JP2006078519A - Nd filter, light quantity diaphragm device, camera equipped with light quantity diaphragm device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ND filter and a light quantity diaphragm device capable of suppressing the deformation of a substrate due to the internal stress of the filter, capable of suppressing the transmission in a visible wavelength region, and also, capable of reducing the transmitted light quantity in a near infrared wavelength region, and to provide a camera equipped with the light quantity diaphragm device. <P>SOLUTION: A thin film 2 having characteristics of attenuating the transmission of a visible region is arranged on a substrate 1 having characteristics of suppressing the transmission of the light in the near-infrared wavelength region as compared with the transmission of the light in the visible wavelength region. In this case, the substrate can be constituted of an infrared cut glass and a resin infrared cut filter or the like, and the thin film can be constituted of a thin film having either of mono-density, multi-density, and gradation in terms of density distribution. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ND filter, a light amount diaphragm device, and a camera having the light amount diaphragm device.

The light amount diaphragm is provided to control the amount of light incident on a solid-state image sensor such as a silver salt film or a CCD, and is configured to be further narrowed down when the object field is bright. Therefore, when photographing a clear or high-luminance field, the aperture becomes a small aperture, which is easily affected by the hunting phenomenon of the aperture and the light diffraction phenomenon, causing deterioration in image performance.
As countermeasures against this, even if the brightness of the object field is the same by arranging an ND filter in the vicinity of the diaphragm or by controlling the light quantity such as directly attaching the ND filter to the diaphragm blade, the aperture of the diaphragm is larger. We are trying to make it possible.

Further, although the solid-state imaging device has a function corresponding to human eyes, the optical response of the device itself is not necessarily the same as that of humans. Therefore, some optical processing is required to achieve almost the same function as humans.
One of them is a method of allowing only the light wavelength region necessary for color reproduction to reach the surface of the solid-state imaging device. This is a measure taken because the solid-state imaging device itself has high sensitivity in the near-infrared region even though the required wavelength region is only the human visual wavelength region. That is, if light is incident on the solid-state imaging device without any processing, signal processing is performed with high sensitivity in the near infrared region, and light amount adjustment and color balance adjustment cannot be appropriately performed. Therefore, when light passes only through the ND filter and enters the solid-state imaging device, image degradation due to the above-described stop hunting phenomenon or light diffraction phenomenon is improved, but infrared light is transmitted, Actually, an image different from the visibility when a person sees with eyes is projected.
For this reason, in addition to the ND filter, an infrared cut filter that controls transmission in the near-infrared wavelength region is usually provided to prevent near-infrared light from entering the solid-state imaging device. It has become common.

Conventionally, in order to suppress transmission in the visible wavelength range and simultaneously limit transmission in the near infrared wavelength range, a configuration having an ND filter and an infrared light cut filter independently is necessary. It was.
On the other hand, in patent document 1, it has an ND filter and an infrared-light cut filter independently by comprising vapor-depositing an ND filter film and an infrared cut filter film on both surfaces of a transparent resin substrate. An ND filter that does not require this has been proposed.
JP 2002-107509 A

However, in Patent Document 1 described above, by forming an ND filter on one surface of the substrate and an infrared cut filter on the other surface, it is not necessary to have each filter independently. There is a problem that the substrate itself is deformed due to the difference in film thickness between the two filters formed.
That is, in order to obtain characteristics satisfying general specifications required for the current infrared cut filter, the number of layers of about 30 to 40 is required. When an ND filter having, for example, about 10 layers is generated on the opposite surface, internal stress is generated due to the difference in film thickness between the ND surface and the infrared cut surface. In particular, in a substrate with low rigidity such as a transparent resin substrate, It will be deformed.

  Therefore, in order to correct the substrate deformation due to internal stress while maintaining the characteristic of cutting the near infrared, the film thickness of the ND surface must be almost close to the infrared cut surface. Although a considerable film thickness is required for each layer of the film, when the film thickness of the ND filter film is increased, other problems such as a decrease in film adhesion and film cracking occur.

  In view of the above problems, the present invention can suppress the deformation of the substrate due to the internal stress of the filter, suppress the transmission in the visible wavelength range, and reduce the amount of transmitted light in the near infrared wavelength range. It is an object of the present invention to provide an ND filter, a light quantity diaphragm device, and a camera having the light quantity diaphragm device.

