JP3816048B2 - Manufacturing method of ND filter, ND filter, light amount diaphragm device and camera having these ND filters - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ND filter manufacturing method and an ND filter, and a light amount diaphragm apparatus and a camera having these ND filters, and more particularly to an ND filter manufacturing method suitable for use in an imaging system such as a video camera or a still video camera. The present invention relates to an ND filter, and a light quantity diaphragm device having these ND filters.
[0002]
[Prior art]
The light amount diaphragm device is provided in the optical path of the photographing optical system to control the amount of light incident on the solid-state image sensor on a silver salt film or CCD, so that the light amount can be reduced to be smaller when the object field is bright. It is configured.
Therefore, when shooting a clear or high-brightness field, the aperture becomes a small aperture, which is easily affected by the hunting phenomenon of the aperture and light diffraction, resulting in degradation 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 is enlarged even if the brightness of the object field is the same.
[0003]
In recent years, as the sensitivity of the image sensor has improved, the density of the ND filter is increased to further reduce the light transmittance, and the aperture of the diaphragm is increased even if the brightness of the object field is the same. .
However, when the density of the ND filter is increased in this way, the light amount difference between the light a that has passed through the ND filter and the light b that has not passed through the ND filter in the state shown in FIG. There are drawbacks such as "shading" phenomenon and resolution reduction. In order to solve this drawback, it has become necessary to adopt a structure in which the transmittance 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 photographing optical system 806, reference numeral 807 denotes a solid-state image sensor, and reference numeral 808 denotes a low-pass filter.
811 to 814 are members constituting the diaphragm device, 811 is an ND filter, 812 and 813 are opposed diaphragm blades, and the two diaphragm blades form a substantially rhombic opening. The ND filter is usually bonded to the diaphragm blade. Reference numeral 814 denotes a diaphragm blade support plate.
[0005]
Generally, as a method for producing an ND filter, an organic dye or pigment that absorbs light in a film-like material (cellulose acetate, PET (polyethylene terephthalate), vinyl chloride, etc.), and a kneading type, There is a type in which an organic dye or pigment that absorbs light is applied to the material.
As a conventional example, a high-quality antireflection light absorbing film that does not cause cracks has been proposed (see Patent Document 1).
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 05-93811
[Problems to be solved by the invention]
However, in the above-described general ND filter manufacturing method, 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.
In addition, what is disclosed in Patent Document 1 is a countermeasure against cracks at a single concentration. When a multi-concentration ND is formed on a single film, the film thickness is increased, which causes cracks. Nothing is disclosed about the solution to this problem.
Furthermore, in order to cope with high image quality such as high sensitivity and miniaturization of CCD in recent years, it is necessary to flatten the spectral transmittance and suppress it to low reflection. Also for such a problem, the above-mentioned Patent Document 1 only discloses a spectral characteristic whose transmittance decreases in the vicinity of the visible light region of 550 nm.
[0008]
Therefore, the present invention solves the above problems, suppresses the generation of cracks, improves the uniformity of the amount of light, and can cope with high image quality, and has a flat spectral characteristic and low reflectance at each concentration. An object of the present invention is to provide an ND filter manufacturing method, an ND filter, and a light quantity diaphragm device and a camera having these ND filters.
[0009]
[Means for Solving the Problems]
The present invention provides a method for manufacturing an ND filter having a gradation density distribution, an ND filter, and a light quantity diaphragm device and a camera having these ND filters, which are configured as follows.
The manufacturing method of the ND filter of the present invention uses a film composed of at least two types of layers stacked on a substrate, and forms a plurality of stepwise density distributions by stacking the films to change the amount of transmitted light. In the manufacturing method of an ND filter as described above, the films are laminated in order from the largest lamination area to the smallest one, and the first layer film facing the substrate is a dielectric film. It is formed and has a mechanical film thickness of 5 nm to 90 nm .
