JP2009116132A - Wide angle lens system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve satisfactory optical performances from infinite distance to near distance with a long back focus with F number of about 4 and a half field angle of about 45° in a retro-focusing wide angle lens system including, in order from an object side, a first lens group having negative refractive power, a diaphragm, and a second lens group having positive refractive power. <P>SOLUTION: In the wide angle lens system, the first lens group includes a negative meniscus lens with the convex surface turned to the object side, a flat convex lens or double convex lens with the convex surface turned to the object side, two negative meniscus lenses with the convex surface turned to the object side, a positive lens, and a cemented lens composed of a positive lens and a negative lens, which are located in order from the object side. The second lens group includes a cemented lens composed of a negative lens and a positive lens, and a positive meniscus lens with the convex surface turned to an image surface side, which are located in order from the object side. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a photographic lens system used for a photographic camera (especially a digital single-lens reflex camera) and a video camera, and more particularly to a wide-angle lens system capable of realizing sufficient aberration correction while sufficiently taking back focus.

In wide-angle lens systems that can take a large angle of view in product fields such as photographic cameras, electronic still cameras, and video cameras, a certain distance (back focus) is ensured between the final lens surface and the imaging surface due to the camera mechanism. From the necessity, a retrofocus type with negative and positive refractive power arrangement from the object side is often adopted.
JP 09-113798 A JP 2005-316014 A JP 2006-301416 A

  However, the retro-focus type is a lens system that is asymmetric with respect to the aperture due to the arrangement of a lens group with a strong negative refractive power in front of the master lens, so various aberrations such as distortion and lateral chromatic aberration that occur in the front group There are also drawbacks that are difficult to correct. Specifically, for example, the lens system proposed in Patent Document 1 shows good performance in terms of optical aberration, but sufficient back focus is obtained because the power (refractive power) arrangement of the most object side group is inappropriate. There are disadvantages that cannot be removed. In Patent Document 2, since the selection of the glass material is inappropriate, flare due to chromatic aberration is generated particularly off-axis, and the power balance of each group is inappropriate and the total length is large. In Patent Document 3, aberrations due to off-axis light such as distortion and curvature of field occur greatly because the refractive power arrangement of the two groups on the object side from the stop is inappropriate, and the glass material for the bonded lens is inappropriate. In the entire system, the lateral chromatic aberration and the curvature of field are greatly generated.

  The present invention has a long back focus compared to the focal length, an F number of about 4, a half angle of view of about 45 degrees, and a retrofocus type wide angle capable of realizing good optical performance from infinity to close range. The object is to obtain a lens system.

  The wide-angle lens system according to the present invention includes, in order from the object side, a first lens group having a negative refractive power, a diaphragm, and a second lens group having a positive refractive power, and the first lens group is positioned in order from the object side. A negative meniscus lens having a convex surface facing the object side, a planoconvex lens or a biconvex lens having a convex surface facing the object side, two negative meniscus lenses having a convex surface facing the object side, a positive lens, and a positive lens and a negative lens The second lens group includes a cemented lens in which a negative lens and a positive lens are cemented, and a positive meniscus lens having a convex surface directed to the image surface side. .

Specifically, the first lens group includes, for example, a negative meniscus lens having a convex surface directed toward the object side in order from the object side, a plano-convex lens having a convex surface directed toward the object side, or a biconvex lens, a first lens group, It is preferable that the first lens unit is composed of the first lens unit after the first lens unit, and the following conditional expressions (1) and (2) are satisfied.
(1) 7.0 <| f1a | / f <13.0
(2) 1.8 <| f1b | / f <6.5
However,
f: focal length of the entire system,
f1a: focal length of the 1a lens group,
f1b; focal length of the 1b lens group,
It is.

  In focusing from an infinitely distant object to a close object, it is possible to move the first lens group and the second lens group independently to the object side.

  Specifically, the first lens group includes, for example, a 1a lens group that does not move during focusing and a 1b lens group that moves, and this 1b lens is used for focusing from an infinite object to a close object. A mode in which the second lens group is independently moved to the object side is possible.

