Optical system, lens device, and imaging device

Abstract

To provide an optical system used in a stereoscopic image pickup device that is small and has the high performance at a lower cost than a conventional technique.SOLUTION: An optical system 101 includes a front lens group N with the negative refractive power, a first reflection member 201, a second reflection member 202 and a rear lens group P with the positive refractive power arranged in the order from an object side to an image side, and has the field angle exceeding 170°. When the focal distance of the front lens group is fn and the focal distance of the rear lens group is fp, a conditional expression of 0.80<|fn / fp|<5.00 is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system suitable for imaging devices such as digital video cameras, digital still cameras, broadcast cameras, cameras for silver halide film, and surveillance cameras. [Background technology]

[0002] In recent years, there has been a demand for imaging devices that can capture images used in content that provides a sense of realism, such as virtual reality. In particular, there is a demand for stereoscopic image (video) imaging devices that have a full angle of view of approximately 180° and can capture images from two viewpoints with parallax similar to that of humans.

[0003] Patent Document 1 describes an imaging device in which two optical systems are arranged in parallel to obtain a captured image that can be viewed stereoscopically. Two reflecting members are arranged in each optical system, and the optical path is bent using the reflecting members, thereby forming optical images from the two optical systems on a single imaging element. In this way, Patent Document 1 proposes a stereoscopic imaging device that is compact yet has a long baseline length. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-008629 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the optical system used in the imaging device disclosed in Patent Document 1 has a total of three lens groups, located before, after, and between the two reflecting members, which requires a large number of lens elements and tends to make the optical system expensive.

[0006] An object of the present invention is to provide an optical system for use in a small, high-performance stereoscopic imaging device at a lower cost than conventional systems. [Means for solving the problem]

[0007] An optical system according to one aspect of the present invention is an optical system having an angle of view exceeding 170°, comprising, arranged in order from an object side to an image side, a front lens group having negative refractive power, a first reflecting member, a second reflecting member, and a rear lens group having positive refractive power, an aperture stop is disposed between the first reflecting member and the second reflecting member; The focal length of the front lens group is fn, and the focal length of the rear lens group is fp. The distance along the optical axis between the lens surface having refractive power in the rear lens group that is closest to the object side and the aperture stop is Lsp Then, 0.80<|fn / fp|<5.00 , 0.60 <Lsp / fp<2.50 The present invention is characterized in that the following conditional expression is satisfied:

[0008] Other objects and features of the present invention will be described in the following embodiments. [Effects of the Invention]

[0009] According to the present invention, an optical system used in a small, high-performance stereoscopic imaging device can be provided at a lower cost than conventional methods. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of a main part of a lens device in which two optical systems of Example 1 are arranged, showing a state in which an optical path is bent by a reflecting member. [Figure 2] FIG. 1 is a diagram schematically illustrating an image circle formed on one image sensor by two optical systems. [Figure 3] 1 is a cross-sectional view of a lens of an optical system according to a first embodiment. [Figure 4] 3A to 3C are aberration diagrams of the optical system of Example 1. [Figure 5] FIG. 10 is a cross-sectional view of a lens of an optical system according to a second embodiment. [Figure 6] 10A to 10C are aberration diagrams of the optical system of Example 2. [Figure 7] FIG. 10 is a cross-sectional view of a lens of an optical system according to a third embodiment. [Figure 8] 10A to 10C are aberration diagrams of the optical system of Example 3. [Figure 9] FIG. 10 is a cross-sectional view of a lens of an optical system according to a fourth embodiment. [Figure 10] 10A to 10C are aberration diagrams of the optical system of Example 4. [Figure 11] FIG. 1 is a schematic diagram of an imaging device. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. [Example 1] FIG. 1 is a cross-sectional view of a main portion of a lens device according to a first embodiment. As shown in FIG. 1, a lens device 100 according to this embodiment has two optical systems (a first optical system 101 and a second optical system 102) arranged in parallel to each other. The two optical systems 101 and 102 are held by a housing (not shown). In this embodiment, the optical systems 101 and 102 are identical except for the direction of reflection of the reflecting members, and therefore, in the following description, the optical system 101 will be described as a representative. Hereinafter, when the optical systems 101 and 102 are said to be identical, it means that the lens configuration, etc., are identical except for the direction of reflection of the reflecting members. Note that while FIG. 1 shows an example in which two optical systems according to the first embodiment are arranged as a representative example, two optical systems according to other embodiments may also be arranged.

