Imaging lens and imaging device

Abstract

The present invention provides a compact imaging lens with good optical performance and advantages for high-speed focusing, as well as an imaging device equipped with this imaging lens. [Solution] The imaging lens consists of a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group, arranged in order from the object side to the image side. When focusing, only the second lens group moves. The imaging lens satisfies the following condition regarding the focal length f of the imaging lens and the focal length f3 of the third lens group when focused on an object at infinity: -0.166≦f / f3<0.38.

Description

[Technical Field]

[0001] This disclosure relates to imaging lenses and imaging devices. [Background technology]

[0002] Conventionally, the lens systems described in Patent Document 1, Patent Document 2, and Patent Document 3 below are known as imaging lenses used in digital cameras and the like. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2012-159613 [Patent Document 2] Japanese Patent Publication No. 2016-099362 [Patent Document 3] Japanese Patent Publication No. 2014-021341 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In recent years, there has been a demand for imaging lenses that are compact, possess good optical performance, and are advantageous for achieving high-speed focusing.

[0005] This disclosure has been made in view of the above circumstances, and aims to provide an imaging lens that is compact, has good optical performance, and is advantageous for high-speed focusing, as well as an imaging device equipped with this imaging lens. [Means for solving the problem]

[0006] The imaging lens of this disclosure consists of a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group, arranged in order from the object side to the image side. When focusing, the first and third lens groups are fixed relative to the image plane, and the second lens group moves. When the entire system is in focus on an object at infinity, let f be the focal length of the system and let f3 be the focal length of the third lens group. -0.5 <f / f3<0.38 (1) The condition (1) expressed by is satisfied.

[0007] The imaging lens disclosed herein is -0.4 <f / f3<0.3 (1-1) It is preferable that the condition expressed in equation (1-1) is satisfied.

[0008] The first lens group includes, in order from the object side to the image side, a first lens having negative refractive power and a second lens having positive refractive power, and when the refractive index of the first lens with respect to the d line is N1 and the refractive index of the second lens with respect to the d line is N2, 1.6 <N1<2.1 (2) 1.6 <N2<2.1 (3) It is preferable that the conditions (2) and (3) expressed by are satisfied. Furthermore, in addition to satisfying conditions (2) and (3), 1.65 <N1<2 (2-1) It is more preferable to satisfy the condition expressed in equation (2-1).

[0009] In a configuration in which the first lens group includes the first lens and the second lens, if the Abbe number of the first lens with respect to the d line is ν1n and the Abbe number of the second lens with respect to the d line is ν1p, 5 < ν1n - ν1p < 40 (4) It is preferable that the condition expressed in equation (4) is satisfied.

[0010] The first lens group preferably includes an aperture. The first lens group preferably includes, in order from the object side to the image side, a first lens having negative refractive power, a second lens having positive refractive power, and an aperture.

[0011] When one lens component is a single lens or a set of cemented lenses, the lens component closest to the image side in the third lens group may be configured to have a negative refractive power.

[0012] The lens surface closest to the image side in the third lens group may be configured to be concave.

[0013] The second lens group preferably consists of a single lens or a set of cemented lenses.

[0014] When the focal length of the second lens group is f2, It is preferable to satisfy the conditional expression (5) represented by 0.5 < |f / f2| < 2 (5).

[0015] In a configuration where the second lens group consists of a single lens and the third lens group consists of a single positive lens and a single negative lens, when the Abbe number of the positive lens in the third lens group based on the d-line is ν3p and the Abbe number of the negative lens in the third lens group based on the d-line is ν3n, It is preferable to satisfy the conditional expression (6) represented by 5 < ν3n - ν3p < 38 (6).

[0016] In a configuration where the second lens group consists of a single positive lens and a single negative lens and the third lens group consists of a single positive lens and a single negative lens, when the Abbe number of the positive lens in the second lens group based on the d-line is ν2p, the Abbe number of the negative lens in the second lens group based on the d-line is ν2n, the Abbe number of the positive lens in the third lens group based on the d-line is ν3p, and the Abbe number of the negative lens in the third lens group based on the d-line is ν3n, It is preferable to satisfy the conditional expressions (7) represented by 8 < ν2n - ν2p < 35 (7). It is preferable to satisfy the conditional expressions (8) represented by 15 < ν3p - ν3n < 45 (8).

[0017] ​​​The first lens group comprises an aperture and at least one set of cemented lenses positioned on the image side of the aperture, including a negative lens and a positive lens. When the Abbe number of the positive lens of the cemented lens of the first lens group, relative to the d line, is ν1cp, 70 < ν1cp < 110 (9) It is preferable to include at least one positive lens that satisfies the conditional expression (9) represented by .

[0018] If the Abbe numbers of the positive and negative lenses joined together in the first lens group are denoted by ν1cp and ν1cn respectively, based on the d line, then 50 < ν1cp - ν1cn < 85 (10) It is preferable to include at least one set of cemented lenses that satisfy the conditional expression (10) represented by .

[0019] If R2f is the radius of curvature of the lens surface closest to the object in the second lens group, and R2r is the radius of curvature of the lens surface closest to the image in the second lens group, -4<(R2r+R2f) / (R2r-R2f)<-0.5 (11) It is preferable that the conditional expression (11) represented by is satisfied.

[0020] If the radius of curvature of the lens surface closest to the object in the third lens group is R3f, and the radius of curvature of the lens surface closest to the image in the third lens group is R3r, -10<(R3r+R3f) / (R3r-R3f)<10 (12) It is preferable that the conditional expression (12) represented by is satisfied.

[0021] If β2 is the lateral magnification of the second lens group when focused on an object at infinity, and β3 is the lateral magnification of the third lens group when focused on an object at infinity, -7.5<(1-β2 2 )×β3 2 <-4 (13) It is preferable that the conditional expression (13) represented by is satisfied.

[0022] If the focal length of the first lens group is f1, and the distance along the optical axis from the reference point to the principal point on the image side of the first lens group is dH, with respect to dH, the sign of the distance on the object side of the reference point is negative, and the sign of the distance on the image side of the reference point is positive, 0.3 <dH / f1<0.7 (14) It is preferable that the conditional expression (14) represented by is satisfied.

