JP7697216B2 - Single focus lens, interchangeable lens and imaging device - Google Patents

Description

The present invention relates to a single focal length lens, an interchangeable lens, and an imaging device.

In recent years, there has been a demand for lenses that are bright, compact, and have a wide angle of view. For example, a retrofocus lens configuration in which a negative lens group precedes the lens group is already known (Patent Document 1).

JP 2013-054269 A

However, retrofocus lenses generally have an asymmetrical configuration with respect to the aperture, and as the angle of view becomes wider, various aberrations, particularly off-axis aberrations, tend to worsen. Furthermore, there is an issue that the lens on the object side becomes larger, making miniaturization difficult. For example, the optical system of Patent Document 1 has room for improvement in terms of the wide angle of view and correction of various aberrations.

The present invention has been made in consideration of the above points, and aims to provide a small, wide-angle prime lens, an interchangeable lens, and an imaging device in which various aberrations are corrected.

The single focal length lens of this embodiment is composed of, in order from the object side, a front group, a stop, and a rear group with positive refractive power, the axial light beam diameter incident on the front group closest to the object side is smaller than the axial light beam diameter passing through the stop, the front group has, closest to the object side, a negative meniscus lens with a convex surface facing the object side, and adjacent to the image side of the negative meniscus lens located closest to the object side, a negative meniscus lens with a convex surface facing the object side, the front group has, in order from the object side, three or more negative lenses and a cemented lens of a positive lens and a negative lens, the front group has, closest to the image side, a lens component with positive refractive power with a concave surface facing the object side, the front group has two or more positive lenses, and is characterized in that it satisfies the following conditional expressions (1) and (15).
(1) 1.85<NdL1
(15) 4.5<TL/D<12.5
however,
NdL1: the refractive index of the negative meniscus lens located closest to the object in the front group,
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 side to the surface of the rear group closest to the object side at infinity,
It is.
The single focal length lens of this embodiment is characterized in that it is composed of, in order from the object side, a front group, a stop, and a rear group with positive refractive power, the axial light beam diameter incident on the most object side of the front group is smaller than the axial light beam diameter passing through the stop, the front group has, in its most object side position, a negative meniscus lens with a convex surface facing the object side, and has, adjacent to the image side of the negative meniscus lens positioned most object side, a negative meniscus lens with a convex surface facing the object side, the front group has, in order from the most object side, three or more negative lenses and a cemented lens of a positive lens and a negative lens, the front group has, in its most image side position, a lens component with positive refractive power with a concave surface facing the object side, the front group has two or more positive lenses, and satisfies the following conditional expressions (1), (2), and (15).
(1) 1.85<NdL1
(2) 1.0<G1bf/f<100
(15) 4.5<TL/D<12.5
however,
NdL1: the refractive index of the negative meniscus lens located closest to the object in the front group,
G1bf: the object-side focal length of the lens component located closest to the image side in the front group,
f: focal length of the entire system of a single focal length lens,
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 side to the surface of the rear group closest to the object side at infinity,
It is.
The single focal length lens of this embodiment is characterized in that it is composed of, in order from the object side, a front group, a stop, and a rear group with positive refractive power, the axial light beam diameter incident on the most object side of the front group is smaller than the axial light beam diameter passing through the stop, the front group has, in its most object side position, a negative meniscus lens with a convex surface facing the object side, and has, adjacent to the image side of the negative meniscus lens positioned most object side, a negative meniscus lens with a convex surface facing the object side, the front group has, in order from the most object side, three or more negative lenses and a cemented lens of a positive lens and a negative lens, the front group has, in its most image side position, a lens component with positive refractive power with a concave surface facing the object side, the front group has two or more positive lenses, and satisfies the following conditional expressions (1), (7), and (15).
(1) 1.85<NdL1
(7) 1.0<TL/f<10
(15) 4.5<TL/D<12.5
however,
NdL1: the refractive index of the negative meniscus lens located closest to the object in the front group,
TL: distance from the surface of the front group closest to the object to the image plane,
f: focal length of the entire system of a single focal length lens,
D: the distance from the surface of the front group closest to the image side to the surface of the rear group closest to the object side at infinity,
It is.

The interchangeable lens and imaging device of this embodiment have the fixed focal length lens described above.

The present invention provides a small, wide-angle prime lens, an interchangeable lens, and an imaging device with corrected aberrations.

FIG. 2 is a lens configuration diagram of a single focal length lens according to Numerical Example 1 when focused on infinity. 1 is a longitudinal aberration diagram of the single focal length lens of Numerical Example 1 when focused on an object at infinity. 1 is a lateral aberration diagram of the single focal length lens of Numerical Example 1 when focused on an object at infinity. FIG. 11 is a lens configuration diagram of a single focal length lens according to Numerical Example 2 when focused on infinity. 11A to 11C are longitudinal aberration diagrams of the single focal length lens of Numerical Example 2 when focused on an object at infinity. 11A to 11C are diagrams showing lateral aberration of the single focal length lens of Numerical Example 2 when focused on an object at infinity. FIG. 11 is a lens configuration diagram of a single focal length lens according to Numerical Example 3 when focused on infinity. FIG. 11 is a longitudinal aberration diagram of the single focal length lens of Numerical Example 3 when focused on an object at infinity. 13A to 13C are diagrams showing lateral aberration of the single focal length lens of Numerical Example 3 when focused on an object at infinity. FIG. 13 is a lens configuration diagram of a single focal length lens according to Numerical Example 4 when focused on infinity. FIG. 13 is a longitudinal aberration diagram of the single focal length lens of Numerical Example 4 when focused on an object at infinity. 13A to 13C are diagrams showing lateral aberration of the single focal length lens of Numerical Example 4 when focused on an object at infinity. FIG. 13 is a lens configuration diagram of a single focal length lens according to Numerical Example 5 when focused on infinity. FIG. 13 is a longitudinal aberration diagram of the single focal length lens of Numerical Example 5 when focused on an object at infinity. 13A to 13C are diagrams showing lateral aberration of the single focal length lens of Numerical Example 5 when focused on an object at infinity. FIG. 13 is a lens configuration diagram of a single focal length lens according to Numerical Example 6 when focused on infinity. FIG. 13 is a longitudinal aberration diagram of the single focal length lens of Numerical Example 6 when focused on an object at infinity. FIG. 13 is a lateral aberration diagram of the single focal length lens of Numerical Example 6 when focused on an object at infinity. FIG. 13 is a lens configuration diagram of a single focal length lens according to Numerical Example 7 when focused on infinity. FIG. 13 is a longitudinal aberration diagram of the single focal length lens of Numerical Example 7 when focused on an object at infinity. FIG. 13 is a lateral aberration diagram of the single focal length lens of Numerical Example 7 when focused on an object at infinity. FIG. 13 is a lens configuration diagram of a single focal length lens according to Numerical Example 8 when focused on infinity. FIG. 13 is a longitudinal aberration diagram of the single focal length lens of Numerical Example 8 when focused on an object at infinity. FIG. 13 is a lateral aberration diagram of the single focal length lens of Numerical Example 8 when focused on an object at infinity. FIG. 13 is a lens configuration diagram of a single focal length lens according to Numerical Example 9 when focused on infinity. FIG. 13 is a longitudinal aberration diagram of the single focal length lens of Numerical Example 9 when focused on an object at infinity. FIG. 13 is a lateral aberration diagram of the single focal length lens of Numerical Example 9 when focused on an object at infinity. FIG. 1 is a first diagram showing an example of an imaging device equipped with a fixed focal length lens according to an embodiment of the present invention. FIG. 2 is a second diagram showing an example of an imaging device equipped with the fixed focal length lens of the present embodiment. FIG. 1 is an external perspective view showing an example of an interchangeable lens of the present embodiment.

The fixed focal length lens of this embodiment is suitable, for example, as a photographic optical system in an imaging device such as a digital single-lens reflex camera or digital single-lens camera, or as an interchangeable lens for use with such an imaging device.

As shown in the lens configuration diagrams of Figures 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, a light amount adjustment aperture SP, and a rear group G2 with positive refractive power. The front group G1 can have either positive or negative refractive power. For example, in Numerical Examples 2, 8, and 9 described later, the front group G1 has positive refractive power, and in Numerical Examples 1, 3, 4, 5, 6, and 7 described later, the front group G1 has negative refractive power. In addition, for example, when the single focus lens of this embodiment is mounted on a digital camera, a low-pass filter, an infrared cut filter, a cover glass for an image sensor, etc. (which may be collectively called a parallel plane plate) (not shown) can be placed between the rear group G2 and the image surface (designed image surface).

