JP7123383B2 - Imaging optical system - Google Patents

Description

The present invention is most suitable for digital cameras, film cameras, video cameras, and the like, and is particularly suitable for mirrorless cameras with a field angle of about 48° to 77° and an F value of about F1.2, and with a short back focus. image forming optical system.

In general, a large-aperture lens with a bright F-number of about F1.2 has a larger entrance pupil diameter than a lens with a darker F-number, making it difficult to correct spherical aberration and longitudinal chromatic aberration. On the other hand, since the image sensors of recent digital cameras have increased the number of pixels, especially in the case of an imaging optical system in which axial chromatic aberration is insufficiently corrected, the image on the imaging plane becomes colored and the out-of-focus part becomes blurred. becomes more conspicuous. In order to solve such a problem, it is important to correct axial chromatic aberration so as to reduce it.

The following patent documents disclose conventional imaging optical systems.

Patent Document 1 discloses an optical system having an angle of view of about 45° and an F value of about F1.2.

Further, Patent Document 2 discloses an optical system having an angle of view of about 49° and an F value of about F1.4.

JP-A-2007-333790 JP 2016-38418 A

However, the imaging optical system disclosed in Patent Literature 1 is insufficient in longitudinal chromatic aberration correction and has a long back focus, and is not an optimal imaging optical system for mirrorless cameras.

Further, the imaging optical system disclosed in Patent Document 2 has a short back focus and is an optimum imaging optical system for mirrorless cameras. However, since the F-number is about F1.4, it is difficult to correct spherical aberration and axial chromatic aberration with the disclosed imaging optical system when trying to increase the F-number to about F1.2.

Therefore, the present invention solves the problem of the conventional imaging optical system, and by shortening the back focus of the F value of about F1.2, it is possible to suppress the overall length of the optical system and satisfactorily correct axial chromatic aberration. It is an object of the present invention to provide an optimal imaging optical system for a mirrorless camera.

１．０ ＜ ｆｓｆ／ｆ ＜ ２．７ （６）
但し、
Ｙは最大像高、
Ｂｆは第３レンズ群Ｌ３の最も像側面の面頂から像面までの距離、
ｆｓｆは前記レンズ群Ｌｓｆの無限遠合焦時の焦点距離、
ｆはレンズ全系の無限遠合焦時の焦点距離であり、
Ａｃｉは以下の式で表される。
Ａｃｉ ＝ φｃｐｉ／νｄｃｐｉ ＋ φｃｍｉ／νｄｃｍｉ
但し、
φｃｐｉは、前記第１レンズ群Ｌ１に含まれる物体側からｉ番目の接合レンズの正レンズ素子の屈折力、
νｄｃｐｉは、記第１レンズ群Ｌ１に含まれる物体側からｉ番目の接合レンズの正レンズ素子のアッベ数、
φｃｍｉは、前記第１レンズ群Ｌ１に含まれる物体側からｉ番目の接合レンズの負レンズ素子の屈折力、
νｄｃｍｉは、記第１レンズ群Ｌ１に含まれる物体側からｉ番目の接合レンズの負レンズ素子のアッベ数である。
In order to solve the above problems, the imaging optical system of the present invention comprises, in order from the object side to the image side, a first lens unit L1 having positive refractive power and a second lens unit L2 having positive refractive power. and a third lens group L3 having negative refractive power, wherein the first lens group L1 has at least one cemented lens, has a negative lens element closest to the object side, and has a convex surface facing the object side. a positive lens element directed toward the image side of the negative lens element, and the second lens group L2 includes an aperture stop S, and the second lens group L2 moves toward the object side during focusing. In addition, the first lens group L1 and the third lens group L3 are fixed with respect to the image plane, and all the lens element groups arranged on the object side of the aperture stop S in the entire lens system are The lens group Lsf has a positive refractive power and satisfies the following conditional expression.
Y/Bf > 0.70 (1)

1.0 < fsf/f < 2.7 (6)
however,
Y is the maximum image height,
Bf is the distance from the vertex of the surface closest to the image side of the third lens unit L3 to the image plane ;
fsf is the focal length of the lens group Lsf when focusing on infinity;
f is the focal length of the entire lens system when focusing at infinity ,
Aci is represented by the following formula.
Aci = φcpi/νdcpi + φcmi/νdcmi
however,
φcpi is the refractive power of the positive lens element of the i-th cemented lens from the object side included in the first lens unit L1;
νdcpi is the Abbe number of the positive lens element of the i-th cemented lens from the object side included in the first lens unit L1;
φcmi is the refractive power of the negative lens element of the i-th cemented lens from the object side included in the first lens group L1;
νdcmi is the Abbe number of the negative lens element of the i-th cemented lens from the object side included in the first lens unit L1.

A second invention is an imaging optical system according to the first invention, wherein the positive lens element L1p located closest to the image side of the first lens unit L1 further satisfies the following conditional expression: be.
νdL1p < 27 (3)
0.0220 < ΔPgfL1p (4)
however,
ΔPgfL1p is the anomalous dispersion of the positive lens element L1p and is expressed by the following equation.
ΔPgfL1p = PgfL1p + 0.0018 x vdL1p - 0.64833
however,
νdL1p is the Abbe number νd of the positive lens element L1p;
PgfL1p is the partial dispersion ratio Pgf for the g-line and the F-line of the positive lens element L1p.

The third invention is based on the first and second inventions, and further includes a lens element extending from the most object-side surface of the first lens unit L1 to the image-side surface of the negative lens element having a concave surface facing the image side. The imaging optical system is characterized in that the lens component L1f has a negative refractive power and satisfies the following conditional expression.
-3.53 < f1f/f < -0.60 (5)
however,
f1f is the focal length of the lens component L1f;
f is the focal length of the entire lens system when focusing on infinity.

A fourth invention is an imaging optical system according to the first to third inventions, characterized by further satisfying the following conditional expression.
1.0 < f2/f < 2.1 (7)
however,
f2 is the focal length of the second lens group L2;
f is the focal length of the entire lens system when focusing on infinity.

A fifth aspect of the invention is an imaging optical system according to the first to fourth aspects of the invention, characterized by further satisfying the following conditional expression.
β1b < 0.37 (8)
however,
β1b is the lateral magnification of the lens element group located closer to the image side than the first lens group L1 when focusing on infinity.

