JP7697217B2 - 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.

Conventionally, various types of optical systems are known for use in, for example, digital cameras as imaging devices. In particular, optical systems with a wide angle of view generally use a retrofocus lens type with negative refractive power in front of the lens and positive refractive power in the rear of the lens, and there is a demand for a small wide-angle lens with high optical performance over the entire shooting distance range. In addition, there is a demand for the overall length of the lens system and the outer diameter of the lens to be small and lightweight so that it is easy to carry around.

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

JP 2018-185389 A

However, conventional retrofocus optical systems tend to become larger and more expensive as the optical performance is improved due to an increase in the number of lenses and the extensive use of aspheric surfaces. In addition, there is also the problem that the wider the angle of view, the larger the size and the higher the cost. For example, Patent Document 1 has room for improvement in terms of widening the angle of view and correcting off-axis aberrations.

The present invention has been made in consideration of the above points, and aims to provide a single focal length lens, an interchangeable lens, and an imaging device that have high optical performance, are small, lightweight, and have a wide angle of view.

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, an aperture stop, and a rear group with positive refractive power, the axial light beam passing through the stop surface of the aperture stop is greater than the axial light beam incident on the refractive surface of the front group closest to the object, the front group has a negative meniscus lens with a convex surface facing the object side, the front group has a refractive surface closest to the image side that has a convex surface facing the image side, the rear group has at least one negative lens, the rear group has a cemented lens closest to the object side, the cemented lens positioned closest to the object side of the rear group has a cemented surface with a concave surface facing the object side, and the rear group has a refractive surface closest to the object side that has a concave surface facing the object side, and satisfies the following conditional expressions (1), (2'), (3), (5), (6), (7), and (11C).
(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: the distance on the optical axis from the surface of the front group closest to the object to the aperture stop,
DR: the distance on the optical axis from the surface of the rear group closest to the image side to the aperture stop,
fBL: focal length of the cemented lens located closest to the object in the rear group,
fBO: focal length of the cemented surface of the cemented lens closest to the object side in the rear group, the concave surface of which faces the object side;
f: focal length of the entire system of a single focal length lens,
Y: image height of the entire system of a single focal length lens,
Fno: F-number of the entire single focal length lens system,
RF: radius of curvature of the refracting surface of the front group closest to the image side,
RR: radius of curvature of the refracting surface of the rear group closest to the object,
NnRmax: the refractive index of the negative lens having the largest refractive index among the negative lenses included in the rear group,
It is.

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

The present invention provides a single focal length lens, an interchangeable lens, and an imaging device that have high optical performance, are small, lightweight, and have a wide angle of view.

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, an aperture stop SP (for adjusting the amount of light) that can control the F-number, 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, 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 surface (designed image surface). The parallel plane plate CG is composed of, for example, a low-pass filter, an infrared cut filter, and a cover glass of the image sensor.

In this embodiment, based on the above-mentioned basic configuration, the detailed structure and power arrangement of the lens groups and lens elements, as well as the selection of glass materials, are optimized to realize a single focal length lens that has high optical performance, is small, lightweight, and has a wide angle of view. In this specification, "having high optical performance" means, for example, that various aberrations are appropriately corrected. In this specification, "having a wide angle of view" means, for example, that the half angle of view is 40° or more. In this specification, miniaturization and weight reduction can be achieved, for example, by reducing the number of lenses that make up the single focal length lens.

In the single focal length 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 refractive surface of the front group G1 closest to the object. This allows the angle of view of the single focal length lens to be widened, while also ensuring the necessary back focus and peripheral light volume.

For example, in the above-mentioned Patent Document 1, of the first and second lens units sandwiching the aperture, the first lens unit has a strong positive refractive power. In contrast, in the single focal length lens of this embodiment, of the front group G1 and rear group G2 sandwiching the aperture aperture SP, the front group G1 has a relatively weaker refractive power than the rear group G2, and therefore high optical performance can be obtained. In addition, because the aperture aperture SP is positioned near the center of the entire optical system, the number of lenses in the front group G1 can be kept relatively small, making it possible to achieve both a wide angle of view and compact size, while also improving performance.

It is preferable that the single focal length lens of this embodiment 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 rear group,
It is.

