JP2012137648A - Imaging optical unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce degradation of image quality by ghost light caused between an infrared cut filter and an imaging element.SOLUTION: A light absorption structure 4 for absorbing light of an infrared half value wavelength of an infrared cut filter 1 is disposed on a surface opposed to an imaging element 5. Thus, light transmitted through the filter 1 and reflected by the imaging element 5 is transmitted through the light absorption structure 4 before reaching a near infrared reflection structure 3 of the filter 1, so that reflection light by the reflection structure 3 can be reduced. The reflection light reflected by the imaging element 5 and reflected by the reflection structure 3 is transmitted through the light absorption structure 4 again before reaching the imaging element 5, so that reflectance by incident light from the imaging element 5 can be reduced.

Description

  The present invention relates to an imaging optical unit mounted on a video camera, a digital still camera, a surveillance camera, or the like using a solid-state imaging device.

  Conventionally, imaging devices such as CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) sensors have been used in imaging systems such as video cameras and digital still cameras. These image sensors have sensitivity in a relatively wide light wavelength, and also have sensitivity in light in the near-infrared wavelength region in addition to light in the visible wavelength region. However, in an ordinary camera application, an infrared wavelength region that is invisible to the human eye is unnecessary. For this reason, in an imaging optical system such as a camera, an infrared cut filter that shields light in the jump beam region is disposed on the incident light side of the imaging element to prevent infrared light from entering the imaging element. .

  Infrared cut filters include a reflective type that reflects infrared rays and an absorption type that absorbs infrared rays.

  The reflection type infrared cut filter is manufactured by laminating a multilayer film on a transparent substrate by vacuum deposition, IAD, ion plating, sputtering, or the like, and is reflected by light interference. Further, in recent years, substrates made of synthetic resin have been used in response to demands for weight reduction and processing into arbitrary shapes.

  On the other hand, an absorption type infrared cut filter absorbs infrared rays by metal ions, kneads metal ions and pigments in a resin as a base material, or applies a pigment that absorbs infrared rays on a transparent substrate. Have been made.

JP 2003-161831 A JP 2000-7870 A JP 2002-303720 A JP 2002-281515 A JP 2006-301894A JP 2008-51985 A JP 2008-112033 A

  Patent Document 1 discloses a reflection-type infrared cut filter that forms a near-infrared light reflecting structure by laminating a plurality of low-refractive materials and high-refractive materials on a transparent substrate to obtain desired spectral characteristics. ing. The reflection type infrared cut filter can be manufactured thinner than the absorption type, and further has an advantage of high transmittance in the transmission wavelength region and good color reproducibility.

  However, this reflection type infrared cut filter has a transmission wavelength region that transmits light, a non-transmission wavelength region that prevents transmission, and a transition wavelength region that transitions from the transmission wavelength region to the non-transmission wavelength region. The transition wavelength region has a wavelength (infrared light half-value wavelength) at which the transmittance is 50% at a wavelength between 600 and 750 nm, and the reflectance at that wavelength is approximately 50%. For this reason, infrared half-wavelength light in the transition wavelength region causes ghost light and is likely to cause deterioration in image quality.

  The intensity of the ghost light by the infrared cut filter is simply a value calculated by (spectral transmittance of the infrared cut filter) / (spectral reflectance of the surface of the infrared cut filter).

  Patent Document 2 discloses an absorption-type infrared cut filter in which copper ions or the like are contained in a base resin. This produces an infrared cut filter using an infrared absorption action of copper ions or the like, and has a low reflectance at the half-wavelength of infrared light, and does not cause ghost light. However, in order to sufficiently absorb light in the near-infrared wavelength region, a thickness of at least 0.35 mm is required, which is in conflict with the recent demand for miniaturization of optical systems that is particularly required.

  In patent document 3, the absorption type infrared cut filter which apply | coated the pigment | dye on the board | substrate is disclosed, Using the coating liquid which disperse | distributed the pigment | dye which absorbs the light of a near-infrared wavelength range to resin or an organic solvent. I am making it. However, the infrared cut filter produced in this way hardly causes image quality degradation due to ghost light, as in Patent Document 2, but the dye absorbs light in the visible wavelength region slightly, and in the near infrared wavelength region. If it is sufficiently absorbed, the transmittance in the visible wavelength region is lowered.

