JP2007058184A - Neutral density filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a neutral density filter (an ND filter) excellent in a flatness characteristic and a spectral characteristic. <P>SOLUTION: The ND filter 1 comprises: a substrate 10; and a plurality of film layers 20 which have constitution of 0.4M3LmH1.25L0.25H1.25L, and are formed on one surface of the substrate 10. An H layer in film layer structure denotes a high refractive index film layer with an iron nickel chromium alloy as a film material, an L layer in the film layer structure denotes a low refractive index film layer consisting of SiO<SB>2</SB>, an M layer in the film layer structure denotes an intermediate film layer which is directly formed on one surface of the substrate 10 as a film layer formed on the substrate 10 first and which has a refractive index in a range between that of the high refractive index film layer and that of the substrate 10, an mH layer in the film layer structure is a density adjusting layer of the ND filter 1 and an (m) denotes a value determined by density and spectral transmittance of the ND filter 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical filter, and more particularly to an ND filter (Neutral Density Filter) having a very favorable spectral transmittance flatness.

  Optical filters are widely applied to optical equipment such as projectors, conventional still cameras, digital cameras, mobile phones, and astronomical observation telescopes, and are used for the purpose of imparting different optical effects to these optical equipments. ing. When optical filters are classified according to spectral characteristics, they are divided into bass filters, cut filters, two-way spectral filters, reflection filters, ND filters, and the like. The ND filter has a predetermined optical density and decreases the amount of light incident on an optical device and reaching a solid photosensitive unit such as a photosensitive film or a charge-coupled device. Each light action is also different. However, no matter how the density changes, it does not change the color distribution of light rays. For example, when shooting in an environment where the sun's rays are strong, even if you try to increase the aperture value, there is a limit to the shutter speed setting. If sufficient shutter speed cannot be obtained, an ND filter is attached to the lens. The effect of light is obtained.

  An ND filter with a fixed density attenuates it uniformly for all wavelengths of light. That is, all the spectra existing in the visible light range have the same transmittance. Regarding the ND filter having a fixed density, the contents disclosed in US Pat. Nos. 5,715,103, 6,842,302B2, and 6,842,301B2 can be referred to.

  The ND filter disclosed in US Pat. No. 5,715,103 is formed by forming an insulating film layer composed of a multilayer antireflection film layer on a substrate. The multilayer antireflection film layer is selected from materials such as Al2O3 (aluminum oxide), MgF2 (magnesium fluoride), and SiO2 (silicon dioxide). An MgF2 film layer is formed on the surface of the filter that comes into contact with air.

  In the ND filter disclosed in US Pat. Nos. 6,842,302B2 and 6,842,301B2, a nickel chromium alloy film layer and a SiO2 film layer are provided on a transparent plastic substrate, and an MgF2 film layer is provided on the upper surface. Is provided. The nickel chromium alloy film layer comprises 90% nickel and 10% chromium. The SiO2 film layer is an antireflection film layer. However, an ND filter constituted by combining a nickel chromium alloy film layer and a SiO2 film layer lacks stability, and the corresponding manufacturing process is relatively complicated.

  The plating process in the manufacturing process of the ND filter described above employs a method in which an absorption effect of TiO2 (titanium oxide) is generated in an atmosphere where oxygen is insufficient, and then Al2O3 and MgF2 are combined with each other and completed. However, in the above-described conventional technology, no mention is made as to whether or not the film arrangement structure is a target. In addition, the plating process must be calculated in detail in consideration of not only that the manufacturing process is complicated, but also that the amount of TiO2 absorbed becomes unstable due to lack of oxygen. This will easily generate a negative impact on the spectral effect of the product.

  In recent years, as the sensitivity of imaging equipment has increased, the density of ND filters has been increased. This is because by increasing the density of the ND filter, the light transmittance is further lowered and the aperture of the aperture is increased.

