Imaging optical system, imaging apparatus, and camera system

Abstract

To provide an imaging optical system capable of satisfactorily correcting various aberrations, an imaging apparatus, and a camera system.SOLUTION: The imaging optical system includes: an aperture diaphragm; a lens element LF1 with a positive power, which is adjacent to the image side of the aperture diaphragm; a lens element LR1 with a positive power, which is located on the most image side; a lens element LR2 with a negative power, which is adjacent to the object side of a lens element LR1; and a lens element LR3 with a positive power, which is adjacent to the object side of lens element LR2. The imaging optical system satisfies the following conditions (1) and (2): 0.5<Linf / Yinf<2.65...(1) 0.5<BLinf / Yinf<2.0...(2). Here, Linf indicates total optical length when focused at infinity; Yinf indicates image height when focused at infinity; and BLinf indicates distance from the image side of the lens element closest to the image side to the image plane when focused at infinity.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present disclosure generally relates to an imaging optical system, an imaging device, and a camera system, and more particularly to an imaging optical system capable of effectively correcting various aberrations, and an imaging device and a camera system using the imaging optical system. [Background technology]

[0002] Patent Document 1 discloses an optical system having a plurality of lens groups and an aperture stop.

[0003] The optical system includes a first lens group B1 with positive refractive power located on the object side of an aperture stop SP, and a second lens group B2 with positive refractive power located on the image side of the aperture stop SP. The first lens group B1 includes, arranged in order from the object side to the image side, a first positive lens Lp1, a second positive lens Lp2, and a first negative lens Ln1. The second lens group B2 includes, arranged in order from the object side to the image side, at least one lens, a second negative lens Ln2, and a third positive lens Lp3. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-184748 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide an imaging optical system capable of effectively correcting various aberrations, and an imaging device and a camera system that use the imaging optical system. [Means for solving the problem]

[0006] An imaging optical system in one embodiment of the present disclosure includes an aperture stop, a lens element LF1 adjacent to the image side of the aperture stop and having positive power, a lens element LR1 located closest to the image side and having positive power, a lens element LR2 adjacent to the object side of lens element LR1 and having negative power, and a lens element LR3 adjacent to the object side of lens element LR2 and having positive power.

[0007] And the following conditions (1) and (2) are satisfied.

[0008] 0.5 < Linf / Yinf < 2.65 (1) 0.5 < BLinf / Yinf < 2.0 (2) where: Linf: Total optical length when focused at infinity, Yinf: Image height when focused at infinity, BLinf: The distance from the image side of the lens element closest to the image plane when focusing at infinity. is.

[0009] Furthermore, a camera system according to one aspect of the present disclosure is a camera system comprising: an interchangeable lens device including the imaging optical system described above; and a camera body that is detachably connected to the interchangeable lens device via a camera mount portion and includes an image sensor that receives an optical image formed by the imaging optical system and converts it into an electrical image signal, wherein the interchangeable lens device forms an optical image of an object on the image sensor.

[0010] An imaging device according to one aspect of the present disclosure converts an optical image of an object into an electrical image signal and at least one of displays and stores the converted image signal. The imaging device includes the imaging optical system described above and an imaging element. The imaging optical system forms an optical image of the object. The imaging element converts the optical image formed by the imaging optical system into an electrical image signal. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide an imaging optical system capable of effectively correcting various aberrations, and an imaging device and a camera system that use the imaging optical system. [Brief explanation of the drawings]

[0012] [Figure 1A] 1 is a lens arrangement diagram showing an imaging optical system according to the first embodiment (numerical example 1); [Figure 1B] 1 is a longitudinal aberration diagram of the imaging optical system according to Numerical Example 1. [Figure 2A] 1 is a lens arrangement diagram showing an imaging optical system according to a second embodiment (numerical example 2); [Figure 2B] 10A and 10B are longitudinal aberration diagrams of the imaging optical system according to Numerical Example 2. [Figure 3A] 10 is a lens arrangement diagram showing an imaging optical system according to the third embodiment (Numerical Example 3). [Figure 3B] 10A and 10B are longitudinal aberration diagrams of the imaging optical system according to Numerical Example 3. [Figure 4A] 10 is a lens arrangement diagram showing an imaging optical system according to the fourth embodiment (numerical example 4); [Figure 4B] 10A and 10B are longitudinal aberration diagrams of the imaging optical system according to Numerical Example 4. [Figure 5] 1 is a schematic diagram of an imaging device according to a first embodiment; [Figure 6] 1 is a schematic diagram illustrating the configuration of a lens-interchangeable digital camera system according to a first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of well-known matters or redundant explanation of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy in the following explanation and to facilitate understanding by those skilled in the art.

[0014] The applicants provide the accompanying drawings and the following description to enable those skilled in the art to fully understand the present disclosure, and do not intend for them to limit the subject matter described in the claims.

[0015] (Embodiments 1 to 4) 1A, 2A, 3A, and 4A show lens arrangements and operations of the imaging optical systems according to the first to fourth embodiments.

[0016] In this disclosure, unless otherwise specified, "focusing" refers to the imaging optical system "focusing" or "focusing." Also, in this disclosure, unless otherwise specified, "optical axis" refers to the optical axis of the imaging optical system.

[0017] (a) of Figures 1A, 2A, 3A, and 4A all show lens arrangements in an infinity-focused state. In (a) of each figure, the line drawn on the far right indicates the position of the image plane S (the surface facing the object, which corresponds to the surface on which the image sensor, described below, is arranged). Therefore, the left side of these figures corresponds to the object side. Furthermore, for example, a low-pass filter or a parallel plate P is arranged between the image plane S and the final lens group facing the image plane S. Note that the aspect ratio is consistent in (a) of each figure.

[0018] In addition, an asterisk * on the surface of a specific lens element shown in (a) of each figure indicates that the surface is aspherical. If an asterisk * is not attached to the object-side or image-side surface of a lens element, the surface is spherical.

[0019] 1A, 2A, 3A, and 4A(b) all show lens arrangements in the near-focus state.

[0020] (Embodiment 1) The imaging optical system according to the first embodiment will be described below with reference to FIG. 1A.