In addition, the ND filter of the present invention forms a plurality of stepwise density distributions by laminating a film composed of at least two kinds of layers laminated on a substrate on the same transparent member, and reduces the amount of transmitted light. In the ND filter, a single-concentration layer is formed by the film having a large lamination area 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.
In addition, a light quantity diaphragm device or a camera with improved light quantity uniformity can be configured by using the ND filter produced by the ND filter production method of the invention or the ND filter of the invention.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
When creating the multi-concentration film by applying the above configuration, stacking is performed in order from the larger stacking area, so that no cracks occur even after film formation or when cutting with a press, etc. The step ND filter can be manufactured, which is based on the following findings based on the results of intensive studies by the present inventors.
[0011]
When a step ND filter having a three-concentration configuration is produced, simply overlapping two or three layers causes a problem that cracks occur in the overlapped portion after film formation or after cutting.
Therefore, the present inventors created a three-concentration step filter as shown in FIG. 3 by the following film formation 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 two concentrations having a smaller lamination area are laminated on the two sides of the plastic substrate. A three-concentration step filter was created.
The reason why such a stacking order is adopted is that although the plastic material is set at a temperature lower than 150 ° C. at which the plastic material is not thermally contracted depending on the substrate temperature and the temperature of the deposited film, it tends to contract somewhat, and the stacking area The larger is, the more easily affected by the heat shrinkage. For this reason, when a film having a small lamination area is gradually formed from a film having a small lamination area, the film having a small lamination area formed earlier is easily affected by the stress caused by thermal contraction of the large film formed later, and this causes cracks. This is considered to be a major factor in generation, and the present invention has been completed by adopting the above-described stacking order.
[0012]
Hereinafter, the present embodiment will be described in more detail with reference to the drawings. However, the present invention is not limited to these specific embodiments. In particular, the following describes the case where the vacuum deposition method is used as a method for forming a film on the ND filter, but the same effect can be obtained also in the sputtering method, the inkjet printing method, the spray method, and 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 vapor deposition machine, in which 501 is a vapor deposition umbrella, 502 is a substrate on which a film is formed, 503 is a vapor deposition source, 504 is a base material on which actual film formation is performed, and 505 is a base material 504. It is a substrate jig for fixing.
Further, the substrate 502 described as the present embodiment is a state in which the base material 504 is set on the substrate jig 505 as shown in FIG.
[0014]
In general, in the vacuum vapor deposition method, the substrate in the chamber is provided on the vapor deposition umbrella 501 as shown in FIG. 5, and the substrate 502 is rotated together with the vapor deposition umbrella 501 to form a film. For example, as shown in FIG. A laminated film of layers is formed on the substrate.
In the present embodiment, this is configured as a single density, and is doubled and tripled to create a step ND filter having a three density distribution on one sheet. For example, as shown in FIG. 3, the plastic substrate having the largest laminated area is first laminated on one surface side of the plastic substrate, and then the two substrates having the smaller laminated area are laminated on the two surface sides of the plastic substrate to form a double-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 corresponding to high quality without generation of cracks after film formation or when 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 polyethylene terephthalate (hereinafter referred to as PET) base material having a thickness of 75 μm by a vacuum deposition method.
The material of the substrate was selected from PET having high heat resistance (glass transition point Tg), high transparency in the visible wavelength range, and low water absorption.
As the film forming method, the vacuum deposition method was selected because the film thickness can be controlled relatively easily and the scattering is very small in the visible wavelength range.
[0016]
As shown in FIG. 4, Al ₂ O ₃ and Ti _X O _Y are alternately stacked as shown in FIG. 4, and the outermost layer is formed with MgF ₂ and seven layers are stacked, with a single concentration D = 0. It was set to 5. In this embodiment, the film of D = 0.5 is doubled and tripled, and a step ND having a three-density distribution of D = 0.5, 1.0, and 1.5 on one sheet. A filter was produced. At that time, as shown in FIG. 3, the one having the largest laminated area is first laminated on one surface side of the plastic substrate, and then the two substrates having two concentrations are laminated on the two surface sides of the plastic substrate. Formed. In fact, there is a tendency that cracks tend to occur in the portion where the two concentrations on the two sides overlap.