Speaking of existing ND filters, the requirement for the transmittance and flatness is that the difference between the maximum transmittance value (Tmax) and the minimum transmittance value (Tmin) is an average transmittance value (Tavg) × 8%. That is, (Tmax−Tmin) <Tavg * 8%. In addition, when the wavelength range of incident light is calculated as 400 to 700 nm, the high-concentration ND filter has a lower average transmittance value (Tavg) than the average transmittance value (Tavg) of the low-density ND filter. Therefore, the difference value of (Tmax−Tmin) in the high density ND filter is further lower than the difference value of (Tmax−Tmin) in the low density ND filter. For example, when the density of the ND filter is 0.8, the average transmittance value (Tavg) is 15.8, and the difference value of the flatness (Tmax−Tmin) is lower than 1.25%. When the density of the ND filter is 1.6 and the transmittance value (Tavg) is 2.5, the flatness (Tmax−Tmin) difference value is lower than 0.2%.
United States Patent No. 5,715,103 United States Patent No. 6,842,302B2 United States Patent No. 6,842,301B2

It is an object of the present invention to provide an ND filter having excellent flatness characteristics and spectral characteristics.

Accordingly, the inventors of the present invention have made extensive studies in view of the drawbacks found in the prior art, and as a result, the substrate comprises a substrate and a plurality of film layers formed on the surface of the substrate, and the structure of the film layer. Is 0.4M3LmH1.25L0.25H1.25L, the H layer in the film layer structure represents a high refractive index film layer, and the high refractive index film layer is made of iron nickel chrome alloy as a film material, and the film layer The L layer in the structure represents a low refractive index film layer, the low refractive index film layer is made of SiO2, and the M layer in the film layer structure has a refractive index between the high refractive index film layer and the substrate. And the intermediate film layer is formed directly on one surface of the substrate as a film layer that is first formed on the substrate, in the film layer structure. Based on such knowledge, the mH layer is a density adjustment layer of the ND filter, and the m is a value determined by the density and spectral transmittance of the ND filter, and the problem can be solved by the ND filter. The present invention has been completed.

The present invention will be specifically described below.
The ND filter described in claim 1 is an ND filter including a substrate and a plurality of film layers having a structure of 0.4M3LmH1.25L0.25H1.25L and formed on one surface of the substrate. The H layer in the film layer structure represents a high refractive index film layer, the high refractive index film layer is made of iron nickel chrome alloy as a film material, and the L layer in the film layer structure is a low refractive index film layer. And the low refractive index film layer is made of SiO2, and the M layer in the film layer structure represents an intermediate film layer having a refractive index in the range between the high refractive index film layer and the substrate, and The intermediate film layer is directly formed on one surface of the substrate as a film layer that is first formed on the substrate, and the mH in the film layer structure is formed. There a concentration adjusting layer of the ND filter, and is a value wherein m is determined by the concentration and spectral transmittance of the ND filter.

The ND filter according to claim 2 forms a film layer having a structure of 0.4M3LmH1.25L0.25H1.25L on the other surface of the substrate according to claim 1.

In the ND filter according to claim 3, the m value of the film layer structure according to claim 1 or 2 is directly proportional to the spectral transmittance of the ND filter, and the m value increases as the density increases. And the spectral transmittance is low.

In the ND filter according to claim 4, when the spectral transmittance value of the ND lens in claim 3 is reduced by 2.5%, the m value is a value obtained by multiplying the original value by 1.4.

In the ND filter according to claim 5, the refractive index of the material of the intermediate film layer according to claim 1 or 2 is between 1.8 and 2.2.

The ND filter according to claim 6 has iron, nickel, and chromium contents in the high refractive index film layer of the ND filter according to claim 5, wherein iron ≦ 1%, nickel ≧ 75%, and chromium ≦ 19.2%, respectively. It is.

In the ND filter according to claim 7, the substrate of the ND filter according to claim 6 is made of a transmissive plastic material.

In the ND filter according to claim 8, the substrate of the ND filter according to claim 6 is made of PET (polyethylene terephthalate).

The ND filter according to claim 9 is an ND filter including a substrate and a plurality of film layers formed on both surfaces of the substrate, and the film layers formed on both surfaces of the substrate have the same structure. An intermediate film layer in which the refractive index of the material is between 1.8 and 2.2 is directly formed on the surface of the substrate as a first layer formed on the substrate, and further a low refractive index film Layers and high refractive index film layers are alternately laminated on the intermediate layer film.

