JP5545072B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus that forms an image of a subject on an imaging device by an optical system including a lens and the like.

  2. Description of the Related Art Conventionally, there has been proposed an imaging apparatus that enables image photographing with a deep depth of field by regularly dispersing a light beam by a phase plate that is a light wavefront modulation element and restoring it by digital processing. (For example, refer to Patent Documents 1-2 and Non-Patent Document 1).

JP 2003-235794 A JP 2000-98303 A

Edward. R. Dowski, Jr., and W. Thomas. Cathey, “Extended depth of field through wave-front coding”, Applied Optics, Vol. 34, No 11, pp. 1859-1866, 10 April, 1995.

In the above technique, for example, a cubic phase element that gives a shift of exp (iα (x ³ + y ³ )) to the phase of light is used as the phase modulation element (light wavefront modulation element). Here, i is an imaginary unit, α is a constant, and x and y are two-dimensional coordinates of the phase modulation element. If such a phase modulation element is formed integrally, the three-dimensional shape becomes complicated, so that the manufacturability is not good.

  Therefore, an object of the present invention is to improve manufacturability of an imaging device including a phase modulation element.

  The imaging apparatus disclosed in the present application generates a phase difference in a direction perpendicular to the optical axis of the lens system with respect to the lens system that collects light from the subject on the image plane and the light that passes through the lens system. A pair of phase modulation masks including: a first phase modulation mask that provides phase modulation by causing the light to generate a phase difference in a direction different from the first direction; A diaphragm that is provided between the pair of phase modulation masks and adjusts the amount of light passing through the lens system, and an imaging unit that converts the light condensed on the image plane into an electrical signal to obtain an image signal And an image processing unit that performs image processing for restoring the phase modulation on the image signal acquired by the imaging unit.

  According to the disclosure of the present specification, the manufacturability of an imaging device including a phase modulation element can be improved.

FIG. 1 is a functional block diagram illustrating a schematic configuration of the imaging apparatus according to the first embodiment. FIG. 2 is a perspective view showing an arrangement example of the phase modulation mask and the diaphragm. FIG. 3A is a yz sectional view showing an example of the configuration of the optical system. FIG. 3B is a diagram illustrating an example of a phase plane in the phase modulation mask. FIG. 3C is an xz sectional view showing an example of the configuration of the optical system. FIG. 3D is a diagram illustrating an example of a phase plane in the phase modulation mask. FIG. 4 is a graph showing an example of MTF calculation in an optical system without a phase modulation mask. FIG. 5 is a graph showing a calculation example of the MTF of the optical system provided with the phase modulation mask shown in FIGS. 3A to 3D. FIG. 6 is a diagram illustrating an example of specifying an inverse filter. FIG. 7 is a graph showing the MTF intensity distribution after the inverse filter processing shown in FIG. FIG. 8 is a diagram illustrating an example of a cross-sectional configuration of an optical system having an aperture stop outside a pair of phase masks and an example of an optical path. FIG. 9 is a diagram illustrating an example of a cross-sectional configuration of an optical system having an aperture between a pair of phase masks and an example of an optical path. It is a graph which shows intensity distribution of MTF for every angle of view of three patterns in the optical system shown in FIG. 10 is a graph showing MTF intensity distribution for each angle of view of three patterns in the optical system shown in FIG. 9. FIG. 12 is a cross-sectional view of the phase modulation mask in the second embodiment and an enlarged view of a part of the phase plane. FIG. 13 is a cross-sectional view for explaining the configuration of the phase modulation mask in the third embodiment. FIG. 14 is an xy sectional view showing an example of the configuration of the optical system according to the fourth embodiment. FIG. 15 is a cross-sectional view showing a modification of the phase modulation mask and the stop. FIG. 16 is a functional block diagram illustrating a configuration example of the entire system including the imaging device according to the fifth embodiment.

