Optical system and imaging apparatus including the same

Abstract

The invention relates to an optical system and an imaging apparatus including the same. The optical system includes, in order from an object side to an image side, a front group having positive refractive power, an aperture stop, and a rear group having positive refractive power, in which the front group includes, in order from the object side to the image side, a first lens having negative refractive power, a second lens having negative refractive power, a third lens, and a fourth lens having positive refractive power, wherein the rear group includes a balsaming lens and a meniscus lens located closest to the image side, in which at least one of an object-side surface and an image-side surface of the meniscus lens is aspheric, and in which spherical surfaces of both edge portions in an effective region passing through the object-side surface in a cross section including an optical axis have a concave shape toward the object side, and wherein a specific inequality is satisfied.

Description

Technical Field

[0001] Aspects of the embodiments are directed to an optical system suitable for use in an imaging device such as a digital still camera, a digital video camera, a vehicle-mounted camera, a camera for a mobile phone, a surveillance camera, a wearable camera, or a medical camera. Background Art

[0002] An optical system for use in an imaging device such as a vehicle-mounted camera needs to have a wide viewing angle. Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2018-522266 discusses an optical system having a wide viewing angle and consisting of seven lenses, in order from the object side to the image side, including a first lens having negative refractive power, a second lens having negative refractive power, a third lens having negative refractive power, and a fourth lens having positive refractive power. Summary of the invention

[0003] According to one aspect of the embodiment, the optical system includes, from the object side to the image side, a front group having positive refractive power, an aperture stop, and a rear group having positive refractive power, wherein the front group includes, from the object side to the image side, a first lens having negative refractive power, a second lens having negative refractive power, a third lens, and a fourth lens having positive refractive power, wherein the rear group includes a cemented lens and a meniscus lens located closest to the image side, wherein at least one of the object side surface and the image side surface of the meniscus lens is an aspherical surface, wherein a spherical surface of two edge portions in an effective area passing through the object side surface in a cross section including the optical axis has a concave shape toward the object side, and wherein the following inequality is satisfied:

[0004] 0.80<Rd<1.00,

[0005] Here, Rd is a value of a ratio of a diameter of a portion having a positive power in the effective area in a direction perpendicular to the optical axis to a diameter of the effective area of ​​the image side surface.

[0006] Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a schematic diagram illustrating main components of an optical system according to a first embodiment.

[0008] Figure 2 2 are aberration diagrams of the optical system according to the first embodiment.

[0009] Figure 3 is a schematic diagram illustrating main components of an optical system according to a second embodiment.

[0010] Figure 42 are aberration diagrams of the optical system according to the second embodiment.

[0011] Figure 5 is a schematic diagram illustrating main components of an optical system according to a third embodiment.

[0012] Figure 6 2 are aberration diagrams of the optical system according to the third embodiment.

[0013] Figure 7 is a schematic diagram illustrating main components of an optical system according to a fourth embodiment.

[0014] Figure 8 2 are aberration diagrams of the optical system according to the fourth embodiment.

[0015] Fig. 9 : is a diagram illustrating an aspherical shape of an object-side surface of second lens L2 according to an embodiment.

[0016] Fig.10 is a diagram illustrating an aspherical shape of the image-side surface of the meniscus lens LL according to the embodiment.

[0017] Fig.11 is a schematic diagram illustrating an image forming apparatus according to an exemplary embodiment.

[0018] Fig.12 is a diagram schematically illustrating optical characteristics of a mobile device and an optical system according to an exemplary embodiment.

[0019] Fig.13 is a block diagram illustrating an example of a configuration of a display system according to an exemplary embodiment. DETAILED DESCRIPTION

[0020] Various exemplary embodiments of the present disclosure will be described below with reference to the accompanying drawings. For convenience, each of the accompanying drawings may be depicted in a scale different from reality. In the accompanying drawings, corresponding components are assigned the same reference numerals, and their repeated descriptions are omitted.

[0021] Figure 1 , Figure 3 , Figure 5 and Figure 7They are cross-sectional views each including an optical axis OA and illustrating an optical system according to the first to fourth embodiments. In each cross-sectional view, the left side is the object side (front side), and the right side is the image side (rear side). Each of the optical systems according to the first to fourth embodiments is an imaging optical system for use in an imaging device, and the imaging plane of the image sensor is disposed at the position of the image plane IMG. The optical block CG disposed on the object side of the image plane IMG is an optical element that does not contribute to the image formation of the optical system, such as an optical filter or a cover glass. The optical system according to the first to fourth embodiments can be used as a projection optical system in a projection device (such as a projector), and in this case, the display surface of a display element (such as a liquid crystal panel) is disposed at the position of the image plane IMG.

[0022] Figure 2 , Figure 4 , Figure 6 and Figure 8 Each is a longitudinal aberration diagram of the optical system according to the first to fourth embodiments. Each longitudinal aberration diagram shows spherical aberration, field curvature (astigmatism) and distortion in order from the left. In each longitudinal aberration diagram, aberrations with respect to 656.3nm (C line), 587.6nm (d line), 486.1nm (F line) and 435.8nm (g line) are illustrated using different lines.

[0023] Next, features of the optical systems according to the first to fourth embodiments will be described in detail below.

[0024] The optical systems according to the first to fourth embodiments are each composed of a front group G1 having positive refractive power, an aperture stop STO, and a rear group G2 having positive refractive power, in order from the object side to the image side. An optical system without an optical block CG will be discussed below. The front group G1 includes, in order from the object side to the image side, a first lens L1 having negative refractive power, a second lens L2 having negative refractive power, a third lens L3, and a fourth lens L4 having positive refractive power. The rear group G2 is composed of a cemented lens LC and a meniscus lens LL (last lens) disposed closest to the image plane IMG. The lens herein refers to an optical element having refractive power and does not include an optical element (such as parallel plate glass) that does not have refractive power.

[0025] In the optical system according to the first to fourth embodiments, both the front group G1 and the rear group G2 have positive refractive power, and the front group G1 adopts the above-mentioned configuration, so that a wide angle of view is achieved while reducing the total length. By adopting the above-mentioned configuration of the rear group G2, field curvature and magnification chromatic aberration caused by widening the angle of view of the optical system are effectively corrected. In particular, by the rear group G2 consisting of two lenses (which are a cemented lens LC and a meniscus lens LL), the above-mentioned various aberrations are corrected while preventing the total length and weight from increasing.

[0026] According to the first to fourth embodiments, at least one of the object side surface and the image side surface of the meniscus lens LL is an aspherical surface. Providing an aspherical surface to the meniscus lens LL, which serves as the last lens disposed closest to the image plane IMG in the optical system, facilitates the correction of the field curvature caused by the viewing angle of the widening optical system. This beneficial effect can be produced in the case where only one of the object side surface and the image side surface of the meniscus lens LL is an aspherical surface (in one embodiment, as described below, the image side surface, which is the last lens surface in the optical system, is an aspherical surface). In order to provide additional freedom of design of the meniscus lens LL while preventing a sharp change in the shape of the aspherical surface, in another embodiment, both the object side surface and the image side surface are aspherical surfaces.