According to the present invention, spherical aberration and axial chromatic aberration, which have been problems of conventional imaging optical systems, are satisfactorily corrected, and imaging is optimal for a mirrorless camera with a short back focus and an F value of about F1.2. An optical system can be provided.

FIG. 2 is a lens configuration diagram when focusing on infinity according to Example 1 of the present invention; FIG. 4 is a longitudinal aberration diagram when focusing on infinity according to Example 1 of the present invention; FIG. 4 is a longitudinal aberration diagram at a shooting distance of 2059 mm according to Example 1 of the present invention; FIG. 4 is a lateral aberration diagram during focusing at infinity according to Example 1 of the present invention; FIG. 4 is a lateral aberration diagram at a shooting distance of 2059 mm according to Example 1 of the present invention; FIG. 10 is a lens configuration diagram when focusing on infinity according to Example 2 of the present invention; FIG. 10 is a longitudinal aberration diagram when focusing on infinity according to Example 2 of the present invention; FIG. 10 is a longitudinal aberration diagram at a shooting distance of 2058 mm according to Example 2 of the present invention; FIG. 10 is a lateral aberration diagram when focusing on infinity according to Example 2 of the present invention; FIG. 10 is a lateral aberration diagram at a shooting distance of 2058 mm according to Example 2 of the present invention; It is a lens configuration diagram at the time of infinity focusing according to Example 3 of the present invention. FIG. 10 is a longitudinal aberration diagram during focusing at infinity according to Example 3 of the present invention; FIG. 11 is a longitudinal aberration diagram at a shooting distance of 1774 mm according to Example 3 of the present invention; FIG. 11 is a lateral aberration diagram at the time of focusing at infinity according to Example 3 of the present invention; It is a lateral aberration diagram at a shooting distance of 1774 mm according to Example 3 of the present invention. FIG. 11 is a lens configuration diagram when focusing on infinity according to Example 4 of the present invention; FIG. 11 is a longitudinal aberration diagram during focusing at infinity according to Example 4 of the present invention; It is a longitudinal aberration diagram at a shooting distance of 1774 mm according to Example 4 of the present invention. FIG. 11 is a lateral aberration diagram during focusing at infinity according to Example 4 of the present invention; FIG. 12 is a lateral aberration diagram at a shooting distance of 1774 mm according to Example 4 of the present invention; FIG. 11 is a lens configuration diagram when focusing on infinity according to Example 5 of the present invention; FIG. 11 is a longitudinal aberration diagram during focusing at infinity according to Example 5 of the present invention; FIG. 11 is a longitudinal aberration diagram at a shooting distance of 1754 mm according to Example 5 of the present invention; FIG. 11 is a lateral aberration diagram at the time of focusing on infinity according to Example 5 of the present invention; FIG. 12 is a lateral aberration diagram at a shooting distance of 1754 mm according to Example 5 of the present invention; FIG. 11 is a lens configuration diagram when focusing on infinity according to Example 6 of the present invention; FIG. 12 is a longitudinal aberration diagram during focusing at infinity according to Example 6 of the present invention; FIG. 11 is a longitudinal aberration diagram at a photographing distance of 1281 mm according to Example 6 of the present invention; FIG. 11 is a lateral aberration diagram during focusing at infinity according to Example 6 of the present invention; FIG. 11 is a lateral aberration diagram at a photographing distance of 1281 mm according to Example 6 of the present invention;

Examples of the optical system according to the present invention will be described in detail below. It should be noted that the following description of the embodiment is an example of the optical system of the present invention, and the present invention is not limited to the present embodiment without departing from the scope of the invention.

但し、
Ｙは最大像高、
Ｂｆは第３レンズ群Ｌ３の最も像側面の面頂から像面までの距離であり、
Ａｃｉは以下の式で表される。
Ａｃｉ ＝ φｃｐｉ／νｄｃｐｉ ＋ φｃｍｉ／νｄｃｍｉ
但し、
φｃｐｉは、前記第１レンズ群Ｌ１に含まれる物体側からｉ番目の接合レンズの正レンズ素子の屈折力、
νｄｃｐｉは、記第１レンズ群Ｌ１に含まれる物体側からｉ番目の接合レンズの正レンズ素子のアッベ数、
φｃｍｉは、前記第１レンズ群Ｌ１に含まれる物体側からｉ番目の接合レンズの負レンズ素子の屈折力、
νｄｃｍｉは、記第１レンズ群Ｌ１に含まれる物体側からｉ番目の接合レンズの負レンズ素子のアッベ数である。 The imaging optical system of this embodiment has, in order from the object side to the image side, a first lens group L1 having positive refractive power, a second lens group L2 having positive refractive power, and a negative refractive power. The first lens unit L1 has at least one cemented lens, has a negative lens element closest to the object side, and has a positive lens element with a convex surface facing the object side. The second lens unit L2 is arranged adjacent to the image side of the negative lens element, and includes an aperture stop S. During focusing, the second lens unit L2 moves toward the object side and the first lens unit L1 moves toward the object side. and the third lens unit L3 are fixed with respect to the image plane, and the following conditional expression is satisfied.
Y/Bf > 0.70 (1)

however,
Y is the maximum image height,
Bf is the distance from the apex of the surface closest to the image side of the third lens unit L3 to the image plane;
Aci is represented by the following formula.
Aci = φcpi/νdcpi + φcmi/νdcmi
however,
φcpi is the refractive power of the positive lens element of the i-th cemented lens from the object side included in the first lens unit L1;
νdcpi is the Abbe number of the positive lens element of the i-th cemented lens from the object side included in the first lens unit L1;
φcmi is the refractive power of the negative lens element of the i-th cemented lens from the object side included in the first lens group L1;
νdcmi is the Abbe number of the negative lens element of the i-th cemented lens from the object side included in the first lens unit L1.

When the refractive indices of the F-line, d-line, and C-line are NF, Nd, and NC, respectively, the Abbe number νd is expressed by the following equation.
νd = (Nd-1)/(NF-NC)

By arranging a negative lens element closest to the object side in the first lens unit L1 and arranging a positive lens element having a convex surface facing the object side so as to be adjacent to the image side of the negative lens element, the image plane of the entire lens system is Curvature correction and coma aberration correction can be effectively performed. Furthermore, by arranging at least one cemented lens in the first lens unit L1, it is possible to effectively correct longitudinal chromatic aberration of the entire lens system.