(First embodiment)
FIG. 1 is a functional block diagram illustrating a schematic configuration of the imaging apparatus according to the first embodiment. An imaging apparatus 1 shown in FIG. 1 includes a lens 2, a pair of phase modulation masks 3 a and 3 b, a diaphragm 4, an imaging unit 5, and an image processing unit 6. The lens 2 is an example of a lens system that collects light from a subject on an image plane. The pair of phase modulation masks 3a and 3b includes a first phase modulation mask 3a that generates a phase difference in one direction perpendicular to the optical axis of the lens 2 with respect to the light passing through the lens system, and the light. And a second phase modulation mask for generating a phase difference in a direction different from the first direction. The stop is provided between the pair of phase modulation masks 3a and 3b, and adjusts the amount of light passing through the lens system. The imaging unit 5 obtains image data by converting the light collected on the image plane by the lens system into an electrical signal. The imaging unit 5 includes, for example, a two-dimensional imaging device such as a CCD / CMOS, and the lens 2 and the diaphragm 4 form an image of a subject on the two-dimensional imaging device. The two-dimensional image sensor converts the image of the subject into an electronic signal (image signal) and inputs it to the image processing unit 6. The image processing unit 6 performs image processing for restoring the phase modulation on the image acquired by the imaging unit 5.

  As described above, the imaging apparatus 1 includes the optical system 7 that obtains image data by forming light from the subject on the light receiving surface of the imaging unit 5 and the image processing unit 6 that processes the image data. The optical system 7 includes a lens 2, a pair of phase modulation masks 3a and 3b, a diaphragm 4 inserted between the pair of phase modulation masks 3a and 3b, and an imaging unit that captures a subject image that has passed through the optical system 7. 5 is included. The image processing unit 6 performs image processing using, for example, an inverse filter of the optical characteristics of the optical system 7.

  The phase modulation masks 3a and 3b are placed between the subject and the imaging unit, and the optical transfer function (0TF) of the optical system can be constantly deformed regardless of the position of the subject in the optical axis direction. The image processing unit 6 can execute processing for returning the image captured by the imaging unit to 0TF that is not deformed by image processing. Thereby, the image processing unit 6 can output an image having a deep depth of field.

  Specifically, the image processing unit 6 can obtain image data by performing, for example, a digital signal or other necessary conversion by an A / D converter on the image signal. The image processing unit 6 performs image processing for restoring the phase modulation by the phase modulation masks 3a and 3b on the image data. The image processing unit 6 can execute, for example, inverse filter calculation that cancels the optical transfer function modulation effect by the phase modulation mask on the image data. As described above, the image processing unit 6 performs a process of convolving the image obtained by the imaging unit 5 using an inverse function (for example, an inverse filter) of the transfer function of the optical system 7. The data representing the inverse function is preferably recorded in advance by the image processing unit 6.

  The image processing unit 6 can be configured by an IC chip dedicated to image processing, or a processor such as a general-purpose CPU and a computer such as a memory. Alternatively, the image processing unit 6 may be formed of an analog circuit.

  By providing a pair of phase modulation masks 3a and 3b (phase modulation elements) that cause a phase difference in different directions as in the above configuration, the shape of the phase modulation mask is simplified, and the productivity is improved. Moreover, since the diaphragm 4 is provided between the phase modulation masks 3a and 3b, the depth of field can be increased while suppressing the influence of the angle of view.

  FIG. 2 is a perspective view showing an arrangement example of the phase modulation masks 3a and 3b and the diaphragm. In FIG. 2, the optical axis of the lens 2 is the z axis, and two axes perpendicular to the z axis and perpendicular to each other are the x axis and the y axis. One phase modulation mask 3a of the pair of phase modulation masks 3a and 3b shown in FIG. 2 has a shape whose thickness continuously changes in the x-axis direction. Therefore, in the phase modulation mask 3a, the degree of phase modulation given to the passing light changes in one direction (for example, the x direction) perpendicular to the optical axis of the lens system. Of the pair of phase modulation masks 3a and 3b, the other phase modulation mask 3b has a shape whose thickness continuously changes in the y-axis direction. Therefore, in the phase modulation mask 3b, phase modulation applied to light passing only in a direction (for example, the y direction) that is perpendicular to the optical axis of the lens system and also perpendicular to the one direction (for example, the x direction). The degree changes. Here, the phase modulation mask 3a and the phase modulation mask 3b have the same shape, and are arranged in a positional relationship in which the directions are different by 90 °.

