JP2007065109A - Nd filter, light quantity reducing device and camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ND filter, capable of reducing transmission and reflection of harmful light generated on an ND filter edge surface part and suppressing the degradation of resolution due to flare or else, to provide a light quantity reducing device having the ND filter, and to provide a camera that has the light quantity diaphragm device. <P>SOLUTION: The ND filter 1 for controlling the quantity of light is has such a constitution that a coated film having light absorptive properties and anti-reflection properties of light is formed on the edge surface 1e of the ND filter 1. The coated film can be formed on the edge surface of the ND filter according to coating material application or a deposition method. The constitution thus described can be applied to the ND filter, having a continuous or stepwise density distribution for controlling the quantity of light. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ND (Neutral Density) filter, a light amount diaphragm device having the ND filter, and a camera. In particular, the present invention relates to an ND filter suitable for use in an imaging system such as a video camera or a still video camera, and a light amount diaphragm apparatus using the ND filter.

A conventional digital video camera having a photographing optical system as shown in FIG. 11 is known.
In FIG. 11, L1, L2, L3 and L4 are component lenses constituting the imaging optical system 16, 14 is a low-pass filter, and 15 is a solid-state imaging device such as a CCD.
Reference numerals 11 to 13 denote a light quantity diaphragm, 11 is an ND (Neutral Density) filter, 12a and 12b are diaphragm blades, and one ND filter 11 is bonded to the diaphragm blade 12a. Reference numeral 13 denotes a diaphragm blade support plate.

In such a light quantity diaphragm device (light quantity adjusting device), the passing light quantity is adjusted by changing the aperture diameter by a pair of diaphragm blades that open and close on the diaphragm blade support plate. This light amount diaphragm device is provided to control the amount of light incident on a solid-state imaging device such as a CCD, and is further narrowed down when the object field is bright. Therefore, when the subject is photographed in fine weather or with high brightness, the aperture becomes a small aperture, which is easily affected by light diffraction by the aperture, and image performance deteriorates.
As a countermeasure against this, for example, a device has been devised in which the aperture of the aperture is increased even if a film-like ND filter is attached to the aperture blade and the brightness of the object field is the same. This ND filter functions to prevent the aperture from becoming extremely small even during high-intensity shooting by reducing the amount of light by being positioned in the optical path when the aperture is reduced.

By the way, in recent years, as the sensitivity of the imaging device is improved, the density of the ND filter is increased to further reduce the light transmittance, so that the aperture of the diaphragm is increased even if the brightness of the object field is the same. It has become to.
However, when the density of the ND filter is increased in this way, as shown in FIG. 11, the light amount difference between the light “a” that has passed through the film and the light “b” that has not passed through differs greatly, and a “shading” phenomenon occurs in which the brightness varies within the screen. Or the resolution is reduced.
As means for solving such a problem, for example, as is known in Patent Document 1, the ND filter density is devised such that the transmittance gradually increases toward the center of the optical axis. Has been made. Further, for example, a structure in which the transmittance of the ND filter density continuously increases toward the center of the optical axis as in Patent Document 2 is used.

However, even if it is possible to suppress the aperture from becoming extremely small by disposing the ND filter in the aperture opening with the above-described configuration, there is a problem that image performance is deteriorated due to another phenomenon.
That is, as shown in FIG. 12, unnecessary light is generated when light reaching the end face of the ND filter forming a part of the aperture of the diaphragm enters from the end face or unnecessary on the end face. Reflection will occur. Therefore, there arises a problem that flare is generated due to the transmission and reflection of unnecessary light generated at these end portions and the resolution is lowered.

Therefore, various countermeasures have been proposed in order to suppress ghosts caused by unnecessary reflection and unnecessary transmission on the end face of the ND filter.
For example, in Patent Document 3, an inclined surface is provided on the opening end surface of the ND filter, and the generation of flare is suppressed by setting the inclined surface not parallel to the optical axis. In Patent Document 4, an ND filter is disposed on each of the two diaphragm blades, and the shape of the aperture opening formed by the end of each optical filter and the notch portion of each diaphragm blade passes through the optical axis. The configuration is asymmetric with respect to a straight line perpendicular to the moving direction. Thereby, the influence of flare is dispersed and kept small.
Japanese Patent No. 02592949 JP 2004-061899 A JP 2004-138865 A JP 2004-012479 A

