WO2013073502A1

WO2013073502A1 - Nd filter unit, imaging system and method for manufacturing nd filter

Info

Publication number: WO2013073502A1
Application number: PCT/JP2012/079298
Authority: WO
Inventors: 有宏斎田; 潤二宮田; 榎本　淳; 俊峯尾; 吉彦田中
Original assignee: 富士フイルム株式会社
Priority date: 2011-11-15
Filing date: 2012-11-12
Publication date: 2013-05-23

Abstract

[Problem] To provide a low-cost ND filter capable of reducing light scattering. [Solution] An ND filter includes a disk-shaped glass plate (210) and an optical layer (211) which is formed on the base material of the glass plate (210) and has a luminous transmittance that continuously changes toward the circumferential direction. The optical layer (211) is constituted by developed silver acquired by exposing and developing a silver halide photography emulsion.

Description

ND filter unit, photographing system, and manufacturing method of ND filter

The present invention relates to an ND (Neutral Density) filter, an ND filter unit, and an ND filter manufacturing method.

The ND filter is used in a photographing system such as a camera, and is effective when photographing under a strong light and reducing the light amount without affecting the color.

As a ND filter, a gradation type ND filter in which an optical film whose optical density continuously changes in the circumferential direction of a disk-shaped base material is proposed (see Patent Documents 1 to 4).

Patent Document 1 describes an ND filter unit having a configuration in which two ND filters each having a gradation pattern formed of a metal film on a glass substrate are stacked.

Patent Document 2 describes that an emulsion layer of a silver halide photographic light-sensitive film comprising a film base and an emulsion layer is exposed and developed to form an ND filter whose light transmittance changes continuously.

Patent Document 3 discloses an ND filter in which a color material is applied on a transparent base material (for example, a glass base material), then the color material is exposed to active energy rays, developed, and light transmittance continuously changes. Is described.

Patent Document 4 describes that a density pattern is printed on a glass substrate by an ink jet printer to form an ND filter whose light transmittance changes continuously.

Japanese Unexamined Patent Publication No. 3-6511 Japanese Unexamined Patent Publication No. 2003-248107 Japanese Unexamined Patent Publication No. 2003-241251 Japanese Unexamined Patent Publication No. 2007-243928

In the ND filter unit described in Patent Document 1, since a gradation pattern is formed by a metal film, a ghost is generated due to multiple reflection of light by the metal film, and image quality is deteriorated.

In the ND filter described in Patent Document 2, since the base of the silver halide photographic photosensitive film becomes a light scattering source, the resolution of the captured image is deteriorated. In order to use this ND filter as a product, it is necessary to attach this ND filter to a hard substrate such as a glass substrate with an adhesive or the like. The rate may decrease and light may be scattered.

Further, since the ND filter described in Patent Document 3 exposes a color material formed on a glass substrate with active energy rays, the exposure apparatus becomes expensive and the manufacturing cost increases. Further, in order to reduce light scattering, it is necessary to make particles constituting the color material fine, but it is technically difficult to make particles constituting the color material fine.

Further, the ND filter described in Patent Document 4 forms a pigment pattern on a glass substrate, and it is necessary to make the pigment particles fine in order to reduce light scattering. However, it is technically difficult to make the pigment particles fine.

The present invention has been made in view of the above circumstances, and is a low-cost ND filter unit capable of easily reducing reflection and scattering of light, an imaging system including the ND filter unit, and an ND used for the ND filter unit. It aims at providing the manufacturing method of a filter.

The ND filter unit of the present invention includes two ND filters having an optical layer whose light transmittance continuously changes in one direction or one circumferential direction, and the two ND filters are light beams of the optical layer. The transmission gradations are arranged so as to be opposite to each other, and at least one of the two ND filters has the optical layer formed on a transparent substrate, and the optical layer has an average particle diameter. It is composed of developed silver obtained by exposing and developing a silver halide photographic emulsion containing silver halide grains of 0.01 μm or more and 0.2 μm or less.

The imaging system of the present invention includes an imaging lens, an imaging element that captures an optical image that has passed through the imaging lens, and the ND filter unit that is disposed in front of the imaging element.

