JP2012159658A - Optical filter module, and optical filter system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable photographing not only at daytime during which natural light is made incident, but also under night vision such as at nighttime.SOLUTION: In the optical filter module 3 provided on an imaging device 1 including a plurality of filters, the plurality of the filters are a first filter 4 which makes visible light transmit therethrough and shields at least infrared rays, and a second filter 7 which makes only the infrared rays pass therethrough, and the first filter 4 and the second filter 7 are arranged so as to be selectively switched.

Description

  The present invention relates to an optical filter module and an optical filter system.

  In an optical system of an electronic camera typified by a general video camera or a digital still camera, a coupling optical system, an infrared cut filter, an optical low-pass filter, a CCD (Charge Coupled Device), and a MOS from the subject side along the optical axis. Image sensors such as (Metal Oxide Semiconductor) are sequentially arranged (see, for example, Patent Document 1). Note that the imaging element referred to here has a sensitivity characteristic that responds to light having a wider wavelength band than light having a wavelength band (visible light) visible to the human eye. Therefore, in addition to visible light, it also responds to light in the infrared region and ultraviolet region.

  The human eye responds to light having a wavelength in the range of about 400 to 620 nm in a dark place and responds to light having a wavelength in the range of about 420 to 700 nm in a bright place. In contrast, for example, a CCD responds with high sensitivity to light having a wavelength in the range of 400 to 700 nm, and further responds to light having a wavelength of less than 400 nm and light having a wavelength of more than 700 nm.

  For this reason, in the imaging device described in Patent Document 1 described below, an infrared cut filter is provided in addition to the CCD that is the imaging element so that infrared rays do not reach the imaging element, and the captured image is close to the human eye. Is to be obtained.

  In addition, in the conventional optical filter, an antireflection film (AR coating) that reduces the reflection of light in the visible range is provided on the main surface of the optical filter in order to improve the transmittance in the visible range that can be seen by human eyes. Applying is a general filter configuration.

JP 2000-209510 A

  By the way, in addition to general video cameras and digital still cameras, there are imaging devices used for other purposes different from normal shooting such as surveillance cameras.

  For example, in a surveillance camera, it is necessary to perform surveillance photography not only in the daytime but also in night vision such as at night. Under night vision, shooting is performed in a state that cannot be seen by human eyes. Therefore, a camera with a normal visible range for imaging cannot perform imaging under night vision. Therefore, currently, photographing under night vision is performed using infrared rays, but the imaging device described in Patent Document 1 is provided with an infrared cut filter that cuts infrared rays. Therefore, it cannot be used for night vision photography.

  SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to provide an optical filter module and an optical filter system that are capable of photographing not only in daylight when natural light enters but also under night vision such as at night. .

  In order to achieve the above object, an optical filter module according to the present invention is provided in an imaging device. In the optical filter module capable of switching and arranging a plurality of filters, the plurality of filters transmit visible light and cut at least infrared rays. The first filter and the second filter that passes only infrared rays, wherein the first filter and the second filter are selectively switchable.

  According to the present invention, since the first filter and the second filter are selectively switchable, shooting is possible not only in the daytime when natural light enters but also in night vision such as at night. . Specifically, the first filter is arranged at daytime, and the second filter is arranged at night vision so that shooting is possible not only in daytime but also at night. Become. In particular, since daytime shooting can be performed with the first filter that transmits visible light and cuts at least infrared rays interposed, a more natural captured image close to human eyes can be obtained in the daytime. In addition, since the second filter that passes only infrared rays can be used for night photography, there is no occurrence of overexposure when part of natural light in the visible range is incident during night photography. A more stable and clear infrared photographed image can be obtained.

  The said structure WHEREIN: A said 2nd filter may pass only the predetermined specific band of infrared rays, and may cut the other band of infrared rays.

  In this case, in addition to the above-described effects, the second filter passes only a specific band set in advance of infrared rays and cuts other bands of infrared rays, so that shooting under night vision is improved. Is possible.

  The said structure WHEREIN: The said 1st filter may be equipped with the infrared rays absorber which absorbs infrared rays, and the infrared rays reflector which reflects infrared rays.

  In this case, in addition to the above-described effects, the first filter includes an infrared absorber that absorbs infrared rays and an infrared reflector that reflects infrared rays, so color reproduction while suppressing ghosts and flares. Since the image quality can be improved at the same time, it is possible to improve daytime shooting.

  The said structure WHEREIN: The said infrared absorber shows the light transmission characteristic which has a transmittance | permeability of 50% in the wavelength within a wavelength band of 620 nm to 660 nm, and the said infrared reflector transmits at a wavelength within a wavelength band of 670 nm to 690 nm. It shows a light transmission characteristic with a transmittance of 50%, and the combination of the infrared absorber and the infrared reflector results in a transmittance of 50% at a wavelength in the wavelength band of 620 nm to 660 nm, and a transmittance of 5 at a wavelength of 700 nm. The light transmission characteristics may be less than%.

  In this case, the first filter includes the infrared absorber and the infrared reflector, and the infrared absorber exhibits a light transmission characteristic in which a transmittance is 50% at a wavelength in a wavelength band of 620 nm to 660 nm, The infrared reflector exhibits a light transmission characteristic in which the transmittance is 50% at a wavelength in a wavelength band of 670 nm to 690 nm, and a wavelength within a wavelength band of 620 nm to 660 nm is obtained by a combination of the infrared absorber and the infrared reflector. Since the transmittance is 50% at a wavelength and the transmittance is less than 5% at a wavelength of 700 nm, the combination of the infrared absorber and the infrared reflector allows a gentle transmission from the visible range to the infrared range. The light transmission characteristic close to the sensitivity characteristic of the human eye can be obtained in which the light transmission rate is reduced to about 0% at a wavelength of 700 nm.