In this embodiment, based on the basic configuration described above, the detailed structure of the lens groups and lens elements and the selection of glass materials are optimized to realize a small, wide-angle prime lens in which various aberrations are corrected. In this specification, "wide angle of view" means, for example, a half angle of view of 40° or more.

In the single focal length lens of this embodiment, the diameter of the axial light beam incident on the most object-side portion of the front group G1 is smaller than the diameter of the axial light beam passing through the aperture stop SP. This allows the single focal length lens to have a wider angle of view, while also ensuring the necessary back focus and peripheral light volume.

In the single focal length lens of this embodiment, the front group G1 has a negative meniscus lens (for example, L1A, L1B, L1C, L1D, L1E, L1F, L1G, L1H, and L1I described below) closest to the object, with the convex surface facing the object. This allows the single focal length lens to be made compact, and various aberrations, particularly distortion and astigmatism, to be corrected well.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expressions (1), (1A), (1B), and (1C).
(1) 1.85<NdL1
(1A) 1.90<NdL1
(1B) 1.95<NdL1
(1C) 2.00<NdL1
however,
NdL1: the refractive index of the negative meniscus lens located closest to the object in the front group,
It is.

By satisfying conditional expression (1), it is possible to reduce the size of the single focal length lens and to satisfactorily correct various aberrations, particularly distortion and curvature of field. This effect is more pronounced when conditional expressions (1A), (1B), and (1C) are satisfied.
If the lower limit of conditional expression (1) is exceeded, the radius of curvature of the image-side surface of the negative meniscus lens located closest to the object in the front group becomes small, and the lens spacing on the image side in particular becomes wider, making it difficult to reduce the size and to correct distortion and curvature of field.

The front group G1 can have, in order from the object side, two or more negative lenses (for example, L1A and L2A, L1B and L2B, L1C and L2C, L1D and L2D, L1E and L2E, L1F and L2F, L1G and L2G, L1H and L2H, and L1I and L2I, which will be described later). This ensures negative refractive power in the front group G1, and allows distortion to be corrected well. If this lens configuration is not satisfied, the negative refractive power in the front group G1 will be too weak, making it difficult to correct distortion.

The front group G1 can have, in order from the object side, two or more negative lenses and a cemented lens G1a of a positive lens and a negative lens. The order of the positive and negative lenses that make up the cemented lens G1a is not limited, and they may be arranged in the order of positive and negative from the object side, or in the order of negative and positive from the object side. In this way, by dividing the negative refractive power of the front group G1 into two or more lenses in order from the object side, it is possible to minimize the occurrence of various aberrations, and in particular to effectively correct coma aberration. Furthermore, by having a cemented lens G1a of a positive lens and a negative lens on the image side of the two or more negative lenses, chromatic aberration can be effectively corrected.

The front group G1 can have, in order from the object side, three or more negative lenses (for example, L1A, L2A, and L3A, L1B, L2B, and L3B, L1C, L2C, and L3C, L1D, L2D, L3D, and L4D, L1E, L2E, and L3E, L1F, L2F, and L3F, L1G, L2G, and L3G, L1H, L2H, and L3H, and L1I, L2I, and L3I, which will be described later). This allows the light rays entering the front group G1 to be gradually refracted by three or more negative lenses, thereby minimizing the occurrence of various aberrations, and in particular allows for good correction of field curvature aberration and astigmatism. In Numerical Example 4 described later, four negative lenses (L1D, L2D, L3D, and L4D) are arranged in the front group G1 from the object side, but five or more negative lenses may be arranged consecutively in the front group G1 from the object side. In terms of compactness, four or less lenses are preferable.

The front group G1 can have a negative meniscus lens (such as L2A, L2B, L2C, L2D, L2E, L2F, L2G, L2H, and L2I described below) with a convex surface facing the object side, adjacent to the image side of the negative meniscus lens located closest to the object. This allows distortion to be effectively corrected.

The front group G1 can have a lens component G1b closest to the image side, with a concave surface facing the object side. This allows for good correction of field curvature. In this specification, the term "lens component" refers to, for example, a single lens or cemented lens with only two air-contact surfaces, one on the object side and one on the image side. In Numerical Examples 1-4 and 6-9 described below, the lens component G1b is composed of a cemented lens, and in Numerical Example 5 described below, the lens component G1b is composed of a single lens.

The front group G1 can have a lens component G1b with positive refractive power closest to the image side. This allows for excellent correction of spherical aberration and coma aberration.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expressions (2), (2A), and (2B).
(2) 1.0<G1bf/f<100
(2A) 1.0<G1bf/f<50
(2B) 3.0<G1bf/f<10
however,
G1bf: the object-side focal length of the lens component located closest to the image side in the front group,
f: focal length of the entire system of a single focal length lens,
It is.

By satisfying conditional expression (2), it is possible to satisfactorily correct curvature of field, spherical aberration, and coma aberration. This effect is more pronounced when conditional expressions (2A) and (2B) are satisfied.
If the upper limit of condition (2) is exceeded, the refractive power of the lens component located closest to the image side in the front group becomes too weak, making it difficult to correct (undercorrect) curvature of field, spherical aberration, and coma.
If the lower limit of condition (2) is exceeded, the refractive power of the lens component located closest to the image side in the front group becomes too strong, resulting in overcorrection of field curvature, spherical aberration, and coma.

The front group G1 has at least one cemented lens (for example, G1a and G1b, which will be described later), and the cemented lens (for example, G1a, which will be described later) located closest to the object among the cemented lenses in the front group G1 can have positive refractive power. This allows for excellent correction of spherical aberration and coma aberration in addition to chromatic aberration.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expressions (3), (3A), (3B), and (3C).
(3) -1.0<G1af/G1f<1.0
(3A) -0.5<G1af/G1f<1.0
(3B) -0.5<G1af/G1f<0.5
(3C)-0.5<G1af/G1f<0.15
however,
G1af: the focal length of the cemented lens in the front group that is located closest to the object,
G1f: focal length of the front group,
It is.

By satisfying conditional expression (3), chromatic aberration and off-axis aberrations can be corrected satisfactorily. This effect is more pronounced when conditional expressions (3A), (3B), and (3C) are satisfied.
If the upper limit of condition (3) is exceeded, it becomes difficult to correct chromatic aberration and off-axis aberrations (they are undercorrected).
If the lower limit of condition (3) is exceeded, chromatic aberration and off-axis aberrations will be overcorrected.

The front group G1 can have two or more positive lenses. This allows for good correction of spherical aberration. If the front group G1 contained only one positive lens, the correction of spherical aberration would be insufficient.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expressions (4), (4A), (4B), (4C), (4D), (4E), (4F), and (4G).
(4) 0.1<L1SF<1.0
(4A) 0.1<L1SF<0.8
(4B) 0.2<L1SF<0.6
(4C)0.25<L1SF<0.5
(4D)0.1<L1SF<0.3
(4E)0.2<L1SF<0.3
(4F)0.25<L1SF<0.3
(4G) 0.22<L1SF<0.29
however,
L1SF=(L1R1-L1R2)/(L1R1+L1R2)
L1R1: radius of curvature of the object-side surface of the negative meniscus lens located closest to the object in the front group,
L1R2: radius of curvature of the image-side surface of the negative meniscus lens located closest to the object in the front group,
It is.

Conditional expression (4) defines the shape (shaping factor) of the negative meniscus lens located closest to the object in the front group. By satisfying conditional expression (4), various aberrations such as coma aberration can be effectively corrected and the overall lens length can be shortened. This effect is more pronounced when conditional expressions (4A), (4B), (4C), (4D), (4E), (4F), and (4G) are satisfied.
If the upper limit of condition (4) is exceeded, the fluctuations of various aberrations such as coma occurring at the image-side surface of the negative meniscus lens located closest to the object side in the front group become large.
If the lower limit of condition (4) is exceeded, the principal point position of the negative meniscus lens located closest to the object in the front group will be on the image side, so that the distance between the principal points of the lenses becomes long and the overall lens length increases.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expressions (5), (5A), (5B), and (5C).
(5) 0.1<L2SF<0.5
(5A) 0.2<L2SF<0.5
(5B) 0.1<L2SF<0.45
(5C)0.19<L2SF<0.3
however,
L2SF=(L2R1-L2R2)/(L2R1+L2R2)
L2R1: the radius of curvature of the object-side surface of the negative meniscus lens located second closest to the object in the front group,
L2R2: radius of curvature of the image-side surface of the negative meniscus lens located second closest to the object in the front group,
It is.

