WO2023281877A1

WO2023281877A1 - Optical system, image capturing device, and image capturing system

Info

Publication number: WO2023281877A1
Application number: PCT/JP2022/015933
Authority: WO
Inventors: 諒黒崎; 哲也鈴木; 淳村田
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2021-07-05
Filing date: 2022-03-30
Publication date: 2023-01-12
Also published as: JP2024116428A

Abstract

An optical system (2) in which first light (L11) in a visible area forms an image on first image capture elements (11), and second light (L12) in a far infrared area forms an image on second image capture elements (12). The optical system comprises: at least one lens (31-33) for transmitting each of the first and second light; and an aperture diaphragm (4) provided with an aperture (40). The aperture diaphragm is provided with an optical filter (41) that blocks the first light and transmits the second light in the periphery of the aperture. The optical system satisfies t < 2x (4npf) / {(n-1) D}. In the foregoing: t is the optical filter thickness; n is the refractive index of the second light in the optical filter; p is the pixel pitch of the second image capture elements; f is the focal distance of the second light in the optical system; and D is the effective diameter of the optical filter in the aperture diaphragm.

Description

Optical system, imaging device and imaging system

The present disclosure relates to an optical system, an imaging device, and an imaging system that perform imaging in the visible range and imaging in the far infrared range.

Patent Literature 1 discloses an aperture stop in an imaging device that captures both an observation image of fluorescence from an observation site of a subject and a subject image of illumination light. This aperture stop has a filter region that transmits infrared light in the wavelength range of fluorescence from 610 to 720 nm and reduces or blocks the transmission of visible light, and an aperture region formed inside the filter region. In Patent Document 1, in order not to cause a phase difference between the fluorescence transmitted through the filter region and the fluorescence transmitted through the aperture region, a transparent plate-like substrate is provided over the filter region and the aperture region, and the thickness in the optical axis direction is is disclosed to be uniform.

WO2011/007435

The present disclosure is an optical system that suppresses blur due to aberration in the visible range and small aperture blur in the far infrared range, and makes it easy to perform imaging in the visible range and imaging in the far infrared range with light amounts suitable for each. , provides an imaging device and an imaging system.

In the present disclosure, the optical system forms an image of first light having a wavelength in the visible range on the first imaging element, and forms an image of second light having a wavelength in the far-infrared range on the second imaging element. Optical system. The optical system is arranged along the optical axis and includes one or more lenses that transmit the first and second lights, respectively, and an aperture stop provided with an opening through which the optical axis passes. The aperture stop includes an optical filter that blocks the first light and transmits the second light around the aperture. The optical system satisfies the following formula (1a).
t<2×(4npf)/{(n−1)D} (1a)
here,
t: thickness of the optical filter in the direction of the optical axis;
n: refractive index of the second light in the optical filter;
p: pixel pitch of the second imaging element;
f: the focal length of the second light in the optical system;
D: Effective diameter of the optical filter at the aperture stop.

According to the optical system, the imaging device, and the imaging system according to the present disclosure, blurring due to aberration in the visible range and small aperture blurring in the far infrared range are suppressed, and imaging in the visible range and imaging in the far infrared range are respectively suitable. It can be made easier with the amount of light.

1 is a diagram for explaining an imaging device and an imaging system according to Embodiment 1 of the present disclosure; FIG. 1 is a diagram showing the configuration of an optical system according to Embodiment 1; FIG. A diagram illustrating data of various lens materials in an optical system Diagram showing the configuration of an aperture filter in an optical system A diagram for explaining the condition (1) in the optical system. Graph showing simulation results of the optical system in Example 1 of Embodiment 1 Graph showing simulation results of the optical system in Example 2 of Embodiment 1 Graph showing simulation results of the optical system in Example 3 of Embodiment 1 4 is a chart showing numerical examples of the optical system according to Embodiment 1. 4 is a chart showing numerical examples of optical systems in Examples 1 to 3 of Embodiment 1. FIG. 4 is a diagram showing the configuration of an optical system according to Embodiment 2; Graph showing simulation results of the optical system in Example 1 of Embodiment 2 Graph showing simulation results of the optical system in Example 2 of Embodiment 2 Graph showing simulation results of the optical system in Example 3 of Embodiment 2 Chart showing a numerical example of the optical system in Embodiment 2 Graph showing numerical examples of optical systems in Examples 1 to 3 of Embodiment 2 FIG. 10 is a diagram showing the configuration of an optical system according to Embodiment 3; Graph showing simulation results of the optical system in Example 1 of Embodiment 3 Graph showing simulation results of the optical system in Example 2 of Embodiment 3 Graph showing simulation results of the optical system in Example 3 of Embodiment 3 Chart showing a numerical example of the optical system in Embodiment 3 4 is a chart showing numerical examples of optical systems in Examples 1 to 3 of Embodiment 3.

Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed description than necessary may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of substantially the same configurations may be omitted. This is to avoid unnecessary verbosity in the following description and to facilitate understanding by those skilled in the art.

It is noted that Applicants provide the accompanying drawings and the following description for a full understanding of the present disclosure by those skilled in the art and are not intended to limit the claimed subject matter thereby. Absent.

(Embodiment 1)
Embodiment 1 of the present disclosure will be described below with reference to the drawings. In the present embodiment, an imaging apparatus and its optical system that are compatible with imaging in the visible range and imaging in the far infrared range will be described.

1. Imaging Apparatus FIG. 1 is a diagram for explaining an imaging apparatus 1 and an imaging system 20 according to this embodiment. An imaging system 20 of this embodiment includes an imaging device 1 and a control unit 15 .

In this embodiment, the imaging device 1 includes an optical system 2, a visible imaging sensor 11, and a far-infrared imaging sensor 12, as shown in FIG. 1, for example. The imaging apparatus 1 of the present embodiment is a camera device that performs imaging in the visible range, ie, visible imaging, and imaging in the far infrared range, ie, far infrared imaging, coaxially with an optical system 2 . For example, the visible region has a wavelength of 400 nm to 750 nm, and the far infrared region has a wavelength of 3 μm to 20 μm. For example, part of the visible region and part of the far-infrared region are targets for visible imaging and far-infrared imaging by the imaging device 1 . For example, the far infrared region may be 7 μm to 12 μm.

