JP2004246018A - Light quantity adjusting device and optical equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light quantity adjusting device which satisfies optical performance and improves film contact strength. <P>SOLUTION: The light quantity adjusting device which adjusts the quantity of light reaching an image plane has: a plurality of aperture blades; and an ND filter unit which is arranged in at least part of an opposite area in the stop aperture formed of those aperture blades. The ND filter unit has: a plastic substrate; a first filter part which is provided on the plastic substrate and formed of a multi-layered film attenuating the quantity of light; and a second filter part which is provided overlapping with the first filter part and formed of a multi-layered film reducing the quantity of light. The first filter part and the second filter part are provided on the surface opposite to an image-plane side of the plastic substrate. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light amount adjusting device used for an optical device such as a video camera, a digital still camera, and an interchangeable lens.
[0002]
[Prior art]
FIG. 9 shows a conventional ND filter. In FIG. 1B, reference numerals 8-1, 8-2, and 8-3 denote filter units that are attached to a deposition substrate 8-4 made of PET (polyethylene terephthalate). When the ND filter is divided into regions I to III shown in FIG. 9A, the densities of these regions are as follows.
[0003]
The density of the region I is the density of the filter unit 8-1. The density of the region II is a density obtained by adding the density of the filter unit 8-1 and the density of the filter unit 8-3. The density of the region III is a density obtained by adding the density of the filter unit 8-1, the density of the filter unit 8-2, and the density of the filter unit 8-3.
[0004]
That is, the boundary line 8-5 between the region I and the region II, the boundary line 8-6 between the region II and the region III, and the boundary line 8-7 between the region III and the exposed PET for bonding the deposition substrate 8-4. The density changes at three lines.
[0005]
Here, when the ND filter is configured with a single density, when the ND filter enters the fixed opening provided in the diaphragm device, the light passing through the ND filter and the light not passing through the ND filter are interposed. The light amount difference is increased, and the resolution is reduced.
[0006]
Therefore, as described above, the ND filter is configured to have a plurality of densities (regions I to III), and the densities are increased in order from the region close to the fixed opening, thereby reducing the light amount difference and reducing the resolution. It has been reduced.
[0007]
The above-described ND filter is attached to an aperture blade that changes the opening area of the light passage port, and is arranged such that the CCD 21 as an image sensor is located on the A side as shown in FIG. 9B. The B side is the object side.
[0008]
[Patent Document 1]
JP-A-10-096971
[Problems to be solved by the invention]
However, in the above-described configuration of the ND filter, light reflected by the CCD 21 causes increased reflection in the vicinity of the boundary line 8-6, so that a ghost image may be generated.
[0010]
When observing the vicinity of the boundary line 8-6 with a microscope, as shown in FIG. 10B, there is an inclined portion at the end of the filter portion 8-2 where the film thickness gradually decreases. The inclined portion is generated due to the floating of the mask, the elongation of the mask, and the like. Light incident on the vicinity of the boundary line 8-6 from the side A (the side of the CCD 21) is reflected by the inclined portion and the filter portion 8-. It is considered that interference occurred with 1 and increased reflection occurred.
[0011]
In particular, since the film thickness of the inclined portion is small and the light incident on the ND film of the filter portion 8-1 is not attenuated, it is considered that the reflection that goes out is higher.
[0012]
On the other hand, when light from the B side is incident, interference occurs between the inclined portion and the filter portion 8-1 in the same manner as described above. However, since the thickness of the filter portion 8-3 is large, two incident lights are generated. It is considered that the light is attenuated in the film of the filter units (8-1, 8-3) and the reflected light from the film is small.
[0013]
In the case of another boundary, it is considered that interference hardly occurs due to interference between the inclined portion of the ND and the substrate 8-4. That is, reflection is prevented by interference. This is presumably because the thickness of the substrate 8-4 is larger than the thickness of the ND, so that it is not reflection enhancement but antireflection.
