Optical system and imaging apparatus including the same

Abstract

To provide an optical system having high optical performance while having a wide angle.SOLUTION: An optical system (100) comprises a front group (G1), an aperture stop (STO), and a rear group (G2). The front group includes, a first lens (L1), a second lens (L2), and a first cemented lens (CL1) including a third lens (L3) having negative refractive power and a fourth lens (L4) having positive refractive power that are cemented to each other. The rear group includes a fifth lens (L5), a sixth lens (L6), and a seventh lens (L7). The second lens has negative refractive power on an optical axis. The object side surface of the second lens is convex on the optical axis. When the refractive index of the third lens with respect to a d-line is N3, the refractive index of the fourth lens with respect to the d-line is N4, the focal length of the optical system is f, and the focal length of the third lens is f3, conditional expressions 0.20<N4-N3<0.50 and -1.70<f3 / f<-1.10 are satisfied.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical system, and is suitable for imaging devices such as digital still cameras, digital video cameras, in-vehicle cameras, mobile phone cameras, surveillance cameras, wearable cameras, medical cameras, and the like.

Background Art

[0002] An optical system used in an imaging device such as an in-vehicle camera is required to have a wide angle of view. Patent Document 1 discloses a wide-angle lens including a cemented lens disposed on the object side with respect to the aperture stop for chromatic aberration correction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the wide-angle lens of Patent Document 1 is not sufficient for the required optical performance requirements.

[0005] An object of the present invention is to provide an optical system having a wide angle of view and high optical performance.

Means for Solving the Problems

[0006] As an aspect of the present invention, an optical system is composed of a front group, an aperture stop, and a rear group, which are arranged in order from the object side to the image side. The front group has a first lens with a negative refractive power, a second lens including an aspherical surface, and a first cemented lens including a third lens with a negative refractive power and a fourth lens with a positive refractive power that are cemented to each other, which are arranged in order from the object side to the image side. The rear group has a fifth lens with a positive refractive power, a sixth lens with a negative refractive power, and a seventh lens, which are arranged in order from the object side to the image side. The second lens has a negative refractive power on the optical axis, and the object-side surface of the second lens is convex on the optical axis. When the refractive index of the third lens with respect to the d-line is N3, the refractive index of the fourth lens with respect to the d-line is N4, the focal length of the optical system is f, and the focal length of the third lens is f3, 0.20 < N4 - N3 < 0.50 -1.70 < f3 / f < -1.10 satisfies the conditional expression.

[0007] Other objects and features of the present invention will be described in the following examples.

Effect of the Invention

[0008] According to the present invention, an optical system having a wide angle and high optical performance can be provided.

Brief Description of the Drawings

[0009]

Figure 1

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Figure 14

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that each drawing may be drawn at a scale different from the actual one for convenience. Also, in each drawing, the same members are denoted by the same reference numerals, and redundant explanations are omitted.

[0011] Optical systems used in imaging devices such as in-vehicle cameras are required to have a wide angle of view, and mainly fisheye lenses are used. As projection methods of fisheye lenses, an orthographic projection method, an equidistant projection method, and a stereographic projection method are known. 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 is represented by the following formula.

[0012] Orthographic projection method: Y = f×sinθ Equidistant projection method: Y = f×θ Stereographic projection method: Y = 2×ftan(θ / 2) The orthographic projection method has the characteristic of strongly compressing the image near the screen periphery with respect to the image near the optical axis. The equidistant projection method has a constant resolution regardless of the angle of view. The stereographic projection method has the characteristic of compressing the image near the optical axis more than the image near the screen periphery, contrary to the orthographic projection.

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

[0014] FIG. 2, FIG. 4, FIG. 6, FIG. 8, and FIG. 10 are longitudinal aberration diagrams of the optical systems according to Embodiments 1 to 5. Each longitudinal aberration diagram shows, in order from the left, spherical aberration, field curvature (astigmatism), and distortion. In each longitudinal aberration diagram, the aberrations with respect 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.

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

[0016] The optical system according to each embodiment includes, in order from the object side to the image side, a front group G1 having a positive refractive power, an aperture stop STO, and a rear group G2 having a positive refractive power. Here, it is considered that the cover glass CG is not included in each optical system. The front group G1 includes, in order from the object side to the image side, a first lens L1 having a negative refractive power, a second lens L2 including an aspherical surface, a third lens L3 having a negative refractive power, and a fourth lens L4 having a positive refractive power. The third lens L3 and the fourth lens L4 are joined to each other to form a first cemented lens CL1. Note that the first cemented lens CL1 may be formed by joining three or more lenses, but it is preferably formed by joining two lenses for miniaturization.

[0017] The second lens L2 has a negative refractive power near the optical axis OA (on the optical axis), and the object side surface is convex near the optical axis. The rear group G2 includes a fifth lens L5 with a positive refractive power, a sixth lens L6 with a negative refractive power, and a seventh lens L7. The fifth lens L5 and the sixth lens L6 are joined to each other to form a second cemented lens CL2. Here, the lens refers to an optical element having a refractive power, and does not include optical elements such as parallel plate glass having no refractive power.

[0018] In the optical system according to each embodiment, since the second lens L2 disposed at a position away from the aperture stop STO is an aspherical lens, projection characteristics having high resolution in the central region of the screen are achieved, and a wide angle of view is realized by adopting the configuration of the above lenses. Further, by configuring the rear group G2 as described above, it is possible to satisfactorily correct spherical aberration, axial aberration, and field curvature generated by widening the angle of view of the optical system.

[0019] In each embodiment, when the refractive index of the third lens L3 with respect to the d-line is N3 and the refractive index of the fourth lens L4 with respect to the d-line is N4, the following conditional expression (1) is satisfied.

[0020] 0.20 < N4 - N3 < 0.50 (1) Also, 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 (2) is satisfied.

[0021] -1.70 < f3 / f < -1.10 (2) By appropriately setting the refractive index difference between the third lens L3 and the fourth lens L4 and the relationship between the focal length of the third lens L3 and the optical system (entire system) so as to satisfy both conditional expressions (1) and (2), it is possible to satisfactorily correct field curvature and realize an optical system with high imaging performance.

[0022] More specifically, when correcting field curvature, it is important to correct the Petzval sum P represented by the following formula (3).

[0023]

Equation

[0024] Here, fi represents the focal length of each lens, and k represents the number of lenses.

[0025] Generally, an imaging lens has a positive refractive power. In a wide-angle lens, the focal length is short, so in particular, the refractive power of a positive lens becomes large. As can be seen from Equation (3), when the refractive power of a positive lens increases (the focal length decreases), the occurrence of the Petzval sum increases. To correct this, from the perspective of the refractive index, it is necessary to increase the refractive index of the positive lens or decrease the refractive index of the negative lens. From the perspective of the focal length, it is necessary to shorten the focal length of the negative lens.

[0026] When the value is below the lower limit of Conditional Expression (1), the refractive index difference between the fourth lens L4 and the third lens L3 is not sufficient, and it becomes difficult to correct the field curvature of the fourth lens L4 with positive refractive power. On the other hand, when the value exceeds the upper limit of Conditional Expression (1), the refractive index difference between the fourth lens L4 and the third lens L3 becomes too large, and the correction of the field curvature becomes excessive, resulting in deterioration of the imaging performance.

