Imaging lens and imaging device

Abstract

To provide an imaging lens which is compact and nonetheless is suppressed in variation of the performance thereof associated with focusing and has good optical performance, and an imaging apparatus comprising the imaging lens.SOLUTION: An imaging lens is comprised of a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group which are arranged in order from the object side to the image side. Upon focusing, the second lens group moves along an optical axis and the first and third lens groups are stationary relative to the image plane. The second lens group includes a diaphragm. A positive Lp1 lens is located on the most object side of the second lens group. A positive Lp2 lens is located on the most image side of the second lens group. The imaging lens satisfies predefined conditional expressions.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] As an imaging lens applicable to imaging devices such as digital cameras and video cameras, for example, lens systems described in Patent Documents 1 to 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, suppresses performance changes associated with focusing, and has good optical performance.

[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, suppresses performance changes associated with focusing, and has good optical performance, and an imaging device including this imaging lens.

Means for Solving the Problems

[0006] A first aspect of the present disclosure is an imaging lens including, 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 positive refractive power, and a third lens group. When focusing, the second lens group moves along the optical axis, the first lens group and the third lens group are fixed with respect to the image plane, the second lens group includes a diaphragm, an Lp1 lens, which is a positive lens, is disposed on the most object side of the second lens group, and an Lp2 lens, which is a positive lens, is disposed on the most image side of the second lens group. When the average value of the refractive indices of the Lp1 lens and the Lp2 lens with respect to the d-line is Np12, and the average value of the Abbe numbers of all the negative lenses included in the second lens group based on the d-line is νn, the following conditional expressions (1) and (2) are satisfied. 1.94 < Np12 < 2.5 (1) 28.4 < νn < 40 (2)

[0007] The imaging lens according to the first aspect preferably satisfies at least one of the following conditional expressions (1-1) and (2-1). 1.965 < Np12 < 2.2 (1-1) 29 < νn < 35 (2-1)

[0008] A second aspect of the present disclosure is an imaging lens including, 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 positive refractive power, and a third lens group. When focusing, the second lens group moves along the optical axis, the first lens group and the third lens group are fixed with respect to the image plane, the second lens group includes a diaphragm, an Lp1 lens, which is a positive lens, is disposed on the most object side of the second lens group, and an Lp2 lens, which is a positive lens, is disposed on the most image side of the second lens group. When the distance on the optical axis from the most object-side lens surface of the third lens group to the most image-side lens surface of the third lens group is D3, and the back focus at the air-equivalent distance of the entire system in a state of focusing on an infinite object is BF, the following conditional expression (3) is satisfied. 0.5 < D3 / BF < 1 (3)

[0009] The imaging lens according to the second aspect preferably satisfies the following conditional expression (3-1). 0.7 < D3 / BF < 1 (3-1)

[0010] In the first and second aspects described above, when the average value of the Abbe numbers of the Lp1 lens and the Lp2 lens based on the d-line is νp12, it is preferable to satisfy the following conditional expression (4). 15 < νp12 < 30 (4)

[0011] In the first and second aspects described above, when the distance on the optical axis from the most object-side lens surface of the second lens group to the most image-side lens surface of the second lens group is D2, and the distance on the optical axis from the most object-side lens surface of the third lens group to the most image-side lens surface of the third lens group is D3, it is preferable to satisfy the following conditional expression (5). 3 < D2 / D3 < 5 (5)

[0012] In the first and second aspects described above, 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 first lens group is f1, it is preferable to satisfy the following conditional expression (6). 0.1 < f / f1 < 0.3 (6)

[0013] In the first and second aspects described above, it is preferable that the second lens group includes a cemented lens in which a negative lens Ln2 lens and an Lp2 lens are cemented in order from the object side.

[0014] In the first and second aspects described above, when the refractive index of the Lp2 lens with respect to the d-line is Np2, and the refractive index of the Ln2 lens with respect to the d-line is Nn2, it is preferable to satisfy the following conditional expression (7). 0.3 < Np2 - Nn2 < 0.7 (7)

[0015] In the first and second aspects described above, when the Abbe number of the Lp2 lens based on the d-line is νp2, and the Abbe number of the Ln2 lens based on the d-line is νn2, it is preferable to satisfy the following conditional expression (8). 5 < νn2 - νp2 < 30 (8)

[0016] In the first and second aspects described above, the Lp1 lens is preferably a positive meniscus lens with a concave surface facing the image side.

[0017] In the first and second aspects described above, the second lens group preferably includes at least two positive lenses and one negative lens on the object side of the aperture stop, and at least two positive lenses and two negative lenses on the image side of the aperture stop.

[0018] In the first and second aspects described above, the third lens group preferably consists of, in order from the object side to the image side, a cemented lens in which a positive lens and a negative lens are sequentially cemented from the object side, and a negative lens with a concave surface facing the object side.

