Image capturing lens and image capturing device

Abstract

To provide an image capturing lens which has a compact configuration, offers good optical performance, and is advantageous in increasing focusing speed, and to provide an image capturing device having the image capturing lens.SOLUTION: An image capturing lens is provided, comprising 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. Only the second lens group moves while focusing. The image capturing lens satisfies the following conditional expression regarding a focal length f of the image capturing lens while being focused on an object at infinity and a focal length f3 of the third lens group: -0.166≤f / f3<0.38.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an imaging lens and an imaging device.

Background Art

[0002] Conventionally, as an imaging lens used in a digital camera or the like, lens systems described in Patent Document 1, Patent Document 2, and Patent Document 3 below are known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, there has been a demand for an imaging lens that is small in size, has good optical performance, and is advantageous for speeding up focusing.

[0005] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide an imaging lens that is small in size, has good optical performance, and is advantageous for speeding up focusing, and an imaging device including this imaging lens.

Means for Solving the Problems

[0006] The imaging lens of the present disclosure comprises, in order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group. When focusing, the first lens group and the third lens group are fixed with respect to the image plane, the second lens group moves, and when the focal length of the entire system in a state of focusing on an infinite object is f and the focal length of the third lens group is f3, -0.5 < f / f3 < 0.38 (1) It satisfies the conditional expression (1) represented by

[0007] The imaging lens of the present disclosure -0.4 < f / f3 < 0.3 (1-1) Preferably, it satisfies the conditional expression (1-1) represented by

[0008] The first lens group includes, in order from the object side to the image side, a first lens having a negative refractive power and a second lens having a positive refractive power. 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) Preferably, it satisfies the conditional expressions (2) and (3) represented by. Further, on the condition that the conditional expressions (2) and (3) are satisfied, 1.65 < N1 < 2 (2-1) More preferably, it satisfies the conditional expression (2-1) represented by

[0009] In the configuration in which the first lens group includes the first lens and the second lens, when the Abbe number of the first lens based on the d-line is ν1n and the Abbe number of the second lens based on the d-line is ν1p, 5 < ν1n - ν1p < 40 (4) Preferably, it satisfies the conditional expression (4) represented by

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

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

[0012] The lens surface closest to the image side of 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, 0.5 < |f / f2| < 2 (5) It is preferable to satisfy the conditional expression (5) represented by this.

[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 of the third lens group based on the d-line is ν3p and the Abbe number of the negative lens of the third lens group based on the d-line is ν3n, 5 < ν3n - ν3p < 38 (6) It is preferable to satisfy the conditional expression (6) represented by this.

[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 of the second lens group based on the d-line is ν2p, the Abbe number of the negative lens of the second lens group based on the d-line is ν2n, the Abbe number of the positive lens of the third lens group based on the d-line is ν3p, and the Abbe number of the negative lens of the third lens group based on the d-line is ν3n, 8 < ν2n - ν2p < 35 (7) 15 < ν3p - ν3n < 45 (8) It is preferable to satisfy the conditional expressions (7) and (8) represented by this.

[0017] The first lens group includes a diaphragm and at least one set of cemented lenses including a negative lens and a positive lens arranged on the image side of the diaphragm. When the Abbe number of the positive lens of the cemented lens in the first lens group with respect to the d-line is ν1cp, 70 < ν1cp < 110 (9) it preferably includes at least one positive lens that satisfies the conditional expression (9) represented by

[0018] When the Abbe numbers of the positive lens and the negative lens of the cemented lens in the first lens group with respect to the d-line are ν1cp and ν1cn respectively, 50 < ν1cp - ν1cn < 85 (10) it preferably includes at least one set of cemented lenses that satisfies the conditional expression (10) represented by

[0019] When the radius of curvature of the most object-side lens surface of the second lens group is R2f and the radius of curvature of the most image-side lens surface of the second lens group is R2r, -4 < (R2r + R2f) / (R2r - R2f) < -0.5 (11) it is preferable to satisfy the conditional expression (11) represented by

[0020] When the radius of curvature of the most object-side lens surface of the third lens group is R3f and the radius of curvature of the most image-side lens surface of the third lens group is R3r, -10 < (R3r + R3f) / (R3r - R3f) < 10 (12) it is preferable to satisfy the conditional expression (12) represented by

[0021] When the lateral magnification of the second lens group in the state of focusing on an infinite object is β2 and the lateral magnification of the third lens group in the state of focusing on an infinite object is β3, -7.5 < (1 - β2 2 ) × β3 2 < -4 (13) it is preferable to satisfy the conditional expression (13) represented by

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

[0023] The imaging device of the present disclosure includes the imaging lens of the present disclosure.

[0024] Note that in this specification, "consisting of ~" and "comprising ~" are intended to mean that in addition to the listed components, there may be included lenses that substantially have no refractive power, optical elements other than lenses such as diaphragms, filters, and cover glasses, and mechanical parts such as lens flanges, lens barrels, imaging elements, and shake correction mechanisms.