Conditional expression (5) defines the shape (shaping factor) of the negative meniscus lens located second from the object side in the front group. By satisfying conditional expression (5), various aberrations such as coma aberration can be effectively corrected and the overall lens length can be shortened. This effect is more pronounced when conditional expressions (5A), (5B), and (5C) are satisfied.
If the upper limit of condition (5) is exceeded, the fluctuations of various aberrations such as coma occurring at the image-side surface of the negative meniscus lens that is the second most negative meniscus lens from the object side in the front group become large.
If the lower limit of condition (5) is exceeded, the principal point position of the negative meniscus lens that is the second most negative meniscus lens from the object side in the front group will be on the image side, so the distance between the principal points of the lenses will be long and the overall lens length will increase.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expressions (6), (6A), (6B), and (6C).
(6) -8.0<L1f/f<0
(6A) -5.0<L1f/f<-1.0
(6B) -3.0<L1f/f<-1.5
(6C) -2.5<L1f/f<-2.0
however,
L1f: the focal length of the negative meniscus lens located closest to the object in the front group,
f: focal length of the entire system of a single focal length lens,
It is.

By satisfying conditional expression (6), the angle of view of the fixed focal length lens can be increased and coma can be effectively corrected. This effect is more pronounced when conditional expressions (6A), (6B), and (6C) are satisfied.
If the upper limit of condition (6) is exceeded, the refractive power of the negative meniscus lens located closest to the object in the front group becomes too weak, making it difficult to achieve a wide angle of view for a single focal length lens.
If the lower limit of condition (6) is exceeded, the refractive power of the negative meniscus lens located in the front group closest to the object becomes too strong, making it difficult to control coma aberration.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expressions (7), (7A), and (7B).
(7) 1.0<TL/f<10
(7A) 1.0<TL/f<6.0
(7B) 4.5<TL/f<6.0
however,
TL: distance from the surface of the front group closest to the object to the image plane,
f: focal length of the entire system of a single focal length lens,
It is.

By satisfying conditional expression (7), it is possible to reduce the size of the optical system and widen the angle of view, while at the same time making it possible to satisfactorily correct spherical aberration, coma, and distortion. This effect is more pronounced when conditional expressions (7A) and (7B) are satisfied.
If the upper limit of condition (7) is exceeded, distortion and coma aberration will be large, and the optical system will become large.
If the lower limit of condition (7) is exceeded, the focal length becomes long and the angle of view becomes narrow, and it becomes difficult to correct spherical aberration and coma.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expressions (8), (8A), (8B), (8C), and (8D).
(8) 1.0<ZTL/f<12.0
(8A) 1.0<ZTL/f<6.0
(8B) 1.0<ZTL/f<4.0
(8C) 1.0<ZTL/f<2.8
(8D) 1.3<ZTL/f<1.8
however,
ZTL: the distance from the surface of the front group closest to the object to the surface closest to the image,
f: focal length of the entire system of a single focal length lens,
It is.

By satisfying conditional expression (8), the front group and in turn the entire lens system can be made thinner, the overall lens length can be shortened, and spherical aberration can be effectively corrected. This effect is more pronounced when conditional expressions (8A), (8B), (8C), and (8D) are satisfied.
If the upper limit of condition (8) is exceeded, the front group and therefore the entire lens system will become thicker, resulting in an increase in the overall lens length.
If the lower limit of condition (8) is exceeded, it becomes difficult to correct spherical aberration.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expressions (9) and (9A).
(9) 1.80<LSPNd
(9A) 1.85<LSPNd
however,
LSPNd: the refractive index of the lens located closest to the image side in the front group,
It is.

By satisfying conditional expression (9), distortion, curvature of field, coma, and spherical aberration can be corrected satisfactorily. This effect is more pronounced by satisfying conditional expression (9A).
If the lower limit of condition (9) is exceeded, distortion, curvature of field, coma, and spherical aberration will be insufficiently corrected.

In the single focal length lens of this embodiment, it is preferable that the rear group G2 has at least one positive lens and that the following conditional expressions (10), (10A), and (10B) are satisfied.
(10) 70<G2νd
(10A) 80<G2νd
(10B)85<G2νd
however,
G2νd: average Abbe number of the positive lenses in the rear group,
It is.

By satisfying conditional expression (10), longitudinal chromatic aberration can be corrected satisfactorily. This effect is more pronounced when conditional expressions (10A) and (10B) are satisfied.
If the lower limit of condition (10) is exceeded, it becomes difficult to correct longitudinal chromatic aberration.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expressions (11), (11A), (11B), and (11C).
(11) 0.1<L2SF/L1SF<5.0
(11A) 0.5<L2SF/L1SF<3.0
(11B) 0.3<L2SF/L1SF<2.0
(11C)0.9<L2SF/L1SF<1.5
however,
L1SF=(L1R1-L1R2)/(L1R1+L1R2)
L2SF=(L2R1-L2R2)/(L2R1+L2R2)
L1R1: radius of curvature of the object-side surface of the negative meniscus lens located closest to the object side in the front group,
L1R2: radius of curvature of the image-side surface of the negative meniscus lens located closest to the object in the front group,
L2R1: the radius of curvature of the object-side surface of the negative meniscus lens located second closest to the object in the front group,
L2R2: radius of curvature of the image-side surface of the negative meniscus lens located second closest to the object in the front group,
It is.

By satisfying conditional expression (11), various aberrations such as coma can be effectively corrected and the overall lens length can be shortened. This effect is more pronounced when conditional expressions (11A), (11B), and (11C) are satisfied.
If the upper limit of conditional expression (11) is exceeded, the principal point position of the negative meniscus lens that is the second most negative lens element from the object side in the front group will be on the image side, so that the distance between the principal points of the lenses will become long and the overall lens length will increase.
If the lower limit of condition (11) is exceeded, the fluctuations of various aberrations such as coma will become large.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expressions (12), (12A), and (12B).
(12) 1.0<G2f/f<5.0
(12A) 1.0<G2f/f<3.0
(12B) 1.5<G2f/f<2.5
however,
G2f: focal length of the rear group,
f: focal length of the entire system of a single focal length lens,
It is.

By satisfying conditional expression (12), it is possible to reduce the size of the single focal length lens and to satisfactorily correct curvature of field. This effect is more pronounced when conditional expressions (12A) and (12B) are satisfied.
If the upper limit of condition (12) is exceeded, the refractive power of the rear group becomes too weak, the amount of movement required for focusing becomes large, and the single focal length lens becomes large.
If the lower limit of condition (12) is exceeded, the refractive power of the rear group becomes too strong, causing large fluctuations in the curvature of field that accompany focusing.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expression (13).
(13) 25<L1νd
however,
L1νd: Abbe number of the negative meniscus lens located closest to the object in the front group,
It is.

By satisfying conditional expression (13), lateral chromatic aberration can be effectively corrected.
If the lower limit of condition (13) is exceeded, it becomes difficult to correct lateral chromatic aberration.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expression (14).
(14) 1.6<(Y×Fno)/f<4.1
however,
Y: image height of the entire system of a single focal length lens,
Fno: F-number of the entire single focal length lens system,
f: focal length of the entire system of a single focal length lens,
It is.

By satisfying conditional expression (14), coma, astigmatism, and spherical aberration can be well corrected, a bright lens with a small F-number can be realized, and a wide angle of view can be achieved.
If the upper limit of condition (14) is exceeded, it becomes difficult to correct off-axis aberrations, particularly coma and astigmatism, and the F-number becomes large, resulting in a dark lens.
If the lower limit of the condition (14) is exceeded, the diameter of the light beam passing through the fixed focal length lens becomes large, making it difficult to correct spherical aberration and coma, and also narrowing the angle of view.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expression (15).
(15) 4.5<TL/D<12.5
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 side to the surface of the rear group closest to the object side at infinity,
It is.

By satisfying conditional expression (15), it is possible to reduce the size of the single focal length lens and to satisfactorily correct the curvature of field.
If the upper limit of condition (15) is exceeded, the overall lens length increases or the air gap between the front and rear groups becomes too narrow, making it difficult to correct curvature of field.
If the lower limit of condition (15) is exceeded, the overall lens length 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 overall length.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expression (16).
(16) 1.5<ZTL/D<4.5
however,
ZTL: the distance from the surface of the front group closest to the object to the surface closest to the image,
D: the distance from the surface of the front group closest to the image side to the surface of the rear group closest to the object side at infinity,
It is.

