Single-focus lens, interchangeable lens, and imaging device

Abstract

To provide a single focus lens which is compact, light-weight, and wide-angle and offers high optical performance, and to provide an interchangeable lens and image capturing device.SOLUTION: A single focus lens provided herein consists of a front group, an aperture stop, and a rear group having positive refractive power arranged in order from the object side, and is configured such that a diameter of an axial ray incident on the side closest to the object in the front group is less than that of an axial ray passing through the aperture stop. The single focus lens satisfies the following conditional expression (1): 5.0<|fF| / fR ...(1), where fF represents a focal length of the front group and fR represents a focal length of the rear group.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a single-focus lens, an interchangeable lens, and an imaging device.

Background Art

[0002] Conventionally, various types are known as optical systems used in, for example, digital cameras as imaging devices. In particular, as an optical system with a wide angle of view, generally, a retrofocus type lens having a negative refractive power in front of the lens and a positive refractive power behind the lens is used, and it is required to be a small wide-angle lens having high optical performance in the entire shooting distance range. In addition, it is desired that the overall length and outer diameter of the entire lens system are small and lightweight for easy portability.

[0003] For example, Patent Document 1 describes that in a retrofocus type optical system having first and second lens units, focusing is performed by moving the second lens unit toward the object side.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in a conventional retrofocus type optical system, as the optical performance is improved, the number of lenses increases or aspherical surfaces are frequently used, resulting in a tendency to increase in size and cost. In addition, as the angle of view is widened, there is a similar problem of increasing in size and cost. For example, Patent Document 1 has room for improvement from the viewpoints of widening the angle of view and correcting off-axis aberrations.

[0006] The present invention has been made in view of the above points, and an object thereof is to provide a single-focus lens, an interchangeable lens, and an imaging device that have high optical performance, are small, lightweight, and have a wide angle of view.

Means for Solving the Problems

[0007] The single-focus lens of the present embodiment is composed of, in order from the object side, a front group, an aperture stop, and a rear group having a positive refractive power. The axial light beam passing through the aperture surface of the aperture stop is larger than the axial light beam incident on the most object-side refractive surface of the front group. The front group has a negative meniscus lens with a convex surface facing the object side on the most object side, and the front group has a convex surface on the most image side refractive surface facing the image side. The rear group has at least one negative lens. The rear group has a cemented lens on the most object side, and the cemented lens located on the most object side of the rear group has a cemented surface with a concave surface facing the object side. The rear group has a concave surface on the most object side refractive surface facing the object side. It satisfies the following conditional expressions (1), (2’), (3)、(5)、(6)、(7)、 (11C), and is characterized by this. (1) 5.0 < |fF| / fR (2’) 0.8 < DF / DR < 2.0 (3) |fBL| / fBO < -1.0 (5) 1.5 < fR / f < 3.0 (6) 1.6 < (Y × Fno) / f < 4.1 (7) 0.3 < RF / RR < 6.0 (RF < 0, RR < 0) (11C) 1.87 < NnRmax However, fF: Focal length of the front group, fR: Focal length of the rear group, DF: Distance on the optical axis from the most object-side surface of the front group to the aperture stop, DR: Distance on the optical axis from the most image-side surface of the rear group to the aperture stop, fBL: Focal length of the cemented lens located on the most object side of the rear group. fBO: Focal length of the cemented surface with a concave surface facing the object side of the cemented lens located on the most object side of the rear group. f: Focal length of the entire single-focus lens system. Y: Image height of the entire single-focus lens system. Fno: F-number of the entire single-focus lens system. RF: Curvature radius of the most image side refractive surface of the front group. RR: Curvature radius of the most object side refractive surface of the rear group. NnRmax: Refractive index of the negative lens having the largest refractive index among the negative lenses included in the rear group, That is.

[0008] The interchangeable lens and imaging device of the present embodiment have the single-focus lens described above.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a single-focus lens, an interchangeable lens, and an imaging device that have high optical performance, are small, lightweight, and have a wide angle of view.

Brief Description of the Drawings

[0010]

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Embodiments for Carrying Out the Invention

[0011] The single-focus lens of this embodiment is suitable as, for example, a photographing optical system in an imaging device such as a digital single-lens reflex camera / digital single-lens camera, or an interchangeable lens used for the imaging device.

[0012] As shown in the lens configuration diagrams of FIGS. 1, 4, 7, 10, 13, 16, 19, 22, and 25, the single-focus lens of this embodiment is composed of, in order from the object side, a front group G1, an aperture stop SP (for controlling the F-number and adjusting the light amount), and a rear group G2 with positive refractive power. The front group G1 can have either positive refractive power or negative refractive power. For example, in Numerical Examples 2, 3, 4, 7, 8, and 9 described later, the front group G1 has positive refractive power, and in Numerical Examples 1, 5, and 6 described later, the front group G1 has negative refractive power. A parallel plane plate CG is disposed between the rear group G2 and the image plane (the designed image plane). The parallel plane plate CG is composed of, for example, a low-pass filter, an infrared cut filter, a cover glass of an imaging element, etc.

[0013] In this embodiment, on the premise of the above-described basic configuration, in order to realize a single-focus lens having high optical performance, being small-sized, lightweight, and having a wide angle of view, the detailed structure, power arrangement of the lens groups and lens elements, and the selection of optical materials are optimized. In this specification, "having high optical performance" means, for example, that various aberrations are properly corrected. In this specification, "having a wide angle of view" means, for example, that the semi-angle of view is 40° or more. Also in this specification, miniaturization and weight reduction can be realized, for example, by reducing the number of lens elements constituting the single-focus lens.

[0014] In the single-focus lens of this embodiment, the axial light beam passing through the aperture surface of the aperture stop SP is larger than the axial light beam incident on the most object-side refractive surface of the front group G1. Thereby, the angle of view of the single-focus lens can be widened, the necessary back focus can be ensured, and the peripheral light amount can also be ensured.

[0015] For example, in Patent Document 1 described above, among the first and second lens units sandwiching the aperture stop, the first lens unit has a strong positive refractive power. In contrast, in the single-focus lens of the present embodiment, among the front group G1 and the rear group G2 sandwiching the aperture stop SP, since the front group G1 has a relatively weak refractive power with respect to the rear group G2, high optical performance can be obtained. Further, since the position of the aperture stop SP is arranged near the center of the entire optical system, the number of lenses in the front group G1 can be suppressed to be relatively small, so that both wide-angle conversion and miniaturization, as well as high performance, can be achieved.

[0016] The single-focus lens of the present embodiment preferably satisfies the following conditional expressions (1), (1A), and (1B). (1) 5.0 < |fF| / fR (1A) 8.0 < |fF| / fR (1B) 10.0 < |fF| / fR However, fF: Focal length of the front group, fR: Focal length of the rear group, where.

[0017] By satisfying the conditional expression (1), miniaturization (reduction of the front lens diameter) and wide-angle conversion of the single-focus lens can be achieved, and various aberrations, such as spherical aberration and coma aberration, can be corrected well. This effect is more significantly manifested by satisfying the conditional expressions (1A) and (1B). When the front group has a negative refractive power, if it exceeds the lower limit of the conditional expression (1), the negative refractive power of the front group becomes too strong, making it difficult to correct aberrations such as spherical aberration and coma aberration. When the front group has a positive refractive power, if it exceeds the lower limit of the conditional expression (1), the positive refractive power of the front group becomes too strong, increasing the front lens diameter and making wide-angle conversion difficult.

[0018] The single-focus lens of the present embodiment preferably satisfies the following conditional expressions (2), (2A), and (2B). (2) 0.7 < DF / DR < 2.0 (2A) 0.8 < DF / DR < 1.9 (2B) 1.0 < DF / DR < 1.8 However, DF: The distance (absolute value) on the optical axis from the most object-side surface of the front group to the aperture stop, DR: The distance (absolute value) on the optical axis from the most image-side surface of the rear group to the aperture stop, is as follows.

