JP2002303824A - Optical crystal low-pass filer unit and video camera using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the problem of influence in terms of image quality such as the blur of a color due to a wavelength at the time of using an optical crystal low-pass filter in a video camera or the like handling general visible light by having wavelength dependence as the characteristic of a second optical crystal low-pass filter. SOLUTION: The optical crystal low-pass filter unit, in which a wavelength plate 32 is arranged between two optical crystal low-pass filters 31 and 33, has a steep characteristic without having frequency dependence since the thickness of the wavelength plate 32 is defined as 15±15 μm, and also has the advantages in configuration and cost since it is unnecessary that the thickness of the wavelength plate is made large. Also a video camera having performance reduced in color blur is obtained by using the low-pass filter unit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical quartz low-pass filter unit used for a video camera and a video camera using the same.

[0002]

2. Description of the Related Art A solid-state image pickup device such as a CCD two-dimensionally samples an analog image projected on an image pickup surface by a lens. Therefore, when an image signal having a spatial signal higher than the Nyquist frequency determined by the image pitch is projected, the high spatial frequency component becomes a false signal and is turned back to a low frequency. To avoid this phenomenon, C
It is necessary to cut this spatial frequency component before it is projected on the imaging surface of the CD, and an optical low-pass filter is provided between the lens and the imaging device. As a low-pass filter, an optical quartz low-pass filter using a quartz plate is most common. This utilizes the birefringence effect of quartz. References that describe such techniques include “Basics of solid-state imaging devices” (published by Nippon Riko Publishing Co., Ltd.) (by Takao Ando et al.) And technical commentary published by Kinseki Co., Ltd. Here, the birefringence of quartz will be briefly described.

FIG. 5A shows a refractive index ellipsoid of a quartz crystal. Here, 101 is the X axis, 102 is the Y axis, 103 is the Z axis, and the directions of the optical axes of the crystals are nx104, ny, respectively.
Numerals 105 and nz 106 denote refractive indices in the respective directions. In the case of a quartz crystal, since nx = ny since it is a uniaxial crystal, it is represented by a spheroid symmetrical to the Z axis as shown in FIG. Is done.

When light is incident in a specific direction of a crystal, the refractive index for the light is represented by an ellipse perpendicular to the light ray and cut by a plane including the origin of the ellipsoid as shown in FIG. Is done. Here, 107a indicates the direction of the incident light beam.
That is, the light whose ON is the wavefront normal has a vibration surface of OP,
It can be decomposed into two linearly polarized lights in the OQ direction. This is called birefringence. The refractive index of the OP polarized light at this time is ne10
8, assuming that the refractive index of OQ polarized light is no109, no is O
Although N does not change in any direction, ne changes depending on the direction. In general, an OQ polarized component whose refractive index does not change is called an ordinary ray, and an OP polarizing component that changes is called an extraordinary ray. Generally, an extraordinary ray having a high refractive index has a lower propagation speed than an ordinary ray.

Next, the principle of an optical quartz low-pass filter will be described. When natural light (usually approximated by circularly polarized light) is perpendicularly incident on a quartz plate, the light is separated into an ordinary ray and an extraordinary ray with a separation angle (this is mathematically based on Fresnel's assumption and Huygens' principle). Can be explained by
Here, the description is omitted because it is out of the spirit of the invention). By taking advantage of this characteristic and setting the optical axis in the direction that gives the maximum separation width, the light separation width d is obtained by using the thickness t of the quartz plate as a parameter, and d = (no ＾ 2-ne ＾ 2) / (no ＾ 2 + ne ＾ 2) · t (Expression 1) Since the refractive index of the crystal is: no = 1.5443 ne = 1.5534 (Equation 2), the separation width d of the light passing through the crystal plate is d = 5.88 × 10 ＾ (− 3) · t (Formula 3) Since the ordinary ray and the extraordinary ray that have passed through the quartz plate are shifted from each other by the separation width d, the frequency components of the spatial frequency 1 / d cancel each other out of phase with each other by π, and the frequency component of the spatial frequency 2 / d is The phases are mutually shifted by 2π and strengthen each other. It is the principle of an optical quartz low-pass filter that a spatial low-pass filter characteristic is obtained by such interference.