[0027] Figure 1 The bottom graph in the figure shows Figure 1 The top figure in the figure shows the outermost off-axis light beam reaching the maximum off-axis image height and the on-axis light beam reaching the on-axis image height in the cross-sectional view of the optical system according to the first embodiment. Figure 1 In the bottom figure in FIG. 1 , only the outermost off-axis light beams reaching the maximum off-axis image height on one side of the optical axis OA are illustrated, and the outermost off-axis light beams reaching the maximum off-axis image height on the other side of the optical axis OA are omitted. Figure 1 In the bottom diagram in FIG. 1 , only the principal ray passing through the center of the aperture stop STO and the marginal rays (upper ray and lower ray) as the outermost beams are illustrated, and other rays are omitted. Figure 1 In the bottom figure in FIG. 1 , the best-fit spherical surfaces corresponding to the object-side surface and the image-side surface of the meniscus lens LL are indicated by dotted lines. The best-fit spherical surface refers to a spherical surface (an approximate spherical surface of an aspherical surface) passing through two edge portions of the effective area of ​​the lens surface. The effective area refers to an area through which an effective light beam contributing to image formation passes, and the two edge portions of the effective area are portions through which marginal rays of the outermost off-axis light beam pass.

[0028] According to the first to fourth embodiments, in the cross section including the optical axis OA, the best-fit spherical surface in the effective region of the object-side surface of the meniscus lens LL is recessed toward the object side. This shape facilitates positioning the edge portion (lens periphery) of the meniscus lens LL in the radial direction separately from the image plane IMG, which facilitates preventing the holding member for holding the meniscus lens LL from interfering with the image sensor. In one embodiment, the best-fit spherical surface in the effective region of the image-side surface of the meniscus lens LL is convex toward the image side. This further facilitates preventing the holding member from interfering with the image sensor.

[0029] Furthermore, the optical systems according to the first to fourth embodiments satisfy the following inequality (0):

[0030] 0.80≤Rd≤1.00 (0),

[0031] Wherein Rd is a value of a ratio of the diameter of a portion having positive power in the effective area in a direction perpendicular to the optical axis OA to the diameter of the effective area of ​​the image-side surface of the meniscus lens LL.

[0032] Inequality (0) indicates that the proportion of the portion having positive power in the effective area of ​​the image side surface of the meniscus lens LL is large. By satisfying inequality (0), the formation of the image side surface of the meniscus lens LL is facilitated. In the case where inequality (0) is not satisfied, a sharp change in the shape of the image side surface of the meniscus lens LL occurs, which makes it difficult to maintain high surface accuracy during molding.

[0033] Furthermore, in one embodiment, the following inequality (0a) is satisfied:

[0034] 0.85≤Rd≤1.00 (0a).

[0035] In another embodiment, the following inequality (0b) is satisfied:

[0036] 0.90≤Rd≤1.00 (0b).

[0037] In one embodiment, the effective area of ​​the image-side surface of the meniscus lens LL is convex in the entire area from the axis to the outermost axis, as in the first embodiment. In other words, the following equation (0c) is satisfied:

[0038] Rd=1.00 (0c).

[0039] This results in the concave and convex shapes of the image-side surface of the meniscus lens LL remaining constant from the off-axis to the outermost off-axis, which further facilitates lens surface formation.

[0040] If the optical system according to the first to fourth embodiments satisfies at least the above-mentioned configuration, the beneficial effects of the present disclosure are obtained, and a configuration (including a configuration of five or more lenses) can be adopted in which, for example, the front group G1 also includes lenses other than the first lens L1 to the fourth lens L4. However, in order to reduce the size of the entire system, the front group G1 is composed of four lenses. Whether the third lens L3 is to have positive refractive power or negative refractive power can be determined based on the specifications of each optical system. According to the first to fourth embodiments, the meniscus lens LL is a positive lens with positive power. However, the meniscus lens LL can be a negative lens with negative power when appropriate. In one embodiment, the meniscus lens LL is a positive lens so as to achieve both a wide viewing angle and excellent optical performance based on the above-mentioned configuration.

[0041] For an imaging device, such as the vehicle-mounted camera described below, both a wide viewing angle and an increased imaging magnification near the optical axis (central area) are required. For example, in a case where the imaging device is deployed at the rear of a movable device (vehicle), an enlarged image of an image corresponding to a central area to be the main area of ​​interest can be displayed on an electronic rearview mirror, and the entire image including an area other than the central area (peripheral area) can be displayed on an in-vehicle display. For this form, the optical system has different imaging magnifications (focal lengths) for the central area and areas other than the central area. Therefore, in one embodiment, an aspherical surface is provided for the first lens L1, which is the lens that is deployed closest to the object and from which light rays from the object are greatly separated from each other. However, since the lens deployed closest to the object is larger in diameter than other lenses, it is difficult to mold an aspherical surface.

[0042] Therefore, in one embodiment, the object side surface (object side lens surface) of the second lens L2 is an aspherical surface. With this configuration, light from the peripheral portion in the radial direction in the light beam from the first lens L1 is greatly refracted toward the optical axis OA by the object side surface of the second lens L2.

[0043] This facilitates differentiation between imaging magnifications in the central region and the peripheral region of the optical system.

[0044] In this case, the object-side surface of second lens L2 is an aspherical surface having an inflection point in a cross section including the optical axis OA. This facilitates achieving a wide viewing angle and increased imaging magnification in a central area while reducing the number of lenses of the optical system.

[0045] Fig. 9 The aspherical shape of the object-side surface of the second lens L2 according to the first to fourth embodiments is illustrated. Fig. 9 , the horizontal axis represents the radial position of the object-side surface of the second lens L2 in the cross section including the optical axis OA, and the vertical axis represents the curvature [1 / mm] of the object-side surface of the second lens L2. More specifically, Fig. 9 The graph plotting the curvature at each position on the object-side surface of the second lens L2 is illustrated. When the distance from the optical axis OA to the position of the effective diameter (maximum effective diameter) is normalized to 1, the numerical value on the horizontal axis represents the distance (normalized distance) from the optical axis OA to the position within the effective diameter of the object-side surface of the second lens L2.

[0046] In one embodiment, the object-side surface of the second lens L2 is aspherical so that the curvature φ representing the distance from the optical axis OA is Fig. 9 Each curve in includes extreme values. Fig. 9As shown in , the curves according to the first to fourth embodiments each include at least one extreme value. This makes it possible to highlight the difference in imaging magnification between the central area and the peripheral area of ​​the optical system. Specifically, the imaging magnification can be set larger in the central area compared to the peripheral area, which makes it possible to improve the visibility of the image to the user of the imaging device. This beneficial effect is obtained in the case where the above-mentioned curve includes one extreme value, but by including multiple extreme values, the effect becomes more obvious. According to the first to fourth embodiments, the above-mentioned curve includes a first extreme value (maximum value) and a second extreme value (minimum value).

[0047] In one embodiment, the optical systems according to the first to fourth embodiments each satisfy the following inequality (1):

[0048] 0.05≤E1≤0.50 (1),

[0049] Wherein E1 is the normalized distance from the optical axis OA to the position corresponding to the first extreme value on the object-side surface of the second lens L2.