[0027] Preferably, the numerical range of Conditional Expression (1) is set as follows in Conditional Expression (1a). More preferably, the numerical range of Conditional Expression (1) is set as follows in Conditional Expression (1b).

[0028] 0.20 < N4 - N3 < 0.40 (1a) 0.20 < N4 - N3 < 0.30 (1b) When the value is below the lower limit of Conditional Expression (2), the negative refractive power of the third lens L3 is weak, so the correction of the field curvature generated by the fourth lens L4 with positive refractive power becomes insufficient. On the other hand, when the value exceeds the upper limit of Conditional Expression (2), the negative refractive power of the third lens L3 becomes too strong, so the correction of the field curvature becomes excessive.

[0029] Preferably, the numerical range of Conditional Expression (2) is set as follows in Conditional Expression (2a). More preferably, the numerical range of Conditional Expression (2) is set as follows in Conditional Expression (2b).

[0030] -1.65 < f3 / f < -1.10 (2a) -1.60 < f3 / f < -1.10 (2b) Note that, for the optical system according to each embodiment, the effects of the present invention can be obtained as long as at least the above-described configuration is satisfied. For example, the front group G1 may have a configuration having lenses other than the first lens L1 to the fourth lens L4 (a configuration having five or more lenses).

[0031] In each embodiment, when the half field angle of the optical system is θ [deg.], the projection characteristic representing the relationship between the half field angle θ and the image height y is y(θ), and the maximum half field angle of the optical system is θmax, it is preferable to satisfy the following conditional expression (4).

[0032] 1.00 < f × sin(θmax) / y(θmax) ≦ 1.90 (4) Although details will be described later, by configuring the optical system so as to satisfy the conditional expression (4), it is possible to increase the resolution of the subject image of the field angle near the optical axis OA (near the optical axis) while having a wide field angle.

[0033] More preferably, the numerical range of the conditional expression (4) is set as the following conditional expression (4a). Even more preferably, the numerical range of the conditional expression (4) is set as the following conditional expression (4b).

[0034] 1.00 < f × sin(θmax) / y(θmax) ≦ 1.70 (4a) 1.00 < f × sin(θmax) / y(θmax) ≦ 1.40 (4b) Also, in each embodiment, it is preferable to satisfy the following conditional expression (5).

[0035] 0.65 < y(θmax / 2) / y(θmax) < 0.85 (5) The ratio between the image height y(θmax) at the maximum half field angle θmax and the image height y(θmax / 2) at half of the maximum half field angle θmax / 2 is set within the range of conditional expression (5). By doing so, while maintaining a wide field angle, the resolution of the subject image at the field angle near the optical axis OA can be made higher.

[0036] More preferably, the numerical range of conditional expression (5) is set as in the following conditional expression (5a). Even more preferably, the numerical range of conditional expression (5) is set as in the following conditional expression (5b).

[0037] 0.65 < y(θmax / 2) / y(θmax) < 0.83 (5a) 0.65 < y(θmax / 2) / y(θmax) < 0.81 (5b) In imaging devices such as in-vehicle cameras described later, not only is it required to have a wide field angle, but it is also required to increase the imaging magnification in the vicinity of the optical axis (central region). For example, when the imaging device is arranged at the rear of a moving device (vehicle), an image corresponding to the central region, which is the main area of attention, is enlarged and displayed on an electronic rearview mirror, and a form in which the entire image including regions other than the central region (peripheral regions) is displayed on an in-vehicle display is conceivable. Therefore, it is desirable to make the imaging magnification (focal length) of the optical system different between the central region and other regions.

[0038] Figs. 11(A) to (E) show the aspherical shape of the object side surface of the second lens L2 according to each embodiment. In Figs. 11(A) to (E), the vertical axis indicates the position (lens radius) in the radial direction in the cross-section including the optical axis OA of the object side surface of the second lens L2, and the horizontal axis indicates the curvature [1 / mm] of the object side surface of the second lens L2. That is, Figs. 11(A) to (E) show a graph in which the curvature for each position of the object side surface of the second lens L2 is plotted. The numerical values on the vertical axis indicate 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 normalized such that the distance from the optical axis OA to the position of the effective diameter (maximum effective diameter) is 1.

[0039] The object-side surface (the lens surface on the object side) of the second lens L2 including the aspherical surface can greatly refract the light rays from the peripheral portion in the radial direction among the light beams from the first lens L1 toward the optical axis OA. As a result, it becomes 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 has an inflection point in the cross section including the optical axis OA as shown in FIGS. 11(A) to (E). Thereby, while reducing the number of lenses constituting the optical system, it is possible to facilitate wide-angleization and an increase in the imaging magnification in the central region.

[0040] When the focal length of the fourth lens L4 is f4, it is preferable to satisfy the following conditional expression (6).

[0041] -1.80 < f3 / f4 < -1.30 (6) If it exceeds the upper limit value of the conditional expression (6), the negative refractive power of the third lens L3 becomes too strong, so that the correction of the field curvature becomes excessive and the occurrence of the longitudinal chromatic aberration also becomes excessive. On the other hand, if it is below the lower limit value of the conditional expression (6), since the negative refractive power of the third lens L3 is weak, the correction of the field curvature of the fourth lens L4 having a positive refractive power becomes insufficient and the occurrence of the longitudinal chromatic aberration is also insufficient.

[0042] More preferably, the numerical range of the conditional expression (6) is set as the following conditional expression (6a). Even more preferably, the numerical range of the conditional expression (6) is set as the following conditional expression (6b).

[0043] -1.78 < f3 / f4 < -1.30 (6a) -1.85 < f3 / f4 < -1.30 (6b) In the optical system according to each embodiment, since both the front group G1 and the rear group G2 have positive refractive powers and the front group G1 adopts the above configuration, a wide angle of view is realized while shortening the overall length of the optical system.

[0044] When the Abbe number based on the d-line of the third lens L3 is ν3 and the Abbe number based on the d-line of the fourth lens L4 is ν4, it is preferable to satisfy the following conditional expression (7).

[0045] |ν4 - ν3| < 10 (7) When the relative Abbe number difference between the fourth lens L4 and the third lens L3 becomes large, it becomes difficult to correct the chromatic aberration of magnification, and the imaging performance deteriorates.

[0046] More preferably, the numerical range of the conditional expression (7) is set as in the following conditional expression (7a). Even more preferably, the numerical range of the conditional expression (7) is set as in the following conditional expression (7b).

[0047] |ν4 - ν3| < 9 (7a) |ν4 - ν3| < 8 (7b) When the radius of curvature of the joint surface of the first cemented lens CL1 is Rc1 and the distance (interval) on the optical axis from the joint surface of the first cemented lens CL1 to the aperture stop STO is dc1, it is preferable to satisfy the following conditional expression (8).

[0048] 1.20 < Rc1 / dc1 < 2.10 (8) If the upper limit value of the conditional expression (8) is exceeded, the symmetry of the joint surface with respect to the aperture stop STO is greatly deviated, so the occurrence of coma aberration increases. On the other hand, if the lower limit value of the conditional expression (8) is fallen below, the occurrence of spherical aberration increases. That is, by being within the range of the conditional expression (8), it becomes possible to perform appropriate aberration correction.