  Patent Document 4 discloses an imaging optical system in which a color filter that absorbs light of an infrared light half-value wavelength of an infrared cut filter is disposed between the infrared cut filter and the imaging element. With such a configuration, it is possible to significantly reduce the generation of ghost light, but a separate color filter is required, leading to an increase in the size and cost of the imaging optical system.

  Patent Documents 5 and 6 disclose, for the purpose of thinning the filter, a hybrid type infrared cut filter provided with a near-infrared light reflecting structure made of an interference film and a light absorbing structure made of a dye that absorbs infrared light. Yes. By setting it as such a structure, the thin infrared cut filter which shields the light of a near-infrared wavelength range can be produced, maintaining the transmittance | permeability in the visible wavelength range of a wavelength of 400-700 nm.

  However, as shown in Patent Documents 5 and 6, when the transmittance in the visible wavelength region is maintained high, the red of the near-infrared light reflecting structure existing at a wavelength of 600 to 750 nm, which is a main factor of ghost light, It becomes impossible to sufficiently absorb light of half-wavelength of outside light. For this reason, it is difficult to greatly improve image quality degradation due to ghost light. Further, Patent Documents 5 and 6 do not describe the location of the light absorption structure that further reduces the generation of ghost light.

  When using an image sensor with high sensitivity in the near-infrared wavelength region, such as a surveillance camera, ghost light due to the infrared cut filter is likely to be generated, and the arrangement position of the light absorbing structure is optimized, and the ghost light It is desired to reduce the strength of the as much as possible.

  An object of the present invention is to eliminate the above-described problems and optimize the light absorption characteristics and arrangement position of a light absorption structure in a hybrid type infrared cut filter, thereby suppressing image quality deterioration due to ghost light. An optical unit is provided.

  In order to achieve the above object, an imaging optical unit according to the present invention includes an infrared cut filter and an image sensor, and the infrared cut filter has a transparent substrate, a near infrared light reflecting structure, and a predetermined absorption wavelength region. The near-infrared light reflecting structure has a transition wavelength region transitioning from a transmission wavelength region to a non-transmission wavelength region between wavelengths of at least 600 to 750 nm, and the light absorption structure At least part of the absorption wavelength region overlaps with the transition wavelength region, and the light absorption structure is disposed between the near-infrared reflective structure having the transition wavelength region and the imaging device. .

  According to the imaging optical unit according to the present invention, by arranging the light absorption structure between the near-infrared light reflection structure having the half-wavelength of infrared light and the imaging element, the vicinity of the half-wavelength of infrared light is high. Even when an image sensor having sensitivity is used, image quality deterioration due to ghost light can be suppressed.

FIG. 2 is a configuration diagram of an imaging optical unit of Example 1. It is a graph of the optical characteristics of a cyanine dye. It is a graph of the sensitivity characteristic of the image sensor used for the surveillance camera. It is a graph of the intensity characteristic of ghost light. It is a block diagram of the imaging optical unit of a modification. FIG. 6 is a configuration diagram of an imaging optical unit of Example 2. It is a graph of the intensity characteristic of ghost light. It is a block diagram of the imaging optical unit of a modification. FIG. 6 is a configuration diagram of an imaging optical unit of Example 3. It is a block diagram of a near-infrared-light reflection prevention structure. It is a graph of the intensity characteristic of ghost light. It is a block diagram of an imaging optical system.

  The present invention will be described in detail based on the embodiments shown in the drawings.

  FIG. 1 is a configuration diagram of an imaging optical unit according to the first embodiment. The infrared cut filter 1 has a configuration in which a near-infrared light reflecting structure 3 and a light absorbing structure 4 are laminated on a transparent substrate 2, and solid-state imaging is performed on the optical path on the light absorbing structure 4 side of the infrared cut filter 1. Element 5 is arranged.

  In Example 1, a glass substrate having a thickness of 0.2 mm, specifically OA-10G (trade name, manufactured by Nippon Electric Glass Co., Ltd.) is used for the transparent substrate 2. The transparent substrate 2 may be a substrate made of synthetic resin such as polycarbonate, PEN, or polyimide, but considering the change in spectral characteristics due to heat, moisture, etc. due to the film formation of the near-infrared light reflecting structure 3, It is more preferable that the heat resistance, that is, the glass transition point Tg is high and the water absorption is low.