The method for producing an ND filter of the present invention comprises a step of coating a silver halide photographic emulsion containing silver halide grains having an average particle size of 0.01 μm or more and 0.2 μm or less on a transparent substrate, and the coated halide Depending on the pattern of the developed silver obtained by developing the silver photographic emulsion through a mask having a continuously changing light transmittance distribution and developing the silver halide photographic emulsion after exposure, the silver photographic emulsion may be unidirectional or And a step of forming an optical layer whose light transmittance changes continuously in the circumferential direction.

According to the present invention, it is possible to provide a low-cost ND filter unit capable of reducing light reflection and scattering, an imaging system including the ND filter unit, and a method for manufacturing an ND filter used in the ND filter unit.

The figure which shows schematic structure of the imaging | photography system 100 for describing one Embodiment of this invention. Schematic sectional view of the ND filter 21 shown in FIG. 2 is a schematic plan view when the ND filter 21 shown in FIG. 2 is viewed from the optical layer 211 side. The figure which shows the picked-up image obtained as a result of image | photographing spot light with the ND filter unit of the comparative example 1. The figure which shows the picked-up image obtained as a result of image | photographing spot light with the ND filter unit of Example 1. FIG. Partial enlarged view of a photographed image obtained as a result of photographing a resolution chart with the transmittance of the ND filter unit of Comparative Example 1 set to 25% Partial enlarged view of a photographed image obtained as a result of photographing a resolution chart with the transmittance of the ND filter unit of Example 1 set to 25% Partial enlarged view of a photographed image obtained as a result of photographing a resolution chart with the transmittance of the ND filter unit of Example 1 set to 6.3% Partial enlarged view of a photographed image obtained as a result of photographing a resolution chart with the transmittance of the ND filter unit of Example 2 set to 6.3% The figure which shows the transmittance | permeability characteristic for each wavelength of ND filter B of Example 1 and ND filter C of Example 2 in the maximum transmittance | permeability. The figure which shows the transmittance | permeability characteristic for each wavelength of ND filter B of Example 1 and ND filter C of Example 2 in the transmittance | permeability 6.3%. The figure which shows the outline of the reflectance measurement in the position of the transmittance | permeability 6.3% of ND filter B (Example 1). The figure which shows the reflectance characteristic for every wavelength in the position of the transmittance | permeability 6.3% of ND filter B (Example 1).

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

FIG. 1 is a diagram showing a schematic configuration of an imaging system 100 for explaining an embodiment of the present invention.

The imaging system 100 includes a camera body 2 and a lens device 1 that can be attached to and detached from the camera body 2. The camera body 2 and the lens device 1 may be integrated.

The lens apparatus 1 includes a photographing lens 10 such as a zoom lens or a focus lens.

The camera body 2 includes an ND filter unit 20 and a photographing unit 30.

The photographing unit 30 includes a color separation prism 31 that separates the light collected by the photographing lens 10 into three colors of red, green, and blue, an image sensor 31R provided on a red light emission surface of the color separation prism 31, and a color separation. An image sensor 31G provided on the green light exit surface of the prism 31 and an image sensor 31B provided on the blue light exit surface of the color separation prism 31 are provided. An optical image passing through the taking lens 10 is picked up by these

image pickup devices

31R, 31G, and 31B. However, the so-called three-plate configuration including the color separation prism 31 in the camera body 2 is an example, and the so-called single-plate configuration including one image sensor in the camera body 2 is the gist of the present application. Holds.

The ND filter unit 20 includes disk-

shaped ND filters

21 and 22 arranged side by side on the optical axis K of the photographing lens 10, and a rotation mechanism 23 that rotates each of the

ND filters

21 and 22 in the circumferential direction thereof. Prepare.

FIG. 2 is a schematic cross-sectional view of the ND filter 21 shown in FIG. The ND filter 21 includes a glass plate 210 which is a transparent substrate, an optical layer 211 formed on the glass plate 210, an adhesive layer 212 formed on the optical layer 211, and an antireflection coating formed on the adhesive layer 212. (AR) a film 213 with a function. The film with an AR function is a film having a reflective interference film, for example. In this specification, the transparent substrate is not a flexible substrate such as a base of a silver halide photographic photosensitive film, but a transparent hard plate with little light scattering such as a glass plate and a resin plate. Say.