[0021] FIG. 1A shows an imaging optical system according to the first embodiment.

[0022] The imaging optical system is composed of, in order from the object side to the image side, a first lens element L1 having negative power, an aperture stop A, a second lens element L2 having positive power, a third lens element L3 having positive power, a fourth lens element L4 having negative power, and a fifth lens element L5 having positive power.

[0023] A parallel plate P is disposed between the fifth lens element L5 and the image plane S.

[0024] The imaging optical system forms an image at the position of an image plane S.

[0025] Each lens element will now be described.

[0026] The first lens element L1 is a meniscus lens having a convex surface facing the image side. Both surfaces of the first lens element L1 are aspheric. The first lens element L1 is an example of a lens group having negative power.

[0027] The second lens element L2 is a biconvex lens. Both surfaces of the second lens element L2 have aspherical shapes. The second lens element L2 is an example of the lens element LF1.

[0028] The third lens element L3 is a meniscus lens having a convex surface facing the image side. Both surfaces of the third lens element L3 are aspheric. The third lens element L3 is an example of the lens element LR3.

[0029] The fourth lens element L4 is a meniscus lens having a convex surface facing the image side. Both surfaces of the fourth lens element L4 are aspherical. The fourth lens element L4 is an example of the lens element LR2.

[0030] The fifth lens element L5 is a meniscus lens having a convex surface facing the object side. Both surfaces of the fifth lens element L5 are aspherical. The fifth lens element L5 is an example of the lens element LR1.

[0031] In the imaging optical system according to embodiment 1, when focusing from infinity to a close object during imaging, the first lens element L1, the second lens element L2, the third lens element L3, the fourth lens element L4, and the fifth lens element L5 move toward the object side with respect to the image plane S. When focusing from infinity to a close object during imaging, the distance between two adjacent lens elements is constant.

[0032] (Embodiment 2) The imaging optical system according to the second embodiment will be described below with reference to FIG. 2A.

[0033] FIG. 2A shows an imaging optical system according to the second embodiment.

[0034] The imaging optical system is composed of, in order from the object side to the image side, an aperture stop A, a first lens element L1 having positive power, a second lens element L2 having positive power, a third lens element L3 having negative power, and a fourth lens element L4 having positive power.

[0035] A parallel plate P is disposed between the fourth lens element L4 and the image plane S.

[0036] The imaging optical system forms an image at the position of an image plane S.

[0037] Each lens element will now be described.

[0038] The first lens element L1 is a meniscus lens having a convex surface facing the object side. Both surfaces of the first lens element L1 are aspheric. The first lens element L1 is an example of the lens element LF1.

[0039] The second lens element L2 is a meniscus lens having a convex surface facing the image side. The second lens element L2 is an example of the lens element LR3.

[0040] The third lens element L3 is a biconcave lens and is an example of the lens element LR2.

[0041] The fourth lens element L4 is a biconvex lens, and is an example of the lens element LR1.

[0042] In the imaging optical system according to embodiment 2, when focusing from infinity to a close object during imaging, the first lens element L1, the second lens element L2, the third lens element L3, and the fourth lens element L4 move toward the object side with respect to the image plane S. When focusing from infinity to a close object during imaging, the distance between two adjacent lens elements is constant.

[0043] (Embodiment 3) The imaging optical system according to the third embodiment will be described below with reference to FIG. 3A.

[0044] FIG. 3A shows an imaging optical system according to the third embodiment.

[0045] The imaging optical system is composed of, in order from the object side to the image side, an aperture stop A, a first lens element L1 having positive power, a second lens element L2 having negative power, a third lens element L3 having positive power, a fourth lens element L4 having negative power, and a fifth lens element L5 having positive power.

[0046] A parallel plate P is disposed between the fifth lens element L5 and the image plane S.

[0047] The imaging optical system forms an image at the position of an image plane S.

[0048] Each lens element will now be described.

[0049] The first lens element L1 is a meniscus lens having a convex surface facing the object side, and is an example of the lens element LF1.

[0050] The second lens element L2 is a meniscus lens having a convex surface facing the image side.

[0051] The third lens element L3 is a biconvex lens and is an example of the lens element LR3.

[0052] The fourth lens element L4 is a biconcave lens and is an example of the lens element LR2.

[0053] The fifth lens element L5 is a meniscus lens having a convex surface facing the object side, and is an example of the lens element LR1.

[0054] In the imaging optical system according to embodiment 3, when focusing from infinity to a close object during imaging, the first lens element L1, the second lens element L2, the third lens element L3, the fourth lens element L4, and the fifth lens element L5 move toward the object side with respect to the image plane S. When focusing from infinity to a close object during imaging, the distance between two adjacent lens elements is constant.

[0055] (Fourth embodiment) The imaging optical system according to the fourth embodiment will be described below with reference to FIG. 4A.

[0056] FIG. 4A shows an imaging optical system according to the fourth embodiment.

[0057] The imaging optical system is composed of, in order from the object side to the image side, an aperture stop A, a first lens element L1 having positive power, a second lens element L2 having negative power, a third lens element L3 having positive power, a fourth lens element L4 having negative power, and a fifth lens element L5 having positive power.

[0058] A parallel plate P is disposed between the fifth lens element L5 and the image plane S.

[0059] The imaging optical system forms an image at the position of an image plane S.

[0060] Each lens element will now be described.

[0061] The first lens element L1 is a meniscus lens having a convex surface facing the object side, and is an example of the lens element LF1.

[0062] The second lens element L2 is a meniscus lens having a convex surface facing the image side.

[0063] The third lens element L3 is a meniscus lens having a convex surface facing the image side, and is an example of the lens element LR3.

[0064] The fourth lens element L4 is a meniscus lens having a convex surface facing the image side, and is an example of the lens element LR2.

[0065] The fifth lens element L5 is a meniscus lens having a convex surface facing the image side, and is an example of the lens element LR1.

[0066] In the imaging optical system according to embodiment 3, when focusing from infinity to a close object during imaging, the first lens element L1, the second lens element L2, the third lens element L3, the fourth lens element L4, and the fifth lens element L5 move toward the object side with respect to the image plane S. When focusing from infinity to a close object during imaging, the distance between two adjacent lens elements is constant.