By satisfying conditional expression (16), it is possible to reduce the size of the single focal length lens and to satisfactorily correct the curvature of field.
If the upper limit of condition (16) is exceeded, the thickness of the front group increases, resulting in an increase in the overall lens length and outer diameter, or the air gap between the front and rear groups becomes too narrow, making it difficult to correct curvature of field.
If the lower limit of condition (16) is exceeded, the thickness of the front group becomes too short, making it difficult to correct distortion, or the air gap between the front and rear groups becomes too wide, resulting in an increase in the overall length.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expression (17).
(17) 1.0<CTL/D<3.0
however,
CTL: the distance from the surface of the rear group closest to the object to the surface closest to the image,
D: the distance from the surface of the front group closest to the image side to the surface of the rear group closest to the object side at infinity,
It is.

By satisfying conditional expression (17), it is possible to reduce the size of the single focal length lens and to satisfactorily correct the curvature of field.
If the upper limit of condition (17) is exceeded, the thickness of the rear group increases, resulting in an increase in the overall lens length and outer diameter, or the air gap between the front and rear groups becomes too narrow, making it difficult to correct curvature of field.
If the lower limit of condition (17) is exceeded, the thickness of the rear group becomes too short, making it difficult to correct spherical aberration, or the air gap between the front and rear groups becomes too wide, resulting in an increase in the overall length.

When focusing, the single focal length lens of this embodiment prefers the rear focus method over the entire extension, which is advantageous for making the lens smaller, lighter, and faster for autofocusing. For example, a rear focus method can be used in which at least the rear group G2 moves toward the object side. Alternatively, a floating focus method can be used in which the cemented lens G1a and the lens component G1b in the front group G1 move integrally toward the object side or image side by an amount different from that of the rear group G2. The floating focus method is advantageous for correcting spherical aberration and curvature of field when shooting from infinity to a finite distance.

The single focus lens of this embodiment may use an aspheric or diffractive surface on any of the lens surfaces, and the aspheric surface may be a glass molded aspheric surface or a ground aspheric surface formed directly on the lens surface, a composite aspheric lens in which a resin layer is applied to the lens surface and an aspheric surface is then applied on top of that, or a plastic aspheric surface in which the lens itself is made from a resin material.

The fixed focal length lens of this embodiment can be given the function of correcting image blur by moving any one of the lens groups or part of the lens group perpendicular to the optical axis.

Specific numerical examples 1-9 are shown. In the various aberration diagrams and tables, d-line, g-line, and c-line are aberrations for each wavelength, S is sagittal, M is meridional, f is the focal length of the entire system, Fno is the F-number, w is the half angle of view, Y is the image height, R is the radius of curvature, D is the lens thickness or lens spacing, Nd is the refractive index at the d-line, νd is the Abbe number at the d-line, BF is the back focus, L is the total lens length, K is the conic constant of the aspheric surface, A4 is the fourth-order aspheric coefficient, A6 is the sixth-order aspheric coefficient, A8 is the eighth-order aspheric coefficient, and A10 is the tenth-order aspheric coefficient. The unit of length is [mm]. Here, the aspheric surface is defined by the following formula, where C is the reciprocal of the paraxial radius of curvature (paraxial curvature) and H is the height from the optical axis.
x=CH ² /[1+[1-(1+K)C ² H ² ] ^1/2 ]+A ₄ H ⁴ +A ₆ H ⁶ +A ₈ H ⁸ +A ₁₀ H ¹⁰

[Numerical Example 1]
Figures 1 to 3 and Tables 1 to 3 show the single focal length lens of Numerical Example 1. Figure 1 is a diagram of the lens configuration when focusing at infinity, Figure 2 is a diagram of longitudinal aberration when focusing at infinity, and Figure 3 is a diagram of lateral aberration when focusing at infinity. Table 1 shows surface data, Table 2 shows aspheric surface data, and Table 3 shows various data.

The single focal length lens of Numerical Example 1 is composed of, from the object side, a front group G1, a light amount adjustment aperture SP, and a rear group G2 with positive refractive power.

The front group G1 is composed of, in order from the object side, a negative meniscus lens L1A convex toward the object side, a negative meniscus lens L2A convex toward the object side, a negative meniscus lens L3A convex toward the object side, a biconvex positive lens L4A, a negative meniscus lens L5A convex toward the image side, and a positive meniscus lens L6A convex toward the image side. The negative meniscus lens L2A has aspheric surfaces on both sides. The negative meniscus lens L3A and the biconvex positive lens L4A are cemented together to form the cemented lens G1a. The negative meniscus lens L5A and the positive meniscus lens L6A are cemented together to form the lens component G1b.

The rear group G2 is composed of, in order from the object side, a positive meniscus lens L7A convex toward the image side, a negative meniscus lens L8A convex toward the image side, a biconvex positive lens L9A, a negative meniscus lens L10A convex toward the image side, and a biconvex positive lens L11A. The positive meniscus lens L7A and the negative meniscus lens L8A are cemented together. The biconvex positive lens L11A has aspheric surfaces on both sides.

(Table 1)
Surface number RD Nd νd
1 32.748 2.200 2.00100 29.1
2 18.748 4.911
3* 19.816 2.700 1.58313 59.4
4* 11.002 12.650
5 1005.122 1.650 1.49700 81.6
6 29.310 5.411 1.91082 35.2
7 -287.518 3.256
8 -58.070 1.450 1.49700 81.6
9 -234.092 2.601 1.90043 37.4
10 -55.592 8.666
11 aperture INFINITY 4.661
12 -24.432 4.847 1.49700 81.6
13 -12.708 1.300 1.81600 46.6
14 -20.846 0.150
15 43.781 6.840 1.43875 95.0
16 -24.842 2.407
17 -39.399 1.200 2.00100 29.1
18 -677.910 1.353
19* 178.063 4.721 1.49700 81.6
20* -22.859 -
* denotes a rotationally symmetric aspheric surface.
(Table 2)
Surface number K A4 A6 A8 A10
3 -1.000 0.7838E-05 -0.8816E-07 0.1687E-09 -0.1783E-12
4 -1.000 0.2576E-04 -0.1791E-06 -0.1143E-09 0.4059E-12
19 0.000 -0.8030E-05 -0.2489E-08 0.5595E-10 0.0000E+00
20 0.000 0.1778E-04 -0.2700E-08 0.1541E-09 0.0000E+00
(Table 3)
f 21.08
F No. 2.4
w 46.3
Y 21.64
BF 40.88
L 113.86

[Numerical Example 2]
Figures 4 to 6 and Tables 4 to 6 show the single focal length lens of Numerical Example 2. Figure 4 is a lens configuration diagram when focusing at infinity, Figure 5 is a longitudinal aberration diagram when focusing at infinity, and Figure 6 is a lateral aberration diagram when focusing at infinity. Table 4 shows surface data, Table 5 shows aspheric surface data, and Table 6 shows various data.

The front group G1 is composed of, in order from the object side, a negative meniscus lens L1B convex toward the object side, a negative meniscus lens L2B convex toward the object side, a biconvex positive lens L3B, a negative meniscus lens L4B convex toward the image side, a negative meniscus lens L5B convex toward the image side, and a positive meniscus lens L6B convex toward the image side. The negative meniscus lens L1B has aspheric surfaces on both sides. The negative meniscus lens L2B has aspheric surfaces on both sides. The biconvex positive lens L3B and the negative meniscus lens L4B are cemented together to form the cemented lens G1a. The negative meniscus lens L5B and the positive meniscus lens L6B are cemented together to form the lens component G1b.

The rear group G2 is composed of, in order from the object side, a positive meniscus lens L7B convex toward the image side, a negative meniscus lens L8B convex toward the image side, a biconvex positive lens L9B, a biconcave negative lens L10B, and a biconvex positive lens L11B. The positive meniscus lens L7B and the negative meniscus lens L8B are cemented together. The biconvex positive lens L11B has aspheric surfaces on both sides.