The optical layer 211 is a layer composed of developed silver obtained by coating a silver halide photographic emulsion on a glass plate 210, exposing the silver halide photographic emulsion, and developing it. A transparent glass plate may be provided instead of the AR function-added film 213. Needless to say, the glass plate 210 and the glass plate provided in place of the AR function-equipped film 213 may have an AR function added to the interface with the air. Further, the adhesive layer 212 and the AR function-equipped film 213 or a transparent glass plate are not essential and may be omitted.

The ND filter 21 is arranged so that the normal direction of the surface of the glass plate 210 is parallel to the optical axis K. The configuration of the ND filter 22 is the same as that of the ND filter 21, and the ND filter 22 is also arranged so that the normal direction of the surface of the glass plate 210 is parallel to the optical axis K. The ND filters 21 and 22 may be arranged such that either the glass plate 210 or the AR function-equipped film 213 faces the lens device 1.

FIG. 3 is a schematic plan view when the ND filter 21 shown in FIG. 2 is viewed from the optical layer 211 side. In FIG. 3, illustration of the adhesive layer 212 and the AR function-equipped film 213 is omitted.

As shown in FIG. 3, in the optical layer 211 formed on the glass plate 210, the light transmittance continuously changes toward the one circumferential direction of the ND filter 21 (where the color is dark in the figure). The smaller the light transmittance). For example, the optical layer 211 is formed so that the transmittance continuously changes from about 99% to about 1% in the range where the circumferential angle θ of the glass plate 210 is 285 °, and the remaining 75 °. The range is a glass plate 210 having a transmittance of about 100%.

The ND filter 21 and the ND filter 22 have a shaft P connected to the rotation mechanism 23 and can rotate around the shaft P. The ND filter 21 and the ND filter 22 are arranged so that the gradation of the light transmittance of the optical layer 211 is opposite to each other. Reverse phase means that the direction of change in light transmittance is the reverse direction. The ND filters 21 and 22 have the center angle (37.5 °) in the angle range (75 °) of the region where the transmittance is about 100% aligned in the optical axis K direction (in the optical axis K direction). The posture (superimposed) is set as the home position. From that posture, for example, the ND filter 21 is rotated from the larger light transmittance to the smaller light transmission area with respect to the light passage area centered on the optical axis K, and the ND filter 22 is similarly moved to the passage area. On the other hand, the ND filters 21 and 22 are rotated in the opposite directions at the same speed so that the light transmittance is rotated from the larger one toward the smaller one. Then, when arranged in the opposite phase and rotated in the opposite direction, the gradient of concentration change proportional to the angle in the circumferential direction so that the concentration is always uniform over the entire passage area. Are attached to the ND filters 21 and 22. Note that the ND filters 21 and 22 may be rotated independently of each other instead of being rotated in the reverse direction at the same speed. Moreover, the rotation direction is not limited to the reverse direction, and it may be rotated in the same direction. When the ND filters 21 and 22 are rotated in the same direction, a difference may be added to each rotation speed. Alternatively, only one of the ND filters 21 and 22 may be rotated. As the positional relationship and rotation operation between the ND filter 21 and the ND filter 22, those described in Japanese Patent Application Laid-Open No. 2007-243928 can be employed.

In each of the ND filters 21 and 22 used in the photographing system 100, an optical layer 211 whose light transmittance continuously changes in the circumferential direction is formed on the glass plate 210. Further, the optical layer 211 is made of silver halide. It is characterized by being formed by developed silver obtained by exposing and developing a photographic emulsion.

The glass plate 210 scatters less light than plastic bases such as PET (polyethylene terephthalate) and TAC (triacetyl cellulose) used in silver halide photographic photosensitive films. Therefore, light scattering by the glass plate 210 hardly occurs. As described above, the ND filters 21 and 22 have the optical layer 211 formed on the glass plate 210, thereby reducing light scattering as compared with the conventional ND filter using a silver halide photographic photosensitive film. can do.

In the ND filters 21 and 22, the optical layer 211 is formed of developed silver obtained by exposing and developing a silver halide photographic emulsion. Since the silver halide photographic emulsion can easily reduce the diameter of silver halide grains, the diameter (particle diameter) of developed silver grains can also be easily reduced. Therefore, as compared with the prior art in which the optical layer is formed with a dye or the like, it becomes easier to suppress light scattering, and an increase in manufacturing cost can be prevented.