The imaging device 1 of the present embodiment can be applied to various uses such as combining thermal imaging, motion sensors, night vision, or the like using far-infrared imaging, and visible imaging, for example. For example, in this system 20, image analysis such as measuring the temperature of a subject 10 such as a person and performing individual recognition on the same subject 10 can be applied. The imaging device 1 of this system 20 may be incorporated into various electronic devices such as mobile terminals, mounted on moving bodies such as drones or vehicles, or installed as surveillance cameras. be done. In such various application examples, miniaturization of the imaging device 1 is useful.

In the imaging device 1 of this embodiment, the optical system 2 collects the light L10 incident from the subject 10, guides the visible light L11 in the incident light L10 to the visible image sensor 11, and The external light L12 is guided to the far-infrared imaging sensor 12. According to such an optical system 2, it is possible to provide a compact device configuration in which the imaging device 1 has only one lens barrel.

In such an imaging device 1, narrowing down the visible light L11 taken in by the optical system 2 is useful from the viewpoint of suppressing blurring due to aberration and improving imaging performance for visible imaging. On the other hand, in far-infrared imaging, the wavelength of the far-infrared light L12 is long. The effect of "aperture blur" is more likely to occur than in visible imaging. Therefore, in far-infrared imaging, it is useful not to narrow down the intake of the far-infrared light L12 too much, from the viewpoint of the influence of the small-aperture blur on imaging performance.

In addition, since the visible image sensor 11 has a relatively small pixel pitch and a large number of pixels and has high sensor sensitivity, narrowing down the visible light L11 is useful for improving the imaging performance of visible imaging. is. On the other hand, the far-infrared imaging sensor 12 has a relatively large pixel pitch and a small number of pixels, resulting in low sensor sensitivity. For this reason, for far-infrared imaging, it is useful to secure a large amount of light for the optical system 2 to take in the far-infrared light L12.

In the conventional imaging device, the aperture diameter is the same for the visible light L11 and the far-red light L12, and it is difficult to suppress aberration blur in the visible range and small-aperture blur in the far-infrared range, and the amount of each light is also optimized. I had a problem that I couldn't. Therefore, the present embodiment provides an optical system 2 capable of realizing both narrowing down of the visible light L11 suitable for visible imaging and capture of far-infrared light L12 suitable for far-infrared imaging, as described above. The configuration of the optical system 2 will be described later.

The visible image sensor 11 is a variety of image sensors, such as CCD or CMOS image sensors, made of materials such as amorphous silicon having light sensitivity in the visible range. The visible image sensor 11 has an imaging surface in which a plurality of pixels are arranged at a predetermined pitch. The pixel pitch of the visible image sensor 11 is, for example, about 3 μm. The visible image sensor 11 captures an image formed on an imaging surface by the incidence of the visible light L11 through the optical system 2, and generates an image signal representing a captured image in the visible range, that is, a visible image Im1. The visible imaging sensor 11 is an example of the first imaging section in this embodiment.

The far-infrared imaging sensor 12 is an imaging element having light sensitivity in the far-infrared region, such as a bolometer, thermopile, or SOI diode. The far-infrared imaging sensor 12 has an imaging surface in which a plurality of pixels are arranged at a predetermined pitch. The pixel pitch of the far-infrared imaging sensor 12 is, for example, 10 μm to 300 μm. The far-infrared image sensor 12 captures an image formed on an imaging surface by the incidence of the far-infrared light L12 via the optical system 2, and presents a captured image in the far-infrared region, that is, a far-infrared image Im2. Generate an image signal. The far-infrared imaging sensor 12 is an example of a second imaging section in this embodiment.

According to the imaging device 1 configured as described above, the visible image Im1 and the far-infrared image Im2 are output as coaxial imaging results using the optical system 2. Therefore, according to the imaging apparatus 1 of the present embodiment, for example, image shift of the subject 10 between the visible image Im1 and the far-infrared image Im2 can be suppressed, and analysis is easy in various applications that combine visible imaging and far-infrared imaging. You can get the image output.

In this system 20, the control unit 15 receives image signals from the imaging device 1 and performs various image analyzes based on various images Im1 and Im2 indicated by the received image signals. The control unit 15 includes, for example, a CPU or MPU that implements various functions by executing programs stored in an internal memory. Control unit 15 may include dedicated hardware circuitry designed to achieve the desired functionality. The control unit 15 may include a CPU, MPU, GPU, DSP, FPGA, ASIC, or the like.

For example, the control unit 15 of the system 20 performs individual recognition of the subject 10 based on the visible image Im1 captured by the visible image sensor 11 in the imaging device 1, and the far-infrared image captured by the far-infrared image sensor 12. The temperature of the subject 10 is recognized based on Im2. Further, the control unit 15 associates the recognition result from the visible image Im1 and the recognition result from the far-infrared image Im2 based on, for example, the position of the subject 10 in each of the images Im1 and Im2, and outputs the result as information of the analysis result. to manage. According to this system 20, the optical system 2 of the imaging device 1 can suppress the image shift of the same subject 10 between the visible image Im1 and the far-infrared image Im2. can run to

2. Optical System The configuration of the optical system 2 according to this embodiment will be described with reference to FIG.

FIG. 2 is a diagram showing the configuration of the optical system 2 according to Embodiment 1. FIG. The optical system 2 includes a lens group 30 having an optical axis Z0 into which incident light L10 from the outside is incident, an aperture filter 4, a light branching element 21, and a far-infrared transmission filter 22.

Hereinafter, the direction of the optical axis Z0 of the lens group 30 in the optical system 2 is defined as the Z direction, and two directions orthogonal to the Z direction are defined as the X and Y directions. In the Z direction, the object side (or enlargement side) facing outside from the optical system 2 is the -Z side or front, and the opposite image plane side (or reduction side) is the +Z side or rear. In the optical system 2 of this embodiment, the main surface of the light branching element 21 is arranged to be inclined by a predetermined angle (for example, 45°) from the XY plane. The X direction corresponds to the direction in which the main surface of the light branching element 21 is inclined, and the Y direction corresponds to the direction in which the main surface of the light branching element 21 extends. The light branching element 21 is tilted so as to be positioned on the +X side as it goes to the +Z side.

