JP2016133517A - Imaging device and lens module using the same, as well as imaging system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which conventionally, when a phase modulation element is applied to a zoom optical system, a proper addition phase cannot be set for each zoom state, and further when using an element of which a phase modulation pattern is variable, it is necessary to electrically route wiring, thus, a size of an imaging system is large, and manufacturing costs are increased because components of a complex configuration are used.SOLUTION: An imaging device having a zoom function is configured such that at least two phase modulation elements with a function making a change of a point image in an optical axis small are provide. Accordingly, the imaging device has the zoom function of a compact and inexpensive configuration, and allows a desired depth-of-focus enlargement effect to be obtained, respectively in at least two zoom states.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging apparatus having a zoom function, a lens module using the imaging apparatus, and an imaging system.

  As a background art in this technical field, for example, one described in US Pat. No. 5,748,371 (Patent Document 1) is known. In Patent Document 1, a phase modulation element that adds a phase to light is arranged in an optical system, and a point image and an optical transfer function (OTF) are within a certain distance range from a focus position of a subject. A phase modulation element having a function of reducing the change in the optical axis direction, that is, a function of reducing a change in the optical axis direction of the point image, and a modulated intermediate image resulting from the OTF modulated by the phase modulation element. A technique is disclosed in which a processed image is generated by removing the amount of modulation by the phase modulation element, and as a result, the depth of focus is expanded.

  Japanese Patent Laid-Open No. 2008-268937 (Patent Document 2) shows an example in which the technique of Patent Document 1 is applied to an optical system having a zoom function. That is, the phase modulation element has a variable phase modulation pattern, and a technique for switching to an appropriate pattern according to the zoom state is disclosed.

US Pat. No. 5,748,371 JP 2008-268937 A

  In the technique of the above-mentioned patent document 1, the range (substantially insensitive range) in which the change of the point image is small can be set large by increasing the additional phase of the phase modulation element. However, if the substantially insensitive range is increased, the change of the point image is relatively increased and the reproduced image is degraded accordingly, and the noise amplification effect at the time of signal processing is increased and the reproduced image is degraded. If there is a problem and the additional phase is too large, the depth-of-focus expansion effect is reduced as a result. Therefore, in order to obtain a desired focal depth expansion effect, it is necessary to set the additional phase appropriately. However, when the technique of Patent Document 1 is applied to a zoom optical system as it is, there is a problem that an appropriate additional phase cannot be set for each zoom state.

  In addition, when an element having a variable phase modulation pattern as in Patent Document 2 is used, an accurate additional phase can be set for each zoom state, but electrical wiring must be routed and the size of the imaging system can be set. There is a problem that the manufacturing cost increases because of the use of parts having a complicated configuration.

  In order to solve the above problems, for example, the configuration described in the claims is adopted. The present invention includes a plurality of means for solving the above-mentioned problems. For example, an imaging apparatus having a zoom function, which is a phase modulation element having a function of reducing a change in the optical axis direction of a point image It is set as the structure which provided at least two.

  According to the optical system of the present invention, it is an imaging apparatus having a zoom function with a small and inexpensive configuration, and can obtain a desired depth of focus expansion effect in at least two zoom states.

1 is a diagram illustrating a configuration example of an imaging system according to Embodiment 1. FIG. 6 is a diagram illustrating an example of a shape of a phase modulation element in Embodiment 1. FIG. 2 is a diagram illustrating an example of an optical system according to Example 1. FIG. It is a figure which shows the phase on a pupil surface in the 1st structure for demonstrating the effect of the invention in Example 2. FIG. It is a figure which shows the focal depth expansion effect in the 1st structure in Example 2. FIG. It is a figure which shows the phase on a pupil surface in the 2nd structure for demonstrating the effect of the invention in Example 3. FIG. It is a figure which shows the focal depth expansion effect in the 2nd structure in Example 3. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, the configuration of the entire imaging system of the present embodiment will be described with reference to FIG. The imaging system 101 includes an optical system 10, an imaging element 8, an image generation unit 20, a lens position control unit 21, an image processing unit 23, an image correction variable storage unit 24, an output unit 25, and the like. The optical system 10 is an imaging device, and includes a first lens group 1, a second lens group 2, a third lens group 3, a fourth lens group 4, an aperture 5, and a first phase modulation element 6. The first lens group 1 includes a second phase modulation element 7.

