Lens device, camera device, and filter unit

Abstract

Provided is a lens device, an imaging device, and an optical filter unit that can suppress the generation of ghost images and light spots. A lens device (100) includes, in order from an object side in an optical path, a first optical filter (134A, 134B) and a second optical filter (136A, 136B). The first optical filter (134A, 134B) is composed of an optical filter (e.g., a band-pass filter) having a light transmission band in a specific wavelength region. The second optical filter (136A, 136B) is composed of an optical filter (a band-stop filter) having a light absorption band in a wavelength region different from the light transmission band of the first optical filter.

Description

Technical Field

[0001] This invention relates to a lens device, a camera device, and a filter unit. Background Technology

[0002] Patent document 1 describes a camera device having a polarizing filter and a polarizing image sensor with multiple light-transmitting areas having different polarization and color characteristics.

[0003] Previous technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2014 / 020791 Summary of the Invention

[0006] One embodiment of the present invention provides a lens device, a camera device, and a filter unit capable of suppressing ghosting and light spots.

[0007] means for solving technical problems

[0008] (1) A lens device comprising, in an optical path, sequentially from the object side: a first optical filter having a light-transmitting radio frequency band in a specific wavelength region; and a second optical filter having a light-absorbing frequency band in a wavelength region different from the light-transmitting radio frequency band of the first optical filter.

[0009] (2) The lens device according to (1), wherein,

[0010] The first optical filter is a reflective bandpass filter.

[0011] (3) The lens device according to (1) or (2), wherein,

[0012] The optical path has a frame with multiple openings.

[0013] The lens device has: a first optical filter disposed in at least two openings; and a second optical filter disposed in the opening where the first optical filter is disposed.

[0014] (4) The lens device according to (3), wherein,

[0015] The first optical filter disposed in the opening has a different light transmission radio frequency band than the first optical filter disposed in at least one of the other openings.

[0016] (5) The lens device according to (4), wherein,

[0017] The second optical filter disposed in the opening has a light transmission frequency band and a light absorption frequency band that includes the light absorption frequency band of the first optical filter disposed in at least one of the other openings.

[0018] (6) The lens device according to (4), wherein,

[0019] The frame has at least three openings.

[0020] The lens device includes: a first optical filter disposed in at least three openings; and a second optical filter disposed in the openings where the first optical filter is disposed, wherein the second optical filter disposed in at least one opening has a light absorption band that includes the light transmission frequency band of the first optical filter disposed in the other openings.

[0021] (7) The lens device according to (4), wherein,

[0022] The frame has at least three openings.

[0023] The lens device includes: a first optical filter disposed in at least three openings; and a second optical filter disposed in the opening where the first optical filter is disposed. The second optical filter disposed in at least one opening is configured by combining multiple optical filters with different light absorption frequency bands, and has a light absorption frequency band including the light transmission frequency band of the first optical filter disposed in the other openings.

[0024] (8) The lens device according to any one of (1) to (7), wherein,

[0025] The second optical filter has an absorption rate of 0.8 or higher at the wavelength where the absorption rate reaches its peak.

[0026] (9) The lens device according to any one of (1) to (8), wherein,

[0027] The second optical filter has a transmittance of 0.8 or higher at the wavelength where the transmittance reaches its peak.

[0028] (10) The lens device according to any one of (1) to (9), wherein,

[0029] The second optical filter has a reflectivity of less than 0.1 at the wavelength where reflectivity reaches its peak.

[0030] (11) The lens device according to any one of (1) to (10), wherein,

[0031] The second optical filter has a wavelength width of 20 nm or more at which the absorption rate reaches 50% of the peak value.

[0032] (12) The lens device according to (11), wherein,

[0033] The second optical filter has a wavelength width of 20 nm or more and 200 nm or less at which the absorption rate reaches 50% of the peak value.

[0034] (13) The lens device according to any one of (1) to (12), wherein,

[0035] The second optical filter has a layer containing pigment.

[0036] (14) The lens device according to any one of (1) to (13), wherein,

[0037] The second optical filter has a transmittance of 0.8 or higher at the wavelength corresponding to the wavelength at which the transmittance of the first optical filter reaches its peak.

[0038] (15) The lens device according to any one of (3) to (7), wherein,

[0039] The absorption rate of the second optical filter disposed in the opening is 0.8 or higher at the wavelength corresponding to the wavelength at which the transmittance of the first optical filter disposed in at least one of the other openings reaches its peak.

[0040] (16) The lens device according to (3), (4), (5), (6), (7) or (15), wherein,

[0041] The frame is positioned at or near the pupil position.

[0042] (17) The lens device according to (3), (4), (5), (6), (7), (15) or (16) further comprises:

[0043] A polarizing filter is disposed at the opening where the first optical filter is disposed.

[0044] (18) A camera device comprising: (17) the lens device; and a polarization image sensor for receiving light passing through the lens device.

[0045] (19) A filter unit disposed in the optical path of a lens device.

[0046] The filter unit comprises: a frame having a plurality of openings; a first optical filter disposed in at least two openings having a light transmission frequency band in a specific wavelength region; and a second optical filter disposed in the opening where the first optical filter is disposed, having a light absorption frequency band in a wavelength region different from the light transmission frequency band of the first optical filter.

[0047] (20) The filter unit according to (19), wherein,

[0048] The first optical filter disposed in the opening has a different light transmission radio frequency band than the first optical filter disposed in at least one of the other openings.

[0049] (21) The filter unit according to (19) or (20), wherein,

[0050] The second optical filter disposed in the opening has a light transmission frequency band and a light absorption frequency band that includes the light absorption frequency band of the first optical filter disposed in at least one of the other openings.

[0051] (22) The filter unit according to any one of (19) to (21) further comprises:

[0052] A polarizing filter is disposed at the opening where the first optical filter is disposed. Attached Figure Description

[0053] Figure 1 This is a diagram illustrating an example of a camera lens.

[0054] Figure 2 This is a front view showing the general structure of the filter unit.

[0055] Figure 3 This is a graph showing an example of the absorption characteristics of the first band filter.

[0056] Figure 4 This is a chart illustrating an example of the absorption characteristics of the second band filter.

[0057] Figure 5 This is an illustration of the function of a camera lens.

[0058] Figure 6 This is a front view of the filter unit in a camera lens where the pupil area is divided into three regions.

[0059] Figure 7 yes Figure 6 An exploded perspective view of the filter unit shown.

[0060] Figure 8 This is a graph showing an example of the absorption characteristics of the first band filter.

[0061] Figure 9 This is a chart illustrating an example of the absorption characteristics of the second band filter.

[0062] Figure 10 This is a chart illustrating an example of the absorption characteristics of the third band filter.

[0063] Figure 11 This is an illustration of the function of a camera lens.

[0064] Figure 12 This is another example of the shape of the window in a filter unit.

[0065] Figure 13 This is a chart illustrating an example of the absorption characteristics of a sharp cutoff filter.

[0066] Figure 14 This is a graph showing an example of the absorption rate characteristics of a second optical filter when a bandstop filter and a sharp cutoff filter are combined to form a second optical filter.

[0067] Figure 15 This is a chart illustrating an example of the absorptivity characteristics of the second optical filter.

[0068] Figure 16 This is a chart illustrating an example of the transmittance characteristics of the second optical filter.

[0069] Figure 17 This is another example of a graph showing the transmittance characteristics of the second optical filter.

[0070] Figure 18 This is a chart illustrating an example of the reflectivity characteristics of the second optical filter.

[0071] Figure 19 This is a chart illustrating an example of the transmittance characteristics of a second optical filter used in combination with the first optical filter.

[0072] Figure 20 This is another example of a graph showing the transmittance characteristics of a second optical filter used in combination with the first optical filter.

[0073] Figure 21 This is a graph showing an example of the transmittance characteristics of a bandstop filter used in combination with a bandpass filter in the third window.

[0074] Figure 22 This is a graph showing an example of the transmittance characteristics when a sharp cutoff filter is used as a second optical filter.

[0075] Figure 23 This is an exploded stereoscopic view of the filter unit in the imaging lens of a polarization-mode multispectral camera system.

[0076] Figure 24 This is a diagram showing an example of a polarizing filter included in each window of a filter unit.

[0077] Figure 25 This is a diagram showing the general structure of a multispectral camera system.

[0078] Figure 26This is a diagram illustrating an example of the configuration of pixels and polarizers in a polarization image sensor.

[0079] Figure 27 This is a diagram illustrating an example of the hardware structure of a signal processing device.

[0080] Figure 28 It is a block diagram of the main functions of a signal processing device. Detailed Implementation

[0081] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0082] [Camera Lens]

[0083] The invention will be explained using the application of this invention to imaging lenses, particularly pupil-segmented imaging lenses, as an example. A pupil-segmented imaging lens is a lens in which the pupil region is divided into multiple regions. Pupil-segmented imaging lenses are used, for example, in multispectral camera systems. Multispectral camera systems will be described later.

[0084] [structure]

[0085] Figure 1 This is a diagram illustrating an example of a camera lens.

[0086] The imaging lens 100 in this embodiment is a pupil-segmented imaging lens in which the pupil area is divided into two regions. The imaging lens 100 is an example of a lens device.

[0087] like Figure 1 As shown, the camera lens 100 includes a lens barrel 110, multiple lens groups 120A and 120B, and a filter unit 130.

[0088] The lens barrel 110 has a cylindrical shape. Lens groups 120A and 120B and filter unit 130 are disposed in predetermined positions within the lens barrel 110.

[0089] Lens groups 120A and 120B each consist of at least one lens. Figure 1 For simplicity, only two lens groups 120A and 120B are shown in the diagram. Hereinafter, as needed, the lens group 120A, located on the front side of the filter unit 130, will be designated as the first lens group, and the lens group 120B, located on the rear side of the filter unit 130, will be designated as the second lens group to distinguish between the two lens groups 120A and 120B. Furthermore, "front side" refers to the "object side," and "rear side" refers to the "image side."

[0090] The filter unit 130 is disposed in the optical path. More specifically, the filter unit 130 is disposed at or near the pupil position in the imaging lens 100. Furthermore, "near the pupil position" refers to the area that satisfies the following formula.

[0091] |d|<φ / (2tanθ)

[0092] θ: The maximum principal ray angle at the pupil position (the principal ray angle is the angle with respect to the optical axis).

[0093] φ: Pupil diameter

[0094] |d|: Distance from the pupil

[0095] Figure 2 This is a front view showing the general structure of the filter unit.

[0096] The filter unit 130 consists of a filter frame 132 and an optical filter held in the filter frame 132.

[0097] The filter frame 132 has a plate-like shape corresponding to the inner circumferential shape of the lens barrel 110, and has multiple windows. For example... Figure 2 As shown, the filter frame 132 of this embodiment has a disc-shaped form and two windows 132A and 132B. The filter frame 132 is an example of a frame.

[0098] Two windows 132A and 132B are formed by circular openings and are symmetrically arranged around the optical axis Z. Windows 132A and 132B are examples of openings. Hereinafter, as needed, window 132A will be designated as the first window 132A and window 132B as the second window 132B to distinguish between the two windows 132A and 132B.

[0099] The camera lens 100 is positioned at or near the pupil position via a filter frame 132, and the pupil region is divided into multiple regions. That is, the optical path is divided into multiple segments. In this embodiment, the pupil region is divided into two regions. That is, the optical path is divided into two segments.

[0100] In each window 132A and 132B, band-pass filters (BPF) 134A and 134B and band-stop filters (BSF) 136A and 136B are arranged sequentially from the object side (front side) along the optical axis Z.