FIG. 6 specifically shows characteristics of an optical quartz low-pass filter. In FIG. 6, reference numeral 140 denotes the frequency characteristic of the optical quartz low-pass filter, and 141 denotes the state of light beam interference when the spatial frequency is 1 / d.
Reference numeral 42 denotes the state of interference of light rays when the spatial frequency is 2 / d, and reference numerals 143 and 144 denote the waveforms of the respective ordinary light rays.
45 and 146 are the waveforms of the extraordinary rays, 147 and 148, respectively.
Is a composite waveform in which an ordinary ray and an extraordinary ray interfere.

When the spatial frequency is 1 / d in the frequency characteristic 140 of the optical quartz low-pass filter, the ordinary light ray 143 and the extraordinary light ray 145 are out of phase by π, so that the combined waveforms 147 cancel each other out and the response is 0. %It has become.

On the other hand, when the spatial frequency is 2 / d,
44 and the extraordinary ray 146 are out of phase by 2π, so that the combined waveforms 148 strengthen each other and the response is 100%.
It has become.

FIG. 7 shows an example of characteristics when two optical crystal low-pass filters having crystal thicknesses t and t / 2 are stacked in order to obtain a steep low-pass filter characteristic. In FIG. 7, 150 is the characteristic of the first optical crystal low-pass filter having a crystal thickness of t, 151 is the characteristic of the second optical crystal low-pass filter having a crystal thickness of t / 2, and 152 is the product obtained by multiplying the two filters. Represents the characteristics.

As is apparent from the figure, it can be seen that a steep characteristic can be obtained by superimposing the characteristics of the two sheets. However, in fact, when the characteristics of a plurality of optical quartz low-pass filters are multiplied in this way, simply superimposing two optical quartz low-pass filters results in linear polarization of both ordinary and extraordinary rays. The ordinary ray coming out of the first sheet goes straight through the second optical crystal low-pass filter,
The extraordinary ray is refracted to the right or left, and consequently has the same function as one optical quartz low-pass filter corresponding to the sum or difference of the two thicknesses. Therefore,
It is necessary to convert the ordinary light and extraordinary light emitted from the first sheet into circularly polarized light. The wave plate performs this function.

The description of the wave plate will be described later. First, how the light passing through the two optical quartz low-pass filters changes depending on the presence or absence of the wave plate will be described with reference to FIG. FIG. 8A shows the case where there is no wave plate.
FIG. 3B shows the state of light separation when a wave plate is inserted between two optical quartz low-pass filters. 162 and 163 are first optical quartz low-pass filters, 164 and 165 are second optical quartz low-pass filters, 166 and 167 are incident natural light (represented by circularly polarized light), and 168 and 169 are 1 Ordinary rays separated by the first optical quartz low-pass filter, 170 and 171 are extraordinary rays separated by the first optical quartz low-pass filter, 172 is a wave plate, 17
Reference numeral 3 denotes an ordinary ray passed through the wave plate and converted into circularly polarized light;
Are the extraordinary rays passed through the wave plate and converted into circularly polarized light, 175
Reference numerals 176 and 176 denote light beams that have passed through two optical quartz low-pass filters and separated when no wave plate is inserted.
Reference numeral 180 denotes a light beam that has passed through the second optical crystal low-pass filter and is separated when a wave plate is inserted between the two optical crystal low-pass filters.

First, when the wave plate 172 is not inserted (FIG. 8A), the natural light 166 passes through the first optical quartz low-pass filter 162, and the ordinary light 16
8. Separated into extraordinary rays 170. The two separated light beams pass through the second optical crystal low-pass filter 164. However, since the ordinary light and the extraordinary light are linearly polarized, the ordinary light also travels straight in the second optical quartz low-pass filter 164, The extraordinary ray is simply refracted and there is no separation of each ray. As a result, the light beam that passed through the two optical quartz low-pass filters had the same two separation points as one optical quartz low-pass filter corresponding to two thicknesses as shown by light beams 175 and 176. Only a light beam is obtained.