[0019] In the first and second aspects described above, when the back focus at the total system's air equivalent distance is BF, the focal length of the entire system in the state of focusing on an infinite object is f, and the maximum half field angle of the entire system in the state of focusing on an infinite object is ωm, it is preferable to satisfy the following conditional expression (9). 0.5 < BF / (f × tanωm) < 1 (9)

[0020] In the first and second aspects described above, when the sum of the distance on the optical axis from the most object-side lens surface of the first lens group to the most image-side lens surface of the third lens group and the back focus at the total system's air equivalent distance is TL, the focal length of the entire system in the state of focusing on an infinite object is f, and the maximum half field angle of the entire system in the state of focusing on an infinite object is ωm, it is preferable to satisfy the following conditional expression (10), and more preferably to satisfy the following conditional expression (10-1). 7.1 < TL 2 / (f 2 × tanωm) < 11 (10) 8 < TL 2 / (f 2 × tanωm) < 10 (10-1)

[0021] In the first and second aspects described above, when the focal length of the first lens group is f1 and the back focus at the air equivalent distance of the entire system is BF, it is preferable to satisfy the following conditional expression (11). 20 < f1 / BF < 30 (11)

[0022] In the first and second aspects described above, when the distance on the optical axis from the most image-side lens surface of the first lens group to the most object-side lens surface of the second lens group in the state of focusing on an infinite object is D12, the focal length of the entire system in the state of focusing on an infinite object is f, and the maximum half field angle of the entire system in the state of focusing on an infinite object is ωm, it is preferable to satisfy the following conditional expression (12). 1.2 < D12 / (f × tan ωm) < 3 (12)

[0023] The third aspect of the present disclosure is an imaging device including the imaging lens according to the above aspect.

[0024] Note that the expressions “comprising” and “consisting of” in this specification are intended to mean that in addition to the listed components, lenses having substantially 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 may be included.

[0025] “~ group having a positive refractive power” means having a positive refractive power as a whole group. “~ group having a negative refractive power” means having a negative refractive power as a whole group. “~ 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. “Lens having a positive refractive power” and “positive lens” are synonymous. “Lens having a negative refractive power” and “negative lens” are synonymous. “Positive meniscus lens” and “meniscus-shaped positive lens” are synonymous.

[0026] "Single lens" means a single 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 configured and function as a single aspherical lens as a whole) is not regarded as a joined lens and is treated as a single lens. Regarding a lens including an aspherical surface, the sign of the refractive power and the surface shape are considered in the paraxial region unless otherwise specified.

[0027] "Entire system" means an imaging lens. The "focal length" used in the conditional expression is the paraxial focal length. The "distance on the optical axis" used in the conditional expression is considered as the geometric length rather than the air-equivalent length unless otherwise specified. "Back focus at the air-equivalent distance" is the air-equivalent distance on the optical axis from the most image-side lens surface of the imaging lens to the image-side focal position of the imaging lens.

[0028] The values used in the conditional expression are the values based on the d-line in the state of focusing on an infinite object. 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 (nanometer), the wavelength of the C-line is 656.27 nm (nanometer), the wavelength of the F-line is 486.13 nm (nanometer), and the wavelength of the g-line is 435.84 nm (nanometer).

Advantages of the Invention

[0029] According to the present disclosure, it is possible to provide an imaging lens that is small in size, suppresses performance changes associated with focusing, and has good optical performance, and an imaging device including this imaging lens.

Brief Description of the Drawings

[0030]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Mode for Carrying Out the Invention

[0031] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the configuration of an imaging lens and a light beam according to one embodiment of the present disclosure. In FIG. 1, as the light beam, an on-axis light beam 2 and a light beam 3 with a maximum semi-aperture angle ωm are shown. FIG. 2 is a cross-sectional view showing the configuration of the imaging lens of FIG. 1. In FIGS. 1 and 2, a state of focusing on an infinite object is shown, with the left side being the object side and the right side being the image side. In this specification, an object with an infinite distance on the optical axis Z from the object to the image plane Sim is referred to as an "infinite object". The examples shown in FIGS. 1 and 2 correspond to the imaging lens of Example 1 described later.

[0032] In FIGS. 1 and 2, assuming that the imaging lens is applied to an imaging device, an example is shown in which an optical member PP in the shape of a parallel plate is disposed between the imaging lens and the image plane Sim. The optical member PP is a member assuming various filters and / or cover glass, etc. The various filters include a low-pass filter, an infrared cut filter, and / or a filter that cuts a specific wavelength range, etc. The optical member PP is a member having no refractive power. It is also possible to configure the imaging device by omitting the optical member PP.

[0033] The imaging lens according to the present embodiment 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 positive refractive power, and a third lens group G3. Since the first lens group G1 has a positive refractive power, it is advantageous for shortening the overall length of the lens system, and thus advantageous for miniaturization. The second lens group G2 includes the aperture stop St. Note that the aperture stops St in FIGS. 1 and 2 indicate the positions in the optical axis direction, not the shapes and sizes.

[0034] In the example shown in FIGS. 1 and 2, the first lens group G1 consists of two lenses, lenses L11 to L12, in order from the object side to the image side. The second lens group G2 consists of three lenses, lenses L21 to L23, an aperture stop St, and five lenses, lenses L24 to L28, in order from the object side to the image side. The third lens group G3 consists of three lenses, lenses L31 to L33, in order from the object side to the image side.

[0035] In the imaging lens according to the present embodiment, when focusing, the second lens group G2 moves 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. By moving the second lens group G2 together with the aperture stop St during focusing, it is advantageous for suppressing aberration fluctuations associated with focusing. Also, by fixing the first lens group G1 with respect to the image plane Sim during focusing, a lens configuration suitable for a dust and drip proof structure is obtained. Further, by fixing the third lens group G3 with respect to the image plane Sim during focusing, the third lens group G3 moves relatively with respect to the second lens group G2 that moves during focusing, which is advantageous for correcting fluctuations in field curvature associated with focusing.

