JP2009217030A - Optical system, and imaging device and digital apparatus using the optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical system, an imaging device, and a digital apparatus, which can reduce stray light and acquire the information on an original image appropriately. <P>SOLUTION: The optical system 1A includes an imaging lens system 11 which forms an optical image onto a predetermined imaging surface, a linear polarizer 12A which is arranged on any location on the optical axis of the imaging lens system 11, converts incidence light into linear polarizing light and emits the light. The imaging lens system 11 includes a thin film 13 having difference between the reflection factor of p polarized light and the reflection factor of s polarized light upstream of the linear polarizer 12A in the light advancing direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical system capable of reducing stray light, and an imaging apparatus and digital apparatus using the optical system.

  In recent years, cameras have been mounted on various devices such as digital devices such as personal computers (PCs) and mobile phones, and mobile objects such as vehicles and robots.

  When shooting with a camera, if there is a relatively strong light source in or near the shooting screen, when the light passes through the optical system, it does not pass through the expected light passing position as designed. Reflection of light rays may occur on the lens surface, optical flat plate, lens barrel, etc., and stray light may be generated. In such a case, when this stray light reaches the image sensor, an image of the light source may be formed at a position where the image is not originally formed, or information on the image that is originally desired to be formed may be lost. there were. In particular, in the case of shooting at night, if this stray light reaches the image sensor, it will be noticeable. In particular, in the case where the information on the image of the in-vehicle camera, the monitoring camera, the measurement camera, etc. is relatively important, if the stray light reaches the image sensor, the information on the original image is lost. It becomes a problem.

  For this reason, it is desirable to remove the stray light that has reached the image sensor. However, for example, when image signals output from the image sensor are subjected to image processing, stray light reaching the image sensor is to be removed, it is difficult to remove, or an unnatural image is obtained when it is removed. There was a case.

On the other hand, Patent Document 1 discloses a technique called polarization imaging. With the technique disclosed in Patent Document 1, it is possible to remove a reflection including a polarization component such as a window glass. However, in the technique disclosed in Patent Document 1, a general optical system is used, and almost no effect can be obtained in removing stray light.
JP 2007-086720 A

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an optical system that can reduce stray light and more appropriately obtain original image information. Moreover, this invention is providing the imaging device and digital apparatus using this optical system.

  As a result of various studies, the present inventor has found that the above object is achieved by the present invention described below. That is, an optical system according to one aspect of the present invention is disposed at any position on an optical axis of an imaging lens system that forms an optical image on a predetermined imaging plane and the imaging lens system, and includes incident light. The imaging lens system has a difference between the reflectance of p-polarized light and the reflectance of s-polarized light upstream of the linear polarizer in the light traveling direction. It has the thin film which has.

  In general, stray light (ghost flare) is reflected at least once in the optical system before reaching the image sensor. In the optical system having the above configuration, since the optical surface of the imaging lens system is provided with a thin film, the reflectance of the optical surface can be reduced, so that the intensity of stray light can be reduced before reaching the imaging device. It becomes possible. Furthermore, since the thin film is provided, reflection loss can be reduced, and the transmittance is improved correspondingly, so that a brighter original image can be obtained. Further, since the intensity of stray light increases with the intensity of light emitted from the light source, if the intensity of the light itself emitted from the light source is strong, the effect of stray light may be noticeable in the captured image. Even in such a case, in the optical system configured as described above, in addition to the reduction of the stray light intensity due to the thin film, at least one linear polarizer is provided in the optical system, so that polarized light orthogonal to the principal axis of the linear polarizer is provided. It becomes possible to remove the stray light having. In addition, in the optical system configured as described above, since the thin film has a difference between the reflectance of p-polarized light and the reflectance of s-polarized light, a difference occurs between the intensity of p-polarized light and the intensity of s-polarized light. Stray light can be effectively removed by the child. As described above, in the optical system configured as described above, the thin film having the above characteristics and the linear polarizer cooperate with each other, so that stray light can be reduced and information of the original image can be obtained more appropriately.

In the above optical system, the imaging lens system includes at least a glass lens, and the thin film is included in the glass lens, and satisfies the following conditional expressions (1) and (2).
1 [%] ≦ Rs (α) −Rp (α) (1)
40 [°] <α <60 [°] (2)
Where α is the light incident angle [°] to the thin film, Rs (α) is the reflectance [%] of the s-polarized light when incident on the thin film at the light incident angle α [°], and Rp (α) is the reflectance [%] of p-polarized light when incident on the thin film at a light incident angle α [°].

  According to this configuration, the difference between the reflectance of p-polarized light and the reflectance of s-polarized light (= Rs (α) −Rp (α)) is set to 1% or more under the condition where the light incident angle α exceeds 40 degrees. Thus, the stray light intensity can be effectively reduced by the polarizer while the manufacturing difficulty of the thin film is suppressed to the same level as that of the existing thin film. On the other hand, by setting the difference between the reflectance of p-polarized light and the reflectance of s-polarized light to 1% or more under the condition where the light incident angle α is less than 60 degrees, the manufacturing difficulty of the thin film can be made the same as that of the existing thin film While suppressing, the stray light intensity can be reduced by the polarizer.

In the above optical system, the imaging lens system includes at least a resin material lens, and the thin film is included in the resin material lens, and satisfies the following conditional expressions (1) and (2): It is characterized by.
1 [%] ≦ Rs (α) −Rp (α) (1)
40 [°] <α <60 [°] (2)
Where α is the light incident angle [°] to the thin film, Rs (α) is the reflectance [%] of the s-polarized light when incident on the thin film at the light incident angle α [°], and Rp (α) is the reflectance [%] of p-polarized light when incident on the thin film at a light incident angle α [°].

  In general, since a thin film of a resin material lens has a higher reflectance than a glass lens, it is difficult to use a resin material lens for the purpose of preventing stray light. Even if a resin-made lens is used for the imaging lens system as in the above configuration, stray light caused by the resin-made lens can be reduced by adopting the configuration of the optical system according to the present invention. Therefore, it is possible to reduce the cost by using a lens made of a resin material, and it is possible to realize an optical system that is resistant to stray light. Furthermore, under the condition that the light incident angle α exceeds 40 degrees, the difference between the reflectance of p-polarized light and the reflectance of s-polarized light (= Rs (α) −Rp (α)) is set to 1% or more, so that the thin film The stray light intensity can be effectively reduced by the polarizer while suppressing the manufacturing difficulty of the same as that of the existing thin film. On the other hand, by setting the difference between the reflectance of p-polarized light and the reflectance of s-polarized light to 1% or more under the condition where the light incident angle α is less than 60 degrees, the manufacturing difficulty of the thin film can be made the same as that of the existing thin film While suppressing, the stray light intensity can be reduced by the polarizer.

In these optical systems described above, the thin film satisfies the following conditional expression (3) in the wavelength region where the reflectance of p-polarized light is 450 nm to 650 nm.
Rp (50) <1.5 [%] (3)
However, Rp (50) is the reflectance [%] of p-polarized light when incident on the thin film at a light incident angle of 50 [°].