[0014]
Further, the conventional example has the following problem. In the case of stacking the filter portion having a multilayer structure, since the deposition base material is made of plastic such as PET or PEN (polyethylene naphthalate), deposition at a low temperature (about 110 ° C.) is required.
[0015]
Here, the outermost layer of the filter section 8-3 is formed of a MgF2 layer, and when another layer is deposited on this MgF2 layer, there is a possibility that the filter section may be separated from the deposition surface.
[0016]
This is because the MgF2 layer deposited at a low temperature becomes a film that is weak to moisture, causing deliquescence, and the adhesion is extremely reduced. As a result, when a trapezoidal multi-concentration filter as shown in FIG. 8A is pressed from a plastic film, the film may be peeled off.
[0017]
[Means for Solving the Problems]
In order to solve the above problems, the present invention is a light amount adjusting device for adjusting the amount of light reaching an image plane, comprising a plurality of aperture blades and a plurality of aperture blades, each of which has an opposing region in an aperture opening formed by the aperture blades. An ND filter unit disposed at least in part; the ND filter unit includes: a plastic substrate; a first filter unit provided on the plastic substrate and configured by a multilayer film that attenuates a light amount; And a second filter portion made of a multilayer film that attenuates the amount of light, the first filter portion and the second filter portion being provided so as to overlap a part of the filter portion. It is provided on a surface opposite to the surface side.
[0018]
The outermost layer of the first filter portion may be made of Al2O3 or SiO2, and the portion other than the outermost layer may be made of TiOy and Al2O3 arranged alternately.
[0019]
Further, a third filter portion made of a multilayer film for attenuating the light amount may be provided on the surface of the plastic substrate opposite to the surface on which the first filter portion is provided.
[0020]
The light amount adjusting device of the present invention can be provided in an optical device such as a video camera, a digital still camera, and an interchangeable lens.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
(1st Embodiment)
The video camera according to the first embodiment of the present invention has a photographing optical system 2 as shown in FIG. The photographing optical system 2 includes, in order from the object side, a first-group lens 2A, an aperture device 1, a second-group lens 2B, a third-group lens 2C, a fourth-group lens 2D, a low-pass filter 3, and an imaging device such as a CCD or CMOS as an imaging device. The element 4 is arranged and configured.
[0022]
The aperture device 1 has an aperture base plate 1D and two aperture blades 1B and 1C. The aperture blades 1B and 1C can advance and retreat to an opening 1D ′ serving as a light passage opening formed in the aperture base plate 1D by receiving a driving force from an actuator (not shown).
[0023]
As described above, the aperture blades 1B and 1C advance and retreat into the opening 1D ', thereby changing the opening area (aperture diameter) of the light passage opening and controlling the light amount of the photographing light.
[0024]
As shown in FIG. 1, an ND filter 1A is attached to a portion corresponding to a small aperture diameter on the aperture blade 1B.
[0025]
Here, if the captured image is too bright, the aperture blades 1B and 1C move in a direction to reduce the aperture area in order to limit the light amount, but if the aperture area is made smaller than a certain size (that is, the aperture is made smaller). Light diffraction occurs and the resolution of the image is reduced.
[0026]
Therefore, in order to limit the amount of light while maintaining the aperture diameter at a predetermined value, the ND filter 1A is used to reduce the amount of light reaching the image sensor 4, thereby preventing a reduction in resolution.
[0027]
The light received by the imaging element 4 is photoelectrically converted and subjected to predetermined signal processing, and then displayed as a photographed image on a display unit (not shown) provided in a video camera or recorded on a recording medium.
[0028]
Next, the ND filter 1A of the present embodiment will be described with reference to FIG. The filter part of the ND filter 1A is of a type obtained by mixing and kneading an organic dye or pigment that absorbs light into a film-like material (cellulose acetate, PET, vinyl chloride, etc.).
[0029]
Plastic is used for the substrate 3-4 of the ND filter 1A. The reason for using plastic is that plastic is harder to break than glass, so that the diaphragm device 1 can be made thinner. As a result, the distance between the first group lens 2A and the second group lens 2B can be reduced, and higher magnification can be achieved. Is obtained.