  The second lens group 2 and the fourth lens group 4 are movable, the second lens group 2 functions as a zoom lens, and the fourth lens group 4 functions as a focus lens. The positions of the second and fourth lens groups are controlled by a signal from the lens position control unit 21. The lens position control unit 21 controls the lens position based on an input signal from the lens position determination unit 22. The lens position determination unit 22 may determine the lens position based on user input, or may determine the lens position by means for automatically calculating the optimum lens position, such as an autofocus function.

  The light beam emitted from the subject and incident on the optical system 10 forms a subject image on the surface of the image sensor 8 by the function of the optical system 10. At this time, the subject image is blurred due to the effects of the first phase modulation element 6 and the second phase modulation element 7. A configuration in which the optical system 10 (imaging device) and the imaging element 8 are integrated is referred to as a lens module.

  The image sensor 8 has a plurality of pixels on its surface. The subject image formed on the surface of the image sensor 8 is converted into an analog signal for each pixel by the image sensor 8 and further converted into a digital signal by the image generation unit 20 to generate image data corresponding to the subject image. Is done.

  The image processing unit 23 receives the image data, and performs a correction process for removing the blur of the subject image caused by the phase modulation of the first phase modulation element 6 and the second phase modulation element 7. In this way, deliberately blurring increases the depth of focus, and has an effect of, for example, relaxing the position adjustment accuracy of the image sensor.

  The correction processing method may be a method of performing correction processing on an image using an OTF inverse filter of the optical system 10. Information on the inverse filter of the OTF is stored in the image correction variable storage unit 24. However, when the OTF of the optical system 10 differs depending on the positions of the second lens group 2 and the fourth lens group 4, the image processing unit is stored in the image correction variable storage unit 24 based on the lens position information. An appropriate correction variable group is selected from a plurality of correction variable groups, and the image is corrected using the selected correction variable group. Information on the lens position is supplied from the lens position determination unit 22 to the image processing unit 23. The corrected image may be supplied to the output unit 25.

  Next, the shapes of the first phase modulation element and the second phase modulation element in this embodiment will be described with reference to FIG. The first phase modulation element and the second phase modulation element need only have a function of reducing the change in the optical axis direction of the point image. For example, the first phase modulation element and the second phase modulation element may have a surface shape having a cubic function component, and a plurality of annular zones. The surface shape may be constituted by other methods.

  FIGS. 2A-1 and 2A-2 show examples of surface shapes having a cubic function component. (A-1) is the figure which looked at the surface shape of the phase modulation element from the optical axis direction, and the internal line has shown the contour line. The opening of the phase modulation element is rectangular. (A-2) represents an additional phase in the cross section in the x direction in (A-1). The shape of the additional phase has a cubic function component corresponding to the shape of the phase modulation element. The magnitude of the phase change at both ends of the opening is expressed by ± α.

  FIGS. 2B-1 and 2B-2 show examples of the surface shape composed of a plurality of annular zones. (B-1) is a view of the surface shape of the phase modulation element viewed from the optical axis direction, and the internal line represents the boundary line of the annular zone. Note that (B-1) shows the case where the number of annular zones is 4, but the number of annular zones is not necessarily four. Each annular zone has a substantially parabolic cross-sectional shape. (B-2) represents an additional phase in the cross section in the r direction in (B-1). The additional phase has a substantially parabolic shape corresponding to the shape of each annular zone. In addition, although the height of the additional phase by each ring zone is shown with the same height in the figure, it does not necessarily need to be the same height. Moreover, although each ring zone is shown by equal width in FIG. 2 (B-1) (B-2), it does not necessarily need to be equal width.

  Next, how the first phase modulation element and the second phase modulation element function with respect to the light beam in each zoom state in this embodiment will be described with reference to FIG.

  FIG. 3A is a ray diagram at the telephoto end, where f = 136.1 mm and F # = 4.78. The first lens group 1 includes lenses indicated by reference numerals 1-1, 1-2, 1-3, and 1-4 from the first lens 1-1 to the fourth lens. -2 assumes that the lens diameter is smaller than other lenses. At this time, the light beam incident in parallel to the optical axis is limited in size by the second lens 1-2 in the first lens group 1 and passes through only the central portion of the aperture 5 without being limited. Therefore, the second phase modulation element 7 disposed in the vicinity of the second lens 1-2 in the first lens group 1 is subjected to a relatively large phase addition, and the first phase disposed in the vicinity of the opening 5. Some phase modulation elements 6 receive only a relatively small phase addition.