In the ND filter according to claim 10, the structures of the film layers formed on both sides of the substrate are all 0.4M3LmH1.25L0.25H1.25L, and the M layer in the film layer structure is an intermediate film layer. H layer in the film layer structure represents a high refractive index film layer, L layer in the film layer structure represents a low refractive index film layer, and m in the film layer structure represents the density and spectral transmission of the ND filter. It is a value determined by the rate.

In an ND filter according to an eleventh aspect, the high refractive index film according to the tenth aspect uses iron, nickel, and chromium as a film material.

In an ND filter according to a twelfth aspect, the iron, nickel, and chrome contents of the high refractive index film according to the eleventh aspect are iron ≦ 1%, nickel ≧ 75%, and chromium ≦ 19.2%.

In the ND filter according to claim 13, the material of the low refractive index film layer according to claim 10 is SiO2.

The ND filter according to claim 14 is selected from the group consisting of PET, PC (polycarbonate), other plastic materials, glass materials, and other transparent materials in claim 10.

The ND filter according to claim 15 is the density adjusting layer of the ND filter, wherein the mH layer of the film layer structure according to claim 1 or 10 is such that the m value increases as the density increases, and the spectral transmittance. Becomes lower.

In an ND filter according to a sixteenth aspect, the m value of the film layer structure according to the fifteenth aspect is directly proportional to the spectral transmittance.

The ND filter described in claim 17 has an upper limit of 10% for the transmittance of the ND filter in claim 16, and the m value is multiplied by 1.4 to the original value every time the transmittance decreases by 2.5%. obtain.

  The ND filter of the present invention has an advantage that preferable flatness characteristics and spectral characteristics can be obtained, and excellent spectral characteristics can be obtained under different spectral transmittances.

The present invention provides an ND filter having excellent flatness characteristics and spectral characteristics, and has a substrate and a structure of 0.4M3LmH1.25L0.25H1.25L, and is formed on one surface of the substrate. And a plurality of film layers. The H layer in the film layer structure represents a high refractive index film layer, and the high refractive index film layer uses an iron-nickel-chromium alloy film material, the L layer in the film layer structure represents a low refractive index film layer, and The low refractive index film layer is made of SiO2, and the M layer in the film layer structure represents an intermediate film layer having a refractive index in the range between the high refractive index film layer and the substrate, and the intermediate film Forming a layer directly on one surface of the substrate as a film layer first formed on the substrate, the mH layer in the film layer structure being the density adjusting layer of the ND filter, and the m being the ND filter It is a value determined by density and spectral transmittance.
In order to explain the structure and characteristics of the ND filter in detail, a specific example will be given and described below with reference to the drawings.

  As shown in FIG. 1, the ND filter 1 according to the present invention is a high-density ND filter, and includes a substrate 10 and a plurality of film layers 20 plated on the substrate 10. When this invention is actually carried out, the film layer may be formed on only one surface of the substrate 10 or on both surfaces. In order to simplify the explanation, FIG. 1 discloses an embodiment in which a film layer is formed only on one surface of a substrate.

  The substrate 10 in the ND filter 1 is a glass substrate, a transmissive plastic substrate, a substrate made of an acrylic material, or other transmissive substrate. In the embodiment, the substrate 10 is a PET substrate. The thickness of the substrate 10 is about 100 μm. However, as described above, the substrate 10 can be made of PC, other plastic material, glass material, or other transparent material.

  The film layer 20 described above is plated on the substrate 10 by a lamination method of 0.4M3LmH1.25L0.25H1.25L. The H layer represents a high refractive index film layer, and an iron nickel chrome alloy is used as a film material. The contents of iron, nickel, and chromium in the film layer represented by H are iron ≦ 1%, nickel ≧ 75%, and chromium ≦ 19.2%. The optical thickness of 1H is 0.20 nm, the physical thickness is 40 nm, and the center wavelength is 440 nm. The L layer represents a low refractive index film layer. The low refractive index film layer is made of SiO 2 and has an optical thickness of 1 L of 0.20 nm, a physical thickness of 60 nm, and a center wavelength of 440 nm. The M layer represents the intermediate film layer M in the range between the high refractive index film layer having a refractive index represented by H and the substrate 10 made of PET, and the refractive index n is 1.8-2. .2.