[0101] Hereinafter, as needed, the bandpass filter 134A disposed in the first window 132A is designated as the first bandpass filter 134A, and the bandpass filter 134B disposed in the second window 132B is designated as the second bandpass filter 134B to distinguish the bandpass filters 134A and 134B disposed in each window 132A and 132B. Furthermore, the bandstop filter 136A disposed in the first window 132A is designated as the first bandstop filter 136A, and the bandstop filter 136B disposed in the second window 132B is designated as the second bandstop filter 136B to distinguish the bandstop filters 136A and 136B disposed in each window 132A and 132B.

[0102] A bandpass filter is an optical filter that allows light of a specific wavelength range to pass through efficiently while effectively blocking other light, allowing only light of that specific wavelength range to pass through. The bandpass filters 134A and 134B disposed in the windows 132A and 132B have different light transmission frequency bands. The light transmission frequency band of the first bandpass filter 134A is designated as the first light transmission frequency band Λ1. Furthermore, the light transmission frequency band of the second bandpass filter 134B is designated as the second light transmission frequency band Λ2 (Λ1≠Λ2). In this embodiment, the second light transmission frequency band Λ2 is set on the longer wavelength side than the first light transmission frequency band Λ1. The bandpass filters 134A and 134B are examples of the first optical filter.

[0103] Bandpass filters include reflective and absorptive types. Reflective filters reflect a specific frequency band while transmitting other frequency bands. Absorbent filters, on the other hand, absorb a specific frequency band while transmitting other frequency bands. Reflective bandpass filters offer the advantage of achieving a narrow transmission frequency band and a rapid shift from the transmission band to the transmission blocking band. Therefore, when the imaging lens 100 is used in a multispectral camera, a reflective bandpass filter is preferred. In the imaging lens 100 of this embodiment, a reflective bandpass filter is used.

[0104] A band-stop filter is an optical filter that attenuates light in a specific wavelength region (stopband) to a very low level, allowing most other wavelengths of light to pass through with minimal intensity loss. Therefore, a band-stop filter has properties completely opposite to a band-pass filter. Band-stop filters are also called band-rejection filters (BRF), band elimination filters (BEF), and stepped filters. Band-stop filters 136A and 136B are examples of second optical filters.

[0105] In this embodiment, an absorption-type bandstop filter is used as the bandstop filter. An absorption-type bandstop filter has an absorption band in a specific wavelength region, and it blocks the transmission of light in the absorption band by absorbing it.

[0106] Bandstop filters, for example, are optical filters comprising a layer of pigment material on a transparent substrate that absorbs light in a specific wavelength range. By using the pigment material, the desired transmittance, absorptance, and reflectance characteristics can be obtained. Furthermore, bandstop filters based on pigment materials are easily stacked due to their thin-film nature, and by combining multiple pigment materials, the desired transmittance, absorptance, and reflectance characteristics can be obtained.

[0107] The first band filter 136A and the second band filter 136B have the following absorption rate characteristics.

[0108] Figure 3 This is a graph showing an example of the absorption characteristics of the first band filter.

[0109] In this figure, the solid line graph represented by the symbol BSF1 shows the absorption characteristics of the first band-blocking filter 136A.

[0110] Additionally, in this figure, the dashed graph represented by the symbol BPF1 indicates the transmittance characteristics of the first bandpass filter 134A. Furthermore, the dashed graph represented by the symbol BPF2 indicates the transmittance characteristics of the second bandpass filter 134B.

[0111] like Figure 3 As shown, the first band-block filter 136A has the characteristic of allowing light to pass through, said light being light in the wavelength region (first light transmission radio frequency band Λ1) that is allowed to pass through at least the first band-pass filter 134A. On the other hand, it has the characteristic of absorbing light in the wavelength region (second light transmission radio frequency band Λ2) that is allowed to pass through at least the second band-pass filter 134B.

[0112] Figure 4 This is a chart illustrating an example of the absorption characteristics of the second band filter.

[0113] In this figure, the solid line graph represented by the symbol BSF2 shows the absorption characteristics of the second band-blocking filter 136B.

[0114] Additionally, in this figure, the dashed graph represented by the symbol BPF1 indicates the transmittance characteristics of the first bandpass filter 134A. Furthermore, the dashed graph represented by the symbol BPF2 indicates the transmittance characteristics of the second bandpass filter 134B.

[0115] like Figure 4 As shown, the second band-stop filter 136B has the characteristic of allowing light to pass through, said light being light in the wavelength region (second light transmission radio frequency band Λ2) that is allowed to pass through at least the second band-pass filter 134B. On the other hand, it has the characteristic of absorbing light in the wavelength region (first light transmission radio frequency band Λ1) that is allowed to pass through at least the first band-pass filter 134A.

[0116] Thus, the bandstop filters disposed in each window have the characteristic of allowing light to pass through, said light being light in the wavelength region allowed to be transmitted by bandpass filters disposed in at least the same window. On the other hand, light in the wavelength region allowed to be transmitted by bandpass filters disposed in at least one of the other windows has the characteristic of absorption.

[0117] Therefore, the bandstop filter located in each window has an absorption band in a wavelength region different from the light transmission frequency band of the bandpass filter located in the same window. For example, as Figure 3 As shown, the first bandblock filter 136A has an optical absorption band in a wavelength region different from the first light transmission radio frequency band Λ1. Furthermore, as... Figure 4 As shown, the second bandblock filter 136B has an optical absorption band in a wavelength region different from the second light transmission radio frequency band Λ2.

[0118] Furthermore, the bandstop filter disposed in each window has a light absorption band that includes the light transmission frequency band of the bandpass filter disposed in at least one of the other windows. For example, such as Figure 3 As shown, the first bandblock filter 136A has a light absorption band including the second light transmission radio frequency band Λ2. Furthermore, as... Figure 4 As shown, the second bandblock filter 136B has an optical absorption band that includes the first light transmission radio frequency band Λ1.

[0119] [effect]

[0120] Next, the function of the camera lens 100 configured as described above in this embodiment will be explained.

[0121] First, for comparison, we will explain the effect when only bandpass filters are installed in each window. That is, we will explain the effect when there are no bandstop filters.

[0122] In a pupil-segmented imaging lens such as the imaging lens 100 of this embodiment, the light paths that are divided into pupil regions are re-converged on the image sensor.

[0123] Light passing through the first window 132A reaches the image sensor after being confined to wavelength region Λ1 by the first bandpass filter 134A. However, a portion of the light is reflected by a lens (second lens group 120B) located further back than the first bandpass filter 134A and the image sensor. Furthermore, a portion of the reflected light enters the second window 132B. The light entering the second window 132B is reflected again by the second bandpass filter 134B located within the second window 132B before reaching the image sensor. The wavelength region Λ1 of the light reflected by the second bandpass filter 134B differs from the light transmission frequency band (second light transmission frequency band Λ2) of the second bandpass filter 134B. Therefore, almost 100% is reflected. As a result, strong ghosting and light spots are produced.

[0124] The same applies to the light passing through the second window 132B. The light passing through the second window 132B reaches the image sensor after being confined to the wavelength region Λ2 by the second bandpass filter 134B. However, a portion of the light is reflected by the lens (second lens group 120B) located further back than the second bandpass filter 134B and the image sensor. Furthermore, a portion of the reflected light is incident on the first window 132A. The light incident on the first window 132A is reflected again by the first bandpass filter 134A located within the first window 132A before reaching the image sensor. The wavelength region Λ2 of the light reflected by the first bandpass filter 134A differs from the light transmission frequency band (first light transmission frequency band Λ1) of the first bandpass filter 134A. Therefore, almost 100% is reflected. As a result, strong ghosting and light spots are produced.

[0125] Thus, in a structure where each window is equipped with only a bandpass filter, light passing through one window is incident on other windows and reflected again, thereby producing strong ghosting and light spots.

[0126] Anti-reflective coatings are commonly used to reduce ghosting and light spots. However, anti-reflective coatings reduce reflectivity by increasing transmittance. Therefore, for example, if an anti-reflective coating is applied to the second bandpass filter 134B with wavelength region Λ1, light in wavelength region Λ1 will be transmitted. As a result, the light transmission frequency band of the second bandpass filter 134B causes it to transmit light in both wavelength regions Λ1 and Λ2, failing to achieve the desired transmittance characteristics (that only transmit wavelength region Λ1).

[0127] Next, the function of the camera lens 100 in this embodiment will be explained.

[0128] Figure 5 This is an illustration of the function of a camera lens.

[0129] Regarding the light incident on the camera lens 100, the optical path is divided into three by the filter unit 130, and reaches the image sensor (not shown) through the first window 132A and the second window 132B.

[0130] Light incident on the first window 132A first passes through the first bandpass filter 134A. Passing through the first bandpass filter 134A, it is confined to the wavelength region Λ1. Next, it passes through the first bandstop filter 136A. The first bandstop filter 136A absorbs light in the wavelength region Λ2 but allows light in the wavelength region Λ1 to pass through. Thus, light in the wavelength region Λ1 that passed through the first bandpass filter 134A directly passes through the first bandstop filter 136A.

[0131] Similarly, light incident on the second window 132B first passes through the second bandpass filter 134B. Passing through the second bandpass filter 134B, it is confined to the wavelength region Λ2. Next, it passes through the second bandstop filter 136B. The second bandstop filter 136B absorbs light in the wavelength region Λ1 but allows light in the wavelength region Λ2 to pass through. Thus, light in the wavelength region Λ2 that passed through the second bandpass filter 134B directly passes through the second bandstop filter 136B.

[0132] As light passing through the first window 132A and the second window 132B reaches the image sensor, a portion is reflected by lenses (second lens group 120B), etc. Furthermore, a portion of the light reaching the image sensor is reflected by the image sensor.

[0133] Light in wavelength region Λ1, reflected by the lens and image sensor, etc., also enters the second window 132B through the first window 132A. However, a second bandpass filter 136B is disposed in the second window 132B. As described above, the second bandpass filter 136B allows light in wavelength region Λ2 to pass through, but absorbs light in wavelength region Λ1. Therefore, even if light in wavelength region Λ1, reflected by the lens and image sensor, etc., enters the second window 132B, it is absorbed before reaching the second bandpass filter 134B. Thus, it is possible to suppress the re-reflection of light in wavelength region Λ1, reflected by the lens and image sensor, etc., by the second bandpass filter 134B.

[0134] The same applies when light in wavelength region Λ2 passing through the second window 132B is reflected by the lens and image sensor, and then incident on the first window 132A. Before reaching the first bandpass filter 134A, it is absorbed by the first bandstop filter 136A disposed in the first window 132A, thus suppressing the re-reflection of the first bandpass filter 134A.

[0135] Thus, according to the camera lens 100 of this embodiment, even if light passing through one window is reflected by the lens and image sensor and incident on other windows, it can be absorbed by the band-stop filters 136A and 136B provided in each window. As a result, the re-reflection of the band-pass filters 134A and 134B can be suppressed, and the generation of ghosting and light spots can be suppressed.

[0136] [Examples of camera lens modifications]

[0137] (1) Number of segments in the pupil region

[0138] In the above embodiments, the case where the pupil region is divided into two regions was described as an example, but the number of pupil region divisions is not limited to this. It is preferable to set it appropriately according to the application, etc. Hereinafter, as an example, a camera lens in which the pupil region is divided into three regions will be described.

[0139] Compared to the imaging lens 100 of the above embodiment where the pupil region is divided into two regions, the structure of the filter unit differs in the imaging lens where the pupil region is divided into three regions. Therefore, only the structure of the filter unit will be described here.