  In general, in a thin film, when the reflectance of p-polarized light is decreased, the reflectance of s-polarized light tends to increase. Since the optical system having the above configuration includes a linear polarizer, s-polarized stray light can be reduced by a linear polarizer having a principal axis in a direction different from that of s-polarized light. It can be made smaller. In the optical system configured as described above, it is possible to reduce the intensity of the stray light regardless of the wavelength of the stray light by making the p-polarized light reflectance of the thin film less than 1.5% in the substantially visible region. Become. Therefore, a clear image (clear image) can be obtained regardless of the type of light source.

  Further, in the above-described optical systems, at least two linear polarizers are included and are arranged so that their principal axes are directed in different directions.

  According to this configuration, stray light having polarization orthogonal to the main axis of the linear polarizer can be removed, and stray light can be further removed as compared with the case of one linear polarizer.

  In these optical systems described above, the linear polarizer is composed of a photonic crystal.

  According to this configuration, it becomes easy to arrange a plurality of polarizers having different directions as principal axes on the surface of the image sensor, and stray light can be effectively reduced.

  An imaging apparatus according to another aspect of the present invention includes the optical system according to any one of the above-described and an imaging element that converts an optical image into an electrical signal. An optical image can be formed on the light receiving surface of the image sensor.

  According to this configuration, it is possible to provide an imaging apparatus that can reduce stray light and more appropriately obtain original image information.

In the above-described imaging apparatus, the thin film of the optical system satisfies the following conditional expression (3) at the reference wavelength of the imaging element.
Rp (50) <1.5 [%] (3)
However, Rp (50) is the reflectance [%] of p-polarized light when incident on the thin film at a light incident angle of 50 [°].

  In general, in a thin film, when the reflectance of p-polarized light is decreased, the reflectance of s-polarized light tends to increase. Since the imaging device having the above configuration includes a linear polarizer, s-polarized stray light can be reduced by a linear polarizer having a principal axis in a direction different from s-polarized light. It can be made smaller. In the imaging apparatus having the above-described configuration, the p-polarized light reflectance of the thin film is less than 1.5% with respect to the reference wavelength most important in the imaging element, so that stray light can be effectively applied to the captured image. It becomes possible to reduce it.

  In the above-described imaging devices, the thin film is provided on a reflection surface of stray light having a high intensity reaching the imaging element.

  According to this configuration, it is possible to effectively reduce the intensity of stray light that reaches the image sensor. Here, “strong stray light” refers to a state in which the presence of stray light can be easily confirmed visually. For this reason, it is preferable that the thin film has a relatively large difference between the reflectance of p-polarized light and the reflectance of s-polarized light. Further, the thin film has another optical surface (an optical surface not provided with the thin film). In order to reduce stray light components other than the strong stray light such as flare, for example, it is preferable to provide a thin film having a relatively small difference between the reflectance of p-polarized light and the reflectance of s-polarized light.

  The above-described imaging devices further include an image processing unit for removing stray light from the image signal output from the imaging element.

  According to this configuration, stray light can be further reduced by the image processing unit. In particular, the image processing unit can also detect the polarization state of the light beam that has reached the imaging device from the image signal, and can use the information on the detected polarization state. It is possible to remove stray light from an image signal by a technique.

  In the above-described imaging devices, the imaging element and the linear polarizer are a polarization imaging system.

  According to this configuration, the light intensity of the non-polarized component can be calculated regardless of the polarization state of the stray light, and the stray light can be effectively reduced even when it is not substantially perpendicular to the polarization direction of the stray light. Become.

  A digital device according to another aspect of the present invention includes an imaging device according to any one of the above-described devices, and a control unit that causes the imaging device to perform at least one of shooting a still image and moving image shooting of a subject. It is characterized by providing.

  According to such a configuration, it is possible to provide a digital device that can reduce stray light and more appropriately obtain original image information.

  According to the present invention, it is possible to provide an optical system, an imaging apparatus, and a digital device that can reduce stray light and more appropriately obtain information of an original image.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the 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.

(First embodiment)
FIG. 1 is a lens cross-sectional view schematically showing the configuration of the imaging apparatus and the optical system in the first embodiment. In FIG. 1, an imaging device 21A includes an optical system 1A and an imaging element 2 that converts an optical image into an electrical signal. The optical system 1A is an optical element such as an object (subject) on the light receiving surface of the imaging element 2. An image can be formed.

  The optical system 1A forms an optical image on the light receiving surface (image surface) of the image sensor 2, and includes an imaging lens system 11, a linear polarizer 12A, and a thin film 13. In the example shown in FIG. 1, the optical system 1 </ b> A further includes an aperture stop 14.

  The imaging lens system 11 forms an optical image on a predetermined imaging surface, in the present embodiment, on the light receiving surface of the imaging device 2, and is a negative lens convex toward the object side in order from the object side to the image side. A first lens L1, a second lens L1 that is a negative lens convex toward the object side, a third lens L3 that is a positive lens convex toward the object side, and a fourth lens L4 that is a positive lens convex toward the image side It has. The imaging lens system 11 of this embodiment has a four-lens configuration. Similarly, in the second to sixth embodiments described later, the imaging lens system 11 adopts an arbitrary configuration with an arbitrary number of lenses as long as it forms an optical image on a predetermined imaging surface. Is possible.

  Here, in this specification, the notation regarding the surface shape is a notation based on paraxial curvature, and when the notation of “concave”, “convex” or “meniscus” is used for the lens, these are optical It is assumed that the lens shape is expressed near the axis (near the center of the lens) (notation based on paraxial curvature).

  The linear polarizer 12A is an optical element that is disposed at any position on the optical axis AX of the imaging lens system 11 and emits incident light converted into linearly polarized light. In the first embodiment, the linear polarizer 12 </ b> A is disposed on the image side of the imaging lens system 11, more specifically, on the front surface of the imaging device 2. The linear polarizer 12A is constituted by, for example, a polymer polarizing film.

  The thin film 13 is an antireflection film that is provided in the imaging lens system 11 and upstream of the linear polarizer 12A in the light traveling direction and has a difference in reflectance between p-polarized light and s-polarized light. is there. The thin film 13 is composed of, for example, a dielectric multilayer film, and is formed using a known manufacturing method such as a vacuum deposition method such as an ion plating method or a sputtering method. In the present embodiment, the thin film 13 is formed on the object-side optical surface (lens surface) of the second lens L2.

  The aperture stop 14 is a member that determines a light ray that has the largest angle with the optical axis AX among light rays that come out of the point on the optical axis AX of the object surface and reach a point on the optical axis AX of the image surface. In the present embodiment, the aperture stop 14 is disposed between the third lens L3 and the fourth lens L4.

  The image sensor 2 converts an optical image into an electrical signal. For example, the image sensor 2 photoelectrically converts the image signals of R (red), G (green), and B (blue) components into a predetermined image in accordance with the amount of light in the optical image formed by the optical system 1A. This element is output to a processing unit (not shown).

  In the imaging apparatus 21A having such a configuration, the object optical image on the object side is guided to the light receiving surface of the image sensor 2 by the optical system 1A, and the object optical image is captured by the image sensor 2. Then, an image signal is output from the imaging device 2 of the imaging device 21A to an unillustrated image processing unit.