[0050] Inequality (1) defines the appropriate position of the first extreme value. Satisfying inequality (1) facilitates increasing the focal length of the central region of the optical system. Not satisfying inequality (1) is undesirable because it becomes difficult to set appropriate imaging magnifications for the central region and the peripheral region.

[0051] Furthermore, the following inequality (1a) is desirably satisfied:

[0052] 0.08≤E1≤0.45 (1a).

[0053] In another embodiment, the following inequality (1b) is satisfied:

[0054] 0.10≤E1≤0.40 (1b).

[0055] In one embodiment, the optical systems according to the first to fourth embodiments each satisfy the following inequality (2):

[0056] 0.60≤E2≤0.98 (2), where E2 is a normalized distance from the optical axis OA to a position corresponding to the second extreme value on the object-side surface of the second lens L2.

[0057] Inequality (2) defines a suitable position of the second extreme value. Satisfying inequality (2) facilitates achieving both size reduction and wide viewing angle of the optical system while highlighting the difference in imaging magnification between the central area and the peripheral area. Not satisfying inequality (2) is undesirable because it becomes difficult to set suitable imaging magnifications for the central area and the peripheral area.

[0058] Furthermore, in one embodiment, the following inequality (2a) is satisfied:

[0059] 0.65≤E2≤0.96 (2a).

[0060] In another embodiment, the following inequality (2b) is satisfied:

[0061] 0.70≤E2≤0.95 (2b).

[0062] Fig.10 and Fig. 9 1 and 2 illustrate the aspherical shape of the image side surface (convex surface) of the meniscus lens LL according to the first to fourth embodiments. In one embodiment, the image side surface of the meniscus lens LL is an aspherical surface such that the curvature with respect to the distance from the optical axis OA is Fig.10 Each curve in includes extreme values. Fig.10 As shown in , the curves according to the first to fourth embodiments each include a third extreme value (maximum value). This makes it possible to correct the field curvature that occurs when the difference in imaging magnification between the central area and the peripheral area of ​​the highlight optical system, which facilitates high optical performance from the axis to the outermost off-axis.

[0063] In one embodiment, the optical systems according to the first to fourth embodiments each satisfy the following inequality (3):

[0064] 0.05≤E3≤0.50 (3),

[0065] Wherein E3 is the normalized distance from the optical axis OA to the position corresponding to the third extreme value on the image-side surface of the meniscus lens LL.

[0066] Inequality (3) defines the appropriate position of the third extremum on the image-side surface of the meniscus lens LL as the last lens surface. Satisfying inequality (3) facilitates preventing the change of field curvature from the axis to the outermost off-axis in the optical system. Not satisfying inequality (3) is undesirable because it becomes difficult to prevent the change of field curvature from the axis to the outermost off-axis.

[0067] Furthermore, in one embodiment, the following inequality (3a) is satisfied:

[0068] 0.10≤E3≤0.45 (3a).

[0069] In another embodiment, the following inequality (3b) is satisfied:

[0070] 0.15≤E3≤0.40 (3b).

[0071] In one embodiment, as described below, the shape of the second lens L2 on the optical axis OA is a convex meniscus shape toward the object side. In this case, the meniscus lens LL having a convex meniscus shape toward the image side is approximately symmetrical with the second lens L2 relative to the aperture stop STO. Therefore, in order to effectively correct the field curvature caused by the second lens L2 using the meniscus lens LL, the extreme values ​​on the aspherical surfaces of the second lens L2 and the meniscus lens LL are also at positions approximately symmetrical with respect to the aperture stop STO. Therefore, both inequality (1) and inequality (3) are satisfied.

[0072] In one embodiment, the optical systems according to the first to fourth embodiments each satisfy the following inequality (4):

[0073] 3.5≤fal / f≤10.0 (4),

[0074] Wherein fa1 is the focal length of the air lens between the first lens L1 and the second lens L2, and f is the focal length of the optical system (the entire system).

[0075] By satisfying inequality (4), a strong positive power (refractive power) (having a high absolute value) is imparted to the air lens formed by the first lens L1 and the second lens L2, which makes it possible to increase the imaging magnification in the central area of ​​the optical system. It is undesirable to fall below the lower limit of inequality (4) because the positive power of the air lens becomes too strong, which may cause a significant change in the optical performance of the optical system when the lens alignment is offset due to manufacturing errors. It is also undesirable to exceed the upper limit of inequality (4) because the positive power of the air lens becomes too weak, which makes it difficult to increase the imaging magnification in the central area of ​​the optical system.

[0076] Furthermore, in one embodiment, the following inequality (4a) is satisfied:

[0077] 3.7≤fa1 / f≤9.5 (4a).

[0078] In another embodiment, the following inequality (4b) is satisfied:

[0079] 4.0≤fa1 / f≤9.0 (4b).

[0080] In one embodiment, the optical systems according to the first to fourth embodiments each satisfy the following inequality (5):

[0081] 0.40≤fG1 / fG2≤3.50 (5),

[0082] Where fG1 is the focal length of the front group G1, and fG2 is the focal length of the rear group G2.

[0083] By satisfying inequality (5), the power of the front group G1 and the rear group G2 can be appropriately set, which makes it possible to further reduce the size of the optical system. It is undesirable to fall below the lower limit of inequality (5) because the power of the front group G1 becomes too strong, which may cause a significant change in the optical performance of the optical system when the lens alignment is offset due to manufacturing errors. It is also undesirable to exceed the upper limit of inequality (5) because the power of the front group G1 becomes too weak, which makes it difficult to further reduce the size of the optical system.

[0084] Furthermore, in one embodiment, the following inequality (5a) is satisfied:

[0085] 0.45≤fG1 / fG2≤3.45 (5a).

[0086] In another embodiment, the following inequality (5b) is satisfied:

[0087] 0.50≤fG1 / fG2≤3.40 (5b).

[0088] In one embodiment, the optical systems according to the first to fourth embodiments each satisfy the following inequality (6):

[0089] -1.50≤(R2+R1) / (R2-R1)≤-4.00 (6),

[0090] Wherein R1 is the radius of curvature of the best-fit spherical surface in the effective area of ​​the object-side surface of the meniscus lens LL, and R2 is the radius of curvature of the best-fit spherical surface in the effective area of ​​the image-side surface of the meniscus lens LL.

[0091] Inequality (6) defines the desired shape (shape factor) of the meniscus lens LL. It is undesirable to fall below the lower limit of inequality (6) because the aperture angle of the meniscus lens LL becomes too large, which makes it difficult to process the aspherical surface of the meniscus lens LL or increases unwanted light reflected from the aspherical surface. It is also undesirable to exceed the upper limit of inequality (6) because a sharp change occurs in the surface shape of the meniscus lens LL, which makes it difficult to maintain high surface accuracy during molding.

[0092] Furthermore, in one embodiment, the following inequality (6a) is satisfied:

[0093] -1.70≤(R2+R1) / (R2-R1)≤-3.80 (6a).

[0094] In another embodiment, the following inequality (6b) is satisfied:

[0095] -1.90≤(R2+R1) / (R2-R1)≤-3.60 (6b).