[0025] Note that in this specification, "~ group having a positive refractive power" means having a positive refractive power as a whole group. Similarly, "~ group having a negative refractive power" means having a negative refractive power as a whole group. "Lens having a positive refractive power", "positive lens", and "positive lens" are synonymous. "Lens having a negative refractive power", "negative lens", and "negative lens" are synonymous. "~ lens group" is not limited to a configuration consisting of a plurality of lenses, and may also be a configuration consisting of only one lens. "The entire system" means the imaging lens.

[0026] "Single lens" means one lens that is not joined. However, a compound aspherical lens (a lens in which a spherical lens and an aspherical film formed on the spherical lens are integrally formed and function as one aspherical lens as a whole) is not regarded as a joined lens and is treated as one lens. Regarding lenses including an aspherical surface, unless otherwise specified, the sign of the refractive power, the surface shape, and the radius of curvature are considered in the paraxial region. Regarding the sign of the radius of curvature, 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.

[0027] The "focal length" used conditionally is the paraxial focal length. The values used in the conditional expressions are the values based on the d-line when focused on an object at infinity. The "d-line", "C-line", "F-line", and "g-line" described in this specification 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 is 656.27 nm (nanometers), the wavelength of the F-line is 486.13 nm (nanometers), and the wavelength of the g-line is 435.84 nm (nanometers).

Advantages of the Invention

[0028] According to the present disclosure, it is possible to provide an imaging lens that is configured to be small, has good optical performance, and is advantageous for speeding up focusing, and an imaging device including this imaging lens.

Brief Description of the Drawings

[0029]

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Embodiments for Carrying Out the Invention

[0030] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. FIG. 1 shows a cross-sectional view of the configuration of an imaging lens according to an embodiment of the present disclosure in a state of being focused on an infinite object. FIG. 2 shows a cross-sectional view of the configuration and light beam in each focusing state of this imaging lens. In FIG. 2, the upper part marked with "infinity" shows a state of being focused on an object with an infinite object distance, and the lower part marked with "close distance" shows a state of being focused on a close-distance object with an object distance of 21.8 mm (millimeters). Hereinafter, an object with an infinite object distance will be referred to as an infinite object. In FIG. 2, as light beams, an on-axis light beam 2 and a light beam 3 with the maximum angle of view are shown. The examples shown in FIGS. 1 and 2 correspond to the imaging lens of Example 1 described later. In FIGS. 1 and 2, the left side is the object side and the right side is the image side. Hereinafter, an imaging lens according to an embodiment of the present disclosure will be mainly described with reference to FIG. 1.

[0031] In FIG. 1, assuming that the imaging lens is applied to an imaging device, an example is shown in which an optical member PP in the form of a parallel plate is arranged between the imaging lens and the image plane Sim. The optical member PP is a member assuming various filters and / or cover glass, etc. Various filters are, for example, a low-pass filter, an infrared cut filter, and a filter that cuts a specific wavelength range, etc. The optical member PP is a member having no refractive power, and a configuration in which the optical member PP is omitted is also possible.

[0032] This imaging lens is composed of a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 in order from the object side to the image side along the optical axis Z. By making the lens group closest to the object side a lens group having a positive refractive power, it becomes easy to shorten the overall length of the lens system, which is advantageous for miniaturization.

[0033] As an example, the first lens group G1 in FIG. 1 consists of, in order from the object side to the image side, a negative lens L11, a positive lens L12, an aperture stop 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 FIG. 1 consists of only one lens, lens L21, and the third lens group G3 in FIG. 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 of FIG. 1, lens L14 and lens L15 are joined to each other, and lens L31 and lens L32 are joined to each other. The aperture stop St in FIG. 1 indicates the position in the optical axis direction, not the size and shape.

[0034] This imaging lens is an inner focus type lens system in which only the second lens group G2 moves during focusing from an infinite object to the closest object, and the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim. Hereinafter, the lens group that moves during focusing is referred to as the focus group. The arrow pointing downward and to the right of the second lens group G2 shown in FIG. 1 means that the second lens group G2 is the focus group and moves toward the image side during focusing from an infinite object to the closest object. By adopting the inner focus method, the overall length of the lens system can be made constant regardless of the object distance during focusing. Even when photographing a close object, since the overall length of the lens system does not change compared to when photographing a distant object, the concern that the subject and the lens system interfere when photographing a close object can be reduced. Also, by adopting the inner focus method, it becomes easy to miniaturize and reduce the weight of the focus group, which is advantageous for speeding up the focusing.