If the average grain size of the silver halide grains contained in the silver halide photographic emulsion which is the raw material of developed silver constituting the optical layer 211 is large, the size of the developed silver obtained by exposing and developing the emulsion layer is large. Become. For this reason, it is preferable that the average grain size of the silver halide grains is small. As a result of various studies, it has been found that when the average grain size of silver halide grains in a silver halide photographic emulsion is 0.2 μm or less, scattering by developed silver can be reduced. For this reason, the average grain size of the silver halide grains is preferably 0.2 μm or less. The average grain size of the silver halide grains can be obtained by observing with an electron microscope.

However, if the average grain size of the silver halide grains is too small to be less than 0.01 μm, the spectral neutrality of the developed silver obtained by exposing and developing the emulsion layer (flatness of transmittance with wavelength) May be damaged. Various additives have been studied in order to maintain the spectral neutrality of developed silver. However, the additive itself may inhibit the characteristics and stability of the optical layer 211. Therefore, the average grain size of the silver halide grains is preferably 0.01 μm or more, and more preferably 0.1 μm or more. For the halogen composition of the silver halide photographic emulsion, any of silver chloride, silver chlorobromide, silver bromide, silver iodobromide and the like can be used.

ND filters 21 and 22 are manufactured as follows.

First, a silver halide photographic emulsion is coated on a glass plate 210 to a certain thickness to form an emulsion layer. Next, a hard mask is placed on the glass plate 210 on which the emulsion layer is formed, and the emulsion layer is exposed through this mask using a white light source such as a halogen lamp.

As the mask used here, a mask formed by depositing a metal on a transparent glass plate in the same pattern as the optical density gradation of the optical layer 211 as shown in FIG. 3 can be used. In this mask, in the area where the metal is not deposited, the light incident on the area passes as it is and enters the emulsion layer, and in the area where the metal is deposited, the light incident on the area passes through the area. The light passes through the region with a transmission amount corresponding to the thickness of the metal film and enters the emulsion layer. As a result, the emulsion layer is formed such that a portion that is strongly irradiated with exposure light and a portion that is weakly irradiated are continuously formed in the circumferential direction.

Develop after exposure. By this development processing, in the emulsion layer, the portion irradiated with the exposure light forms developed silver according to the irradiation amount, and a gradation pattern of optical density corresponding to the mask is formed. After the development processing, the optical layer 211 is formed by sequentially performing fixing, washing with water, and drying.

After the formation of the optical layer 211, the thickness that can be smoothed by filling the optical layer 211 with the fine irregularities formed on the surface of the optical layer 211, that is, the thickness greater than the depth from the apex portion of the irregularities to the bottom of the valley A colorless transparent resin layer (adhesive layer 212) having a thickness is formed. By this step, generation of scattered light due to the unevenness of the surface of the optical layer 211 can be prevented. In addition, it is possible to prevent adhesion of dust or the like that causes image defects on the surface of the optical layer 211.

Finally, a transparent antireflection film 213 (or transparent glass plate) is placed on the adhesive layer 212, the optical layer 211 and the antireflection film 213 (or transparent glass plate) are adhered, and the ND filter 21 is attached. Finalize.

As described above, by providing the adhesive layer 212 and the film 213 with an antireflection function, it is possible to prevent foreign matter from adhering to the surface of the optical layer 211 and to protect the optical layer 211 and maintain the quality of the ND filter. be able to. Note that, when a film is pasted on the optical layer 211, it is desirable to use a film with little image degradation because the film may cause degradation of resolution and image quality.

As described above, since the ND filters 21 and 22 can form the optical layer 211 by exposure using white light, the exposure apparatus is not expensive and the manufacturing cost can be suppressed.

Further, according to the ND filters 21 and 22, the ND filter can be completed with only two components of the glass plate 210 and the optical layer 211. In the conventional method of producing an ND filter using a silver halide photographic photosensitive film, the silver halide photographic photosensitive film itself is composed of two components, a base and an optical layer. Furthermore, since the silver halide photographic photosensitive film itself is not rigid, it is necessary to affix the silver halide photographic photosensitive film to a transparent substrate such as a glass plate with an adhesive. Therefore, at least four members (base, optical layer, adhesive, transparent substrate) constituting the ND filter are required. As the number of components constituting the ND filter increases, there is a concern that the image quality is degraded due to the reflection of light at the interface of the components. Since the ND filters 21 and 22 of the present embodiment can be configured with a minimum of two components, it is possible to reduce the reflection of light at the interface between the components and to prevent deterioration of the video quality.

