JP2007225735A - Nd filter, light quantity control device using the same and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ND filter capable of suppressing surface reflection, at the same time, suppressing transmission light quantity from visible light up to infrared light and making a device small in size and light in weight, to provide a light quantity control device using the ND filter and to provide an imaging apparatus comprising the light quantity control device. <P>SOLUTION: The ND filter of controlling transmission light quantity is constituted so that ND filter films 12, 14 that absorbs visible light are formed on both surface sides of a transparent substrate 11 and an infrared ray attenuating film 13 is formed on the lower surface of the ND filter 12 on either one surface side of the substrate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ND filter, a light quantity stop device using the ND filter, and an imaging device. In particular, the present invention relates to an ND filter suitable for use in a photographing system such as a video camera or a still video camera.

The light amount diaphragm is provided to control the amount of light incident on an image pickup device such as a silver salt film or a CCD or CMOS sensor, and has a structure in which the light field is further reduced as the object field becomes brighter.
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.
Conventionally, as a countermeasure, for example, a device as shown in FIG. 8 has been devised.
In other words, a ND (Neutral Density) filter 101 is attached to the diaphragm blade 102 so as to increase the aperture of the diaphragm even if the brightness of the object field is the same (for example, see Patent Document 1). .
In particular, an image pickup device such as a CCD or CMOS sensor has high sensitivity to infrared light, so that an image captured by the camera becomes reddish.
Therefore, for example, in Patent Document 2, a proposal has been made in which a coating for attenuating infrared rays is provided on a protective glass of a lens or an image sensor.

On the other hand, with the progress of miniaturization of the imaging device, the above-described filters are also required to be thinner and smaller.
For example, in a video camera or the like equipped with a galvanometer type diaphragm device, a diaphragm device having a structure in which an ND filter is attached to a diaphragm blade is known in order to widen the control range of the amount of transmitted light. It is becoming difficult to deal with some of them.
That is, even in such a diaphragm device, as the image pickup device is further downsized, a device having a relatively small driving torque is used, and it is a resin-based ND that is light and not heavy and not easily broken like glass. A filter has been put into practical use (for example, see Patent Document 3).
In addition, video cameras, digital cameras, and the like are used such that an infrared cut filter is driven in front of an image sensor (see, for example, Patent Document 4 and Patent Document 5).
Further, unlike the sensitivity of the human eye that does not sense light having a wavelength longer than 700 nm, the solid-state imaging device has a sensitivity of the imaging device up to a wavelength of about 1100 nm in the infrared region.
For this reason, an infrared cut filter is used in order to prevent the image from being imaged differently from unnecessary light due to unnecessary light.
The following types of known infrared cut filters used in the optical system of such an imaging apparatus are known.
That is, the infrared absorption glass type in which the transmittance characteristic changes depending on the thickness and the amount of the absorbent and the multilayer coating type in which the transmittance characteristic changes by alternately laminating two or more kinds of thin films having different refractive indexes. There is something.
Patent registration No. 2592949 Japanese Patent Laid-Open No. 5-110938 JP-A-10-133253 Japanese Patent Laid-Open No. 11-95092 JP 2002-16838 A

By the way, as described above, the downsizing of the image pickup apparatus proceeds, and in order to reduce the size of the optical system, it is necessary to bring the lens, the image pickup element, the filter, and the like as close as possible.
Therefore, in order to cut infrared rays, those using infrared absorbing glass, or those in which a glass substrate is provided with a coating that attenuates infrared rays have a thickness of glass itself and are difficult to downsize.

On the other hand, a filter having a flat spectral transmittance characteristic in visible light can be manufactured by a vapor deposition method.
However, an ND filter used at the time of photographing in the daytime or a bright place needs to have a high optical density. However, it is difficult to form such an ND filter so as to obtain a desired transmittance.
That is, in order to obtain such an ND filter, it is extremely difficult to accurately control and form an ND filter having a low light transmittance even if it is manufactured using an optical film thickness control device.
In such a case, it is necessary to configure the ND filter and the infrared light cut filter independently of each other, and the glass type infrared cut filter is driven separately to secure a space for taking in and out in the optical path. Then, it becomes difficult to reduce the size of the optical system.
In addition, when a plurality of ND filters are stacked, the density can be increased. However, not only the drive space by the separate drive as described above is increased, but also it becomes heavier due to the bonding, which conflicts with downsizing and weight reduction. It will be.