Also in this focusing mode, it is preferable to satisfy the conditional expressions (1) and (2).
(1) 7.0 <| f1a | / f <13.0
(2) 1.8 <| f1b | / f <6.5
However,
f: focal length of the entire system,
f1a: focal length of the 1a lens group,
f1b; focal length of the 1b lens group,
It is.

The wide-angle lens system of the present invention preferably satisfies the following conditional expression (3).
(3) -3.9 <SF <-2.0
However,
SF = (R2 + R1) / (R2-R1)
R1: radius of curvature of the object side surface of the negative meniscus lens located closest to the object side,
R2: radius of curvature of the image side surface of the negative meniscus lens located closest to the object side,
It is.

Moreover, it is desirable to satisfy the following conditional expressions (4) and (5).
(4) -0.15 <np-nn <-0.07
(5) -21 <νp-νn <-16
However,
np: refractive index of a positive lens constituting the cemented lens in the first lens group,
νp: Abbe number of the positive lens constituting the cemented lens in the first lens group,
nn: refractive index of the negative lens constituting the cemented lens in the first lens group,
νn: Abbe number of the negative lens constituting the cemented lens in the first lens group,
It is.

  In the specific configuration example, the first lens group further includes a negative meniscus lens having a convex surface facing the image side between the cemented lens and the positive lens on the object side.

  In the specific configuration example, the second lens group includes a positive lens having a convex surface on the image side and further on the image side of a positive meniscus lens having a convex surface on the image surface side.

  According to the retrofocus type wide-angle lens system of the present invention, the back focus is long compared to the focal length, the F-number is about 4, the half angle of view is about 45 degrees, and good optical performance is obtained from infinity to close distance. Can be realized.

  The wide-angle lens system according to the present invention is shown in FIG. 1 (FIG. 3), FIG. 5 (FIG. 7), FIG. 9 (FIG. 11), FIG. 13 (FIG. 15), FIG. 25 (FIG. 27), the first lens unit 10 having negative refractive power on the object side and the second lens having positive refractive power on the image side, separated by the stop S, are used. It consists of a lens group 20. I is the image plane.

  In this embodiment, focusing is performed by floating, and there are two modes of floating. The first mode is that the first lens group 10 has a negative refractive power that does not move during focusing, as indicated by an arrow at the bottom of each lens configuration diagram of FIG. 1, FIG. 5, FIG. 9, FIG. The first-b lens group 11 and the first-b lens group 12 having the same negative refractive power that are moved are divided into the first-b lens group 11 and the first-b lens group 20 respectively. In this mode, the second lens group 20 is moved to the object side independently (the movement amount of the second lens group 20 is larger than that of the first b lens group 11). In the second mode, the first lens group 10 and the second lens group 20 are integrated when focusing from an object at infinity to a short distance object, as indicated by an arrow at the bottom of each lens configuration diagram of FIGS. Are moved independently to the object side (the amount of movement of the second lens group 20 is larger than that of the first lens group 10). Any floating focus can reduce the weight of the moving group and facilitate AF.

  In addition, the wide-angle lens system of the present embodiment has a retrofocus configuration in which negative and positive refractive powers are arranged in order from the object side in order to obtain sufficient back focus. The wide-angle lens system of this embodiment has a first lens group 10 having a negative refractive power and a second lens group 20 having a positive refractive power, and has a retrofocus structure. Further, when the first lens group 10 is divided into a stationary group (first a lens group 11) and a movable group (first b lens group 12) during focusing as described above, the first lens group 11 is negative. The first-b lens group 12 and the second lens group 20 have a positive refractive power in combination and have a retrofocus structure.

  In a mode in which the entire first lens group 10 is a focus group, the 1a lens group 11 is defined as including a negative meniscus lens having a convex surface facing the object side and a plano-convex lens or a biconvex lens having a convex surface facing the object side. To do. Even in accordance with this definition, the first-a lens group 11 has a negative refractive power, and the combined refractive power of the first-b lens group 12 and the second lens group 20 is positive. In other words, the 1a lens group 11 is a negative portion of a retrofocus type lens.