[0067] (Conditions and effects, etc.) Below, we will explain conditions that can be satisfied by the imaging optical systems according to, for example, Embodiments 1 to 4. Note that, although multiple possible conditions are defined for the imaging optical systems according to Embodiments 1 to 4, the imaging optical system configuration that satisfies all of these multiple conditions is the most effective. However, it is also possible to obtain imaging optical systems that achieve the respective effects by satisfying individual conditions.

[0068] For example, like the imaging optical systems according to Embodiments 1 to 4, the imaging optical system according to the present disclosure includes an aperture stop, a lens element LF1 having positive power and adjacent to the image side of the aperture stop, a lens element LR1 having positive power and positioned closest to the image side, a lens element LR2 having negative power and adjacent to the object side of lens element LR1, and a lens element LR3 having positive power and adjacent to the object side of lens element LR2. This configuration is the basic configuration.

[0069] This basic configuration makes it possible to realize a compact, high-performance lens.

[0070] Furthermore, for example, it is desirable that the imaging optical system satisfy the following condition (1).

[0071] 0.5 < Linf / Yinf < 2.65 (1) where: Linf: Total optical length when focused at infinity, Yinf: Image height when focused at infinity, is.

[0072] Condition (1) is a condition for specifying the ratio of the total optical length when focusing at infinity in an imaging optical system (the distance on the optical axis from the object-side surface of the lens element closest to the object, between the surface on which aperture stop A is located and the object-side surface of the lens element closest to the object, to image plane S) to the image height when focusing at infinity (approximately equal to the length from the center to the diagonal of the image sensor).

[0073] If the lower limit of condition (1) is exceeded, the optical system becomes too small, making it difficult to correct aberrations, which is undesirable, whereas if the upper limit of condition (1) is exceeded, the optical system becomes too large, which is undesirable.

[0074] Preferably, the above-mentioned effects can be further enhanced by satisfying either one or both of the following conditions (1a) and (1b):

[0075] 0.80 < Linf / Yinf (1a) Linf / Yinf < 2.40 (1b) More preferably, the above-mentioned effect can be further enhanced by satisfying either one or both of the following conditions (1c) and (1d):

[0076] 1.30 < Linf / Yinf (1c) Linf / Yinf < 2.20 (1d) Furthermore, for example, it is desirable that the imaging optical system satisfy the following condition (2).

[0077] 0.5 < BLinf / Yinf < 2.0 (2) where: Yinf: Image height when focused at infinity, BLinf: Distance from the image side of the lens element closest to the image plane S when focused at infinity, is.

[0078] Condition (2) is a condition for specifying the ratio of the image height (approximately equal to the length from the center to the diagonal of the image sensor) when focused at infinity in an imaging optical system to the distance from the image side surface of the lens element closest to the image side to the image plane S when focused at infinity.

[0079] If the lower limit of condition (2) is exceeded, the distance from the image side surface of the lens element closest to the image to the image plane S becomes narrow. This makes it difficult to arrange the components that fasten the imaging optical system to the imaging element located at the image plane S, which is undesirable. On the other hand, if the upper limit of condition (2) is exceeded, the distance from the image side surface of the lens element closest to the image to the image plane S becomes wide. This makes the imaging optical system too large, which is undesirable.

[0080] Preferably, the above-mentioned effect can be further enhanced by satisfying either one or both of the following conditions (2a) and (2b).

[0081] 0.6 < BLinf / Yinf (2a) BLinf / Yinf < 1.5 (2b) More preferably, the above-mentioned effect can be further enhanced by satisfying either one or both of the following conditions (2c) and (2d):

[0082] 0.7 < BLinf / Yinf (2a) BLinf / Yinf < 1.0 (2b) Also, for example, it is desirable that the imaging optical system comprises, in order from the object side, a lens group having negative power and an aperture stop A.

[0083] By locating aperture stop A on the object side of lens element LF1 with positive power, the distance from the lens element closest to the object to the lens element closest to the image can be made small. Furthermore, by locating a lens group with negative power on the object side of aperture stop A, the compact design facilitates aberration correction for the lens group located on the image side of the aperture stop with strong positive power.

[0084] Furthermore, for example, the imaging optical system may include a lens element with negative power adjacent to the aperture stop A on the object side.

[0085] This allows the distance from the lens element with negative power adjacent to the object side of aperture stop A to the lens element closest to the image side to be reduced, and the reduction in size makes it easier to correct aberrations in the lens group that has strong positive power and is positioned on the image side of aperture stop A.

[0086] Furthermore, for example, it is desirable that the imaging optical system satisfy the following condition (3):

[0087] nd_LF1 < 1.65 (3) where: nd_LF1: refractive index of lens element LF1, is.

[0088] Condition (3) is a condition for defining the refractive index of the lens element LF1.

[0089] If the upper limit of the condition (3) is exceeded, the spherical aberration will undesirably increase to the positive side.

[0090] Preferably, the following condition (3a) is satisfied, so that the above effect can be further enhanced.

[0091] nd_LF1 < 1.60 (3a) More preferably, the above-mentioned effect can be further enhanced by satisfying the following condition (3b):

[0092] nd_LF1 < 1.55 (3b) It is more preferable to satisfy the following condition (3c) in addition to any one of the conditions (3), (3a), and (3b).

[0093] 1.40 < nd_LF1 (3c) If the lower limit of the condition (3c) is not reached, there is a risk that spherical aberration will become large on the negative side.

[0094] Furthermore, for example, it is desirable that the imaging optical system satisfy the following condition (4):

[0095] 50 < vd_LF1 (4) where: vd_LF1: Abbe number of lens element LF1, is.

[0096] Condition (4) is a condition for defining the Abbe number of lens element LF1.

[0097] If the lower limit of the condition (4) is not met, the longitudinal chromatic aberration becomes large, which is not preferable.

[0098] Preferably, the above effect can be further enhanced by satisfying the following condition (4a):

[0099] 60 < vd_LF1 (4a) It is more preferable to satisfy the following condition (4b) in addition to either condition (3) or condition (3a).

