according to the present invention forms a fine uneven periodic structure on at least a part of a surface of a transparent substrate, and the fine uneven periodic structure contains a substance that attenuates light of a predetermined wavelength. , characterized in that it have a smaller pitch and height than the wavelength of visible light range for preventing reflection of light.

The optical filter according to the present invention suppresses reflection on the substrate surface by using a material containing a light-absorbing material on a transparent substrate and forming a fine uneven periodic structure having a pitch and height below the visible light wavelength. However, the light attenuation effect can be obtained.

It is a block diagram of an imaging optical system. It is a schematic diagram of a fine uneven | corrugated periodic structure. It is a schematic diagram of a fine uneven | corrugated periodic structure. It is a schematic diagram of a fine uneven | corrugated periodic structure. It is explanatory drawing of the manufacturing method of a fine uneven | corrugated periodic structure. It is explanatory drawing of the manufacturing method of a fine uneven | corrugated periodic structure. It is a cross-sectional schematic diagram of an optical element. It is a cross-sectional schematic diagram of an optical element. It is a cross-sectional schematic diagram of an optical element. It is a cross-sectional schematic diagram of an optical element. It is a block diagram of the conventional ND filter. It is a film | membrane structural view of the conventional ND filter.

The present invention will be described in detail based on the embodiment shown in FIGS.
FIG. 1 is a configuration diagram of a photographing optical system of an image pickup apparatus in the present embodiment, and is a solid-state image pickup composed of a lens 11, a light amount diaphragm device 12, lenses 13 to 15, a low-pass filter 16 as an infrared cut filter, a CCD, and the like. Elements 17 are sequentially arranged. In the light quantity diaphragm device 12 for adjusting the light quantity, a pair of diaphragm blades 19a and 19b are movably attached to the diaphragm blade support plate 18, and an ND filter 20 is attached to the diaphragm blade 19a.

  The light amount diaphragm device 12 attenuates the light in the visible light region passing through the substantially rhombic opening formed by the diaphragm blade 19a to which the ND filter 20 is attached and the diaphragm blade 19b to attenuate the light substantially uniformly. Can do. Further, the ND filter 20 can be inserted into the opening alone without being attached to the aperture blade 19a.

  In such an imaging optical system, the amount of light passing through the lens 11 is adjusted through the light amount diaphragm device 12 and imaged on the surface of the solid-state image sensor 17 to be converted into an electrical signal.

  FIG. 2 is a schematic diagram of a fine concavo-convex periodic structure having a Moth eye structure formed on the surface of the ND filter 20. On a transparent substrate 21 made of a PET (polyethylene terephthalate) resin film having a thickness of about 100 μm, which serves as a base material for the ND filter 20, an infinite number of conical protrusions 22 having a pitch P and a height D are arranged at equal intervals. Thus, a fine uneven periodic structure 23 is formed.

  As the substrate 21, a PET resin film having a light transmittance of 80% or more in the visible light region is used, but in addition to PET, a film-like synthetic resin substrate or glass substrate having transparency and mechanical strength is used. It is also possible to use it. For example, PEN (polyethylene naphthalate), acrylic resin, polycarbonate, polyimide resin, norbornene resin, polystyrene, polyvinyl chloride, polyarylate, polysulfone, polyethersulfone, polyetherimide, or the like may be used.

  Further, the thickness of the substrate 21 is desirably as thin as possible while maintaining the rigidity as the ND filter 20, and is specifically preferably 300 μm or less, more preferably 50 to 100 μm.

  The volume of each protrusion 22 gradually increases from the top to the bottom, and the corresponding effective refractive index is also distributed continuously from the top to the bottom of the protrusion 22. Therefore, there is a smooth effective refractive index distribution from the air layer toward the substrate 21, and the light incident on the fine uneven periodic structure 23 has no abrupt refractive index difference. To reach.

  In order to obtain a good antireflection effect, the protrusion 22 is preferably formed in a conical shape as shown in FIG. 2, but the quadrangular pyramid-shaped protrusion 24 shown in FIG. Furthermore, a fine uneven periodic structure 23 having an inverted conical recess 25 shown in FIG. 4 may be used.