  In general, stray light (ghost / flare) is reflected at least once in the optical system before reaching the image sensor. In the optical system 1A and the imaging device 21A configured as described above, since the optical surface of the imaging lens system 11 includes the thin film 13, the reflectance of the optical surface can be reduced. In addition, the intensity of stray light can be reduced. Furthermore, since the thin film 13 is provided, the reflection loss can be reduced, and the transmittance is improved correspondingly, so that a brighter original optical image of the subject can be obtained. In addition, since the intensity of stray light increases with the intensity of light emitted from the light source, if the intensity of the light itself emitted from the light source is strong, the influence of stray light is caused by the captured image formed from the image signal. It may stand out. Even in such a case, in the optical system 1A and the imaging device 21A configured as described above, in addition to the reduction of the stray light intensity by the thin film 13, at least one linear polarizer 12A is provided in the optical system 1A. It becomes possible to remove stray light having polarized light orthogonal to the main axis of 12A. In addition, in the optical system 1A and the imaging device 21A configured as described above, the thin film 13 has a difference between the reflectance of p-polarized light and the reflectance of s-polarized light, and thus there is a difference between the intensity of p-polarized light and the intensity of s-polarized light. As a result, the stray light can be effectively removed by the linear polarizer 12A. As described above, in the optical system 1A and the imaging device 21A configured as described above, the thin film 13 and the linear polarizer 12A having the above characteristics cooperate with each other, thereby effectively reducing stray light and making the information of the original image more appropriate. Can be obtained.

  In the optical system 1A and the imaging device 21A configured as described above, the thin film 13 is formed on the object-side optical surface of the second lens L2. Light rays that become stray light are incident on the thin film 13 relatively obliquely, and by providing the thin film 13, the reflectance of p-polarized light and s-polarized light is greatly different, and stray light can be effectively reduced. It becomes.

  Next, another embodiment will be described.

(Second Embodiment)
FIG. 2 is a lens cross-sectional view schematically showing the configuration of the imaging apparatus and the optical system in the second embodiment. In the optical system 1A and the imaging device 21A in the first embodiment, the linear polarizer 12A is disposed on the image side of the imaging lens system 11, but as shown in FIG. 2, the optical system 1B in the second embodiment and The imaging device 21B is provided in the imaging lens system 11, more specifically between the third lens L3 and the fourth lens L4, and more specifically between the aperture stop 14 and the fourth lens L4 ( Arranged on the image side of the aperture stop 14. The optical system 1B and the imaging device 21B in the second embodiment are the same as the optical system 1A and the imaging device 21A in the first embodiment except for the arrangement position of the linear polarizer 12A. Is omitted.

  Even with such a configuration, the optical system 1B and the imaging device 21B in the second embodiment can effectively reduce stray light and display the information of the original image, similarly to the optical system 1A and the imaging device 21A in the first embodiment. It becomes possible to obtain more appropriately.

  In particular, since the linear polarizer 12A is disposed in the vicinity of the aperture stop 14, the size of the linear polarizer 12A can be reduced and the cost can be reduced as compared with the case where the linear polarizer 12A is disposed in front of the imaging device. It becomes possible to plan.

  In the first embodiment, the linear polarizer 12A is disposed on the image side of the imaging lens system 11, and in the second embodiment, the linear polarizer 12A is disposed on the image side of the aperture stop 14. However, the present invention is not limited to this. In short, the linear polarizer 12A is downstream of the thin film 13 and upstream of the imaging device 2 in the light traveling direction, that is, the thin film 13 and the imaging device 2. It suffices to be disposed between the two.

  Next, another embodiment will be described.

(Third embodiment)
FIG. 3 is a lens cross-sectional view schematically illustrating the configuration of an imaging apparatus and an optical system according to the third embodiment. In the optical system 1C and the imaging device 21C in the third embodiment, the linear polarizer 12B is made of a photonic crystal as shown in FIG. The optical system 1C and the imaging device 21C in the third embodiment only use a linear polarizer 12B made of a photonic crystal in place of the linear polarizer 12A, and the others are the optical system 1A and the optical system 1A in the first embodiment. Since it is the same as that of the imaging device 21A, the description thereof is omitted.

  A photonic crystal refers to a structure in which materials having different refractive indexes are periodically arranged, and a two-dimensional or three-dimensional periodic structure is particularly called a photonic crystal. Unlike a material crystal, a photonic crystal is an artificial optical element that has a periodic refractive index distribution generally equal to or smaller than the wavelength of light. Similar to the phenomenon in which electrons (electron waves) are reflected by Bragg reflections due to the periodic potential of nuclei in a semiconductor and a band gap is formed in a photonic crystal, light waves are subjected to Bragg reflections due to a periodic refractive index distribution, resulting in a band for light. A gap (photonic band gap) is formed. In this photonic band gap, the existence of light itself becomes impossible, so that the light can be controlled by a photonic crystal, and a linear polarizer can be formed.

  The linear polarizer 12B made of a photonic crystal is made of a two-dimensional optical multilayer film having an effective refractive index that differs in the axial direction.

  In the optical system 1C and the imaging device 21C in the third embodiment, since the linear polarizer 12B is composed of a photonic crystal, a plurality of linear polarizers having different directions as principal axes are arranged on the surface of the imaging device 2. Thus, stray light can be effectively reduced, and original image information can be obtained more appropriately.

  Next, another embodiment will be described.

(Fourth embodiment)
FIG. 4 is a lens cross-sectional view schematically showing the configuration of the imaging device and the optical system in the fourth embodiment. As shown in FIG. 4, the optical system 1D and the imaging device 21D in the fourth embodiment include the thin film 13-1 formed on the object-side optical surface of the second lens L2, and the image side of the first lens L1. The thin film 13-2 formed on the optical surface is also provided. The thin film 13-1 and the thin film 13-2 are antireflection films having a difference between the reflectance of p-polarized light and the reflectance of s-polarized light, and the thin film 13-1 and the thin film 13-2 may be the same. Well, it can be different. In the case where they are the same, different lenses can be vapor-deposited simultaneously, which is suitable for mass production and leads to cost reduction. If they are different, the optimum film design can be performed in consideration of the incident angle of the stray light to each lens, and the stray light can be further reduced.

  In the present 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.

  Since the optical system 1D and the imaging device 21D in the fourth embodiment are the same as the optical system 1A and the imaging device 21A in the first embodiment except that the number of thin films 13 is large, the description thereof is omitted. .

  In the optical system 1D and the imaging device 21D according to the fourth embodiment, since the imaging lens system 11 includes the plurality of thin films 13, the stray light can be more effectively reduced and the original image information can be obtained more appropriately. It becomes possible.

  In the first to third embodiments, one thin film 13 is formed on the object-side optical surface of the second lens L2, and in the fourth embodiment, the two thin films 13-1 and 13-2 are formed. Although formed on each of the object-side optical surface of the second lens L2 and the image-side optical surface of the first lens L1, the present invention is not limited to this. It is sufficient that at least one thin film 13 is provided on the upstream side of the linear polarizer 12 (12A, 12B) in the traveling direction.

  Next, another embodiment will be described.