By satisfying conditional expression (1), it is possible to reduce the size of the single focal length lens (reducing the diameter of the front lens) and to widen the angle of view, while at the same time making it possible to satisfactorily correct various aberrations, such as spherical aberration and coma aberration. This effect is more pronounced when conditional expressions (1A) and (1B) are satisfied.
When the front group has negative refractive power, if the lower limit of conditional expression (1) is exceeded, the negative refractive power of the front group becomes too strong, making it difficult to correct aberrations such as spherical aberration and coma.
In the case where the front group has positive refractive power, if the lower limit of conditional expression (1) is exceeded, the positive refractive power of the front group becomes too strong, the front lens diameter increases, and it becomes difficult to achieve a wide angle of view.

It is preferable that the single focal length lens of this embodiment 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: (absolute value of) the distance on the optical axis from the surface of the front group closest to the object to the aperture stop,
DR: (absolute value of) the distance on the optical axis from the surface of the rear group closest to the image side to the aperture stop,
It is.

By satisfying conditional expression (2), it is possible to reduce the size of the single focal length lens (shortening the overall lens length and suppressing the outer diameter) and to widen the angle of view. This effect is more pronounced when conditional expressions (2A) and (2B) are satisfied.
If the upper limit of condition (2) is exceeded, the overall length and outer diameter of the front group become too large, making it difficult to simultaneously achieve compact size and a wide angle of view.
If the lower limit of condition (2) is exceeded, the overall length of the rear group becomes too large, making it difficult to achieve compact size.

The rear group G2 has a cemented lens BL closest to the object, and the cemented lens BL located closest to the object in 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 (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: focal length of the cemented lens located closest to the object in the rear group,
fBO: focal length of the cemented surface of the cemented lens closest to the object side in the rear group, the concave surface of which faces the object side;
It is.

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.

In the rear group, the on-axis light beam becomes large, so by providing a cemented lens closest to the object, spherical aberration and on-axis chromatic aberration can be effectively corrected. In addition, by providing a cemented surface with a concave surface facing the object side, off-axis aberrations such as coma, astigmatism, and chromatic aberration of magnification can be effectively corrected while correcting the above aberrations.

The cemented lens BL can have either positive or negative refractive power. For example, in Numerical Example 8 described below, the front group G1 has positive refractive power, and in Numerical Examples 1-7 and 9 described below, the front group G1 has negative refractive power.

When the cemented lens BL has positive refractive power, it acts to shorten the focal length of the entire optical system, making it easier to achieve a wide angle of view. Also, when the cemented lens BL has negative refractive power, it can more effectively correct spherical aberration.

By satisfying conditional expression (3), it is possible to effectively correct aberrations such as spherical aberration and coma aberration. This effect is more pronounced when conditional expressions (3A), (3B), and (3C) are satisfied.
If the upper limit of condition (3) is exceeded, the refractive power of the cemented surface of the cemented lens element located closest to the object in the rear group, the cemented surface having a concave surface facing the object side, becomes too weak, making it difficult to correct aberrations such as spherical aberration and coma.
If the lower limit of condition (3A) is exceeded, the refractive power of the cemented surface of the cemented lens element located closest to the object in the rear group, the cemented surface having a concave surface facing the object side, becomes too strong, making it difficult to correct aberrations such as spherical aberration and coma.

It is preferable that the single focal length lens of this embodiment 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: 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 (4), 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, coma, and distortion. This effect is more pronounced when conditional expressions (4A) and (4B) are satisfied.
If the upper limit of condition (4) is exceeded, distortion and coma aberration will be significant, and the optical system will become large (the total lens length will become long).
If the lower limit of condition (4) 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 (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 system of a single focal length lens,
It is.

By satisfying conditional expression (5), the angle of view can be increased and spherical aberration and coma can be effectively corrected. This effect is more pronounced when conditional expressions (5A) and (5B) are satisfied.
If the upper limit of condition (5) is exceeded, the refractive power of the rear group becomes too weak, and the focal length becomes too long, making it difficult to achieve a wide angle of view.
If the lower limit of condition (5) is exceeded, the refractive power of the rear group becomes too strong, making it difficult to correct spherical aberration, coma, and the like.

It is preferable that the single focal length lens of this embodiment satisfies the following conditional expression (6).
(6) 1.6<(Y×Fno)/f<4.1
however,
Y: image height of the entire system of a single focal length lens (maximum image height that a single focal length lens forms on the image plane),
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 (6), 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 (6) 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 (6) 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.

