JP2014174325A - Imaging optical system unit, imaging device and digital device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging optical system unit, an imaging device and a digital device that reduce color shading, while attaining miniaturization and reduction in costs, and enable reduction in intensity of unwanted light arising from an infrared cut filter (IRCF).SOLUTION: An imaging optical system unit SUa comprises: an imaging optical system OSa; and an IRCFFT. The imaging optical system OSa includes an optical element that has an anti-reflection layer, in which average reflectance of wavelengths 600 to 650 nm of 5-degree incident light is less than 1.8%, formed on at least one surface, and the IRCFFT is configured to satisfy |λ(0, 50;600 to 700)-λ(30, 50;600 to 700)|≤15 nm as to a wavelength λ(α, 50;600 to 700) where reflectance of α-degree incident light in wavelengths 600 to 700 nm is 50%, and 0.4%/nm≤|▵R|≤8%/nm as to a tilt ▵R of reflectance differences to a difference in respective wavelengths where reflectance of 0-degree incident light in wavelengths 600 to 650 nm is 30% and 70%.

Description

  The present invention relates to an imaging optical system that forms an optical image of a subject on a predetermined surface and an imaging optical system unit that includes an infrared cut filter. The present invention relates to an imaging apparatus and a digital device using the imaging optical system unit.

  In recent years, imaging devices using solid-state imaging devices such as CCD (Charged Coupled Device) type image sensors and CMOS (Complementary Metal Oxide Semiconductor) type image sensors have become more sophisticated and miniaturized. Digital devices such as mobile phones and personal digital assistants equipped with devices have become widespread. Since such a solid-state imaging device is usually formed of a silicon semiconductor, it has light receiving sensitivity not only in the visible light wavelength band but also in the near-infrared (IR) wavelength band. For this reason, when light including visible light and near-infrared light is incident on the image sensor, the near-infrared light is also captured in the image. Therefore, there is a problem such that the obtained image includes a pseudo color due to the near-infrared light. Arise. In order to eliminate such problems, an infrared cut filter that cuts (filters) an infrared wavelength region corresponding to the light receiving sensitivity of the solid-state image sensor is generally disposed between the imaging optical system and the solid-state image sensor. The

  This infrared cut filter is roughly classified into an absorption type infrared cut filter that cuts infrared rays by absorbing infrared rays and a reflection type infrared cut filter that cuts infrared rays by reflecting infrared rays.

  This absorption type infrared cut filter is formed of a material to which an infrared absorbing material that absorbs infrared rays is added. This infrared absorbing material includes, for example, Lumogen IR765 and Lumogen IR788 manufactured by BASF, ABS643, ABS654, ABS667, ABS670T, IRA693N and IRA735, manufactured by Exciton. W. SDA3598, SDA6075, SDA8030, SDA8303, SDA8470, SDA3039, SDA3040, SDA3922 and SDA7257 manufactured by SANDS, TAP-15 and IR-706 manufactured by Yamada Chemical Co., Ltd., CIR-1080 and CIR-1081 manufactured by Nippon Carlit, manufactured by Yamamoto Chemical YKR-3080 and YKR-3081, Nippon Shokubai EEX Color IR-10, IR-12 and IR-14, Mitsui Chemicals Fine SIR-128, SIR-130, SIR-159, PA-1001, PA- 1005 etc. can be mentioned.

The reflective infrared cut filter includes a layer made of a relatively high refractive index material such as TiO ₂ , Nb ₂ O _5, and Ta ₂ O ₅ by a thin film forming method such as a vacuum evaporation method and a sputtering method. And an optical thin film (multilayer film) in which layers made of a relatively low refractive index material such as SiO ₂ and MgF ₂ are alternately laminated. Accordingly, the reflective infrared cut filter has spectral characteristics (transmittance characteristics) that transmit visible light and reflect near-infrared light.

  An imaging apparatus having this infrared cut filter is disclosed in Patent Document 1, for example. The imaging apparatus disclosed in Patent Document 1 is provided with an imaging element that receives light from an object and picks up an image, an imaging optical system that guides light to the imaging element, and the imaging optical system, and an infrared region. An infrared cut filter for blocking the light, and an antireflection coat provided on the infrared cut filter and having a reflectance of substantially 1% or less with respect to light in the visible light region. More specifically, the imaging optical system in the imaging apparatus disclosed in Patent Document 1 includes an optical aperture, a lens, and a parallel plate-shaped infrared cut filter in order from the object side to the image side, and an image of the infrared cut filter. An antireflection coating is formed on the side surface. An image sensor is arranged on the image side of the infrared cut filter. Therefore, the light from the subject imaged by the lens enters the image sensor through the infrared cut filter and the antireflection coat. In the imaging apparatus disclosed in Patent Document 1 having such a configuration, the antireflection coating is configured so that reflected light that is incident on the infrared cut filter and reflected on the image side surface and the object side surface of the infrared cut filter enters the image sensor. It is preventing. As a result, the antireflection coating suppresses the generation of ghosts that occur when the reflected light enters the image sensor.

JP 2006-313121 A

  By the way, since the reflection type infrared cut filter described above utilizes interference of light, the infrared cut characteristic (infrared transmission characteristic) representing the relationship between the incident angle of the incident light and the infrared cut amount (infrared transmission amount) is Depending on the incident angle of the incident light, it changes with respect to the change of the incident angle. As a result, in the reflective infrared cut filter, when the incident angle of incident light incident on the reflective infrared cut filter via the imaging optical system is different between the central portion and the peripheral portion, the central portion and the peripheral portion Infrared cut amount differs depending on the part. For this reason, in the image obtained through the reflective infrared cut filter, color unevenness (color shading) in which the central portion becomes red occurs. In particular, since the imaging optical system of the imaging device mounted on a mobile phone such as a smartphone has a relatively wide angle of view and a low profile, the incident angle is about 30 degrees in the peripheral portion. Serious.

  On the other hand, the above-described absorption-type infrared cut filter does not have the dependency of the incident angle on such infrared cut characteristics, but the price of the infrared absorber is high and the cost is high. Further, in order to obtain a desired infrared absorption amount, it is necessary to increase the thickness of the absorption type infrared cut filter mixed with the infrared absorbing material, which is inconvenient for shortening the optical total length. In particular, since an imaging device mounted on a mobile phone such as a smartphone has an optical total length of several millimeters, it is desired that the imaging optical system unit can be made as thin as possible, and this problem is serious.

  In addition, when the reflective infrared cut filter is arranged on the image side of the imaging optical system, light incident on the reflective infrared cut filter from the imaging optical system is reflected according to the reflectance characteristics of the reflective infrared cut filter. The reflected light returns to the imaging optical system, is reflected mainly by the optical element arranged closest to the image side of the imaging optical system, and enters the reflective infrared cut filter again. The light (referred to as “unnecessary light” or “harmful light”) that is incident on the reflective infrared cut filter again by being reflected between the reflective infrared cut filter and the imaging optical system is so-called. A flare (lens flare) is generated, and a position that should be originally incident by reflection between the reflective infrared cut filter and the imaging optical system (light that directly reaches the image sensor from the imaging optical system via the reflective infrared cut filter ( The incident light enters the image sensor at a position different from the position on the light-receiving surface of the image sensor in direct light), thereby causing a ghost in the image. The antireflection coating disclosed in Patent Document 1 prevents reflected light reflected by the image side surface and the object side surface of the infrared cut filter from entering the image sensor, and such a reflection type infrared cut filter and It does not prevent reflected light due to reflection with the imaging optical system.

  The present invention has been made in view of the above-described circumstances, and its object is to reduce color unevenness and reduce the intensity of unnecessary light caused by an infrared cut filter while reducing size and cost. An imaging optical system unit capable of performing imaging, and an imaging apparatus and a digital device using the imaging optical system unit are provided.

  In order to solve the above technical problem, the present invention provides an imaging optical system unit, an imaging apparatus, and a digital device having the following configurations.

An imaging optical system unit according to an aspect of the present invention includes: an imaging optical system that forms an optical image of a subject on a predetermined surface; and an infrared cut filter that is disposed on an image side of the imaging optical system. The optical system includes an optical element formed on at least one antireflection layer that satisfies the following conditional expression (A1), and the infrared cut filter satisfies the following conditional expressions (B1) and (B2): It is characterized by.
RCAR (5, 600 to 650) ≦ 1.8% (A1)
| Λ (0, 50; 600 to 700) −λ (30, 50; 600 to 700) | ≦ 15 nm (B1)
0.4% / nm ≦ | ΔR | ≦ 8% / nm (B2)
However, RCAR (5, 600 to 650) is an average reflectance of the antireflection layer from a wavelength of 600 nm to 650 nm in incident light incident at 5 degrees, and λ (0, 50; 600 to 700) is a wavelength. It is a wavelength (nm) at which the reflectance of incident light incident at 0 degree incidence is 50% between 600 nm and a wavelength of 700 nm, and λ (30, 50; 600 to 700) is from a wavelength of 600 nm to a wavelength of 700 nm. Is the wavelength (nm) at which the reflectance of incident light incident at 30 degrees is 50%, and ΔR is the incident light incident at 0 degrees between wavelengths 600 nm and 700 nm. The wavelength at which the reflectance is 30% is λ (0, 30; 600 to 700), and the reflection of incident light that is incident at 0 degrees between the wavelength 600 nm and the wavelength 700 nm. ΔR = (70−30) / (λ (0,70; 600 to 700) −λ (0,30; 600) where λ (0,70; 600 to 700) is a wavelength at which is 70%. ~ 700)) The slope of the reflectance change with respect to the wavelength change expressed in (% / nm).

  Since the infrared cut filter of such an imaging optical system unit satisfies the conditional expression (B1), the incident angle dependency of the infrared cut characteristic is low. For this reason, the imaging optical system unit uses an infrared cut filter having a low incident angle-dependent infrared cut characteristic, so that the infrared cut characteristic can be obtained even when the difference in incident angle between the central part and the peripheral part is large. The change between the central portion and the peripheral portion becomes small (the infrared cut amount becomes substantially uniform), color unevenness can be reduced, and the height can be reduced. Moreover, since conditional expression (B2) is satisfy | filled, an infrared cut characteristic and productivity can be made compatible. By falling below the lower limit of the conditional expression (B2), it is not necessary to laminate an excessively thin film, and it is possible to prevent warpage of the infrared cut filter and decrease in yield. On the other hand, exceeding the upper limit of the conditional expression (B2) can prevent unnecessary infrared rays from entering the image sensor.

  Here, while the color unevenness can be reduced as described above, since the light reflected by the infrared cut filter is reflected by the lens surface of the imaging optical system, the intensity of unnecessary light returning to the infrared cut filter again is general. It becomes stronger than the case of a simple infrared cut filter. However, since the imaging optical system unit includes an optical element on which at least one antireflection layer that satisfies the conditional expression (A1) is formed, the intensity of unnecessary light can be reduced.