[0096] In one embodiment, the optical systems according to the first to fourth embodiments each satisfy the following inequality (7):

[0097] 1.0≤fLC / f≤6.0 (7),

[0098] Where fLC is the focal length of the cemented lens LC.

[0099] Satisfying inequality (7) makes it possible to effectively correct field curvature and astigmatism in the entire region of a wide viewing angle. Falling below inequality (7) is undesirable because the positive power of the cemented lens LC becomes too strong, which makes it easier for high-order aberrations to occur. Exceeding the upper limit of inequality (4) is also undesirable because the positive power of the cemented lens LC becomes too weak, which results in insufficient correction of field curvature or astigmatism.

[0100] Furthermore, in one embodiment, the following inequality (7a) is satisfied:

[0101] 1.1≤fLC / f≤5.9 (7a).

[0102] In another embodiment, the following inequality (7b) is satisfied:

[0103] 1.2≤fLC / f≤5.8 (7b).

[0104] In one embodiment, the optical systems according to the first to fourth embodiments each satisfy the following inequality (8):

[0105] -2.20≤Ds / rLC≤-0.60 (8),

[0106] Wherein rLC is the radius of curvature of the cemented surface of the cemented lens LC, and Ds is the distance from the aperture stop STO to the cemented surface of the cemented lens LC.

[0107] By satisfying inequality (8), the cemented surface of the cemented lens LC becomes concentric with respect to the aperture stop STO, which makes it possible to prevent halo from occurring in the entire region of a wide viewing angle. It is undesirable to fall below the lower limit of inequality (8) because the radius of curvature of the cemented surface of the cemented lens LC becomes too small, which makes it easier for high-order aberrations to occur. It is also undesirable to exceed the upper limit of inequality (8) because the radius of curvature of the cemented surface of the cemented lens LC becomes too large, which results in insufficient correction of halo.

[0108] Furthermore, in one embodiment, the following inequality (8a) is satisfied:

[0109] -2.10≤Ds / rLC≤-0.70 (8a).

[0110] In another embodiment, the following inequality (8b) is satisfied:

[0111] -2.00≤Ds / rLC≤-0.80 (8b).

[0112] In one embodiment, the optical systems according to the first to fourth embodiments each satisfy the following inequality (9):

[0113] 2.0≤fLL / f≤22.0 (9),

[0114] where fLL is the focal length of the meniscus lens LL.

[0115] By satisfying inequality (9), an appropriate positive power is given to the meniscus lens LL, which makes it possible to prevent field curvature from occurring in the entire region of a wide viewing angle and achieve excellent telecentricity. It is undesirable to fall below the lower limit of inequality (9) because the power of the meniscus lens LL becomes too large, which makes it difficult to correct the field curvature. It is also undesirable to exceed the upper limit of inequality (9) because the power of the meniscus lens LL becomes too small, which makes it difficult to achieve excellent telecentricity.

[0116] Furthermore, in one embodiment, the following inequality (9a) is satisfied:

[0117] 2.2≤fLL / f≤21.0 (9a).

[0118] In another embodiment, the following inequality (9b) is satisfied:

[0119] 2.4≤fLL / f≤20.0 (9b).

[0120] In one embodiment, on the optical axis OA, the first lens L1 and the second lens L2 each have a convex meniscus shape toward the object side, the third lens L3 has a concave shape toward the object side, and the fourth lens L4 has a biconvex shape. With this configuration, the incident angle of each light ray on the rear group G2 is reduced, and changes in optical performance due to alignment errors (manufacturing errors) of each lens, etc., are prevented. In another embodiment, the shapes of the lenses other than the shapes on the optical axis OA are also configured as described above. Specifically, each of the first lens L1 and the second lens L2 is a meniscus lens (negative meniscus lens) having a convex shape toward the object side, the third lens L3 is a lens having a concave shape toward the object side, and the fourth lens L4 is a biconvex lens.

[0121] In one embodiment, the cemented lens LC of the rear group G2 also includes a positive lens and a negative lens in sequence from the object side to the image side, so as to facilitate the reduction of chromatic aberration of magnification. In addition, on the optical axis OA, the positive lens of the cemented lens LC has a biconvex shape, and the negative lens of the cemented lens LC has a convex meniscus shape toward the image side. This makes it possible to effectively correct the chromatic aberration of magnification while reducing the size of the cemented lens LC. In one embodiment, the shapes of the lenses other than the shapes on the optical axis OA are also configured as described above. Specifically, the positive lens of the cemented lens LC is a biconvex lens, and the negative lens of the cemented lens LC is a meniscus lens with a convex shape toward the image side. The cemented lens LC can be composed of three or more lenses. However, in order to reduce the size of the entire system and facilitate manufacturing, the cemented lens LC is composed of two lenses.

[0122] The detailed configurations of the optical systems according to the first to fourth embodiments will be described below.

[0123] [First embodiment]

[0124] like Figure 1 As shown in FIG. 1 , the optical system 100 according to the first embodiment is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, an aperture stop STO, a cemented lens LC, and a meniscus lens LL from the object side to the image side. A light beam from an object (not shown) is focused onto an image plane IMG through the lens and the cover glass CG, thereby forming an image of the object. The optical system 100 according to this embodiment has a sufficiently wide total viewing angle of 180° (with a half viewing angle of ±90°), and a sufficiently long focal length (center focal length) of 4.4 mm on the optical axis OA.

[0125] According to the present embodiment, the third lens L3 has negative refractive power, and the cemented lens LC is composed of a positive lens L5 and a negative lens L6 in order from the object side to the image side. The second lens L2 and the meniscus lens LL each have an aspherical surface. Specifically, the object side surface and the image side surface of the second lens L2 and the meniscus lens LL are each aspherical surfaces, and the object side surface of the second lens L2 and the image side surface of the meniscus lens LL are each aspherical surfaces including an inflection point in a cross section including the optical axis OA.

[0126] like Figure 2 As shown in FIG. 1 , in the optical system 100 according to the present embodiment, spherical aberration and field curvature are effectively corrected. The distortion in the peripheral area increases as the viewing angle (image height) increases, while the distortion in the central area is relatively small. This makes it possible to achieve high resolution in the central area compared to the peripheral area, which makes it possible to improve the visibility of the image for the user of the imaging device.

[0127] [Second embodiment]

[0128] like Figure 3As shown in , the optical system 200 according to the second embodiment is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, an aperture stop STO, a cemented lens LC and a meniscus lens LL from the object side to the image side. As in the first embodiment, according to this embodiment, the third lens L3 has a negative refractive power, and the cemented lens LC is composed of a positive lens L5 and a negative lens L6 from the object side to the image side. However, the difference between this embodiment and the first embodiment is that the third lens L3 and the fourth lens L4 are bonded together to form a cemented lens. The optical system 200 according to this embodiment has a sufficiently wide total viewing angle of 180° (including a half viewing angle of ±90°), and a sufficiently long focal length of 4.6 mm on the optical axis OA.

[0129] like Figure 4 As shown in , in the optical system 200 according to the present embodiment, spherical aberration and field curvature are effectively corrected. The distortion in the peripheral area increases as the viewing angle increases, while the distortion in the central area is relatively small.

