JP7418134B1 - Optical system and imaging device equipped with the same - Google Patents

Abstract

An object of the present invention is to provide a compact optical system with a wide angle of view and an imaging device equipped with the same. SOLUTION: An optical system 100 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 order from the object side to the image side. G1 is a first lens L1 with negative refractive power, a second lens L2 with negative refractive power, a third lens L3, and a fourth lens with positive refractive power, which are arranged in order from the object side to the image side. The rear group G2 has a cemented lens LC and a positive lens LL disposed closest to the image side, and the combined focal length of the second lens and the third lens is f23, and the rear group G2 has a cemented lens LC and a positive lens LL arranged closest to the image side. When the focal length of the air lens between the lens and the third lens is fa1, the following conditional expression is satisfied: 2.4≦f23/fa1≦16.0. [Selection diagram] Figure 1

Description

The present invention relates to an optical system, and is suitable for imaging devices such as digital still cameras, digital video cameras, vehicle-mounted cameras, mobile phone cameras, surveillance cameras, wearable cameras, and medical cameras.

Optical systems used in imaging devices such as in-vehicle cameras are required to have a wide angle of view. Patent Documents 1 and 2 disclose a first lens with a negative refractive power, a second lens with a negative refractive power, a third lens with a negative refractive power, and a third lens with a positive refractive power, which are arranged in order from the object side to the image side. An optical system with a wide angle of view is disclosed which is composed of seven lenses including a fourth lens.

Special table 2018-522266 publication US Patent Application Publication No. 2020/0142158

However, in the optical systems of Patent Documents 1 and 2, it is difficult to reduce the diameter of the first lens and second lens disposed closest to the object side or to shorten the entire system.

An object of the present invention is to provide a compact optical system with a wide angle of view, and an imaging device equipped with the optical system.

In order to achieve the above object, an optical system as one aspect of the present invention includes a front group with positive refractive power, an aperture stop, and a rear group with positive refractive power, which are arranged in order from the object side to the image side. The front group includes a first lens with a negative refractive power, a second lens with a negative refractive power, a third lens with a positive refractive power, and a third lens with a positive refractive power, which are arranged in order from the object side to the image side. The rear group includes a cemented lens and a positive lens disposed closest to the image side, and the object side surface of the second lens has an inflection point in a cross section including the optical axis. The combined focal length of the second lens and the third lens is f23, the focal length of the air lens between the second lens and the third lens is fa1, and the focal length of the optical system is is characterized by satisfying the following conditional expressions: 2.4≦f23/fa1≦16.0, −1.20≦fa1/f≦−0.50.

According to the present invention, it is possible to provide a compact optical system with a wide angle of view and an imaging device equipped with the optical system.

Schematic diagram of main parts of the optical system according to Example 1 Aberration diagram of the optical system according to Example 1 Schematic diagram of main parts of the optical system according to Example 2 Aberration diagram of the optical system according to Example 2 Schematic diagram of main parts of the optical system according to Example 3 Aberration diagram of the optical system according to Example 3 Schematic diagram of main parts of the optical system according to Example 4 Aberration diagram of the optical system according to Example 4 A diagram showing the aspherical shape of the object side surface of the second lens L2 according to each example. Schematic diagram of an imaging device according to an embodiment A schematic diagram of a moving device according to an embodiment and a diagram showing optical characteristics of an optical system. Block diagram showing a configuration example of an in-vehicle system according to an embodiment

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Note that each drawing may be drawn on a scale different from the actual scale for convenience. Moreover, in each drawing, the same reference numerals are given to the same members, and overlapping explanations will be omitted.

1, 3, 5, and 7 are cross-sectional views including the optical axis OA of the optical systems according to Examples 1 to 4. In each cross-sectional view, the left side is the object side (front side), and the right side is the image side (back side). The optical system of each embodiment is an imaging optical system used in an imaging device, and the imaging surface of the imaging element is arranged at the position of the imaging surface IMG. The optical block CG arranged on the object side of the image plane IMG is an optical element such as an optical filter or a cover glass that does not contribute to image formation in the optical system. Note that the optical system of each embodiment may be used as a projection optical system in a projection device such as a projector, and in that case, a display surface of a display element such as a liquid crystal panel will be placed at the position of the image plane IMG.

2, 4, 6, and 8 are longitudinal aberration diagrams of the optical systems according to Examples 1 to 4. Each longitudinal aberration diagram shows spherical aberration, field curvature (astigmatism), and distortion in order from the left. In each longitudinal aberration diagram, aberrations related to 656.3 nm (C line), 587.6 nm (d line), 486.1 nm (F line), and 435.8 nm (g line) are shown by different lines.

Next, the characteristics of the optical system according to each embodiment will be described in detail.

The optical system according to each 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 order from the object side to the image side. Here, it is assumed that the optical block CG is not included in each 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 with positive refractive power, and a third lens L3 with positive refractive power, which are arranged in order from the object side to the image side. 4 lens L4. The rear group G2 includes a cemented lens LC and a positive lens LL (last lens) disposed closest to the image side. The lens here refers to an optical element that has refractive power, and does not include optical elements such as parallel flat glass that does not have refractive power.

In the optical system according to each embodiment, both the front group G1 and the rear group G2 have positive refractive power, and the front group G1 adopts the above configuration, thereby shortening the overall length of the optical system and widening the angle of view. has been realized. Furthermore, by configuring the rear group G2 as described above, it is possible to satisfactorily correct field curvature and chromatic aberration of magnification that occur when the optical system has a wide angle of view. Then, when the combined focal length of the second lens L2 and the third lens L3 is f23, and the focal length of the air lens between the second lens L2 and the third lens L3 is fa1, the optical system according to each example is The following conditional expression (1) is satisfied.
2.4≦f23/fa1≦16.0 (1)

By appropriately setting the relationship between the focal lengths f23 and fa1 so as to satisfy conditional expression (1), the total length of the optical system can be shortened, and the entire system can be made smaller. When the lower limit of conditional expression (1) is exceeded, the absolute value of the power of the air lens between the second lens L2 and the third lens L3 becomes too small, making it difficult to shorten the total length of the optical system. Alternatively, the absolute value of the combined power of the second lens L2 and the third lens L3 becomes too large, making it difficult to suppress changes in the optical performance of the optical system when the arrangement of each lens is misaligned due to manufacturing errors, etc. become. Furthermore, if the upper limit of conditional expression (1) is exceeded, the absolute value of the power of the air lens between the second lens L2 and the third lens L3 will become too large, and the arrangement of each lens will shift due to manufacturing errors. It becomes difficult to suppress changes in the optical performance of the optical system when Alternatively, the absolute value of the combined power of the second lens L2 and the third lens L3 becomes too small, making it difficult to widen the angle of view of the optical system.

Furthermore, it is preferable that the following conditional expression (1a) is satisfied, and it is more preferable that the conditional expression (1b) is satisfied.
2.6≦f23/fa1≦15.0 (1a)
2.8≦f23/fa1≦14.0 (1b)

Note that the optical system according to each embodiment can obtain the effects of the present invention if it satisfies at least the above-mentioned configuration. For example, the front group G1 includes lenses other than the first lens L1 to the fourth lens L4. (a configuration including five or more lenses). However, in order to downsize the entire system, it is preferable that the front group G1 is composed of four lenses. Regarding the third lens L3, since the absolute value of the power is small as described later, whether it has positive refractive power or negative refractive power can be determined depending on the specifications of each optical system.