[0100] vd_LF1 < 100 (4b) If the upper limit of the condition (4b) is exceeded, there are few glass materials having the desired Abbe number, which may make it difficult to select the material for the lens elements.

[0101] Furthermore, for example, in an imaging optical system, it is desirable that the lens element adjacent to the image side of the lens element LF1 has an object side surface that is convex toward the image side.

[0102] This makes it possible to easily correct various aberrations, particularly spherical aberration.

[0103] Furthermore, for example, in an imaging optical system, it is desirable to have three to six lens elements on the image side of the aperture stop A.

[0104] It is not preferable to use two or fewer lens elements on the image side of aperture stop A, as this makes it difficult to correct aberrations. It is also not preferable to use seven or more lens elements on the image side of aperture stop A, as this increases the size of the optical system.

[0105] Furthermore, for example, in focusing operations from infinity to close range, it is desirable that at least the lens element adjacent to the image side of aperture stop A to the lens element closest to the image side move as a single unit.

[0106] This makes it easier to correct aberrations when focusing from an object focused at infinity to a close object. Furthermore, the lens elements from the lens element adjacent to the image side of aperture diaphragm A to the lens element closest to the image may move integrally with aperture diaphragm A. By moving aperture diaphragm A integrally, the spacing required during focusing can be reduced, making it easier to make the lens smaller.

[0107] Furthermore, for example, it is desirable that the imaging optical system satisfy the following condition (5):

[0108] -1.0 < (R1_LR2 - R2_LR3) / (R1_LR2 + R2_LR3) < 0.5 (5) where: R1_LR2: radius of curvature of the object-side surface of lens element LR2, R2_LR3: Radius of curvature of the image side surface of lens element LR3, is.

[0109] Condition (5) is a condition for defining the form factor of the air lens between the radius of curvature of the object-side surface of lens element LR2 and the radius of curvature of the image-side surface of lens element LR3.

[0110] If the lower limit of condition (5) is exceeded, the spherical aberration will undesirably become too large on the positive side, whereas if the upper limit of condition (5) is exceeded, the spherical aberration will undesirably become too large on the negative side.

[0111] Preferably, the above-mentioned effects can be further enhanced by satisfying either one or both of the following conditions (5a) and (5b):

[0112] -0.7 < (R1_LR2 - R2_LR3) / (R1_LR2 + R2_LR3) ···(5a) (R1_LR2 - R2_LR3) / (R1_LR2 + R2_LR3) < 0.2 ···(5b) More preferably, the above-mentioned effect can be further enhanced by satisfying either one or both of the following conditions (5c) and (5d):

[0113] -0.5 < (R1_LR2 - R2_LR3) / (R1_LR2 + R2_LR3) ···(5c) (R1_LR2 - R2_LR3) / (R1_LR2 + R2_LR3) < 0.0 ···(5d) Furthermore, for example, it is desirable that the imaging optical system satisfy the following condition (6):

[0114] 0.5 < L_ss_LR1R2 / Yinf < 3.0 (6) where: L_ss_LR1R2: The distance from the aperture stop A to the image side of the lens element LR1 when focusing at infinity, Yinf: Image height when focused at infinity, is.

[0115] Condition (6) is a condition for specifying the ratio in an imaging optical system between the distance from aperture stop A to the image side surface of lens element LR1 when focusing at infinity and the image height (approximately equal to the length from the center to the diagonal of the imaging element) when focusing at infinity.

[0116] If the lower limit of condition (6) is not met, aperture stop A will be too close to image plane S, which will increase the angle of incidence on the imaging surface too much and reduce the efficiency of incidence on the image sensor, which is undesirable. Furthermore, if the upper limit of condition (6) is exceeded, the optical system will become too large, which is undesirable.

[0117] Preferably, the above-mentioned effect can be further enhanced by satisfying either one or both of the following conditions (6a) and (6b):

[0118] 0.6 < L_ss_LR1R2 / Yinf (6a) L_ss_LR1R2 / Yinf < 2.0 (6b) More preferably, the above-mentioned effect can be further enhanced by satisfying either one or both of the following conditions (6c) and (6d):

[0119] 0.7 < L_ss_LR1R2 / Yinf (6c) L_ss_LR1R2 / Yinf < 1.1 (6d) Furthermore, for example, it is desirable that the imaging optical system satisfy the following condition (7):

[0120] 0.2 < L_tsum / L_LR1R2 < 0.9 (7) where: L_tsum: the sum of the thicknesses of all lens elements in the imaging optical system, L_LR1R2: The distance on the optical axis from the surface closest to the object to the image side of the lens element located closest to the image, is.

[0121] Condition (7) is a condition that specifies the ratio between the sum of the thicknesses of all lens elements in the imaging optical system and the distance on the optical axis from the surface closest to the object (the surface closest to the object among the surface on which aperture stop A is located and the object-side surface of the lens element closest to the object) to the image-side surface of the lens element closest to the image.

[0122] If the lower limit of condition (7) is exceeded, the lens elements will become too thin, which is undesirable because it will be difficult to form the shape required for aberration correction. If the upper limit of condition (7) is exceeded, the air gap between the lens elements will become too narrow, which is undesirable because it will be difficult to hold the lens elements.

[0123] Preferably, the above-mentioned effect can be further enhanced by satisfying either one or both of the following conditions (7a) and (7b):

[0124] 0.3 < L_tsum / L_LR1R2 ···(7a) L_tsum / L_LR1R2 < 0.8 (7b) More preferably, the above-mentioned effect can be further enhanced by satisfying either one or both of the following conditions (7c) and (7d):

[0125] 0.4 < L_tsum / L_LR1R2 ···(7c) L_tsum / L_LR1R2 < 0.7 (7d) Furthermore, for example, it is desirable that the imaging optical system satisfy the following condition (8):

[0126] 0.03 < EA_L1R1 / finfo < 0.50 ···(8) where: EA_L1R1: Effective diameter of the object-side surface of the lens element closest to the object, finf: focal length when focused at infinity, is.

[0127] Condition (8) sets forth the ratio between the effective diameter of the object-side surface of the lens element closest to the object (which can be regarded as the radius of the front lens element of the imaging optical system) and the focal length when focused at infinity.