In the single focal length lens of this embodiment, the front group G1 has a negative meniscus lens (for example, L1A, L1B, L1C, L1D, and L1E described below) with a convex surface facing the object side, located closest to the object side. By providing a negative lens closest to the object side in the front group G1, it is possible to reduce the lens outer diameter and achieve both a wide angle of view and compact size. By making the negative lens closest to the object side in the front group G1 a meniscus shape with a convex surface facing the object side, coma, astigmatism, and distortion can be effectively corrected.

In the single focal length lens of this embodiment, the refractive surface closest to the image of the front group G1 has a convex surface facing the image side, and the refractive surface closest to the object of the rear group G2 has a concave surface facing the object side. This allows distortion to be well corrected, and spherical aberrations and other aberrations that occur on the refractive surface closest to the image of the front group G1 can be effectively corrected.

It is preferable that the single focal length lens of this embodiment 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 refracting surface of the front group closest to the image side,
RR: radius of curvature of the refracting surface of the rear group closest to the object,
It is.

By satisfying conditional expression (7), spherical aberration can be corrected well. This effect is more pronounced by satisfying conditional expressions (7A) and (7B).
If the upper limit of condition (7) is exceeded, the radius of curvature of the refracting surface (convex surface) of the front group closest to the image side becomes too large, causing excessive spherical aberration.
If the lower limit of condition (7) is exceeded, the radius of curvature of the refracting surface (convex surface) of the front group closest to the image side becomes too small, causing spherical aberration to be under-corrected.

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, it is possible to effectively correct mainly off-axis aberrations such as coma, astigmatism, and chromatic aberration of magnification. In Numerical Example 8 described later, three positive lenses (L4D, L6D, and L7D) are arranged in the front group G1, but four or more positive lenses may be arranged in the front group G1. In terms of compactness, three or less lenses are preferable.

The front group G1 can have at least three negative lenses. This allows for a wider angle of view and effectively corrects off-axis aberrations such as coma, astigmatism, and chromatic aberration of magnification.

The front group G1 can have three or more negative lenses in order from the object side. This allows the principal point position to be lowered backward, making it easier to achieve a wide angle of view while keeping the front lens diameter small. In addition, by gradually refracting the light rays entering the front group G1 with three or more negative lenses, the occurrence of various aberrations can be minimized, and in particular, curvature of field aberration and astigmatism can be corrected well. In addition, in 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 arranged consecutively in order from the object side of the front group G1. In terms of compactness, four or less lenses are preferable.

In the single focal length lens of this embodiment, it is preferable that the front group has at least one negative lens 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,
It is.

By satisfying conditional expression (8), various aberrations such as coma and astigmatism can be effectively corrected. This effect is more pronounced when conditional expressions (8A), (8B), (8C), and (8D) are satisfied.
If the lower limit of condition (8) is exceeded, it becomes difficult to correct various aberrations such as coma and astigmatism.

In the single focal length lens of this embodiment, it is preferable that the front group has at least one negative lens 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: average value of refractive index of negative lenses included in the front group,
It is.

By satisfying conditional expression (9), various aberrations such as coma, astigmatism, distortion, etc. can be well corrected. Furthermore, by satisfying conditional expressions (9A) and (9B), various aberrations such as coma, astigmatism, distortion, etc. can be corrected to a certain degree, and field curvature can be well corrected.
If the lower limit of condition (9) is exceeded, it becomes difficult to correct various aberrations such as coma, astigmatism, and distortion.
If the upper limit of condition (9A) is exceeded, the Petzval sum will have a negative value, resulting in overcorrection of the field curvature.
If the lower limits of conditional expressions (9A) and (9B) are exceeded, it becomes extremely difficult to correct various aberrations such as coma, astigmatism, and distortion.

In the single focal length lens of this embodiment, it is preferable that the front group has at least one positive lens and satisfies the following conditional expression (10).
(10) 30<νpFave<50
however,
νpFav: average Abbe number of the positive lenses included in the front group,
It is.

By satisfying conditional expression (10), spherical aberration can be corrected satisfactorily.
If the upper limit of condition (10) is exceeded, lateral chromatic aberration will be insufficiently corrected.
If the lower limit of condition (10) is exceeded, lateral chromatic aberration will be overcorrected.

In the single focal length lens of this embodiment, it is preferable that the rear group has 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 having the largest refractive index among the negative lenses included in the rear group,
It is.

By satisfying conditional expression (11), it is possible to satisfactorily correct various aberrations such as spherical aberration, coma aberration, etc. This effect is more pronounced when conditional expressions (11A), (11B), (11C), and (11D) are satisfied.
If the lower limit of condition (11) is exceeded, it becomes difficult to correct various aberrations such as spherical aberration and coma.