  Each of the pair of phase modulation masks 3a, 3b is formed with a curved surface (phase surface) for changing the degree of phase modulation of light passing therethrough, and the pair of phase modulation masks 3a, 3b is opposed to each other. Phase modulation masks 3a and 3b are arranged.

  The diaphragm 4 is provided between these opposed phase surfaces. The diaphragm 4 is provided in parallel to a plane (for example, xy plane) perpendicular to the optical axis. In the example shown in FIG. 2, the diaphragm 4 has a circular opening. Note that the opening is not limited to a circle, and may be a square, for example.

  In the example shown in FIG. 2, as described above, the first phase surface for causing the phase difference in only one direction is provided on one surface of the phase modulation mask 3a, and the phase surface is set at a position orthogonal to the optical axis. A phase modulation mask 3b having a second phase plane that is arranged and generates a phase difference in the one direction and a direction orthogonal to the optical axis is further arranged. Thereby, the shape of the phase modulation mask can be further simplified. For example, compared to a case where the same phase modulation is realized with a single phase modulation mask, the height difference in one direction can be halved without an acute angle portion. As a result, manufacturability is further improved. Further, by arranging the pair of phase modulation masks 3a and 3b so that the phase planes face each other and providing the diaphragm 4 at a position between the phase planes, the position of the diaphragm 4 can be brought close to the phase plane. When the aperture surface and the phase surface are close, the influence of the angle of view becomes smaller. That is, by placing the diaphragm surface between the pair of phase surfaces, the influence of the angle of view can be reduced, and performance deterioration due to the angle of view can be suppressed.

  3A to 3D are diagrams showing further detailed examples of the configuration of the optical system 7. FIG. 3A is an xz sectional view showing an example of the configuration of the optical system 7. FIG. 3B is a diagram illustrating an example of a phase plane in the phase modulation mask 3a. FIG. 3C is a yz sectional view showing an example of the configuration of the optical system 7. FIG. 3D is a diagram illustrating an example of a phase plane in the phase modulation mask 3b.

In the example shown in FIG. 3A and FIG. 3B, the phase modulation mask 3a has a plane parallel to the xy plane, and the surface facing this surface (the back surface of this surface) is z = kx ³ (where k is a constant). ). Therefore, the light that has passed through the phase modulation mask 3a undergoes phase modulation of exp (iα (x ³ ) / 2). That is, when the center (x, y) = (0, 0) of the phase modulation mask 3a is used as a reference, the phase difference of light passing through the point (x, y) is expressed by exp (iα (x ³ ) / 2). Is done. The light that has passed through the phase modulation mask 3a is obtained by multiplying the wave function of the light before passing by exp (iα (x ³ ) / 2). Here, α / 2 can be expressed by, for example, α / 2 = 2π (n−1) k / λ (n is the refractive index of the phase modulation mask).

In the example shown in FIGS. 3C and 3D, the phase modulation mask 3b has a plane parallel to the xy plane, and the surface facing this surface is a curved surface represented by z = ky ³ . Therefore, the light that has passed through the phase modulation mask 3b undergoes phase modulation with a phase difference exp (iα (y ³ ) / 2). When the center (x, y) = (0, 0) of the phase modulation mask 3b is used as a reference, the phase difference of the light passing through the point (x, y) is expressed by exp (iα (y ³ ) / 2). . The light that has passed through the phase modulation mask 3b is obtained by multiplying the wave function of the light before passing by exp (iα (y ³ ) / 2). Here, α / 2 can be expressed by, for example, α / 2 = 2π (n−1) k / λ.

Therefore, the light passing through the phase modulation mask 3a and the phase modulation mask 3b shown in FIGS. 3A to 3D undergoes phase modulation of exp (iα (x ³ ) / 2) · exp (iα (y ³ ) / 2). It will be. The shape of the phase plane of the phase modulation mask shown in FIGS. 3A to 3D is an example, and is not limited to this. For example, the phase plane of the phase modulation mask 3a is other curved surface represented by z = kx ^3, it may be a curved surface represented by an odd function of x. Assuming that the phase difference provided by the phase modulation mask 3b is exp (iφ (x)), φ (x) is not limited to the cube of x and may be another odd function. Similarly, φ (y) of the phase difference exp (iφ (y)) may be another odd function of y on the phase plane of the phase modulation mask 3b.

