Optical system and imaging device including the same

Abstract

To provide a compact optical system while having a wide angle of view.SOLUTION: An optical system (100) comprises, in order from an object side to an image side, a front group (G1) and a rear group (G2). The front group includes, in order from the object side to the image side, a first lens (L1) having negative refractive power and a second lens (L2) having an aspherical surface. The rear group includes, in order from the object side to the image side, a third lens (L3) having positive refractive power, a fourth lens (L4) having positive refractive power, a fifth lens (L5) having negative refractive power, and a sixth lens (L6) having an aspherical surface. On an optical axis, the object side surface of the first lens is convex, the object side surface of the second lens is convex, and the object side surface of the sixth lens is concave. When the focal length of the optical system is f and the focal length of the third lens is f3, a conditional expression 1.00<f3 / f<1.80 is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system suitable for imaging devices such as digital still cameras, digital video cameras, vehicle-mounted cameras, cameras for mobile phones, surveillance cameras, wearable cameras, and medical cameras. [Background technology]

[0002] Optical systems used in imaging devices such as vehicle-mounted cameras are required to have a wide angle of view. Patent Document 1 discloses a wide-angle lens having projection characteristics similar to those of an orthogonal projection system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-9028 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the wide-angle lens of Patent Document 1 is not sufficient to meet the demand for miniaturization.

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide a wide-angle yet compact optical system. [Means for solving the problem]

[0006] An optical system according to one aspect of the present invention includes, arranged in order from the object side to the image side, a first lens having negative refractive power, a second lens including an aspherical surface, a third lens having positive refractive power, a fourth lens having positive refractive power, a fifth lens having negative refractive power, and a sixth lens including an aspherical surface. It consists of , an object side surface of the first lens is a convex surface, an object side surface of the second lens is a convex surface, and an object side surface of the sixth lens is a concave surface on an optical axis; The focal length of the optical system is f, and the focal length of the third lens is f3 t23 is the distance on the optical axis from the image side surface of the second lens to the object side surface of the third lens, fR is the composite focal length of the lens arranged closer to the image side than the second lens, and f1 is the focal length of the first lens. When 1.00 <f3 / f<1.80 0.80 <t23 / fR<1.50 -6.0 <f1 / f<-3.0 The following condition is satisfied.

[0007] Other objects and features of the present invention are illustrated in the following examples. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a wide-angle yet compact optical system. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of a main part of an optical system according to Example 1. FIG. [Figure 2] 3A to 3C are aberration diagrams of the optical system according to Example 1. [Figure 3] FIG. 10 is a schematic diagram of a main part of an optical system according to Example 2. [Figure 4] 10A to 10C are aberration diagrams of the optical system according to Example 2. [Figure 5] FIG. 10 is a schematic diagram of a main part of an optical system according to Example 3. [Figure 6] 10A to 10C are aberration diagrams of the optical system according to Example 3. [Figure 7] FIG. 10 is a schematic diagram of a main part of an optical system according to Example 4. [Figure 8] 10A to 10C are aberration diagrams of the optical system according to Example 4. [Figure 9] FIG. 10 is a schematic diagram of a main part of an optical system according to a fifth embodiment. [Figure 10] 10A to 10C are aberration diagrams of the optical system according to Example 5. [Figure 11] FIG. 4 is a diagram showing the aspherical shape of the object side surface of the second lens in each example. [Figure 12] FIG. 10 is a diagram showing the inclination of the object side surface of the sixth lens in each example. [Figure 13] FIG. 10 is a diagram showing the inclination of the image side surface of the sixth lens in each example. [Figure 14] FIG. 1 is a schematic diagram of an imaging device according to an embodiment. [Figure 15]1A and 1B are diagrams illustrating a schematic diagram of a moving device according to an embodiment and optical characteristics of an optical system. [Figure 16] 1 is a block diagram showing an example of the configuration of an in-vehicle system according to an embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings may be drawn at a scale different from the actual scale for convenience. In addition, the same reference numerals are used for the same components in the drawings, and duplicated descriptions will be omitted.

[0011] Optical systems used in imaging devices such as vehicle-mounted cameras are required to have a wide angle of view, and fisheye lenses are mainly used for this purpose. Known projection methods for fisheye lenses include orthogonal projection, equidistant projection, and stereoscopic projection. Here, when the image height on the projection plane is Y, the focal length of the entire optical system is f, and the half angle of view is θ, each projection method can be expressed by the following equation:

[0012] Orthographic projection method: Y=f×sinθ Equidistant projection method: Y=f×θ Stereoscopic projection method: Y=2×ftan(θ / 2) The orthogonal projection method has the characteristic of compressing the image at the periphery of the screen more strongly than the image near the optical axis. The equidistant projection method maintains a constant resolution regardless of the angle of view. The stereographic projection method is the opposite of orthogonal projection, compressing the image near the optical axis more than the image at the periphery of the screen.

[0013] 1, 3, 5, 7, and 9 are cross-sectional views of optical systems according to Examples 1 to 5, each including an optical axis OA. In 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 of each Example is an imaging optical system used in an imaging device, and the imaging surface of an imaging element is located at the position of the image plane IMG. A cover glass (optical block) CG located on the object side of the image plane IMG is an optical element such as an optical filter or cover glass that does not contribute to the imaging of the optical system. Note that the optical system of each Example may be used as a projection optical system in a projection device such as a projector, in which case the display surface of a display element such as a liquid crystal panel would be located at the position of the image plane IMG.

[0014] 2, 4, 6, 8, and 10 are longitudinal aberration diagrams of the optical systems according to Examples 1 to 5, respectively. Each longitudinal aberration diagram shows, from left to right, spherical aberration, field curvature (astigmatism), and distortion. In each longitudinal aberration diagram, aberrations for 656.3 nm (C-line), 587.6 nm (d-line), 486.1 nm (F-line), and 435.8 nm (g-line) are indicated by different lines.

[0015] Next, the features of the optical systems according to the respective examples will be described in detail.

[0016] The optical system according to each embodiment is composed of a front group G1 with negative refractive power and a rear group G2 with positive refractive power, arranged in this order from the object side to the image side. Here, it is assumed that a cover glass CG is not included in each optical system. The front group G1 has, arranged in this order from the object side to the image side, a first lens L1 with negative refractive power and a second lens L2 including an aspherical surface. The object-side surface of the first lens L1 is a convex surface. The second lens L2 has negative refractive power near (on) the optical axis OA. The object-side surface of the second lens L2 is a convex surface near the optical axis OA.

[0017] The rear group G2 includes, arranged in order from the object side to the image side, a third lens L3 with positive refractive power, a fourth lens L4 with positive refractive power, a fifth lens L5 with negative refractive power, and a sixth lens L6 including an aspherical surface. The fourth lens L4 and the fifth lens L5 are cemented together to form a cemented lens CL. The object-side surface of the sixth lens L6 is concave near the optical axis. Here, "lens" refers to an optical element with refractive power and does not include optical elements such as parallel plate glass that do not have refractive power. The rear group G2 also includes an aperture stop STO.

[0018] In the optical systems according to the examples, the second lens L2, which is positioned away from the aperture stop STO, is an aspherical lens, thereby achieving projection characteristics with high resolution in the central region of the screen (near the optical axis), and the above lens configuration achieves a wide angle of view. Also, by configuring the rear group G2 as described above, it is possible to effectively correct spherical aberration, axial aberration, and field curvature that occur when the optical system has a wide angle of view.

[0019] In each embodiment, when the focal length of the third lens L3 is f3 and the focal length of the optical system (entire system) is f, the following conditional expression (1) is satisfied.