[0049] More preferably, the numerical range of the conditional expression (8) is set as in the following conditional expression (8a). Even more preferably, the numerical range of the conditional expression (8) is set as in the following conditional expression (8b).

[0050] 1.25 < Rc1 / dc1 < 2.08 (8a) 1.30 < Rc1 / dc1 < 2.05 (8b) When the focal length of the first lens L1 is f1, it is preferable to satisfy the following conditional expression (9).

[0051] -5.00 < f1 / f < -3.00 (9) If it exceeds the upper limit value of conditional expression (9), the negative refractive power of the first lens L1 becomes too strong, and various aberrations generated by this lens are excessively generated. On the other hand, if it is below the lower limit value of conditional expression (9), the negative refractive power of the first lens L1 is weak, the generation of pupil aberration is suppressed, and the amount of incident light of off-axis rays decreases.

[0052] 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).

[0053] -4.80 < f1 / f < -3.50 (9a) -4.60 < f1 / f < -4.00 (9b) The fifth lens L5 and the sixth lens L6 are the second cemented lens CL2 cemented to each other. When the radius of curvature of the cemented surface of the second cemented lens CL2 is Rc2 and the distance (interval) on the optical axis from the aperture stop STO to the cemented surface of the second cemented lens CL2 is dc2, it is preferable to satisfy the following conditional expression (10).

[0054] -0.90 < Rc2 / dc2 < -0.50 (10) If it exceeds the upper limit value of conditional expression (10), the symmetry of the cemented surface with respect to the aperture stop STO is greatly deviated, so the generation of coma aberration increases. On the other hand, if it is below the lower limit value of conditional expression (10), the generation of spherical aberration increases. That is, by being within the range of conditional expression (10), it becomes possible to perform appropriate aberration correction.

[0055] More preferably, the numerical range of conditional expression (10) is set as in the following conditional expression (10a). Even more preferably, the numerical range of conditional expression (10) is set as in the following conditional expression (10b).

[0056] -0.88 < Rc2 / dc2 < -0.55 (10a) -0.86 < Rc2 / dc2 < -0.60 (10b) When the radius of curvature of the object side surface of the third lens L3 is R31, it is preferable to satisfy the following conditional expression (11).

[0057] -0.70 < f / R31 < -0.20 (11) If it exceeds the upper limit value of conditional expression (11), the negative power (refractive power) of the object side surface of the third lens L3 becomes weak, resulting in insufficient correction of field curvature. On the other hand, if it is below the lower limit value of conditional expression (11), the light reflected from the object side surface of the third lens L3 is reflected again by the second lens L2 and then forms an image after the third lens L3, easily generating unnecessary ghosts.

[0058] More preferably, the numerical range of conditional expression (11) is set as in the following conditional expression (11a). Even more preferably, the numerical range of conditional expression (11) is set as in the following conditional expression (11b).

[0059] -0.68 < f / R31 < -0.21 (11a) -0.65 < f / R31 < -0.22 (11b) The seventh lens L7 preferably has a positive refractive power on the optical axis OA (in the vicinity of the optical axis). By adopting such a configuration, the field curvature generated by the first lens L1 and the second lens L2 having negative refractive powers can be corrected.

[0060] The imaging device includes an optical system of each embodiment that forms a subject image, and an imaging sensor that photoelectrically converts the subject image (images a subject as an object through the optical system). A plurality of pixels arranged in a two-dimensional array are provided on the imaging surface of the imaging sensor.

[0061] Hereinafter, the detailed configuration of the optical system according to each embodiment will be described.

Embodiment

[0062] The optical system 100 of Example 1 shown in FIG. 1 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, an aperture stop STO, a fifth lens L5, a sixth lens L6, and a seventh lens L7, which are arranged in order from the object side to the image side. The first lens L1 has a convex object side surface and is a meniscus lens with a negative refractive power. The second lens L2 is an aspherical lens. The third lens L3 is a biconcave lens with a negative power (refractive power). The fourth lens L4 and the fifth lens L5 are each a biconvex lens with a positive power. The sixth lens L6 has a convex image side surface and is a meniscus lens with a negative power. The seventh lens L7 is an aspherical lens.

[0063] On the image plane IMG, the imaging surface of an imaging sensor such as a CMOS (Complementary Metal - Oxide - Semiconductor) sensor is arranged and has a cover glass CG of the imaging sensor. In the imaging device, image data is generated from the output of the imaging sensor.

[0064] The third lens L3 and the fourth lens L4 form a first cemented lens CL1 that is cemented to each other. The fifth lens L5 and the sixth lens L6 form a second cemented lens CL2 that is cemented to each other.

[0065] The object side surface of the second lens L2 is convex (near the optical axis) on the optical axis OA, and the image side surface is concave. As shown in FIG. 11(a), the object side surface of the second lens L2 is an aspherical surface having an inflection point in the cross - section including the optical axis OA. The object side surface of the seventh lens L7 is concave near the optical axis, the image side surface is convex, and the focal length of the seventh lens L7 is 93.44 mm.

[0066] The first lens L1 to the fourth lens L4 form a front group G1, and the focal length of the front group G1 is 16.32 mm. The fifth lens L5 to the seventh lens L7 form a rear group G2, and the focal length of the rear group G2 is 10.18 mm.

[0067] As shown in Fig. 2, in the optical system 100 according to this embodiment, spherical aberration and field curvature are well corrected in the wavelength range of 400 to 700 nm. Also, regarding distortion, while it increases as the angle of view (image height) increases in the peripheral region, it is relatively small in the central region. As a result, the resolution in the central region can be made higher than that in the peripheral region, and as described above, it becomes possible to improve the visibility of the image for the user of the imaging device.

[0068] Numerical Example 1 shows specific numerical values of the optical system 100 of this embodiment. Table 1 shows the numerical values of each conditional expression. The optical system 100 of this embodiment satisfies conditional expressions (1), (2), (4) to (11).

Embodiment

[0069] The optical system 200 of Embodiment 2 shown in Fig. 3 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, an aperture stop STO, a fifth lens L5, a sixth lens L6, and a seventh lens L7, which are arranged in order from the object side to the image side. 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 is a biconcave lens with negative power (refractive power). The fourth lens L4 and the fifth lens L5 are each biconvex lenses with positive power. The sixth lens L6 has a convex image-side surface and is a meniscus lens with negative power. The seventh lens L7 is an aspherical lens.

[0070] On the image plane IMG, the imaging surface of an imaging sensor such as a CMOS sensor is arranged, and it has a cover glass CG of the imaging sensor. In the imaging device, image data is generated from the output of the imaging sensor.

[0071] The third lens L3 and the fourth lens L4 form a first cemented lens CL1 that is cemented to each other. The fifth lens L5 and the sixth lens L6 form a second cemented lens CL2 that is cemented to each other.

[0072] 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 Fig. 11(b), the object side surface of the second lens L2 is an aspherical surface having an inflection point in the cross section including the optical axis OA. The object side surface of the seventh lens L7 is concave near the optical axis, and the image side surface is convex, and the focal length of the seventh lens L7 is 14.99 mm.

[0073] The first lens L1 to the fourth lens L4 constitute the front group G1, and the focal length of the front group G1 is 44.35 mm. The fifth lens L5 to the seventh lens L7 constitute the rear group G2, and the focal length of the rear group G2 is 8.46 mm.