  FIG. 3B is a ray diagram at the wide-angle end, where f = 4.50 mm and F # = 1.46. At this time, the light beam incident in parallel to the optical axis is limited in size by the aperture 5, and is not limited in the first lens group 1 and passes through only a part of the region. Therefore, the first phase modulation element 6 disposed in the vicinity of the opening 5 receives a relatively large phase addition, and the second phase modulation element 7 receives only a relatively small phase addition.

  As described above, the present embodiment is an image pickup apparatus having a zoom function, and has a configuration in which at least two phase modulation elements having a function of reducing a change in the optical axis direction of a point image are provided.

  Further, one of the phase modulation elements is arranged in the vicinity of a component (the opening 5 in this embodiment) that restricts the size of a light beam incident parallel to the optical axis at the wide angle end.

  In addition, one of the phase modulation elements is disposed in the vicinity of a component (in this embodiment, the second lens 1-2 in the first lens group 1) that limits the size of the light beam incident parallel to the optical axis at the telephoto end. The configuration is as follows.

  Therefore, according to the present embodiment, by arranging the second phase modulation element in addition to the first phase modulation element, the additional phase at the telephoto end is hardly affected by the additional phase at the wide angle end. Can be changed. In other words, the additional phase at the wide-angle end can be appropriately set according to the surface shape of the first phase modulation element, and the additional phase at the telephoto end should be appropriately set according to the surface shape of the second phase modulation element. Is possible. As a result, a desired focal depth expansion effect can be obtained at the wide-angle end and the telephoto end, respectively.

  Since the phase modulation element is made in advance with a member such as glass or plastic, there is no need for electrical control, and there is no problem that the size of the imaging system is increased because it is necessary to route electrical wiring. In addition, the problem that the manufacturing cost increases due to the use of parts having complicated structures is also solved.

  Therefore, according to the present embodiment, the image pickup apparatus having a zoom function with a small and inexpensive configuration can obtain a desired depth of focus expansion effect in at least two zoom states.

  In this embodiment, the surface-shaped phase modulation element having the cubic function component shown in FIG. 2A-1 is applied to both the first phase modulation element and the second phase modulation element in the optical system shown in FIG. A simulation result of the phase on the pupil plane and the depth of focus expansion effect in the first configuration will be described.

  The first phase modulation element is α = 7.3λ, and the second phase modulation element is α = 1.8λ (λ = 560 nm). FIG. 4 is a simulation result of the phase at the pupil coordinates for each zoom state. 4A and 4B, the broken line a indicates the case where only the first phase modulation element is disposed in the optical system, and the solid line b indicates the case where both the first phase modulation element and the second phase modulation element are disposed. Is shown. FIG. 4A shows that the additional phase can be increased by disposing the second phase modulation element at the telephoto end. On the other hand, according to FIG. 4B, it can be seen that the additional phase hardly changes even when the second phase modulation element is arranged at the wide angle end.

  FIG. 5 shows a simulation result of the depth of focus. PSNR (Peak Signal-to-Noise Ratio) was used for evaluation of image quality. The input image was an image of a female model (Lena), and the range of defocus from the in-focus position where the PSNR was 35 dB or more even when the reproduced image was degraded was defined as the depth of focus. The sensor pitch was 7.5 μm, and the quantization bit of the sensor was 12 bits. For reference, the PSNR of an image when no phase modulation element is arranged in the same optical system (normal system) is also shown. In the normal system, the point image becomes blurred and the output image deteriorates with defocus. Similarly, the range of defocus where the PSNR is 35 dB or more is set as the focal depth. The range indicated as DOF (N) in the figure is the focal depth of the normal system. Further, a plot of the reproduced image in a state where only the first phase modulation element is arranged in the optical system is a broken line a, the depth of focus in that state is DOF (a), the first phase modulation element and the second phase modulation element A plot of the reproduced image in a state where both of these are arranged is shown as a solid line b, and the depth of focus in that state is shown as DOF (b). According to FIG. 5A, it can be seen that the focal depth expansion effect can be set larger by disposing the second phase modulation element at the telephoto end than when only the first phase modulation element is disposed. On the other hand, according to FIG. 5B, it can be seen that, at the wide-angle end, the focal depth expansion effect is hardly changed even when the second phase modulation element is arranged.

  Therefore, according to the present embodiment, similarly to the first embodiment, by arranging the second phase modulation element in addition to the first phase modulation element, the desired focal depth expansion effect at the wide-angle end and the telephoto end, respectively. Can be obtained.