[0020] 1.00 <f3 / f<1.80 (1) To shorten the overall length of the optical system, it is effective to strengthen the power of the lens with positive refractive power located at a position where the axial ray height is high. In each embodiment, since the first lens L1 and the second lens L2 have negative refractive power, the axial ray is diverged and the position at which it is incident on the third lens L3 is high. Furthermore, by appropriately setting the third lens L3 with positive refractive power, it is possible to shorten the overall length of the optical system. If the upper limit of conditional formula (1) is exceeded, the positive refractive power of the third lens L3 is weak, and the effect of shortening the overall length is reduced. On the other hand, if the lower limit of conditional formula (1) is not met, the positive refractive power of the third lens L3 becomes too strong, making it difficult to correct field curvature.

[0021] Preferably, the numerical range of conditional expression (1) is set as shown in the following conditional expression (1a): More preferably, the numerical range of conditional expression (1) is set as shown in the following conditional expression (1b):

[0022] 1.20 <f3 / f<1.75 (1a) 1.30 <f3 / f<1.70 (1b) The optical systems according to the examples can obtain the effects of the present invention as long as they satisfy at least the above-described configuration, and for example, the front group G1 may have a configuration including lenses other than the first lens L1 and the second lens L2 (a configuration including three or more lenses).

[0023] In each embodiment, when the half angle of view of the optical system is θ [deg.], the projection characteristic expressing 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, it is preferable to satisfy the following conditional expression (2):

[0024] 1.00 <f×sin(θmax) / y(θmax)≦1.90 (2) Although details will be described later, by configuring the optical system so as to satisfy conditional expression (2), it is possible to have a wide angle of view while increasing the resolution of the subject image in the angle of view near the optical axis OA (near the optical axis).

[0025] More preferably, the numerical range of conditional expression (2) is set as shown in the following conditional expression (2a): Even more preferably, the numerical range of conditional expression (2) is set as shown in the following conditional expression (2b):

[0026] 1.00 <f×sin(θmax) / y(θmax)≦1.70 (2a) 1.00 <f×sin(θmax) / y(θmax)≦1.40 (2b) In each embodiment, it is preferable to satisfy the following conditional expression (3).

[0027] 0.65 <y(θmax / 2) / y(θmax)<0.85 (3) The ratio of the image height y(θmax) at the maximum half angle of view θmax to the image height y(θmax / 2) at the angle of view θmax / 2, which is half the maximum half angle of view θmax, is set within the range of conditional expression (3), thereby making it possible to further increase the resolution of the subject image at the angle of view near the optical axis OA while maintaining a wide angle of view.

[0028] More preferably, the numerical range of conditional expression (3) is set as shown in the following conditional expression (3a): Even more preferably, the numerical range of conditional expression (3) is set as shown in the following conditional expression (3b):

[0029] 0.65 <y(θmax / 2) / y(θmax)<0.83 (3a) 0.65 <y(θmax / 2) / y(θmax)<0.81 (3b) Imaging devices such as in-vehicle cameras, which will be described later, are required to have not only a wide angle of view but also a large imaging magnification in the vicinity of the optical axis (central region). For example, when an imaging device is installed at the rear of a mobile device (vehicle), an image corresponding to the central region, which is the main focus area, may be enlarged and displayed on an electronic rearview mirror, and the entire image including the region other than the central region (peripheral region) may be displayed on an 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 region other than the central region.

[0030] Figures 11(A) to 11(E) show the aspheric shape of the object-side surface of the second lens L2 in each example. In Figures 11(A) to 11(E), the vertical axis represents the radial position (lens radius) of the object-side surface of the second lens L2 in a cross section including the optical axis OA, and the horizontal axis represents the curvature [1 / mm] of the object-side surface of the second lens L2. That is, Figures 11(A) to 11(E) are graphs plotting the curvature for each position on the object-side surface of the second lens L2. The values ​​on the vertical axis represent 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, when the distance from the optical axis OA to the position of the effective diameter (maximum effective diameter) is normalized to 1.

[0031] The object-side surface (the lens surface facing the object) of the second lens L2, which is an aspherical lens, can significantly refract light rays from the radial periphery of the light beam from the first lens L1 toward the optical axis OA. This makes it easy to differentiate the imaging magnification between the central region and the peripheral region of the optical system. In this case, it is preferable that the object-side surface of the second lens L2 has an inflection point in a cross section including the optical axis OA, as shown in Figures 11(A) to 11(E). This makes it easy to widen the angle of view and increase the imaging magnification in the central region while reducing the number of lenses constituting the optical system.

[0032] When the distance (spacing) on ​​the optical axis from the image side surface of the second lens L2 to the object side surface of the third lens L3 is t23 and the focal length of the rear group is fR, it is preferable to satisfy the following conditional expression (4):

[0033] 0.80 <t23 / fR<1.50 (4) Generally, when an optical system is considered to be divided into a front group and a rear group, where the focal length of the front group is fF and the distance on the optical axis between the front group and the rear group is d, the power (refractive power) Φ of the optical system (entire system) is expressed by the following equation (5):

[0034]

number

[0035] In each embodiment, the refractive power of the front group G1 is negative and the refractive power of the rear group G2 is positive. Therefore, the third term in equation (5) is positive, and the value of the third term increases as the distance between the front group G1 and the rear group G2 increases. When setting the power (or focal length) of the optical system (entire system) to a desired value, the value of the third term increases as the distance between the front group G1 and the rear group G2 increases. This eliminates the need to excessively strengthen the power of the rear group G2, which has positive refractive power, which is advantageous for aberration correction.

[0036] If the lower limit of conditional expression (4) is exceeded, the distance between the front group G1 and the rear group G2 is insufficient, causing the refractive power of the rear group G2 to become too strong, making it difficult to correct aberrations.On the other hand, if the upper limit of conditional expression (4) is exceeded, the distance between the front group G1 and the rear group G2 becomes too wide, causing the optical system to become large.

[0037] More preferably, the numerical range of conditional expression (4) is set as in the following conditional expression (4a): Even more preferably, the numerical range of conditional expression (4) is set as in the following conditional expression (4b):

[0038] 0.81 <t23 / fR<1.35 (4a) 0.82 <t23 / fR<1.20 (4b) When the focal length of the fourth lens L4 is f4, it is preferable to satisfy the following conditional expression (6).

[0039] 1.20 <f3 / f4<1.70 (6) The third lens L3 and the fourth lens L4, each having a positive refractive power, share the optical power, thereby suppressing the occurrence of aberrations in each lens. If the lower limit or upper limit of conditional expression (6) is exceeded, the power will be biased toward one of the lenses, making it difficult to correct spherical aberration and astigmatism.

[0040] More preferably, the numerical range of conditional expression (6) is set as in the following conditional expression (6a): Even more preferably, the numerical range of conditional expression (6) is set as in the following conditional expression (6b):

[0041] 1.30 <f3 / f4<1.65 (6a) 1.40 <f3 / f4<1.60 (6b) When the Abbe number of the third lens L3 with respect to the d-line is ν3, it is preferable that the following conditional expression (7) be satisfied.

[0042] 30<ν3<100 (7) If the lower limit of condition (7) is exceeded, the amount of lateral chromatic aberration will be too large and difficult to correct, whereas if the upper limit of condition (7) is exceeded, the material will have low dispersion, making it difficult to manufacture.

[0043] More preferably, the numerical range of conditional expression (7) is set as in the following conditional expression (7a): Even more preferably, the numerical range of conditional expression (7) is set as in the following conditional expression (7b):

[0044] 40<ν3<85 (7a) 50<ν3<70 (7b) Figures 12(A) to 12(E) are diagrams showing the inclination of the object-side surface of the sixth lens L6 in each example. Figures 13(A) to 13(E) are diagrams showing the inclination of the image-side surface of the sixth lens L6 in each embodiment. In Figures 12(A) to 12(E) and 13(A) to 13(E), the vertical axis indicates the radial position (lens radius) of each surface of the sixth lens L6 in a cross section including the optical axis OA, and the horizontal axis indicates the radial derivative of the lens with respect to the amount of sag of the surface. The values ​​on the vertical axis indicate the distance (normalized distance) from the optical axis OA to each position within the effective diameter of each surface of the sixth lens L6 when the distance from the optical axis OA to the position of the effective diameter (maximum effective diameter) is normalized to be 1.