[0023] The imaging device of this disclosure comprises an imaging lens of this disclosure.

[0024] Furthermore, the terms "~consisting of" and "~consisting of" in this specification are intended to include, in addition to the listed components, lenses that substantially have no refractive power, optical elements other than lenses such as apertures, filters, and cover glass, and mechanical parts such as lens flanges, lens barrels, image sensors, and image stabilization mechanisms.

[0025] In this specification, "a group of lenses with positive refractive power" means that the group as a whole has positive refractive power. Similarly, "a group of lenses with negative refractive power" means that the group as a whole has negative refractive power. "A lens with positive refractive power," "positive lens," and "positive lens" are synonymous. "A lens with negative refractive power," "negative lens," and "negative lens" are synonymous. A "lens group" is not limited to a configuration consisting of multiple lenses, but may also consist of a single lens. "Entire system" means the imaging lens.

[0026] A "single lens" refers to a single, unbonded lens. However, a composite aspherical lens (a lens in which a spherical lens and an aspherical film formed on that spherical lens are integrally constructed and function as a single aspherical lens as a whole) is not considered a bonded lens and is treated as a single lens. For lenses including aspherical surfaces, the sign of refractive power, surface shape, and radius of curvature will be considered in the paraxial region unless otherwise specified. Regarding the sign of the radius of curvature, the sign of the radius of curvature of a surface with a convex shape facing the object side is considered positive, and the sign of the radius of curvature of a surface with a convex shape facing the image side is considered negative.

[0027] The "focal length" used in the conditional equations is the paraxial focal length. The values ​​used in the conditional equations are those with the d-line as the reference when the image is in focus on an object at infinity. The "d-line," "C-line," "F-line," and "g-line" described herein are emission lines. In this specification, the wavelength of the d-line is treated as 587.56 nm (nanometers), the wavelength of the C-line as 656.27 nm (nanometers), the wavelength of the F-line as 486.13 nm (nanometers), and the wavelength of the g-line as 435.84 nm (nanometers). [Effects of the Invention]

[0028] According to this disclosure, it is possible to provide an imaging lens that is compact, has good optical performance, and is advantageous for high-speed focusing, as well as an imaging device equipped with this imaging lens. [Brief explanation of the drawing]

[0029] [Figure 1] This is a cross-sectional view corresponding to the imaging lens of Example 1, showing the configuration of an imaging lens according to one embodiment. [Figure 2] Figure 1 is a cross-sectional view showing the configuration and light beam of the imaging lens in each focus state. [Figure 3] These are aberration diagrams of the imaging lens in Example 1. [Figure 4] This is a cross-sectional view showing the configuration of the imaging lens in Example 2. [Figure 5] These are aberration diagrams for the imaging lens of Example 2. [Figure 6] This is a cross-sectional view showing the configuration of the imaging lens in Example 3. [Figure 7] These are aberration diagrams for the imaging lens of Example 3. [Figure 8] This is a cross-sectional view showing the configuration of the imaging lens in Example 4. [Figure 9] These are aberration diagrams for the imaging lens of Example 4. [Figure 10] This is a cross-sectional view showing the configuration of the imaging lens in Example 5. [Figure 11]These are aberration diagrams for the imaging lens of Example 5. [Figure 12] This is a cross-sectional view showing the configuration of the imaging lens in Embodiment 6. [Figure 13] These are aberration diagrams for the imaging lens of Example 6. [Figure 14] This is a cross-sectional view showing the configuration of the imaging lens in Example 7. [Figure 15] These are aberration diagrams for the imaging lens of Example 7. [Figure 16] This is a cross-sectional view showing the configuration of the imaging lens in Example 8. [Figure 17] These are aberration diagrams for the imaging lens of Example 8. [Figure 18] This is a cross-sectional view showing the configuration of the imaging lens in Example 9. [Figure 19] These are aberration diagrams for the imaging lens of Example 9. [Figure 20] This is a cross-sectional view showing the configuration of the imaging lens in Example 10. [Figure 21] These are aberration diagrams for the imaging lens of Example 10. [Figure 22] This is a cross-sectional view showing the configuration of the imaging lens in Example 11. [Figure 23] These are aberration diagrams of the imaging lens in Example 11. [Figure 24] This is a front perspective view of an imaging device according to one embodiment of the present disclosure. [Figure 25] This is a perspective view of the rear side of an imaging device according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0030] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Figure 1 shows a cross-sectional view of the configuration of an imaging lens according to one embodiment of the present disclosure when it is in focus on an object at infinity. Figure 2 shows cross-sectional views of the configuration and light beam of this imaging lens in each focus state. In Figure 2, the upper section labeled "Infinity" shows the state in focus on an object at infinity, and the lower section labeled "Near" shows the state in focus on a nearby object at a distance of 21.8 mm (millimeters). Hereinafter, an object at infinity will be referred to as an "infinity object". In Figure 2, the light beams shown are the on-axial light beam 2 and the light beam 3 at the maximum angle of view. The examples shown in Figures 1 and 2 correspond to the imaging lens of Embodiment 1 described later. In Figures 1 and 2, the left side is the object side and the right side is the image side. Hereinafter, the imaging lens according to one embodiment of the present disclosure will be described mainly with reference to Figure 1.

[0031] Figure 1 shows an example where a parallel plate-shaped optical element PP is placed between the imaging lens and the image plane Sim, assuming that the imaging lens is applied to an imaging device. The optical element PP is a component that is intended to be various filters and / or cover glass, etc. Various filters include, for example, low-pass filters, infrared cut filters, and filters that cut out a specific wavelength range. The optical element PP is a component that does not have refractive power, and a configuration without the optical element PP is also possible.

[0032] This imaging lens consists of a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, and a third lens group G3, arranged in order from the object side to the image side along the optical axis Z. By making the lens group closest to the object the group with positive refractive power, the overall length of the lens system can be easily shortened, which is advantageous for miniaturization.