[0019] By satisfying the conditional expression (2), miniaturization of the single-focus lens (reduction of the overall lens length and suppression of the outer diameter) and wide-angle conversion can be achieved. This operational effect is more significantly manifested by satisfying the conditional expressions (2A) and (2B). If the upper limit of the conditional expression (2) is exceeded, the overall length and outer diameter of the front group become too large, making it difficult to achieve both miniaturization and wide-angle conversion. If the lower limit of the conditional expression (2) is exceeded, the overall length of the rear group becomes too large, making miniaturization difficult.

[0020] The rear group G2 has a cemented lens BL on the most object side, and the cemented lens BL located on the most object side of the rear group G2 has a cemented surface facing the concave surface on the object side. Based on this configuration, the single-focus lens of the present embodiment preferably satisfies the following conditional expressions (3), (3A), (3B), and (3C). (3) |fBL| / fBO < -1.0 (3A) -45.0 < |fBL| / fBO < -1.0 (3B) -30.0 < |fBL| / fBO < -1.5 (3C) -20.0 < |fBL| / fBO < -1.7 However, fBL: The focal length of the cemented lens located on the most object side of the rear group, fBO: The focal length of the cemented surface facing the concave surface on the object side of the cemented lens located on the most object side of the rear group, is as follows.

[0021] The focal length of the cemented surface indicated by fBO is defined by the formula fBO = RB / (n' - n), where n is the refractive index of the lens on the object side, n' is the refractive index of the lens on the image side, and RB is the radius of curvature of the cemented surface.

[0022] In the rear group, since the on-axis light beam becomes large, by providing the cemented lens closest to the object side, spherical aberration and axial chromatic aberration can be effectively corrected. Further, by providing a cemented surface with a concave surface facing the object side, while correcting the above-mentioned aberrations, off-axis aberrations such as coma aberration, astigmatism, and lateral chromatic aberration can be effectively corrected.

[0023] Also, the cemented lens BL can have either a positive refractive power or a negative refractive power. For example, in Numerical Example 8 described later, the front group G1 has a positive refractive power, and in Numerical Examples 1-7 and 9 described later, the front group G1 has a negative refractive power.

[0024] When the cemented lens BL has a positive refractive power, it has the effect of shortening the focal length of the entire optical system and making it easier to widen the angle of view. Also, when the cemented lens BL has a negative refractive power, spherical aberration can be more effectively corrected.

[0025] By satisfying Conditional Expression (3), aberrations such as spherical aberration and coma aberration can be corrected well. This effect is more significantly manifested by satisfying Conditional Expressions (3A), (3B), and (3C). When exceeding the upper limit of Conditional Expression (3), the refractive power of the cemented surface with a concave surface facing the object side of the cemented lens located closest to the object side in the rear group becomes too weak, making it difficult to correct aberrations such as spherical aberration and coma aberration. When exceeding the lower limit of Conditional Expression (3A), the refractive power of the cemented surface with a concave surface facing the object side of the cemented lens located closest to the object side in the rear group becomes too strong, making it difficult to correct aberrations such as spherical aberration and coma aberration.

[0026] The single-focus lens of this embodiment preferably satisfies the following Conditional Expressions (4), (4A), and (4B). (4) 1.0 < TL / f < 10.0 (4A) 1.0 < TL / f < 8.0 (4B) 1.0 < TL / f < 7.0 However, TL: The distance from the surface closest to the object side of the front group to the image plane, f: Focal length of the entire single-focus lens system, is as follows.

[0027] By satisfying conditional expression (4), miniaturization of the optical system (shortening of the overall lens length) and wide-angle magnification can be achieved, and spherical aberration, coma aberration, and distortion aberration can be corrected well. This effect is more significantly manifested by satisfying conditional expressions (4A) and (4B). When exceeding the upper limit of conditional expression (4), large amounts of distortion aberration and coma aberration occur, and the optical system becomes large (the overall lens length becomes long). When exceeding the lower limit of conditional expression (4), the focal length becomes long and the angle of view becomes narrow. Also, correction of spherical aberration and coma aberration becomes difficult.

[0028] The single-focus lens of this embodiment preferably satisfies the following conditional expressions (5), (5A), and (5B). (5) 1.5 < fR / f < 3.0 (5A) 1.6 < fR / f < 2.8 (5B) 1.7 < fR / f < 2.7 However, fR: Focal length of the rear group, f: Focal length of the entire single-focus lens system, is as follows.

[0029] By satisfying conditional expression (5), wide-angle magnification can be achieved, and spherical aberration and coma aberration can be corrected well. This effect is more significantly manifested by satisfying conditional expressions (5A) and (5B). When exceeding the upper limit of conditional expression (5), the refractive power of the rear group becomes too weak and the focal length becomes long, making wide-angle magnification difficult. When exceeding the lower limit of conditional expression (5), the refractive power of the rear group becomes too strong, making correction of spherical aberration, coma aberration, etc. difficult.

[0030] The single-focus lens of this embodiment preferably satisfies the following conditional expression (6). (6) 1.6 < (Y × Fno) / f < 4.1 However, Y: Image height of the entire single-focus lens (the maximum image height formed by the single-focus lens on the image plane), Fno: F-number of the entire single-focus lens, f: Focal length of the entire single-focus lens, is.

[0031] By satisfying conditional expression (6), coma aberration, astigmatism, and spherical aberration can be corrected well, and a bright lens with a small F-number can be realized, achieving a wide-angle effect. When exceeding the upper limit of conditional expression (6), off-axis correction, especially coma aberration and astigmatism correction, becomes difficult, and the lens becomes a large F-number and dark one. When exceeding the lower limit of conditional expression (6), the beam diameter passing through the single-focus lens becomes large, making it difficult to correct spherical aberration and coma aberration. Also, the angle of view becomes narrow.

[0032] In the single-focus lens of this embodiment, the front group G1 has, on the most object side, a negative meniscus lens (for example, L1A, L1B, L1C, L1D, L1E described later) with a convex surface facing the object side. By providing a negative lens on the most object side of the front group G1, the outer diameter of the lens can be reduced, and both wide-angle and miniaturization can be achieved. By forming the negative lens on the most object side of the front group G1 into a meniscus shape with a convex surface facing the object side, coma aberration, astigmatism, and distortion aberration can be effectively corrected.

[0033] In the single-focus lens of this embodiment, the most image-side refracting surface of the front group G1 can have a convex surface on the image side, and the most object-side refracting surface of the rear group G2 can have a concave surface on the object side. Thereby, distortion aberration can be corrected well, and spherical aberration generated at the most image-side refracting surface of the front group G1 can be effectively corrected.

[0034] The single-focus lens of this embodiment preferably satisfies the following conditional expressions (7), (7A), and (7B). (7) 0.3 < RF / RR < 6.0 (RF < 0, RR < 0) (7A) 0.5 < RF / RR < 5.5 (7B)0.6 < RF / RR < 5.0 However, RF: Radius of curvature of the most image-side refracting surface of the front group, RR: Radius of curvature of the most object-side refracting surface of the rear group, is as follows.

[0035] By satisfying the conditional expression (7), spherical aberration can be corrected well. This effect is more significantly manifested by satisfying the conditional expressions (7A) and (7B). When exceeding the upper limit of the conditional expression (7), the radius of curvature of the most image-side refracting surface (convex surface) of the front group becomes too large, resulting in overcorrected spherical aberration. When exceeding the lower limit of the conditional expression (7), the radius of curvature of the most image-side refracting surface (convex surface) of the front group becomes too small, resulting in undercorrected spherical aberration.