  Therefore, such an imaging optical system unit can reduce color unevenness and reduce the intensity of unnecessary light due to the infrared cut filter while reducing the size and cost.

According to another aspect, in the above-described imaging optical system unit, the antireflection layer satisfies a conditional expression (A2) below.
RCAR (5, 420 to 600) ≦ 2% (A2)
However, RCAR (5, 420 to 600) is an average reflectance of the antireflection layer from a wavelength of 420 nm to 600 nm in incident light incident at 5 degrees incidence.

  In such an imaging optical system unit, when the antireflection layer satisfies the conditional expression (A2), reflection of the antireflection layer with respect to light reflected by the infrared cut filter and incident on the antireflection layer can be effectively reduced. The generation of unnecessary light due to the infrared cut filter can be effectively reduced by the antireflection layer.

  In another aspect, in the above-described imaging optical system unit, the optical element having the antireflection layer is a flat plate or a lens having a light-transmitting property with respect to visible light.

  According to this configuration, it is possible to provide an imaging optical system unit including a flat plate or a lens that has an antireflection layer and has a translucency for visible light.

  According to another aspect, in the above-described imaging optical system unit, the optical element having the antireflection layer is arranged on the most image side.

  In general, reflection of light occurs at an interface where materials having different refractive indexes contact each other. In such an imaging optical system unit, since the optical element having the antireflection layer is disposed closest to the image side, the interface between the infrared cut filter and the antireflection layer can be reduced. The generation of unnecessary light due to the anti-reflection layer can be reduced more effectively.

  According to another aspect, in the above-described imaging optical system unit, the antireflection layer is formed on a lens surface on the image side of the optical element.

  In such an imaging optical system unit, since the antireflection layer is formed on the image side surface of the optical element disposed closest to the image side, the interface between the infrared cut filter and the antireflection layer should be minimized. The generation of unnecessary light due to the infrared cut filter can be further effectively reduced by the antireflection layer.

  According to another aspect, in the above-described imaging optical system unit, all the lenses included in the imaging optical system are formed of a resin material.

  In recent years, the entire solid-state imaging device has been required to be further downsized, and even a solid-state imaging device having the same number of pixels has a small pixel pitch, and as a result, an imaging surface size has been reduced. In such an imaging optical system unit for a solid-state imaging device having a small imaging surface size, it is necessary to relatively shorten the focal length of the entire system, so that the radius of curvature and the outer diameter of each lens are considerably reduced. Therefore, the imaging optical system of such an imaging optical system unit is composed of a resin material lens manufactured by injection molding, and compared with a glass lens manufactured by time-consuming polishing. Even a lens having a small radius of curvature or outer diameter can be produced in large quantities at a low cost. Moreover, since the lens made of a resin material can lower the press temperature, it is possible to suppress the wear of the molding die, and as a result, the number of times of replacement and maintenance of the molding die is reduced, thereby reducing the cost. be able to.

In another aspect, in the above-described imaging optical system unit, the substrate refractive index of the optical element having the antireflection layer satisfies the following conditional expression (A3).
1.4 ≦ nd ≦ 1.7 (A3)
Where nd is the refractive index of the d line.

  In such an imaging optical system unit, the antireflective layer can be formed with a small film configuration when the substrate refractive index of the optical element having the antireflective layer satisfies the conditional expression (A3). For this reason, such an imaging optical system unit can form an antireflection layer more easily, and can reduce cost.

  According to another aspect, in the above-described imaging optical system unit, the antireflection layer is a multilayer film having a total film thickness of 600 nm or less and a number of layers of 15 or less.

  According to this configuration, it is possible to provide an imaging optical system unit including a lens having a multilayer antireflection layer having a total film thickness of 600 nm or less and a number of layers of 15 or less.

  An imaging apparatus according to another aspect of the present invention includes any one of the above-described imaging optical system units and an imaging element that converts an optical image into an electrical signal, and the imaging optical system unit includes: The imaging optical system is capable of forming an optical image of an object on the light receiving surface of the imaging element as the predetermined surface.

  Such an imaging apparatus uses an imaging optical system unit that can reduce color unevenness and reduce the intensity of unnecessary light caused by the infrared cut filter while reducing the size and cost, so that the size, Cost reduction and high image quality can be achieved. That is, a high-quality image pickup apparatus with a small size, low cost, and reduced color unevenness is provided.

  According to another aspect of the present invention, a digital apparatus includes the above-described imaging device, and a control unit that causes the imaging device to perform at least one of photographing a still image and a moving image of the subject. The imaging optical system is assembled so that an optical image of an object can be formed on a light receiving surface of the imaging element. Preferably, the digital device comprises a mobile terminal.

  Since such digital devices and portable terminals use an imaging optical system unit that can reduce color unevenness and reduce the intensity of unnecessary light due to the infrared cut filter while reducing size and cost. Miniaturization, cost reduction, and high image quality can be achieved. That is, a small-sized, low-cost and high-quality digital device or portable terminal with reduced color unevenness is provided.

  The imaging optical system unit according to the present invention can reduce color unevenness and reduce the intensity of unnecessary light due to the infrared cut filter while reducing the size and cost. The imaging apparatus and digital device according to the present invention can be reduced in size, cost, and image quality.

It is sectional drawing of the optical element which showed the structure typically for description of the imaging optical system unit in embodiment. It is the figure which showed typically the structure of the infrared cut filter in the imaging optical system unit of embodiment. It is the partial cross section figure which showed typically the structure of the optical element and infrared cut filter of the image side most in the imaging optical system of 1st Embodiment. It is a figure for demonstrating the characteristic of the imaging optical system unit of 1st Embodiment. It is the partial cross section figure which showed typically the structure of the optical element and infrared cut filter of the image side most in the imaging optical system of a comparative example. It is a figure for demonstrating the characteristic of the imaging optical system unit of a comparative example. It is a figure which shows the characteristic of each infrared cut filter in 1st Embodiment and a comparative example. It is a figure for demonstrating the characteristic of the imaging optical system unit of 2nd Embodiment. It is a figure for demonstrating the characteristic of the imaging optical system unit of 3rd Embodiment. It is a figure for demonstrating the characteristic of the imaging optical system unit of 4th Embodiment. It is a partial sectional view showing typically composition of an optical element on the most image side and an infrared cut filter in an imaging optical system of a 5th embodiment. It is a figure for demonstrating the characteristic of the imaging optical system unit of 5th Embodiment. It is a block diagram which shows the structure of the digital device in 6th Embodiment. It is an external appearance block diagram of the mobile telephone with a camera (an example of a digital device) in 7th Embodiment.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted suitably. Further, in this specification, when referring generically, it is indicated by a reference symbol without a suffix, and when referring to an individual configuration, it is indicated by a reference symbol with a suffix.

(First embodiment)
FIG. 1 is a cross-sectional view of an optical element schematically showing the configuration for explaining an imaging optical system unit in the embodiment. FIG. 2 is a diagram schematically illustrating the configuration of an infrared cut filter in the imaging optical system unit of the embodiment.

  In FIG. 1, the imaging optical system unit SUa forms an optical image of an object (subject) on a light receiving surface of an imaging element IS that converts an optical image into an electrical signal. An imaging optical system OSa that forms an optical image of a subject on a predetermined surface and an infrared cut filter FT disposed on the image side of the imaging optical system OSa are provided.

  The imaging optical system OSa is an optical system composed of one or more lenses La1 to Lan in order from the object side to the image side (n is an integer of 1 or more). The imaging optical system OSa includes, for example, about 3 to 7 lenses in order to realize desired optical characteristics with various aberrations corrected. Since the aberration can be easily corrected, the larger the number of lenses, the better. The lens La1 included in the imaging optical system OSa may be a glass lens formed of a glass material of glass material, but in the present embodiment, all of them are resin material lenses formed of a resin material. The resin material of the lens made of this resin material is a thermoplastic resin and an energy curable resin (for example, a thermosetting resin and an ultraviolet curable resin), and the like, for example, plastic, more specifically an acrylic resin (with a refractive index of 1. 49), cycloolefin resin (refractive index 1.54), polycarbonate resin (refractive index 1.59), and fluorene polyester resin (refractive index 1.61).

The imaging optical system OSa has the following (A1) when the average reflectance of the antireflection layer from the wavelength of 600 nm to 650 nm in the incident light incident at 5 degrees is RCAR (5, 600 to 650). It includes an optical element La having an antireflection layer ARa that satisfies the conditional expression formed on at least one surface.
RCAR (5, 600 to 650) ≦ 1.8% (A1)

The antireflection layer ARa has the following (A2) when the average reflectance of the antireflection layer from the wavelength of 420 nm to 600 nm in the incident light incident at 5 degrees is RCAR (5, 420 to 600). Satisfies the conditional expression.
RCAR (5, 420 to 600) ≦ 2% (A2)

  The optical element La on which such an antireflection layer ARa is formed on at least one surface is a parallel plate or a lens having translucency for visible light. In the example shown in FIG. 1, the optical element La is a parallel plate that is a plane in which both surfaces facing each other are parallel. The parallel plate may have a predetermined refractive power by changing the refractive index from the optical axis toward the end of the effective region. Note that the case where the optical element La on which at least one such antireflection layer AR is formed is a lens will be described in detail in a fifth embodiment to be described later.

  Further, the optical element La having such an antireflection layer ARa formed on at least one surface may be any optical element La of the imaging optical system OSa. In the present embodiment, as shown in FIG. It is arranged on the most image side. The antireflection layer ARa may be formed on the object side surface of the optical element Lan arranged on the most image side or on both the object side surface and the image side surface. In the example shown in FIG. Is formed.

  The antireflection layer ARa may be, for example, a rough surface having a fine concavo-convex structure having a size corresponding to light in a wavelength band for preventing reflection, and has a predetermined refractive index with respect to the d-line, for example. For example, it may be a multilayer film in which one or a plurality of pairs of a low refractive index layer having a relatively low refractive index and a high refractive index layer having a relatively high refractive index are laminated (see above). The refractive index of the high refractive index layer is higher than the refractive index of the low refractive index layer: the refractive index of the low refractive index layer <the refractive index of the high refractive index layer).

In addition, the substrate refractive index of the optical element La satisfies the following conditional expression (A3) when the refractive index of the d-line is nd.
1.4 ≦ nd ≦ 1.7 (A3)

More specifically, as shown in Table 1, the antireflection layer ARa of the first embodiment has a refractive index of 1.41, a thickness of 103 nm (design value), and a substrate refractive index of 1.55. Such a single antireflection layer ARa is formed of, for example, SiO ₂ , MgF ₂ or the like. In general, thin film design can be performed by automatic design, and the above-described antireflection layer ARa is also designed by automatic design using the conditional expression (A1) as a target condition.