[0074] As shown in Fig. 4, in the optical system 200 according to the present embodiment, spherical aberration and field curvature are well corrected at wavelengths of 400 to 700 nm. Also, with regard to distortion, it increases as the angle of view (image height) increases in the peripheral region, while it is 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 becomes possible to improve the visibility of the image for the user of the imaging device.

[0075] Numerical Example 2 shows specific numerical values of the optical system 200 of the present embodiment. Table 1 shows the numerical values of each conditional expression. The optical system 200 of the present embodiment satisfies conditional expressions (1), (2), (4) to (11).

Embodiment

[0076] The optical system 300 of Embodiment 3 shown in Fig. 5 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, an aperture stop STO, a fifth lens L5, a sixth lens L6, and a seventh lens L7 arranged in order from the object side to the image side. 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 is a biconcave lens with negative power (refractive power). The fourth lens L4 and the fifth lens L5 are each a biconvex lens with positive power. The sixth lens L6 has a convex image side surface and is a meniscus lens with negative power. The seventh lens L7 is an aspherical lens.

[0077] On the image plane IMG, the imaging surface of an imaging sensor such as a CMOS sensor is disposed, and it has a cover glass CG of the imaging sensor. In the imaging device, image data is generated from the output of the imaging sensor.

[0078] The third lens L3 and the fourth lens L4 form a first cemented lens CL1 that is cemented to each other. The fifth lens L5 and the sixth lens L6 form a second cemented lens CL2 that is cemented to each other.

[0079] 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 FIG. 11(c), 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. The object side surface of the seventh lens L7 is convex near the optical axis, the image side surface is convex, and the focal length of the seventh lens L7 is 22.39 mm.

[0080] The first lens L1 to the fourth lens L4 constitute a front group G1, and the focal length of the front group G1 is 86.06 mm. The fifth lens L5 to the seventh lens L7 constitute a rear group G2, and the focal length of the rear group G2 is 7.99 mm.

[0081] As shown in FIG. 6, in the optical system 300 according to the present embodiment, spherical aberration and field curvature are favorably corrected at wavelengths of 400 to 700 nm. Also, with respect to distortion, while it increases as the angle of view (image height) increases in the peripheral region, it is 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 becomes possible to improve the visibility of the image for the user of the imaging device.

[0082] Numerical Example 3 shows specific numerical values of the optical system 300 of the present embodiment. Table 1 shows the numerical values of each conditional expression. The optical system 300 of the present embodiment satisfies conditional expressions (1), (2), (4) to (11).

Embodiment

[0083] The optical system 400 of Example 4 shown in FIG. 7 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, an aperture stop STO, a fifth lens L5, a sixth lens L6, and a seventh lens L7, which are arranged in order from the object side to the image side. 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 is a biconcave lens with negative power (refractive power). The fourth lens L4 and the fifth lens L5 are each a biconvex lens with positive power. The sixth lens L6 has a convex image side surface and is a meniscus lens with negative power. The seventh lens L7 is an aspherical lens.

[0084] On the image plane IMG, the imaging surface of an imaging sensor such as a CMOS sensor is arranged and has a cover glass CG of the imaging sensor. In the imaging device, image data is generated from the output of the imaging sensor.

[0085] The third lens L3 and the fourth lens L4 form a first cemented lens CL1 that is cemented to each other. The fifth lens L5 and the sixth lens L6 form a second cemented lens CL2 that is cemented to each other.

[0086] 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 FIG. 11(d), the object side surface of the second lens L2 is an aspherical surface having an inflection point in the cross section including the optical axis OA. The object side surface of the seventh lens L7 is convex near the optical axis, the image side surface is convex, and the focal length of the seventh lens L7 is 24.63 mm.

[0087] The first lens L1 to the fourth lens L4 form a front group G1, and the focal length of the front group G1 is 40.97 mm. The fifth lens L5 to the seventh lens L7 form a rear group G2, and the focal length of the rear group G2 is 8.32 mm.

[0088] As shown in FIG. 8, in the optical system 400 according to this embodiment, spherical aberration and field curvature are well corrected at wavelengths of 400 to 700 nm. Also, regarding distortion, while it increases as the angle of view (image height) increases in the peripheral region, it is relatively small in the central region. Thereby, the resolution in the central region can be made higher than that in the peripheral region, and as described above, it becomes possible to improve the visibility of the image for the user of the imaging device.

[0089] Numerical Example 4 shows specific numerical values of the optical system 400 of this embodiment. Table 1 shows the numerical values of each conditional expression. The optical system 400 of this embodiment satisfies conditional expressions (1), (2), (4) to (11).

Embodiment

[0090] The optical system 500 of Embodiment 5 shown in FIG. 9 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, an aperture stop STO, a fifth lens L5, a sixth lens L6, and a seventh lens L7, which are arranged in order from the object side to the image side. 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 is a biconcave lens with negative power (refractive power). The fourth lens L4 and the fifth lens L5 are each a biconvex lens with positive power. The sixth lens L6 has a convex image-side surface and is a meniscus lens with negative power. The seventh lens L7 is an aspherical lens.

[0091] On the image plane IMG, the imaging surface of an imaging sensor such as a CMOS sensor is arranged, and it has a cover glass CG of the imaging sensor. In the imaging device, image data is generated from the output of the imaging sensor.

[0092] The third lens L3 and the fourth lens L4 form a first cemented lens CL1 that is cemented to each other. The fifth lens L5 and the sixth lens L6 form a second cemented lens CL2 that is cemented to each other.

[0093] 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 Fig. 11(e), the object side surface of the second lens L2 is an aspherical surface having an inflection point in the cross-section including the optical axis OA. The object side surface of the seventh lens L7 is concave near the optical axis, and the image side surface is convex, and the focal length of the seventh lens L7 is 23.79 mm.

[0094] The first lens L1 to the fourth lens L4 constitute the front group G1, and the focal length of the front group G1 is 18.17 mm. The fifth lens L5 to the seventh lens L7 constitute the rear group G2, and the focal length of the rear group G2 is 9.81 mm.

[0095] As shown in Fig. 10, in the optical system 500 according to this embodiment, spherical aberration and field curvature are well corrected in the wavelength range of 400 to 700 nm. Regarding distortion, it increases as the angle of view (image height) increases in the peripheral region, while it is 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, the visibility of the image for the user of the imaging device can be improved.

[0096] Numerical Example 5 shows specific numerical values of the optical system 500 of this embodiment. Table 1 shows the numerical values of each conditional expression. The optical system 500 of this embodiment satisfies conditional expressions (1), (2), (4) to (11).

[0097] The numerical examples 1 to 5 corresponding to Embodiments 1 to 5 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 of the i-th (the i-th surface) (unit: mm), di is the interval from the (i + 1)-th (unit: mm), ndi and νdi respectively indicate the refractive index and Abbe number of the i-th optical member based on the d-line (wavelength 587.6 nm). The Abbe number νd is a value defined by the following formula when the refractive indices for the F-line, d-line, and C-line are nF, nd, and nC, respectively.

[0098] νd=(nd-1) / (nF-nC) The surface interval is positive when going towards the image side along the optical path and negative when going towards the object side. Also, in Numerical Examples 1 to 5, the two surfaces on the most image side are planes corresponding to the optical block.