[0035] When the focal length of the entire system in a state where the imaging lens is focused on an infinite object is f and the focal length of the third lens group G3 is f3, it is configured to satisfy the following conditional expression (1). By preventing the corresponding value of the conditional expression (1) from falling below the lower limit, the negative refractive power of the third lens group G3 does not become too strong, so it is possible to suppress an increase in the incident angle of the chief ray of the maximum angle of view onto the image plane Sim. By preventing the corresponding value of the conditional expression (1) from exceeding the upper limit, the positive refractive power of the third lens group G3 does not become too strong, which is advantageous for suppressing field curvature and is also advantageous for shortening the overall length of the lens system. In order to obtain better characteristics, it is preferable for the imaging lens to satisfy the following conditional expression (1-1). -0.5 < f / f3 < 0.38 (1) -0.4 < f / f3 < 0.3 (1-1)

[0036] It is preferable that the first lens group G1 includes the aperture stop St. By adopting a configuration in which the aperture stop St is arranged within the first lens group, it becomes easy to reduce the outer diameter of the lenses in the first lens group G1, which is advantageous for miniaturization.

[0037] It is preferable that the first lens group G1 includes, in order from the object side to the image side in the most continuous manner, a first lens having a negative refractive power, a second lens having a positive refractive power, and the aperture stop St. By limiting the number of lenses arranged on the object side of the aperture stop St to only two, it becomes easy to reduce the outer diameter of the lenses on the object side of the aperture stop St, which is advantageous for miniaturization. Also, by arranging both a negative lens and a positive lens on the object side of the aperture stop St, it is advantageous for correcting various aberrations. In the example of FIG. 1, the lens L11 corresponds to the first lens and the lens L12 corresponds to the second lens.

[0038] When the first lens group G1 includes the aperture stop St, it is preferable that the first lens group G1 includes at least one cemented lens including a negative lens and a positive lens arranged on the image side of the aperture stop St. In this case, it is advantageous for correcting axial chromatic aberration.

[0039] The second lens group G2 preferably consists of one lens component. Here, one lens component means a single lens or a set of cemented lenses. By configuring the focus group to consist of a single lens or a set of cemented lenses, it becomes easy to reduce the weight of the focus group, which is advantageous for faster focusing.

[0040] When the second lens group G2 consists of a single lens, it is easier to reduce the weight of the focus group compared to the case where the second lens group G2 consists of a set of cemented lenses, which is more advantageous for faster focusing. When the second lens group G2 consists of a set of cemented lenses formed by joining a single positive lens and a single negative lens, it is advantageous for suppressing fluctuations in chromatic aberration during focusing.

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

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

[0043] The lens component closest to the image side of the third lens group G3 may be configured to have a negative refractive power. By arranging a lens component with a negative refractive power closest to the image side of the third lens group G3, the off-axis light beam incident on the image plane Sim from the lens component closest to the image side can be emitted in a direction away from the optical axis Z. As a result, the diameter of the lens component closest to the image side can be reduced, and it becomes easy to configure the mount used when mounting the imaging lens on the imaging device so that this off-axis light beam is not blocked.

[0044] The most image-side lens surface of the third lens group G3 may be configured to be concave. In this case, similar to the case where a lens component having a negative refractive power is arranged on the most image side of the third lens group G3 described above, while avoiding light shielding by the mount, as a result, it is advantageous for reducing the diameter of the most image-side lens component of the third lens group G3.

[0045] Next, a preferable configuration regarding the conditional expressions will be described. However, the conditional expressions that the imaging lens preferably satisfies are not limited to the conditional expressions described in the form of equations, and include all conditional expressions obtained by arbitrarily combining the lower limit and the upper limit from among the conditional expressions regarded as preferable and more preferable.

[0046] In a configuration in which the first lens group G1 includes a first lens having a negative refractive power on the most object side, when 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 conditional expression (2). By preventing the corresponding value of the conditional expression (2) from falling below the lower limit, even when the first lens has the necessary negative refractive power, it is possible to suppress the absolute value of the curvature radius of the first lens from becoming too small, which is advantageous for correcting field curvature. By preventing the corresponding value of the conditional expression (2) from exceeding the upper limit, it becomes possible to select a low-dispersion material as the material of the first lens, which is advantageous for chromatic aberration correction. In order to obtain better characteristics, it is more preferable that the imaging lens satisfies the following conditional expression (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 a positive refractive power, when 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 conditional expression (3). By preventing the corresponding value of the conditional expression (3) from falling 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, and thus it becomes easy to ensure the thickness of the peripheral portion of the second lens. By preventing the corresponding value of the conditional expression (3) from exceeding the upper limit, it becomes possible to select a low-dispersion material as the material of the second lens, which is advantageous for chromatic aberration correction. In order to obtain better characteristics, it is more preferable that the imaging lens satisfies the following conditional expression (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, in order from the object side to the image side, a first lens having a negative refractive power and a second lens having a positive refractive power, it is preferable that the imaging lens satisfies the conditional expressions (2) and (3) simultaneously. Further, it is more preferable that at least one of the conditional expressions (2-1) and (3-1) is satisfied after the conditional expressions (2) and (3) are satisfied simultaneously.