  In the present embodiment, the surface-shaped phase modulation element constituted by a plurality of annular zones shown in FIG. 2 (B-1) is used for both the first phase modulation element and the second phase modulation element in the optical system shown in FIG. A simulation result of the phase on the pupil plane and the depth of focus expansion effect in the applied second configuration will be described.

  The first phase modulation element has four ring zones, h = 2.5λ for all four ring zones, the second phase modulation element has two ring zones, and h = 5λ for both ring zones (λ = 560 nm). ). In each of the first phase modulation element and the second phase modulation element, each annular zone is set to have an equal width. Symbols such as a, b, DOF (N), DOF (a), and DOF (b) in FIGS. 6 and 7 are the same as those in FIGS. The definition of the depth of focus and the sensor setting are the same conditions.

  FIG. 6 is a simulation result of the phase at the pupil coordinates for each zoom state. 6A shows that the additional phase can be increased by disposing the second phase modulation element at the telephoto end. On the other hand, according to FIG. 6B, it can be seen that the change in the additional phase due to the arrangement of the second phase modulation element is relatively small at the wide angle end.

  FIG. 7 shows a simulation result of the depth of focus. According to FIG. 7A, it can be seen that the effect of expanding the depth of focus can be set larger by disposing the second phase modulation element at the telephoto end than when only the first phase modulation element is disposed. On the other hand, according to FIG. 7B, it can be seen that, at the wide-angle end, the effect of extending the depth of focus is slightly reduced by disposing the second phase modulation element, but hardly changes.

  As described above, according to the present embodiment, similarly to the second embodiment, by arranging the second phase modulation element in addition to the first phase modulation element, the desired values can be obtained at the wide-angle end and the telephoto end, respectively. A depth of focus expansion effect can be obtained.

  In Example 2, an example in which a surface-shaped phase modulation element having a cubic function component is applied to both the first phase modulation element and the second phase modulation element, and in Example 3, the first phase modulation element, The example in which the phase modulation element having the annular zone structure is applied to the second phase modulation element has been described. However, the present invention is not limited to this combination. For example, the first phase modulation element has a surface-shaped phase modulation having a cubic function component. It is an element, and the second phase modulation element may be a phase modulation element having an annular structure, or may be a reverse combination.

  Moreover, although the example which used two phase modulation elements was demonstrated in the above Example, it is not limited to this, For example, you may use three. Specifically, by providing a third phase modulation element in the vicinity of the lens group that is not fixed, that is, the second lens group 2 in FIG. 3, the degree of freedom in setting the focal depth expansion effect is further improved. You can also.

  Although the embodiments have been described above, the present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 ... 1st lens group 2 ... 2nd lens group 3 ... 3rd lens group 4 ... 4th lens group 5 ... Aperture 6 ... 1st phase modulation element 7 ... 2nd phase modulation element 8 ... Imaging element 10 ... Optical System 20 ... Image generation unit 21 ... Lens position control unit 22 ... Lens position determination unit 23 ... Image processing unit 24 ... Image correction variable storage unit 25 ... Output unit 101 ... Imaging system

Claims (8)

An imaging device having a zoom function,
An imaging apparatus comprising at least two phase modulation elements having a function of reducing a change in the optical axis direction of a point image. The imaging apparatus according to claim 1,
One of the phase modulation elements is disposed in the vicinity of a component that restricts the size of a light beam incident parallel to the optical axis at the wide-angle end. The imaging apparatus according to any one of claims 1 and 2,
One of the phase modulation elements is disposed in the vicinity of a component that restricts the size of a light beam incident parallel to the optical axis at the telephoto end. The imaging apparatus according to any one of claims 1 to 3,
At least one of the phase modulation elements has a surface shape having a cubic function component. The imaging apparatus according to any one of claims 1 to 3,
An image pickup apparatus, wherein at least one of the phase modulation elements has a surface shape having an annular structure.   6. A lens module, wherein the imaging device according to claim 1 and an imaging element are integrated. An imaging device that converts a subject image from the imaging device according to any one of claims 1 to 5 into an analog signal;
An image generation unit that converts an analog signal from the image sensor into a digital signal and generates image data corresponding to the subject image;
An imaging system comprising: a signal processing unit that performs signal processing of image data from the image generation unit. The imaging system according to claim 7,
The image processing system, wherein the signal processing unit performs a correction process for removing blur of a subject image caused by phase modulation of the phase modulation element.

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