In addition, in an imaging device such as a vehicle-mounted camera to be described later, it is required not only to have a wide angle of view but also to increase the imaging magnification near the optical axis (center area). For example, when an imaging device is placed at the rear of a moving device (vehicle), the image corresponding to the center area, which is the main area of interest, is enlarged and displayed on the electronic rearview mirror, and the area other than the center area (peripheral area) is enlarged and displayed on the electronic rearview mirror. A possible configuration would be to display the entire image including the vehicle on the in-vehicle display. Therefore, it is desirable to make the imaging magnification (focal length) of the optical system different between the central region and the other regions.

Therefore, it is desirable that the object side surface (lens surface on the object side) of the second lens L2 be an aspherical surface. According to this configuration, among the light beams from the first lens L1, light rays from the peripheral portion in the radial direction can be largely refracted toward the optical axis OA side by the object side surface of the second lens L2. This makes it easy to make the imaging magnification different between the central region and the peripheral region of the optical system. At this time, it is preferable that the object side surface of the second lens L2 is an aspherical surface having an inflection point in a cross section including the optical axis OA. Thereby, it is possible to easily widen the angle of view and increase the imaging magnification in the central region while reducing the number of lenses constituting the optical system.

FIG. 9 shows the aspherical shape of the object side surface of the second lens L2 according to each example. In FIG. 9, the horizontal axis indicates the position of the object side surface of the second lens L2 in the radial direction in a 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. There is. That is, FIG. 9 shows a graph in which the curvature of the second lens L2 at each position on the object side is plotted. The numerical value on the horizontal axis is the effective diameter of the object side of the second lens L2 from the optical axis OA when normalized so that the distance from the optical axis OA to the position of the effective diameter (maximum effective diameter) is 1. The distance (normalized distance) to each position within is shown.

The object side surface of the second lens L2 is preferably an aspheric surface such that the graph of curvature versus distance from the optical axis OA shown in FIG. 9 has a plurality of extreme values. As shown in FIG. 9, the graphs according to each example each have a first extreme value (maximum value) and a second extreme value (minimum value). This makes it possible to highlight the difference in imaging magnification between the central area and the peripheral area of the optical system, and specifically, it is possible to make the imaging magnification of the central area larger than that of the peripheral area, so the imaging It becomes possible to improve the visibility of the image for the user of the device.

Further, when the normalized distances from the optical axis OA to the positions corresponding to the first extreme value and the second extreme value, respectively, on the object side surface of the second lens L2 are E1 and E2, the optical system according to each embodiment It is desirable that the following conditional expressions (2) and (3) be satisfied.
0.02≦E1≦0.40 (2)
0.60≦E2≦0.98 (3)

Conditional expressions (2) and (3) define appropriate positions of the first extreme value and the second extreme value. By satisfying conditional expression (2), it is possible to easily increase the focal length of the central region of the optical system, and by satisfying conditional expression (3), it is easy to achieve both miniaturization and widening of the angle of view of the optical system. It can be done. If conditional expressions (2) and (3) are not satisfied, it is not preferable because it becomes difficult to appropriately set the imaging magnification of each of the central region and the peripheral region.

Furthermore, it is preferable that the following conditional expressions (2a) and (3a) are satisfied, and it is more preferable that the following conditional expressions (2b) and (3b) are satisfied.
0.04≦E1≦0.35 (2a)
0.65≦E2≦0.96 (3a)
0.06≦E1≦0.30 (2b)
0.70≦E2≦0.94 (3b)

Further, when the focal length of the optical system (the entire system) is f, it is desirable that the optical system according to each embodiment satisfies the following conditional expression (4).
-1.20≦fa1/f≦-0.50 (4)

By satisfying conditional expression (4), the air lens formed by the second lens L2 and the third lens L3 can have strong (large absolute value) negative power (refractive power), and the optical system Further downsizing is possible. If the lower limit of conditional expression (4) is not reached, the negative power of the air lens will become too strong, which is undesirable because the change in the optical performance of the optical system will increase if the arrangement of each lens is deviated due to manufacturing errors. . Moreover, if the upper limit of conditional expression (4) is exceeded, the negative power of the air lens becomes too weak, making it difficult to further downsize the optical system, which is not preferable.

Furthermore, it is preferable that conditional expression (4a) below be satisfied, and it is more preferable that conditional expression (4b) be satisfied.
-1.10≦fa1/f≦-0.55 (4a)
-1.00≦fa1/f≦-0.60 (4b)

Further, when the focal length of the image side surface of the second lens L2 is f2R2, and the focal length of the object side surface of the third lens L3 is f3R1, the optical system according to each embodiment must satisfy the following conditional expression (5). is desirable.
2.0≦f3R1/f2R2≦7.0 (5)

By appropriately setting the focal length (power) of the image side surface of the second lens L2 and the object side surface of the third lens L3 so as to satisfy conditional expression (5), it is possible to reduce the outer diameter of the first lens L1. This makes it possible to downsize the entire system. If the lower limit of conditional expression (5) is not reached, the absolute value of the power on the image side surface of the second lens L2 becomes too small, making it difficult to reduce the diameter of the first lens L1, which is not preferable. Furthermore, if the upper limit of conditional expression (5) is exceeded, the absolute value of the power on the image side surface of the second lens L2 will become too large, and the optical performance of the optical system will deteriorate even if the arrangement of each lens is shifted due to manufacturing errors. This is not preferable because it becomes difficult to suppress changes in .

Furthermore, it is preferable that the following conditional expression (5a) is satisfied, and it is more preferable that the conditional expression (5b) is satisfied.
2.3≦f3R1/f2R2≦6.7 (5a)
2.5≦f3R1/f2R2≦6.5 (5b)

Furthermore, when the focal length of the front group G1 is fG1 and the focal length of the rear group G2 is fG2, it is desirable that the optical system according to each embodiment satisfy the following conditional expression (6).
0.60≦fG1/fG2≦1.50 (6)

By satisfying conditional expression (6), the powers of the front group G1 and the rear group G2 can be appropriately set, and further miniaturization of the optical system becomes possible. If the lower limit of conditional expression (6) is not reached, the power of the front group G1 becomes too strong, which is not preferable because the change in the optical performance of the optical system becomes large when the arrangement of each lens is deviated due to manufacturing errors or the like. Furthermore, if the upper limit of conditional expression (6) is exceeded, the power of the front group G1 becomes too weak, making it difficult to further downsize the optical system, which is not preferable.

Furthermore, it is preferable that the following conditional expression (6a) is satisfied, and it is more preferable that the conditional expression (6b) is satisfied.
0.65≦fG1/fG2≦1.45 (6a)
0.70≦fG1/fG2≦1.40 (6b)

Further, when the radius of curvature of the object side surface of the first lens L1 is R1, and the radius of curvature of the image side surface of the first lens L1 is R2, the optical system according to each embodiment must satisfy the following conditional expression (7). is desirable.
-3.50≦(R2+R1)/(R2-R1)≦-1.85 (7)

Conditional expression (7) expresses a preferable shape (shape factor) of the first lens L1. If the lower limit of conditional expression (7) is not reached, the outer diameter of the first lens L1 becomes large, which is not preferable because it becomes difficult to further downsize the optical system. Furthermore, if the upper limit of conditional expression (7) is exceeded, it becomes difficult for the first lens L1 to take in the light rays directed toward the most off-axis image height (most off-axis rays), making it difficult to further widen the field of view of the optical system. This is not desirable.