[0012] The optical system 101 has two reflecting members 201 and 202, which will be described later. The first reflecting member 201 has a reflecting surface R1 that bends the optical path. The second reflecting member 202 has a reflecting surface R2 that bends the optical path. An aperture stop SP is provided between the first reflecting member 201 and the second reflecting member 202. The two reflecting members 201 and 202 bend the optical path twice at right angles. Therefore, the optical system 101 is an optical system with a bent optical axis. Here, the optical axis refers to the central axis of the optical system.

[0013] In Fig. 1, IP denotes an image plane (paraxial imaging position). When the optical system 101 of this embodiment is used as the photographic optical system of a digital still camera or digital video camera, the imaging surface of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor is placed on the image plane IP. When the optical system 101 of this embodiment is used as the photographic optical system of a silver halide film camera, a photosensitive surface corresponding to the film surface is placed on the image plane IP.

[0014] An image (optical image) is formed on an image plane IP by the optical systems 101 and 102. That is, in the lens apparatus 100 of this embodiment, two optical images by the two optical systems 101 and 102 are formed on one image sensor 200.

[0015] 2 is a diagram schematically illustrating two image circles IC1 and IC2 formed on an image plane IP by two optical systems 101 and 102 of the lens apparatus 100 of this embodiment. The rectangular area shown in FIG. 2 represents the effective area of ​​the image sensor 200, with IC1 being the image circle formed by the optical system 101 and IC2 being the image circle formed by the optical system 102.

[0016] With the lens device 100 of this embodiment, two optical images with parallax can be formed on one image sensor 200 due to the above configuration.

[0017] Next, the optical system 101 of this embodiment will be specifically described.

[0018] FIG. 3 is a cross-sectional view of the optical system 101 of this embodiment. The optical path bent by the reflecting members 201 and 202 is shown unfolded. In the cross-sectional view of the lens, the left side is the object side (front) and the right side is the image side (rear). The optical system of this embodiment is configured with multiple lens groups. Each lens group may consist of a single lens or multiple lenses. The lens group may also include an aperture stop. Although not shown, the optical system 101 of this embodiment may also include optical blocks corresponding to an optical filter, face plate, low-pass filter, infrared cut filter, etc., on the object side of the image plane IP. This also applies to the subsequent cross-sectional views of the lens.

[0019] The optical system 101 of this embodiment has a total angle of view of 190°, which is a so-called fisheye lens having an angle of view exceeding 170°.

[0020] FIG. 4 shows aberration diagrams of the optical system 101 of this embodiment when focused at infinity. In each aberration diagram, Fno is the F-number, and ω is the half angle of view (°). In the spherical aberration diagrams, the solid line represents the amount of spherical aberration for the d-line (wavelength 587.6 nm), and the dashed line represents the amount of spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagrams, the solid line (S) represents the amount of astigmatism for the sagittal image plane at the d-line, and the dashed line (M) represents the amount of astigmatism for the meridional image plane at the d-line. The distortion diagrams show the amount of distortion for the d-line and also show distortion relative to equidistant projection. Equidistant projection is a projection method that satisfies the equation y = fθ when forming an image. Here, y is the image height (height) on the image plane, f is the focal length of the optical system, and θ is the angle of view (angle). The chromatic aberration diagrams show the amount of chromatic aberration of magnification for the g-line. These same principles apply to the subsequent aberration diagrams.

[0021] The optical system 101 of this embodiment comprises, arranged in order from the object side to the image side, a front lens group N, a first reflecting member 201, a second reflecting member 202, and a rear lens group P. The front lens group N has negative refractive power. The first reflecting member 201 has a first reflecting surface R1. The second reflecting member 202 has a second reflecting surface R2. The rear lens group P has positive refractive power. Unlike the optical system illustrated in Patent Document 1, the optical system 101 of this embodiment does not have positive refractive power between the first reflecting surface R1 and the second reflecting surface R2. In Patent Document 1, this positive refractive power is provided by the intermediate group M. In Patent Document 1, the intermediate group M reduces the ray angle of off-axial light beams and brings the light rays closer to being parallel to the optical axis, thereby reducing the effective diameter of the rear lens group P and preventing interference between optical systems. In the optical system 101 of this embodiment, in order to reduce the element corresponding to this intermediate group M, the first reflecting member 201 and the second reflecting member 202 are arranged close to each other, and the focal length of the front lens group N and the focal length of the rear lens group P are optimized to satisfy the following conditional expression (1).

[0022] 0.80<|fn / fp|<5.00 (1) Here, fn is the focal length of the front lens group N, and fp is the focal length of the rear lens group P.