  In addition, the infrared absorber has a light transmission characteristic in which the transmittance is 50% at a wavelength in a wavelength band of 620 nm to 660 nm, for example, an infrared having a light transmission characteristic indicated by L11 in FIG. Absorptive glass is used, and the transmittance becomes about 0% (less than 5%) by combining the infrared absorbing action of the infrared absorber with the infrared reflecting action of the infrared reflector to 700 nm. It is matched. For this reason, the first filter of the present invention is higher in the visible region, particularly in the wavelength range of 600 nm to 700 nm, compared to the conventional infrared cut filter made of the infrared absorbing glass having the light transmission characteristics shown in L12 of FIG. The transmittance can be maintained. That is, it is possible to transmit a sufficient amount of red light (wavelength of 600 nm to 700 nm) that can be sensed by the imaging device of the imaging device while cutting infrared rays having a wavelength exceeding 700 nm. Therefore, by applying the first filter of the present invention to the infrared cut filter of the imaging device, the red sensitivity of the imaging device is weak, and the image captured by the imaging device tends to be a dark image. It can be solved.

  In the first filter, the amount of light reflected by the infrared reflector is suppressed by combining the infrared absorber with the infrared reflector. For this reason, it becomes possible to suppress generation | occurrence | production of the ghost by reflection of the light in the said infrared reflector.

  Further, the thickness of the infrared absorbing glass having the light transmission characteristic shown in L11 of FIG. 10 having a transmittance of 50% at a wavelength of 640 nm has the light transmission characteristic shown in L12 of FIG. 10 used as a conventional infrared cut filter. As it is taught that the thickness is less than half of the thickness of the infrared-absorbing glass, it has a light transmission characteristic that the transmittance is 50% at a wavelength within the wavelength band of 620 nm to 660 nm constituting the first filter of the present invention. As the infrared absorber, the one having a thickness smaller than that of an infrared cut filter made of a conventional infrared absorbing glass having a light transmission characteristic shown in L12 of FIG. 10 can be used. For this reason, according to the first filter of the present invention, the infrared ray is cut while sufficiently transmitting red visible light with the same thickness or a thin thickness as a conventional infrared cut filter composed only of an infrared absorber. And the infrared cut filter which has the light transmission characteristic close | similar to a human eye in visible region can be provided.

  In order to achieve the above-described object, the optical filter system according to the present invention can switch and arrange at least a coupling optical system for entering light from the outside and a plurality of filters from the outside subject side along the optical axis. In the optical filter system of the imaging device in which the optical filter system, the optical filter, and the imaging device are sequentially arranged, the plurality of filters transmit a visible light and at least a first filter that cuts infrared rays, and a first filter that passes only infrared rays. 2 filters, and either one of the first filter and the second filter is selectively switched on the optical axis.

  According to the present invention, since either one of the first filter and the second filter is selectively switched on the optical axis, it is not only in daytime when natural light enters but also under night vision such as at night. Even shooting is possible. Specifically, the first filter is switched on the optical axis during daytime, and the second filter is switched on the optical axis during night vision so that not only daytime but also nighttime. Shooting is possible even under night vision. In particular, since daytime shooting can be performed with the first filter that transmits visible light and cuts at least infrared rays interposed, a more natural captured image close to human eyes can be obtained in the daytime. In addition, since the second filter that passes only infrared rays can be used for night photography, there is no occurrence of overexposure when part of natural light in the visible range is incident during night photography. A more stable and clear infrared photographed image can be obtained.

  The said structure WHEREIN: A said 2nd filter may pass only the predetermined specific band of infrared rays, and may cut the other band of infrared rays.

  In this case, in addition to the above-described effects, the second filter passes only a specific band set in advance of infrared rays and cuts other bands of infrared rays, so that shooting under night vision is improved. Is possible.

  The said structure WHEREIN: The said 1st filter may be equipped with the infrared rays absorber which absorbs infrared rays, and the infrared rays reflector which reflects infrared rays.

  In this case, in addition to the above-described effects, the first filter includes an infrared absorber that absorbs infrared rays and an infrared reflector that reflects infrared rays, so color reproduction while suppressing ghosts and flares. Since the image quality can be improved at the same time, it is possible to improve daytime shooting.

  The said structure WHEREIN: The said infrared absorber shows the light transmission characteristic which has a transmittance | permeability of 50% in the wavelength within a wavelength band of 620 nm to 660 nm, and the said infrared reflector transmits at a wavelength within a wavelength band of 670 nm to 690 nm. It shows a light transmission characteristic with a transmittance of 50%, and the combination of the infrared absorber and the infrared reflector results in a transmittance of 50% at a wavelength in the wavelength band of 620 nm to 660 nm, and a transmittance of 5 at a wavelength of 700 nm. The light transmission characteristics may be less than%.

  In this case, the first filter includes the infrared absorber and the infrared reflector, and the infrared absorber exhibits a light transmission characteristic in which a transmittance is 50% at a wavelength in a wavelength band of 620 nm to 660 nm, The infrared reflector exhibits a light transmission characteristic in which the transmittance is 50% at a wavelength in a wavelength band of 670 nm to 690 nm, and a wavelength within a wavelength band of 620 nm to 660 nm is obtained by a combination of the infrared absorber and the infrared reflector. Since the transmittance is 50% at a wavelength and the transmittance is less than 5% at a wavelength of 700 nm, the combination of the infrared absorber and the infrared reflector allows a gentle transmission from the visible range to the infrared range. The light transmission characteristic close to the sensitivity characteristic of the human eye can be obtained in which the light transmission rate is reduced to about 0% at a wavelength of 700 nm.