From the above viewpoint, the conditional expression (A3) is preferably the following conditional expression (A3a).
1.45 ≦ nd ≦ 1.6 (A3a)

  When the antireflection layer ARa is a multilayer film, the antireflection layer ARa is preferably a multilayer film having a total film thickness of 600 nm or less and a number of layers of 15 or less. Such a multilayer antireflection layer AR will be described in detail in second to fifth embodiments described later.

  The infrared cut filter FT is a reflective infrared cut filter, and includes, for example, a multilayer film 12 formed on a substrate 11 as shown in FIG. The substrate 11 is a support that supports the multilayer film 12, and may be omitted if the multilayer film 12 has sufficient mechanical strength. In the present embodiment, the substrate 11 is, for example, a glass substrate formed in a plate shape with a transparent glass material (for example, BK7), but may be a resin substrate formed in a plate shape with a transparent resin material. . A separate multilayer film may be formed on the back surface of the substrate 11 and on the opposite side of the multilayer film 12. By forming the multilayer film on both surfaces of the substrate 11, the internal stresses of the multilayer films on both surfaces can be balanced, and the warpage of the substrate 11 can be reduced. The multilayer film 12 is an optical thin film in which a high refractive index layer 121 having a relatively high refractive index and a low refractive index layer 122 having a relatively low refractive index are alternately stacked. That is, the refractive index of the high refractive index layer 121 is higher than the refractive index of the low refractive index layer 122. In the example shown in FIG. 2, the multilayer film 12 has the most substrate side layer as the high refractive index layer 121, but the most substrate side layer may be the low refractive index layer 122.

  The high refractive index layer 121 has a refractive index equal to or higher than the average value of the refractive indexes of a plurality of materials forming the multilayer film 12, and the low refractive index layer 122 has a refractive index lower than the average value. ing. When a plurality of low refractive index materials having different refractive indexes are laminated side by side (continuously), it is optically equivalent to the presence of one low refractive index layer. Similarly, when a plurality of high refractive index materials having different refractive indexes are laminated side by side (continuously), it is optically equivalent to the presence of one high refractive index layer.

Here, the multilayer film 12 of the infrared cut filter FT is formed so as to satisfy the following conditional expressions (B1) and (B2). Conditional expression (B1) is an expression that prescribes a wavelength difference of 50% reflectivity exerted by the incident angle.
| Λ (0, 50; 600 to 700) −λ (30, 50; 600 to 700) | ≦ 15 nm (B1)
0.4% / nm ≦ | ΔR | ≦ 8% / nm (B2)
However, λ (0, 50; 600 to 700) is a wavelength (nm) at which the reflectance of incident light incident at 0 degree incidence is 50% between a wavelength of 600 nm and a wavelength of 700 nm, and λ (30 , 50; 600 to 700) is a wavelength (nm) at which the reflectance of incident light incident at 30 degrees incidence is 50% between the wavelength 600 nm and the wavelength 700 nm, and ΔR is the wavelength from the wavelength 600 nm to the wavelength 700 nm. The wavelength at which the reflectance of incident light incident at 0 degree incidence is 30% in the range up to 700 nm is λ (0, 30; 600 to 700), and the incident light is incident at 0 degree between wavelength 600 nm and wavelength 700 nm. ΔR = (70−30) / (λ (0,70; 600 to 700) −, where λ (0,70; 600 to 700) is a wavelength at which the reflectance of incident light is 70%. λ (0,3 ; 600~700)) (% / nm) is the slope of the reflectance change to the wavelength change represented by. That is, the slope ΔR is the reflectivity of incident light that is incident at 0 degrees, and the reflectivity between the wavelength of 600 nm to 700 nm is 30% and the reflectivity between the wavelength of 600 nm to 700 nm. It is the slope of the reflectance between the wavelength of 70%.

  Generally, as described above, thin film design can be executed by automatic design, and the multilayer film 12 is also automatically designed by using the conditional expressions (B1) and (B2) as target conditions. Designed. According to such automatic design, the multilayer film 12 has a ratio (SH / SL) of the optical film thickness SH of the high refractive index layer 121 and the optical film thickness SL of the low refractive index layer 122 adjacent to each other to 3 or more. If there are at least four cutoff adjustment pairs and Δn × nH ≧ 1.5 is satisfied, the conditional expressions (B1) and (B2) are satisfied. Here, Δn is a value of nH−nL when the maximum refractive index among the refractive indexes of the layers constituting the multilayer film 12 is nH and the minimum refractive index is nL. The cut-off adjustment pair includes the high refractive index layer 121 and the low refractive index layer 122 that are adjacent to each other, the high refractive index layer 121 that is close to the substrate 11, and the next low layer (which is stacked thereon). It is defined as a pair with the refractive index layer 122.

For example, the high refractive index layer 121 is, for example, can be used Ti0 ₂ having a refractive index of 2.4, the low refractive index layer 122 is, for example, Al of Si0 ₂ and the refractive index 1.6 of the refractive index 1.46 (a mixture of _Al 2 _{O 3} and _{La 2 O 3)} 2 _{O 3} and a refractive index of 1.7 Merck substance M2 or the like can be used. As an example of a multilayer film 12 including a material such a dielectric, for example, with use of Ti0 ₂ having a refractive index of 2.4 as the high refractive index layer 121, the refractive index as a low refractive index layer 122 1.46 When SiO ₂ is used, the multilayer film 12 includes 13 cutoff adjustment pairs having SH / SL of 3 or more, and Δn × nH ≧ 2.26. Further, for example, with use of Ti0 ₂ having a refractive index of 2.4 as the high refractive index layer 121, when using a Merck Substance M2 refractive index of 1.7 as a low refractive index layer 122, the multilayer film 121, SH Eighteen cut-off adjustment pairs with / SL of 3 or more are provided, and Δn × nH ≧ 1.68.

  In the image pickup optical system OSa, for example, an optical stop ST such as an aperture stop is arranged on the object side of the lens La1 arranged closest to the object side, and the image pickup optical system OSa is a front stop type. The optical diaphragm ST may be a medium diaphragm type disposed between predetermined lenses. Furthermore, an image sensor IS is disposed on the image side of the imaging optical system unit SUa, that is, on the image side of the infrared cut filter FT. The imaging element IS is arranged so that its light receiving surface substantially coincides with the image plane of the imaging optical system OSa (image plane = imaging plane). Therefore, the predetermined surface of the imaging optical system OSa is a light receiving surface of the imaging element IS in the present embodiment. The image sensor IS is an image signal of each component of R (red), G (green), and B (blue) according to the amount of light in the optical image of the subject imaged by the imaging optical system OSa of the imaging optical system unit SUa. This is an element that performs photoelectric conversion to a predetermined image processing circuit (not shown). The image sensor IS is a solid-state image sensor such as a CCD image sensor or a CMOS image sensor. Thus, the optical image of the object on the object side is guided to the light receiving surface of the image sensor IS along the optical axis AX by the imaging optical system unit SUa, and the optical image of the object is captured by the image sensor IS. The

  A parallel plate-like optical element may be further arranged on at least one of the object side and the image side of the infrared cut filter FT. This parallel plate-like optical element may be, for example, various optical filters excluding an infrared cut filter, a cover glass (seal glass) of the imaging element IS, or the like. This parallel plate-shaped optical element is appropriately arranged according to the use application, the imaging element IS, the configuration of the camera, and the like.

  Since the infrared cut filter FT in the imaging optical system unit SUa of the first embodiment satisfies the conditional expression (B1), the incident angle dependency of the infrared cut characteristic is low. For this reason, the imaging optical system unit SUa uses the infrared cut filter FT having a low incident angle-dependent infrared cut characteristic, so that the infrared cut characteristic can be obtained even if the difference in incident angle between the central portion and the peripheral portion is large. However, the change between the central portion and the peripheral portion becomes small (the infrared cut amount becomes substantially uniform), color unevenness can be reduced, and the height can be reduced.

  Here, while the color unevenness can be reduced as described above, since the light reflected by the infrared cut filter FT is reflected by the lens surface of the imaging optical system OSa, unnecessary light (harmful light) returning to the infrared cut filter again. ) Is stronger than that of a general infrared cut filter. However, since the imaging optical system unit SUa of the first embodiment satisfies the conditional expression (B1), the incident angle dependency of the infrared cut characteristics is low. For this reason, the imaging optical system unit uses an infrared cut filter having a low incident angle-dependent infrared cut characteristic, so that the infrared cut characteristic can be obtained even when the difference in incident angle between the central part and the peripheral part is large. The change between the central portion and the peripheral portion becomes small (the infrared cut amount becomes substantially uniform), and the color unevenness can be reduced. Moreover, since conditional expression (B2) is satisfy | filled, an infrared cut characteristic and productivity can be made compatible. Furthermore, since the imaging optical system OSa includes the optical element Lan on which at least one antireflection layer ARa that satisfies the conditional expression (A1) is formed, the intensity of unnecessary light can be reduced.

  Therefore, such an imaging optical system unit SUa can reduce color unevenness and reduce the intensity of unnecessary light caused by the infrared cut filter FT while reducing the size and cost.

From the above viewpoint, the conditional expression (A1) is preferably the following conditional expression (A1a), and more preferably the following conditional expression (A1b).
RCAR (5, 600 to 650) ≦ 1.4% (A1a)
RCAR (5, 600 to 650) ≦ 1% (A1b)

  Further, since the conditional expression (A2) is satisfied, the reflection of the antireflection layer ARa with respect to visible light reflected by the infrared cut filter FT and incident on the antireflection layer ARa can be effectively reduced, resulting from the infrared cut filter FT. The intensity of unnecessary light can be effectively reduced by the antireflection layer ARa.

From the above viewpoint, the conditional expression (A2) is preferably the following conditional expression (A2a), and more preferably the following conditional expression (A2b).
RCAR (5, 420 to 600) ≦ 1.5% (A2a)
RCAR (5, 420 to 600) ≦ 1% (A2b)

  In general, reflection of light occurs at an interface where materials having different refractive indexes contact each other. In the imaging optical system unit SUa of the first embodiment, since the optical element La having the antireflection layer ARa is arranged on the most image side, the interface between the infrared cut filter FT and the antireflection layer ARa is reduced. The intensity of unnecessary light resulting from the infrared cut filter FT can be more effectively reduced by the antireflection layer.

  In the imaging optical system unit SUa of the first embodiment, since the antireflection layer ARa is formed on the image side surface of the optical element La arranged closest to the image side, the infrared cut filter FT, the antireflection layer ARa, The interface between the two can be minimized, and the intensity of unnecessary light caused by the infrared cut filter FT can be further effectively reduced by the antireflection layer ARa.