Next, when a wave plate is inserted between the two optical quartz low-pass filters (FIG. 8B), natural light 167 is applied to the first optical quartz low-pass filter 1.
When passing through 63, the ordinary ray 169 and the extraordinary ray 17
It is separated into 1. Although the two separated light beams are linearly polarized light, they pass through the wave plate 172 to become circularly polarized light beams 17.
3 and 174. Accordingly, each ray is separated into an ordinary ray and an extraordinary ray when passing through the two optical quartz low-pass filters 165 in the same manner as when passing through the first optical quartz low-pass filter 163. Rays 177, 178, 17 with four separation points
9, and 180. As a result, the effect of the second optical quartz low-pass filter can be exerted, and as a result, a steep low-pass filter characteristic can be obtained.

Next, the structure of the wave plate will be described with reference to FIGS. FIG. 9 is a diagram showing a phase difference in a crystal between an ordinary ray and an extraordinary ray. FIG. 10 illustrates the relationship between the crystal plate thickness and the phase difference. 9 in FIG.
0 is an ordinary ray, 111 is an extraordinary ray, 112 is a quartz crystal serving as a refraction medium, 113 is a distance in the Y-axis direction representing a thickness dimension of quartz, 114 is a phase difference, and an important phase difference λ / 4 described later. It represents the image of. Since the ordinary ray 110 and the extraordinary ray 111 have different refractive indexes in the quartz crystal 112, the velocity of the extraordinary ray having a large refractive index in the crystal is slowed, and the phase difference is changed at the exit of the crystal at Y = t. Have.
FIG. 9 shows that there is a phase difference λ / 4.

Next, in FIG. 10, reference numeral 120 denotes a quartz plate, 121 denotes an X axis of a quartz crystal, and 122 denotes a Z axis. In quartz, the Z axis is an optical axis. 123 is the polarization direction of the linearly polarized incident light beam, and 124 is the thickness t of the quartz plate.

First, the X axis 121 and the Z axis 1
When the linearly polarized light 123 inclined at 45 ° with respect to 22 is made incident, the vibration direction in the crystal is changed to the X component along the X axis 121 and Z
It is divided into a Z-axis component along the axis 122. Quartz plate thickness d
When the surface of the quartz plate is set as the origin of the Y coordinate using 124 as a parameter, the X component reaches time τ = τx, and the Z component reaches τ = τz (> τx). Therefore, the phase difference に お け る at Y = t can be written as: Γ = ω * (τz−τx) = ω * (t / vz−t / vx) (Equation 4) Here, vz and vx are the speed of light in the crystal, respectively, and ω is the angular frequency. ω is invariant regardless of the medium, and can be written as ω = 2πC / λ (Equation 5). Here, C and λ are the speed of light and the wavelength in vacuum, respectively. Further, since C / vz = ne C / vx = no (Equation 6) is the refractive index for each light ray, the phase difference に お け る at Y = t is: Γ = (2π / λ) * (ne−no) * T (Expression 7)

Since the two linearly polarized light beams along the X and Z axes have different phases, at the exit Y = t of the quartz plate, the light beam is a combined beam using the wavelength λ and the thickness t of the quartz plate as parameters. Further, since these two linearly polarized lights are in an orthogonal relationship, the combined light beam behaves as so-called elliptically polarized light that rotates helically with respect to the traveling direction. A quartz plate that converts the linearly polarized light into elliptically polarized light is generally called a wave plate.