[0036] The front group G1 can have at least two positive lenses. For example, when the front group G1 has a strong negative refractive power, by including at least two positive lenses in the front group G1, mainly off-axis aberrations such as coma aberration, astigmatism, and lateral chromatic aberration can be effectively corrected. In the numerical example 8 described later, three positive lenses (L4D, L6D, and L7D) are arranged in the front group G1. However, four or more Positive lenses may be arranged in the front group G1. Considering miniaturization, three or less is preferable.

[0037] The front group G1 can have at least three negative lenses. Thereby, while achieving wide-angle imaging, mainly off-axis aberrations such as coma aberration, astigmatism, and lateral chromatic aberration can be effectively corrected.

[0038] The front group G1 can have three or more negative lenses in order from the object side. As a result, the principal point position can be lowered rearward, making it easier to widen the angle of view while suppressing the front lens diameter. Also, by gradually refracting the light rays incident on the front group G1 with three or more negative lenses, the occurrence of various aberrations can be minimized, and in particular, field curvature aberration and astigmatism can be corrected well. In the numerical example 7 described later, four negative lenses (L1C, L2C, L3C, and L4C) are arranged in order from the object side of the front group G1, but five or more negative lenses may be continuously arranged in order from the object side of the front group G1. Considering miniaturization, four or less is preferable.

[0039] The single-focus lens of the present embodiment preferably has at least one negative lens in the front group and satisfies the following conditional expressions (8), (8A), (8B), (8C), and (8D). (8) 1.60 < NnFmax (8A) 1.70 < NnFmax (8B) 1.80 < NnFmax (8C) 1.85 < NnFmax (8D) 1.90 < NnFmax However, NnFmax: The refractive index of the negative lens having the largest refractive index among the negative lenses included in the front group is.

[0040] By satisfying the conditional expression (8), various aberrations such as coma aberration and astigmatism can be corrected well. This effect is more significantly manifested by satisfying the conditional expressions (8A), (8B), (8C), and (8D). When exceeding the lower limit of the conditional expression (8), it becomes difficult to correct various aberrations such as coma aberration and astigmatism.

[0041] The single-focus lens of the present embodiment preferably has at least one negative lens in the front group and satisfies the following conditional expressions (9), (9A), and (9B). (9) 1.60 < NnFave (9A) 1.60 < NnFave < 1.80 (9B) 1.60 < NnFave < 1.75 However, NnFave: The average refractive index of the negative lenses included in the front group, is.

[0042] By satisfying conditional expression (9), various aberrations such as coma aberration, astigmatism, and distortion aberration can be corrected well. Also, by satisfying conditional expressions (9A) and (9B), various aberrations such as coma aberration, astigmatism, and distortion aberration can be corrected to a certain extent, and field curvature can be corrected well. If it exceeds the lower limit of conditional expression (9), it becomes difficult to correct various aberrations such as coma aberration, astigmatism, and distortion aberration. If it exceeds the upper limit of conditional expression (9A), the Petzval sum becomes a negative value, and field curvature becomes overcorrected. If it exceeds the lower limit of conditional expressions (9A) and (9B), it becomes extremely difficult to correct various aberrations such as coma aberration, astigmatism, and distortion aberration.

[0043] The single-focus lens of this embodiment preferably has a front group having at least one positive lens and satisfies the following conditional expression (10). (10) 30 < νpFave < 50 However, νpFave: The average Abbe number of the positive lenses included in the front group, is.

[0044] By satisfying conditional expression (10), spherical aberration can be corrected well. If it exceeds the upper limit of conditional expression (10), the longitudinal chromatic aberration becomes undercorrected. If it exceeds the lower limit of conditional expression (10), the longitudinal chromatic aberration becomes overcorrected.

[0045] The single-focus lens of this embodiment preferably has a rear group having at least one negative lens and satisfies the following conditional expressions (11), (11A), (11B), (11C), and (11D). (11) 1.75 < NnRmax (11A) 1.8 < NnRmax (11B) 1.85 < NnRmax (11C) 1.87 < NnRmax (11D) 1.90 < NnRmax However, NnRmax: The refractive index of the negative lens with the largest refractive index among the negative lenses included in the rear group. That is.

[0046] By satisfying the conditional expression (11), various aberrations such as spherical aberration and coma aberration can be corrected well. This effect is more significantly manifested by satisfying the conditional expressions (11A), (11B), (11C), and (11D). When exceeding the lower limit of the conditional expression (11), it becomes difficult to correct various aberrations such as spherical aberration and coma aberration.

[0047] The single-focus lens of this embodiment preferably has a rear group having at least one negative lens and satisfies the following conditional expressions (12), (12A), and (12B). (12) 30 < νnRave < 50 (12A) 30 < νnRave < 45 (12B) 30 < νnRave < 40 However, νnRave: The average value of the Abbe numbers of the negative lenses included in the rear group. That is.

[0048] By satisfying the conditional expression (12), axial chromatic aberration can be corrected well. This effect is more significantly manifested by satisfying the conditional expressions (12A) and (12B). When exceeding the upper limit of the conditional expression (12), the axial chromatic aberration becomes under-corrected. When exceeding the lower limit of the conditional expression (12), the axial chromatic aberration becomes over-corrected.

[0049] The single-focus lens of this embodiment preferably has a rear group having at least one positive lens and satisfies the following conditional expression (13). (13) 60 < νpRave However, νpRave: The average Abbe number of the positive lenses in the rear group. It is.

[0050] By satisfying condition (13), longitudinal chromatic aberration can be effectively corrected. If the lower limit of condition (13) is exceeded, axial chromatic aberration will be insufficiently corrected.

[0051] It is preferable that the single focal length lens of this embodiment satisfies the following conditional expressions (14), (14A), and (14B). (14)5.0 <TL / D<20.0 (14A)6.0 <TL / D<15.0 (14B)7.0 <TL / D<10.0 however, TL: Distance from the surface of the front group closest to the object to the image plane, D: The distance from the surface of the front group closest to the image to the surface of the rear group closest to the object at infinity. It is.

[0052] By satisfying conditional expression (14), it is possible to reduce the size of the optical system (shorten the overall lens length) and widen the angle of view, while at the same time making it possible to satisfactorily correct spherical aberration and coma aberration. This effect is more pronounced when conditional expressions (14A) and (14B) are satisfied. If the upper limit of condition (14) is exceeded, the optical system becomes large in size or the air space between the front and rear groups becomes too narrow, making it difficult to correct curvature of field. If the lower limit of condition (14) is exceeded, the optical system becomes too short, making it difficult to correct spherical aberration and coma, or the air gap between the front and rear groups becomes too wide, resulting in an increase in the size of the optical system.

[0053] The rear group G2 has a cemented lens BL closest to the object, and the cemented lens BL closest to the object of the rear group G2 has a cemented surface with a concave surface facing the object. With this configuration as a premise, it is preferable that the single focal length lens of this embodiment satisfies the following conditional expressions (15), (15A), and (15B). (15)-1.5 <fR / fBO<-0.6 (15A) - 1.4 < fR / fBO < -0.7 (15B) - 1.3 < fR / fBO < -0.8 However, fR: Focal length of the rear group, fBO: Focal length of the joint surface facing concave on the object side of the joint lens located closest to the object side of the rear group, is as follows.

[0054] The focal length of the joint surface indicated by fBO is defined by the formula fBO = RB / (n' - n), where n is the refractive index of the lens on the object side, n' is the refractive index of the lens on the image side, and RB is the radius of curvature of the joint surface.

[0055] By satisfying the conditional expression (15), it is possible to satisfactorily correct aberrations such as spherical aberration and coma aberration. This effect is more significantly manifested by satisfying the conditional expressions (15A) and (15B). When exceeding the upper limit of the conditional expression (15), the refractive power of the joint surface facing concave on the object side of the joint lens located closest to the object side of the rear group becomes too weak, making it difficult to correct aberrations such as spherical aberration and coma aberration. When exceeding the lower limit of the conditional expression (15), the refractive power of the joint surface facing concave on the object side of the joint lens located closest to the object side of the rear group becomes too strong, making it difficult to correct aberrations such as spherical aberration and coma aberration.