(Fifth embodiment)
FIG. 5 is a lens cross-sectional view schematically illustrating the configuration of an imaging apparatus and an optical system according to a fifth embodiment. As shown in FIG. 5, the optical system 1E and the imaging device 21E in the fifth embodiment are an imaging lens system 11 excluding the object-side optical surface of the second lens L2 on which the thin film 13 (13-1) is formed. A general antireflection film 15 (15-1 to 15-6) formed on each optical surface is provided.

  The optical system 1E and the imaging device 21E in the fifth embodiment are generally used for each optical surface in the imaging lens system 11 excluding the object-side optical surface in the second lens L2 on which the thin film 13 (13-1) is formed. Except for the point that the antireflection film 15 (15-1 to 15-6) is formed, the rest is the same as the optical system 1A and the imaging device 21A in the first embodiment, and the description thereof is omitted.

  In the imaging lens system 11 having the configuration shown in FIG. 5, the object-side optical surface of the second lens L <b> 2 is a reflection surface of stray light with high intensity that reaches the imaging device 2. “Strong stray light” is a state in which the presence of stray light can be easily confirmed visually as described above. The “general antireflection film” is a film to be compared with the thin film 13 and is not intended to make the reflectance of each polarized light different. For example, the stray light having a strong intensity such as a flare is used. The purpose is to reduce stray light components other than the above. The general antireflection film 15 may have a difference between the reflectances of both polarized lights, but is smaller than the difference between the reflectances of both polarized lights in the thin film 13.

  Therefore, it is preferable that the thin film 13 has a relatively large difference between the reflectance of p-polarized light and the reflectance of s-polarized light. Further, the general anti-reflection film 15 is formed of the stray light having high intensity such as flare, for example. It is preferable that the difference between the reflectance of p-polarized light and the reflectance of s-polarized light is relatively small enough to reduce stray light components other than the above.

  In the optical system 1E and the imaging device 21E in the fifth embodiment, the thin film 13 is provided on the optical surface on the object side in the second lens L2, which is a reflection surface of stray light having a high intensity reaching the imaging device 2, It is possible to effectively reduce the intensity of the stray light that reaches the image pickup device 2, to obtain information of the original image more appropriately, and to provide a general antireflection film 15 for other optical surfaces in the image pickup lens system 11. Since -1 to 15-6 are provided, the intensity of the stray light that reaches the image sensor 2 can be reduced more effectively, and the original image information can be obtained more appropriately.

  Next, another embodiment will be described.

(Sixth embodiment)
FIG. 6 is a lens cross-sectional view schematically showing the configuration of the imaging apparatus and the optical system in the sixth embodiment. As shown in FIG. 6, the optical system 1 </ b> F and the imaging device 21 </ b> F according to the sixth embodiment include two linear polarizers 12 </ b> A- 1 and 12 </ b> A- 2 arranged so that their principal axes are directed in different directions. Yes.

  More specifically, the imaging device 21F in the sixth embodiment includes an optical system 1F, two imaging elements 2-1 and 2-2 that convert an optical image into an electrical signal, and an optical system. 1F can form optical images of objects (subjects), for example, on the light receiving surfaces of the image sensor 2-1 and the image sensor 2-2.

  The optical system 1F forms an optical image on each light receiving surface (image surface) of each of the image pickup devices 2-1, 2-2, and includes an image pickup lens system 11, a beam splitter 17, and two pieces. The linear polarizers 12A-1 and 12A-2 and the thin film 13 are provided. In the example illustrated in FIG. 6, the optical system 1 </ b> F further includes an aperture stop 14.

  The imaging lens system 11, the thin film 13 and the aperture stop 14 are the same as the imaging lens system 11, the thin film 13 and the aperture stop 14 in the first embodiment, respectively.

  The beam splitter 17 is an optical element that divides incident light into two and emits it. In the present embodiment, as shown in FIG. 6, the beam splitter 17 includes two declination prisms that deviate the traveling direction of the light beam by 90 degrees, and these two declination surfaces face each other. These declination prisms are joined together, and a half mirror (semi-transparent mirror) is formed on the joined surface.

  The linear polarizers 12A-1 and 12A-2 are optical elements that are disposed at any position on the optical axis AX of the imaging lens system 11 and emit incident light converted into linearly polarized light. First Embodiment This is the same as the linear polarizer 12A in FIG. In the present embodiment, one linear polarizer 12A-1 is arranged so that one light beam branched by the beam splitter 17 is incident, and the other linear polarizer 12A-2 is the other beam branched by the beam splitter 17. Are arranged so as to be incident. In the present embodiment, since the beam splitter 17 is configured to include two declination prisms having a right angled isosceles triangle cross section joined at a declination surface as described above, the cross section of the beam splitter 17 is a square. One linear polarizer 12A-1 is disposed on the first exit surface facing the entrance surface of the beam splitter 17 so that the entrance surface is parallel, and the other linear polarizer 12A-2 The incident surface is arranged in parallel to the second exit surface orthogonal to the incident surface of the splitter 17. Note that one or both of the linear polarizers 12A-1 and 12A-2 may be a linear polarizer 12B made of a photonic crystal.

  The image sensors 2-1 and 2-2 convert an optical image into an electrical signal, and are the same as the image sensor 2 in the first embodiment. One image sensor 2-1 is arranged so that one light beam branched by the beam splitter 17 is incident through one linear polarizer 12A-1, and the other image sensor 2-2 is provided with the beam splitter 17. Is arranged so that the other light beam branched in the direction enters through the other linear polarizer 12A-2.

  Since the optical system 1F and the imaging device 21F in the sixth embodiment include two linear polarizers 12A-1 and 12A-2, polarized light orthogonal to the main axes of the linear polarizers 12A-1 and 12A-2. And stray light can be removed more than in the case of one linear polarizer 12A. Therefore, in the optical system 1F and the imaging device 21F in the sixth embodiment, the intensity of the stray light that reaches the imaging elements 2-1 and 2-2 can be more effectively reduced, and the original image information can be obtained more appropriately. Is possible.

  Although the optical system 1F and the imaging device 21F in the present embodiment are configured to include two linear polarizers 12A-1 and 12A-2, they may be configured to include more linear polarizers 12A. Good.

  In each of the imaging devices 21A to 21F in the first to sixth embodiments, on the image side of the optical systems 1A to 1F, for example, depending on the intended use, the imaging device 2, the configuration of the imaging devices 21A to 21F, and the like. For example, an optical filter such as a low-pass filter or an infrared cut filter may be appropriately disposed.

In each of the optical systems 1A to 1F and the imaging devices 21A to 21F in the first to sixth embodiments, the second lens L2 on which the thin film 13 is formed may be a glass lens or made of a resin material. It may be a lens. In such a case, the thin film 13 has a light incident angle on the thin film 13 as α [°], and the reflectance of s-polarized light when incident on the thin film at a light incident angle α [°] is Rs (α ) [%], And when the reflectance of p-polarized light is Rp (α) [%] when incident on the thin film at a light incident angle α [°], the following conditions (1) and (2) It is preferable to satisfy the formula.
1 [%] ≦ Rs (α) −Rp (α) (1)
40 [°] <α <60 [°] (2)
By making the difference between the reflectance of p-polarized light and the reflectance of s-polarized light 1% or more under the condition where the light incident angle α exceeds 40 degrees, the manufacturing difficulty of the thin film is suppressed to the same level as the existing thin film, The polarizer can effectively reduce the stray light intensity. On the other hand, by setting the difference between the reflectance of p-polarized light and the reflectance of s-polarized light to 1% or more under the condition where the light incident angle α is less than 60 degrees, the manufacturing difficulty of the thin film can be made the same as that of the existing thin film. While suppressing, the stray light intensity can be reduced by the polarizer.