  In any embodiment, the first-b lens group 12 is arranged in order from the object side, two negative meniscus lenses having a convex surface facing the object side, a thick positive meniscus lens or a biconvex positive lens, and a positive lens and a negative lens. Each has one cemented lens and has negative refractive power as a whole. In Numerical Examples 6 and 7, a negative meniscus lens having a convex surface facing the image side is disposed between a thick positive meniscus lens or a biconvex positive lens and a cemented lens.

  In any embodiment, the second lens group 20 is arranged in order from the object side, a cemented lens of one negative lens and one positive lens, a positive meniscus lens having a convex surface on the image side, and a convex surface on the image side. It has a positive refractive power as a whole.

  Conditional expressions (1) and (2) are conditions that the first a lens group 11 and the first b lens group 12 of the first lens group 10 should satisfy in order to ensure back focus and realize good aberration correction. . If the lower limit of the conditional expression (1) is exceeded or the lower limit of the conditional expression (2) is not reached, large aberrations mainly due to off-axis rays occur in the first lens group, making correction in the second lens group 20 difficult. Become. On the contrary, if the upper limit of conditional expression (1) is exceeded or the upper limit of conditional expression (2) is exceeded, the back focus is insufficient.

  Conditional expression (3) is a conditional expression related to the shape factor (lens shape) of a negative meniscus lens having a convex surface facing the object side closest to the object side, and achieves both distortion and productivity that occur in the negative meniscus lens. It is a condition for. If the lower limit of conditional expression (3) is not reached, the amount of distortion aberration generated will be reduced, but the concave shape of the negative meniscus lens will become deep, causing a problem in productivity. If the upper limit of conditional expression (3) is exceeded, a lot of distortion will occur and correction by the subsequent lens system will be difficult.

  Conditional expressions (4) and (5) are conditions for correcting the chromatic aberration and the curvature of field in a well-balanced manner under the conditions regarding the refractive index and Abbe number of the cemented lens in the 1b lens group. If the upper limit of conditional expression (4) regarding the refractive index is exceeded, correction of field curvature becomes difficult, and if the lower limit is not reached, there is no room for selecting a glass material or correction of chromatic aberration caused by the preceding negative meniscus lens becomes difficult. . Further, unless conditional expression (5) regarding the Abbe number is satisfied, correction of chromatic aberration is similarly difficult.

Next, specific numerical examples will be shown. In the various aberration diagrams and tables, SA in the chromatic aberration (axial chromatic aberration) diagram and magnification chromatic aberration diagram represented by spherical aberration, SC is spherical aberration, SC is a sine condition, d-line, g-line, and C-line are aberrations for each wavelength. Where S is sagittal, M is meridional, F _NO. Is F number, FE is effective F number, Y is image height, f is the focal length of the entire system, M is lateral magnification, W is half angle of view (°) , FB Is the back focus, r is the radius of curvature, d is the lens thickness or lens spacing, Nd is the refractive index of the d-line, and ν is the Abbe number. D that varies depending on M, fB, and shooting distance is shown in the order of infinity-shortest object shooting distance.
A rotationally symmetric aspherical surface is defined by the following equation.
x = cy ² / [1+ [1- (1 + K) c ² y ² ] ^1/2 ] + A4y ⁴ + A6y ⁶ + A8y ⁸ + A10y ¹⁰ + A12y ¹² ...
(Where x is an aspherical shape, c is a curvature (1 / r), y is a height from the optical axis, K is a conical coefficient, A4, A6, A8,... Are aspherical coefficients of respective orders. )

[Numerical Example 1]
1 to 4 and Table 1 show Numerical Example 1 of the wide-angle lens system of the present invention. 1 and FIG. 3 are lens configuration diagrams when the object at infinity is in focus and when the object is focused at the shortest (shooting distance), respectively, and FIGS. 2 and 4 are various aberration diagrams in the lens configuration of FIGS. Table 1 shows the numerical data.