In the single focal length lens of this embodiment, it is preferable that the rear group has 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: average Abbe number of the negative lenses included in the rear group,
It is.

By satisfying conditional expression (12), longitudinal chromatic aberration can be corrected satisfactorily. This effect is more pronounced when conditional expressions (12A) and (12B) are satisfied.
If the upper limit of condition (12) is exceeded, axial chromatic aberration will be insufficiently corrected.
If the lower limit of condition (12) is exceeded, the longitudinal chromatic aberration will be overcorrected.

In the single focal length lens of the present embodiment, it is preferable that the rear group has at least one positive lens and satisfies the following conditional expression (13).
(13) 60<νpRave
however,
νpRave: average Abbe number of the positive lenses included in the rear group,
It is.

By satisfying conditional expression (13), longitudinal chromatic aberration can be corrected satisfactorily.
If the lower limit of condition (13) is exceeded, axial chromatic aberration will be insufficiently corrected.

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.

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, 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 (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.

The rear group G2 has a cemented lens BL closest to the object, and the cemented lens BL located closest to the object of the rear group G2 has a cemented surface with a concave surface facing the object side. 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 rear group,
fBO: focal length of the cemented surface of the cemented lens closest to the object side in the rear group, the concave surface of which faces the object side;
It is.

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.

By satisfying conditional expression (15), it is possible to effectively correct aberrations such as spherical aberration and coma aberration. This effect is more pronounced when conditional expressions (15A) and (15B) are satisfied.
If the upper limit of condition (15) is exceeded, the refractive power of the cemented surface of the cemented lens element located closest to the object in the rear group, the cemented surface having a concave surface facing the object side, becomes too weak, making it difficult to correct aberrations such as spherical aberration and coma.
If the lower limit of condition (15) is exceeded, the refractive power of the cemented surface of the cemented lens element located closest to the object in the rear group, the cemented surface having a concave surface facing the object side, becomes too strong, making it difficult to correct aberrations such as spherical aberration and coma.

The fixed focal length lenses of Numerical Examples 1-4 described below can have a focusing lens group in which at least a portion of the rear group G2 moves on the optical axis when focusing from infinity to a close distance. By making at least a portion of the rear group G2, which is a relatively small lens group, the focusing lens group is made lighter, and the focusing speed during AF (autofocus) can be increased.

The fixed focal length lenses of Numerical Examples 5-9 described below can have a focusing lens group in which the lens closest to the image in the front group G1 moves on the optical axis when focusing from infinity to a close distance. By using the single lens (or cemented lens) closest to the image in the front group G1, which is a relatively small lens group, as the focusing lens group, the weight of the focusing lens group can be reduced, and the focusing speed during AF (autofocus) can be increased.

The single focal length lens of this embodiment, throughout all embodiments (for example, Numerical Examples 1-9 described below), can have at least one aberration correction lens group that moves on the optical axis on a different movement trajectory from the focusing lens group when focusing from infinity to a close distance. The focusing lens group has a strong refractive power in order to increase the AF speed, so aberration generally increases at close distances. By having an aberration correction lens group that moves other than the focusing lens group, it is possible to effectively correct aberration fluctuations at close distances. The aberration correction lens group can be provided in at least one of the front group G1 and the rear group G2.

The fixed focal length lens of this embodiment can have at least one aberration correction lens group that moves on the optical axis on a different movement trajectory from the focusing lens group when focusing from infinity to a close distance. The focusing lens group has a strong refractive power in order to increase the AF speed, so aberration generally increases at close distances. By having an aberration correction lens group that moves other than the focusing lens group, it is possible to effectively correct aberration fluctuations at close distances. The aberration correction lens group can be provided in at least one of the front group G1 and the rear group G2.

In the single focal length lens of this embodiment, when focusing from infinity to a close distance, the front group G1 is divided into sub lens group A on the object side and sub lens group B on the image side with the widest air gap, and when focusing from infinity to a close distance, sub lens group A can be fixed. Since a relatively large lens is arranged in the sub lens group A on the object side to achieve a wide angle of view, the lens weight becomes heavy. Therefore, in order to increase the AF speed, it is preferable to fix the sub lens group A during focusing operations. Also, by making the internal lenses into movable groups, the overall lens length does not change, there is no collision with the subject during focusing operations, and it also has excellent airtightness.