[0023] Conditional expression (1) defines the ratio of the focal length of the front lens group N to the focal length of the rear lens group P in the optical system 101. By satisfying conditional expression (1), the optical system has no refractive power between the first reflecting surface R1 and the second reflecting surface R2, but the ray angle of the off-axis light beam is reduced, making the light beam more parallel to the optical axis and enabling a smaller effective diameter of the rear lens group P. Below the lower limit of conditional expression (1), the refractive power of the front lens group N becomes too strong, widening the on-axis light beam and increasing the size of the reflecting members 201 and 202. To avoid interference between the two optical systems 101 and 102, the size of the reflecting members 201 and 202 is limited. This makes it difficult to ensure a sufficient distance required for bending the optical path, i.e., a sufficient distance between the lens surface of the front lens group N closest to the image and the lens surface of the rear lens group P closest to the object. If the upper limit of conditional expression (1) is exceeded, the refractive power of the front lens unit N will be weakened, making it difficult to reduce the size of the optical system 101. Also, the Petzval sum of the optical system 101 will be increased, resulting in increased curvature of field.

[0024] With the above configuration, a small, high-performance stereoscopic imaging device can be realized at a lower cost than conventional devices.

[0025] It is more preferable that the numerical range of conditional expression (1) is within the range of the following conditional expression (1a), and even more preferable that it is within the range of conditional expression (1b).

[0026] 0.83<|fn / fp|<4.00 (1a) 0.85<|fn / fp|<3.50 (1b) Next, conditions and configurations that are preferably satisfied by the optical system 101 of this embodiment will be described. The following preferred conditions and configurations may be satisfied by at least one of the two optical systems 101 and 102. More preferably, the two optical systems 101 and 102 may have the same configuration, so that both the two optical systems 101 and 102 satisfy the following preferred conditions and configurations.

[0027] In the optical system 101, when the refractive index of the first reflecting member 201 at the d-line is N1 and the refractive index of the second reflecting member 202 at the d-line is N2, it is preferable that at least one of N1 and N2 satisfy the following conditional expression (2):

[0028] 1.55 <Ni<2.20 i=1または2 (2) The equivalent length of a plane-parallel plate with a thickness s and a refractive index Ni is given by s / Ni. Therefore, fabricating the reflecting members 201 and 202 from a glass material with a high refractive index has the effect of shortening the equivalent length. This is desirable for reducing the effective diameter of the rear lens group P, which is determined by the off-axial light beam. Furthermore, this is also advantageous for correcting spherical aberration and axial chromatic aberration.

[0029] If the lower limit of conditional expression (2) is not satisfied, the diameter of the rear lens unit P becomes too large, which is undesirable, and the two optical systems 101 and 102 interfere with each other. Also, optical materials that exceed the upper limit of conditional expression (2) are undesirable because they are difficult to process and expensive.

[0030] It is more preferable that the numerical range of conditional expression (2) is within the range of the following conditional expression (2a), and even more preferable that it is within the range of conditional expression (2b).

[0031] 1.60 <Ni<2.10 i=1または2 (2a) 1.65 <Ni<2.05 i=1または2 (2b) It is preferable that the optical system 101 satisfy the following conditional expression (3), where fM is the focal length between the lens surface of the front lens group N closest to the image and the lens surface of the rear lens group P closest to the object, and f is the focal length of the optical system 101.

[0032] -0.010 <f / fM<0.010 (3) Conditional expression (3) defines the focal length of the optical path bending section. In this embodiment, the first reflecting surface R1 and the second reflecting surface R2 are formed as flat surfaces and have no refractive power. If the reflecting surfaces, entrance surfaces, and exit surfaces of the reflecting members 201 and 202 have refractive power beyond the range of conditional expression (3), the reflecting members 201 and 202 will have to be processed into curved surfaces, which increases manufacturing costs and is undesirable. Furthermore, if the reflecting surfaces are curved, the focal lengths in the meridional and sagittal directions will differ, which is undesirable as astigmatism will occur due to the on-axial angle of view and will degrade image quality.

[0033] It is more preferable that the numerical range of conditional expression (3) be within the range of the following conditional expression (3a), and even more preferable that it be within the range of conditional expression (3b).

[0034] -0.005 <f / fM<0.005 (3a) -0.002 <f / fM<0.002 (3b) It is preferable that the optical system 101 has a positive focal length as a whole, that is, does not have an intermediate image point.

[0035] When the focal length of the entire optical system 101 is negative, i.e., when an intermediate image point is present, the total optical length increases compared to when there is no intermediate image point, making it difficult to achieve compactness, which is not preferable. Also, the number of required lens elements increases, which is not preferable as it increases costs.