For a certain wavelength λ, the phase difference π is π /
By adjusting the thickness t124 to be 2, linearly polarized light can be converted to perfect circularly polarized light. Such a wave plate is generally called a “１ ／ λ plate”. That is, when π / 2 = (2π / λ) * (ne−no) * t → t = (１ ／) λ * (1 / (ne−no)) (Equation 8), the linearly polarized light is completely converted. Can be converted to circularly polarized light.

Next, an example in which the optical quartz low-pass filter and the wave plate are arranged in a video camera will be described with reference to FIG. In FIG. 11, 130 is a lens, 131 is a first optical crystal low-pass filter, 132 is a wave plate,
133 is a second optical quartz low-pass filter, 13
4 is a CCD which is a solid-state imaging device, 135 is incident light, 13
Reference numeral 6 denotes an ordinary ray and an extraordinary ray that have passed through the first optical quartz low-pass filter, 137 denotes a ray that has passed through the wave plate and has been converted into circularly polarized light, and 138 has passed through the second optical quartz low-pass filter. The light beam is divided into four points.

The incident light 135 passes through the lens 130 and the first optical crystal low-pass filter 131, and is separated into two points, an ordinary ray and an extraordinary ray, which are linearly polarized light, so that a spatial low-pass filter is applied. . The ordinary ray and the extraordinary ray that are linearly polarized light are converted into circularly polarized light by the wave plate 132,
The incident light passes through the second optical crystal low-pass filter 133 and is separated into four points, whereby a sharper spatial low-pass filter is applied. The light beam that has passed through the second optical crystal low-pass filter 133 is a CCD 134
And is converted into an electric signal. Here, the first optical quartz low-pass filter 131 and the wave plate 13 are used.
The second and second optical crystal low-pass filters 133 are individually described, but they are generally bonded together as a unit to form a unit.

[0021]

However, in the case of a video camera, the wavelength range of visible light (360 nm to 360 nm) is generally used.
760 nm), but the wavelength plate that can convert linearly polarized light into circularly polarized light is a wavelength that satisfies the relationship of Expression 8 that acts as a λλ plate, and can be completely converted over the entire visible light wavelength range. Not necessarily.

FIG. 12 shows a case where a wave plate is inserted between two deflectors whose polarization planes are orthogonal to each other (referred to as orthogonal Nicol condition). FIG. The thickness t of the wave plate is t = 0.5 mm
Is assumed. Since the two deflectors are in an orthogonal relationship, the transmittance is 0% if there is no wavelength plate. However, due to the influence of the wavelength plate, the light is converted into elliptically polarized light according to the wavelength and transmitted. The transmitted light rate T is represented by the following equation: T = (sin (π / λ * (ne-no) * t)) 数 式 2 (Equation 9). It shows that the plate functions as a λλ plate at the time of. FIG. 12 shows that a large number of wavelengths that cannot be converted into circularly polarized light in the visible light range (wavelengths deviating from the transmittance of 50%) are generated.

When the above-described wavelength plate is used, the characteristics of the second optical quartz low-pass filter have wavelength wavelength dependence. There is a problem in that the image quality is affected, such as color bleeding.

Also, the thickness of the wave plate is made as thick as possible,
In some cases, a method of increasing the number of wavelengths serving as a １ ／ λ plate in the wavelength range of visible light is used. FIG. 13 shows the transmittance T at the time of t = 1.5 mm under the orthogonal Nicols condition. It can be seen that by increasing the thickness, the interval between wavelengths that are not circularly polarized is reduced. As a result, it behaves as though it has been improved as an impression, although it has wavelength dependence. However, it is not a sufficient solution because the wavelength dependence has not been eliminated fundamentally, and there is no other way but to increase the thickness in order to improve the effect, which is disadvantageous in terms of structure and cost.

In view of the above-mentioned problems, the present invention has an optical quartz low-pass filter unit that has sharp characteristics without frequency dependence, and does not need to increase the thickness of a wave plate, so that it is advantageous in terms of structure and cost. The present invention also provides an optical quartz low-pass filter unit having less color bleeding in performance and a video camera using the same.