  In the embodiment, the intermediate film layer M is a layer to be formed first, and is plated directly on the substrate 10. Further, the low refractive index film layer L and the high refractive index film layer H are alternately laminated on the intermediate film layer M. The structure of the film layer 20 formed by such a method is that the first film layer is the intermediate film layer M, the second film layer is the low refractive index film layer L, and the third film layer is the high refractive index film. The fourth film layer is a low refractive index film layer L, the fifth film layer is a high refractive index film layer H, and the sixth film layer is a low refractive index film layer L.

  The intermediate film layer M of the first film layer (0.4M) plating a 0.4 times quarter wave film on the substrate. The low-refractive index film layer L of the second film layer (3L) plating a triple quarter-wave film on the first film layer. The high refractive index film layer H of the third film layer (mH) plating a m-fold quarter-wave film on the second film layer. The film layer (mH) is a filter density adjusting layer, and the m value is determined based on the necessity of density and the requirement of spectral transmittance (described later). The low refractive index film layer L of the fourth film layer (1.25L) plating a 1.25-fold quarter-wave film on the third film layer. The high refractive index film layer H of the fifth film layer (0.25H) plating a 0.25-fold quarter-wave film on the fourth film layer. The low refractive index film layer L of the sixth film layer (1.25L) plating a 1.25-fold quarter-wave film on the fifth film layer. By laminating the film layers in such a manner, an ND filter having preferable spectral characteristics can be obtained.

  Each film layer in the above-described film layer 20 sets a specific numerical value of the film thickness according to a specific requirement and an environment to be applied.

  The third film layer (mH) in the film layer 20 described above is a density adjusting layer, and the m value increases as the density increases, and the spectral transmittance T (%) decreases as the density increases. . T (%) and the m value are in a directly proportional relationship. When the T (%) value decreases by 2.5%, the m value multiplies the original numerical value by 1.4. Preferably, the ND filter is calculated by using a program for inputting the design value of the film layer so that a preferable flatness of transmittance can be obtained.

Based on T = 10% as a reference, the proportional relationship between the two will be described as follows.
T = 10% → m = 0.4
T = 7.5% → m = 0.55
T = 5% → m = 0.75
T = 2.5% → m = 1.05
T = 1% → m = 1.5

  FIG. 2 discloses a graph of spectral transmittance characteristics obtained when the spectral transmittance is T = 10% and the film layer 20 of the ND filter 1 is designed within a wavelength range of 400 to 700 nm. A graph relating to the characteristics of spectral reflectance is disclosed in FIG. Of course, even if the spectral transmittance is, for example, 7.5%, 5%, 2.5%, 1%, or other values, a preferable flatness characteristic of the spectral transmittance can be obtained. The graph regarding these is omitted.

  In the plating process described above, plating is performed using a general vapor deposition method. In the plating process, the spectral flatness of the ND filter according to the present invention can be adjusted based on the manufacturing process conditions. For example, (Tmax−Tmin) <1% and R <2% are obtained by plating the first surface of the ND filter. Tmax is the maximum transmittance value through which incident light passes through the ND filter, and Tmin represents the minimum transmittance value through which incident light passes through the ND filter. R represents the reflectance. The flatness characteristic of the actual transmittance in the wavelength range of 400 to 700 nm is as disclosed in FIG.

  In order to obtain a preferable flatness characteristic by going further one step according to the design value described above, the ND filter 1 plated on both sides may be used in the present invention. According to such a format, a flatness characteristic (see FIG. 5) of (Tmax−Tmin) <0.5% and a reflectance characteristic (see FIG. 6) of R <2% are obtained. In other words, by forming a film layer having the same structure as the film layer 20 on the other surface of the substrate 10 and complementing each other's spectral spectrum by the design of forming the film layer on both surfaces, a more preferable transmitted light flatness characteristic is obtained. It is done.

The above is a preferred embodiment of the present invention and does not limit the scope of the present invention. Therefore, any modifications or changes that can be made by those skilled in the art, which are made within the spirit of the present invention and have an equivalent effect on the present invention, shall belong to the scope of the claims of the present invention. To do.