The near-infrared light reflecting structure 3 is formed on the transparent substrate 2 by laminating a plurality of SiO ₂ and TiO ₂ having different refractive indexes by a vacuum deposition method. The spectral characteristics of the reflective structure 3 are determined by the optical film thickness n · d (n: refractive index, d: physical film thickness) of SiO ₂ and TiO ₂ . The reflection structure 3 has a wavelength at which both the transmittance and the reflectance are approximately 50% in the transition wavelength region where the transmittance continuously decreases from the transmission wavelength region to the non-transmission wavelength region between wavelengths of 600 to 750 nm. (Infrared light half-value wavelength). The reflecting structure 3 is designed as a film so as to shield light in the near infrared wavelength region.

In the present embodiment, SiO ₂ and TiO ₂ are used for the near-infrared light reflecting structure 3. For example, MgF ₂ , Al ₂ O ₃ , MgO, ZrO ₂ , Nb ₂ O ₅ , Ta ₂ O _{5 are used.} May be used, and a material suitable for a desired spectral characteristic may be selected as appropriate. In this embodiment, the reflective structure 3 is formed by a vacuum vapor deposition method, but can also be formed by a film formation method other than the vacuum vapor deposition method, such as an ion plating method, an ion assist vapor deposition method, or a sputtering method. A film formation method most suitable for the purpose and conditions may be selected.

  The light absorbing structure 4 is formed by applying a coating solution obtained by dissolving and dispersing a pigment, which is a dye having a predetermined absorption wavelength region in an organic solvent, onto the near infrared light reflecting structure 3. It is filming.

  In the present embodiment, a cyanine dye having optical characteristics such as transmittance and absorptivity as shown in FIG. 2 is used as the dye of the light absorption structure 4, and a styrene resin is used as the resin. These dyes and resins are dissolved in an organic solvent composed of a ketone mixture such as methyl ethyl ketone and methyl isobutyl ketone to prepare a coating solution, and this coating solution is applied onto the near-infrared light reflecting structure 3 by a spin coating method. Apply. Further, the light absorbing structure 4 is formed by drying in a heating furnace and volatilizing the solvent. The light absorbing structure 4 may be formed by a dip method, a spray method, a gravure method, a bar coater method or the like instead of the spin coating method.

  In addition, the dye is not limited to cyanine, but may be any one having absorption in the near infrared wavelength region, for example, phthalocyanine, naphthalocyanine, pyrylium, squarylium, polymethine, diimonium, azo compound Or anthraquinone may be used, or these may be used by mixing a plurality of n pigments.

  As long as the resin has high transmittance in the visible wavelength region, the resin is not limited to styrene, and may be a polyester or acrylic resin, or a mixture of a plurality of resins.

  Furthermore, the organic solvent is not limited to a ketone type, and may be a hydrocarbon type such as cyclohexane, an ester type such as ethyl acetate, an ether type such as methyl cellosolve, an alcohol type such as methanol, or an amine type organic solvent such as dimethylformamide. A mixture may be used.

  As described above, the intensity of the ghost light of the infrared cut filter is simply calculated by (spectral transmittance of the infrared cut filter) · (spectral reflectance of the infrared cut filter). In the infrared cut filter comprising the near-infrared light reflecting structure 3, the intensity of the ghost light is maximum in the transition wavelength region where the transmission wavelength region transitions to the non-transmission wavelength region, and is approximately 25%.

  Practically, the intensity of the ghost light needs to be about 15 to 16% or less although it depends on the sensitivity of the imaging optical system and the imaging device. Therefore, for example, in order to reduce the intensity to 16% or less, when the light absorbing structure 4 is combined, at least the transmittance is 40% and the reflectance is 40%. Therefore, at least part of the absorption wavelength region of the light absorption structure 4 overlaps the transition wavelength region of the near-infrared light reflection structure 3, and a characteristic having an absorption rate of 20% or more is required.

  Thus, the selection of the pigment, resin, and organic solvent may be appropriately selected in accordance with the purpose and conditions.

  FIG. 3 is a graph of sensitivity characteristics of the image sensor 5 for each of red, green, and blue colors. For example, the image sensor 5 used in the monitoring camera has a characteristic particularly sensitive to red so that it can be monitored at night. It is preferable to use one.

  FIG. 4 is a graph showing the intensity characteristics of ghost light near the half-wavelength of infrared light (660 nm) generated by the infrared cut filter and the image sensor 5 having the characteristics shown in FIG.

  And as shown to A of FIG. 4, the intensity | strength of the ghost light in the imaging optical unit using the infrared cut filter comprised only by the near-infrared-light reflection structure 3 without providing the light absorption structure 4 is about maximum. 24%.