[0026]

According to the present invention, there is provided an optical quartz low-pass filter unit comprising a wave plate disposed between at least two optical quartz low-pass filters, the optical quartz low-pass filter unit comprising: Board thickness is 15
It is characterized by being ± 5 μm.

With such a configuration, there is provided an optical quartz low-pass filter unit having a sharp characteristic without frequency dependence and having an advantage in terms of configuration and cost because it is not necessary to increase the thickness of the wave plate. It is possible to obtain an optical quartz low-pass filter unit with little color bleeding in performance by using the same.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is described. An optical quartz low-pass filter unit comprising a wave plate disposed between at least two optical quartz low-pass filters, wherein the thickness of the wave plate is 15 ± 5 μm. Therefore, it is possible to provide an optical quartz low-pass filter unit which has a steep characteristic without frequency dependence, and has an advantage in terms of constitution and cost because it is not necessary to increase the thickness of the wave plate, and uses it. This makes it possible to obtain an optical quartz low-pass filter with little color fringing in terms of performance.

According to a second aspect of the present invention, the thickness between the at least two optical quartz low-pass filters is 15 ± 5.
An optical quartz low-pass filter unit having a wavelength plate of μm arranged therein, and an image sensor that converts an optical signal from the optical quartz low-pass filter unit into an electric signal and outputs the electric signal, and includes the optical quartz low-pass filter unit. A video camera characterized in that it is arranged in front of the imaging means, has sharp characteristics without frequency dependency, and does not need to increase the thickness of a wave plate, which is advantageous in terms of configuration and cost. An optical quartz low-pass filter unit with good quality can be provided, and by using it, a video camera with less color fringing in performance can be obtained.

According to the third aspect of the present invention, two different thicknesses are provided.
An optical quartz low-pass filter unit, comprising: a wave plate unit bonded so that the optical axes of the respective wave plates are substantially orthogonal to each other, disposed between at least two optical quartz low-pass filters. An optical quartz low-pass filter unit characterized in that the difference between the thicknesses of two wave plates is set to 15 ± 5 μm, which has steep characteristics without frequency dependence and increases the thickness of the wave plate. Since there is no need, an optical crystal low-pass filter unit having advantages in terms of configuration and cost can be provided, and by using the same, an optical crystal low-pass filter with less color blur in performance can be obtained.

[0031] The invention according to claim 4 is a method according to claim 2, wherein
At least two or more wave plate units are attached such that the difference between the thicknesses of the two wave plates is 15 ± 5 μm and the optical axes of the two wave plates are substantially orthogonal. An optical crystal low-pass filter unit disposed between the crystal low-pass filters, and an image sensor that converts an optical signal from the optical crystal low-pass filter unit into an electric signal and outputs the electric signal, and includes the optical crystal low-pass filter unit. A video camera characterized in that it is arranged in front of the imaging means, has sharp characteristics without frequency dependency, and does not need to increase the thickness of a wave plate, which is advantageous in terms of configuration and cost. Can provide an optical quartz low-pass filter unit with high quality, and by using it, it is possible to obtain a video camera with less color fringing in terms of performance. Wear.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) In order to realize a wavelength plate having a small wavelength dependence, the parameter of the thickness t is varied by using the above-mentioned equation (9), and the thickness t at which the wavelength dependence is minimized in the visible light region is obtained. I asked for. As a result, t = 15 ± 5μ
It has been found that a wavelength plate having a small wavelength dependence can be realized with a wavelength of about m.

FIG. 1 shows the thickness t of the wave plate under the orthogonal Nicols condition.
= 10, 15, 20 μm. In the case of a wavelength plate having a thickness in the above range, since the transmittance is localized in the vicinity of 50% in the visible light region, the wavelength plate has the effect of converting a linearly polarized light into a circularly polarized light into a quarter-λ plate. It can be seen that this can be achieved by dependency. Therefore,
The above-mentioned problem can be solved by disposing a wave plate having a thickness in this range between two or more optical quartz low-pass filters.