[0130] [Third embodiment]

[0131] like Figure 5 As shown in FIG. 1 , the optical system 300 according to the third embodiment is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, an aperture stop STO, a cemented lens LC, and a meniscus lens LL in order from the object side to the image side. The optical system 300 according to this embodiment has a sufficiently wide total viewing angle of 180° (including a half viewing angle of ±90°) and a sufficiently long focal length of 4.5 mm on the optical axis OA.

[0132] like Figure 6 As shown in , in the optical system 300 according to the present embodiment, spherical aberration and field curvature are effectively corrected. The distortion in the peripheral area increases as the viewing angle increases, while the distortion in the central area is relatively small.

[0133] [Fourth embodiment]

[0134] like Figure 7 As shown in FIG. 1 , the optical system 400 according to the fourth embodiment is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, an aperture stop STO, a cemented lens LC, and a meniscus lens LL in order from the object side to the image side. The optical system 400 according to this embodiment has a sufficiently wide total viewing angle of 120° (with a half viewing angle of ±60°) and a sufficiently long focal length of 4.4 mm on the optical axis OA.

[0135] like Figure 8 As shown in , in the optical system 400 according to the present embodiment, spherical aberration and field curvature are effectively corrected. The distortion in the peripheral area increases as the viewing angle increases, while the distortion in the central area is relatively small.

[0136] The first to fourth numerical examples for the above-mentioned first to fourth embodiments will be described below. In each numerical example, each surface number indicates the order of the corresponding optical surface counted from the object plane, r [mm] indicates the radius of curvature of the i-th optical surface, and d [mm] indicates the distance between the i-th optical surface and the (i + 1)-th optical surface (the distance on the optical axis). In addition, nd indicates the refractive index of the medium between the i-th surface and the (i + 1)-th surface for the d-line, and νd indicates the Abbe number of the medium based on the d-line. The Abbe number νd is a value defined by the following equation:

[0137] vd=(nd-1) / (nF-nC),

[0138] wherein nF, nd and nC indicate the refractive indices for the F line, d line and C line, respectively.

[0139] In each numerical example, an asterisk (*) is added to the end of each surface number of the aspherical surface. In the numerical value, "E±P" indicates "×10±P". The shape of each aspherical surface is expressed by the following equation 1:

[0140] Equation 1

[0141]

[0142] Wherein z is the amount of displacement from the surface vertex in the direction of the optical axis, h is the height from the optical axis OA in a direction perpendicular to the optical axis, c is the curvature (the inverse of the radius of curvature r), k is the cone coefficient, and A, B, C, D, E, F, G, H, I... are aspherical coefficients.

[0143] The optical systems according to the numerical examples are each a single focus optical system in which the focal length is fixed (zooming is not performed) and adopt a configuration in which focusing is not performed. Specifically, the distance between the lenses of the optical systems according to the numerical examples is always fixed. This makes it possible to avoid changes in optical performance caused by the movement of the lenses. However, the optical system can be configured to perform at least one of zooming and focusing when appropriate, and in order to do this, the distance between the lenses can be set to be variable.

[0144] (First numerical example)

[0145] Various data

[0146] Center focal length 4.4mm

[0147] Fno 2.8

[0148] Half viewing angle ±90°

[0149] Surface data

[0150]

[0151] Aspheric coefficient

[0152]

[0153] (Second numerical example)

[0154] Various data

[0155] Center focal length 4.6mm

[0156] Fno 2.8

[0157] Half viewing angle ±90°

[0158] Surface data

[0159]

[0160] Aspheric coefficient

[0161]

[0162]

[0163] (Third numerical example)

[0164] Various data

[0165] Center focal length 4.5mm

[0166] Fno 2.8

[0167] Half viewing angle ±90°

[0168] Surface data

[0169]

[0170] Aspheric coefficient

[0171]

[0172]

[0173] (Fourth Numerical Example)

[0174] Various data

[0175] Center focal length 4.4mm

[0176] Fno 2.8

[0177] Half viewing angle ±60°

[0178] Surface data

[0179]

[0180] Aspheric coefficient

[0181]

[0182]

[0183] Table 1 presents values ​​associated with inequalities associated with the optical systems according to the first to fourth embodiments. Table 1 also presents values ​​associated with inequalities (10) and (11). As shown in Table 1, the optical systems according to the first to fourth embodiments satisfy the inequalities.

[0184] Table 1

[0185] First embodiment First embodiment Second embodiment Fourth embodiment (0) Rd 1.00 1.00 0.90 1.00 (1) E1 0.20 0.24 0.30 0.22 (2) E2 0.84 0.90 0.90 0.94 (3) E3 0.24 0.22 0.22 0.26 fal 21.2 28.5 33.7 22.6 f 4.40 4.57 4.52 4.40 (4) fal / f 4.81 6.24 7.46 5.13 fG1 8.84 25.18 17.46 8.25 fG2 11.47 9.36 10.69 11.22 (5) fG1 / fG2 0.77 2.69 1.63 0.74 R1 -13.03 -15.07 -14.09 -2.17E+01 R2 -6.49 -7.38 -7.69 -7.40 (6) (R2+R1) / (R2-R1) -2.98 -2.92 -3.41 -2.03 f 19.55 10.01 11.34 22.44 (7) fLC / f 4.44 2.19 2.51 5.10 Ds 4.55 5.04 4.40 4.60 LqCy -3.47 -3.32 -3.2 -3.4 (8) Ds / R -1.31 -1.52 -1.38 -1.35 f 18.34 52.14 76.16 15.98 (9) fLL / f 4.17 11.42 16.86 3.63 (10) f×sin(θmax) / y(θmax) 1.13 1.17 1.15 1.10 (11) y(θmax / 2) / y(θmax) 0.77 0.78 0.78 0.67

[0186] [Imaging device]

[0187] Fig.11 is a schematic diagram illustrating main components of an imaging device 70 according to an exemplary embodiment of the present disclosure. The imaging device 70 according to the present exemplary embodiment includes an optical system (imaging optical system) 71 according to any one of the above-described embodiments, a light receiving element 72 configured to perform photoelectric conversion on an object image formed by the optical system 71, and a camera body (housing) 73 configured to hold the light receiving element 72. The optical system 71 is held by a lens barrel (holding member) and connected to the camera body 73. Fig.11 As shown in FIG. 7 , a display unit 74 for displaying an image acquired by the light receiving element 72 may be connected to the camera body 73. As the light receiving element 72, an image sensor (photoelectric conversion element) such as a charge coupled device (CCD) sensor or a complementary metal oxide semiconductor (CMOS) sensor may be used.

[0188] In the case of using the imaging device 70 as the distance measuring device, for example, an image sensor (imaging plane phase difference sensor) including pixels capable of splitting a light beam from an object into two and photoelectrically converting the split beams can be adopted as the light receiving element 72. In the case where the subject is located on the front focal plane of the optical system 71, positional deviation does not occur in the image corresponding to the two split light beams on the image plane of the optical system 71. However, in the case where the subject is located outside the front focal plane of the optical system 71, positional deviation occurs in the image. In this case, since the positional deviation in each image corresponds to the amount of displacement of the subject from the front focal plane, the distance to the subject can be measured by acquiring the amount of positional deviation in each image and the direction of each positional deviation using the imaging plane phase difference sensor.