[0049] Also, in a configuration where the first lens group G1 includes, in order from the object side to the image side, a first lens having a negative refractive power and a second lens having a positive refractive power, it is preferable that the imaging lens satisfies the following conditional expression (4). In the conditional expression (4), the Abbe number of the first lens based on the d-line is ν1n, and the Abbe number of the second lens based on the d-line is ν1p. By preventing the corresponding value of the conditional expression (4) from falling below the lower limit, it becomes easy to correct the magnification chromatic aberration. By preventing the corresponding value of the conditional expression (4) from exceeding the upper limit, it is possible to suppress the overcorrection of the magnification chromatic aberration. In order to obtain better characteristics, it is more preferable that the imaging lens satisfies the following conditional expression (4-1). 5 < ν1n - ν1p < 40 (4) 6 < ν1n - ν1p < 35 (4-1)

[0050] When the focal length of the entire system in the state of focusing on an infinite object is f and the focal length of the second lens group G2 is f2, the imaging lens preferably satisfies the following conditional expression (5). By ensuring that the corresponding value of the conditional expression (5) does not fall below the lower limit, the refractive power of the second lens group G2 does not become too weak, so that the movement amount of the second lens group G2 during focusing can be shortened, which is advantageous for shortening the overall length of the lens system. By ensuring that the corresponding value of the conditional expression (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 variation during focusing. In order to obtain better characteristics, the imaging lens more preferably satisfies the following conditional expression (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 a single positive lens and a single negative lens, the imaging lens preferably satisfies the following conditional expression (6). In the conditional expression (6), the Abbe number of the positive lens of the third lens group G3 based on the d-line is ν3p, and the Abbe number of the negative lens of the third lens group G3 based on the d-line is ν3n. By satisfying the conditional expression (6), it is advantageous for good correction of longitudinal chromatic aberration. In order to obtain better characteristics, the imaging lens more preferably satisfies the following conditional expression (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 conditional expressions (7) and (8). In conditional expressions (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. By satisfying conditional expression (7), it is advantageous for suppressing fluctuations in chromatic aberration during focusing. By satisfying conditional expression (8), it is advantageous for achieving good correction of magnification chromatic aberration. In order to obtain better characteristics, it is more preferable that the imaging lens satisfies at least one of conditional expressions (7-1) and (8-1) after simultaneously satisfying conditional expressions (7) and (8). 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 includes an aperture stop St and at least one set of cemented lenses including a negative lens and a positive lens arranged on the image side of the aperture stop St, it is preferable that the imaging lens includes at least one positive lens that satisfies the following conditional expression (9). In conditional expression (9), the Abbe number of the positive lens of the cemented lens of the first lens group G1 with respect to the d-line is ν1cp. By satisfying conditional expression (9), it is advantageous for correcting chromatic aberration, and particularly advantageous for achieving good correction of axial chromatic aberration. In order to obtain better characteristics, it is preferable that the imaging lens includes at least one positive lens that satisfies the following conditional expression (9-1). 70 < ν1cp < 110 (9) 75 < ν1cp < 105 (9-1)

[0054] In a configuration where the first lens group G1 includes the aperture stop St and at least one set of cemented lenses including a negative lens and a positive lens arranged on the image side of the aperture stop St, it is preferable that the imaging lens includes at least one set of cemented lenses that satisfy the following conditional expression (10). In the conditional expression (10), the Abbe numbers based on the d-line of the positive lens and the negative lens respectively joined to each other of the cemented lenses of the first lens group G1 arranged on the image side of the aperture stop St are denoted as ν1cp and ν1cn. By satisfying the conditional expression (10), it is advantageous for correcting chromatic aberration, and particularly advantageous for achieving good correction of axial chromatic aberration. In order to obtain better characteristics, it is preferable that the imaging lens includes at least one set of cemented lenses that satisfy the following conditional expression (10-1). 50 < ν1cp - ν1cn < 85 (10) 55 < ν1cp - ν1cn < 83 (10-1)