Furthermore, it is preferable that conditional expression (7a) below be satisfied, and it is more preferable that conditional expression (7b) be satisfied.
-3.20≦(R2+R1)/(R2-R1)≦-1.88 (7a)
-3.00≦(R2+R1)/(R2-R1)≦-1.90 (7b)

In addition, on the optical axis OA, the first lens L1 and the second lens L2 are meniscus lenses having a convex shape toward the object side (negative meniscus lenses), and the third lens L3 is a meniscus lens having a concave shape toward the object side. It is desirable that the fourth lens L4 be a biconvex lens. With such a configuration, it is possible to reduce the angle of incidence of each light beam on the rear group G2, and to suppress changes in optical performance caused by placement errors (manufacturing errors) of each lens.

Note that the cemented lens LC of the rear group G2 desirably includes a positive lens and a negative lens in order to facilitate reduction of lateral chromatic aberration. Although the cemented lens LC may be composed of three or more lenses, it is preferably composed of two lenses in order to downsize the entire system and facilitate manufacturing. Furthermore, the rear group G2 may include lenses other than the cemented lens LC and the positive lens LL. For example, the lens L5 may be arranged on the object side of the cemented lens LC as in Example 3 shown in FIG. It is desirable to decide whether or not to provide lenses other than the cemented lens LC and the positive lens LL in the rear group G2, depending on the specifications of each optical system and the required optical performance. For example, in order to easily reduce field curvature and lateral chromatic aberration with a small number of lenses while suppressing the influence of manufacturing errors, it is preferable that the rear group G2 is composed of a cemented lens LC and a positive lens LL.

Here, it is desirable that the positive lens LL of the rear group G2 also include an aspherical surface. In other words, it is desirable that at least one of the object side surface or the image side surface of the positive lens LL be an aspheric surface. Furthermore, like the aspherical surface of the second lens L2 of the front group G1, it is preferable that the aspherical surface of the positive lens LL also have an inflection point in the cross section including the optical axis OA. Thereby, it is possible to reduce the curvature of field caused by the aspheric surface of the second lens L2 while reducing the number of lenses constituting each optical system. At this time, it is preferable that the aspheric surface of the positive lens LL also has a plurality of extreme values, and it is more preferable that the above-mentioned conditional expressions (2) and (3) are satisfied.

As described above, since optical performance can be improved by making the second lens L2 and the positive lens LL aspherical lenses, it is desirable to make each lens a lens made of a resin material (resin lens). Here, the resin material refers to a material whose main component is resin (plastic), and includes not only a material made only of resin but also a material containing a minute amount of a substance other than resin (impurity). By constructing each lens from a resin material, it is possible to form an aspherical surface more easily than when constructing each lens from a glass material, and manufacturing costs can be reduced.

However, the temperature coefficient of the refractive index of a resin lens is larger than that of a glass lens made of a general glass material. Therefore, if only the second lens L2 and the positive lens LL having strong negative power are made of resin lenses, there is a possibility that the focus fluctuations caused by temperature changes cannot be completely canceled out by each lens. Therefore, in order to suppress focus fluctuations caused by temperature changes, it is desirable that the third lens L3 is also made of a resin lens. Furthermore, when the focal length of the third lens L3 is f3 and the focal length of the entire system is f, it is desirable that the optical system according to each embodiment satisfy the following conditional expression (8).
|f/f3|≦0.15 (8)

By appropriately setting the power of the third lens L3 so as to satisfy conditional expression (8), it becomes easy to suppress changes in focus of each optical system due to temperature changes. If the range of conditional expression (8) is exceeded, the absolute value of the power of the third lens L3 becomes too large, making it difficult to suppress changes in focus of each optical system due to temperature changes, which is not preferable.

Furthermore, it is preferable that the following conditional expression (8a) is satisfied, and it is more preferable that the conditional expression (8b) is satisfied.
|f/f3|≦0.13 (8a)
|f/f3|≦0.12 (8b)

Note that lenses other than the second lens L2, the third lens L3, and the positive lens LL may be made of resin lenses as necessary. However, as mentioned above, the temperature coefficient of the refractive index of the resin lens is relatively large, so in order to suppress focus fluctuations caused by temperature changes, it is preferable that at least one lens is a glass lens. As described above, it is more preferable that only the second lens L2 having an aspherical surface, the positive lens LL, and the third lens L3 for canceling the focus fluctuation caused by them are made of resin lenses. Note that since resin lenses are easier to process than glass lenses, it is desirable that both the object side surface and the image side surface of the resin lens be aspherical. This makes it easy to achieve good optical performance while reducing the number of lenses constituting each optical system.

Further, when the focal length of the first lens L1 is f1, and the distance (interval) between the first lens L1 and the second lens L2 on the optical axis OA is d12, the optical system according to each example is under the following conditions. It is desirable that equation (9) be satisfied.
f1/d12≦-8.50 (9)

By appropriately setting the relationship between the focal length f1 and the distance d12 so as to satisfy conditional expression (9), the outer diameters of the first lens L1 and the second lens L2 can be reduced, and the entire system can be made smaller. can be realized. Exceeding the upper limit of conditional expression (9) is not preferable because the distance between the first lens L1 and the second lens L2 becomes too wide, making it difficult to reduce the diameters of the first lens L1 and the second lens L2.

Note that if the distance d12 is made infinitely small by bringing the first lens L1 and the second lens L2 close together, the absolute value of f1/d12 will approach infinity. However, except when the first lens L1 and the second lens L2 form a cemented lens, it is desirable that the first lens L1 and the second lens L2 be arranged apart from each other. Therefore, it is desirable that the following conditional expression (9a) be satisfied.
-1.00×10 ³ ≦f1/d12≦-8.50 (9a)

If the lower limit of conditional expression (9a) is not reached, the distance between the first lens L1 and the second lens L2 will become too narrow, and there is a possibility that the first lens L1 and the second lens L2 will come into contact with each other due to manufacturing errors, etc. This is undesirable because it causes sexual problems. Furthermore, it is preferable that the following conditional expression (9b) is satisfied, and it is more preferable that the following conditional expression (9c) is satisfied.
-8.00×10 ² ≦f1/d12≦-9.00 (9b)
-3.00×10 ² ≦f1/d12≦-9.50 (9c)

The detailed configuration of the optical system according to each embodiment will be described below.

[Example 1]
As shown in FIG. 1, the optical system 100 according to the first embodiment includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and an aperture stop arranged in order from the object side to the image side. It is composed of an STO, a cemented lens LC, and a positive lens LL. A light flux from an object (not shown) is condensed onto an image plane IMG via each lens and a cover glass CG, thereby forming an image of the object. The optical system 100 of this embodiment has a sufficiently wide full angle of view of 180° (half angle of view of ±90°), and a sufficiently wide focal length (center focal length) on the optical axis OA of 4.4 mm. It has a long structure.

In this 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. Further, the second lens L2 and the positive lens LL have aspherical surfaces. Specifically, each of the object side surface and image side surface of the second lens L2 and the object side surface and image side surface of the positive lens LL is an aspheric surface having an inflection point in a cross section including the optical axis OA. Note that each lens according to this embodiment is a glass lens made of a glass material, and each aspherical surface is molded with a glass mold.

As shown in FIG. 2, in the optical system 100 according to this embodiment, spherical aberration and field curvature are well corrected. Furthermore, while distortion increases as the angle of view (image height) increases in the peripheral region, it becomes relatively small in the central region. Thereby, the resolution of the central region can be made higher than that of the peripheral region, and as described above, it is possible to improve the visibility of the image for the user of the imaging device.

[Example 2]
As shown in FIG. 3, the optical system 200 according to the second embodiment includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and an aperture stop arranged in order from the object side to the image side. It is composed of an STO, a cemented lens LC, and a positive lens LL. Similarly to Example 1, in this example as well, 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. has been done. The optical system 200 of this embodiment has a sufficiently wide full angle of view of 180° (half angle of view of ±90°) and a sufficiently long focal length of 4.4 mm on the optical axis OA. There is.