[0045] The object-side surface of sixth lens L6 is preferably aspherical and has no extreme value in the radial direction in the cross section including the optical axis OA. As shown in Figures 12(A) to 12(e), the slope of the object-side surface of sixth lens L6 is always negative in the radial direction of the lens and has no extreme value, so no depressions are formed on the surface, which is advantageous in manufacturing.

[0046] It is desirable that the tilt of the object-side surface of sixth lens L6 (the tilt with respect to a plane perpendicular to the optical axis OA) monotonically increases in the radial direction in a cross section including the optical axis OA. More off-axis rays from fifth lens L5 are incident on this surface at an oblique angle, and as shown in Figures 12(A) to 12(e), the tilt of the object-side surface of sixth lens L6 monotonically increases in negative value. This reduces the angle of incidence on this surface, suppressing the occurrence of astigmatic difference.

[0047] The image side surface of sixth lens L6 is aspherical, and it is desirable that it has no extreme value in the radial direction in the cross section including the optical axis OA. As shown in Figures 13(A) to 13(e), the slope of the image side surface of sixth lens L6 is always negative in the radial direction of the lens and has no extreme value, so no depressions are formed on the surface, which is advantageous in manufacturing.

[0048] It is desirable that the slope of the image-side surface of the sixth lens L6 monotonically increases in the radial direction in a cross section including the optical axis OA. Off-axis rays from the object surface of the sixth lens L6 are obliquely incident on this surface, and as shown in Figures 13(A) to 13(e), the slope of the image-side surface of the sixth lens L6 monotonically increases in negative value. This reduces the angle of incidence on this surface, thereby suppressing the occurrence of astigmatic difference.

[0049] When the radius of curvature of the object side surface of the third lens L3 is R31 and the radius of curvature of the image side surface of the third lens L3 is R32, it is preferable to satisfy the following conditional expression (8).

[0050] -0.30<(R32+R31) / (R32-R31)<0.15 (8) If the upper limit of conditional expression (8) is exceeded, the spherical aberration generated by the third lens L3 will not be shared between the object-side and image-side surfaces, making the lens more susceptible to the generation of higher-order aberrations and manufacturing errors.On the other hand, if the lower limit of conditional expression (8) is not reached, the generation of coma will increase, making correction difficult.

[0051] More preferably, the numerical range of conditional expression (8) is set as in the following conditional expression (8a): Even more preferably, the numerical range of conditional expression (8) is set as in the following conditional expression (8b):

[0052] -0.30<(R32+R31) / (R32-R31)<0.12 (8a) -0.30<(R32+R31) / (R32-R31)<0.10 (8b) When the focal length of the first lens L1 is f1, it is preferable to satisfy the following conditional expression (9).

[0053] -6.0 <f1 / f<-3.0 (9) If the upper limit of conditional expression (9) is exceeded, the negative refractive power of the first lens L1 becomes too strong, causing excessive aberrations to occur in the first lens L1. On the other hand, if the lower limit of conditional expression (9) is not reached, the negative refractive power of the first lens L1 becomes too weak, suppressing the occurrence of pupil aberrations and reducing the amount of off-axis light taken in.

[0054] More preferably, the numerical range of conditional expression (9) is set as in the following conditional expression (9a): Even more preferably, the numerical range of conditional expression (9) is set as in the following conditional expression (9b):

[0055] -5.9 <f1 / f<-3.2 (9a) -5.8 <f1 / f<-3.4 (9b) The imaging device includes an optical system according to each embodiment that forms a subject image, and an imaging sensor that photoelectrically converts the subject image (capturing the subject as an object via the optical system). The imaging surface of the imaging sensor is provided with a plurality of pixels that are two-dimensionally arranged.

[0056] The detailed configuration of the optical system according to each example will be described below. [Example]

[0057] The optical system 100 of Example 1 shown in FIG. 1 is composed of, arranged in order from the object side to the image side, a first lens L1, a second lens L2, a third lens L3, an aperture stop STO, a fourth lens L4, a fifth lens L5, and a sixth lens L6. The first lens L1 has a convex object-side surface and is a meniscus lens with negative refractive power. The second lens L2 is an aspherical lens. The third lens L3 and the fourth lens L4 are each biconvex lenses with positive refractive power. The fifth lens L5 has a convex image-side surface and is a meniscus lens with negative refractive power. The sixth lens L6 is an aspherical lens.

[0058] The imaging surface of an imaging sensor such as a CMOS (Complementary Metal-Oxide-Semiconductor) sensor is disposed on the image plane IMG, and the imaging sensor has a cover glass CG. In the imaging device, image data is generated from the output of the imaging sensor.

[0059] The fourth lens L4 and the fifth lens L5 are cemented together to form a cemented lens CL.

[0060] The object-side surface of the second lens L2 is convex near the optical axis OA (on the optical axis), and the image-side surface is concave. As shown in FIG. 11A, the object-side surface of the second lens L2 is aspheric, with an inflection point in a cross section including the optical axis OA. The object-side surface of the sixth lens L6 is concave near the optical axis, and as shown in FIG. 12A, the inclination of the surface increases monotonically with no extreme value in the radial direction in the cross section including the optical axis OA. The image-side surface of the sixth lens L6 is convex near the optical axis, and as shown in FIG. 13A, the inclination of the surface increases monotonically with no extreme value in the radial direction in the cross section including the optical axis OA.

[0061] The first lens L1 and the second lens L2 constitute a front group G1, and the focal length of the front group G1 is -5.01 mm. The third lens L3 to the sixth lens L6 constitute a rear group G2, and the focal length of the rear group G2 is 5.53 mm.

[0062] As shown in Fig. 2, in the optical system 100 according to this embodiment, spherical aberration and curvature of field are well corrected in the wavelength range of 400 to 700 nm. Furthermore, while distortion increases as the angle of view (image height) increases in the peripheral region, it is relatively small in the central region. This allows the resolution in the central region to be higher than that in the peripheral region, thereby improving the visibility of the image for the user of the imaging device, as described above.

[0063] Numerical Example 1 shows specific numerical values ​​of the optical system 100 of this example. Table 1 shows the numerical values ​​of each conditional expression. The optical system 100 of this example satisfies conditional expressions (1) to (4) and (6) to (9). [Example]

[0064] The optical system 200 of Example 2 shown in FIG. 3 is composed of a first lens L1, a second lens L2, a third lens L3, an aperture stop STO, a fourth lens L4, a fifth lens L5, and a sixth lens L6, arranged in this order from the object side to the image side. The first lens L1 is a meniscus lens with a convex object-side surface and negative refractive power. The second lens L2 is an aspherical lens. The third lens L3 and the fourth lens L4 are each biconvex lenses with positive power (refractive power). The fifth lens L5 is a meniscus lens with a convex image-side surface and negative refractive power. The sixth lens L6 is an aspherical lens.

[0065] An imaging surface of an imaging sensor such as a CMOS sensor is disposed on the image plane IMG, and the imaging device has a cover glass CG for the imaging sensor. Image data is generated from the output of the imaging sensor.

[0066] The fourth lens L4 and the fifth lens L5 are cemented together to form a cemented lens CL.