  In general, since a thin film of a resin material lens has a higher reflectance than a glass lens, it is difficult to use a resin material lens for the purpose of preventing stray light. However, since the optical systems 1A to 1F and the imaging devices 21A to 21F are configured as described above, even if a resin material lens is used for the second lens L2 on which the thin film 13 is formed, a resin material lens is used. The stray light caused by can be reduced. Therefore, it is possible to reduce the cost by using a lens made of a resin material, and it is possible to realize the optical system 1A and the imaging device 21A that are resistant to stray light.

In such a case, it is more preferable that the thin film 13 satisfies the following conditional expressions (1 ′) and (2 ′).
1.2 [%] ≦ Rs (α) −Rp (α) (1 ′)
40 [°] <α <60 [°] (2 ′)
By satisfying the above conditional expressions (1 ′) and (2 ′), it becomes possible to more effectively reduce stray light and obtain information of the original image more appropriately.

Further, in such a case, it is more preferable that the thin film 13 satisfies the following conditional expressions (1 ″) and (2 ″).
1.5 [%] ≦ Rs (α) −Rp (α) (1 ″)
40 [°] <α <60 [°] (2 ”)
By satisfying the above conditional expressions (1 ″) and (2 ″), it becomes possible to further reduce stray light more effectively and obtain information of the original image more appropriately.

  In such a case, one or a plurality of lenses in the lens (the first lens L1, the third lens, and the fourth lens) other than the second lens L2 in which the thin film 13 is formed in the imaging lens system 11 It may be a lens made of a resin material.

In each of the optical systems 1A to 1F and the imaging devices 21A to 21F in the first to sixth embodiments, the thin film 13 has a reflectance of p-polarized light when incident on the thin film 13 at a light incident angle of 50 [°]. Is set to Rp (α) [%], it is preferable to satisfy the following conditional expression (3) at the reference wavelength of the image sensor 2.
Rp (50) <1.5 [%] (3)
In general, in a thin film, when the reflectance of p-polarized light is decreased, the reflectance of s-polarized light tends to increase. Since each of the optical systems 1A to 1F and the imaging devices 21A to 21F having such a configuration includes the linear polarizers 12A and 12B, the s-polarized stray light is generated by the linear polarizer having a principal axis in a direction different from the s-polarized light. Therefore, it is possible to reduce the reflectance of p-polarized light. In each of the optical systems 1A to 1F and the imaging devices 21A to 21F configured as described above, the reflectance of the p-polarized light of the thin film 13 is less than 1.5% with respect to the reference wavelength most important in the imaging device 2. Thus, stray light can be effectively reduced with respect to the captured image.

In such a case, it is more preferable that the thin film 13 satisfies the following conditional expression (3 ′).
Rp (50) <1.0 [%] (3 ′)
When the conditional expression (3 ′) is satisfied, stray light can be more effectively reduced, and original image information can be obtained more appropriately.

Furthermore, in such a case, it is even more preferable that the thin film 13 satisfies the following conditional expression (3 ″).
Rp (50) <0.5 [%] (3 ")
By satisfying the conditional expression (3 ″), it is possible to further reduce stray light more effectively and obtain information of the original image more appropriately.

  In each of the optical systems 1A to 1F and the imaging devices 21A to 21F in the first to sixth embodiments, the thin film 13 has a reflectance of p-polarized light when incident on the thin film 13 at a light incident angle of 50 [°]. Is preferably Rp (α) [%], the p-polarized light reflectance preferably satisfies the conditional expression (3) in the wavelength region of 450 nm to 650 nm, and the conditional expression (3 ′) above. Is more preferable, and it is even more preferable that the conditional expression (3 ″) is satisfied.

  Since each of the optical systems 1A to 1F and the imaging devices 21A to 21F having such a configuration includes the linear polarizers 12A and 12B, the s-polarized stray light is generated by the linear polarizer having a principal axis in a direction different from the s-polarized light. Therefore, it is possible to reduce the reflectance of p-polarized light. In each of the optical systems 1A to 1F and the imaging devices 21A to 21F configured as described above, the p-polarized light reflectance of the thin film 13 is less than 1.5% in the substantially visible region, so that it does not depend on the wavelength of stray light. In addition, the intensity of the stray light can be reduced. Therefore, a clear image (clear image) can be obtained regardless of the type of light source.

  The optical systems 1A to 1F and the imaging devices 21A to 21F in the first to sixth embodiments may further include an image processing unit for removing stray light from the image signal output from the imaging device 2. . In each of the optical systems 1A to 1F and the imaging devices 21A to 21F having such a configuration, stray light can be further reduced by the image processing unit. In particular, the image processing unit can also detect the polarization state of the light beam that has reached the imaging device 2 from the image signal, and can use the information on the detected polarization state. It is possible to remove stray light from an image signal by a technique.

  For example, as disclosed in Japanese Patent Application Laid-Open No. 2007-086720, at least two polarizers oriented in different directions are arranged in front of the image sensor 2, so that images with different polarization states in the image sensor 2 are displayed. Are acquired simultaneously, and the polarization state can be detected based on the difference between them. Then, stray light is removed based on the detected polarization state. For example, a non-polarized image can be easily obtained by comparing a plurality of images and extracting the darkest part of each pixel.

  Further, in each of the optical systems 1A to 1F and the imaging devices 21A to 21F in the first to sixth embodiments, the imaging element 2 and the linear polarizer 12 (12A, 12B) may be a polarization imaging system. The polarization imaging system is a polarization imaging system including an imaging element 2 in which at least two polarizers facing different directions are arranged in front thereof. In each of the optical systems 1A to 1F and the imaging devices 21A to 21F having such a configuration, the light intensity of the non-polarized component can be calculated regardless of the polarization state of the stray light, and is not substantially perpendicular to the polarization direction of the stray light. Even in this case, stray light can be effectively reduced.

  For example, as disclosed in Japanese Patent Application Laid-Open No. 2007-086720, at least two polarizers oriented in different directions are arranged in front of the image sensor 2, so that images with different polarization states in the image sensor 2 are displayed. Are acquired at the same time. Here, the transmitted light that has passed through the polarizer includes a polarization component A corresponding to the polarizer and a uniform non-polarization component B that does not depend on the polarizer (common to each polarizer). Therefore, the image is subjected to predetermined image processing (information processing) to separate the image into a polarized component A and a non-polarized component B, and the separated polarized component A and non-polarized component B are reconstructed. Thus, an image with reduced stray light can be obtained.

  The polarization component A refers to a component whose intensity changes depending on the rotation angle of the polarizer when light is passed through the polarizer, and so-called linearly polarized light and elliptically polarized light. The non-polarized component B is a component whose intensity does not change depending on the rotation angle of the polarizer when light passes through the polarizer, and is so-called non-polarized light and circularly polarized light.

