JP5391565B2 - Optical system, optical system focusing method, and imaging apparatus having these - Google Patents

Description

  The present invention relates to an optical system, a focusing method of the optical system, and an imaging apparatus having these.

Conventionally, an inner focus type optical system suitable for a photographic camera, an electronic still camera, a video camera, and the like has been proposed (see, for example, Patent Documents 1 and 2).
Japanese Patent Laid-Open No. 7-199066 JP-A-3-200909

  The conventional inner focus optical system has not been optimized for the lens glass used in the focusing group, so it has high focusing performance while maintaining good optical performance from infinity to close range. It was difficult to achieve.

  The present invention has been made in view of the above problems, an optical system having good optical performance and focusing performance from an infinite distance to a close distance, a focusing method of the optical system, and an imaging apparatus having these. The purpose is to provide.

In order to solve the above problems, the present invention provides:
In order from the object side, a first lens group having a positive refractive power and a second lens group having a positive refractive power,
In a state where the first lens group is fixed in the optical axis direction, the second lens group is moved in the optical axis direction, the distance between adjacent lens groups is changed, and the object is focused.
An optical system is provided in which at least two negative lenses of the second lens group and at least three positive lenses of the second lens group satisfy the following conditions.
νdA <50
0.00913 × νdA + ndA−2.16043 <0
ndA <1.66000
1.64000 <ndB <1.86000
0 <0.00667 × νdB + ndB−1.88333
Where νdA is the Abbe number with respect to the d-line (wavelength λ = 587.6 nm) of the medium of the negative lens, ndA is the refractive index with respect to the d-line (wavelength λ = 587.6 nm) of the medium of the negative lens, and νdB is the positive The Abbe number for the d-line (wavelength λ = 587.6 nm) of the lens medium, and ndB is the refractive index for the d-line (wavelength λ = 587.6 nm) of the medium of the positive lens .

The present invention also provides:
In order from the object side, a first lens group having a positive refractive power and a second lens group having a positive refractive power,
At least two negative lenses of the second lens group and at least three positive lenses of the second lens group satisfy the following conditions:
The second lens group is moved in the optical axis direction while the first lens group is fixed in the optical axis direction, and an object is focused by changing the interval between adjacent lens groups. An optical system focusing method is provided.
νdA <50
0.00913 × νdA + ndA−2.16043 <0
ndA <1.66000
1.64000 <ndB <1.86000
0 <0.00667 × νdB + ndB−1.88333
Where νdA is the Abbe number with respect to the d-line (wavelength λ = 587.6 nm) of the medium of the negative lens, ndA is the refractive index with respect to the d-line (wavelength λ = 587.6 nm) of the medium of the negative lens, and νdB is the positive The Abbe number for the d-line (wavelength λ = 587.6 nm) of the lens medium, and ndB is the refractive index for the d-line (wavelength λ = 587.6 nm) of the medium of the positive lens.

  The present invention also provides an imaging apparatus having the optical system.

  In addition, the present invention provides an imaging apparatus characterized by including the focusing method of the optical system.

  According to the present invention, it is possible to provide an optical system having good optical performance and focusing performance from an infinite distance to a close distance, a focusing method for the optical system, and an imaging apparatus having these.

  Hereinafter, an optical system according to an embodiment of the present invention will be described.

The optical system according to the embodiment includes, in order from the object side, a first lens group having a positive refractive power and a second lens group having a positive refractive power, and focuses the object on the second lens. This is performed by moving the group in the optical axis direction, and at least two negative lenses of the second lens group satisfy the following conditional expressions (1), (2), and (3).
(1) νdA <50
(2) 0.00913 × νdA + ndA −2.16043 <0
(3) ndA <1.66000
Where νdA is the Abbe number with respect to the d-line (wavelength λ = 587.6 nm) of the negative lens medium of the second lens group, and ndA is the d-line (wavelength λ = 587.6 nm) of the negative lens medium of the second lens group. Is the refractive index.

  Conditional expression (1) defines the Abbe number of the medium of the negative lens of the second lens group. By satisfying conditional expression (1), the off-axis chromatic aberration can be corrected well, and good optical performance can be achieved.