(Table 4)
Surface number RD Nd νd
1* 34.054 2.200 2.00100 29.1
2* 19.030 4.910
3* 19.607 2.700 1.58080 59.2
4* 10.815 12.650
5 373.720 5.410 1.91082 35.2
6 -33.388 1.650 1.49700 81.6
7 -128.250 3.260
8 -45.002 1.450 1.49700 81.6
9 -250.000 2.600 1.90043 37.4
10 -46.001 8.886
11 aperture INFINITY 4.660
12 -23.663 4.850 1.49700 81.6
13 -12.108 1.300 1.81600 46.6
14 -19.911 0.150
15 67.506 6.840 1.43875 95.0
16 -21.670 2.410
17 -40.395 1.200 2.00100 29.1
18 9241.387 1.350
19* 126.733 6.350 1.49700 81.6
20* -24.151 -
* denotes a rotationally symmetric aspheric surface.
(Table 5)
Surface number K A4 A6 A8 A10
1 0.000 0.6602E-05 -0.3640E-08 -0.1822E-10 -0.4486E-14
2 0.000 0.1348E-04 0.3867E-07 -0.1447E-10 0.4218E-12
3 -1.000 -0.2328E-05 -0.7287E-07 0.2559E-09 -0.5481E-12
4 -1.000 0.8666E-06 -0.2855E-06 0.1343E-09 0.2490E-12
19 0.000 -0.2411E-05 0.2624E-07 0.1630E-12 0.0000E+00
20 0.000 0.1986E-04 0.3576E-07 0.9209E-10 0.0000E+00
(Table 6)
f 21.20
F No. 2.5
w 46.2
Y 21.64
BF 40.68
L 115.51

[Numerical Example 3]
7 to 9 and Tables 7 to 9 show the single focal length lens of Numerical Example 3. Fig. 7 is a diagram of the lens configuration when focusing at infinity, Fig. 8 is a diagram of longitudinal aberration when focusing at infinity, and Fig. 9 is a diagram of transverse aberration when focusing at infinity. Table 7 shows surface data, Table 8 shows aspheric surface data, and Table 9 shows various data.

The front group G1 is composed of, in order from the object side, a negative meniscus lens L1C convex toward the object side, a negative meniscus lens L2C convex toward the object side, a negative meniscus lens L3C convex toward the object side, a biconvex positive lens L4C, a negative meniscus lens L5C convex toward the image side, a negative meniscus lens L6C convex toward the image side, and a positive meniscus lens L7C convex toward the image side. The negative meniscus lens L1C has aspheric surfaces on both sides. The negative meniscus lens L2C has aspheric surfaces on both sides. The negative meniscus lens L3C has aspheric surfaces on both sides. The biconvex positive lens L4C and the negative meniscus lens L5C are cemented together to form a cemented lens G1a. The negative meniscus lens L6C and the positive meniscus lens L7C are cemented together to form a lens component G1b.

The rear group G2 is composed of, in order from the object side, a positive meniscus lens L8C convex toward the image side, a negative meniscus lens L9C convex toward the image side, a biconvex positive lens L10C, a biconcave negative lens L11C, and a biconvex positive lens L12C. The positive meniscus lens L8C and the negative meniscus lens L9C are cemented together. The biconvex positive lens L12C has aspheric surfaces on both sides.

(Table 7)
Surface number RD Nd νd
1* 34.054 2.200 2.00100 29.1
2* 19.030 4.910
3* 19.607 2.700 1.58080 59.2
4* 10.815 2.650
5* 17.009 3.000 1.58080 59.2
6* 15.413 7.000
7 373.720 5.410 1.91082 35.2
8 -33.388 1.650 1.49700 81.6
9 -128.250 3.260
10 -45.002 1.450 1.49700 81.6
11 -250.000 2.600 1.90043 37.4
12 -46.001 0.100
13 aperture INFINITY 13.446
14 -28.072 4.850 1.49700 81.6
15 -14.134 1.300 1.81600 46.6
16 -24.753 0.150
17 30.340 6.840 1.43875 95.0
18 -28.341 2.410
19 -85.623 1.200 2.00100 29.1
20 90.631 1.350
21* 96.109 6.350 1.49700 81.6
22* -27.321 -
* denotes a rotationally symmetric aspheric surface.
(Table 8)
Surface number K A4 A6 A8 A10
1 0.000 0.1457E-05 0.9938E-10 0.1226E-10 -0.4887E-13
2 0.000 -0.1340E-05 0.3256E-07 0.9660E-11 0.3799E-12
3 -1.000 -0.1534E-04 -0.8417E-07 0.2146E-09 0.1891E-12
4 -1.000 0.1821E-04 -0.4206E-06 -0.6877E-09 -0.7451E-11
5 0.000 -0.5384E-04 -0.1927E-06 -0.1480E-08 -0.2415E-11
6 0.000 -0.8035E-04 -0.3021E-06 0.3476E-09 0.4630E-11
21 0.000 0.1052E-04 0.1383E-06 0.4348E-10 0.0000E+00
22 0.000 0.3492E-04 0.1468E-06 0.4775E-09 0.0000E+00
(Table 9)
f 21.45
F No. 2.5
w 45.9
Y 21.64
BF 40.60
L 115.42

[Numerical Example 4]
10 to 12 and Tables 10 to 12 show the single focal length lens of Numerical Example 4. Fig. 10 is a diagram of the lens configuration when focusing at infinity, Fig. 11 is a diagram of longitudinal aberration when focusing at infinity, and Fig. 12 is a diagram of lateral aberration when focusing at infinity. Table 10 shows surface data, Table 11 shows aspheric surface data, and Table 12 shows various data.

The front group G1 is composed of, in order from the object side, a negative meniscus lens L1D convex toward the object side, a negative meniscus lens L2D convex toward the object side, a negative meniscus lens L3D convex toward the object side, a negative meniscus lens L4D convex toward the object side, a biconvex positive lens L5D, a negative meniscus lens L6D convex toward the image side, and a positive meniscus lens L7D convex toward the image side. The negative meniscus lens L1D has aspheric surfaces on both sides. The negative meniscus lens L2D has aspheric surfaces on both sides. The negative meniscus lens L3D has aspheric surfaces on both sides. The negative meniscus lens L4D and the biconvex positive lens L5D are cemented together to form a cemented lens G1a. The negative meniscus lens L6D and the positive meniscus lens L7D are cemented together to form a lens component G1b.

The rear group G2 is composed of, in order from the object side, a positive meniscus lens L8D convex toward the image side, a negative meniscus lens L9D convex toward the image side, a biconvex positive lens L10D, a biconcave negative lens L11D, and a biconvex positive lens L12D. The positive meniscus lens L8D and the negative meniscus lens L9D are cemented together. The biconvex positive lens L12D has aspheric surfaces on both sides.

(Table 10)
Surface number RD Nd νd
1* 34.054 2.200 2.00100 29.1
2* 19.030 4.910
3* 19.607 2.700 1.58080 59.2
4* 10.815 2.650
5* 15.767 3.000 1.58080 59.2
6* 14.832 7.000
7 128.250 1.650 1.49700 81.6
8 33.388 5.410 1.91082 35.2
9 -373.720 3.260
10 -45.002 1.450 1.49700 81.6
11 -250.000 2.600 1.90043 37.4
12 -46.001 0.100
13 aperture INFINITY 13.446
14 -20.104 4.850 1.49700 81.6
15 -17.129 1.300 1.81600 46.6
16 -26.120 0.150
17 23.554 6.840 1.43875 95.0
18 -36.311 2.410
19 -155.791 1.200 2.00100 29.1
20 53.829 1.350
21* 41.369 6.350 1.49700 81.6
22* -29.151 -
* denotes a rotationally symmetric aspheric surface.
(Table 11)
Surface number K A4 A6 A8 A10
1 0.000 0.2450E-05 -0.7174E-08 0.1574E-10 -0.2170E-13
2 0.000 -0.2538E-05 0.2938E-07 -0.1222E-09 0.3620E-12
3 -1.000 -0.1071E-04 -0.8756E-07 0.1696E-10 0.7235E-12
4 -1.000 0.4062E-04 -0.4848E-06 0.1877E-09 -0.5732E-11
5 0.000 -0.4292E-04 -0.2190E-06 -0.1378E-08 -0.7973E-12
6 0.000 -0.8154E-04 -0.2085E-06 -0.1370E-08 0.8714E-11
21 0.000 -0.6926E-05 0.8489E-07 0.2076E-10 0.0000E+00
22 0.000 0.2759E-04 0.1048E-06 0.3796E-09 0.0000E+00
(Table 12)
f 21.39
F No. 2.4
w 45.9
Y 21.64
BF 40.64
L 115.47

[Numerical Example 5]
13 to 15 and Tables 13 to 15 show the single focal length lens of Numerical Example 5. Fig. 13 is a diagram of the lens configuration when focusing at infinity, Fig. 14 is a diagram of longitudinal aberration when focusing at infinity, and Fig. 15 is a diagram of lateral aberration when focusing at infinity. Table 13 shows surface data, Table 14 shows aspheric surface data, and Table 15 shows various data.