[0036] Hereinafter, in this specification, the group that moves during focusing is referred to as the "focus group". Focusing is performed by the movement of the focus group. The leftward arrow below the second lens group G2 in FIG. 2 indicates that the second lens group G2 is a focus group that moves toward the object side during focusing from an infinite object to a close-distance object.

[0037] On the most object side of the second lens group G2, a positive lens Lp1, the Lp1 lens, is arranged. Since the Lp1 lens, which is the most object-side lens of the second lens group G2, is a positive lens, the height of the light ray incident on the lens on the image side from the optical axis Z can be reduced, which is advantageous for reducing the diameter of the lens, and thus advantageous for miniaturization. Also, correction of various aberrations becomes easy. In the example of FIG. 1, the lens L21 corresponds to the Lp1 lens Lp1.

[0038] The Lp1 lens Lp1 is preferably a positive meniscus lens with a concave surface facing the image side. By making the Lp1 lens Lp1, which is the most object-side lens of the second lens group G2, a positive meniscus lens with a concave surface facing the image side, it is advantageous for suppressing the occurrence of spherical aberration.

[0039] On the most image side of the second lens group G2, a positive lens Lp2, the Lp2 lens, is arranged. Since the Lp2 lens, which is the most image-side lens of the second lens group G2, is a positive lens, the height of the off-axis light ray incident on the third lens group G3 on the image side from the optical axis Z can be reduced, which is advantageous for reducing the diameter of the lens, and thus advantageous for miniaturization. In the example of FIG. 1, the lens L28 corresponds to the Lp2 lens Lp2.

[0040] The second lens group G2 preferably includes a cemented lens in which a negative lens Ln2 lens Ln2 and an Lp2 lens Lp2 are cemented in order from the object side. That is, the Lp2 lens Lp2 disposed on the most image side of the second lens group G2 is preferably cemented to the Ln2 lens Ln2. By disposing the cemented lens on the most image side of the second lens group G2, while shortening the distance D2 on the optical axis Z from the most object-side lens surface of the second lens group G2 to the most image-side lens surface of the second lens group G2, axial chromatic aberration can be preferably corrected. In the example of FIG. 1, the lens L27 corresponds to the Ln2 lens Ln2 and is cemented to the lens L28 corresponding to the Lp2 lens Lp2.

[0041] The second lens group G2 preferably includes at least two positive lenses and one negative lens on the object side of the aperture stop St, and at least two positive lenses and two negative lenses on the image side of the aperture stop St. By adopting such a configuration, various aberrations generated within the second lens group G2 can be sufficiently corrected, which is advantageous for suppressing aberration variations associated with focusing. Note that the arrangement order of the at least two positive lenses and the one negative lens disposed on the object side of the aperture stop St within the second lens group G2 is not particularly limited. Similarly, the arrangement order of the at least two positive lenses and the two negative lenses disposed on the image side of the aperture stop St within the second lens group G2 is not particularly limited.

[0042] The third lens group G3 preferably consists of, in order from the object side to the image side, a cemented lens in which a positive lens and a negative lens are cemented in order from the object side, and a negative lens with a concave surface facing the object side. Since the third lens group G3 with a high height from the optical axis Z of the off-axis ray includes a cemented lens, it is advantageous for correcting magnification chromatic aberration while shortening the distance D3 on the optical axis Z from the most object-side lens surface of the third lens group G3 to the most image-side lens surface of the third lens group G3. Further, by disposing a negative lens with a concave surface facing the object side on the most image side of the third lens group G3, the Petzval sum can be reduced, which is advantageous for suppressing the occurrence of field curvature.

[0043] For the imaging lens according to this embodiment, when the average value of the refractive indices of the Lp1 lens Lp1 and the Lp2 lens Lp2 with respect to the d-line is defined as Np12, it is preferable to satisfy the following conditional expression (1). By preventing the corresponding value of the conditional expression (1) from falling below the lower limit, even for positive lenses (i.e., the Lp1 lens Lp1 and the Lp2 lens Lp2) that require strong refractive power, it is possible to suppress an excessive decrease in the absolute value of the radius of curvature, which is advantageous for suppressing the occurrence of spherical aberration. Also, it is possible to reduce the Petzval sum, which is advantageous for suppressing the occurrence of field curvature. By preventing the corresponding value of the conditional expression (1) from exceeding the upper limit, it is possible to select materials with an appropriate Abbe number for the Lp1 lens Lp1 and the Lp2 lens Lp2, which is advantageous for correcting axial chromatic aberration. To obtain better characteristics, it is more preferable to satisfy the following conditional expression (1-1), and even more preferable to satisfy the following conditional expression (1-2). 1.94 < Np12 < 2.5 (1) 1.965 < Np12 < 2.2 (1-1) 1.975 < Np12 < 2.15 (1-2)

[0044] For the imaging lens according to this embodiment, when the average value of the Abbe numbers of all the negative lenses included in the second lens group G2 with respect to the d-line is defined as νn, it is preferable to satisfy the following conditional expression (2). By preventing the corresponding value of the conditional expression (2) from falling below the lower limit, it is advantageous for suppressing the occurrence of magnification chromatic aberration. By preventing the corresponding value of the conditional expression (2) from exceeding the upper limit, it is advantageous for correcting axial chromatic aberration. To obtain better characteristics, it is more preferable to satisfy the following conditional expression (2-1), and even more preferable to satisfy the following conditional expression (2-2). 28.4 < νn < 40 (2) 29 < νn < 35 (2-1) 29.5 < νn < 32 (2-2)