[0140] Figure 6 This is a front view of the filter unit within a camera lens whose pupil area is divided into three regions. Furthermore, Figure 7 yes Figure 6 An exploded perspective view of the filter unit shown.

[0141] like Figure 6 and Figure 7 As shown, in the filter unit 140 of this example, three windows 142A, 142B, and 142C are provided in the filter frame 142. Each window 142A, 142B, and 142C is arranged at a predetermined interval on a concentric circle centered on the optical axis. Hereinafter, as needed, window 142A is designated as the first window 142A, window 142B as the second window 142B, and window 142C as the third window 142C to distinguish the three windows 142A, 142B, and 142C. The imaging lens 100 is positioned at or near the pupil position through the filter frame 142, dividing the pupil region into three regions. That is, the optical path is divided into three parts.

[0142] Bandpass filters 144A, 144B, and 144C and bandstop filters 146A, 146B, and 146C are provided in each window 142A, 142B, and 142C. In the filter unit 140 of this example, bandpass filters 144A, 144B, and 144C and bandstop filters 146A, 146B, and 146C are arranged sequentially along the optical axis Z from the object side (front side).

[0143] Hereinafter, as needed, the bandpass filter 144A configured in the first window 142A is designated as the first bandpass filter 144A, the bandpass filter 144B configured in the second window 142B is designated as the second bandpass filter 144B, and the bandpass filter 144C configured in the third window 142C is designated as the third bandpass filter 144C to distinguish the bandpass filters 144A, 144B, and 144C configured in each window 142A, 142B, and 142C. Furthermore, the band-stop filter 146A disposed in the first window 142A is designated as the first band-stop filter 146A, the band-stop filter 146B disposed in the second window 142B is designated as the second band-stop filter 146B, and the band-stop filter 146C disposed in the third window 142C is designated as the third band-stop filter 146C, so as to distinguish the band-stop filters 146A, 146B, and 146C disposed in each window 142A, 142B, and 142C.

[0144] The bandpass filters 144A, 144B, and 144C configured in each of the windows 142A, 142B, and 142C have different light transmission radio frequency bands. The light transmission radio frequency band of the first bandpass filter 144A is designated as the first light transmission radio frequency band Λ1. The light transmission radio frequency band of the second bandpass filter 144B is designated as the second light transmission radio frequency band Λ2 (Λ1≠Λ2). The light transmission radio frequency band of the third bandpass filter 144C is designated as the third light transmission radio frequency band Λ3 (Λ1≠Λ3, Λ2≠Λ3). In this example, the third light transmission radio frequency band Λ3 is set on a longer wavelength side than the second light transmission radio frequency band Λ2. The second light transmission radio frequency band Λ2 is set on a longer wavelength side than the first light transmission radio frequency band Λ1. Furthermore, reflective bandpass filters are used in bandpass filters 144A, 144B, and 144C.

[0145] Absorption-type bandstop filters are used in bandstop filters 146A, 146B, and 146C. The bandstop filters 146A, 146B, and 146C disposed in each window 142A, 142B, and 142C have the following absorption characteristics.

[0146] Figure 8 This is a graph showing an example of the absorption characteristics of the first band filter.

[0147] In this figure, the solid line graph represented by the symbol BSF1 shows the absorption characteristics of the first band-blocking filter 146A.

[0148] Furthermore, in this figure, the dashed graph represented by symbol BPF1 shows the transmittance characteristics of the first bandpass filter 144A. The dashed graph represented by symbol BPF2 shows the transmittance characteristics of the second bandpass filter 144B. And the dashed graph represented by symbol BPF3 shows the transmittance characteristics of the third bandpass filter 144C.

[0149] like Figure 8 As shown, the first band-stop filter 146A has the characteristic of allowing light to pass through, said light being light in the wavelength region (first light-transmitting radio frequency band Λ1) that is allowed to pass through at least the first band-pass filter 144A. On the other hand, it has the characteristic of absorbing light in the wavelength region (second light-transmitting radio frequency band Λ2) that is allowed to pass through at least the second band-pass filter 144B, and light in the wavelength region (third light-transmitting radio frequency band Λ3) that is allowed to pass through the third band-pass filter 144C.

[0150] Regarding the first bandpass filter 146A, it can be implemented, for example, using a single pigment material. That is, the wavelength region transmitted by the first bandpass filter 136A (the first light-transmitting radio frequency band Λ1) is not between the two wavelength regions absorbed by the first bandpass filter 136A (the second light-transmitting radio frequency band Λ2 and the third light-transmitting radio frequency band Λ3), therefore it can be constructed using a single pigment material. Specifically, a pigment material that absorbs light from the second light-transmitting radio frequency band Λ2 and the third light-transmitting radio frequency band Λ3 is used.

[0151] Figure 9 This is a chart illustrating an example of the absorption characteristics of the second band filter.

[0152] In this figure, the solid line graph represented by the symbol BSF2 shows the absorption characteristics of the second band-blocking filter 146B.

[0153] Furthermore, in this figure, the dashed graph represented by symbol BPF1 shows the transmittance characteristics of the first bandpass filter 144A. The dashed graph represented by symbol BPF2 shows the transmittance characteristics of the second bandpass filter 144B. And the dashed graph represented by symbol BPF3 shows the transmittance characteristics of the third bandpass filter 144C.

[0154] like Figure 9 As shown, the second band-stop filter 146B has the characteristic of allowing light to pass through, said light being light in the wavelength region (second light-transmitting radio frequency band Λ2) that is allowed to be transmitted by at least the second band-pass filter 144B. On the other hand, it has the characteristic of absorbing light in the wavelength region (first light-transmitting radio frequency band Λ1) that is allowed to be transmitted by at least the first band-pass filter 144A, and light in the wavelength region (third light-transmitting radio frequency band Λ3) that is allowed to be transmitted by the third band-pass filter 144C.

[0155] The second bandstop filter 146B is configured, for example, by combining two bandstop filters. Specifically, a bandstop filter that absorbs light in the wavelength region (first light-transmitting radio frequency band Λ1) allowed to be transmitted by the first bandpass filter 144A (the second bandstop filter of the first bandpass filter) and a bandstop filter that absorbs light in the wavelength region (third light-transmitting radio frequency band Λ3) allowed to be transmitted by the third bandpass filter 144C (the second bandstop filter of the second bandpass filter) are combined to achieve a bandstop filter with the desired absorptivity characteristics as a whole. In this case, for example, the second bandstop filter of the first bandpass filter is configured using a pigment material that absorbs light in the first light-transmitting radio frequency band Λ1. And the second bandstop filter of the second bandpass filter is configured using a pigment material that absorbs light in the third light-transmitting radio frequency band Λ3. Figure 9 In the diagram, the solid line graph represented by the symbol BSF21 shows the absorptivity characteristics of the first second bandblock filter. Furthermore, the solid line graph represented by the symbol BSF22 shows the absorptivity characteristics of the second second bandblock filter.

[0156] Figure 10 This is a chart illustrating an example of the absorption characteristics of the third band filter.

[0157] In this figure, the solid line graph represented by the symbol BSF3 shows the absorption characteristics of the third band-blocking filter 146C.

[0158] Furthermore, in this figure, the dashed graph represented by symbol BPF1 shows the transmittance characteristics of the first bandpass filter 144A. The dashed graph represented by symbol BPF2 shows the transmittance characteristics of the second bandpass filter 144B. And the dashed graph represented by symbol BPF3 shows the transmittance characteristics of the third bandpass filter 144C.

[0159] like Figure 10 As shown, the third bandstop filter 146C has the characteristic of allowing light to pass through the wavelength region (third light-transmitting radio frequency band Λ3) that is transmitted by at least the third bandpass filter 144C. On the other hand, it has the characteristic of absorbing light in the wavelength region (first light-transmitting radio frequency band Λ1) that is allowed to pass through by at least the first bandpass filter 144A, and light in the wavelength region (second light-transmitting radio frequency band Λ2) that is allowed to pass through by the second bandpass filter 144B.

[0160] Regarding the third bandblock filter 146C, it can also be made of a single pigment material. That is, by using a pigment material that absorbs light from the first light-transmitting radio frequency band Λ1 and the second light-transmitting radio frequency band Λ2, it can be made of a single pigment material.

[0161] As described above, the bandstop filter disposed in each window has the characteristic of allowing light in the wavelength range transmitted by the bandpass filter disposed in at least the same window to pass through. On the other hand, the bandpass filter disposed in at least one of the other windows allows light in the wavelength range transmitted to have absorption characteristics. Thus, as Figure 8 As shown, the first bandblock filter 146A has an optical absorption band in a wavelength region different from the first light-transmitting radio frequency band Λ1, and on the other hand, it has an optical absorption band in a wavelength region including the second light-transmitting radio frequency band Λ2 and the third light-transmitting radio frequency band Λ3. Furthermore, as... Figure 9 As shown, the second bandblock filter 146B has an optical absorption band in a wavelength region different from the second light-transmitting radio frequency band Λ2, and on the other hand, it has an optical absorption band in a wavelength region including the first light-transmitting radio frequency band Λ1 and the third light-transmitting radio frequency band Λ3. Furthermore, as... Figure 10 As shown, the third bandblock filter 146C has an optical absorption band in a wavelength region different from the third optical transmission radio frequency band Λ3, and on the other hand, it has an optical absorption band in a wavelength region that includes the first optical transmission radio frequency band Λ1 and the second optical transmission radio frequency band Λ2.

[0162] Figure 11 This is an illustration of the function of a camera lens.

[0163] Light incident on the camera lens 100 passes through the filter unit 140, through the first window 142A, the second window 142B, and the third window 142C, and reaches the image sensor (not shown).

[0164] Light incident on the first window 142A first passes through the first bandpass filter 144A. Passing through the first bandpass filter 144A, it is confined to the wavelength region Λ1. Next, it passes through the first bandstop filter 146A. The first bandstop filter 146A absorbs light in wavelength regions Λ2 and Λ3, but allows light in wavelength region Λ1 to pass through. Therefore, light in wavelength region Λ1 that has passed through the first bandpass filter 144A directly passes through the first bandstop filter 146A.

[0165] Light incident on the second window 142B first passes through the second bandpass filter 144B. Passing through the second bandpass filter 144B, it is confined to the wavelength region Λ2. Next, it passes through the second bandstop filter 146B. The second bandstop filter 146B absorbs light in wavelength regions Λ1 and Λ3, but allows light in wavelength region Λ2 to pass through. Therefore, light in wavelength region Λ2 that has passed through the second bandpass filter 144B directly passes through the second bandstop filter 146B.

[0166] Light incident on the third window 142C first passes through the third bandpass filter 144C. Passing through the third bandpass filter 144C, it is confined to the wavelength region Λ3. Next, it passes through the third bandstop filter 146C. The third bandstop filter 146C absorbs light in wavelength regions Λ1 and Λ2, but allows light in wavelength region Λ3 to pass through. Therefore, light in wavelength region Λ3 that has passed through the third bandpass filter 144C directly passes through the third bandstop filter 146C.

[0167] As light passing through the first window 142A, the second window 142B, and the third window 142C reaches the image sensor, a portion of it is reflected by lenses (second lens group 120B), etc. Furthermore, a portion of the light reaching the image sensor is reflected by the image sensor.

