Optical system and image pickup apparatus having the same

Abstract

An optical system (100) includes a front group (G1) having a positive refractive power, an aperture stop (STO), and a rear group (G2) having a positive refractive power arranged in this order from an object side toward an image side, in which the front group (G1) includes a first lens (L1) having a negative refractive power, a second lens (L2) having a negative refractive power, a third lens (L3), and a fourth lens (L4) having a positive refractive power arranged in this order from the object side toward the image side, wherein the rear group (G2) includes a cemented lens (LC) and a positive lens (LL) arranged closest to the image side, and wherein the object-side surface of the second lens (L2) is aspheric, and wherein a predetermined conditional expression is satisfied.

Description

Technical Field

[0001] The present invention relates to an optical system and is suitable for imaging equipment including a digital still camera, a digital video camera, a car-mounted camera, a portable phone camera, a surveillance camera, a wearable camera, and a camera for medical applications. Background Art

[0002] Optical systems used in imaging devices such as vehicle-mounted cameras are required to have a wide viewing angle. Patent Documents 1 and 2 discuss optical systems that have a wide viewing angle and are composed of seven different lenses 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, which are sequentially arranged from the object side to the image side.

[0003] Citation List

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application No. 2018-522266

[0006] Patent Document 2: U.S. Patent Application Publication No. 2020 / 0142158 Summary of the invention

[0007] Problem that the invention aims to solve

[0008] The optical systems disclosed in Patent Document 1 and Patent Document 2 still have difficulty in reducing the diameters of the second lens and the first lens disposed closest to the object side, and in shortening the length of the entire system.

[0009] The present invention is directed to providing a compact optical system having a wide angle of view and an image pickup apparatus including the compact optical system having a wide angle of view.

[0010] Solutions for solving problems

[0011] According to one aspect of the present invention, an optical system includes a front group with positive refractive power, an aperture stop, and a rear group with positive refractive power, which are arranged in sequence from the object side to the image side, wherein the front group includes a first lens with negative refractive power, a second lens with negative refractive power, a third lens, and a fourth lens with positive refractive power, which are arranged in sequence from the object side to the image side, wherein the rear group includes a cemented lens and a positive lens arranged closest to the image side, wherein the object side surface of the second lens is an aspherical surface, and wherein the following conditional expression is satisfied:

[0012] f1 / d12≤-8.50

[0013] Wherein, f1 is the focal length of the first lens, and d12 is the distance between the first lens and the second lens on the optical axis.

[0014] According to another aspect of the present invention, an optical system includes a front group with positive refractive power, an aperture stop, and a rear group with positive refractive power, which are arranged in sequence from the object side to the image side, wherein the front group includes a first lens with negative refractive power, a second lens with negative refractive power, a third lens, and a fourth lens with positive refractive power, which are arranged in sequence from the object side to the image side, wherein the rear group includes a cemented lens and a positive lens arranged closest to the image side, wherein the object side surface of the second lens is an aspherical surface, and wherein the following conditional expression is satisfied:

[0015] 2.4≤f23 / fa1≤16.0

[0016] Wherein, f23 is the combined focal length of the second lens and the third lens, and fa1 is the focal length of the air lens between the second lens and the third lens.

[0017] Effects of the Invention

[0018] According to the present invention, a compact optical system having a wide angle of view and an image pickup apparatus including the compact optical system having a wide angle of view can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a diagram schematically illustrating a main portion of an optical system according to a first exemplary embodiment.

[0020] Figure 2 ] are diagrams illustrating aberrations of the optical system according to the first exemplary embodiment.

[0021] Figure 3 is a diagram schematically illustrating a main portion of an optical system according to a second exemplary embodiment.

[0022] Figure 4 : are diagrams illustrating aberrations of the optical system according to the second exemplary embodiment.

[0023] Figure 5 is a diagram schematically illustrating a main portion of an optical system according to a third exemplary embodiment.

[0024] Figure 6 ] are diagrams illustrating aberrations of the optical system according to the third exemplary embodiment.

[0025] Figure 7 is a diagram schematically illustrating a main portion of an optical system according to a fourth exemplary embodiment.

[0026] Figure 8: are diagrams illustrating aberrations of the optical system according to the fourth exemplary embodiment.

[0027] Fig. 9 : is a diagram illustrating the shape of the aspherical surface on the object-side surface of the second lens according to each typical embodiment.

[0028] Fig.10 is a schematic diagram illustrating an imaging apparatus according to an exemplary embodiment.

[0029] Fig.11A is a schematic diagram illustrating a movable device according to an exemplary embodiment.

[0030] Fig. 11B Optical characteristics of the optical system according to the typical embodiment are illustrated.

[0031] Fig.12 is a block diagram illustrating an example structure of an in-vehicle system according to an exemplary embodiment. DETAILED DESCRIPTION

[0032] The following will describe the desired typical embodiments of the present invention with reference to the accompanying drawings. For convenience, the drawings may be drawn in a scale different from the actual scale. In the drawings, the same components are represented by the same reference numerals, and repeated descriptions will be omitted.

[0033] Figure 1 , Figure 3 , Figure 5 and Figure 7 It is a cross-sectional view (including the optical axis OA) of the optical system according to the first typical embodiment to the fourth typical embodiment. Referring to each cross-sectional view, the left side is the object side (front side), and the right side is the image side (rear side). The optical system according to each typical embodiment is an imaging optical system for an imaging device. The imaging surface of the image sensor is arranged in the position of the image plane IMG. The optical block CG arranged on the object side of the image plane IMG is an optical element (such as a filter and a cover glass) that does not contribute to the imaging of the optical system. The optical system according to each typical embodiment can also be used as a projection optical system in a projection device such as a projector. In this case, a display surface of a display element such as a liquid crystal panel is arranged in the position of the image plane IMG.

[0034] Figure 2 , Figure 4 , Figure 6 and Figure 8 1 is a diagram illustrating vertical aberrations according to the first exemplary embodiment to the fourth exemplary embodiment. Each vertical aberration illustrates spherical aberration, field curvature (astigmatism), and distortion from left to right. In each vertical aberration diagram, aberrations for 656.3nm (C line), 587.6nm (d line), 486.1nm (F line), and 435.8nm (g line) are plotted with different lines.

[0035] Features of the optical system according to each typical embodiment will be described in detail below.

[0036] The optical system according to each typical embodiment includes a front group G1 with positive refractive power, an aperture stop STO, and a rear group G2 with positive refractive power, which are arranged in sequence from the object side to the image side. In each typical embodiment, the optical block CG is not included in the optical system. The front group G1 includes a first lens L1 with negative refractive power, a second lens L2 with negative refractive power, a third lens L3, and a fourth lens L4 with positive refractive power, which are arranged in sequence from the object side to the image side. The rear group G2 includes a cemented lens LC and a positive lens LL (final lens) arranged closest to the image side. A lens refers to an optical element with refractive power, rather than an optical element without refractive power such as a parallel plane glass.