[0055] When the radius of curvature of the most object-side lens surface of the second lens group G2 is R2f and the radius of curvature of the most image-side lens surface of the second lens group G2 is R2r, it is preferable that the imaging lens satisfies the following conditional expression (11). The conditional expression (11) is an expression regarding the shape factor of the second lens group G2. By preventing the corresponding value of the conditional expression (11) from falling below the lower limit, it is advantageous for suppressing fluctuations in spherical aberration during focusing. By preventing the corresponding value of the conditional expression (11) from exceeding the upper limit, it is advantageous for suppressing fluctuations in field curvature during focusing. In order to obtain better characteristics, it is more preferable that the imaging lens satisfies the following conditional expression (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 side of the third lens group G3 is R3f and the radius of curvature of the lens surface closest to the image side of the third lens group G3 is R3r, the imaging lens preferably satisfies the following conditional expression (12). The conditional expression (12) is an expression regarding the shape factor of the third lens group G3. By ensuring that the corresponding value of the conditional expression (12) does not fall below the lower limit, it is advantageous for good correction of spherical aberration. By ensuring that the corresponding value of the conditional expression (12) does not exceed the upper limit, it is advantageous for good correction of field curvature. In order to obtain better characteristics, the imaging lens more preferably satisfies the following conditional expression (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 in the state of focusing on an infinite object is β2 and the lateral magnification of the third lens group G3 in the state of focusing on an infinite object is β3, the imaging lens preferably satisfies the following conditional expression (13). By ensuring that the corresponding value of the conditional expression (13) does not fall below the lower limit, it is possible to suppress the change in the image position per unit movement amount of the second lens group G2, which is the focusing group, in the optical axis direction from becoming too large. By ensuring that the corresponding value of the conditional expression (13) does not exceed the upper limit, it is possible to shorten the movement amount of the second lens group G2 during focusing, which is advantageous for shortening the overall length of the lens system. In order to obtain better characteristics, the imaging lens more preferably satisfies the following conditional expression (13-1). -7.5 < (1 - β2 2 ) × β3 2 < -4 (13) -6.5 < (1 - β2 2 ) × β3 2 < -4.5 (13-1)

[0058] When the focal length of the first lens group G1 is f1 and the distance on the optical axis from a reference to the image-side principal point of the first lens group G1 is dH with respect to the most image-side lens surface of the first lens group G1, it is preferable that the imaging lens satisfies the following conditional expression (14). Regarding the sign of dH, the sign of the distance on the object side from the above reference is negative, and the sign of the distance on the image side from the above reference is positive. As an example, FIG. 1 shows the image-side principal point H and dH of the first lens group G1. By preventing the corresponding value of the conditional expression (14) from falling below the lower limit, it is advantageous for suppressing fluctuations in field curvature during focusing. This is due to the following reasons. If the corresponding value of the conditional expression (14) falls below the lower limit, the image-side principal point H of the first lens group G1 will be located more on the object side, so the back focus of the first lens group G1 will become shorter. This means that the object point of the second lens group G2 will be located more on the object side. In order to keep the image point of the second lens group G2 constant, 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 focus group, increases, the aberration fluctuations during focusing become larger, and in particular, the fluctuations in field curvature during focusing become larger. By preventing the corresponding value of the conditional expression (14) from exceeding the upper limit, it is advantageous for suppressing an increase in the diameter of the image-side lens within the first lens group and is also advantageous for suppressing spherical aberration. 0.3 < dH / f1 < 0.7 (14) 0.35 < dH / f1 < 0.65 (14-1)

[0059] Note that the example shown in FIG. 1 is just an example, and various modifications are possible without departing from the gist of the technology of the present disclosure. For example, the number of lenses constituting each lens group may be different from the example in FIG. 1.

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

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

[0062] The third lens group G3 can be configured to be composed of a cemented lens in which a positive lens and a negative lens are sequentially cemented from the object side. Alternatively, the third lens group G3 can be configured to be composed of a cemented lens in which a negative lens and a positive lens are sequentially cemented from the object side. Alternatively, the third lens group G3 can be configured to be composed of a negative meniscus lens with a convex surface facing the object side.

[0063] The above-described preferred configurations and possible configurations, including the configuration related to the conditional expression, can be combined arbitrarily, and it is preferable to selectively adopt them as appropriate according to the required specifications.

[0064] Next, an embodiment of the imaging lens of the present disclosure will be described. [Embodiment 1] A cross-sectional view showing the configuration of the imaging lens of Embodiment 1 is shown in FIG. 1, and the illustration method and configuration are as described above, so duplicate explanations are partially omitted here. The imaging lens of Embodiment 1 includes, in order from the object side to the image side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a negative refractive power. When focusing from an infinite object to the closest object, only the second lens group G2 moves toward the image side along the optical axis Z, and the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim. The first lens group G1 includes six lenses, namely, lenses L11 to L16, and an aperture stop St. The aperture stop St is disposed between the lens L12 and the lens L13. The second lens group G2 includes only the lens L21. The third lens group G3 includes two lenses, namely, lenses L31 to L32. The above is the outline of the imaging lens of Embodiment 1.

[0065] For the imaging lens of Example 1, the basic lens data is shown in Table 1, the specifications and variable surface intervals are shown in Table 2, and the aspherical coefficients are shown in Table 3. In Table 1, in the column of Sn, the surface numbers are shown when the surface closest to the object side is defined as the first surface and the numbers are incremented one by one toward the image side. In the column of R, the radius of curvature of each surface is shown. In the column of D, the axial surface interval between each surface and the surface adjacent to it on the image side is shown. In the column of Nd, the refractive index of each component with respect to the d-line is shown. In the column of νd, the Abbe number of each component based on the d-line is shown.