Therefore, in the present embodiment, the thickness is 1
An optical quartz low-pass filter unit in which a 5 ± 5 μm wave plate is arranged between two optical quartz low-pass filters is proposed. Furthermore, a video camera is proposed in which the above-mentioned optical quartz low-pass filter unit is arranged in front of an imaging means.

FIG. 2 is a diagram showing an embodiment of an optical quartz low-pass filter unit according to the first embodiment and a video camera according to a second invention using the same. FIG.
Reference numeral 30 denotes a lens, 31 denotes a first optical quartz low-pass filter which is a first optical quartz low-pass filter, 32 denotes a wave plate having a thickness of 15 μm, and 33 denotes a second optical quartz low-pass filter. A second optical quartz low-pass filter 34 is a CCD which is a solid-state imaging device which forms a light beam from the second optical quartz low-pass filter 33, converts the light beam into an electric signal, and outputs the electric signal. The incident light, 36, is a light that has passed through the first optical quartz low-pass filter 31, and is composed of an ordinary light 36a and an extraordinary light 36b. Reference numeral 37 denotes a light beam that has passed through the wavelength plate 32 and has been converted into circularly polarized light without wavelength dependence, and reference numeral 38 denotes a light beam that has passed through the second optical quartz low-pass filter and has been separated into four points.

The operation of the optical crystal low-pass filter unit of the present embodiment configured as described above and a video camera using the same will be described below.

The incident light 35 passes through the lens 30 and the first optical quartz low-pass filter 31, and is separated into two points, an ordinary ray 36a and an extraordinary ray 36b, which are linearly polarized light, so that a spatial low-pass filter is applied. Can be The ordinary ray 36a and the extraordinary ray 36b, which are linearly polarized light, are converted into circularly polarized light 37 without wavelength dependence by the wavelength plate 32 having a thickness of 15 μm, incident on the second optical quartz low-pass filter 33, passed through and separated into four points. Is done. As a result, a sharper spatial low-pass filter is applied. The light beam 38 passing through the second optical quartz low-pass filter 33 is transmitted to the CCD 3
4 and is converted into an electric signal.

Although the first optical quartz low-pass filter 31, the wave plate 32, and the second optical quartz low-pass filter 33 are shown individually here, they are united by being bonded together as a unit. No problem at all.

Although only the structure in which the wave plate 32 is arranged between the two optical quartz low-pass filters 31 and 33 has been described here, the wave plate is arranged between a plurality of optical quartz low-pass filters. The same effect can be obtained even in the case of doing so, and any of them does not depart from the gist of the present invention.

Further, an optical quartz low-pass filter unit for obtaining a two-dimensional spatial low-pass characteristic by orthogonalizing the optical axes of two optical quartz low-pass filters is also available.
Although a wave plate is required between the sheets, this does not depart from the gist of the present invention.

As described above, according to the present embodiment, an optical device having steep characteristics without frequency dependence and having no necessity of increasing the thickness of the wave plate is advantageous in terms of constitution and cost. A crystal low-pass filter unit can be provided, and by using the same, a video camera with less color fringing in performance can be obtained.

(Embodiment 2) Next, Embodiment 2 of the present invention will be described.

The production of a quartz plate having a thickness of about 15 μm is not easy because it is very thin. Therefore, it is proposed to use a wave plate that utilizes the fact that two wave plates having different thicknesses behave as wave plates having a difference in thickness when the optical axes of the two wave plates are orthogonal to each other.

FIG. 3 shows a unit in which the optical axes of two different wavelength plates are orthogonally bonded. In FIG. 3, reference numeral 20 denotes a first wave plate as a first wave plate, and reference numeral 21 denotes a second wave plate as a second wave plate, and their thicknesses have a difference of Δt. 22 and 23 are the X and Z axes of the first and second wave plates 20 and 21, 24 is the Z axis of the second wave plate 21, and the first wave plate 20 and the second wave plate 21 are The Z axes 23 and 24, which are the respective optical axes, are bonded in an orthogonal arrangement. 25 is the polarization direction of the linearly polarized incident light beam, 26 is the thickness t of the first wave plate 20, and 27 is the thickness (t + Δt) of the second wave plate 21. The extraordinary light component in the first wave plate 20 is treated as an ordinary light component in the second wave plate 21, so that the phase shifted is returned, and equivalently the thickness difference Δt between the two wave plates. Behave equivalently.