[0067] The object-side surface of the second lens L2 is convex near the optical axis, and the image-side surface is concave. As shown in Figure 11(B), the object-side surface of the second lens L2 is aspheric, with an inflection point in a cross section including the optical axis OA. The object-side surface of the sixth lens L6 is concave near the optical axis, and as shown in Figure 12(B), the inclination of the surface does not have an extreme value in the radial direction in the cross section including the optical axis OA, and increases monotonically. The image-side surface of the sixth lens L6 is convex near the optical axis, and as shown in Figure 13(B), the inclination of the surface does not have an extreme value in the radial direction in the cross section including the optical axis OA, and increases monotonically.

[0068] The first lens L1 and the second lens L2 constitute a front group G1, and the focal length of the front group G1 is -5.52 mm. The third lens L3 to the sixth lens L6 constitute a rear group G2, and the focal length of the rear group G2 is 6.75 mm.

[0069] As shown in Fig. 4, in the optical system 200 according to this embodiment, spherical aberration and curvature of field are well corrected in the wavelength range of 400 to 700 nm. Furthermore, while distortion increases as the angle of view (image height) increases in the peripheral region, it is relatively small in the central region. This allows the resolution in the central region to be higher than that in the peripheral region, thereby improving the visibility of the image for the user of the imaging device, as described above.

[0070] Numerical Example 2 shows specific numerical values ​​of the optical system 200 of this example. Table 1 shows the numerical values ​​of each conditional expression. The optical system 200 of this example satisfies the conditional expressions (1) to (4) and (6) to (9). [Example]

[0071] The optical system 300 of Example 3 shown in FIG. 5 is composed of a first lens L1, a second lens L2, a third lens L3, an aperture stop STO, a fourth lens L4, a fifth lens L5, and a sixth lens L6, arranged in this order from the object side to the image side. The first lens L1 is a meniscus lens with a convex object-side surface and negative refractive power. The second lens L2 is an aspherical lens. The third lens L3 and the fourth lens L4 are each biconvex lenses with positive refractive power. The fifth lens L5 is a meniscus lens with a convex image-side surface and negative refractive power. The sixth lens L6 is an aspherical lens.

[0072] An imaging surface of an imaging sensor such as a CMOS sensor is disposed on the image plane IMG, and the imaging device has a cover glass CG for the imaging sensor. Image data is generated from the output of the imaging sensor.

[0073] The fourth lens L4 and the fifth lens L5 are cemented together to form a cemented lens CL.

[0074] The object-side surface of the second lens L2 is convex near the optical axis, and the image-side surface is concave. As shown in Figure 11(C), the object-side surface of the second lens L2 is aspheric, with an inflection point in a cross section including the optical axis OA. The object-side surface of the sixth lens L6 is concave near the optical axis, and as shown in Figure 12(C), the inclination of the surface does not have an extreme value in the radial direction in the cross section including the optical axis OA, and increases monotonically. The image-side surface of the sixth lens L6 is convex near the optical axis, and as shown in Figure 13(C), the inclination of the surface does not have an extreme value in the radial direction in the cross section including the optical axis OA, and increases monotonically.

[0075] The first lens L1 and the second lens L2 constitute a front group G1, and the focal length of the front group G1 is -5.07 mm. The third lens L3 to the sixth lens L6 constitute a rear group G2, and the focal length of the rear group G2 is 5.58 mm.

[0076] As shown in Fig. 6, in the optical system 300 according to this embodiment, spherical aberration and curvature of field are well corrected in the wavelength range of 400 to 700 nm. Furthermore, while distortion increases as the angle of view (image height) increases in the peripheral region, it is relatively small in the central region. This allows the resolution in the central region to be higher than that in the peripheral region, thereby improving the visibility of the image for the user of the imaging device, as described above.

[0077] Numerical Example 3 shows specific numerical values ​​of the optical system 300 of this example. Table 1 shows the numerical values ​​of each conditional expression. The optical system 300 of this example satisfies the conditional expressions (1) to (4) and (6) to (9). [Example]

[0078] The optical system 400 of Example 4 shown in FIG. 7 is composed of a first lens L1, a second lens L2, an aperture stop STO, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6, arranged in this order from the object side to the image side. The first lens L1 is a meniscus lens with a convex object-side surface and negative refractive power. The second lens L2 is an aspheric lens. The third lens L3 and the fourth lens L4 are each biconvex lenses with positive refractive power. The fifth lens L5 is a meniscus lens with a convex image-side surface and negative refractive power. The sixth lens L6 is an aspheric lens.

[0079] An imaging surface of an imaging sensor such as a CMOS sensor is disposed on the image plane IMG, and the imaging device has a cover glass CG for the imaging sensor. Image data is generated from the output of the imaging sensor.

[0080] The fourth lens L4 and the fifth lens L5 are cemented together to form a cemented lens CL.

[0081] The object-side surface of the second lens L2 is convex near the optical axis, and the image-side surface is concave. As shown in Figure 11(D), the object-side surface of the second lens L2 is aspheric, with an inflection point in a cross section including the optical axis OA. The object-side surface of the sixth lens L6 is concave near the optical axis, and as shown in Figure 12(D), the inclination of the surface does not have an extreme value in the radial direction in the cross section including the optical axis OA, and increases monotonically. The image-side surface of the sixth lens L6 is convex near the optical axis, and as shown in Figure 13(D), the inclination of the surface does not have an extreme value in the radial direction in the cross section including the optical axis OA, and increases monotonically.

[0082] The first lens L1 and the second lens L2 constitute a front group G1, and the focal length of the front group G1 is -6.53 mm. The third lens L3 to the sixth lens L6 constitute a rear group G2, and the focal length of the rear group G2 is 5.59 mm.

[0083] As shown in Fig. 8, in the optical system 400 according to this embodiment, spherical aberration and curvature of field are well corrected in the wavelength range of 400 to 700 nm. Furthermore, while distortion increases as the angle of view (image height) increases in the peripheral region, it is relatively small in the central region. This allows the resolution in the central region to be higher than that in the peripheral region, thereby improving the visibility of the image for the user of the imaging device, as described above.

[0084] Numerical Example 4 shows specific numerical values ​​of the optical system 400 of this example. Table 1 shows the numerical values ​​of each conditional expression. The optical system 400 of this example satisfies the conditional expressions (1) to (4) and (6) to (9). [Example]

[0085] The optical system 500 of Example 5 shown in FIG. 9 is composed of a first lens L1, a second lens L2, an aperture stop STO, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6, arranged in this order from the object side to the image side. The first lens L1 is a meniscus lens with a convex object-side surface and negative refractive power. The second lens L2 is an aspherical lens. The third lens L3 and the fourth lens L4 are each biconvex lenses with positive refractive power. The fifth lens L5 is a meniscus lens with a convex image-side surface and negative refractive power. The sixth lens L6 is an aspherical lens.

[0086] An imaging surface of an imaging sensor such as a CMOS sensor is disposed on the image plane IMG, and the imaging device has a cover glass CG for the imaging sensor. Image data is generated from the output of the imaging sensor.

[0087] The fourth lens L4 and the fifth lens L5 are cemented together to form a cemented lens CL.

[0088] The object-side surface of the second lens L2 is convex near the optical axis, and the image-side surface is concave. As shown in Figure 11(e), the object-side surface of the second lens L2 is aspheric, with an inflection point in a cross section including the optical axis OA. The object-side surface of the sixth lens L6 is concave near the optical axis, and as shown in Figure 12(e), the inclination of the surface increases monotonically with no extreme value in the radial direction in a cross section including the optical axis OA. The image-side surface of the sixth lens L6 is convex near the optical axis, and as shown in Figure 13(e), the inclination of the surface increases monotonically with no extreme value in the radial direction in a cross section including the optical axis OA.

[0089] The first lens L1 and the second lens L2 constitute a front group G1, and the focal length of the front group G1 is -6.16 mm. The third lens L3 to the sixth lens L6 constitute a rear group G2, and the focal length of the rear group G2 is 5.39 mm.