[0168] Light in wavelength region Λ1, reflected by the lens and image sensor, etc., also enters the second window 142B and the third window 142C through the first window 142A. However, a second band-block filter 146B and a third band-block filter 146C are respectively disposed in the second window 142B and the third window 142C. As described above, the second band-block filter 146B disposed in the second window 142B allows light in wavelength region Λ2 to pass through, but absorbs light in wavelength regions Λ1 and Λ3. Therefore, even if light in wavelength region Λ1, reflected by the lens and image sensor, etc., enters the second window 142B, it is absorbed before reaching the second band-pass filter 144B. Therefore, it is possible to suppress the re-reflection of light in wavelength region Λ1, reflected by the lens and image sensor, etc., by the second band-pass filter 144B. Furthermore, the third band-stop filter 146C, disposed in the third window 142C, allows light in wavelength region Λ3 to pass through, but absorbs light in wavelength regions Λ1 and Λ2. Therefore, even if reflected light, i.e., light in wavelength region Λ1, is incident on the third window 142C, it is absorbed before reaching the third band-pass filter 144C. Thus, it is possible to suppress the reflection of reflected light and light in wavelength region Λ1 by the third band-pass filter 144C.

[0169] The same applies when light of wavelength region Λ2 passing through the second window 142B is reflected by the lens and image sensor, and then incident on the first window 142A and the third window 142C. When the reflected light and light of wavelength region Λ2 are incident on the first window 142A, they are absorbed by the first band-stop filter 146A before reaching the first band-pass filter 144A. Therefore, it is possible to suppress the light of wavelength region Λ2 from being reflected again by the first band-pass filter 144A. Furthermore, when light of wavelength region Λ2 is incident on the third window 142C, it is absorbed by the third band-stop filter 146C before reaching the third band-pass filter 144C. Therefore, it is possible to suppress the light of wavelength region Λ2 from being reflected again by the third band-pass filter 144C.

[0170] The same applies when light of wavelength region Λ3 passing through the third window 142C is reflected by the lens and image sensor, and then incident on the first window 142A and the second window 142B. When the reflected light and light of wavelength region Λ3 are incident on the first window 142A, they are absorbed by the first band-stop filter 146A before reaching the first band-pass filter 144A. This prevents light of wavelength region Λ3 from being reflected again by the first band-pass filter 144A. Similarly, when light of wavelength region Λ3 is incident on the second window 142B, it is absorbed by the second band-stop filter 146B before reaching the second band-pass filter 144B. Therefore, it prevents light of wavelength region Λ3 from being reflected again by the second band-pass filter 144B.

[0171] Thus, according to the camera lens 100 of this embodiment, even if light passing through one window is reflected by the lens and image sensor and incident on other windows, it can be absorbed by the band-stop filters 146A and 146B provided in each window. As a result, the re-reflection of the band-pass filters 144A and 144B can be suppressed, and the generation of ghosting and light spots can be suppressed.

[0172] (2) Shape of the window

[0173] In the above embodiments, the shape (opening shape) of the window portion in the filter unit is set to a circular shape, but the shape of the window portion is not limited to this.

[0174] Figure 12 This is another example of the shape of the window in a filter unit.

[0175] In this figure, the disc-shaped filter frame 142 is divided into three equal parts along the circumference to form windows 142A, 142B, and 142C with fan-shaped openings. Each window 142A, 142B, and 142C is equipped with a fan-shaped bandpass filter and a bandstop filter.

[0176] (3) Structure of bandpass filter and bandstop filter

[0177] The functions of a bandpass filter and a bandstop filter can also be achieved with a single optical filter. For example, a layer or film with the function of a bandpass filter can be provided on one side of a transparent substrate, and a layer or film with the function of a bandstop filter can be provided on the other side. Thus, an optical filter that has the functions of a bandpass filter and a bandstop filter can be achieved with a single piece.

[0178] Furthermore, when the bandpass filter and bandstop filter are composed of different optical filters, the two optical filters are preferably arranged without an air layer. In this case, for example, the optical filters can be joined by optical contact and arranged in an integrated manner.

[0179] (4) Filter unit

[0180] The filter unit can be detachable from the lens barrel. This allows for the replacement of the filter unit.

[0181] Furthermore, the structure allows for the individual replacement of optical filters installed in each window. This enables free selection of the number and combination of wavelengths used for beam splitting. Additionally, it is not necessary to use all windows. For example, in a filter unit with four windows in the filter frame, when capturing an image split into three wavelengths, one window can be used to block light.

[0182] (5) Second optical filter

[0183] In the above embodiment, an example was given using a bandstop filter with a limited width in the light absorption band as the second optical filter; however, the optical filter used as the second optical filter is not limited to this. Furthermore, for example, optical filters that absorb light above or below a specific wavelength while allowing light in other wavelength regions to pass through can also be used. A sharp cut-off filter (SCF) can be exemplified as such an optical filter. Sharp cut-off filters are also called long-pass filters, etc.

[0184] Figure 13 This is a chart illustrating an example of the absorption characteristics of a sharp cutoff filter.

[0185] The diagram shows... Figure 6 An example of the absorptivity characteristics of the sharp-cutoff filter disposed in the first window of the filter unit shown (a filter unit having three windows) is presented. That is, an example of the absorptivity characteristics of the sharp-cutoff filter used in conjunction with the first bandpass filter 144A is shown.

[0186] In this figure, the solid line graph represented by the symbol SCF1 represents the absorption characteristics of the sharp cutoff filter.

[0187] Furthermore, in this figure, the dashed graph represented by symbol BPF1 shows the transmittance characteristics of the first bandpass filter 144A. The dashed graph represented by symbol BPF2 shows the transmittance characteristics of the second bandpass filter 144B. And the dashed graph represented by symbol BPF3 shows the transmittance characteristics of the third bandpass filter 144C.

[0188] like Figure 13As shown, the sharp cutoff filter in this example has the following characteristics: it sets the wavelength range (first transmittance RF band Λ1) between the first bandpass filter 144A and the second bandpass filter 144B (second transmittance RF band Λ2) as the boundary, absorbing light from the longer wavelength side. Therefore, it can transmit light from the wavelength range (first transmittance RF band Λ1) allowed by the first bandpass filter 144A, and absorb light from the wavelength range (second transmittance RF band Λ2) allowed by the second bandpass filter 144B and the wavelength range (third transmittance RF band Λ3) allowed by the third bandpass filter 144C.

[0189] Figure 14 This is a graph showing an example of the absorption rate characteristics of a second optical filter when a bandstop filter and a sharp cutoff filter are combined to form a second optical filter.

[0190] The diagram shows... Figure 6 An example of the absorptivity characteristics of the second optical filter disposed in the first window of the filter unit shown.

[0191] In this figure, the dashed graph represented by symbol BPF1 shows the transmittance characteristics of the first bandpass filter 144A. The dashed graph represented by symbol BPF2 shows the transmittance characteristics of the second bandpass filter 144B. And the dashed graph represented by symbol BPF3 shows the transmittance characteristics of the third bandpass filter 144C.

[0192] In this example, a second optical filter with the desired absorptivity characteristics can be achieved by combining a bandstop filter that absorbs light in the wavelength region (second light-transmitting radio frequency band Λ2) allowed to be transmitted by at least the second bandpass filter 144B and allows light in other wavelength regions to be transmitted, and a sharp cutoff filter that absorbs light in the wavelength region (third light-transmitting radio frequency band Λ3) allowed to be transmitted by at least the third bandpass filter 144C and allows light in other wavelength regions to be transmitted.

[0193] exist Figure 14 In the diagram, the solid line graph, denoted by the symbol BSF11, represents the absorptivity characteristics of the bandstop filter. The bandstop filter has a finite optical absorption bandwidth in the wavelength region encompassing the second transmission frequency band Λ2.

[0194] Furthermore, in Figure 14 In the diagram, the solid line graph represented by the symbol SCF12 shows the absorptivity characteristics of the sharp cutoff filter. The sharp cutoff filter has the characteristic of absorbing light on the long wavelength side by setting the wavelength set on the short wavelength side, which is shorter than the third light transmission radio frequency band Λ3.

[0195] Thus, by combining a band-stop filter and a sharp-cutoff filter, a second optical filter with the desired absorption characteristics can also be achieved.

[0196] In addition, this example illustrates the case of combining a bandstop filter and a sharp cutoff filter to achieve a second optical filter with the desired absorptivity characteristics, but it is also possible to combine two sharp cutoff filters to achieve a second optical filter with the desired absorptivity characteristics.

[0197] [Optical characteristics of the second optical filter]

[0198] The preferred optical characteristics that the second optical filter should have are described.

[0199] (1) Absorption characteristics of the second optical filter

[0200] Figure 15 This is a chart illustrating an example of the absorptivity characteristics of the second optical filter.

[0201] This figure illustrates an example of preferred absorptivity characteristics when using a bandstop filter with a limited optical absorption bandwidth as a second optical filter.

[0202] In the so-called visible to near-infrared region (400-1000 nm), the wavelength at which the absorption rate reaches its peak (peak absorption wavelength) is set as λabs, and the absorption rate in the peak absorption wavelength λabs is set as αmax.

[0203] The second optical filter is preferably an absorbance αmax of 0.8 or higher (αmax≥0.8) at the peak absorbance wavelength λabs.

[0204] In an optical filter, if the absorptivity is α, the transmittance is τ, and the reflectivity is ρ, then the relationship α + τ + ρ = 1 holds. When a wavelength near the peak absorptivity wavelength λabs is incident on the second optical filter, the unabsorbed light is divided into transmitted and reflected light. However, if there is a reflective component behind the direction of light travel, the transmitted component will also be reflected. By ensuring an absorptivity α above a specified value, the reflected component of light, which also includes the reflected component accompanying transmission, can be reduced.

[0205] Figure 15 This is an example of a band-block filter, but the same applies to the case where a sharp cut-off filter is used as the second optical filter, preferably with an absorptivity αmax of 0.8 or higher at the peak absorptivity wavelength λabs.

[0206] Furthermore, when using a bandstop filter with a limited width in the optical absorption band as the second optical filter, it is preferable to further satisfy the following condition: That is, if the width of the wavelength at which the absorptivity αmax reaches 50% (αmax / 2) at the peak absorptivity wavelength λabs is defined as δλabs, then its width δλabs is preferably 20 nm or more and 200 nm or less (20 [nm] ≤ δλabs ≤ 200 [nm]). The width of the wavelength at which the absorptivity reaches 50% (half-value) at the peak absorptivity wavelength refers to the bandwidth between the long wavelength side and the short wavelength side of the value at which the absorptivity reaches 50% of the peak value (so-called full width at half maximum).

[0207] If the absorption wavelength range is too narrow, the desired wavelength cannot be fully absorbed, resulting in insufficient suppression of ghosting and light spots. On the other hand, if the absorption wavelength range is too wide, the wavelength intended for use will be absorbed, leading to a decrease in brightness. Therefore, when using a bandstop filter as a second optical filter, its full width at half maximum (δλabs) is preferably 20 nm or more and 200 nm or less.

[0208] (2) Transmittance characteristics of the second optical filter

[0209] Figure 16 This is a chart illustrating an example of the transmittance characteristics of the second optical filter.

[0210] This figure illustrates an example of preferred transmittance characteristics when using a bandstop filter with a limited optical absorption bandwidth as a second optical filter.

[0211] In the so-called visible to near-infrared region (400-1000 nm), the wavelength at which the transmittance reaches its peak (transmittance peak wavelength) is set as λtra, and the transmittance in the transmittance peak wavelength λtra is set as τmax.

[0212] The second optical filter is preferably one with a transmittance τmax of 0.8 or higher (τmax≥0.8) at the peak transmittance wavelength λtra.