Wavelength plates bonded so that the thickness difference between the two crystal waveplates having different thicknesses is 15 ± 5 μm, and the optical axes of these two crystal waveplates are substantially orthogonal. An optical quartz low-pass filter unit in which the units are arranged between optical quartz low-pass filters is proposed. Furthermore, a video camera in which the optical quartz low-pass filter unit is arranged in front of an imaging unit is proposed.

FIG. 4 is a schematic diagram showing a configuration of a video camera using the optical quartz low-pass filter unit of the present embodiment. 4, 30 is a lens, 31
Denotes a first optical quartz low-pass filter which is a first optical quartz low-pass filter, 40 denotes a first wave plate which is a first wave plate, and 41 denotes a second wave plate which is a second wave plate.
A first wave plate 40 and a second wave plate 41
Have a thickness difference of 15 μm, and their optical axes are arranged in a substantially orthogonal relationship. Reference numeral 33 denotes a second optical quartz low-pass filter which is a second optical quartz low-pass filter, and reference numeral 34 denotes a second optical quartz low-pass filter.
CCD which is a solid-state imaging device for converting an optical signal from the optical signal into an electric signal and outputting the electric signal; 35, incident light incident through a lens 30; 36, a first optical quartz low-pass filter 3;
The light beam passing through No. 1 is composed of an ordinary light beam 36a and an extraordinary light beam 36b. Reference numeral 37 denotes a light beam that has passed through the wave plates 40 and 41 and has been converted into circularly polarized light without wavelength dependence, and reference numeral 38 denotes a light beam that has passed through the second optical quartz low-pass filter 33 and has been separated into four points.

The operation of the optical crystal low-pass filter unit of the present embodiment configured as described above and a video camera using the same will be described below.

The incident light 35 passes through the lens 30 and the first optical quartz low-pass filter 31, and is separated into two points, an ordinary ray 36a and an extraordinary ray 36b, which are linearly polarized light. Can be hung. The ordinary ray 36a and the extraordinary ray 36b that are linearly polarized light are first and second rays.
Are converted into circularly polarized light 37 without wavelength dependence by the wave plates 40 and 41, and are incident on and passed through the second optical quartz low-pass filter 33 to be separated into four points, so that a sharper spatial low-pass filter is applied. Can be The light beam 38 that has passed through the second optical quartz low-pass filter 33 is
34, and is converted into an electric signal.

Although the first optical quartz low-pass filter 31, the wave plates 40 and 41, and the second optical quartz low-pass filter 33 are individually described here, they are united as a single unit. There is no problem at all.

Although only the structure in which the wave plates 40 and 41 are disposed between the two optical quartz low-pass filters 31 and 33 has been described, the wave plate is further interposed between a plurality of optical quartz low-pass filters. The same effect can be obtained even if is arranged, and any of them does not depart from the gist of the present invention.

Also, the optical quartz low-pass filter unit that obtains a two-dimensional spatial low-pass characteristic by making the optical axes of the two optical quartz low-pass filters 31 and 33 orthogonal requires a wave plate between the two. However, this does not depart from the gist of the present invention.

As described above, according to the present embodiment, the difference between the thicknesses of the two quartz wave plates having different thicknesses is 15 ± 5 μm, and the optical axis of each of these two quartz wave plates is By using an optical quartz low-pass filter unit in which the wave plate units that are bonded so as to have a substantially orthogonal relationship are arranged between the optical quartz low-pass filters, an effect of facilitating manufacture can be obtained.