  In recent years, the entire solid-state imaging device has been required to be further downsized, and even a solid-state imaging device having the same number of pixels has a small pixel pitch, and as a result, an imaging surface size has been reduced. In such an imaging optical system unit for a solid-state imaging device having a small imaging surface size, it is necessary to relatively shorten the focal length of the entire system, so that the radius of curvature and the outer diameter of each lens are considerably reduced. Accordingly, the imaging optical system OSa of such an imaging optical system unit SUa is compared with a glass lens manufactured by a time-consuming polishing process by constituting all lenses with resin material lenses manufactured by injection molding. If so, even a lens having a small radius of curvature or outer diameter can be produced in large quantities at a low cost. Moreover, since the lens made of a resin material can lower the press temperature, it is possible to suppress the wear of the molding die, and as a result, the number of times of replacement and maintenance of the molding die is reduced, thereby reducing the cost. be able to.

  In the imaging optical system unit SUa of the first embodiment, the antireflection layer ARa can be formed as a single layer (one layer). For this reason, the imaging optical system unit SUa of the first embodiment can form the antireflection layer ARa more easily, and can reduce the cost.

  Next, the effect of the imaging optical system unit of the first embodiment will be described in more detail while comparing with the comparative example. FIG. 3 is a partial cross-sectional view schematically showing the configurations of the optical element on the most image side and the infrared cut filter in the imaging optical system of the first embodiment. FIG. 4 is a diagram for explaining the characteristics of the imaging optical system unit according to the first embodiment. FIG. 4A is a diagram showing the reflectance wavelength characteristic of the image side surface (the reflectance wavelength characteristic of the antireflection layer ARa) in the optical element arranged closest to the image side. The horizontal axis of FIG. 4A is the wavelength expressed in nm unit, and the vertical axis is the reflectance expressed in% unit. FIG. 4A shows the reflectivity (solid line) with respect to 5 ° incident light and the reflectivity (broken line) with respect to 30 ° incident light. FIG. 4B is a diagram illustrating wavelength characteristics of harmful light with respect to incident light incident at 5 degrees, and FIG. 4C is a diagram illustrating wavelength characteristics of harmful light with respect to incident light incident at 30 degrees. 4B and 4C, the horizontal axis represents a wavelength expressed in nm, and the vertical axis represents the average intensity of harmful light. 4B and 4C, the case of the first embodiment is indicated by a broken line, and the case of the comparative example shown in FIGS. 5 and 6 is indicated by a solid line. FIG. 5 is a partial cross-sectional view schematically showing configurations of the optical element on the most image side and the infrared cut filter in the imaging optical system of the comparative example. FIG. 6 is a diagram for explaining the characteristics of the imaging optical system unit of the comparative example. FIG. 6A is a diagram showing the reflectance wavelength characteristics of the image side surface in the optical element arranged closest to the image side. The horizontal axis in FIG. 6A is the wavelength expressed in nm, and the vertical axis is the reflectance expressed in%. FIG. 6A shows the reflectivity (solid line) with respect to 5 ° incident light and the reflectivity (broken line) with respect to 30 ° incident light. FIG. 6B is a diagram showing the wavelength characteristics of each harmful light with respect to each incident light at 5 degrees incident and 30 degrees incident. The horizontal axis in FIG. 6B is the wavelength expressed in nm, and the vertical axis is the average intensity of harmful light. The solid line is the case of 5 degree incidence, and the broken line is the case of 30 degree incidence. FIG. 7 is a diagram illustrating the characteristics of each infrared cut filter in the first embodiment and the comparative example. FIG. 7A shows reflectance wavelength characteristics, and FIG. 7B shows transmittance wavelength characteristics. Each of the horizontal axes in FIGS. 7A and 7B is the wavelength expressed in nm units, the vertical axis in FIG. 7A is the reflectance expressed in% units, and the vertical axis in FIG. 7B is , The transmittance expressed in%. The solid line is the case of the hybrid type infrared cut filter in which the reflection type infrared cut filter is formed on the surface of the substrate containing the infrared absorbing material, and the broken line is the case of 5 degree incidence in the absorption type infrared cut filter of the first embodiment. The alternate long and short dash line is the case of 30-degree incidence in the reflective infrared cut filter of the first embodiment.

  First, the imaging optical system unit of the comparative example will be described. The imaging optical system unit SUref of this comparative example is different from the imaging optical system unit SUa of the first embodiment in that the antireflection layer AR is not provided, but the other is the same as the imaging optical system unit SUa of the first embodiment. is there. That is, the imaging optical system unit SUref of this comparative example is disposed on the image side of the imaging optical system OSref and the imaging optical system OSref composed of one or a plurality of lenses Lref1 to Lrefn, as shown in FIG. The imaging optical system OSref includes an infrared cut filter FT and does not include the antireflection layer AR. Therefore, the image side surface of the optical element Lrefn arranged closest to the image side in the imaging optical system OSref of the comparative example has a relatively high reflectance in the wavelength range of 350 nm to 800 nm as shown in FIG. . Although the reflectivity of incident light at 5 degrees is gradually decreased as the wavelength increases, it is about 4.5 or more in the wavelength range, and the reflectivity of incident light at 30 degrees is also gradually increased as the wavelength increases. However, it is about 4.6 or more in the wavelength range.

  In the imaging optical system unit SUref of this comparative example, as shown in FIG. 5, the light beam of the optical image of the subject imaged by the imaging optical system OSref is incident on the infrared cut filter FT, and a part of the light beam Is transmitted through the infrared cut filter FT according to the transmittance wavelength characteristic of the infrared cut filter FT, and the other part of the light beam is reflected by the infrared cut filter FT according to the reflectance wavelength characteristic of the infrared cut filter FT. . The reflected light returns to the imaging optical system OSref, is mainly reflected by the optical element Lrefn arranged closest to the image side of the imaging optical system OSref, and enters the infrared cut filter FT again.

  The light (unnecessary light, harmful light) that is incident again on the infrared cut filter FT by being reflected between the infrared cut filter FT and the imaging optical system OSref causes so-called flare (lens flare), and the infrared cut. Light receiving surface of the image sensor IS at a position where light should be incident by reflection between the filter FT and the image pickup optical system OSref (light that reaches the image sensor IS directly from the image pickup optical system OSref via the infrared cut filter FT (direct light)) The incident light enters the imaging element IS at a position different from the upper position), causing a ghost in the image. Since this harmful light is generated by the above-described process, its intensity Ph is equal to the light intensity P0, the reflectance RIR of the infrared cut filter, the reflectance RC of the image side surface of the optical element Lrefn, and the transmittance TIR of the infrared cut filter. (Ph = RIR × RC × TIR × P0).

  The reflectance and transmittance of the infrared cut filter FT in the first embodiment and the comparative example are shown in FIGS. 7A and 7B, respectively. 7A and 7B show, for reference, the reflectance wavelength characteristic and the transmittance wavelength characteristic in a hybrid infrared cut filter in which a reflective infrared cut filter is formed on a substrate with an infrared absorbing material, respectively. Has been.

  As shown in FIG. 7A, the reflectance of the infrared cut filter FT in the first embodiment and the comparative example is approximately 100% up to a wavelength of about 400 nm in the case of incident light incident at 5 degrees, and at a wavelength of about 400 nm. It is a profile that suddenly decreases and is about 10% or less of the wavelength from about 420 nm to about 600 nm, but increases and decreases from about 600 nm, and becomes 100% again at a wavelength of about 700 nm or more. In the case of incident light with an incident angle of 30 degrees, the wavelength is about 100% up to a wavelength of about 385 nm, rapidly decreases at a wavelength of about 385 nm, and increases and decreases slightly from about 420 nm to a wavelength of about 600 nm. There is a profile that increases from a wavelength of about 600 nm and becomes 100% again at a wavelength of about 670 nm or more. Further, the reflectance and the transmittance are in a relation of the front and back, and the transmittance is substantially opposite to the reflectance profile as shown in FIG. 7B.

  As described above, the reflectivity of the infrared cut filter FT in the first embodiment and the comparative example exists even from a wavelength of about 420 nm to a wavelength of about 600 nm, but increases from about 600 nm. The light is reflected by the infrared cut filter FT and returns to the imaging optical system OSref. As shown in FIG. 6A, the reflectance of the optical element Lrefn arranged closest to the image side of the imaging optical system OSref is constant regardless of the wavelength and is constant, so that the image is reflected by the infrared cut filter FT. The harmful light reflected by the optical element Lrefn of the optical system OSref has an intensity even at a wavelength of about 420 nm to a wavelength of about 600 nm, as shown in FIG. In the case of incident light with an incident angle of 5 degrees, between about 0.1 and an intensity of about 0.5, in the case of incident light with an incident angle of 30 degrees In the wavelength range of about 600 nm to about 660 nm, it exists with a relatively large intensity. The intensity peak has a wavelength of about 650 nm in the case of incident light incident at 5 degrees, and has a wavelength of about 645 nm in the case of incident light incident at 30 degrees.

  Table 2 summarizes the reflectance and harmful light of the optical element Lrefn. In the case of 5 degree incidence, the average reflectance RC (5, 420 to 600) of the optical element Lrefn from the wavelength of 420 nm to the wavelength of 600 nm is 4.65, and harmful light having a wavelength of 420 nm to 600 nm has an average intensity of 0.8. 20. In the case of incidence at 5 degrees, the average reflectance RC (5, 600 to 650) of the optical element Lrefn from the wavelength 600 nm to the wavelength 650 nm is 4.56, and harmful light having a wavelength of 600 nm to 650 nm has an average intensity of 0. 67. In the case of 30-degree incidence, the average reflectance RC (30, 420 to 600) of the optical element Lrefn from the wavelength 420 nm to the wavelength 600 nm is 4.82, and harmful light having a wavelength of 420 nm to 600 nm has an average intensity of 0.8. 28. In the case of 30 degree incidence, the average reflectance RC (5, 600 to 650) of the optical element Lrefn from the wavelength 600 nm to the wavelength 650 nm is 4.56, and the harmful light having the wavelength 600 nm to the wavelength 650 nm has an average intensity of 0.1. 67.

  As described above, in the imaging optical system unit SUref of the comparative example, the reflection of the infrared cut filter having a wavelength of about 600 nm to a wavelength of about 650 nm shown by a triangle in FIG. 7B is a main cause of harmful light.

  On the other hand, the imaging optical system unit SUa of the first embodiment includes an optical element La having an antireflection layer ARa formed on at least one surface. More specifically, the imaging optical system unit SUa of the first embodiment has an antireflection layer on the image side surface of the optical element Lan arranged closest to the image side in the imaging optical system OSa in the example shown in FIGS. It has ARa. For this reason, even if the reflected light reflected by the infrared cut filter FT enters the image pickup optical system OSa, the reflection by the image pickup optical system OSa is suppressed, and the incidence on the infrared cut filter FT again is reduced.

