Imaging lens and imaging device

Abstract

To provide an imaging lens having excellent optical performance while being compact and light-weight and an imaging apparatus including the imaging lens.SOLUTION: The imaging lens comprises, in order from an object side, a first lens group having refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power. In focusing, the second lens group is moved. The second lens group includes a diaphragm and at least three negative lenses. The imaging lens satisfies a predetermined conditional expression.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology of the present disclosure relates to an imaging lens and an imaging device. [Background technology]

[0002] 2. Description of the Related Art Conventionally, imaging lenses that can be used in imaging devices such as digital cameras are known from the following Patent Documents 1 and 2. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-156431 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-146607 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for imaging lenses that are small and lightweight yet have good optical performance, and the level of these requirements is increasing year by year.

[0005] An object of the present disclosure is to provide an imaging lens that is small and lightweight yet has good optical performance, and an imaging device that includes this imaging lens. [Means for solving the problem]

[0006] An imaging lens according to one embodiment of the present disclosure includes, in order from the object side to the image side, a first lens group having refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power, and during focusing, the first lens group and the third lens group are fixed with respect to an image plane, and the second lens group moves along an optical axis, and the second lens group includes a diaphragm and at least three negative lenses, 5 <TTL 2 / (f 2 ×tanωm)<15 (1) The following conditional expression (1) is satisfied. The symbols in conditional expression (1) are defined as follows: TTL is the sum of the distance on the optical axis from the lens surface in the first lens group closest to the object to the lens surface in the third lens group closest to the image, and the back focal length in air equivalent of the entire system. f is the focal length of the entire system when focused on an object at infinity. ωm is the maximum half angle of view when focused on an object at infinity.

[0007] When the back focus of the entire system in terms of air equivalent distance is Bf, the imaging lens of the above embodiment has the following characteristics: 0.1 <Bf / f<0.6 (2) It is preferable to satisfy conditional expression (2) below.

[0008] The first lens group may be configured to be a lens group having negative refractive power.

[0009] When the focal length of the second lens group is f2 and the focal length of the third lens group is f3, the imaging lens of the above aspect has the following characteristics: -18.5 <f3 / f2<-1 (3) It is preferable to satisfy conditional expression (3) below.

[0010] When the refractive index of the positive lens closest to the object among the positive lenses in the second lens group is N2po for the d-line, and the refractive index of the positive lens closest to the image among the positive lenses in the second lens group is N2pi for the d-line, the imaging lens of the above aspect has the following properties: 1.86<(N2po+N2pi) / 2<2.2 (4) It is preferable to satisfy conditional expression (4) below.

[0011] When the Abbe number based on the d-line of the positive lens closest to the object among the positive lenses in the second lens group is ν2po, and the Abbe number based on the d-line of the positive lens closest to the image among the positive lenses in the second lens group is ν2pi, the imaging lens of the above aspect has the following properties: 15<(ν2po+ν2pi) / 2<40 (5) It is preferable to satisfy conditional expression (5) below.

[0012] When the focal length of the first lens group is f1 and the focal length of the third lens group is f3, the imaging lens of the above aspect has the following characteristics: 1.5 <f3 / f1<3.5 (6) It is preferable to satisfy conditional expression (6) below.

[0013] When the focal length of the entire system is in focus on an object at infinity, f is the focal length of the first lens group, and f1 is the focal length of the first lens group. In the imaging lens of the above aspect, -0.35 <f / f1<-0.08 (7) It is preferable to satisfy conditional expression (7) below.

[0014] Of the positive lenses in the second lens group, the positive lens closest to the image side is preferably cemented with a negative lens.

[0015] Of the positive lenses in the second lens group, the positive lens closest to the object side is preferably a meniscus lens whose image-side surface is concave.

[0016] The second lens group preferably includes at least one aspherical lens surface, and the third lens group preferably includes at least one aspherical lens surface.

[0017] It is preferable that the third lens group includes a cemented lens formed by cementing a positive lens and a negative lens together in this order from the object side, and a negative lens arranged closest to the image side and having a concave surface on the object side. In such a configuration, when the Abbe number based on the d-line of the positive lens in the cemented lens of the third lens group is v3p and the Abbe number based on the d-line of the negative lens in the cemented lens of the third lens group is v3n, the imaging lens of the above aspect has the following properties: 1<ν3p-ν3n<10 (8) It is preferable to satisfy conditional expression (8) below.

[0018] When the distance on the optical axis from the lens surface of the third lens group closest to the object side to the lens surface of the third lens group closest to the image side is DG3 and the back focus in terms of the air-equivalent distance of the entire system is Bf, the imaging lens of the above aspect has the following characteristics: 0.85 <DG3 / Bf<2 (9) It is preferable to satisfy conditional expression (9) below.

[0019] The lens closest to the object in the first lens group may be configured to be a negative lens with a concave surface on the object side. In such a configuration, it is preferable that a positive lens is arranged adjacent to the image side of the negative lens closest to the object in the first lens group. Furthermore, when a positive lens is arranged adjacent to the image side of the negative lens closest to the object in the first lens group, it is preferable that the negative lens closest to the object in the first lens group is a biconcave lens.

[0020] An imaging device according to another aspect of the present disclosure includes the imaging lens according to the above aspect of the present disclosure.

[0021] In this specification, the terms "consisting of" and "consisting of" are intended to mean that, in addition to the listed components, other components may also be included, such as lenses that have substantially no refractive power, optical elements other than lenses, such as apertures, filters, and cover glasses, and mechanical parts, such as lens flanges, lens barrels, image sensors, and image stabilization mechanisms.

[0022] In this specification, "a group having positive refractive power" means that the group as a whole has positive refractive power. Similarly, "a group having negative refractive power" means that the group as a whole has negative refractive power. "A lens having positive refractive power" and "a positive lens" are synonymous. "A lens having negative refractive power" and "a negative lens" are synonymous. In this specification, the "first lens group" and "third lens group" are not limited to configurations consisting of multiple lenses, and may be configured to consist of only one lens.

[0023] A "single lens" refers to a single lens that is not cemented. However, a compound aspherical lens (a lens that is integrally constructed with a spherical lens and an aspherical film formed on that spherical lens, functioning as a single aspherical lens as a whole) is not considered a cemented lens, but is treated as a single lens. Unless otherwise specified, the sign of the refractive power and surface shape of lenses that include aspherical surfaces are those in the paraxial region.

[0024] In this specification, "total system" refers to the imaging lens. The "focal length" used in the conditional expressions is the paraxial focal length. The "distance on the optical axis" used in the conditional expressions is the geometric distance unless otherwise specified. The values ​​used in the conditional expressions are values ​​based on the d-line when focused on an object at infinity unless otherwise specified. The "d-line," "C-line," and "F-line" used in this specification are emission lines, and the wavelength of the d-line is treated as 587.56 nm (nanometers), the wavelength of the C-line is treated as 656.27 nm (nanometers), and the wavelength of the F-line is treated as 486.13 nm (nanometers). [Effects of the Invention]