Conditional expression (1) defines the back focus of the entire lens system for miniaturization.

If the lower limit of conditional expression (1) is exceeded and the back focus of the entire lens system becomes long, the total length of the entire lens system increases, which is disadvantageous for downsizing.

By setting the lower limit of conditional expression (1) to 0.75, the above effect can be more reliably obtained.

Conditional expression (2) defines the sum of primary achromatic conditions of the cemented lens included in the first lens unit L1 for high performance.

When the upper limit of conditional expression (2) is exceeded and the sum of the achromatic conditions of the cemented lenses included in the first lens unit L1 becomes large, the first-order achromatization becomes insufficient, and longitudinal chromatic aberration worsens. put away.

By limiting the upper limit of conditional expression (2) to 0.0016, the aforementioned effect can be more reliably obtained.

Further, the positive lens element L1p located closest to the image side in the first lens unit L1 satisfies the following conditional expression.
νdL1p < 27 (3)
0.0220 < ΔPgfL1p (4)
however,
ΔPgfL1p is the anomalous dispersion of the positive lens element L1p and is expressed by the following equation.
ΔPgfL1p = PgfL1p + 0.0018 x vdL1p - 0.64833
however,
νdL1p is the Abbe number νd of the positive lens element L1p;
PgfL1p is the partial dispersion ratio Pgf for the g-line and the F-line of the positive lens element L1p.

Conditional expressions (3) and (4) define the Abbe number νd and the anomalous dispersion ΔPgf of the positive lens element L1p for high performance.

When the refractive indices of g-line, F-line, d-line, and C-line are Ng, NF, Nd, and NC, respectively, the partial dispersion ratio Pgf is expressed by the following equation.
Pgf = (Ng-NF)/(NF-NC)

If the upper limit of conditional expression (3) is exceeded and the lower limit of conditional expression (4) is exceeded, and the Abbe number νd of the positive lens element L1p increases and the anomalous dispersion ΔPgf decreases, correction of the secondary spectrum is particularly difficult. If it is insufficient, axial chromatic aberration will be worsened.

By limiting the upper limit of conditional expression (3) to 23 and the lower limit of conditional expression (4) to 0.0260, the above effect can be more reliably achieved.

Further, a lens component L1f is defined from the most object-side surface of the first lens unit L1 to the image-side surface of the negative lens element having a concave surface facing the image side, and the lens component L1f has negative refractive power. , is characterized by satisfying the following conditional expressions.
-3.53 < f1f/f < -0.60 (5)
however,
f1f is the focal length of the lens component L1f;
f is the focal length of the entire lens system when focusing on infinity.

Conditional expression (5) defines the refractive power of the lens component L1f for miniaturization.

If the upper limit of conditional expression (5) is exceeded and the refractive power of the lens component L1f becomes stronger, the divergence action of the lens component L1f becomes stronger. Since the height of the light rays at the lens element increases and the lens diameter increases, the diameter of the product increases.

If the lower limit of conditional expression (5) is exceeded and the refractive power of the lens component L1f becomes weak, the divergence effect of the lens component L1f becomes weak. Although the height of light rays at the lens component does not increase, the height of light rays at the lens component L1f itself increases and the diameter of the lens increases, resulting in an increase in the diameter of the product.

By restricting the upper limit of conditional expression (5) to -0.70 and the lower limit to -3.20, the above effects can be more reliably achieved.

Further, in the entire lens system, all lens element groups arranged on the object side of the aperture stop S are defined as a lens group Lsf, and the lens group Lsf has a positive refractive power and satisfies the following conditional expression: It is characterized by
1.0 < fsf/f < 2.7 (6)
however,
fsf is the focal length of the lens group Lsf when focusing on infinity;
f is the focal length of the entire lens system when focusing on infinity.

Conditional expression (6) defines the refractive power of the lens group Lsf for miniaturization and high performance.

When the upper limit of conditional expression (6) is exceeded and the refractive power of the lens unit Lsf becomes weak, the diameter of the F-number luminous flux at the aperture stop S increases, so the diameter of the aperture increases when trying to maintain the F-number. This leads to an increase in the diameter of the diaphragm unit, which leads to an increase in the diameter of the product, which is disadvantageous for miniaturization.

If the lower limit of conditional expression (6) is exceeded and the refractive power of the lens unit Lsf becomes strong, the diameter of the F-number luminous flux at the aperture stop S will decrease, so the diameter of the stop unit will decrease, which is advantageous for miniaturization. On the other hand, the curvature of field, which mainly occurs in the lens unit Lsf, becomes worse, and it becomes difficult to satisfactorily correct this in the entire lens system, which is disadvantageous in achieving high performance.

By restricting the lower limit of conditional expression (6) to 1.2 and the upper limit to 2.2, the above effect can be more assured.

Furthermore, it is characterized by satisfying the following conditional expressions.
1.0 < f2/f < 2.1 (7)
however,
f2 is the focal length of the second lens group L2;
f is the focal length of the entire lens system when focusing on infinity.

Conditional expression (7) defines the refractive power of the second lens unit L2 for high performance and miniaturization.

When the lower limit of conditional expression (7) is exceeded and the refractive power of the second lens unit L2 becomes strong, the amount of movement during focusing becomes small, which is advantageous for miniaturization, but astigmatism during focusing. , spherical aberration, etc., and the sensitivity to manufacturing errors increases, which is disadvantageous for achieving high performance.

If the upper limit of conditional expression (7) is exceeded and the refracting power of the second lens unit L2 is weakened, fluctuations in various aberrations during focusing are reduced, which is advantageous for high performance. Since the amount of movement increases, it is disadvantageous for miniaturization.

By restricting the lower limit of conditional expression (7) to 1.1 and the upper limit to 1.8, the above effect can be more reliably achieved.

Furthermore, it is characterized by satisfying the following conditional expressions.
β1b < 0.37 (8)
however,
β1b is the lateral magnification of the lens element group located closer to the image side than the first lens group L1 when focusing on infinity.