  Further, as Comparative Example 1, the stacking order of the near-infrared light reflecting structure 3 and the light absorbing structure 4 of the infrared cut filter 1 shown in FIG. 1 is reversed, and the light absorbing structure 4 and the reflection are reflected on the transparent substrate 2. The structures 3 were stacked in this order. In the imaging optical unit using such an infrared cut filter, the maximum ghost light intensity was about 12.5% as shown in FIG. 3B.

  On the other hand, in the imaging optical unit using the infrared cut filter 1 in which the near-infrared light reflection structure 3 and the light absorption structure 4 are sequentially laminated on the transparent substrate 2 as in the first embodiment, FIG. As shown in C, the intensity of the ghost light is about 6% at the maximum.

  In the infrared cut filter 1 of the first embodiment, a light absorbing structure 4 that absorbs light in the transition wavelength region of the near infrared light reflecting structure 3 is disposed on a surface facing the imaging element 5.

  Thereby, the light transmitted through the infrared cut filter 1 and reflected by the image sensor 5 passes through the light absorption structure 4 before reaching the near infrared light reflection structure 3 of the infrared cut filter 1. Light reflected by the reflective structure 3 can be reduced.

  Further, the reflected light reflected by the imaging element 5 and reflected by the near-infrared light reflecting structure 3 passes through the light absorbing structure 4 again before reaching the imaging element 5, The reflectance from the image sensor 5 due to incident light can be reduced.

  In the first embodiment, the configuration as shown in FIG. 1 is adopted. However, as shown in the modification of FIG. 5A, the light absorption structure 4 is provided on the surface of the transparent substrate 2 on the imaging element 5 side, and the opposite side. The near-infrared light reflecting structure 3 may be formed on the surface. Alternatively, as shown in FIG. 5B, the light absorption structure 4 and the reflection structure 3 may be sequentially formed on the surface of the transparent substrate 2 opposite to the imaging element 5. That is, a structure in which the light absorption structure 4 is disposed between the near-infrared light reflection structure 3 and the imaging element 5 may be used.

  Moreover, when providing the some light absorption structure 4, at least one should just be arrange | positioned between the near-infrared-light reflection structure 3 and the image pick-up element 5. FIG.

  FIG. 6 is a configuration diagram of the imaging optical unit of Example 2, and a near-infrared light reflecting structure 3a that shields light having a half-wavelength of infrared light is formed on the surface of the transparent substrate 2 opposite to the imaging element 5. is doing. Further, a light absorption structure 4 is formed on the surface of the transparent substrate 2 on the image pickup element 5 side, and light in an opaque wavelength region that cannot be shielded by the reflection structure 3a on the light absorption structure 4 is further formed. The near-infrared light reflecting structure 3b to be shielded is formed.

  As the transparent substrate 2, a synthetic resin film substrate, specifically, Arton (trade name, manufactured by JSR), which is a norbornene-based resin having a thickness of 0.1 mm, is used. However, if the transparency in the visible wavelength region is high, not only Arton but also other norbornene resins such as Zeonex, Zeonor (trade name, manufactured by Nippon Zeon Co., Ltd.), F1 (trade name, manufactured by Gunze Co., Ltd.) are used. Also good. In addition to norbornene resins, various synthetic resin film substrates such as PMMA, PC (polycarbonate), PET, PEN, and polyimide resins can also be used.

  Considering thermal stress and film stress due to film formation of the near-infrared light reflecting structure 3, and changes in the spectrum due to moisture, the heat resistance, that is, the glass transition point Tg is high, the bending elasticity is high, and the water absorption is low. More preferred. Considering these conditions, norbornene resin and polyimide resin are one of the most suitable materials.

  A synthetic resin film substrate is thinner and more flexible than a normal glass substrate or the like, and has an advantage that it can be thinned and processed into an arbitrary shape. However, since it is easily affected by film stress or the like, it is preferable to form the near-infrared light reflecting structure 3 on both surfaces of the substrate so as to cancel each other's film stress as disclosed in Patent Document 7. .

  FIG. 7 is a graph showing the intensity characteristics of ghost light in the vicinity of the half-wavelength of infrared light (660 nm) of the imaging optical unit in the second embodiment. The intensity of the ghost light in the imaging optical unit using the infrared cut filter composed only of the near-infrared light reflecting structures 3a and 3b without providing the light absorbing structure 4 is about 24% at the maximum like A. is there.