Next, examples of the thin film 13 (13A to 13D) will be described.
(First Example of Thin Film 13)
The thin film 13A of the first embodiment is an antireflection film having a seven-layer structure with respect to light having a design center wavelength λ0 = 550 nm, and is formed on the substrate of BK7 from the first layer with the materials and optical film thicknesses shown in Table 1. Up to 7 layers were sequentially laminated. In Table 1, ZrTiO ₄ is “OH-5” manufactured by Optron Corporation. The same applies to Tables 2 and 3.

  7 to 9 are diagrams showing the reflection characteristics with respect to the incident angle in the thin film of the first embodiment. 7 shows the case of an incident light wavelength of 450 nm, FIG. 8 shows the case of an incident light wavelength of 550 nm, and FIG. 9 shows the case of an incident light wavelength of 650 nm. The horizontal axis in FIGS. 7 to 9 is the incident angle expressed in degrees, and the vertical axis is the reflectance expressed in percentage. A solid line indicates s-polarized light, and a broken line indicates p-polarized light. 10 to 12 are diagrams showing reflection characteristics with respect to wavelength in the thin film of the first embodiment. 10 shows the case of a light incident angle of 0 degrees on the thin film 13A, FIG. 11 shows the case of a light incident angle of 20 degrees on the thin film 13A, and FIG. 12 shows a case where the light incident angle on the thin film 13A is 40 degrees. Show the case. The horizontal axis of FIGS. 10 to 12 is the wavelength expressed in nm, and the vertical axis thereof is the reflectance expressed in percentage. A solid line indicates s-polarized light, and a broken line indicates p-polarized light.

  The reflection characteristics of the thin film 13A designed in this way are shown in FIGS. As can be seen from FIGS. 7 to 12, when the light incident angle α to the thin film 13A is 40 [°] to 60 [°] at a wavelength of 550 nm, the difference between the reflectance of s-polarized light and the reflectance of p-polarized light is as follows. When the light incident angle α to the thin film 13A is 50 [°] in the substantially visible region having a wavelength of 450 nm to 650 nm, the reflectance of p-polarized light is 1.0 [%]. %] Or less.

(Second Example of Thin Film 13)
The thin film 13B of the second embodiment is an antireflection film having a four-layer structure with respect to light having a design center wavelength λ0 = 850 nm, and is formed on the substrate of BK7 from the first layer with the materials and optical film thicknesses shown in Table 2. Up to four layers were sequentially stacked.

  FIG. 13 is a diagram showing the reflection characteristics with respect to the incident angle in the thin film of the second embodiment. FIG. 13 shows the case of an incident light wavelength of 850 nm, the horizontal axis is the incident angle expressed in degrees, and the vertical axis is the reflectance expressed in percentage units. A solid line indicates s-polarized light, and a broken line indicates p-polarized light. 14 to 16 are diagrams showing reflection characteristics with respect to wavelength in the thin film of the second embodiment. FIG. 14 shows the case of a light incident angle of 0 degrees on the thin film 13B, FIG. 15 shows the case of a light incident angle of 20 degrees on the thin film 13B, and FIG. 16 shows the case of a light incident angle of 40 degrees on the thin film 13B. Show the case. The horizontal axis of FIGS. 14 to 16 is the wavelength expressed in nm, and the vertical axis thereof is the reflectance expressed in percent. A solid line indicates s-polarized light, and a broken line indicates p-polarized light.

  The reflection characteristics of the thin film 13B designed in this way are shown in FIGS. As can be seen from FIGS. 13 to 16, in the near-infrared region of the design center wavelength of 850 nm, when the light incident angle α to the thin film 13B is 40 [°] to 60 [°], the reflectance of s-polarized light. And the reflectance of the p-polarized light is 2.0 [%] or more, and the light incident angle α to the thin film 13B is 50 [° in the near-infrared region with a wavelength of 850 nm, which is the design center wavelength. ], The reflectance of p-polarized light is 0.2 [%] or less.

(Third embodiment of thin film 13)
The thin film 13C of the first embodiment is an antireflection film having a three-layer structure with respect to light having a design center wavelength λ0 = 550 nm, and is formed on the substrate of BK7 from the first layer with the materials and optical film thicknesses shown in Table 3. Up to three layers were sequentially stacked.

  17 to 19 are diagrams showing the reflection characteristics with respect to the incident angle in the thin film of the third embodiment. FIG. 17 shows the case of an incident light wavelength of 450 nm, FIG. 18 shows the case of an incident light wavelength of 550 nm, and FIG. 19 shows the case of an incident light wavelength of 650 nm. The horizontal axis in FIGS. 17 to 19 is the incident angle expressed in degrees, and the vertical axis is the reflectance expressed in percent. A solid line indicates s-polarized light, and a broken line indicates p-polarized light. 20 to 22 are diagrams showing the reflection characteristics with respect to the wavelength in the thin film of the third embodiment. 20 shows the case of a light incident angle of 0 degrees on the thin film 13C, FIG. 21 shows the case of a light incident angle of 20 degrees on the thin film 13C, and FIG. 22 shows a light incident angle of 40 degrees on the thin film 13C. Show the case. The horizontal axis in FIGS. 20 to 22 is the wavelength expressed in nm, and the vertical axis thereof is the reflectance expressed in percent. A solid line indicates s-polarized light, and a broken line indicates p-polarized light.

  The reflection characteristics of the thin film 13C designed in this way are shown in FIGS. As can be seen from FIGS. 17 to 22, when the light incident angle α to the thin film 13C is 40 ° to 60 ° in the substantially visible region with a wavelength of 450 nm to 650 nm, the reflectivity of s-polarized light and the p-polarized light. The difference from the reflectance is 4.0 [%] or more.

(First Example of Thin Film 13)
The thin film 13D of the fourth embodiment is an antireflection film having a four-layer structure with respect to light having a design center wavelength λ0 = 550 nm. The thin film 13D has the materials and optical film thicknesses shown in Table 4 on a ZEONEX ™ E48R substrate. The first layer to the fourth layer were sequentially stacked.

  23 to 25 are diagrams showing the reflection characteristics with respect to the incident angle in the thin film of the fourth embodiment. FIG. 23 shows the case where the incident light wavelength is 450 nm, FIG. 24 shows the case where the incident light wavelength is 550 nm, and FIG. 25 shows the case where the incident light wavelength is 650 nm. The horizontal axis of FIGS. 23 to 25 is the incident angle expressed in degrees, and the vertical axis thereof is the reflectance expressed in percentage. A solid line indicates s-polarized light, and a broken line indicates p-polarized light. 26 to 28 are diagrams showing the reflection characteristics with respect to the wavelength in the thin film of the fourth embodiment. 26 shows the case of a light incident angle of 0 degree on the thin film 13D, FIG. 27 shows the case of a light incident angle of 20 degrees on the thin film 13D, and FIG. 28 shows a case of a light incident angle of 40 degrees on the thin film 13D. Show the case. The horizontal axis of FIGS. 26 to 28 is the wavelength expressed in nm, and the vertical axis thereof is the reflectance expressed in percent. A solid line indicates s-polarized light, and a broken line indicates p-polarized light.

