JP2004117718A - Method for manufacturing nd filter, nd filter, and light quantity adjusting device and camera having the nd filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an ND filter which have less cracks, improve uniformity of light quantity, are capable of dealing with high image quality and have flat spectral characteristics at each density, and to provide the ND filter, and a light quantity adjusting device and a camera having the ND filters. <P>SOLUTION: In this method for manufacturing ND filters, a plurality of stepwise optical density distributions are formed by stacking films consisting of at least two or more kinds of layers stacked on a substrate onto the same transparent member to change the amount of transmitted light. A single density layer consisting of the above films and having a larger stacking area is formed on one face of the member, and a two-density layer of a smaller stacking area is formed on the opposite face of the member. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of manufacturing an ND filter, an ND filter, and a light amount diaphragm device and a camera having the ND filter. The present invention relates to an ND filter and a light amount stop device having the ND filter.
[0002]
[Prior art]
The light amount aperture device is provided in the optical path of the photographing optical system in order to control the amount of light incident on the solid-state imaging device such as a silver halide film or a CCD, and to reduce the amount of light to be smaller when the field is bright. Is configured.
Therefore, when shooting a sunny or high-brightness scene, the aperture becomes small, which is easily affected by the hunting phenomenon of the aperture and the diffraction of light, resulting in deterioration of image performance.
As a countermeasure against this, a film-like ND (Neutral Density) filter is attached to the aperture blade so that the aperture of the aperture becomes large even if the brightness of the field is the same.
[0003]
In recent years, as the sensitivity of an image sensor has been improved, the density of the ND filter has been increased to further reduce the light transmittance, and the aperture of the diaphragm has been increased even if the brightness of the object field is the same. .
However, when the density of the ND filter is increased as described above, the light quantity difference between the light a passing through the ND filter and the light b not passing through the ND filter in the state shown in FIG. There are drawbacks such as the "shading" phenomenon and the reduction in resolution. In order to solve this drawback, it has become necessary to adopt a structure in which the transmittance of the density of the ND filter increases gradually toward the center of the optical axis.
[0004]
In FIG. 8, reference numerals 806A, 806B, 806C, and 806D denote lenses constituting the imaging optical system 806, 807 denotes a solid-state image sensor, and 808 denotes a low-pass filter.
Reference numerals 811 to 814 denote members constituting an aperture device, 811 denotes an ND filter, and 812 and 813 move in opposite directions. The two aperture blades form a substantially rhombic opening. The ND filter is usually bonded to the diaphragm blade. 814 is a diaphragm blade support plate.
[0005]
Generally, ND filters are manufactured by mixing and kneading an organic dye or pigment that absorbs light into a film-like material (cellulose acetate, PET (polyethylene terephthalate), vinyl chloride, etc.), There is a type in which an organic dye or pigment that absorbs light is applied to the material.
Further, as a conventional example, a high-quality antireflection light absorbing film which does not cause cracks has been proposed (see Patent Document 1).
[0006]
[Patent Document 1] Japanese Patent Application Laid-Open No. 05-93811
[Problems to be solved by the invention]
However, according to the above-described general method of manufacturing an ND filter, a filter having a uniform density can be manufactured, but a step ND filter of a type in which the density changes in the same filter is extremely difficult to manufacture.
The technique disclosed in Patent Document 1 is a countermeasure against cracking at a single concentration. When a multi-concentration ND is formed on a single film, the film thickness becomes large, and thus cracks occur. Nothing is disclosed about the solution to this problem.
Furthermore, in recent years, in order to respond to high image quality such as high sensitivity and miniaturization of CCD, it is necessary to flatten the spectral transmittance and suppress the reflection to low. Even with respect to such a problem, Patent Document 1 described above only discloses one having spectral characteristics in which the transmittance is reduced near a visible light region of 550 nm.
[0008]
Therefore, the present invention solves the above problems, suppresses the occurrence of cracks, improves the uniformity of light quantity, and can respond to high image quality. At each density, the spectral characteristics are flat and the reflectance is low. An object of the present invention is to provide a method of manufacturing an ND filter, an ND filter, and a light-amount aperture device and a camera having these ND filters.
[0009]
[Means for Solving the Problems]
The present invention provides a method of manufacturing an ND filter having a gradation density distribution configured as follows, an ND filter, and a light amount diaphragm device and a camera having these ND filters.