  The first-a lens group 11 includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side and a biconvex lens. A resin aspherical layer is formed on the image side surface of the negative meniscus lens. The first-b lens group 12 includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side, a biconvex positive lens, and a cemented lens including one biconvex positive lens and one biconcave lens. The second lens group 20 includes, in order from the object side, one cemented lens for each of a biconcave negative lens and a biconvex positive lens, and two positive meniscus lenses having a convex surface facing the image side. Focusing from an infinite object to a close object is performed by fixing the 1a lens group 11 with respect to the image plane and moving the 1b lens group 12 and the second lens group 20 individually (independently) to the object side. Do it. The aperture stop S is located at the front (object side) 1.00 of the second lens group 20 (fifteenth surface) and moves together with the second lens group 20 during focusing.

(Table 1)
F _NO. = 1: 4.0
f = 15.00
M = 0.000--0.145
W = 43.5
fB = 37.49-39.90
Surface No. rd Nd ν
1 57.113 1.40 1.72916 54.7
2 29.738 0.10 1.52972 42.7
3 * 23.318 3.09
4 54.208 4.16 1.50000 63.9
5 -1024.688 3.12-1.49
6 18.316 1.00 1.81000 47.5
7 9.300 5.28
8 103.971 1.35 1.81000 47.5
9 11.668 1.71
10 32.873 7.48 1.74076 27.4
11 -214.919 0.10
12 15.689 4.50 1.66240 31.9
13 -11.373 1.68 1.80000 50.2
14 8815.245 2.95-2.17
15 -123.963 3.00 1.80000 26.1
16 13.286 3.02 1.49700 81.6
17 -21.288 0.50
18 -66.932 1.64 1.50000 69.6
19 -19.357 0.50
20 -175.426 1.91 1.48749 70.2
21 -18.294-
* Aspheric data (Aspheric coefficient not shown is 0.00);
Surface No.
K A4 A6 A8
NO.3 0.0 -0.24221 × 10 ^-4 0.91040 × 10 ^-8 -0.30083 × 10 ^-10
[Numerical Example 2]
5 to 8 and Table 2 show Numerical Example 2 of the wide-angle lens system of the present invention. FIGS. 5 and 7 are lens configuration diagrams when focusing on an object at infinity and focusing on the shortest (shooting distance) object, respectively, and FIGS. 6 and 8 are various aberration diagrams in the lens configuration of FIGS. 5 and 7, respectively. Table 2 shows the numerical data. The basic lens configuration and focusing mode are that the second lens from the object side of the 1a lens group 12 is a positive meniscus lens having a convex surface facing the object side, and three lenses from the object side of the 1b lens group 12 Except that the eye lens is a positive meniscus lens having a convex surface facing the object side, and that the cemented negative lens of the first lens group 12 is a negative meniscus lens having a concave surface facing the image side, Numerical Example 1 It is the same. The aperture stop S is located at the front (object side) 1.00 of the second lens group 20 (15th surface), and moves together with the second lens group 20 during focusing.
(Table 2)
F _NO. = 1: 4.0
f = 15.00
M = 0.000--0.142
W = 43.6
fB = 37.50-39.72
Surface No. rd Nd ν
1 45.303 1.40 1.72916 54.7
2 24.970 0.10 1.52972 42.7
3 * 20.449 4.51
4 47.785 3.81 1.50000 66.4
5 717.096 3.10-1.51
6 18.071 1.00 1.81000 47.5
7 9.300 5.06
8 48.824 1.00 1.81000 47.5
9 10.132 2.17
10 28.931 6.87 1.80886 25.2
11 82.673 0.10
12 16.190 4.50 1.68943 30.2
13 -10.323 1.00 1.79939 50.2
14 -54.109 2.63-2.00
15 -44.370 3.00 1.80000 25.1
16 13.644 3.02 1.50000 71.3
17 -15.745 0.50
18 -56.007 1.64 1.50000 69.6
19 -18.225 0.50
20 -78.196 1.91 1.48749 70.2
21 -19.732-
* Aspheric data (Aspheric coefficient not shown is 0.00);
Surface No.
K A4 A6 A8
NO.3 0.0 -0.24888 × 10 ^-4 0.14867 × 10 ^-7 -0.11364 × 10 ^-9