Conditional expression (8) defines the lateral magnification of the lens element group located closer to the image side than the first lens group L1 in order to improve performance.

When the lateral magnification of the lens element group located closer to the image side than the first lens unit L1 exceeds the upper limit of conditional expression (8), the aberration generated in the first lens unit L1 is magnified. unfavorable for conversion.

By limiting the upper limit of conditional expression (8) to 0.31, the aforementioned effect can be more reliably achieved.

Numerical data of Examples 1 to 6 of the imaging optical system according to the present invention are shown below.

In [Surface data], the surface number is the number of the lens surface or aperture stop counted from the object side, r is the radius of curvature of each surface, d is the distance between each surface, and nd is the d line (wavelength λ = 587.56 nm) A refractive index and νd indicate the Abbe number for the d-line. Also, BF represents back focus, and the description of the refractive index n=1.0000 of air is omitted.

The surface numbered (aperture) indicates the radius of curvature ∞ (infinity) with respect to a plane or an aperture stop.

[Aspheric surface data] shows each coefficient value that gives the aspheric shape of the lens surface marked with * in [Surface data]. As for the shape of the aspherical surface, y is the displacement in the direction orthogonal to the optical axis, z is the displacement (sag amount) in the optical axis direction from the intersection of the aspherical surface and the optical axis, and K, 4, 6, 8 is the conic coefficient. Let A4, A6, A8, A10, and A12 be the 10th and 12th order aspherical coefficients, respectively, and the coordinates of the aspherical surface are represented by the following equations.

[Various data] shows values such as the focal length in each focal length state.

[Variable distance data] shows the variable distance and BF (back focus) values in each focal length state.

[Lens group data] indicates the number of the surface closest to the object side constituting each lens group and the combined focal length of the entire group. In addition, in the values of all the specifications below, unless otherwise specified, millimeters (mm) are used for the focal length f, radius of curvature r, distance between lens surfaces d, and other lengths. The system is not limited to this because the same optical performance can be obtained in both proportional enlargement and proportional reduction.

In the aberration diagrams corresponding to each example, d, g, and C represent the d-line, g-line, and C-line, respectively, and .DELTA.S and .DELTA.M represent the sagittal image plane and the meridional image plane, respectively.
1, 6, 11, 16, 21, and 26, S is an aperture stop, I is an image plane, LPF is a low-pass filter, and a dashed line passing through the center is an optical axis.

FIG. 1 is a lens configuration diagram of an imaging optical system according to Example 1 at infinity. The imaging optical system of Example 1 includes, in order from the object side to the image side, a first lens unit L1 having a fixed positive refractive power during focusing and a second lens unit L1 having a positive refractive power that moves toward the object side during focusing. It consists of a lens group L2 and a third lens group L3 having a fixed negative refractive power during focusing.

The first lens unit L1 includes, in order from the object side to the image side, a lens component L1f composed of a concave meniscus lens with a convex surface facing the object side, a convex meniscus lens with a convex surface facing the object side, and a biconcave lens. It is composed of a convex lens, a cemented lens of a biconcave lens and a biconvex lens, a cemented lens of a biconcave lens and a biconvex lens, and a biconvex lens element L1p.

The second lens unit L2 includes, in order from the object side to the image side, a biconvex lens whose surface R2 is aspheric, a cemented lens composed of a biconvex lens and a biconcave lens, a diaphragm S, a biconcave lens, and a convex surface facing the object side. It is composed of a cemented meniscus lens, a biconvex lens, and a convex meniscus lens in which both the R1 and R2 surfaces are aspheric and the concave surface faces the object side.

The third lens unit L3 is composed of a biconvex lens and a biconcave lens in order from the object side to the image side.

Next, the specification values of the imaging optical system according to Example 1 are shown below.

Numerical example 1
Unit: mm
[Surface data]
Face number rd nd vd
Object plane ∞ (d0)
1 259.2005 3.9656 1.49700 81.61
2 36.0489 1.8284
3 40.4512 6.7840 2.00069 25.46
4 48.7346 13.5960
5 -50.0535 2.0000 1.49700 81.61
6 444.9340 0.1500
7 102.4616 9.9748 1.77250 49.62
8 -57.2347 0.7113
9 -52.7837 1.5000 1.80518 25.46
10 62.5000 11.0746 1.77250 49.62
11 -70.2116 3.1864
12 -72.1569 1.5000 1.92119 23.96
13 90.1742 5.8741 1.77250 49.62
14 -1000.0000 0.1500
15 132.7624 7.8334 1.98612 16.48
16 -112.3961 d16
17 42.1510 10.6553 1.69350 53.20
18* -192.5256 0.4054
19 2870.6010 7.9394 1.59349 67.00
20 -41.6908 1.0000 1.67300 38.26
21 43.2474 6.3397
22 (Aperture) ∞ 6.8810
23 -30.4885 1.0000 1.69895 30.05
24 152.7244 2.8633 1.55032 75.50
25 683.1561 0.2000
26 72.4204 8.5969 1.77250 49.62
27 -45.9138 3.9524
28* -442.9462 4.3093 1.77250 49.50
29* -68.8452 d29
30 71.3653 4.3854 2.00069 25.46
31 -244.4417 0.7125
32 -146.9124 0.8000 1.78470 26.29
33 41.7634 20.9913
34 ∞ 2.5000 1.51680 64.20
35∞BF
Image plane ∞

[Aspheric Data]
18 faces 28 faces 29 faces
K 0.0000E+00 0.0000E+00 0.0000E+00
A4 1.7905E-06 -4.1058E-06 1.9868E-06
A6 -1.7282E-09 -7.3230E-09 -5.1825E-09
A8 9.5181E-13 3.9434E-11 3.9444E-11
A10 -5.0029E-16 -5.8666E-14 -5.0984E-14
A12 0.0000E+00 0.0000E+00 0.0000E+00

[Various data]
INF
Focal length 48.30
F number 1.26
Full angle of view 2ω 48.80
Image height Y 21.63
Lens length 165.00

[Variable interval data]
INF shooting distance 2059mm
d0 ∞ 1894.2816
d16 8.8392 7.7209
d29 1.5000 2.6183
BF 1.0000 1.0000

[Lens group data]
Group Starting surface Focal length
L1 1 187.14
L2 17 64.05
L3 30 -200.77
L1f1-54.52
Lsf 1 69.94

FIG. 6 is a lens configuration diagram of the imaging optical system according to Example 2 at infinity. The imaging optical system of Example 2 includes, in order from the object side to the image side, a first lens unit L1 having a fixed positive refractive power during focusing and a second lens unit L1 having a positive refractive power that moves toward the object side during focusing. It consists of a lens group L2 and a third lens group L3 having a fixed negative refractive power during focusing.