It is explanatory drawing which showed the cross-section of the ND filter of this invention. It is the graph which showed the spectrum transmittance | permeability characteristic obtained when the transmittance | permeability is set to T = 10% in the spectrum of the film layer of the ND filter disclosed in FIG. 1 within the wavelength range of 400-700 nm. It is the graph which showed the characteristic of the spectral reflectance of the ND filter disclosed in FIG. It is the graph which showed the flatness characteristic of the actual transmittance | permeability when the wavelength range of the ND filter disclosed in FIG. 1 is 400-700 nm. It is the graph which showed the flatness characteristic at the time of plating the ND film disclosed in FIG. 1 on both surfaces. It is the graph which showed the reflectance characteristic at the time of plating the ND film disclosed in FIG. 1 on both surfaces.

Explanation of symbols

1 ND filter 10 Substrate 20 Film layer

Claims (17)

An ND filter comprising a substrate and a plurality of film layers having a structure of 0.4M3LmH1.25L0.25H1.25L and formed on one surface of the substrate;
The H layer in the film layer structure represents a high refractive index film layer, and the high refractive index film layer is an iron nickel chrome alloy film material,
L layer in the film layer structure represents a low refractive index film layer, and the low refractive index film layer is made of SiO2,
The M layer in the film layer structure represents an intermediate film layer having a refractive index in the range between the high refractive index film layer and the substrate, and the intermediate film layer is first formed on the substrate as a film layer Forming directly on one surface of the substrate,
The ND filter, wherein the mH layer in the film layer structure is a density adjustment layer of the ND filter, and the m is a value determined by the density and spectral transmittance of the ND filter. The ND filter according to claim 1, wherein a film layer having a structure of 0.4M3LmH1.25L0.25H1.25L is formed on the other surface of the substrate. The m value in the film layer structure is directly proportional to the spectral transmittance of the ND filter, and the m value increases and the spectral transmittance decreases as the density increases. Alternatively, the ND filter according to claim 2. The ND filter according to claim 3, wherein when the spectral transmittance value of the ND lens decreases by 2.5%, the m value is a value obtained by multiplying an original value by 1.4. The ND filter according to claim 1, wherein a refractive index of a material of the intermediate film layer is between 1.8 and 2.2. 6. The content of iron, nickel, and chromium in the high refractive index film layer in the ND filter is iron ≦ 1%, nickel ≧ 75%, and chromium ≦ 19.2%, respectively. ND filter. The ND filter according to claim 6, wherein the substrate in the ND filter is made of a transmissive plastic material. The ND filter according to claim 6, wherein the substrate in the ND filter is made of PET. An ND filter comprising a substrate and a plurality of film layers formed on both sides of the substrate,
The film layers formed on both surfaces of the substrate are each formed in an intermediate film layer having the same structure and the refractive index of the material between 1.8 and 2.2. The ND filter is formed directly on the surface of the substrate as a layer, and further, a low refractive index film layer and a high refractive index film layer are alternately laminated on the intermediate layer film. The structures of the film layers formed on both sides of the substrate are all 0.4M3LmH1.25L0.25H1.25L,
M layer in the film layer structure represents an intermediate film layer,
The H layer in the film layer structure represents a high refractive index film layer,
L layer in the film layer structure represents a low refractive index film layer,
The ND filter according to claim 9, wherein m in the film layer structure is a value determined by the density and spectral transmittance of the ND filter. The ND filter according to claim 10, wherein the high refractive index film layer uses iron, nickel, or chromium as a film material. 12. The ND filter according to claim 11, wherein the content of iron, nickel, and chromium in the high refractive index film layer is iron ≦ 1%, nickel ≧ 75%, and chromium ≦ 19.2%. The ND filter according to claim 10, wherein a material of the low refractive index film layer is SiO 2. 11. The ND filter according to claim 10, wherein the substrate is selected from PET, PC, other plastic materials, glass materials, and other materials having transparency. The mH layer in the film layer structure is a density adjusting layer of the ND filter, and as the density increases, the m value increases and the spectral transmittance decreases. The ND filter according to 10. The ND filter according to claim 15, wherein the m value in the film layer structure is directly proportional to the spectral transmittance. The transmittance of the ND filter is 10% as an upper limit value, and the m value is obtained by multiplying an original value by 1.4 every time the transmittance decreases by 2.5%. ND filter.

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