  In view of the above-described problems, the present invention can suppress surface reflection and the amount of transmitted light from visible light to infrared light, and can be reduced in size and weight, and the ND filter. An object of the present invention is to provide a light quantity diaphragm device and an imaging device using a filter.

In order to achieve the above object, the present invention provides a light quantity stop device and an imaging device using an ND filter configured as follows.
The ND filter of the present invention is an ND filter that adjusts the amount of transmitted light,
An ND filter film that absorbs visible light and an infrared attenuation film that absorbs or reflects infrared light and attenuates are formed on the transparent substrate.
In the ND filter of the present invention, the transparent substrate is a plastic substrate.
In the ND filter of the present invention, the ND filter film is formed on both sides of the substrate, and an infrared attenuation film is formed on the lower surface of the ND filter film on one side of the substrate. It is characterized by.
In addition, the ND filter of the present invention is characterized in that the ND filter film on at least one surface side of the substrate on which the ND filter film is formed has a region portion where no film that absorbs visible light exists.
The ND filter according to the present invention is characterized in that the ND filter film is composed of a multilayer film in which a dielectric film and a metal oxide film are laminated.
In the ND filter according to the present invention, the multilayer ND filter film has a visible light wavelength of 400 to 700 nm having a transmittance of 50% or less and an infrared light transmittance lower than that of visible light. It is said.
The ND filter according to the present invention is characterized in that the ND filter film has a density distribution by any one of a single density, a continuous density change, and a multistage density change.
The ND filter of the present invention is characterized in that the reflectance of the surface facing the image sensor is 3% or less in the visible light region.
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 aperture, and an ND filter disposed at least in a part of the aperture formed by the diaphragm blades. In a light quantity diaphragm device having
The ND filter is configured by any of the ND filters described above.
The image pickup apparatus of the present invention includes an image pickup element and the light amount diaphragm device.

According to the present invention, it is possible to suppress surface reflection and to suppress the amount of transmitted light from visible light to infrared light, and to reduce the size and weight.
In particular, according to the present invention, it is possible to reduce the occurrence of ghost, flare and the like due to visible light and infrared light.

Next, an embodiment of the present invention will be described.
In the embodiment of the present invention, when producing the ND filter having the above-described configuration, specifically, a film that attenuates the amount of light is coated on both surfaces of the plastic substrate, and the wavelength from the visible light to the infrared wavelength region is coated. Thus, an ND filter having a wide adjustment range of the amount of transmitted light can be obtained.
In the present embodiment, cellulose acetate, PET (polyethylene terephthalate), PEN, PC, or the like can be used as the plastic substrate.
On both sides of such a plastic substrate, a dielectric film and a metal oxide film are laminated, and an ND filter film having the function of attenuating visible light and limiting the amount of transmitted light is coated, as well as a film that attenuates infrared rays. Thus, an ND filter configured as described above can be obtained.
Here, the infrared attenuating film may be either an absorption type or a reflection type, but when it is provided on the image sensor side, it is preferably an absorption type in order to suppress multiple reflection.
In addition, an ND filter film having a flat spectral transmittance characteristic in visible light can be manufactured by an evaporation method.