The first lens unit L1 includes, in order from the object side to the image side, a lens component L1f composed of a concave meniscus lens with a convex surface facing the object side, a convex meniscus lens with a convex surface facing the object side, and a biconcave lens. It is composed of a convex lens, a cemented lens of a biconcave lens and a biconvex lens, a cemented lens of a biconcave lens and a biconvex lens, and a biconvex lens element L1p.

The second lens unit L2 includes, in order from the object side to the image side, a biconvex lens having an aspheric R2 surface, a cemented lens composed of a convex meniscus lens with a concave surface facing the object side and a biconcave lens, an aperture stop S, and a biconcave lens. It is composed of a cemented double convex lens, a double convex lens, and a convex meniscus lens in which both the R1 and R2 surfaces are aspheric and the concave surface faces the object side.

The third lens unit L3 is composed of a biconvex lens and a biconcave lens in order from the object side to the image side.

Next, the specification values of the imaging optical system according to Example 2 are shown below.

Numerical example 2
Unit: mm
[Surface data]
Face number rd nd vd
Object plane ∞ (d0)
1 329.2217 2.5000 1.49700 81.61
2 37.8223 1.5392
3 41.4152 6.6962 2.00069 25.46
4 49.9917 13.5883
5 -57.1815 2.0000 1.49700 81.61
6 754.3452 0.1500
7 98.1553 9.5005 1.77250 49.62
8 -69.9522 0.5964
9 -64.9402 1.5000 1.80518 25.46
10 62.5000 12.1207 1.77250 49.62
11 -80.2691 7.6735
12 -67.4612 1.5000 1.92119 23.96
13 90.1864 5.5629 1.77250 49.62
14 -1000.0000 0.1500
15 113.4358 7.4188 1.98612 16.48
16 -131.3073 d16
17 46.3689 9.9520 1.77377 47.17
18* -197.7804 1.2969
19 -303.0475 7.7510 1.62041 60.34
20 -36.9798 1.0000 1.63980 34.46
21 44.2758 4.8849
22 (Aperture) ∞ 6.9054
23 -30.1848 1.0000 1.69895 30.05
24 194.4879 3.3785 1.55032 75.50
25 -270.8956 0.2000
26 74.8673 8.0566 1.77250 49.62
27 -50.0318 5.7227
28* -845.2086 4.2281 1.77250 49.50
29* -74.7984 d29
30 68.2901 4.4272 2.00069 25.46
31 -257.0025 0.7402
32 -148.0556 0.8000 1.78470 26.29
33 38.8678 19.3766
34 ∞ 2.5000 1.51680 64.20
35∞BF
Image plane ∞

[Aspheric data]
18 faces 28 faces 29 faces
K 0.0000E+00 0.0000E+00 0.0000E+00
A4 1.4731E-06 -5.4481E-06 1.1966E-06
A6 -1.3492E-09 -5.6829E-09 -3.8825E-09
A8 8.1394E-13 3.2756E-11 3.3851E-11
A10 -4.5812E-16 -4.5885E-14 -4.1154E-14
A12 0.0000E+00 0.0000E+00 0.0000E+00

[Various data]
INF
Focal length 48.30
F number 1.26
Full angle of view 2ω 48.26
Image height Y 21.63
Lens length 165.00

[Variable interval data]
INF shooting distance 2058mm
d0 ∞ 1892.8607
d16 7.7833 6.6929
d29 1.5000 2.5904
BF 1.0000 1.0000

[Lens group data]
Group Starting surface Focal length
L1 1 209.80
L2 17 60.78
L3 30 -173.23
L1f1-60.78
Lsf 1 71.87

FIG. 11 is a lens configuration diagram of the imaging optical system according to Example 3 at infinity. The imaging optical system of Example 11 includes, in order from the object side to the image side, a first lens unit L1 having a fixed positive refractive power during focusing, and a second lens unit L1 moving toward the object side during focusing and having positive refractive power. It consists of a lens group L2 and a third lens group L3 having a fixed negative refractive power during focusing.

The first lens unit L1 includes, in order from the object side to the image side, a cemented lens composed of a concave meniscus lens with a convex surface facing the object side, a convex meniscus lens with a convex surface facing the object side, and a concave meniscus lens with a convex surface facing the object side. A lens component L1f composed of a convex meniscus lens with a concave surface facing the object side, a cemented lens of a biconcave lens and a biconvex lens, a cemented lens of a concave meniscus lens with a convex surface facing the object side and a biconvex lens, and a biconvex lens element L1p.

The second lens unit L2 includes, in order from the object side to the image side, a biconvex lens having an aspheric R2 surface, a cemented lens composed of a convex meniscus lens with a concave surface facing the object side and a biconcave lens, an aperture stop S, and a biconcave lens. It is composed of a cemented double convex lens, a double convex lens, and a convex meniscus lens in which both the R1 and R2 surfaces are aspheric and the concave surface faces the object side.

The third lens unit L3 is composed of a cemented lens of a biconvex lens and a biconcave lens in order from the object side to the image side.

Next, the specification values of the imaging optical system according to Example 3 are shown below.