[0033] As an example, the first lens group G1 in Figure 1 consists of, in order from the object side to the image side, a negative lens L11, a positive lens L12, an aperture diaphragm St, a negative lens L13, a negative lens L14, a positive lens L15, and a positive lens L16. Also as an example, the second lens group G2 in Figure 1 consists of only one lens, L21, and the third lens group G3 in Figure 1 consists of two lenses, a positive lens L31 and a negative lens L32, in order from the object side to the image side. In the example in Figure 1, lenses L14 and L15 are joined to each other, and lenses L31 and L32 are joined to each other. The aperture diaphragm St in Figure 1 indicates its position in the optical axis direction, not its size and shape.

[0034] This imaging lens is an inner-focusing lens system in which only the second lens group G2 moves when focusing from an object at infinity to the nearest object, while the first lens group G1 and the third lens group G3 remain fixed relative to the image plane Sim. Hereafter, the lens group that moves during focusing will be referred to as the focus group. The arrow pointing to the right below the second lens group G2 in Figure 1 indicates that the second lens group G2 is the focus group and moves toward the image when focusing from an object at infinity to the nearest object. By adopting an inner-focusing system, the total length of the lens system can be kept constant regardless of the object distance during focusing. Even when photographing close-range objects, the total length of the lens system does not change from when photographing distant objects, thus reducing concerns about interference between the subject and the lens system when photographing close-range objects. Furthermore, by adopting an inner-focusing system, it is easy to miniaturize and lighten the focus group, which is advantageous for faster focusing.

[0035] This imaging lens is configured to satisfy the following condition (1) when the total focal length of the entire system is f and the focal length of the third lens group G3 is f3, in a state where it is focused on an object at infinity. By ensuring that the corresponding value in condition (1) does not fall below the lower limit, the negative refractive power of the third lens group G3 does not become too strong, thereby suppressing an increase in the angle of incidence of the principal ray at the maximum angle of view onto the image plane Sim. By ensuring that the corresponding value in condition (1) does not exceed the upper limit, the positive refractive power of the third lens group G3 does not become too strong, which is advantageous in suppressing image field curvature and also advantageous in shortening the overall length of the lens system. To obtain better characteristics, it is preferable that the imaging lens satisfies the following condition (1-1). -0.5 <f / f3<0.38 (1) -0.4 <f / f3<0.3 (1-1)

[0036] The first lens group G1 preferably includes an aperture diaphragm St. By arranging the aperture diaphragm St within the first lens group, it becomes easier to reduce the outer diameter of the lenses in the first lens group G1, which is advantageous for miniaturization.

[0037] The first lens group G1 preferably includes, in order from the object side to the image side, a first lens having negative refractive power, a second lens having positive refractive power, and an aperture diaphragm St. By limiting the number of lenses positioned on the object side of the aperture diaphragm St to only two, it becomes easier to reduce the outer diameter of the lenses on the object side of the aperture diaphragm St, which is advantageous for miniaturization. Furthermore, by positioning both a negative lens and a positive lens on the object side of the aperture diaphragm St, it is advantageous for correcting various aberrations. In the example in Figure 1, lens L11 corresponds to the first lens and lens L12 corresponds to the second lens.

[0038] When the first lens group G1 includes an aperture diaphragm St, it is preferable that the first lens group G1 includes at least one set of cemented lenses, which are positioned on the image side of the aperture diaphragm St and include a negative lens and a positive lens. This is advantageous for correcting axial chromatic aberration.

[0039] The second lens group G2 preferably consists of a single lens component. A single lens component refers to either a single lens or a pair of cemented lenses. Configuring the focusing group to consist of a single lens or a pair of cemented lenses facilitates weight reduction of the focusing group, which is advantageous for achieving faster focusing.

[0040] If the second lens group G2 consists of a single lens element, it is easier to reduce the weight of the focusing group compared to if the second lens group G2 consists of a pair of cemented lenses, which is advantageous for faster focusing. If the second lens group G2 consists of a pair of cemented lenses formed by joining one positive lens and one negative lens, it is advantageous for suppressing fluctuations in chromatic aberration during focusing.

[0041] The third lens group G3 preferably consists of one positive lens and one negative lens. Having both a negative lens and a positive lens in the third lens group G3 is advantageous for correcting chromatic aberration compared to cases where the third lens group G3 consists only of a negative lens or only of a positive lens.

[0042] The third lens group G3 preferably consists of a single lens component. If the third lens group G3 consists of a set of cemented lenses formed by joining one positive lens and one negative lens, it is advantageous for correcting chromatic aberration. If the third lens group G3 consists of a single lens, it is advantageous for miniaturization.

[0043] The lens component closest to the image in the third lens group G3 may be configured to have negative refractive power. By placing a lens component with negative refractive power closest to the image in the third lens group G3, the off-axis light beam incident on the image plane Sim from the lens component closest to the image can be emitted in a direction away from the optical axis Z. This makes it possible to reduce the diameter of the lens component closest to the image, and also makes it easier to configure the system so that this off-axis light beam is not blocked by the mount used when attaching the imaging lens to the imaging device.

[0044] The lens surface on the image side of the third lens group G3 may be configured to be concave. In this case, similar to the case where a lens component with negative refractive power is placed on the image side of the third lens group G3 described above, light shielding by the mount is avoided, and as a result, it is advantageous to reduce the diameter of the lens component on the image side of the third lens group G3.

[0045] Next, preferred configurations for the conditional expressions will be described. However, the preferred conditional expressions that the imaging lens should satisfy are not limited to those written in formula form, but include all conditional expressions that can be obtained by arbitrarily combining lower and upper limits from among the preferred and more preferred conditional expressions.