Conventionally, an ND filter used for photographing in the daytime or in a bright place needs to have a high optical density. When producing an ND filter, an ND filter having a low light transmittance is used with an optical film thickness control device. Thus, it was difficult to perform control film formation.
Further, conventionally, an infrared cut filter used for an optical system of an image pickup apparatus is known as an infrared absorption glass type whose transmittance characteristics change depending on the thickness and the amount of an absorbent. The glass itself is thick and difficult to downsize.
However, according to the present embodiment described above, it can be easily manufactured and downsizing can be achieved.
That is, according to the present embodiment described above, the adjustment range can be widened toward the high density side of the transmitted light amount by coating the both surfaces of the plastic substrate with the film that attenuates the light amount.
This makes it possible to easily manufacture V-shaped and arc-shaped shapes that are difficult with glass because the plastic substrate has excellent workability and flexibility of the outer shape, and can be miniaturized. Can do.
In addition, according to the present embodiment, since it is possible to produce a filter with a high density, there is no influence of hunting phenomenon or light diffraction caused by a small stop in a clear day or in a high-luminance field, and Degradation can be eliminated.
In addition, by arranging films that attenuate visible light on both sides of the substrate, the reflectance of the filter can be kept low, so that the occurrence of flare and ghost can be reduced.
Further, according to the configuration of the ND filter of the present embodiment in which the ND filter and the infrared cut filter are provided on the same filter, image degradation due to a small aperture state can be avoided not only in the daytime or in a bright place, but also at night. There is no problem in shooting in the dark.
That is, the dark filter is not necessary when photographing at night or in a dark place and is removed from the optical path. At the same time, the infrared cut filter is also removed, so there is no problem in photographing at night or in a dark place.
In addition, when the ND filter of the present embodiment is applied to the imaging apparatus, an ND filter and an infrared cut filter can be formed on the diaphragm blades, so that the size of the imaging apparatus can be reduced by reducing the number of parts and saving space. And cost reduction.

Examples of the present invention will be described below.
[Example 1]
In the first embodiment, a configuration example in the case where a single concentration ND filter film is used will be described.
First, a configuration example of an optical system of an imaging apparatus having an ND filter in this embodiment will be described with reference to FIG.
In FIG. 1, 6A, 6B, 6C and 6D are lenses constituting the photographing optical system 6, 7 is a solid-state image sensor, and 5 is a low-pass filter.
Further, 1 is an ND filter, 2 and 3 are diaphragm blades that move oppositely, 4 is a diaphragm blade support plate, and the diaphragm device of this embodiment is constituted by these.
The ND filter 1 of this embodiment is bonded to the diaphragm blade 2, and a substantially diamond-shaped opening is formed by the two diaphragm blades 2 and 3.
In the ND filter 1, a filter film having an infrared cut filter function for cutting infrared light and a filter film having an ND filter function for reducing visible light transmittance are integrally formed by coating means. .
Depending on the brightness of the object field, the diaphragm blades 2 and 3 to which the ND filter is bonded open and close the aperture to limit the amount of light incident on the image sensor.
Examples of a method for forming such an ND filter include a vapor deposition method, a sputtering method, an ink jet printing method, and a spray method.
Among these, the vacuum deposition method is selected here because the film thickness can be controlled relatively easily and the scattering is very small in the visible wavelength region.

Next, a specific configuration of the ND filter in this embodiment will be described. FIG. 2 shows a schematic cross-sectional view of the ND filter of this embodiment.
In FIG. 2, reference numeral 10 denotes an ND filter. The ND filter 10 includes a substrate 11, ND filter films 12 and 14 provided on both surfaces of the substrate, and an infrared cut filter film provided on the lower surface of the one ND filter film 12. 13.
The material of the plastic base material is not particularly limited, but it is desirable that the plastic base material has high transparency in the visible wavelength range (low haze value) and low water absorption. Here, a PET substrate having a thickness of 75 μm was used.

The ND filter is for obtaining a desired transmittance, and it is desirable that the transmittance is constant in the visible light region.
Since thin film ND filters with deposited metal have 9 to 13 layers, all metal films made of Ti, Cr, or Ni are extremely thin films with a thickness of 10 nm or less, making it difficult to control film thickness and reproducibility. Good flat spectral characteristics cannot be obtained.
In addition, the interference type filter is preferably a light absorption type filter because stray light is generated in the optical path and the image is deteriorated.
Here, a multilayer film deposition filter using a titanium oxide such as TiO or Ti ₂ O ₃ was formed to constitute the ND filter.
The concentration of the ND filter can be changed by the film thickness of the titanium oxide. However, when the light transmittance is lowered, it becomes difficult to control to a predetermined optical density using an optical film thickness controller.
Therefore, in this embodiment, an ND filter film is provided on both sides of the substrate, and either side is coated with an infrared cut filter that cuts infrared light.
That is, this made it possible to produce an ND filter having a lower light transmittance than when an ND filter film was provided on one side.