[0017]
In addition, as countermeasures against cracks in this embodiment, the following conditions (1) to (3) are changed in addition to devising the above-described stacking order.
(1) The film thickness of the first layer Al ₂ O ₃ is set to 5 nm to 90 nm. Actually, it is preferable that the film thickness is 10 nm to 60 nm, and if it is less than the range, it is difficult to control the film thickness, and if it is above, the film thickness becomes thick and cracks occur. Therefore, the incidence of cracks is lower when the film thickness is made as thin as possible. Therefore, the first layer Al ₂ O ₃ which is not affected by the spectral characteristics of transmittance and reflectance was thinned.
FIG. 15 shows the relationship of the crack rate when the film thickness of the first layer is varied. As can be seen from this result, the crack rate can be lowered only by thinning the first layer film. As a synergistic effect, the cross-cut test (in which the deposited film was cut at intervals of 1 to 2 mm in length and width and peeled off by Nichiban tape), the adhesion of the film was improved.
(2) At the time of forming a film having the largest area, a three-concentration step ND filter as shown in FIG. 1A is formed by using a dividing mask 201 as shown in FIG.
According to this, as compared with the case of the 3-concentration step ND filter shown in FIG. 1B formed on the entire surface with the entire surface mask, the warping of the entire plastic substrate can be suppressed, and the stress is dispersed and the low stress is obtained. can get.
(3) Since the adhesiveness is lowered when the outermost layer is MgF ₂ at the portion where two concentrations on the two surfaces side having a small area are overlapped, Al ₂ O ₃ is used for the adhesion surface. Although a method of stacking three layers on one side is also conceivable, it is considered better to reduce the overlapping part as much as possible.
[0018]
The step ND filter having a three-concentration distribution completed under the above conditions can be used by cutting it into various shapes, for example, cutting it into a shape as shown in FIG. The cutting result is shown in FIG.
In FIG. 7, the left side (a) shows the crack rate when no countermeasure against cracks is applied, the middle side (b) shows the crack rate when using the dividing mask 201, and the right side shows (c). The thing shows the crack rate when forming into a film in order of the area.
[0019]
From the results shown in FIG. 7, when the film is formed and cut out under the conditions of using the stacking order and the dividing mask 201 of this embodiment, there is a remarkable effect as compared with a film that does not take such measures at all. I understand.
Further, from the result shown in FIG. 7, when cutting from the one surface side having a large area as shown in FIG. 6 (b), when cutting from the two surface side having a small area as shown in FIG. 6 (a), It can be seen that the crack rate is much lower.
[0020]
In this way, the best case is when cutting from one side with a large area. The reason may be that the film tends to be convex on one side when the film is first deposited on one side as a tendency of vapor deposition. I know. On the other hand, if the film is formed on the two surfaces first, the film becomes convex on the two surfaces.
As an example, when the first side is first deposited and cut out from the first side, the shape before and after cutting is the same as convex ⇒ 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 is increased.
[0021]
FIG. 9, FIG. 10, FIG. 11, FIG. 12, FIG. 13, and FIG. 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 region, and the reflectance is less than 3%, which is suppressed to low reflection.
In the D = 1.0 film (FIGS. 11 and 12), since the other layer D = 0.5 is laminated, the outermost layer is not MgF ₂ that suppresses the reflectance but Al ₂ O _3. Similarly, the transmittance was flat and the reflectance was kept low.
In the D = 1.5 film (FIGS. 13 and 14), the same results as described above were obtained for both transmittance and reflectance.
It should be noted that flattening the transmittance of the ND filter is indispensable as a measure for high image quality such as high sensitivity and miniaturization of the CCD in recent years.
[0022]
【The invention's effect】
According to the present invention, the generation of cracks is suppressed, the uniformity of the light quantity is improved, and it is possible to cope with high image quality, and the manufacturing method of the ND filter having flat spectral characteristics and low reflectance at each concentration, and It is possible to realize an ND filter, and 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 fabricated with a split mask in an embodiment of the present invention, and FIG. 1B is a diagram of a three-density step ND filter fabricated with a full-face mask.