[0099] Also, when the optical surface is an aspherical surface, a "*" sign is attached to the right side of the surface number. Each of the aspherical optical surfaces in this embodiment has a rotationally symmetric shape centered on the optical axis and is expressed by the following aspherical formula.

[0100]

Number

[0101] Here, z is the sag amount (mm) in the optical axis direction of the aspherical shape, c is the curvature (1 / mm) on the optical axis AX, k is the conic coefficient, h is the radial interval (mm) from the optical axis OA, and each of A, B, C, ··· is the aspherical coefficient of the 4th term, 6th term, 8th term, ···. 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. Also, the terms from the second term onwards indicate the sag amount of the aspherical component applied on the base sphere. "E±P" in each numerical example means "×10 ±P ".

[0102] Note that each optical system according to each numerical example is a single-focus optical system with a constant focal length (without zooming) and has a configuration that does not perform focusing. That is, the interval between each lens constituting the optical system according to each numerical example is always fixed. Thereby, it is possible to avoid fluctuations in optical performance due to the movement of each lens. However, if necessary, the optical system may be configured to perform at least one of zooming and focusing, and for that purpose, the interval between each lens may be configured to change.

[0103] [Numerical Example 1] Surface Data Surface Number r d nd νd 1 32.135 2.00 1.703 52.4 2 9.864 0.82 3* 5.077 1.64 1.583 59.5 4* 2.297 2.89 5 -18.118 2.00 1.517 52.4 6 4.676 1.99 1.772 49.6 7 -7.949 0.80 8(STO) ∞ 0.90 9 8.286 3.70 1.595 67.7 10 -3.153 0.84 1.847 23.8 11 -7.892 1.78 12 -88.975 3.31 1.583 59.5 13 -34.257 0.93 14 ∞ 0.90 1.560 56.0 15 ∞ 0.50 16(IMG) ∞ Aspherical data Surface number K A B C 3 -2.4958E+00 4.9339E-03 -4.4683E-04 -2.8159E-05 4 -4.7405E-01 7.1885E-03 3.0608E-04 -1.1058E-03 12 0.0000E+00 3.1395E-04 -1.4632E-03 3.6623E-04 13 0.0000E+00 7.5965E-03 -2.8378E-03 3.3669E-04 D E F G 3 4.0165E-06 -1.6918E-07 2.7067E-09 0.0000.E+00 4 2.6062E-04 -2.9008E-05 1.2573E-06 0.0000.E+00 12 -5.0963E-05 3.5310E-06 -9.8030E-08 0.0000.E+00 13 -2.2526E-05 8.0952E-07 -1.2139E-08 0.0000.E+00 Various data Focal length (mm) 4.52 Fno 2.80 Half field angle (deg.) 90.0 Overall length (mm) 25.02 [Numerical Example 2] Surface data Surface number r d nd νd 1 35.117 2.00 1.703 52.4 2 9.996 0.83 3* 4.854 1.80 1.583 59.5 4* 2.290 2.58 5 -19.216 2.01 1.620 36.3 6 4.136 2.12 1.834 37.2 7 -9.984 1.00 8(STO) ∞ 1.00 9 7.606 3.00 1.618 63.3 10 -3.348 0.60 1.847 23.8 11 -7.851 2.20 12 -197.087 3.55 1.583 59.5 13 -33.493 0.87 14 ∞ 1.00 1.560 56.0 15 ∞ 0.50 16(IMG) ∞ Aspherical data Surface number K A B C 3 -2.0555E+00 2.9797E-03 -1.4630E-04 -5.6253E-05 4 -5.8540E-01 4.3897E-03 1.0111E-03 -1.2289E-03 12 0.0000E+00 -4.3508E-04 -1.2523E-03 3.1940E-04 13 0.0000E+00 7.2846E-03 -2.5525E-03 2.9193E-04 D E F G 3 5.5854E-06 -2.1591E-07 3.2717E-09 0.0000.E+00 4 2.7508E-04 -2.9317E-05 1.2539E-06 0.0000.E+00 12 -4.6867E-05 3.3157E-06 -9.3447E-08 0.0000.E+00 13 -1.9271E-05 6.8799E-07 -1.0252E-08 0.0000.E+00 Various data Focal length (mm) 4.54 Fno 2.80 Half angle of view (deg.) 90.0 Overall length (mm) 25.06 [Numerical Example 3] Surface data Surface number r d nd νd 1 26.553 2.00 1.703 52.4 2 8.888 1.14 3* 5.211 2.14 1.583 59.5 4* 2.591 2.46 5 -7.405 1.41 1.517 52.4 6 5.020 1.80 1.804 46.5 7 -8.273 0.70 8 (STO) ∞ 0.80 9 7.685 3.92 1.603 65.4 10 -3.328 0.60 1.847 23.8 11 -8.710 2.15 12 11.575 3.53 1.583 59.5 13 90.605 0.91 14 ∞ 1.00 1.560 56.0 15 ∞ 0.50 16(IMG) ∞ Aspherical data Surface number K A B C 3 -1.9177E+00 2.8036E-03 -2.7397E-04 -3.8091E-05 4 -2.0363E-01 3.7896E-03 -9.3777E-04 -7.0617E-04 12 0.0000E+00 1.6440E-03 -1.2704E-03 2.7718E-04 13 0.0000E+00 1.1407E-02 -3.9015E-03 5.4596E-04 D E F G 3 6.5909E-06 -4.3316E-07 1.3533E-08 -1.6182.E-10 4 2.2359E-04 -2.5177E-05 3.1358E-07 7.1354.E-08 12 -3.4612E-05 2.4731E-06 -9.7237E-08 1.6328.E-09 13 -4.4544E-05 2.1148E-06 -5.4328E-08 5.8556.E-10 Various data Focal length (mm) 4.65 Fno 2.80 Half angle of view (deg.) 90.0 Overall length (mm) 25.05 [Numerical Example 4] Surface data Surface number r d nd νd 1 24.580 2.00 1.703 52.4 2 8.333 1.15 3* 5.148 2.19 1.583 59.5 4* 2.517 2.47 5 -8.445 1.25 1.532 48.8 6 4.618 1.94 1.772 49.6 7 -7.133 0.70 8(STO) ∞ 0.80 9 7.417 4.90 1.618 63.3 10 -3.451 0.60 1.847 23.8 11 -10.662 1.11 12 11.668 3.56 1.583 59.5 13 55.177 1.02 14 ∞ 0.80 1.560 56.0 15 ∞ 0.50 16(IMG) ∞ Aspherical Data Surface Number K A B C 3 -1.2249E+00 2.8781E-03 -2.0560E-04 -3.8740E-05 4 -1.9754E-01 4.2162E-03 1.3282E-03 -1.9463E-03 12 0.0000E+00 8.0272E-04 -1.2465E-03 2.8266E-04 13 0.0000E+00 1.1002E-02 -4.0891E-03 5.6714E-04 D E F G 3 5.1762E-06 -3.1130E-07 9.6101E-09 -1.1626.E-10 4 6.0634E-04 -9.8114E-05 7.7613E-06 -2.4233.E-07 12 -3.4491E-05 2.2398E-06 -7.3186E-08 8.9940.E-10 13 -4.5575E-05 2.1332E-06 -5.3826E-08 5.6431.E-10 Various Data Focal Length (mm) 4.60 Fno 2.80 Half Angle of View (deg.) 90.0 Full length (mm) 24.98 [Numerical Example 5] Surface data Surface number r d nd νd 1 33.346 2.00 1.703 52.4 2 9.829 0.80 3* 4.984 1.77 1.583 59.5 4* 2.263 2.65 5 -18.773 2.20 1.517 52.4 6 4.833 1.97 1.772 49.6 7 -8.058 1.00 8(STO) ∞ 1.00 9 9.035 3.34 1.595 67.7 10 -3.246 0.60 1.847 23.8 11 -7.264 2.06 12 -218.170 3.30 1.583 59.5 13 -65.298 0.94 14 ∞ 0.90 1.560 56.0 15 ∞ 0.50 16(IMG) ∞ Aspherical data Surface number K A B C 3 -1.9613E+00 3.6169E-03 -1.9596E-04 -4.4423E-05 4 -5.2288E-01 5.9504E-03 1.1802E-03 -1.2704E-03 12 0.0000E+00 -1.1895E-04 -1.2350E-03 3.1268E-04 13 0.0000E+00 6.1252E-03 -2.4177E-03 2.8228E-04 D E F G 3 4.2327E-06 -1.5383E-07 2.2392E-09 0.0000.E+00 4 2.7519E-04 -2.9533E-05 1.2734E-06 0.0000.E+00 12 -4.3465E-05 2.9460E-06 -7.9229E-08 0.0000.E+00 13 -1.8804E-05 6.7427E-07 -1.0067E-08 0.0000.E+00 Various data Focal length (mm) 4.53 Fno 2.80 Half angle of view (deg.) 60.0 Overall length (mm) 25.02