  In addition, the infrared absorber has a light transmission characteristic in which the transmittance is 50% at a wavelength in a wavelength band of 620 nm to 660 nm, for example, an infrared having a light transmission characteristic indicated by L11 in FIG. Absorptive glass is used, and the transmittance becomes about 0% (less than 5%) by combining the infrared absorbing action of the infrared absorber with the infrared reflecting action of the infrared reflector to 700 nm. It is matched. For this reason, the first filter of the present invention is higher in the visible region, particularly in the wavelength range of 600 nm to 700 nm, compared to the conventional infrared cut filter made of the infrared absorbing glass having the light transmission characteristics shown in L12 of FIG. The transmittance can be maintained. That is, it is possible to transmit a sufficient amount of red light (wavelength of 600 nm to 700 nm) that can be sensed by the imaging device of the imaging device while cutting infrared rays having a wavelength exceeding 700 nm. Therefore, by applying the first filter of the present invention to the infrared cut filter of the imaging device, the red sensitivity of the imaging device is weak, and the image captured by the imaging device tends to be a dark image. It can be solved.

  In the first filter, the amount of light reflected by the infrared reflector is suppressed by combining the infrared absorber with the infrared reflector. For this reason, it becomes possible to suppress generation | occurrence | production of the ghost by reflection of the light in the said infrared reflector.

  Further, the thickness of the infrared absorbing glass having the light transmission characteristic shown in L11 of FIG. 10 having a transmittance of 50% at a wavelength of 640 nm has the light transmission characteristic shown in L12 of FIG. 10 used as a conventional infrared cut filter. As it is taught that the thickness is less than half of the thickness of the infrared-absorbing glass, it has a light transmission characteristic that the transmittance is 50% at a wavelength within the wavelength band of 620 nm to 660 nm constituting the first filter of the present invention. As the infrared absorber, the one having a thickness smaller than that of an infrared cut filter made of a conventional infrared absorbing glass having a light transmission characteristic shown in L12 of FIG. 10 can be used. For this reason, according to the first filter of the present invention, the infrared ray is cut while sufficiently transmitting red visible light with the same thickness or a thin thickness as a conventional infrared cut filter composed only of an infrared absorber. And the infrared cut filter which has the light transmission characteristic close | similar to a human eye in visible region can be provided.

  In the above-described configuration of the present invention, the infrared reflector exhibits a light transmission characteristic with a transmittance of 10% to 40% at a wavelength of 700 nm, and the infrared reflector has a transmittance of 15 at a wavelength of 700 nm. The light transmission characteristics may be less than%.

  In this case, the infrared absorber exhibiting a light transmission characteristic having a transmittance of 10% to 40% at a wavelength of 700 nm, and the infrared reflector exhibiting a light transmission characteristic having a transmittance of less than 15% at a wavelength of 700 nm; With this combination, it is possible to reliably obtain a high transmittance in the wavelength band of red visible light (600 nm to 700 nm).

  In the configuration of the present invention, the infrared reflector may exhibit a light transmission characteristic having a transmittance of 90% or more in a wavelength band of 430 nm to 650 nm.

  In this case, since the light transmission characteristic depending on the light transmission characteristic of the infrared absorber is obtained in the wavelength band of 430 nm to 650 nm, the transmittance gradually decreases from the visible range to the infrared range, and at a wavelength of 700 nm. Light transmission characteristics close to the sensitivity characteristics of the human eye with a transmittance of about 0% can be obtained, and a high transmittance is obtained in the visible region, particularly in the wavelength band of red visible light (600 nm to 700 nm). It becomes possible.

  According to the present invention, shooting is possible not only in the daytime when natural light enters but also under night vision such as at night.

FIG. 1 is a schematic diagram illustrating a schematic configuration of an imaging device according to an embodiment. FIG. 2 is a diagram illustrating light transmission characteristics of the first filter according to the embodiment. FIG. 3 is a schematic diagram illustrating a schematic configuration of the first filter according to the embodiment. FIG. 4 is a partially enlarged view showing a schematic configuration of the infrared reflector of the first filter according to the embodiment. FIG. 5 is a diagram illustrating light transmission characteristics of the second filter according to the embodiment. FIG. 6 is a schematic diagram illustrating a schematic configuration of the second filter according to the embodiment. FIG. 7 is a partially enlarged view showing a schematic configuration of the infrared transmitting body of the second filter according to the embodiment. FIG. 8 is a diagram illustrating the light transmission characteristics of the infrared cut filter according to the example. FIG. 9 is a schematic diagram illustrating a schematic configuration of an imaging device according to another embodiment. FIG. 10 is a diagram showing the light transmission characteristics of the infrared absorbing glass.

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

<Embodiment>
As shown in FIG. 1, the imaging device 1 according to the present embodiment includes a lens 2, which is a coupled optical system that enters light from the outside along the optical axis 11, at least from the outside subject side, and a plurality of filters ( An optical filter module 3 that can be switched and arranged, an optical filter 8 that is an OLPF, and an image sensor 9 are sequentially arranged.

  The optical filter module 3 includes a first filter 4 that transmits visible light and cuts at least infrared rays, and a second filter 7 that passes only infrared rays. Either one of the first filter 4 and the second filter 7 is selectively switched on the optical axis 11 by known switching means (not shown). Specifically, when natural light such as daytime enters, the first filter 4 is disposed on the optical axis 11, and the second filter 7 is disposed on the optical axis 11 under night vision such as nighttime. When the second filter 7 is disposed on the optical axis 11, the subject is irradiated with light from an LED (not shown) whose light peak wavelength is 850 to 900 nm (870 nm in the present embodiment). . The definition of daytime in the present embodiment refers to a case where the illuminance exceeds 400 lx, and the definition of night refers to a case where the illuminance is 400 lx or less. Here, 400 lx is an example, and a person skilled in the art can freely set the boundary illuminance between daytime and nighttime. Alternatively, you can define only the nighttime and judge that the illuminance deviates from the nighttime definition as daytime, or just define the daytime and set the illuminance outside the daytime definition to be judged as nighttime. Also good. That is, the illuminance reference may be set in advance, and the first filter 4 and the second filter 7 may be switched based on the set illuminance.