  Moreover, it is preferable that the pitch P of the protrusion parts 22 and 24 of the fine uneven | corrugated periodic structure 23 and the recessed part 25 is smaller than the wavelength ((lambda) = 400-700 nm) of a visible region, and is 300 nm in a present Example. As the pitch P becomes smaller, the wavelength at which the antireflection effect can be obtained is expanded to the lower wavelength side. However, as the pitch P becomes smaller, it becomes more difficult to form the fine uneven periodic structure 23, so the pitch P is about 100 to 300 nm. preferable.

  Further, the larger the D / P which is the ratio (aspect ratio) of the height D of the protrusions 22 and 24 and the depth D of the recesses 25 and the pitch P, the greater the antireflection effect, and the D / P becomes 0. It is preferably 2 or more, more preferably 1 or more.

  In order to form the protrusions 22 and 24 and the recess 25 constituting the fine uneven periodic structure 23, the surface of the substrate 21 or a transfer mold surface having a shape opposite to that of the fine uneven periodic structure 23 to be formed can be solidified. There is a method in which a film is applied and brought into close contact with the substrate 21 to solidify the solidifiable material.

  In this embodiment, as shown in FIG. 5, a small amount of a solidifiable material 33 is applied to a transfer mold 32 having a fine uneven periodic structure 31 having a pattern opposite to that of the fine uneven periodic structure 23, and the substrate 21 is placed under the transfer mold 32. The mold 34 is used for close contact. Then, after irradiating ultraviolet rays from the outside of the transfer mold 32 and photocuring the solidifiable material 33, the substrate 21 is peeled from the transfer mold 32, whereby the ND filter 20 having the fine uneven periodic structure 23 can be obtained. it can.

  After forming one surface, the fine uneven periodic structure 23 may be formed in the same manner on the opposite surface. In addition, as shown in FIG. 6, the fine uneven periodic structure 23 can be formed simultaneously on both surfaces by using a pair of upper and lower transfer molds 32 and closely contacting the substrate 21 from above and below.

  There are various methods for forming the fine uneven periodic structure 31 on the transfer mold 32. For example, a resist pattern is formed on the mold base by electron beam drawing, and this is etched by reactive ion etching to form the fine uneven periodic structure. Can be formed. In the present embodiment, a fine uneven periodic structure 31 having a height of 350 nm and a pitch of 300 nm is formed on a quartz mold base material.

  In this embodiment, a transparent quartz plate is used as the transfer mold 32, and light is transmitted through the transfer mold 32 when the solidifiable material 33 is solidified, but light is irradiated from the substrate 21 side. Therefore, it is also possible to use a metal transfer mold.

  As the solidifiable material 33, there is used a curable composition that has fluidity in the initial state and solidifies by irradiation with light such as ultraviolet rays, active energy rays such as heat and electron beams. Moreover, it can prepare by mix | blending the component which accelerates | stimulates or adjusts a reaction, and another component, The mixture of a polymeric compound and a polymerization initiator is contained as a main component.

  Examples of the polymerizable compound include esterified products obtained from 1 mol of a polyhydric alcohol and 2 mol or more of (meth) acrylic acid or a derivative thereof; a polyhydric alcohol, a polyvalent carboxylic acid or an anhydride thereof, ( Examples include esterified products obtained from (meth) acrylic acid or derivatives thereof. Specifically, 1,9-nonanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, Trimethylolethane tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, glycerin tri (meth) acrylate, dipentaerythritol penta (meth) acrylate, Obtained from 1 mol of polyhydric alcohol such as tripentaerythritol hexa (meth) acrylate, tripentaerythritol hepta (meth) acrylate, and 2 mol or more of (meth) acrylic acid or a derivative thereof. Stealides: polyhydric alcohols such as trimethylolethane, glycerin, trimethylolpropane, pentaerythritol, and polyvalent alcohols such as malonic acid, succinic acid, sebacic acid, fumaric acid, itaconic acid, adipic acid, glutaric acid, maleic anhydride Examples thereof include esterified products obtained by a combination arbitrarily selected from carboxylic acid or its anhydride and (meth) acrylic acid or its derivative. These may be used alone or in combination of two or more.