[0045] For the imaging lens according to this embodiment, when the distance on the optical axis Z from the lens surface closest to the object side of the third lens group G3 to the lens surface closest to the image side of the third lens group G3 is D3, and the back focus at the air-equivalent distance of the entire system is BF, it is preferable to satisfy the following conditional expression (3). By ensuring that the corresponding value of the conditional expression (3) does not fall below the lower limit, a sufficient D3 can be ensured to correct various aberrations by the third lens group G3, which is advantageous for suppressing aberration fluctuations associated with focusing. By ensuring that the corresponding value of the conditional expression (3) does not exceed the upper limit, D3 does not become excessive, which is advantageous for shortening the overall length of the lens system and thus for miniaturization. To obtain better characteristics, it is more preferable to satisfy the following conditional expression (3-1), and even more preferable to satisfy the following conditional expression (3-2). 0.5 < D3 / BF < 1 (3) 0.7 < D3 / BF < 1 (3-1) 0.7 < D3 / BF < 0.98 (3-2)

[0046] For the imaging lens according to this embodiment, when the average value of the Abbe numbers of the Lp1 lens Lp1 and the Lp2 lens Lp2 based on the d-line is νp12, it is preferable to satisfy the following conditional expression (4). By ensuring that the corresponding value of the conditional expression (4) does not fall below the lower limit, it is advantageous for suppressing the occurrence of axial chromatic aberration. By ensuring that the corresponding value of the conditional expression (4) does not exceed the upper limit, appropriate materials can be selected for the Lp1 lens Lp1 and the Lp2 lens Lp2. To obtain better characteristics, it is more preferable to satisfy the following conditional expression (4-1), and even more preferable to satisfy the following conditional expression (4-2). 15 < νp12 < 30 (4) 20 < νp12 < 25 (4-1) 21.7 < νp12 < 23.5 (4-2)

[0047] For the imaging lens according to this embodiment, when the distance on the optical axis Z from the lens surface closest to the object side of the second lens group G2 to the lens surface closest to the image side of the second lens group is D2, and the distance on the optical axis Z from the lens surface closest to the object side of the third lens group G3 to the lens surface closest to the image side of the third lens group G3 is D3, it is preferable to satisfy the following conditional expression (5). By ensuring that the corresponding value of the conditional expression (5) does not fall below the lower limit, D3 will not become excessively large, 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, D2 will not become excessively large, which is also advantageous for shortening the overall length of the lens system. If the corresponding value of the conditional expression (5) exceeds the upper limit, D2 will become excessively large. Therefore, if an attempt is made to secure a movable range during focusing of the second lens group G2, which is the focusing group, the overall length of the lens system will increase. To obtain better characteristics, it is more preferable to satisfy the following conditional expression (5-1), and even more preferable to satisfy the following conditional expression (5-2). 3 < D2 / D3 < 5 (5) 3.2 < D2 / D3 < 4.8 (5-1) 3.3 < D2 / D3 < 4.6 (5-2)

[0048] For the imaging lens according to this embodiment, when the focal length of the entire system in a state of being focused on an infinite object is f, and the focal length of the first lens group G1 is f1, it is preferable to satisfy the following conditional expression (6). By ensuring that the corresponding value of the conditional expression (6) does not fall below the lower limit, the refractive power of the first lens group G1 will not become too weak, which is advantageous for shortening the overall length of the lens system. By ensuring that the corresponding value of the conditional expression (6) does not exceed the upper limit, the refractive power of the first lens group G1 will not become too strong, which is advantageous for suppressing aberration variation associated with focusing. To obtain better characteristics, it is more preferable to satisfy the following conditional expression (6-1), and even more preferable to satisfy the following conditional expression (6-2). 0.1 < f / f1 < 0.3 (6) 0.15 < f / f1 < 0.3 (6-1) 0.2 < f / f1 < 0.25 (6-2)

[0049] For the imaging lens according to the present embodiment, when the refractive index of the Lp2 lens Lp2 with respect to the d-line is Np2 and the refractive index of the Ln2 lens Ln2 with respect to the d-line is Nn2, it is preferable to satisfy the following conditional expression (7). By preventing the corresponding value of the conditional expression (7) from falling below the lower limit, it is advantageous for correcting various aberrations excluding axial chromatic aberration. By preventing the corresponding value of the conditional expression (7) from exceeding the upper limit, a material with an appropriate Abbe number can be selected for the Lp2 lens Lp2 and the Ln2 lens Ln2, which is advantageous for correcting axial chromatic aberration. To obtain better characteristics, it is more preferable to satisfy the following conditional expression (7-1), and it is even more preferable to satisfy the following conditional expression (7-2). 0.3 < Np2 - Nn2 < 0.7 (7) 0.4 < Np2 - Nn2 < 0.5 (7-1) 0.4 < Np2 - Nn2 < 0.45 (7-2)