In this example, unlike Example 1, not only the second lens L2 and the positive lens LL but also the third lens L3 have an aspherical surface. Specifically, the object side surface and the image side surface of each of the second lens L2, the third lens L3, and the positive lens LL are aspheric. Note that 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, but the aspheric surface of the third lens L3 does not have an inflection point. Further, in this example, unlike Example 1, 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. . That is, each aspherical surface is molded using a plastic mold.

As shown in FIG. 4, in the optical system 200 according to this embodiment, spherical aberration and field curvature are well corrected. Furthermore, while distortion increases as the angle of view increases in the peripheral area, it becomes relatively small in the central area.

[Example 3]
As shown in FIG. 5, the optical system 300 according to the third embodiment includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and an aperture stop arranged in order from the object side to the image side. It is composed of an STO, a fifth lens L5, a cemented lens LC, and a positive lens LL. In this example, unlike Example 1, the third lens L3 has a positive refractive power, and the fifth lens L5 with a positive refractive power is arranged on the object side of the cemented lens LC. The LC is composed of a negative lens L6 and a positive lens L7 arranged in order from the object side to the image side. The optical system 300 of this embodiment has a sufficiently wide full angle of view of 180° (half angle of view of ±90°) and a sufficiently long focal length of 4.4 mm on the optical axis OA. There is.

In this example, unlike Example 1, not only the second lens L2 and the positive lens LL but also the third lens L3 and the fifth lens L5 have aspheric surfaces. Specifically, the object side surface and the image side surface of each of the second lens L2, the third lens L3, the fifth lens L5, and the positive lens LL are aspheric. Note that 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, but the aspheric surfaces of the third lens L3 and the fifth lens L5 do not have an inflection point. Further, in this example, unlike Example 1, 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. . Note that each aspherical surface of the second lens L2, third lens L3, and positive lens LL is molded with a plastic mold, and each aspherical surface of the fifth lens L5 is molded with a glass mold.

As shown in FIG. 6, in the optical system 300 according to this embodiment, spherical aberration and field curvature are well corrected. Furthermore, while distortion increases as the angle of view increases in the peripheral area, it becomes relatively small in the central area.

[Example 4]
As shown in FIG. 7, the optical system 400 according to the fourth embodiment includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and an aperture stop arranged in order from the object side to the image side. It is composed of an STO, a cemented lens LC, and a positive lens LL. The optical system 400 of this embodiment has a sufficiently wide full angle of view of 180° (half angle of view of ±90°) and a sufficiently long focal length of 4.4 mm on the optical axis OA. There is.

In this example as well as in Example 2, 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. ing. The object side surface and the image side surface of each of the second lens L2, the third lens L3, and the positive lens LL have an aspheric surface. Further, in this example as well as in Example 2, each of the second lens L2, the third lens L3, and the positive lens LL is made of a resin material.

As shown in FIG. 8, in the optical system 400 according to this embodiment, spherical aberration and field curvature are well corrected. Furthermore, while distortion increases as the angle of view increases in the peripheral area, it becomes relatively small in the central area.

Numerical Examples 1 to 4 corresponding to Examples 1 to 4 described above will be shown below. In each numerical example, the surface number is the order of each optical surface when counted from the object surface. r [mm] indicates the radius of curvature of the i-th optical surface, and d [mm] indicates the interval (distance on the optical axis) between the i-th optical surface and the (i+1)-th optical surface. There is. nd represents the refractive index of the medium between the i-th surface and the (i+1)-th surface with respect to the d-line, and νd represents the Abbe number of the medium with respect to the d-line. Note that the Abbe number νd is a value defined by the following formula, where the refractive indices for the F line, d line, and C line are respectively nF, nd, and nC.
νd=(nd-1)/(nF-nC)

Furthermore, in each numerical example, for aspherical surfaces, an asterisk (*) is attached after the surface number. Further, "E±P" in each numerical value means "×10 ^±P ". The shape of each aspherical surface is as follows: z is the displacement from the apex of the surface 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 (reciprocal of the radius of curvature r), and is conical. When the coefficient is k and the aspheric coefficients are A, B, C, D, E, F, G, H, I..., it is expressed by the following formula.

It should be noted that the optical systems according to each numerical example are all single-focus optical systems in which the focal length remains unchanged (no zooming is performed), and have a configuration in which no focusing is performed. That is, the distance between the lenses constituting the optical system according to each numerical example is always fixed. This makes it possible to avoid fluctuations in optical performance due to movement of each lens. However, if necessary, the optical system may be configured to perform at least one of zooming and focusing, and for this purpose, the distance between each lens may be configured to change.

(Numerical Example 1)
Various data center focal length 4.4mm
Fno 2.8
Half angle of view ±90°

Surface data surface number rd nd νd
1 24.64 1.00 1.703 52.4
2 12.20 0.67
3* 4.86 1.87 1.583 59.5
4* 2.44 3.13
5 -5.08 3.11 1.595 67.7
6 -7.50 0.20
7 8.20 1.56 1.583 59.4
8 -13.98 0.70
9(STO) ∞ 1.12
10 11.26 3.75 1.603 65.4
11 -3.40 0.60 1.785 25.7
12 -12.99 2.27
13* 9.44 2.58 1.583 59.5
14* -1697.27 0.70
15 ∞ 0.90 1.560 56.0
16 ∞ 0.85

Aspheric coefficient surface number KABCDE
3 -4.499E-01 5.138E-03 -1.389E-03 2.223E-04 -3.240E-05 3.183E-06
4 -8.597E-01 1.547E-02 -5.648E-03 1.575E-03 -4.610E-04 1.122E-04
13 0.000E+00 6.276E-03 -3.280E-03 9.788E-04 -2.079E-04 3.009E-05
14 0.000E+00 2.784E-02 -1.002E-02 2.165E-03 -3.424E-04 3.840E-05

Surface number FGHI
3 -1.933E-07 7.002E-09 -1.390E-10 1.165E-12
4 -1.915E-05 2.114E-06 -1.361E-07 3.895E-09
13 -2.816E-06 1.613E-07 -5.130E-09 6.926E-11
14 -2.873E-06 1.340E-07 -3.504E-09 3.913E-11

(Numerical Example 2)
Various data center focal length 4.4mm
Fno 2.8
Half angle of view ±90°

Surface data surface number rd nd νd
1 27.36 1.00 1.703 52.4
2 13.37 0.05
3* 4.92 2.40 1.536 56.0
4* 2.42 4.20
5* -3.99 2.58 1.536 56.0
6* -5.38 0.20
7 5.71 1.62 1.583 59.4
8 -29.74 0.98
9(STO) ∞ 1.15
10 17.63 2.74 1.603 65.4
11 -3.35 0.60 1.785 25.7
12 -19.47 1.55
13* 6.80 3.38 1.536 56.0
14* -43.69 0.66
15 ∞ 0.90 1.560 56.0
16 ∞ 0.85

Aspheric coefficient surface number KABCDE
3 -4.634E-01 4.868E-03 -7.845E-04 1.348E-04 -1.747E-05 1.253E-06
4 -6.958E-01 1.742E-02 -5.776E-03 3.092E-03 -1.201E-03 2.696E-04
5 0.000E+00 4.533E-03 -1.467E-03 6.577E-04 -2.115E-04 4.871E-05
6 0.000E+00 1.574E-03 -1.185E-04 -1.584E-04 1.443E-04 -5.423E-05
13 0.000E+00 1.330E-03 -1.183E-03 2.994E-04 -4.603E-05 4.955E-06
14 0.000E+00 1.670E-02 -5.403E-03 8.838E-04 -9.971E-05 8.862E-06