  Examples of the photopolymerization initiator when using the photocuring reaction include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, benzyl, benzophenone, ethylphenylglyoxylate, p-methoxybenzophenone, 4 , 4′-bis (dimethylamino) benzophenone, 2,2-diethoxyacetophenone, α, α-dimethoxy-α-phenylacetophenone, methylphenylglyoxylate, 2-hydroxy-2-methyl-1-phenylpropane-1 Carbonyl compounds such as -one; sulfur compounds such as tetramethylthiuram monosulfide and tetramethylthiuram disulfide; 2,4,6-trimethylbenzoyldiphenylphosphine oxide, benzoyl Ethoxy phosphine oxide, and the like. Commercially available photopolymerization initiators may be used, and these may be used alone or in combination of two or more.

  Examples of the thermal polymerization initiator when using the thermosetting reaction include t-butyl hydroperoxide, cumene hydroperoxide, methyl ethyl ketone peroxide, benzoyl peroxide, dicumyl peroxide, t-butyl peroxyoctate, t -Organic peroxides such as butyl peroxybenzoate and lauroyl peroxide; azo compounds such as azobisisobutyronitrile; N, N-dimethylaniline, N, N-dimethyl-p-toluidine as the organic peroxide And redox polymerization initiators combined with amines such as Commercially available thermal polymerization initiators may be used, and these may be used alone or in combination of two or more.

  Examples of the electron beam curing initiator when using the electron beam curing reaction include benzophenone, 4-phenylbenzophenone, t-butylanthraquinone, 2-ethylanthraquinone, 2,4-diethylthioxanthone, and 4,4-bis (diethylamino). Thioxanthone such as benzophenone, 2,4,6-trimethylbenzophenone, methylorthobenzoylbenzoate, isopropylthioxanthone, 2,4-dichlorothioxanthone; diethoxyacetophenone, 2-methyl-2-morpholino (4-thiomethylphenyl) propane-1 -One, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethyl ketal, 1-hydroxycyclohexyl-phenylketone, 2-benzyl-2-dimethylamino-1- (4-mol Acetophenone such as linophenyl) -butanone; benzoin ether such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether; 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis (2,6-dimethoxybenzoyl)- Acylphosphine oxides such as 2,4,4-trimethylpentylphosphine oxide and bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide; methylbenzoylformate, 1,7-bisacridinylheptane, 9-phenyl Examples include acridine. Moreover, a commercially available electron beam curing initiator may be used, and these may be used alone or in combination of two or more.

  The photopolymerization initiator, thermal polymerization initiator, and electron beam curing initiator described above may be used alone or in any desired combination. Specific examples of the active energy rays include visible light, ultraviolet rays, electron beams, infrared rays, and the like, and generally ultraviolet rays using a high-pressure mercury lamp or the like are often used.

  In the optical element in the present embodiment, a light-absorbing material is contained in the solidifiable material 33 described above as a substance that attenuates light of a predetermined wavelength. The light absorbing material is not particularly limited, and commonly used dyes, pigments, and the like can be used. These may be used alone or in combination. When an optical filter is used as an ND filter, a black light absorbing material is used. For example, even if a black pigment is used alone, a mixture of cyan, magenta, and yellow pigments is used. Also good.

  The following are examples of commercially available black, cyan, magenta, and yellow pigments. Black pigments include Raven1060, Raven1080, Raven1170, Raven1200, Raven1250, Raven1255, Raven1500, Raven2000, Raven3500, Raven5250, Raven5750, Raven7000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000U. MOGUL-L, Regal 400R, Regal 660R, Regal 330R, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1300, Monarch 1400 (above, manufactured by Cabot), Color Black F 1, Color Black FW2, Color Black FW200, Color Black 18, Color Black S160, Color Black S170, Special Black 4P, Special Black 4A, Special BlackP No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Corporation) and the like can be mentioned, but are not limited thereto.