[0030]
By using plastic, the thickness of the substrate 3-4 can be reduced to 100 μm or less, and in some cases can be reduced to 50 μm.
[0031]
FIG. 4 shows a cross section of a filter portion deposited on a surface of the plastic substrate 3-4 opposite to the image sensor 4.
[0032]
In FIG. 4, the portion I (the portion where only the filter portion 3-1 is arranged) is a low density portion, and the portion II (the portion where the filter portion 3-1 and the filter portion 3-2 overlap) is a high density portion. Department.
[0033]
The filter unit 3-1 has a multilayer structure in which Al2O3 layers and TiOy (y is an arbitrary value, for example, 1) layers are alternately arranged, and the first layer and the outermost layer in contact with the substrate 3-4 are Al2O3. It is composed of layers.
[0034]
The thickness (optical thickness) of the Al2O3 layer, which is the outermost layer, is about ４λ (λ = 550 nm). The transmittance of the TiOy layer can be changed by changing the film thickness.
[0035]
Here, the outermost layer of the filter unit 3-1 may be made of SiO2. The refractive indexes of Al2O3 and SiO2 are 1.65 and 1.46, respectively, which are close to the refractive index of air, so that they are effective as antireflection films. In addition, any material can be formed at a low temperature and has no deliquescence.
[0036]
Therefore, even when a filter section 3-2 described later is superimposed on the surface of the Al2O3 (or SiO2) layer that is the outermost layer of the filter section 3-1, film peeling that occurs when the MgF2 layer is the outermost layer is prevented. be able to.
[0037]
The filter section (second filter section) 3-2 is alternately arranged in order from the first layer in contact with the outermost layer of the filter section 3-1 to the TiOy layer and the Al2O3 layer, and the outermost layer is an MgF2 layer. . However, the first layer and the outermost layer of the filter section 3-2 may be Al2O3 layers.
[0038]
By the way, when two filters (filter parts 3-1 and 3-2) are stacked on the plastic substrate 3-4, the film thickness becomes thicker than when one filter having the same density is formed.
[0039]
This is because, when two filter units are stacked, it is required that the reflectance of the filter unit 3-1 disposed on the lower side (the side of the substrate 3-4) is low, so that the lower filter unit 3-1 is required. This is because an anti-reflection film is required in both the upper and lower filter sections 3-2.
[0040]
When the film thickness is increased, the ND filters formed by overlapping may warp. In order to solve this problem, it is necessary to lower the deposition temperature and the total film thickness.
[0041]
Here, using Al2O3 as the outermost layer can make the film thickness thinner than using MgF2. Therefore, it is preferable to use an Al2O3 layer as the outermost layer of the filter section 3-2.
[0042]
On the other hand, on the surface of the substrate 3-4 opposite to the surface on which the filter portions 3-1 and 3-2 are formed, a filter portion (third filter portion) 3-3 is formed.
[0043]
The ND filter of the present embodiment has a three-density structure shown in FIG. The method for manufacturing the ND filter is as follows.
[0044]
First, a plastic substrate 3-4 having high transparency and a thickness of 75 μm is prepared. Thereafter, the filter section 3-1 is vacuum-deposited by using the plastic substrate 3-4 as a mask.
[0045]
The cross-sectional structure of the filter section 3-1 is as shown in FIG. 4, and specifically has a structure in which the layers are superimposed in the following order.
First layer Al2O3 20 nm
Second layer TiO 5 nm
Third layer Al2O3 38 nm
4th layer TiO 8 nm
Fifth layer Al2O3 32 nm
Sixth layer TiO 12 nm
7th layer (outermost layer) Al2O3 55 nm
The filter unit 3-1 is formed by low-temperature film formation at a film formation temperature of 110 ° C. The thicknesses of the first to seventh layers are described in terms of a mechanical film thickness.