[0189] The optical system 71 and the camera body 73 can be configured to be attachable to and detachable from each other. Specifically, the optical system 71 and the lens barrel can be configured as an interchangeable lens (lens device). The optical system according to the above-mentioned first to fourth embodiments can be applied not only to imaging devices such as digital still cameras, cameras for silver halide films, video cameras, vehicle-mounted cameras, and surveillance cameras, but also to various optical devices such as telescopes, binoculars, projectors (projection devices), and digital copiers.

[0190] [In-vehicle system]

[0191] Fig.12 The top diagram in FIG. 1 is a schematic diagram illustrating an imaging device 20 (vehicle-mounted camera) and a movable device 10 capable of moving while holding the imaging device 20 according to an exemplary embodiment of the present disclosure. Fig.12 The top figure in illustrates a case where the mobile device 10 is a car (vehicle). The mobile device 10 includes a driving unit (such as a motor) (not shown) for moving the mobile device 10 and an on-board system (driving assistance device) (not shown) for assisting a user 40 (such as a driver or a passenger) of the mobile device 10 using an image acquired by the imaging device 20. Although the present exemplary embodiment describes a case where the imaging device 20 is deployed to capture the rear of the mobile device 10, the imaging device 20 may be deployed to capture the front or side of the mobile device 10. Two or more imaging devices 20 may be deployed at two or more locations on the mobile device 10.

[0192] The imaging device 20 includes an optical system 201 and an imaging unit 210 according to any one of the above-described embodiments. The optical system 201 is an optical system (different-angle lens) having different imaging magnifications between a first angle of view (first field of view) 30 and a second angle of view (second field of view) 31 greater than the first angle of view 30. The imaging plane (light receiving surface) of the imaging unit 210 includes a first area for imaging an object within the first angle of view 30 and a second area for imaging an object within the second angle of view 31. In this case, the number of pixels per unit angle of view is larger in the first area than in the second area excluding the first area. In other words, the first angle of view 30 (first area) of the imaging device 20 is higher in resolution than the second angle of view 31 (second area).

[0193] The optical characteristics of the optical system 201 will be described in detail below. Fig.12 The lower left figure in FIG. 1 illustrates the image height y [mm] at different half viewing angles θ [deg.] on the imaging plane of the imaging unit 210 in the form of contour lines. Fig.12 The lower right figure in is a graph showing the relationship between the half viewing angle θ and the image height y in the first quadrant of the left figure (the projection characteristics of the optical system 201).

[0194] like Fig.12 As shown in the bottom figure in , the optical system 201 is configured so that the projection characteristic y(θ) of the viewing angle less than the predetermined half viewing angle θa overlaps with the projection characteristic y(θ) of the viewing angle greater than or equal to the half viewing angle θa. Therefore, the amount of increase (resolution) of the image height y per unit half viewing angle θ changes for each viewing angle. The local resolution of the optical system 201 is expressed as the differential value dy(θ) / dθ of the projection characteristic y(θ) with respect to the half viewing angle θ. Fig.12 The lower left figure in indicates that the larger the spacing between the contour lines of the image height y relative to the half viewing angle θ, the higher the resolution. Fig.12 The lower right graph in indicates that the larger the slope of the curve of the projection characteristic y(θ), the higher the resolution.

[0195] exist Fig.12 In the lower left figure of FIG. 1 , the first area 201a is the central area and corresponds to a viewing angle less than half the viewing angle θa, and the second area 201b is the peripheral area and corresponds to a viewing angle greater than or equal to half the viewing angle θa. Fig.12 The first viewing angle 30 in the top figure corresponds to the first viewing angle 30 in the top figure, and the viewing angle less than half the viewing angle θa and the viewing angle greater than or equal to half the viewing angle θa are combined with Fig.12 31 in the top diagram of FIG. As described above, the first region 201a is a high-resolution, low-distortion region, and the second region 201b is a low-resolution, high-distortion region.

[0196] In one embodiment, the value of the half viewing angle θa is greater than or equal to 13.5° and less than or equal to 31.5°, and in another embodiment, greater than or equal to 14.4° and less than or equal to 22.5°.

[0197] The optical system 201 is configured so that the projection characteristic y(θ) in the first region 2θ1a is different from f×θ (equidistant projection method) and from the projection characteristic in the second region 201b. In this case, the projection characteristic y(θ) of the optical system 201 satisfies the following inequality (10):

[0198] 1.0 <f×sin(θmax) / y(θmax)≤1.9 (10).

[0199] By satisfying inequality (10), the resolution is reduced in the second region 201b, thereby achieving a wide viewing angle of the optical system 201. In addition, a higher resolution is achieved in the first region 201a than in the central region of a general fisheye lens using an orthographic projection method (y(θ)=f×sinθ). It is undesirable to fall below the lower limit of inequality (10) because it results in a lower resolution in the first region 201a compared to the fisheye lens of the orthographic projection method, or an increased maximum image height, thereby resulting in an increase in the size of the optical system. It is also undesirable to exceed the upper limit of inequality (10) because it results in an excessively high resolution in the first region 201a, which makes it difficult to achieve a wide viewing angle equivalent to that of the fisheye lens of the orthographic projection method or to maintain excellent optical performance.

[0200] Furthermore, in one embodiment, the following inequality (10a) is satisfied:

[0201] 1.0 <f×sin(θmax) / y(θmax)≤1.7 (10a).

[0202] In another embodiment, the following inequality (10b) is satisfied:

[0203] 1.0<f×sin(θmax) / y(θmax)≤1.4 (10b).

[0204] In one embodiment, the optical system according to the present exemplary embodiment satisfies the following inequality (11):

[0205] 0.55<y(θmax / 2) / y(θmax)<0.85 (11).

[0206] Inequality (11) represents the value of the ratio of the image height y(θmax / 2) at the viewing angle θmax / 2 which is half of the maximum half viewing angle θmax to the image height y(θmax) at the maximum half viewing angle θmax. By satisfying inequality (11), a higher resolution is achieved near the optical axis OA in the first region 201a while maintaining a wide viewing angle. Not satisfying inequality (11) is undesirable because it results in a lower resolution in the first region 201a than the fisheye lens of the orthographic projection method, or makes it difficult to achieve a wide viewing angle equivalent to that of the fisheye lens of the orthographic projection method.

[0207] Furthermore, in another embodiment, the following inequality (11a) is satisfied:

[0208] 0.60<y(θmax / 2) / y(θmax)<0.83 (11a).

[0209] In yet another embodiment, the following inequality (11b) is satisfied:

[0210] 0.65 <y(θmax / 2) / y(θmax)<0.81 (11b).

