JP2006154395A - Optical filter and imaging device having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical filter which is a thin type tough for environmental changes and is high-quality, and to provide an imaging device having the optical filter. <P>SOLUTION: The optical filter 4 disposed in an optical path of an imaging optical system 1 is made by alternately joining two or more respective ones of optical anisotropic members 42, 44 consisting of organic material constituted in a film shape and inorganic base plates 41, 43 consisting of inorganic material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical filter disposed in an optical path when an image is formed using an imaging device, and is suitable for an imaging device such as a digital camera or a video camera.

  Conventionally, in an imaging apparatus using a solid-state imaging device such as a CCD or a CMOS, an object is to reduce a false signal generated depending on a sampling frequency of the imaging device when an object having a high frequency component is imaged. Various optical low-pass filters have been proposed.

  An optical low-pass filter uses a birefringence action of a uniaxial single crystal of quartz to separate subject light into ordinary rays and extraordinary rays, and lowers the response to the spatial frequency component corresponding to this separation width. Even now, various applications of this property are widely used (conventional example 1).

  In addition, there are uniaxial crystals other than quartz, such as those utilizing the birefringence action of a single crystal plate of lithium niobate (Conventional Example 2).

  Conventional Example 2 uses the birefringence action of a uniaxial single crystal as in Conventional Example 1, but the single crystal of lithium niobate has a difference (ΔN) between the refractive index of ordinary light and the refractive index of extraordinary light. Due to the large size, the thickness of the substrate required to obtain an equivalent separation width when compared with the configuration of Conventional Example 1 can be reduced.

  Other than using a single-crystal substrate as a birefringent material, various types of optical low-pass filters have been proposed by utilizing the birefringence action of organic substances such as liquid crystal materials (Patent Documents 1, 2, and 5). 3).

  In Patent Documents 1, 2, and 3, a method for producing a material that has birefringence by applying an electric field or a magnetic field to the molecular orientation of the liquid crystalline material as a predetermined direction, and this material is used as an optical low-pass filter. To the effect.

  In the optical low-pass filter, the above-described examples of materials used for the function of separating the subject image include the above-described materials, but in actual use, an optical low-pass filter is realized by using a plurality of these materials. It has become common.

  Since an image pickup device such as a CCD or CMOS has pixels and color filters regularly arranged two-dimensionally, it is desirable to configure so as to appropriately control the spatial frequency response in at least two directions. From such a background, the first crystal birefringence plate, the crystal phase plate, and the second crystal birefringence so as to control the response in two horizontal and vertical directions which are general arrangement directions of the image sensor. An optical low-pass filter in which plates are arranged in this order is known (conventional example 3).

  The first quartz birefringent plate of Conventional Example 3 has its optical axis inclined by a predetermined angle (often set at 45 °, which is most efficient) with respect to the normal of the incident surface, and its substrate The orthogonal projection onto the incident surface is configured to face the first direction (here, the horizontal direction) that reduces the response to the spatial frequency. In the first quartz birefringent plate, incident light is separated into a linearly polarized ordinary ray and an extraordinary ray having a predetermined vibration surface, and only the extraordinary ray is moved by a predetermined amount in the horizontal direction of the imaging screen. Has function. The quartz phase plate has its optical axis arranged in a direction orthogonal to the incident surface (that is, in the plane of the substrate) and 45 with respect to the orthogonal projection of the optical axis of the first quartz birefringent plate on the substrate incident surface. It is configured to face in a direction rotated by ° (here, a direction rotated 45 ° from the horizontal direction). The quartz phase plate has an effect of converting the phase of a set of linearly polarized light beams emitted from the first quartz birefringent plate, and has a phase corresponding to the phase difference determined by the thickness of the phase plate and the wavelength of the light beam. It is ejected by changing.