The present invention provides an ND filter, a light quantity diaphragm device, and a camera having the light quantity diaphragm device configured as follows.
That is, the ND filter of the present invention has a thin film having a characteristic of attenuating transmission in the visible range on a substrate having characteristics of low transmission compared to the visible wavelength range for light in the near infrared wavelength range. It is a feature. In the present invention, the substrate can be composed of an infrared cut glass, a resin infrared cut filter, or the like, and the thin film is a thin film having a single concentration, multiple concentration, or gradation concentration distribution. Can be configured.
In addition, the light quantity diaphragm device of the present invention includes a plurality of diaphragm blades that are relatively driven to change the size of the diaphragm opening, and a light quantity adjustment device that is disposed on at least a part of the aperture formed by the diaphragm blades. In the light quantity reduction device provided with the ND filter for
The ND filter is constituted by the ND filter described above.
In addition, a camera of the present invention is characterized by having an optical system, the above-described light amount diaphragm device that limits the amount of light that passes through the optical system, and a solid-state imaging device that receives an image formed by the optical system.

  ADVANTAGE OF THE INVENTION According to this invention, the deformation | transformation of the board | substrate by the internal stress of a filter can be suppressed, transmission in a visible wavelength range can be suppressed, and the ND filter which can reduce the transmitted light amount in a near-infrared wavelength range. Further, it is possible to realize a light amount diaphragm device and a camera having the light amount diaphragm device.

Next, an embodiment of the present invention will be described.
FIG. 1 is a cross-sectional view showing one example of the configuration of an ND filter in the present embodiment, and FIG. 2 is a cross-sectional view showing a configuration example of an ND filter different from FIG.
1 and 2, 1 is a substrate, and 2 is an ND filter film.
Here, an infrared cut glass or a plastic infrared cut filter capable of cutting the transmission of light in the near infrared wavelength region to about 5% or less is used for the substrate 1. Moreover, the near-infrared area | region here has shown the light wavelength area | region of 700 nm-1100 nm.
Since the substrate is used as an ND filter, the substrate is not limited to obtain a high transmittance of, for example, 90% or more with respect to the transmittance in the visible wavelength region, but is higher than the minimum density specification required for the ND filter. Need to be. The minimum value of the density specification is, for example, a density of about 0.5 in a gradation ND filter in which the density gradually changes from 0.5 to 1.0, and the transmittance is about 32%. Refers to the degree.

  As shown in FIG. 1, an ND filter film is generated on a substrate such as the above-described infrared cut glass or plastic infrared cut filter by a vacuum deposition method. At this time, when the deformation of the substrate due to the internal stress of the film becomes a problem, improvement can be achieved by forming ND filter films on both surfaces of the substrate as shown in FIG. The plastic infrared cut filter described here is a resin substrate that contains high-concentration copper ions, etc., and means a filter that can sufficiently suppress transmission in the near infrared region. ing.

FIG. 3, FIG. 4 and FIG. 5 show examples of concentration distribution when an ND filter film is formed on the infrared cut filter substrate.
An ND filter film formed on an infrared cut glass or plastic infrared cut filter substrate is a single concentration film whose entire surface has a uniform transmitted light amount as shown in FIG. 3, on the same substrate as shown in FIG. Further, a multi-concentration film having several different concentrations, and a gradation concentration film in which the density sequentially changes from small to large, or from large to small, as shown in FIG.
Similarly, various appearances of the ND filter can be formed. In multi-density and gradation density, the density pattern can also be varied depending on the application and specifications.

  While the present embodiment has been described above, the present invention is not limited to these embodiments. In particular, in the above-described embodiment, the case where the vacuum deposition method is used as the method for forming the ND filter film on the infrared cut glass has been described. However, a sputtering method, a spray method, or the like can also be applied. It is. In addition, since these film-forming methods are generally known, the description is abbreviate | omitted here.

[Example 1]
As Example 1, an ND filter film was laminated on an infrared absorbing glass to produce an ND filter.
FIG. 6 shows the spectral transmittance characteristics of the infrared absorption glass used for the substrate in this example.
As shown in FIG. 6, an infrared absorbing glass having a transmittance of 5% or less in a wavelength range of about 700 nm to 1100 nm and capable of substantially cutting light transmission in the near infrared region was used for the substrate. This infrared absorbing glass has a transmittance of 50% near 610 nm, and a transmittance of from 400 nm to 600 nm is 85% or more.

FIG. 7 shows the layer structure of the ND filter film in this embodiment.
On the infrared absorbing glass substrate, an ND filter film having an 11-layer film structure as shown in FIG. 7 was formed on one side as shown in FIG. As shown in FIG. 3, the formed ND filter film was a single concentration film having a uniform transmitted light amount on the entire surface. Specifically, the film has a concentration of about 0.5, that is, a transmittance of about 32% over the entire visible wavelength range. Here, the relationship between transmission (T) and density (D) is D = −log ₁₀ T.
The vacuum deposition method was selected because the film thickness can be controlled relatively easily and the scattering is very small.