[0056] The single - focus lens in Numerical Examples 1 - 4 described later can have a focusing lens group in which at least a part of the rear group G2 moves on the optical axis when focusing from infinity to a short distance. By using at least a part of the relatively small - sized rear group G2 as the focusing lens group, the focusing lens group can be lightened, and the focusing speed during AF (Auto Focus) can be increased.

[0057] The single-focus lenses of Numerical Examples 5-9 described below can have a focusing lens group in which the most image-side lens of the front group G1 moves on the optical axis when focusing from infinity to a short distance. By using the single lens (or cemented lens) that is the most image-side lens of the relatively small front group G1 as the focusing lens group, the focusing lens group can be lightened and the focusing speed during AF (auto focus) can be increased.

[0058] The single-focus lens of this embodiment can have at least one aberration correction lens group that moves on the optical axis along a movement locus different from that of the focusing lens group when focusing from infinity to a short distance throughout all embodiments (for example, Numerical Examples 1-9 described below). Since the focusing lens group has a stronger refractive power for the purpose of increasing the AF speed, generally the aberration at a short distance increases. By having an aberration correction lens group that moves other than the focusing lens group, the aberration variation at a short distance can be effectively corrected. Note that the aberration correction lens group can be provided in at least one of the front group G1 and the rear group G2.

[0059] The single-focus lens of this embodiment can have at least one aberration correction lens group that moves on the optical axis along a movement locus different from that of the focusing lens group when focusing from infinity to a short distance. Since the focusing lens group has a stronger refractive power for the purpose of increasing the AF speed, generally the aberration at a short distance increases. By having an aberration correction lens group that moves other than the focusing lens group, the aberration variation at a short distance can be effectively corrected. Note that the aberration correction lens group can be provided in at least one of the front group G1 and the rear group G2.

[0060] In the single-focus lens of this embodiment, when focusing from infinity to a short distance, the front group G1 is partitioned into a sub-lens group A on the object side and a sub-lens group B on the image side with the widest air gap therebetween, and when focusing from infinity to a short distance, the sub-lens group A can be fixed. Since relatively large lenses are arranged in the sub-lens group A on the object side for wide-angle conversion, the lens weight increases. Therefore, for the purpose of increasing the AF speed, it is preferable that the sub-lens group A be fixed during the focusing operation. Also, by making the internal lenses a movable group, the overall lens length remains unchanged, there is no collision with the subject during the focusing operation, and the sealing performance is also excellent.

[0061] For the single-focus lens of this embodiment, an aspherical surface or a diffractive surface may be used on any lens surface. The aspherical surface may be a glass-molded aspherical surface or a ground aspherical surface directly formed on the lens surface, a composite aspherical lens in which a resin layer is applied on the lens surface and an aspherical surface is formed thereon, a plastic aspherical surface in which the lens itself is made of a resin material, or the like.

[0062] The single-focus lens of this embodiment can be provided with a function of correcting image blur by moving any lens group or a part of a lens group in a direction perpendicular to the optical axis.

[0063] Specific numerical examples 1-9 are shown. In the aberration diagrams and tables, d-line, g-line, and c-line represent aberrations for their respective wavelengths, S represents sagittal, M represents meridional, f represents the focal length of the entire system, Fno represents the F-number, w represents the semi-field angle, Y represents the image height, R represents the radius of curvature, D represents the lens thickness or the lens interval, Nd represents the refractive index at the d-line, νd represents the Abbe number at the d-line, BF represents the back focus, L represents the overall lens length, K represents the conic constant of the aspherical surface, A4 represents the 4th-order aspherical coefficient, A6 represents the 6th-order aspherical coefficient, A8 represents the 8th-order aspherical coefficient, and A10 represents the 10th-order aspherical coefficient, respectively. The unit of length is [mm]. Here, the aspherical surface is defined by the following formula when the reciprocal of the paraxial radius of curvature (paraxial curvature) is C and the height from the optical axis is H. x = CH 2 / [1 + [1 - (1 + K)C 2 H 2 1 / 2 + A4H​4 +A6H 6 +A8H 8 +A 10 H 10

[0064] [Numerical Example 1] Figures 1 to 3 and Tables 1 to 3 show the single-focus lens of Numerical Example 1. Figure 1 is a lens configuration diagram at infinity focus, Figure 2 is a longitudinal aberration diagram at infinity focus, and Figure 3 is a lateral aberration diagram at infinity focus. Table 1 is surface data, Table 2 is aspherical data, and Table 3 is various data.

[0065] The single-focus lens of Numerical Example 1 is composed of, in order from the object side, a front group G1, an aperture stop SP (for controlling the F number and adjusting the light amount), and a rear group G2 with positive refractive power. A parallel plane plate CG is arranged between the rear group G2 and the image plane (the designed image plane). The parallel plane plate CG is composed of, for example, a low-pass filter, an infrared cut filter, a cover glass of an image sensor, etc.

[0066] The front group G1 is composed of, in order from the object side, a negative meniscus lens L1A convex on the object side, a negative meniscus lens L2A convex on the object side, a negative meniscus lens L3A convex on the object side, a biconvex positive lens L4A, a negative meniscus lens L5A convex on the image side, and a positive meniscus lens L6A convex on the image side. The negative meniscus lens L2A has aspherical surfaces on both sides. The negative meniscus lens L3A and the biconvex positive lens L4A are joined. The negative meniscus lens L5A and the positive meniscus lens L6A are joined.

[0067] The rear group G2 is composed of, in order from the object side, a positive meniscus lens L7A convex on the image side, a negative meniscus lens L8A convex on the image side, a biconvex positive lens L9A, a negative meniscus lens L10A convex on the image side, and a biconvex positive lens L11A. The positive meniscus lens L7A and the negative meniscus lens L8A are joined to form a cemented lens BL. The cemented surface of the cemented lens BL faces concave on the object side. The biconvex positive lens L11A has aspherical surfaces on both sides.

[0068] (Table 1) Surface number R D Nd νd 1 33.991 2.200 2.00100 29.1 2 19.117 4.910 3* 19.000 2.700 1.58080 59.2 4* 10.532 12.932 5 114.302 1.650 1.49700 81.6 6 33.318 5.410 1.91082 35.2 7 -449.604 3.260 8 -45.215 1.450 1.49700 81.6 9 -254.812 2.600 1.90043 37.4 10 -46.047 8.510 11 Strangled INFINITY 5.125 12 -22.025 4.850 1.49700 81.6 13 -12.497 1.300 1.81600 46.6 14 -19.227 0.150 15 51.792 6.650 1.43875 95.0 16 -23.010 2.410 17 -31.290 1.200 2.00100 29.1 18 -181.145 1.350 19* 117.398 6.350 1.49700 81.6 20* -24.237 38.340 21 INFINITY 1.500 1.51633 64.1 22 INFINITY - * represents an axially symmetric aspherical surface. (Table 2) Surface number K A4 A6 A8 A10 3 -1.000 -0.1268E-04 -0.4615E-07 0.1479E-09 -0.2507E-12 4 -1.000 -0.1307E-05 -0.1753E-06 0.2686E-09 -0.5280E-12 19 0.000 -0.2287E-05 0.2084E-07 0.1124E-10 0.0000E+00 20 0.000 0.1927E-04 0.2797E-07 0.7616E-10 0.0000E+00 (Table 3) f 21.32 Fno 2.45 w 46.1 Y 21.64 BF 40.33 L 115.34

[0069] [Numerical Example 2] Figures 4 to 6 and Tables 4 to 6 show the single-focus lens of Numerical Example 2. Figure 4 is the lens configuration diagram at infinity focus, Figure 5 is the longitudinal aberration diagram at infinity focus, and Figure 6 is the lateral aberration diagram at infinity focus. Table 4 is the surface data, Table 5 is the aspherical data, and Table 6 is the various data.