[0128] If the lower limit of condition (8) is exceeded, the diameter of the incident light beam becomes too small, which is undesirable. Therefore, it becomes difficult to provide a practical F-number, and it is also undesirable to exceed the upper limit of condition (8), which makes it difficult to construct a compact optical system.

[0129] Preferably, the above-mentioned effect can be further enhanced by satisfying either one or both of the following conditions (8a) and (8b):

[0130] 0.05 < EA_L1R1 / finfo (8a) EA_L1R1 / finf < 0.30 (8b) More preferably, the above-mentioned effect can be further enhanced by satisfying either one or both of the following conditions (8c) and (8d):

[0131] 0.07 < EA_L1R1 / finfo (8a) EA_L1R1 / finf < 0.26 (8b) Furthermore, for example, it is desirable that the imaging optical system satisfy the following condition (9):

[0132] 0.01 < L_ss_LF1R1 / Yinf < 0.2 (9) where: L_ss_LF1R1: The distance on the optical axis from the aperture stop A to the object side of the lens element LF1 when focused at infinity, Yinf: Image height when focused at infinity, is.

[0133] Condition (9) specifies the ratio between the distance on the optical axis from aperture stop A to the object side surface of lens element LF1 when focusing at infinity and the image height (approximately equal to the length from the center to the diagonal of the image sensor) when focusing at infinity.

[0134] If the lower limit of condition (9) is exceeded, the distance between lens element LF1 and aperture diaphragm A becomes too narrow, which makes it difficult to position aperture diaphragm A, which is undesirable. On the other hand, if the upper limit of condition (9) is exceeded, the distance between lens element LF1 and aperture diaphragm A becomes too wide, which makes it difficult to position aperture diaphragm A, which is undesirable.

[0135] Preferably, the above effect can be further enhanced by satisfying the following condition (9a):

[0136] L_ss_LF1R1 / Yinf < 0.15 ···(9a) More preferably, the above-mentioned effect can be further enhanced by satisfying the following condition (9b):

[0137] L_ss_LF1R1 / Yinf < 0.10 ···(9b) Furthermore, for example, in the basic configuration of an imaging optical system, it is desirable that aperture stop A or a lens element having power adjacent to aperture stop A on the object side be located closest to the object side.

[0138] This makes it possible to provide a compact optical system.

[0139] (Schematic configuration of an imaging device to which the first embodiment is applied) 5 shows a schematic configuration of an imaging device to which the imaging optical system according to Embodiment 1 is applied. Note that the imaging optical systems according to Embodiments 2 to 4 can also be applied to imaging devices.

[0140] The imaging device 100 is made up of a housing 104, an imaging element 102, and an imaging optical system 101 according to Embodiment 1. A specific example of the imaging device 100 is a digital camera.

[0141] The lens barrel 302 holds each lens element of the imaging optical system 101 and an aperture stop A.

[0142] The image pickup element 102 is disposed at the position of the image plane S in the image pickup optical system according to the first embodiment.

[0143] The imaging optical system 101 is configured so that a lens frame included in the lens barrel 302 is attached to or engages with the first lens element L1, the second lens element L2, the third lens element L3, the fourth lens element L4, and the fifth lens element L5 so that they move together during focusing from infinity to close object focusing during imaging. Note that the aperture diaphragm A may be attached to or engaged with the lens frame included in the lens barrel 302 so that the aperture diaphragm A also moves together with the first lens element L1, the second lens element L2, the third lens element L3, the fourth lens element L4, and the fifth lens element L5 during focusing.

[0144] The imaging optical system 301, which has each lens element held by the lens barrel 302, is configured with actuators and lens frames controlled by a controller within the imaging device 100 so that the first lens element L1, the second lens element L2, the third lens element L3, the fourth lens element L4, and the fifth lens element L5 move during focusing.

[0145] This makes it possible to realize an imaging device that can effectively correct various aberrations.

[0146] Although the imaging optical system according to the first embodiment described above is applied to a digital camera, it can also be applied to a digital video camera, a surveillance camera, a smartphone, and the like.

[0147] (Schematic configuration of a camera system to which the first embodiment is applied) 6 shows a schematic configuration of a camera system to which the imaging optical system according to Embodiment 1 is applied. Note that the imaging optical systems according to Embodiments 2 to 4 can also be applied to a camera system.

[0148] The camera system 200 includes a camera body 201 and an interchangeable lens device 300 that is detachably connected to the camera body 201 .

[0149] The camera body 201 includes an image sensor 202 that receives an optical image formed by the imaging optical system of the interchangeable lens device 300 and converts it into an electrical image signal, a monitor 203 that displays the image signal converted by the image sensor 202, a memory (not shown) that stores the image signal, a camera mount unit 204, and a viewfinder 205.

[0150] The imaging optical system of the interchangeable lens device 300 is the imaging optical system according to the first embodiment.

[0151] The lens barrel 302 holds each lens element of the imaging optical system 301 and an aperture stop A, and includes a lens mount section 304 that is connected to the camera mount section 204 of the camera body 201 .

[0152] The camera mount unit 204 and the lens mount unit 304 not only provide a physical connection, but also function as an interface that electrically connects a controller (not shown) in the camera body 201 and a controller (not shown) in the interchangeable lens device 300, enabling the exchange of signals between them.

[0153] The imaging optical system 301 is configured so that the lens frames included in the lens barrel 302 can be attached to or engaged with the lens barrel 302 so that the lens frames holding the first lens element L1, the second lens element L2, the third lens element L3, the fourth lens element L4, and the fifth lens element L5 can move together during focusing. Note that the aperture diaphragm A may be attached to or engaged with the lens frame included in the lens barrel 302 so that the aperture diaphragm A also moves together during focusing.

[0154] This makes it possible to realize an imaging device that can effectively correct various aberrations.

[0155] Although the imaging optical system according to the first embodiment described above is applied to a digital camera, it can also be applied to a digital video camera, a surveillance camera, a smartphone, and the like.

[0156] (Other embodiments) As described above, embodiments 1 to 4 have been described as examples of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate.