The method for manufacturing an ND filter according to the present invention uses a film composed of at least two or more layers laminated on a substrate, and forms a plurality of stepwise concentration distributions by laminating the films to change the amount of transmitted light. A method of manufacturing an ND filter as described above, wherein the films are stacked in order from a larger stacking area to a smaller stacking area.
Further, the ND filter of the present invention forms a plurality of stepwise concentration distributions by laminating films composed of at least two or more types of layers laminated on a substrate on the same transparent member, and reduces the amount of transmitted light. An ND filter adapted to be changed, wherein a single-concentration layer of the film having a large lamination area is formed on one side of the member, and a two-concentration layer having a small lamination area is formed on the opposite side of the member. It is characterized by being.
Further, the ND filter manufactured by the method of manufacturing an ND filter of the present invention or the ND filter of the present invention can be used to configure a light-aperture stop device or a camera with improved uniformity of light amount.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Applying the above configuration, when creating a multi-concentration film, by laminating in order from the larger lamination area, high quality without cracking even after film formation or cutting by pressing etc. The above-described step ND filter can be manufactured, but it is based on the following findings based on the results of intensive studies by the present inventors.
[0011]
In the case of manufacturing a step ND filter having a three-concentration configuration, a problem arises that cracks are generated in the overlapped portion after film formation or cutting, if the layers are simply doubled and tripled.
Therefore, the present inventors have created a three-density step filter as shown in FIG. 3 by the following film forming method.
First, a single-concentration film having the largest lamination area is laminated on one side of the plastic substrate shown in FIG. 3, and then a two-density film having a small lamination area is laminated on the two sides of the plastic substrate. A three density step filter was created.
The reason why such a lamination order is adopted is that although the plastic material is set at a temperature of less than 150 ° C. at which the plastic material does not thermally shrink due to the substrate temperature or the temperature of the vapor-deposited film, the plastic material still tends to slightly shrink. The greater the value, the more susceptible to the heat shrinkage. Therefore, when a film having a small lamination area is gradually formed from a film having a small lamination area, a film having a small lamination area formed earlier is easily affected by stress due to thermal shrinkage of a large film which is formed later. This is considered to be a major factor of occurrence, and the present invention has been completed by adopting the above-described lamination order.
[0012]
Hereinafter, the present embodiment will be described in more detail with reference to the drawings, but the present invention is not limited to these specific embodiments. In particular, in the following, a case is described in which a vacuum deposition method is used as a method for forming a film on an ND filter. However, a similar effect can be obtained in a sputtering method, an inkjet printing method, a spray method, or the like. Since this is presumed to be generally known, the description is omitted.
[0013]
FIG. 5 is a simplified view of the inside of a chamber in a vacuum deposition machine, where 501 is a deposition umbrella, 502 is a substrate on which a film is to be formed, 503 is a deposition source, 504 is a substrate on which a film is actually formed, and 505 is a substrate 504 This is a substrate jig for fixing.
In addition, the substrate 502 described in this embodiment is assumed to be in a state where the substrate 504 is set on the substrate jig 505 as shown in FIG.
[0014]
Generally, in a vacuum deposition method, a substrate in a chamber is provided on a deposition umbrella 501 as shown in FIG. 5, and a substrate 502 rotates together with the deposition umbrella 501 to form a film. A laminated film of layers is formed on the substrate.
In the present embodiment, this is configured to have a single density, and is superimposed twice or three times to create a step ND filter having three density distributions on one sheet. For example, as shown in FIG. 3, a plastic substrate having the largest lamination area is first laminated on one surface side of a plastic substrate, and then a plastic substrate having a smaller lamination area is laminated on the two surface sides of the plastic substrate to form a two-concentration substrate. Thus, a step ND filter having a three density distribution is created. With such a configuration, it is possible to produce a step ND filter that is compatible with high quality without generating cracks even after the film is formed or cut by a press or the like.
[0015]
【Example】
Next, examples of the present invention will be described.
First, a film is formed on a 75 μm-thick polyethylene terephthalate (hereinafter referred to as PET) substrate by a vacuum evaporation method.
As the material of the substrate, PET having high heat resistance (glass transition point Tg), high transparency in the visible wavelength range, and low water absorption was selected.
As a film forming method, a vacuum deposition method was selected because the film thickness can be controlled relatively easily and scattering is very small in a visible wavelength range.