[0025] According to the present disclosure, it is possible to provide an imaging lens that is small and lightweight yet has good optical performance, and an imaging device that includes this imaging lens. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a cross-sectional view showing the configuration of an imaging lens according to one embodiment, corresponding to the imaging lens of Example 1. FIG. [Figure 2] 2A to 2C are cross-sectional views showing the configuration and light beams of the imaging lens of FIG. 1 in each focus state. [Figure 3] 3A to 3C are diagrams showing various aberrations of the imaging lens of Example 1. [Figure 4] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens according to a second embodiment. [Figure 5] 10A to 10C are diagrams showing various aberrations of the imaging lens of Example 2. [Figure 6] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens according to a third embodiment. [Figure 7] 10A to 10C are diagrams showing various aberrations of the imaging lens of Example 3. [Figure 8] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens according to a fourth embodiment. [Figure 9] 10A to 10C are diagrams showing various aberrations of the imaging lens of Example 4. [Figure 10] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens according to a fifth embodiment. [Figure 11] 10A to 10C are diagrams showing various aberrations of the imaging lens of Example 5. [Figure 12] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens according to a sixth embodiment. [Figure 13] 10A to 10C are diagrams showing various aberrations of the imaging lens of Example 6. [Figure 14] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens according to a seventh embodiment. [Figure 15] 13A to 13C are cross-sectional views showing the configuration and light beams in each focus state of the imaging lens of Example 7. [Figure 16] 10A to 10C are diagrams showing various aberrations of the imaging lens of Example 7. [Figure 17] FIG. 13 is a cross-sectional view showing the configuration of an imaging lens according to an eighth embodiment. [Figure 18] 13A to 13C are diagrams showing various aberrations of the imaging lens of Example 8. [Figure 19] FIG. 13 is a cross-sectional view showing the configuration of an imaging lens according to a ninth embodiment. [Figure 20] 13A to 13C are diagrams showing various aberrations of the imaging lens of Example 9. [Figure 21] FIG. 20 is a cross-sectional view showing the configuration of an imaging lens according to a tenth embodiment. [Figure 22] 20A to 20C are diagrams showing various aberrations of the imaging lens of Example 10. [Figure 23] FIG. 20 is a cross-sectional view showing the configuration of an imaging lens according to an eleventh embodiment. [Figure 24] 13A to 13C are diagrams showing various aberrations of the imaging lens of Example 11. [Figure 25] 1 is a perspective view of the front side of an imaging device according to an embodiment. [Figure 26] FIG. 2 is a perspective view of the rear side of the imaging device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0028] FIG. 1 shows a cross-sectional view of the configuration of an imaging lens according to an embodiment of the present disclosure when focused on an object at infinity. FIG. 2 shows cross-sectional views of the configuration and light beams of the imaging lens in each focus state of FIG. 1. In FIG. 2, the upper row labeled "infinity" shows a state focused on an object at infinity, and the lower row labeled "closest" shows a state focused on a closest object, 0.3 m (meters) from the lens surface closest to the object. Note that in this specification, an object at infinity is referred to as an "infinite object," and an object at the closest distance is referred to as a "closest object." The upper row of FIG. 2 shows an axial light beam 2 and a light beam 3 with a maximum half angle of view ωm when focused on an object at infinity. The lower row of FIG. 2 shows an axial light beam and a light beam with a maximum half angle of view ωm when focused on a closest object. The example shown in FIGS. 1 and 2 corresponds to the imaging lens of Example 1, which will be described later. 1 and 2, the left side is the object side and the right side is the image side. The following description will be mainly made with reference to FIG.

[0029] FIG. 1 shows an example in which a parallel-plate optical member PP is arranged between the imaging lens and the image plane Sim, assuming that the imaging lens is applied to an imaging device. The optical member PP is a member that is assumed to include various filters and / or cover glass. The various filters are low-pass filters, infrared cut filters, and / or filters that cut off specific wavelength ranges. The optical member PP is a member that does not have refractive power. It is also possible to configure an imaging device without the optical member PP.

[0030] The imaging lens of the present disclosure comprises, in order from the object side to the image side along the optical axis Z, a first lens group G1 having refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. During focusing, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim, and the second lens group G2 moves along the optical axis Z. In this specification, the group that moves along the optical axis Z during focusing is referred to as the focus group. Focusing is achieved by moving the focus group. In the imaging lens of the present disclosure, the second lens group G2 is the focus group.

[0031] A configuration in which the first lens group G1 is fixed during focusing is advantageous for dustproof and drip-proof properties. A configuration in which the third lens group G3 is fixed during focusing means that the third lens group G3 moves relative to the second lens group G2 during focusing, effectively suppressing fluctuations in field curvature that accompany focusing. A configuration in which only the second lens group G2 moves during focusing allows the focus group to be made smaller and lighter than a configuration in which other groups move in addition to the second lens group G2, and this also reduces the load on the drive system.

[0032] The second lens group G2 and the third lens group G3 have refractive powers of opposite signs. By having the third lens group G3 have negative refractive power, the positive refractive power of the second lens group G2 can be strengthened, which contributes to shortening the movement distance of the focus group during focusing and increasing the focusing speed. The sign of the refractive power of the first lens group G1 may be negative or positive. Configuring the first lens group G1 to have negative refractive power is advantageous for achieving a wider angle of view. Configuring the first lens group G1 to have positive refractive power is advantageous for achieving a smaller size.

[0033] As an example, each lens group in the imaging lens in FIG. 1 is configured as follows: The first lens group G1, from the object side to the image side, consists of two lenses, lenses L11 and L12. The second lens group G2, from the object side to the image side, consists of three lenses, lenses L21 to L23, an aperture stop St, and five lenses, lenses L24 to L28. Note that the aperture stop St in FIG. 1 does not indicate its size or shape, but rather its position in the optical axis direction. The third lens group G3, from the object side to the image side, consists of four lenses, lenses L31 to L34. The left-pointing arrow below the second lens group G2 in FIG. 1 indicates that the second lens group G2 is a focus group that moves toward the object side when focusing from an object at infinity to the closest object.

[0034] In this specification, a "lens group" is a component of an imaging lens that includes at least one lens and is separated by an air gap that changes during focusing. During focusing, each lens group is moved or fixed, and the mutual spacing between lenses within each lens group does not change. In other words, in this specification, a group in which the spacing between adjacent groups changes during focusing, but the total spacing between adjacent lenses within itself does not change, is defined as one lens group.

[0035] The first lens group G1 preferably includes one negative lens and one positive lens. This is advantageous for correcting chromatic aberration. The first lens group G1 may also be configured with one negative lens and one positive lens. This is advantageous for correcting chromatic aberration and for compactness.

[0036] The second lens group G2 preferably includes an aperture stop St and at least three negative lenses. A configuration in which the second lens group G2 includes an aperture stop St is advantageous for achieving a compact size in the radial direction compared to a configuration in which the first lens group G1 or the third lens group G3 includes an aperture stop St. Including at least three negative lenses in the second lens group G2 is advantageous for achieving good correction of various aberrations.

[0037] Of the positive lenses in the second lens group G2, the positive lens closest to the object side may be configured as a meniscus lens with a concave surface on the image side, which is advantageous for suppressing the occurrence of spherical aberration.

[0038] Of the positive lenses in the second lens group G2, the positive lens closest to the image side is preferably cemented with a negative lens. By forming a cemented lens with these positive and negative lenses, it is possible to effectively correct axial chromatic aberration while reducing the axial thickness of the second lens group G2.

[0039] The second lens group G2 preferably includes at least one aspherical lens surface, and by using an aspherical surface in the second lens group G2, spherical aberration can be effectively corrected.

[0040] The third lens group G3 preferably includes a cemented lens formed by cementing a positive lens and a negative lens together in that order from the object side, and a negative lens positioned closest to the image side and having a concave surface facing the object side. By locating the cemented lens in the third lens group G3, where the height from the optical axis Z of the off-axial light beam is high, it is possible to effectively correct lateral chromatic aberration while reducing the axial thickness of the third lens group G3. Furthermore, by locating a negative lens with its concave surface facing the object side closest to the image side, it is possible to reduce the Petzval sum, which is advantageous for suppressing the occurrence of field curvature.