  If the upper limit of conditional expression (1) is exceeded, the Abbe number of the medium of the negative lens in the second lens group becomes too large, and the off-axis chromatic aberration of the optical system cannot be corrected well. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (1) to 46.

  Conditional expression (2) defines the range of the refractive index and Abbe number of the medium of the negative lens of the second lens group. By satisfying conditional expression (2), the off-axis chromatic aberration can be corrected well, and good optical performance can be achieved. Further, the second lens group can be reduced in weight, and high focusing performance can be achieved.

  If the upper limit of conditional expression (2) is exceeded, the Abbe number of the medium of the negative lens of the second lens group becomes too large, and axial chromatic aberration of the optical system cannot be corrected well. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (2) to −0.01500.

  Conditional expression (3) defines the refractive index of the medium of the negative lens of the second lens group. Satisfying conditional expression (3) makes it possible to maintain good optical performance from an infinite distance to a close distance. Further, the second lens group can be reduced in weight, and high focusing performance can be achieved.

  If the upper limit of conditional expression (3) is exceeded, the refractive power of the medium of the negative lens in the second lens group becomes weak, so the positive refractive power becomes relatively strong, and the field curvature aberration at the time of focusing becomes good. Cannot be corrected. In addition, the refractive index of the medium of the negative lens increases and the specific gravity of the lens increases too much, making it difficult to achieve high focusing performance. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (3) to 1.65000.

In the optical system according to the embodiment, it is desirable that the positive lens of the second lens group satisfies the following conditional expressions (4) and (5).
(4) 1.64000 <ndB <1.86000
(5) 0 <0.00667 × νdB + ndB − 1.88333
Where ndB is the refractive index of the positive lens medium d-line (wavelength λ = 587.6 nm) of the second lens group, and νdB is the positive lens medium d-line (wavelength λ = 587.6 nm) of the second lens group. Is the Abbe number.

  Conditional expression (4) defines the refractive index of the medium of the positive lens in the second lens group. Satisfying conditional expression (4) makes it possible to achieve good optical performance from an infinite distance to a close distance.

  If the upper limit of conditional expression (4) is exceeded, the refractive power of the second lens group becomes too strong, so that axial chromatic aberration cannot be corrected well. In addition, the refractive index of the medium of the positive lens increases and the specific gravity of the lens increases too much, making it difficult to achieve high focusing performance. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (4) to 1.84000.

  If the lower limit value of conditional expression (4) is not reached, the refractive power of the second lens group becomes too weak, and spherical aberration cannot be corrected well. In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (4) to 1.65000.

  Conditional expression (5) defines the range of the refractive index and Abbe number of the medium of the positive lens in the second lens group. Satisfying conditional expression (5) makes it possible to achieve good optical performance from an infinite distance to a close distance.

  If the lower limit value of conditional expression (5) is not reached, the Abbe number of the medium of the positive lens in the second lens group becomes small and off-axis chromatic aberration cannot be corrected well. In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (5) to 0.01000.

  In addition, the optical system according to the embodiment desirably has an aperture stop between the first lens group and the second lens group. With such a configuration, off-axis chromatic aberration can be corrected satisfactorily.

  In the optical system according to the present embodiment, it is desirable that the first lens group is fixed in the optical axis direction during focusing. With such a configuration, downsizing can be achieved.

  In the optical system according to the present embodiment, it is desirable that the second lens group has a cemented lens. With such a configuration, axial chromatic aberration and lateral chromatic aberration can be favorably corrected.

  In the optical system according to this embodiment, each lens surface of the optical system is preferably a spherical surface or a flat surface. With such a configuration, lens processing becomes easy, and deterioration of optical performance due to processing errors can be prevented. In addition, even when the image plane is deviated, it is possible to reduce the degradation of the drawing performance.

  In the optical system according to the present embodiment, it is desirable that the second lens group is lighter than the first lens group. With such a configuration, it is possible to reduce the load at the time of focusing with the second lens group than when focusing with the first lens group. It is also suitable for driving a motor such as an ultrasonic motor.