[0037] In the optical system according to each typical embodiment, the front group G1 and the rear group G2 have positive refractive power, and the front group G1 has the above-mentioned structure, thereby achieving a wide viewing angle with a shortened total length of the optical system. With the rear group G2 configured as described above, image surface curvature and chromatic aberration of magnification caused by the optical system having a wide viewing angle are well corrected. The optical system according to each typical embodiment satisfies the following conditional expression (1), wherein: f1 is the focal length of the first lens L1, and d12 is the distance (interval) between the first lens L1 and the second lens L2 on the optical axis OA.

[0038] f1 / d12 ≤ -8.50 (1)

[0039] The relationship between the focal length f1 and the distance d12 is appropriately set to satisfy the conditional expression (1), which reduces the outer diameters of the first lens L1 and the second lens L2, which enables miniaturization of the entire system. If the upper limit of the conditional expression (1) is exceeded, the interval between the first lens L1 and the second lens L2 increases excessively, and it is difficult to reduce the diameters of the first lens L1 and the second lens L2.

[0040] If the first lens L1 and the second lens L2 are brought close to each other to reduce the distance d12, the absolute value of f1 / d12 approaches infinity. However, except in the case where a cemented lens is formed by the first lens L1 and the second lens L2, it is desirable that the first lens L1 and the second lens L2 are arranged separately. Thus, it is desirable to satisfy the following conditional expression (1a).

[0041] -1.00×10 3 ≤f1 / d12≤-8.50(1a)

[0042] If the lower limit of conditional expression (1a) is exceeded downward, the distance between first lens L1 and second lens L2 is excessively reduced, which may cause first lens L1 and second lens L2 to contact each other undesirably due to, for example, a manufacturing error. It is also desirable to satisfy the following conditional expression (1b), and it is more desirable to satisfy the following conditional expression (1c).

[0043] -8.00×10 2 ≤f1 / d12≤-9.00(1b)

[0044] -3.00×10 2 ≤f1 / d12≤-9.50(1c)

[0045] As long as the optical system according to each typical embodiment satisfies at least the above-mentioned structure, the effect of the present invention can be obtained. For example, the front group G1 may include lenses other than the first lens L1 to the fourth lens L4 (a total of five or more lenses). However, in order to achieve miniaturization of the entire system, it is desirable that the front group G1 consists of four lenses. Since the absolute value of the power of the third lens L3 as described below is small, the determination of which of the positive refractive power and the negative refractive power is provided for the third lens L3 is performed according to the specifications of each optical system.

[0046] In an imaging device such as a vehicle-mounted camera (described below), not only a wide viewing angle but also a large imaging magnification in the vicinity of the optical axis (central area) is required. In an example case where the imaging device is arranged at the rear of a movable device (vehicle), the implementation structure may be in the form of displaying an enlarged image corresponding to the central area as the main object area in an electronic rearview mirror, and displaying the entire image including the peripheral area other than the central area on an in-vehicle display. Thus, it is desirable that the imaging magnification (focal length) of the optical system be set to be different between the central area and the area other than the central area.

[0047] Therefore, it is desirable that the object side surface (lens surface on the object side) of the second lens L2 is an aspherical surface. With this structure, the light from the radial peripheral portion in the light beam from the first lens L1 is greatly deflected toward the optical axis OA side by the object side surface of the second lens L2. Therefore, the imaging magnification between the central area and the peripheral area of ​​the optical system is easily set to be different from each other. In this case, it is desirable that the object side surface of the second lens L2 is an aspherical surface having an inflection point in the cross section including the optical axis OA. Therefore, in the case where the number of lenses included in the optical system is small, it is easy to increase the viewing angle (field angle) and the imaging magnification in the central area.

[0048] Fig. 9 The shape of the aspherical surface on the object side of the second lens L2 according to each exemplary embodiment is exemplified. Fig. 9, the horizontal axis indicates 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 indicates the curvature [1 / mm] of the object-side surface of the second lens L2. Fig. 9 A graph in which curvature is plotted for different positions on the object-side surface of the second lens L2 is illustrated. The numerical value on the horizontal axis indicates the distance (normalized distance) from the optical axis OA to each position within the effective diameter of the object-side surface of the second lens L2, where the distance from the optical axis OA to the effective diameter (maximum effective diameter) is normalized to 1.

[0049] It is desirable that the object side surface of the second lens L2 is an aspherical surface as follows: Fig. 9 The illustrated graph showing the curvature versus distance from the optical axis OA has a plurality of extreme values. Fig. 9 As illustrated, the graph according to each typical embodiment has a first extreme value (maximum value) and a second extreme value (minimum value). With this structure, the difference in imaging magnification between the central area and the peripheral area of ​​the optical system is highlighted, and more specifically, the imaging magnification of the central area is set to be greater than the imaging magnification of the peripheral area, which improves the image visibility to the user of the imaging device.

[0050] It is expected that the optical system according to each typical embodiment satisfies the following conditional expressions (2) and (3), wherein: on the object side of the second lens L2, E1 is a normalized distance from the optical axis OA to a position corresponding to the first extreme value, and E2 is a normalized distance from the optical axis OA to a position corresponding to the second extreme value.

[0051] 0.02 ≤ E1 ≤ 0.40 (2)

[0052] 0.60 ≤ E2 ≤ 0.98 (3)

[0053] Conditional expressions (2) and (3) define appropriate positions of the first extreme value and the second extreme value, respectively. Satisfying conditional expression (2) makes it easy to increase the focal length of the central area of ​​the optical system, and satisfying conditional expression (3) makes it easy to miniaturize the optical system and to increase the viewing angle. If conditional expressions (2) and (3) are not satisfied, it is difficult to appropriately set the imaging magnification of the central area and the peripheral area, which is undesirable.

[0054] It is also desirable to satisfy the following conditional expressions (2a) and (3a), and it is more desirable to satisfy the following conditional expressions (2b) and (3b).

[0055] 0.04≤E1≤0.35(2a)

[0056] 0.65≤E2≤0.96(3a)

[0057] 0.06≤E1≤0.30(2b)

[0058] 0.70≤E2≤0.94(3b)

[0059] Furthermore, it is desirable that the optical system according to each exemplary embodiment satisfies the following conditional expression (4), where fa1 is the focal length of the air lens between second lens L2 and third lens L3, and f is the focal length of the optical system (entire system).