The optical system 2 has an imaging position P1 where the visible light L11 is imaged by the optical system 2 and an imaging position P2 where the far infrared light L12 is imaged by the optical system 2 on the +Z side, ie, the rear. The imaging plane of the visible image sensor 11 is arranged at the imaging position P1, and the imaging plane of the far-infrared imaging sensor 12 is arranged at the imaging position P2. In the optical system 2 , the light branching element 21 is provided between the lens group 30 and the

imaging sensors

11 and 12 . The far-infrared transmission filter 22 is provided between the light branching element 21 and the far-infrared imaging sensor 12 .

The lens group 30 in the optical system 2 is made of a lens material that has optical transparency in both the visible range and the far infrared range. Due to the wavelength dependence of the refractive index of lens materials, the focal length of lens group 30 can vary according to the wavelength of the light to be imaged. The lens group 30 functions as an imaging optical system by applying a refractive power according to the focal length to the incident light L10 from the outside. The incident light L10 after passing through the lens group 30 includes visible light L11 and far-infrared light L12, and enters the light branching element 21 . The visible light L11 and the far-infrared light L12 are examples of first and second light, respectively, in this embodiment.

In the optical system 2 of Embodiment 1, the lens group 30 is composed of three

lens elements

31 , 32 and 33 . In the lens group 30, a first lens element 31, a second lens element 32, and a third lens element 33 are arranged in order from the front along the optical axis Z0.

In Embodiment 1, as an example of the lens material, the first and

third lens elements

31 and 33 are made of chalcohalide glass (CH), and the second lens element 32 is made of zinc sulfide (ZnS) (FIG. 9). reference). Data for these various lens materials are exemplified in FIG. The lens material in the lens group 30 is not limited to the above. It can be material. For example, the wavelength band transmitted by the lens material may be from 0.4 μm to 12 μm.

The aperture filter 4 is an example of an aperture stop in the present embodiment, and limits the amount of visible light L11 and the amount of far-infrared light L12 in the incident light L10. In the present embodiment, the aperture filter 4 has a configuration for achieving both an aperture diameter that relatively reduces the amount of visible light L11 and an aperture diameter that relatively increases the amount of far-infrared light L12. The configuration of the aperture filter 4 will be described later.

The aperture filter 4 is arranged between the second and

third lens elements

32 and 33 in the first embodiment. The aperture filter 4 may be arranged at any position in the lens group 30 in the optical system 2 . Hereinafter, of the entire lens group 30 of the optical system 2, the lens group consisting of the

lens elements

31 and 32 in front of the aperture filter 4 will be referred to as a front group 30a, and the lens group consisting of the lens element 33 behind the aperture filter 4 will be referred to as a rear group 30b. There is a case. Each lens group may consist of one lens element.

The light branching element 21 is arranged, for example, behind the rear group 30b, and branches the optical path of the visible light L11 and the optical path of the far-infrared light L12. For example, as shown in FIG. 2, the light branching element 21 transmits the visible light L11 in the incident light L10 from the −Z side and emits it to the +Z side, while reflecting the far infrared light L12 to the +X side. configured to emit. For example, the light branching element 21 has a specific wavelength band (that is, a transmission band) that selectively transmits light, and is a band-pass filter having an optical characteristic that reflects light outside the transmission band. It is configured by setting the band to the transmission band.

The far-infrared transmission filter 22 is arranged, for example, between the light branching element 21 and the far-infrared imaging sensor 12 in the configuration example of FIG. 2, and selectively transmits the far-infrared light L12. The far-infrared transmission filter 22 is composed of various filter elements such as a bandpass filter whose transmission band is set in advance to the wavelength band of the far-infrared light L12.

The optical system 2 of this embodiment is configured so that, for example, no lens element having refractive power is provided between the light branching element 21 and each of the

imaging sensors

11 and 12 . With this configuration, it is possible to reduce the size of the optical system 2 from the viewpoint of the overall length or the number of parts, etc., and the cost can be reduced by reducing the alignment process of the lens after the light splitting. In the present embodiment, in order to achieve both visible imaging and far-infrared imaging in such a compact configuration, the lens group 30 on the -Z side (that is, in front) of the light branching element 21 is arranged so that the visible light included in the incident light L10 is An imaging optical system for each of L11 and far-infrared light L12 is configured. In other words, each imaging position P1, P2 is set corresponding to the focal length of the lens group 30. FIG.

2-1. Aperture Filter The configuration of the aperture filter 4 in the optical system 2 of this embodiment will be described with reference to FIG.

FIG. 4 is a front view of the configuration of the aperture filter 4 in the optical system 2, viewed from the Z direction. For example, as shown in FIG. 4, the aperture filter 4 is provided with an aperture 40 surrounding the optical axis Z0. The aperture filter 4 includes a filter portion 41 surrounding the aperture portion 40 and a light blocking portion 42 surrounding the filter portion 41 . In the aperture filter 4, the aperture portion 40, the filter portion 41 and the light shielding portion 42 are formed concentrically, for example.

The aperture 40 defines an area in the aperture filter 4 for passing both the visible light L11 and the far infrared light L12 in the incident light L1. The opening 40 is formed, for example, in a circular shape around the optical axis Z0. The aperture diameter Dap of the aperture 40 defines the aperture value (F number) of the visible light L11. In this embodiment, the opening 40 is configured by providing a hollow hole in the filter portion 41 . Thereby, in the optical system 2, the function of transmitting the visible light L11 and the far-infrared light L12 can be easily realized without using a special optical member.

The filter section 41 is made of various optical materials having optical properties of blocking the visible light L11 and transmitting the far-infrared light L12. For example, various materials such as silicon, germanium and chalcogenide glass can be employed. Examples 1 to 3 in which the filter portion 41 is made of various materials will be described later. The filter section 41 is an example of an optical filter in this embodiment. Hereinafter, the thickness of the filter portion 41 in the direction of the optical axis Z0 will be referred to as "filter thickness".