Numerical example 3
Unit: mm
[Surface data]
Face number rd nd vd
Object plane ∞ (d0)
1 200.9822 1.8000 1.49700 81.61
2 43.4726 6.5224 1.85026 32.27
3 70.0835 4.0432
4 126.2598 2.0000 1.51742 52.15
5 39.8554 9.8773
6 -158.2148 3.1251 1.77250 49.62
7 -79.5276 2.9894
8 -45.6289 1.5000 1.85478 24.80
9 37.7292 12.5622 1.77250 49.62
10 -632.3971 0.4149
11 2107.4248 1.0000 1.63980 34.46
12 93.2276 5.4458 1.77250 49.62
13 -1000.0000 0.1500
14 98.7068 8.1636 1.92286 20.88
15 -112.0714 d15
16 50.4845 9.5645 1.77377 47.17
17* -137.8916 0.2961
18 -1734.9315 9.1393 1.62041 60.34
19 -45.1824 1.0000 1.63980 34.46
20 43.0199 9.1027
21 (Aperture) ∞ 11.6205
22 -26.9583 1.0000 1.69895 30.05
23 53.1245 5.2119 1.55032 75.50
24 -132.8172 0.2000
25 86.7699 7.0512 1.77250 49.62
26 -40.0307 0.2000
27* -324.7949 2.8048 1.77250 49.50
28* -65.1019 d28
29 83.6872 4.6258 2.00069 25.46
30 -230.4316 1.5000 1.78470 26.29
31 45.1994 22.9280
32 ∞ 2.5000 1.51680 64.20
33∞BF
Image plane ∞

[Aspheric data]
17 planes 27 planes 28 planes
K 0.0000E+00 0.0000E+00 0.0000E+00
A4 2.4425E-06 -3.4754E-06 2.8623E-06
A6 -1.3075E-09 -2.8304E-09 -1.9050E-09
A8 6.1584E-13 3.3147E-11 3.3778E-11
A10 -2.2459E-16 -7.6000E-14 -7.1102E-14
A12 0.0000E+00 0.0000E+00 0.0000E+00

[Various data]
INF
Focal length 41.35
F number 1.26
Full angle of view 2ω 57.17
Image height Y 21.63
Lens length 157.00

[Variable interval data]
INF shooting distance 1774mm
d0 ∞ 1617.3263
d15 6.1614 5.2301
d28 1.5000 2.4313
BF 1.0000 1.0000

[Lens group data]
Group Starting surface Focal length
L1 1 347.73
L2 16 56.46
L3 29-261.51
L1f1-104.33
Lsf 1 67.09

FIG. 16 is a lens configuration diagram of the imaging optical system according to Example 4 at infinity. The imaging optical system of Example 4 comprises, in order from the object side to the image side, a first lens unit L1 having a fixed positive refractive power during focusing and a second lens unit L1 having a positive refractive power that moves toward the object side during focusing. It consists of a lens group L2 and a third lens group L3 having a fixed negative refractive power during focusing.

The first lens unit L1 includes, in order from the object side to the image side, a lens component L1f composed of a concave meniscus lens with a convex surface facing the object side, a convex meniscus lens with a convex surface facing the object side, and a biconcave lens. It is composed of a convex lens, a cemented lens of a biconcave lens and a biconvex lens, a cemented lens of a biconcave lens and a biconvex lens, and a biconvex lens element L1p.

The second lens unit L2 includes, in order from the object side to the image side, a biconvex lens having an aspheric R2 surface, a cemented lens composed of a convex meniscus lens with a concave surface facing the object side and a biconcave lens, an aperture stop S, and a biconcave lens. It is composed of a cemented double convex lens, a double convex lens, and a convex meniscus lens in which both the R1 and R2 surfaces are aspheric and the concave surface faces the object side.

The third lens unit L3 is composed of a cemented lens of a biconvex lens and a biconcave lens in order from the object side to the image side.

Next, the specification values of the imaging optical system according to Example 4 are shown below.

Numerical example 4
Unit: mm
[Surface data]
Face number rd nd vd
Object plane ∞ (d0)
1 222.3721 1.8000 1.49700 81.61
2 34.3733 1.5298
3 37.6422 3.8385 2.00069 25.46
4 42.1300 14.1236
5 -51.5735 2.0000 1.58144 40.89
6 122.0687 0.1500
7 70.9733 10.7653 1.80610 40.93
8 -61.1105 0.7239
9 -55.6180 1.5000 1.85478 24.80
10 40.8062 15.5122 1.77250 49.62
11 -61.0719 1.5640
12 -54.5483 1.0000 1.63980 34.46
13 76.3102 6.3012 1.77250 49.62
14 -981.9588 0.1500
15 85.3542 6.6457 1.98612 16.48
16 -433.5515 d16
17 52.3247 9.1585 1.77377 47.17
18* -141.5547 0.6202
19 -593.8396 5.9536 1.62041 60.34
20 -55.2310 4.2677 1.63980 34.46
21 47.8028 5.4564
22 (Aperture) ∞ 11.1877
23 -27.4538 1.0000 1.69895 30.05
24 48.7275 4.8646 1.55032 75.50
25 -194.7129 0.2000
26 79.5877 6.5984 1.77250 49.62
27 -39.6483 1.3762
28* -702.3955 3.9400 1.77250 49.50
29* -66.0217 d29
30 248.0233 3.3994 2.00069 25.46
31 -178.8404 1.5000 1.78470 26.29
32 61.7251 19.1129
33 ∞ 2.5000 1.51680 64.20
34∞BF
Image plane ∞

[Aspheric Data]
18 faces 28 faces 29 faces
K 0.0000E+00 0.0000E+00 0.0000E+00
A4 2.5132E-06 -2.8168E-06 5.0736E-06
A6 -1.7612E-09 -1.2444E-08 -1.0663E-08
A8 1.2109E-12 5.7415E-11 5.4065E-11
A10 -5.5710E-16 -1.1822E-13 -1.0223E-13
A12 0.0000E+00 0.0000E+00 0.0000E+00

[Various data]
INF
Focal length 41.35
F number 1.26
Full angle of view 2ω 57.17
Image height Y 21.63
Lens length 157.00

[Variable interval data]
INF shooting distance 1774mm
d0 ∞ 1616.8603
d16 5.5884 4.7640
d29 1.6726 2.4970
BF 1.0000 1.0000

[Lens group data]
Group Starting surface Focal length
L1 1 157.05
L2 17 53.18
L3 30 -136.32
L1f1 -37.66
Lsf 1 53.87

FIG. 21 is a lens configuration diagram of the imaging optical system according to Example 5 at infinity. The imaging optical system of Example 5 comprises, in order from the object side to the image side, a first lens unit L1 having a fixed positive refractive power during focusing, and a second lens unit L1 moving toward the object side during focusing and having positive refractive power. It consists of a lens group L2 and a third lens group L3 having a fixed negative refractive power during focusing.