[Numerical Example 3]
9 to 12 and Table 3 show Numerical Example 3 of the wide-angle lens system of the present invention. FIGS. 9 and 11 are lens configuration diagrams when focusing on an object at infinity and focusing on the shortest (shooting distance) object, respectively, and FIGS. 10 and 12 are aberration diagrams in the lens configuration of FIGS. 9 and 11, respectively. Table 3 shows the numerical data. The basic lens configuration and focusing mode are the same as those in Numerical Example 2. The aperture stop S is located at the front (object side) 1.00 of the second lens group 20 (15th surface), and moves together with the second lens group 20 during focusing.
(Table 3)
F _NO. = 1: 4.1
f = 15.00
M = 0.000--0.144
W = 43.4
fB = 37.50-39.88
Surface No. rd Nd ν
1 78.420 1.40 1.80 400 46.6
2 29.567 0.10 1.52972 42.7
3 * 22.216 1.58
4 34.896 5.38 1.53172 48.9
5 793.317 3.02-1.50
6 17.700 1.00 1.80 400 46.6
7 9.883 4.38
8 62.422 1.00 1.80 400 46.6
9 10.753 1.70
10 25.442 6.81 1.76182 26.5
11 230.236 2.69
12 19.107 3.90 1.69895 30.1
13 -10.782 1.43 1.80 400 46.6
14 -379.992 2.87-2.00
15 -128.017 3.00 1.80518 25.4
16 12.879 3.02 1.49700 81.6
17 -27.349 0.50
18 -49.469 1.64 1.48749 70.2
19 -17.327 0.50
20 -292.976 1.91 1.48749 70.2
21 -16.485-
* Aspheric data (Aspheric coefficient not shown is 0.00);
Surface No.
K A4 A6 A8
NO.3 0.0 -0.30400 × 10 ^-4 0.14389 × 10 ^-7 -0.54718 × 10 ^-10

[Numerical Example 4]
13 to 16 and Table 4 show Numerical Example 4 of the wide-angle lens system of the present invention. FIG. 13 and FIG. 15 are diagrams of lens configurations when focusing on an object at infinity and focusing on the shortest (shooting distance) object, respectively, and FIG. 14 and FIG. 16 are various aberration diagrams in the lens configurations of FIG. Table 4 shows the numerical data. The basic lens configuration and focusing mode are the same as those in Numerical Example 2. The aperture stop S is located at the front (object side) 1.00 of the second lens group 20 (15th surface), and moves together with the second lens group 20 during focusing.
(Table 4)
F _NO. = 1: 4.1
f = 15.45
M = 0.000--0.148
W = 42.7
fB = 37.50-39.99
Surface No. rd Nd ν
1 68.944 1.40 1.80 400 46.6
2 29.739 0.10 1.52972 42.7
3 * 23.464 1.75
4 36.047 5.15 1.53172 48.9
5 613.864 3.20-1.50
6 17.091 1.00 1.80 400 46.6
7 9.732 4.37
8 43.905 1.00 1.80 400 46.6
9 10.300 2.80
10 35.048 6.81 1.76182 26.5
11 225.065 1.22
12 17.376 4.06 1.69895 30.1
13 -10.584 1.59 1.80 400 46.6
14 -938.503 2.79-2.00
15 -73.266 3.00 1.80518 25.4
16 14.003 3.02 1.49700 81.6
17 -18.481 0.50
18 -67.277 1.64 1.48749 70.2
19 -19.218 0.50
20 -119.433 1.91 1.48749 70.2
21 -18.651-
* Aspheric data (Aspheric coefficient not shown is 0.00);
Surface No.
K A4 A6 A8
NO.3 0.0 -0.23016 × 10 ^-4 0.49713 × 10 ^-8 0.25709 × 10 ^-10