Surface number FGHI
3 -5.205E-08 1.265E-09 -1.681E-11 9.454E-14
4 -3.679E-05 3.043E-06 -1.405E-07 2.785E-09
5 -7.65E-06 7.686E-07 -4.394E-08 1.079E-09
6 1.1252E-05 -1.341E-06 8.630E-08 -2.328E-09
13 -3.906E-07 2.128E-08 -6.966E-10 1.010E-11
14 -6.139E-07 2.924E-08 -8.120E-10 9.729E-12

(Numerical Example 3)
Various data center focal length 4.4mm
Fno 2.8
Half angle of view ±90°

Surface number rd nd νd
1 26.80 1.12 1.703 52.4
2 8.47 0.98
3* 3.86 3.20 1.536 56.0
4* 1.83 3.54
5* -6.87 1.92 1.536 56.0
6* -5.73 0.20
7 3.63 1.74 1.539 55.6
8 13.12 1.69
9(STO) ∞ 0.22
10* 35.10 1.20 1.583 59.4
11* -5.79 0.40
12 -7.68 0.33 1.742 25.7
13 6.23 1.84 1.589 61.1
14 -9.36 0.72
15* 23.06 2.88 1.536 56.0
16* -9.62 0.69
Sphere ∞ 0.90 1.569 56.4
Sphere ∞ 1.43

Aspheric coefficient surface number KABCDE
3 -5.513E-01 1.621E-03 -4.817E-04 8.237E-05 -1.292E-05 1.073E-06
4 -8.615E-01 5.511E-03 -1.955E-03 -1.456E-04 -2.832E-05 3.229E-05
5 0.000E+00 -2.677E-03 1.363E-04 -1.769E-04 1.235E-04 -3.507E-05
6 0.000E+00 -6.872E-04 -3.457E-04 2.432E-04 -6.088E-05 8.232E-06
10 0.000E+00 -8.697E-03 -1.594E-03 3.830E-04 -1.179E-04 0.000E+00
11 0.000E+00 -4.873E-03 -4.025E-04 -7.694E-05 2.965E-05 0.000E+00
15 0.000E+00 2.170E-03 -1.611E-03 1.453E-04 7.909E-05 -3.374E-05
16 0.000E+00 1.445E-02 -5.089E-03 8.968E-04 -1.162E-04 1.118E-05

Surface number FGHI
3 -5.062E-08 1.380E-09 -2.026E-11 1.228E-13
4 -7.139E-06 7.722E-07 -4.358E-08 1.034E-09
5 5.4319E-06 -4.927E-07 2.477E-08 -5.312E-10
6 -6.181E-07 2.074E-08 1.389E-10 -2.085E-11
10 0.000E+00 0.000E+00 0.000E+00 0.000E+00
11 0.000E+00 0.000E+00 0.000E+00 0.000E+00
15 6.0816E-06 -5.992E-07 3.159E-08 -6.970E-10
16 -7.948E-07 3.965E-08 -1.235E-09 1.792E-11

(Numerical Example 4)
Various data center focal length 4.4mm
Fno 2.8
Half angle of view ±90°

Surface data surface number rd nd νd
1 23.47 1.17 1.703 52.4
2 7.57 1.31
3* 3.82 3.25 1.536 56.0
4* 1.99 3.30
5* -7.32 1.81 1.536 56.0
6* -6.04 0.72
7 5.80 1.75 1.514 69.5
8 -10.77 1.33
9(STO) ∞ 1.61
10 13.56 1.73 1.589 61.1
11 -3.65 1.01 1.878 25.7
12 -20.26 0.62
13* 9.91 2.39 1.536 56.0
14* -10.47 0.66
15 ∞ 0.90 1.569 56.4
16 ∞ 1.43

Aspheric coefficient surface number KABCDE
3 -5.553E-01 2.035E-03 -4.672E-04 7.196E-05 -1.144E-05 8.964E-07
4 -7.682E-01 5.504E-03 -1.152E-03 -1.293E-03 5.350E-04 -1.181E-04
5 0.000E+00 -3.664E-03 -4.244E-04 4.473E-04 -8.862E-05 5.675E-06
6 0.000E+00 -1.413E-03 -4.265E-04 6.189E-04 -2.342E-04 4.960E-05
13 0.000E+00 1.133E-02 -5.796E-03 1.694E-03 -3.406E-04 4.642E-05
14 0.000E+00 2.836E-02 -7.958E-03 1.011E-03 -1.905E-05 -1.504E-05

Surface number FGHI
3 -3.696E-08 7.803E-10 -6.415E-12 -8.093E-15
4 1.707E-05 -1.562E-06 8.018E-08 -1.731E-09
5 5.5065E-07 -1.298E-07 9.501E-09 -2.564E-10
6 -6.471E-06 5.148E-07 -2.282E-08 4.308E-10
13 -4.141E-06 2.245E-07 -6.385E-09 6.590E-11
14 2.5115E-06 -1.928E-07 7.525E-09 -1.203E-10

The table below shows values for each conditional expression for the optical system according to each of the embodiments described above. Note that the table below also shows values related to conditional expression (10), which will be described later. As shown in the table, the optical system according to each example satisfies each conditional expression.

[Imaging device]
FIG. 10 is a schematic diagram of main parts of an imaging device 70 according to an embodiment of the present invention. The imaging device 70 according to the present embodiment includes an optical system (imaging optical system) 71 according to any of the above-described embodiments, a light receiving element 72 that photoelectrically converts an image of an object formed by the optical system 71, and a light receiving element 72 that photoelectrically converts an image of an object formed by the optical system 71. A camera body (housing) 73 that holds an element 72 is provided. The optical system 71 is held by a lens barrel (holding member) and connected to a camera body 73. As shown in FIG. 7, a display section 74 that displays images acquired by the light receiving element 72 may be connected to the camera body 73. As the light receiving element 72, an imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor can be used.

When the imaging device 70 is used as a distance measuring device, for example, an imaging device (imaging surface phase difference sensor) having a pixel that can split a luminous flux from an object into two and perform photoelectric conversion can be employed as the light receiving device 72. When the subject is on the front focal plane of the optical system 71, no positional shift occurs in the images corresponding to the two divided light beams on the image plane of the optical system 71. However, when the subject is located at a position other than the front focal plane of the optical system 71, a positional shift occurs in each image. At this time, the positional deviation of each image corresponds to the amount of displacement from the front focal plane of the subject, so by obtaining the positional deviation amount and direction of each image using the imaging plane phase difference sensor, The distance to the subject can be measured.

Note that the optical system 71 and the camera body 73 may be configured to be detachable from each other. That is, the optical system 71 and the lens barrel may be configured as an interchangeable lens (lens device). Further, the optical system according to each of the embodiments described above is not limited to imaging devices such as digital still cameras, silver halide film cameras, video cameras, in-vehicle cameras, and surveillance cameras, but also telescopes, binoculars, projectors (projection devices), digital It can be applied to various optical devices such as copying machines.

[In-vehicle system]
FIG. 11(A) is a schematic diagram of the moving device 10 and the imaging device 20 (vehicle camera) held by the moving device 10 according to the embodiment of the present invention. FIG. 11A shows a case where the mobile device 10 is an automobile (vehicle). The mobile device 10 includes an in-vehicle system (driving support device), not shown, for supporting a user 40 (driver, passenger, etc.) of the mobile device 10 using images acquired by the imaging device 20. There is. In this embodiment, a case is shown in which the imaging device 20 is installed to image the rear of the moving device 10, but the imaging device 20 is installed so as to image the front or side of the moving device 10. may have been done. Furthermore, two or more imaging devices 20 may be installed at two or more locations on the mobile device 10.