[0104]

Table 1

[0105] [Imaging device] FIG. 12 is a schematic diagram of the 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 one 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 is connected to the camera body 73. As shown in FIG. 12, a display unit 74 for displaying an image acquired by the light receiving element 72 may be connected to the camera body 73. As the light receiving element 72, an imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor can be used.

[0106] When the imaging device 70 is used as a distance measuring device, for example, an imaging element (imaging plane phase difference sensor) having pixels capable of splitting a light beam from the object side into two and performing photoelectric conversion can be adopted as the light receiving element 72. When the subject is on the front focal plane of the optical system 71, there is no displacement in the positions of the respective images corresponding to the two split light beams on the image plane of the optical system 71. However, when the subject is at a position other than the front focal plane of the optical system 71, displacement occurs in each image. At this time, since the displacement of each image corresponds to the amount of displacement from the front focal plane of the subject, the distance to the subject can be measured by acquiring the amount and direction of displacement of each image using the imaging plane phase difference sensor.

[0107] 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 systems according to the above-described embodiments are not limited to imaging devices such as digital still cameras, silver halide film cameras, video cameras, in-vehicle cameras, and surveillance cameras, and can be applied to various optical devices such as telescopes, binoculars, projectors (projection devices), and digital copiers.

[0108] [In-vehicle system] FIG. 13(A) is a schematic view of a mobile device 10 and an imaging device 20 (in-vehicle camera) held by the same according to an embodiment of the present invention. FIG. 13(A) 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 assisting a user 40 (such as a driver or a passenger) of the mobile device 10 using an image acquired by the imaging device 20. In the present embodiment, a case where the imaging device 20 is installed so as to image the rear of the mobile device 10 is shown, but the imaging device 20 may be installed so as to image the front or side of the mobile device 10. Further, two or more imaging devices 20 may be installed at two or more locations on the mobile device 10.

[0109] The imaging device 20 includes the optical system 201 and the imaging unit 210 according to any of the above-described embodiments. The optical system 201 is an optical system (a variable-angle lens) in which the imaging magnification is different between a first angle of view (a first field of view) 30 and a second angle of view (a 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 that images an object included in the first angle of view 30 and a second region that images an object included in the second angle of view 31. At this time, the number of pixels per unit angle of view in the first region is larger than the number of pixels per unit angle of view in the second region excluding the first region. In other words, the resolution in the first angle of view (the first region) of the imaging device 20 is higher than the resolution in the second angle of view (the second region).

[0110] Hereinafter, the optical characteristics of the optical system 201 will be described in detail. The left diagram in FIG. 13(B) shows the image height y [mm] at each half angle of view θ [deg.] on the imaging surface of the imaging unit 210 in the form of contour lines. The right diagram in FIG. 13(B) graphically shows 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.

[0111] As shown in FIG. 13(B), the optical system 201 is configured such that the projection characteristics y(θ) are different between an angle of view less than a predetermined half angle of view θa and an angle of view greater than or equal to the half angle of view θa. Therefore, the increase amount (resolution) of the image height y with respect to the half angle of view θ per unit is also different for each angle of view. The local resolution of the optical system 201 is represented by the differential value dy(θ) / dθ of the projection characteristics y(θ) with respect to the half angle of view θ. In the left diagram of FIG. 13(B), it shows that the higher the resolution, the larger the interval between the contour lines of the image height y for each half angle of view θ. Also, in the right diagram of FIG. 13(B), it shows that the higher the resolution, the larger the slope of the graph of the projection characteristics y(θ).

[0112] In the left figure of FIG. 13(B), the first region 201a, which is the central region, corresponds to an angular coverage less than the half angular coverage θa, and the second region 201b, which is the peripheral region, corresponds to an angular coverage of θa or more. The angular coverage less than the half angular coverage θa corresponds to the first angular coverage 30 in FIG. 13(A), and the combined angular coverage of the angular coverage less than the half angular coverage θa and the angular coverage of θa or more corresponds to the second angular coverage 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.

[0113] The optical system 201 is configured such 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 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 above conditional expression (2).

[0114] By satisfying the conditional expression (2), it is possible to achieve a wide-angle conversion 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 that of the central region of a general fisheye lens adopting the orthographic projection method. If it is below the lower limit of the conditional expression (2), compared with the fisheye lens of the orthographic projection method, the resolution in the first region 201a becomes low or the maximum image height becomes large, leading to an increase in the size of the optical system, which is not preferable. If it exceeds the upper limit of the conditional expression (2), the resolution in the first region 201a becomes too high, making it difficult to achieve a wide-angle coverage equivalent to that of the fisheye lens of the orthographic projection method or to maintain good optical performance, which is not preferable.

[0115] 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 as compared with the second region 201b. Therefore, good visibility can be obtained by setting the first region 201a (first viewing angle 30) as the region of interest of the user 40. For example, when the imaging device 20 is arranged at the rear part of the moving device 10 as shown in Fig. 13(A), by displaying the image corresponding to the first viewing angle 30 on the electronic rearview mirror, a natural perspective can be obtained when the user 40 gazes at a vehicle behind or the like. On the other hand, for the second region 201b (second viewing angle 31), it corresponds to a wide viewing angle including the first viewing angle 30. Therefore, for example, when the moving device 10 is moving backward, by displaying the image corresponding to the second viewing angle 31 on the in-vehicle display, driving assistance for the user 40 can be provided.

[0116] Fig. 14 is a functional block diagram for explaining a configuration example of the in-vehicle system 2 according to the present embodiment. The in-vehicle system 2 is a system for displaying an image obtained by an imaging device 20 installed behind the moving device 10 to the user 40. The in-vehicle system 2 includes an imaging device 20, a processing device 220, and a display device (display unit) 230. The imaging device 20 has an optical system 201 and an imaging unit 210 as described above. The imaging unit 210 includes an imaging element 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 it to the processing device 220.