[0213] The second optical filter has absorption characteristics in λabs to prevent reflected light, but has high transmittance near the wavelength to be transmitted, thereby suppressing the reduction in brightness.

[0214] Figure 17 This is another example of a graph showing the transmittance characteristics of the second optical filter.

[0215] This figure illustrates an example of preferred transmittance characteristics when using a sharp cutoff filter as a second optical filter.

[0216] The same applies to the case where a sharp cutoff filter is used as the second optical filter, preferably with a transmittance τmax of 0.8 or higher at the peak transmittance wavelength λtra.

[0217] (3) Reflectivity characteristics of the second optical filter

[0218] Figure 18 This is a chart illustrating an example of the reflectivity characteristics of the second optical filter.

[0219] In the so-called visible to near-infrared region (400-1000 nm), the wavelength at which the reflectivity reaches its peak (peak reflectivity wavelength) is set as λref, and the transmittance in the peak reflectivity wavelength λref is set as ρmax.

[0220] The second optical filter is preferably one with a reflectance ρmax less than 0.1 at the peak reflectance wavelength λref (ρmax < 0.1).

[0221] By suppressing the reflectivity of the second optical filter, ghosting and light spots caused by reflection from the second optical filter can be suppressed.

[0222] (4) Transmittance characteristics of the second optical filter used in combination with the first optical filter

[0223] Figure 19 This is a chart illustrating an example of the transmittance characteristics of a second optical filter used in combination with the first optical filter.

[0224] This figure illustrates an example of using a bandpass filter as the first optical filter and a bandstop filter as the second optical filter.

[0225] In the so-called visible to near-infrared region (400–1000 nm), the wavelength at which the transmittance of a bandpass filter reaches its peak (peak transmittance wavelength) is defined as λBPF. In a bandstop filter, the transmittance at the wavelength corresponding to the peak transmittance wavelength λBPF is defined as τBSF(λBPF).

[0226] The bandstop filter used as the second optical filter is preferably one with a transmittance τBSF(λBPF) of 0.8 or more at the wavelength corresponding to the peak transmittance wavelength λBPF (τBSF(λBPF)≥0.8).

[0227] When used in combination with the first optical filter, by increasing the transmittance of the wavelength region corresponding to the light transmission radio frequency band of the first optical filter, it is possible to suppress the reduction in brightness at the wavelength actually used.

[0228] Figure 20This is another example of a graph showing the transmittance characteristics of a second optical filter used in combination with the first optical filter.

[0229] This figure illustrates an example of using a bandpass filter as the first optical filter and a sharp cutoff filter as the second optical filter.

[0230] In a sharp cutoff filter, the transmittance at the wavelength corresponding to the peak transmittance wavelength λBPF is set as τSCF(λBPF).

[0231] Even when a sharp cutoff filter is used as the second optical filter, it is preferable that the transmittance τSCF(λBPF) at the wavelength corresponding to the peak transmittance wavelength λBPF is 0.8 or higher (τSCF(λBPF)≥0.8). By increasing the transmittance in the wavelength region corresponding to the light transmission frequency band of the first optical filter, the reduction in brightness at the wavelength actually used can be suppressed.

[0232] (5) Transmittance characteristics of the second optical filter disposed in each region of the imaging lens in the pupil region divided into multiple regions.

[0233] In a camera lens where the pupil region is divided into multiple regions, the transmittance characteristics of the second optical filter configured in each region are set as follows.

[0234] In this case, we assume that the pupil region is divided into three regions. That is, we assume that the optical path is divided into three parts. In this case, the filter unit has three windows.

[0235] Furthermore, the following example will be used: a bandpass filter is used in the first optical filter and a bandstop filter is used in the second optical filter.

[0236] Let j = 1, 2, 3, and set the peak transmittance wavelength of the bandpass filter configured in the j-th window to λBPFj.

[0237] Let i = 1, 2, 3, and let the absorbance of the bandstop filter in the wavelength λ of the i-th window be αBSFi(λ).

[0238] If i, j ∈ {1, 2, 3}, then the bandstop filter configured in each window preferably has an absorption rate characteristic that satisfies the following conditions.

[0239] αBSFi(λBPFj)≥0.8

[0240] However, i≠j

[0241] That is, the bandstop filter configured in each window is preferably an absorbance of 0.8 or more at the wavelength corresponding to the peak transmittance wavelength of the bandpass filter configured in other windows (optical path).

[0242] Figure 21 This is a graph showing an example of the transmittance characteristics of a bandstop filter used in combination with a bandpass filter in the third window.

[0243] As shown in the figure, the absorptivity αBSF3(λBPF1) of the bandstop filter located in the third window is almost close to its peak value at the wavelength corresponding to the peak transmittance wavelength λBPF1 of the bandpass filter located in the first window, and at the wavelength corresponding to the peak transmittance wavelength λBPF2 of the bandpass filter located in the second window. That is, it has the characteristic of reaching its peak value near the wavelength corresponding to the peak transmittance wavelength λBPF1 of the bandpass filter located in the first window and near the wavelength corresponding to the peak transmittance wavelength λBPF2 of the bandpass filter located in the second window.

[0244] Figure 22 This is a graph showing an example of the transmittance characteristics when a sharp cutoff filter is used as a second optical filter.

[0245] The peak transmittance wavelength of the bandpass filter configured in the first window is set as λBPF1, and the peak transmittance wavelength of the bandpass filter configured in the second window is set as λBPF2. In the sharp cutoff filter configured in the third window, the absorptivity at the wavelength corresponding to the peak transmittance wavelength λBPF1 of the bandpass filter configured in the first window is set as αSCF3(λBPF1), and the absorptivity at the wavelength corresponding to the peak transmittance wavelength λBPF2 of the bandpass filter configured in the second window is set as αSCF3(λBPF2).

[0246] As shown in the figure, the absorptivity αSCF3(λBPF1) of the sharp cutoff filter located in the third window is almost close to its peak value at the wavelength corresponding to the peak transmittance wavelength λBPF1 of the bandpass filter located in the first window and the wavelength corresponding to the peak transmittance wavelength λBPF2 of the bandpass filter located in the second window. That is, it has the characteristic of reaching its peak value near the wavelength corresponding to the peak transmittance wavelength λBPF1 of the bandpass filter located in the first window and near the wavelength corresponding to the peak transmittance wavelength λBPF2 of the bandpass filter located in the second window.

[0247] Thus, by using a second optical filter with a specified absorption rate characteristic (a second optical filter with an absorption rate of a specified value or higher at or near the wavelength corresponding to the peak transmittance wavelength of the first optical filter disposed in other windows) in each window, ghosting and light spots can be suppressed. Specifically, the following effects are achieved.

[0248] Consider the light that passes through the first window and is reflected by the lens and image sensor, and then enters the third window.

[0249] The light passing through the first window is limited to light with a wavelength near λBPF1 by the second optical filter configured in the first window.

[0250] On the other hand, the second optical filter configured in the third window reaches its peak absorption rate at or near the wavelength corresponding to wavelength λBPF1.

[0251] Therefore, if light reflected from the first window is incident on the third window, most of it will be absorbed by the second optical filter located in the third window.

[0252] The same effect applies to light that passes through the second window and is reflected by the lens and image sensor before entering the third window. That is, most of it is absorbed by the second optical filter located in the third window.

[0253] Thus, most of the light incident on the third window through reflections from other windows, such as lenses and image sensors, is absorbed by the second optical filter located in the third window. This reduces reflections caused by the first optical filter located in the third window, or by the second optical filter itself located in the third window, suppressing ghosting and light spots.

[0254] The same applies to light that passes through other windows and is reflected by lenses and image sensors, etc., and then enters the first and second windows. That is, most of it is absorbed by the second optical filters located in the first and second windows.

[0255] Next, consider the light that passes through the first window and is reflected by the lens and image sensor, etc., and enters the first window. That is, consider the light that is reflected back to the same window.

[0256] As described above, the light passing through the first window is limited to light with a wavelength near λBPF1 by the second optical filter positioned in the first window. The first and second optical filters positioned in the first window generally transmit light with a wavelength near λBPF1. Therefore, the light is not reflected again by the first and second optical filters positioned in the first window. Thus, it does not contribute to the generation of ghosting or increased light spots.

[0257] The same applies to light that passes through the second window and is reflected by the lens and image sensor, and light that passes through the third window and is reflected by the lens and image sensor, and light that passes through the third window and is reflected, and light that passes through the third window ...

[0258] Thus, by arranging a second optical filter with a specified absorption rate characteristic in the window where the first optical filter is located, reflections from the first optical filter are reduced. Consequently, as a whole, the optical system can achieve a reduction in ghosting and light spots.

[0259] [Imaging lens for polarization-based multispectral camera systems]

[0260] A multispectral camera system is a system that simultaneously captures images (multispectral images) of light split into multiple wavelengths. Polarization refers to the method by which a multispectral camera system utilizes polarized light.

[0261] In a polarization-based multispectral camera system, the imaging lens has polarization filters configured in each window of the filter unit. The following explanation will focus on the case of imaging an image split into three wavelengths (three rings).

[0262] In addition, except for the fact that polarizing filters are arranged in each window of the filter unit, the structure is the same as that of the imaging lens in the above embodiment. Therefore, only the structure of the filter unit will be described here.

[0263] Figure 23 This is an exploded stereoscopic view of the filter unit in the imaging lens of a polarization-mode multispectral camera system.

[0264] As shown in the figure, in the filter unit 150 of this example, three windows 152A, 152B, and 152C are provided in the filter frame 152. Each window 152A, 152B, and 152C is arranged at a predetermined interval on a concentric circle centered on the optical axis. Hereinafter, as needed, window 152A is designated as the first window 152A, window 152B as the second window 152B, and window 152C as the third window 152C to distinguish the three windows 152A, 152B, and 152C. The imaging lens 100 is positioned at or near the pupil position through the filter frame 152, and the pupil area is divided into three regions. That is, the optical path is divided into three parts.

[0265] In each window 152A, 152B, and 152C, bandpass filters 154A, 154B, and 154C, bandstop filters 156A, 156B, and 156C, and polarizing filters 158A, 158B, and 158C are arranged. In the filter unit 150 of this example, polarizing filters 158A, 158B, and 158C, bandpass filters 154A, 154B, and 154C, and bandstop filters 156A, 156B, and 156C are arranged sequentially along the optical axis Z from the object side (front side).

[0266] Hereinafter, as needed, the bandpass filter 154A configured in the first window 152A is designated as the first bandpass filter 154A, the bandpass filter 154B configured in the second window 152B is designated as the second bandpass filter 154B, and the bandpass filter 154C configured in the third window 152C is designated as the third bandpass filter 154C to distinguish the bandpass filters 154A, 154B, and 154C configured in each window 152A, 152B, and 152C. Furthermore, the band-stop filter 156A disposed in the first window 152A is designated as the first band-stop filter 156A, the band-stop filter 156B disposed in the second window 152B is designated as the second band-stop filter 156B, and the band-stop filter 156C disposed in the third window 152C is designated as the third band-stop filter 156C, so as to distinguish the band-stop filters 156A, 156B, and 156C disposed in each window 152A, 152B, and 152C. Furthermore, the polarizing filter 158A disposed in the first window 152A is designated as the first polarizing filter 158A, the polarizing filter 158B disposed in the second window 152B is designated as the second polarizing filter 158B, and the polarizing filter 158C disposed in the third window 152C is designated as the third polarizing filter 158C, so as to distinguish the polarizing filters 158A, 158B, and 158C disposed in each window 152A, 152B, and 152C.