Here, for example, when forming with one phase modulation mask, the phase plane of the phase modulation mask can be set to z = k ′ (x ³ + y ³ ). The phase modulation mask applies exp (iα (x ³ + y ³ ) / 2) phase modulation to the light passing therethrough. In this case, the shape of the phase plane becomes complicated, and the manufacturability deteriorates. In addition, since a sharp point with a single point is formed on the phase plane, it is easily broken. In contrast, in the example shown in FIGS. 3A to 3D, the direction of the phase difference is separated into a pair of phase modulation masks 3a and 3b, so that the shape is not complicated and there is no acute angle portion. The height difference in direction can be set in half. As a result, manufacturability is improved. Furthermore, by separating the phase difference, positioning is only performed in one direction, and assemblability is improved.

[Expansion effect of depth of field]
FIG. 4 is a graph showing an example of MTF calculation in an optical system in which the phase modulation masks 3a and 3b are not provided. FIG. 5 is a graph showing a calculation example of the MTF of the optical system provided with the phase modulation masks 3a and 3b shown in FIGS. 3A to 3D. 4 and 5, the horizontal axis indicates the spatial frequency, and the vertical axis indicates the MTF. 4 and 5, R1 and W1 are MTF intensity distributions when the subject is at the focal position, R2 and W2 are MTF intensity distributions when the subject is deviated from the focal position, and R3 and W2 are The intensity distribution of the MTF when the subject is further deviated from the focal position is shown.

  As in the example shown in FIG. 4, in an optical system that does not have a phase modulation mask, the MTF deteriorates when the subject is out of focus and the focus is out of focus. On the other hand, as in the example shown in FIG. 5, in the optical system 7 including the phase modulation masks 3a and 3b, the change in MTF is small even when the focus is out of focus.

  By performing processing using an inverse filter having the characteristics shown in FIG. 6 on the image captured by the optical system 7 including the phase modulation masks 3a and 3b, the MTF intensity distributions W1a and W3a shown in FIG. can get. That is, the MTF intensity distributions W1, W2, and W3 in FIG. 5 correspond to the intensity distributions W1a, W2a, and W3a after the inverse filter processing shown in FIG. Each of the MTF intensity distributions shown in FIG. 7 has a shape close to the MTF intensity distribution (for example, R1 in FIG. 4) when the subject is at the focal length. As described above, the image obtained by the optical system having the phase modulation masks 3a and 3b can be corrected to an image with little defocus by the inverse filter even when the focus is out of focus.

[Performance evaluation by diaphragm surface]
FIG. 8 is a diagram illustrating an example of a cross-sectional configuration of an optical system having an aperture stop outside a pair of phase masks and an example of an optical path. FIG. 9 is a diagram illustrating an example of a cross-sectional configuration of an optical system having an aperture between a pair of phase masks and an example of an optical path. In FIG. 8 and FIG. 9, the optical paths of three patterns having different angles of view (large, medium, and small patterns) are indicated by thick lines, medium thick lines, and thin lines in descending order of the angle of view.

  In the example shown in FIG. 8, the diaphragm 4 is provided outside the pair of phase masks 3 a and 3 b and on the imaging unit 6 side. In the example shown in FIG. 9, the diaphragm 4 is provided between the pair of phase masks 3a and 3b. In the example shown in FIG. 9, the diaphragm surface is disposed between the two phase planes, and therefore the optical path is different from the example shown in FIG.

  FIG. 10 is a graph showing the MTF intensity distribution for each angle of view of the three patterns in the optical system shown in FIG. FIG. 11 is a graph showing the MTF intensity distribution for each angle of view of the three patterns in the optical system shown in FIG. 10 and 11, the MTF when the angle of view is large is indicated by a thick line, the MTF when the angle of view is medium is indicated by a thick line, and the MTF when the angle of view is small is indicated by a thin line. The solid line represents the MTF in the Y direction, and the alternate long and short dash line represents the MTF in the X direction. The dotted line indicates the diffraction limit.