The focusing method of the optical system according to the embodiment includes, in order from the object side, a first lens group having a positive refractive power and a second lens group having a positive refractive power. At least two negative lenses satisfy the following conditions (1), (2), and (3), and the second lens group is moved in the optical axis direction to focus on the object.
(1) νdA <50
(2) 0.00913 × νdA + ndA −2.16043 <0
(3) ndA <1.66000
Where νdA is the Abbe number for the d-line (wavelength λ = 587.6 nm) of the negative lens medium, and ndA is the refractive index for the d-line (wavelength λ = 587.6 nm) of the negative lens medium.

  With such a configuration, an inner focus optical system having high imaging performance can be achieved.

(Example)
Hereinafter, each example according to the present embodiment will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a cross-sectional view of the lens configuration of the optical system according to Example 1 in an infinitely focused state.

  The optical system according to the first example includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a positive refractive power. ing.

  An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 includes, in order from the object side, a positive meniscus lens L11 having a convex surface facing the object side, a positive meniscus lens L12 having a convex surface facing the object side, and a negative meniscus lens L13 having a convex surface facing the object side. Consists of.

  The second lens group G2 includes, in order from the object side, a positive meniscus lens L21 having a convex surface directed toward the object side, a biconcave negative lens L22, a biconcave negative lens L23, and a biconvex positive lens L24. It consists of a cemented lens and a biconvex positive lens L25.

  The third lens group G3 is composed of a positive meniscus lens L31 having a convex surface directed toward the object side.

  Focusing from an object at infinity to an object at a short distance is performed by moving the second lens group G2 to the object side along the optical axis.

  Table 1 below lists specifications of the optical system according to the first example.

  In (surface data) in the table, the surface number is the surface number from the object side, r is the radius of curvature, d is the surface spacing, nd is the refractive index at the d-line (wavelength λ = 587.6 nm), and νd is the d-line. The Abbe number at (wavelength λ = 587.6 nm), the object plane represents the object plane, (variable) represents the variable plane spacing in focus, (diaphragm) represents the aperture stop S, and the image plane represents the image plane I. Note that the description of the refractive index nd of air = 1.000 is omitted. Further, “∞” in the radius of curvature r column indicates a plane.

  In (various data), f is the focal length, f1 is the focal length of the first lens group, f2 is the focal length of the second lens group, f3 is the focal length of the third lens group, FNO is the F number, and 2ω is the angle of view. (Unit: “°”), Y represents the image height, TL represents the total lens length, and Bf represents the back focus in the infinitely focused state.

  In (variable distance data), f is the focal length, β is the magnification, d0 is the distance between the object surface and the most object side lens surface (first surface), di is the variable surface distance value at surface number i, and Bf is Represents back focus.

  (Conditional expression corresponding value) indicates the corresponding value of each conditional expression.

  In all the following specification values, “mm” is generally used as the focal length f, radius of curvature r, surface interval d and other lengths, etc. unless otherwise specified, but the optical system is proportional. Even if it is enlarged or proportionally reduced, the same optical performance can be obtained. Further, the unit is not limited to “mm”, and other appropriate units may be used. Further, the explanation of these symbols is the same in the other embodiments, and the explanation is omitted.

(Table 1)
(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 48.8417 11.20 1.60300 65.47
2 448.8233 0.10
3 44.0159 7.60 1.80400 46.58
4 67.5908 4.64
5 204.7044 2.30 1.67270 32.11
6 28.5061 10.70
7 (Aperture) ∞ (Variable)
8 52.1712 3.60 1.77250 49.61
9 14443.5010 3.30
10 -49.7521 1.50 1.58144 40.75
11 48.8814 6.00
12 -43.0322 1.40 1.58144 40.75
13 62.8163 7.30 1.77250 49.61
14 -41.0534 0.10
15 100.8291 3.40 1.69680 55.52
16 -187.3176 (variable)
17 329.9899 2.00 1.77250 49.61
18 780.7371 Bf
Image plane ∞ ∞

(Various data)
f = 86.0
f1 = 219.1428
f2 = 71.9802
f3 = 715.7011
FNO = 1.44
2ω = 28.39
Y = 21.60
TL = 120.98
Bf = 38.12

(Variable interval data)
Infinite focus state Short range focus state
f or β 85.1452 -0.11598
d0 ∞ 731.5216
d7 14.91346 2.53213
d16 3.60003 15.98136
Bf 38.12 38.12