[0267] The bandpass filters 154A, 154B, and 154C, configured in each of the windows 152A, 152B, and 152C, have different light transmission radio frequency bands. The light transmission radio frequency band of the first bandpass filter 154A is designated as the first light transmission radio frequency band Λ1. The light transmission radio frequency band of the second bandpass filter 154B is designated as the second light transmission radio frequency band Λ2 (Λ1≠Λ2). The light transmission radio frequency band of the third bandpass filter 154C is designated as the third light transmission radio frequency band Λ3 (Λ1≠Λ3, Λ2≠Λ3). In this example, the third light transmission radio frequency band Λ3 is set on the longer wavelength side than the second light transmission radio frequency band Λ2. Furthermore, the second light transmission radio frequency band Λ2 is set on the longer wavelength side than the first light transmission radio frequency band Λ1. Furthermore, reflective bandpass filters are used in bandpass filters 154A, 154B, and 154C.

[0268] The bandstop filters 156A, 156B, and 156C disposed in each of the windows 152A, 152B, and 152C have the characteristic of allowing light to pass through, wherein the light is light in the wavelength region allowed to be transmitted by the bandpass filter disposed in at least the same window. On the other hand, the light in the wavelength region allowed to be transmitted by the bandpass filter disposed in at least one of the other windows has the characteristic of absorption. Specifically, it is composed of an absorption-type bandstop filter having the following optical characteristics.

[0269] The first bandpass filter 146A has the characteristic of allowing light to pass through, said light being light in the wavelength region (first light-transmitting radio frequency band Λ1) that is allowed to pass through at least the first bandpass filter 144A. On the other hand, it has the characteristic of absorbing light in the wavelength region (second light-transmitting radio frequency band Λ2) that is allowed to pass through at least the second bandpass filter 144B, and light in the wavelength region (third light-transmitting radio frequency band Λ3) that is allowed to pass through the third bandpass filter 144C (see reference). Figure 8 ).

[0270] The second bandpass filter 146B has the characteristic of allowing light to pass through, said light being light in the wavelength region (second light-transmitting radio frequency band Λ2) that is allowed to be transmitted by at least the second bandpass filter 144B. On the other hand, it has the characteristic of absorbing light in the wavelength region (first light-transmitting radio frequency band Λ1) that is allowed to be transmitted by at least the first bandpass filter 144A, and light in the wavelength region (third light-transmitting radio frequency band Λ3) that is allowed to be transmitted by the third bandpass filter 144C. Figure 9 Reference).

[0271] The third bandpass filter 146C has the characteristic of allowing light to pass through, said light being light in the wavelength region (third light-transmitting radio frequency band Λ3) that is allowed to be transmitted by at least the third bandpass filter 144C. On the other hand, it has the characteristic of absorbing light in the wavelength region (first light-transmitting radio frequency band Λ1) that is allowed to be transmitted by at least the first bandpass filter 144A, and light in the wavelength region (second light-transmitting radio frequency band Λ2) that is allowed to be transmitted by the second bandpass filter 144B (see reference). Figure 10 ).

[0272] Each window 152A, 152B, and 152C includes a polarizing filter 158A, 158B, and 158C with a different transmission axis angle. In the polarizing filter 158A in the first window 152A, the transmission axis is set to a first angle β1. In the polarizing filter 158B in the second window 152B, the transmission axis is set to a second angle β2 (β2≠β1). In the polarizing filter 158C in the third window 152C, the transmission axis is set to a third angle β3 (β3≠β1, β3≠β1).

[0273] Figure 24This is a diagram showing an example of the polarizing filters included in each window of the filter unit. The diagram shows the transmission axis settings of each polarizing filter 158A, 158B, and 158C when the filter unit 150 is viewed from the object side.

[0274] As shown in the figure, in the filter unit 150 of this embodiment, the transmission axis of the polarizing filter 158A provided in the first window 152A is set to β1 = 0°, the transmission axis of the polarizing filter 158B provided in the second window 152B is set to β2 = 60°, and the transmission axis of the polarizing filter 158C provided in the third window 152C is set to β3 = 120°.

[0275] Furthermore, regarding angles, the state parallel to the X-axis is defined as 0°, and the counter-clockwise direction is defined as positive (+) when viewed from the object's side (front side). Therefore, a transmission axis of 60° refers to a state tilted 60° counter-clockwise relative to the X-axis. And a transmission axis of 120° refers to a state tilted 120° counter-clockwise relative to the X-axis. Additionally, 120° has the same meaning as -60°. That is, a transmission axis of 120° refers to a state tilted 60° clockwise relative to the X-axis.

[0276] The X-axis is an axis defined in a plane orthogonal to the optical axis Z. In the same plane orthogonal to the optical axis Z, the Y-axis is defined as an axis orthogonal to the X-axis. The image sensor within the camera body of the multispectral camera system is configured such that the top and bottom edges of its light-receiving surface are parallel to the X-axis, and the left and right edges are parallel to the Y-axis.

[0277] In polarization filters 158A, 158B, and 158C, either reflective or absorptive types can be used, but from the viewpoint of suppressing ghosting, absorptive types are preferred.

[0278] The function of the camera lens in this example, as described above, is as follows.

[0279] Regarding the light incident on the camera lens, the optical path is divided into three by the filter unit 150, and reaches the image sensor (not shown) through the first window 152A, the second window 152B and the third window 152C.

[0280] Light incident on the first window 152A passes through the first polarizing filter 158A, the first bandpass filter 154A, and the first bandstop filter 156A disposed in the first window 152A, and exits from the first window 152A. At this time, the light incident on the first window 152A passes sequentially through the first polarizing filter 158A, the first bandpass filter 154A, and the first bandstop filter 156A. First, it passes through the first polarizing filter 158A, thus becoming linearly polarized light with an azimuth angle of 0°. Next, it passes through the first bandpass filter 154A, thus confining it to the wavelength region Λ1. The first bandstop filter 156A absorbs light in the wavelength regions Λ2 and Λ3, but allows light in the wavelength region Λ1 to pass through. Therefore, the light in the wavelength region Λ1 that passed through the first bandpass filter 154A directly passes through the first bandstop filter 156A. Thus, linearly polarized light with a wavelength region Λ1 and an azimuth angle of 0° is emitted from the first window 152A.

[0281] Light incident on the second window 152B passes through the second polarizing filter 158B, the second bandpass filter 154B, and the second bandstop filter 156B disposed in the second window 152B, and exits from the second window 152B. At this time, the light incident on the second window 152B passes sequentially through the second polarizing filter 158B, the second bandpass filter 154B, and the second bandstop filter 156B. First, it passes through the second polarizing filter 158B, thus becoming linearly polarized light with an azimuth angle of 60°. Next, it passes through the second bandpass filter 154B, thus confining it to the wavelength region Λ2. The second bandstop filter 156B absorbs light in wavelength regions Λ1 and Λ3, but allows light in wavelength region Λ2 to pass through. Therefore, the light in wavelength region Λ2 that has passed through the second bandpass filter 154B directly passes through the second bandstop filter 156B. Thus, linearly polarized light with a wavelength region Λ2 and an azimuth angle of 60° is emitted from the second window 152B.

[0282] Light incident on the third window 152C passes through the third polarization filter 158C, the third bandpass filter 154C, and the third bandstop filter 156C disposed in the third window 152C, and exits from the third window 152C. At this time, the light incident on the third window 152C sequentially passes through the third polarization filter 158C, the third bandpass filter 154C, and the third bandstop filter 156C. First, it passes through the third polarization filter 158C, thus becoming linearly polarized light with an azimuth angle of 120°. Next, it passes through the third bandpass filter 154C, thus confining it to the wavelength region Λ2. The third bandstop filter 156C absorbs light in wavelength regions Λ1 and Λ2, but allows light in wavelength region Λ3 to pass through. Therefore, light in wavelength region Λ3 passing through the third bandpass filter 154C directly passes through the third bandstop filter 156C. Consequently, linearly polarized light with wavelength region Λ3 and azimuth angle of 120° is emitted from the third window 152C.

[0283] Thus, according to the imaging lens of this example, by arranging polarizing filters 158A, 158B, and 158C in each window 152A, 152B, and 152C of the filter unit 150, light with a predetermined polarization direction from each window 152A, 152B, and 152C can be obtained. Furthermore, the effect of suppressing ghosting and light spots by arranging band-stop filters 156A, 156B, and 156C is the same as that of the imaging lens 100 in the above embodiment.

[0284] In this example, in each window, the bandpass filter, bandstop filter, and bandstop filter are arranged along the optical axis from the object side in the order of polarization filter, bandpass filter, and bandstop filter. However, the order in which the optical filters are arranged is not limited to this. For example, the bandpass filter, bandstop filter, and polarization filter can be arranged sequentially from the object side along the optical axis. Furthermore, for example, the bandpass filter, polarization filter, and bandstop filter can be arranged sequentially from the object side along the optical axis.

[0285] Furthermore, the bandpass filter, bandstop filter, and polarizing filter configured in each window are preferably configured without an air layer.

[0286] Furthermore, a sharp cutoff filter can be used instead of a band-stop filter for the second optical filter.

[0287] Furthermore, the number of windows (the number of pupil area divisions) in the filter unit is set according to the number of wavelengths of the beam splitting. For example, when imaging is performed by splitting the beam into 2 wavelengths, at least 2 windows are provided. And when imaging is performed by splitting the beam into 4 wavelengths, at least 4 windows are provided.

[0288] [Multispectral Camera System]

[0289] Next, a multispectral camera system using the imaging lens applicable to this invention will be described.

[0290] As described above, a multispectral camera system is a system that simultaneously captures images of light divided into multiple wavelengths.

[0291] The example described uses a multispectral camera system based on polarization. Furthermore, the example of capturing images split into three wavelengths will be used.

[0292] Figure 25 This is a diagram showing the general structure of a multispectral camera system.

[0293] As shown in the figure, the multispectral camera system 1 of this embodiment mainly consists of a multispectral camera 10 and a signal processing device 300. The multispectral camera 10 consists of an imaging lens 100 and a camera body 200. The multispectral camera 10 is an example of an imaging device.

[0294] [Camera Lens]

[0295] The camera lens 100 is equipped with Figure 23 The image lens of the filter unit 150 shown. That is, the filter frame 152 has three windows 152A, 152B, and 152C, and the image lens uses the filter unit 150 which has bandpass filters 154A, 154B, and 154C, bandstop filters 156A, 156B, and 156C, and polarizing filters 158A, 158B, and 158C arranged in each window 152A, 152B, and 152C.

[0296] [Camera Body]

[0297] like Figure 25 As shown, the camera body 200 includes an image sensor 210. The image sensor 210 is positioned on the optical axis of the imaging lens 100 and receives light passing through the imaging lens 100. This image sensor 210 is composed of a polarization image sensor. A polarization image sensor is an image sensor equipped with a polarizer, with each pixel having a polarizer. For example, a polarizer is provided between a microlens and a photodiode. Furthermore, such polarization image sensors are well known (e.g., refer to International Publication No. 2020 / 071253, etc.), therefore, a detailed description of its contents is omitted.

[0298] The orientation (angle of the transmission axis) of the polarizer mounted on the polarization image sensor is selected according to the number of wavelengths being captured. In this embodiment, an image split into three wavelengths is captured. Therefore, a polarization image sensor with polarizers in at least three directions is used. In this embodiment, a polarization image sensor with polarizers in four directions is used.