[0060] -1.20 ≤ fa1 / f ≤ -0.50 (4)

[0061] Satisfying the conditional expression (4) provides the air lens formed between the second lens L2 and the third lens L3 with a negative power (refractive power) having a large value (large absolute value), which enables further miniaturization of the optical system. If the lower limit of the conditional expression (4) is exceeded downward, the negative power of the air lens increases excessively, which is undesirable because if the configuration of each lens deviates due to manufacturing errors, the optical performance variation of the optical system increases. If the upper limit of the conditional expression (4) is exceeded, the negative power of the air lens decreases excessively, which is undesirable because it is difficult to further miniaturize the optical system.

[0062] It is desirable that the following conditional expression (4a) is satisfied, and it is more desirable that the following conditional expression (4b) is satisfied.

[0063] -1.10≤fa1 / f≤-0.55(4a)

[0064] -1.00≤fa1 / f≤-0.60(4b)

[0065] Furthermore, it is desirable that the optical system according to each exemplary embodiment satisfies the following conditional expression (5), where: fG1 is the focal length of the front group G1 , and fG2 is the focal length of the rear group G2 .

[0066] 0.60 ≤ fG1 / fG2 ≤ 1.50 (5)

[0067] Satisfying the conditional expression (5) allows the power of the front group G1 and the rear group G2 to be appropriately set, which allows further miniaturization of the optical system. If the lower limit of the conditional expression (5) is exceeded downward, the power of the front group G1 is excessively increased, which is not desirable because if the configuration of each lens deviates due to manufacturing errors, the optical performance variation of the optical system increases. If the upper limit of the conditional expression (5) is exceeded, the power of the front group G1 is excessively reduced, which is not desirable because it is difficult to further miniaturize the optical system.

[0068] It is desirable that the following conditional expression (5a) is satisfied, and it is more desirable that the following conditional expression (5b) is satisfied.

[0069] 0.65≤fG1 / fG2≤1.45(5a)

[0070] 0.70≤fG1 / fG2≤1.40(5b)

[0071] Furthermore, it is desirable that the optical system according to each exemplary embodiment satisfies the following conditional expression (6), wherein: R1 is the curvature radius of the image-side surface of first lens L1 , and R2 is the curvature radius of the object-side surface of first lens L1 .

[0072] -3.50 ≤ (R2 + R1) / (R2 - R1) ≤ -1.85 (6)

[0073] Conditional expression (6) represents a desired shape (form factor) of first lens L1. If the lower limit of conditional expression (6) is exceeded downward, the outer diameter of first lens L1 increases, which is undesirable because it is difficult to further miniaturize the optical system. If the upper limit of conditional expression (6) is exceeded, it is difficult to capture light traveling toward the outermost off-axis image height from first lens L1 (outermost off-axis ray), which is undesirable because it is difficult to further increase the angle of view of the optical system.

[0074] It is desirable that the following conditional expression (6a) is satisfied, and it is more desirable that the following conditional expression (6b) is satisfied.

[0075] -3.20≤(R2+R1) / (R2-R1)≤-1.88(6a)

[0076] -3.00≤(R2+R1) / (R2-R1)≤-1.90(6b)

[0077] On the optical axis OA, it is desirable that the first lens L1 and the second lens L2 are meniscus lenses (negative meniscus lenses) having a convex shape toward the object side, the third lens L3 is a meniscus lens having a concave shape toward the object side, and the fourth lens L4 is a double convex lens. With this structure, the incident angle of each light beam to the rear group G2 is reduced, and the optical performance variation caused by the configuration error (manufacturing error) of each lens is prevented.

[0078] While it is desirable that the cemented lens LC of the rear group G2 includes a positive lens and a negative lens to easily reduce chromatic aberration of magnification, the cemented lens LC may include three or more lenses, however, it is desirable that the cemented lens LC is composed of two lenses to miniaturize the entire system and facilitate manufacturing. In addition, the rear group G2 may include lenses other than the cemented lens LC and the positive lens LL. For example, Figure 5As in the third exemplary embodiment illustrated, lens L5 may be arranged on the object side of cemented lens LC. It is desirable to make a determination as to whether to set lenses other than cemented lens LC and positive lens LL in rear group G2 according to the specifications of each optical system and the required optical performance. For example, in order to easily reduce curvature of field and chromatic aberration of magnification with a small number of lenses while reducing the influence of manufacturing errors, it is desirable that rear group G2 is composed of cemented lens LC and positive lens LL.

[0079] It is desirable that the positive lens LL of the rear group G2 also includes an aspherical surface. In other words, it is desirable that at least one of the object side surface and the image side surface of the positive lens LL is an aspherical surface. Furthermore, like the aspherical surface of the second lens L2 of the front group G1, it is desirable that the aspherical surface of the positive lens LL also includes an inflection point in a cross section including the optical axis OA. This reduces the field curvature caused by the aspherical surface of the second lens L2 when the number of lenses in each optical system is small. It is desirable that the aspherical surface of the positive lens LL also has a plurality of extreme values, and it is more desirable that the above-mentioned conditional expressions (2) and (3) are satisfied.

[0080] As described above, since the use of aspherical lenses for the second lens L2 and the positive lens LL improves the performance of the optical system, it is desirable that each lens is made of a resin material (resin lens). Resin material refers to a material mainly composed of resin (plastic), but is not limited to a material composed only of resin, and resin materials include materials containing a trace amount of non-resin materials (impurities). Compared with using glass materials for each lens, using resin materials for each lens makes it easier to mold the aspherical surface, thereby reducing the manufacturing cost.

[0081] However, the temperature coefficient of the refractive index of the resin lens is greater than the temperature coefficient of the refractive index of the glass lens made of a common glass material. Therefore, if the resin lens is used only for the second lens L2 and the positive lens LL having a high negative optical power, the focus variation due to temperature variation may not be fully offset by each lens. Therefore, it is desirable to use the resin lens also for the third lens L3 to prevent the focus variation due to temperature variation. It is also desirable that the optical system according to each typical embodiment satisfies the following conditional expression (7), where f3 is the focal length of the third lens L3, and f is the focal length of the entire system.

[0082] |f / f3| ≤ 0.15 (7)

[0083] Properly setting the power of the third lens L3 to satisfy the conditional expression (7) makes it easy to prevent focus changes of each optical system caused by temperature changes. If the conditional expression (7) is not satisfied, the absolute value of the power of the third lens L3 increases excessively, which is undesirable because it is difficult to prevent focus changes of each optical system caused by temperature changes.

[0084] It is also desirable that the following conditional expression (7a) is satisfied, and it is more desirable that the following conditional expression (7b) is satisfied.