[0090] 10, in the optical system 500 according to this embodiment, spherical aberration and curvature of field are well corrected in the wavelength range of 400 to 700 nm. Furthermore, while distortion increases as the angle of view (image height) increases in the peripheral region, it is relatively small in the central region. This allows the resolution in the central region to be higher than that in the peripheral region, thereby improving the visibility of the image for the user of the imaging device, as described above.

[0091] Numerical Example 5 shows specific numerical values ​​of the optical system 500 of this example. Table 1 shows the numerical values ​​of each conditional expression. The optical system 500 of this example satisfies the conditional expressions (1) to (4) and (6) to (9).

[0092] Numerical Examples 1 to 5 corresponding to Examples 1 to 5, respectively, are shown below. In each numerical example, i indicates the order of the surface (optical surface) from the object side. ri is the radius of curvature (unit: mm) of the ith surface (its surface), di is the distance (unit: mm) from the i+1th surface, and ndi and vdi are the refractive index and Abbe number of the ith optical member based on the d-line (wavelength 587.6 nm), respectively. The Abbe number vd is a value defined by the following equation when nF, nd, and nC are the refractive indices for the F-line, d-line, and C-line, respectively.

[0093] νd=(nd-1) / (nF-nC) The surface spacing is positive along the optical path toward the image side and negative along the optical path toward the object side. In Numerical Examples 1 to 5, the two surfaces closest to the image side are flat surfaces that correspond to optical blocks.

[0094] Furthermore, if the optical surface is aspherical, a symbol "*" is added to the right of the surface number. Each of the aspherical optical surfaces in this embodiment has a rotationally symmetric shape about the optical axis, and is expressed by the following aspherical formula:

[0095]

number

[0096] Here, z is the sag amount (mm) of the aspherical shape in the optical axis direction, c is the curvature (1 / mm) on the optical axis AX, k is the conic coefficient, h is the radial distance (mm) from the optical axis OA, and A, B, C, ... are aspherical coefficients of the fourth order, sixth order, eighth order, ... respectively. In this aspherical formula, the first term indicates the sag amount of the base sphere, and the radius of curvature of this base sphere is R = 1 / c. The second and subsequent terms indicate the sag amount of the aspherical component imparted to the base sphere. In each numerical example, "E±P" is "×10 ±P " means.

[0097] The optical systems according to the numerical examples are all single-focus optical systems with a fixed focal length (no zooming) and are configured without focusing. That is, the spacing between the lenses constituting the optical systems according to the numerical examples is always fixed. This prevents fluctuations in optical performance due to movement of the lenses. However, the optical systems may be configured to perform at least one of zooming and focusing, as needed, and the spacing between the lenses may be configured to change for this purpose.

[0098] [Numerical Example 1] Surface Data Surface number rd nd νd 1 32.135 2.00 1.703 52.4 2 8.988 1.00 3* 4.779 2.20 1.583 59.5 4* 2.002 4.82 5 8.502 1.41 1.639 55.4 6 -7.468 0.31 7(STO)∞ 1.90 8 9.144 3.35 1.595 67.7 9 -3.329 0.62 1.847 23.8 10 -10.605 0.86 11* -71.758 4.22 1.583 59.5 12* -34.349 0.87 13 ∞ 1.00 1.560 56.0 14 ∞ 0.50 15(IMG)∞ Aspheric data Floor number KABC 3 -3.9571E+00 5.0632E-03 -5.8613E-04 3.0001E-05 4 -5.9485E-01 5.2028E-03 -2.2066E-03 9.7470E-05 11 0.0000E+00 -8.3736E-04 -1.3504E-03 4.4466E-04 12 0.0000E+00 5.6639E-03 -2.2098E-03 2.8026E-04 DEFG 3 -2.7899E-06 2.1270E-07 -8.0836E-09 1.2197.E-10 4 -4.0398E-05 1.3020E-05 -1.9419E-06 1.0674.E-07 11 -8.3883E-05 8.3421E-06 -4.0932E-07 6.9235.E-09 12 -2.2691E-05 1.1328E-06 -3.1237E-08 3.5844.E-10 Various data Focal length (mm) 4.53 Fno 2.80 Half angle of view (deg.) 90.0 Total length (mm) 25.05 [Numerical Example 2] Surface Data Surface number rd nd νd 1 34.938 2.00 1.703 52.4 2 10.110 0.77 3* 4.750 2.20 1.583 59.5 4* 2.054 5.03 5 11.194 1.51 1.589 61.1 6 -6.610 0.58 7(STO)∞ 2.00 8 7.974 3.85 1.618 63.3 9 -3.898 0.60 1.893 20.4 10 -8.919 1.15 11* -15.532 2.98 1.583 59.5 12* -28.493 1.01 13 ∞ 0.80 1.560 56.0 14 ∞ 0.50 15(IMG)∞ Aspheric data Floor number KABC 3 -3.2078E+00 5.8684E-03 -7.2302E-04 6.7335E-05 4 -5.2267E-01 7.6289E-03 -2.5226E-03 1.0393E-04 11 0.0000E+00 -5.9387E-04 -2.4198E-03 7.6714E-04 12 0.0000E+00 8.6149E-03 -4.1195E-03 6.6355E-04 DEFG 3 -7.5321E-06 4.8581E-07 -1.5022E-08 1.7928.E-10 4 -2.1161E-06 -9.2832E-06 1.9917E-06 -1.2574.E-07 11 -1.3401E-04 1.2410E-05 -5.4646E-07 8.1343.E-09 12 -6.3876E-05 3.6376E-06 -1.1135E-07 1.4060.E-09 Various data Focal length (mm) 4.50 Fno 2.80 Half angle of view (deg.) 90.0 Total length (mm) 24.98 [Numerical Example 3] Surface Data Surface number rd nd νd 1 26.038 2.00 1.703 52.4 2 7.679 1.30 3* 4.812 2.20 1.583 59.5 4* 2.127 4.63 5 10.499 1.34 1.603 60.6 6 -6.153 0.10 7(STO)∞ 1.90 8 9.568 3.91 1.618 63.3 9 -3.300 0.60 1.847 23.8 10 -11.555 1.37 11* -202.515 3.33 1.583 59.5 12* -29.735 0.93 13 ∞ 0.90 1.560 56.0 14 ∞ 0.50 15(IMG)∞ Aspheric data Floor number KABC 3 -3.2011E+00 4.3512E-03 -3.1831E-04 -3.9417E-05 4 -4.9624E-01 4.2044E-03 1.9513E-04 -1.4432E-03 11 0.0000E+00 9.8265E-04 -1.6503E-03 3.6134E-04 12 0.0000E+00 1.1233E-02 -3.8988E-03 5.1119E-04 DEFG 3 5.4456E-06 -3.0417E-07 8.6181E-09 -9.4548.E-11 4 4.3074E-04 -5.9822E-05 3.3205E-06 -1.9937.E-08 11 -4.1290E-05 1.8553E-06 1.6565E-08 -2.7170.E-09 12 -4.0265E-05 1.8953E-06 -4.8930E-08 5.3120.E-10 Various data Focal length (mm) 4.51 Fno 2.80 Half angle of view (deg.) 90.0 Total length (mm) 25.02 [Numerical Example 4] Surface Data Surface number rd nd νd 1 34.209 2.00 1.703 52.4 2 11.603 0.45 3* 4.774 2.20 1.583 59.5 4* 2.172 6.51 5(STO) ∞ 0.06 6 7.945 1.39 1.639 55.4 7 -9.380 1.52 8 8.217 3.46 1.618 63.3 9 -3.801 0.60 1.893 20.4 10 -11.556 0.48 11* -12.241 3.87 1.583 59.5 12* -20.824 0.95 13 ∞ 1.00 1.560 56.0 14 ∞ 0.50 15(IMG)∞ Aspheric data Floor number KABC 3 -3.4765E+00 5.7781E-03 -3.3546E-04 1.4620E-06 4 -5.1905E-01 5.7961E-03 7.3257E-04 -1.0837E-03 11 0.0000E+00 -1.1472E-03 -2.4170E-03 9.1354E-04 12 0.0000E+00 8.4354E-03 -3.6764E-03 5.4299E-04 DEFG 3 -7.9186E-07 9.2678E-08 -3.2853E-09 3.9399.E-11 4 2.5070E-04 -3.5513E-05 2.8905E-06 -1.0453.E-07 11 -1.9869E-04 2.4179E-05 -1.5176E-06 3.7679.E-08 12 -4.6569E-05 2.3197E-06 -6.0101E-08 5.9285.E-10 Various data Focal length (mm) 4.50 Fno 2.80 Half angle of view (deg.) 90.0 Total length (mm) 24.99 [Numerical Example 5] Surface Data Surface number rd nd νd 1 32.807 2.00 1.703 52.4 2 11.088 0.52 3* 4.753 2.20 1.583 59.5 4* 2.107 6.04 5(STO) ∞ 0.05 6 8.182 1.59 1.518 58.9 7 -7.016 1.77 8 6.468 3.61 1.618 63.3 9 -4.623 0.60 1.893 20.4 10 -21.471 0.62 11* -21.926 3.68 1.583 59.5 12* -47.506 1.00 13 ∞ 0.80 1.560 56.0 14 ∞ 0.50 15(IMG)∞ Aspheric data Floor number KABC 3 -2.9034E+00 4.8820E-03 -3.0036E-04 6.5621E-06 4 -5.2350E-01 5.9449E-03 2.2764E-04 -8.0585E-04 11 0.0000E+00 -2.9052E-03 -1.4403E-03 4.2903E-04 12 0.0000E+00 4.8230E-03 -2.3005E-03 2.3993E-04 DEFG 3 -1.7356E-06 1.5460E-07 -5.1659E-09 6.1697.E-11 4 1.6304E-04 -2.1492E-05 1.7398E-06 -6.7600.E-08 11 -7.3305E-05 6.5268E-06 -2.5091E-07 2.0664.E-09 12 -1.0497E-05 -6.8424E-08 2.2720E-08 -5.7428.E-10 Various data Focal length (mm) 4.52 Fno 2.80 Half angle of view (deg.) 60.0 Total length (mm) 24.95