In the example of FIG. 1, the two ND filters included in the ND filter unit 20 have the same configuration, but one of the two ND filters has a cross-sectional configuration shown in FIG. 2 and the other is, for example, The ND filter described in Patent Document 1 may be used. Even in this case, compared with the case of using two ND filters of the conventional configuration, it is possible to reduce the ghost due to light reflection.

In the example of FIG. 1, the ND filter unit 20 is built in the camera body 2, but the ND filter unit 20 may be built in the lens device 1. In this case, the ND filter unit 20 may be disposed on the object side or the opposite side of the photographing lens 10 of the lens apparatus 1. When the photographing lens 10 is composed of a plurality of lenses, the ND filter unit 20 may be disposed between the plurality of lenses.

Further, the ND filter unit 20 may be built in the adapter, and the adapter may be attached to the subject side of the lens apparatus 1 or may be attached between the lens apparatus 1 and the camera body 2.

Although the ND filters 21 and 22 have a disk shape, as described in Patent Document 4, they have a rectangular plate shape, and the ND filters 21 and 22 are moved in a direction perpendicular to the optical axis K, respectively. You may be able to do it. Furthermore, shapes other than a disk shape or a rectangular plate shape are possible. In such a case, the light transmittance may be continuously changed in one direction within the surface.

Further, the ND filter unit 20 shown in FIG. 1 is configured to be applied to a commercial camera system for television and movie shooting. However, the present invention is not limited to this, and a single-lens reflex camera, a handheld type camera system, or the like. However, it is generally applicable to any imaging optical system.

Hereinafter, examples of the present invention will be described. Hereinafter, materials, usage amounts, ratios, processing contents, and processing procedures shown in the examples can be appropriately changed without departing from the gist of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

(Comparative Example 1)
A sample H1 was prepared by coating an undercoat layer, an emulsion layer, and a protective layer in this order on a PET support having a thickness of 125 μm from the support side.

The emulsion is composed of 55 mol% of silver chloride and 45 mol% of silver bromide. Physically ripened and desalted Lippmann-type silver halide photographic emulsion having an average particle size of 0.17 μm according to a conventional method to obtain sodium thiosulfate and gold chloride [ III] Prepared by adding chemical acid aging.

In the above emulsion, 1,2-bis (vinylsulfonylacetamido) ethane as a hardening agent, 4-hydroxy-6-methyl-1,3,3a, 7-tetrazaindene as a stabilizer, 1-phenyl-as an antifoggant Add 5-mercaptotetrazole, sodium bis (2-ethylhexyl) sulfosuccinate as the surfactant, poly (potassium p-styrenesulfonate) as the thickener, and subbing layer (gelatin 50 mg / mg) on the PET support. The above emulsion layer was formed by coating on m ² ) so as to be 3.5 g / m ² silver and 5.0 g / m ² gelatin.

Sample H1 was exposed while adjusting the amount of light with an incandescent lamp light source through an ND filter preparation mask prepared in advance, and developed with a commercial FT-803R developer manufactured by FUJIFILM Corporation for 3 minutes at 20 ° C. Then, it was immersed in a commercial Fuji acetic acid stop solution manufactured by FUJIFILM Corporation for 30 seconds at 20 ° C. Further, after fixing for 3 minutes at 20 ° C. with a commercially available LF-308 fixing solution manufactured by FUJIFILM Corporation, the film was washed with running water for 3 minutes at room temperature and dried naturally. As a result, an optical layer made of developed silver was formed. Thus, the glass plate was affixed on both surfaces of the sample obtained with the adhesive agent, and ND filter A was formed.

In a state where the two ND filters A are arranged in opposite phases on the lens tip of a camera having a recording pixel of 2 megapixels, and the light transmittance of the ND filter unit YA including the two ND filters A is 25%. I took a spotlight. Further, with the same system configuration, the resolution chart was taken in a state where the light transmittance of the ND filter unit YA was 25%.