[0085] |f / f3|≤0.13(7a)

[0086] |f / f3|≤0.12(7b)

[0087] For lenses other than the second lens L2, the third lens L3 and the positive lens LL, resin lenses can be appropriately used. However, since the temperature coefficient of the refractive index of the resin lens is relatively large as described above, it is desirable to use a glass lens for at least one lens to prevent focus changes due to temperature changes. As described above, it is also desirable to use a resin lens only for the second lens L2 and the positive lens LL having aspheric surfaces, and to use the third lens L3 to offset focus changes caused by the second lens L2 and the positive lens LL. Since resin lenses are easier to process than glass lenses, it is desirable that both the object side and the image side of the resin lens are aspheric. This enables good optical performance to be achieved with a small number of lenses in each optical system.

[0088] When the second lens L2 and the third lens L3 have a combined focal length f23, even if the optical system according to each typical embodiment does not satisfy the conditional expression (1), satisfying the following conditional expression (8) enables similar effects of achieving a wide viewing angle and miniaturization to be obtained.

[0089] 2.4 ≤ f23 / fa1 ≤ 16.0 (8)

[0090] Properly setting the relationship between the focal lengths f23 and fa1 to satisfy the conditional expression (8) shortens the total length of the optical system, which enables miniaturization of the entire system. If the lower limit of the conditional expression (8) is exceeded downward, the absolute value of the focal length of the air lens between the second lens L2 and the third lens L3 is excessively reduced, which makes it difficult to shorten the total length of the optical system. Alternatively, the absolute value of the focal length of the composite focal length of the second lens L2 and the third lens L3 is excessively increased, which makes it difficult to prevent the optical performance of the optical system from changing when the configuration of each lens deviates due to a manufacturing error. In addition, if the upper limit of the conditional expression (8) is exceeded, the absolute value of the focal length of the air lens between the second lens L2 and the third lens L3 is excessively increased, which makes it difficult to prevent the optical performance of the optical system from changing when the configuration of each lens deviates due to a manufacturing error. Alternatively, the absolute value of the focal length of the composite focal length of the second lens L2 and the third lens L3 is excessively reduced, which makes it difficult to increase the viewing angle of the optical system.

[0091] It is desirable that the following conditional expression (8a) is satisfied, and it is more desirable that the following conditional expression (8b) is satisfied.

[0092] 2.6≤f23 / fa1≤15.0(8a)

[0093] 2.8≤f23 / fa1≤14.0(8b)

[0094] Desirably, the optical system according to each exemplary embodiment satisfies the following conditional expression (9), where: f2R2 is the focal length of the image-side surface of second lens L2, and f3R1 is the focal length of the object-side surface of third lens L3.

[0095] 2.0 ≤ f3R1 / f2R2 ≤ 7.0 (9)

[0096] The focal lengths (optical power) of the image side surface of the second lens L2 and the object side surface of the third lens L3 are appropriately set to satisfy the conditional expression (9), which reduces the outer diameter of the first lens L1, thereby miniaturizing the entire system. If the lower limit of the conditional expression (9) is exceeded downward, the absolute value of the optical power of the image side surface of the second lens L2 is excessively reduced, which is undesirable because it is difficult to reduce the diameter of the first lens L1. If the upper limit of the conditional expression (9) is exceeded, the absolute value of the optical power of the image side surface of the second lens L2 is excessively increased, which is undesirable because it is difficult to prevent the optical performance of the optical system from changing when the configuration of each lens deviates due to manufacturing errors.

[0097] It is desirable that the following conditional expression (9a) is satisfied, and it is more desirable that the following conditional expression (9b) is satisfied.

[0098] 2.3≤f3R1 / f2R2≤6.7(9a)

[0099] 2.5≤f3R1 / f2R2≤6.5(9b)

[0100] The structure of an optical system according to each exemplary embodiment will be described below.

[0101] [First exemplary embodiment]

[0102] like Figure 1 As illustrated, the optical system 100 according to the first exemplary embodiment includes 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 positive lens LL arranged in sequence from the object side to the image side. Light beams from an object (not illustrated) are converged on an image plane IMG through each lens and a cover glass CG, and an image of the object is formed. The optical system 100 according to the present exemplary embodiment has a sufficiently wide total viewing angle of 180 degrees (a half viewing angle of ±90 degrees) and a sufficiently long focal length (center focal length) of 4.4 mm on the optical axis OA.

[0103] According to the present typical 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 arranged in sequence from the object side to the image side. The second lens L2 and the positive lens LL have aspherical surfaces. More specifically, for each of the second lens L2 and the positive lens LL, the object side surface and the image side surface are aspherical surfaces having an inflection point in a cross section including the optical axis OA. Each lens according to the present typical embodiment is a glass lens made of a glass material, and each aspherical surface is formed by glass molding.

[0104] like Figure 2 As illustrated, in the optical system 100 according to the present exemplary embodiment, spherical aberration and field curvature are well corrected. Distortion increases in the peripheral area as the viewing angle (image height) increases, and relatively decreases in the central area. This results in a higher resolution in the central area than in the peripheral area, thereby improving the image visibility to the user of the imaging device as described above.

[0105] [Second exemplary embodiment]

[0106] like Figure 3 As illustrated, the optical system 200 according to the second exemplary embodiment includes 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 positive lens LL arranged in sequence from the object side to the image side. According to the present exemplary embodiment, as in the first exemplary 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 arranged in sequence from the object side to the image side. The optical system 200 according to the present exemplary embodiment has a sufficiently wide viewing angle of 180 degrees (half viewing angle of ±90 degrees) and a sufficiently long focal length of 4.4 mm on the optical axis OA.

[0107] According to the present typical embodiment, unlike the first typical embodiment, not only the second lens L2 and the positive lens LL have aspheric surfaces, but also the third lens L3 has an aspheric surface. More specifically, in each of the second lens L2, the third lens L3 and the positive lens LL, the image side surface and the object side surface are aspheric surfaces. The aspheric surfaces of the second lens L2 and the positive lens LL have an inflection point in a cross section including the optical axis OA, while the aspheric surface of the third lens L3 does not have an inflection point. According to the present typical embodiment, unlike the first typical embodiment, the second lens L2, the third lens L3 and the positive lens LL are each made of a resin material, and the other lenses are made of a glass material. More specifically, each aspheric surface is formed by plastic molding.

[0108] like Figure 4 As illustrated, in the optical system 200 according to the present exemplary embodiment, spherical aberration and field curvature are well corrected. Distortion increases in the peripheral region as the angle of view increases, and relatively decreases in the central region.