[0099] [Table 1]

[0100] [Imaging device] FIG. 14 is a schematic diagram of a main part of an imaging device 70 according to an embodiment of the present invention. The imaging device 70 according to this 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 camera body (housing) 73 that holds the light receiving element 72. The optical system 71 is held by a lens barrel (holding member) and connected to the camera body 73. As shown in FIG. 14, a display unit 74 that displays an image acquired by the light receiving element 72 may be connected to the camera body 73. The light receiving element 72 may be an imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor.

[0101] When the imaging device 70 is used as a distance measuring device, for example, an imaging element (image plane phase difference sensor) having pixels that can split a light beam from the object side into two and perform photoelectric conversion can be used as the light receiving element 72. When the object is on the front focal plane of the optical system 71, no positional shift occurs between the images corresponding to the two split light beams on the image plane of the optical system 71. However, when the object is located at a position other than the front focal plane of the optical system 71, a positional shift occurs between the images. In this case, the positional shift between the images corresponds to the amount of displacement from the front focal plane of the object, so the distance to the object can be measured by obtaining the amount and direction of the positional shift between the images using the image plane phase difference sensor.

[0102] 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). The optical systems according to the above-described embodiments are not limited to imaging devices such as digital still cameras, silver halide film cameras, video cameras, vehicle-mounted cameras, and surveillance cameras, but can also be applied to various optical devices such as telescopes, binoculars, projectors (projection devices), and digital copiers.

[0103] [In-vehicle system] FIG. 15(A) is a schematic diagram of a mobile device 10 according to an embodiment of the present invention and an imaging device 20 (on-board camera) held therein. FIG. 15(A) shows a case where the mobile device 10 is an automobile (vehicle). The mobile device 10 is equipped with an on-board system (driving assistance device) (not shown) for assisting a user 40 (driver, passenger, etc.) of the mobile device 10 using images acquired by the imaging device 20. In this embodiment, the imaging device 20 is installed so as to capture an image of the rear of the mobile device 10, but the imaging device 20 may also be installed so as to capture an image of the front or side of the mobile device 10. Furthermore, two or more imaging devices 20 may be installed in two or more locations on the mobile device 10.

[0104] The imaging device 20 includes an optical system 201 according to any one of the above-described embodiments and an imaging unit 210. The optical system 201 is an optical system (different-angle-of-view lens) having different imaging magnifications at a first angle of view (first field of view) 30 and a second angle of view (second field of view) 31 larger than the first angle of view 30. The imaging surface (light-receiving surface) of the imaging unit 210 includes a first region for capturing an image of an object included in the first angle of view 30 and a second region for capturing an image of an object included in the second angle of view 31. In this case, the number of pixels per unit angle of view in the first region is greater than the number of pixels per unit angle of view in the second region excluding the first region. 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).

[0105] The optical characteristics of the optical system 201 will be described in detail below. The left diagram in Fig. 15(B) shows, in contour lines, the image height y [mm] at each half angle of view θ [deg.] on the imaging plane of the imaging unit 210. The right diagram in Fig. 15(B) shows, in graph form, the relationship between each half angle of view θ and the image height y (the projection characteristics of the optical system 201) in the first quadrant of the left diagram.

[0106] As shown in FIG. 15B, the optical system 201 is configured so that the projection characteristic y(θ) differs between angles of view less than a predetermined half angle of view θa and angles of view equal to or greater than the half angle of view θa. Therefore, the increase in image height y per unit half angle of view θ (resolution) also differs for each angle of view. The local resolution of the optical system 201 is expressed as the differential value dy(θ) / dθ of the projection characteristic y(θ) with respect to the half angle of view θ. The left diagram of FIG. 15B indicates 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. The right diagram of FIG. 15B indicates that the larger the slope of the graph of the projection characteristic y(θ), the higher the resolution.

[0107] In the left diagram of Fig. 15(B), the first region 201a, which is the central region, corresponds to an angle of view less than half the angle of view θa, and the second region 201b, which is the peripheral region, corresponds to an angle of view equal to or greater than half the angle of view θa. The angle of view less than half the angle of view θa corresponds to the first angle of view 30 in Fig. 15(A), and the angle of view obtained by combining the angle of view less than half the angle of view θa and the angle of view equal to or greater than half the angle of view θa corresponds to the second angle of view 31 in Fig. 11(A). 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.

[0108] The optical system 201 is configured so that the projection characteristic y(θ) in the first region 201a is different from that of the equidistant projection method and is also different from that in the second region 201b. In this case, it is desirable that the projection characteristic y(θ) of the optical system 201 satisfy the above-mentioned conditional expression (2).

[0109] By satisfying conditional expression (2), the resolution in the second region 201b can be reduced, thereby realizing a wider angle of view for the optical system 201. Furthermore, the resolution in the first region 201a can be higher than that in the central region of a typical fisheye lens that employs an orthogonal projection system. Falling below the lower limit of conditional expression (2) is undesirable because the resolution in the first region 201a becomes lower than that of an orthogonal projection fisheye lens, or the maximum image height becomes larger, resulting in an increase in the size of the optical system. Exceeding the upper limit of conditional expression (2) is undesirable because the resolution in the first region 201a becomes too high, making it difficult to achieve a wide angle of view equivalent to that of an orthogonal projection fisheye lens or because good optical performance cannot be maintained.