[0036] In the optical system 101, it is preferable that an aperture diaphragm SP be disposed between the first reflecting surface R1 and the second reflecting surface R2. Placing the aperture diaphragm SP closer to the object than the first reflecting surface R1 increases the distance between the rear lens group P and the aperture diaphragm SP, increasing the lens diameter of the rear lens group P and causing physical interference between the two optical systems 101 and 102 in the lens device 100, which is undesirable. Placing the aperture diaphragm SP closer to the image than the second reflecting surface R2 increases the distance between the front lens group N and the aperture diaphragm SP, increasing the diameter of the first lens, which is disposed closest to the object in the optical system 101. Because the first lens has a large volume, increasing the diameter of the first lens undesirably increases costs. Therefore, it is preferable that the aperture diaphragm SP be disposed between the first reflecting surface R1 and the second reflecting surface R2.

[0037] It is preferable that the optical system 101 satisfy at least one of the following conditional expressions (4) to (9).

[0038] 0.60 <Lsp / fp<2.50 (4) 0.75 <Emax / ICD<0.95 (5) 2.0<|fn / f|<20.0 (6) 2.0<|fp / f|<10.0 (7) 170° <FOV<200° (8) 0.05 <Dout / Din<0.50 (9) Here, Lsp is the distance along the optical axis between the lens surface having refractive power in the rear lens group P that is closest to the object and the aperture stop SP, and fp is the focal length of the rear lens group P. Emax is the maximum effective beam diameter in the rear lens group P, and ICD is the diameter of the image circle of the optical system 101. fn is the focal length of the front lens group N. FOV is the total angle of view of the optical system 101. Dout is the distance between the vertices of the surfaces of the lenses that are located closest to the image in the two optical systems 101 and 102 provided in the lens device 100. Din is the distance between the vertices of the surfaces of the lenses that are located closest to the object in the two optical systems 101 and 102 provided in the lens device 100.

[0039] Conditional expression (4) defines the ratio of the distance along the optical axis between the lens surface of the rear lens group P that has refractive power and is closest to the object and the aperture stop SP to the focal length of the rear lens group P. If the lower limit of conditional expression (4) is not satisfied, the refractive power of the rear lens group P becomes too weak, which increases the overall length of the optical system 101 and makes it unsuitable for compactness, undesirably. Furthermore, the diameter of the rear lens group P becomes too large, which causes interference between the two optical systems 101 and 102, undesirably. If the upper limit of conditional expression (4) is exceeded, the rear lens group P becomes too far from the aperture stop SP, which increases axial chromatic aberration and spherical aberration, resulting in a deterioration in image quality, undesirably.

[0040] It is more preferable that the numerical range of conditional expression (4) be within the range of the following conditional expression (4a), and even more preferable that it be within the range of conditional expression (4b).

[0041] 0.62 <Lsp / fp<2.00 (4a) 0.65 <Lsp / fp<1.50 (4b) Conditional formula (5) defines the ratio between the maximum effective diameter of light rays in the rear lens group P and the diameter of the image circle of the optical system 101. If the lower limit of conditional formula (5) is not met, the image circles IC1 and IC2 will interfere with each other on the image plane of the lens device 100, which is undesirable. If the upper limit of conditional formula (5) is met, the image circle IC1 will become too small, which will reduce the number of pixels relative to the angle of view and degrade image quality, which is undesirable. Alternatively, the diameter of the rear lens group P will become too large, which will cause physical interference between the two optical systems 101 and 102 of the lens device 100, which is undesirable.

[0042] It is more preferable that conditional expression (5) be set within the range of the following conditional expression (5a), and even more preferable that conditional expression (5b) be set within the range of the following conditional expression (5b).

[0043] 0.76 <Emax / ICD<0.92 (5a) 0.77 <Emax / ICD<0.90 (5b) Conditional expression (6) defines the absolute value of the ratio between the focal length of the front lens group N and the focal length of the optical system 101. If the lower limit of conditional expression (6) is not satisfied, the refractive power of the front lens group N becomes too strong, the diameter of the rear lens group P becomes large, and the two optical systems 101, 102 of the lens device 100 physically interfere with each other, which is undesirable. If the upper limit of conditional expression (6) is exceeded, the refractive power of the front lens group N becomes too weak, and the overall length of the optical system 101 becomes large, which is unsuitable for miniaturization, which is undesirable. Furthermore, the diameter of the first lens arranged closest to the object in the optical system 101 becomes large, which is undesirable as it increases costs.

[0044] It is more preferable that conditional expression (6) be set within the range of the following conditional expression (6a), and even more preferable that conditional expression (6b) be set within the range of the following conditional expression (6b).