However, the above-mentioned conventional example of Patent Document 3 has the following problems. That is, since the inclined surface at the end of the ND filter is inclined toward the solid-state image sensor side, the light beam reflected by the light incident surface of the solid-state image sensor is incident on the inclined surface at the end of the ND filter and re-reflected. . When the re-reflected light beam is incident on the solid-state image sensor again, a ghost is generated.
Also in the structure of Patent Document 4, there are two ND filter end faces in the opening, and unnecessary transmission and reflection of light that occurs when light enters these ND filter ends are completely suppressed. It is difficult. Accordingly, there remains a problem that flare occurs and the resolving power decreases. In particular, in the case of adopting a structure in which the transmittance of the ND filter described above gradually increases toward the center of the optical axis, the transmittance of the ND filter near the center of the optical axis is high.
Therefore, not only unnecessary reflection on the surface of the end of the ND filter as shown in FIG. 12, but the transmittance of light incident from the end surface of the ND filter is increased, so that unnecessary light reaches the imaging surface as flare. It will be easy to do.
In addition, as shown in FIG. 13, even if the light is incident from the surface of the ND filter, the light that has passed through the inside of the ND filter reaches the image plane as unnecessary reflection and transmission on the inner end face, resulting in degradation of image quality. It will be.

  In view of the above-described problems, the present invention provides an ND filter, a light amount diaphragm device, and a camera that can reduce the transmission and reflection of harmful light generated at the end face of the ND filter and suppress a decrease in resolution due to flare and the like. It is intended to provide.

In order to solve the above problems, the present invention provides an ND filter, a light quantity diaphragm device, and a camera configured as follows.
That is, the ND filter of the present invention is an ND filter that adjusts the amount of light, and is characterized in that a film having light absorption and antireflection properties is formed on the end face of the ND filter. .
In the present invention, the coating film can be formed on the end face of the ND filter by applying a paint or by vapor deposition. Further, the present invention can be applied to an ND filter having a continuous or stepwise density distribution in order to adjust the amount of light.
According to the present invention, there is provided a diaphragm blade having an aperture blade for forming an aperture, and an ND filter that is attached to the diaphragm blade and adjusts an amount of light passing through the aperture. It is characterized by comprising an ND filter. That is, the ND filter of the present invention described above is provided as the ND filter, and an end face of the ND filter on which the coating is formed is arranged facing an opening formed by the diaphragm blades.
In addition, the light amount diaphragm device of the present invention includes 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. Yes.

  According to the present invention, it is possible to realize an ND filter, a light amount diaphragm device, and a camera that can reduce the transmission and reflection of harmful light generated at the end face of the ND filter and can suppress a decrease in resolution due to flare and the like. Can do.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a side sectional view of a configuration example of a light quantity diaphragm device in the present embodiment.
In FIG. 1, 1 is an ND filter, 2a and 2b are aperture blades.
As shown in FIG. 1, the light quantity diaphragm device of this embodiment includes two diaphragm blades 2a and 2b, and the diaphragm blades reciprocate on a plane perpendicular to the optical axis in accordance with the amount of incident light. Thus, the size of the aperture opening is changed.
The two diaphragm blades 2a and 2b are close to each other when the object scene is bright, and have a small aperture, so that the amount of passing light is reduced, and when the object field is dark, they are separated from each other to increase the amount of passing light. It has become.

An ND filter 1 is attached to the diaphragm blade 2a.
FIG. 3 is a perspective view of the diaphragm blade 2a in which the ND filter 1 is disposed.
As shown in FIG. 3, the ND filter 1 is bonded to the blade so as to cover the concave notch of the diaphragm blade 2a.
The end 1e of the ND filter 1 bonded to the diaphragm blades forms a part of the outer peripheral part that determines the size of the diaphragm opening.
In the light quantity diaphragm device according to the present embodiment, a light-absorbing and anti-reflection film is formed on the end 1e of the ND filter facing the aperture of the diaphragm aperture.
Therefore, as shown in FIG. 1, among the incident light entering from the front (left side of the drawing), most of the light incident on the end face of the ND filter is a light-absorbing and anti-reflective coating formed on the end face. Is absorbed by. In addition, the light reflected on the coating is reduced as much as possible for the antireflection effect of the coating.
Further, as shown in FIG. 2, most of the light incident from the ND filter surface and entering the inner end face is also absorbed by the light-absorbing and anti-reflective coating formed on the end face. . As a result, most of the light that reaches the end face is prevented from entering rearward (right side of the drawing), so that flare does not occur substantially.