The light blocking part 42 is made of various materials that block both the visible light L11 and the far infrared light L12, and is made of various metal members, for example. The light shielding portion 42 is formed, for example, in an annular shape that is concentric with the opening portion 40 . The inner diameter of the light shielding portion 42 corresponds to the outer diameter of the filter portion 41, that is, the effective diameter D. As shown in FIG. This effective diameter D defines the aperture value of the far-infrared light L12. The light shielding portion 42 is not limited to an annular shape, and may be formed, for example, in a rotationally symmetrical polygonal shape. The light shielding part 42 may be configured to have a variable aperture value with a structure such as a blade aperture.

According to the aperture filter 4 configured as described above, the visible light L11 is narrowed down by the aperture diameter Dap of the aperture 40, thereby suppressing aberration blurring, and the effective diameter D of the filter section 41, which is larger than the aperture diameter Dap, The amount of light can be ensured while suppressing the small-aperture blur of the far-infrared light L12. In addition, for example, since the respective portions 40 to 42 of the aperture filter 4 are concentric, the eccentricity of the optical system 2 can be suppressed with respect to each of the visible light L11 and the far-infrared light L12.

2-2. Regarding optimization conditions According to the intensive research of the inventors of the present application, in adopting the configuration of the aperture filter 4 as described above in the imaging device 1 capable of both visible imaging and far-infrared imaging, optical A new problem has been found that can lead to a decrease in performance. In order to solve such a new problem, the inventors of the present application conducted extensive research and came up with the optical system 2 in which the filter thickness of the aperture filter 4 is optimized. Various conditions for optimizing the aperture filter 4 in the optical system 2 will be described below.

In the optical system 2 of this embodiment, the aperture filter 4 satisfies the condition (1) represented by the following equations (1a) and (1b).
t<2×(4npf)/{(n−1)D} (1a)
0.1<t (1b)

　In the above formulas (1a) and (1b), t is the filter thickness of the filter portion 41 of the aperture filter 4 in the direction of the optical axis Z0, for example in units of mm. n is the refractive index of the filter portion 41 of the filter portion 41 in the far infrared region. p is the pixel pitch of the far-infrared imaging sensor 12 (or the pixel pitch in the imaging of the far-infrared light L12). f is the focal length of the far-infrared light L12 in the optical system 2; D is the effective diameter of the filter portion 41 in the aperture filter 4 .

Condition (1) is for avoiding deterioration in optical performance that may occur when the far-infrared light L12 passes through the filter portion 41 and the aperture portion 40 of the aperture filter 4 in the optical system 2 of the imaging device 1. It is a condition. Condition (1) in the optical system 2 will be described with reference to FIG.

In FIG. 5, the far-infrared rays L12a that pass through the filter portion 41 of the aperture filter 4 and the far-infrared rays L12a that pass through the aperture portion 40 without passing through the filter portion 41 ray L12b are illustrated.

Depending on the presence or absence of the filter section 41 , the focal position changes due to the influence of light refraction in the filter section 41 . For this reason, in the aperture filter 4 which is hollow at the aperture 40, as shown in FIG. are offset from each other. As a result, a new problem was found that the optical performance of the optical system 2 could be lowered. With respect to this problem, the optical system 2 of this embodiment can suppress deterioration of the optical performance of the optical system 2 by falling below the upper limit of the condition (1).

First, in the aperture filter 4 of the optical system 2, there is The amount of deviation Δt is represented by the difference in air-equivalent length between the far-infrared rays L12a and L12b, as in the following equation (11).
Δt=t(1−1/n) (11)

If the amount of deviation Δt between the far-infrared rays L12a and L12b is within the range of the depth of focus d in the imaging device 1, the optical performance of the optical system 2 can be substantially maintained. The focal depth d is represented by the following equation (12) using the permissible circle of confusion diameter ε in the far-infrared imaging sensor 12 of the imaging device 1 .
d=2εf/D=4pf/D (12)

From the above theoretical viewpoint, the optical system 2 of this embodiment may satisfy the following formula (1c).
t<(4npf)/{(n−1)D} (1c)

By satisfying the above formula (1c), it is possible to ideally ensure good optical performance of the optical system 2 . On the other hand, the optical system 2 of the present embodiment does not necessarily have to satisfy the above formula (1c), and may fall below the upper limit of the condition (1) as in the above formula (1a). Numerical simulations by the inventors of the present application have confirmed that, even in this case, it is possible to sufficiently suppress deterioration in the optical performance of the optical system 2 in practice. This point will be described later. Hereinafter, the right side of the above equation (1c) may be referred to as a factor Q.

Regarding the condition (1), the pixel pitch p included in the factor Q is various pixels that can be used to obtain an optical image formed by the far-infrared light L12 without necessarily having the far-infrared imaging sensor 12. may be set at intervals. For example, the pixel pitch p may be about a representative wavelength of the far-infrared light L12, for example, 10 μm to 12 μm, from the viewpoint of the physical limit of pixels that form an image of the far-infrared light L12. good. Also, the pixel pitch p may be 10 μm or more and 300 μm or less from the viewpoint of making it possible to use various far-infrared imaging sensors 12 .

Further, the lower limit of the condition (1) based on the above formula (1b) is that the filter thickness t is too thin, and the far-infrared imaging is affected from a different point of view from the defocus amount Δt between the far-infrared rays L12a and L12b. To solve a problem that can degrade optical performance. That is, when the filter thickness t is extremely thin, the far-infrared light L12 transmitted through the filter portion 41 and the far-infrared light L12 reflected inside the filter portion 41 (for example, reflected on the +Z side surface and then reflected on the -Z side surface This is thought to be due to the interference with the light emitted from the light, which causes unevenness in luminance.

On the other hand, if the filter thickness t is 10 times or more the average wavelength (for example, 10 μm) of the far-infrared light L12, the effect can be ignored. Therefore, the optical system 2 of this embodiment can solve the problem of the influence of such interference by exceeding the lower limit of the condition (1).