[0045] 2.5<|fn / f|<18.0 (6a) 3.0<|fn / f|<16.0 (6b) Conditional expression (7) defines the absolute value of the ratio between the focal length of the rear lens group P and the focal length of the optical system 101. If the lower limit of conditional expression (7) is not satisfied, the refractive power of the rear lens group P becomes too strong, increasing the Petzval sum of the entire system and increasing the curvature of field, which is undesirable. If the upper limit of conditional expression (7) is exceeded, the refractive power of the rear lens group P becomes too weak, increasing the overall length of the optical system 101 and making it unsuitable for size reduction, which is undesirable.

[0046] It is more preferable that conditional expression (7) be within the range of the following conditional expression (7a), and even more preferable that conditional expression (7b) be within the range:

[0047] 2.5<|fp / f|<7.0 (7a) 3.0<|fp / f|<5.0 (7b) Conditional expression (8) defines a preferred angle of view for the optical system 101. To achieve a high sense of realism in virtual reality, it is preferable to have a wider angle of view. If the lower limit of conditional expression (8) is exceeded, the angle of view becomes narrow and a sufficient sense of realism cannot be achieved during viewing, which is undesirable. Furthermore, if the upper limit of conditional expression (8) is exceeded, the number of pixels per degree of angle of view decreases, which is undesirable as the image quality deteriorates. Furthermore, as the image height increases, the parallax between the two optical systems 101 and 102 decreases, which reduces the stereoscopic effect, so there is no need to use an optical system with an unnecessarily large angle of view.

[0048] It is more preferable that conditional expression (8) be set within the range of the following conditional expression (8a), and even more preferable that conditional expression (8b) be set within the range of the following conditional expression (8b).

[0049] 180° <FOV<195° (8a) 185° <FOV<192° (8b) Conditional expression (9) defines the ratio of the distance between the optical axes on the object side and the image side of the lens device 100. Below the lower limit of conditional expression (9), the base length becomes insufficient, making it impossible to obtain a sufficient three-dimensional effect, which is undesirable. Above the upper limit of conditional expression (9), the parallax becomes excessively large, which is undesirable. In this embodiment, Din is 60 mm, and Dout is 18.1 mm.

[0050] It is more preferable that conditional expression (9) be within the range of the following conditional expression (9a), and even more preferable that conditional expression (9b) be within the range:

[0051] 0.15 <Dout / Din<0.40 (9a) 0.20 <Dout / Din<0.35 (9b) Next, a description will be given of another embodiment in which the configuration of the optical system 101 is different. Here, only the differences from the first embodiment will be described. [Example 2] 5 is a cross-sectional view of the lenses of the optical system 101 in Example 2. However, the optical path bent by the first reflecting member 201 and the second reflecting member 202 is shown in an expanded form.

[0052] In Example 2, the value of conditional expression (6) is 15.56, which is significantly different from the values ​​of 3 to 4.5 of conditional expression (6) in the other examples. As a result, in the optical system 101 of Example 2, the front lens group N can be configured with three lenses. In the other examples, the front lens group N is configured with four lenses. In this way, in this example, the number of lenses can be reduced compared to the other examples, resulting in further cost reduction.

[0053] FIG. 6 is a diagram showing aberrations of the optical system 101 of the second embodiment when focused at infinity. [Example 3] 7 is a cross-sectional view of the lenses of the optical system 101 in Example 3. However, the optical path bent by the first reflecting member 201 and the second reflecting member 202 is shown in an expanded form.

[0054] In Example 3, the refractive indexes of the first reflecting member 201 and the second reflecting member 202 that bend the optical path are both 1.658, which is lower than the value of 2.001 in Examples 1 and 2. If the refractive indexes of the reflecting members 201 and 202 are lowered, the converted length of the reflecting members 202 and 202 becomes longer, making aberration correction more difficult; however, there are more types of optical glass available with a refractive index of around 1.7 than with a refractive index of around 2, making it easier to select inexpensive ones. For this reason, in this example, the reflecting members 202 and 202 can be made more inexpensive.

[0055] FIG. 8 is a diagram showing aberrations of the optical system 101 of the third embodiment when focused at infinity. [Example 4] 9 is a cross-sectional view of the lenses of the optical system 101 in Example 4. However, the optical path bent by the first reflecting member 201 and the second reflecting member 202 is shown in an expanded form.

[0056] In Example 4, the size of first reflecting member 201 is 22 mm in distance along the optical axis, which is larger than the value of 14.6 mm in the other Examples. Therefore, the value of Din is also 67 mm, which is larger than the value of Din of 60 mm in the other Examples. Increasing the base length increases the three-dimensional effect obtained from the image.