The coating formed on the end of the ND filter facing the opening must be a coating having both light absorption and antireflection properties.
As the material for forming the film, it is preferable to use an acrylic or urethane phenolic resin containing acrylic resin fine particles, styrene resin fine particles, inorganic filler, or the like as an antireflection agent. In that case, acrylic type and urethane type phenol resin can be made to contain crosslinking agents, such as a urea resin and a melamine resin, as needed. Further, a coating material in which a substance such as a black pigment such as carbon black having a light absorbing function is appropriately mixed is formed. By applying the coating material thus obtained to the end portion 1e of the ND filter facing the opening of the aperture opening, a film having light absorption and antireflection properties is formed.
In addition, although it does not specifically limit regarding a film thickness, it is necessary for the film of the previous period to completely cover the end part surface of the ND filter facing the opening.

The formation of the coating on the end face of the ND filter facing the opening can increase the efficiency of the work by, for example, the following coating formation method.
FIG. 4 shows an example of a method for applying and producing a coating film in the present embodiment.
As shown in FIG. 4, a large number of ND filters 1 punched by a press or the like are bundled, a plurality of ND filters 1 are bundled so that the end faces are aligned, and the ND filter end faces facing the openings are collectively sprayed by a nozzle 7. To do. Thereby, when forming the said film, it becomes possible to aim at the work efficiency improvement.

On the other hand, as a method other than the method for forming a film by applying a paint as described above, a vacuum film forming method typified by a vapor deposition method can also be applied.
As one of the preferred embodiments, with respect to the number of layers and the film thickness of each layer, a light-absorbing material and a material for lowering the reflectance with respect to the end surface of the ND filter facing the above-described opening are used. The method of laminating appropriately is mentioned. Here, materials such as titanium oxide and chromium metal can be used as the light-absorbing material. A material such as Al ₂ O ₃ , SiO ₂ , or MgF ₂ can be used as a material for reducing the reflectance. As a result, a film having both light absorption and antireflection properties can be formed. In that case, it is more preferable that the laminated coating has performance as an ND filter.

Next, a method for forming a film by a vacuum film forming method typified by such a vapor deposition method will be described.
FIG. 5 shows a simplified view of the inside of a chamber in a vacuum vapor deposition machine for forming the coating film. In FIG. 5, 8 is a vapor deposition umbrella, 9 is a vapor deposition source, and 10 is a substrate jig on which an ND filter for forming a film is set.
The deposition surface on which the film is formed is a deposition umbrella such that a large number of ND filters punched by a press or the like are bundled, and a plurality of ND filters are bundled so that the end surfaces are aligned, so that the ND filter end surface to be deposited faces the evaporation source. 8 is provided. The substrate 10 is rotated together with the vapor deposition umbrella 8 around the Z axis to perform film formation.

FIG. 6 shows a cross-sectional view of a configuration example of an ND filter formed as a light-absorbing and anti-reflective coating in the present embodiment.
In FIG. 6, the second, fourth, sixth and eighth layers are TiOx films for lowering the transmittance. The transmittance varies depending on the total thickness of the three layers, and the transmittance decreases as the thickness increases.
Further, the neutrality of the transmittance within the wavelength range of 400 nm to 700 nm varies depending on the x of the TiOx film composition, and the transmittance distribution becomes neutral when appropriately selected.
A preferable numerical value of x is in a range of 0.5 or more and 2 or less, and when x = 1.2 or less, a phenomenon occurs in which the transmittance at a low wavelength is lowered with a wavelength of about 550 nm as a boundary. On the other hand, when x = 1.2 or more, it is inclined to increase the transmittance of the low wavelength. For this reason, it is preferable to make a transmittance | permeability neutral by monitoring the transmittance | permeability at the time of vapor deposition.

The first, third, fifth and seventh layers are antireflection films for reducing the reflectance, and are Al ₂ O ₃ films. By monitoring the reflectivity during vapor deposition, the reflectivity can be reduced by controlling the film thickness of Al ₂ O ₃ .
Further, MgF ₂ or SiO ₂ , which is a low refractive material, is used as the outermost layer under the film formation conditions of optical film thickness n × d (n: refractive index, d: physical film thickness) and ¼λ (λ = 500 nm to 600 nm). By vapor deposition, it is possible to further enhance the antireflection effect.