[0117] 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), a reverse gear detection unit 225 (second detection unit), and a display angle 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 operations of each component based on a computer program. At least one component in the processing device 220 may be implemented by hardware such as an ASIC (Application Specific Integrated Circuit) or a PLA (Programmable Logic Array).

[0118] 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 the 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 the image when it is displayed on the display device 230, and also improves the detection rate of the rear vehicle in the rear vehicle distance detection unit 223. Note that the distortion correction may not be performed on the imaging data corresponding to the first region 201a. The image processing unit 221 outputs the image data generated by executing the above-described image processing to the display angle change unit 222 and the rear vehicle distance detection unit 223.

[0119] The rear vehicle distance detection unit 223 uses the image data output from the image processing unit 221 to obtain information regarding the distance to a rear vehicle included in the image data corresponding to a range that does not include the first angle of view 30 in the second angle of view 31. For example, the rear vehicle distance detection unit 223 can detect a rear vehicle based on the image data corresponding to the second region 201b in 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 the calculated distance information to the display angle determination unit 224.

[0120] Furthermore, the rear vehicle distance detection unit 223 may determine the vehicle type of the rear vehicle based on data regarding feature information such as the shape and color for each vehicle type, 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 regarding the vehicle type of the rear vehicle to the display angle determination unit 224. The reverse gear detection unit 225 detects whether the transmission of the moving device 10 (own vehicle) is in the reverse gear, and outputs the detection result to the display angle determination unit 224.

[0121] Based on the output from at least one of the rear vehicle distance detection unit 223 or the reverse gear detection unit 225, the display angle determination unit 224 determines whether to set the angle of the image to be displayed on the display device 230 (display angle) to either the first angle 30 or the second angle 31. Then, the display angle determination unit 224 outputs to the display angle change unit 222 according to the determination result. For example, when the value of the distance in the distance information is equal to or less than a certain threshold value (for example, 3 m), the display angle determination unit 224 can determine to set the display angle to the second angle 31, and when it becomes larger than the threshold value, determine to set the display angle to the first angle 30. Alternatively, when notified by the reverse gear detection unit 225 that the transmission of the moving device 10 is in the reverse gear, the display angle determination unit 224 can determine to set the display angle to the second angle 31. Also, when not in the reverse gear, the display angle determination unit 224 can determine to set the display angle to the first angle 30.

[0122] Furthermore, when the transmission of the mobile device 10 is in the reverse gear, the display angle determination unit 224 can determine that the display angle is set to the second angle 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 the reverse gear, the display angle determination unit 224 can determine that the display angle is determined according to the detection result of the rear vehicle distance detection unit 223. Note that the display angle determination unit 224 may change the determination criteria for angle change 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, since the braking distance is longer than that of a normal vehicle, it is desirable to set the above-mentioned threshold value longer (for example, 10 m) than that of a normal vehicle.

[0123] The user setting change unit 226 is for allowing the user 40 to change the determination criteria for whether the display angle is changed to the second angle 31 by the display angle determination unit 224. The determination criteria set (changed) by the user 40 are input from the user setting change unit 226 to the display angle determination unit 224.

[0124] The display angle change unit 222 generates a display image to be displayed on the display device 230 according to the determination result of the display angle determination unit 224. For example, when it is determined that the first angle 30 is to be set, the display angle change unit 222 cuts out a rectangular included angle image (the first image) from the image data corresponding to the first angle 30 and outputs it to the display device 230. Also, when there is a rear vehicle satisfying a predetermined condition in the image data corresponding to the second angle 31, the display angle change unit 222 outputs an image (the second image) including the rear vehicle to the display device 230. Note that the second image may include an image corresponding to the first area 201a. The display angle change unit 222 functions as a display control unit that performs display control to switch between a first display state in which the display device 230 displays the first image and a second display state in which the display device 230 displays the second image.

[0125] The cropping of the image by the viewing 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 therefrom. Note that the region corresponding to the first image in the image data is a rectangular region in the first viewing angle 30 corresponding to the first region 201a. Also, the region corresponding to the second image in the image data is a rectangular region including the rear vehicle in the second viewing angle 31 corresponding to the second region 201b.

[0126] The display device 230 has a display unit such as a liquid crystal display or an organic EL, and displays the display image output from the viewing angle changing unit 222. For example, the display device 230 has a first display unit as an electronic rearview mirror disposed above the windshield (front glass) of the moving device 10, and a second display unit as an operation panel (monitor) disposed below the windshield of the moving device 10. According to this configuration, the first image and the second image generated from the above-described image data can be respectively displayed on the first display unit and the second display unit. The first display unit may be configured to be able to be used as a mirror when not used as a display, for example, by including a half mirror or the like. The second display unit may also serve as a display of a navigation system or an audio system, for example.

[0127] Note that the moving device 10 is not limited to a vehicle such as an automobile, and may be a moving body such as a ship, an aircraft, an industrial robot, or a drone, for example. Also, although the in-vehicle system 2 according to the present embodiment is used for displaying an image to the user 40, it is not limited thereto and may be used for driving support such as cruise control (including a function of following the vehicle speed) and automatic driving. Furthermore, the in-vehicle system 2 is not limited to a moving device and can be applied to various devices that utilize object recognition such as an advanced road traffic system (ITS).

[0128] [Modification Example] The preferred embodiments and examples of the present invention have been described above. However, 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 thereof.

[0129] For example, the optical systems according to the above-described examples are assumed to be used in the visible range and are configured to perform good aberration correction over the entire visible range. However, the wavelength range for performing aberration correction may be changed as necessary. For example, each optical system may be configured to perform aberration correction only in a specific wavelength range within the visible range, or may be configured to perform aberration correction in a wavelength range in the infrared range outside the visible range.

[0130] In addition, in the in-vehicle system 2 described above, a distance measuring device as described above may be adopted 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 the information on the distance to the object acquired by the imaging device 20. Further, a stereo camera including two imaging units 210 may be adopted 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 same processing as described above can be performed by using the two image data. However, if the difference in the imaging time by each imaging unit is known, it is not necessary to synchronize each imaging unit.