  The second crystal birefringent plate is tilted by a predetermined angle (often set at 45 °, which is most efficient) with respect to the normal line of the incident surface of the second crystal birefringent plate, and toward the substrate incident surface. The orthogonal projection is directed in the second direction (in this case, the vertical direction) that reduces the response to the spatial frequency. In the second crystal birefringent plate, incident light is separated into linearly polarized ordinary rays and extraordinary rays having a predetermined vibration surface, and only the extraordinary rays are moved by a predetermined amount in the horizontal direction of the imaging screen. Has function.

  As described above, in the conventional example 3, the three crystal substrates are combined to be arranged, and the orientation of the optical axis of each crystal substrate is appropriately set and arranged to arrange the subject image in four horizontal and vertical directions. The image is separated, and the spatial frequency response in the horizontal and vertical directions corresponding to the separation width is reduced.

  The crystal phase plate used here converts the light in the entire visible wavelength range by λ / 4 around the wavelength near 550 nm, which is an intermediate wavelength in the visible wavelength range, to a circularly polarized state. When trying to do so, the thickness needs to be about 15 μm.

  Therefore, by increasing the thickness of the quartz phase plate sufficiently and sufficiently increasing the wavelength dependence of the phase of the light beam emitted from the phase plate, a general subject image having a predetermined wavelength range has substantially the same intensity. A technique is used in which the image is separated into four images.

Further, in the conventional example 3, the depolarization function is realized with a sufficiently thick quartz phase plate. However, an optical low-pass using a film-like organic material having optical anisotropy instead of the quartz phase plate. A filter has been proposed (see Patent Document 4).
JP-A-6-317776 JP-A-8-122708 JP-A-11-305168 JP 2002-303826 A

  The conventional low-pass filter and the optical low-pass filter disclosed in Patent Document 4 use a uniaxial single crystal birefringent plate and a phase plate, so that it is possible to stably produce materials, substrates, and processing at a relatively low price. There are advantages. However, since the difference in refractive index between ordinary rays and extraordinary rays is not so large, even when the single crystal substrate is used most efficiently, the thickness of the single crystal substrate required to obtain a desired beam separation width is small. There is a problem that the camera structure becomes difficult due to the increase in thickness.

  In general, in an image pickup apparatus using a solid-state image pickup device such as a CCD or CMOS, a space up to the image pickup surface on the image side of the photographing lens is used to protect the visibility correction filter and the image pickup device in addition to the optical low-pass filter. A cover glass or the like is arranged, and these flat plates have a problem that they change the light aberration of the photographing lens.

  For this reason, this problem cannot be ignored when constructing a single-lens reflex camera using an image sensor assuming that an interchangeable lens designed on the assumption of using a silver salt film is used as a photographic lens. It was.

  The separation width of the ordinary ray and the extraordinary ray is determined by the refractive index of the ordinary ray and the extraordinary ray of the single crystal material itself, the orientation with respect to the crystal axis of the single crystal substrate, and the thickness of the substrate. Assuming that the orientation with respect to the axis is set efficiently, it is generally determined by the refractive index of the ordinary ray and extraordinary ray of the single crystal material itself.

  In Conventional Example 2, since the single crystal substrate uses lithium niobate having a large difference in refractive index between ordinary light and extraordinary light compared to quartz, even when the separation width of ordinary light and extraordinary light is equal, Compared with the case of using the crystal of Conventional Example 1, the entire optical low-pass filter can be made thin.

  However, the lithium niobate single crystal material, on the contrary, needs to be processed thinly, and it is difficult to process the polishing substrate depending on the hardness of the material itself, and it is a material with a high refractive index. In addition, there is a problem that it is difficult to manufacture because it requires an advanced antireflection treatment.

  Patent Documents 1, 2, and 3 focus on the action that certain organic materials used for liquid crystals and the like change the orientation direction of the molecules by applying an electric field or magnetic field, and the orientation direction is uniform. In this state, the characteristic that this material exhibits anisotropy similar to that of the single crystal material used in the conventional examples 1 and 2 is applied to the optical low-pass filter.

  Among these, in Patent Document 1, the uniformity of the material is changed by applying an electric field so that the function as an optical low-pass filter is variable. However, an additional configuration such as a voltage application unit is required to reduce the thickness. Not suitable.