  According to the present embodiment described above, harmful transmission and reflection generated at the end face portion are formed by forming a film having light absorption and anti-reflection properties on the end face portion of the ND filter that forms the outer periphery of the opening. Can be reduced. Therefore, it is possible to suppress a decrease in resolution such as flare.

Examples of the present invention will be described below.
[Example 1]
In Example 1, an ND filter film having a nine-layer structure as shown in FIG. 7 was formed on a transparent PET film substrate having a thickness of 100 μm by a vacuum deposition method.
The formed ND filter film is a gradation density film in which the density sequentially changes from small to large from the aperture opening as shown in FIG.
The gradation portion was formed by using a mask or the like in which the hole diameter of the dot-like pattern and the distance between the hole centers as described in Patent Document 2 change stepwise or steplessly.
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%. However, MgF ₂ which is a low refractive index material for further improving the antireflection property which is the outermost layer has an optical film thickness n × d (n: refractive index, d: physical film thickness), 1 over the entire surface without using a mask. Vapor deposition was performed under a film forming condition of / 4λ (λ = 540 nm). Here, the relationship between transmission (T) and density (D) is D = −log ₁₀ T.

Next, a plurality of ND filters prepared by the above method were punched into a shape for attaching to the diaphragm blades by pressing. Furthermore, in order to efficiently form a coating on the end face of the opening of the ND filter, a plurality of ND filters punched out by a press were bundled and held so that the end faces were aligned.
After that, a black paint containing acrylic resin, carbon black, anti-reflective agent, dispersion aid, and curing agent is prepared, applied to the end face of the opening using a spray air gun, and black on the end face of the ND filter opening. A film was formed.
As described above, when an ND filter having a film having both light absorption and antireflection properties is formed on the end face of the opening, the image is evaluated by attaching the ND filter to the diaphragm blade of the light quantity diaphragm device. It became possible to suppress.

[Example 2]
In Example 2, an ND filter film having two different concentrations as shown in FIG. 9 was formed on a transparent PET film substrate having a thickness of 100 μm by a vacuum deposition method.
The formed ND filter has a low density in the region A including the aperture opening and a high density in the region B away from the aperture opening.
As a vapor deposition method, as shown in FIG. 10, first, an ND filter film having a 9-layer structure as shown in FIG.
Next, a mask is applied to the aperture opening portion A on the other surface so that the vapor deposition film does not adhere to the region B away from the aperture opening portion. An ND filter film was deposited so as to have a concentration of 0.6.
The formed ND filter had a density in the region A of about 0.4 and a density in the region B of about 1.0.

Next, a plurality of the produced ND filters were punched into a shape for attaching to the diaphragm blades by press working, and a black film was formed on the end face of the opening by the same method as in Example 1.
When the ND filter produced above was attached to the diaphragm blades of the light quantity diaphragm device and the image was evaluated, the influence of flare was reduced, and it was possible to suppress deterioration in image quality.

[Example 3]
In Example 2, the concentration as shown in FIG. 8 is changed from about 0.2 to about 1.0 by vacuum deposition on a transparent PET film substrate having a thickness of 100 μm by the same method as in Example 1. An ND filter film having a gradation density that changes sequentially was produced. A plurality of this was punched out into a shape to be attached to the aperture blade by press working.
In order to efficiently form a coating on the end face of the opening of the ND filter, a plurality of ND filters punched out by a press were bundled so that the end faces were aligned, and the end face corresponding to the opening of the ND filter was used as a vapor deposition surface.

After the prepared plurality of ND filters are set on the vapor deposition umbrella of the vapor deposition apparatus shown in FIG. 5 so that a film can be formed on the end face of the ND filter, the film configuration shown in FIG. 6 has the characteristics of the ND filter. A film was formed by a vacuum evaporation method.
The second, fourth, sixth and eighth TiOx (1 ≦ x ≦ 2) layers were formed as materials having a function of absorbing light.
In addition, the 1, 3, 5 and 7 layers are Al ₂ O ₃ , and when TiOx is laminated with an appropriate layer thickness, it has the property of reducing the reflectance in the wavelength range of 400 nm to 700 nm. Was used to form a film.
In this example, four conditions of 0.6, 1.0, 1.5, and 2.0 were prepared with respect to the coating concentration.