The front group G1 is composed of, in order from the object side, a negative meniscus lens L1E convex toward the object side, a negative meniscus lens L2E convex toward the object side, a negative meniscus lens L3E convex toward the object side, a biconvex positive lens L4E, and a positive meniscus lens L5E convex toward the image side. The negative meniscus lens L2E has aspheric surfaces on both sides. The negative meniscus lens L3E and the biconvex positive lens L4E are cemented together to form the cemented lens G1a. The positive meniscus lens L5E forms the lens component G1b.

The rear group G2 is composed of, in order from the object side, a positive meniscus lens L6E convex toward the image side, a negative meniscus lens L7E convex toward the image side, a biconvex positive lens L8E, a biconcave negative lens L9E, and a biconvex positive lens L10E. The positive meniscus lens L6E and the negative meniscus lens L7E are cemented together. The biconvex positive lens L10E has aspheric surfaces on both sides.

(Table 13)
Surface number RD Nd νd
1 34.054 2.200 2.00100 29.1
2 19.030 4.910
3* 19.607 2.700 1.58080 59.2
4* 10.815 12.650
5 128.250 1.650 1.49700 81.6
6 33.388 5.410 1.91082 35.2
7 -373.720 3.260
8 -57.410 3.050 1.95906 17.5
9 -44.186 8.886
10 aperture INFINITY 4.660
11 -20.811 4.850 1.49700 81.6
12 -12.688 1.300 1.81600 46.6
13 -18.804 0.150
14 38.869 6.840 1.43875 95.0
15 -25.761 2.410
16 -40.470 1.200 2.00100 29.1
17 289.417 1.350
18* 73.078 6.350 1.49700 81.6
19* -24.858 -
* denotes a rotationally symmetric aspheric surface.
(Table 14)
Surface number K A4 A6 A8 A10
3 -1.000 0.7570E-05 -0.1061E-06 0.2252E-09 -0.2661E-12
4 -1.000 0.2697E-04 -0.2334E-06 0.8845E-10 0.1194E-12
18 0.000 -0.6810E-05 0.1394E-07 -0.1213E-11 0.0000E+00
19 0.000 0.1828E-04 0.2146E-07 0.5656E-10 0.0000E+00
(Table 15)
f 21.09
F No. 2.5
w 46.3
Y 21.64
BF 40.69
L 114.51

[Numerical Example 6]
16 to 18 and Tables 16 to 18 show the single focal length lens of Numerical Example 6. Fig. 16 is a diagram of the lens configuration when focusing at infinity, Fig. 17 is a diagram of longitudinal aberration when focusing at infinity, and Fig. 18 is a diagram of lateral aberration when focusing at infinity. Table 16 shows surface data, Table 17 shows aspheric surface data, and Table 18 shows various data.

The front group G1 is composed of, in order from the object side, a negative meniscus lens L1F convex toward the object side, a negative meniscus lens L2F convex toward the object side, a negative meniscus lens L3F convex toward the object side, a positive meniscus lens L4F convex toward the object side, a biconcave negative lens L5F, and a biconvex positive lens L6F. The negative meniscus lens L2F has aspheric surfaces on both sides. The negative meniscus lens L3F and the positive meniscus lens L4F are cemented together to form the cemented lens G1a. The biconcave negative lens L5F and the biconvex positive lens L6F are cemented together to form the lens component G1b.

The rear group G2 is composed of, in order from the object side, a positive meniscus lens L7F convex toward the image side, a biconcave negative lens L8F, a biconvex positive lens L9F, a negative meniscus lens L10F convex toward the image side, and a biconvex positive lens L11F. The positive meniscus lens L7F and the biconcave negative lens L8F are cemented together. The biconvex positive lens L11F has aspheric surfaces on both sides.

(Table 16)
Surface number RD Nd νd
1 29.681 1.800 2.00069 25.5
2 16.294 5.907
3* 25.005 2.200 1.58913 60.9
4* 9.930 5.463
5 42.315 1.500 1.49700 81.6
6 19.234 5.129 1.90043 37.4
7 190.660 4.338
8 -32.433 1.400 1.49700 81.6
9 71.521 3.122 1.85150 40.8
10 -40.263 8.004
11 aperture INFINITY 5.559
12 -262.056 4.814 1.49700 81.6
13 -11.747 1.250 1.77250 49.6
14 1870.094 0.100
15 43.154 6.540 1.53775 74.7
16 -19.001 2.274
17 -29.504 1.200 2.00069 25.5
18 -88.434 0.100
19* 108.178 6.315 1.58913 60.9
20* -21.291 -
* denotes a rotationally symmetric aspheric surface.
(Table 17)
Surface number K A4 A6 A8 A10
3 -1.000 -0.3357E-04 0.9053E-07 -0.2124E-09 0.2304E-12
4 -1.000 -0.3497E-04 -0.1830E-07 -0.1178E-09 -0.1059E-12
19 0.000 -0.1054E-04 0.3162E-07 -0.4110E-10 0.0000E+00
20 0.000 0.2101E-04 0.2702E-07 0.1680E-09 0.0000E+00
(Table 18)
f 19.40
F No. 3.6
w 48.6
Y 21.64
BF 38.45
L 105.47

[Numerical Example 7]
19 to 21 and Tables 19 to 21 show the single focal length lens of Numerical Example 7. Fig. 19 is a diagram of the lens configuration when focused at infinity, Fig. 20 is a diagram of longitudinal aberration when focused at infinity, and Fig. 21 is a diagram of lateral aberration when focused at infinity. Table 19 shows surface data, Table 20 shows aspheric surface data, and Table 21 shows various data.

The front group G1 is composed of, in order from the object side, a negative meniscus lens L1G convex toward the object side, a negative meniscus lens L2G convex toward the object side, a negative meniscus lens L3G convex toward the object side, a biconvex positive lens L4G, a negative meniscus lens L5G convex toward the image side, and a positive meniscus lens L6G convex toward the image side. The negative meniscus lens L1G has aspheric surfaces on both sides. The negative meniscus lens L2G has aspheric surfaces on both sides. The negative meniscus lens L3G and the biconvex positive lens L4G are cemented together to form a cemented lens G1a. The negative meniscus lens L5G and the positive meniscus lens L6G are cemented together to form a lens component G1b.

The rear group G2 is composed of, in order from the object side, a positive meniscus lens L7G convex toward the image side, a negative meniscus lens L8G convex toward the image side, a biconvex positive lens L9G, a biconcave negative lens L10G, and a biconvex positive lens L11G. The positive meniscus lens L7G and the negative meniscus lens L8G are cemented together. The biconvex positive lens L11G has aspheric surfaces on both sides.

(Table 19)
Surface number RD Nd νd
1* 32.214 2.200 1.95906 17.5
2* 18.226 4.910
3* 19.607 2.700 1.58080 59.2
4* 10.581 13.600
5 112.780 1.650 1.49700 81.6
6 33.451 5.410 1.91082 35.2
7 -450.820 3.260
8 -45.002 1.450 1.49700 81.6
9 -250.000 2.600 1.90043 37.4
10 -46.001 18.779
11 aperture INFINITY 5.125
12 -46.128 4.850 1.49700 81.6
13 -13.501 1.300 1.81600 46.6
14 -19.594 0.150
15 25.891 6.650 1.43875 95.0
16 -32.443 2.410
17 -39.001 1.200 2.00100 29.1
18 97.988 1.350
19* 29.953 6.350 1.49700 81.6
20* -263.658 -
* denotes a rotationally symmetric aspheric surface.
(Table 20)
Surface number K A4 A6 A8 A10
1 0.000 0.1435E-04 -0.2070E-07 -0.6273E-10 0.1176E-12
2 0.000 0.2488E-05 0.4598E-07 -0.4491E-09 0.2116E-12
3 -1.000 -0.1068E-03 0.4939E-06 -0.1202E-08 0.1188E-11
4 -1.000 -0.8123E-04 0.3544E-06 0.4263E-09 -0.3878E-11
19 0.000 0.7102E-05 0.4652E-07 0.5553E-10 0.0000E+00
20 0.000 0.3215E-04 0.6473E-07 0.1328E-09 0.0000E+00
(Table 21)
f 21.38
F No. 2.5
w 46.1
Y 21.64
BF 29.68
L 115.62

[Numerical Example 8]
Figures 22 to 24 and Tables 22 to 24 show the single focal length lens of Numerical Example 8. Figure 22 is a lens configuration diagram when focusing at infinity, Figure 23 is a longitudinal aberration diagram when focusing at infinity, and Figure 24 is a lateral aberration diagram when focusing at infinity. Table 22 shows surface data, Table 23 shows aspheric surface data, and Table 24 shows various data.