[0016]
As shown in FIG. 4, the film configuration is such that Al ₂ O ₃ and Ti _X O _Y are alternately laminated, and the outermost layer is formed of MgF ₂ , and seven layers are laminated. It was set to 5. In the present embodiment, the film having D = 0.5 is superimposed twice or three times, and one sheet has three density distributions of D = 0.5, 1.0, 1.5 in step ND. A filter was made. At this time, as shown in FIG. 3, the plastic substrate having the largest lamination area is first laminated on one surface side of the plastic substrate, and then the plastic substrate having the smaller lamination area is laminated on the two surface sides of the plastic substrate to obtain a two-density substrate. Formed. Actually, cracks tend to easily occur in the portions where the two concentrations on the two surfaces overlap each other.
[0017]
As a countermeasure against cracks in the present embodiment, the following conditions (1) to (3) are changed in addition to devising the above stacking order.
(1) The film thickness of the first layer Al ₂ O ₃ is set to 5 nm to 90 nm. Actually, the film thickness is preferably from 10 nm to 60 nm. If the thickness is less than the range, it is difficult to control the film thickness. If the thickness is more than the range, the film thickness becomes large and cracks occur. Therefore, the smaller the film thickness is, the lower the rate of occurrence of cracks is. Therefore, the first layer Al ₂ O ₃ which is not affected by the spectral characteristics of the transmittance and the reflectance was thinned.
FIG. 15 shows the relationship between the crack rates when the thickness of the first layer is varied. As can be seen from this result, the crack rate can be reduced only by reducing the thickness of the first layer film. As a synergistic effect, a cross-cut test (cuts made at intervals of 1 to 2 mm in the vertical and horizontal directions in the deposited film and peeled off with a Nichiban tape) resulted in improved adhesion of the film.
(2) When forming a film having the largest area, a film is formed using a dividing mask 201 as shown in FIG. 2B to form a three-density step ND filter as shown in FIG. 1A.
According to this, the warpage of the entire plastic substrate can be suppressed, and the stress is dispersed and the one with low stress can be suppressed, as compared with the case of the three-density step ND filter shown in FIG. can get.
(3) In the portion where the two concentrations are overlapped on the two surfaces having a small area, the adhesiveness is reduced when the outermost layer is MgF ₂ , and therefore, Al ₂ O ₃ is used for the adhesive surface. In addition, although a method of stacking three layers on one side surface is also conceivable, it is considered that it is better to reduce the overlapping portion as much as possible.
[0018]
The step ND filter having the three-density distribution completed under the above conditions can be cut out into various shapes, for example, cut out into a shape as shown in FIG. FIG. 7 shows the cutting results.
In FIG. 7, (a) on the left side shows the crack rate when no crack countermeasures are taken, (b) in the center shows the crack rate when the dividing mask 201 is used, and (c) on the right side. Those indicate the crack ratios when the films were formed in the descending order of the area.
[0019]
From the results shown in FIG. 7, when a film is formed and cut out under the conditions of using the above-described lamination order and the dividing mask 201 of the present embodiment, there is a remarkable effect as compared with a film that does not take such measures at all. I understand.
Also, from the results shown in FIG. 7, when cutting out from one side having a large area as shown in FIG. 6B, compared with cutting out from two sides having a small area as shown in FIG. 6A. It can be seen that the crack rate is much lower.
[0020]
As described above, the optimal case is to cut out from one side having a large area. One possible reason for this is that when a film is formed on the first side as a tendency of vapor deposition, the film becomes convex on the one side. I know. Conversely, if the film is formed on the two surfaces first, it becomes convex on the two surfaces.
For example, when the film is first formed on one side and cut out from the first side, the shape before and after cutting is not changed from convex to convex, but when cut out from the second side, the shape reverses from concave to convex before and after cutting. It is considered that the crack rate increases.
[0021]
9, 10, 11, 12, 13, and 14 show the transmittance and reflectance at each density of the three-density step ND filter.
In the D = 0.5 film (FIGS. 9 and 10), the transmittance is flat in the visible light range, and the reflectance is less than 3%, which is low reflection.
In the D = 1.0 film (FIGS. 11 and 12), since another layer D = 0.5 is laminated, the outermost layer is not MgF ₂ for suppressing the reflectance but Al ₂ O _3. Similarly, the transmittance was flat and the reflectance was low.
Also in the case of the D = 1.5 film (FIGS. 13 and 14), the same results as described above were obtained for both transmittance and reflectance.
Making the transmittance of the ND filter flat is indispensable in response to high image quality such as recent high sensitivity and miniaturization of CCD.