(Values for conditional expressions)
Lens code L22 L23
(1) νdA = 40.75, 40.75
(2) 0.00913 × νdA + ndA −2.16043 = -0.20694, -0.20694
(3) ndA = 1.58144, 1.58144
Lens code L21 L24 L25
(4) ndB = 1.77250, 1.77250, 1.69680
(5) 0.00667 × νdB + ndB − 1.88333 = 0.22007, 0.22007, 0.18379

  FIG. 2 shows various aberration diagrams of the optical system according to the first example. (A) shows various aberration diagrams when focusing on infinity, and (b) shows various aberration diagrams when focusing on short distance (β = −0.11598). Show. The image height is Y = 21.60.

  In each aberration diagram, FNO is an F number, A is a half angle of view (unit: “°”), NA is a numerical aperture, and H0 is an object height. D represents the d-line (wavelength λ = 587.6 nm), and g represents the g-line (wavelength λ = 435.8 nm). In the spherical aberration diagram and the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. In the following examples, the same symbols are used, and the following description is omitted.

  It can be seen from the respective aberration diagrams that the optical system according to the first example has excellent imaging performance with various aberrations corrected well.

(Second embodiment)
FIG. 3 is a cross-sectional view of the lens configuration of the optical system according to Example 2 in an infinitely focused state.

  The optical system according to the second example includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a positive refractive power. ing.

  An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 includes, in order from the object side, a positive meniscus lens L11 having a convex surface facing the object side, a positive meniscus lens L12 having a convex surface facing the object side, and a negative meniscus lens L13 having a convex surface facing the object side. Consists of.

  The second lens group G2 includes, in order from the object side, a positive meniscus lens L21 having a convex surface directed toward the object side, a biconcave negative lens L22, a biconcave negative lens L23, and a biconvex positive lens L24. It consists of a cemented lens and a biconvex positive lens L25.

  The third lens group G3 is composed of a positive meniscus lens L31 having a convex surface directed toward the object side.

  Focusing from an object at infinity to an object at a short distance is performed by moving the second lens group G2 to the object side along the optical axis.

  Table 2 below lists specifications of the optical system according to the second example.

(Table 2)
(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 49.6722 11.20 1.60300 65.47
2 357.8769 0.10
3 43.3361 7.60 1.80400 46.58
4 66.3322 4.42
5 161.8658 2.30 1.67270 32.11
6 28.5061 10.70
7 (Aperture) ∞ (Variable)
8 51.3573 3.60 1.80400 46.58
9 2180.315 3.30
10 -52.2845 1.50 1.60342 38.00
11 48.3972 6.00
12 -43.1588 1.40 1.60342 38.00
13 62.8163 7.30 1.80400 46.58
14 -41.997 0.10
15 105.218 3.40 1.69680 55.52
16 -187.318 (variable)
17 306.5836 2.00 1.77250 49.61
18 819.5894 Bf
Image plane ∞ ∞

(Various data)
f = 85.0
f1 = 218.15933
f2 = 73.20767
f3 = 616.32650
FNO = 1.44
2ω = 28.75
Y = 21.60
TL = 120.76
Bf = 38.12

(Variable interval data)
Infinite focus state Short range focus state
f or β 84.9999 -0.11475
d0 ∞ 731.5216
d7 14.91346 2.53213
d16 2.29346 14.67479
Bf 38.12 38.12

(Values for conditional expressions)
Lens code L22 L23
(1) νdA = 38.00, 38.00
(2) 0.00913 × νdA + ndA −2.16043 = -0.21007, -0.21007
(3) ndA = 1.60342, 1.60342
Lens code L21 L24 L25
(4) ndB = 1.80400, 1.80400, 1.69680
(5) 0.00667 × νdB + ndB − 1.88333 = 0.23136, 0.23136, 0.18379

  4A and 4B show various aberration diagrams of the optical system according to the second example. FIG. 4A shows various aberration diagrams when focusing on infinity, and FIG. 4B shows various aberration diagrams when focusing on short distance (β = −0.11475). Show. The image height is Y = 21.60.