[0109] [Third exemplary embodiment]

[0110] like Figure 5 As illustrated, the optical system 300 according to the third typical embodiment includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, an aperture stop STO, a fifth lens L5, a cemented lens LC, and a positive lens LL, which are arranged in sequence from the object side to the image side. According to the present typical embodiment, unlike the first typical embodiment, the third lens L3 has a positive refractive power, and a fifth lens L5 having a positive refractive power is arranged on the object side of the cemented lens LC. The cemented lens LC is composed of a negative lens L6 and a positive lens L7, which are arranged in sequence from the object side to the image side. The optical system 300 according to the present typical embodiment has a sufficiently wide total viewing angle of 180 degrees (a half viewing angle of ±90 degrees) and a sufficiently long focal length of 4.4 mm on the optical axis OA.

[0111] According to the present typical embodiment, unlike the first typical embodiment, not only the second lens L2 and the positive lens LL have aspheric surfaces, but also the third lens L3 and the fifth lens L5 have aspheric surfaces. More specifically, in each of the second lens L2, the third lens L3, the fifth lens L5 and the positive lens LL, the object side surface and the image side surface are aspheric surfaces. The aspheric surfaces of the second lens L2 and the positive lens LL have an inflection point in a cross section including the optical axis OA, while the aspheric surfaces of the third lens L3 and the fifth lens L5 do not have an inflection point. According to the present typical embodiment, unlike the first typical embodiment, the second lens L2, the third lens L3 and the positive lens LL are each made of a resin material, and the other lenses are made of a glass material. The aspheric surfaces of the second lens L2, the third lens L3 and the positive lens LL are each formed by plastic molding, and the aspheric surface of the fifth lens L5 is formed by glass molding.

[0112] like Figure 6 As illustrated, in the optical system 300 according to the present exemplary embodiment, spherical aberration and field curvature are well corrected. Distortion increases in the peripheral region as the angle of view increases, and relatively decreases in the central region.

[0113] [Fourth exemplary embodiment]

[0114] like Figure 7 As illustrated, the optical system 400 according to the fourth exemplary embodiment includes 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 positive lens LL, which are arranged in sequence from the object side to the image side. The optical system 400 according to the present exemplary embodiment has a sufficiently wide total viewing angle of 180 degrees (a half viewing angle of ±90 degrees) and a sufficiently long focal length of 4.4 mm on the optical axis OA.

[0115] According to the present exemplary embodiment, as in the second exemplary 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 arranged in order from the object side to the image side. In each of the second lens L2, the third lens L3, and the positive lens LL, the object side surface and the image side surface have an aspherical surface. According to the present exemplary embodiment, unlike the second exemplary embodiment, the second lens L2, the third lens L3, and the positive lens LL are each made of a resin material.

[0116] like Figure 8 As illustrated, in the optical system 400 according to the present exemplary embodiment, spherical aberration and field curvature are well corrected. Distortion increases in the peripheral region as the angle of view increases, and relatively decreases in the central region.

[0117] The first numerical exemplary embodiment to the fourth numerical exemplary embodiment corresponding to the first exemplary embodiment to the fourth exemplary embodiment described above, respectively, will be described below. In each numerical exemplary embodiment, the surface number indicates the order of each optical surface when counting from the object plane, r [mm] is the radius of curvature of the i-th optical surface, d [mm] is the distance (on the optical axis) between the i-th optical surface and the (i + 1)-th optical surface, nd is the refractive index of the medium between the i-th optical surface and the (i + 1)-th optical surface with respect to the d-line, and νd is the Abbe number of the medium with respect to the d-line. The Abbe number νd is a value defined by the following expression when the refractive indices for the F-line, d-line, and C-line are nF, nd, and nC, respectively.

[0118] νd=(nd-1) / (nF-nC)

[0119] For the aspheric surfaces in each numerical exemplary embodiment, the surface number is indicated by a trailing asterisk (*). The “E±P” in each numerical value means “×10 ±P ". The shape of each aspherical surface is expressed by the following expression, wherein: z is the displacement from the surface vertex in the optical axis direction, h is the height from the optical axis OA in the direction perpendicular to the optical axis direction, c is the curvature (the inverse of the curvature radius r), k is the cone constant, and A, B, C, D, E, F, G, H, I... are aspherical coefficients.

[0120] [Formula 1]

[0121]

[0122] The optical system according to each numerical typical embodiment is a single-focus optical system with a constant focal length that is configured to neither zoom nor focus. This means that the distance between the lenses constituting the optical system according to each numerical typical embodiment is constant and fixed. In this structure, the change in optical performance with the movement of each lens is avoided. However, the optical system is capable of at least one of zooming and focusing as needed, and is therefore configured to change the distance between the lenses.

[0123] (First Numerical Example)

[0124] Various data

[0125] Center focal length 4.4mm

[0126] Fno 2.8

[0127] Half viewing angle ±90°

[0128] Area data

[0129]

[0130]

[0131] Aspheric coefficient

[0132]

[0133] (Second numerical typical embodiment) Various data centers focal length 4.4mm Fno 2.8

[0134] Half viewing angle ±90°

[0135] Area data

[0136]

[0137]

[0138] Aspheric coefficient

[0139]

[0140] (Third Numerical Typical Embodiment) Various Data Center Focal Length 4.4mm Fno 2.8

[0141] Half viewing angle ±90°

[0142] Area data

[0143]

[0144]

[0145] Aspheric coefficient

[0146]

[0147] (Fourth Numerical Typical Embodiment) Various Data Center Focal Length 4.4mm Fno 2.8

[0148] Half viewing angle ±90°

[0149] Area data

[0150]

[0151] Aspheric coefficient

[0152]

[0153]

[0154] The following table illustrates values ​​associated with conditional expressions for the optical system according to each typical embodiment described above. The following table also illustrates values ​​associated with conditional expression (10) (described below). As illustrated in the table, the optical system according to each typical embodiment satisfies the associated conditional expression.

[0155] [Table 1]

[0156]

[0157] [Camera equipment]

[0158] Fig.10 : is a schematic diagram illustrating the main parts of an image pickup device 70 according to an exemplary embodiment of the present invention. The image pickup device 70 according to the present exemplary embodiment includes an optical system (image pickup optical system) 71 according to one of the above-described exemplary embodiments, a light receiving element 72 for photoelectrically converting an object image formed by the optical system 71, and a camera body (casing) 73 for holding the light receiving element 72. The optical system 71 is held by a lens barrel (holding member) and is connected to the camera body 73. Figure 7 As illustrated, the camera body 73 may be connected to a display unit 74 for displaying an image captured by the light receiving element 72. As the light receiving element 72, an image sensor (photoelectric conversion element) such as a charge coupled device (CCD) sensor and a complementary metal oxide semiconductor (CMOS) sensor is used.