[0046] In a configuration where the first lens group G1 includes a first lens having the most negative refractive power on the object side, and the refractive index of the first lens with respect to the d line is N1, it is preferable that the imaging lens satisfies the following condition (2). By ensuring that the corresponding value in condition (2) does not fall below the lower limit, even when the first lens is given the necessary negative refractive power, it is possible to suppress the absolute value of the radius of curvature of the first lens from becoming too small, which is advantageous for correcting field curvature. By ensuring that the corresponding value in condition (2) does not exceed the upper limit, it becomes possible to select a low-dispersion material for the first lens, which is advantageous for correcting chromatic aberration. To obtain even better characteristics, it is more preferable that the imaging lens satisfies the following condition (2-1). 1.6 <N1<2.1 (2) 1.65 <N1<2 (2-1)

[0047] In a configuration where the second lens from the object side of the first lens group G1 is a second lens having positive refractive power, if the refractive index of the second lens with respect to the d line is N2, it is preferable that the imaging lens satisfies the following condition (3). By ensuring that the corresponding value in condition (3) does not fall below the lower limit, it is possible to suppress the absolute value of the radius of curvature of the second lens from becoming too small, making it easier to secure the thickness of the peripheral part of the second lens. By ensuring that the corresponding value in condition (3) does not exceed the upper limit, it becomes possible to select a low-dispersion material as the material for the second lens, which is advantageous for chromatic aberration correction. To obtain even better characteristics, it is more preferable that the imaging lens satisfies the following condition (3-1). 1.6 <N2<2.1 (3) 1.8 <N2<2 (3-1)

[0048] In a configuration where the first lens group G1 includes a first lens having negative refractive power and a second lens having positive refractive power, arranged sequentially from the object side to the image side, it is preferable that the imaging lens simultaneously satisfies conditions (2) and (3). Furthermore, it is more preferable that the imaging lens simultaneously satisfies conditions (2) and (3) and satisfies at least one of conditions (2-1) and (3-1).

[0049] Furthermore, in a configuration where the first lens group G1 includes a first lens having negative refractive power and a second lens having positive refractive power, arranged sequentially from the object side to the image side, it is preferable that the imaging lens satisfies the following conditional equation (4). In conditional equation (4), the Abbe number of the first lens with respect to the d line is ν1n, and the Abbe number of the second lens with respect to the d line is ν1p. By ensuring that the corresponding value in conditional equation (4) does not fall below the lower limit, correction of lateral chromatic aberration becomes easier. By ensuring that the corresponding value in conditional equation (4) does not exceed the upper limit, excessive correction of lateral chromatic aberration can be suppressed. To obtain even better characteristics, it is more preferable that the imaging lens satisfies the following conditional equation (4-1). 5 < ν1n - ν1p < 40 (4) 6 < ν1n - ν1p < 35 (4-1)

[0050] When the focal length of the entire system is f and the focal length of the second lens group G2 is f2, it is preferable that the imaging lens satisfies the following condition (5). By ensuring that the corresponding value in condition (5) does not fall below the lower limit, the refractive power of the second lens group G2 does not become too weak, thus shortening the amount of movement of the second lens group G2 during focusing, which is advantageous for shortening the overall length of the lens system. By ensuring that the corresponding value in condition (5) does not exceed the upper limit, the refractive power of the second lens group G2 does not become too strong, which is advantageous for suppressing aberration fluctuations during focusing. To obtain even better characteristics, it is more preferable that the imaging lens satisfies the following condition (5-1). 0.5 < |f / f²| < 2 (5) 0.7 < |f / f²| < 1.6 (5-1)

[0051] In a configuration where the second lens group G2 consists of a single lens and the third lens group G3 consists of one positive lens and one negative lens, it is preferable that the imaging lens satisfies the following condition (6). In condition (6), the Abbe number of the positive lens of the third lens group G3 with respect to the d line is ν3p, and the Abbe number of the negative lens of the third lens group G3 with respect to the d line is ν3n. Satisfying condition (6) is advantageous for good correction of chromatic aberration. To obtain even better characteristics, it is more preferable that the imaging lens satisfies the following condition (6-1). 5 < ν³n - ν³p < 38 (6) 9 < ν3n - ν3p < 35 (6-1)

[0052] In a configuration where the second lens group G2 consists of one positive lens and one negative lens, and the third lens group G3 consists of one positive lens and one negative lens, it is preferable that the imaging lens satisfies the following conditions (7) and (8). In conditions (7) and (8), the Abbe number of the positive lens of the second lens group G2 with respect to the d line is ν2p, the Abbe number of the negative lens of the second lens group G2 with respect to the d line is ν2n, the Abbe number of the positive lens of the third lens group G3 with respect to the d line is ν3p, and the Abbe number of the negative lens of the third lens group G3 with respect to the d line is ν3n. Satisfying condition (7) is advantageous in suppressing fluctuations in chromatic aberration during focusing. Satisfying condition (8) is advantageous in achieving good correction of lateral chromatic aberration. To obtain better characteristics, it is more preferable for the imaging lens to satisfy conditions (7) and (8) simultaneously, as well as at least one of conditions (7-1) and (8-1). 8 < ν²n - ν²p < 35 (7) 12 < ν²n - ν²p < 30 (7-1) 15 < ν3p - ν3n < 45 (8) 20 < ν3p - ν3n < 40 (8-1)

[0053] In a configuration where the first lens group G1 comprises an aperture diaphragm St and at least one set of cemented lenses arranged on the image side of the aperture diaphragm St, including a negative lens and a positive lens, it is preferable that the imaging lens includes at least one positive lens that satisfies the following condition (9). In condition (9), the d-line reference Abbe number of the positive lens of the cemented lens of the first lens group G1 is ν1cp. Satisfying condition (9) is advantageous for correcting chromatic aberration, and is particularly advantageous for good correction of axial chromatic aberration. To obtain even better characteristics, it is preferable that the imaging lens includes at least one positive lens that satisfies the following condition (9-1). 70 < ν1cp < 110 (9) 75 < ν1cp < 105 (9-1)