[0050] For the imaging lens according to the present embodiment, when the Abbe number of the Lp2 lens Lp2 based on the d-line is νp2 and the Abbe number of the Ln2 lens based on the d-line is νn2, it is preferable to satisfy the following conditional expression (8). By preventing the corresponding value of the conditional expression (8) from falling below the lower limit, even if the absolute value of the radius of curvature of the joint surface between the Lp2 lens Lp2 and the Ln2 lens Ln2 is not made too small, axial chromatic aberration can be preferably corrected. Also, since the absolute value of the radius of curvature of the joint surface between the Lp2 lens Lp2 and the Ln2 lens Ln2 does not become too small, it is advantageous for suppressing the occurrence of spherical aberration. By preventing the corresponding value of the conditional expression (8) from exceeding the upper limit, a material with an appropriate refractive index can be selected for the Ln2 lens Ln2, so that the absolute value of the radius of curvature of the object-side surface of the Ln2 lens Ln2 does not need to be made too small to ensure refractive power, which is advantageous for suppressing the occurrence of spherical aberration. To obtain better characteristics, it is more preferable to satisfy the following conditional expression (8-1), and it is even more preferable to satisfy the following conditional expression (8-2). 5 < νn2 - νp2 < 30 (8) 10 < νn2 - νp2 < 25 (8-1) 15 < νn2 - νp2 < 20 (8-2)

[0051] For the imaging lens according to this embodiment, when the back focus at the air equivalent distance of the entire system is BF, the focal length of the entire system in the state of focusing on an infinite object is f, and the maximum half angle of view of the entire system in the state of focusing on an infinite object is ωm, it is preferable to satisfy the following conditional expression (9). By preventing the corresponding value of the conditional expression (9) from falling below the lower limit, it is possible to suppress an increase in the incident angle of off-axis light rays to the image plane Sim, which is advantageous for suppressing the occurrence of color shading. By preventing the corresponding value of the conditional expression (9) from exceeding the upper limit, BF does not become too long, which is advantageous for shortening the overall length of the lens system. In order to obtain better characteristics, it is more preferable to satisfy the following conditional expression (9-1), and it is even more preferable to satisfy the following conditional expression (9-2). 0.5 < BF / (f × tan ωm) < 1 (9) 0.65 < BF / (f × tan ωm) < 0.9 (9-1) 0.7 < BF / (f × tan ωm) < 0.9 (9-2)

[0052] For the imaging lens according to this embodiment, when the distance on the optical axis Z from the most object-side lens surface of the first lens group G1 to the most image-side lens surface of the third lens group G3 and the back focus at the air equivalent distance of the entire system are TL, the focal length of the entire system in the state of focusing on an infinite object is f, and the maximum half angle of view of the entire system in the state of focusing on an infinite object is ωm, it is preferable to satisfy the following conditional expression (10). By preventing the corresponding value of the conditional expression (10) from falling below the lower limit, TL can be ensured, which is advantageous for achieving good optical performance and for ensuring the movable range of the focus group during focusing. By preventing the corresponding value of the conditional expression (10) from exceeding the upper limit, TL does not become too long, which is advantageous for shortening the overall length of the lens system and for miniaturization. In order to obtain better characteristics, it is more preferable to satisfy the following conditional expression (10-1), and it is even more preferable to satisfy the following conditional expression (10-2). 7.1 < TL 2 / (f 2 × tan ωm) < 11 (10) 8 < TL 2 / (f2 ×tan ωm) < 10 (10 - 1) 8.5 < TL 2 / (f 2 ×tan ωm) < 9.5 (10 - 2)

[0053] When the focal length of the first lens group G1 is f1 and the back focus at the air equivalent distance of the entire system is BF, the imaging lens according to the present embodiment preferably satisfies the following conditional expression (11). By preventing the corresponding value of the conditional expression (11) from falling below the lower limit, the refractive power of the first lens group G1 does not become too strong, which is advantageous for suppressing aberration variation during focusing. By preventing the corresponding value of the conditional expression (11) from exceeding the upper limit, the refractive power of the first lens group G1 does not become too weak, which is advantageous for shortening the overall length of the lens system. In order to obtain better characteristics, it is more preferable to satisfy the following conditional expression (11 - 1), and it is even more preferable to satisfy the following conditional expression (11 - 2). 20 < f1 / BF < 30 (11) 20 < f1 / BF < 26 (11 - 1) 20 < f1 / BF < 22 (11 - 2)

[0054] When the distance on the optical axis from the most image - side lens surface of the first lens group G1 to the most object - side lens surface of the second lens group G2 in the state of focusing on an infinite object is D12, the focal length of the entire system in the state of focusing on an infinite object is f, and the maximum semi - field angle of the entire system in the state of focusing on an infinite object is ωm, the imaging lens according to the present embodiment preferably satisfies the following conditional expression (12). By preventing the corresponding value of the conditional expression (12) from falling below the lower limit, D12 can be ensured, so that a movable region during focusing of the second lens group G2, which is a focus group, can be ensured, and photographing at a closest distance becomes possible. By preventing the corresponding value of the conditional expression (12) from exceeding the upper limit, it is advantageous for shortening the overall length of the lens system and for miniaturization. In order to obtain better characteristics, it is more preferable to satisfy the following conditional expression (12 - 1), and it is even more preferable to satisfy the following conditional expression (12 - 2). 1.2 < D12 / (f × tan ωm) < 3 (12) 1.2 < D12 / (f × tan ωm) < 1.5 (12-1) 1.2 < D12 / (f × tan ωm) < 1.3 (12-2)

[0055] The preferable configurations and possible configurations described above, including the configuration related to the conditional expressions, can be combined arbitrarily, and it is preferable to selectively adopt them as appropriate according to the required specifications. Note that the conditional expressions that the imaging lens of the present disclosure preferably satisfies are not limited to 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 that are described as preferable, more preferable, and even more preferable. Also, the examples shown in FIGS. 1 and 2 are merely examples, and various modifications are possible within the scope not 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 examples of FIGS. 1 and 2.