[0157] Each lens group constituting the imaging optical system according to Embodiments 1 to 4 is composed solely of refractive lens elements that deflect incident light rays by refraction (i.e., lens elements that deflect incident light rays at the interface between media with different refractive indices), but is not limited to this. For example, each lens group may be composed of diffractive lens elements that deflect incident light rays by diffraction, hybrid refractive-diffractive lens elements that deflect incident light rays by combining diffractive and refractive effects, gradient index lens elements that deflect incident light rays by the refractive index distribution within the medium, or a combination of two or more of these. In particular, in a hybrid refractive-diffractive lens element, forming a diffractive structure at the interface between media with different refractive indices is preferable because it improves the wavelength dependence of diffraction efficiency. This makes it possible to realize a camera with good aberration correction.

[0158] In the first embodiment, the first lens element L1 is shown as an example of a lens group with negative power located on the object side of the aperture stop A. The lens group with negative power may be composed of a plurality of single lens elements or cemented lenses, and may have a negative composite power. Therefore, the lens group with negative power is not limited to a negative single lens element.

[0159] However, if the lens group having negative power is configured, from the object side, with a lens element having negative power and another lens element having negative power, it becomes easier to correct aberrations that occur in the lens element having positive power that is located on the image side of the aperture stop A. Furthermore, the image side surface of the first lens element having negative power from the object side in the lens group having negative power may be made convex toward the object side, which makes it even easier to correct aberrations up to the periphery.

[0160] Furthermore, if the lens group having negative power is configured, from the object side, with a lens element having positive power, a lens element having negative power, and a lens element having negative power, the back focus of the imaging optical system can be prevented from becoming too large. Furthermore, the image side surface of the second lens element having negative power from the object side of the lens group having negative power may be made convex toward the object side. This makes it easy to correct aberrations up to the periphery.

[0161] Furthermore, if the lens group having negative power is configured, in order from the object side, with a lens element having negative power, a lens element having positive power, and a lens element having negative power, this makes it easier to correct aberrations occurring in the lens element LF1 having positive power located on the image side of the aperture stop A, while also making it easier to correct aberrations in the lens group having negative power located on the object side of the aperture stop A. Furthermore, the image side surface of the first lens element having negative power from the object side in the lens group having negative power may be made convex toward the object side, which makes it even easier to correct aberrations up to the periphery.

[0162] Furthermore, if the lens group having negative power is configured, in order from the object side, with a lens element having negative power, a lens element having negative power, a lens element having positive power, and a lens element having negative power, it is possible to easily correct aberrations in the peripheral areas even in a wide-angle imaging optical system with an angle of view ranging from 40 to 60 degrees. Furthermore, the image side surface of the first lens element having negative power from the object side in the lens group having negative power may be made convex toward the object side. This makes it even easier to correct aberrations in the peripheral areas.

[0163] (Numerical example) Numerical examples that specifically implement the imaging optical systems according to Embodiments 1 to 4 will be described below. In each numerical example, all lengths in the tables are in "mm" and all angles of view are in "°". In each numerical example, r is the radius of curvature, d is the surface spacing, nd is the refractive index for the d-line, νd (also written as vd) is the Abbe number for the d-line, and the effective diameter is the distance from the optical axis to the maximum height of a peripheral ray passing through that surface, perpendicular to the optical axis. In each numerical example, surfaces marked with an * are aspherical, and the aspherical shape is defined by the following equation:

[0164]

number

[0165] where: Z: The distance from a point on the aspheric surface at a height h from the optical axis to the tangent plane of the vertex of the aspheric surface. h: height from the optical axis, r: apex curvature radius, κ: conic constant, An: n-th order aspheric coefficient is.

[0166] 1B, 2B, 3B, and 4B are longitudinal aberration diagrams of the imaging optical systems according to Numerical Examples 1 to 4, respectively.

[0167] In each longitudinal aberration diagram, (a) shows the aberrations at infinity, and (b) shows the aberrations at a close position. From left to right, each longitudinal aberration diagram shows spherical aberration (SA (mm)), astigmatism (AST (mm)), and distortion (DIS (%)). In each spherical aberration diagram, the vertical axis represents the F-number (denoted by F in the diagram), with the solid line representing the d-line, the short dashed line representing the F-line, and the long dashed line representing the C-line characteristics. In each astigmatism diagram, the vertical axis represents the image height (denoted by H in the diagram), with the solid line representing the sagittal plane (denoted by s) and the dashed line representing the meridional plane (denoted by m). In each distortion diagram, the vertical axis represents the image height (denoted by H in the diagram).