The imaging device 20 includes an optical system 201 and an imaging section 210 according to any of the embodiments described above. The optical system 201 is an optical system in which the imaging magnification is different between 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. (different angle of view lens). The imaging surface (light-receiving surface) of the imaging unit 210 has a first area for imaging an object included in the first angle of view 30 and a second area for imaging an object included in the second angle of view 31. include. At this time, 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 excluding the first area. In other words, the resolution at the first angle of view (first region) of the imaging device 20 is higher than the resolution at the second angle of view (second region).

The optical characteristics of the optical system 201 will be explained in detail below. The left diagram in FIG. 11B shows each half angle of view θ [deg. ] The image height y [mm] is shown in contour lines. The right diagram in FIG. 11B is a graph showing the relationship between each half angle of view θ and the image height y (projection characteristics of the optical system 201) in the first quadrant of the left diagram.

As shown in FIG. 11(B), the optical system 201 is configured such that the projection characteristic y(θ) differs between the angle of view less than a predetermined half-angle θa and the angle of view greater than or equal to the half-angle θa. . Therefore, the amount of increase (resolution) in the image height y with respect to the half angle of view θ per unit also differs depending on the angle of view. The local resolution of the optical system 201 is expressed by the differential value dy(θ)/dθ of the projection characteristic y(θ) with respect to the half angle of view θ. The left diagram in FIG. 11B shows that the larger the interval between the contour lines of the image height y for each half angle of view θ, the higher the resolution. Further, in the right diagram of FIG. 11(B), the larger the slope of the graph of the projection characteristic y(θ), the higher the resolution.

In the left diagram of FIG. 11(B), the first area 201a, which is the central area, corresponds to an angle of view less than half the angle of view θa, and the second area 201b, which is the peripheral area, corresponds to an angle of view greater than or equal to the half angle θa. It corresponds to the corner. The angle of view less than half the angle of view θa corresponds to the first angle of view 30 in FIG. corresponds to the second angle of view 31 in FIG. 11(A). As described above, the first region 201a is a high resolution and low distortion region, and the second region 201b is a low resolution and high distortion region.

The value θa/θmax of the ratio of the half angle of view θa to the maximum half angle of view θmax is preferably 0.15 or more and 0.35 or less, more preferably 0.16 or more and 0.25 or less. preferable. For example, in each of the above embodiments, the maximum half angle of view θmax=90°, so the value of the half angle of view θa is preferably 13.5° or more and 31.5° or less, and 14.4° or more. It is more preferable that the angle is 22.5° or less.

Further, the optical system 201 is configured such that the projection characteristic y(θ) in the first region 201a is different from f×θ (equidistant projection method) and also different from the projection characteristic in the second region 201b. . At this time, it is desirable that the projection characteristic y(θ) of the optical system 201 satisfies the following conditional expression (10).
1.0<f×sin(θmax)/y(θmax)≦1.9 (10)

y(θmax) corresponds to the image height (maximum image height) corresponding to the maximum half-field angle θmax. By satisfying conditional expression (10), it is possible to realize a wide angle of view of the optical system 201 by reducing the resolution in the second region 201b. Furthermore, in the first region 201a, the resolution can be made higher than the central region of a general fisheye lens that employs the orthographic projection method (y(θ)=f×sinθ). If the lower limit of conditional expression (10) is exceeded, the resolution in the first region 201a will be lower than that of an orthogonal projection type fisheye lens, and the maximum image height will be large, leading to an increase in the size of the optical system. Undesirable. If the upper limit of conditional expression (10) is exceeded, the resolution in the first region 201a will become too high, making it difficult to achieve a wide angle of view equivalent to that of an orthographic projection fisheye lens, and making it difficult to achieve good optical performance. This is not desirable because it may become unsustainable.

Further, it is preferable that the following conditional expression (10a) is satisfied, and it is more preferable that the following conditional expression (10b) is satisfied.
1.0<f×sin(θmax)/y(θmax)≦1.7 (10a)
1.0<f×sin(θmax)/y(θmax)≦1.4 (10b)

As described above, in the first region 201a, the distortion of the optical system 201 is small and the resolution is high, so a high-definition image can be obtained compared to the second region 201b. Therefore, good visibility can be obtained by setting the first area 201a (first angle of view 30) to be the user's 40 attention area. For example, when the imaging device 20 is placed at the rear of the mobile device 10 as shown in FIG. This allows users to obtain a natural sense of perspective when looking at objects such as vehicles behind them. On the other hand, the second area 201b (second angle of view 31) corresponds to a wide angle of view including the first angle of view 30. Therefore, for example, by displaying an image corresponding to the second angle of view 31 on the in-vehicle display when the mobile device 10 is traveling in reverse, driving support for the user 40 can be provided.

FIG. 12 is a functional block diagram for explaining a configuration example of the in-vehicle system 2 according to this embodiment. The in-vehicle system 2 is a system for displaying images obtained by an imaging device 20 installed at the rear of the mobile device 10 to a user 40. The in-vehicle system 2 includes an imaging device 20, a processing device 220, and a display device (display section) 230. The imaging device 20 includes the optical system 201 and the imaging section 210 as described above. The imaging unit 210 includes an imaging device such as a CCD sensor or a CMOS sensor, generates imaging data by photoelectrically converting the optical image formed by the optical system 201, and outputs the data to the processing device 220.

The processing device 220 includes an image processing unit 221, a display 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), and a back gear. It has a detecting section 225 (second detecting section) and a display angle changing section 222 (second changing section). The processing device 220 is, for example, a computer such as a CPU (Central Processing Unit) microcomputer, and functions as a control unit that controls the operation of each component based on a computer program. At least one component in the processing device 220 may be realized by hardware such as an ASIC (Application Specific Integrated Circuit) or a PLA (Programmable Logic Array).

The image processing unit 221 generates image data by performing image processing such as WDR (Wide Dynamic Range) correction, gamma correction, LUT (Look Up Table) processing, and distortion correction on the imaging data acquired from the imaging unit 210. do. Note that distortion correction is performed on at least the imaging data corresponding to the second region 201b. This makes it easier for the user 40 to visually recognize an image when it is displayed on the display device 230, and also improves the detection rate of the rear vehicle by the rear vehicle distance detection unit 223. Note that it is not necessary to perform distortion correction on the imaging data corresponding to the first region 201a. The image processing unit 221 outputs image data generated by performing the image processing as described above to the display angle changing unit 222 and the rear vehicle distance detecting unit 223.

The rear vehicle distance detection unit 223 uses the image data output from the image processing unit 221 to detect the rear vehicle included in the image data corresponding to the range that does not include the first angle of view 30 of the second angle of view 31. Get information about the distance to. For example, the rear vehicle distance detection unit 223 detects a rear vehicle based on the image data corresponding to the second area 201b among the image data, and detects the distance to the host vehicle based on changes in the position and size of the detected rear vehicle. Distance can be calculated. The rear vehicle distance detection section 223 outputs information on the calculated distance to the display angle of view determination section 224.

Further, the rear vehicle distance detection unit 223 detects the vehicle type of the rear vehicle based on data regarding characteristic information such as the shape and color of each vehicle type, which is output as a result of machine learning (deep learning) based on images of a large number of vehicles. You may make a judgment. At this time, the rear vehicle distance detection section 223 may output information regarding the vehicle type of the rear vehicle to the display angle determination section 224. Back gear detection unit 225 detects whether the transmission of mobile device 10 (self-vehicle) is in reverse gear, and outputs the detection result to display angle determination unit 224 .