[0056] As an example, a preferable aspect of the present disclosure 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 positive refractive power, and a third lens group G3. When focusing, the second lens group G2 moves along the optical axis Z, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim, the second lens group G2 includes the aperture stop St, the most object-side of the second lens group G2 is provided with a positive lens Lp1 lens Lp1, and the most image-side of the second lens group G2 is provided with a positive lens Lp2 lens Lp2, and it is an imaging lens that satisfies the above conditional expressions (1) and (2).

[0057] As another example, a preferred embodiment of the present disclosure 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 positive refractive power, and a third lens group G3. When focusing, the second lens group G2 moves along the optical axis Z, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane Sim, the second lens group G2 includes the aperture stop St, the most object-side of the second lens group G2 is provided with a positive lens Lp1 lens Lp1, and the most image-side of the second lens group G2 is provided with a positive lens Lp2 lens Lp2, which is an imaging lens satisfying the above conditional expression (3).

[0058] Next, an embodiment of the imaging lens of the present disclosure will be described with reference to the drawings. Note that the reference numerals attached to the lenses in the cross-sectional views of each embodiment are used independently for each embodiment in order to avoid complicating the description and the drawings due to an increase in the number of digits of the reference numerals. Therefore, even if the same reference numeral is attached in the drawings of different embodiments, it is not necessarily the same configuration.

[0059] [Embodiment 1] The configuration of the imaging lens of Embodiment 1 is shown in FIGS. 1 and 2, and the illustration method and configuration are as described above, so duplicate description will be 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 positive refractive power, and a third lens group G3 having a negative refractive power. The first lens group G1 includes two lenses, lenses L11 to L12, in order from the object side to the image side. The second lens group G2 includes, in order from the object side to the image side, three lenses, lenses L21 to L23, an aperture stop St, and five lenses, lenses L24 to L28. The third lens group G3 includes three lenses, lenses L31 to L33, in order from the object side to the image side.

[0060] 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. Table 1 is described as follows. 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 with respect to the d-line of each component is shown. In the column of νd, the Abbe number based on the d-line of each component is shown. In the column of θgF, the partial dispersion ratio between the g-line and the F-line of each component is shown. The partial dispersion ratio θgF between the g-line and the F-line of a certain lens is defined as θgF = (Ng - NF) / (NF - NC), where Ng, NF, and NC are the refractive indices of the lens with respect to the g-line, F-line, and C-line, respectively.

[0061] 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. 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. In Table 1, for the variable surface interval during focusing, the symbol DD[ ] is used, and the surface number on the object side of this interval is appended in [ ] and described in the column of D.

[0062] Table 2 shows the values of the focal length f of the entire system, the back focus BF, the F-number FNo., the maximum full angle of view 2ωm, and the variable surface intervals. The [°] in the column of 2ωm means that the unit is degrees. For the back focus BF, the value in the state of focusing on an infinite object is 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 closest object with a distance of 0.5 m (meter) from the object to the image plane Sim on the optical axis Z are shown in the column marked "0.5 m". The values shown in Table 2 are the values based on the d-line.

[0063] In Table 1, an asterisk is attached to the surface number of the aspheric surface, and the numerical value of the paraxial radius of curvature is described in the column of the radius of curvature of the aspheric surface. In Table 3, the row of Sn shows the surface number of the aspheric surface, and the rows of KA and Am (m is an integer of 4 or more) show the numerical values of the aspheric coefficients for each aspheric surface. The "E±n" (n is an integer) of the numerical value of the aspheric coefficient in Table 3 means "×10 ±n ". KA and Am are the aspheric coefficients in the aspheric formula represented by the following formula. Zd = C × h 2 / {1 + (1 - KA × C 2 × h 2 ) 1 / 2}+ ΣAm × h m However, Zd: Aspheric depth (the length of the perpendicular line dropped from the point on the aspheric surface with height h to the plane perpendicular to the optical axis where the aspheric vertex touches) h: Height (the distance from the optical axis to the lens surface) C: Reciprocal of the paraxial radius of curvature KA, Am: Aspheric coefficients where Σ in the aspheric formula means the sum with respect to m.

[0064] 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, the numerical values rounded to a predetermined number of digits are described in each of the following tables.

[0065]

Table 1

[0066]

Table 2

[0067]

Table 3

[0068] 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 part marked "Distance: Infinity" shows the aberration diagrams in the state of focusing on an object at infinity, and the lower part marked "Distance: 0.5 m" shows the aberration diagrams in the state of focusing on a close object with a distance of 0.5 m (meter) on the optical axis Z from the object to the image plane Sim. In the spherical aberration diagram, the aberrations at the d-line, C-line, and F-line are shown by solid line, long dashed line, and short dashed line, respectively. In the astigmatism diagram, the aberration at the d-line in the sagittal direction is shown by a solid line, and the aberration at the d-line in the tangential direction is shown by a short dashed line. In the distortion diagram, the aberration at the d-line is shown by a solid line. In the chromatic aberration of magnification diagram, the aberrations at the C-line and F-line are shown by a long dashed line and a short dashed line, respectively. In the spherical aberration diagram, the value of the F-number is shown after "FNo. =", and in the other aberration diagrams, the value of the semi-field angle corresponding to the upper end of the vertical axis is shown after "ω =".

[0069] The symbols, meanings, description methods, and illustration methods of the respective data regarding the above Example 1 are the same in the following examples unless otherwise specified, so duplicate explanations are omitted below.