[0057] FIG. 10 is a diagram showing aberrations of the optical system 101 of the fourth embodiment when focused at infinity.

[0058] Next, Numerical Examples 1 to 4 corresponding to the optical system 101 of each example will be shown.

[0059] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial spacing (distance on the optical axis) between the mth surface and the (m+1)th surface. Here, m is the surface number counted from the light incident side. Also, nd represents the refractive index of each optical element with respect to the d-line, and vd represents the Abbe number of the optical element. Note that the Abbe number vd of a certain material is given by the following when the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines are Nd, NF, and NC, respectively: νd=(Nd-1) / (NF-NC) It is expressed as:

[0060] In each numerical example, d, focal length (mm), F-number, and half angle of view (°) are all values ​​when the optical system of each example is focused on an object at infinity. "Back focus BF" is the distance on the optical axis from the final lens surface (the lens surface closest to the image) to the paraxial image plane, expressed as an air-equivalent length. "Total lens length" is the distance on the optical axis from the forefront lens surface (the lens surface closest to the object) to the final lens surface plus the back focus. "Lens group" is not limited to cases where it is composed of multiple lenses, but also includes cases where it is composed of a single lens.

[0061] In Numerical Examples 1 to 4, the entire optical system is extended when focusing from an object at infinity to an object at a close distance. However, in order to reduce the weight of the drive unit, it is also possible to perform focusing by driving only some of the lenses in the optical system.

[0062] If the optical surface is aspherical, an asterisk (*) is added to the right of the surface number. The aspherical shape is expressed as follows: X is the displacement from the vertex of the surface in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, and A10 are the aspherical coefficients of each order. x=(h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 ]+A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 It should be noted that "e±XX" in each aspherical coefficient means "×10±XX."