[Numerical Example 5]
17 to 20 and Table 5 show Numerical Example 5 of the wide-angle lens system of the present invention. FIGS. 17 and 19 are lens configuration diagrams at the time of focusing on the object at infinity and the shortest (shooting distance) object focusing, respectively, and FIGS. 18 and 20 are aberration diagrams in the lens configuration of FIGS. 17 and 19, respectively. Table 5 shows the numerical data. The basic lens configuration and focusing mode are the same as those in Numerical Example 1 except that the third lens from the object side of the 1b lens group 12 is a positive meniscus lens having a convex surface facing the object side. The aperture stop S is located at the front (object side) 1.57 of the second lens group 20 (fifteenth surface), and moves together with the second lens group 20 during focusing.
(Table 5)
F _NO. = 1: 4.1
f = 15.45
M = 0.000--0.152
W = 42.9
fB = 37.50-40.14
Surface No. rd Nd ν
1 68.051 2.00 1.77250 49.6
2 29.129 0.15 1.52972 42.7
3 * 23.181 3.32
4 63.136 4.55 1.53172 48.9
5 -377.110 3.31-1.47
6 17.007 1.00 1.80 400 46.6
7 9.300 4.97
8 38.612 1.00 1.80 400 46.6
9 11.119 2.26
10 31.207 6.54 1.76182 26.5
11 122.835 0.59
12 16.757 3.91 1.69895 30.1
13 -11.654 1.00 1.80 400 46.6
14 684.227 3.65-2.87
15 -125.109 3.00 1.80518 25.4
16 14.066 3.02 1.49700 81.6
17 -19.090 0.50
18 -117.839 1.64 1.48749 70.2
19 -18.256 0.50
20 -68.457 1.91 1.48749 70.2
21 -20.774-
* Aspheric data (Aspheric coefficient not shown is 0.00);
Surface No.
K A4 A6 A8
NO.3 0.0 -0.23794 × 10 ^-4 0.21028 × 10 ^-8 -0.20581 × 10 ^-10

[Numerical Example 6]
21 to 24 and Table 6 show Numerical Example 6 of the wide-angle lens system of the present invention. FIG. 21 and FIG. 23 are lens configuration diagrams when the object at infinity is in focus and the shortest (shooting distance) object focus, and FIG. 21 and FIG. 23 are various aberration diagrams in the lens configuration of FIG. Table 6 shows the numerical data. Focusing from an infinitely distant object to a close object is performed by moving the first lens group 10 and the second lens group 20 individually (independently) to the object side. The basic lens configuration is that a negative meniscus lens having a convex surface facing the image side is disposed between the cemented lens of the third biconvex positive lens and positive / negative lens from the object side of the first-b lens group 12. The negative lens of the cemented lens in the first-b lens group 12 is the same as in Numerical Example 1 except that the negative lens is a negative meniscus lens having a convex surface facing the object side. The aperture stop S is located at the front (object side) 1.00 of the second lens group 20 (17th surface), and moves together with the second lens group 20 during focusing.
(Table 6)
F _NO. = 1: 4.0
f = 15.45
M = 0.000--0.151
W = 43.2
fB = 37.47-40.12
Surface No. rd Nd ν
1 46.940 1.40 1.72916 54.7
2 27.608 0.10 1.52972 42.7
3 * 22.997 3.40
4 47.608 4.21 1.50051 69.1
5 -8733.782 1.50
6 15.563 1.01 1.80 400 46.6
7 8.989 4.31
8 51.012 1.00 1.80 400 46.6
9 11.044 2.02
10 25.718 7.00 1.80518 25.4
11 -73.792 0.81
12 -28.796 1.00 1.80 400 46.6
13 -1343.137 0.20
14 25.369 4.81 1.60000 38.2
15 -8.850 2.78 1.67586 58.3
16 -46.229 2.77-1.99
17 -128.466 2.48 1.80518 25.4
18 17.979 2.74 1.49700 81.6
19 -18.131 0.50
20 -70.014 1.48 1.51633 64.1
21 -23.188 1.00
22 -217.392 2.01 1.48749 70.2
23 -20.642-
* Aspheric data (Aspheric coefficient not shown is 0.00);
Surface No.
K A4 A6 A8
NO.3 0.0 -0.19163 × 10 ^-4 0.59264 × 10 ^-8 -0.31481 × 10 ^-10