  It can be seen from the respective aberration diagrams that the optical system according to the second example has excellent imaging performance with various aberrations corrected well.

(Third embodiment)
FIG. 5 is a cross-sectional view of the lens configuration of the optical system according to Example 3 in an infinitely focused state.

  The optical system according to the third example includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a positive refractive power. ing.

  An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 includes, in order from the object side, a positive meniscus lens L11 having a convex surface facing the object side, a positive meniscus lens L12 having a convex surface facing the object side, and a negative meniscus lens L13 having a convex surface facing the object side. Consists of.

  The second lens group G2, in order from the object side, includes a positive meniscus lens L21 having a convex surface directed toward the object side, a biconcave negative lens L22, a negative meniscus lens L23 having a concave surface directed toward the object side, and the image plane I side. A cemented lens with a positive meniscus lens L24 having a convex surface facing the surface, and a biconvex positive lens L25.

  The third lens group G3 is composed of a positive meniscus lens L31 having a convex surface directed toward the object side.

  Focusing from an object at infinity to an object at a short distance is performed by moving the second lens group G2 to the object side along the optical axis.

  Table 3 below lists specifications of the optical system according to the third example.

(Table 3)
(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 48.8417 11.20 1.60300 65.47
2 448.8233 0.10
3 44.0159 7.60 1.80400 46.58
4 67.5908 4.64
5 204.7044 2.30 1.67270 32.11
6 28.5061 10.70
7 (Aperture) ∞ (Variable)
8 44.3052 4.20 1.83481 42.72
9 701.4073 2.50
10 -84.1675 1.50 1.62004 36.30
11 40.6158 7.00
12 -34.0106 1.50 1.67270 32.11
13 -156.805 7.60 1.83481 42.72
14 -43.4693 0.10
15 97.7847 3.60 1.69680 55.52
16 -81.5801 (variable)
17 329.9899 2.00 1.77250 49.61
18 780.7371 Bf
Image plane ∞ ∞

(Various data)
f = 86.0
f1 = 219.14277
f2 = 71.98016
f3 = 715.70110
FNO = 1.44
2ω = 28.38
Y = 21.60
TL = 120.87
Bf = 38.12

(Variable interval data)
Infinite focus state Short range focus state
f or β 86.0011 -0.11579
d0 ∞ 731.5216
d7 13.60145 1.22012
d16 2.09728 14.47861
Bf 38.12 38.12

(Values for conditional expressions)
Lens code L22 L23
(1) νdA = 36.30, 33.79
(2) 0.00913 × νdA + ndA −2.16043 = -0.20897, -0.20424
(3) ndA = 1.62004, 1.64769
Lens code L21 L24 L25
(4) ndB = 1.83481, 1.83481, 1.69680
(5) 0.00667 × νdB + ndB − 1.88333 = 0.23642, 0.23642, 0.18379

  6A and 6B are graphs showing various aberrations of the optical system according to the third example. FIG. 6A is a diagram showing various aberrations when focusing on infinity, and FIG. 6B is a diagram showing various aberrations when focusing on short distance (β = −0.11579). Show. The image height is Y = 21.60.

  It can be seen from the respective aberration diagrams that the optical system according to the third example has excellent imaging performance with various aberrations corrected well.

(Fourth embodiment)
FIG. 7 is a sectional view of the lens configuration of the optical system according to the fourth example in the infinitely focused state.

  The optical system according to the fourth example includes, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power.

  An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 includes, in order from the object side, a positive meniscus lens L11 having a convex surface facing the object side, a positive meniscus lens L12 having a convex surface facing the object side, and a negative meniscus lens L13 having a convex surface facing the object side. Consists of.

  The second lens group G2 includes, in order from the object side, a biconvex positive lens L21, a biconcave negative lens L22, a cemented lens of a biconcave negative lens L23, and a biconvex positive lens L24. And a positive biconvex lens L25 and a negative meniscus lens L26 having a concave surface facing the object side.

  Focusing from an object at infinity to an object at a short distance is performed by moving the second lens group G2 to the object side along the optical axis.

  Table 4 below lists specifications of the optical system according to the fourth example.