  Moreover, since the antireflection layer ARa in the imaging optical system unit SUa of the first embodiment satisfies the conditional expression (A1), the wavelength of about 600 nm to about 650 nm of the portion indicated by the triangle in FIG. Reflected light by the infrared cut filter is effectively prevented, and generation of harmful light due to visible light having a wavelength of about 600 nm to about 650 nm is suppressed.

  Furthermore, since the antireflection layer ARa in the imaging optical system unit SUa of the first embodiment also satisfies the conditional expression (A2), reflection with respect to visible light having a wavelength of about 420 nm to about 600 nm is effectively prevented, and the wavelength of about Generation | occurrence | production of the harmful light resulting from the visible light of 420 nm-wavelength about 600 nm is suppressed.

  More specifically, as described above, the antireflection layer ARa in the imaging optical system unit SUa of the first embodiment has a refractive index of 1.41 and a thickness of 103 nm (design value) (Table 1). As shown in FIG. 4A, the reflectance wavelength characteristic decreases as the wavelength increases from 350 nm, both when the reflectivity is incident at 5 degrees and when incident at 30 degrees, and is incident at 30 degrees. In this case, the reflectance is about 1.6 at the minimum at a wavelength of about 525 nm. On the other hand, in the case of 5 degree incidence, the reflectance is about 1.55 at the wavelength of about 560 nm, and then the profile gradually increases.

  In the imaging optical system unit SUa of the first embodiment using the antireflection layer ARa having the reflectance wavelength characteristic shown in FIG. 4A, harmful light when incident at 5 degrees is shown in FIG. The harmful light when incident at 30 degrees becomes a profile indicated by a broken line in FIG. In both cases of 5 degree incidence and 30 degree incidence, as shown in FIGS. 4B and 4C, the harmful light is reduced from the comparative example at any wavelength, and is shown in Table 3. Thus, it is greatly reduced as compared with the above-described comparative example. That is, with respect to incident light with an incident angle of 5 degrees, harmful light having a wavelength of 420 nm to 600 nm has an average intensity of 0.08, which is about 39.6% compared to an intensity of 0.20 in the comparative example (comparison). When the harmful light intensity of the example is 1, the harmful light intensity of the first embodiment is 39.6% (the same applies hereinafter), which is improved by about 60.4%. The harmful light having a wavelength of 600 nm to 650 nm has an average intensity of 0.24 compared to the intensity of 0.67 of the comparative example, and is about 36.1% with respect to incident light of 5 degrees incident. 9% improvement. For incident light with an incident angle of 30 degrees, harmful light with a wavelength of 420 nm to 600 nm has an average intensity of 0.10, which is about 37.3% compared to an average intensity of 0.28 of the comparative example, and about 62 .7% improvement. The harmful light having a wavelength of 600 nm to 650 nm has an average intensity of 0.34 with respect to incident light of 30 degrees incident, which is about 38.9% compared to the average intensity of 0.87 of the comparative example. .1% improvement.

  In the above case, the reflectance of the antireflection layer ARa is 1.81 in the average reflectance RC (5, 420 to 600) from the wavelength 420 nm to the wavelength 600 nm in the incident light incident at 5 degrees incidence, The average reflectivity RC (5, 600 to 650) from the wavelength 600 nm to 650 nm in the incident light incident at 5 degrees incidence is 1.63, and the average from the wavelength 420 nm to 600 nm in the incident light incident at 30 degrees incidence. The reflectivity RC (30, 420 to 600) is 1.78, and the average reflectivity RC (30, 600 to 650) from the wavelength 600 nm to 650 nm in the incident light incident at 30 degrees is 1. 82.

  As described above, in the imaging optical system unit SUa of the first embodiment, harmful light is significantly reduced as compared with the imaging optical system unit of the comparative example. For this reason, the imaging optical system unit SUa of the first embodiment can reduce color unevenness while reducing the size and cost, and can reduce the generation of harmful light due to the infrared cut filter.

  Next, another embodiment will be described.

(Second Embodiment)
FIG. 8 is a diagram for explaining the characteristics of the imaging optical system unit according to the second embodiment. FIG. 8A is a diagram showing the reflectance wavelength characteristic of the image side surface (the reflectance wavelength characteristic of the antireflection layer ARb) in the optical element arranged closest to the image side. The horizontal axis in FIG. 8A is the wavelength expressed in nm unit, and the vertical axis is the reflectance expressed in% unit. FIG. 8A shows the reflectance (solid line) with respect to 5 ° incident light and the reflectance (broken line) with respect to 30 ° incident light. FIG. 8B is a diagram illustrating wavelength characteristics of harmful light with respect to incident light incident at 5 degrees, and FIG. 8C is a diagram illustrating wavelength characteristics of harmful light with respect to incident light incident at 30 degrees. The horizontal axis of FIGS. 8B and 8C is the wavelength expressed in nm, and the vertical axis is the average intensity of harmful light. In FIGS. 8B and 8C, the case of the second embodiment is indicated by a broken line, and the case of the comparative example is indicated by a solid line.

  The imaging optical system unit SUb of the second embodiment has a different antireflection layer ARb. That is, the imaging optical system unit SUb of the second embodiment includes an imaging optical system OSb and an infrared cut filter FT. The infrared cut filter FT in the imaging optical system unit SUb of the second embodiment is the same as the infrared cut filter FT in the imaging optical system unit SUa of the first embodiment, and in the imaging optical system unit SUb of the second embodiment. The imaging optical system OSb is different from the antireflection layer ARa in the imaging optical system unit SUa of the first embodiment, except that the antireflection layer ARb is formed on the image side surface of the optical element Lbn arranged closest to the image side. Since it is the same as the imaging optical system OSa, the description thereof is omitted.

As shown in Table 4, the antireflection layer ARb in the second embodiment has a refractive index of 2.08 and a thickness of 8 nm stacked on the optical element body LMb of the optical element Lbn arranged closest to the image side. A first high refractive index layer having a (design value) and a first low refractive index layer having a refractive index of 1.41 and a thickness of 122 nm (design value) stacked in the first high refractive index layer. It has two layers. The first high refractive index layer is made of, for example, TiO ₂ or Nb ₂ O ₅ , and the first low refractive index layer is made of, for example, SiO ₂ or MgF ₂ . More specifically, when the antireflection layer AR in which the A layer and the B layer are laminated in the thickness direction from the substrate is represented by // substrate // A / B, the antireflection layer ARb is, for example, / Optical element (substrate) / TiO ₂ / SiO ₂ , and for example, the antireflection layer ARb is // optical element (substrate) / Nb ₂ O ₅ / MgF ₂ .

  Such an antireflection layer ARb exhibits the reflectance wavelength characteristic shown in FIG. That is, the reflectance wavelength characteristic of the antireflection layer ARb decreases in both cases where the reflectance is 5 degrees incident and 30 degrees incident as the wavelength increases from 350 nm, and is reflected at a wavelength of about 490 nm in the case of 30 degrees incident. On the other hand, when the incidence is 5 degrees, the reflectance is about 0.9, and the reflectance is about 0.9 at a wavelength of about 530 nm. Thereafter, the profile gradually increases.

  In the imaging optical system unit SUb of the second embodiment using the antireflection layer ARb having the reflectance wavelength characteristic shown in FIG. 8A, harmful light in the case of 5 degree incidence is shown in FIG. The harmful light when incident at 30 degrees becomes the profile indicated by the broken line in FIG. 8C. In both cases of 5 degree incidence and 30 degree incidence, as shown in FIGS. 8B and 8C, the harmful light is reduced in comparison with the comparative example at any wavelength, as shown in Table 5. Thus, it is greatly reduced as compared with the above-described comparative example. That is, the harmful light having a wavelength of 420 nm to 600 nm has an average intensity of 0.05 with respect to incident light of 5 ° incidence, which is about 27.2% compared to the average intensity of 0.20 in the comparative example ( When the noxious light intensity of the comparative example is 1, the noxious light intensity of the second embodiment is improved by about 72.8%, 27.2% (the same applies hereinafter). The harmful light having a wavelength of 600 nm to 650 nm has an average intensity of 0.19 compared to the average intensity of 0.67 of the comparative example, and is about 27.8% with respect to the incident light of 5 degrees incident. .2% improvement. The harmful light having a wavelength of 420 nm to 600 nm with respect to the incident light of 30 degrees incident has an average intensity of 0.07, which is about 23.5% compared to the average intensity of 0.28 of the comparative example, and is about 76. .5% improvement. The harmful light having a wavelength of 600 nm to 650 nm has an average intensity of 0.29 compared to the average intensity of 0.87 of the comparative example, which is about 34.0% with respect to the incident light of 30 degrees incident, and about 66 0.0% improvement.

  In the case described above, the reflectance of the antireflection layer ARb is 1.21, and the average reflectance RC (5, 420 to 600) from the wavelength 420 nm to 600 nm in the incident light incident at 5 degrees is 1.21. The average reflectance RC (5, 600 to 650) from the wavelength 600 nm to 650 nm in the incident light incident at an angle of incidence is 1.23, and the average reflection from the wavelength 420 nm to 600 nm in the incident light incident at an incident angle of 30 degrees. The rate RC (30, 420 to 600) is 1.09, and the average reflectance RC (30, 600 to 650) from the wavelength 600 nm to 650 nm in the incident light incident at 30 degrees is 1.57. It is.

  Next, another embodiment will be described.

(Third embodiment)
FIG. 9 is a diagram for explaining the characteristics of the imaging optical system unit according to the third embodiment. FIG. 9A is a diagram illustrating the reflectance wavelength characteristic of the image side surface (the reflectance wavelength characteristic of the antireflection layer ARc) in the optical element arranged closest to the image side. The horizontal axis of FIG. 9A is the wavelength expressed in nm unit, and the vertical axis is the reflectance expressed in% unit. FIG. 9A shows the reflectivity with respect to 5 ° incident light (solid line) and the reflectivity with respect to 30 ° incident light (broken line). FIG. 9B is a diagram illustrating wavelength characteristics of harmful light with respect to incident light incident at 5 degrees, and FIG. 9C is a diagram illustrating wavelength characteristics of harmful light with respect to incident light incident at 30 degrees. The horizontal axis of FIGS. 9B and 9C is the wavelength expressed in nm, and the vertical axis is the average intensity of harmful light. In FIGS. 9B and 9C, the case of the third embodiment is indicated by a broken line, and the case of the comparative example is indicated by a solid line.

  The imaging optical system unit SUc of the third embodiment is different in the antireflection layer ARc. That is, the imaging optical system unit SUc of the third embodiment includes an imaging optical system OSc and an infrared cut filter FT. The infrared cut filter FT in the imaging optical system unit SUc of the third embodiment is the same as the infrared cut filter FT in the imaging optical system unit SUa of the first embodiment, and in the imaging optical system unit SUc of the third embodiment. The imaging optical system OSc is different from the antireflection layer ARa in the imaging optical system unit SUa of the first embodiment except that the antireflection layer ARc is formed on the image side surface of the optical element Lcn arranged closest to the image side. Since it is the same as the imaging optical system OSa, the description thereof is omitted.