  Further, as Comparative Example 2, the positions of the near-infrared light reflecting structures 3a and 3b shown in FIG. 6 are reversed, and the reflecting structure 3b is formed on the surface of the transparent substrate 2 on the opposite side of the image pickup device 5 to be transparent. The light absorption structure 4 and the reflection structure 3a were formed on the surface of the substrate 2 on the image sensor 5 side. The intensity of the ghost light in the imaging optical unit using such an infrared cut filter was a maximum of about 12.5% as shown in B.

  On the other hand, the intensity of the ghost light in the imaging optical unit using the infrared cut filter 1 in the second embodiment is about 7.5% at the maximum like C.

  This is because the reflection of the infrared cut filter 1 with respect to the reflected light in the vicinity of the half-wavelength of infrared light from the imaging element 5 is predominantly due to the near-infrared light reflecting structure 3a, and reaches the reflecting structure 3a. This is because the light absorbing structure 4 absorbs light in the vicinity of the half-wavelength of infrared light.

  In the second embodiment, the configuration shown in FIG. 6 is used. However, as shown in the modification of FIG. 8A, the near-infrared light reflecting structure 3b is provided on the surface of the transparent substrate 2 on the image sensor 5 side. The light absorbing structure 4 and the near-infrared light reflecting structure 3a may be sequentially formed on the opposite surface. Alternatively, as shown in FIG. 8B, the near-infrared light reflecting structure 3b and the light absorbing structure 4 are sequentially formed on the surface of the transparent substrate 2 on the image pickup device 5 side, and on the opposite surface. The reflective structure 3a may be formed. Even in these cases, the intensity of the ghost light can be reduced as compared with an infrared cut filter in which the light absorption structure 4 is not located between the reflection structure 3a and the imaging element 5 as in Comparative Example 2. .

  When a plurality of light absorbing structures 4 are configured, at least one of the light absorbing structures 4 may be disposed between the near-infrared light reflecting structure 3 a and the image sensor 5.

  FIG. 9 shows a configuration diagram of the imaging optical unit in Example 3. Further, an antireflection structure 6 is further formed on the outermost layer on the imaging element 5 side of the infrared cut filter 1 shown in FIG. 8B. Yes. As the antireflection structure 6, an acrylic resin having a plurality of conical protrusions 6 a whose projections are shorter than the wavelength of light as shown in FIG.

  The volume of the conical protrusion 6a gradually changes from the top to the bottom, and the corresponding effective refractive index also changes continuously from the top to the bottom of the protrusion 6a. Therefore, when light enters the conical protrusion 6a from above, since there is a smooth effective refractive index distribution, there is no abrupt refractive index difference, and almost no light is reflected on the surface of the antireflection structure 6. There is nothing.

  In the third embodiment, the protrusion 6a of the antireflection structure 6 has a conical shape, but the same effect can be obtained even when a pyramid-shaped protrusion or an inverted conical recess is used.

  The antireflection structure 6 uses a mold having a fine uneven periodic structure, is filled with a resin composition containing a polymerizable compound and a polymerization initiator, is cured, and the mold is peeled off. Molding.

  In the third embodiment, an acrylic resin is used for the antireflection structure 6, but any resin having a high light transmittance may be used. For example, a urethane resin, a polystyrene resin, an olefin resin, or the like may be used. it can.

  In Example 3, the resin composition to be the antireflection structure 6 was thermally cured, but the resin composition was cured by using other active energy rays such as visible light, electron beam, plasma, infrared rays, and ultraviolet rays. It may be used. The irradiation amount of active energy rays should just be the energy amount which hardening of a resin composition advances. Further, for the production of the antireflection structure 6, an injection molding method or the like may be used as long as a fine uneven structure is finally obtained.

  The antireflection structure 6 may be made of a fine concavo-convex structure made of an oxide such as alumina or zirconia, or may be made of a single layer or a plurality of thin films. As a method for producing the antireflection structure 6, for example, a coating solution in which a material that is a component of a fine concavo-convex structure such as an aluminum compound or a zinc compound is dissolved in an organic solvent is prepared, and this coating solution is applied at room temperature or under pressure. It is obtained by heating and drying or heat treatment. For applying the solution, a dipping method, a spin coating method, a spray method, a printing method, a flow coating method, or the like is used.