  Further, since the optical filter module 3 includes the first filter 4, the optical filter 8 that is an OLPF is not formed with an infrared cut filter, and light rays in two wavelength bands (visible range and infrared range). Only a single-layer antireflection film 81 for preventing the reflection of light is formed on both main surfaces. In the present embodiment, only the single-layer antireflection film 81 is formed on both main surfaces of the optical filter 8, but the present invention is not limited to this, and is not limited to this. It is sufficient that an antireflection film capable of preventing reflection of light having a wavelength is formed.

  According to the imaging device 1 shown in FIG. 1, the lens 2, the first filter 4, the optical filter 8, and the imaging element 9 are sequentially arranged from the outside subject side along the optical axis 11 at daytime. With the configuration in which the first filter 4 is disposed on the optical 11, the imaging device 1 (optical filter module 3) has the light transmission characteristics shown in FIG. On the other hand, at night, the lens 2, the second filter 7, the optical filter 8, and the image sensor 9 are sequentially arranged from the outside subject side along the optical axis 11. With the configuration in which the second filter 7 is disposed on the optical 11, the imaging device 1 (optical filter module 3) has the light transmission characteristics shown in FIG.

  As described above, according to the imaging device 1 shown in FIG. 1, either one of the first filter 4 and the second filter 7 is selectively switched on the optical axis 11. A spectral characteristic close to the sensitivity characteristic of the eye can be obtained, and light in only a desired band in the infrared region can be transmitted. As a result, according to the imaging device 1 shown in FIG. 1, it is possible to suitably perform shooting in the daytime in which infrared rays are cut and shooting under night vision such as nighttime in which only infrared rays are passed. That is, it is possible to shoot not only in the daytime when natural light enters but also under night vision such as at night. Specifically, the first filter 4 is switched and arranged on the optical axis 11 during the daytime, and the second filter 7 is switched and arranged on the optical axis 11 in the night vision state. You can shoot even under night vision. In particular, since daytime shooting can be performed with the first filter 4 that transmits visible light and cuts at least infrared rays interposed, a more natural captured image close to human eyes can be obtained in the daytime. In addition, since night photography can be performed with the second filter 7 that passes only infrared rays, whiteout does not occur when a part of natural light in the visible range is incident during night photography. A more stable and clear infrared photographed image can be obtained.

  Next, the optical filter module 3 will be described with reference to FIGS. The optical filter module 3 is provided with a first filter 4, a second filter 7, and known switching means (not shown).

  As shown in FIGS. 2 and 3, the first filter 4 includes an infrared absorber 5 that transmits visible light and absorbs infrared light, and an infrared reflector 6 that transmits visible light and reflects infrared light. Bonded.

  The infrared absorber 5 is formed by forming an antireflection film 54 (AR coat) on one main surface 52 of the infrared absorbing glass 51.

  The infrared absorbing glass 51 is a blue glass in which a pigment such as copper ions is dispersed. For example, a rectangular thin glass having a thickness of 0.2 mm to 1.2 mm is used.

Further, the antireflection film 54, to the one main surface 52 of the infrared absorbing glass 51, a single layer made of MgF _2, multilayer film made of Al ₂ O ₂ and ZrO ₂ and MgF ₂ Prefecture, TiO ₂ and SiO ₂ It is formed by vacuum-depositing any one of the multilayer films composed of the above by a known vacuum deposition apparatus (not shown). The antireflection film 54 performs a vapor deposition operation while monitoring the film thickness, and closes a shutter (not shown) provided in the vicinity of the vapor deposition source (not shown) when the predetermined film thickness is reached. This is done by stopping the deposition.

  The infrared absorber 5 exhibits light transmission characteristics such that the transmittance is 50% at a wavelength in the wavelength band of 620 nm to 660 nm and the transmittance is 10% to 40% at a wavelength of 700 nm. In the light transmission characteristics of the infrared absorber 5 as described above, the transmittance has a maximum value of 90% or more at a wavelength within the wavelength band of 400 nm to 550 nm.

  The infrared reflector 6 is formed by forming an infrared reflecting film 64 on one main surface 62 of the transparent substrate 61.

  As the transparent substrate 61, it is a colorless transparent glass which permeate | transmits visible light and infrared rays, for example, square-shaped plate-shaped glass with a thickness of 0.2 mm-1.0 mm is used.

As shown in FIG. 4, the infrared reflective film 64 is a multilayer film in which a plurality of first thin films 65 made of a high refractive index material and a plurality of second thin films 66 made of a low refractive index material are alternately laminated. In this embodiment, the TiO ₂ used in the first film 65 has been used SiO ₂ to the second thin film 66, ₂ odd layer TiO, but an even layer is in the SiO _2, the odd layer May be SiO ₂ and the even layer may be TiO ₂ .

As a manufacturing method of the infrared reflecting film 64, TiO ₂ and SiO ₂ are alternately vacuum-deposited on a main surface 62 of the transparent substrate 61 by a known vacuum deposition apparatus (not shown), as shown in FIG. A method of forming an infrared reflection film 64 is used. The film thickness adjustment of the first thin film 65 and the second thin film 66 is performed by performing a vapor deposition operation while monitoring the film thickness. (Omitted) is closed to stop the vapor deposition of the vapor deposition material (TiO ₂ , SiO ₂ ).