As shown in Table 6, the antireflection layer ARc in the third embodiment has a refractive index of 2.08 and a thickness of 16 stacked on the optical element body LMc of the optical element Lcn arranged closest to the image side. A first high refractive index layer having a thickness of 0.02 nm (design value) and a first low refractive index having a refractive index of 1.475 and a thickness of 33.08 nm (design value) laminated in the first high refractive index layer. An index layer, a second high refractive index layer having a refractive index of 2.08 and a thickness of 67.95 nm (design value) laminated on the first low refractive index layer, and the second high refractive index layer shape A second low refractive index layer having a refractive index of 1.475 and a thickness of 12 nm (design value), and a refractive index of 2.08 laminated on the second low refractive index layer. A third high refractive index layer having a thickness of 40.6 nm (design value), and a refractive index of 1.3 laminated on the third high refractive index layer. A 85 and a third low refractive index layer is a thick 104.11Nm (design value), a six-layer. The first to third high refractive index layers are made of, for example, TiO ₂ or Nb ₂ O ₅ , and the first to third low refractive index layers are made of, for example, SiO ₂ or MgF ₂ . For example, the antireflection layer ARc is, for example, // optical element (substrate) / TiO ₂ / SiO ₂ / TiO ₂ / SiO ₂ / TiO ₂ / MgF ₂ .

  Such an antireflection layer ARc exhibits the reflectance wavelength characteristic shown in FIG. In other words, the reflectance wavelength characteristic of the antireflection layer ARc decreases as the wavelength increases from 350 nm, both when the reflectance is incident at 5 degrees and when incident at 30 degrees, and is reflected at a wavelength of about 410 nm when incident at 30 degrees. On the other hand, in the case of 5 degree incidence, the reflectance is about 0.1, and the reflectance is about 0.2 at a wavelength of about 420 nm. Thereafter, the reflectance starts to increase, and in the case of 30 degree incidence, the reflectance is about 0 at a wavelength of about 445 nm. In the case of 5 degree incidence, the reflectance becomes about 0.5 at a wavelength of about 470 nm, and then the reflectance starts to decrease. In the case of 30 degree incidence, the reflectance is about 0.05 at a wavelength of about 645 nm again. On the other hand, in the case of 5 degree incidence, the reflectance is almost zero again at a wavelength of about 670 nm, and thereafter the profile increases relatively slowly.

  In the imaging optical system unit SUc of the third embodiment using the antireflection layer ARc having the reflectance wavelength characteristic shown in FIG. 9A, harmful light when incident at 5 degrees is shown in FIG. The harmful light when incident at 30 degrees becomes a profile indicated by a broken line in FIG. 9C. In both cases of 5 degree incidence and 30 degree incidence, as shown in FIGS. 9 (B) and (C), the harmful light is almost 0, which is lower than the comparative example at any wavelength, As shown in Table 7, it is greatly reduced as compared with the above-described comparative example. That is, the harmful light having a wavelength of 420 nm to 600 nm has an average intensity of 0.02 with respect to incident light of 5 degrees incident, and is about 8.2% compared to the average intensity of 0.20 in the comparative example ( When the noxious light intensity of the comparative example is 1, the noxious light intensity of the third embodiment is 8.2% (the same applies hereinafter), which is an improvement of about 91.8%. The harmful light having a wavelength of 600 nm to 650 nm has an average intensity of 0.01 with respect to incident light of 5 degrees incident, which is about 1.7% compared to the average intensity of 0.67 in the comparative example, and is about 98. .3% improvement. The harmful light having a wavelength of 420 nm to 600 nm with respect to incident light of 30 degrees incident has an average intensity of 0.02, which is about 5.9% compared to the average intensity of 0.28 of the comparative example, and is about 94. .1% improvement. The harmful light having a wavelength of 600 nm to 650 nm has an average intensity of 0.02 with respect to incident light of 30 degrees incident, which is about 2.2% compared to the average intensity of 0.87 of the comparative example, and about 97 .8% improvement.

  In the case described above, the reflectance of the antireflection layer ARc is 0.39, and the average reflectance RC (5, 420 to 600) from the wavelength of 420 nm to 600 nm in the incident light incident at 5 degrees is 0.39. The average reflectivity RC (5, 600 to 650) from the wavelength 600 nm to 650 nm in the incident light incident at an incident angle of 0.1 is 0.1, and the average reflection from the wavelength 420 nm to 600 nm in the incident light incident at an incident angle of 30 degrees is 0.1. The rate RC (30, 420 to 600) is 0.3, and the average reflectance RC (30, 600 to 650) from the wavelength 600 nm to 650 nm in the incident light incident at 30 degrees is 0.11. It is.

  Next, another embodiment will be described.

(Fourth embodiment)
FIG. 10 is a diagram for explaining the characteristics of the imaging optical system unit of the fourth embodiment. FIG. 10A is a diagram showing the reflectance wavelength characteristic of the image side surface (the reflectance wavelength characteristic of the antireflection layer ARd) in the optical element arranged closest to the image side. In FIG. 10A, the horizontal axis represents the wavelength expressed in nm, and the vertical axis represents the reflectance expressed in%. FIG. 10A shows the reflectance (solid line) with respect to 5 degree incident light and the reflectance (broken line) with respect to 30 degree incident light. FIG. 10B is a diagram illustrating wavelength characteristics of harmful light with respect to incident light incident at 5 degrees, and FIG. 10C is a diagram illustrating wavelength characteristics of harmful light with respect to incident light incident at 30 degrees. In FIGS. 10B and 10C, the horizontal axis represents the wavelength expressed in nm, and the vertical axis represents the average intensity of harmful light. In FIGS. 10B and 10C, the case of the fourth embodiment is indicated by a broken line, and the case of the comparative example is indicated by a solid line.

  The imaging optical system unit SUd of the fourth embodiment has a different antireflection layer ARd. That is, the imaging optical system unit SUd of the fourth embodiment includes an imaging optical system OSd and an infrared cut filter FT. The infrared cut filter FT in the imaging optical system unit SUd of the fourth embodiment is the same as the infrared cut filter FT in the imaging optical system unit SUa of the first embodiment, and in the imaging optical system unit SUd of the fourth embodiment. The imaging optical system OSd is different from the antireflection layer ARa in the imaging optical system unit SUa of the first embodiment except that the antireflection layer ARd is formed on the image side surface of the optical element Ldn arranged closest to the image side. Since it is the same as the imaging optical system OSa, the description thereof is omitted.

As shown in Table 8, the antireflection layer ARd in the fourth embodiment has a refractive index of 1.475 and a thickness of 18 laminated on the optical element body LMd of the optical element Ldn arranged closest to the image side. A first low-refractive index layer having a thickness of 1.31 nm (design value) and a first high-refractive index having a refractive index of 2.316 and a thickness of 10.00 nm (design value) stacked in the first low-refractive index layer. The refractive index layer and the low refractive index layer and the high refractive index layer shown in Table 8 below are sequentially laminated, and finally the refractive index is 1.385 and the thickness is laminated on the seventh high refractive index layer. And an eighth low refractive index layer having a value of 103.00 nm (design value), and 15 layers. The first to seventh high refractive index layers are made of, for example, TiO ₂ or Nb ₂ O ₅ , and the first to eighth low refractive index layers are made of, for example, SiO ₂ or MgF ₂ . For example, the antireflection layer ARc is, for example, // optical element (substrate) / SiO ₂ / TiO ₂ /... / TiO ₂ / MgF ₂ .

  Such an antireflection layer ARd exhibits the reflectance wavelength characteristic shown in FIG. That is, the reflectance wavelength characteristic of the antireflection layer ARd decreases as the wavelength increases from 350 nm, both when the reflectance is incident at 5 degrees and when incident at 30 degrees, and decreases at a wavelength of about 400 nm when incident at 30 degrees. The rate decreases slowly and decreases to a minimum of about 0.1 reflectance at a wavelength of about 425 nm, while it becomes a minimum of about 0.2 reflectance at a wavelength of about 405 nm in the case of 5 degree incidence, and then reflects in both cases. Although the rate of increase and decrease is repeated between about 0 and 0.5, the overall rate decreases to almost 0. In the case of 30 degree incidence, the wavelength starts to increase again from about 700 nm. In the case of 5 degree incidence, the wavelength starts from about 725 nm. The profile starts to increase again, and the profile increases relatively slowly. While repeating the increase / decrease, in the case of 30 degree incidence, the wavelength is about 450 nm and the wavelength is about 545 nm, and the wavelength is about 480 nm, and in the case of the 5 degree incidence, the wavelength is about 420 nm, the wavelength is about 470 nm, and It has a maximum at a wavelength of about 555 nm, and a minimum at a wavelength of about 440 nm and a wavelength of about 510 nm.

  In the imaging optical system unit SUd of the fourth embodiment using the antireflection layer ARd having the reflectance wavelength characteristic shown in FIG. 10A, harmful light when incident at 5 degrees is shown in FIG. The harmful light when incident at 30 degrees becomes a profile indicated by a broken line in FIG. 10C. In both cases of 5 degree incidence and 30 degree incidence, as shown in FIGS. 10 (B) and 10 (C), the harmful light is almost 0, which is lower than the comparative example at any wavelength, As shown in Table 9, it is greatly reduced as compared with the comparative example described above. That is, the harmful light having a wavelength of 420 nm to 600 nm has an average intensity of 0.01 with respect to incident light of 5 ° incidence, which is about 6.3% compared to the average intensity of 0.20 in the comparative example ( When the harmful light intensity of the comparative example is 1, the harmful light intensity of the fourth embodiment is improved by about 63.7% (the same applies hereinafter) and about 93.7%. The harmful light having a wavelength of 600 nm to 650 nm has an average intensity of 0.01 with respect to incident light of 5 degrees incident, which is about 0.8% compared to the average intensity of 0.67 in the comparative example, and about 99 .2% improvement. For incident light with an incident angle of 30 degrees, harmful light having a wavelength of 420 nm to 600 nm has an average intensity of 0.01, which is about 3.3% compared to an average intensity of 0.28 in the comparative example, and is about 96. .7% improvement. The harmful light having a wavelength of 600 nm to 650 nm has an average intensity of 0.02 with respect to the incident light of 30 degrees incident, which is about 2.5% as compared with the average intensity of 0.87 of the comparative example. .5% improvement.