The outermost layer is a layer provided for the purpose of preventing reflection, and was formed under the condition of λ / 4 λ: 540 nm with an optical film thickness n × d (n is a refractive index, d is a mechanical film thickness).
The refractive index n of the outermost layer film was selected to be 1.5 or less in the visible wavelength range. Specifically, MgF ₂ was used.

FIG. 8 shows the spectral transmittance of the ND filter thus created.
The transmittance is about 32% in the wavelength range from 400 nm to 600 nm, the transmittance is 5% or less in the near infrared wavelength range from 700 nm to 1100 nm, and the transmittance is 1% or less particularly in the region from 700 nm to 1000 nm. An ND filter having a rate characteristic could be obtained.
As described above, in this example, even with the film configuration shown in FIG. 13 or FIG. 14, an ND filter having substantially the same transmission characteristics as the above-described ND filter film could be produced.

[Example 2]
As Example 2, an ND filter film was laminated on a plastic infrared cut filter to produce an ND filter. This embodiment will be described below.
An infrared absorption filter made of plastic having substantially the same characteristics as the infrared absorption glass shown in FIG. 6 is used as a substrate, and ND filters each having 11 layers as shown in FIG. 9 are formed on both sides of the substrate as shown in FIG. A film was formed by a vacuum evaporation method. The formed ND filter film was a single concentration film having a uniform transmitted light amount as shown in FIG. Specifically, an ND filter film having a density of about 0.5 on one side in the entire visible wavelength region and a film having a density of about 1.0 on both sides, that is, a transmittance of about 10%.
The vacuum deposition method was selected because the film thickness can be controlled relatively easily and the scattering is very small.

On both surfaces, the outermost layer is a layer provided for the purpose of preventing reflection, and was formed under the condition of λ / 4 λ: 540 nm with an optical film thickness n × d (where n is a refractive index and d is a mechanical film thickness). The refractive index n of the outermost layer film was selected to be 1.5 or less in the visible wavelength range. Specifically, MgF ₂ was used.
After the film formation from the first layer to the outermost layer as described above, heat treatment was performed in air at 110 ° C. and 1H. The reason for selecting 110 ° C. is that the effect of improving the environmental stability is insufficient if the temperature is less than 100 ° C., and if the temperature exceeds 130 ° C., problems such as thermal degradation of the base material and cracks in the film occur. is there. Under the conditions of Example 2, the heat treatment temperature is suitably between 110 ° C and 130 ° C.

In order to investigate environmental stability, the plastic ND filter was subjected to a standing test at 60 ° C., 85%, 240 hours, and the transmittance before and after the test was measured. As a result, the difference was almost 0.2% or less. . As a reference, when the same environmental test was performed on the sample without heat treatment, and the transmittance before and after the test was measured, it increased by about 2%.
In general, when a glass substrate is used, the substrate temperature is 200 ° C. to 250 ° C., preferably about 300 ° C. for film formation. However, when the substrate is plastic as in this embodiment, it is necessary to form the film at a temperature at which the substrate does not cause thermal shrinkage, and the substrate temperature is limited to less than 150 ° C.

The spectral transmittance of the ND filter thus created is shown in FIG.
The transmittance is about 10% in the wavelength region of 400 nm to 600 nm, the transmittance is 5% or less in the near infrared wavelength region of 700 nm to 1100 nm, and the transmission of 1% or less particularly in the region of 700 nm to 1000 nm. An ND filter having a rate characteristic could be obtained.
As described above, in this example, even with the film configuration shown in FIG. 15 or FIG. 16, an ND filter having substantially the same transmission characteristics as the above-described ND filter film could be produced.

[Example 3]
As Example 3, an ND filter film having a gradation density distribution was laminated on a plastic infrared cut filter to produce an ND filter.
An infrared absorption filter made of plastic having substantially the same characteristics as the infrared absorption glass shown in FIG. 6 is used as a substrate, and ND filters each having 11 layers as shown in FIG. 9 are formed on both sides of the substrate as shown in FIG. A film was formed by a vacuum evaporation method. The formed ND filter film was a gradation density film in which the density gradually changed from small to large or from large to small as shown in FIG. Specifically, the film has a concentration that gradually changes from about 0.2 to about 1.0, that is, from about 63% to about 10%.
The vacuum deposition method was selected because the film thickness can be controlled relatively easily and the scattering is very small.