[0041] The third lens group G3 preferably includes at least one aspherical lens surface, which effectively suppresses fluctuations in field curvature and distortion caused by focusing.

[0042] A preferred configuration of the imaging lens of the present disclosure in relation to the conditional expressions will be described below. In the following description of the conditional expressions, "the imaging lens of the present disclosure" will be simply referred to as "the imaging lens" to avoid redundancy.

[0043] It is preferable that the imaging lens satisfy the following conditional expression (1). Here, TTL is the sum of the distance on the optical axis from the lens surface of the first lens group G1 closest to the object to the lens surface of the third lens group G3 closest to the image and the back focus in terms of the air equivalent distance of the entire system. f is the focal length of the entire system when focused on an object at infinity. ωm is the maximum half angle of view when focused on an object at infinity. In conditional expression (1), tan is the tangent. Ensuring that the corresponding value of conditional expression (1) is not equal to or less than the lower limit is advantageous for ensuring good optical performance. Ensuring that the corresponding value of conditional expression (1) is not equal to or greater than the upper limit is advantageous for reducing the size of the lens system. This is particularly advantageous for configuring a lens system with a short overall optical length relative to the image size. In order to obtain better characteristics, it is more preferable that the imaging lens satisfy the following conditional expression (1-1), and it is even more preferable for it to satisfy the following conditional expression (1-2). 5 <TTL 2 / (f 2 ×tanωm)<15 (1) 7.2 <TTL 2 / (f 2 ×tanωm)<11.8 (1-1) 8 <TTL 2 / (f 2 ×tanωm)<10 (1-2)

[0044] If the back focal length of the entire system in air equivalent distance is Bf and the focal length of the entire system when focused on an object at infinity is f, it is preferable that the imaging lens satisfy the following conditional expression (2). Ensuring that the corresponding value of conditional expression (2) does not become equal to or less than the lower limit is advantageous for ensuring an appropriate back focal length. This is particularly advantageous for ensuring a back focal length when the imaging lens is used as an interchangeable lens. Ensuring that the corresponding value of conditional expression (2) does not become equal to or greater than the upper limit is advantageous for shortening the overall optical length. In order to obtain better characteristics, it is more preferable that the imaging lens satisfy the following conditional expression (2-1), and it is even more preferable for the imaging lens to satisfy the following conditional expression (2-2). 0.1 <Bf / f<0.6 (2) 0.2 <Bf / f<0.5 (2-1) 0.3 <Bf / f<0.45 (2-2)

[0045] Assuming that the focal length of the second lens group G2 is f2 and the focal length of the third lens group G3 is f3, it is preferable that the imaging lens satisfy the following conditional expression (3). By ensuring that the corresponding value of conditional expression (3) is not below the lower limit, the refractive power of the second lens group G2 does not become too strong, which is advantageous for simultaneously correcting spherical aberration and curvature of field associated with focusing. By ensuring that the corresponding value of conditional expression (3) is not above the upper limit, the refractive power of the third lens group G3 does not become too strong, which prevents the angle change between the light rays entering the third lens group G3 and the light rays emerging from the third lens group G3 from becoming too steep. This is advantageous for suppressing breathing. To obtain better characteristics, it is more preferable that the imaging lens satisfy the following conditional expression (3-1), and even more preferable that the imaging lens satisfy the following conditional expression (3-2). -18.5 <f3 / f2<-1 (3) -17.5 <f3 / f2<-7 (3-1) -16.5 <f3 / f2<-8 (3-2)

[0046] It is preferable that the imaging lens satisfy the following conditional expression (4). Here, the refractive index of the positive lens closest to the object in the second lens group G2 at the d-line is N2po. The refractive index of the positive lens closest to the image in the second lens group G2 at the d-line is N2pi. By ensuring that the corresponding value of conditional expression (4) is not below the lower limit, the absolute value of the radius of curvature of the positive lens, which is required to have particularly strong refractive power, does not become too small, which is advantageous for reducing spherical aberration. It also makes it easier to suppress the Petzval sum, which is advantageous for reducing field curvature. Generally, optical materials with high refractive indices have small Abbe numbers. Therefore, by ensuring that the corresponding value of conditional expression (4) is not above the upper limit, it becomes easier to select a material with an appropriate Abbe number, which is advantageous for correcting axial chromatic aberration. To obtain better characteristics, it is more preferable that the imaging lens satisfy the following conditional expression (4-1), and even more preferable that the imaging lens satisfy the following conditional expression (4-2). 1.86<(N2po+N2pi) / 2<2.2 (4) 1.9<(N2po+N2pi) / 2<2.15 (4-1) 1.92<(N2po+N2pi) / 2<2.1 (4-2)

[0047] It is preferable that the imaging lens satisfy the following conditional expression (5). Here, the Abbe number based on the d-line of the positive lens in the second lens group G2 that is closest to the object is denoted as ν2po. The Abbe number based on the d-line of the positive lens in the second lens group G2 that is closest to the image is denoted as ν2pi. By ensuring that the corresponding value of conditional expression (5) is not equal to or less than the lower limit, the occurrence of longitudinal chromatic aberration can be suppressed, which is advantageous for correcting longitudinal chromatic aberration and other aberrations. By ensuring that the corresponding value of conditional expression (5) is not equal to or greater than the upper limit, it becomes easier to select an appropriate material. In order to obtain better characteristics, it is more preferable that the imaging lens satisfy the following conditional expression (5-1), and it is even more preferable that the imaging lens satisfy the following conditional expression (5-2). 15<(ν2po+ν2pi) / 2<40 (5) 20<(ν2po+ν2pi) / 2<35 (5-1) 25<(ν2po+ν2pi) / 2<30 (5-2)

[0048] Assuming that the focal length of the first lens group G1 is f1 and the focal length of the third lens group G3 is f3, it is preferable that the imaging lens satisfy the following conditional expression (6). By ensuring that the corresponding value of conditional expression (6) is not below the lower limit, the negative refractive power of the first lens group G1 does not become too weak, and the positive refractive power of the second lens group G2 does not become relatively too weak. This makes it possible to reduce the amount of movement of the focus group during focusing, which is advantageous for compactness. By ensuring that the corresponding value of conditional expression (6) is not above the upper limit, the negative refractive power of the first lens group G1 does not become too strong, and this makes it possible to prevent the overall optical length from becoming too long. Furthermore, by ensuring that the corresponding value of conditional expression (6) is not above the upper limit, the negative refractive power of the first lens group G1 does not become too strong, and the positive refractive power of the second lens group G2 does not become relatively too strong. This helps to prevent the angle between the light beam entering the second lens group G2 and the light beam emerging from the second lens group G2 from changing too sharply, which is advantageous for suppressing breathing. To obtain better characteristics, it is more preferable that the imaging lens satisfy the following conditional expression (6-1), and it is even more preferable that the imaging lens satisfy the following conditional expression (6-2): 1.5 <f3 / f1<3.5 (6) 1.6 <f3 / f1<3.4 (6-1) 1.7 <f3 / f1<3.3 (6-2)