[0070] [Example 2] Fig. 4 is a cross-sectional view of the configuration of the imaging lens of Example 2 in the state of focusing on an object at infinity. The imaging lens of Example 2 is composed of a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power, in order from the object side to the image side. The first lens group G1 is composed of two lenses, lenses L11 to L12, in order from the object side to the image side. The second lens group G2 is composed of three lenses, lenses L21 to L23, an aperture stop St, and five lenses, lenses L24 to L28, in order from the object side to the image side. The third lens group G3 is composed of three lenses, lenses L31 to L33, in order from the object side to the image side.

[0071] Regarding 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 respective aberration diagrams are shown in Fig. 5.

[0072]

Table 4

[0073]

Table 5

[0074]

Table 6

[0075] [Example 3] Figure 6 is a cross-sectional view of the configuration of the imaging lens of Example 3 in a state where it is focused on an infinite object. The imaging lens of Example 3 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 positive refractive power, and a third lens group G3 having a negative refractive power. The first lens group G1 includes three lenses, lenses L11 to L13, in order from the object side to the image side. The second lens group G2 includes three lenses, lenses L21 to L23, an aperture stop St, and four lenses, lenses L24 to L27, in order from the object side to the image side. The third lens group G3 includes three lenses, lenses L31 to L33, in order from the object side to the image side.

[0076] Regarding 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 Figure 7.

[0077]

Table 7

[0078]

Table 8

[0079]

Table 9

[0080] [Example 4] FIG. 8 is a cross-sectional view of the configuration of the imaging lens according to Example 4 in a state of being focused on an infinite object. The imaging lens according to Example 4 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 positive refractive power, and a third lens group G3 having a negative refractive power. The first lens group G1 includes two lenses, lenses L11 to L12, in order from the object side to the image side. The second lens group G2 includes, in order from the object side to the image side, three lenses, lenses L21 to L23, an aperture stop St, and four lenses, lenses L24 to L27. The third lens group G3 includes three lenses, lenses L31 to L33, in order from the object side to the image side.

[0081] For the imaging lens according to 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.

[0082]

Table 10

[0083]

Table 11

[0084]

Table 12

[0085] [Example 5] FIG. 10 is a cross-sectional view of the configuration of the imaging lens according to Example 5 in a state of being focused on an infinite object. The imaging lens according to Example 5 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 positive refractive power, and a third lens group G3 having a positive refractive power. The first lens group G1 includes two lenses, lenses L11 to L12, in order from the object side to the image side. The second lens group G2 includes, in order from the object side to the image side, three lenses, lenses L21 to L23, an aperture stop St, and four lenses, lenses L24 to L27. The third lens group G3 includes three lenses, lenses L31 to L33, in order from the object side to the image side.

[0086] Regarding the imaging lens according to 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.

[0087]

Table 13

[0088]

Table 14

[0089]

Table 15

[0090] Table 16 shows the corresponding values of the conditional expressions (1) to (12) of the imaging lenses according to Examples 1 to 5.

[0091]

Table 16

[0092] As can be seen from the data described above, the imaging lenses according to Examples 1 to 5 are configured to have good optical performance while suppressing performance changes associated with focusing, despite being small in size.

[0093] Next, an imaging device according to an embodiment of the present disclosure will be described. FIGS. 12 and 13 show external views of a camera 30 which is an imaging device according to an embodiment of the present disclosure. FIG. 12 shows a perspective view of the camera 30 seen from the front side, and FIG. 13 shows a perspective view of the camera 30 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.

[0094] 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 an image that has been captured and an image within the angle of view before being captured.

[0095] A photographing aperture through which light from a photographing object enters 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.

[0096] 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 a 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. In 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.

[0097] 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, the interval between surfaces, the refractive index, the Abbe number, the aspherical coefficient, etc. of each lens are not limited to the values shown in the above numerical examples, and other values can be taken.

[0098] Also, the imaging device according to the embodiment of the present disclosure is not limited to the above example, and can be in various forms, for example, cameras other than the mirrorless type, film cameras, video cameras, etc.

Explanation of Reference Numerals

[0099] 1 Imaging lens 2 On-axis light beam 3 Light beam at the maximum half field angle 20 Interchangeable lens 30 Camera 31 Camera body 32 Shutter button 33 Power button 34, 35 Operation unit 36 Display unit 37 Mount D2, D3, D12 Distance G1 First lens group G2 Second lens group G3 Third lens group L11~L33 Lenses Ln2 Ln2 lens Lp1 Lp1 lens Lp2 Lp2 lens PP Optical member Sim Image plane St Aperture stop Z Optical axis ωm Maximum half field angle

Claims

1. It consists of a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group, in order from the object side to the image side. During focusing, the second lens group moves along the optical axis, and the first lens group and the third lens group are fixed with respect to the image plane. The second lens group includes a diaphragm. On the most object side of the second lens group, an Lp1 lens, which is a positive lens, is arranged. On the most image side of the second lens group, an Lp2 lens, which is a positive lens, is arranged. The third lens group consists of, in order from the object side to the image side, a cemented lens in which a positive lens and a negative lens are cemented in order from the object side, and a negative lens having a concave surface facing the object side. Let the average value of the refractive indices of the Lp1 lens and the Lp2 lens with respect to the d-line be Np12. When the average value of the Abbe numbers of all the negative lenses included in the second lens group with respect to the d-line is νn. 1.94 < Np12 < 2.5 (1) 28.4 < νn < 40 (2) An imaging lens that satisfies the conditional expressions (1) and (2) represented by the above.