  In addition, as disclosed in Patent Documents 2 and 3, when a liquid crystalline organic material is solidified with an electric or magnetic field applied, and a film-like organic material having uniform birefringence is used as an optical low-pass filter The majority of organic materials have a coefficient of linear expansion of about 10 times that of inorganic materials such as optical glass and optical single crystal materials. For this reason, it tends to expand or contract with respect to the temperature change of the outside world. For this reason, in general, when an organic material and an inorganic material are bonded, it is necessary to devise an adhesive and a bonding method so that distortion and peeling of the bonding in the vicinity of the bonded portion do not occur when the temperature changes.

  When selecting an optical filter with a wavelength-selective member made of an organic material and having an optical function of transmitting only light of a predetermined wavelength or an optical member having a phase conversion function, the wavelength selection made of an organic material is used. In general, the characteristic member has a problem that the wavelength selection characteristic is easily changed by the change in the humidity of the outside due to the water absorption of the organic material.

  An object of the present invention is to provide a high-quality optical filter that is resistant to environmental changes and is thin, and an imaging apparatus having the same.

The optical filter of the present invention is
An optical filter disposed in the optical path of the imaging optical system,
It is characterized in that two or more optically anisotropic members made of an organic material made of a film and inorganic substrates made of an inorganic material are alternately joined.

  According to the present invention, it is possible to obtain a high-quality optical filter that is thin and highly environmentally changing while taking advantage of the thinness of the organic material.

  First, an outline of the present embodiment will be described.

  In this embodiment, an optical filter suitable for a camera (imaging device) that forms a color image with a single imaging device configured by arranging color filters in a mosaic pattern as the imaging device is realized.

  A camera that forms a color image with a single image sensor configured by arranging color filters in a mosaic pattern as the image sensor, and is applied to a single lens reflex camera that uses a silver salt film In a camera that has been made possible, the arrangement of the color filters is generally configured to have a predetermined regularity, and the luminance signals of the pixels where the corresponding color filters are not arranged are present in the surroundings and the color filters are arranged. The pixel is formed by appropriately interpolating using the luminance signal of the pixel. At this time, the signal formed by interpolation generates a false signal at a relatively high spatial frequency corresponding to the interpolation pitch, and appears in the image as a false color signal determined by the arrangement of the color filters. Become. In the image pickup device in which pixels and color filters are arranged in a two-dimensional manner, the false color signal is generated at a specific spatial frequency in a direction in which the arrangement is regular, generally in the horizontal, vertical, and diagonal directions. Become.

  Therefore, an image pickup system using an image pickup element may include an optical low-pass filter to reduce the response to the spatial frequency of these two-dimensional orientations in order to reduce the intensity of such false color signals. Desired. In order to reduce the response in a two-dimensional manner as described above, it is necessary to two-dimensionally manipulate the light beam from the photographing lens to the image sensor.

  In this embodiment, two or more optical members (optically anisotropic members) made of an organic material formed in a film shape are used as an optical member (single crystal substrate) (an inorganic substrate) made of an inorganic material formed in a substrate shape. ) Are arranged on both sides. Thus, the optical low-pass filter that reduces the response to a predetermined spatial frequency in a two-dimensional manner by separating light rays from the photographing lens to the image sensor in a two-dimensional manner is configured to be sufficiently thin. Further, a suitable optical filter is realized by arranging an optical member (wavelength selective member) having a wavelength selection action on the outer side (light incident side) (object side).

  In an image pickup device that generally has square pixels and uses a mosaic color filter, as a technique for reducing the intensity of a false color signal generated by the arrangement of the color filters, for example, from an imaging lens to an image pickup device There is known a method of providing an optical low-pass filter having a function of separating light rays reaching 1 to 2 in two directions, horizontal and vertical, and forming four subject images on an image sensor. With such a configuration, it is possible to appropriately reduce the response to a specific spatial frequency that generates a false color signal in each of horizontal, vertical, and diagonal directions.