[0054] In a configuration where the first lens group G1 comprises an aperture diaphragm St and at least one set of cemented lenses, including a negative lens and a positive lens, positioned on the image side of the aperture diaphragm St, it is preferable that the imaging lens includes at least one set of cemented lenses that satisfy the following condition (10). In condition (10), the d-line reference Abbe numbers of the positive and negative lenses, respectively, of the cemented lenses of the first lens group G1 positioned on the image side of the aperture diaphragm St are ν1cp and ν1cn. Satisfying condition (10) is advantageous for correcting chromatic aberration, and is particularly advantageous for good correction of axial chromatic aberration. To obtain even better characteristics, it is preferable that the imaging lens includes at least one set of cemented lenses that satisfy the following condition (10-1). 50 < ν1cp - ν1cn < 85 (10) 55 < ν1cp - ν1cn < 83 (10-1)

[0055] When R2f is the radius of curvature of the lens surface closest to the object in the second lens group G2, and R2r is the radius of curvature of the lens surface closest to the image in the second lens group G2, it is preferable that the imaging lens satisfies the following condition (11). Condition (11) is an equation relating to the shape factor of the second lens group G2. By ensuring that the corresponding value of condition (11) does not fall below the lower limit, it is advantageous to suppress fluctuations in spherical aberration during focusing. By ensuring that the corresponding value of condition (11) does not exceed the upper limit, it is advantageous to suppress fluctuations in field curvature during focusing. To obtain even better characteristics, it is more preferable that the imaging lens satisfies the following condition (11-1). -4<(R2r+R2f) / (R2r-R2f)<-0.5 (11) -3.5<(R2r+R2f) / (R2r-R2f)<-1 (11-1)

[0056] When the radius of curvature of the lens surface closest to the object in the third lens group G3 is R3f, and the radius of curvature of the lens surface closest to the image in the third lens group G3 is R3r, it is preferable that the imaging lens satisfies the following condition (12). Condition (12) is an equation relating to the shape factor of the third lens group G3. Ensuring that the corresponding value of condition (12) does not fall below the lower limit is advantageous for good correction of spherical aberration. Ensuring that the corresponding value of condition (12) does not exceed the upper limit is advantageous for good correction of field curvature. To obtain even better characteristics, it is more preferable that the imaging lens satisfies the following condition (12-1). -10<(R3r+R3f) / (R3r-R3f)<10 (12) -6<(R3r+R3f) / (R3r-R3f)<1 (12-1)

[0057] When the lateral magnification of the second lens group G2 is in focus on an object at infinity, and the lateral magnification of the third lens group G3 is in focus on an object at infinity, it is preferable that the imaging lens satisfies the following condition (13). By ensuring that the corresponding value of condition (13) does not fall below the lower limit, it is possible to suppress the amount of change in image position per unit of movement in the optical axis direction of the second lens group G2, which is the focusing group, from becoming too large. By ensuring that the corresponding value of condition (13) does not exceed the upper limit, the amount of movement of the second lens group G2 during focusing can be shortened, which is advantageous for shortening the overall length of the lens system. To obtain even better characteristics, it is more preferable that the imaging lens satisfies the following condition (13-1). -7.5<(1-β2 2 )×β3 2 <-4 (13) -6.5<(1-β2 2 )×β3 2 <-4.5 (13-1)

[0058] If the focal length of the first lens group G1 is f1, and the distance on the optical axis from the reference to the image-side principal point of the first lens group G1 is dH, then it is preferable that the imaging lens satisfies the following condition (14). Note that the sign of dH is negative for distances closer to the object than the reference, and positive for distances closer to the image than the reference. As an example, Figure 1 shows the image-side principal point H and dH of the first lens group G1. By ensuring that the corresponding value of condition (14) does not fall below the lower limit, it is advantageous to suppress fluctuations in field curvature during focusing. This is due to the reasons described below. If the corresponding value of condition (14) falls below the lower limit, the image-side principal point H of the first lens group G1 will be located closer to the object, thus shortening the back focus of the first lens group G1. This means that the object point of the second lens group G2 will be located closer to the object. To maintain a constant image point for the second lens group G2, it is necessary to increase the refractive power of the second lens group G2. When the refractive power of the second lens group G2, which is the focusing group, increases, the aberration fluctuations during focusing become larger, and in particular, the fluctuations in field curvature during focusing become larger. By ensuring that the corresponding value in conditional equation (14) does not exceed the upper limit, it is advantageous to suppress the enlargement of the image-side lens within the first lens group, and also advantageous to suppress spherical aberration. 0.3 <dH / f1<0.7 (14) 0.35 <dH / f1<0.65 (14-1)

[0059] The example shown in Figure 1 is just one example, and various modifications are possible without departing from the spirit of the technology disclosed herein. For example, the number of lenses constituting each lens group may be different from the example in Figure 1.

[0060] Each lens group can have, for example, the following configuration: The first lens group G1 can be configured, in order from the object side to the image side, to consist of a biconcave lens, a biconvex lens, an aperture diaphragm St, a negative meniscus lens with its concave surface facing the object side, a negative lens with its concave surface facing the image side, a biconvex lens, and a positive lens with its convex surface facing the image side.

[0061] The second lens group G2 can be configured to consist of a negative meniscus lens with its convex surface facing the object. Alternatively, the second lens group G2 can be configured to consist of a cemented lens in which a biconvex lens and a biconcave lens are joined in order from the object side.

[0062] The third lens group G3 can be configured as a cemented lens in which a positive lens and a negative lens are joined in order from the object side. Alternatively, the third lens group G3 can be configured as a cemented lens in which a negative lens and a positive lens are joined in order from the object side. Alternatively, the third lens group G3 can be configured as a negative meniscus lens with its convex surface facing the object side.

[0063] The preferred and possible configurations described above, including the configurations related to conditional expressions, can be combined in any way and are preferably selected as appropriate according to the required specifications.