[0299] Figure 26 This is a diagram illustrating an example of the configuration of pixels and polarizers in a polarization image sensor.

[0300] As shown in the figure, for pixels arranged in a matrix, four polarizers with different transmission axis angles are regularly arranged. The polarizer with a transmission axis angle of γ1 is designated as the first polarizer, the polarizer with a transmission axis angle of γ2 as the second polarizer, the polarizer with a transmission axis angle of γ3 as the third polarizer, and the polarizer with a transmission axis angle of γ4 as the fourth polarizer. As an example, in this embodiment, the transmission axis angle γ1 of the first polarizer is set to 0°, the transmission axis angle γ2 of the second polarizer is set to 45°, the transmission axis angle γ3 of the third polarizer is set to 90°, and the transmission axis angle γ4 of the fourth polarizer is set to 135°.

[0301] Pixel P1, which has the first polarizer, is designated as the first pixel; pixel P2, which has the second polarizer, is designated as the second pixel; pixel P3, which has the third polarizer, is designated as the third pixel; and pixel P4, which has the fourth polarizer, is designated as the fourth pixel. A 2×2 pixel group consisting of the first pixel P1, the second pixel P2, the third pixel P3, and the fourth pixel P4 is designated as a unit (pixel unit) PU, and this pixel unit PU is repeatedly arranged along the X-axis and Y-axis.

[0302] Thus, in a polarization image sensor equipped with polarizers in four directions, it is possible to capture polarization images in four directions at once.

[0303] The image sensor 210 is, for example, a CMOS (Complementary Metal Oxide Semiconductor) type comprising a driving unit, an ADC (Analog-to-Digital Converter), and a signal processing unit. In this case, the image sensor 210 is driven by the built-in driving unit. Furthermore, the signal of each pixel is converted into a digital signal by the built-in ADC and output. Additionally, the signal of each pixel undergoes correlation double sampling, gain processing, and correction processing by the built-in signal processing unit before being output. The signal processing can be performed after conversion to a digital signal or before conversion to a digital signal.

[0304] The camera body 200 includes, in addition to the image sensor 210, an output unit (not shown) that outputs data of the image captured by the image sensor 210, and a camera control unit (not shown) that controls the overall movement of the camera body 200. The camera control unit may be configured as a processor. The processor functions as the camera control unit by executing a predetermined control program.

[0305] Furthermore, the image data output from the camera body 200 is so-called RAW image data, that is, unprocessed image data. This RAW image data is processed by the signal processing unit 300 to generate an image split into multiple wavelengths.

[0306] [Signal Processing Device]

[0307] As described above, the signal processing device 300 processes the image data (RAW image data) output from the camera body 200 to generate an image split into multiple wavelengths. More specifically, it generates an image of a wavelength region corresponding to the light transmission frequency band of the bandpass filter provided in each window of the imaging lens 100. In this embodiment, an image of three wavelengths is generated, consisting of an image (first image) of a wavelength region (first wavelength region Λ1) corresponding to the first light transmission frequency band Λ1, an image (second image) of a wavelength region (second wavelength region Λ2) corresponding to the second light transmission frequency band Λ2, and an image (third image) of a wavelength region (third wavelength region Λ3) corresponding to the third light transmission frequency band Λ3.

[0308] Figure 27 This is a diagram illustrating an example of the hardware structure of a signal processing device.

[0309] As shown in the figure, the signal processing device 300 includes a CPU (Central Processing Unit) 311, a ROM (Read Only Memory) 312, a RAM (Random Access Memory) 313, an auxiliary storage device 314, an input device 315, an output device 316, and an input / output interface 317. This signal processing device 300 is, for example, composed of a general-purpose computer such as a personal computer.

[0310] Regarding the signal processing device 300, it functions as a signal processing device by executing a predetermined program (signal processing program) by the CPU 311, which acts as a processor. The program executed by the CPU 311 is stored in the ROM 312 or the auxiliary storage device 314.

[0311] The auxiliary storage device 314 constitutes the storage unit of the signal processing device 300. The auxiliary storage device 314 may be, for example, an HDD (Hard Disk Drive) or an SSD (Solid State Drive).

[0312] The input device 315 constitutes the operation unit of the signal processing device 300. The input device 315 may be, for example, a keyboard, a mouse, a touch panel, etc.

[0313] The output device 316 constitutes the display unit of the signal processing device 300. The output device 316 may be, for example, a liquid crystal display, an organic light-emitting diode display, or the like.

[0314] The input / output interface 317 forms the connection part of the signal processing device 300. The signal processing device 300 is connected to the camera body 200 via the input / output interface 317.

[0315] Figure 28 It is a block diagram of the main functions of a signal processing device.

[0316] As shown in the figure, the signal processing device 300 has functions such as an image data acquisition unit 320, an image generation unit 330, an output control unit 340, and a recording control unit 350. These functions are implemented by the CPU 311 executing a predetermined program.

[0317] The image data acquisition unit 320 acquires image data obtained through photography from the camera body 200. As described above, the image data acquired from the camera body 200 is RAW image data.

[0318] The image generation unit 330 performs prescribed signal processing on the image data acquired by the image data acquisition unit 320 to generate images of wavelength regions corresponding to the light transmission frequency bands of the bandpass filters provided in each window of the imaging lens 100. In this embodiment, images of the first wavelength region Λ1 (first image), the second wavelength region Λ2 (second image), and the third wavelength region Λ3 (third image) are generated. The image generation unit 330 performs interference removal processing on the image data acquired by the image data acquisition unit 320 at the pixel unit level to generate images of each wavelength region Λ1, Λ2, and Λ3. The processing will be summarized below.

[0319] As described above, in a polarization image sensor equipped with polarizers in four directions, it is possible to capture polarized images in four directions simultaneously. Each of these four polarized images contains image components of wavelength regions Λ1, Λ2, and Λ3 at a predetermined ratio (interference rate). The interference rate is determined and is known by the angle of the transmission axis of the polarization filter in each window of the filter unit 120 and the angle of the transmission axis of the polarizer in each pixel. Furthermore, by utilizing this interference rate information, images of each wavelength region can be generated.

[0320] The pixel value of the first pixel P1 in the image captured by the image sensor 210 is set to x1, the pixel value of the second pixel P2 is set to x2, the pixel value of the third pixel P3 is set to x3, and the pixel value of the fourth pixel P4 is set to x4.

[0321] Furthermore, the pixel value of the corresponding pixel in the generated first image is set to X1, the pixel value of the corresponding pixel in the second image is set to X2, and the pixel value of the corresponding pixel in the third image is set to X3.

[0322] If we set the ratio of light from the first wavelength region Λ1 to light received by the first pixel P1 as b11, the ratio of light from the second wavelength region Λ2 to light received by the first pixel P1 as b12, and the ratio of light from the third wavelength region Λ3 to light received by the first pixel P1 as b13, then the following relationship holds between X1, X2, X3 and x1.

[0323] b11*X1+b12*X2+b13*X3=x1… (Equation 1)

[0324] Furthermore, if the ratio of light from the first wavelength region Λ1 to light received by the second pixel P2 is set to b21, the ratio of light from the second wavelength region Λ2 to light received by the second pixel P2 is set to b22, and the ratio of light from the third wavelength region Λ3 to light received by the second pixel P2 is set to b23, then the following relationship holds between X1, X2, X3 and x2.

[0325] b21*X1+b22*X2+b23*X3=x2… (Formula 2)

[0326] Furthermore, if the ratio of light from the first wavelength region Λ1 to light received by the third pixel P3 is set to b31, the ratio of light from the second wavelength region Λ2 to light received by the third pixel P3 is set to b32, and the ratio of light from the third wavelength region Λ3 to light received by the third pixel P3 is set to b33, then the following relationship holds between X1, X2, X3 and x3.

[0327] b31*X1+b32*X2+b33*X3=x3… (Formula 3)

[0328] Furthermore, if the ratio of light from the first wavelength region Λ1 to light received by the fourth pixel P4 is set to b41, the ratio of light from the second wavelength region Λ2 to light received by the fourth pixel P4 is set to b42, and the ratio of light from the third wavelength region Λ3 to light received by the fourth pixel P4 is set to b43, then the following relationship holds between X1, X2, X3 and x4.

[0329] b41*X1+b42*X2+b43*X3=x4… (Equation 4)

[0330] Regarding X1, X2, and X3, by solving the simultaneous equations 1 to 4 above, the pixel values ​​X1, X2, and X3 of the corresponding pixels in the first, second, and third images can be obtained.

[0331] Thus, by utilizing information about the interference rate, it is possible to generate images of various wavelength regions from images captured by an image sensor.

[0332] The aforementioned simultaneous equations can be expressed using matrices. Furthermore, X1, X2, and X3 can be calculated by multiplying both sides of the inverse matrix. The signal processing device 300 retains the elements of the inverse matrix as a coefficient set. Information about the coefficient set is stored, for example, in the auxiliary storage device 314. The image generation unit 330 retrieves the coefficient set information from the auxiliary storage device 314, thereby generating images for each wavelength region.

[0333] The output control unit 340 controls the output of images (first image, second image, and third image) of each wavelength region generated by the image generation unit 330. In this embodiment, it controls the output (display) to the display, which is the output device 316.

[0334] The recording control unit 350 controls the recording of images of each wavelength region generated by the image generation unit 330 according to commands from the user. The generated images of each wavelength region are recorded in the auxiliary storage device 314.

[0335] The multispectral camera system 1 of this embodiment, configured as described above, is capable of simultaneously capturing images split into three wavelengths. The three wavelengths correspond to the light transmission radio frequency bands (first light transmission radio frequency band Λ1, second light transmission radio frequency band Λ2, and third light transmission radio frequency band Λ3) of the bandpass filters 154A, 154B, and 154C disposed in the respective windows 152A, 152B, and 152C of the imaging lens 100. Therefore, by changing the bandpass filters disposed in each window 152A, 152B, and 152C, images of combinations of different wavelength regions can be captured.

[0336] [Example of a multispectral camera system]

[0337] [Suitable for multispectral camera systems other than those based on polarization]

[0338] The imaging lens to which this invention is applicable can also be used in multispectral camera systems other than those using polarization. For example, it can also be used in multispectral camera systems that use a directional sensor in the image sensor. A directional sensor is an image sensor that selectively receives light by using microlenses and a light-shielding film to perform pupil segmentation on a light beam incident through the imaging lens (e.g., refer to International Publication No. 2019 / 073881, etc.). A directional sensor is also called a pupil-selective sensor, etc. In principle, a polarization filter is not required in imaging lenses used in multispectral camera systems other than those using polarization.

[0339] [Camera lens and camera body]

[0340] The camera lens and camera body can be an integrated structure, and for example, it can be configured to allow the camera lens to be replaced with the camera body via a bayonet mount.

[0341] Image sensor

[0342] Color polarized image sensors can also be used in image sensors. For example, a color polarized image sensor can be used when capturing an image with four wavelengths of light. A color polarized image sensor is a polarized image sensor that has a color filter in each pixel. The color filter is disposed at a predetermined position in each pixel unit. For example, such as... Figure 26 The image sensor shown, in which a pixel unit PU is composed of four pixels P1 to P4, has a first color filter (e.g., a color filter that allows light in the green wavelength region to pass through) disposed in the first pixel P1, a second color filter (e.g., a color filter that allows light in the red wavelength region to pass through) disposed in the second pixel P2, a third color filter (e.g., a color filter that allows light in the blue wavelength region to pass through) disposed in the third pixel P3, and a fourth color filter (e.g., a color filter that allows light in the infrared region to pass through) disposed in the fourth pixel P4. In each pixel, the color filter is, for example, disposed between a microlens and a polarizer.