[0070] The lens configuration of the single-focus lens of Numerical Example 2 is different from that of the single-focus lens of Numerical Example 1 in the following points. (1) In the front group G1, the negative lens L5A is a biconcave negative lens, and the positive lens L6A is a biconvex positive lens. (2) In the rear group G2, the negative lens L10A is a biconcave negative lens.

[0071] (Table 4) Surface number R D Nd νd 1 30.582 2.200 2.00100 29.1 2 19.030 6.072 3* 26.081 2.700 1.58080 59.2 4* 11.578 15.631 5 88.610 1.650 1.66382 27.4 6 33.534 4.410 1.80610 33.3 7 -148.022 3.256 8 -52.910 3.600 1.55332 71.7 9 21.127 7.029 1.61266 44.5 10 -42.757 9.232 11 aperture INFINITY 5.125 12 -32.561 4.850 1.49700 81.6 13 -13.923 1.300 1.81600 46.6 14 -23.123 0.150 15 30.410 6.650 1.49700 81.6 16 -33.124 2.410 17 -51.716 1.200 2.00100 29.1 18 100.282 1.350 19* 206.686 6.350 1.49700 81.6 20* -29.263 38.665 21 INFINITY 1.500 1.51633 64.1 22 INFINITY - * is a rotationally symmetric aspheric surface. (Table 5) Surface number K A4 A6 A8 A10 3 -1.000 -0.2600E-04 0.6768E-07 -0.1084E-09 0.4042E-13 4 -1.000 -0.1484E-04 -0.1036E-07 0.2671E-09 -0.1214E-11 19 0.000 -0.2402E-05 0.8054E-07 0.4918E-10 0.0000E+00 20 0.000 0.1913E-04 0.7639E-07 0.2449E-09 0.0000E+00 (Table 6) f 21.30 Fno 2.45 w 46.1 Y 21.64 BF 40.65 L 125.82

[0072] [Numerical Example 3] Figures 7 to 9 and Tables 7 to 9 show the single-focus lens of Numerical Example 3. Figure 7 is a lens configuration diagram at infinite focus, Figure 8 is a longitudinal aberration diagram at infinite focus, and Figure 9 is a lateral aberration diagram at infinite focus. Table 7 is surface data, Table 8 is aspherical data, and Table 9 is various data.

[0073] The lens configuration of the single-focus lens of Numerical Example 3 is different from that of the single-focus lens of Numerical Example 1 in the following points. (1) In the front group G1, the negative lens L3A is a biconcave negative lens, and the positive lens L4A is a biconvex positive lens. (2) In the rear group G2, the positive lens L11A is a positive meniscus lens convex on the image side.

[0074] (Table 7) Surface number R D Nd νd 1 30.223 2.200 2.00100 29.1 2 19.030 7.654 3* 20.992 2.700 1.58080 59.2 4* 11.077 15.775 5 -247.224 1.650 1.43875 95.0 6 27.721 4.410 1.85026 32.3 7 -103.826 3.256 8 -55.871 1.450 1.75575 24.7 9 -185.136 3.600 1.55298 55.1 10 -37.694 9.232 11 Stop INFINITY 5.125 12 -22.334 4.850 1.49700 81.6 13 -12.049 1.300 1.81600 46.6 14 -19.331 0.150 15 65.108 6.650 1.49700 81.6 16 -22.848 2.410 17 -26.446 1.200 2.00100 29.1 18 -71.876 1.350 19* -759.184 6.350 1.49700 81.6 20* -24.487 39.489 21 INFINITY 1.500 1.51633 64.1 22 INFINITY - * indicates an axially symmetric aspherical surface. (Table 8) Surface number K A4 A6 A8 A10 3 -1.000 -0.1115E-04 0.1432E-07 -0.1942E-10 -0.1548E-13 4 -1.000 0.7925E-05 -0.4817E-07 0.1072E-09 -0.8099E-12 19 0.000 -0.3608E-05 0.8766E-08 0.1660E-10 0.0000E+00 20 0.000 0.1353E-04 0.1018E-07 0.5994E-10 0.0000E+00 (Table 9) f 21.26 Fno 2.45 w 46.6 Y 21.64 BF 41.48 L 122.79

[0075] [Numerical Example 4] Figures 10 to 12 and Tables 10 to 12 show the single-focus lens of Numerical Example 4. Figure 10 is a lens configuration diagram at infinity focus, Figure 11 is a longitudinal aberration diagram at infinity focus, and Figure 12 is a lateral aberration diagram at infinity focus. Table 10 is surface data, Table 11 is aspherical surface data, and Table 12 is various data.

[0076] The lens configuration of the single-focus lens in Numerical Example 4 is the same as that of the single-focus lens in Numerical Example 3.

[0077] (Table 10) Surface number R D Nd νd 1 28.567 2.200 2.00069 25.5 2 19.030 7.391 3* 22.176 2.700 1.58080 59.2 4* 11.013 16.610 5 -187.025 1.650 1.43875 95.0 6 27.985 4.410 1.85026 32.3 7 -104.117 3.256 8 -56.210 1.450 1.75575 24.7 9 -133.930 3.600 1.55298 55.1 10 -38.199 9.232 11 Stop INFINITY 5.125 12 -23.093 4.850 1.49700 81.6 13 -12.067 1.300 1.81600 46.6 14 -19.359 0.150 15 60.401 6.650 1.49700 81.6 16 -22.869 2.410 17 -25.808 1.200 2.00100 29.1 18 -74.847 1.350 19* -823.817 6.350 1.49700 81.6 20* -24.233 39.213 21 INFINITY 1.500 1.51633 64.1 22 INFINITY - * indicates an axially symmetric aspherical surface. (Table 11) Surface number K A4 A6 A8 A10 3 -1.000 -0.1279E-04 0.1347E-07 -0.1789E-10 -0.1664E-13 4 -1.000 0.9704E-05 -0.4781E-07 0.1084E-09 -0.7853E-12 19 0.000 -0.3529E-05 0.1017E-07 0.1352E-10 0.0000E+00 20 0.000 0.1350E-04 0.1148E-07 0.5876E-10 0.0000E+00 (Table 12) f 21.29 Fno 2.45 w 46.6 Y 21.64 BF 41.20 L 123.09

[0078] [Numerical Example 5] Figures 13 to 15 and Tables 13 to 15 show the single-focus lens of Numerical Example 5. Figure 13 is a lens configuration diagram at infinity focus, Figure 14 is a longitudinal aberration diagram at infinity focus, and Figure 15 is a lateral aberration diagram at infinity focus. Table 13 is surface data, Table 14 is aspherical surface data, and Table 15 is various data.

[0079] The front group G1 is composed of, in order from the object side, a negative meniscus lens L1B convex on the object side, a negative meniscus lens L2B convex on the object side, a biconcave negative lens L3B, a biconvex positive lens L4B, a biconvex positive lens L5B, and a negative meniscus lens L6B convex on the image side. The negative meniscus lens L2B has aspherical surfaces on both sides. The biconcave negative lens L3B and the biconvex positive lens L4B are joined. The biconvex positive lens L5B and the negative meniscus lens L6B are joined.

[0080] The rear group G2 is composed of, in order from the object side, a positive meniscus lens L7B convex on the image side, a biconcave negative lens L8B, a biconvex positive lens L9B, a biconvex positive lens L10B, a biconvex positive lens L11B, a biconcave negative lens L12B, a negative meniscus lens L13B convex on the image side, and a biconvex positive lens L14B. The positive meniscus lens L7B, the biconcave negative lens L8B, and the biconvex positive lens L9B are joined together to form a cemented lens BL. The biconvex positive lens L11B and the biconcave negative lens L12B are joined together. The biconvex positive lens L14B has aspherical surfaces on both sides.