  The reflection characteristics of the thin film 13D designed in this way are shown in FIGS. As can be seen from FIGS. 23 to 28, in the substantially visible region with a wavelength of 450 nm to 650 nm, when the light incident angle α to the thin film 13D is 40 [°] to 60 [°], the reflectivity of s-polarized light and p-polarized light. When the difference from the reflectivity is 1.0 [%] or more and the light incident angle α to the thin film 13D is 50 [°] in the substantially visible region with a wavelength of 450 nm to 650 nm, the reflection of p-polarized light The rate is 1.0 [%] or less.

  Next, digital devices incorporating the optical systems 1A to 1F in the first to sixth embodiments will be described.

  FIG. 29 is a block diagram illustrating a configuration of a digital device according to the embodiment. In FIG. 29, 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, a storage unit 36, and an I / F unit for the imaging function. 37. Examples of the digital device 3 include a digital still camera, a digital video camera, a monitor camera for monitoring and mounting on a mobile object, a portable terminal such as a mobile phone and a personal digital assistant (PDA), a personal computer, and a mobile computer. These peripheral devices (eg, mouse, scanner, printer, etc.) may be included.

  The imaging unit 30 includes the imaging device 21 (21A to 21F) and the imaging element 2. The imaging device 21 includes an optical system 1 (1A to 1F) as shown in FIGS. 1 to 6, and the optical system 1 is on a predetermined imaging surface, in these examples, an optical image of a subject on the imaging device 2. The imaging lens device (not shown) is configured to be capable of forming the lens, and the lens driving device (not shown) for driving the lens in the optical axis direction for focusing. The light beam from the subject is imaged on the light receiving surface of the image sensor 2 by the optical system 1 and becomes an optical image of the subject.

  The imaging element 2 is an element that converts an optical image of the subject guided by the imaging lens device of the imaging device 21 into an electrical signal. As described above, the optical image of the subject imaged by the optical system 1 is obtained. The signals are converted into electrical signals (image signals) of R, G, and B color components and output to the image generation unit 31 as image signals of R, G, and B colors. The imaging device 2 is controlled by the control unit 35 for imaging operation such as imaging of either a still image or a moving image, or reading of output signals of each pixel (horizontal synchronization, vertical synchronization, transfer) in the imaging device 2. . The image sensor 2 may be a solid-state image sensor such as a CCD or a CMOS, or may be a color image sensor or a monochrome image sensor.

  The image generation unit 31 performs amplification processing, digital conversion processing, and the like on the analog output signal from the image sensor 2 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 of each pixel 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. It is composed of a RAM (Random Access Memory).

  The image processing unit 33 is a circuit that performs image processing such as resolution conversion on the image data in the image data buffer 32. Further, if necessary, the image processing unit 33 can correct aberrations that cannot be corrected by the optical system 1 such as known distortion correction processing for correcting distortion in the optical image of the subject formed on the light receiving surface of the image sensor 2. May be configured to correct. 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 2 by the imaging lens device of the imaging device 21 is distorted, it is possible to generate a natural image with almost no distortion. It becomes. Further, the image processing unit 33 may perform a process of removing stray light from the image signal output from the image sensor 2 as necessary. This image processing unit 33 can further reduce stray light. In particular, the image processing unit 33 may detect the polarization state of the light beam that has reached the imaging device 2 from the image signal, and remove stray light from the image signal by using information on the detected polarization state. With this configuration, stray light can be removed from the image signal by a simpler method.

  The driving unit 34 is a circuit that performs focusing of the optical system 1 by operating the lens driving device (not shown) based on a control signal output from the control unit 35.

  The control unit 35 includes, for example, a microprocessor, a storage element, and peripheral circuits thereof, 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. The operation of each part of the / F unit 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, a rewritable nonvolatile memory, or the like. 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 shooting a still image, the control unit 35 controls the imaging device 21 to shoot a still image and operates the lens driving device (not shown) of the imaging device 21 via the driving unit 34. , Do the focusing. As a result, the focused optical image is periodically and repeatedly formed on the light receiving surface of the image sensor 2, converted into R, G, and B color component image signals, 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 (display device) (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. In this state, when a so-called unillustrated shutter button is pressed, 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 device 21 to perform moving image shooting. Thereafter, in the same manner as in the case of still image shooting, the photographer refers to the display and adjusts the image of the subject obtained through the imaging device 21 to be in a desired position on the screen. Can do. In this case, as with still image shooting, moving image shooting is started by pressing the shutter button.

  At the time of moving image shooting, the control unit 35 controls the imaging device 21 to take a moving image, and operates the lens driving device of the imaging device 21 via the driving unit 34 to perform focusing. As a result, a focused optical image is periodically and repeatedly formed on the light receiving surface of the image sensor 2, 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 the display (not shown). Then, when the shutter button 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.

  In such a digital device 3 and the imaging device 21, stray light can be reduced, information on the original image can be obtained more appropriately, and a better image can be obtained.

  Next, as a specific example of a digital device including the optical system 1 and the imaging device 21, a case where it is mounted on a mobile phone and a case where it is mounted on an in-vehicle monitor camera will be described below.

  FIG. 30 is an external configuration diagram of a camera-equipped mobile phone showing an embodiment of a digital device. FIG. 30A shows the operation surface of the mobile phone, and FIG. 30B shows the back surface of the operation surface, that is, the back surface.

  In FIG. 30, the cellular phone 5 is provided with an antenna 51 at the top, and on its operation surface, as shown in FIG. 30 (A), a rectangular display 52, image shooting mode activation, still image shooting and moving image An image shooting button 53 for switching to shooting, a shutter button 55, and a dial button 56 are provided. The cellular phone 5 incorporates a circuit for realizing a telephone function using a cellular phone network, and includes the above-described imaging unit 30, image generating unit 31, image data buffer 32, image processing unit 33, and driving unit. 34, the control part 35, and the memory | storage part 36 are incorporated, and the imaging device 21 of the imaging part 30 faces the back.

  When the image capturing button 53 is operated, a control signal indicating the operation content is output to the control unit 35, and the control unit 35 executes an operation corresponding to the operation content. When the shutter button 55 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. In this way, a still image or a moving image is captured.

  The optical system 1 and the imaging device 21 are attached to a predetermined position, and are suitable for a monitor camera that images a subject in a predetermined area around the attached position, for example, an in-vehicle monitor camera that images a peripheral area of the vehicle. Mounted on.

  FIG. 31 is a diagram for explaining an overview of an in-vehicle monitor camera showing an embodiment of a digital device. In FIG. 31, the in-vehicle monitor camera 7 is installed at a predetermined position on the rear part of the vehicle 9 so as to image the rear of the vehicle 9, for example, and the captured image of the subject is installed on the dashboard, for example. Is displayed on the monitor (not shown). The in-vehicle monitor camera 7 is normally attached to the vehicle 9 in a posture inclined obliquely downward so that the optical axis AX faces obliquely downward because an upward visual field of the vehicle 9 is not required. And in the vertical direction, it has an angle of view 2φ with the horizontal line passing through the mounting position of the monitor camera 7 as the upper end. In this specification, the angle of view in the left-right direction is also 2φ as in the up-down direction. However, the angle of view may be different between the up-down direction and the left-right direction without being limited thereto.