The front group G1 is composed of, in order from the object side, a negative meniscus lens L1H convex toward the object side, a negative meniscus lens L2H convex toward the object side, a negative meniscus lens L3H convex toward the object side, a biconvex positive lens L4H, a negative meniscus lens L5H convex toward the image side, and a positive meniscus lens L6H convex toward the image side. The negative meniscus lens L2H has aspheric surfaces on both sides. The negative meniscus lens L3H and the biconvex positive lens L4H are cemented together to form the cemented lens G1a. The negative meniscus lens L5H and the positive meniscus lens L6H are cemented together to form the lens component G1b.

The rear group G2 is composed of, in order from the object side, a positive meniscus lens L7H convex toward the image side, a negative meniscus lens L8H convex toward the image side, a biconvex positive lens L9H, a negative meniscus lens L10H convex toward the image side, and a biconvex positive lens L11H. The positive meniscus lens L7H and the negative meniscus lens L8H are cemented together. The biconvex positive lens L11H has aspheric surfaces on both sides.

(Table 22)
Surface number RD Nd νd
1 30.616 2.200 1.91082 35.2
2 17.302 4.910
3* 19.816 2.700 1.58313 59.4
4* 10.581 15.883
5 112.780 1.650 1.49700 81.6
6 33.451 5.410 1.91082 35.2
7 -450.820 3.260
8 -45.002 1.450 1.49700 81.6
9 -250.000 2.600 1.90043 37.4
10 -46.001 4.154
11 aperture INFINITY 5.125
12 -23.664 4.850 1.49700 81.6
13 -11.418 1.300 1.81600 46.6
14 -20.100 0.150
15 88.031 6.650 1.43875 95.0
16 -19.444 2.410
17 -27.659 1.200 2.00100 29.1
18 -98.090 1.350
19* 187.995 6.350 1.49700 81.6
20* -21.999 -
* denotes a rotationally symmetric aspheric surface.
(Table 23)
Surface number K A4 A6 A8 A10
3 -1.000 -0.1509E-04 -0.3182E-07 0.1519E-09 -0.3193E-12
4 -1.000 -0.7861E-05 -0.1811E-06 0.3404E-09 -0.9676E-12
19 0.000 -0.3113E-05 0.3833E-07 -0.1438E-10 0.0000E+00
20 0.000 0.2035E-04 0.4251E-07 0.1139E-09 0.0000E+00
(Table 24)
f 20.20
F No. 2.5
w 47.7
Y 21.64
BF 42.22
L 115.82

[Numerical Example 9]
Figures 25 to 27 and Tables 25 to 27 show the single focal length lens of Numerical Example 9. Figure 25 is a lens configuration diagram when focusing at infinity, Figure 26 is a longitudinal aberration diagram when focusing at infinity, and Figure 27 is a lateral aberration diagram when focusing at infinity. Table 25 shows surface data, Table 26 shows aspheric surface data, and Table 27 shows various data.

The front group G1 is composed of, in order from the object side, a negative meniscus lens L1I convex toward the object side, a negative meniscus lens L2I convex toward the object side, a negative meniscus lens L3I convex toward the object side, a biconvex positive lens L4I, a negative meniscus lens L5I convex toward the image side, and a positive meniscus lens L6I convex toward the image side. The negative meniscus lens L2I has aspheric surfaces on both sides. The negative meniscus lens L3I and the biconvex positive lens L4I are cemented together to form the cemented lens G1a. The negative meniscus lens L5I and the positive meniscus lens L6I are cemented together to form the lens component G1b.

The rear group G2 is composed of, in order from the object side, a positive meniscus lens L7I convex toward the image side, a negative meniscus lens L8I convex toward the image side, a biconvex positive lens L9I, a negative meniscus lens L10I convex toward the image side, and a biconvex positive lens L11I. The positive meniscus lens L7I and the negative meniscus lens L8I are cemented together. The biconvex positive lens L11I has aspheric surfaces on both sides.

(Table 25)
Surface number RD Nd νd
1 30.379 2.200 1.90366 31.3
2 17.165 4.910
3* 19.816 2.700 1.58313 59.4
4* 10.581 14.308
5 112.780 1.650 1.49700 81.6
6 33.451 5.410 1.91082 35.2
7 -450.820 3.260
8 -45.002 1.450 1.49700 81.6
9 -250.000 2.600 1.90043 37.4
10 -46.001 6.280
11 aperture INFINITY 5.125
12 -24.208 4.850 1.49700 81.6
13 -12.152 1.300 1.81600 46.6
14 -20.596 0.150
15 66.663 6.650 1.43875 95.0
16 -20.991 2.410
17 -29.672 1.200 2.00100 29.1
18 -129.296 1.350
19* 131.919 6.350 1.49700 81.6
20* -23.046 -
* denotes a rotationally symmetric aspheric surface.
(Table 26)
Surface number K A4 A6 A8 A10
3 -1.000 -0.1683E-04 -0.3963E-07 0.1687E-09 -0.3188E-12
4 -1.000 -0.8717E-05 -0.2080E-06 0.4009E-09 -0.8585E-12
19 0.000 -0.2695E-05 0.2379E-07 -0.1161E-10 0.0000E+00
20 0.000 0.1968E-04 0.3488E-07 0.5897E-10 0.0000E+00
(Table 27)
f 20.78
F No. 2.5
w 46.8
Y 21.64
BF 41.69
L 115.84

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 (17).
(Table 28)
Example 1 Example 2 Example 3
Condition (1) 2.00100 2.00100 2.00100
Condition (2) 7.57 6.33 6.26
Condition (3) -0.21 0.03 -0.31
Condition (4) 0.27 0.28 0.28
Condition (5) 0.29 0.29 0.29
Condition (6) -2.26 -2.19 -2.17
Condition (7) 5.39 5.45 5.38
Condition (8) 1.75 1.74 1.72
Condition (9) 1.9004 1.9004 1.9004
Condition (10) 86.01 86.01 86.01
Condition (11) 1.05 1.02 1.02
Condition (12) 1.82 1.92 1.81
Condition (13) 29.10 29.10 29.10
Condition (14) 2.46 2.55 2.52
Condition (15) 8.54 8.53 8.23
Condition (16) 2.76 2.72 2.72
Condition (17) 1.71 1.80 1.80
Example 4 Example 5 Example 6
Condition (1) 2.00100 2.00100 2.00069
Condition (2) 6.28 8.52 4.47
Condition (3) -0.34 -0.24 -0.11
Condition (4) 0.28 0.28 0.29
Condition (5) 0.29 0.29 0.43
Condition (6) -2.17 -2.20 -2.00
Condition (7) 5.40 5.43 5.44
Condition (8) 1.72 1.70 1.59
Condition (9) 1.9004 1.9591 1.8515
Condition (10) 86.01 86.01 72.47
Condition (11) 1.02 1.02 1.48
Condition (12) 1.79 1.64 2.11
Condition (13) 29.10 29.10 25.50
Condition (14) 2.43 2.57 4.02
Condition (15) 8.52 8.45 7.78
Condition (16) 2.72 2.65 2.28
Condition (17) 1.80 1.80 1.67
Example 7 Example 8 Example 9
Condition (1) 1.95906 1.91082 1.90366
Condition (2) 6.28 6.65 6.46
Condition (3) -0.01 0.11 0.02
Condition (4) 0.28 0.28 0.28
Condition (5) 0.30 0.30 0.30
Condition (6) -2.22 -2.35 -2.28
Condition (7) 5.41 5.73 5.58
Condition (8) 1.77 1.98 1.85
Condition (9) 1.9004 1.9004 1.9004
Condition (10) 86.01 86.01 86.01
Condition (11) 1.08 1.09 1.09
Condition (12) 1.92 2.06 1.96
Condition (13) 17.50 35.20 31.30
Condition (14) 2.53 2.68 2.60
Condition (15) 4.84 12.48 10.16
Condition (16) 1.58 4.32 3.37
Condition (17) 1.01 2.61 2.13

With reference to Figures 28 and 29, we will explain a digital camera (imaging device) 100 equipped with a fixed focal length lens of this embodiment.