The first lens unit L1 is composed of, in order from the object side to the image side, a concave meniscus lens whose R1 surface is aspheric and whose convex surface faces the object side, a convex meniscus lens whose convex surface faces the object side, and a biconcave lens. It is composed of a lens component L1f, a biconvex lens, a cemented lens of a biconcave lens and a biconvex lens, a cemented lens of a biconcave lens and a biconvex lens, and a biconvex lens element L1p.

The second lens unit L2 includes, in order from the object side to the image side, a biconvex lens whose R2 surface is aspheric, a cemented lens composed of a biconvex lens and a biconcave lens, an aperture stop S, and a convex meniscus lens with a concave surface facing the object side. It is composed of a cemented double-concave lens, a double-convex lens, and a convex meniscus lens in which both the R1 and R2 surfaces are aspheric and the concave surface faces the object side.

The third lens unit L3 is composed of a cemented lens of a convex meniscus lens with a convex surface facing the object side and a concave meniscus lens with a convex surface facing the object side in order from the object side to the image side.

Next, the specification values of the imaging optical system according to Example 5 are shown below.

Numerical example 5
Unit: mm
[Surface data]
Face number rd nd vd
Object plane ∞ (d0)
1* 139.6509 1.8000 1.55332 71.72
2 31.3080 3.3519
3 40.1764 3.0537 2.00069 25.46
4 42.3174 14.1738
5 -41.6381 2.0000 1.75520 27.53
6 382.0476 0.1500
7 111.9078 9.4662 1.96300 24.11
8 -57.1565 2.0984
9 -44.8777 1.5000 1.69895 30.05
10 47.2106 13.4687 1.77250 49.62
11 -52.4616 1.3809
12 -48.0680 1.0000 1.85478 24.80
13 214.4413 6.4438 1.77250 49.62
14 -86.3080 0.1500
15 99.2021 5.5781 1.98612 16.48
16 -1000.0000 d16
17 49.7362 9.5105 1.77250 49.50
18* -139.0619 0.1500
19 3282.6280 5.8767 1.60311 60.69
20 -60.6030 4.4210 1.69895 30.05
21 44.8147 5.8050
22 (Aperture) ∞ 11.1520
23 -34.6547 3.8628 1.45860 90.20
24 -20.6907 1.0000 1.73800 32.33
25 1885.5546 0.2000
26 90.5393 6.6762 1.78590 43.93
27 -35.7077 1.5067
28* -765.1479 2.6780 1.88202 37.11
29* -75.0558 d29
30 98.7964 3.2313 1.77250 49.62
31 548.6746 1.5000 1.63980 34.46
32 55.0055 20.4705
33 ∞ 2.5000 1.51680 64.20
34∞BF
Image plane ∞

[Aspheric data]
1 side 18 side 28 side 29 side
K 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00
A4 9.0624E-07 2.5314E-06 -4.0336E-06 1.9377E-06
A6 -4.6241E-11 -1.6401E-09 -1.1965E-08 -9.6277E-09
A8 9.1123E-13 9.1729E-13 8.4262E-11 8.4381E-11
A10 -1.3268E-15 -2.8599E-16 -1.8017E-13 -1.6731E-13
A12 9.0487E-19 0.0000E+00 0.0000E+00 0.0000E+00

[Various data]
INF
Focal length 36.19
F number 1.25
Full angle of view 2ω 64.18
Image height Y 21.63
Lens length 157.00

[Variable interval data]
INF shooting distance 1754mm
d0 ∞ 1416.9900
d16 8.3439 7.5156
d29 1.5000 2.3283
BF 1.0000 1.0000

[Lens group data]
Group Starting surface Focal length
L1 1 163.04
L2 17 57.63
L3 30 -262.85
L1f1 -27.86
Lsf 1 53.74

FIG. 26 is a lens configuration diagram of the imaging optical system according to Example 6 at infinity. The imaging optical system of Example 6 comprises, in order from the object side to the image side, a first lens unit L1 having a fixed positive refractive power during focusing, and a second lens unit L1 moving toward the object side during focusing and having positive refractive power. It consists of a lens group L2 and a third lens group L3 having a fixed negative refractive power during focusing.

The first lens unit L1 includes, in order from the object side to the image side, a lens component L1f composed of a concave meniscus lens whose surfaces R1 and R2 are both aspherical surfaces and whose convex surface faces the object side, a biconvex lens, and a biconcave lens. , a biconvex lens, a cemented lens of a biconcave lens and a biconvex lens, a cemented lens of a biconcave lens and a biconvex lens, and a biconvex lens element L1p.

The second lens unit L2 includes, in order from the object side to the image side, a biconvex lens whose R2 surface is an aspherical surface, a cemented lens composed of a convex meniscus lens with a concave surface facing the object side and a biconcave lens, an aperture stop S, and a It consists of a cemented lens composed of a convex meniscus lens with a concave surface and a biconcave lens cemented, a biconvex lens, and a convex meniscus lens with both R1 and R2 surfaces being aspheric and concave to the object side.

The third lens unit L3 is composed of, in order from the object side to the image side, a concave meniscus lens with a convex surface facing the object side and a concave meniscus lens with a concave surface facing the object side.

Next, the specification values of the imaging optical system according to Example 6 are shown below.

Numerical Example 6
Unit: mm
[Surface data]
Face number rd nd vd
Object plane ∞ (d0)
1* 497.7501 3.8955 1.55332 71.72
2* 27.0268 9.5737
3 177.2296 3.5743 2.00069 25.46
4 -1650.6743 8.5003
5 -35.1153 5.0986 1.75520 27.53
6 3650.2461 0.1500
7 91.8368 9.0944 1.96300 24.11
8 -62.8278 1.4724
9 -49.5290 1.5000 1.69895 30.05
10 39.9398 13.0709 1.77250 49.62
11 -54.6718 5.2590
12 -42.4436 1.0000 1.85478 24.80
13 217.0651 5.5505 1.77250 49.62
14 -79.6234 0.1500
15 82.6353 5.2089 1.98612 16.48
16 -1000.0000 d16
17 55.2793 7.4436 1.77250 49.50
18* -104.7961 0.9456
19 -243.8387 4.1503 1.60311 60.69
20 -62.2588 1.0000 1.69895 30.05
21 43.1707 4.7727
22 (Aperture) ∞ 8.8160
23 -668.0246 7.3315 1.45860 90.20
24 -20.2908 2.5051 1.73800 32.33
25 271.3960 0.2000
26 74.4126 7.9008 1.78590 43.93
27 -38.5560 1.9168
28* -957.5724 4.1375 1.88202 37.22
29* -82.1503 d29
30 33.6124 1.0000 1.53172 48.84
31 25.7096 8.1281
32 -80.2924 1.0000 1.49700 81.61
33 -253.4720 12.5001
34 ∞ 2.5000 1.51680 64.20
35∞BF
Image plane ∞