(Table 4)
(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 47.1005 11.20 1.60300 65.47
2 389.6297 0.10
3 43.2050 7.60 1.80400 46.58
4 64.2685 4.23
5 193.6555 2.30 1.67270 32.11
6 28.1335 10.70
7 (Aperture) ∞ (Variable)
8 51.1641 3.60 1.77250 49.61
9 -1655.5923 3.30
10 -46.1050 1.50 1.58144 40.75
11 49.8060 6.00
12 -44.6366 1.40 1.58144 40.75
13 62.8163 7.30 1.77250 49.61
14 -38.9308 0.10
15 93.9046 3.40 1.69680 55.52
16 -187.3176 2.29
17 -57.0412 2.00 1.77250 49.61
18 -59.6536 (variable)
Image plane ∞ ∞

(Various data)
f = 86.0
f1 = 219.14277
f2 = 65.48955
FNO = 1.45
2ω = 28.40
Y = 21.60
TL = 120.20

(Variable interval data)
Infinite focus state Short range focus state
f or β 86.05184 -0.11454
d0 ∞ 731.5216
d7 15.10219 4.28681
d18 (Bf) 38.08 48.89

(Values for conditional expressions)
Lens code L22 L23
(1) νdA = 40.75, 40.75
(2) 0.00913 × νdA + ndA −2.16043 = -0.20694, -0.220694
(3) ndA = 1.58144, 1.58144
Lens code L21 L24 L25
(4) ndB = 1.77250, 1.77250, 1.69680
(5) 0.00667 × νdB + ndB − 1.88333 = 0.22007, 0.22007, 0.18379

  8A and 8B show various aberration diagrams of the optical system according to the fourth example. FIG. 8A shows various aberration diagrams when focusing on infinity, and FIG. 8B shows various aberration diagrams when focusing on short distance (β = −0.11454). Show. The image height is Y = 21.60.

  It can be seen from the respective aberration diagrams that the optical system according to the fourth example has excellent imaging performance with various aberrations corrected well.

(Example 5)
FIG. 9 is a cross-sectional view of the lens configuration of the optical system according to Example 5 in an infinitely focused state.

  The optical system according to Example 5 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3.

  An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 includes, in order from the object side, a positive meniscus lens L11 having a convex surface facing the object side, a positive meniscus lens L12 having a convex surface facing the object side, and a negative meniscus lens L13 having a convex surface facing the object side. Consists of.

  The second lens group G2 includes, in order from the object side, a biconvex positive lens L21, a biconcave negative lens L22, a cemented lens of a biconcave negative lens L23, and a biconvex positive lens L24. And a positive biconvex lens L25.

  The third lens group G3 is composed of a positive meniscus lens L31 having a convex surface directed toward the object side.

  Focusing from an object at infinity to an object at a short distance is performed by moving the second lens group G2 to the object side along the optical axis.

  Table 5 below lists specifications of the optical system according to the fifth example.

(Table 5)
(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 49.1219 11.20 1.60300 65.47
2 383.8573 0.10
3 43.0298 7.60 1.80400 46.58
4 65.1701 4.19
5 168.3702 2.30 1.67270 32.11
6 28.3841 10.70
7 (Aperture) ∞ (Variable)
8 51.6258 3.60 1.79500 45.30
9 -11753.4240 3.30
10 -52.1126 1.50 1.60342 38.00
11 49.5651 6.00
12 -41.8483 1.40 1.64769 33.79
13 62.8163 7.30 1.80610 40.94
14 -40.3613 0.10
15 92.9455 3.40 1.65160 58.54
16 -164.6403 (variable)
17 306.5836 2.00 1.77250 49.61
18 819.5894 Bf
Image plane ∞ ∞

(Various data)
f = 85.0
f1 = 218.15933
f2 = 73.20767
f3 = 616.32350
FNO = 1.45
2ω = 28.76
Y = 21.60
TL = 120.69
Bf = 38.12

(Variable interval data)
Infinite focus state Short range focus state
f or β 85.0000 -0.11475
d0 ∞ 731.5216
d7 14.76993 2.38860
d16 2.60043 14.98176
Bf 38.12 38.12

(Values for conditional expressions)
Lens code L22 L23
(1) νdA = 38.00, 33.79
(2) 0.00913 × νdA + ndA − 2.16043 = -0.21007, -0.20424
(3) ndA = 1.60342, 1.64769
Lens code L21 L24 L25
(4) ndB = 1.79500, 1.80610, 1.65160
(5) 0.00667 × νdB + ndB − 1.88333 = 0.21382, 0.19584, 0.15873

  FIG. 10 shows various aberration diagrams of the optical system according to Example 5. (a) shows various aberration diagrams when focusing on infinity, and (b) shows various aberration diagrams when focusing on short distance (β = −0.11475). Show. The image height is Y = 21.60.