  Comparing FIG. 10 and FIG. 11, it can be seen that in the optical system in which the diaphragm surface is disposed between the phase surfaces, variation due to the MTF angle of view is small as compared with the configuration in which the diaphragm surface is not between the phase surfaces. For this reason, for example, as shown in FIG. 8, when the diaphragm surface is outside the pair of phase modulation masks, it can be said that the MTF variation is large due to the influence of the angle of view, and the performance is deteriorated. On the other hand, MTF variation can be suppressed by placing the diaphragm surface between the pair of phase modulation masks. As a result, the influence of the angle of view can be reduced and performance degradation can be suppressed.

(Second Embodiment)
In the first embodiment, the phase planes of the phase modulation masks 3a and 3b are curved surfaces. However, the phase planes may be formed in a step shape. For example, the phase plane can be formed such that the thickness of the phase modulation mask in the optical axis direction (for example, z direction) changes stepwise in one direction (for example, x direction or y direction). That is, the phase surface of each phase modulation mask 3a, 3b is a staircase having a step parallel to a surface perpendicular to the optical axis direction at each step, and has a staircase shape stepping up in the above-mentioned one direction. be able to. Thereby, a phase difference can be generated in the direction 1 with respect to the passing light. That is, in the phase modulation mask, the phase difference in one direction can be stepped. Thus, the configuration in which the phase surface is stepped is easier to make than the configuration in which the phase surface is a curved surface.

  As in the first embodiment, the step-up directions on the phase planes of the phase modulation masks 3a and 3b are preferably orthogonal to each other. Moreover, it is preferable that the width | variety in said 1 direction of each step does not exceed the wavelength of light. By setting the width of one step to be equal to or less than the wavelength, it becomes difficult to see the effect of making it stepped.

  FIG. 12 is a sectional view of the phase modulation mask 3a in the present embodiment and an enlarged view of a part of the phase plane. The enlarged view of FIG. 12 is an enlarged view of a portion of a region T indicated by a dotted line in the phase modulation mask 3a. In the example shown in FIG. 12, the phase plane of the phase modulation mask 3a is formed by steps that step up along the x direction. The width L in the x direction of each step of the staircase is formed so as not to exceed the wavelength of light. Similarly, a step that steps up in the y direction is also formed on the phase plane of the phase modulation mask 3b. By making the phase surface stepped in this way, manufacturing becomes easier than making the phase surface curved.

(Third embodiment)
In the first and second embodiments, the phase modulation mask is formed such that the thickness in the optical axis direction changes in one direction within a vertical plane. When the thickness changes, the optical path length changes, so that a phase difference occurs in the direction 1 described above. In the present embodiment, the phase modulation mask is divided into, for example, a plurality of regions having substantially the same width as the wavelength of light in the one direction where the phase difference occurs, and the thickness is changed independently in each region. Let Thereby, the thickness of the phase modulation mask can be reduced.

  FIG. 13A is a cross-sectional view for explaining the configuration of the phase modulation mask 3a1 in the third embodiment. In the example shown in the upper part of FIG. 13A, the phase modulation mask 3a1 is divided into a plurality of regions having the same width H as the wavelength of light in the x direction, and the thickness is changed independently for each region. That is, the thickness of the phase modulation mask 3a1 is reset for each region, and changes in each region based on a predetermined level. Therefore, the xz cross section of the phase modulation mask 3a1 has a saw-like shape whose thickness changes periodically at least in part.

  The phase modulation mask 3a1 shown in the upper part of FIG. 13A has the same phase modulation function as the phase modulation mask 3a shown in the lower part. The phase modulation mask 3a shown in the lower part of FIG. 13A has the same configuration as the phase modulation mask 3a in the first or second embodiment. The phase modulation mask 3a1 shown in the upper stage is divided into widths H in the x direction in a region where the change in thickness of the phase modulation mask 3a shown in the lower stage is relatively steep, that is, a constant region from both ends. It is the structure which changed thickness. In each divided region, the thickness changes based on a predetermined level.

  As described above, the entire thickness of the phase modulation mask 3a1 can be kept small by dividing the wavelength width like a Fresnel lens and changing the thickness for each divided region to form a sawtooth shape.