The display angle of view determination unit 224 determines the angle of view (display angle of view) of the image displayed on the display device 230 based on the output from at least one of the rear vehicle distance detection unit 223 and the back gear detection unit 225. It is determined whether to use the angle 30 or the second angle of view 31. Then, the display angle of view determining section 224 outputs an output to the display angle of view changing section 222 according to the determination result. For example, the display angle of view determination unit 224 determines that the display angle of view is to be set to the second angle of view 31 when the distance value in the distance information is less than or equal to a certain threshold value (for example, 3 m), and when the distance value in the distance information becomes larger than the threshold value. In this case, it can be determined that the display angle of view is set to the first angle of view 30. Alternatively, the display angle of view determination unit 224 determines that the display angle of view is to be set to the second angle of view 31 if the reverse gear detection unit 225 reports that the transmission of the mobile device 10 is in reverse gear. be able to. Further, the display angle of view determination unit 224 can determine that the display angle of view is set to the first angle of view 30 when the vehicle is not in reverse gear.

Further, the display angle of view determination unit 224 determines that the display angle of view is to be set to the second angle of view 31 regardless of the result of the rear vehicle distance detection unit 223 when the transmission of the moving device 10 is in reverse gear. be able to. Furthermore, if the transmission of the mobile device 10 is not in reverse gear, the display angle of view determination unit 224 can determine that the display angle of view is determined according to the detection result of the rear vehicle distance detection unit 223. Note that the display angle of view determination section 224 may change the criterion for changing the angle of view according to the vehicle type of the mobile device 10 by receiving vehicle type information from the rear vehicle distance detection section 223. For example, when the moving device 10 is a large vehicle such as a truck, the braking distance is longer than that of a regular car, so it is desirable to set the above-mentioned threshold value to be longer than that of a regular car (for example, 10 m).

The user setting change unit 226 is for allowing the user 40 to change the criterion for determining whether or not to change the display angle of view to the second angle of view 31 in the display angle of view determination unit 224 . The criterion set (changed) by the user 40 is input from the user setting changing section 226 to the display angle determining section 224 .

The display angle changing unit 222 generates a display image to be displayed on the display device 230 according to the determination result by the display angle determining unit 224. For example, when it is determined that the first angle of view is 30, the display angle of view changing unit 222 cuts out a rectangular included angle image (first image) from the image data corresponding to the first angle of view 30. and outputs it to the display device 230. Further, if 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 displays an image (second image) including the rear vehicle on the display device 230. Output for. Note that the second image may include an image corresponding to the first area 201a. The display angle changing unit 222 functions as a display control unit that performs display control to switch the display device 230 between a first display state in which the first image is displayed and a second display state in which the second image is displayed. do.

Clipping of an image by the display angle changing unit 222 is executed by storing the image data output from the image processing unit 221 in a storage unit (memory) such as a RAM, and reading out the image to be cropped from there. Ru. Note that the area corresponding to the first image in the image data is a rectangular area at the first angle of view 30 corresponding to the first area 201a. Further, the area corresponding to the second image in the image data is a rectangular area including the rear vehicle at the second angle of view 31 corresponding to the second area 201b.

The display device 230 has a display section such as a liquid crystal display or an organic EL display, and displays the display image output from the display angle changing section 222. For example, the display device 230 includes a first display section as an electronic room mirror placed above the windshield (windshield) of the moving device 10, and an operation panel placed below the windshield of the moving device 10. It has a second display unit (monitor). According to this configuration, the first image and the second image generated from the image data described above can be displayed on the first display section and the second display section, respectively. The first display section may be configured to include, for example, a half mirror so that it can be used as a mirror when not being used as a display. The second display unit may also serve as a display for a navigation system or an audio system, for example.

Note that the mobile device 10 is not limited to a vehicle such as a car, but may be a mobile object such as a ship, an aircraft, an industrial robot, or a drone. Further, the in-vehicle system 2 according to the present embodiment is used to display images to the user 40, but is not limited to this, and can be used for driving support such as cruise control (including an all-vehicle speed tracking function) and automatic driving. You can. Furthermore, the in-vehicle system 2 can be applied not only to mobile devices but also to various devices that utilize object recognition, such as intelligent transportation systems (ITS).

[Modified example]
Although preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes can be made within the scope of the gist.

For example, the optical systems according to each of the embodiments described above are assumed to be used in the visible range, and are configured to perform good aberration correction throughout the visible range, but aberration correction may be performed as necessary. The wavelength range to be used may be changed. For example, each optical system may be configured to perform aberration correction only in a specific wavelength range in the visible range, or may be configured to perform aberration correction in a wavelength range in the infrared range other than the visible range. Good too.

Further, in the vehicle-mounted system 2 described above, a distance measuring device as described above may be employed as the imaging device 20. At this time, the in-vehicle system 2 may include a determination unit that determines the possibility of collision with the object based on information on the distance to the object acquired by the imaging device 20. Further, a stereo camera including two imaging units 210 may be employed as the imaging device 20. In this case, even without using the imaging plane phase difference sensor, image data can be acquired simultaneously by each of the synchronized imaging units, and the same processing as described above can be performed using the two image data. Can be done. However, if the difference in imaging time between each imaging unit is known, it is not necessary to synchronize each imaging unit.

Note that the embodiment of the present invention includes the following configuration.

(Configuration 1)
It consists of a front group with positive refractive power, an aperture stop, and a rear group with positive refractive power, which are arranged in order from the object side to the image side.
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 order from the object side to the image side. has
The rear group includes a cemented lens and a positive lens located closest to the image side,
When the combined focal length of the second lens and the third lens is f23, and the focal length of the air lens between the second lens and the third lens is fa1,
2.4≦f23/fa1≦16.0
An optical system characterized by satisfying the following conditional expression.

(Configuration 2)
The optical system according to configuration 1, wherein the object side surface of the second lens is an aspherical surface.

(Configuration 3)
The optical system according to configuration 2, wherein the aspherical surface has an inflection point in a cross section that includes the optical axis.

(Configuration 4)
2. The optical system according to configuration 2, wherein the graph representing curvature versus position in the radial direction in a cross section including the optical axis of the aspherical surface has a first extreme value and a second extreme value.

(Configuration 5)
In the aspherical surface, when normalized distances from the optical axis to positions corresponding to the first extreme value and the second extreme value, respectively, are E1 and E2,
0.02≦E1≦0.40
0.60≦E2≦0.98
The optical system according to configuration 4, which satisfies the following conditional expression.

(Configuration 6)
When the focal length of the optical system is f,
-1.20≦fa1/f≦-0.50
6. The optical system according to any one of configurations 1 to 5, which satisfies the following conditional expression.

(Configuration 7)
When the focal length of the image side surface of the second lens is f2R2, and the focal length of the object side surface of the third lens is f3R1,
2.0≦f3R1/f2R2≦7.0
7. The optical system according to any one of configurations 1 to 6, which satisfies the following conditional expression.

(Configuration 8)
When the focal length of the front group is fG1 and the focal length of the rear group is fG2,
0.6≦fG1/fG2≦1.5
8. The optical system according to any one of configurations 1 to 7, which satisfies the following conditional expression.

(Configuration 9)
When the radius of curvature of the object side surface of the first lens is R1, and the radius of curvature of the image side surface of the first lens is R2,
-3.50≦(R2+R1)/(R2-R1)≦-1.85
9. The optical system according to any one of configurations 1 to 8, which satisfies the following conditional expression.