[0046]
Next, the substrate 3-4 on which the filter unit 3-1 is formed is taken out of the vacuum apparatus, and the deposition jig and the mask are changed to predetermined ones to form the filter unit 3-3.
[0047]
Here, a method of forming the filter section 3-2 before forming the filter section 3-3 is also conceivable. However, if the film is continuously formed on the same side, the film stress increases, and the plastic substrate 3-3 is formed. 4 may warp.
[0048]
Therefore, after forming the filter unit 3-3 on the surface of the plastic substrate 3-4 opposite to the surface on which the filter unit 3-1 is deposited, the filter unit 3-2 is formed and the entire plastic substrate is formed. It is necessary to balance the stress.
[0049]
The cross-sectional structure of the filter section 3-3 is as shown in FIG. 5, and specifically, has a structure in which the respective layers are overlapped in the following order.
First layer Al2O3 20 nm
Second layer TiO 13 nm
Third layer Al2O3 43 nm
4th layer TiO 4 nm
Fifth layer Al2O3 35 nm
6th layer TiO 5 nm
7th layer (outermost layer) MgF2 87 nm
[0050]
The cross-sectional structure of the filter section 3-2 is as shown in FIG. 4, and specifically, has a structure in which the respective layers are overlapped in the following order.
First layer TiO 13 nm
Second layer Al2O3 43 nm
Third layer TiO 4 nm
Fourth layer Al2O3 35 nm
Fifth layer TiO 5 nm
6th layer (outermost layer) MgF2 87 nm
[0051]
In this case, even if the first layer is made of Al2O3, almost no optical change occurs. In this embodiment, the density of each of the three filters (3-1, 3-2, 3-3) is approximately 0.5.
[0052]
FIG. 6 shows the transmittance of the region I, the region II, and the region III in FIG. As can be seen from FIG. 6, the area I has a transmittance of about 31% at a density of 0.5, the area II has a transmittance of 10% at a density of 1.0, and the area III has a transmittance of about 3.2% at a density of 1.5. The transmittance is flat at a wavelength of visible light of 400 nm to 700 nm.
[0053]
FIG. 7 shows the reflectance at that time. As shown in the figure, the reflectance is suppressed to 3% or less at a wavelength of 400 nm to 700 nm, whereby the probability of occurrence of a ghost can be reduced.
[0054]
Further, the warpage generated when the deposition process was repeated three times could be suppressed to within 0.15 mm.
[0055]
In FIG. 3A, the width of each of the regions I to III is 2 mm, and has a density portion of 6 mm in total.
[0056]
The density increases as the area shifts from the area I to the area III. It has been found that the resolution of the video camera using the aperture device having the three-density ND filter according to the present embodiment is improved by about 15% as compared with the aperture device having the one-density ND filter.
[0057]
When the ND filter of this embodiment was scratched to a 1 mm square with a cutter and a tape peeling test was performed, the phenomenon that the deposited film was peeled at the intermediate layer did not occur.
[0058]
In addition, since a boundary portion formed by overlapping the ND film on the ND film is provided on the surface (object side) of the plastic substrate 3-4 opposite to the image sensor 4 side, a ghost image is generated. Did not.
[0059]
(Modification)
The ND filter of this modification is obtained by changing the outermost layer of the filter section 3-1 of the first embodiment from Al2O3 to SiO2, and the other filter sections 3-2 and 3-3 have the first configuration. This is the same as the embodiment.
[0060]
That is, in the present modification, the film configuration of the filter unit 3-1 in the first embodiment is modified as follows.
First layer Al2O3 20 nm
Second layer TiO 5 nm
Third layer Al2O3 38 nm
4th layer TiO 8 nm
Fifth layer Al2O3 32 nm
Sixth layer TiO 12 nm
7th layer SiO2 75 nm
[0061]
It has been found that the transmittance and the reflectance of the ND filter of the present modified example are not inferior to those of the ND filter of the first embodiment. Since SiO2 is brittle compared to Al2O3, it is necessary to pay attention to cracks and the like. When a tape peeling test was performed in the same manner as in the first embodiment, peeling could be suppressed to a practically acceptable level.