[0211] As described above, since the first area 201a of the optical system 201 is low in distortion and high in resolution, a high-resolution image can be obtained compared to the second area 201b. Therefore, by setting the first area 201a (first viewing angle 30) as the area of ​​interest of the user 40, excellent visibility can be achieved. Fig.12 In the case where the imaging device 20 shown in the top figure in FIG. 1 is disposed at the rear of the mobile device 10, displaying an image corresponding to the first viewing angle 30 on the electronic rearview mirror allows a natural sense of perspective to be obtained when the user 40 is looking at the rear vehicle. In contrast, the second area 201b (second viewing angle 31) corresponds to a wide viewing angle including the first viewing angle 30. Therefore, for example, displaying an image corresponding to the second viewing angle 31 on the in-vehicle display when the mobile device 10 is reversing assists the user 40 in driving.

[0212] Fig.13 1 is a functional block diagram illustrating an example of the configuration of the vehicle-mounted system (display system) 2 according to the present exemplary embodiment. The vehicle-mounted system 2 is a system that displays an image acquired by the imaging device 20 positioned behind the mobile device 10 to the user 40. The vehicle-mounted system 2 includes the imaging device 20, a processing device 220, and a display device (display unit) 230. The imaging device 20 includes the optical system 201 and the imaging unit 210 as described above. The imaging unit 210 includes an image sensor (such as a CCD sensor or a CMOS sensor), performs photoelectric conversion on an optical image formed by the optical system 201 to generate captured image data, and outputs the captured image data to the processing device 220.

[0213] The processing device 220 includes an image processing unit 221, a display viewing angle determination unit 224 (determination unit), a user setting change unit 226 (first change unit), a rear vehicle distance detection unit 223 (first detection unit), a reverse gear detection unit 225 (second detection unit), and a display viewing angle change unit 222 (second change unit). The processing device 220 is a computer such as a central processing unit (CPU) microcontroller and serves as a control unit that controls the operation of each component based on a computer program. At least one component of the processing device 220 may be implemented by hardware such as an application specific integrated circuit (ASIC) or a programmable logic array (PLA).

[0214] The image processing unit 221 generates image data by performing image processing (such as wide dynamic range (WDR) correction, gamma correction, lookup table (LUT) processing, and distortion correction) on the captured image data obtained from the imaging unit 210. Distortion correction is performed on at least the captured image data corresponding to the second area 201b. This makes it easier for the user 40 to visually recognize the image displayed on the display device 230, and in addition, improves the detection rate of the rear vehicle distance detection unit 223 for the rear vehicle. Distortion correction can be omitted for the captured image data corresponding to the first area 201a. The image processing unit 221 outputs the image data generated by performing the above-mentioned image processing to the display viewing angle change unit 222 and the rear vehicle distance detection unit 223.

[0215] The rear vehicle distance detection unit 223 acquires information on the distance to the rear vehicle included in the image data corresponding to the range within the second viewing angle 31 but excluding the first viewing angle 30 using the image data output from the image processing unit 221. For example, the rear vehicle distance detection unit 223 is capable of detecting the rear vehicle based on the image data corresponding to the second area 201b and calculating the distance from the rear vehicle to the vehicle including the in-vehicle system 2 based on the changes in the position and size of the detected rear vehicle. The rear vehicle distance detection unit 223 outputs the calculated distance information to the display viewing angle determination unit 224.

[0216] In addition, the rear vehicle distance detection unit 223 can determine the vehicle type of the rear vehicle based on feature information data (such as shape and color) for each vehicle type output as a result of machine learning (deep learning) based on a large number of vehicle images. In this case, the rear vehicle distance detection unit 223 can output the vehicle type information about the rear vehicle to the display angle determination unit 224. The reverse gear detection unit 225 detects whether the transmission device of the mobile device 10 (including the vehicle of the vehicle-mounted system 2) is in reverse gear and outputs the detection result to the display angle determination unit 224.

[0217] The display angle determination unit 224 determines which of the first angle of view 30 and the second angle of view 31 is to be set as the angle of view (display angle of view) of the image to be displayed on the display device 230 based on the output from at least one of the rear vehicle distance detection unit 223 and the reverse gear detection unit 225. The display angle of view determination unit 224 outputs to the display angle of view change unit 222 based on the determination result. For example, in the case where the distance value in the distance information becomes equal to or less than a threshold value (for example, 3m), the display angle of view determination unit 224 determines to set the display angle of view to the second angle of view 31, and in the case where the distance value exceeds the threshold value, the display angle of view determination unit 224 determines to set the display angle of view to the first angle of view 30. In addition, in the case where a notification indicating that the transmission device of the mobile device 10 is in the reverse gear is received from the reverse gear detection unit 225, the display angle of view determination unit 224 may determine to set the display angle of view to the second angle of view 31. In the case where the transmission device is not in the reverse gear, the display angle of view determination unit 224 may determine to set the display angle of view to the first angle of view 30.

[0218] In addition, in a state where the transmission device of the mobile device 10 is in reverse gear, the display viewing angle determination unit 224 can determine to set the display viewing angle to the second viewing angle 31 regardless of the result of the rear vehicle distance detection unit 223. In a case where the transmission device of the mobile device 10 is not in reverse gear, the display viewing angle determination unit 224 can determine to set the display viewing angle based on the detection result of the rear vehicle distance detection unit 223. The display viewing angle determination unit 224 can change the determination criteria for determining whether to change the viewing angle based on the vehicle type of the mobile device 10 by receiving vehicle type information from the rear vehicle distance detection unit 223. For example, in a case where the mobile device 10 is a large-sized vehicle such as a truck, since the braking distance is longer than that of a normal-sized vehicle, in one embodiment, the threshold is set to be longer than the threshold for a normal-sized vehicle (e.g., 10 m).

[0219] The user setting change unit 226 enables the user 40 to change the determination criterion used by the display angle determination unit 224 to determine whether to change the display angle to the second angle 31. The determination criterion set (changed) by the user 40 is input from the user setting change unit 226 to the display angle determination unit 224.

[0220] The display angle changing unit 222 generates a display image to be displayed on the display device 230 based on the determination result of the display angle determining unit 224. For example, in the case where it is determined that the first angle of view 30 is set, the display angle of view changing unit 222 crops a rectangular narrow-angle image (first image) from the image data corresponding to the first angle of view 30 and outputs the cropped image to the display device 230. In the case where there is a rear vehicle that satisfies a predetermined condition in the image data corresponding to the second angle of view 31, the display angle of view changing unit 222 outputs an image (second image) including the rear vehicle to the display device 230. The second image may include an image corresponding to the first area 201a. The display angle of view changing unit 222 functions as a display control unit that performs display control that switches between a first display state in which the display device 230 displays the first image and a second display state in which the display device 230 displays the second image.

[0221] The display angle of view changing unit 222 performs image cropping by storing the image data output from the image processing unit 221 in a storage unit (memory) such as a random access memory (RAM), and then reading the image to be cropped from the stored image data. The area corresponding to the first image in the image data is a rectangular area within the first angle of view 30 corresponding to the first area 201a. The area corresponding to the second image in the image data is a rectangular area including the rear vehicle within the second angle of view 31 corresponding to the second area 201b.