  It can be seen from the respective aberration diagrams that the optical system according to the fifth example has excellent imaging performance with various aberrations corrected well.

  As described above, according to the embodiment, the second lens group, which is a light focusing group with a large aperture ratio, can be focused quickly, has high focusing accuracy, and has spherical aberration and image quality. It is possible to provide an optical system having good optical performance in which fluctuations in surface curvature are sufficiently corrected.

  Next, a camera equipped with the optical system according to the embodiment will be described. Although the case where the inner focus type optical system according to the first example is mounted will be described, the same applies to other examples.

  FIG. 11 is a diagram illustrating a configuration of a camera including the optical system according to the first example.

  In FIG. 11, a camera 1 is a digital single-lens reflex camera provided with the optical system according to the first embodiment as a photographing lens 2. In the camera 1, light from an object (subject) (not shown) is collected by the photographic lens 2 of the optical system according to the first embodiment and is imaged on the focusing screen 4 via the quick return mirror 3. The light imaged on the focusing screen 4 is reflected in the pentaprism 5 a plurality of times and guided to the eyepiece lens 6. Thus, the photographer can observe the subject image as an erect image through the eyepiece 6.

  When the release button (not shown) is pressed by the photographer, the quick return mirror 3 is retracted out of the optical path, and light from the subject (not shown) reaches the image sensor 7. As a result, light from the subject is picked up by the image sensor 7 and recorded as a subject image in a memory (not shown). In this way, the photographer can shoot the subject with the camera 1.

  By mounting the inner focus type optical system according to the first embodiment as the photographing lens 2 on the camera 1, a camera having high imaging performance can be realized.

  The contents described below can be appropriately adopted as long as the optical performance is not impaired.

  In the embodiment, a two-group or three-group configuration is shown, but the present invention can also be applied to other group configurations such as a 4-group and 5-group.

  Alternatively, a single lens group, a plurality of lens groups, or a partial lens group may be moved in the optical axis direction to be a focusing lens group that performs focusing from an object at infinity to a near object.

  The focusing lens group can also be applied to autofocus, and is also suitable for driving a motor for autofocus (such as an ultrasonic motor). In particular, the second lens group is preferably a focusing lens group.

  Alternatively, the lens group or the partial lens group may be vibrated in a direction perpendicular to the optical axis so as to correct an image blur caused by camera shake. In particular, it is preferable that at least a part of the second lens group or the third lens group is an anti-vibration lens group.

  The lens surface may be an aspherical surface. The aspherical surface may be any of an aspherical surface by grinding, a glass mold aspherical surface in which a glass is formed into an aspherical shape, or a composite aspherical surface in which a resin is formed in an aspherical shape on the glass surface.

  The aperture stop is preferably disposed between the first lens group and the second lens group. However, the role of the aperture stop may be substituted by a lens frame without providing a member as the aperture stop.

  If each lens surface is provided with an antireflection film having a high transmittance in a wide wavelength range, flare and ghost can be reduced and high contrast and high optical performance can be achieved.

  In addition, the first lens group, the second lens group, and the third lens group may be used as a zoom lens with variable intervals.

  In addition, in order to explain the present invention in an easy-to-understand manner, the configuration requirements of the embodiment have been described, but it goes without saying that the present invention is not limited to this.