Example 1
Sample H1 was produced in the same manner as in Comparative Example 1 except that the PET support was changed to a glass support having a thickness of 1.6 mm. The sample H1 was obtained by exposing, developing, fixing, washing and drying the sample H1 in the same manner as in Comparative Example 1, and a glass plate was attached to the opposite surface of the glass support with an adhesive to produce an ND filter B. did. In a state where the two ND filters B are arranged in opposite phases on the lens tip of a camera having a recording pixel of 2 megapixels, and the light transmittance of the ND filter unit YB including the two ND filters B is 25%. The spotlight was photographed. Further, with the same system configuration, the resolution chart was photographed with the light transmittance of the ND filter unit YB being 25% and 6.3%. Further, the light transmittance of the ND filter B alone was measured. Further, the reflectance of light at a position where the transmittance of the ND filter B with respect to light having a wavelength of 550 nm was 6.3% was measured.

FIG. 4 is a diagram showing a photographed image obtained by photographing spot light in a state where the light transmittance of the ND filter unit YA of Comparative Example 1 is 25%. FIG. 5 is a diagram illustrating a photographed image obtained by photographing spot light in a state where the light transmittance of the ND filter unit YB of Example 1 is 25%.

4 and 5, the ND filter unit YA of Comparative Example 1 composed of an ND filter in which glass plates are attached to both surfaces of a sample in which an optical layer is formed on a PET support has a large range of image turbidity. It can be seen that light scattering is increased.

FIG. 6 is a partially enlarged view of a photographed image obtained by photographing a resolution chart in a state where the light transmittance of the ND filter unit YA of Comparative Example 1 is 25%. FIG. 7 is a partially enlarged view of a photographed image obtained by photographing a resolution chart in a state where the light transmittance of the ND filter unit YB of Example 1 is 25%. FIG. 8 is a partially enlarged view of a photographed image obtained by photographing a resolution chart in a state where the light transmittance of the ND filter unit YB of Example 1 is set to 6.3%.

As can be seen from FIG. 6 to FIG. 8, in the ND filter unit YA of Comparative Example 1, the resolution of the image is 600 TV lines or less, and the resolution degradation is remarkable. On the other hand, the ND filter unit YB of the first embodiment has an image resolution of 800 TV lines or more regardless of the transmittance.

(Example 2)
An ND filter C was prepared in the same manner as in Example 1 except that the average grain size of silver halide in the emulsion was changed to 0.06 μm. About this ND filter C, the light transmittance was measured. In addition, two ND filters C are arranged in the opposite phase on the lens tip of a camera having a recording pixel of 2 megapixels, and the light transmittance of the ND filter unit YC including the two ND filters C is 6.3%. The resolution chart was taken in the state.

FIG. 9 is a partially enlarged view of a photographed image obtained by photographing a resolution chart in a state where the light transmittance of the ND filter unit YC of Example 2 is set to 6.3%. The ND filter unit YC of the second embodiment has an image resolution of 800 TV lines or more.

FIG. 10 is a diagram showing the transmittance characteristics for each wavelength at the positions of the maximum transmittances of the ND filter B (Example 1) and the ND filter C (Example 2). FIG. 11 is a diagram showing the transmittance characteristics for each wavelength at the position where the light transmittance is 6.3% with respect to the wavelength of 550 nm of the ND filter B (Example 1) and the ND filter C (Example 2).

As can be seen from FIG. 11, in the ND filter C (Example 2), the transmittance of the transmittance on the short wavelength side is lowered. This indicates that the spectral neutrality of the developed silver forming the optical layer is slightly reduced.

On the other hand, in the ND filter B (Example 1), the decrease in the transmittance on the short wavelength side is small, and it can be seen that the spectral neutrality of the developed silver forming the optical layer is sufficiently maintained. From this result, it can be seen that the average grain size of silver halide used as the raw material of the optical layer 211 in the ND filters 21 and 22 is preferably 0.1 μm or more. Further, since the ND filter B has an average grain size of silver halide of 0.2 μm or less, a decrease in resolution due to an excessively large average grain size is also suppressed.

FIG. 12 is a diagram showing an outline of reflectance measurement at a position where the transmittance of the ND filter B is 6.3%. Light incident from the upper side of the AR film 213 is reflected mainly at the interface between the AR film 213 and air and the interface between the adhesive layer 212 and the optical layer 211. In this example, the reflectance of the two reflected lights was measured with a spectrophotometer.

FIG. 13 is a diagram showing the reflectance characteristics for each wavelength at the position where the transmittance of the ND filter B is 6.3%. In general, when a film with a transmittance of 6.3% is formed of a metal film such as chromium, a reflectance of 30% or more cannot be avoided. When incorporated in an optical instrument, the amount of ghosts cannot be ignored. Deteriorate. However, in the ND filter B, the reflectance is less than 0.5% in the wavelength region of 420 nm to 670 nm, and the ghost caused by this reflection is a negligible minute amount.