  In each region divided by the wavelength width, the phase plane may be a curved surface as in the first embodiment, or the thickness may be changed stepwise as in the second embodiment. Also good. For example, the region T in the phase modulation mask 3a1 shown in the upper part of FIG. 13A can be configured in a stepped manner as in the enlarged view of the region T in FIG.

  FIG. 13A shows an example in which the phase modulation mask 3a according to the first or second embodiment is divided into a plurality of regions in the x direction. Similarly, the phase modulation mask 3b is divided into a plurality of regions in the y direction. In each region, the thickness can be changed in the y direction.

  FIG. 13B is a cross-sectional view for explaining the configuration of a phase modulation mask 3a2 according to a modification. The example shown in the upper part of FIG. 13B is a configuration in which the phase modulation mask 3a shown in the lower part of FIG. 13B is divided so as to be a Fresnel lens having a constant thickness (L). In this case, the division width in the x direction is not constant and becomes narrower toward the outside.

(Fourth embodiment)
FIG. 14 is an xy sectional view showing an example of the configuration of the optical system 7 in the fourth embodiment. In the example shown in FIG. 14, the polarizing element 8 is provided on the surface of the phase modulation mask 3b that faces the phase surface. In other words, the back surface of the polarizing element 8 is the phase modulation mask 3b.

  As described above, the phase modulation mask 3b can be configured to have one optical element having another function in a direction orthogonal to the optical axis, and the rear surface thereof serves as a phase plane that causes a phase difference in one direction. Alternatively, the phase modulation mask 3b can have a configuration in which an element having a phase plane and an optical element having another function are bonded to each other. Examples of the optical element include a polarizing filter (polarizing element) and a plano-convex lens, but are not limited to specific ones.

  By combining the phase modulation mask and an optical element having another function, the structure can be simplified and the cost can be reduced.

  In the example shown in FIG. 14, the pair of phase modulation masks 3a and 3b are arranged so that the phase planes of the pair of phase modulation masks 3a and 3b face each other, and the back side of the phase plane, that is, the pair of phase modulation masks 3a. Other optical elements are formed outside 3b. A diaphragm 4 is provided between the opposing phase surfaces. Thus, by providing the phase plane on the diaphragm surface side, it becomes possible to couple with other optical elements while reducing the influence of the angle of view.

  FIG. 15 is a cross-sectional view showing a modification of the phase modulation masks 3a and 3b and the diaphragm 4. As shown in FIG. In the example shown in FIG. 15, each of the phase modulation masks 3a and 3b has a phase plane and a plane located on the back side of the phase plane, and the planes of the phase modulation masks 3a and 3b are opposed to each other. A pair of phase modulation masks 3a and 3b are arranged so that the surface is located outside. A diaphragm 4 is provided between the opposing planar surfaces. Further, an optical element 8 having a function other than the phase modulation is formed on the plane on the back side of the phase plane of one phase modulation mask 3a. In this case, the diaphragm 4 may not be separate from the phase modulation masks 3a and 3b. For example, the diaphragm 4 can be directly formed on the phase modulation masks 3a and 3b by vapor deposition.

(Fifth embodiment)
FIG. 16 is a functional block diagram illustrating a configuration example of the entire system including the imaging device 1 according to the fifth embodiment. In FIG. 16, the same functional blocks as those in FIG. In the configuration example shown in FIG. 16, a variable diaphragm 4a is provided between the phase modulation masks 3a and 3b. In addition, the system illustrated in FIG. 16 further includes a control unit 9, a recording unit 11, a display unit 12, and an operation unit 13.

  The controller 9 controls the aperture (aperture) of the variable aperture 4a. In addition, the operation of the imaging apparatus 1 can be determined and controlled according to an operation input from the user via the operation unit 13. Similar to the image processing unit 6, the control unit 9 can be configured by an IC chip dedicated to image processing, or a processor such as a general-purpose CPU and a computer such as a memory.