In order to form a coating film having a function as an ND filter as described above and further improve the antireflection property, MgF ₂ as a low refractive index material is changed to an optical film thickness n × d (n: refractive index, d: Physical film thickness) Vapor deposition was performed under a film forming condition of ¼λ (λ = 540 nm).
As described above, an ND filter in which coatings of four different concentrations were formed on the end face of the opening by vapor deposition was attached to the diaphragm blades of the light quantity diaphragm device, and the image was evaluated. The results are shown in Table 1.

  As shown in Table 1, the effect of flare cannot be sufficiently reduced under the condition of the coating concentration of 0.6, and the deterioration of the image quality is not sufficiently suppressed. On the other hand, the effect of flare is further reduced as the coating concentration increases, and the effect of flare is most reduced under the highest 2.0 conditions, and the highest effect is obtained in suppressing deterioration in image quality. I was able to.

[Example 4]
In Example 4, on the transparent PET film substrate having a thickness of 100 μm, the same ND as shown in FIG. 9 and FIG. A filter was produced. Here, two types of ND filters having different densities, in which the density of the area including the aperture opening is 0.4 and the density of the area away from the aperture opening is 1.0, were manufactured. After punching a plurality of sheets into a shape to be attached to the diaphragm blades by press working, the density of 0.6, 1.0, 1.5, 2. Four types of coatings of 0 were formed.
As described above, an ND filter in which coatings of four different concentrations were formed on the end face of the opening by vapor deposition was attached to the diaphragm blades of the light quantity diaphragm device, and the image was evaluated.
The results are shown in Table 2.

As shown in Table 2, the influence of flare cannot be sufficiently reduced under the condition of the coating concentration of 0.6, and the deterioration of the image quality is not sufficiently suppressed. On the other hand, the effect of flare is further reduced as the coating concentration increases, and the effect of flare is most reduced under the highest 2.0 conditions, and the highest effect is obtained in suppressing deterioration in image quality. did it.
As described above, by applying the light quantity diaphragm device of each embodiment to a photographing apparatus of a type that forms a subject image on a solid-state image sensor such as a video camera or a digital still camera, it is possible to realize a light quantity diaphragm apparatus with good performance.

The sectional side view which shows the structural example of the light quantity aperture device in embodiment of this invention. The sectional side view which shows the structural example of the light quantity aperture device in embodiment of this invention. The perspective view of the aperture blade which arrange | positioned the ND filter in embodiment of this invention. The schematic diagram which shows an example of the coating production method of the film in embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS The simple figure which shows the structure in the chamber in the vacuum evaporation machine explaining embodiment of this invention. Sectional drawing which shows the structural example of the ND filter in embodiment of this invention. Sectional drawing which shows the structural example of the ND filter in Example 1, 2 and 3 and 4 of this invention. The figure which shows the density distribution example of the gradation ND filter in Example 1 and 3 of this invention. The figure which shows the density distribution example of the 2 density | concentration ND filter in Example 2 and 4 of this invention. FIG. 6 is a cross-sectional configuration diagram of a two-concentration ND filter in Examples 2 and 4 of the present invention. Schematic showing the imaging optical system used for the video camera in a prior art example. The sectional side view which shows the structural example of the light quantity diaphragm | throttle device in a prior art example. The sectional side view which shows the structural example of the light quantity diaphragm | throttle device in a prior art example.

Explanation of symbols

1: ND filter 1e: end of ND filter 1 2a: diaphragm blade to which ND filter is bonded 2b: diaphragm blade

Claims (7)

  An ND filter that adjusts the amount of light, wherein an ND filter is formed with a film having light absorption and antireflection properties on an end face thereof.   The ND filter according to claim 1, wherein the coating is formed on an end face of the ND filter by applying a paint.   The ND filter according to claim 1, wherein the coating is formed on an end face of the ND filter by a vapor deposition method.   4. The coating film according to claim 1, wherein the coating film is made of a paint formed by mixing a black pigment or the like with a material containing an antireflection agent in an acrylic or urethane phenol resin. The ND filter according to item 1.   The ND filter according to claim 1, wherein the ND filter has a continuous or stepwise density distribution for adjusting the amount of light.   6. A light quantity diaphragm apparatus having a diaphragm blade for forming an opening and an ND filter attached to the diaphragm blade for adjusting the amount of light passing through the opening, wherein the ND filter is any one of claims 1 to 5. The ND filter according to the above item is provided, and an end face of the ND filter on which the film is formed is disposed so as to face an opening formed by the diaphragm blades.   A camera, comprising: an optical system; a light quantity diaphragm device according to claim 6 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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