[0049] When the focal length of the entire system is f and the focal length of the first lens group G1 is f1 when focused on an object at infinity, it is preferable that the imaging lens satisfy the following conditional expression (7): By ensuring that the corresponding value of conditional expression (7) is not below the lower limit, the negative refractive power of the first lens group G1 does not become too strong, thereby preventing an increase in the overall optical length. Furthermore, by ensuring that the corresponding value of conditional expression (7) is not below the lower limit, the negative refractive power of the first lens group G1 does not become too strong, thereby preventing the positive refractive power of the second lens group G2 from becoming too strong relatively. This prevents the angle between the light beam entering the second lens group G2 and the light beam emerging from the second lens group G2 from becoming too sharp, which is advantageous for suppressing breathing. By ensuring that the corresponding value of conditional expression (7) is not above the upper limit, the negative refractive power of the first lens group G1 does not become too weak, thereby preventing the positive refractive power of the second lens group G2 from becoming too weak relatively. This makes it possible to reduce the amount of movement of the focus group during focusing, which is advantageous for miniaturization. In order to obtain better characteristics, it is more preferable that the imaging lens satisfy the following conditional expression (7-1), and it is even more preferable that the imaging lens satisfy the following conditional expression (7-2): -0.35 <f / f1<-0.08 (7) -0.32 <f / f1<-0.11 (7-1) -0.28 <f / f1<-0.15 (7-2)

[0050] When the third lens group G3 includes a cemented lens formed by cementing a positive lens and a negative lens together in this order from the object side, it is preferable that the imaging lens satisfy the following conditional expression (8). Here, the Abbe number based on the d-line of the positive lens in the cemented lens of the third lens group G3 is v3p, and the Abbe number based on the d-line of the negative lens in the cemented lens of the third lens group G3 is v3n. By ensuring that the corresponding value of conditional expression (8) is not below the lower limit, it is possible to obtain the effect of correcting longitudinal chromatic aberration without reducing the absolute value of the radius of curvature of the cemented surface of the cemented lens of the third lens group G3. Generally, if the absolute value of the radius of curvature of the lens surface becomes too small, spherical aberration will worsen. In other words, by ensuring that the corresponding value of conditional expression (8) is not below the lower limit, it is possible to obtain the effect of correcting longitudinal chromatic aberration without worsening spherical aberration. Generally, optical materials with large Abbe numbers have low refractive indices, so by ensuring that the corresponding value of conditional expression (8) does not exceed the upper limit, it becomes easy to select a material with an appropriate refractive index for the positive lens of the cemented lens. This prevents the absolute value of the radius of curvature of the lens surface of this positive lens that is in contact with air from becoming too small, which is advantageous for preventing deterioration of spherical aberration and maintaining good performance. In order to obtain better characteristics, it is more preferable that the imaging lens satisfy the following conditional expression (8-1), and even more preferable that it satisfy the following conditional expression (8-2). 1<ν3p-ν3n<10 (8) 2.5<ν3p-ν3n<8 (8-1) 4<ν3p-ν3n<6 (8-2)

[0051] It is preferable that the imaging lens satisfy the following conditional expression (9). Here, DG3 is the distance on the optical axis from the lens surface of the third lens group G3 closest to the object to the lens surface of the third lens group G3 closest to the image. Bf is the back focus in terms of the air-equivalent distance of the entire system. By ensuring that the corresponding value of conditional expression (9) is not below the lower limit, it becomes easy to ensure the axial thickness of the third lens group G3 necessary for aberration correction, which is advantageous for reducing aberration fluctuations associated with focusing. By ensuring that the corresponding value of conditional expression (9) is not above the upper limit, the axial thickness of the third lens group G3 does not become too thick, which is advantageous for miniaturization. In order to obtain better characteristics, it is more preferable that the imaging lens satisfy the following conditional expression (9-1), and it is even more preferable that it satisfy the following conditional expression (9-2). 0.85 <DG3 / Bf<2 (9) 0.88 <DG3 / Bf<1.7 (9-1) 0.9 <DG3 / Bf<1.4 (9-2)

[0052] 1 is merely an example, and various modifications are possible without departing from the spirit of the technology of the present disclosure. For example, the number of lens groups constituting the imaging lens and the number of lenses included in each lens group may be different from those in the example of FIG. 1. Furthermore, the shape of the lenses included in each lens group may also be different from those in the example of FIG. 1.

[0053] For example, in the example of FIG. 1 , the object-side surface of the lens closest to the object in the first lens group G1 is convex. However, in the technology of the present disclosure, the lens closest to the object in the first lens group G1 may be configured to be a negative lens with a concave object-side surface. This is advantageous mainly for correcting field curvature. If the lens closest to the object in the first lens group G1 is a negative lens with a concave object-side surface, it is preferable that the second lens from the object side in the first lens group G1 be a positive lens. Placing a positive lens adjacent to the image side of the negative lens closest to the object in the first lens group G1 is advantageous for suppressing the occurrence of spherical aberration. Furthermore, if the second lens from the object side in the first lens group G1 is a positive lens, it is preferable that the negative lens closest to the object in the first lens group G1 be a biconcave lens. The image-side surface of the lens closest to the object in the first lens group G1 faces the positive lens. Making this facing surface concave is advantageous for correcting chromatic aberration.

[0054] Each lens group of the imaging lens of the present disclosure may be configured as follows.

[0055] The first lens group G1 may be configured to consist of two lenses. The first lens group G1 may be configured to consist, in order from the object side to the image side, of a negative lens and a positive lens. In this case, the negative lens in the first lens group G1 may be a meniscus lens with a convex surface facing the object side or a biconcave lens, and the positive lens in the first lens group G1 may be a meniscus lens with a convex surface facing the object side or a biconvex lens. Furthermore, when the first lens group G1 consists, in order from the object side to the image side, of a negative lens and a positive lens, these negative lens and positive lens may be configured to be single lenses.

[0056] The first lens group G1 may be configured to include an aspherical lens. If the first lens group G1 includes an aspherical lens, the lens in the first lens group G1 closest to the image may be an aspherical lens. By using an aspherical lens for a lens with a relatively small diameter in the first lens group G1, it becomes easier to effectively correct various aberrations while reducing costs.

[0057] The second lens group G2 may be configured to include five positive lenses, three negative lenses, and an aperture stop St. For example, the second lens group G2 may be configured to include, in order from the object side to the image side, a positive lens, a cemented lens, the aperture stop St, a positive lens, a cemented lens, and another cemented lens. In this case, the cemented lens in the second lens group G2 located closer to the object side than the aperture stop St may be configured by cementing a positive lens and a negative lens together in that order from the object side, or may be configured by cementing a negative lens and a positive lens together in that order from the object side. Furthermore, each of the two cemented lenses in the second lens group G2 located closer to the image side than the aperture stop St may be configured by cementing a negative lens and a positive lens together in that order from the object side.

[0058] The second lens group G2 may be configured to include five positive lenses, four negative lenses, and an aperture stop St. For example, the second lens group G2 may be configured to include, in order from the object side to the image side, a positive lens, a cemented lens, the aperture stop St, a negative lens, a cemented lens, and another cemented lens. In this case, the cemented lens in the second lens group G2 closer to the object than the aperture stop St may be configured by cementing together a positive lens, a negative lens, and a positive lens. Furthermore, the two cemented lenses in the second lens group G2 closer to the image than the aperture stop St may each be configured by cementing together a negative lens and a positive lens, in that order from the object side.

[0059] The second lens group G2 may be configured to include four positive lenses, four negative lenses, and an aperture stop St. For example, the second lens group G2 may be configured to include, in order from the object side to the image side, a positive lens, a cemented lens, the aperture stop St, a negative lens, a cemented lens, and another cemented lens. In this case, the cemented lens in the second lens group G2 located closer to the object side than the aperture stop St may be configured by cementing a positive lens and a negative lens together in that order from the object side. Furthermore, each of the two cemented lenses in the second lens group G2 located closer to the image side than the aperture stop St may be configured by cementing a negative lens and a positive lens together in that order from the object side.