Further, the antireflection structure 6 composed of a single layer or a plurality of layers of thin films uses a relatively low refractive index such as MgF ₂ or SiO _{2 in} the case of a single layer, and the refractive index in the case of a plurality of layers. Obtained by alternately laminating thin films having different thicknesses. As a film forming method, a vacuum deposition method, an ion plating method, an ion assist deposition method, a sputtering method, or the like is used.

  FIG. 11 is a graph of intensity characteristics comparing the intensity of ghost light of the imaging optical unit with and without the antireflection structure 6, and the structure without the antireflection structure 6 is shown in FIG. The structure 6 has a structure shown in FIG.

  From this graph, it can be seen that the imaging optical unit having the antireflection structure 6 has lower ghost light intensity. This is because the reflectance of the surface of the infrared cut filter 1 on the image sensor 5 side is reduced by the antireflection structure 6.

  In each of the first and second embodiments, the antireflection structure 6 can be provided on the surface of the infrared cut filter 1 on the image sensor 5 side.

  FIG. 12 shows an image pickup optical system used for a monitoring camera or the like, and the image pickup optical units of Embodiments 1 to 3 are used. On the optical path, the lens 11, the light quantity diaphragm 12, the lenses 13 to 15, the infrared cut filter 1, and the image sensor 5 are sequentially arranged.

  In the light quantity diaphragm device 12, a pair of diaphragm blades 17a and 17b are movably attached to the diaphragm blade support plate 16, and the light quantity is adjusted by changing the area of the opening. An ND (Neutral Density) filter 18 for reducing the amount of light is attached to the diaphragm blade 17a.

  The diaphragm blades 17a and 17b and the ND filter 18 adjust the amount of incident light so that the aperture of the diaphragm can be maintained as large as possible even with the same amount of light. As a result, it is possible to reduce deterioration in image quality due to a hunting phenomenon or a light diffraction phenomenon.

  Further, the infrared cut filter 1 can be freely advanced and retracted with respect to the optical path by the filter drive unit 20 according to the output of the control means 19, and the amount of infrared light is limited in accordance with the characteristics of the image sensor 5 to obtain an appropriate image. Be able to.

  The light that has passed through the light amount diaphragm 12 enters the infrared cut filter 1, but when the subject is bright, that is, when the amount of visible light is sufficient, the infrared cut filter 1 is placed on the optical path of the imaging optical system by the filter drive unit 20. Insert into. On the other hand, when the subject is dark, such as at night, that is, when the amount of visible light is insufficient, the infrared cut filter 1 is retracted out of the optical path of the imaging optical system by the filter driving unit 20.

  At this time, by using the infrared cut filter 1 shown in the first to third embodiments, it is possible to further reduce ghost light due to the wavelength of light in the vicinity of the half-wavelength of infrared light in the transition wavelength region.

DESCRIPTION OF SYMBOLS 1 Infrared cut filter 2 Transparent substrate 3, 3a, 3b Near-infrared light reflection structure 4 Light absorption structure 5 Imaging element 6 Antireflection structure 6a Protrusion 12 Light quantity diaphragm 17a, 17b Diaphragm blade 18 ND filter 20 Filter drive Part

Claims (6)

  The infrared cut filter comprises an infrared cut filter and an imaging device, and the infrared cut filter includes a transparent substrate, a near infrared light reflection structure, and a light absorption structure having a predetermined absorption wavelength region, and the near infrared light reflection structure. The body has a transition wavelength region that transitions from a transmission wavelength region to a non-transmission wavelength region between wavelengths of at least 600 to 750 nm, and at least a part of the absorption wavelength region of the light absorption structure overlaps the transition wavelength region. The imaging optical unit, wherein the light absorbing structure is disposed between a near infrared light reflecting structure having the transition wavelength region and the imaging element.   The imaging optical unit according to claim 1, wherein the light absorbing structure is a resin in which a pigment is dispersed.   The light absorbing structure has an absorptivity of 20% or more at a wavelength at which the transmittance is approximately 50% within the transition wavelength region of the near infrared light reflecting structure. The imaging optical unit described in 1.   The imaging optical unit according to any one of claims 1 to 3, wherein an antireflection structure is provided on a surface layer on the imaging element side of the infrared cut filter.   The imaging optical unit according to any one of claims 1 to 4, wherein the transparent substrate is a synthetic resin film.   A diaphragm blade having an opening, an imaging optical unit according to any one of claims 1 to 5, and a drive unit that drives the infrared cut filter so that the infrared cut filter can freely move back and forth in the opening. An imaging optical system characterized by the above.

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