[0159] In the case of using the imaging device 70 as a distance measuring device, for example, an image sensor (imaging surface phase difference sensor) having pixels capable of splitting a light beam from an object into two for photoelectric conversion can be applied as the light receiving element 72. In the case where the subject is located on the front focal plane of the optical system 71, no positional deviation occurs in the images 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 at a position other than the front focal plane of the optical system 71, a positional deviation occurs in each image. Since the positional deviation of each image corresponds to the displacement from the front focal plane of the subject, the positional deviation amount and the positional deviation direction are acquired for each image by using the imaging surface phase difference sensor, so that the distance to the subject is measured.

[0160] The optical system 71 and the camera body 73 may be configured to be attachable to and detachable from each other. More specifically, the optical system 71 and the lens barrel may be configured as an interchangeable lens (lens device). The optical system according to each of the above-described exemplary embodiments is applicable not only to imaging devices such as digital still cameras, silver film cameras, video cameras, vehicle-mounted cameras, and surveillance cameras, but also to various types of optical devices such as telescopes, binoculars, projectors (projection devices), and digital copiers.

[0161] [In-vehicle system]

[0162] Fig.11A 2 is a schematic diagram illustrating a movable device 10 and an imaging device 20 (vehicle-mounted camera) according to an exemplary embodiment of the present invention. Fig.11A The case where the movable device 10 is a car (vehicle) is illustrated. The movable device 10 includes an in-vehicle system (driving assistance device, not illustrated) for assisting a user 40 (driver or fellow passenger) of the movable device 10 by using an image captured by the camera device 20. Although the present typical embodiment indicates a case where the camera device 20 is arranged to capture an image of the rear of the movable device 10, the camera device 20 may be arranged to capture images of the front and sides of the movable device 10. Two or more camera devices 20 may be arranged at two or more different positions on the movable device 10.

[0163] The imaging device 20 includes an optical system 201 and an imaging unit 210 according to one of the above-described typical embodiments. The optical system 201 is a different-angle lens having different imaging magnifications in a first angle of view (first field of view) 30 and a second angle of view (second field of view) 31 that is larger than the first angle of view 30. The imaging surface (light-receiving surface) of the imaging unit 210 includes a first area (in which objects included in the first angle of view 30 are photographed) and a second area (in which objects included in the second angle of view 31 are photographed). In this structure, the number of pixels per unit angle of view in the first area is greater than the number of pixels per unit angle of view in the second area except for the first area. In other words, the resolution in the first angle of view (first area) of the imaging device 20 is higher than the resolution in the second angle of view (second area).

[0164] The optical characteristics of the optical system 201 will be described in detail below. Fig. 11B The left figure illustrates the image height y [mm] at different half angles of view θ [deg.] on the imaging plane of the imaging unit 210 using contour lines. Fig. 11B The right figure illustrates the relationship between different half angles of view θ and image height y (projection characteristics of the optical system 201) in the first quadrant of the left figure.

[0165] like Fig. 11B As illustrated, the optical system 201 is configured to have a projection characteristic y(θ) that is different between a viewing angle less than a predetermined half viewing angle θa and a viewing angle greater than or equal to the half viewing angle θa. Thus, the increase in image height y per unit of half viewing angle θ (resolution) is also different for each viewing angle. The local resolution of the optical system 201 is represented by the derivative dy(θ) / dθ of the projection characteristic y(θ) with respect to the half viewing angle θ. Fig. 11B The left figure of illustrates that the resolution increases as the distance between the contour lines of the image height y increases for different half-viewing angles θ. Fig. 11B The right figure of exemplifies that the resolution increases as the gradient of the graph of the projection characteristic y(θ) increases.

[0166] refer to Fig. 11B In the left figure, the first area 201a as the central area corresponds to a viewing angle less than the half viewing angle θa, and the second area 201b as the peripheral area corresponds to a viewing angle equal to or greater than the half viewing angle θa. Fig.11A The total viewing angle of the viewing angle smaller than the half viewing angle θa and the viewing angle equal to or greater than the half viewing angle θa is Fig.11A 31. As described above, the first region 201a is a region with high resolution and low distortion, and the second region 201b is a region with low resolution and high distortion.

[0167] It is desirable that the ratio of the half viewing angle θa to the maximum viewing angle θmax, that is, θa / θmax, is 0.15 degrees or more and 0.35 degrees or less, and more desirably 0.16 degrees or more and 0.25 degrees or less. For example, since the maximum viewing angle θmax=90 degrees in each of the above-mentioned typical embodiments, it is desirable that the value of the half viewing angle θa is 13.5 degrees or more and 31.5 degrees or less, and more desirably 14.4 degrees or more and 22.5 degrees or less.

[0168] The optical system 201 is configured so that the projection characteristic y(θ) in the first region 201a is different from f×θ (equidistant projection method), and the projection characteristic y(θ) is also different from the projection characteristic in the second region 201b. In this case, it is desirable that the projection characteristic y(θ) of the optical system 201 satisfies the following conditional expression (10).

[0169] 1.0 < f × sin(θmax) / y(θmax) ≤ 1.9 (10)

[0170] Satisfying the conditional expression (10) enables a wide viewing angle of the optical system 201 by reducing the resolution in the second region 201b. In addition, the resolution in the first region 201a is set higher than the resolution in the central region of a general fisheye lens using the orthographic projection method (y(θ)=f×sinθ). If the lower limit of the conditional expression (2) is exceeded downward, this is undesirable because the resolution in the first region 201a decreases and the maximum image height therein is higher compared to the fisheye lens using the orthographic projection method, which increases the size of the optical system. If the upper limit of the conditional expression (2) is exceeded, the resolution in the first region 201a increases excessively, which is undesirable because it is difficult to achieve a wide viewing angle equivalent to that of a fisheye lens using the orthographic projection method, and good optical performance cannot be maintained.

[0171] It is desirable that the following conditional expression (10a) is satisfied, and it is more desirable that the following conditional expression (10b) is satisfied.

[0172] 1.0 <f×sin(θmax) / y(θmax)≤1.7(10a)

[0173] 1.0 <f×sin(θmax) / y(θmax)≤1.4(10b)

[0174] As described above, the optical system 201 has small distortion and high resolution in the first area 201a, so an image is obtained with higher definition in the first area 201a than in the second area 201b. Thus, setting the first area 201a (first viewing angle 30) as the object area of ​​the user 40 enables good visibility. Fig.11AIn the illustrated case where the camera device 20 is arranged at the rear of the movable device 10, displaying an image corresponding to the first viewing angle 30 on the electronic rearview mirror provides a natural sense of perspective when the user 40 views the rear vehicle. On the other hand, the second area 201b (second viewing angle 31) corresponds to a wide viewing angle including the first viewing angle 30. For example, when the movable device 10 is traveling backward, displaying an image corresponding to the second viewing angle 31 on the in-vehicle display assists the user 40 in driving.