[0060] Alternatively, when the second lens group G2 consists of four positive lenses, four negative lenses, and an aperture stop St, the second lens group G2 may be configured to consist, in order from the object side to the image side, of a cemented lens, the aperture stop St, a cemented lens, a negative lens, a positive lens, and another cemented lens. In this case, the cemented lens in the second lens group G2 closer to the object than the aperture stop St may be configured by cementing a positive lens and a negative lens together in that order from the object side. Furthermore, each of the two cemented lenses in the second lens group G2 closer to the image side than the aperture stop St may be configured by cementing a negative lens and a positive lens together in that order from the object side.

[0061] In the second lens group G2, if a single lens is disposed adjacent to the image side of the aperture stop St, that single lens may be configured to be an aspherical lens. By using an aspherical lens in the vicinity of the aperture stop St in this way, spherical aberration can be effectively corrected.

[0062] The third lens group G3 may be configured to include four lenses. For example, the third lens group G3 may be configured to include one positive lens and three negative lenses. The third lens group G3 may be configured to include, in order from the object side to the image side, a cemented lens, a negative lens, and a negative lens. In this case, the cemented lens of the third lens group G3 may be configured by cementing a positive lens and a negative lens together in order from the object side.

[0063] The third lens group G3 may be configured to consist of three lenses. For example, the third lens group G3 may be configured to consist of one positive lens and two negative lenses. The third lens group G3 may be configured to consist, in order from the object side to the image side, of a cemented lens and a negative lens. In this case, the cemented lens of the third lens group G3 may be configured by cementing a positive lens and a negative lens together in order from the object side.

[0064] Alternatively, when the third lens group G3 consists of three lenses, it may be configured to include two positive lenses and one negative lens. The third lens group G3 may be configured to include, in order from the object side to the image side, a positive lens and a cemented lens. In this case, the cemented lens of the third lens group G3 may be configured by cementing, in order from the object side, a negative lens and a positive lens.

[0065] If a single lens is located closest to the image in the third lens group G3, that single lens may be configured to be an aspherical lens. If no single lens is located closest to the image in the third lens group G3, the single lens closest to the image in the third lens group G3 may be configured to be an aspherical lens. In the third lens group G3, the off-axis light rays and on-axis light rays become more separated the closer to the image, so by using an aspherical lens for the lens closest to the image, various aberrations can be effectively corrected, and off-axis aberrations in particular can be effectively corrected.

[0066] The above-described preferred configurations and possible configurations can be arbitrarily combined, and are preferably selectively adopted as appropriate according to the required specifications. Note that the conditional expressions that the imaging lens of the present disclosure preferably satisfies are not limited to conditional expressions written in the form of an equation, and include all conditional expressions obtained by arbitrarily combining lower limits and upper limits from among the conditional expressions that are deemed preferred, more preferred, and even more preferred.

[0067] As an example, one preferred embodiment of the imaging lens of the present disclosure comprises, in order from the object side to the image side, a first lens group G1 having refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power, and during focusing, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim, and the second lens group G2 moves along the optical axis Z, and the second lens group G2 includes an aperture stop St and at least three negative lenses, and satisfies the above conditional formula (1).

[0068] Next, examples of the imaging lens of the present disclosure will be described with reference to the drawings. The reference symbols assigned to the lenses in the cross-sectional views of each example are used independently for each example to avoid cluttering the explanation and drawings due to an increase in the number of digits in the reference symbols. Therefore, even if common reference symbols are assigned in drawings of different examples, this does not necessarily mean that the configuration is the same.

[0069] [Example 1] A cross-sectional view of the configuration of the imaging lens of Example 1 is shown in Figure 1, and since the illustration method and configuration are as described above, some overlapping explanations will be omitted here. The imaging lens of Example 1 comprises, in order from the object side to the image side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. When focusing from an object at infinity to a closest object, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim, and the second lens group G2 moves toward the object side.

[0070] For the imaging lens of Example 1, basic lens data is shown in Table 1, specifications and variable surface spacing in Table 2, and aspherical coefficients in Table 3. The table of basic lens data is written as follows: The Sn column shows the surface number, with the surface closest to the object being surface 1 and the numbers increasing by one toward the image side. The R column shows the radius of curvature of each surface. The D column shows the surface spacing on the optical axis between each surface and its adjacent surface on the image side. The Nd column shows the refractive index for the d-line of each component element. The νd column shows the Abbe number based on the d-line of each component element.

[0071] In the basic lens data table, the sign of the radius of curvature of a surface with a convex surface facing the object side is positive, and the sign of the radius of curvature of a surface with a convex surface facing the image side is negative. The surface number column for the surface corresponding to the aperture stop St is entered with the surface number and the phrase (St). The basic lens data table also shows the optical element PP. The value in the bottom column of the surface spacing column in the table is the distance between the surface in the table closest to the image side and the image plane Sim. The symbol DD[ ] is used for variable surface spacing during focusing, and the surface number on the object side of this distance is entered in the [ ] in the surface spacing column.

[0072] Table 2 shows the focal length, back focus at the air-equivalent distance, maximum aperture F-number, maximum full-field angle, and variable surface spacing based on the d-line. The [°] in the maximum full-field angle column indicates that the unit is degrees. In Table 2, the "Infinity" column shows the values ​​when focused on an object at infinity, and the "Closest" column shows the values ​​when focused on the closest object. However, only the values ​​when focused on an object at infinity are shown for the back focus at the air-equivalent distance. Below the term "Closest" in Table 2, the distance on the optical axis from the closest object to the lens surface closest to the object is shown. In Example 1, this distance is 0.4 m (meters).

[0073] In the basic lens data, the surface numbers of aspherical surfaces are marked with an *, and the numerical value of the paraxial radius of curvature is entered in the column for the radius of curvature of the aspherical surface. In Table 3, the Sn row shows the surface numbers of aspherical surfaces, and the KA and Am rows show the numerical values ​​of the aspherical coefficients for each aspherical surface. Note that m in Am is an integer of 3 or more, and varies depending on the surface. For example, for the 11th surface of Example 1, m = 4, 6, 8, ..., 20. The numerical values ​​of the aspherical coefficients in Table 3, "E±n" (n: integer), are expressed as "×10 ±n " KA and Am are aspherical coefficients in the aspherical formula given below. Zd=C×h 2 / {1+(1-KA×C 2 ×h 2 ) 1 / 2}+ΣAm×h m however, Zd: Aspheric depth (length of the perpendicular line drawn from a point on the aspheric surface at height h to a plane perpendicular to the optical axis Z where the vertex of the aspheric surface is in contact) h: Height (distance from optical axis Z to lens surface) C: Reciprocal of paraxial radius of curvature KA, Am: aspherical coefficients In the aspherical formula, Σ means the summation over m.

[0074] In the data in each table, the angle unit is degrees and the length unit is mm (millimeters), but since the optical system can be used with proportional enlargement or reduction, other appropriate units can also be used. Also, in each table below, the values ​​are rounded to a predetermined number of decimal places.

[0075] [Table 1]

[0076] [Table 2]

[0077] [Table 3]

[0078] FIG. 3 shows aberration diagrams for the imaging lens of Example 1. From left to right, FIG. 3 shows spherical aberration, astigmatism, distortion, and lateral chromatic aberration. In FIG. 3, the upper row labeled "Infinity" shows aberration diagrams for a state focused on an object at infinity, while the lower row labeled "Closest" shows aberration diagrams for a state focused on a very close object. The distance on the optical axis from the very close object to the lens surface closest to the object in the data for each aberration diagram is the same as the value listed in the specifications table. In the spherical aberration diagram, aberrations for the d-line, C-line, and F-line are shown by solid lines, long-dashed lines, and short-dashed lines, respectively. In the astigmatism diagram, aberrations for the d-line in the sagittal direction are shown by solid lines, and aberrations for the d-line in the tangential direction are shown by short-dashed lines. In the distortion diagram, aberrations for the d-line are shown by solid lines. In the lateral chromatic aberration diagram, the aberrations for the C-line and F-line are shown with long and short dashed lines, respectively. In the spherical aberration diagram, the maximum F-number value for each state is shown after "FNo.=". In the other aberration diagrams, the maximum half angle of view value for each state is shown after "ω=".