Further, the optical system 2 of this embodiment may satisfy the condition represented by the following formula (2).
0.2×|fa|>f (2)

In the above formula (2), f is the focal length of the far-infrared light L12 in the entire optical system 2. fa is the synthetic focal length of the far-infrared light L12 synthesized in the front group in the optical system 2, that is, in the lens group on the object side (-Z side) of the aperture filter 4;

The above equation (2) is obtained by increasing the composite focal length fa on the object side of the aperture filter 4 compared to the focal length f of the entire optical system 2, so that the shift amount Δt between the far infrared rays L12a and L12b described above is is a condition for suppressing the occurrence of

That is, according to the combined focal length fa that satisfies the above formula (2), the far-infrared light L12 incident on the optical system 2 from the object side causes the light beam directions of the light beams incident on the aperture filter 4 to be parallel to each other in the Z direction. can get closer. According to such a light beam of substantially parallel far-infrared light L12, in the aperture filter 4, the angle difference between the far-infrared light L12a refracted by the filter portion 41 and the far-infrared light L12b traveling straight through the aperture 40 is can be suppressed. Thereby, the defocus amount Δt between the two light beams L12a and L12b can be reduced.

From the viewpoint of obtaining such effects more remarkably, the optical system 2 of this embodiment may further satisfy the following formula (2a).
0.05×|fa|>f (2a)

Further, the optical system 2 of this embodiment may satisfy the condition represented by the following formula (3).
D≤f/2 (3)

That is, in the optical system 2 of the present embodiment, the F value for the far-infrared light L12 may be 2 or less as in the above formula (3). Thereby, the far-infrared light L12 can be easily taken into the optical system 2. FIG.

Moreover, the optical system 2 of this embodiment may satisfy the condition represented by the following formula (4).
Dap≧fvis/4 (4)

In the above formula (4), Dap is the aperture diameter of the aperture 40 in the aperture filter 4 (see FIG. 4). fvis is the focal length of the visible light L11 in the optical system 2; In the optical system 2 of the present embodiment, the F value for the visible light L11 may be 4 or more as in the above formula (4). As a result, it is easy to narrow down the visible light L11 and improve the imaging performance of the optical system 2 for visible imaging.

2-3. Simulation of Optical Performance A numerical simulation of the optical system 2 in which the effect of the optical performance under the condition (1) as described above has been confirmed will be described with reference to FIGS. 6 to 8. FIG.

FIG. 6 is a graph showing simulation results of the optical system 2 in Example 1 of Embodiment 1. FIG. In FIG. 6, the horizontal axis indicates the filter thickness t of the aperture filter 4 in the optical system 2, and the vertical axis indicates the MTF (modulation transfer function). The unit of filter thickness t is mm.

In Example 1 of FIG. 6, silicon is used as the optical material of the filter portion 41 in the aperture filter 4 of the optical system 2 . In this simulation, the MTF was calculated on-axis in the image plane, using a spatial frequency of 10 lp/mm (lp: line pairs). The pixel pitch p of the far-infrared imaging sensor 12 was assumed to be 50 μm, and the Nyquist frequency was taken into consideration in calculating the MTF. In this simulation, the factor Q (=(4npf)/{(n-1)D}) was calculated in the configuration of the optical system 2 in Embodiment 1 and compared with the filter thickness t.

According to this simulation, as shown in FIG. 6, when the filter thickness t is near the upper limit Q of the theoretical formula (1c) described above, the MTF is constant and good optical performance can be maintained. Also, the decrease in MTF occurs after the upper limit 2Q of condition (1) is exceeded (see formula (1a)). In other words, it was confirmed that the optical performance of the optical system 2 can be maintained up to the upper limit 2Q of the condition (1) even if the filter thickness t exceeds the upper limit Q of the above formula (1c).

FIG. 7 is a graph showing simulation results of the optical system 2 in Example 2 of Embodiment 1. FIG. FIG. 8 is a graph showing simulation results of the optical system 2 in Example 3 of the first embodiment.

In Example 2, germanium was adopted as the optical material of the filter portion 41 instead of silicon in Example 1. In Example 3, chalcogenide glass was used as the optical material of the filter section 41 (specifically, IRG203 manufactured by Hubei Xinhua Optical Information Materials Co., Ltd.). Graphs in FIGS. 7 and 8 show simulation results for Examples 2 and 3, respectively, similarly to FIG. 6 for Example 1. FIG.

In the optical system 2 of the present embodiment, as illustrated in FIGS. 7 and 8, the same tendency as in FIG. 6 was confirmed even when the optical material of the filter portion 41 was changed. That is, it was confirmed that the deterioration of the optical performance of the optical system 2 can be suppressed when the filter thickness t is less than the upper limit of the condition (1). Moreover, it was confirmed that the optical performance of the optical system 2 can be stably ensured by falling below the upper limit of the above formula (1c).

2-2. Numerical Examples Numerical examples showing Examples 1 to 3 of the optical system 2 of Embodiment 1 as described above will be described with reference to FIGS.

FIG. 9 is a chart showing a numerical example of the optical system 2 in Embodiment 1. FIG. The chart in FIG. 9 includes surface data D11, aspheric surface data D12, and various data D13 of the optical system 2 in this embodiment. In addition, in FIG. 9, the focal length f, the total angle of view 2ω, and the aperture diameter D of the optical system 2 of this embodiment are illustrated above the surface data D11.

The surface data D11 indicates the shape, radius of curvature, surface interval, and material of each surface S1 to S14 arranged in order from the object side in the optical system 2, and includes a remark column. For example, the surface number S2 is the object-side lens surface of the first lens element 31 and has an aspherical shape. Note that the surface number S1 represents an object such as the subject 10 positioned at infinity (see remarks). In the surface data D11 of FIG. 9, the surface number S10 is the surface of the light branching element 21 on the object side. and respectively (see FIG. 2).

The aspherical surface data D12 indicates various coefficients of the following equation (20) that defines the shape of the aspherical surface for each of the aspherical surfaces S2, S3, S8, and S9 in the surface data D11.