As described above, after forming the film from the first layer to the front of the outermost layer, the outermost layer has a constant film thickness with no concentration gradient on both surfaces, specifically, the optical film thickness nxd (n is the refractive index, d is the refractive index) The film thickness was λ / 4 λ: 540 nm. Here, the film thickness shape of the outermost layer can be variously configured depending on the required specifications such as a concentration gradient up to the front of the outermost layer and a reverse taper shape.
For both surfaces, the outermost layer was a layer provided for the purpose of preventing reflection, and a layer having a refractive index n of 1.5 or less in the visible wavelength range was selected. Specifically, MgF ₂ was used. As described above, after both layers of the substrate were formed from the first layer to the outermost layer, heat treatment was performed in air at 110 ° C. for 1 hour.

FIG. 11 shows the relationship between the position on the substrate and the transmittance of the ND filter thus created, and FIG. 12 shows the spectral transmittance. X1, X2, and X3 in FIGS. 11 and 12 correspond to each other.
Accordingly, in the wavelength range from 400 nm to 600 nm, X1 is about 63%, X2 is about 31%, and X3 is about 10%. In the near infrared wavelength range from 700 nm to 1100 nm, X1, X2 , X3 has a transmittance of 5% or less, and an ND filter having a transmittance characteristic of 1% or less can be obtained particularly in the region of 700 nm to 1000 nm.
As described above, in this example, even with the film configuration shown in FIG. 15 or FIG. 16, an ND filter having substantially the same transmission characteristics as the above-described ND filter film could be produced.

Sectional drawing which shows one of the structural examples of ND filter in embodiment of this invention. Sectional drawing which shows another structural example of ND filter in embodiment of this invention. The figure which shows the density distribution example of the single density | concentration ND filter in embodiment of this invention. The figure which shows the density distribution example of the multi-density ND filter in embodiment of this invention. The figure which shows the density distribution example of the gradation ND filter in embodiment of this invention. The figure which shows the spectral transmittance characteristic of the infrared rays absorption glass used for the board | substrate in Example 1 of this invention. The figure which shows the layer structure of the ND filter film | membrane in Example 1 of this invention. The figure which shows the spectral transmittance characteristic of the ND filter in Example 1 of this invention. The figure which shows the layer structure of the ND filter film | membrane in Example 2 of this invention. The figure which shows the spectral transmittance characteristic of the ND filter in Example 2 of this invention. The figure which shows the transmittance | permeability characteristic of the ND filter in Example 3 of this invention. The figure which shows the spectral transmittance characteristic of the ND filter in Example 3 of this invention. The figure which shows the layer structure of the ND filter film | membrane in Example 1 of this invention. The figure which shows the layer structure of the ND filter film | membrane in Example 1 of this invention. The figure which shows the layer structure of the ND filter film | membrane in Example 2 and Example 3 of this invention. The figure which shows the layer structure of the ND filter film | membrane in Example 2 and Example 3 of this invention.

Explanation of symbols

1: Substrate 2: ND filter film

Claims (11)

For light in the near-infrared wavelength region, on a substrate with low transmission characteristics compared to the visible wavelength region,
An ND filter comprising a thin film having a characteristic of attenuating transmission in the visible range.   The ND filter according to claim 1, wherein the substrate is an infrared cut glass or a resin infrared cut filter.   The ND filter according to claim 1, wherein the substrate has a light transmittance of about 5% or less with respect to light in the near-infrared wavelength region.   The ND filter according to any one of claims 1 to 3, wherein the thin film is a thin film having a density distribution of single density, multiple density, or gradation.   The ND filter according to claim 1, wherein the thin film is formed on one side or both sides of the substrate.   5. The ND filter according to claim 4, wherein the single-concentration thin film is formed on one surface of the substrate, and the light transmittance in the visible wavelength region of the thin film is about 32%.   5. The ND filter according to claim 4, wherein the single-concentration thin film is formed on both surfaces of the substrate, and light transmittance in the visible wavelength region of the thin film is about 10%.   The thin film having the gradation density distribution is formed on both surfaces of the substrate, and the light transmittance in the visible wavelength region of the thin film sequentially changes from about 10% to about 63% according to the gradation density distribution. The ND filter according to claim 4, wherein   9. The ND filter according to claim 8, wherein the thin film having the gradation density distribution has an outermost layer having a constant film thickness, or an inversely tapered shape with a density gradient before the outermost layer. 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 ND filter is constituted by the ND filter according to claim 1.   11. A camera comprising: an optical system; a light quantity diaphragm device according to claim 10 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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