[0079] The symbols, meanings, notation methods, and illustration methods of each data item related to the above-mentioned Example 1 are basically the same in the following Examples unless otherwise specified, and therefore, redundant explanations will be omitted below.

[0080] [Example 2] FIG. 4 shows a cross-sectional view of the configuration of the imaging lens of Example 2. The imaging lens of Example 2 comprises, in order from the object side to the image side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. The first lens group G1 comprises, in order from the object side to the image side, two lenses, lenses L11 and L12. The second lens group G2 comprises, in order from the object side to the image side, three lenses, lenses L21 to L23, an aperture stop St, and five lenses, lenses L24 to L28. The third lens group G3 comprises, in order from the object side to the image side, four lenses, lenses L31 to L34. When focusing from an object at infinity to a closest object, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim, and the second lens group G2 moves toward the object side.

[0081] For the imaging lens of Example 2, basic lens data is shown in Table 4, specifications and variable surface spacings are shown in Table 5, aspherical coefficients are shown in Table 6, and each aberration diagram is shown in FIG.

[0082] [Table 4]

[0083] [Table 5]

[0084] [Table 6]

[0085] [Example 3] FIG. 6 shows a cross-sectional view of the configuration of the imaging lens of Example 3. The imaging lens of Example 3 comprises, in order from the object side to the image side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. The first lens group G1 comprises, in order from the object side to the image side, two lenses, lenses L11 and L12. The second lens group G2 comprises, in order from the object side to the image side, three lenses, lenses L21 to L23, an aperture stop St, and five lenses, lenses L24 to L28. The third lens group G3 comprises, in order from the object side to the image side, four lenses, lenses L31 to L34. When focusing from an object at infinity to a closest object, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim, and the second lens group G2 moves toward the object side.

[0086] For the imaging lens of Example 3, basic lens data is shown in Table 7, specifications and variable surface spacing are shown in Table 8, aspherical coefficients are shown in Table 9, and each aberration diagram is shown in FIG.

[0087] [Table 7]

[0088] [Table 8]

[0089] [Table 9]

[0090] [Example 4] FIG. 8 shows a cross-sectional view of the configuration of the imaging lens of Example 4. The imaging lens of Example 4 comprises, in order from the object side to the image side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. The first lens group G1 comprises, in order from the object side to the image side, two lenses, lenses L11 and L12. The second lens group G2 comprises, in order from the object side to the image side, three lenses, lenses L21 to L23, an aperture stop St, and five lenses, lenses L24 to L28. The third lens group G3 comprises, in order from the object side to the image side, four lenses, lenses L31 to L34. When focusing from an object at infinity to a closest object, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim, and the second lens group G2 moves toward the object side.

[0091] For the imaging lens of Example 4, basic lens data is shown in Table 10, specifications and variable surface spacings are shown in Table 11, aspherical coefficients are shown in Table 12, and each aberration diagram is shown in FIG.

[0092] [Table 10]

[0093] [Table 11]

[0094] [Table 12]

[0095] [Example 5] FIG. 10 shows a cross-sectional view of the configuration of the imaging lens of Example 5. The imaging lens of Example 5 comprises, in order from the object side to the image side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. The first lens group G1 comprises, in order from the object side to the image side, two lenses, lenses L11 and L12. The second lens group G2 comprises, in order from the object side to the image side, three lenses, lenses L21 to L23, an aperture stop St, and five lenses, lenses L24 to L28. The third lens group G3 comprises, in order from the object side to the image side, four lenses, lenses L31 to L34. When focusing from an object at infinity to a closest object, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim, and the second lens group G2 moves toward the object side.

[0096] For the imaging lens of Example 5, basic lens data is shown in Table 13, specifications and variable surface spacings are shown in Table 14, aspherical coefficients are shown in Table 15, and aberration diagrams are shown in FIG.

[0097] [Table 13]

[0098] [Table 14]

[0099] [Table 15]

[0100] [Example 6] FIG. 12 shows a cross-sectional view of the configuration of the imaging lens of Example 6. The imaging lens of Example 6 comprises, in order from the object side to the image side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. The first lens group G1 comprises, in order from the object side to the image side, two lenses, lenses L11 and L12. The second lens group G2 comprises, in order from the object side to the image side, three lenses, lenses L21 to L23, an aperture stop St, and five lenses, lenses L24 to L28. The third lens group G3 comprises, in order from the object side to the image side, three lenses, lenses L31 to L33. When focusing from an object at infinity to a closest object, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim, and the second lens group G2 moves toward the object side.

[0101] For the imaging lens of Example 6, basic lens data is shown in Table 16, specifications and variable surface spacing are shown in Table 17, aspherical coefficients are shown in Table 18, and each aberration diagram is shown in FIG.

[0102] [Table 16]

[0103] [Table 17]

[0104] [Table 18]

[0105] [Example 7] FIG. 14 shows a cross-sectional view of the configuration of the imaging lens of Example 7. FIG. 15 shows the configuration and light beams of the imaging lens of Example 7 in each focus state. The imaging lens of Example 7 consists of, in order from the object side to the image side, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. The first lens group G1 consists of, in order from the object side to the image side, two lenses, lenses L11 and L12. The second lens group G2 consists of, in order from the object side to the image side, three lenses, lenses L21 to L23, an aperture stop St, and five lenses, lenses L24 to L28. The third lens group G3 consists of, in order from the object side to the image side, three lenses, lenses L31 to L33. When focusing from an object at infinity to a closest object, the first lens group G1 and the third lens group G3 are fixed relative to the image plane Sim, and the second lens group G2 moves toward the object.

[0106] For the imaging lens of Example 7, basic lens data is shown in Table 19, specifications and variable surface spacings are shown in Table 20, aspherical coefficients are shown in Table 21, and various aberration diagrams are shown in FIG.

[0107] [Table 19]

[0108] [Table 20]

[0109] [Table 21]

[0110] [Example 8] FIG. 17 shows a cross-sectional view of the configuration of the imaging lens of Example 8. The imaging lens of Example 8 comprises, in order from the object side to the image side, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. The first lens group G1 comprises, in order from the object side to the image side, two lenses, lenses L11 and L12. The second lens group G2 comprises, in order from the object side to the image side, three lenses, lenses L21 to L23, an aperture stop St, and five lenses, lenses L24 to L28. The third lens group G3 comprises, in order from the object side to the image side, three lenses, lenses L31 to L33. When focusing from an object at infinity to a closest object, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim, and the second lens group G2 moves toward the object side.

[0111] For the imaging lens of Example 8, basic lens data is shown in Table 22, specifications and variable surface spacings are shown in Table 23, aspherical coefficients are shown in Table 24, and each aberration diagram is shown in FIG.

[0112] [Table 22]

[0113] [Table 23]

[0114] [Table 24]

[0115] [Example 9] FIG. 19 shows a cross-sectional view of the configuration of the imaging lens of Example 9. The imaging lens of Example 9 comprises, in order from the object side to the image side, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. The first lens group G1 comprises, in order from the object side to the image side, two lenses, lenses L11 and L12. The second lens group G2 comprises, in order from the object side to the image side, four lenses, lenses L21 to L24, an aperture stop St, and five lenses, lenses L25 to L29. The third lens group G3 comprises, in order from the object side to the image side, three lenses, lenses L31 to L33. When focusing from an object at infinity to a closest object, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim, and the second lens group G2 moves toward the object side.