[0063] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 39.239 1.90 2.00100 29.1 38.00 2 11.346 6.06 21.91 3* 38.557 1.05 1.53110 55.9 20.80 4* 19.011 7.05 18.23 5 -16.669 0.85 1.76385 48.5 17.06 6 32.370 2.92 17.19 7 89.803 5.79 1.91082 35.3 18.32 8 -20.149 6.04 18.79 9 ∞ 7.30 2.00100 29.1 12.25 10 ∞(reflective surface)7.30 2.00100 29.1 9.55 11 ∞ 4.00 6.89 12 (Aperture) ∞ 2.15 7.21 13 ∞ 7.30 2.00100 29.1 7.38 14 ∞(reflective surface)7.30 2.00100 29.1 8.53 15 ∞ 0.50 11.47 16* 13.540 3.42 1.53110 55.9 13.40 17* -74.993 0.66 13.52 18 17.465 2.90 1.49700 81.6 13.75 19 105.012 0.70 13.39 20 40.435 0.75 2.00100 29.1 13.13 21 8.751 6.63 1.43700 95.1 12.32 22 -19.518 13.50 13.46 Image plane ∞ Aspheric data 3rd page K = 0.00000e+000 A 4= 1.47379e-004 A 6=-1.41900e-007 A 8= 1.19814e-009 Side 4 K = 0.00000e+000 A 4= 1.66511e-004 A 6= 2.19570e-007 A 8= 2.54840e-009 Page 16 K = 0.00000e+000 A 4=-1.88452e-005 A 6= 5.38815e-008 A 8= 6.15195e-010 Page 17 K = 0.00000e+000 A 4= 6.23581e-005 A 6=-2.92064e-008 A 8= 1.41252e-009 Various data Focal length 5.23 F-number 2.91 Half angle of view (°) 95.2 Image height 8.55 Lens length 96.07 BF 13.50 Entrance pupil position 10.99 Exit pupil position -40.08 Front principal point position 15.70 Back principal point position 8.27 Lens group data Group starting plane focal length N 1 -22.73 P 16 19.15 [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 33.427 1.90 2.00100 29.1 39.54 2 11.724 10.86 22.85 3 -58.739 1.00 1.88300 40.8 21.25 4 17.768 16.53 18.69 5 346.991 6.54 1.89254 30.8 18.76 6 -31.423 9.55 18.64 7 ∞ 6.68 2.00100 29.1 11.37 8 ∞(reflective surface) 8.20 2.00100 29.1 9.24 9∞2.80 8.75 10 (Aperture) ∞ 1.55 8.81 11 ∞ 8.20 2.00100 29.1 8.84 12 ∞(reflective surface) 6.68 2.00100 29.1 8.93 13 ∞ 0.50 10.67 14 13.897 5.09 1.49700 81.5 11.92 15 -11.357 0.15 12.09 16 -11.370 1.00 1.86163 42.5 11.98 17 -26.444 2.63 12.55 18 22.711 0.75 1.91650 31.6 13.12 19 9.223 6.10 1.49700 81.5 12.62 20 -44.718 16.44 13.39 Image plane ∞ Various data Focal length 5.20 F-number 2.91 Half angle of view (°) 95.1 Image height 8.55 Lens length 113.15 BF 16.44 Entrance pupil position 11.97 Exit pupil position -32.39 Front principal point position 16.62 Back principal point position 11.23 Lens group data Group starting plane focal length N 1 -81.01 P 14 24.66 [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 46.645 1.90 2.00069 25.5 35.87 2 11.823 8.67 21.91 3* 124.690 1.05 1.53110 55.9 20.91 4* 12.426 6.55 18.87 5 -21.391 0.85 1.75500 52.3 18.85 6 -39.510 1.15 19.56 7 -60.866 4.89 1.85025 30.1 20.04 8 -17.516 6.00 20.78 9 ∞ 7.30 1.65844 50.9 13.33 10 ∞ (reflective surface) 7.30 1.65844 50.9 10.01 11 ∞ 4.00 6.89 12 (Aperture) ∞ 2.15 7.21 13 ∞ 7.30 1.65844 50.9 7.37 14 ∞(reflective surface)7.30 1.65844 50.9 9.03 15 ∞ 0.50 12.56 16 28.608 1.41 2.00069 25.5 13.69 17 57.221 0.15 13.81 18* 15.283 3.01 1.53110 55.9 14.60 19* 172.931 0.15 14.55 20 22.986 3.57 1.58913 61.1 14.60 21 -37.765 0.30 14.23 22 526.011 0.75 2.00069 25.5 13.60 23 8.518 5.94 1.49700 81.6 12.53 24 -32.581 13.21 13.33 Image plane ∞ Aspheric data 3rd page K = 0.00000e+000 A 4=-6.25154e-005 A 6=-2.44737e-008 A 8=-1.05285e-009 Side 4 K = 0.00000e+000 A 4=-6.14589e-005 A 6=-2.59819e-007 A 8=-4.67418e-009 Page 18 K = 0.00000e+000 A 4=-1.50169e-005 A 6= 4.77191e-007 A 8=-1.08530e-008 Page 19 K = 0.00000e+000 A 4= 5.91324e-005 A 6= 4.75199e-007 A 8=-1.26414e-008 Various data Focal length 5.31 F-number 2.91 Half angle of view (°) 93.6 Image height 8.55 Lens length 95.39 BF 13.21 Entrance pupil position 11.03 Exit pupil position -38.51 Front principal point position 15.80 Back principal point position 7.90 Lens group data Group starting plane focal length N 1 -23.95 P 16 19.12 [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 41.874 1.90 2.00100 29.1 38.05 2 11.318 10.21 21.91 3* 168.222 1.05 1.53110 55.9 21.01 4* 17.906 4.38 19.97 5 -26.508 0.85 1.76385 48.5 19.59 6 410.337 1.15 19.99 7 423.771 4.49 2.00330 28.3 20.31 8 -26.645 6.00 20.58 9 ∞ 11.00 1.85150 40.8 15.01 10 ∞ (reflective surface) 11.00 1.85150 40.8 11.08 11 ∞ 4.00 7.15 12 (Aperture) ∞ 2.15 7.58 13 ∞ 7.30 1.85150 40.8 7.82 14 ∞(reflective surface) 7.30 1.85150 40.8 9.27 15 ∞ 0.50 12.36 16 12.153 4.10 1.43875 94.7 14.90 17 -50.487 0.15 14.88 18* 19.544 2.02 1.53110 55.9 14.60 19* 84.188 1.51 14.28 20 -201.996 2.86 1.43875 94.7 14.19 21 -19.998 0.30 14.10 22 33.675 0.75 2.00069 25.5 13.15 23 10.331 1.27 12.28 24 19.091 3.08 1.43875 94.7 12.50 25 -91.914 13.21 12.96 Image plane ∞ Aspheric data 3rd page K = 0.00000e+000 A 4=-1.27473e-004 A 6= 3.97577e-007 A 8=-1.63372e-009 Side 4 K = 0.00000e+000 A 4=-1.59268e-004 A 6= 7.23736e-008 A 8=-1.39198e-010 Page 18 K = 0.00000e+000 A 4=-4.88438e-005 A 6=-2.89995e-006 A 8= 2.12575e-008 Page 19 K = 0.00000e+000 A 4= 1.23695e-004 A 6=-2.88957e-006 A 8= 3.57708e-008 Various data Focal length 5.32 F-number 2.91 Half angle of view (°) 93.4 Image height 8.55 Lens length 102.54 BF 13.21 Entrance pupil position 11.51 Exit pupil position -33.17 Front principal point position 16.23 Back principal point position 7.89 Lens group data Group starting plane focal length N 1 -16.21 P16 18.99 The various values ​​in each numerical example are summarized in Table 1 below.