[0175] Fig.12 1 is a functional block diagram illustrating an example structure of a vehicle-mounted system 2 according to the present exemplary embodiment. The vehicle-mounted system 2 displays an image captured by a camera device 20 installed at a rear position of a movable device 10 to a user 40. The vehicle-mounted system 2 includes the camera device 20, a processing device 220, and a display device (display unit) 230. As described above, the camera device 20 includes an optical system 201 and a camera unit 210. The camera unit 210 including an image sensor such as a CCD sensor and a CMOS sensor generates camera data by photoelectrically converting an optical image formed by the optical system 201, and outputs the data to the processing device 220.

[0176] The processing device 220 includes an image processing unit 221, a display viewing angle judgment unit 224 (judgment 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). For example, the processing device 220 is a computer such as a central processing unit (CPU) and a microcomputer, and serves as a control unit for controlling the operation of different components based on a computer program. At least one component of the processing device 220 may be implemented by a hardware component such as an application specific integrated circuit (ASIC) and a programmable logic array (PLA).

[0177] The image processing unit 221 performs image processing (such as wide dynamic range (WDR) correction, gamma correction, lookup table (LUT) processing and distortion correction, etc.) on the camera data obtained from the camera unit 210 to generate image data. At least the camera data corresponding to the second area 201b is subjected to distortion correction. This makes it easier for the user 40 to visually recognize the image displayed on the display device 230, which improves the detection rate of the rear vehicle distance detection unit 223 for the rear vehicle. The distortion correction of the camera data corresponding to the first area 201a can be skipped. The image processing unit 221 outputs the image data generated by the above-mentioned image processing to the display viewing angle change unit 222 and the rear vehicle distance detection unit 223.

[0178] By using the image data output from the image processing unit 221, the rear vehicle distance detection unit 223 acquires information related to the distance to the rear vehicle included in the image data corresponding to the range excluding the first angle of view 30 in the second angle of view 31. For example, the rear vehicle distance detection unit 223 detects the rear vehicle based on the image data corresponding to the second area 201b in the image data, and calculates the distance from the rear vehicle to the self-vehicle based on the changes in the position and size of the detected rear vehicle. The rear vehicle distance detection unit 223 outputs the information related to the calculated distance to the display angle of view determination unit 224.

[0179] In addition, the rear vehicle distance detection unit 223 can determine the model of the rear vehicle based on data related to feature information (shape, color, etc.) for each model output as a result of machine learning (deep learning) based on images of a large number of vehicles. In this case, the rear vehicle distance detection unit 223 can output information related to the model of the rear vehicle to the display viewing angle determination unit 224. The reverse gear detection unit 225 detects whether the transmission of the movable device 10 (self-vehicle) is in reverse gear, and outputs the detection result to the display viewing angle determination unit 224.

[0180] The display angle of view determination unit 224 determines which of the first angle of view 30 and the second angle of view 31 the angle of view (display angle of view) of the image to be displayed on the display device 230 is 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 information to the display angle of view change unit 222 according to the determination result. For example, in the case where the distance value in the distance information reaches below a threshold value (for example, 3 m) downward, the display angle of view determination unit 224 determines to set the second angle of view 31 as the display angle of view, and in the case where the distance value exceeds the threshold value, the display angle of view determination unit 224 determines to set the first angle of view 30 as the display angle of view. Alternatively, in the case where the display angle of view determination unit 224 receives a notification from the reverse gear detection unit 225 that the transmission of the movable device 10 is in reverse gear, the display angle of view determination unit 224 determines to set the second angle of view 31 as the display angle of view. In the case where the transmission is not in reverse gear, the display angle of view determination unit 224 determines to set the first angle of view 30 as the display angle of view.

[0181] When the transmission of the movable device 10 is in reverse gear, the display angle judgment unit 224 judges to set the second angle 31 as the display angle regardless of the judgment result of the rear vehicle distance detection unit 223. When the transmission of the movable device 10 is not in reverse gear, the display angle judgment unit 224 judges to set the display angle according to the detection result of the rear vehicle distance detection unit 223. In response to receiving the vehicle information from the rear vehicle distance detection unit 223, the display angle judgment unit 224 can change the judgment basis of whether to change the angle according to the model of the movable device 10. For example, in the case where the movable device 10 is a large vehicle such as a truck, the braking distance is generally longer than that of an ordinary vehicle, and it is desirable to set the above threshold to be longer than the threshold for ordinary vehicles (for example, 10m).

[0182] The user setting change unit 226 allows the user 40 to change the judgment criterion of whether to change the display angle of view to the second angle of view 31 via the display angle of view judgment unit 224. The judgment criterion set (changed) by the user 40 is input from the user setting change unit 226 to the display angle of view judgment unit 224.

[0183] The display angle changing unit 222 generates a display image to be displayed on the display device 230 according to the judgment result of the display angle judging unit 224. For example, in the case where the display angle judging unit 224 judges that the first angle of view 30 is set as the display angle of view, the display angle of view changing unit 222 cuts out a rectangular narrow-angle image (first image) from the image data corresponding to the first angle of view 30, and outputs the cut-out 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 relevant 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 serves as a display control unit for performing display control to change 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.

[0184] The display perspective changing unit 222 cuts out the image data output from the image processing unit 221 by storing it in a storage unit (memory) such as a RAM and reading the image to be cut out. The area corresponding to the first image in the image data is a rectangular area in the first perspective 30 corresponding to the first area 201a. The area corresponding to the second image in the image data is a rectangular area including the relevant rear vehicle in the second perspective 31 corresponding to the second area 201b.

[0185] The display device 230 includes a display unit such as a liquid crystal display and an organic electroluminescent 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 as an electronic rearview mirror arranged on the upper part of the windshield of the movable device 10, and a second display unit as an operation panel (monitor) arranged on the lower part of the windshield of the movable device 10. With this structure, the first image and the second image generated from the above-mentioned image data are displayed on the first display unit and the second display unit, respectively. The first display unit may include, for example, a half mirror, and may be configured to be used as a reflector when not used as a display. The second display unit may also be used, for example, as a display for a navigation system or an audio system.