[0116] For the imaging lens of Example 9, basic lens data is shown in Table 25, specifications and variable surface spacing are shown in Table 26, aspherical coefficients are shown in Table 27, and each aberration diagram is shown in FIG.

[0117] [Table 25]

[0118] [Table 26]

[0119] [Table 27]

[0120] [Example 10] FIG. 21 shows a cross-sectional view of the configuration of the imaging lens of Example 10. The imaging lens of Example 10 comprises, in order from the object side to the image side, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. The first lens group G1 comprises, in order from the object side to the image side, two lenses, L11 and L12. The second lens group G2 comprises, in order from the object side to the image side, two lenses, L21 and L22, an aperture stop St, and six lenses, L23 to L28. The third lens group G3 comprises, in order from the object side to the image side, three lenses, L31 to L33. When focusing from an object at infinity to a closest object, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim, and the second lens group G2 moves toward the object side.

[0121] For the imaging lens of Example 10, basic lens data is shown in Table 28, specifications and variable surface spacings are shown in Table 29, aspherical coefficients are shown in Table 30, and various aberration diagrams are shown in FIG.

[0122] [Table 28]

[0123] [Table 29]

[0124] [Table 30]

[0125] [Example 11] A cross-sectional view of the configuration of the imaging lens of Example 11 is shown in Figure 23. The imaging lens of Example 11 consists of, in order from the object side to the image side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. The first lens group G1 consists of, in order from the object side to the image side, two lenses, lenses L11 and L12. The second lens group G2 consists of, in order from the object side to the image side, two lenses, lenses L21 and L22, an aperture stop St, and six lenses, lenses L23 to L28. The third lens group G3 consists of, in order from the object side to the image side, three lenses, lenses L31 to L33. When focusing from an object at infinity to a closest object, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim, and the second lens group G2 moves toward the object side.

[0126] For the imaging lens of Example 11, basic lens data is shown in Table 31, specifications and variable surface spacings are shown in Table 32, aspherical coefficients are shown in Table 33, and each aberration diagram is shown in FIG.

[0127] [Table 31]

[0128] [Table 32]

[0129] [Table 33]

[0130] Table 34 shows the corresponding values ​​of conditional expressions (1) to (9) for the imaging lenses of Examples 1 to 11. In Table 34, a "-" is entered in any column for which there is no corresponding lens. The corresponding values ​​of the Examples shown in Table 34 may be used as the upper or lower limits of the conditional expressions to set preferred ranges for the conditional expressions.

[0131] [Table 34]

[0132] The imaging lenses of Examples 1 to 11 are small and lightweight, yet maintain good optical performance with various aberrations suppressed. Furthermore, the maximum aperture F-number when focused on an object at infinity is smaller than 2 for the imaging lenses of Examples 1 to 11, and is particularly smaller than 1.8 for the imaging lenses of Examples 1 to 7 and 9 to 11. The imaging lenses of Examples 1 to 11 achieve a large aperture ratio.

[0133] Imaging devices such as digital cameras require interchangeable lenses that are high-performance, exhibit minimal changes in performance with focusing, and are capable of capturing images at close range. However, in the past, suppressing performance fluctuations with focusing in high-performance lens systems made it difficult to achieve compact and lightweight designs. Alternatively, attempts to achieve compact and lightweight designs made it difficult to ensure sufficient movement of the focus group, resulting in a long minimum focusing distance. In contrast, Examples 1 to 11 of the present disclosure provide compact and lightweight lens systems that are high-performance, exhibit minimal changes in performance with focusing, are capable of capturing images at close range, and are also compact and lightweight.

[0134] Next, an imaging device according to an embodiment of the present disclosure will be described. Fig. 25 and Fig. 26 show external views of a camera 30, which is an imaging device according to an embodiment of the present disclosure. Fig. 25 shows a perspective view of the camera 30 as seen from the front side, and Fig. 26 shows a perspective view of the camera 30 as seen from the rear side. The camera 30 is a so-called mirrorless digital camera, to which an interchangeable lens 20 can be removably attached. The interchangeable lens 20 is configured to include an imaging lens 1 according to an embodiment of the present disclosure housed in a lens barrel.

[0135] The camera 30 includes a camera body 31, and a shutter button 32 and a power button 33 are provided on the top surface of the camera body 31. An operation unit 34, an operation unit 35, and a display unit 36 ​​are provided on the back surface of the camera body 31. The display unit 36 ​​can display a captured image and an image within the angle of view before the image was captured.

[0136] A photographic opening through which light from the subject to be photographed enters is provided in the center of the front face of the camera body 31, and a mount 37 is provided at a position corresponding to the photographic opening, and an interchangeable lens 20 is attached to the camera body 31 via the mount 37.

[0137] Inside the camera body 31 are provided an imaging element such as a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) that outputs an imaging signal corresponding to the subject image formed by the interchangeable lens 20, a signal processing circuit that processes the imaging signal output from the imaging element to generate an image, and a recording medium for recording the generated image. With the camera 30, it is possible to take still images or videos by pressing the shutter button 32, and the image data obtained by this shooting is recorded on the recording medium.

[0138] Although the technology of the present disclosure has been described above using embodiments and examples, the technology of the present disclosure is not limited to the above embodiments and examples and can be modified in various ways. For example, the radius of curvature, surface spacing, refractive index, Abbe number, aspherical coefficient, etc. of each lens are not limited to the values ​​shown in the above examples and can take other values.

[0139] Furthermore, the imaging device according to the embodiment of the present disclosure is not limited to the above example, and can take various forms, such as a camera other than a mirrorless type, a film camera, and a video camera.