[0168] (Numerical Example 1) (Table 1A: Surface data) Surface number rd nd vd Effective diameter Object surface ∞ variable 1* -8.65700 1.00000 1.53504 55.7 5.372 2* -32.87850 0.76690 4.592 3 (Aperture) ∞ 0.33000 3.900 4* 11.22640 2.83530 1.53504 55.7 4.746 5* -21.40270 2.76000 4.500 6* -43.36530 3.40360 1.53504 55.7 5.556 7* -8.90430 2.57790 6.231 8* -3.84940 3.70670 1.65731 21.2 6.397 9* -9.45130 1.19510 8.563 10* 7.58240 2.92440 1.53504 55.7 12.999 11* 16.52250 Variable 13.227 12 ∞ 2.10000 1.51680 64.2 13∞1.00000 14∞BF Image plane ∞ (Table 1B: Aspheric Data) Front page K= 5.31630E-01, A4= 2.22724E-03, A6=-6.20115E-05, A8= 2.03677E-06 A10=-3.97029E-08, A12= 3.85282E-10, A14=-1.09379E-16 2nd side K= 0.00000E+00, A4= 1.16869E-03, A6=-2.66816E-06, A8=-4.18934E-07 A10= 2.65515E-08, A12= 0.00000E+00, A14= 0.00000E+00 Side 4 K= 0.00000E+00, A4=-1.20138E-03, A6= 3.53432E-05, A8=-1.76419E-06 A10= 2.59025E-08, A12= 0.00000E+00, A14= 0.00000E+00 5th page K= 0.00000E+00, A4=-7.66982E-04, A6=-4.51133E-06, A8=-1.24786E-08 A10=-7.28084E-09, A12= 9.99430E-11, A14= 0.00000E+00 Side 6 K= 0.00000E+00, A4=-6.52331E-04, A6=-1.17374E-05, A8= 2.13956E-07 A10=-3.43681E-09, A12= 2.02053E-10, A14=-3.41283E-12 Side 7 K=-4.53181E-01, A4=-2.87799E-04, A6=-6.07098E-06, A8=-3.30975E-07 A10= 1.70395E-08, A12=-2.48554E-10, A14= 3.67673E-14 Side 8 K=-7.74103E-01, A4= 2.16786E-03, A6=-6.33393E-05, A8= 1.70626E-06 A10=-1.00326E-08, A12=-2.86534E-10, A14= 4.16765E-12 9th page K= 0.00000E+00, A4= 8.56406E-05, A6= 8.27047E-06, A8=-2.31563E-07 A10= 5.44602E-09, A12=-6.18853E-11, A14= 3.02930E-13 Side 10 K=-4.57568E+00, A4= 6.88528E-05, A6=-2.04899E-06, A8=-3.67590E-09 A10= 1.51362E-10, A12=-6.54998E-13, A14= 8.80953E-16 Page 11 K= 0.00000E+00, A4=-1.53882E-05, A6=-3.02341E-06, A8= 1.90678E-08 A10=-4.84851E-11, A12= 6.32345E-14, A14= 0.00000E+00 (Table 1C: Various data when focused at infinity and when focused on a close object) Infinity Close Focal length 21.3171 21.3171 F-number 2.91374 3.13378 Angle of view 45.4058 43.2589 Image height 19.0940 19.4950 Optical total length 37.0000 40.0321 BF -0.09987 -0.09987 d0 ∞ 159.9625 d11 12.5000 15.5321 Entrance pupil position 1.3122 1.3122 Exit pupil position -39.9407 -42.9727 Front principal point position 11.2235 11.2235 Back principal point position 15.6830 15.6830 (Table 1D: Single lens data) Lens starting surface focal length 1 1 -22.2838 2 4 14.1931 3 6 20.2456 4 8 -13.3961 5 10 23.5107 (Numerical Example 2) (Table 2A: Surface data) Surface number rd nd vd Effective diameter Object surface ∞ variable 1 (Aperture) ∞ 0.33000 1.771 2* 11.49150 1.87640 1.53504 55.7 2.182 3* 24.41460 3.69120 2.795 4 -22.60080 2.95790 1.81600 46.6 4.853 5 -8.23450 2.74910 5.485 6 -6.87890 1.00000 1.60817 29.3 5.749 7 143.98310 2.24020 8.203 8 110.41290 3.50520 2.00100 29.1 12.400 9 -59.95300 Variable 12.911 10 ∞ 2.10000 1.51680 64.2 11∞1.00000 12∞BF Image plane ∞ (Table 2B: Aspheric Data) 2nd side K= 0.00000E+00, A4=-2.29466E-04, A6= 1.46226E-04, A8=-4.10743E-05 A10= 3.70762E-06 3rd page K= 0.00000E+00, A4= 3.80191E-04, A6=-3.17775E-05, A8= 1.95653E-06 A10=-4.91767E-08 (Table 2C: Various data when focused at infinity and when focused on a close object) Infinity Close Focal length 28.3752 28.3752 F-number 8.01107 9.61345 Angle of view 37.3263 32.4236 Image height 21.1950 20.9720 Optical total length 34.0002 40.0404 BF 0.05019 0.05019 d0 ∞ 159.9598 d9 12.5000 18.5403 Entrance pupil position 0.0000 0.0000 Exit pupil position -30.1479 -36.1882 Front principal point position 1.7129 1.7129 Back principal point position 5.6250 5.6250 (Table 2D: Single lens data) Lens starting surface focal length 1 2 38.6220 2 4 14.5311 3 6 -10.7681 4 8 39.2200 (Numerical Example 3) (Table 3A: Surface data) Surface number rd nd vd Effective diameter Object surface ∞ variable 1 (Aperture) ∞ 0.33000 1.936 2 17.30230 1.54630 1.43700 95.1 2.423 3 197.03810 3.12200 3.085 4 -4.63680 1.43620 2.00100 29.1 3.880 5 -5.58620 0.30000 4.789 6 213.84700 4.17130 1.81600 46.6 7.065 7 -11.97070 2.46280 7.518 8 -9.65220 1.00000 1.65388 26.1 7.471 9 168.93730 1.21500 9.420 10 31.69380 2.86650 1.81055 41.1 12.601 11* 300.00000 Variable 12.764 12 ∞ 2.10000 1.51680 64.2 13∞1.00000 14∞BF Image plane ∞ (Table 3B: Aspheric data) Page 11 K= 0.00000E+00, A4= 5.03539E-05, A6=-1.84261E-07, A8= 6.79258E-10 A10=-1.25416E-12 (Table 3C: Various data when focused at infinity and when focused on a close object) Infinity Close Focal length 22.6563 22.6563 F-number 5.85131 6.51229 Angle of view 43.8222 41.0683 Image height 19.5960 19.9170 Optical total length 34.0001 37.5161 BF -0.05000 -0.05000 d0 ∞ 162.4840 d11 12.5000 16.0160 Entrance pupil position 0.0000 0.0000 Exit pupil position -31.1753 -34.6913 Front principal point position 6.1646 6.1646 Back principal point position 11.3438 11.3438 (Table 3D: Single Lens Data) Lens starting surface focal length 1 2 43.2915 2 4 -112.0470 3 6 14.0086 4 8 -13.9327 5 10 43.5125 (Numerical Example 4) (Table 4A: Surface data) Surface number rd nd vd Effective diameter Object surface ∞ variable 1 (Aperture) ∞ 0.33000 1.552 2 11.62450 1.48810 1.43700 95.1 2.001 3 40.11130 2.44460 2.595 4 -4.77310 1.00000 1.94595 18.0 3.336 5 -5.78950 0.30000 3.987 6 -67.46760 3.13000 1.81600 46.6 5.250 7 -9.80600 4.02770 5.813 8 -7.36270 1.00000 1.69513 24.0 6.205 9 -61.66430 1.29370 8.586 10 -59.76830 3.43580 2.00100 29.1 10.031 11 -21.52680 Variable 10.798 12 ∞ 2.10000 1.51680 64.2 13∞1.00000 14∞BF Image plane ∞ (Table 4B: Aspheric data) none (Table 4C: Various data when focused at infinity and when focused on a close object) Infinity Close Focal length 24.7165 24.7165 F-number 7.96280 9.00883 Angle of view 41.1960 37.7225 Image height 19.7600 19.9200 Optical total length 33.9990 38.2727 BF -0.05087 -0.05087 d0 ∞ 161.7260 d11 12.5000 16.7736 Entrance pupil position 0.0000 0.0000 Exit pupil position -32.5834 -36.8571 Front principal point position 5.9382 5.9382 Back principal point position 9.2825 9.2825 (Table 4D: Single Lens Data) Lens starting surface focal length 1 2 36.8697 2 4 -55.0887 3 6 13.7260 4 8 -12.1195 5 10 32.1653 (Condition's corresponding value) Table 1 below shows the corresponding values ​​for conditions (1) to (9).