Next, the spectral characteristics of the ND filter of this embodiment will be described.
FIG. 3 shows the spectral characteristics of the ND filter of this example.
The ND filter film of this example is shown by a one-dot chain line in FIG. 3 in the case where light transmittance is suppressed and surface reflection is suppressed with respect to light in a visible light region, that is, a wavelength region from approximately 400 nm to approximately 700 nm. As shown, it has a spectral characteristic of a transmittance of 50% or less.
Here, assuming that the outermost surfaces of both surfaces of the filter are ND filter films with a transmittance of 50%, a filter with a transmittance of 25% is obtained as shown by the dotted line in FIG.
Furthermore, by providing an infrared cut filter, the transmittance of infrared light can be lowered as shown by the solid line in FIG.
In the ND filter of the present embodiment, the surface reflectance is 3% or less with respect to light in the wavelength region of about 400 nm to about 1000 nm by configuring the ND filter surface with the absorption-type vapor deposition ND filter film. A filter can be manufactured.
Here, the infrared cut filter is for cutting infrared light of 700 nm or more, and is formed by laminating using a transparent oxide such as TiO ₂ , ZrO ₂ , ITO, SiO ₂ , The present invention is not particularly limited to this.
For example, inorganic and organic materials having infrared absorbing ability may be coated.
Further, when vapor deposition is performed on a plastic substrate, a tensile or compressive stress is generated between the substrate and the vapor deposition multilayer film according to the type of the vapor deposited material, and curling occurs in which the substrate is bent either on the front or back.
However, curling can also be suppressed by dividing the light attenuation amount of the ND filter film into the front and back sides and adjusting the balance of stresses between the front and back sides of the substrate.
Therefore, according to the present embodiment, it is possible to obtain a filter with good flatness that has less reflection on the filter surface and can effectively prevent the occurrence of ghosts and flares due to reflected light and infrared light.

[Example 2]
In the second embodiment, a configuration example in the case of using an ND filter film having a concentration distribution due to a continuous concentration change or a multistage concentration change will be described.
FIG. 4 shows the configuration of the ND filter in this embodiment.
In FIG. 4, reference numeral 20 denotes an ND filter. The ND filter 20 includes a substrate 21, ND filter films 22 and 24 provided on both surfaces of the substrate, and an infrared cut filter film provided on the lower surface of the one ND filter film 22. 23.
FIG. 5 shows a configuration in which the ND filter 31 thus configured is attached to the diaphragm blade 32.

As this ND filter, a filter in which the concentration distribution is continuously changed as shown in FIG. 6 (a) may be used, or a filter which is changed in multiple steps as shown in FIG. 6 (b). May be used.
When the brightness of the object field is bright and the aperture of the aperture must be reduced, inserting a dark ND filter to increase the aperture diameter of the aperture even if the amount of light is the same will increase the aperture of the aperture and degrade the image. It is possible to avoid a small aperture state without inviting.
When the ND filter 31 having such characteristics is provided on the diaphragm blade 32 as shown in FIG. 5 and mounted on an imaging device having sensitivity in the infrared light region, even if the amount of light is changed depending on the position where the filter is used. Harmful infrared light can be attenuated. As a result, it is possible to effectively prevent the occurrence of ghosts and flares.

[Example 3]
In the third embodiment, a configuration example of an ND filter having a different form from the above embodiments will be described.
FIG. 7 shows the configuration of the ND filter of this embodiment.
In FIG. 7, reference numeral 40 denotes an ND filter. The ND filter 40 includes a substrate 41, ND filter films 42 and 44 provided on both surfaces of the substrate, and an infrared cut filter film provided on the lower surface of the one ND filter film 42. 43.
At this time, in this embodiment, the ND filter 40 is provided with an infrared cut filter region without the ND filter films 42 and 44.
By providing the infrared cut filter region without the ND filter films 42 and 44 in this way, even when the open aperture value of the image pickup apparatus is used in the open state, when it is desired to attenuate harmful infrared light, it is large enough to cover the aperture diameter. Can be adapted to
Even when the amount of light is not reduced, the infrared light is cut and the amount of incident light is changed by the ND filter in accordance with the amount of incident light.
In this case, if the ND filter films 42 and 44 are spectral transmittance characteristics ND filter films having a continuous density change, it is desirable that the density change is not steep even when the aperture is gradually narrowed from the open stop.
In this embodiment, the infrared region has a wavelength of about 700 nm or more, preferably about 700 nm to 1000 nm. However, the wavelength region of the infrared region may be more or less, and is not limited.