  Examples of cyan pigments include C.I. I. Pigment Blue-1, C.I. I. Pigment Blue-2, C.I. I. Pigment Blue-3, C.I. I. Pigment Blue-15, C.I. I. Pigment Blue-15: 2, C.I. I. Pigment Blue-15: 3, C.I. I. Pigment Blue-15: 4, C.I. I. Pigment Blue-16, C.I. I. Pigment Blue-22, C.I. I. Pigment Blue-60 etc. are mentioned, but it is not limited to these.

  Examples of magenta pigments include C.I. I. Pigment Red-5, C.I. I. Pigment Red-7, C.I. I. Pigment Red-12, C.I. I. Pigment Red-48, C.I. I. Pigment Red-48: 1, C.I. I. Pigment Red-57, C.I. I. Pigment Red-112, C.I. I. Pigment Red-122, C.I. I. Pigment Red-123, C.I. I. Pigment Red-146, C.I. I. Pigment Red-168, C.I. I. Pigment Red-184, C.I. I. Pigment Red-202, C.I. I. Pigment Red-207 and the like, but are not limited thereto.

  Examples of yellow pigments include C.I. I. Pigment Yellow-12, C.I. I. Pigment Yellow-13, C.I. I. Pigment Yellow-14, C.I. I. Pigment Yellow-16, C.I. I. Pigment Yellow-17, C.I. I. Pigment Yellow-74, C.I. I. Pigment Yellow-83, C.I. I. Pigment Yellow-93, C.I. I. Pigment Yellow-95, C.I. I. Pigment Yellow-97, C.I. I. Pigment Yellow-98, C.I. I. Pigment Yellow-114, C.I. I. Pigment Yellow-128, C.I. I. Pigment Yellow-129, C.I. I. Pigment Yellow-151, C.I. I. Pigment Yellow-154 and the like, but are not limited thereto.

  In this embodiment, a black pigment is dispersed in an acrylic polymerization photosensitive resin composition comprising an acrylic resin copolymer, a polyfunctional acrylic monomer, a methacrylic monomer, a photopolymerization initiator, a sensitizer, and additives as the solidifiable material 33. We use what we let. In the present embodiment, the light having a wavelength in the visible light region can be attenuated substantially uniformly by adding the black pigment to the fine uneven periodic structure 23.

  In this embodiment, the content of the black pigment is adjusted, and the fine uneven periodic structure 23 having an optical density of 0.25 is formed on both surfaces of the substrate 21 to obtain the ND filter 20 having an optical density of 0.5. it can.

  As shown in FIG. 7A, the fine uneven periodic structure 23 to which the fine uneven periodic structure 31 of the transfer mold 32 is transferred is transferred to the surface of the ND filter 20, and the ND filter 20 has λ = 400 to 700 nm. The maximum reflectance for light of a wavelength is 0.5%.

  In addition, when an optical element is used as an infrared cut filter, a material having an absorption effect on infrared rays, such as an anthraquinone compound and a naphthalocyanine compound, should be used as a substance that absorbs (attenuates) light in the infrared light region. Can do.

  In this way, the ND filter 20 shown in FIG. 7A can be obtained, but as shown in FIG. 7B, the fine uneven periodic structure 41 on one side does not contain a light absorbing material, It may be used simply as an antireflection film. The optical density of the ND filter 20 can be adjusted by the content of the light absorbing material having a function of attenuating light, and the ND filter 20 having different optical densities on both sides can be formed.

  By forming the fine concavo-convex periodic structures 23 and 41 with different areas on at least a part of the surface of the ND filter 20, it is possible to form the ND filter 20 having a plurality of regions with different amounts of transmitted light. Further, by changing the concentration of the light-absorbing material that attenuates light within the same surface of the substrate 21, the multi-concentration type ND filter 20 having a plurality of regions with different attenuation rates as shown in FIG. It can also be created. Also, a gradation type ND filter 20 having a region where the attenuation factor continuously changes as shown in FIG. 9A can be produced.

  FIGS. 8B and 9B show the relationship between the position of the ND filter 20 in FIGS. 8A and 9A and the optical density.