  In the case described above, the reflectance of the antireflection layer ARd is 0.29, and the average reflectance RC (5, 420 to 600) from the wavelength 420 nm to 600 nm in the incident light incident at 5 degrees incidence is 0.29. The average reflectivity RC (5, 600 to 650) from the wavelength 600 nm to 650 nm in the incident light incident at an incident angle of 0.05 is 0.05, and the average reflection from the wavelength 420 nm to 600 nm in the incident light incident at an incident angle of 30 degrees. The rate RC (30, 420 to 600) is 0.17, and the average reflectance RC (30, 600 to 650) from the wavelength 600 nm to 650 nm in the incident light incident at 30 degrees is 0.12. It is.

  Next, another embodiment will be described.

(Fifth embodiment)
FIG. 11 is a partial cross-sectional view schematically showing the configuration of the most image-side optical element and the infrared cut filter in the imaging optical system of the fifth embodiment. FIG. 12 is a diagram for explaining the characteristics of the imaging optical system unit according to the fifth embodiment. FIG. 12A is a diagram showing the reflectance wavelength characteristic of the image side surface (the reflectance wavelength characteristic of the antireflection layer ARe) in the optical element arranged closest to the image side. The horizontal axis in FIG. 12A is the wavelength expressed in nm units, and the vertical axis is the reflectance expressed in% units. FIG. 12A shows the reflectivity (solid line) with respect to 5 ° incident light and the reflectivity (broken line) with respect to 37.5 ° incident light. FIG. 12B is a diagram illustrating wavelength characteristics of harmful light with respect to incident light incident at 5 degrees, and FIG. 12C is a diagram illustrating wavelength characteristics of harmful light with respect to incident light incident at 30 degrees. In FIGS. 12B and 12C, the horizontal axis represents the wavelength expressed in nm, and the vertical axis represents the average intensity of harmful light. In FIGS. 12B and 12C, the case of the fifth embodiment is indicated by a broken line, and the case of the comparative example is indicated by a solid line.

  The imaging optical system unit SUe of the fifth embodiment is different in the optical element Len arranged on the most image side in the imaging optical system OSe and the antireflection layer ARe formed on the side surface of the image. That is, the imaging optical system unit SUe of the fifth embodiment includes an imaging optical system OSe and an infrared cut filter FT. The infrared cut filter FT in the imaging optical system unit SUe of the fifth embodiment is the same as the infrared cut filter FT in the imaging optical system unit SUa of the first embodiment, and in the imaging optical system unit SUe of the fifth embodiment. As shown in FIG. 11, the imaging optical system OSe includes a lens optical element Len instead of the parallel plate optical element Lan arranged closest to the image side, and the antireflection layer ARe is the most antireflection layer ARa. This is the same as the imaging optical system OSa in the imaging optical system unit SUa of the first embodiment except that it is formed on the image side surface of the optical element Len of this lens arranged on the side. To do.

  The optical element Len in the fifth embodiment is a lens having positive or negative refractive power. The lens which is the optical element Len may be spherical on one side (single flat lens), spherical on both sides and aspheric on at least one side. In the example shown in FIG. 11, the optical element Len has a positive refractive power, and when the optical element Len moves from the intersection of the optical axes toward the effective region end along the optical axis along the contour line of the lens cross section including the optical axis. It is a lens having an aspherical surface having at least one inflection point. The inflection point is within the effective radius of the lens, and at each point on the contour line of the lens cross section (the lens cross section including the optical axis along the optical axis) along the optical axis, the contour line is arranged on the second floor. The point where the sign of the sign is reversed when differentiated. The effective area refers to an area set as an area that is optically used as a lens by design.

  As shown in Table 10, the antireflection layer ARe in the fifth embodiment is the same as the antireflection layer ARc in the third embodiment, and is on the optical element body LMe of the optical element Len arranged on the most image side. Laminated.

  Such an antireflection layer ARd exhibits the reflectance wavelength characteristic shown in FIG. That is, the reflectance wavelength characteristics of the antireflection layer ARe are as shown in FIG. 11 on the aspheric surface when the reflectance is 5 degrees incident (paraxial) and 30 degrees incident as the wavelength increases from 350 nm. (In the case of a specific location) both decrease, and in the case of 30 degree incidence, the reflectance is about 0.1 at a wavelength of about 400 nm, while in the case of 5 degree incidence, the reflectance is about 0.1 at a wavelength of about 420 nm. After that, when the incidence is 30 degrees, the reflectance is approximately constant from about 450 nm to about 540 nm, and the reflectance is about 0.45, whereas in the case of 5 degrees incidence, the reflectance is about 470 nm and the reflectance is about 0.55. After that, it turned to decrease, and in the case of 30 degree incidence, the reflectance was about 0.25 nm again at a wavelength of about 625 nm, whereas in the case of 5 degree incidence, the reflectance was almost zero again at a wavelength of about 670 nm. Next, then, it has a profile which increases relatively slowly.

  In the imaging optical system unit SUe of the fifth embodiment using the antireflection layer ARe having the reflectance wavelength characteristic shown in FIG. 12A, the harmful light in the case of entering the infrared cut filter at 5 degrees is shown in FIG. 12 (B) has a profile indicated by a broken line, and harmful light in the case of 30-degree incidence on the infrared cut filter has a profile indicated by a broken line in FIG. 12 (C). In both cases of 5 degree incidence and 30 degree incidence, as shown in FIGS. 12 (B) and 12 (C), the harmful light is almost 0, which is lower than the comparative example at any wavelength, As shown in Table 11, it is greatly reduced as compared with the comparative example described above. That is, with respect to incident light at 5 degrees incident (paraxial), harmful light having a wavelength of 420 nm to 600 nm has an average intensity of 0.02 and is about 8.2% compared to an average intensity of 0.20 in the comparative example. (When the harmful light intensity of the comparative example is 1, the harmful light intensity of the fifth embodiment is 8.2%, the same applies hereinafter), which is an improvement of about 91.8%. With respect to incident light at 5 degrees incident (paraxial), harmful light having a wavelength of 600 nm to 650 nm has an average intensity of 0.01, which is about 1.7% compared to an average intensity of 0.67 in the comparative example. That is about 98.3% improvement. The harmful light having a wavelength of 420 nm to 600 nm has an average intensity of 0.02 with respect to incident light of 30 degrees incident (the specific portion shown in FIG. 11), which is about 7. 0%, an improvement of about 93.0%. The harmful light having a wavelength of 600 nm to 650 nm has an average intensity of 0.02 with respect to the incident light of 30 degrees incident (the specific portion shown in FIG. 11), which is about 4. 7%, an improvement of about 95.3%.

  In the case described above, the reflectance of the antireflection layer ARe is 0.39 in the average reflectance RC (5, 420 to 600) from the wavelength of 420 nm to 600 nm in the incident light incident at 5 degrees incidence (paraxial). The average reflectivity RC (5, 600 to 650) from the wavelength 600 nm to 650 nm in the incident light incident at 5 degrees incident (paraxial) is 0.1 and incident at 30 degrees (the above-described case shown in FIG. 11). The average reflectance RC (30, 420 to 600) from the wavelength 420 nm to 600 nm in the incident light incident at the specific location is 0.37, and incident at 30 degrees incident (the specific location shown in FIG. 11). The average reflectance RC (30, 600 to 650) from a wavelength of 600 nm to 650 nm in the incident light is 0.24.

  As described above, the imaging optical system units SUb to SUe of the second to fifth embodiments are substantially similar to the imaging optical system unit SUa of the first embodiment as compared to the imaging optical system unit of the comparative example. Toxic light has been reduced. For this reason, the imaging optical system units SUb to SUe of the second to fifth embodiments reduce color unevenness while reducing the size and cost, and reduce the intensity of unnecessary light caused by the infrared cut filter. Can do.

  Next, another embodiment will be described.

<Description of digital equipment incorporating imaging optical system unit>
Next, a digital apparatus in which any of the imaging optical system units SUa to SUe of the first to fifth embodiments described above is incorporated will be described.

  FIG. 13 is a block diagram illustrating a configuration of a digital device according to the embodiment. For example, as illustrated in FIG. 13, the digital device 3 has an imaging unit 30, an image generation unit 31, an image data buffer 32, an image processing unit 33, a drive unit 34, a control unit 35, and a storage unit 36 for the imaging function. And an interface unit (I / F unit) 37. Examples of the digital device 3 include a digital still camera, a video camera, a surveillance camera (monitor camera), a portable terminal such as a mobile phone or a personal digital assistant (PDA), a personal computer, and a mobile computer. Mouse, scanner and printer, etc.). In particular, the imaging optical system unit SU (SUa to SUe) of the present embodiment is sufficiently compact when mounted on a mobile terminal such as a mobile phone or a personal digital assistant (PDA), and is suitable for this mobile terminal. Installed.

  The imaging unit 30 is an example of the imaging device 21 and includes an imaging optical system unit SU that functions as an imaging lens and an imaging element IS. As described above, the imaging optical system unit SU is one of the imaging optical system units SUa to SUe of the first to fifth embodiments, and includes the imaging optical system OS (OSa to OSe) and the infrared cut filter FT. In the present embodiment, the imaging optical system OS is provided with a lens driving device (not shown) for performing focusing by driving a lens for focusing in the optical axis direction. The light beam from the subject is imaged on the light receiving surface of the imaging element IS by the imaging optical system OS of the imaging optical system unit SU to become an optical image of the subject.

  As described above, the imaging element IS converts the optical image of the subject formed by the imaging optical system OS of the imaging optical system unit SU into an electrical signal (image signal) of R, G, B color components, and R , G, and B are output to the image generator 31 as image signals of respective colors. In the imaging device IS, the imaging unit IS controls imaging operations such as imaging of either a still image or a moving image, or reading (horizontal synchronization, vertical synchronization, transfer) of an output signal of each pixel in the imaging device IS. .

  The image generation unit 31 performs amplification processing, digital conversion processing, and the like on the analog output signal from the image sensor IS, and determines an appropriate black level, γ correction, and white balance adjustment (WB adjustment) for the entire image. Then, known image processing such as contour correction and color unevenness correction is performed to generate image data from the image signal. The image data generated by the image generation unit 31 is output to the image data buffer 32.

  The image data buffer 32 is a memory that temporarily stores image data and is used as a work area for performing processing described later on the image data by the image processing unit 33. For example, the image data buffer 32 is a volatile storage element. A RAM (Random Access Memory) or the like is used.

  The image processing unit 33 is a circuit that performs predetermined image processing such as resolution conversion on the image data in the image data buffer 32.