[0222] The display device 230 includes a display unit such as a liquid crystal display or an organic electroluminescent (organic EL) display, and displays a display image output from the display viewing angle changing unit 222. For example, the display device 230 includes a first display unit positioned on the upper side of the windshield (front glass) of the movable device 10 and acting as an electronic rearview mirror, and a second display unit positioned on the lower side of the windshield of the movable device 10 and acting as an operation panel (monitor). This configuration makes it possible to display the first and second images generated from the image data on the first and second display units, respectively. The first display unit may include, for example, a semi-transparent reflector so that the first display unit is used as a reflector when not used as a display. The second display unit may also be used as, for example, a display for a navigation system or an audio system.

[0223] The movable device 10 is not limited to vehicles such as cars, and may be a movable object such as a ship, an airplane, an industrial robot, or a drone. The vehicle-mounted system 2 according to this exemplary embodiment is used to display images to the user 40. However, this is not a limitation, and the vehicle-mounted system 2 may be used for driving assistance, such as cruise control (including full-range adaptive cruise control) or autonomous driving. In addition, the vehicle-mounted system 2 may be applied not only to movable devices, but also to various devices using object recognition, such as an intelligent transportation system (ITS).

[0224] [Modification example]

[0225] Various exemplary embodiments and embodiments of the present disclosure have been described above. However, the present disclosure is not limited to these exemplary embodiments and embodiments, and various combinations, modifications, and changes may be made without departing from the scope of the present disclosure.

[0226] For example, the optical systems according to the above-described embodiments are intended to be used in the visible range and are configured to perform appropriate aberration correction over the entire visible range. However, the wavelength range for which aberration correction is performed can be appropriately changed. For example, each optical system can be configured to perform aberration correction specifically for a specific wavelength range in the visible range, or can be configured to perform aberration correction in an infrared range excluding the visible range.

[0227] The vehicle-mounted system 2 may adopt the above-mentioned distance measuring device as the imaging device 20. In this case, the vehicle-mounted system 2 may include a method for determining the possibility of collision with an object based on information about the distance to the object obtained by the imaging device 20. A stereo camera including two imaging units 210 may be adopted as the imaging device 20. In this case, a process similar to the above process may be performed by simultaneously acquiring image data using synchronized imaging units 210 and using two pieces of image data without using an imaging plane phase difference sensor. However, if the difference in imaging time between the imaging units 210 is known, the imaging units 210 do not have to be synchronized.

Claims

1. An optical system, comprising, from the object side to the image side, the following: the front group with positive refractive power; Aperture diaphragm; as well as The rear group has positive refractive power, The front group includes, from the object side to the image side, a first lens having negative refractive power, a second lens having negative refractive power, a third lens, and a fourth lens having positive refractive power. The rear group includes a cemented lens and a meniscus lens disposed closest to the image plane. wherein at least one of the object side surface and the image side surface of the meniscus lens is an aspherical surface, wherein a spherical surface of two edge portions passing through the effective area of ​​the object-side surface in a cross section including the optical axis has a concave shape toward the object side, and The following inequalities are satisfied: 0.80≤Rd≤1.00, Here, Rd is a value of a ratio of a diameter of a portion having positive power in the effective area of ​​the image-side surface to a diameter of the effective area of ​​the image-side surface in a direction perpendicular to the optical axis. 2 . The optical system of claim 1 , wherein the object-side surface of the meniscus lens is aspherical. 3 . The optical system according to claim 1 , wherein an object-side surface of the second lens is an aspherical surface including an inflection point in a cross section including the optical axis.

4. The optical system according to claim 3, wherein a curve representing the curvature of the object-side surface of the second lens with respect to the radial position in the cross section including the optical axis includes a first extreme value, and the following inequality is satisfied: 0.05≤E1≤0.50, Wherein E1 is the normalized distance from the optical axis to the position corresponding to the first extreme value.

5. The optical system of claim 4, wherein the curve includes a second extreme value, and the following inequality is satisfied: 0.60≤E2≤0.98, Wherein E2 is the normalized distance from the optical axis to the position corresponding to the second extreme value.

6. The optical system according to claim 1, wherein a curve representing the curvature of the image-side surface of the meniscus lens with respect to the radial position in the cross section including the optical axis includes a third extreme value, and the following inequality is satisfied: 0.05≤E3≤0.50, Wherein E3 is the normalized distance from the optical axis to the position corresponding to the third extreme value.

7. The optical system of claim 1, wherein the following inequality is satisfied: 3.5≤fa1 / f≤10.0, Wherein fa1 is the focal length of the air lens between the first lens and the second lens, and f is the focal length of the optical system.

8. The optical system of claim 1, wherein the following inequality is satisfied: 0.4≤fG1 / fG2≤3.5, Where fG1 is the focal length of the front group, and fG2 is the focal length of the rear group.

9. The optical system of claim 1, wherein the following inequality is satisfied: -1.50≤(R2+R1) / (R2-R1)≤-4.00, Wherein R1 is the radius of curvature of the spherical surface passing through two edge portions in the effective area of ​​the object-side surface of the meniscus lens, and R2 is the radius of curvature of the spherical surface passing through two edge portions in the effective area of ​​the image-side surface of the meniscus lens.

10. The optical system of claim 1, wherein the following inequality is satisfied: 1.0≤fLC / f≤6.0, Where fLC is the focal length of the cemented lens, and f is the focal length of the optical system.

11. The optical system of claim 1 , wherein the following inequality is satisfied: -2.20≤Ds / rLC≤-0.60, Where rLC is the radius of curvature of the cemented surface of the cemented lens, and Ds is the distance from the aperture stop to the cemented surface.

12. The optical system of claim 1, wherein the following inequality is satisfied: 2.0≤fLL / f≤22.0, Where fLL is the focal length of the meniscus lens and f is the focal length of the optical system. 13 . The optical system according to claim 1 , wherein on an optical axis, the first lens and the second lens each have a convex meniscus shape toward the object side, the third lens has a concave shape toward the object side, and the fourth lens has a biconvex shape.

14. The optical system according to claim 1, wherein the cemented lens includes a positive lens and a negative lens in order from the object side to the image side, and on the optical axis, the positive lens has a biconvex shape and the negative lens has a convex meniscus shape toward the image side.

15. The optical system of claim 1, wherein the following inequality is satisfied: 1.0 <f×sin(θmax) / y(θmax)≤1.9, Wherein y(θ) is a projection characteristic of the optical system representing the relationship between the half viewing angle θ and the image height y, θmax is the maximum half viewing angle of the optical system, and f is the focal length of the optical system.

16. The optical system of claim 1, wherein the following inequality is satisfied: 0.65 <y(θmax / 2) / y(θmax)<0.85, Wherein y(θ) is the projection characteristic of the optical system representing the relationship between the half viewing angle θ and the image height y, and θmax is the maximum half viewing angle of the optical system.

17. An apparatus comprising the optical system according to any one of claims 1 to 6 and a sensor configured to capture an image of an object through the optical system.

18. A display system comprising the apparatus according to claim 17 and a display device configured to display an image obtained based on an output from the apparatus.

19. A display system according to claim 18, wherein the display device includes a first display unit and a second display unit, the first display unit is configured to display a first area of ​​the image corresponding to a first viewing angle, and the second display unit is configured to display a second area of ​​the image corresponding to a second viewing angle, and the second viewing angle includes the first viewing angle.

20. A movable device comprising the device according to claim 17 and configured to be moved while holding the device.

Images