(Configuration 10)
On the optical axis, the first lens and the second lens are meniscus lenses that are convex toward the object side, the third lens is a meniscus lens that is concave toward the object side, and the fourth lens is a meniscus lens that is concave toward the object side. 10. The optical system according to any one of configurations 1 to 9, wherein is a biconvex lens.

(Configuration 11)
11. The optical system according to any one of configurations 1 to 10, wherein the rear group includes the cemented lens and the positive lens.

(Configuration 12)
12. The optical system according to any one of configurations 1 to 11, wherein the cemented lens includes a positive lens and a negative lens arranged in order from the object side to the image side.

(Configuration 13)
13. The optical system according to any one of configurations 1 to 12, wherein the positive lens disposed closest to the image side in the rear group includes an aspherical surface having an inflection point in a cross section including the optical axis. .

(Configuration 14)
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 the focal length of the third lens is f3, and the focal length of the optical system is f3. When f,
|f/f3|≦0.15
14. The optical system according to any one of configurations 1 to 13, which satisfies the following conditional expression.

(Configuration 15)
When the focal length of the first lens is f1, and the distance between the first lens and the second lens on the optical axis is d12,
f1/d12≦-8.50
15. The optical system according to any one of configurations 1 to 14, wherein the optical system satisfies the following conditional expression.

(Configuration 16)
When the projection characteristic of the optical system representing the relationship between the half angle of view θ and the image height y is y(θ), the maximum half angle of view of the optical system is θmax, and the focal length of the optical system is f,
1.0<f×sin(θmax)/y(θmax)≦1.9
16. The optical system according to any one of configurations 1 to 15, which satisfies the following conditional expression.

(Configuration 17)
An imaging device comprising: the optical system according to any one of Configurations 1 to 16; and an imaging element that images an object via the optical system.

(Configuration 18)
An in-vehicle system comprising the imaging device according to configuration 17 and a display device that displays an image obtained based on the output of the imaging device.

(Configuration 19)
The display device includes a first display section that displays a first image corresponding to a first angle of view among the images, and a second display section that displays a first image that corresponds to a first angle of view among the images, and a second display section that displays a first image that corresponds to a first angle of view that includes the first angle of view. 19. The in-vehicle system according to configuration 18, further comprising a second display unit that displays an image of the image.

(Configuration 20)
A moving device comprising the imaging device according to configuration 17 and being movable while holding the imaging device.

100 Optical system G1 Front group G2 Rear group L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens LC Cemented lens LL Positive lens (final lens)
STO aperture diaphragm

Claims (18)

It consists of a front group with positive refractive power, an aperture stop, and a rear group with positive refractive power, which are arranged in order from the object side to the image side.
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 order from the object side to the image side. has
The rear group is composed of a cemented lens and a positive lens disposed closest to the image side,
The object side surface of the second lens is an aspherical surface having an inflection point in a cross section including the optical axis,
When the combined focal length of the second lens and the third lens is f23, the focal length of the air lens between the second lens and the third lens is fa1, and the focal length of the optical system is f,
2.4≦f23/fa1≦16.0
-1.20≦fa1/f≦-0.50
An optical system characterized by satisfying the following conditional expression. It consists of a front group with positive refractive power, an aperture stop, and a rear group with positive refractive power, which are arranged in order from the object side to the image side.
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 order from the object side to the image side. has
The rear group includes a cemented lens and a positive lens located closest to the image side,
The object side surface of the second lens is an aspherical surface having an inflection point in a cross section including the optical axis,
A graph representing curvature versus position in the radial direction in the cross section of the aspherical surface has a first extreme value and a second extreme value,
When the combined focal length of the second lens and the third lens is f23, the focal length of the air lens between the second lens and the third lens is fa1, and the focal length of the optical system is f,
2.4≦f23/fa1≦16.0
-1.20≦fa1/f≦-0.50
An optical system characterized by satisfying the following conditional expression. It consists of a front group with positive refractive power, an aperture stop, and a rear group with positive refractive power, which are arranged in order from the object side to the image side.
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 order from the object side to the image side. has
The rear group includes a cemented lens and a positive lens located closest to the image side,
The object side surface of the second lens is an aspherical surface having an inflection point in a cross section including the optical axis,
The combined focal length of the second lens and the third lens is f23, the focal length of the air lens between the second lens and the third lens is fa1, the focal length of the optical system is f, and the half angle of view θ When the projection characteristic of the optical system representing the relationship between
2.4≦f23/fa1≦16.0
-1.20≦fa1/f≦-0.50
1.0<f×sin(θmax)/y(θmax)≦1.9
An optical system characterized by satisfying the following conditional expression. 4. The optical system according to claim 1, wherein the graph representing curvature versus position in the radial direction in the cross section of the aspherical surface has a first extreme value and a second extreme value. In the aspherical surface, when normalized distances from the optical axis to positions corresponding to the first extreme value and the second extreme value, respectively, are E1 and E2,
0.02≦E1≦0.40
0.60≦E2≦0.98
3. The optical system according to claim 2 , wherein the optical system satisfies the following conditional expression. When the focal length of the image side surface of the second lens is f2R2, and the focal length of the object side surface of the third lens is f3R1,
2.0≦f3R1/f2R2≦7.0
4. The optical system according to claim 1, wherein the optical system satisfies the following conditional expression. When the focal length of the front group is fG1 and the focal length of the rear group is fG2,
0.6≦fG1/fG2≦1.5
4. The optical system according to claim 1, wherein the optical system satisfies the following conditional expression. When the radius of curvature of the object side surface of the first lens is R1, and the radius of curvature of the image side surface of the first lens is R2,
-3.50≦(R2+R1)/(R2-R1)≦-1.85
4. The optical system according to claim 1, wherein the optical system satisfies the following conditional expression. On the optical axis, the first lens and the second lens are meniscus lenses that are convex toward the object side, the third lens is a meniscus lens that is concave toward the object side, and the fourth lens is a meniscus lens that is concave toward the object side. 4. The optical system according to claim 1, wherein is a biconvex lens. 4. The optical system according to claim 1 , wherein the cemented lens includes a positive lens and a negative lens arranged in order from the object side to the image side. 4. The optical system according to claim 1, wherein the positive lens includes an aspheric surface having an inflection point in the cross section . Each of the second lens, the third lens, and the positive lens is made of a resin material, and when the focal length of the third lens is f3,
|f/f3|≦0.15
4. The optical system according to claim 1, wherein the optical system satisfies the following conditional expression. When the focal length of the first lens is f1, and the distance between the first lens and the second lens on the optical axis is d12,
f1/d12≦-8.50
4. The optical system according to claim 1, wherein the optical system satisfies the following conditional expression. When the projection characteristic of the optical system representing the relationship between the half angle of view θ and the image height y is y(θ), and the maximum half angle of view of the optical system is θmax,
1.0<f×sin(θmax)/y(θmax)≦1.9
3. The optical system according to claim 1, wherein the optical system satisfies the following conditional expression. An imaging device comprising: the optical system according to any one of claims 1 to 3 ; and an imaging element that images an object via the optical system. A display system comprising: the imaging device according to claim 15 ; and a display device that displays an image obtained based on the output of the imaging device. The display device includes a first display section that displays a first image corresponding to a first angle of view among the images, and a second display section that displays a first image that corresponds to a first angle of view among the images, and a second display section that displays a first image that corresponds to a first angle of view that includes the first angle of view. 17. The display system according to claim 16 , further comprising a second display section that displays an image of. A moving device comprising the imaging device according to claim 15 and being movable while holding the imaging device.

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