[0064] [Table 1]

[0065] [Imaging device] Next, an embodiment of the imaging device of the present invention will be described. FIG. 11 is a schematic diagram of an imaging device (digital still camera) 300 of this embodiment. The imaging device 300 includes a camera body 320 having an imaging element 310 and a lens apparatus 100 having an optical system 101 similar to any of the above-described embodiments 1 to 4. The lens apparatus 100 and the camera body 320 may be integrally configured or detachably configured. The camera body 320 may be a so-called single-lens reflex camera having a quick-turn mirror, or a so-called mirrorless camera having no quick-turn mirror. The imaging element 310 is a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that receives and photoelectrically converts the optical image formed by the optical system 101. Note that only one optical system is shown in FIG. 11 because two optical systems are arranged side by side in the depth direction. FIG. 11 is a schematic side view of the imaging device 300, with two optical systems 101 and 102 arranged side by side in the depth direction.

[0066] In this embodiment, by using the lens device 100 equipped with the optical system 101 of each of the above embodiments, it is possible to provide a small, high-performance stereoscopic imaging device at a lower cost than conventional devices.

[0067] The lens device of each of the above-described embodiments can be applied not only to the digital still camera shown in FIG. 11 but also to various other imaging devices such as broadcast cameras, cameras for silver halide film, and surveillance cameras.

[0068] Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0069] Front lens group N Rear lens group P First reflecting member 201 Second reflecting member 202

Claims

1. An optical system having an angle of view exceeding 170°, comprising a front lens group having negative refractive power, a first reflecting member, a second reflecting member, and a rear lens group having positive refractive power, which are arranged in this order from the object side to the image side, an aperture stop is disposed between the first reflecting member and the second reflecting member; Let fn be the focal length of the front lens group, fp be the focal length of the rear lens group, and Lsp be the distance along the optical axis between the lens surface in the rear lens group that has refractive power and is closest to the object side and the aperture stop. 0.80<|fn / fp|<5.00 0.60<Lsp / fp<2.50 An optical system characterized by satisfying the following conditional expression:

2. When the refractive index of the first reflecting member at the d-line is N1 and the refractive index of the second reflecting member at the d-line is N2, for at least one of N1 and N2, 1.55<Ni<2.20 i=1 or 2 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. When the focal length between the lens surface of the front lens group closest to the image side and the lens surface of the rear lens group closest to the object side is fM and the focal length of the optical system is f, -0.010<f / fM<0.010 3. The optical system according to claim 1, wherein the following condition is satisfied:

4. 4. The optical system according to claim 1, wherein the focal length of the optical system is positive.

5. When the maximum effective diameter of light rays in the rear lens group is Emax and the diameter of the image circle of the optical system is ICD, 0.75<Emax / ICD<0.95 5. The optical system according to claim 1, wherein the following is satisfied:

6. When the focal length of the optical system is f, 2.0<|fn / f|<20.0 6. The optical system according to claim 1, wherein the following condition is satisfied:

7. When the focal length of the optical system is f, 2.0<|fp / f|<10.0 7. The optical system according to claim 1, wherein the following condition is satisfied:

8. When the total angle of view of the optical system is FOV, 170°<FOV<200° 8. The optical system according to claim 1, wherein the following condition is satisfied:

9. 9. The optical system according to claim 1, wherein the front lens group is made up of three or four lenses.

10. 10. A lens device comprising two optical systems: a first optical system as the optical system according to any one of claims 1 to 9; and a second optical system as the optical system according to any one of claims 1 to 9.

11. 11. The lens device according to claim 10, wherein the two optical systems are arranged in parallel.

12. When the distance between the vertices of the lenses located closest to the object side in the two optical systems is Din and the distance between the vertices of the lenses located closest to the image side in the two optical systems is Dout, 0.05<Dout / Din<0.50 12. The lens device according to claim 10, wherein the following condition is satisfied:

13. A lens device according to any one of claims 10 to 12; an imaging element that captures an optical image formed by the two optical systems.

14. 14. The imaging device according to claim 13, wherein the optical images formed by the two optical systems are captured by one of the imaging elements.

Images