[Numerical Example 7]
25 to 28 and Table 7 show Numerical Example 6 of the wide-angle lens system of the present invention. FIGS. 25 and 27 are diagrams of lens configurations when the object is focused at infinity and when the object is focused at the shortest (shooting distance), and FIGS. 26 and 28 are graphs showing various aberrations in the lens configurations of FIGS. Table 7 shows the numerical data. The basic lens configuration and focusing mode are that the second lens from the object side of the 1a lens group 12 is a positive meniscus lens having a convex surface facing the object side, and the most image side lens of the second lens group 20 Is the same as Numerical Example 6 except that is a biconvex lens. The aperture stop S is located at the front (object side) 1.00 of the second lens group 20 (17th surface), and moves together with the second lens group 20 during focusing.
(Table 7)
F _NO. = 1: 4.0
f = 15.45
M = 0.000--0.147
W = 43.2
fB = 37.49-40.13
Surface No. rd Nd ν
1 74.826 1.40 1.68565 34.2
2 38.276 0.10 1.52972 42.7
3 * 27.328 2.03
4 58.274 3.80 1.60423 53.4
5 402.268 1.50
6 15.367 1.00 1.80958 47.5
7 9.598 5.86
8 84.990 1.00 1.80975 47.5
9 11.493 1.65
10 21.976 7.00 1.83617 24.1
11 -76.405 1.10
12 -21.576 1.00 1.80000 49.8
13 -83.668 0.20
14 28.896 4.81 1.56841 40.9
15 -8.310 1.62 1.64957 60.8
16 -46.008 2.76-2.00
17 -126.569 3.24 1.80518 25.4
18 17.603 2.74 1.49700 81.6
19 -21.511 0.50
20 -45.019 1.48 1.51633 64.1
21 -19.690 1.00
22 189.892 2.01 1.48749 70.2
23 -19.717-
* Aspheric data (Aspheric coefficient not shown is 0.00);
Surface No.
K A4 A6 A8
NO.3 0.0 -0.26650 × 10 ^-4 0.21338 × 10 ^-7 -0.19772 × 10 ^-10

Table 8 shows values for the conditional expressions of the numerical examples.
(Table 8)

  As apparent from Table 8, Examples 1 to 7 satisfy the conditional expressions (1) to (5), and various aberrations are relatively well corrected as is apparent from the various aberration diagrams.

It is a lens block diagram at the time of infinity object focusing of Numerical Example 1 of the wide-angle lens system by this invention. FIG. 2 is a diagram illustrating various aberrations of the lens configuration in FIG. 1. FIG. 3 is a lens configuration diagram in the shortest object in-focus state in Numerical Example 1. FIG. 4 is a diagram illustrating various aberrations in the lens configuration in FIG. 3. It is a lens block diagram at the time of infinity object focusing of Numerical Example 2 of the wide angle lens system by this invention. FIG. 6 is a diagram illustrating various aberrations of the lens configuration in FIG. 5. It is a lens block diagram in the shortest object focusing state of Numerical Example 2. FIG. 8 is a diagram illustrating various aberrations in the lens configuration in FIG. 7. It is a lens block diagram at the time of infinity object focusing of Numerical Example 3 of the wide angle lens system by this invention. FIG. 10 is a diagram illustrating various aberrations of the lens configuration in FIG. 9. It is a lens block diagram in the shortest object focusing state of Numerical Example 3. FIG. 12 is a diagram illustrating various aberrations in the lens configuration in FIG. 11. It is a lens block diagram at the time of infinity object focusing of Numerical Example 4 of the wide angle lens system by this invention. FIG. 14 is a diagram illustrating various aberrations of the lens configuration in FIG. 13. FIG. 9 is a lens configuration diagram in a shortest object in-focus state according to Numerical Example 4. FIG. 16 is a diagram illustrating various aberrations in the lens configuration in FIG. 15. It is a lens block diagram at the time of infinity object focusing of Numerical Example 5 of the wide angle lens system by this invention. FIG. 18 is a diagram illustrating various aberrations of the lens configuration in FIG. 17. FIG. 9 is a lens configuration diagram in a shortest object in-focus state according to Numerical Example 5. FIG. 20 is a diagram illustrating various aberrations in the lens configuration in FIG. 19. It is a lens block diagram at the time of an infinite object focusing of numerical example 6 of the wide angle lens system by this invention. FIG. 22 is a diagram illustrating various aberrations of the lens configuration in FIG. 21. FIG. 10 is a lens configuration diagram of Numerical Example 6 in the shortest object in-focus state. FIG. 24 is a diagram illustrating various aberrations in the lens configuration in FIG. 23. It is a lens block diagram at the time of infinity object focusing of Numerical Example 7 of the wide angle lens system by this invention. FIG. 26 is a diagram illustrating various aberrations of the lens configuration in FIG. 25. FIG. 10 is a lens configuration diagram in a shortest object in-focus state according to Numerical Example 7. FIG. 28 is a diagram illustrating various aberrations in the lens configuration in FIG. 27.