  When the ND filter 20 manufactured by the above-described method is used in the light amount diaphragm device 12, the change in the light amount can be moderated, the surface reflection of the ND filter 20 can be reduced, and a good captured image can be obtained. The method of insertion into the light quantity diaphragm device 12 may be attached to the diaphragm blade 19a, or may be able to be taken in and out separately from the diaphragm blade 19a.

  Furthermore, as shown in FIG. 10, the fine uneven periodic structure 23 containing the light absorbing material can be formed on the ND filter 20 containing the light absorbing material in the substrate 21 ′ itself. Thereby, since attenuation of the transmitted light amount as the whole ND filter 20 can be increased, it is possible to manufacture the ND filter 20 having a high concentration relatively easily.

  Further, by using an infrared cut glass instead of the substrate 21 ′ shown in FIG. 10 and using a filter in a region other than the wavelength attenuated by the fine uneven periodic structure 23, the wavelengths in various regions can be attenuated. An optical element can be configured. For example, the ND filter and the infrared cut filter can be configured by one member. In this case, it goes without saying that the embodiment described above can be applied to the fine uneven periodic structure 23.

  The ND filter 20 produced in this way and the ND filter 1 of the conventional example were separately attached to the diaphragm blade 19a of the light quantity diaphragm device 12, and the captured image was evaluated.

  Table 1 shows the ND filter 20 having an optical density of 0.25 produced in the present embodiment, which is a conventional example, and the ND filter 1 in which a vapor deposition film having an optical density of 0.25 is formed on the substrate surface shown in FIG. A comparison table is shown. As shown in Table 1, the ND filter 20 in which the fine uneven periodic structure 23 is formed on the substrate 21 has a low reflectance and no ghost, but the ND filter 1 in which the fine uneven periodic structure 23 is not formed. Some ghost was seen.

Table 1
Fine irregular periodic structure Ghost Maximum reflectance (λ = 400-700nm)
ND filter 20 Yes No 0.5%
ND filter 1 None Available (Minor) 4%

  The optical element of the present invention can be applied to the surfaces of various optical members such as lenses and glass plates in addition to the filters of the embodiments.

DESCRIPTION OF SYMBOLS 12 Light quantity diaphragm device 20 ND filter 21, 21 'Board | substrate 22, 24 Protrusion part 23, 31, 41 Fine uneven | corrugated periodic structure 25 Recessed part 32 Transfer mold 33 Solidifiable material 34 Lower mold | type

Claims (9)

A fine uneven periodic structure is formed on at least a part of the surface of the transparent substrate, the fine uneven periodic structure contains a substance that attenuates light of a predetermined wavelength, and the wavelength of the visible light region for preventing light reflection optical filter characterized by chromatic even smaller pitch and height. The optical filter according to claim 1, wherein the substance that attenuates the light having the predetermined wavelength attenuates at least a wavelength in a visible light region. The optical filter according to claim 1, wherein the fine uneven periodic structure has a function as an ND filter that attenuates the wavelength in the visible light region substantially uniformly. The optical filter according to claim 3, wherein the fine uneven periodic structure that attenuates the wavelength of the visible light region substantially uniformly has a plurality of regions having different attenuation factors. The optical filter according to claim 3, wherein the fine concavo-convex periodic structure that attenuates the wavelength of the visible light region substantially uniformly has a region in which an attenuation factor continuously changes. The optical filter according to claim 1, wherein the substance that attenuates the light having the predetermined wavelength attenuates a wavelength in an infrared light region. A light amount adjustment comprising: aperture blades for forming an opening; and the optical filter according to any one of claims 1 to 5 for adjusting a light amount of light passing through the opening. apparatus. The solid-state image sensor that converts an image formed by the imaging optical system of the light amount adjusting device according to claim 7 into an electrical signal, and the wavelength of an infrared light region incident on the solid-state image sensor is attenuated. An imaging apparatus comprising: an optical filter .   An imaging apparatus comprising: the light amount adjusting device according to claim 7 that adjusts the amount of light that passes through the imaging optical system; and a solid-state imaging device that converts an image formed by the imaging optical system into an electrical signal.