  Alternatively, as another technique, an optical low-pass filter having a function of separating light rays into two directions of a first oblique 45 ° direction and a second oblique 45 ° direction with respect to a horizontal line, and also forming four subject images. There is also known a technique of comprising

  In an imaging device having a square pixel and using a mosaic color filter, the direction in which a false color signal is strongly generated is both horizontal, vertical, and diagonal 45 °. In order to efficiently reduce the color signal, it is desirable that the image is separated in two directions orthogonal to each other as in the above two methods.

  A solid-state imaging device such as a CCD or CMOS has a spectral sensitivity that is generally determined by the photoelectric conversion characteristics of silicon, although there is a difference depending on the detailed structure of the imaging device itself because it uses the photoelectric conversion action of silicon. Therefore, when configuring the photographing apparatus, it is necessary to provide a visibility correction filter for correcting the difference between the spectral sensitivity and the visibility of the image sensor. Therefore, it is common to use a colored glass filter or a dielectric deposited film as an optical filter mainly for the purpose of blocking near infrared rays for correcting visibility.

  Attempting to block light in the harmful wavelength range using only the colored glass filter results in a decrease in transmittance in the visible wavelength range, that is, a reduction in sensitivity. May occur. Therefore, it is desired to use a wavelength selective member in which a colored glass filter and a dielectric deposited film are used in combination.

Next, when paying attention to the linear expansion coefficient of the material of the film or substrate used in this example, in an organic material such as polycarbonate resin, about 7.0 × 10 ⁻⁵ / ° C., a general optical glass or colored glass filter, An inorganic material such as a single crystal substrate of quartz has a value different from about 7.0 × 10 ⁻⁶ / ° C. to 1.5 × 10 ⁻⁵ / ° C. by about 5 to 10 times.

  This example is based on the assumption that a film-like organic material is used to make the optical filter thin, and has high reliability against temperature changes in the outside world based on the difference in the linear expansion coefficient of such a material. A configuration that can maintain the performance is proposed.

  Therefore, in this embodiment, in order from the light incident side (object side), a wavelength selective member (colored glass filter substrate) that is an inorganic material, an organic material, a film-like first optical anisotropic member, and an inorganic material A phase substrate (optically anisotropic member) composed of a single crystal substrate and a film-like second optically anisotropic member are arranged and bonded in this order. At this time, the first and second optically anisotropic members are fixed by being stuck between the single crystal substrates having a predetermined thickness, or are bonded and fixed to the surface of the single crystal substrate.

  In this embodiment, the expansion and contraction of the organic material is substantially suppressed even when a change in temperature of the outside world occurs as such a configuration.

  Here, the configuration on the image plane side from the second optically anisotropic member is not particularly defined, but an air layer can be used, but it is better if an inorganic material substrate is bonded. can do. In addition, a more preferred embodiment can be realized if the structure is such that the surface of the image sensor is bonded and held when mounted on the camera.

  In addition, further features of this embodiment are described in the following embodiments.

  FIG. 1 is a cross-sectional view of a main part of a single-lens reflex camera (imaging device) having an optical filter according to a first embodiment of the present invention.

  In the figure, reference numeral 1 denotes a photographic optical system as an interchangeable photographic lens, and 2 denotes a rotating mirror (QR mirror), which is rotated and retracted from the optical path of the photographic optical system 1 during photographing. A focal plane shutter 3 mechanically limits the exposure time. An optical filter 4 according to the present invention is disposed in the optical path on the image plane side of the imaging optical system 1 and is configured by bonding a plurality of optically anisotropic members described later and an inorganic substrate. Reference numeral 5 denotes an image pickup device (configured by a solid-state image pickup device such as a CCD or CMOS) as an image pickup means, which is disposed on a planned focal plane of the image pickup optical system 1. Reference numeral 6 denotes a focusing screen on which a subject image is formed. Reference numeral 7 denotes a finder optical system, which includes a penta roof prism 8 and an eyepiece 9 as image inverting means for inverting the subject image formed on the focusing screen 6.