Claims (9)

In order from the object side, a first lens group having a negative refractive power, a diaphragm and a second lens group having a positive refractive power,
The first lens group includes a negative meniscus lens having a convex surface facing the object side, a plano-convex lens or a biconvex lens having a convex surface facing the object side, and two negative meniscus lenses having a convex surface facing the object side. A positive lens, and a cemented lens of a positive lens and a negative lens,
The second lens group includes a cemented lens in which a negative lens and a positive lens are cemented in order from the object side, and a positive meniscus lens having a convex surface directed toward the image plane side. 2. The wide-angle lens system according to claim 1, wherein the first lens group includes a negative meniscus lens having a convex surface directed toward the object side and a plano-convex lens having a convex surface directed toward the object side or a biconvex lens in order from the object side. A wide-angle lens system that includes the first lens group and the first lens group after the first lens group, and satisfies the following conditional expressions (1) and (2).
(1) 7.0 <| f1a | / f <13.0
(2) 1.8 <| f1b | / f <6.5
However,
f: focal length of the entire system,
f1a: focal length of the 1a lens group,
f1b: focal length of the 1b lens group. 3. The wide-angle lens system according to claim 1, wherein the first lens group and the second lens group move independently toward the object side during focusing from an object at infinity to a short-distance object. 2. The wide-angle lens system according to claim 1, wherein the first lens group includes a 1a lens group that does not move during focusing and a 1b lens group that moves, and the first lens group is used for focusing from an infinite object to a short-distance object. The 1b lens and the second lens group are a wide-angle lens system that independently moves toward the object side. 5. The wide angle lens system according to claim 4, wherein the following conditional expressions (1) and (2) are satisfied.
(1) 7.0 <| f1a | / f <13.0
(2) 1.8 <| f1b | / f <6.5
However,
f: focal length of the entire system,
f1a: focal length of the 1a lens group,
f1b: focal length of the 1b lens group. The wide-angle lens system according to any one of claims 1 to 5, wherein the wide-angle lens system satisfies the following conditional expression (3).
(3) -3.9 <SF <-2.0
However,
SF = (R2 + R1) / (R2-R1)
R1: radius of curvature of the object side surface of the negative meniscus lens located closest to the object side,
R2: radius of curvature of the image side surface of the negative meniscus lens located closest to the object side. The wide-angle lens system according to any one of claims 1 to 6, wherein the wide-angle lens system satisfies the following conditional expressions (4) and (5).
(4) -0.15 <np-nn <-0.07
(5) -21 <νp-νn <-16
However,
np: refractive index of a positive lens constituting the cemented lens in the first lens group,
νp: Abbe number of the positive lens constituting the cemented lens in the first lens group,
nn: refractive index of the negative lens constituting the cemented lens in the first lens group,
νn: Abbe number of the negative lens constituting the cemented lens in the first lens group. 8. The wide-angle lens system according to claim 1, wherein the first lens group further includes a negative meniscus lens having a convex surface facing the image side between the cemented lens and the positive lens on the object side. Wide-angle lens system. 9. The wide-angle lens system according to claim 1, wherein the second lens group includes a positive lens having a convex surface on the image side and further on the image side of a positive meniscus lens having a convex surface on the image surface side. Wide-angle lens system.

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