[0131] The disclosure of each example includes the following configurations. (Configuration 1) An optical system composed of a front group, an aperture stop, and a rear group arranged in order from the object side to the image side, The front group has a first lens with a negative refractive power, a second lens including an aspherical surface, and a first cemented lens including a third lens with a negative refractive power and a fourth lens with a positive refractive power, which are cemented to each other, arranged in order from the object side to the image side, The rear group has a fifth lens with a positive refractive power, a sixth lens with a negative refractive power, and a seventh lens, arranged in order from the object side to the image side, The second lens has a negative refractive power on the optical axis, The object side surface of the second lens is convex on the optical axis, When the refractive index of the third lens with respect to the d-line is N3, the refractive index of the fourth lens with respect to the d-line is N4, the focal length of the optical system is f, and the focal length of the third lens is f3, 0.20 < N4 - N3 < 0.50 -1.70 < f3 / f < -1.10 An optical system characterized by satisfying the conditional expression. (Configuration 2) When the half field angle of the optical system is θ [deg.], the projection characteristic representing the relationship between the half field angle θ and the image height y is y(θ), and the maximum half field angle of the optical system is θmax, 1.00 < f × sin(θmax) / y(θmax) ≤ 1.90 The optical system according to Configuration 1, characterized by satisfying the conditional expression. (Configuration 3) When the half field angle of the optical system is θ [deg.], the projection characteristic representing the relationship between the half field angle θ and the image height y is y(θ), and the maximum half field angle of the optical system is θmax, 0.65 < y(θmax / 2) / y(θmax) < 0.85 The optical system according to Configuration 1 or 2, characterized by satisfying the conditional expression. (Configuration 4) The optical system according to any one of Configurations 1 to 3, characterized in that the object side surface of the second lens is an aspherical surface having an inflection point in a cross section including the optical axis. (Configuration 5) When the focal length of the fourth lens is f4, -1.80 < f3 / f4 < -1.30 The optical system according to any one of Configurations 1 to 4, characterized by satisfying the conditional expression. (Configuration 6) The optical system according to any one of Configurations 1 to 5, characterized in that both the front group and the rear group have positive refractive power. (Configuration 7) When the Abbe number of the third lens with respect to the d-line is ν3 and the Abbe number of the fourth lens with respect to the d-line is ν4, |ν4 - ν3| < 10 The optical system according to any one of Configurations 1 to 6, characterized by satisfying the following conditional expression. (Configuration 8) When the radius of curvature of the joint surface of the first joint lens is Rc1 and the distance on the optical axis from the joint surface of the first joint lens to the aperture stop is dc1, 1.20 < Rc1 / dc1 < 2.10 The optical system according to any one of Configurations 1 to 7, characterized by satisfying the following conditional expression. (Configuration 9) When the focal length of the first lens is f1, -5.00 < f1 / f < -3.00 The optical system according to any one of Configurations 1 to 8, characterized by satisfying the following conditional expression. (Configuration 10) The fifth lens and the sixth lens are a second joint lens joined to each other, When the radius of curvature of the joint surface of the second joint lens is Rc2 and the distance on the optical axis from the aperture stop to the joint surface of the second joint lens is dc2, -0.90 < Rc2 / dc2 < -0.50 The optical system according to any one of Configurations 1 to 9, characterized by satisfying the following conditional expression. (Configuration 11) When the radius of curvature of the object side surface of the third lens is R31, -0.7 < f / R31 < -0.2 The optical system according to any one of Configurations 1 to 10, characterized by satisfying the following conditional expression. (Configuration 12) The seventh lens is an aspherical lens and has a positive refractive power on the optical axis. The imaging device according to any one of Configurations 1 to 11. (Configuration 13) An imaging device comprising the optical system according to any one of Configurations 1 to 12 and an imaging element that images an object through the optical system. (Configuration 14) An in-vehicle system comprising the imaging device according to Configuration 13 and a display device that displays an image obtained based on the output of the imaging device. (Configuration 15) The display device includes a first display unit that displays a first image corresponding to a first viewing angle among the images, and a second display unit that displays a second image corresponding to a second viewing angle including the first viewing angle. The in-vehicle system according to Configuration 14 is characterized by this. (Configuration 16) A mobile device comprising the imaging device according to Configuration 13, characterized in that the imaging device can be held and moved.

Explanation of Signs

[0132] 100, 200, 300, 400, 500 Optical System CL1 First Bonding Lens G1 Front Group G2 Rear Group L1 First Lens L2 Second Lens L3 Third Lens L4 Fourth Lens L5 Fifth Lens L6 Sixth Lens L7 Seventh Lens STO Aperture Stop

Claims

1. An optical system composed of a front group, an aperture stop, and a rear group, arranged in order from the object side to the image side, The front group has, arranged in order from the object side to the image side, a first lens with a negative refractive power, a second lens including an aspherical surface, and a first cemented lens including a third lens with a negative refractive power and a fourth lens with a positive refractive power, which are cemented to each other. The rear group has, arranged in order from the object side to the image side, a fifth lens with a positive refractive power, a sixth lens with a negative refractive power, and a seventh lens. The second lens has a negative refractive power on the optical axis. The object-side surface of the second lens is convex on the optical axis. When the refractive index of the third lens with respect to the d-line is N3, the refractive index of the fourth lens with respect to the d-line is N4, the focal length of the optical system is f, and the focal length of the third lens is f3, 0.20 < N4 - N3 < 0.50 -1.70 < f3 / f < -1.10 An optical system characterized by satisfying the conditional expression.

2. When the half field angle of the optical system is θ [deg.], the projection characteristic representing the relationship between the half field angle θ and the image height y is y(θ), and the maximum half field angle of the optical system is θmax, 1.00 < f × sin(θmax) / y(θmax) ≤ 1.90 The optical system according to claim 1, characterized by satisfying the conditional expression.

3. When the half field angle of the optical system is θ [deg.], the projection characteristic representing the relationship between the half field angle θ and the image height y is y(θ), and the maximum half field angle of the optical system is θmax, 0.65 < y(θmax / 2) / y(θmax) < 0.85 The optical system according to claim 1, characterized by satisfying the conditional expression.

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

5. When the focal length of the fourth lens is f4, -1.80 < f3 / f4 < -1.30 The optical system according to claim 1, characterized in that the conditional expression is satisfied.

6. The optical system according to any one of claims 1 to 5, characterized in that both the front group and the rear group have positive refractive power.

7. When the Abbe number of the third lens based on the d-line is ν3 and the Abbe number of the fourth lens based on the d-line is ν4, |ν4 - ν3| < 10 The optical system according to any one of claims 1 to 5, characterized in that the conditional expression is satisfied.

8. When the radius of curvature of the joint surface of the first joint lens is Rc1 and the distance on the optical axis from the joint surface of the first joint lens to the aperture stop is dc1, 1.20 < Rc1 / dc1 < 2.10 The optical system according to any one of claims 1 to 5, characterized in that the conditional expression is satisfied.

9. When the focal length of the first lens is f1, -5.00 < f1 / f < -3.00 The optical system according to any one of claims 1 to 5, characterized in that the conditional expression is satisfied.

10. The fifth lens and the sixth lens are the second joint lens joined to each other. When the radius of curvature of the joint surface of the second joint lens is Rc2 and the distance on the optical axis from the aperture stop to the joint surface of the second joint lens is dc2, -0.90 < Rc2 / dc2 < -0.50 The optical system according to any one of claims 1 to 5, characterized in that the conditional expression is satisfied.

11. When the radius of curvature of the object side surface of the third lens is R31, -0.7 < f / R31 < -0.2 The optical system according to any one of claims 1 to 5, characterized by satisfying the conditional expression:

12. The optical system according to any one of claims 1 to 5, characterized in that the seventh lens includes an aspherical surface and has a positive refractive power on the optical axis.

13. An imaging device comprising the optical system according to any one of claims 1 to 5, and an imaging element that images an object through the optical system.

14. An in-vehicle system comprising the imaging device according to claim 13, and a display device that displays an image obtained based on the output of the imaging device.

15. The in-vehicle system according to claim 14, characterized in that the display device includes 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 including the first angle of view.

16. A mobile device comprising the imaging device according to claim 13, and being movable while holding the imaging device.

Images