[0081] (Table 13) Surface number R D Nd νd 1 30.974 2.200 1.92286 20.9 2 18.264 8.000 3* 16.400 2.700 1.55332 71.7 4* 9.115 10.995 5 -53.839 1.650 1.59410 60.5 6 23.771 6.450 1.72047 34.7 7 -122.909 5.050 8 48.753 6.400 1.72047 34.7 9 -29.598 2.000 1.80400 46.5 10 -97.966 9.132 11 Stop INFINITY 5.125 12 -68.409 5.400 1.49700 81.6 13 -16.178 1.300 1.90043 37.4 14 25.078 5.300 1.73800 32.3 15 -31.129 0.000 16 38.270 5.500 1.59349 67.0 17 -30.739 0.200 18 81.771 4.300 1.53775 74.7 19 -29.000 1.400 1.72047 34.7 20 40.087 6.561 21 -39.560 1.200 1.90366 31.3 22 -198.722 0.200 23* 60.349 7.350 1.69350 53.2 24* -33.919 38.851 25 INFINITY 1.500 1.51633 64.1 26 INFINITY - * indicates an axially symmetric aspherical surface. (Table 14) Surface number K A4 A6 A8 A10 3 -1.000 -0.6476E-04 0.2359E-06 -0.4852E-09 0.4698E-12 4 -1.000 -0.6729E-04 0.2167E-06 -0.3477E-09 -0.7233E-12 23 0.000 -0.4141E-05 0.1163E-07 0.0000E+00 0.0000E+00 24 0.000 0.9336E-05 0.9261E-08 0.2832E-10 0.0000E+00 (Table 15) f 19.36 Fno 2.40 w 49.7 Y 21.64 BF 40.84 L 139.25

[0082] [Numerical Example 6] Figures 16 to 18 and Tables 16 to 18 show the single-focus lens of Numerical Example 6. Figure 16 is the lens configuration diagram at infinity focus, Figure 17 is the longitudinal aberration diagram at infinity focus, and Figure 18 is the lateral aberration diagram at infinity focus. Table 16 is the surface data, Table 17 is the aspherical surface data, and Table 18 is the various data.

[0083] The lens configuration of the single-focus lens in Numerical Example 6 is the same as that of the single-focus lens in Numerical Example 5.

[0084] (Table 16) Surface number R D Nd νd 1 30.140 2.200 1.92286 20.9 2 17.801 8.000 3* 17.580 2.700 1.55332 71.7 4* 9.309 10.995 5 -52.450 1.650 1.59410 60.5 6 24.240 6.450 1.72047 34.7 7 -124.145 5.050 8 45.360 6.400 1.72047 34.7 9 -26.515 2.000 1.80400 46.5 10 -99.003 9.132 11 Stop INFINITY 5.125 12 -107.303 5.400 1.49700 81.6 13 -16.209 1.300 1.90043 37.4 14 23.105 5.300 1.73800 32.3 15 -35.948 0.000 16 37.736 5.500 1.59349 67.0 17 -30.053 0.200 18 85.947 4.300 1.53775 74.7 19 -29.000 1.400 1.72047 34.7 20 39.137 6.561 21 -41.238 1.200 1.90366 31.3 22 -158.120 0.200 23* 60.093 7.350 1.69350 53.2 24* -33.149 38.452 25 INFINITY 1.500 1.51633 64.1 26 INFINITY - * is a rotationally symmetric aspherical surface. (Table 17) Surface number K A4 A6 A8 A10 3 -1.000 -0.6525E-04 0.2367E-06 -0.4837E-09 0.4436E-12 4 -1.000 -0.7182E-04 0.2068E-06 -0.3608E-09 -0.7608E-12 23 0.000 -0.4301E-05 0.1367E-07 0.0000E+00 0.0000E+00 24 0.000 0.9844E-05 0.1004E-07 0.3459E-10 0.0000E+00 (Table 18) f 18.51 Fno 2.40 w 50.6 Y 21.64 BF 40.44 L 138.85

[0085] [Numerical Example 7] Figures 19 to 21 and Tables 19 to 21 show the single-focus lens of Numerical Example 7. Figure 19 is a lens configuration diagram at infinity focus, Figure 20 is a longitudinal aberration diagram at infinity focus, and Figure 21 is a lateral aberration diagram at infinity focus. Table 19 is surface data, Table 20 is aspherical surface data, and Table 21 is various data.

[0086] The front group G1 is composed of, in order from the object side, a negative meniscus lens L1C convex on the object side, a negative meniscus lens L2C convex on the object side, a negative meniscus lens L3C convex on the object side, a biconcave negative lens L4C, a biconvex positive lens L5C, and a biconvex positive lens L6C. The negative meniscus lens L2C has aspherical surfaces on both sides. The biconcave negative lens L4C and the biconvex positive lens L5C are joined.

[0087] The rear group G2 is composed of, in order from the object side, a positive meniscus lens L7C convex on the image side, a negative meniscus lens L8C convex on the image side, a biconcave negative lens L9C, a biconvex positive lens L10C, a biconvex positive lens L11C, a biconcave negative lens L12C, and a biconvex positive lens L13C. The positive meniscus lens L7C and the negative meniscus lens L8C are joined together to form a cemented lens BL. The biconvex positive lens L10C has aspherical surfaces on both sides. The biconvex positive lens L13C has an aspherical surface on the image-side surface.

[0088] (Table 19) Surface number R D Nd νd 1 30.226 2.200 1.92286 20.9 2 17.950 8.000 3* 21.599 2.700 1.69350 53.2 4* 11.166 8.950 5 55.023 1.500 1.49700 81.6 6 30.470 5.000 7 -87.301 1.650 1.49700 81.6 8 22.257 6.450 1.68376 37.6 9 -132.670 2.153 10 45.385 3.400 1.80518 25.4 11 -330.248 9.132 12 Stop INFINITY 5.125 13 -74.037 5.400 1.49700 81.6 14 -14.174 2.276 1.90043 37.4 15 -28.500 1.000 16 -29.192 1.200 1.87070 40.7 17 150.450 0.200 18* 41.612 5.500 1.49710 81.6 19* -30.541 0.200 20 32.274 5.300 1.49700 81.6 21 -32.692 5.560 22 -26.743 1.200 1.91082 35.2 23 108.223 0.200 24 53.426 7.350 1.76802 49.2 25* -29.761 35.905 26 INFINITY 1.500 1.51633 64.1 27 INFINITY - * is a rotationally symmetric aspherical surface. (Table 20) Surface number K A4 A6 A8 A10 3 -1.000 -0.4474E-04 0.1064E-06 -0.1734E-09 0.1258E-12 4 -1.000 -0.5208E-04 0.5356E-07 -0.5263E-10 -0.2494E-12 18 0.000 0.1527E-04 -0.5562E-07 0.0000E+00 0.0000E+00 19 0.000 0.1116E-04 -0.2212E-07 0.0000E+00 0.0000E+00 25 0.000 0.2089E-04 0.3682E-07 0.0000E+00 0.0000E+00 (Table 21) f 16.45 Fno 2.40 w 54.2 Y 21.64 BF 37.89 L 129.54

[0089] [Numerical Example 8] Figures 22 to 24 and Tables 22 to 24 show the single-focus lens of Numerical Example 8. Figure 22 is a lens configuration diagram at infinity focus, Figure 23 is a longitudinal aberration diagram at infinity focus, and Figure 24 is a lateral aberration diagram at infinity focus. Table 22 is surface data, Table 23 is aspherical data, and Table 24 is various data.

[0090] The front group G1 is composed of, in order from the object side, a negative meniscus lens L1D convex on the object side, a negative meniscus lens L2D convex on the object side, a negative meniscus lens L3D convex on the object side, a biconvex positive lens L4D, a biconcave negative lens L5D, a biconvex positive lens L6D, and a biconvex positive lens L7D. The negative meniscus lens L2D has aspherical surfaces on both sides. The biconcave negative lens L5D and the biconvex positive lens L6D are joined together.