[0064] Next, embodiments of the imaging lens of this disclosure will be described. Examples 3, 5, 6, 10, and 11 below are embodiments of this disclosure, while Examples 1, 2, 4, 7, 8, and 9 are reference embodiments. [Example 1] A cross-sectional view showing the configuration of the imaging lens of Example 1 is shown in Figure 1, and its illustration method and configuration are as described above, so some redundant explanations will be omitted here. The imaging lens of Example 1 consists of a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with negative refractive power, in order from the object side to the image side. When focusing from an object at infinity to the nearest object, only the second lens group G2 moves towards the image side along the optical axis Z, while the first lens group G1 and the third lens group G3 are fixed relative to the image plane Sim. The first lens group G1 consists of six lenses, L11 to L16, and an aperture diaphragm St. The aperture diaphragm St is positioned between lenses L12 and L13. The second lens group G2 consists of only lens L21. The third lens group G3 consists of two lenses, L31 to L32. The above is an overview of the imaging lens of Example 1.

[0065] Table 1 shows the basic lens data for the imaging lens of Example 1, Table 2 shows the specifications and variable plane spacing, and Table 3 shows the aspherical coefficient. In Table 1, the Sn column indicates the plane number when the plane closest to the object is designated as the first plane and the number increases by one as you move toward the image side, the R column indicates the radius of curvature of each plane, and the D column indicates the plane spacing on the optical axis between each plane and the plane adjacent to it on the image side. The Nd column indicates the refractive index of each component with respect to the d line, and the νd column indicates the Abbe number of each component with respect to the d line.

[0066] In Table 1, the sign of the radius of curvature of a surface with a convex face towards the object is positive, and the sign of the radius of curvature of a surface with a convex face towards the image is negative. Table 1 also shows the aperture diaphragm St and the optical element PP. In the column for the surface number corresponding to the aperture diaphragm St, the surface number and the phrase (St) are written. The value in the bottom column of D in Table 1 is the distance between the surface closest to the image in the table and the image plane Sim. In Table 1, for variable surface spacings that change during focusing, the symbol DD[ ] is used, and the surface number on the object side for this spacing is written in column D with the [ ] inside.

[0067] Table 2 shows the values ​​for focal length f, F-number FNo., maximum angle of view 2ω, and variable plane spacing. The (°) in the 2ω column indicates that the unit is degrees. For focal length and maximum angle of view, the values ​​shown are for when the lens is in focus on an object at infinity. For the other items, the values ​​for when the lens is in focus on an object at infinity are shown in the column labeled "Infinity," and the values ​​for when the lens is in focus on a nearby object with an object distance of 21.8 mm (millimeters) are shown in the column labeled "Nearby." The object distance is the distance along the optical axis from the object to the lens surface of the first lens group G1 closest to the object. The values ​​shown in Table 2 are based on the d line.

[0068] In Table 1, the aspherical surface numbers are marked with an asterisk (*), and the column for the radius of curvature of the aspherical surface shows the value of the paraxial radius of curvature. In Table 3, the column Sn shows the aspherical surface number, and the columns KA and Am (m=4, 6, 8, 10, 12, 14, 16) show the numerical values ​​of the aspherical coefficient for each aspherical surface. In Table 3, the numerical values ​​of the aspherical coefficient "E±n" (n: integer) are multiplied by 10.±n It means "". KA and Am are the aspherical coefficients in the aspherical formula represented by the following formula. Zd = C × h 2 / {1+(1 - KA × C 2 × h 2 ) 1 / 2}+ ΣAm × h m However, Zd: Aspherical depth (the length of the perpendicular line dropped from the point on the aspherical surface at height h to the plane perpendicular to the optical axis Z where the aspherical vertex touches) h: Height (the distance from the optical axis Z to the lens surface) C: Reciprocal of the paraxial radius of curvature KA, Am: Aspherical coefficients where Σ in the aspherical formula means the sum with respect to m.

[0069] In the data of each table, degrees are used as the unit of angle and mm (millimeter) is used as the unit of length. However, since the optical system can be used even with proportional magnification or reduction, other appropriate units can also be used. Also, in each of the following tables, the numerical values are rounded to a predetermined number of digits.

[0070]

Table 1

[0071]

Table 2

[0072] !

Table 3

[0073] Figure 3 shows the aberration diagrams for the imaging lens of Example 1. From left to right in Figure 3, the diagrams show spherical aberration, astigmatism, distortion, and chromatic aberration. In Figure 3, the upper section labeled "Infinity" shows the aberration diagrams when the lens is focused on an object at infinity, while the lower section labeled "Near Distance" shows the aberration diagrams when the lens is focused on a nearby object at a distance of 21.8 mm (millimeters). In the spherical aberration diagram, the aberrations along the d, C, F, and g lines are shown as solid lines, long dashed lines, short dashed lines, and dashed lines, respectively. In the astigmatism diagram, the aberration along the d line in the sagittal direction is shown as a solid line, and the aberration along the d line in the tangential direction is shown as a short dashed line. In the distortion diagram, the aberration along the d line is shown as a solid line. In the chromatic aberration diagram, the aberrations along the C, F, and g lines are shown by long dashed lines, short dashed lines, and dashed lines, respectively. In the spherical aberration diagram, FNo. refers to the F number, and in the other aberration diagrams, ω refers to the half-angle of view. Figure 3 shows the FNo. and ω values ​​corresponding to the top of the vertical axis in each diagram.

[0074] The symbols, meanings, methods of description, methods of illustration, and object distances of nearby objects for each data point in Example 1 described above are the same in the following examples unless otherwise specified, so redundant explanations will be omitted below.

[0075] [Example 2] Figure 4 shows a cross-sectional view illustrating the configuration of the imaging lens of Example 2. The imaging lens of Example 2 has a configuration similar to that of the imaging lens of Example 1. For the imaging lens of Example 2, the basic lens data is shown in Table 4, the specifications and variable plane spacing are shown in Table 5, the aspherical coefficient is shown in Table 6, and the aberration diagrams are shown in Figure 5. In Figure 5, the aberration diagrams are shown in the upper row when the lens is focused on an object at infinity, and in the lower row when the lens is focused on a nearby object.