  Further, if necessary, the image processing unit 33 performs an imaging optical system OS of the imaging optical system unit SU such as a known distortion correction process for correcting distortion in an optical image of a subject formed on the light receiving surface of the imaging element IS. Then, it may be configured to correct aberrations that could not be corrected. In the distortion correction, an image distorted by aberration is corrected to a natural image having a similar shape similar to a sight seen with the naked eye and having substantially no distortion. With this configuration, even if the optical image of the subject guided to the image sensor IS by the imaging optical system OS is distorted, it is possible to generate a natural image with substantially no distortion. Further, in the configuration in which such distortion is corrected by image processing based on information processing, in particular, only other aberrations other than distortion aberration need to be considered, so that the degree of freedom in designing the imaging optical system OS is increased and the design is improved. It becomes easier. In addition, in the configuration in which such distortion is corrected by image processing based on information processing, the aberration burden due to the lens close to the image plane is reduced, so that the exit pupil position can be easily controlled, and the lens shape is easy to process. It can be shaped.

  Further, the image processing unit 33 may include a known peripheral illuminance decrease correction process for correcting the peripheral illuminance decrease in the optical image of the subject formed on the light receiving surface of the image sensor IS as necessary. The digital device 3 can obtain a better image by further including such a peripheral illumination fall correction process. The peripheral illuminance drop correction (shading correction) is executed by storing correction data for performing the peripheral illuminance drop correction in advance and multiplying the image (pixel) after photographing by the correction data. Since the decrease in ambient illuminance mainly occurs due to the incident angle dependency of the sensitivity in the image sensor IS, the vignetting of the lens, the cosine fourth law, and the like, the correction data has a predetermined value that corrects the decrease in illuminance caused by these factors. Is set. With such a configuration, even if the peripheral illuminance drops in the optical image of the subject guided to the image sensor IS by the imaging optical system OS of the imaging optical system unit SU, an image having sufficient illuminance to the periphery. Can be generated.

  The drive unit 34 operates the lens driving device (not shown) based on a control signal output from the control unit 35 to focus on the imaging optical system OS of the imaging optical system unit SU so as to perform desired focusing. Drive the lens for.

  The control unit 35 includes, for example, a microprocessor and its peripheral circuits, and includes an imaging unit 30, an image generation unit 31, an image data buffer 32, an image processing unit 33, a drive unit 34, a storage unit 36, and an I / F unit. The operation of each part 37 is controlled according to its function. In other words, the imaging device 21 is controlled by the control unit 35 to execute at least one of the still image shooting and the moving image shooting of the subject.

  The storage unit 36 is a storage circuit that stores image data generated by still image shooting or moving image shooting of a subject. For example, a ROM (Read Only Memory) that is a nonvolatile storage element or a rewritable nonvolatile memory It comprises an EEPROM (Electrically Erasable Programmable Read Only Memory) that is a storage element, a RAM, and the like. That is, the storage unit 36 has a function as a still image memory and a moving image memory.

  The I / F unit 37 is an interface that transmits / receives image data to / from an external device. For example, the I / F unit 37 is an interface that conforms to a standard such as USB or IEEE1394.

  Next, the imaging operation of the digital device 3 having such a configuration will be described.

  When capturing a still image, the control unit 35 controls the imaging unit 30 (imaging device 21) to capture a still image, and the lens (not shown) of the imaging unit 30 via the drive unit 34. Focusing is performed by operating the driving device and moving all balls. As a result, a focused optical image is periodically and repeatedly formed on the light receiving surface of the image sensor IS, converted into image signals of R, G, and B color components, and then output to the image generator 31. . The image signal is temporarily stored in the image data buffer 32, and after image processing is performed by the image processing unit 33, an image based on the image signal is displayed on a display (not shown). The photographer can adjust the main subject so as to be within a desired position on the screen by referring to the display. When a so-called shutter button (not shown) is pressed in this state, image data is stored in the storage unit 36 as a still image memory, and a still image is obtained.

  In addition, when performing moving image shooting, the control unit 35 controls the imaging unit 30 to perform moving image shooting. After that, as in the case of still image shooting, the photographer refers to the display (not shown) so that the image of the subject obtained through the imaging unit 30 is in a desired position on the screen. Can be adjusted. When a shutter button (not shown) is pressed, moving image shooting is started. At the time of moving image shooting, the control unit 35 controls the imaging unit 30 to shoot a moving image and operates the lens driving device (not shown) of the imaging unit 30 via the driving unit 34 to perform focusing. Do. As a result, a focused optical image is periodically and repeatedly formed on the light receiving surface of the image sensor IS, converted into image signals of R, G, and B color components, and then output to the image generation unit 31. . The image signal is temporarily stored in the image data buffer 32, and after image processing is performed by the image processing unit 33, an image based on the image signal is displayed on a display (not shown). Then, when the shutter button (not shown) is pressed again, the moving image shooting is completed. The captured moving image is guided to and stored in the storage unit 36 as a moving image memory.

  Such a digital device 3 and the imaging device 21 (imaging unit 30) can reduce color unevenness and reduce the intensity of unnecessary light caused by the infrared cut filter FT while reducing the size and cost. Since the imaging optical system unit SU is used, size reduction, cost reduction, and high image quality can be achieved. That is, the high-quality digital device 3 and the imaging device 21 (imaging unit 30) with small size, low cost, and reduced color unevenness are provided. For this reason, it is suitable for mobile phones that are becoming thinner, particularly so-called smartphones. As an example, a case where the imaging device 21 is mounted on a mobile phone will be described below.

  FIG. 14 is an external configuration diagram of a camera-equipped mobile phone showing an embodiment of a digital device. 14A shows an operation surface of the mobile phone, and FIG. 14B shows a back surface of the operation surface, that is, a back surface.

  For example, as shown in FIG. 14, the mobile phone 5 includes a display unit 51 that displays predetermined information, an input operation unit 52 that receives an input of a predetermined instruction, and a telephone function that performs communication using a mobile phone network. The communication part 53 of the omission of illustration which implement | achieves, each part 30-37 shown in FIG. 13, and the thin plate-shaped housing | casing HS which accommodates these each part 51-53, 30-37 are provided. A rectangular display surface of the display unit 51 faces one main surface (front surface) of the housing HS, and an input operation unit 52 is disposed on one end side (lower side) of the display surface. The display surface of the display unit 51 is provided with a touch panel that accepts input by touching the display surface with a fingertip or a pen, and an instruction input that cannot be input by the input operation unit 52 is displayed on the touch panel and the display unit 51. It is realized by combining it with information. For example, the display unit 51 displays an image shooting mode start button, an image shooting button for switching between still image shooting and moving image shooting, a shutter button, and the like, and touching the display surface of the position of the displayed button. The instruction indicated by the button is input to the mobile phone 5. The touch panel may be of a known type such as a so-called capacitance type. The imaging unit 30 (imaging device 21) faces the other main surface (back surface) of the housing HS.

  In such a cellular phone 5, when the start button of the image capturing mode is operated, a control signal indicating the operation content is output to the control unit 35, and the control unit 35 activates the image capturing function. When the image shooting button is operated, a control signal indicating the operation content is output to the control unit 35, and the control unit 35 activates and executes the still image shooting mode and starts and executes the moving image shooting mode. The operation according to the operation content is executed. When the shutter button is operated, a control signal indicating the operation content is output to the control unit 35, and the control unit 35 performs an operation corresponding to the operation content such as still image shooting or moving image shooting. .

  In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not covered by the claims. To be construed as inclusive.

SUa to SUe, SUref Imaging optical system units OSa to OSe, OSref Imaging optical system FT Infrared cut filter ARa to ARe Antireflection layer La to Le, Lref Optical element IS Imaging element 3 Digital device 5 Mobile phone

Claims (11)

An imaging optical system for forming an optical image of a subject on a predetermined surface;
An infrared cut filter disposed on the image side of the imaging optical system,
The imaging optical system includes an optical element having an antireflection layer that satisfies the following conditional expression (A1) formed on at least one surface:
The imaging optical system unit, wherein the infrared cut filter satisfies the following conditional expressions (B1) and (B2).
RCAR (5, 600 to 650) ≦ 1.8% (A1)
| Λ (0, 50; 600 to 700) −λ (30, 50; 600 to 700) | ≦ 15 nm (B1)
0.4% / nm ≦ | ΔR | ≦ 8% / nm (B2)
However,
RCAR (5, 600 to 650); average reflectance of antireflection layer from wavelength 600 nm to 650 nm in incident light incident at 5 degrees incidence λ (0, 50; 600 to 700); between wavelength 600 nm and wavelength 700 nm , The wavelength at which the reflectance of incident light incident at 0 degree incidence is 50% (nm)
λ (30, 50; 600 to 700); a wavelength (nm) at which the reflectance of incident light incident at 30 degrees is 50% between a wavelength of 600 nm and a wavelength of 700 nm
ΔR: The wavelength at which the reflectance of incident light incident at 0 degree incidence is 30% between the wavelength 600 nm and the wavelength 700 nm is λ (0,30; 600 to 700), and the wavelength from the wavelength 600 nm to the wavelength 700 nm. When the wavelength at which the reflectance of incident light incident at 0 degree is 70% is λ (0, 70; 600 to 700), ΔR = (70−30) / (λ (0, 70; 600 to 700) -λ (0, 30; 600 to 700)) (% / nm) slope of reflectance change with respect to wavelength change The imaging optical system unit according to claim 1, wherein the antireflection layer satisfies the following conditional expression (A2).
RCAR (5, 420 to 600) ≦ 2% (A2)
However,
RCAR (5, 420 to 600): average reflectance of the antireflection layer from a wavelength of 420 nm to 600 nm in incident light incident at 5 degrees incidence The imaging optical system unit according to claim 1, wherein the optical element having the antireflection layer is a flat plate or a lens having translucency with respect to visible light. The imaging optical system unit according to any one of claims 1 to 3, wherein the optical element having the antireflection layer is disposed closest to the image side. The imaging optical system unit according to claim 4, wherein the antireflection layer is formed on a lens surface on an image side of the optical element. The imaging optical system unit according to any one of claims 1 to 5, wherein the optical element having the antireflection layer is made of a resin material. The imaging optical system unit according to any one of claims 1 to 6, wherein a substrate refractive index of the optical element having the antireflection layer satisfies the following conditional expression (A3).
1.4 ≦ nd ≦ 1.7 (A3)
However,
nd: d-line refractive index The imaging optical system according to any one of claims 1 to 7, wherein the antireflection layer is a multilayer film having a total film thickness of 600 nm or less and a number of layers of 15 or less. unit. The imaging optical system unit according to any one of claims 1 to 8,
An image sensor that converts an optical image into an electrical signal,
An image pickup apparatus, wherein the image pickup optical system of the image pickup optical system unit is capable of forming an optical image of an object on the light receiving surface of the image pickup element on the predetermined surface. An imaging device according to claim 9,
A controller that causes the imaging device to perform at least one of still image shooting and moving image shooting of a subject;
The digital apparatus, wherein the imaging optical system of the imaging device is assembled so that an optical image of an object can be formed on a light receiving surface of the imaging device.   The digital device according to claim 10, comprising a mobile terminal.

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