  In this embodiment, the subject image formed by the imaging optical system 1 is formed on the focusing screen 6 and observed as a finder image by the finder optical system 6 when the rotating mirror 2 is disposed in the optical path. When a photographing operation is started by a release switch (not shown), the rotating mirror 2 is retracted out of the optical path of the photographing optical system 1, and the focal plane shutter 3 performs an opening operation, so that the image sensor is connected via the optical filter 4. 5 on the imaging surface. An imaging signal is output from the imaging device 5 and stored in a memory (not shown).

  2A and 2B are explanatory views of the optical filter 4 shown in FIG. 1, respectively. FIG. 2A is a cross-sectional view of the main part of the optical filter 4, and FIG. It is a disassembled perspective view.

  2A and 2B, reference numeral 41 denotes an inorganic substrate made of an inorganic material configured in a substrate shape. The inorganic substrate 41 is made of a colored glass filter substrate (filter substrate) as a wavelength selective member, and an optical thin film (dielectric vapor deposition film) that blocks harmful light of near ultraviolet rays and near infrared rays is deposited on the surface of the substrate. .

  Reference numeral 42 denotes a first optically anisotropic member, which has optical anisotropy and is made of an organic material configured in a film shape.

  Reference numeral 43 denotes a quartz phase plate (filter substrate), which is made of an inorganic material configured in a substrate shape, and has a single crystal quartz (single crystal substrate) in a predetermined orientation so as to have a phase conversion action (or birefringence action). It is cut out and formed.

  Reference numeral 44 denotes a second optically anisotropic member, which has an optical anisotropy and is made of an organic material configured in a film shape.

  In this embodiment, the first optically anisotropic member 42, the quartz phase plate 43, and the second optically anisotropic member 44 are arranged in this order, thereby reducing the response to a predetermined spatial frequency. Configure the filter. The colored glass filter substrate 41 blocks light in an unnecessary wavelength range.

  The first optically anisotropic member 42 is a film-like organic substance formed by aligning molecules of a liquid crystal compound with a characteristic angle with respect to the surface, and incident light is vibrated to a predetermined vibration level by birefringence. It has a function of separating the ordinary ray and the extraordinary ray in a linearly polarized state having a surface, and moving only the extraordinary ray in the horizontal direction of the photographing screen by a predetermined amount.

  The quartz phase plate 43 is composed of a phase plate arranged with its optical axis rotated by 45 ° from the horizontal line in the film plane, and is separated from the first optical anisotropic member 42 by a phase difference conversion action (or birefringence action). It has a function to convert the emitted linearly polarized light into various polarization states.

  The second optically anisotropic member 44 is made of the same material as the first optically anisotropic member 42. The second optically anisotropic member 44 is an ordinary ray in a linearly polarized state having a predetermined vibration surface due to birefringence. And has a function of moving only the extraordinary ray by a predetermined amount in the vertical direction of the photographing screen.

  In this embodiment, the first optical anisotropic member 42, the crystal phase plate 43, and the second optical anisotropic member 44 are combined in this way, so that the incident light is transmitted in the horizontal direction and the vertical direction. Thus, an optical low-pass filter that reduces the response at a predetermined spatial frequency is realized by having a function of converting and emitting four emitted lights having substantially equal intensities at positions separated by a predetermined amount.

The linear expansion coefficient of the first and second optically anisotropic members 42 and 44 in this embodiment is about 7.0 × 10 ⁻⁵ / ° C., and the linear expansion coefficient of the crystal phase plate 43 is the crystal axis direction. Although it differs in the orthogonal direction, it is about 7.0 × 10 ⁻⁶ / ° C. to 1.2 × 10 ⁻⁵ / ° C.

In the optical filter 4 of this embodiment, a color glass filter substrate 41 made of an inorganic material in which a material having an action of absorbing light in a predetermined wavelength region is mixed with an optically anisotropic member having an optical low-pass filter action is joined. It is configured. In addition, the linear expansion coefficient of the colored glass filter substrate of this example is about 1.5 × 10 ⁻⁵ / ° C.