[0110] As described above, the distortion of the optical system 201 is small and the resolution is high in the first region 201a, so a higher-resolution image can be obtained in comparison with the second region 201b. Therefore, good visibility can be obtained by setting the first region 201a (first angle of view 30) to be the region of interest of the user 40. For example, when the imaging device 20 is disposed at the rear of the mobile device 10 as shown in FIG. 15(A), an image corresponding to the first angle of view 30 can be displayed on the electronic rearview mirror, thereby providing a natural sense of perspective when the user 40 focuses on a vehicle behind. On the other hand, the second region 201b (second angle of view 31) corresponds to a wide angle of view that includes the first angle of view 30. Therefore, for example, when the mobile device 10 is backing up, driving assistance can be provided to the user 40 by displaying an image corresponding to the second angle of view 31 on an in-vehicle display.

[0111] 16 is a functional block diagram for explaining an example of the configuration of an in-vehicle system 2 according to this embodiment. The in-vehicle system 2 is a system for displaying to a user 40 an image obtained by an imaging device 20 installed behind a mobile device 10. The in-vehicle system 2 has the imaging device 20, a processing device 220, and a display device (display unit) 230. As described above, the imaging device 20 has the optical system 201 and the imaging unit 210. The imaging unit 210 includes an imaging element such as a CCD sensor or a CMOS sensor, and generates imaging data by photoelectrically converting an optical image formed by the optical system 201, and outputs the imaging data to the processing unit 220.

[0112] The processing device 220 has an image processing unit 221, a display angle of view determination unit 224 (determination unit), a user setting change unit 226 (first change unit), a rear vehicle distance detection unit 223 (first detection unit), a reverse gear detection unit 225 (second detection unit), and a display angle of view change unit 222 (second change unit). The processing device 220 is 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 of the processing device 220 may be realized by hardware such as an ASIC (Application Specific Integrated Circuit) or a PLA (Programmable Logic Array).

[0113] 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. 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 recognize an image when it is displayed on the display device 230, and also improves the detection rate of a rear vehicle by the rear vehicle distance detection unit 223. Note that distortion correction does not need to be performed on the imaging data corresponding to the first region 201a. The image processing unit 221 outputs the image data generated by performing the image processing described above to the display angle of view change unit 222 and the rear vehicle distance detection unit 223.

[0114] Using the image data output from the image processing unit 221, the rear vehicle distance detection unit 223 acquires information about the distance to the rear vehicle included in image data corresponding to a range of the second angle of view 31 that does not include the first angle of view 30. For example, the rear vehicle distance detection unit 223 can detect a rear vehicle based on image data corresponding to the second region 201b among the image data, and calculate the distance to the host vehicle from changes in the position and size of the detected rear vehicle. The rear vehicle distance detection unit 223 outputs information about the calculated distance to the display angle of view determination unit 224.

[0115] Furthermore, the rear vehicle distance detection unit 223 may determine the type of vehicle of the rear vehicle based on data relating to characteristic information such as the shape and color of each vehicle model, which is output as a result of machine learning (deep learning) based on images of a large number of vehicles. At this time, the rear vehicle distance detection unit 223 may output information relating to the type of vehicle of the rear vehicle to the display field of view determination unit 224. The reverse gear detection unit 225 detects whether the transmission of the mobility device 10 (host vehicle) is in reverse gear, and outputs the detection result to the display field of view determination unit 224.

[0116] The display angle of view determination unit 224 determines whether the angle of view (display angle of view) of an image to be displayed on the display device 230 should be the first angle of view 30 or the second angle of view 31, based on output from at least one of the rear vehicle distance detection unit 223 or the reverse gear detection unit 225. Then, the display angle of view determination unit 224 outputs the determination result to the display angle of view change unit 222. For example, the display angle of view determination unit 224 can determine that the display angle of view should be the second angle of view 31 when the distance value in the distance information is equal to or less than a certain threshold value (e.g., 3 m), and can determine that the display angle of view should be the first angle of view 30 when the distance value exceeds the threshold value. Alternatively, the display angle of view determination unit 224 can determine that the display angle of view should be the second angle of view 31 when the reverse gear detection unit 225 notifies the user that the transmission of the mobile device 10 is in reverse gear. Furthermore, the display angle of view determination unit 224 can determine that the display angle of view should be set to the first angle of view 30 when the reverse gear is not engaged.

[0117] Furthermore, when the transmission of the mobile device 10 is in reverse gear, the display angle of view determination unit 224 can determine to set the display angle of view to the second angle of view 31 regardless of the result of the rear vehicle distance detection unit 223. Also, when the transmission of the mobile device 10 is not in reverse gear, the display angle of view determination unit 224 can determine to determine the display angle of view according to the detection result of the rear vehicle distance detection unit 223. Note that the display angle of view determination unit 224 may change the determination criteria 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 unit 223. For example, when the mobile device 10 is a large vehicle such as a truck, the braking distance is longer compared to that of an ordinary vehicle, so it is desirable to set the above-mentioned threshold longer than that of an ordinary vehicle (for example, 10 m).

[0118] The user setting change unit 226 allows the user 40 to change the criteria for determining whether or not the display angle of view is to be changed to the second angle of view 31 by the display angle of view determination unit 224. The criteria set (changed) by the user 40 is input from the user setting change unit 226 to the display angle of view determination unit 224.

[0119] Display angle of view change unit 222 generates a display image to be displayed on display device 230 according to the determination result of display angle of view determination unit 224. For example, if it is determined that first angle of view 30 should be used, display angle of view change unit 222 cuts out a rectangular narrow-angle image (first image) from image data corresponding to first angle of view 30 and outputs it to display device 230. Furthermore, if a following vehicle that satisfies a predetermined condition is present in image data corresponding to second angle of view 31, display angle of view change unit 222 outputs an image (second image) including the following vehicle to display device 230. Note that the second image may include an image corresponding to first region 201a. Display angle of view change unit 222 functions as a display control unit that performs display control to switch 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.

[0120] The image cropping by the display angle of view changing unit 222 is performed by storing the image data output from the image processing unit 221 in a storage unit (memory) such as a RAM, and then reading out the image to be cropped from there. The area in the image data corresponding to the first image is a rectangular area in the first angle of view 30 corresponding to the first area 201a. The area in the image data corresponding to the second image is a rectangular area including the following vehicle in the second angle of view 31 corresponding to the second area 201b.

[0121] The display device 230 has a display unit such as a liquid crystal display or an organic EL display, and displays the display image output from the display angle of view changing unit 222. For example, the display device 230 has a first display unit as an electronic rearview mirror arranged above the windshield (front glass) of the mobile device 10, and a second display unit as an operation panel (monitor) arranged below the windshield of the mobile device 10. With this configuration, the first image and the second image generated from the image data described above can be displayed on the first display unit and the second display unit, respectively. The first display unit may be configured to be equipped with, for example, a half mirror so that it can be used as a mirror when not used as a display. The second display unit may also serve as a display for, for example, a navigation system or an audio system.

[0122] The mobile device 10 is not limited to a vehicle such as an automobile, but may be a mobile object such as a ship, an airplane, an industrial robot, or a drone. The in-vehicle system 2 according to this embodiment is used to display images to the user 40, but may also be used for driving assistance such as cruise control (including full-speed tracking function) and autonomous driving. The in-vehicle system 2 is not limited to a mobile device and can be applied to various devices that use object recognition, such as an intelligent transport system (ITS).

[0123] [Variations] Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist of the present invention.

[0124] For example, although the optical systems according to the above-described embodiments are intended for use in the visible range and are configured to perform good aberration correction throughout the entire visible range, the wavelength range in which aberration correction is performed may be changed as necessary. 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 outside the visible range.