[0091] The rear group G2 is composed of, in order from the object side, a positive meniscus lens L8D convex on the image side, a negative meniscus lens L9D convex on the image side, a biconcave negative lens L10D, a biconvex positive lens L11D, a biconvex positive lens L12D, a biconcave negative lens L13D, and a biconvex positive lens L14D. The positive meniscus lens L8D and the negative meniscus lens L9D are joined together to form a cemented lens BL. The biconvex positive lens L11D has aspherical surfaces on both sides. The biconvex positive lens L14D has an aspherical surface on the image-side surface.

[0092] (Table 22) Surface number R D Nd νd 1 33.036 2.200 1.92286 20.9 2 19.621 8.000 3* 22.478 2.700 1.69350 53.2 4* 11.425 8.950 5 822.572 1.500 1.49700 81.6 6 34.153 3.000 7 96.088 3.000 1.62588 35.7 8 -71.301 1.614 9 -38.852 1.650 1.49700 81.6 10 22.479 6.450 1.68376 37.6 11 -113.768 2.153 12 54.049 3.400 1.62588 35.7 13 -127.803 9.132 14 Twist INFINITY 5.125 15 -68.119 5.400 1.49700 81.6 16 -14.067 2.276 1.90043 37.4 17 -23.168 1.000 18 -25.193 1.200 1.87070 40.7 19 544.700 0.200 20* 48.277 5.500 1.49710 81.6 21* -40.520 0.200 22 30.210 5.300 1.49700 81.6 23 -34.264 5.560 24 -30.224 1.200 1.91082 35.2 25 121.191 0.200 26 55.097 7.350 1.76802 49.2 27* -34.604 34.726 28 Twist INFINITY 1.500 1.51633 64.1 29 Twist INFINITY - * indicates a rotationally symmetric aspherical surface. (Table 23) Surface number K A4 A6 A8 A10 3 -1.000 -0.4398E-04 0.1181E-06 -0.1775E-09 0.1376E-12 4 -1.000 -0.4831E-04 0.8531E-07 0.1661E-10 -0.2401E-12 20 0.000 0.1736E-04 -0.6330E-07 0.0000E+00 0.0000E+00 21 0.000 0.1069E-04 -0.3659E-07 0.0000E+00 0.0000E+00 27 0.000 0.2303E-04 0.3642E-07 0.0000E+00 0.0000E+00 (Table 24) f 16.45 Fno 2.40 w 54.2 Y 21.64 BF 36.71 L 130.97

[0093] [Numerical Example 9] Figures 25 to 27 and Tables 25 to 27 show the single-focus lens of Numerical Example 9. Figure 25 is a lens configuration diagram at infinity focus, Figure 26 is a longitudinal aberration diagram at infinity focus, and Figure 27 is a lateral aberration diagram at infinity focus. Table 25 is surface data, Table 26 is aspherical surface data, and Table 27 is various data.

[0094] The front group G1 is composed of, in order from the object side, a negative meniscus lens L1E convex on the object side, a negative meniscus lens L2E convex on the object side, a biconcave negative lens L3E, a biconvex positive lens L4E, a negative meniscus lens L5E convex on the object side, and a biconvex positive lens L6E. The negative meniscus lens L2E has aspherical surfaces on both sides. The biconcave negative lens L3E and the biconvex positive lens L4E are cemented. The negative meniscus lens L5E and the biconvex positive lens L6E are cemented.

[0095] The rear group G2 is composed of, in order from the object side, a positive meniscus lens L7E convex on the image side, a negative meniscus lens L8E convex on the image side, a double concave negative lens L9E, a double convex positive lens L10E, a double convex positive lens L11E, a negative meniscus lens L12E convex on the image side, and a negative meniscus lens L13E convex on the object side. The positive meniscus lens L7E and the negative meniscus lens L8E are joined together to form a cemented lens BL. The double convex positive lens L10E has aspherical surfaces on both sides. The negative meniscus lens L12E has an aspherical surface on the object-side surface. The negative meniscus lens L13E has an aspherical surface on the object-side surface.

[0096] (Table 25) Surface number R D Nd νd 1 42.899 2.200 1.95375 32.3 2 19.706 5.697 3* 20.825 2.200 1.59201 67.0 4* 10.862 16.230 5 -39.482 2.075 1.49700 81.6 6 27.600 7.450 1.73211 46.2 7 -53.697 2.153 8 99.709 1.400 1.49700 81.6 9 17.398 5.400 1.57099 50.8 10 -159.126 9.132 11 Stop INFINITY 5.125 12 -238.568 4.400 1.49700 81.6 13 -12.953 2.276 1.90043 37.4 14 -33.936 1.000 15 -41.319 1.200 1.87070 40.7 16 3789.651 0.200 17* 44.883 5.500 1.49710 81.6 18* -22.923 0.200 19 23.959 5.300 1.49700 81.6 20 -49.787 5.560 21* -23.294 1.200 1.88202 37.2 22 -31.431 3.300 23* 29.598 1.200 1.85135 40.1 24 21.829 18.768 25 INFINITY 1.500 1.51633 64.1 26 INFINITY - * indicates an axially symmetric aspherical surface. (Table 26) Surface number K A4 A6 A8 A10 3 -1.000 -0.6507E-05 0.2577E-07 -0.9930E-10 0.1134E-12 4 -1.000 0.1678E-04 0.6599E-07 -0.3890E-09 0.3727E-13 17 0.000 0.2612E-05 -0.1351E-07 0.0000E+00 0.0000E+00 18 0.000 0.6048E-06 0.9071E-08 0.0000E+00 0.0000E+00 21 0.000 -0.3241E-05 -0.2408E-07 0.2285E-09 0.0000E+00 23 0.000 -0.3015E-04 -0.2688E-07 -0.3905E-09 0.0000E+00 (Table 27) f 14.04 Fno 2.40 w 58.1 Y 21.64 BF 20.76 L 111.15

[0097] The values for each conditional expression of each numerical example are shown in Table 28. As shown in Table 28, numerical examples 1 to 9 satisfy conditional expressions (1) to (15). (Table 28) Example 1 Example 2 Example 3 Conditional expression (1) 46.00 33.55 22.48 Conditional expression (2) 1.55 1.20 1.77 Conditional expression (3) -8.81 -17.88 -6.87 Conditional expression (4) 5.41 5.91 5.78 Conditional expression (5) 1.87 2.18 1.98 Conditional expression (6) 2.49 2.49 2.49 Conditional expression (7) 2.09 1.31 1.69 Conditional expression (8) 2.00100 2.00100 2.00100 Conditional expression (9) 1.64395 1.69974 1.69408 Conditional expression (10) 36.31 38.87 43.71 Conditional expression (11) 2.00100 2.00100 2.00100 Conditional expression (12) 37.88 37.88 37.88 Conditional expression (13) 86.01 81.55 81.55 Conditional expression (14) 8.46 8.76 8.55 Conditional expression (15) -1.02 -1.06 -1.12 Example 4 Example 5 Example 6 Conditional expression (1) 21.67 11.88 11.96 Conditional expression (2) 1.79 1.25 1.25 Conditional expression (3) -8.24 -2.09 -1.83 Conditional expression (4) 5.78 7.19 7.50 Conditional expression (5) 1.99 2.17 2.23 Conditional expression (6) 2.49 2.68 2.81 Conditional expression (7) 1.65 1.43 0.92 Conditional expression (8) 2.00069 1.92286 1.92286 Conditional expression (9) 1.69400 1.71857 1.68441 Conditional expression (10) 43.71 34.71 34.71 Conditional expression (11) 2.00100 1.90366 1.90366 Conditional expression (12) 37.88 34.46 34.46 Conditional expression (13) 81.55 61.75 61.69 Conditional expression (14) 8.57 9.77 9.74 Conditional expression (15) -1.12 -1.05 -1.03 Example 7 Example 8 Example 9 Conditional expression (1) 39.50 39.11 11.97 Conditional expression (2) 1.35 1.33 1.48 Conditional expression (3) -13.24 -5.89 -5.50 Conditional expression (4) 7.87 7.96 7.92 Conditional expression (5) 2.31 2.34 2.48 Conditional expression (6) 3.16 3.16 3.70 Conditional expression (7) 4.46 1.88 0.67 Conditional expression (8) 1.92286 1.92286 1.95375 Conditional expression (9) 1.65259 1.65259 1.63494 Conditional expression (10) 31.54 36.35 48.49 Conditional expression (11) 1.91082 1.91082 1.90043 Conditional expression (12) 37.78 37.78 38.86 Conditional expression (13) 73.48 73.48 81.55 Conditional expression (14) 9.09 9.19 7.80 Conditional expression (15) -1.08 -1.10 -1.08

[0098] Referring to FIGS. 28 and 29, the digital camera (imaging device) 100 equipped with the single-focus lens of the present embodiment will be described.