  As described above, the optical filter 4 of the present embodiment includes, in order from the light incident side (object side), the colored glass filter substrate 41 of the substrate (inorganic substrate) made of an inorganic material, and the first optical anisotropy of the organic film material. The member 42, the phase substrate 43 made of an inorganic material, and the second optically anisotropic member 44 made of an organic material are combined. That is, in this embodiment, an optical member made of an inorganic material and an optical member made of an organic material are alternately joined.

  In such a configuration, the organic material having a relatively large linear expansion coefficient has a film shape, a small volume, and is bonded to an adjacent inorganic material having a relatively small linear expansion coefficient. On the other hand, it is possible to reduce problems such as peeling of the bond.

  Moreover, since the optical filter 4 of the present embodiment is finally configured as described above, in the manufacturing process, the first and second optical anisotropic members 42, which are organic film materials, 44 may be bonded to the inorganic substrate, and can be manufactured without increasing the difficulty in the bonding process.

  The colored glass filter substrate 41 uses an optical material that absorbs near ultraviolet rays and near infrared rays as a substrate, and an optical thin film that reflects near ultraviolet rays and near infrared rays is deposited on the light transmission surface. Here, the near-ultraviolet rays are blocked in order to prevent chemical changes in the first and second optical anisotropic members 42 and 44 made of an organic material, and the near-infrared rays are blocked in the imaging device 5. This is because the spectral sensitivity is approximated to the visual sensitivity.

  Polymeric materials with liquid crystallinity are used as film-like organic materials with optical anisotropy, but these materials have the problem of causing yellowing deterioration due to chemical changes in response to near-ultraviolet irradiation. There is. Therefore, it is necessary to adopt a configuration in which near-ultraviolet rays are blocked before reaching the first and second optical anisotropic members 42 and 44.

  On the other hand, a general imaging device using the photoelectric conversion action of silicon has a spectral sensitivity that is generally determined by the photoelectric conversion characteristics of silicon, although there are differences depending on the detailed structure of the imaging device itself. The spectral sensitivity determined here tends to be much higher in the infrared wavelength range than the visual sensitivity of the human eye. It is necessary to properly block the light in the area.

  The colored glass filter substrate 41 of the present embodiment is a filter having a property of transmitting light in a wavelength region having spectral transmittance characteristics that are approximately close to visual sensitivity and absorbing other light. When the first and second optically anisotropic members 42 and 44 are insufficient to block harmful near-ultraviolet rays, and are insufficient to block near-infrared rays that are harmful to color reproduction of a photographing result It is preferable that an optical thin film having a predetermined spectral transmittance characteristic is deposited on the light transmission surface of the colored glass filter substrate 41 to reflect near ultraviolet and near infrared harmful light.

  FIG. 3 shows the spectral characteristics of the optical filter 4 of this embodiment. In the figure, 411 is the spectral transmittance characteristic of the colored glass filter substrate 41 itself, 412 is the spectral transmittance characteristic of the optical thin film deposited on the object side surface of the colored glass filter substrate 41, and 413 is the colored glass filter substrate 41 and its object. The spectral transmittance characteristic of the whole optical filter 4 which synthesize | combined the optical thin film vapor-deposited on the side surface is represented. At this time, the decrease in spectral transmittance in other optical members and other surfaces constituting the optical filter 4 is ignored as being small.

  In the present embodiment, by using the optical filter 4 having the spectral transmittance characteristic as shown in FIG. 3, the transmittance in the near ultraviolet wavelength region below the wavelength of about 350 nm is lowered, and the wavelength from around 400 nm to around 650 nm is reduced. The transmittance in the visible wavelength region is kept high, and the transmittance in the near-infrared wavelength region from near the wavelength of 700 nm to 1100 nm is lowered. In particular, in this embodiment, the spectral transmittance characteristics of the optical thin film deposited on the object side surface of the colored glass filter substrate 41 are as shown by the dotted line 412 in FIG. Thus, the first and second optically anisotropic members 42 and 44 made of an organic material are prevented from being deteriorated due to a chemical change.