  In addition, as shown in FIG. 4, the infrared reflective film 64 includes a plurality of layers defined by ordinal numbers in order from the one main surface 62 side of the transparent substrate 61, in this embodiment, one layer, two layers, three layers,. It is composed of Each of the first layer, the second layer, the third layer,... Is formed by laminating a first thin film 65 and a second thin film 66. The first thin film 65 and the second thin film 66 to be laminated have different optical film thicknesses, so that the thicknesses of the first layer, the second layer, the third layer,. In addition, the optical film thickness here is calculated | required by following Numerical formula 1.

[Formula 1]
Nd = d × N × 4 / λ (Nd: optical film thickness, d: physical film thickness, N: refractive index, λ: center wavelength)
In the present embodiment, the infrared reflector 6 has a transmittance of 90% or more in the wavelength band of 430 nm to 650 nm, a transmittance of 50% at a wavelength in the wavelength band of 660 nm to 690 nm, and transmits at a wavelength of 700 nm. The number of layers of the infrared reflection film 64 and the optical film thickness of each layer are appropriately adjusted so as to have a light transmission characteristic with a rate of less than 15%.

  The 1st filter 4 which consists of such an infrared absorber 5 and the infrared reflector 6 has thickness of 0.4 mm-1.6 mm, for example. That is, the thickness of the infrared absorbing glass 51 constituting the infrared absorbing body 5 and the thickness of the transparent substrate 61 constituting the infrared reflecting body 6 are the sum of the thicknesses of the infrared absorbing body 5 and the infrared reflecting body 6 being, for example, 0. It adjusts suitably so that it may be set to 4 mm-1.6 mm.

  The first filter 4 has a maximum transmittance at a wavelength within a wavelength band of 400 nm to 550 nm, and a wavelength band of 620 nm to 660 nm due to the combination of the light transmission characteristics of the infrared absorber 5 and the infrared reflector 6 described above. The transmittance is 50% at an inner wavelength, and the transmittance is less than 5% at a wavelength of 700 nm.

  As described above, the first filter 4 having the above configuration includes the infrared absorber 5 that absorbs infrared rays and the infrared reflector 6 that reflects infrared rays, so that color reproduction is achieved while suppressing ghosts and flares. Since it is possible to improve the quality at the same time, it is possible to improve daytime shooting.

  As shown in FIGS. 5 and 6, the second filter 7 passes only a specific band set in advance for infrared rays (in this embodiment, the half value is 850 nm or more), and cuts the visible range. The second filter 7 is provided with an LED (not shown) whose light peak wavelength is 850 to 900 nm (870 nm in the present embodiment), and the second filter 7 is disposed on the optical axis 11. The object is irradiated with light from the LED. As described above, the second filter 7 is a filter dedicated to shooting under night vision and is not intended for shooting under visible conditions such as daytime, and cannot perform shooting under visible conditions. Note that the present invention is not limited to this embodiment, and only a specific band close to 870 nm may be passed. In this case, noise can be further eliminated and better night vision photography can be performed.

The second filter 7 passes only the specific band set in advance of infrared rays (corresponding to the wavelength of light emitted from the LED in this embodiment), and cuts the other band of infrared rays in the transparent substrate 71. An infrared pass coat 74 (IR pass coat) is formed on one main surface 72. An antireflection film 77 is formed on the other main surface 73 of the second filter 7. Antireflection film 77 with respect to the other main surface 73 of the second filter 7, a multilayer film, TiO ₂ and SiO ₂ Metropolitan consisting of a single layer, Al ₂ O ₂ and ZrO ₂ and MgF ₂ Metropolitan consisting MgF ₂ Any one of the multilayer films is formed by vacuum deposition using a known vacuum deposition apparatus (not shown). According to the second filter 7, only a specific band set in advance for infrared rays (corresponding to the wavelength of light emitted from the LED in this embodiment) is passed, and other bands of infrared rays are cut. It is possible to make the shooting in better.

  As the transparent substrate 71, it is a colorless transparent glass which permeate | transmits visible light and infrared rays, for example, square-shaped plate-shaped glass with a thickness of 0.4 mm-1.6 mm is used.

As shown in FIG. 7, the infrared path coat 74 is a multilayer film in which a plurality of first thin films 75 made of a high refractive index material and a plurality of second thin films 76 made of a low refractive index material are alternately laminated. In this embodiment, the TiO ₂ used in the first film 75, the second thin film 76 has been used SiO _{2, 2} odd layer TiO, but an even layer is in the SiO _2, the odd layer May be SiO ₂ and the even layer may be TiO ₂ .

As a manufacturing method of the infrared pass coat 74, TiO ₂ and SiO ₂ are alternately vacuum-deposited on a main surface 72 of the transparent substrate 71 by a known vacuum deposition apparatus (not shown), as shown in FIG. A method for forming an infrared path coat 74 is used. The film thickness adjustment of the first thin film 75 and the second thin film 76 is performed by performing a vapor deposition operation while monitoring the film thickness. (Omitted) is closed to stop the vapor deposition of the vapor deposition material (TiO ₂ , SiO ₂ ).

  In addition, as shown in FIG. 7, the infrared path coat 74 has a plurality of layers defined by ordinal numbers in order from the one main surface 72 side of the transparent substrate 71, in this embodiment, one layer, two layers, three layers,. It is composed of Each of the first layer, the second layer, the third layer,... Is formed by laminating a first thin film 75 and a second thin film 76. The first thin film 75 and the second thin film 76 to be laminated have different optical thicknesses so that the thicknesses of the first layer, the second layer, the third layer,. In addition, the optical film thickness here is calculated | required by said Numerical formula 1.