In the above equation (20), h is the height in the radial direction, k is the conic constant, and An is the n-th order aspheric coefficient. In the second term on the right side of the above equation (20), n is an even number of 4 or more and 20 or less, and the sum of each n is taken. According to the above formula (20), the sag amount z at the height h in the radial direction on the target surface is defined rotationally symmetrically.

The various data D13 include the F-number for the visible light L11 of the aperture filter 4 in the optical system 2, the F-number for the far-infrared light L12, the total angle of view, the absolute value of the combined focal length fa by the front group, The focal length f of the entire optical system 2 is shown. Also, the optical system 2 of this embodiment has a focal length fvis=8.8 mm for the visible light L11.

FIG. 10 is a chart showing numerical examples of the optical system 2 in Examples 1 to 3 of the first embodiment. The chart in FIG. 10 shows interplanar spacing data D14 and factor data D15 for various filter thicknesses t in Examples 1-3.

As shown in the surface distance data D14 in FIG. 10, in the numerical simulation described above, the filter thickness t was varied within the range of 0 to 1.6 mm in this embodiment. In accordance with this, the surface distances dA, dB, dC before and after the aperture filter 4 and the surface distance dD between the light branching element 21 and the far-infrared transmission filter 22 were changed. In Examples 1, 2, and 3, changes in the interplanar spacing dD with respect to changes in the filter thickness t were set separately.

Further, the factor data D15 indicates the calculation results of the factors Q and 2Q of condition (1) according to the optical material of the filter section 41 in Examples 1 to 3 of the present embodiment. According to the above numerical examples, the simulation results shown in FIGS. 6 to 8 were obtained for the optical system 2 of this embodiment.

3. Summary As described above, the optical system 2 according to the present embodiment forms an image of the visible light L11, which is an example of the first light having a wavelength in the visible range, on the visible image sensor 11, which is an example of the first imaging element. do. Further, the optical system 2 forms an image of far-infrared light L12, which is an example of second light having a wavelength in the far-infrared region, on a far-infrared imaging sensor 12, which is an example of a second imaging element. The optical system 2 is arranged along the optical axis Z0, and includes first to third lens elements 31 to 33 as an example of one or more lenses that respectively transmit the visible light L11 and the far infrared light L12, and an aperture stop. and an aperture filter 4 as an example. The aperture filter 4 is provided with an aperture 40 through which the optical axis Z0 passes, and defines the amount of emitted visible light L11 and far-infrared light L12 incident on the optical system 2 . For example, the aperture 40 defines the amount of visible light L11. The aperture filter 4 includes a filter section 41 as an example of an optical filter that shields the visible light L11 around the aperture 40 and transmits the far-infrared light L12. The optical system 2 satisfies the following formula (1a).
t<2×(4npf)/{(n−1)D} (1a)
Here, t is the thickness of the filter section 41 in the direction of the optical axis Z0. n is the refractive index of the far-infrared light L12 in the filter section 41; p is the pixel pitch of the far-infrared imaging sensor 12 (or the pixel pitch in the imaging of the far-infrared light L12). f is the focal length of the far-infrared light L12 in the optical system 2; D is the effective diameter of the filter portion 41 in the aperture filter 4 .

According to the above-described optical system 2, the filter thickness t is optimized in the aperture filter 4 that captures a larger amount of far-infrared light L12 while limiting the amount of visible light L11 in the filter portion 41 and the aperture 40. It is possible to solve the problem that the optical performance of far-infrared imaging can be degraded. Accordingly, it is possible to provide the optical system 2 that makes it easy to perform imaging in the visible range and imaging in the far-infrared range with light amounts suitable for each.

In this embodiment, the optical system 2 satisfies the following formula (1b).
0.1<t (1b)
Thereby, the influence of the interference of the far-infrared light L12 can be suppressed in the aperture filter 4, and the optical performance of far-infrared imaging can be easily obtained.

In this embodiment, the optical system 2 satisfies the following formula (1c).
t<(4npf)/{(n−1)D} (1c)
As a result, in the aperture filter 4, the amount of deviation Δt between the far-infrared rays L12a that pass through the filter section 41 and the far-infrared rays L12b that do not pass through the filter section 41 is kept within the range of the depth of focus d, and the optical performance of far-infrared imaging is improved. can be stably secured.

In this embodiment, the optical system 2 satisfies the following formula (2).
0.2×|fa|>f (2)
Here, fa is the far-infrared light generated by the lens group, ie, the front group 30a, arranged on the incident side, ie, the enlargement side, of the visible light L11 and the far-infrared light L12, relative to the aperture filter 4 in the entire lens group 30 of the optical system 2. It is the combined focal length of the external light L12. According to the above formula (2), the luminous flux of the far-infrared light L12 incident on the aperture filter 4 can be totally collimated, the shift amount Δt can be reduced, and the optical performance of far-infrared imaging can be improved.

In this embodiment, the optical system 2 satisfies the following formulas (3) and (4).
D≤f/2 (3)
Dap≧fvis/4 (4)
Here, Dap is the opening diameter of the opening 40 . fvis is the focal length of the visible light L11 in the optical system 2; As a result, the optical system 2 can narrow down the visible light L11 by setting the F value to 2 or less while taking in the amount of light by setting the F value to 4 or more for the far infrared rays L12 in the optical system 2 . As a result, visible imaging and far-infrared imaging can be easily performed with the optimum amount of light for each.

In the optical system 2 of this embodiment, the aperture filter 4 is hollow at the aperture 40 . This makes it possible to easily obtain a configuration that transmits both the visible light L11 and the far-infrared light L12. Even in this case, according to the optical system 2 of the present embodiment, the problem that the optical performance of far-infrared imaging may be degraded is solved, and visible imaging and far-infrared imaging are suitable for each. It can be done easily with the amount of light.

In the optical system 2 of this embodiment, the aperture 40 of the aperture stop 4 and the filter section 41 are provided concentrically around the optical axis Z0. Thereby, the eccentricity of the optical system 2 can be suppressed for each of the visible light L11 and the far-infrared light L12, and it is possible to easily perform both visible imaging and far-infrared imaging.