  At a wavelength of 350 nm, the transmittance of the colored glass filter substrate 41 itself of this embodiment is about 58%, and the transmittance of the optical thin film deposited on the object side surface of the colored glass filter substrate 41 is about 0%. In this embodiment, the optical thin film substantially blocks near ultraviolet rays.

  The subject light transmitted through the optical filter 4 of this embodiment reaches the image sensor 5 and outputs an image signal. The spectral sensitivity of the subject image formed at this time is shown in FIG.

  In the figure, reference numeral 413 denotes a relative sensitivity corresponding to the spectral transmittance of light transmitted through the entire optical filter 4 shown in FIG. 3, 511 denotes a spectral sensitivity of the photoelectric conversion unit of the image sensor 5, and 512 denotes a spectral transmission of the entire optical filter 4. The spectral sensitivity of the imaging apparatus according to the present exemplary embodiment, which is obtained by multiplying the ratio 413 and the spectral sensitivity 511 of the imaging device 5, is shown.

  As shown in FIG. 4, the optical filter 4 of this embodiment is configured to reduce the transmittance in the near-infrared wavelength region from near the wavelength 700 (nm) to near 1100 (nm), mainly depending on the characteristics of silicon. A correction function for the difference in spectral sensitivity between the determined image sensor 5 and the sensitivity of the human eye is also provided.

  FIG. 5 shows a comparison between the spectral sensitivity of the color signal of the imaging apparatus to which the optical filter 4 of this embodiment is applied and the spectrum tristimulus value of the human eye.

  In the figure, CB, CG, and CR are spectral sensitivities of three color signals of the imaging apparatus to which this embodiment is applied, and EB, EG, and ER are human eyes. Represents a spectrum tristimulus value. As shown in the figure, the optical filter 4 of the present embodiment enables good color reproduction so that the spectral sensitivity of the color signal of the imaging device has characteristics similar to those of the human eye.

  As described above, in the present embodiment, in consideration of the characteristics of the organic material, it is particularly suitable for a single-lens reflex camera using a large-area image sensor configured by arranging color filters in a mosaic pattern. A thin and high quality optical filter is realized.

  Next, a second embodiment of the present invention will be described.

  In this embodiment, the difference from the first embodiment is that a substrate (inorganic substrate) made of an inorganic material is bonded to the surface of the second optical anisotropic member 44 on the imaging element 5 side (light emission side). It is configured. Other configurations and optical actions are substantially the same as those in the first embodiment, and the same effects are obtained.

  That is, in the first embodiment, the second optically anisotropic member 44 is arranged facing the air layer on the most image pickup element 5 side of the optical filter 4, but the environmental resistance is further improved. In other words, it is effective to join another inorganic substrate. Of course, instead of newly arranging and joining another inorganic substrate here, it is possible to use the protective glass of the image sensor 5 that is generally used for the purpose of protecting the imaging surface of the image sensor 5 as this inorganic substrate. Is desirable.

  In Examples 1 and 2, the single crystal substrate (quartz phase plate) 43 of quartz is used as the inorganic material having the phase conversion action. However, the influence of the wavelength dependence of the phase conversion action is substantially reduced. In order to reduce the thickness of the substrate and reduce the thickness of the substrate, a single crystal substrate of lithium niobate may be used.

  In the first and second embodiments, a configuration in which an optical member made of an organic material formed in a film shape and an optical member made of an inorganic material are joined substantially alternately is disclosed. It is also possible to use an organic film constructed as described above. For example, two or more optically anisotropic members made of an organic material formed in a film shape, and two made of an inorganic material provided on the light incident side and the light emission side of the two or more optically anisotropic members. A structure sandwiched between two inorganic substrates is also applicable.

  In the case of such a configuration, in a strict sense, it is not a configuration in which an optical member made of a film-like organic material and an optical member made of an inorganic material are alternately combined and joined, but such an embodiment is also a technique of the present invention. This is an example of the idea.