  In the present embodiment, the second filter has a transmittance of 90% or more in the wavelength band of 860 nm, a transmittance of 50% at a wavelength in the wavelength band of 850 nm, and a transmittance of less than 15% at a wavelength of 840 nm. The number of layers of the infrared pass coat 74 and the optical film thickness of each layer are appropriately adjusted so as to have the light transmission characteristics.

  Such a second filter 7 has a thickness of 0.4 mm to 1.6 mm, for example.

  The second filter 7 has a maximum transmittance at a wavelength in the wavelength band of 860 nm or more and a transmittance of 50% at a wavelength in the wavelength band of 850 nm due to the light transmission characteristics of the infrared path coat 74. , The light transmission characteristics with a transmittance of less than 5% at a wavelength of 830 nm.

  Next, the wavelength characteristics of the first filter 4 and the second filter 5 are actually measured, and the results and configurations are shown in FIG.

-First filter according to the embodiment 4-
In the 1st filter 4 concerning a present Example, as infrared rays absorption glass 51, it is blue glass which disperse | distributed pigment | dyes, such as a copper ion, thickness is 0.8 mm, and the refractive index in N air | atmosphere is about 1.5. A glass plate is used. Then, an Al ₂ O ₃ film having a refractive index of 1.6 in the N atmosphere, a ZrO ₂ film having a refractive index of 2.0 in the N atmosphere, and a Nr atmosphere in the main surface 52 of the infrared absorbing glass 51 Each film constituting the antireflection film 54 was formed by vacuum deposition in the order of the MgF ₂ film having a refractive index of 1.4 to obtain the infrared absorber 5.

  The infrared absorber 5 has light transmission characteristics as indicated by L1 in FIG. In this embodiment, the incident angle of the light beam is 0 degree, that is, the light beam is vertically incident.

  As shown in FIG. 8, the infrared absorbing glass 51 has a transmittance of 90% or more in the wavelength band of 400 nm to 550 nm, a decrease in the transmittance in the wavelength band of 550 nm to 700 nm, and a transmittance at a wavelength of about 640 nm. The light transmission characteristic is 50%, and the transmittance is about 17% at a wavelength of 700 nm.

As the transparent substrate 61 of the infrared reflector 6, a glass plate having a refractive index of 1.5 in the N atmosphere and a thickness of 0.3 mm is used. Further, as the first thin film 65 constituting the infrared reflecting film 64, TiO ₂ having a refractive index of 2.30 in the N atmosphere is used, and as the second thin film 66, the refractive index in the N atmosphere is 1.46. Using SiO ₂ , their center wavelength is 688 nm.

  The optical film thickness of each of the first thin film 65 and the second thin film 66 is set to the one main surface 62 of the transparent substrate 61 by the manufacturing method of the infrared reflecting film 64 composed of the 40 layers shown in Table 1. The first thin film 65 and the second thin film 66 are formed (laminated), and the infrared reflector 6 is obtained.

  Table 1 shows the composition of the infrared reflecting film 64 of the first filter 4 and the optical film thickness of each thin film (the first thin film 65 and the second thin film 66).

  The infrared reflector 6 has a light transmission characteristic as indicated by L2 in FIG. In other words, the light transmission characteristics of the infrared reflecting film 64 show a transmittance of about 100% in the wavelength band of 395 nm to 670 nm (wavelength band including the wavelength band of 430 nm to 650 nm), and sharply when the wavelength exceeds about 670 nm. The transmittance is reduced, and the transmittance is 50% at a wavelength of about 680 nm and the transmittance is about 4% at a wavelength of 700 nm.

  And as shown in FIG. 8, the 1st filter 4 which concerns on the Example whose thickness is 1.1 mm is obtained by adhere | attaching the other main surface 63 of the transparent substrate 61 to the other main surface 53 of the infrared rays absorption glass 51. It was.

  The first filter 4 has a light transmission characteristic indicated by L3 in FIG. 8 in which the light transmission characteristics of the infrared absorber 5 and the infrared reflector 6 are combined. In other words, the first filter 4 of the embodiment has a transmittance of 90% or more in the wavelength band of 400 nm to 550 nm, a decrease in the transmittance in the wavelength band of 550 nm to 700 nm, and a transmittance of 50% at a wavelength of about 640 nm. Thus, the light transmission characteristic is shown in which the transmittance is about 0% at a wavelength of 700 nm.

  As shown in the light transmission characteristics of the first filter 4 of this example, the first filter 4 according to the present embodiment has a wavelength band of 400 nm to 550 nm depending on the combination of the infrared absorber 5 and the infrared reflector 6. The transmittance is 90% or more at the maximum wavelength, the transmittance is 50% at the wavelength in the wavelength range of 620 nm to 660 nm, and the transmittance is about 0% (less than 5%) at the wavelength of 700 nm. The light transmission characteristics can be obtained. That is, it is possible to obtain a light transmission characteristic close to the sensitivity characteristic of the human eye in which the transmittance gradually decreases from the visible region to the infrared region, and the transmittance is about 0% at a wavelength of 700 nm.

  The light transmission characteristic L3 of the first filter 4 according to the embodiment shown in FIG. 8 will be described more specifically by comparison with the light transmission characteristic L4 of the conventional infrared cut filter.

  The conventional infrared cut filter having the light transmission characteristic indicated by L4 in FIG. 8 is composed of an infrared absorber in which an antireflection film is formed on both surfaces of an infrared absorption glass. In this conventional infrared cut filter, the point at which the transmittance becomes 0% is adjusted to 700 nm by setting the thickness of the infrared absorbing glass as an infrared absorber to 1.6 mm.