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, an aperture stop SP that can control the F-number (for adjusting the amount of light), and a rear group G2 with positive refractive power. A parallel plane plate CG is disposed between the rear group G2 and the image plane (designed image plane). The parallel plane plate CG is composed of, for example, a low-pass filter, an infrared cut filter, and a cover glass for the image sensor.

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. The negative meniscus lens L5A and the positive meniscus lens L6A are cemented together.

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 to form a cemented lens BL. The cemented surface of the cemented lens BL faces the concave surface toward the object side. The biconvex positive lens L11A has aspheric surfaces on both sides.

(Table 1)
Surface number RD 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 aperture 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 -
* denotes a rotationally symmetric aspheric 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
F No. 2.45
w 46.1
Y 21.64
BF 40.33
L 115.34

[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 lens configuration of the single focal length lens of Numerical Example 2 differs from the lens configuration of the single focal length 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.

(Table 4)
Surface number RD 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 -
* denotes 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
F No. 2.45
w 46.1
Y 21.64
BF 40.65
L 125.82

[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 lens configuration of the single focal length lens of Numerical Example 3 differs from the lens configuration of the single focal length 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 toward the image side.

(Table 7)
Surface number RD 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 aperture 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 -
* denotes a rotationally symmetric aspheric 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
F No. 2.45
w 46.6
Y 21.64
BF 41.48
L 122.79

[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 lens configuration of the single focus lens in Numerical Example 4 is similar to the lens configuration of the single focus lens in Numerical Example 3.

(Table 10)
Surface number RD 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 aperture 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 -
* denotes a rotationally symmetric aspheric 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
F No. 2.45
w 46.6
Y 21.64
BF 41.20
L 123.09

[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 L1B convex toward the object side, a negative meniscus lens L2B convex toward 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 toward the image side. The negative meniscus lens L2B has aspheric surfaces on both sides. The biconcave negative lens L3B and the biconvex positive lens L4B are cemented together. The biconvex positive lens L5B and the negative meniscus lens L6B are cemented together.

The rear group G2 is composed of, in order from the object side, a positive meniscus lens L7B convex toward 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 toward 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 cemented together to form a cemented lens BL. The biconvex positive lens L11B and the biconcave negative lens L12B are cemented together. The biconvex positive lens L14B has aspheric surfaces on both sides.

(Table 13)
Surface number RD 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 aperture 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 -
* denotes a rotationally symmetric aspheric 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
F No. 2.40
w 49.7
Y 21.64
BF 40.84
L 139.25

[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 lens configuration of the single focus lens in Numerical Example 6 is the same as the lens configuration of the single focus lens in Numerical Example 5.

(Table 16)
Surface number RD 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 aperture 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 -
* denotes a rotationally symmetric aspheric 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
F No. 2.40
w 50.6
Y 21.64
BF 40.44
L 138.85

[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 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 biconcave negative lens L4C, a biconvex positive lens L5C, and a biconvex positive lens L6C. The negative meniscus lens L2C has aspheric surfaces on both sides. The biconcave negative lens L4C and the biconvex positive lens L5C are cemented together.

The rear group G2 is composed of, in order from the object side, a positive meniscus lens L7C convex toward the image side, a negative meniscus lens L8C convex toward 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 cemented together to form a cemented lens BL. The biconvex positive lens L10C has aspheric surfaces on both sides. The biconvex positive lens L13C has an aspheric surface on the image side surface.

(Table 19)
Surface number RD 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 aperture 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 -
* denotes a rotationally symmetric aspheric 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
F No. 2.40
w 54.2
Y 21.64
BF 37.89
L 129.54

[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 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 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 aspheric surfaces on both sides. The biconcave negative lens L5D and the biconvex positive lens L6D are cemented together.

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 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 cemented together to form a cemented lens BL. The biconvex positive lens L11D has aspheric surfaces on both sides. The biconvex positive lens L14D has an aspheric surface on the image side surface.

(Table 22)
Surface number RD 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 aperture 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 INFINITY 1.500 1.51633 64.1
29 INFINITY -
* denotes a rotationally symmetric aspheric 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
F No. 2.40
w 54.2
Y 21.64
BF 36.71
L 130.97

[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 L1E convex toward the object side, a negative meniscus lens L2E convex toward the object side, a biconcave negative lens L3E, a biconvex positive lens L4E, a negative meniscus lens L5E convex toward the object side, and a biconvex positive lens L6E. The negative meniscus lens L2E has aspheric surfaces on both sides. The biconcave negative lens L3E and the biconvex positive lens L4E are cemented together. The negative meniscus lens L5E and the biconvex positive lens L6E are cemented together.