[0022]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of a crack is suppressed, the uniformity of light quantity improves, it becomes possible to respond to high image quality, and the spectral characteristic is flat in each density | concentration, and the manufacturing method of the ND filter of low reflectance. It is possible to realize an ND filter, a light amount diaphragm device and a camera having these ND filters.
[Brief description of the drawings]
FIG. 1A is a diagram of a three-density step ND filter manufactured using a dividing mask according to an embodiment of the present invention, and FIG. 1B is a diagram of a three-density step ND filter manufactured using an entire surface mask.
FIG. 2A is a diagram illustrating a step ND filter obtained by punching after vapor deposition in an example, and FIG. 2B is a diagram illustrating a dividing mask.
FIG. 3 is a side view showing a three-concentration film formation structure of a step ND filter according to the embodiment and examples of the present invention.
FIG. 4 is a diagram illustrating a laminated structure of thin films with a single concentration D = 0.5 of the step ND filter according to the embodiment and the examples of the present invention.
FIG. 5 is a simplified view of the inside of a chamber in a vacuum deposition machine for describing an embodiment of the present invention.
FIG. 6A is a cutout diagram of a three-density step ND filter cut from two sides, and FIG. 6B is a cutout diagram of a three-density step ND filter according to the present embodiment cut from one side.
FIG. 7 is a diagram showing a crack occurrence rate by a cutout test.
FIG. 8 is a diagram illustrating a photographing optical system used in a video camera.
FIG. 9 is a graph showing a spectral transmittance at D = 0.5 in an example of the present invention.
FIG. 10 is a graph showing a spectral reflectance at D = 0.5 in an example of the present invention.
FIG. 11 is a graph showing a spectral transmittance at D = 1.0 in an example of the present invention.
FIG. 12 is a graph showing a spectral reflectance at D = 1.0 in an example of the present invention.
FIG. 13 is a graph showing a spectral transmittance at D = 1.5 in an example of the present invention.
FIG. 14 is a graph showing a spectral reflectance at D = 1.5 in an example of the present invention.
FIG. 15 is a graph showing the relationship between the thickness of the first layer Al ₂ O ₃ and the crack rate.
[Explanation of symbols]
201: division mask 501: vapor deposition umbrella 502: substrate 503: vapor deposition source 504: base material 505: substrate jigs 806A, 806B, 806C,
806D: Lens 807 constituting imaging optical system 6: Solid-state image sensor 808: Low-pass filter 8011: ND filters 812, 813: Aperture blade 814: Aperture blade support plate

Claims (9)

A method of manufacturing an ND filter using a film composed of at least two or more types of layers laminated on a substrate, and forming a plurality of stepwise density distributions by changing the laminated amount to change the amount of transmitted light. Wherein the films are stacked in ascending order of lamination area. 2. The method according to claim 1, wherein a dividing mask for dispersing and reducing stress is used when stacking the large-area films. The method for manufacturing an ND filter according to claim 1, wherein the ND filter is cut from a side of the film having a large area. 4. The film according to claim 1, wherein the first film facing the member on which the film is laminated is formed of a dielectric film, and has a mechanical thickness of 5 nm to 90 nm. The method for manufacturing an ND filter according to any one of the above items. An ND filter in which a film composed of at least two or more types of layers laminated on a substrate is laminated on the same transparent member to form a plurality of stepwise density distributions, thereby changing the amount of transmitted light. ,
An ND filter characterized in that a single-layered layer of the film having a large lamination area is formed on one side of the member, and a two-density layer having a small lamination area is formed on the opposite side of the member. . The ND filter according to claim 5, wherein the single-concentration layer has a structure that becomes convex toward the single-concentration layer by film formation. 6. The film according to claim 5, wherein a first film facing the transparent member on which the film is laminated is formed of a dielectric film, and has a mechanical thickness of 5 nm to 90 nm. Or the ND filter according to claim 6. A light amount aperture provided with a plurality of aperture blades that are relatively driven to change the size of the aperture opening, and an ND filter for adjusting a light amount disposed at least in a part of the opening formed by the aperture blades In the device,
The ND filter is configured by the ND filter manufactured by the manufacturing method according to any one of claims 1 to 4, or the ND filter according to any one of claims 5 to 7. Characteristic light stop device. 9. A camera, comprising: an optical system; a light amount stop device according to claim 8 for restricting an amount of light passing through the optical system; and a solid-state imaging device for receiving an image formed by the optical system.

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