  On the other hand, in the first filter 4 of the embodiment, the thickness is half that of the conventional infrared cut filter (infrared absorber) showing the light transmission characteristics of L4, and the visible region, particularly the wavelength band of 600 nm to 700 nm. In the infrared absorber 5 showing a higher transmittance than the conventional infrared cut filter, that is, the infrared reflector 5 is combined with the infrared absorber 5 showing the light transmission characteristics shown in L1, the transmittance is 0%. The point is adjusted to 700 nm.

  For this reason, the light transmission characteristic L3 of the first filter 4 according to the embodiment shows a higher transmittance than the light transmission characteristic L4 of the conventional infrared cut filter in the visible light region, particularly in the wavelength band of 600 nm to 700 nm. . Further, in the light transmission characteristic L3 of the first filter 4 according to the example, the transmittance with respect to a light beam having a wavelength of 700 nm is closer to 0% than the light transmission characteristic L4 of the conventional infrared cut filter. Yes.

  Specifically, in the light transmission characteristic L4 of the conventional infrared cut filter, the transmittance at a wavelength of 600 nm is about 55%, the transmittance is about 50% at a wavelength of about 605 nm, and the transmittance is about 605 nm. 7.5%, and the transmittance is about 3% at a wavelength of 700 nm.

  On the other hand, in the light transmission characteristic L3 of the first filter 4 according to the embodiment, the transmittance at a wavelength of 600 nm is about 75%, the transmittance is about 50% at a wavelength of about 640 nm, and the transmittance is at a wavelength of 675 nm. Is about 20%, and the transmittance is about 0% at a wavelength of 700 nm.

  As described above, the light transmission characteristic L3 of the first filter 4 according to the embodiment has a wavelength band of 600 nm to 700 nm, in particular, a wavelength band of 600 nm to 675 nm, compared with the light transmission characteristic L4 of the conventional infrared cut filter. The transmittance is high and the transmittance at a wavelength of 700 nm is close to 0%. That is, the 1st filter 4 which concerns on an Example can fully permeate | transmit red visible light with a wavelength of 600 nm-700 nm, fully cutting the infrared rays over 700 nm compared with the conventional infrared cut filter. It is recognized that For this reason, when the first filter 4 according to the embodiment is mounted on the imaging device, the imaging device 9 can capture an image with a stronger shade of red than in the past, and an image in a dark place can be brightened. Imaging can be performed.

  Further, as described above, in the first filter 4 according to the present embodiment, the amount of light reflected by the infrared reflector 6 is suppressed by combining the infrared reflector 5 with the infrared reflector 6. For this reason, generation | occurrence | production of the ghost by reflection of the light by the infrared reflector 6 can be suppressed.

  In addition, the infrared reflector 6 has a transmittance of 90% or more with respect to the light of the half-value wavelength of the infrared absorber 5 so that the half-value wavelength of the first filter 4 and the half-value wavelength of the infrared absorber 5 substantially coincide. Therefore, the infrared cut filter is provided with a light transmission characteristic close to the sensitivity characteristic of the human eye whose transmittance gradually decreases at a wavelength of 550 nm to 700 nm of the infrared absorber 5. The light transmission characteristic close to the sensitivity characteristic is obtained.

  Furthermore, in the 1st filter 4 which concerns on embodiment, the infrared absorber 5 can be comprised by thickness thinner than the conventional infrared cut filter which has the light transmission characteristic shown to L4. For this reason, the thickness of the 1st filter 4 can be made the same as the conventional infrared cut filter, or can be made thinner than this conventional infrared cut filter.

-Second filter 7 according to the embodiment-
In the second filter 7 according to the present embodiment, a glass plate having a refractive index of 1.5 in the N atmosphere and a thickness of 1.1 mm is used as the transparent substrate 71. Further, as the first thin film 75 constituting the infrared pass coat 74, TiO ₂ having a refractive index of 2.30 in the N atmosphere is used, and as the second thin film 76, the refractive index in the N atmosphere is 1.46. Using SiO ₂ , their center wavelength is 720 nm.

  The optical film thickness of each of the first thin film 75 and the second thin film 76 is set on the one main surface 72 of the transparent substrate 71 by the manufacturing method of the above-described 48-layer infrared pass coat 74 shown in Table 2. The first thin film 75 and the second thin film 76 are formed (laminated) to obtain the second filter 7.

  Table 2 shows the composition of the second filter 7 and the optical film thickness of each thin film (the first thin film 75 and the second thin film 76). The second filter 7 has a light transmission characteristic as shown in FIG. An antireflection film 77 is formed on the other main surface 73 of the transparent substrate 71.

  In the above embodiment, the optical filter module 3 is provided with the first filter 4, the second filter 7, and the switching means (not shown). However, the present invention is not limited to this, and is modularized. Instead, the optical filter system shown in FIG. 9 in which the first filter 4, the second filter 7, and switching means (not shown) are directly provided in the imaging device 1 may be constructed.

  Moreover, although the glass plate is used as the transparent substrate 61, it is not limited to this, For example, if it is a board | substrate which can permeate | transmit light, a quartz plate may be sufficient. The transparent substrate 61 may be a birefringent plate or a birefringent plate composed of a plurality of sheets. Moreover, you may comprise the transparent substrate 61 combining a quartz plate and a glass plate.

In the embodiment, TiO ₂ is used for the first thin film 65. However, the present invention is not limited to this, and it is sufficient that the first thin film 65 is made of a highly refractive material. For example, ZrO ₂ , TaO ₂ , Nb ₂ O ₂ or the like may be used. In addition, although SiO ₂ is used for the second thin film 66, the present invention is not limited to this, and the second thin film 66 may be made of a low refractive material, and for example, MgF ₂ or the like may be used.

  Moreover, although the 1st filter 4 of embodiment is arrange | positioned so that the infrared absorber 5 may be located in the lens 2 side rather than the infrared reflector 6 in an imaging device, it is not limited to this. . That is, the first filter 4 may be arranged such that the infrared reflector 6 is positioned closer to the lens 2 than the infrared absorber 5.