[0140] The following supplementary items are further disclosed regarding the above embodiments and examples. [Additional note 1] The lens comprises, in order from the object side to the image side, a first lens group having a refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power, During focusing, the first lens group and the third lens group are fixed with respect to an image plane, and the second lens group moves along an optical axis; the second lens group includes a stop and at least three negative lenses, the sum of the distance on the optical axis from the lens surface of the first lens group closest to the object side to the lens surface of the third lens group closest to the image side and the back focus in terms of the air equivalent distance of the entire system, The focal length of the entire system when focused on an object at infinity is f. When the maximum half angle of view when focused on an object at infinity is ωm, 5 <TTL 2 / (f 2 ×tanωm)<15 (1) An imaging lens that satisfies conditional expression (1) expressed as follows: [Additional note 2] If the back focus in air equivalent distance of the entire system is Bf, 0.1 <Bf / f<0.6 (2) The imaging lens according to claim 1, which satisfies conditional expression (2) shown below. [Additional note 3] The imaging lens according to claim 1 or 2, wherein the first lens group is a lens group having negative refractive power. [Additional note 4] The focal length of the second lens group is f2, If the focal length of the third lens group is f3, -18.5 <f3 / f2<-1 (3) The imaging lens according to any one of supplementary items 1 to 3, which satisfies conditional expression (3) shown below. [Additional note 5] Among the positive lenses in the second lens group, the refractive index of the positive lens closest to the object side for the d-line is N2po, When the refractive index of the positive lens closest to the image side among the positive lenses in the second lens group is N2pi for the d-line, 1.86<(N2po+N2pi) / 2<2.2 (4) The imaging lens according to any one of supplementary items 1 to 4, which satisfies conditional expression (4) shown below. [Additional note 6] Among the positive lenses in the second lens group, the positive lens closest to the object side has an Abbe number based on the d-line of ν2po, When the Abbe number of the positive lens closest to the image side among the positive lenses in the second lens group is ν2pi based on the d-line, 15<(ν2po+ν2pi) / 2<40 (5) The imaging lens according to any one of supplementary items 1 to 5, which satisfies conditional expression (5) shown below. [Additional note 7] The focal length of the first lens group is f1, If the focal length of the third lens group is f3, 1.5 <f3 / f1<3.5 (6) The imaging lens according to any one of supplementary items 1 to 6, which satisfies conditional expression (6) shown below. [Additional note 8] If the focal length of the first lens group is f1, then -0.35 <f / f1<-0.08 (7) The imaging lens according to any one of supplementary items 1 to 7, which satisfies conditional expression (7) shown below. [Additional note 9] The imaging lens according to any one of supplementary items 1 to 8, wherein the positive lens closest to the image side among the positive lenses in the second lens group is cemented with a negative lens. [Additional Note 10] The imaging lens according to any one of Supplementary Items 1 to 9, wherein the positive lens closest to the object side among the positive lenses in the second lens group is a meniscus lens whose surface on the image side is concave. [Additional Note 11] The imaging lens according to any one of supplementary items 1 to 10, wherein the second lens group includes at least one lens surface having an aspherical shape. [Additional Note 12] The imaging lens according to any one of supplementary items 1 to 11, wherein the third lens group includes at least one lens surface having an aspherical shape. [Additional Note 13] The imaging lens according to any one of Supplementary Items 1 to 12, wherein the third lens group includes a cemented lens formed by cementing a positive lens and a negative lens together in this order from the object side, and a negative lens that is arranged closest to the image side and has a concave surface on the object side. [Additional Note 14] the Abbe number of the positive lens of the cemented lens based on the d-line is ν3p, When the Abbe number of the negative lens of the cemented lens based on the d-line is ν3n, 1<ν3p-ν3n<10 (8) The imaging lens according to claim 13, which satisfies conditional expression (8) shown below. [Additional Note 15] The distance on the optical axis from the lens surface of the third lens group closest to the object side to the lens surface of the third lens group closest to the image side is DG3, If the back focus in air equivalent distance of the entire system is Bf, 0.85 <DG3 / Bf<2 (9) The imaging lens according to any one of supplementary items 1 to 14, which satisfies conditional expression (9) shown below. [Additional Note 16] The imaging lens according to any one of Supplementary Items 1 to 15, wherein the lens closest to the object side in the first lens group is a negative lens whose surface on the object side is concave. [Additional Note 17] The imaging lens according to appended item 16, wherein a positive lens is disposed adjacent to the image side of the negative lens closest to the object side in the first lens group. [Additional Note 18] The imaging lens according to Supplementary Item 17, wherein the negative lens in the first lens group closest to the object side is a biconcave lens. [Additional Note 19] An imaging device comprising the imaging lens according to any one of supplementary items 1 to 18. [Explanation of symbols]

[0141] 1 Imaging lens 2 On-axis luminous flux 3. Maximum half-angle luminous flux 20 Interchangeable Lenses 30 Camera 31 Camera Body 32 Shutter button 33 Power button 34 Control section 35 Control section 36 Display section 37 Mount G1 First lens group G2 Second lens group G3 Third lens group L11~L34 lenses PP optical components Sim image plane St aperture stop Z optical axis ωm Maximum half angle of view

Claims

1. The lens comprises, in order from the object side to the image side, a first lens group having a refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power, During focusing, the first lens group and the third lens group are fixed with respect to an image plane, and the second lens group moves along an optical axis; the second lens group includes a stop and at least three negative lenses, The sum of the distance on the optical axis from the lens surface of the first lens group closest to the object side to the lens surface of the third lens group closest to the image side and the back focus in terms of the air equivalent distance of the entire system is defined as TTL, The focal length of the entire system when focused on an object at infinity is f. The maximum half angle of view when focused on an object at infinity is ωm. The focal length of the second lens group is f2, The focal length of the third lens group is f3, The distance on the optical axis from the lens surface of the third lens group closest to the object side to the lens surface of the third lens group closest to the image side is DG3, When the back focus of the entire system in terms of air is Bf, 5<TTL ２ / (f ２ ×tanωm)<15 (1) -18.5<f3 / f2<-1 (3) 0.85<DG3 / Bf≦1.19 (9-3) An imaging lens that satisfies conditional expressions (1), (3), and (9-3) expressed by the following formulas.

2. 0.1<Bf / f<0.6 (2) 2. The imaging lens according to claim 1, which satisfies conditional expression (2) expressed as follows:

3. The imaging lens according to claim 1 , wherein the positive lens closest to the image side among the positive lenses in the second lens group is cemented with a negative lens.

4. 2. The imaging lens according to claim 1, wherein the positive lens closest to the object side among the positive lenses in the second lens group is a meniscus lens having a concave surface facing the image side.

5. The imaging lens according to claim 1 , wherein the second lens group includes at least one aspherical lens surface.

6. The imaging lens according to claim 1 , wherein the third lens group includes at least one aspherical lens surface.

7. 2. The imaging lens according to claim 1, wherein the lens closest to the object side in the first lens group is a negative lens whose surface on the object side is concave.

8. 8. The imaging lens according to claim 7, wherein a positive lens is disposed adjacent to the image side of the negative lens closest to the object side in the first lens group.

9. The imaging lens according to claim 8 , wherein the negative lens in the first lens group closest to the object side is a biconcave lens.

10. The lens comprises, in order from the object side to the image side, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power, During focusing, the first lens group and the third lens group are fixed with respect to an image plane, and the second lens group moves along an optical axis; the second lens group includes a stop and at least three negative lenses, The sum of the distance on the optical axis from the lens surface of the first lens group closest to the object side to the lens surface of the third lens group closest to the image side and the back focus in terms of the air equivalent distance of the entire system is defined as TTL, The focal length of the entire system when focused on an object at infinity is f. The maximum half angle of view when focused on an object at infinity is ωm. The focal length of the first lens group is f1, When the focal length of the third lens group is f3, 5<TTL ２ / (f ２ ×tanωm)<15 (1) 1.5<f3 / f1<3.5 (6) -0.35<f / f1<-0.08 (7) An imaging lens that satisfies conditional expressions (1), (6), and (7) expressed by the following formulas.

11. When the back focus of the entire system in terms of air is Bf, 0.1<Bf / f<0.6 (2) 11. The imaging lens according to claim 10, which satisfies conditional expression (2) expressed as follows:

12. The refractive index of the positive lens closest to the object side among the positive lenses in the second lens group is N2po for the d-line, When the refractive index of the positive lens closest to the image side among the positive lenses in the second lens group is N2pi with respect to the d-line, 1.86<(N2po+N2pi) / 2<2.2 (4) 11. The imaging lens according to claim 10, which satisfies conditional expression (4) expressed as follows:

13. Among the positive lenses in the second lens group, the Abbe number of the positive lens closest to the object side based on the d-line is ν2po, When the Abbe number of the positive lens closest to the image side among the positive lenses in the second lens group is ν2pi based on the d-line, 15<(ν2po+ν2pi) / 2<40 (5) 11. The imaging lens according to claim 10, which satisfies conditional expression (5) expressed as follows:

14. 11. The imaging lens according to claim 10, wherein the third lens group includes a cemented lens formed by cementing a positive lens and a negative lens together in this order from the object side, and a negative lens that is disposed closest to the image side and has a concave surface facing the object side.

15. the Abbe number of the positive lens of the cemented lens based on the d-line is ν3p, When the Abbe number of the negative lens of the cemented lens based on the d-line is ν3n, 1<ν3p−ν3n<10 (8) 15. The imaging lens according to claim 14, which satisfies conditional expression (8) expressed as follows:

16. An imaging device comprising the imaging lens according to any one of claims 1 to 15.

Images