  In Examples 1 and 2 described above, the organic material and the inorganic material are used to represent usable optical materials, but the purpose is to form an optical filter by joining materials having greatly different linear expansion coefficients. Therefore, it may be appropriate to define another definition.

That is, the organic material of Examples 1 and 2 has a linear expansion coefficient in the range of 3.0 × 10 ⁻⁴ / ° C. to 3.0 × 10 ⁻⁵ / ° C., and the inorganic material has a linear expansion coefficient. The material in the range of 3.0 × 10 ⁻⁵ / ° C. to 3.0 × 10 ⁻⁶ / ° C. is substantially meant.

  As described above, in the first and second embodiments, in an imaging apparatus using a solid-state imaging device such as a CCD or a CMOS, a low-pass filter that reduces a false signal generated by a subject having a high frequency component and a wavelength selection that blocks harmful light. An optical filter such as a filter can be made thin and high in quality so that it can be placed in a narrow space in the optical path of the photographing optical system of the camera. In particular, an optical filter that is suitable not only in terms of performance but also in terms of manufacturing cost can be realized in an interchangeable lens type imaging apparatus using a large-sized imaging element that requires an optical filter with a large area.

Sectional drawing of the principal part of the single-lens reflex camera using the optical filter of Example 1 of this invention Explanatory drawing of the optical filter shown in FIG. FIG. 3 is a spectral characteristic diagram of the optical filter according to the first embodiment of the present invention. Explanatory drawing of spectral sensitivity, such as an image sensor of Example 1 of the present invention Explanatory drawing of the color signal of the imaging device of Example 1 of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shooting lens 2 QR mirror 3 Focal plane shutter 4 Optical filter 5 Image pick-up element 6 Focusing plate 7 Finder optical system 8 Penta roof prism 9 Eyepiece 41, 42, 43, 44 Optical member

Claims (10)

An optical filter disposed in the optical path of the imaging optical system,
An optical filter characterized in that two or more optically anisotropic members made of an organic material composed of a film and inorganic substrates made of an inorganic material are alternately joined.   2. The birefringence function according to claim 1, wherein at least one of the two or more optically anisotropic members has a birefringence function in which the orientation direction of molecules is uniform and incident light is separated into ordinary rays and extraordinary rays. Optical filter.   The two or more inorganic substrates include a wavelength selective substrate that restricts transmission of a light beam in a predetermined wavelength region, and a phase substrate formed by processing a single crystal material in a predetermined orientation. The optical filter according to 1 or 2.   The optical filter according to claim 1, wherein an inorganic substrate is disposed on the outermost side.   5. The optical filter according to claim 1, wherein a linear expansion coefficient of the optically anisotropic member is larger than a linear expansion coefficient of the inorganic substrate.   The wavelength selective substrate includes a substrate that absorbs near ultraviolet rays and near infrared rays, and an optical thin film that reflects near ultraviolet rays and near infrared rays provided on a light transmission surface of the substrate. 4. The optical filter according to 3.   The optical filter according to any one of claims 1 to 6, wherein at least one of the two or more optically anisotropic members is formed by laminating a film-like organic material. . An optical filter disposed in the optical path of the imaging optical system,
The optical filter is a wavelength-selective substrate made of an inorganic material that controls the transmission of a light flux in a predetermined wavelength range in order from the light incident side, and a film that divides incident light into ordinary rays and extraordinary rays by birefringence. A first optically anisotropic member made of a shaped organic material, a phase substrate made of a single crystal material with an inorganic material that converts the phase of incident light by birefringence or phase conversion, and incident light by birefringence An optical filter comprising a second optically anisotropic member made of a film-like organic material that is emitted after being separated into an ordinary ray and an extraordinary ray. An optical filter disposed in the optical path of the imaging optical system,
Two or more optically anisotropic members made of a film-like organic material, and two inorganic materials made of an inorganic material provided on the light incident side and light emission side of the two or more optically anisotropic members An optical filter comprising a substrate.   An imaging apparatus comprising the optical filter according to any one of claims 1 to 9.