The digital camera 100 has a camera body (housing) 101, a photographing lens 102, a viewfinder 103, a flash 104, a shutter button 105, a power button 106, an LCD monitor 107, operation buttons 108, and a memory card slot 109.

The camera body 101 houses each component of the digital camera 100. The photographing lens 102 is, for example, a unit formed by incorporating the fixed focal length lens of this embodiment into a lens barrel and/or an interchangeable lens. The viewfinder 103 is a viewing window for determining the subject and composition. The flash 104 emits a flash of light when photographing at night or in a dark place. The shutter button 105 is a physical switch for executing photographing with 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 images photographed by the digital camera 100, etc. The operation button 108 is a physical switch for setting the photographing mode of the digital camera 100, etc. The memory card slot 109 is a slot for inserting a memory card (not shown) that stores images photographed by the digital camera 100, etc.

The digital camera 100 has 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 as internal functional components of the camera body 101.

The central processing unit 111 performs various types of arithmetic processing within the digital camera 100. The image processing unit 112 performs various types of image processing on images captured 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 types of signal processing such as shooting instruction signals and image processing signals. The semiconductor memory 115 forms a temporary storage area for images captured by the digital camera 100. The communication card 116 enables wireless communication with an external device (not shown).

Figure 30 is an external perspective view showing an example of an interchangeable lens (lens barrel) 102 of this embodiment. As shown in Figure 30, the interchangeable lens 102 has a lens holding barrel 102X and a fixed focal length lens held by this lens holding barrel 102X. Figure 30 depicts lenses L1A to L1I of the fixed focal length lens that are positioned closest to the object in the front group G1.

This embodiment makes it possible to provide a small, wide-angle prime lens, an interchangeable lens, and an imaging device in which various aberrations are corrected.

The configuration of the digital camera 100 described here is merely one example, and various design changes are possible (there is a degree of freedom in the specific form of the digital camera 100).

The fixed focal length lens of this embodiment can be applied to devices other than the digital camera 100 described above, such as interchangeable lenses, portable information terminal devices, video cameras, silver halide cameras, optical sensors, and projection optical systems (projectors).

G1: front group G1a: cemented lens G1b: lens components L1A to L1I: negative meniscus lens with a convex surface facing the object side L2A to L2I: negative meniscus lens with a convex surface facing the object side G2: rear group SP: aperture 100: digital camera (imaging device)
102 Photographic lenses (lens barrels, interchangeable lenses)

Claims (13)

From the object side, it is composed of a front group, a stop, and a rear group with positive refractive power,
The diameter of the axial light beam incident on the front group closest to the object is smaller than the diameter of the axial light beam passing through the aperture stop.
the front group has a negative meniscus lens closest to the object side and having a convex surface facing the object side, and has a negative meniscus lens closest to the object side and having a convex surface facing the object side adjacent to the image side of the negative meniscus lens closest to the object side,
the front group includes, in order from the object side, three or more negative lenses and a cemented lens of a positive lens and a negative lens;
The front group has a lens component with positive refractive power, the lens component being closest to the image side and having a concave surface facing the object side.
The front group has two or more positive lenses,
The following conditional expressions (1) and (15) are satisfied:
A single focal length lens.
(1) 1.85<NdL1
(15) 4.5<TL/D<12.5
however,
NdL1: the refractive index of the negative meniscus lens located closest to the object in the front group,
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 side to the surface of the rear group closest to the object side at infinity. From the object side, it is composed of a front group, a stop, and a rear group with positive refractive power,
The diameter of the axial light beam incident on the front group closest to the object is smaller than the diameter of the axial light beam passing through the aperture stop.
the front group has a negative meniscus lens closest to the object side and having a convex surface facing the object side, and has a negative meniscus lens closest to the object side and having a convex surface facing the object side adjacent to the image side of the negative meniscus lens closest to the object side,
the front group includes, in order from the object side, three or more negative lenses and a cemented lens of a positive lens and a negative lens;
The front group has a lens component with positive refractive power, the lens component being closest to the image side and having a concave surface facing the object side.
The front group has two or more positive lenses,
The following conditional expressions (1), (2), and (15) are satisfied:
A single focal length lens.
(1) 1.85<NdL1
(2) 1.0<G1bf/f<100
(15) 4.5<TL/D<12.5
however,
NdL1: the refractive index of the negative meniscus lens located closest to the object in the front group,
G1bf: the object-side focal length of the lens component located closest to the image side in the front group,
f: focal length of the entire system of a single focal length lens,
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 side to the surface of the rear group closest to the object side at infinity. From the object side, it is composed of a front group, a stop, and a rear group with positive refractive power,
The diameter of the axial light beam incident on the front group closest to the object is smaller than the diameter of the axial light beam passing through the aperture stop.
the front group has a negative meniscus lens closest to the object side and having a convex surface facing the object side, and has a negative meniscus lens closest to the object side and having a convex surface facing the object side adjacent to the image side of the negative meniscus lens closest to the object side,
the front group includes, in order from the object side, three or more negative lenses and a cemented lens of a positive lens and a negative lens;
The front group has a lens component with positive refractive power, the lens component being closest to the image side and having a concave surface facing the object side.
The front group has two or more positive lenses,
The following conditional expressions (1), (7), and (15) are satisfied:
A single focal length lens.
(1) 1.85<NdL1
(7) 1.0<TL/f<10
(15) 4.5<TL/D<12.5
however,
NdL1: the refractive index of the negative meniscus lens located closest to the object in the front group,
TL: distance from the surface of the front group closest to the object to the image plane,
f: focal length of the entire system of a single focal length lens,
D: The distance from the surface of the front group closest to the image side to the surface of the rear group closest to the object side at infinity. the front group has at least one cemented lens;
Among the cemented lenses in the front group, the cemented lens located closest to the object has positive refractive power.
4. The single focal length lens according to claim 1 , the front group has at least one cemented lens;
The following condition (3) is satisfied:
4. The single focal length lens according to claim 1 ,
(3) -1.0<G1af/G1f<1.0
however,
G1af: the focal length of the cemented lens in the front group that is located closest to the object,
G1f: focal length of the front group. The following condition (4) is satisfied:
4. The single focal length lens according to claim 1 ,
(4) 0.1<L1SF<1.0
however,
L1SF=(L1R1-L1R2)/(L1R1+L1R2)
L1R1: radius of curvature of the object-side surface of the negative meniscus lens located closest to the object side in the front group,
L1R2: The radius of curvature of the image-side surface of the negative meniscus lens located closest to the object in the front group. the front group has a negative meniscus lens with a convex surface facing the object side, adjacent to the image side of the negative meniscus lens located closest to the object side;
The following condition (5) is satisfied:
4. The single focal length lens according to claim 1 ,
(5) 0.1<L2SF<0.5
however,
L2SF=(L2R1-L2R2)/(L2R1+L2R2)
L2R1: the radius of curvature of the object-side surface of the negative meniscus lens located second closest to the object in the front group,
L2R2: The radius of curvature of the image-side surface of the negative meniscus lens that is the second most negative lens from the object side in the front group. The following condition (6) is satisfied:
4. The single focal length lens according to claim 1 ,
(6) -8.0<L1f/f<0
however,
L1f: the focal length of the negative meniscus lens located closest to the object in the front group,
f: focal length of the entire system of a prime lens. The following condition (8) is satisfied:
4. The single focal length lens according to claim 1 ,
(8) 1.0<ZTL/f<12.0
however,
ZTL: the distance from the surface of the front group closest to the object to the surface closest to the image,
f: focal length of the entire system of a prime lens. The following condition (9) is satisfied:
4. The single focal length lens according to claim 1 ,
(9) 1.80<LSPNd
however,
LSPNd: the refractive index of the lens in the front group that is located closest to the image side. the rear group has at least one positive lens;
The following condition (10) is satisfied:
4. The single focal length lens according to claim 1 ,
(10) 70<G2νd
however,
G2νd: the average Abbe number of the positive lenses in the rear group. An interchangeable lens comprising the single focal length lens according to any one of claims 1 to 3 . An imaging device comprising the single focal length lens according to any one of claims 1 to 3 .

Images