[0066] In Table 1, the sign of the radius of curvature of the surface with a convex surface facing the object side is positive, and the sign of the radius of curvature of the surface with a convex surface facing the image side is negative. Table 1 also shows the aperture stop St and the optical member PP. In the column of the surface number corresponding to the aperture stop St, the surface number and the phrase (St) are described. The value in the bottommost column of D in Table 1 is the interval between the surface closest to the image side in the table and the image plane Sim. In Table 1, for the variable surface interval whose interval changes during focusing, the symbol DD[ ] is used, and the surface number on the object side of this interval is appended in [ ] and entered in the column of D.

[0067] Table 2 shows the values of the focal length f, F-number FNo., maximum full angle of view 2ω, and variable surface intervals. The (°) in the column of 2ω means that the unit is degrees. For the focal length and the maximum full angle of view, the values in the state of focusing on an infinite object are shown. For the other items, the values in the state of focusing on an infinite object are shown in the column marked "infinity", and the values in the state of focusing on a close object with an object distance of 21.8 mm (millimeters) are shown in the column marked "close distance". Note that the object distance is the axial distance from the object to the lens surface closest to the object side of the first lens group G1. The values shown in Table 2 are the values based on the d-line.

[0068] In Table 1, an asterisk is attached to the surface numbers of the aspherical surfaces, and the numerical values of the paraxial radii of curvature are described in the column of the radii of curvature of the aspherical surfaces. In Table 3, in the column of Sn, the surface numbers of the aspherical surfaces are shown. In the columns of KA and Am (m = 4, 6, 8, 10, 12, 14, 16), the numerical values of the aspherical coefficients for each aspherical surface are shown. The "E±n" (n: integer) of the numerical values of the aspherical coefficients in Table 3 is "×10 ±nIt means "」". KA and Am are 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 dropped from a point on the aspherical surface at height h to the plane perpendicular to the optical axis Z where the aspherical vertex touches) to the optical axis Z) 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 if it is proportionally enlarged or reduced, 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] Fig. 3 shows the aberration diagrams of the imaging lens of Example 1. In Fig. 3, from left to right, spherical aberration, astigmatism, distortion, and chromatic aberration of magnification are shown. In Fig. 3, the upper row marked with "infinity" shows the aberration diagrams in the state of focusing on an object at infinity, and the lower row marked with "close distance" shows the aberration diagrams in the state of focusing on a close-distance object with an object distance of 21.8 mm (millimeters). In the spherical aberration diagram, the aberrations at the d-line, C-line, F-line, and g-line are indicated by solid line, long dashed line, short dashed line, and one-dot chain line respectively. In the astigmatism diagram, the aberration at the d-line in the sagittal direction is indicated by a solid line, and the aberration at the d-line in the tangential direction is indicated by a short dashed line. In the distortion diagram, the aberration at the d-line is indicated by a solid line. In the chromatic aberration of magnification diagram, the aberrations at the C-line, F-line, and g-line are indicated by long dashed line, short dashed line, and one-dot chain line respectively. The FNo. in the spherical aberration diagram means the F-number, and ω in the other aberration diagrams means the semi-field angle. Fig. 3 shows the values of FNo. and ω corresponding to the upper end of the vertical axis of each figure.

[0074] The symbols, meanings, description methods, illustration methods of the respective data related to Example 1 above, and the object distance of the close-distance object are the same in the following examples unless otherwise specified, so the repeated explanations are omitted below.

[0075] [Example 2] A cross-sectional view showing the configuration of the imaging lens of Example 2 is shown in Fig. 4. The imaging lens of Example 2 has the same configuration as the outline 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 surface intervals are shown in Table 5, the aspherical coefficients are shown in Table 6, and the aberration diagrams are shown in Fig. 5. In Fig. 5, the upper row shows the aberration diagrams in the state of focusing on an object at infinity, and the lower row shows the aberration diagrams in the state of focusing on a close-distance object.

[0076]

Table 4

[0077]

Table 5

[0078]

Table 6

[0079] [Example 3] A cross-sectional view showing the configuration of the imaging lens of Example 3 is shown in Fig. 6. The imaging lens of Example 3 has the same configuration as the outline of the imaging lens of Example 1, except that the third lens group G3 has a positive refractive power. For the imaging lens of Example 3, the basic lens data is shown in Table 7, the specifications and variable surface intervals are shown in Table 8, the aspherical coefficients are shown in Table 9, and each aberration diagram is shown in Fig. 7. In Fig. 7, the upper part shows each aberration diagram in the state of focusing on an infinite object, and the lower part shows each aberration diagram in the state of focusing on a near-distance object.