In this embodiment, the optical system 2 further includes a light branching element 21 arranged between the lens group 30, the visible image sensor 11, and the far-infrared light L12. The light splitting element 21 splits the visible light L11 and the far-infrared light L12 incident along the optical axis Z0 from the lens group 30, guides the visible light L11 to the visible imaging sensor 11, and L12 is guided to the far-infrared imaging sensor 12. FIG. Thus, the visible light L11 and the far-infrared light L12 can be guided to different imaging positions P1 and P2 via the light branching element 21, making it easy to achieve both visible imaging and far-infrared imaging.

In this embodiment, the imaging device 1 includes an optical system 2, a visible imaging sensor 11 that is an example of a first imaging section, and a far-infrared imaging sensor 12 that is an example of a second imaging section. The visible image sensor 11 captures an image of visible light L11 formed via the optical system 2 . The far-infrared imaging sensor 12 captures an image formed by far-infrared light L12 through the optical system 2 . According to the imaging apparatus 1 of the present embodiment, the optical system 2 makes it easy to perform visible imaging and far-infrared imaging with the amount of light suitable for each. In addition, it is possible to reduce the size of the configuration that achieves both visible imaging and far-infrared imaging, and to improve the imaging performance of both.

In this embodiment, the imaging system 20 includes an imaging device 1 and a control unit 15 that analyzes various images Im1 and Im2 captured by the imaging device 1. According to the present system 20, the optical system 2 of the imaging device 1 can facilitate visible imaging and far-infrared imaging with the amount of light suitable for each. Accordingly, it is possible to easily perform both analysis of the visible image Im1 and analysis of the far-infrared image Im2.

(Embodiment 2)
Embodiment 2 will be described below with reference to FIGS. 11 to 16. FIG. Although the example of the optical system 2 having three lenses has been described in the first embodiment, the present disclosure is not limited to this. In the second embodiment, an example of an optical system 2A having two lenses will be described.

Hereinafter, the optical system 2A according to the present embodiment will be described, omitting the same description as in the first embodiment as appropriate.

FIG. 11 shows the configuration of an optical system 2A according to the second embodiment. An optical system 2A according to this embodiment has the same configuration as the optical system 2 according to the first embodiment, but includes two

lens elements

31 and 32 instead of the three lens elements 31-33. The aperture filter 4 of this embodiment is arranged, for example, between two

lens elements

31 and 32 .

For the optical system 2A of the present embodiment as described above, numerical simulations were performed in the same manner as in FIGS. 6 to 8 of the first embodiment. At this time, various materials were adopted for the filter portion 41 of the aperture filter 4 in the same manner as in Examples 1 to 3 of the first embodiment.

FIG. 12 shows simulation results of the optical system 2A in Example 1 of Embodiment 2, similarly to FIG. 13 and 14 show simulation results of the optical system 2A in Examples 2 and 3 of Embodiment 2, respectively, similarly to FIGS. 7 and 8. FIG.

15 and 16 show numerical examples of the optical system 2A according to the second embodiment, similarly to the first embodiment. Specifically, surface data D21, aspheric surface data D22, and various data D23 in FIG. 15 respectively indicate information about the optical system 2A in this embodiment, similarly to each data D11 to D13 in FIG. Further, the surface distance data D24 and the factor data D25 in FIG. 16 respectively show information about the optical system 2A in Examples 1 to 3 of the present embodiment, similarly to the data D14 and D15 in FIG.

As shown in FIGS. 12 to 14, it was confirmed that the optical system 2A of the present embodiment also provided the same effects as those of the first embodiment under condition (1).

(Embodiment 3)
Embodiment 3 will be described below with reference to FIGS. 17 to 22. FIG. In the first embodiment, an example in which the lens materials of the lens elements in the optical system 2 are different has been described. In Embodiment 3, an optical system 2B composed of lens elements made of the same lens material will be described.

Hereinafter, descriptions similar to those of

Embodiments

1 and 2 will be omitted as appropriate, and an optical system 2B according to this embodiment will be described.

FIG. 17 shows the configuration of an optical system 2B according to the third embodiment. In Embodiment 1, zinc sulfide is exemplified as the lens material of the second lens element 32 . In the optical system 2B according to this embodiment, the lens material of the second lens element 32B is the same chalcohalide glass as that of the first lens element 31 in the same configuration as the optical system 2 of the first embodiment. According to the optical system 2B of the present embodiment, the lens group 30 can be made of glass with high productivity and workability, and can be easily used in various applications.

Also for the optical system 2B of this embodiment as described above, numerical simulations were performed in the same manner as in the first and second embodiments. At this time, as in Examples 1 to 3 of

Embodiments

1 and 2, various materials were used for the filter portion 41 of the opening portion 4 . 18 to 20 show simulation results of the optical system 2B in Examples 1 to 3 of the third embodiment, respectively, similarly to FIGS. 6 to 8. FIG.

FIGS. 21 and 22 show numerical examples of the optical system 2B in Embodiment 3, similarly to Embodiment 1. FIG. Specifically, the surface data D31, the aspheric data D32, and the various data D33 in FIG. 21 each indicate information about the optical system 2B in this embodiment, similarly to the data D11 to D13 in FIG. Also, the surface distance data D34 and the factor data D35 in FIG. 22 respectively show information about the optical system 2B in Examples 1 to 3 of the present embodiment, similarly to the data D14 and D15 in FIG.

As shown in FIGS. 18 to 20, it was confirmed that the optical system 2B of the present embodiment also provided the same effects as those of the first and second embodiments under condition (1).

(Other embodiments)
As described above, Embodiments 1 to 3 have been described as examples of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can also be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. Moreover, it is also possible to combine the constituent elements described in the above embodiments to form a new embodiment. Therefore, other embodiments will be exemplified below.