  The recording unit 11 stores the image data output from the image processing unit 6. The display unit 12 displays the image data stored in the recording unit 11. The display unit 12 can be formed of, for example, a liquid crystal display panel. The operation unit 13 includes, for example, a button, a dial, a keyboard, and other input devices, and functions as an interface that enables user operation input.

  In the above-described configuration, when photographing is performed with the variable aperture 4a stopped down, the phase of the light that passes through the aperture is covered with the phase modulation mask. Therefore, it is preferable that the control unit 9 notifies the image processing unit 6 of aperture information such as the degree of aperture. Thereby, the image processing unit 6 can restore an appropriate image according to the phase modulation by the phase modulation masks 3a and 3b based on the aperture information. For example, the image processing unit 6 records in advance values indicating the degree of aperture at a plurality of levels and data relating to the inverse filter corresponding to each level, and performs an inverse filter corresponding to the aperture level received from the control unit 9. Can be applied to the image.

(Other variations)
As mentioned above, although embodiment of this invention was described, this invention is not limited to the said 1st-5th embodiment.

  In the above-described embodiment, the case where the optical element phase plate whose thickness is changed is used as the phase modulation masks 3a and 3b. However, the phase modulation masks 3a and 3b are not limited to this, and other wavefronts are deformed. A wavefront modulation element can be used. For example, use an optical element whose refractive index changes depending on the location, such as a gradient index wavefront modulation lens, or an optical element whose thickness and refractive index change due to coding on the lens surface, such as a wavefront modulation hybrid lens. Can do. Furthermore, a liquid crystal element capable of modulating the phase distribution, such as liquid crystal spatial phase modulation element light, can be used as the phase modulation mask.

  Further, the use of the imaging device is not particularly limited. The imaging device can be used for, for example, a digital still camera, a mobile phone camera, a mobile information terminal camera, an image inspection device, an industrial camera for automatic control, an information code reader, and the like.

Claims (5)

A lens system that focuses light from the subject onto the image plane;
To light passing through the lens system, a first phase surface comprising a curved surface for changing the degree of phase modulation to be given to the first direction perpendicular to the optical axis in the light passing through only Oite of the lens system a first phase modulation mask having, with respect to the optical phase modulation to be given to the lens system of the light passing through only the even vertical second direction relative to the vertical a and the first direction to the optical axis look including a second phase modulation mask having a second phase plane consisting of a curved surface for changing the degree of the pair of the second phase surface and the first phase surface is disposed to face A phase modulation mask of
A diaphragm for adjusting the amount of light passing through the lens system, provided between the pair of phase modulation masks to suppress the influence of the angle of view and increase the depth of field ;
An imaging unit that obtains an image by converting the light collected on the image plane into an electrical signal; and
An image processing unit that performs a process of restoring the phase modulation on the image acquired by the imaging unit;
An imaging apparatus comprising: The first phase modulation mask has exp (iαx ³ ) for light passing there (where i is an imaginary unit, α is a constant, and x is x when a plane perpendicular to the optical axis is an xy plane) Coordinate) phase modulation,
The second phase modulation mask has exp (iαy ³ ) for light passing there (where i is an imaginary unit, α is a constant, y is y when a plane perpendicular to the optical axis is an xy plane) The imaging apparatus according to claim 1, wherein phase modulation of coordinates) is applied . The first phase modulation mask has a shape whose thickness changes stepwise only in the first direction, and the width of each step of the step in the first direction exceeds the wavelength of light passing therethrough. Not
The second phase modulation mask has a shape whose thickness changes stepwise only in the second direction, and the width of each step of the step in the second direction exceeds the wavelength of light passing therethrough. not, the imaging apparatus according to claim 1 or 2. At least one phase modulation mask of the pair of phase modulation masks is provided on a phase plane for realizing a phase modulation function and a surface on the back side of the phase plane, and has an optical function different from the phase modulation function and a device, an imaging apparatus according to claim 1. Each of the pair of phase modulation masks is formed with a curved surface or a stepped phase surface for changing the degree of phase modulation of light passing therethrough,
The pair of phase modulation masks are arranged so that the phase surfaces formed with curved surfaces or stepped shapes of the pair of phase modulation masks face each other,
The imaging device according to claim 1 , wherein the diaphragm is provided between the facing phase surfaces .

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