FIG. 2A is a view showing a step ND filter obtained by punching after vapor deposition in an embodiment, and FIG. 2B is a view showing a dividing mask.
FIG. 3 is a side view showing a three-concentration film-forming structure of a step ND filter in the embodiments and examples of the present invention.
FIG. 4 is a diagram showing a laminated structure of thin films with a single concentration D = 0.5 of a step ND filter in the embodiments and examples of the present invention.
FIG. 5 is a simplified view inside a chamber in a vacuum vapor deposition machine for explaining an embodiment of the present invention.
FIG. 6A is a cutout view of a 3 density step ND filter cut from the second surface side, and FIG. 6B is a cutout view of a 3 concentration step ND filter according to the present embodiment cut from the first surface side.
FIG. 7 is a diagram showing a crack occurrence rate by a cut-out test.
FIG. 8 is a diagram illustrating a photographing optical system used in a video camera.
FIG. 9 is a graph showing the spectral transmittance at D = 0.5 in the example of the present invention.
FIG. 10 is a graph showing the spectral reflectance at D = 0.5 in the example of the present invention.
FIG. 11 is a graph showing the spectral transmittance at D = 1.0 in the example of the present invention.
FIG. 12 is a graph showing the spectral reflectance at D = 1.0 in the example of the present invention.
FIG. 13 is a graph showing the spectral transmittance at D = 1.5 in an example of the present invention.
FIG. 14 is a graph showing the spectral reflectance at D = 1.5 in the example of the present invention.
FIG. 15 is a graph showing the relationship between the film thickness of the first layer Al ₂ O ₃ and the crack rate.
[Explanation of symbols]
201: Dividing mask 501: Deposition umbrella 502: Substrate 503: Deposition source 504: Base material 505: Substrate jigs 806A, 806B, 806C,
806D: Lens constituting the photographing optical system 6 807: Solid-state imaging device 808: Low-pass filter 8011: ND filter 812, 813: Diaphragm blade 814: Diaphragm blade support plate

Claims (8)

An ND filter manufacturing method using a film composed of at least two types of layers stacked on a substrate, and forming a plurality of stepwise density distributions by stacking the films to change the amount of transmitted light. The films are laminated in order from the largest lamination area to the smallest, and the film is formed of a dielectric film as the first film facing the substrate, and the mechanical film thickness is 5 nm to ND filter manufacturing method characterized by being 90 nm . 2. The method of manufacturing an ND filter according to claim 1, wherein a dividing mask for dispersing and reducing stress is used when laminating the film having a large area. 3. The method of manufacturing an ND filter according to claim 1, wherein the ND filter is cut from a side of the film having a large area. An ND filter in which a film composed of at least two types of layers stacked on a substrate is stacked on the same transparent member to form a plurality of stepwise density distributions and change the amount of transmitted light. ,
An ND filter characterized in that a single-concentration layer made 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. . The ND filter according to claim 4 , wherein the single-concentration layer has a structure that protrudes toward the single-concentration layer by film formation. The membrane, according to claim first layer of film facing the transparent member to laminate the membrane is formed of a dielectric film, its mechanical thickness, characterized in that there is a 5Nm～90nm 4 Alternatively, the ND filter according to claim 5 . A light quantity diaphragm comprising a plurality of diaphragm blades that are relatively driven to vary the size of the diaphragm aperture, and an ND filter for adjusting the light quantity disposed at least in part of the aperture formed by the diaphragm blades In the device
The said ND filter is comprised by the ND filter manufactured by the manufacturing method of any one of Claims 1-3 , or the ND filter of any one of Claims 4-6. A featured light diaphragm device. A camera, comprising: an optical system; a light quantity diaphragm device according to claim 7 that limits an amount of light that passes through the optical system; and a solid-state imaging device that receives an image formed by the optical system.

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