In Embodiments 1 to 3 above, the optical systems 2 to 2B in which the light branching element 21 transmits the visible light L11 and reflects the far-infrared light L12 are illustrated, but the present disclosure is not limited to this. For example, the optical system 2 of this embodiment may include a light branching element 23 that reflects the visible light L11 and transmits the far-infrared light L12 instead of the light branching element 21 described above. For example, the optical branching element of this embodiment is configured by a bandpass filter in which the wavelength band of the far-infrared light L12 is set in advance to the transmission band. Further, in the optical system 2 of the present embodiment, the far-infrared transmission filter 22 is arranged, for example, on the +Z side of the light branching element. With the optical system 2 of the present embodiment as well, the aperture filter 4 can be used in the same manner as in the above-described embodiments to facilitate the realization of the imaging apparatus 1 capable of both visible imaging and far-infrared imaging.

In each of the above embodiments, an example in which the optical branching element 21 is composed of a bandpass filter has been described. In this embodiment, the optical branching element 21 is not limited to a band-pass filter, and can be configured by various band splitters, for example, a high-pass filter or a low-pass filter. Moreover, in the present embodiment, the optical branching element 21 does not necessarily have to be provided in the optical system 2 .

In each of the above-described embodiments, an example in which the respective portions 40 to 42 of the aperture filter 4 are configured concentrically has been described. In this embodiment, the parts 40 to 42 of the aperture filter 4 do not necessarily have to be concentrically arranged. Moreover, the parts 40 to 42 of the aperture filter 4 may not be formed in a circular shape, but may be formed in an elliptical or polygonal shape, for example.

In each of the above embodiments, an example in which the aperture filter 4 includes the light shielding portion 42 has been described. In this embodiment, the aperture filter 4 does not necessarily have to include the light shielding portion 42 . In the aperture filter 4 of the present embodiment, the light shielding section 42 may be omitted when, for example, the aperture value of the far-infrared light L12 is set to open.

In each of the above embodiments, the optical material that blocks the visible light L11 and transmits the far-infrared light L12 in the filter portion 41 of the aperture filter 4 is exemplified. In the present embodiment, the filter portion 41 of the aperture filter 4 is configured by applying a coating or the like that blocks the visible light L11 to a base material made of an optical material that transmits the visible light L11 and the far-infrared light L12. good too.

In each of the above embodiments, an example in which the far-infrared transmission filter 22 is provided in the optical systems 2 to 2B has been described. In this embodiment, the far-infrared transmission filter 22 may be provided integrally with the far-infrared imaging sensor 12 or the light branching element 21 . The far-infrared transmission filter 22 may be omitted from the optical systems 2-2B.

In each of the above embodiments, an example in which no optical element other than the far-infrared transmission filter 22 is arranged between the light branching element 21 and each of the imaging positions P1 and P2 has been described, but the present disclosure is not limited thereto. . In this embodiment, various optical elements may be arranged between the light branching element 21 and the image forming positions P1 and P2. For example, various wavelength filters, polarizing filters, polarizing plates, and mirrors may be arranged. may Further, in this embodiment, it is not always necessary to exclude lens elements from the optical elements that can be arranged between the light branching element 21 and the image forming positions P1 and P2. can also place lens elements.

In each of the above embodiments, optical systems 2 to 2B including aspherical lens surfaces are illustrated. The optical system of this embodiment may not include an aspherical lens surface, and for example, all of the lens elements included in the lens group 30 may be spherical lenses. Further, the optical system of this embodiment may include a lens element having a free-form surface that is not rotationally symmetrical in the lens group 30 .

As described above, the embodiment has been described as an example of the technology of the present disclosure. To that end, the accompanying drawings and detailed description have been provided.

Therefore, among the components described in the attached drawings and detailed description, there are not only components essential for solving the problem, but also components not essential for solving the problem in order to illustrate the above technology. can also be included. Therefore, it should not be immediately recognized that those non-essential components are essential just because they are described in the attached drawings and detailed description.

In addition, since the above-described embodiment is for illustrating the technology in the present disclosure, various changes, substitutions, additions, omissions, etc. can be made within the scope of claims or equivalents thereof.

The present disclosure is applicable to various applications that combine visible imaging and far-infrared imaging.

Claims

An optical system that forms an image of a first light having a wavelength in the visible range on a first imaging device and forms an image of a second light having a wavelength in the far-infrared region on a second imaging device,
one or more lenses arranged along an optical axis and transmitting the first and second lights, respectively;
an aperture stop provided with an opening through which the optical axis passes;
The aperture stop comprises an optical filter that blocks the first light and transmits the second light around the opening,
satisfying the following formula (1a),
t<2×(4npf)/{(n−1)D} (1a)
here,
t: the thickness of the optical filter in the direction of the optical axis;
n: refractive index of the wavelength of the second light in the optical filter;
p: pixel pitch of the second imaging element;
f: the focal length of the second light in the optical system;
D: Optical system, which is the effective diameter of the optical filter at the aperture stop.
satisfying the following formula (1b),
0.1<t (1b)
The optical system according to claim 1.
satisfying the following formula (1c),
t<(4npf)/{(n−1)D} (1c)
3. The optical system according to claim 1 or 2.
satisfying the following formula (2),
0.2×|fa|>f (2)
here,
fa: any of claims 1 to 3, wherein fa is a synthetic focal length of the second light by a lens group arranged on the expansion side of the first and second lights with respect to the aperture stop in the one or more lenses. 1. The optical system according to item 1.
satisfying the following formulas (3) and (4),
D≤f/2 (3)
Dap≧fvis/4 (4)
here,
Dap: opening diameter of the opening;
The optical system according to any one of claims 1 to 4, wherein fvis is the focal length of the first light in the optical system.
The optical system according to any one of claims 1 to 5, wherein the aperture stop is hollow at the aperture.
The optical system according to any one of claims 1 to 6, wherein the opening and the optical filter are provided concentrically about the optical axis.
arranged between the one or more lenses and the first and second imaging units, and splitting the first and second lights incident from the one or more lenses along the optical axis to 8. The device according to claim 1, further comprising an optical branching element that guides the first light to the first imaging section and guides the second light to the second imaging section. optics.
an optical system according to any one of claims 1 to 8;
a first imaging unit that captures an image formed by the first light and formed via the optical system;
and a second imaging unit that captures an image formed by the second light and formed via the optical system.
an imaging device according to claim 9;
and a control unit that analyzes an image captured by the imaging device.