2. It consists of a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group, in order from the object side to the image side. During focusing, the second lens group moves along the optical axis, and the first lens group and the third lens group are fixed with respect to the image plane. The second lens group includes a diaphragm. On the most object side of the second lens group, an Lp1 lens, which is a positive lens, is arranged. On the most image side of the second lens group, an Lp2 lens, which is a positive lens, is arranged. Let the average value of the refractive indices of the Lp1 lens and the Lp2 lens with respect to the d-line be Np12. Let the average value of the Abbe numbers of all the negative lenses included in the second lens group with respect to the d-line be νn. In the state of focusing on an infinite object, the distance on the optical axis from the most image-side lens surface of the first lens group to the most object-side lens surface of the second lens group is D12. The focal length of the entire system in the state of focusing on an infinite object is f. When the maximum half field angle of the entire system in the state of focusing on an infinite object is ωm. 1.94 < Np12 < 2.5 (1) 28.4 < νn < 40 (2) 1.2 < D12 / (f × tan ωm) < 3 (12) An imaging lens that satisfies the conditional expressions (1), (2), and (12) represented by the above.

3. It consists of a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group, in order from the object side to the image side. When focusing, the second lens group moves along the optical axis, and the first lens group and the third lens group are fixed with respect to the image plane. The second lens group includes a diaphragm. On the most object side of the second lens group, an Lp1 lens, which is a positive lens, is arranged. On the most image side of the second lens group, an Lp2 lens, which is a positive lens, is arranged. Let the average value of the refractive indices of the Lp1 lens and the Lp2 lens with respect to the d-line be Np12. When the average value of the Abbe numbers of all the negative lenses included in the second lens group based on the d-line is νn. 1.965 < Np12 < 2.2 (1-1) 28.4 < νn < 40 (2) An imaging lens that satisfies the conditional expressions (1-1) and (2) represented by the above.

4. When the average value of the Abbe numbers of the Lp1 lens and the Lp2 lens based on the d-line is νp12. 15 < νp12 < 30 (4) The imaging lens according to any one of Claims 1 to 3, which satisfies the conditional expression (4) represented by the above.

5. Let the distance on the optical axis from the most object-side lens surface of the second lens group to the most image-side lens surface of the second lens group be D2. When the distance on the optical axis from the most object-side lens surface of the third lens group to the most image-side lens surface of the third lens group is D3. 3 < D2 / D3 < 5 (5) The imaging lens according to any one of Claims 1 to 4, which satisfies the conditional expression (5) represented by the above.

6. Let the focal length of the entire system in the state of focusing on an infinite object be f. When the focal length of the first lens group is f1. 0.1 < f / f1 < 0.3 (6) The imaging lens according to any one of Claims 1 to 5, which satisfies the conditional expression (6) represented by the above.

7. The second lens group includes a cemented lens in which an Ln2 lens, which is a negative lens, and the Lp2 lens are cemented in order from the object side. The imaging lens according to any one of Claims 1 to 6.

8. Let the refractive index of the Lp2 lens with respect to the d-line be Np2. When the refractive index of the Ln2 lens with respect to the d-line is Nn2. 0.3 < Np2 - Nn2 < 0.7 (7) The imaging lens according to Claim 7, which satisfies the conditional expression (7) represented by the above.

9. Let the Abbe number of the Lp2 lens based on the d-line be νp2. When the Abbe number of the Ln2 lens based on the d-line is νn2. 5 < νn2 - νp2 < 30 (8) The imaging lens according to Claim 7 or Claim 8, which satisfies the conditional expression (8) represented by the above.

10. The Lp1 lens is a positive meniscus lens with a concave surface facing the image side. The imaging lens according to any one of claims 1 to 9.

11. The second lens group includes at least two positive lenses and one negative lens on the object side of the aperture, and includes at least two positive lenses and two negative lenses on the image side of the aperture. The imaging lens according to any one of claims 1 to 10.

12. Let the back focus at the air equivalent distance of the entire system be BF, Let the focal length of the entire system in the state of focusing on an infinite object be f, When the maximum half angle of view of the entire system in the state of focusing on an infinite object is ωm, 0.5 < BF / (f × tan ωm) < 1 (9) The imaging lens according to any one of claims 1 to 11 that satisfies the conditional expression (9) represented by the above.

13. Let the distance on the optical axis from the most object-side lens surface of the first lens group to the most image-side lens surface of the third lens group be TL, Let the focal length of the entire system in the state of focusing on an infinite object be f, When the maximum half angle of view of the entire system in the state of focusing on an infinite object is ωm, 7.1 < TL ２ / (f ２ × tan ωm) < 11 (10) The imaging lens according to any one of claims 1 to 12 that satisfies the conditional expression (10) represented by the above.

14. Let the focal length of the first lens group be f1, When the back focus at the air equivalent distance of the entire system is BF, 20 < f1 / BF < 30 (11) The imaging lens according to any one of claims 1 to 13 that satisfies the conditional expression (11) represented by the above.

15. 29 < νn < 35 (2-1) The imaging lens according to any one of claims 1 to 3 that satisfies the conditional expression (2-1) represented by the above.

16. 8 < TL ２ / (f ２ ×tan ωm) < 10 (10 - 1) The imaging lens according to claim 13 that satisfies the conditional expression (10-1) represented by the above.

17. An imaging device including the imaging lens according to any one of claims 1 to 16.

Images