[0125] Furthermore, in the above-described in-vehicle system 2, the above-described distance measuring device may be employed as the imaging device 20. In this case, the in-vehicle system 2 may include a determination unit that determines the possibility of a collision with an object based on information about the distance to the object acquired by the imaging device 20. Also, a stereo camera having two imaging units 210 may be employed as the imaging device 20. In this case, even without using an imaging surface phase difference sensor, image data can be simultaneously acquired by each of the synchronized imaging units, and the two image data can be used to perform processing similar to that described above. However, if the difference in imaging time between each imaging unit is known, the imaging units do not need to be synchronized.

[0126] The disclosure of each embodiment includes the following configuration. (Configuration 1) An optical system composed of a front group and a rear group arranged in this order from the object side to the image side, the front group is composed of, arranged in order from the object side to the image side, a first lens element having negative refractive power and a second lens element including an aspherical surface; the rear group includes, arranged in order from the object side to the image side, a third lens element having positive refractive power, a fourth lens element having positive refractive power, a fifth lens element having negative refractive power, and a sixth lens element including an aspherical surface; an object side surface of the first lens is a convex surface, an object side surface of the second lens is a convex surface, and an object side surface of the sixth lens is a concave surface on an optical axis; When the focal length of the optical system is f and the focal length of the third lens is f3, 1.00 <f3 / f<1.80 An optical system characterized by satisfying the following conditional expression: (Configuration 2) When the half angle of view of the optical system is θ [deg.], the projection characteristic 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, 1.00 <f×sin(θmax) / y(θmax)≦1.90 The optical system according to configuration 1, characterized in that the following condition is satisfied: (Configuration 3) When the half angle of view of the optical system is θ [deg.], the projection characteristic 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, 0.65 <y(θmax / 2) / y(θmax)<0.85 3. The optical system according to configuration 1 or 2, wherein the following condition is satisfied: (Configuration 4) 4. The optical system according to any one of configurations 1 to 3, wherein the object side surface of the second lens is an aspheric surface having an inflection point in a cross section including the optical axis. (Configuration 5) When the distance on the optical axis from the image side surface of the second lens to the object side surface of the third lens is t23 and the focal length of the rear group is fR, 0.80 <t23 / fR<1.50 5. The optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) When the focal length of the fourth lens is f4, 1.20 <f3 / f4<1.70 6. The optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) When the Abbe number of the third lens based on the d-line is ν3, 30<ν3<100 7. The optical system according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) 8. The optical system according to any one of configurations 1 to 7, wherein the object side surface of the sixth lens is aspherical and has no extremum in the radial direction in a cross section including the optical axis. (Configuration 9) The optical system described in any one of configurations 1 to 8, characterized in that the inclination of the object-side surface of the sixth lens with respect to a plane perpendicular to the optical axis increases monotonically in the radial direction in a cross section including the optical axis. (Configuration 10) 10. The optical system according to any one of configurations 1 to 9, wherein the image side surface of the sixth lens is aspherical and has no extremum in the radial direction in a cross section including the optical axis. (Configuration 11) 11. The optical system according to any one of configurations 1 to 10, wherein the inclination of the image side surface of the sixth lens relative to a plane perpendicular to the optical axis increases monotonically in the radial direction in a cross section including the optical axis. (Configuration 12) When the radius of curvature of the object side surface of the third lens is R31 and the radius of curvature of the image side surface of the third lens is R32, -0.30<(R32+R31) / (R32-R31)<0.15 12. The optical system according to any one of configurations 1 to 11, wherein the following condition is satisfied: (Configuration 13) When the focal length of the first lens is f1, -6.0 <f1 / f<-3.0 13. The optical system according to any one of configurations 1 to 12, wherein the following condition is satisfied: (Configuration 14) 14. The optical system according to any one of configurations 1 to 13, wherein the rear group has an aperture stop. (Configuration 15) 15. The optical system according to any one of configurations 1 to 14, wherein the front group has negative refractive power, and the rear group has positive refractive power. (Configuration 16) 16. The optical system according to any one of configurations 1 to 15, wherein the fourth lens and the fifth lens are cemented together to form a cemented lens. (Configuration 17) 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) 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 in-vehicle system according to configuration 18, wherein the display device has a first display unit that displays a first image corresponding to a first angle of view among the images, and a second display unit that displays a second image corresponding to a second angle of view that includes the first angle of view. (Configuration 20) A moving device comprising the imaging device according to configuration 17, and capable of moving while holding the imaging device. [Explanation of symbols]

[0127] 100, 200, 300, 400, 500 optics G1 front group G2 rear group L1 First lens L2 Second lens L3 Third lens L4 4th lens L5 Fifth lens L6 6th lens

Claims

1. An optical system including, arranged in order from an object side to an image side, a first lens having negative refractive power, a second lens including an aspherical surface, a third lens having positive refractive power, a fourth lens having positive refractive power, a fifth lens having negative refractive power, and a sixth lens including an aspherical surface, an object side surface of the first lens is a convex surface, an object side surface of the second lens is a convex surface, and an object side surface of the sixth lens is a concave surface on an optical axis; When the focal length of the optical system is f, the focal length of the third lens is f3, the distance on the optical axis from the image side surface of the second lens to the object side surface of the third lens is t23, the composite focal length of the lens disposed closer to the image side than the second lens is fR, and the focal length of the first lens is f1, 1.00<f3 / f<1.80 0.80<t23 / fR<1.50 -6.0<f1 / f<-3.0 An optical system characterized by satisfying the following conditional expression:

2. When the projection characteristic of the optical system, which represents 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, 1.00<f×sin(θmax) / y(θmax)≦1.90 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. When the projection characteristic of the optical system, which represents 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, 0.65<y(θmax / 2) / y(θmax)<0.85 2. The optical system according to claim 1, wherein the following condition is satisfied:

4. 2. The optical system according to claim 1, wherein the object side surface of the second lens is an aspheric surface having an inflection point in a cross section including the optical axis.

5. When the focal length of the fourth lens is f4, 1.20<f3 / f4<1.70 2. The optical system according to claim 1, wherein the following condition is satisfied:

6. When the Abbe number of the third lens based on the d-line is ν3, 30<ν3<100 2. The optical system according to claim 1, wherein the following condition is satisfied:

7. 7. The optical system according to claim 1, wherein the object side surface of the sixth lens is an aspheric surface that has no extremum in a cross section including the optical axis.

8. 7. The optical system according to claim 1, wherein the inclination of the object-side surface of the sixth lens relative to a plane perpendicular to the optical axis varies monotonically in a cross section including the optical axis.

9. 7. The optical system according to claim 1, wherein the image side surface of the sixth lens is an aspheric surface that has no extremum in a cross section including the optical axis.

10. 7. The optical system according to claim 1, wherein the inclination of the image side surface of the sixth lens relative to a plane perpendicular to the optical axis varies monotonically in a cross section including the optical axis.

11. When the radius of curvature of the object side surface of the third lens is R31 and the radius of curvature of the image side surface of the third lens is R32, -0.30<(R32+R31) / (R32-R31)<0.15 7. The optical system according to claim 1, wherein the following condition is satisfied:

12. 7. The optical system according to claim 1, further comprising an aperture stop arranged closer to the image side than the second lens.

13. 7. The optical system according to claim 1, wherein the fourth lens and the fifth lens are cemented together.

14. An imaging device comprising: the optical system according to claim 1; and an imaging element that images an object via the optical system.

15. 15. A system comprising: the imaging device according to claim 14; and a display device that displays an image obtained based on an output of the imaging device.

16. The system described in claim 15, characterized in that the display device has a first display unit that displays a first image of the images corresponding to a first angle of view, and a second display unit that displays a second image of the images corresponding to a second angle of view that includes the first angle of view.

17. A moving device comprising the imaging device according to claim 14, and capable of moving while holding the imaging device.

Images