[0343] When using a color polarized image sensor, the interference rate is calculated by further considering the spectral transmittance information of the color filters in each pixel.

[0344] [Signal Processing Device]

[0345] In the multispectral camera system described above, the camera body and the signal processing device are separate components, but the signal processing device function can also be integrated into the camera body. Furthermore, it is also possible to configure the camera body to have only signal processing functionality.

[0346] Furthermore, the various functions of a signal processing device are implemented by various processors. These processors include general-purpose processors that execute programs and function as various processing units, such as CPUs and / or GPUs (Graphics Processing Units); FPGAs (Field Programmable Gate Arrays), which are processors whose circuit structure can be modified after manufacturing, i.e., Programmable Logic Devices (PLDs); and ASICs (Application Specific Integrated Circuits), which are processors with circuit structures specifically designed to perform specific processes, i.e., dedicated circuits. The terms "program" and "software" have the same meaning.

[0347] A processing unit can be composed of one of these various processors, or it can be composed of two or more processors of the same or different types. For example, a processing unit can be constructed using multiple FPGAs or a combination of a CPU and an FPGA. Furthermore, multiple processing units can be constructed using a single processor. As examples of multiple processing units constructed using a single processor, firstly, there is the following: Represented by computers used for clients and servers, a single processor is constructed using a combination of one or more CPUs and software, and this processor functions as multiple processing units. Secondly, there is the following: Represented by systems on a single chip (SoC), a processor is used to implement the overall system functionality including multiple processing units using a single IC (Integrated Circuit) chip. Thus, regarding various processing units, as a hardware structure, one or more of the aforementioned processors are used.

[0348] [Suitable for other lens devices and camera devices]

[0349] This invention is also applicable to lens devices used in imaging devices other than multispectral cameras. Imaging devices include those mounted on other equipment, such as digital cameras mounted on smartphones, personal computers, etc. Furthermore, it is also applicable to lens devices used in optical devices other than imaging devices.

[0350] Symbol Explanation

[0351] 1 - Multispectral camera system; 10 - Multispectral camera; 100 - Camera lens; 110 - Lens barrel; 120 - Filter unit; 120A - Lens group (first lens group); 120B - Lens group (second lens group); 130 - Filter unit; 132 - Filter frame; 132A - Window (first window); 132B - Window (second window); 134A - Bandpass filter (first bandpass filter); 134B - Bandpass filter (second bandpass filter); 136A - Bandstop filter (first bandstop filter); 136B - Bandstop filter (second bandstop filter); 140 - Filter unit; 142 - Filter frame; 142A - Window (first window); 142B - Window (second window) 142C - Window (3rd Window), 144A - Bandpass Filter (1st Bandpass Filter), 144B - Bandpass Filter (2nd Bandpass Filter), 144C - Bandpass Filter (3rd Bandpass Filter), 146A - Bandstop Filter (1st Bandstop Filter), 146B - Bandstop Filter (2nd Bandstop Filter), 146C - Bandstop Filter (Third bandpass filter), 150 - Filter unit, 152 - Filter frame, 152A - Window (First window), 152B - Window (Second window), 152C - Window (Third window), 154A - Bandpass filter (First bandpass filter), 154B - Bandpass filter (Second bandpass filter), 154C - Bandpass filter (Third bandpass filter) 156A-Band-stop filter (first band-stop filter), 156B-Band-stop filter (second band-stop filter), 156C-Band-stop filter (third band-stop filter), 158A-Polarizing filter (first polarizing filter), 158B-Polarizing filter (second polarizing filter), 158C-Polarizing filter (third polarizing filter), 200-Camera body, 210-Image sensor, 300-Signal processing unit, 311-CPU, 312-ROM, 314-Auxiliary storage device, 315-Input device, 316-Output device, 317-Input / output interface, 320-Image data acquisition unit, 330-Image generation unit, 340-Output control unit, 350-Recording unit Control unit, P1 - pixel (1st pixel), P2 - pixel (2nd pixel), P3 - pixel (3rd pixel), P4 - pixel (4th pixel), PU - pixel unit, Z - optical axis, β1 - angle of the transmission axis of the polarizing filter in the 1st window, β2 - angle of the transmission axis of the polarizing filter in the 2nd window, β3 - angle of the transmission axis of the polarizing filter in the 3rd window, Λ1 - light transmission radio frequency band of the 1st bandpass filter (1st light transmission radio frequency band), Λ2 - light transmission radio frequency band of the 2nd bandpass filter (2nd light transmission radio frequency band), Λ3 - light transmission radio frequency band of the 3rd bandpass filter (3rd light transmission radio frequency band), γ1 - angle of the transmission axis of the 1st polarizer, γ2 - angle of the transmission axis of the 2nd polarizer.γ3 - Angle of the transmission axis of the third polarizer, γ4 - Angle of the transmission axis of the fourth polarizer, λBPF - Peak transmittance wavelength of the bandpass filter, λBPF1 - Peak transmittance wavelength of the bandpass filter located in the first window, λBPF2 - Peak transmittance wavelength of the bandpass filter located in the second window, λabs - Peak absorptivity wavelength of the bandstop filter, λref - Peak reflectivity wavelength of the bandstop filter, λtra - Peak transmittance wavelength of the bandstop filter, αmax - Absorption at the peak absorptivity wavelength λabs, ρmax - Transmittance at the peak reflectivity wavelength λref, τBSF(λBPF) - Transmittance at the wavelength corresponding to the peak transmittance wavelength λBPF, τSCF(λBPF) - Transmittance at the wavelength corresponding to the peak transmittance wavelength λBPF, τmax - Transmittance at the peak transmittance wavelength λtra, αBSF3(λBPF1) - Transmittance at the wavelength corresponding to the peak transmittance wavelength λBPF. Absorbance at the wavelength corresponding to the long λBPF1, αBSF3(λBPF2) - absorbance at the wavelength corresponding to the peak transmittance wavelength λBPF2, BPF1 - graph representing the transmittance characteristics of the first bandpass filter, BPF2 - graph representing the transmittance characteristics of the second bandpass filter, BPF3 - graph representing the transmittance characteristics of the third bandpass filter, BSF1 - graph representing the absorbance characteristics of the first bandstop filter, BSF2 - graph representing the absorbance characteristics of the second bandstop filter, BSF21 - graph representing the absorbance characteristics of the first and second bandstop filters, BSF22 - graph representing the absorbance characteristics of the second and second bandstop filters, BSF3 - graph representing the absorbance characteristics of the third bandstop filter, SCF1 - graph representing the absorbance characteristics of the sharp cutoff filter, BSF11 - graph representing the absorbance characteristics of the bandstop filter, SCF12 - graph representing the absorbance characteristics of the sharp cutoff filter.

Claims

1. A lens device comprising: The component, positioned in the optical path, has multiple openings; A first optical filter is disposed in at least two of the openings and has a light-transmitting radio frequency band in a specific wavelength region; A second optical filter is disposed at the opening where the first optical filter is disposed, and is positioned closer to the image side than the first optical filter. It has a light absorption band in a wavelength region different from the light transmission frequency band of the first optical filter. A polarizing filter is disposed at the opening where the first optical filter is located. The transmission axes of the two polarizing filters disposed in the opening are at different angles.

2. The lens device according to claim 1, wherein, The first optical filter is a reflective bandpass filter.

3. The lens device according to claim 1 or 2, wherein, The first optical filter disposed in the opening has a light transmission radio frequency band that is different from that of the first optical filter disposed in at least one of the other openings.

4. The lens device according to claim 3, wherein, The second optical filter disposed in the opening has the light absorption band of the light transmission radio frequency band that includes the first optical filter disposed in at least one of the other openings.

5. The lens device according to claim 3, wherein, The component has at least three openings. The lens device has: The first optical filter is disposed at at least three of the openings; and The second optical filter is disposed at the opening where the first optical filter is disposed. The second optical filter disposed in at least one of the openings has the light absorption band that includes the light transmission radio frequency band of the first optical filter disposed in the other openings.

6. The lens device according to claim 3, wherein, The component has at least three openings. The lens device has: The first optical filter is disposed at at least three of the openings; and The second optical filter is disposed at the opening where the first optical filter is disposed. The second optical filter, configured in at least one of the openings, is composed of a plurality of optical filters having different light absorption frequency bands, and has a light absorption frequency band including the light transmission frequency band of the first optical filter configured in the other openings.

7. The lens device according to claim 1 or 2, wherein, The second optical filter has an absorption rate of 0.8 or higher at the wavelength where the absorption rate reaches its peak.

8. The lens device according to claim 1 or 2, wherein, The second optical filter has a transmittance of 0.8 or higher at the wavelength where the transmittance reaches its peak.

9. The lens device according to claim 1 or 2, wherein, The second optical filter has a reflectivity of less than 0.1 at the wavelength where the reflectivity reaches its peak.

10. The lens device according to claim 1 or 2, wherein, The second optical filter has a wavelength width of 20 nm or more at which the absorption rate reaches 50% of the peak value.

11. The lens device according to claim 10, wherein, The second optical filter has a wavelength width of 20 nm or more and 200 nm or less at which the absorption rate reaches 50% of the peak value.

12. The lens device according to claim 1 or 2, wherein, The second optical filter has a layer containing pigment.

13. The lens device according to claim 1 or 2, wherein, The second optical filter has a transmittance of 0.8 or higher at the wavelength corresponding to the wavelength at which the transmittance of the first optical filter reaches its peak.

14. The lens device according to claim 1 or 2, wherein, The absorption rate of the second optical filter disposed in the opening is 0.8 or higher at the wavelength corresponding to the wavelength at which the transmittance of the first optical filter disposed in at least one of the other openings reaches its peak.

15. A camera device comprising: The lens device according to claim 1; and A polarization image sensor that receives light passing through the lens device.

16. A filter unit disposed in the optical path of a lens assembly. The filter unit includes: The component has multiple openings; A first optical filter is disposed in at least two of the openings and has a light-transmitting radio frequency band in a specific wavelength region; A second optical filter is disposed at the opening where the first optical filter is disposed, and has a light absorption band in a wavelength region different from the light transmission frequency band of the first optical filter; and A polarizing filter is disposed at the opening where the first optical filter is disposed.

17. The filter unit according to claim 16, wherein, The first optical filter disposed in the opening has a light transmission radio frequency band that is different from that of the first optical filter disposed in at least one of the other openings.

18. The filter unit according to claim 16 or 17, wherein, The second optical filter disposed in the opening has the light absorption band of the light transmission radio frequency band that includes the first optical filter disposed in at least one of the other openings.

19. A filter unit disposed in or near the pupil position in the optical path of a lens device. The filter unit includes: The component has a plurality of openings that divide the pupil region of the pupil; A first optical filter is disposed in at least two of the openings, and has a light-transmitting radio frequency band in a specific wavelength region; and The second optical filter is disposed at the opening where the first optical filter is disposed, and has a light absorption band in a wavelength region different from the light transmission frequency band of the first optical filter. In each of the plurality of openings, the first optical filter and the second optical filter are configured to overlap each other.

20. The filter unit according to claim 19, wherein, The first optical filter disposed in the opening has a light transmission radio frequency band that is different from that of the first optical filter disposed in at least one of the other openings.

21. The filter unit according to claim 19 or 20, wherein, The second optical filter disposed in the opening has the light absorption band of the light transmission radio frequency band that includes the first optical filter disposed in at least one of the other openings.

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