[0076] [Table 4]

[0077] [Table 5]

[0078] [Table 6]

[0079] [Example 3] Figure 6 shows a cross-sectional view illustrating the configuration of the imaging lens of Example 3. The imaging lens of Example 3 has the same configuration as the imaging lens of Example 1, except that the third lens group G3 has positive refractive power. For the imaging lens of Example 3, the basic lens data is shown in Table 7, the specifications and variable plane spacing are shown in Table 8, the aspherical coefficient is shown in Table 9, and the aberration diagrams are shown in Figure 7. In Figure 7, the aberration diagrams are shown in the upper row when focused on an object at infinity, and in the lower row when focused on a nearby object.

[0080] [Table 7]

[0081] [Table 8]

[0082] [Table 9]

[0083] [Example 4] Figure 8 shows a cross-sectional view illustrating the configuration of the imaging lens of Example 4. The imaging lens of Example 4 has the same configuration as the imaging lens of Example 1, except that the third lens group G3 has positive refractive power. For the imaging lens of Example 4, the basic lens data is shown in Table 10, the specifications and variable plane spacing are shown in Table 11, the aspherical coefficient is shown in Table 12, and the various aberration diagrams are shown in Figure 9. In Figure 9, the upper row shows the various aberration diagrams when focused on an object at infinity, and the lower row shows the various aberration diagrams when focused on a nearby object.

[0084] [Table 10]

[0085] [Table 11]

[0086] [Table 12]

[0087] [Example 5] Figure 10 shows a cross-sectional view illustrating the configuration of the imaging lens of Example 5. The imaging lens of Example 5 has the same configuration as the imaging lens of Example 1, except that the third lens group G3 has positive refractive power and the second lens group G2 consists of two lenses, L21 and L22. For the imaging lens of Example 5, the basic lens data is shown in Table 13, the specifications and variable plane spacing are shown in Table 14, the aspherical coefficient is shown in Table 15, and the various aberration diagrams are shown in Figure 11. In Figure 11, the upper row shows the various aberration diagrams when focused on an object at infinity, and the lower row shows the various aberration diagrams when focused on a nearby object.

[0088] [Table 13]

[0089] [Table 14]

[0090] [Table 15]

[0091] [Example 6] Figure 12 shows a cross-sectional view illustrating the configuration of the imaging lens of Example 6. The imaging lens of Example 6 has the same configuration as the imaging lens of Example 1, except that the second lens group G2 consists of two lenses, L21 and L22. For the imaging lens of Example 6, the basic lens data is shown in Table 16, the specifications and variable plane spacing are shown in Table 17, the aspherical coefficient is shown in Table 18, and the various aberration diagrams are shown in Figure 13. In Figure 13, the upper row shows the various aberration diagrams when focused on an object at infinity, and the lower row shows the various aberration diagrams when focused on a nearby object.

[0092] [Table 16]

[0093] [Table 17]

[0094] [Table 18]

[0095] [Example 7] Figure 14 shows a cross-sectional view illustrating the configuration of the imaging lens of Example 7. The imaging lens of Example 7 has a configuration similar to that of the imaging lens of Example 1. For the imaging lens of Example 7, the basic lens data is shown in Table 19, the specifications and variable plane spacing are shown in Table 20, the aspherical coefficient is shown in Table 21, and the aberration diagrams are shown in Figure 15. In Figure 15, the aberration diagrams are shown in the upper row when the lens is focused on an object at infinity, and in the lower row when the lens is focused on a nearby object.

[0096] [Table 19]

[0097] [Table 20]

[0098] [Table 21]

[0099] [Example 8] Figure 16 shows a cross-sectional view illustrating the configuration of the imaging lens of Example 8. The imaging lens of Example 8 has a configuration similar to that of the imaging lens of Example 1. For the imaging lens of Example 8, the basic lens data is shown in Table 22, the specifications and variable plane spacing in Table 23, the aspherical coefficient in Table 24, and the aberration diagrams in Figure 17. In Figure 17, the aberration diagrams are shown in the upper row when the lens is focused on an object at infinity, and in the lower row when the lens is focused on a nearby object.

[0100] [Table 22]

[0101] [Table 23]

[0102] [Table 24]

[0103] [Example 9] Figure 18 shows a cross-sectional view illustrating the configuration of the imaging lens of Example 9. The imaging lens of Example 9 has the same configuration as the imaging lens of Example 1, except that the second lens group G2 consists of two lenses, L21 and L22, and the third lens group G3 consists of only one lens, L31. For the imaging lens of Example 9, the basic lens data is shown in Table 25, the specifications and variable plane spacing are shown in Table 26, the aspherical coefficient is shown in Table 27, and the aberration diagrams are shown in Figure 19. In Figure 19, the upper row shows the aberration diagrams when focused on an object at infinity, and the lower row shows the aberration diagrams when focused on a nearby object.

[0104] [Table 25]

[0105] [Table 26]

[0106] [Table 27]

[0107] [Example 10] Figure 20 shows a cross-sectional view illustrating the configuration of the imaging lens of Example 10. The imaging lens of Example 10 has the same configuration as the imaging lens of Example 1, except that the second lens group G2 consists of two lenses, L21 and L22. For the imaging lens of Example 10, the basic lens data is shown in Table 28, the specifications and variable plane spacing are shown in Table 29, the aspherical coefficient is shown in Table 30, and the various aberration diagrams are shown in Figure 21. In Figure 21, the upper row shows the various aberration diagrams when focused on an object at infinity, and the lower row shows the various aberration diagrams when focused on a nearby object.

[0108] [Table 28]

[0109] [Table 29]

[0110] [Table 30]

[0111] [Example 11] Figure 22 shows a cross-sectional view illustrating the configuration of the imaging lens of Example 11. The imaging lens of Example 11 has the same configuration as the imaging lens of Example 1, except that the third lens group G3 has a positive refractive power. For the imaging lens of Example 11, the basic lens data is shown in Table 31, the specifications and variable plane spacing are shown in Table 32, the aspherical coefficient is shown in Table 33, and the aberration diagrams are shown in Figure 23. In Figure 23, the aberration diagrams are shown in the upper row when focused on an object at infinity, and in the lower row when focused on a nearby object.