[0186] The movable device 10 is not limited to vehicles such as automobiles, but may be a mobile body such as a ship, an airplane, an industrial robot, a drone, etc. Although the in-vehicle system 2 according to the present typical embodiment is used to display an image to the user 40, the use of the in-vehicle system 2 is not limited thereto. The in-vehicle system 2 may be used for cruise control (including a full vehicle speed tracking function) and driving assistance such as automatic driving. In addition, the in-vehicle system 2 is applicable not only to movable devices but also to various types of devices utilizing object recognition such as an intelligent transportation system (ITS).

[0187] [Modifications]

[0188] The optical system according to each of the above-described typical embodiments is to be used in the visible region and is configured to perform good aberration correction in the entire visible region. However, the wavelength region in which aberration correction is performed can be appropriately changed. For example, each optical system can be configured to perform aberration correction only in a specific wavelength region in the visible region, or to perform aberration correction in a wavelength region in the infrared region other than the visible region.

[0189] The vehicle-mounted system 2 may adopt the above-mentioned distance measuring device as the camera device 20. In this case, the vehicle-mounted system 2 may include a judgment unit for judging the possibility of collision with the object based on the information related to the distance to the object acquired by the camera device 20. A stereo camera including two camera units 210 may be adopted as the camera device 20. In this case, even in the case where the camera surface phase difference sensor is not used, it is possible to perform processing similar to the above-mentioned processing by synchronously acquiring image data through two different camera units and using the two image data. In the case where the difference in the shooting time between the two camera units is known, the camera units do not need to be synchronized.

[0190] Although the preferred exemplary embodiments and examples of the present invention are described above, the present invention is not limited to these exemplary embodiments and examples, and various combinations, modifications and changes can be made within the scope of the gist of the present invention. To disclose the scope of the present invention, the following claims are attached.

[0191] This application claims the benefit of Japanese Patent Application No. 2022-096787, filed on Jun. 15, 2022, and Japanese Patent Application No. 2022-167466, filed on Oct. 19, 2022, which are hereby incorporated by reference in their entirety.

Claims

1. An optical system comprising a front group having positive refractive power, an aperture stop, and a rear group having positive refractive power, which are arranged in sequence from the object side to the image side, in, The front group includes 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, which are arranged in sequence from the object side to the image side. wherein the rear group includes a cemented lens and a positive lens arranged closest to the image side, The object side surface of the second lens is an aspherical surface, and Among them, the following conditional expressions are satisfied: f1 / d12≤-8.50, Wherein, f1 is the focal length of the first lens, and d12 is the distance between the first lens and the second lens on the optical axis.

2. The optical system according to claim 1, wherein: The following conditional expressions are satisfied: 2.4≤f23 / fa1≤16.0, Wherein, f23 is the combined focal length of the second lens and the third lens, and fa1 is the focal length of the air lens between the second lens and the third lens.

3. An optical system comprising a front group having positive refractive power, an aperture stop, and a rear group having positive refractive power, which are arranged in sequence from the object side to the image side, in, The front group includes 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, which are arranged in sequence from the object side to the image side. wherein the rear group includes a cemented lens and a positive lens arranged closest to the image side, The object side surface of the second lens is an aspherical surface, and Among them, the following conditional expressions are satisfied: 2.4≤f23 / fa1≤16.0, Wherein, f23 is the combined focal length of the second lens and the third lens, and fa1 is the focal length of the air lens between the second lens and the third lens.

4. The optical system according to any one of claims 1 to 3, wherein: The aspherical surface has an inflection point in a cross section including the optical axis.

5. The optical system according to claim 4, wherein: A graph representing the curvature of the aspherical surface with respect to the radial position in a cross section including the optical axis includes a first extreme value and a second extreme value.

6. The optical system according to claim 5, wherein: The following conditional expressions are satisfied: 0.02≤E1≤0.40, 0.60≤E2≤0.98, Wherein, E1 is the normalized distance from the optical axis to the position corresponding to the first extreme value on the aspherical surface.

7. The optical system according to claim 5 or 6, wherein: The following conditional expressions are 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 on the aspherical surface.

8. The optical system according to any one of claims 1 to 7, wherein: The following conditional expressions are satisfied: -1.20≤fa1 / f≤-0.50, Wherein, fa1 is the focal length of the air lens between the second lens and the third lens, and f is the focal length of the optical system.

9. The optical system according to any one of claims 1 to 8, wherein: The following conditional expressions are satisfied: 0.6≤fG1 / fG2≤1.5, Wherein, fG1 is the focal length of the front group, and fG2 is the focal length of the rear group.

10. The optical system according to any one of claims 1 to 9, wherein: The following conditional expressions are satisfied: -3.50≤(R2+R1) / (R2-R1)≤-1.85, Wherein, R1 is the curvature radius of the object-side surface of the first lens, and R2 is the curvature radius of the image-side surface of the first lens.

11. The optical system according to any one of claims 1 to 10, wherein: The following conditional expressions are satisfied: 2.0≤f3R1 / f2R2≤7.0, Wherein, f2R2 is the focal length of the image side of the second lens, and f3R1 is the focal length of the object side of the third lens.

12. An optical system according to any one of claims 1 to 11, wherein: On the optical axis, the first lens and the second lens are meniscus lenses having a convex shape toward the object side, the third lens is a meniscus lens having a concave shape toward the object side, and the fourth lens is a biconvex lens.

13. An optical system according to any one of claims 1 to 12, wherein: The rear group is composed of the cemented lens and the positive lens.

14. An optical system according to any one of claims 1 to 13, wherein: The positive lens in the rear group, which is arranged closest to the image side, has an aspherical surface having an inflection point in a cross section including the optical axis.

15. An optical system according to any one of claims 1 to 14, in, The second lens, the third lens, and the positive lens disposed closest to the image side in the rear group are each made of a resin material, and Among them, the following conditional expressions are satisfied: |f / f3|≤0.15, Wherein, f3 is the focal length of the third lens, and f is the focal length of the optical system.

16. An optical system according to any one of claims 1 to 15, wherein: The following conditional expressions are 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 a half viewing angle θ and an image height, θmax is the maximum half viewing angle of the optical system, and f is the focal length of the optical system.

17. A camera device, comprising: An optical system according to any one of claims 1 to 16; as well as An image sensor is configured to capture an image of an object via the optical system.

18. A vehicle-mounted system, comprising: The imaging device according to claim 17; as well as A display device is configured to display an image acquired based on the output of the imaging device.

19. The vehicle-mounted system according to claim 18, wherein: The display device includes: a first display unit configured to display a first image corresponding to a first viewing angle; and a second display unit configured to display a second image corresponding to a second viewing angle including the first viewing angle.

20. A movable device comprising: The imaging device according to claim 17, The movable device can be moved while holding the camera device.

Images