As described above, the following items are disclosed in this specification.

The disclosed ND filter unit includes two ND filters each having an optical layer whose light transmittance continuously changes in one direction or one circumferential direction, and the two ND filters include light of the optical layer. The transmission gradations are arranged so as to be opposite to each other, and at least one of the two ND filters has the optical layer formed on a transparent substrate, and the optical layer has an average particle diameter. It is composed of developed silver obtained by exposing and developing a silver halide photographic emulsion containing silver halide grains of 0.01 μm or more and 0.2 μm or less.

The disclosed ND filter unit includes one in which the transparent substrate is a glass plate.

The disclosed ND filter unit includes a transparent plate on the optical layer.

In the disclosed ND filter unit, the transparent plate is attached to the optical layer via an adhesive.

In the disclosed ND filter unit, the transparent plate has an antireflection function.

The disclosed ND filter unit includes those in which the average grain size of the silver halide grains is 0.1 μm to 0.2 μm.

The disclosed ND filter unit includes a mechanism for moving the two ND filters in opposite directions.

The disclosed imaging system includes an imaging lens, an imaging element that captures an optical image that passes through the imaging lens, and the ND filter unit that is disposed in front of the imaging element.

The disclosed manufacturing method of the ND filter includes a step of coating a silver halide photographic emulsion containing silver halide having an average grain size of 0.01 μm or more and 0.2 μm or less on a transparent substrate, and the coated silver halide. Depending on the pattern of the developed silver obtained by developing the photographic emulsion through a mask having a continuously varying light transmittance distribution and developing the silver halide photographic emulsion after exposure, the photographic emulsion is unidirectional or Forming an optical layer whose light transmittance continuously changes in the circumferential direction.

The ND filter unit of the present invention can be mounted on an imaging device such as a digital camera, for example, and can contribute to improvement of imaging image quality.

Although the present invention has been described in detail and with specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the technical spirit of the disclosed invention. This application is based on a Japanese patent application filed on November 15, 2011 (Japanese Patent Application No. 2011-250157) and a Japanese patent application filed on October 16, 2012 (Japanese Patent Application No. 2012-229093). Captured here.

20

ND filter unit

21, 22 ND filter 210 Glass plate 211 Optical layer 212 Adhesive layer 213 Film with antireflection function

Claims

Comprising two ND filters having an optical layer whose light transmittance continuously changes in one direction or one circumferential direction;
The two ND filters are arranged so that gradations of light transmittance of the optical layer are opposite to each other,
At least one of the two ND filters has the optical layer formed on a transparent substrate, and the optical layer contains silver halide grains having an average grain size of 0.01 μm or more and 0.2 μm or less. An ND filter unit composed of developed silver obtained by exposing and developing a silver photographic emulsion.
The ND filter unit according to claim 1,
The ND filter unit, wherein the transparent substrate is a glass plate.
The ND filter unit according to claim 1 or 2,
An ND filter unit comprising a transparent plate on the optical layer.
The ND filter unit according to claim 3,
The transparent plate is an ND filter unit that is attached to the optical layer via an adhesive.
The ND filter unit according to claim 3 or 4,
The transparent plate is an ND filter unit having an antireflection function.
An ND filter unit according to any one of claims 1 to 5,
An ND filter unit in which an average particle diameter of the silver halide grains is 0.1 μm or more and 0.2 μm or less.
The ND filter unit according to any one of claims 1 to 6,
An ND filter unit comprising a mechanism for moving the two ND filters in opposite directions.
A taking lens,
An image pickup device for picking up an optical image passing through the photographing lens;
An imaging system comprising: the ND filter unit according to any one of claims 1 to 7 disposed in front of the imaging device.
Coating a silver halide photographic emulsion containing silver halide having an average grain size of 0.01 μm or more and 0.2 μm or less on a transparent substrate;
Exposing the coated silver halide photographic emulsion through a mask having a continuously varying light transmittance distribution;
Forming an optical layer whose light transmittance continuously changes in one direction or one circumferential direction by a developed silver pattern obtained by developing the exposed silver halide photographic emulsion. Manufacturing method of ND filter.