[0112] [Table 31]

[0113] [Table 32]

[0114] [Table 33]

[0115] Table 34 shows the corresponding values ​​for the imaging lens condition equations (1) to (14) in Examples 1 to 11. Examples 1 to 11 use the d-line as the reference wavelength. Table 34 shows the values ​​based on the d-line.

[0116] [Table 34]

[0117] The imaging lenses of Examples 1 to 11 are compact in design, and their focus group consists of one or two lenses, which is advantageous for achieving high-speed focusing. The imaging lenses of Examples 1 to 11 maintain high optical performance, with aberrations being well corrected not only when focused on objects at infinity but also when focused on objects at close range.

[0118] Next, an imaging device according to an embodiment of the present disclosure will be described. Figures 24 and 25 show external views of a camera 30, which is an imaging device according to one embodiment of the present disclosure. Figure 24 shows a perspective view of the camera 30 from the front, and Figure 25 shows a perspective view of the camera 30 from the rear. The camera 30 is a so-called mirrorless type digital camera, and an interchangeable lens 20 can be detachably attached. The interchangeable lens 20 is configured to include an imaging lens 1 according to one embodiment of the present disclosure, which is housed in the lens barrel.

[0119] The camera 30 comprises a camera body 31, the top of which is provided a shutter button 32 and a power button 33. The rear of the camera body 31 is provided with an operation unit 34, an operation unit 35, and a display unit 36. The display unit 36 ​​can display captured images and images within the field of view before capture.

[0120] A shooting aperture is provided in the center of the front of the camera body 31, into which light from the subject to be photographed enters. A mount 37 is provided at a position corresponding to the shooting aperture, and an interchangeable lens 20 is attached to the camera body 31 via the mount 37.

[0121] The camera body 31 contains an image sensor 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 image sensor to generate an image, and a recording medium for recording the generated image. The camera 30 can take still images or videos by pressing the shutter button 32, and the image data obtained from this shooting is recorded on the recording medium.

[0122] Although the technology of this disclosure has been described above with reference to embodiments and examples, the technology of this disclosure is not limited to the above embodiments and examples, and various modifications are possible. For example, the radius of curvature, interplanar spacing, refractive index, Abbe number, and aspheric coefficient of each lens are not limited to the values ​​shown in each of the above embodiments, but can take other values.

[0123] Furthermore, the imaging device according to the embodiments of this disclosure is not limited to the above example, and can take various forms, such as cameras other than mirrorless cameras, film cameras, and video cameras. [Explanation of Symbols]

[0124] 1 imaging lens 2 On-axis luminous flux 3. Light beam at the maximum angle of view 20 interchangeable lenses 30 Cameras 31 Camera Body 32 Shutter button 33 Power button 34, 35 Operation section 36 Display section 37 Mount dH: Distance along the optical axis from the image-side lens surface of the first lens group to the image-side principal point of the first lens group. G1 First Lens Group G2 2nd lens group G3 3rd lens group H First lens group image-side principal point L11-L16, L21-L22, L31-L32 lenses PP optical components Sim image plane St aperture diaphragm Z optical axis

Claims

1. It consists of a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group, arranged in order from the object side to the image side. When focusing, the first lens group and the third lens group are fixed to the image plane, and the second lens group moves. The first lens group includes, in order from the object side to the image side, a first lens having negative refractive power, a second lens having positive refractive power, and an aperture. f is the focal length of the entire system when it is in focus on an object at infinity. The focal length of the third lens group is f3, The refractive index of the first lens with respect to the d line is N1, The refractive index of the second lens with respect to the d line is N2, The focal length of the second lens group is f2, The radius of curvature of the lens surface closest to the object in the third lens group is R3f. When the radius of curvature of the image-side lens surface of the third lens group is R3r, -0.5<f / f3<0.38 (1) 1.65<N1<2 (2-1) 1.64769 ≤ N² < 2 (3-2) 0.7<|f / f2|<2 (5-3) -0.61≦(R3r+R3f) / (R3r-R3f)<10 (12-3) An imaging lens that satisfies the following conditions: (1), (2-1), (3-2), (5-3), and (12-3).

2. -0.4<f / f3<0.38 (1-2) The imaging lens according to claim 1, satisfying the conditional expression (1-2) represented by .

3. -0.4<f / f3<0.3 (1-1) An imaging lens according to claim 1 or 2 that satisfies the conditional expression (1-1) represented by .

4. 1.65 < N1 ≤ 1.88202 (2-2) An imaging lens according to any one of claims 1 to 3 that satisfies the conditional expression (2-2) represented by .

5. 1.69350 ≤ N1 ≤ 1.88202 (2-3) An imaging lens according to any one of claims 1 to 4 that satisfies the conditional expression (2-3) represented by .

6. 1.72903 ≤ N1 ≤ 1.88202 (2-4) An imaging lens according to any one of claims 1 to 5 that satisfies the conditional expression (2-4) represented by .

7. 1.64769 ≤ N2 ≤ 1.86966 (3-3) An imaging lens according to any one of claims 1 to 6 that satisfies the conditional expression (3-3) represented by .

8. 0.7<|f / f2|<1.6 (5-1) An imaging lens according to any one of claims 1 to 7 that satisfies the conditional expression (5-1) represented by .

9. 0.7<|f / f2|≦1.358 (5-4) An imaging lens according to any one of claims 1 to 8 that satisfies the conditional expression (5-4) represented by .

10. -0.61≦(R3r+R3f) / (R3r-R3f)<1 (12-2) An imaging lens according to any one of claims 1 to 9 that satisfies the conditional expression (12-2) represented by .

11. -0.4<f / f3<0.38 (1-2) 1.72903 ≤ N1 ≤ 1.88202 (2-4) 1.64769 ≤ N2 ≤ 1.86966 (3-3) 0.7<|f / f2|≦1.358 (5-4) -0.61≦(R3r+R3f) / (R3r-R3f)<1 (12-2) The imaging lens according to claim 1, satisfying the conditional expressions (1-2), (2-4), (3-3), (5-4), and (12-2) represented by .

12. An imaging device comprising an imaging lens according to any one of claims 1 to 11.

Images