[0080]

Table 7

[0081]

Table 8

[0082]

Table 9

[0083] [Example 4] A cross-sectional view showing the configuration of the imaging lens of Example 4 is shown in Fig. 8. The imaging lens of Example 4 has the same configuration as the outline of the imaging lens of Example 1, except that the third lens group G3 has a positive refractive power. For the imaging lens of Example 4, the basic lens data is shown in Table 10, the specifications and variable surface intervals are shown in Table 11, the aspherical coefficients are shown in Table 12, and each aberration diagram is shown in Fig. 9. In Fig. 9, the upper part shows each aberration diagram in the state of focusing on an infinite object, and the lower part shows each aberration diagram in the state of focusing on a near-distance object.

[0084]

Table 10

[0085]

Table 11

[0086]

Table 12

[0087] [Example 5] A cross-sectional view showing the configuration of the imaging lens of Example 5 is shown in FIG. 10. The imaging lens of Example 5 has the same configuration as the outline of the imaging lens of Example 1, except that the third lens group G3 has a positive refractive power and the second lens group G2 consists of two lenses, namely lens L21 and lens L22. For the imaging lens of Example 5, the basic lens data is shown in Table 13, the specifications and variable surface intervals are shown in Table 14, the aspherical coefficients are shown in Table 15, and each aberration diagram is shown in FIG. 11. In FIG. 11, the upper row shows each aberration diagram in the state of focusing on an infinite object, and the lower row shows each aberration diagram in the state of focusing on a near-distance object.

[0088]

Table 13

[0089]

Table 14

[0090]

Table 15

[0091] [Example 6] Fig. 12 shows a cross-sectional view showing the configuration of the imaging lens of Example 6. The imaging lens of Example 6 has the same configuration as the outline of the imaging lens of Example 1, except that the second lens group G2 consists of two lenses, lens L21 and lens L22. For the imaging lens of Example 6, the basic lens data is shown in Table 16, the specifications and variable surface intervals are shown in Table 17, the aspherical coefficients are shown in Table 18, and each aberration diagram is shown in Fig. 13. In Fig. 13, the upper row shows each aberration diagram in a state of focusing on an infinite object, and the lower row shows each aberration diagram in a state of focusing on a close object.

[0092]

Table 16

[0093]

Table 17

[0094]

Table 18

[0095] [Example 7] Fig. 14 shows a cross-sectional view showing the configuration of the imaging lens of Example 7. The imaging lens of Example 7 has the same configuration as the outline 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 surface intervals are shown in Table 20, the aspherical coefficients are shown in Table 21, and each aberration diagram is shown in Fig. 15. In Fig. 15, the upper row shows each aberration diagram in a state of focusing on an infinite object, and the lower row shows each aberration diagram in a state of focusing on a close object.

[0096]

Table 19

[0097]

Table 20

[0098]

Table 21

[0099] [Example 8] A cross-sectional view showing the configuration of the imaging lens of Example 8 is shown in FIG. 16. The imaging lens of Example 8 has the same configuration as the outline 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 surface intervals are shown in Table 23, the aspherical coefficients are shown in Table 24, and each aberration diagram is shown in FIG. 17. In FIG. 17, the upper row shows each aberration diagram in a state focused on an infinite object, and the lower row shows each aberration diagram in a state focused on a near-distance object.

[0100]

Table 22

[0101]

Table 23

[0102]

Table 24

[0103] [Example 9] A cross-sectional view showing the configuration of the imaging lens of Example 9 is shown in FIG. 18. The imaging lens of Example 9 has the same configuration as the outline of the imaging lens of Example 1, except that the second lens group G2 consists of two lenses, lens L21 and lens L22, and the third lens group G3 consists of only one lens, lens L31. For the imaging lens of Example 9, the basic lens data is shown in Table 25, the specifications and variable surface intervals are shown in Table 26, the aspherical coefficients are shown in Table 27, and each aberration diagram is shown in FIG. 19. In FIG. 19, the upper row shows each aberration diagram in a state focused on an infinite object, and the lower row shows each aberration diagram in a state focused on a near-distance object.

[0104]

Table 25

[0105]

Table 26

[0106]

Table 27

[0107] [Example 10] A cross-sectional view showing the configuration of the imaging lens of Example 10 is shown in FIG. 20. The imaging lens of Example 10 has the same configuration as the outline of the imaging lens of Example 1, except that the second lens group G2 consists of two lenses, lens L21 and lens L22. For the imaging lens of Example 10, the basic lens data is shown in Table 28, the specifications and variable surface intervals are shown in Table 29, the aspherical coefficients are shown in Table 30, and each aberration diagram is shown in FIG. 21. In FIG. 21, the upper row shows each aberration diagram in the state of focusing on an infinite object, and the lower row shows each aberration diagram in the state of focusing on a near-distance object.