[0054]

As described above, according to the present invention, it is possible to provide a steep characteristic without frequency dependence, and it is not necessary to increase the thickness of the wave plate. We can provide a crystal low-pass filter unit,
In addition, by using such a video camera, it is possible to provide a video camera with little color fringing in terms of performance, and the effect is extremely large.

[Brief description of the drawings]

FIG. 1 shows a thickness t = 10, 1 of a wave plate under orthogonal Nicols conditions.
Characteristic diagram showing transmitted light ratio T at 5, 20 μm

FIG. 2 is a schematic diagram showing the configuration of an optical quartz low-pass filter unit according to the first embodiment of the present invention and a video camera using the same.

FIG. 3 is a perspective view showing a unit according to a second embodiment of the present invention in which two different wavelength plates are bonded with their optical axes orthogonal to each other.

FIG. 4 is a schematic diagram showing a configuration of an optical quartz low-pass filter unit of the embodiment and a video camera using the same.

FIG. 5 is a characteristic diagram showing a refractive index ellipsoid of a quartz crystal.

FIG. 6 is a characteristic diagram showing frequency characteristics of an optical quartz low-pass filter.

FIG. 7 is a characteristic diagram showing an example of characteristics when two optical quartz low-pass filters having quartz pressures t and t / 2 are stacked.

FIG. 8 is a schematic diagram for explaining a change in a light beam depending on the presence or absence of a wave plate;

FIG. 9 is a characteristic diagram showing a phase difference in a crystal between an ordinary ray and an extraordinary ray.

FIG. 10 is a perspective view showing a relationship between a crystal plate thickness and a phase difference.

FIG. 11 is a schematic diagram showing a configuration of a video camera using a conventional optical quartz low-pass filter.

FIG. 12 is a characteristic diagram showing the relationship between wavelength and transmittance based on orthogonal Nicol conditions in a conventional optical quartz low-pass filter.

FIG. 13 is a characteristic diagram showing a relationship between wavelength and transmittance when t = 15 mm under the same orthogonal Nicols condition.

[Explanation of symbols]

 Reference Signs List 30 lens 31 first optical quartz low-pass filter 32 wave plate 33 second optical quartz low-pass filter 34 CCD 35 incident light 36a ordinary ray 36b extraordinary ray 37 circularly polarized light 40 first wave plate 41 second wave plate

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 BA05 BA06 BA07 BA42 BB03 BC21 2H083 AA09 2H099 AA00 BA00 CA07 5C022 AC41 AC55

Claims (4)

[Claims] 1. An optical quartz low-pass filter unit comprising a wave plate disposed between at least two optical quartz low-pass filters, wherein the wave plate has a thickness of 15 ± 1.
An optical quartz low-pass filter unit having a size of 5 μm. 2. An optical quartz low-pass filter unit in which a wave plate having a thickness of 15 ± 5 μm is arranged between at least two optical quartz low-pass filters, and an optical signal from the optical quartz low-pass filter unit is electrically transmitted. A video camera, comprising: an image sensor that converts the signal into a signal and outputs the signal; and wherein the optical quartz low-pass filter unit is disposed on a front surface of the image capturing unit. 3. An optical system comprising: a wave plate unit in which two wave plates having different thicknesses are bonded so that the optical axes of the wave plates are substantially orthogonal to each other. A quartz low-pass filter unit, wherein the difference between the thicknesses of the two wave plates is 15 ± 5 μm.
An optical quartz low-pass filter unit characterized in that: 4. A wave plate unit wherein two wave plates having different thicknesses have a thickness difference of 15 ± 5 μm, and are bonded so that the optical axes of the two wave plates are substantially orthogonal. An optical quartz low-pass filter unit disposed between at least two or more optical quartz low-pass filters, and an image sensor that converts an optical signal from the optical quartz low-pass filter unit into an electric signal and outputs the electric signal. A video camera, wherein the optical quartz low-pass filter unit is disposed in front of the imaging means.