[0062]
(2nd Embodiment)
FIG. 8 shows a throw-in type ND filter used for a digital camera or the like.
[0063]
This ND filter has a filter section 7-2 formed on the surface of a substrate 7-3, a filter section 7-1 formed on the surface of the filter section 7-2, and the filter sections 7-1 and 7-2. , Arranged on concentric circles.
[0064]
With this configuration, the ND filter of the present embodiment is a two-density ND filter having different densities in the first region I and the second region II.
[0065]
The ND filter is capable of moving back and forth into an opening serving as a light passage provided in the diaphragm device, and covers the entire opening when entering. When limiting the amount of light, the center of the first circular region I is aligned with the optical axis, so that the first region I having a higher concentration than the second region II covers the region around the optical axis. .
[0066]
The cross-sectional structure of the ND filter of the present embodiment has the same structure as the ND filter of the first embodiment. Specifically, the filter unit 7-2 has the same layer structure as the filter unit 3-1 of FIG. The filter unit 7-1 has the same layer structure as the filter unit 3-2 in FIG.
[0067]
The ND filter of the present embodiment is also arranged in the imaging optical system 2 shown in FIG. 2, and the filter units 7-1 and 7-2 are provided on the surface of the substrate 7-3 opposite to the image sensor 4 side. I have.
[0068]
【The invention's effect】
As described above, according to the present invention, the first filter portion and the second filter portion that are attached to part of the first filter portion on the surface of the plastic substrate opposite to the image surface side. Is disposed, the reflection increase is prevented, and the occurrence of a ghost image can be prevented.
[Brief description of the drawings]
FIG. 1 is a perspective view of an aperture blade according to a first embodiment.
FIG. 2 is a diagram illustrating a photographing optical system including an aperture device.
FIG. 3A is a front view of an ND filter according to the first embodiment, and FIG. 3B is a diagram showing a positional relationship between the ND filter and an image sensor.
FIG. 4 is a partial cross-sectional view of the ND filter according to the first embodiment.
FIG. 5 is a partial cross-sectional view of the ND filter according to the first embodiment.
FIG. 6 is a spectral characteristic diagram of transmittance of the ND filter of the first embodiment.
FIG. 7 is a spectral characteristic diagram of the reflectance of the ND filter according to the first embodiment.
FIG. 8 is a front view (a) and a side view (b) of an ND filter according to the second embodiment.
FIG. 9A is a front view of an ND filter according to the related art, and FIG. 9B is a diagram illustrating a positional relationship between the ND filter and an image sensor.
FIG. 10 is a diagram showing a state in which the film thickness of the ND is gradually reduced in the prior art.
[Explanation of symbols]
1: aperture device 2: photographing optical system 3: low-pass filter 4: image sensor

Claims (4)

A light amount adjusting device for adjusting the amount of light reaching the image plane,
A plurality of aperture blades,
An ND filter unit disposed in at least a part of an opposing region in an aperture opening formed by these aperture blades,
The ND filter unit is provided on a plastic substrate, a first filter unit provided on the plastic substrate, the multilayer filter attenuating the light amount, and provided so as to overlap a part of the first filter unit. And a second filter section made of a multilayer film for attenuating the
The light amount adjusting device according to claim 1, wherein the first filter unit and the second filter unit are provided on a surface of the plastic substrate opposite to an image surface side. The said 1st filter part is an outermost layer comprised by Al2O3 or SiO2, The part other than this outermost layer is comprised by alternately arrange | positioning TiOy and Al2O3, The Claim 1 characterized by the above-mentioned. Light control device. 3. A third filter unit comprising a multilayer film for attenuating the amount of light is provided on a surface of the plastic substrate opposite to a surface on which the first filter unit is provided. The light amount adjusting device according to the above. An optical apparatus comprising the light amount adjusting device according to claim 1.

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