[0169] [Table 1] [Industrial Applicability]

[0170] The imaging optical system according to the present disclosure is applicable to digital still cameras, digital cameras with interchangeable lenses, digital video cameras, cameras in mobile phone devices, cameras in PDAs (Personal Digital Assistances), surveillance cameras in surveillance systems, web cameras, and in-vehicle cameras, and is particularly suitable for imaging optical systems that require high image quality, such as digital still camera systems and digital video camera systems. [Explanation of symbols]

[0171] L1 First lens element L2 Second lens element L3 Third lens element L4 Fourth lens element L5 Fifth lens element A aperture stop P parallel plate S image plane 100 Imaging device 101 Imaging optical system 102 Image sensor 104 Case 200 Camera System 201 Camera body 202 Image sensor 203 Monitor 204 Camera mount 205 Finder 300 Interchangeable lens device 301 Imaging Optical System 302 Telescope tube 304 Lens mount

Claims

1. An aperture stop, a lens element LF1 having a positive power and adjacent to the image side of the aperture stop; a lens element LR1 having a positive power and located closest to the image side; a lens element LR2 having negative power and adjacent to the object side of the lens element LR1; a lens element LR3 having a positive power and adjacent to the object side of the lens element LR2; Equipped with the object side surface of the lens element LR2 has a convex shape toward the image side, the image side surface of the lens element LR3 has a convex shape toward the image side; The following conditions (1) and (2) are satisfied: 0.5<Linf / Yinf<2.65...(1) 0.5<BLinf / Yinf<2.0...(2) where: Linf: total optical length when focused at infinity, Yinf: Image height when focused at infinity, BLinf: distance from the image side of the lens element closest to the image plane when focusing at infinity, That is, Imaging optical system.

2. and a lens group having negative power and the aperture stop, in that order from the object side. The imaging optical system according to claim 1 .

3. a negative power lens element adjacent to the object side of the aperture stop; The imaging optical system according to claim 1 .

4. The following condition (3) is satisfied: nd_LF1 < 1.65...(3) where: nd_LF1: the refractive index of the lens element LF1, That is, The imaging optical system according to claim 1 .

5. The following condition (4) is satisfied: 50 < vd_LF1 ... (4) where: vd_LF1: Abbe number of the lens element LF1, That is, The imaging optical system according to claim 1 .

6. a lens element adjacent to the lens element LF1 on the image side has an object side surface having a shape convex toward the image side; The imaging optical system according to claim 1 .

7. There are three to six lens elements on the image side of the aperture stop. The imaging optical system according to claim 1 .

8. During focusing from infinity to close range, at least the lens element adjacent to the image side of the aperture stop to the lens element closest to the image side moves as a single unit. The imaging optical system according to claim 1 .

9. The following condition (5) is satisfied: -1.0 < (R1_LR2 - R2_LR3) / (R1_LR2 + R2_LR3) < 0.5...(5) where: R1_LR2: radius of curvature of the object-side surface of the lens element LR2, R2_LR3: radius of curvature of the image-side surface of the lens element LR3, That is, The imaging optical system according to claim 1 .

10. The following condition (6) is satisfied: 0.5 < L_ss_LR1R2 / Yinf < 3.0 (6) where: L_ss_LR1R2: the distance from the aperture stop to the image side of the lens element LR1 when focused at infinity, Yinf: Image height when focused at infinity, That is, The imaging optical system according to claim 1 .

11. The following condition (7) is satisfied: 0.2 < L_tsum / L_LR1R2 < 0.9 (7) where: L_tsum: the sum of the thicknesses of all lens elements in the imaging optical system, L_LR1R2: the distance on the optical axis from the surface closest to the object to the image-side surface of the lens element located closest to the image, That is, The imaging optical system according to claim 1 .

12. The following condition (8) is satisfied: 0.03<EA_L1R1 / finf<0.50...(8) where: EA_L1R1: effective diameter of the object-side surface of the lens element closest to the object, finf: focal length when focused at infinity, That is, The imaging optical system according to claim 1 .

13. The following condition (9) is satisfied: 0.01 < L_ss_LF1R1 / Yinf < 0.2 (9) where: L_ss_LF1R1: the distance on the optical axis from the aperture stop to the object side surface of the lens element LF1 when focused at infinity, Yinf: Image height when focused at infinity, That is, The imaging optical system according to claim 1 .

14. the aperture stop or a lens element having power adjacent to the aperture stop on the object side is located closest to the object side; The imaging optical system according to claim 1 .

15. 1. An imaging device that converts an optical image of an object into an electrical image signal and at least one of displays and stores the converted image signal, an imaging optical system according to claim 1 that forms an optical image of an object; an imaging element that converts an optical image formed by the imaging optical system into an electrical image signal; Equipped with Imaging device.

16. an interchangeable lens device including the imaging optical system according to claim 1; a camera body that is detachably connected to the interchangeable lens device via a camera mount and includes an image sensor that receives an optical image formed by the image pickup optical system and converts it into an electrical image signal; A camera system comprising: The interchangeable lens device forms an optical image of an object on the imaging element. Camera system.

Images