[0099] The digital camera 100 includes a camera body (housing) 101, a photographing lens 102, a viewfinder 103, a flash 104, a shutter button 105, a power button 106, a liquid crystal monitor 107, operation buttons 108, and a memory card slot 109.

[0100] The camera body 101 houses each component of the digital camera 100. The photographing lens 102 is, for example, a unit in which a single-focus lens of the present embodiment is incorporated into a lens barrel and / or an interchangeable lens. The viewfinder 103 is a viewing window for determining a subject and composition. The flash 104 emits a flash during night photography or photography in a dark place. The shutter button 105 is a physical switch for executing photography by the digital camera 100. The power button 106 is a physical switch for switching the power of the digital camera 100 on and off. The liquid crystal monitor 107 displays a photographed image or the like by the digital camera 100. The operation buttons 108 are physical switches for setting the photographing mode or the like of the digital camera 100. The memory card slot 109 is a slot for inserting a memory card (not shown) that stores a photographed image or the like by the digital camera 100.

[0101] As functional components inside the camera body 101, the digital camera 100 includes a central processing unit 111, an image processing unit 112, a light receiving element 113, a signal processing unit 114, a semiconductor memory 115, and a communication card 116.

[0102] The central processing unit 111 performs various arithmetic processes inside the digital camera 100. The image processing unit 112 performs various image processes on the photographed image by the digital camera 100. The light receiving element 113 takes in and receives external light used for photometry processing. The signal processing unit 114 performs various signal processes such as a photographing instruction signal and an image processing signal. The semiconductor memory 115 constitutes a temporary storage area for the photographed image by the digital camera 100. The communication card 116 is for enabling wireless communication with an external device (not shown).

[0103] Figure 30 is an external perspective view showing an example of the interchangeable lens (lens barrel) 102 of the present embodiment. As shown in Figure 30, the interchangeable lens 102 has a lens holding cylinder 102X and a single-focus lens held by this lens holding cylinder 102X. In Figure 30, among the single-focus lenses, the lenses L1A to L1E arranged on the most object side of the front group G1 are depicted.

[0104] According to the present embodiment, it is possible to provide a single-focus lens, an interchangeable lens, and an imaging device that have high optical performance, are small, lightweight, and have a wide angle of view.

[0105] The configuration of the digital camera 100 described here is merely an example, and various design changes are possible (there is freedom in the specific form of the digital camera 100).

[0106] The single-focus lens of the present embodiment can be applied not only to the digital camera 100 described above, but also to, for example, an interchangeable lens, a portable information terminal device, a video camera, a silver halide camera, an optical sensor, a projection optical system (projector), etc.

Explanation of Reference Numerals

[0107] G1 Front group L1A~L1E Negative meniscus lens with a convex surface facing the object side G2 Rear group BL Bonding lens SP Aperture stop CG Parallel plate 100 Digital camera (imaging device) 102 Photographing lens (lens barrel, interchangeable lens)

Claims

1. Composed of, in order from the object side, a front group, an aperture stop, and a rear group with positive refractive power, The chief ray passing through the stop surface of the aperture stop is larger than the chief ray incident on the most object-side refractive surface of the front group, The front group has, on the most object side, a negative meniscus lens with a convex surface facing the object side, The most image-side refractive surface of the front group has a convex surface on the image side, The rear group has at least one negative lens, The rear group has, on the most object side, a cemented lens, The cemented lens located on the most object side of the rear group has a cemented surface with a concave surface facing the object side, The most object-side refractive surface of the rear group has a concave surface on the object side, Satisfying the following conditional expressions (1), (2'), (3), (5), (6), (7), (11C), A single-focus lens characterized by this. (1) 5.0 < |fF| / fR (2') 0.8 < DF / DR < 2.0 (3) |fBL| / fBO < -1.0 (5) 1.5 < fR / f < 3.0 (6) 1.6 < (Y × Fno) / f < 4.1 (7) 0.3 < RF / RR < 6.0 (RF < 0, RR < 0) (11C) 1.87 < NnRmax However, fF: Focal length of the front group, fR: Focal length of the rear group, DF: Axial distance on the optical axis from the most object-side surface of the front group to the aperture stop, DR: Axial distance on the optical axis from the most image-side surface of the rear group to the aperture stop, fBL: Focal length of the cemented lens located on the most object side of the rear group, fBO: Focal length of the cemented surface with a concave surface facing the object side of the cemented lens located on the most object side of the rear group, f: Focal length of the entire single-focus lens system, Y: Image height of the entire single-focus lens system, Fno: F-number of the entire single-focus lens system, RF: Curvature radius of the most image-side refractive surface of the front group, RR: Curvature radius of the most object-side refractive surface of the rear group, NnRmax: Refractive index of the negative lens with the largest refractive index among the negative lenses included in the rear group.

2. Satisfying the following conditional expression (4), The single-focus lens according to Claim 1, characterized by this. (4) 1.0 < TL / f < 10.0 However, TL: Distance from the most object-side surface of the front group to the image plane, f: Focal length of the entire single-focus lens system.

3. The front group has at least two positive lenses, The single-focus lens according to Claim 1 or Claim 2, characterized by this.

4. The front group has at least three negative lenses, The single-focus lens according to any one of Claims 1 to 3, characterized by this.

5. The front group has, in order from the most object side, three or more negative lenses, The single-focus lens according to any one of Claims 1 to 4, characterized by this.

6. The front group has at least one negative lens and satisfies the following conditional expression (8), The single-focus lens according to any one of Claims 1 to 5, characterized in that. (8) 1.60 < NnFmax However, NnFmax: The refractive index of the negative lens having the largest refractive index among the negative lenses included in the front group.

7. The front group has at least one negative lens and satisfies the following conditional expression (9), The single-focus lens according to any one of Claims 1 to 6, characterized in that. (9) 1.60 < NnFave However, NnFave: The average value of the refractive indices of the negative lenses included in the front group.

8. The front group has at least one positive lens and satisfies the following conditional expression (10), The single-focus lens according to any one of Claims 1 to 7, characterized in that. (10) 30 < νpFave < 50 However, νpFave: The average value of the Abbe numbers of the positive lenses included in the front group.

9. Satisfies the following conditional expression (12), The single-focus lens according to any one of Claims 1 to 8, characterized in that. (12) 30 < νnRave < 50 However, νnRave: The average value of the Abbe numbers of the negative lenses included in the rear group.

10. The rear group has at least one positive lens and satisfies the following conditional expression (13), The single-focus lens according to any one of Claims 1 to 9, characterized in that. (13) 60 < νpRave However, νpRave: The average value of the Abbe numbers of the positive lenses included in the rear group.

11. An interchangeable lens having the single-focus lens according to any one of Claims 1 to 10.

12. An imaging device having the single-focus lens according to any one of Claims 1 to 10.

Images