The rear group G2 is composed of, in order from the object side, a positive meniscus lens L7E convex toward the image side, a negative meniscus lens L8E convex toward the image side, a biconcave negative lens L9E, a biconvex positive lens L10E, a biconvex positive lens L11E, a negative meniscus lens L12E convex toward the image side, and a negative meniscus lens L13E convex toward the object side. The positive meniscus lens L7E and the negative meniscus lens L8E are cemented together to form a cemented lens BL. The biconvex positive lens L10E has aspheric surfaces on both sides. The negative meniscus lens L12E has an aspheric surface on the object side surface. The negative meniscus lens L13E has an aspheric surface on the object side surface.

(Table 25)
Surface number RD 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 aperture 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 -
* denotes a rotationally symmetric aspheric 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
F No. 2.40
w 58.1
Y 21.64
BF 20.76
L 111.15

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

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 L1E 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 single focal length lens, an interchangeable lens, and an imaging device that have high optical performance, are small, lightweight, and have a wide angle of view.

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 L1A to L1E: negative meniscus lens with a convex surface facing the object side G2: rear group BL: cemented lens SP: aperture stop CG: plane-parallel plate 100: digital camera (imaging device)
102 Photographic lenses (lens barrels, interchangeable lenses)

Claims (12)

From the object side, it is composed of a front group, an aperture stop, and a rear group having positive refractive power,
The axial light beam that passes through the aperture stop surface is larger than the axial light beam that is incident on the refractive surface closest to the object in the front group.
The front group has a negative meniscus lens with a convex surface facing the object side,
the front group has a refracting surface closest to the image side that is convex toward the image side;
The rear group has at least one negative lens,
The rear group has a cemented lens closest to the object,
the cemented lens in the rear group located closest to the object has a cemented surface with a concave surface facing the object side,
the rear group has a refracting surface closest to the object side that is concave toward the object side;
The following conditional expressions (1), (2'), (3), (5), (6), (7), and (11C) are satisfied.
A single focal length lens.
(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: the distance on the optical axis from the surface of the front group closest to the object to the aperture stop,
DR: the distance on the optical axis from the surface of the rear group closest to the image side to the aperture stop,
fBL: focal length of the cemented lens located closest to the object in the rear group,
fBO: focal length of the cemented surface of the cemented lens closest to the object side in the rear group, the concave surface of which faces the object side;
f: focal length of the entire system of a single focal length lens,
Y: image height of the entire system of a single focal length lens,
Fno: F-number of the entire single focal length lens system,
RF: radius of curvature of the refracting surface of the front group closest to the image side,
RR: radius of curvature of the refracting surface of the rear group closest to the object,
NnRmax: the refractive index of the negative lens having the largest refractive index among the negative lenses included in the rear group. The following condition (4) is satisfied:
2. The single focal length lens according to claim 1 .
(4) 1.0<TL/f<10.0
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 prime lens. The front group has at least two positive lenses.
3. The single focal length lens according to claim 1 or 2 . The front group has at least three negative lenses.
4. The single focal length lens according to claim 1 , The front group includes, in order from the object side, three or more negative lenses.
5. The single focal length lens according to claim 1 . the front group has at least one negative lens;
The following condition (8) is satisfied:
6. The single focal length lens according to claim 1 ,
(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. the front group has at least one negative lens;
The following condition (9) is satisfied:
7. The single focal length lens according to claim 1 .
(9) 1.60<NnFave
however,
NnFave: The average value of the refractive index of the negative lenses included in the front group. the front group has at least one positive lens;
The following condition (10) is satisfied:
8. The single focal length lens according to claim 1 ,
(10) 30<νpFave<50
however,
νpFav: the average value of the Abbe number of the positive lenses included in the front group. The following condition (12) is satisfied:
9. The single focal length lens according to claim 1,
(12) 30<νnRave<50
however,
νnRave: the average Abbe number of the negative lenses included in the rear group. the rear group has at least one positive lens;
The following condition (13) is satisfied:
10. The single focal length lens according to claim 1 .
(13) 60<νpRave
however,
νpRave: the average value of the Abbe number of the positive lenses included in the rear group. An interchangeable lens comprising the single focal length lens according to any one of claims 1 to 10 . An imaging device comprising the single focal length lens according to any one of claims 1 to 10 .

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