  For example, in the imaging device, when the first filter 4 is arranged so that the infrared absorber 5 is positioned on the lens 2 side, the light reflected by the infrared reflector 6 can be absorbed by the infrared absorber 5. Therefore, compared with the case where the infrared reflector 6 is disposed on the lens 2 side, the amount of light reflected by the infrared reflector 6 and scattered by the lens 2 can be reduced, and the occurrence of ghost is suppressed. can do. On the other hand, when the first filter 4 is arranged so that the infrared reflector 6 is located on the lens 2 side, the infrared filter is more reflective than when the first absorber 4 is arranged so that the infrared absorber 5 is located on the lens 2 side. Since the distance between the body 6 and the imaging element 9, specifically, the distance between the foreign matter generated in the infrared reflector 6 and the imaging element 9 during the manufacturing process is increased, image degradation due to the foreign matter can be suppressed.

  Further, in the embodiment, as the infrared absorber 5, one having the antireflection film 54 formed on one main surface 52 or both main surfaces 211 and 212 of the infrared absorbing glass 2 is used. The infrared absorber 5 is not limited to this. For example, when the refractive index of the infrared absorbing glass 51 in the atmosphere is substantially the same as the refractive index of the atmosphere, the antireflection film 54 may not be formed. That is, you may use the infrared rays absorption glass in which the antireflection film is not formed as an infrared rays absorber.

  In the embodiment, the infrared reflector 6 is formed by forming the infrared reflecting film 64 on one main surface 62 of the transparent substrate 61 bonded to the other main surface 53 of the infrared absorbing glass 51. The infrared reflector 6 referred to in the present invention is not limited to this. For example, an infrared reflecting film formed on the surface of infrared absorbing glass may be used as an infrared reflector. In this case, it becomes easy to reduce the size of the optical filter module and the optical filter system, simplify the switching mechanism, and save power.

  That is, in the embodiment, the infrared reflecting film 64 is formed on one main surface 62 of the transparent substrate 61 bonded to the other main surface 53 of the infrared absorbing glass 51, but the other main surface 53 of the infrared absorbing glass 51 is formed. An infrared reflection film 64 as an infrared absorber may be directly formed. Thus, if the infrared reflective film 64 is formed directly on the other main surface 53 of the infrared absorbing glass 51, the first filter 4 can be thinned.

  It should be noted that the present invention can be implemented in various other forms without departing from the spirit, gist, or main features. For this reason, the above-described embodiments and examples are merely examples in all respects and should not be interpreted in a limited manner. The scope of the present invention is indicated by the claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  The present invention can be applied to an optical filter used in an imaging device.

DESCRIPTION OF SYMBOLS 1 Imaging device 11 Optical axis 2 Lens 3 Optical filter module 4 1st filter 5 Infrared absorber 51 Infrared absorption glass 52,53 Main surface 54 Antireflection film 6 Infrared reflector 61 Transparent substrate 62,63 Main surface 64 Infrared reflection film 65 First thin film 66 Second thin film 7 Second filter 71 Transparent substrates 72 and 73 Main surface 74 Infrared pass coat 75 First thin film 76 Second thin film 77 Antireflection film 8 Optical filter 81 Antireflection film 9 Imaging element

Claims (8)

In an optical filter module provided in an imaging device and capable of switching and arranging a plurality of filters,
The plurality of filters are a first filter that transmits visible light and cuts at least infrared rays, and a second filter that passes only infrared rays, and the first filter and the second filter can be selectively switched. An optical filter module characterized by being arranged. The optical filter module according to claim 1.
The optical filter module, wherein the second filter passes only a predetermined specific band of infrared rays and cuts other bands of infrared rays. The optical filter module according to claim 1 or 2,
The first filter includes an infrared absorber that absorbs infrared rays and an infrared reflector that reflects infrared rays. The optical filter module according to claim 3,
The infrared absorber exhibits a light transmission characteristic in which a transmittance is 50% at a wavelength within a wavelength band of 620 nm to 660 nm,
The infrared reflector exhibits a light transmission characteristic in which a transmittance is 50% at a wavelength in a wavelength band of 670 nm to 690 nm,
By combining the infrared absorber and the infrared reflector, the transmittance is 50% at a wavelength in the wavelength band of 620 nm to 660 nm, and the transmittance is less than 5% at a wavelength of 700 nm. An optical filter module. Optical of an imaging device in which a coupling optical system in which at least light is incident from the outside along the optical axis, an optical filter system capable of switching and arranging a plurality of filters, an optical filter, and an imaging device are arranged in this order. In the filter system,
The plurality of filters are a first filter that transmits visible light and cuts at least infrared rays, and a second filter that passes only infrared rays, and either one of the first filter and the second filter is selective. And an optical filter system that is switched on the optical axis. The optical filter system according to claim 5.
The optical filter system, wherein the second filter passes only a predetermined specific band of infrared rays and cuts other bands of infrared rays. The optical filter system according to claim 5 or 6,
The first filter includes an infrared absorber that absorbs infrared rays and an infrared reflector that reflects infrared rays. The optical filter system according to claim 7.
The infrared absorber exhibits a light transmission characteristic in which a transmittance is 50% at a wavelength within a wavelength band of 620 nm to 660 nm,
The infrared reflector exhibits a light transmission characteristic in which a transmittance is 50% at a wavelength in a wavelength band of 670 nm to 690 nm,
By combining the infrared absorber and the infrared reflector, the transmittance is 50% at a wavelength in the wavelength band of 620 nm to 660 nm, and the transmittance is less than 5% at a wavelength of 700 nm. Optical filter system.

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