[0108]

Table 28

[0109]

Table 29

[0110]

Table 30

[0111] [Example 11] A cross-sectional view showing the configuration of the imaging lens of Example 11 is shown in FIG. 22. The imaging lens of Example 11 has the same configuration as the outline of 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 surface intervals are shown in Table 32, the aspherical coefficients are shown in Table 33, and each aberration diagram is shown in FIG. 23. In FIG. 23, the upper row shows each aberration diagram in a state of focusing on an infinite object, and the lower row shows each aberration diagram in a state of focusing on a near-distance object.

[0112]

Table 31

[0113]

Table 32

[0114]

Table 33

[0115] Table 34 shows the corresponding values of the conditional expressions (1) to (14) of the imaging lenses of 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 reference.

[0116]

Table 34

[0117] The imaging lenses of Examples 1 to 11 are configured to be small, and since the focus group is composed of one or two lenses, it is advantageous for speeding up focusing. The imaging lenses of Examples 1 to 11 maintain high optical performance with good correction of various aberrations not only in a state of focusing on an infinite object but also in a state of focusing on a near-distance object.

[0118] Next, an imaging device according to an embodiment of the present disclosure will be described. FIGS. 24 and 25 show external views of a camera 30 which is an imaging device according to an embodiment of the present disclosure. FIG. 24 shows a perspective view of the camera 30 as seen from the front side, and FIG. 25 shows a perspective view of the camera 30 as seen from the back side. The camera 30 is a so-called mirrorless type digital camera, and an interchangeable lens 20 can be detachably attached thereto. The interchangeable lens 20 includes an imaging lens 1 according to an embodiment of the present disclosure housed in a lens barrel.

[0119] The camera 30 includes a camera body 31, and a shutter button 32 and a power button 33 are provided on the upper surface of the camera body 31. Further, 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 the captured image and the image within the angle of view before being captured.

[0120] A photographing aperture through which light from a photographing object is incident is provided at the center of the front surface of the camera body 31, and a mount 37 is provided at a position corresponding to the photographing aperture. The interchangeable lens 20 is attached to the camera body 31 via the mount 37.

[0121] Inside the camera body 31, an imaging element such as a CCD (Charge Coupled Device) or a 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 are provided. With the camera 30, it is possible to take a still image or a moving image by pressing the shutter button 32, and the image data obtained by this photographing is recorded on the above recording medium.

[0122] The above has described the technology of the present disclosure by way of embodiments and examples. However, the technology of the present disclosure is not limited to the above embodiments and examples, and various modifications are possible. For example, the radius of curvature, surface interval, refractive index, Abbe number, aspherical coefficient, etc. of each lens are not limited to the values shown in the above examples, and other values can be taken.

[0123] Also, the imaging device according to the embodiment of the present disclosure is not limited to the above example. For example, it can be in various forms such as cameras other than the mirrorless type, film cameras, and video cameras.

Explanation of Reference Numerals

[0124] 1 Imaging lens 2 On-axis light beam 3 Light beam of maximum picture angle 20 Interchangeable lens 30 Camera 31 Camera body 32 Shutter button 33 Power button 34, 35 Operation unit 36 Display unit 37 Mount dH Distance on the optical axis from the most 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 Second lens group G3 Third lens group H Image-side principal point of the first lens group L11~L16, L21~L22, L31~L32 Lenses PP Optical member Sim Image plane St Aperture stop Z Optical axis

Claims

1. The optical system comprises, in order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group, 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; the first lens group includes a single lens that is disposed closest to the image side and has a positive refractive power with a convex surface facing the image side, and a biconvex lens that is disposed adjacent to the single lens on the object side, the second lens group is composed of one meniscus lens having a negative refractive power and a convex surface facing the object side, the third lens group comprises, in order from the object side to the image side, one positive lens and one negative lens, The focal length of the entire system when focused on an object at infinity is f. The focal length of the third lens group is f3. The focal length of the second lens group is f2. The radius of curvature of the lens surface of the third lens group closest to the object is R3f. If the radius of curvature of the lens surface closest to the image side in the third lens group is R3r, -0.166≦f / f3<0.38 (1-3) 0.5<|f / f2|<2 (5) -4.81≦(R3r+R3f) / (R3r-R3f)<1 (12-2) An imaging lens that satisfies the conditional expressions (1-3), (5), and (12-2) expressed by the following formulas.

2. The imaging lens according to claim 1 , wherein the first lens group includes a diaphragm.

3. 3. The imaging lens according to claim 1, wherein the first lens group is made up of six lenses.

4. The imaging lens according to claim 1 , wherein the first lens group includes only one cemented lens.

5. 5. The imaging lens according to claim 4, wherein the cemented lens comprises, in order from the object side to the image side, one negative lens and one positive lens.

6. An imaging device comprising the imaging lens according to claim 1 .

Images