[Aspheric Data]
1 side 2 side 18 side 28 side 29 side
K 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00
A4 2.2184E-06 -1.9337E-06 4.3977E-06 -6.9997E-06 -1.6405E-06
A6 -2.0858E-09 -6.2114E-09 -3.3590E-09 -1.6027E-09 8.1756E-11
A8 3.4379E-12 5.5145E-12 2.7509E-12 4.1894E-11 4.5542E-11
A10 -3.1012E-15 -1.4533E-14 -2.0239E-15 -7.8139E-14 -7.1688E-14
A12 1.5381E-18 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00

[Various data]
INF
Focal length 28.90
F number 1.25
Full angle of view 2ω 76.94
Image height Y 21.63
Lens length 157.00

[Variable interval data]
INF shooting distance 1281mm
d0 ∞ 1124.3538
d16 5.1534 4.5949
d29 1.5000 2.0585
BF 1.0000 1.0000

[Lens group data]
Group Starting surface Focal length
L1 1 101.14
L2 17 44.54
L3 30 -111.36
L1f1 -24.83
Lsf 1 59.09

[Conditional Expression Corresponding Values] below shows a list of corresponding values of each embodiment corresponding to each conditional expression.

[Value corresponding to conditional expression]
Conditional expression 1 Conditional expression 2 Conditional expression 3 Conditional expression 4
Example Y/Bf |ΣAci| νdL1p ΔPgfL1p
1 0.88 0.0014 16.48 0.0470
2 0.95 0.0014 16.48 0.0470
3 0.82 0.0011 20.88 0.0283
4 0.96 0.0012 16.48 0.0470
5 0.90 0.0011 16.48 0.0470
6 1.35 0.0011 16.48 0.0470

Conditional expression 5 Conditional expression 6 Conditional expression 7 Conditional expression 8
Example f1f/f fsf/f f2/f β1b
1 -1.13 1.4 1.3 0.26
2 -1.26 1.5 1.3 0.23
3 -2.52 1.6 1.4 0.12
4 -0.91 1.3 1.3 0.26
5 -0.77 1.5 1.6 0.22
6 -0.86 2.0 1.5 0.29

As is clear from the various aberration diagrams in each example, the present invention provides an optimal imaging optical system for mirrorless cameras by satisfactorily correcting longitudinal chromatic aberration, which has been a problem with conventional imaging optical systems. can do.

L1 First lens group L2 Second lens group L3 Third lens group L1f Lens component L1f
Lsf lens group Lsf
L1p lens element L1p
S open aperture LPF low pass filter I image plane

Claims (5)

From the object side to the image side,
a first lens group L1 having positive refractive power;
a second lens group L2 having positive refractive power;
a third lens group L3 having negative refractive power;
consists of
The first lens unit L1 has at least one cemented lens, has a negative lens element closest to the object side, and has a positive lens element having a convex surface facing the object side so as to be adjacent to the image side of the negative lens element. arranged,
The second lens group L2 includes an aperture stop S,
During focusing, the second lens group L2 moves toward the object side, and the first lens group L1 and the third lens group L3 are fixed with respect to the image plane,
In the entire lens system, all lens element groups arranged on the object side of the aperture stop S are referred to as a lens group Lsf, and the lens group Lsf has a positive refractive power,
An imaging optical system characterized by satisfying the following conditional expression.
Y/Bf > 0.70 (1)

1.0 < fsf/f < 2.7 (6)
however,
Y is the maximum image height,
Bf is the distance from the vertex of the surface closest to the image side of the third lens unit L3 to the image plane ;
fsf is the focal length of the lens group Lsf when focusing on infinity;
f is the focal length of the entire lens system when focusing at infinity ,
Aci is represented by the following formula.
Aci = φcpi/νdcpi + φcmi/νdcmi
however,
φcpi is the refractive power of the positive lens element of the i-th cemented lens from the object side included in the first lens unit L1;
νdcpi is the Abbe number of the positive lens element of the i-th cemented lens from the object side included in the first lens unit L1;
φcmi is the refractive power of the negative lens element of the i-th cemented lens from the object side included in the first lens group L1;
νdcmi is the Abbe number of the negative lens element of the i-th cemented lens from the object side included in the first lens unit L1. 2. An imaging optical system according to claim 1, wherein the positive lens element L1p located closest to the image side in said first lens unit L1 satisfies the following conditional expression.
νdL1p < 27 (3)
0.0220 < ΔPgfL1p (4)
however,
ΔPgfL1p is the anomalous dispersion of the positive lens element L1p and is expressed by the following equation.
ΔPgfL1p = PgfL1p + 0.0018 x vdL1p - 0.64833
however,
νdL1p is the Abbe number νd of the positive lens element L1p;
PgfL1p is the partial dispersion ratio Pgf for the g-line and the F-line of the positive lens element L1p. A lens component L1f is defined from the most object-side surface of the first lens unit L1 to the image-side surface of the negative lens element having a concave surface facing the image side, and the lens component L1f has negative refractive power. 3. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
-3.53 < f1f/f < -0.60 (5)
however,
f1f is the focal length of the lens component L1f;
f is the focal length of the entire lens system when focusing on infinity. 4. An imaging optical system according to claim 1 , wherein the following conditional expression is satisfied.
1.0 < f2/f < 2.1 (7)
however,
f2 is the focal length of the second lens group L2;
f is the focal length of the entire lens system when focusing on infinity. 5. An imaging optical system according to claim 1 , wherein the following conditional expression is satisfied.
β1b < 0.37 (8)
however,
β1b is the lateral magnification of the lens element group located closer to the image side than the first lens group L1 when focusing on infinity.

Images