As described above, according to the ND filter of each of the above embodiments, the reflectance of the surface of the filter can be suppressed to about 3% or less by disposing the ND filter film on both surfaces of the substrate. The occurrence of flare and the like can be reduced.
Furthermore, the structure provided with the infrared cut filter film can reduce the occurrence of ghosts, flares and the like due to infrared light.
Thereby, size reduction and price reduction of an imaging device are realizable.

1 is a diagram illustrating a configuration example of an optical system of an imaging apparatus having an ND filter in Embodiment 1 of the present invention. 1 is a schematic cross-sectional view showing a configuration of an ND filter in Embodiment 1 of the present invention. FIG. 3 is a diagram illustrating spectral characteristics of an ND filter according to Embodiment 1 of the present invention. The schematic sectional drawing which shows the structure by the ND filter film | membrane which has density distribution by the continuous density change in Example 2 of this invention or multistage density | concentration change. The figure which shows the structure by which the ND filter in Example 2 of this invention was adhere | attached on the aperture blade. It is a figure which shows the distance-concentration characteristic of ND filter in Example 2 of this invention, (a) was made to change in multiple steps, (a) when changing density distribution continuously. The figure explaining a case. It is a schematic sectional drawing which shows the ND filter in Example 3 of this invention. The figure explaining the imaging optical system which uses the ND filter in a prior art example.

Explanation of symbols

1: ND filter 2, 3: diaphragm blade 4: diaphragm blade support plate 5: low-pass filters 6A, 6B, 6C, 6D: lens 7 constituting imaging optical system 6: solid-state imaging device 10: ND filter 11: substrate 12: ND filter film 13: Infrared cut filter film (infrared attenuating film)
14: ND filter film 20: ND filter 21: Substrate 22: ND filter film 23: Infrared cut filter film (infrared attenuating film)
24: ND filter film 31: ND filter 32: Diaphragm blade 40: ND filter 41: Substrate 42: ND filter film 43: Infrared cut filter film (infrared attenuating film)
44: ND filter film 45: Aperture blade

Claims (10)

An ND filter that adjusts the amount of transmitted light,
An ND filter, wherein an ND filter film that absorbs visible light and an infrared attenuation film that absorbs or reflects infrared light and attenuates are formed on a transparent substrate.   The ND filter according to claim 1, wherein the transparent substrate is a plastic substrate.   The ND filter film is formed on both surfaces of the substrate, and an infrared attenuation film is formed on the lower surface of the ND filter film on one surface side of the substrate. Item 3. The ND filter according to Item 2.   4. The ND filter according to claim 3, wherein the ND filter film on at least one surface side of the substrate on which the ND filter film is formed has a region portion in which a film that absorbs visible light does not exist.   5. The ND filter according to claim 1, wherein the ND filter film is formed of a multilayer film in which a dielectric film and a metal oxide film are laminated.   6. The ND filter according to claim 5, wherein the ND filter film using the multilayer film has a visible light wavelength of 400 to 700 nm having a transmittance of 50% or less and an infrared light transmittance lower than that of visible light. filter.   The ND filter according to claim 5 or 6, wherein the ND filter film has a concentration distribution according to any one of a single concentration, a continuous concentration change, and a multistage concentration change.   8. The ND filter according to claim 1, wherein a reflectance of a surface facing the image sensor is 3% or less in a visible light region. In a light quantity diaphragm apparatus having a plurality of diaphragm blades that are relatively driven to change the size of the diaphragm aperture, and an ND filter disposed in at least a part of the aperture formed by the diaphragm blades,
9. The light quantity stop device, wherein the ND filter is configured by the ND filter according to claim 1.   An image pickup apparatus comprising: an image pickup element; and the light quantity diaphragm device according to claim 9.

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