  The flow of processing when the vehicle-mounted camera 7 having such a configuration is used as a back monitor will be outlined below. For example, the user (driver) turns the vehicle body 7 back while looking at a monitor (display device) (not shown) installed on the dashboard of the vehicle body 9. At this time, if the area that the driver wants to check is different from the area that the in-vehicle camera 7 captures, the driver performs a predetermined operation such as operating an operation button (not shown) provided on the dashboard. I do.

  In response to this operation, the control unit 35 controls the drive unit 34 to adjust the orientation of the imaging unit 30. Subsequently, the control unit 35 drives the lens driving device of the imaging device 21 to perform focusing of the optical system 1. As a result, a focused optical image is formed on the light receiving surface of the image sensor 2, 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 image processing is performed by the image processing unit 33. Thus, a substantially natural image of the area that the driver wants to confirm is displayed on the monitor installed on the dashboard.

  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. Accordingly, 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. It is interpreted that it is included in

It is a lens sectional view showing the composition typically for explanation of an imaging device and an optical system in a 1st embodiment. It is lens sectional drawing which showed the structure typically for description of the imaging device and optical system in 2nd Embodiment. It is lens sectional drawing which showed the structure typically for description of the imaging device and optical system in 3rd Embodiment. It is lens sectional drawing which showed the structure typically for description of the imaging device and optical system in 4th Embodiment. It is a lens sectional view showing the composition typically for explanation of an imaging device and an optical system in a 5th embodiment. It is lens sectional drawing which showed the structure typically for description of the imaging device and optical system in 6th Embodiment. It is a figure (the 1) which shows the reflective characteristic with respect to the incident angle in the thin film of 1st Example. It is FIG. (2) which shows the reflection characteristic with respect to the incident angle in the thin film of 1st Example. FIG. 6 is a diagram (part 3) illustrating reflection characteristics with respect to an incident angle in the thin film of the first example. It is a figure (the 1) which shows the reflective characteristic with respect to the wavelength in the thin film of 1st Example. It is a figure (the 2) which shows the reflective characteristic with respect to the wavelength in the thin film of 1st Example. FIG. 6 is a diagram (part 3) illustrating reflection characteristics with respect to wavelength in the thin film of the first example. It is a figure which shows the reflection characteristic with respect to the incident angle in the thin film of 2nd Example. It is FIG. (1) which shows the reflective characteristic with respect to the wavelength in the thin film of 2nd Example. It is a figure (the 2) which shows the reflective characteristic with respect to the wavelength in the thin film of 2nd Example. It is a figure (the 3) which shows the reflective characteristic with respect to the wavelength in the thin film of 2nd Example. It is a figure (the 1) which shows the reflective characteristic with respect to the incident angle in the thin film of 3rd Example. It is FIG. (2) which shows the reflection characteristic with respect to the incident angle in the thin film of 3rd Example. It is the figure (the 3) which shows the reflective characteristic with respect to the incident angle in the thin film of 3rd Example. It is FIG. (1) which shows the reflective characteristic with respect to the wavelength in the thin film of 3rd Example. It is a figure (the 2) which shows the reflective characteristic with respect to the wavelength in the thin film of 3rd Example. It is the figure (the 3) which shows the reflective characteristic with respect to the wavelength in the thin film of 3rd Example. It is FIG. (1) which shows the reflection characteristic with respect to the incident angle in the thin film of 4th Example. It is FIG. (2) which shows the reflection characteristic with respect to the incident angle in the thin film of 4th Example. It is the figure (the 3) which shows the reflective characteristic with respect to the incident angle in the thin film of 4th Example. It is a figure (the 1) which shows the reflective characteristic with respect to the wavelength in the thin film of 4th Example. It is a figure (the 2) which shows the reflective characteristic with respect to the wavelength in the thin film of 4th Example. It is the figure (the 3) which shows the reflective characteristic with respect to the wavelength in the thin film of 4th Example. It is a block diagram which shows the structure of the digital device in embodiment. It is an external appearance block diagram of the mobile phone with a camera which shows one Embodiment of a digital device. It is a figure for demonstrating the outline | summary of the vehicle-mounted monitor camera which shows one Embodiment of digital equipment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 (1A-1F) Optical system 2 Image pick-up element 3 Digital equipment 11 Imaging lens system 12 (12A, 12B) Linear polarizer 13 Thin film 21 Imaging device

Claims (12)

An imaging lens system that forms an optical image on a predetermined imaging surface;
A linear polarizer that is disposed at any position on the optical axis of the imaging lens system and emits incident light converted into linearly polarized light; and
The image pickup lens system includes a thin film having a difference in reflectance between p-polarized light and s-polarized light upstream of the linear polarizer in the light traveling direction. The optical system according to claim 1, wherein the imaging lens system includes at least a glass lens, and the thin film is included in the glass lens, and satisfies the following conditional expressions (1) and (2).
1 [%] ≦ Rs (α) −Rp (α) (1)
40 [°] <α <60 [°] (2)
However,
α: Light incident angle on the thin film [°]
Rs (α): s-polarized light reflectance [%] when incident on a thin film at a light incident angle α [°]
Rp (α): p-polarized light reflectance [%] when incident on a thin film at a light incident angle α [°] The imaging lens system includes at least a resin material lens,
The optical system according to claim 1, wherein the thin film is provided in the lens made of the resin material and satisfies the following conditional expressions (1) and (2).
1 [%] ≦ Rs (α) −Rp (α) (1)
40 [°] <α <60 [°] (2)
However,
α: Light incident angle on the thin film [°]
Rs (α): s-polarized light reflectance [%] when incident on a thin film at a light incident angle α [°]
Rp (α): p-polarized light reflectance [%] when incident on a thin film at a light incident angle α [°] The optical system according to any one of claims 1 to 3, wherein the thin film satisfies the following conditional expression (3) in a wavelength range where the reflectance of p-polarized light is 450 nm to 650 nm.
Rp (50) <1.5 [%] (3)
However,
Rp (50): p-polarized light reflectance [%] when incident on a thin film at a light incident angle of 50 [°] The optical system according to any one of claims 1 to 4, wherein at least two linear polarizers are included and are arranged so that their principal axes are directed in different directions. The optical system according to claim 1, wherein the linear polarizer is made of a photonic crystal. An optical system according to any one of claims 1, 2, 3, 5, and 6;
An image sensor that converts an optical image into an electrical signal,
An image pickup apparatus, wherein the optical system is capable of forming an optical image on a light receiving surface of the image pickup device. The imaging apparatus according to claim 7, wherein the thin film of the optical system satisfies the following conditional expression (3) at a reference wavelength of the imaging element.
Rp (50) <1.5 [%] (3)
However,
Rp (50): p-polarized light reflectance [%] when incident on a thin film at a light incident angle of 50 [°] The imaging device according to claim 7, wherein the thin film is provided on a reflection surface of stray light having a high intensity that reaches the imaging element. The image pickup apparatus according to claim 7, further comprising an image processing unit for removing stray light from the image signal output from the image pickup element. The imaging device according to any one of claims 7 to 10, wherein the imaging device and the linear polarizer are a polarization imaging system. An imaging device according to any one of claims 7 to 11,
A digital apparatus comprising: a control unit that causes the imaging device to perform at least one of still image shooting and moving image shooting of a subject.

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