It is sectional drawing in the infinite point focusing state of the lens structure of the optical system which concerns on 1st Example. The aberration diagrams of the optical system according to Example 1 are shown. (A) shows various aberration diagrams when focusing on infinity, and (b) shows various aberration diagrams when focusing on short distance (β = −0.11598). It is sectional drawing in the infinite point focusing state of the lens structure of the optical system which concerns on 2nd Example. The aberration diagrams of the optical system according to Example 2 are shown. (A) shows various aberration diagrams when focusing on infinity, and (b) shows various aberration diagrams when focusing on short distance (β = −0.11475). It is sectional drawing which shows the structure in the infinite point focusing state of the optical system which concerns on 3rd Example. The aberration diagrams of the optical system according to Example 3 are shown. (A) shows various aberration diagrams when focusing on infinity, and (b) shows various aberration diagrams when focusing on short distance (β = −0.11579). It is sectional drawing which shows the structure in the infinite point focusing state of the optical system which concerns on 4th Example. The aberration diagrams of the optical system according to Example 4 are shown. (A) shows various aberration diagrams at the time of focusing on infinity, and (b) shows the various aberration diagrams at the time of focusing at short distance (β = −0.11454). It is sectional drawing which shows the structure in the infinite point focusing state of the optical system which concerns on 5th Example. The aberration diagrams of the optical system according to Example 5 are shown. (A) shows various aberration diagrams when focusing on infinity, and (b) shows various aberration diagrams when focusing on short distance (β = −0.11475). It is a figure which shows the structure of the camera provided with the inner-focus-type optical system which concerns on 1st Example.

Explanation of symbols

G1 1st lens group G2 2nd lens group G3 3rd lens group S Aperture stop I Image plane L11 Positive meniscus lens L12 Positive meniscus lens L13 Negative meniscus lens L21 Positive lens L22 Negative lens L23 Negative lens L24 Positive lens L25 Positive lens L26 Negative lens Lens L31 Positive lens 1 Camera 2 Shooting lens 3 Quick return mirror 4 Focus plate 5 Penta prism 6 Eyepiece 7 Imaging element

Claims (8)

In order from the object side, a first lens group having a positive refractive power and a second lens group having a positive refractive power,
In a state where the first lens group is fixed in the optical axis direction, the second lens group is moved in the optical axis direction, the distance between adjacent lens groups is changed, and the object is focused.
An optical system, wherein at least two negative lenses of the second lens group and at least three positive lenses of the second lens group satisfy the following conditions.
νdA <50
0.00913 × νdA + ndA−2.16043 <0
ndA <1.66000
1.64000 <ndB <1.86000
0 <0.00667 × νdB + ndB−1.88333
However,
νdA: Abbe number with respect to d-line (wavelength λ = 587.6 nm) of the medium of the negative lens
ndA: Refractive index for the negative lens medium d-line (wavelength λ = 587.6 nm) ν dB: Abbe number for the positive lens medium d-line (wavelength λ = 587.6 nm)
ndB: refractive index with respect to d-line (wavelength λ = 587.6 nm) of the medium of the positive lens   The optical system according to claim 1, wherein the second lens group includes a cemented lens. Optical system according to claim 1 or 2, characterized in that there is an aperture stop between the second lens group and the third lens group. Wherein each lens surface of the optical system according to any one of claims 1 to 3, characterized in that the spherical or planar. The second lens group, an optical system according to claim 1, any one of 4, characterized in that lighter than the first lens group. Imaging apparatus characterized by having an optical system according to any one of claims 1 to 5. In order from the object side, a first lens group having a positive refractive power and a second lens group having a positive refractive power,
At least two negative lenses of the second lens group and at least three positive lenses of the second lens group satisfy the following conditions:
The second lens group is moved in the optical axis direction while the first lens group is fixed in the optical axis direction, and an object is focused by changing the interval between adjacent lens groups. Optical system focusing method.
νdA <50
0.00913 × νdA + ndA−2.16043 <0
ndA <1.66000
1.64000 <ndB <1.86000
0 <0.00667 × νdB + ndB−1.88333
However,
νdA: Abbe number with respect to d-line (wavelength λ = 587.6 nm) of the medium of the negative lens
ndA: Refractive index for the negative lens medium d-line (wavelength λ = 587.6 nm) ν dB: Abbe number for the positive lens medium d-line (wavelength λ = 587.6 nm)
ndB: refractive index with respect to d-line (wavelength λ = 587.6 nm) of the medium of the positive lens An imaging apparatus comprising the optical system focusing method according to claim 7 .

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