JP4796829B2 - Zoom lens system - Google Patents

Description

The present invention relates to a zoom lens system suitable for a single-lens reflex (SLR) camera, particularly a digital SLR camera.

Currently, an SLR zoom lens system (so-called standard zoom lens system) that has a zoom ratio of about 2 to 3 times and covers the angle of view from the wide-angle range to the telephoto range from the object side. A negative positive retrofocus type two-group zoom lens system is used in this order. Digital S
Since it is difficult to increase the size of the image sensor of the LR camera, an image sensor having a smaller screen size than the so-called Leica (35 mm version) silver salt film SLR camera is widely used. Therefore, for interchangeable lenses having the same focal length, the digital SLR camera has a narrower angle of view than the silver salt SLR camera, so an optical system with a shorter focal length is preferred. In addition, in order to maintain the compatibility with the interchangeable lens for the conventional SLR camera for silver halide film, which is already widely used, in order to make the lens mount and the flange back common, the back focus is longer than the focal length. Need. Therefore, a zoom lens system for a digital SLR camera is more difficult to widen than a conventional silver salt SLR camera, and the image sensor is small, but the frequency is often viewed on a personal computer. Therefore, high performance is required over the entire screen.
Japanese Patent Laid-Open No. 2002-082283 JP-A-11-160619 JP 2001-350089 A Japanese Patent Laid-Open No. 10-282417

However, the conventional negative and positive two-group type zoom lens system has a large number of lenses, is not sufficiently small and low in cost, and has a zoom ratio (zoom ratio) of 2 times or less at the short focal length end. The angle of view is not enough.

The present invention is a negative-positive two-group zoom lens system in order from the object side. Even in a camera using a small image pickup element, by arranging the refractive power of each lens group appropriately, at the short focal length end. It has a sufficient angle of view of 75 ° or more, a zoom ratio of about 3 times, a long back focus compared to the focal length at the short focal length end, and a necessary peripheral light amount at the short focal length end. Above,
A good balance between off-axis aberrations at the short focal length end and on-axis aberrations at the long focal length end side,
An object is to obtain a compact and low-cost zoom lens system.

The present invention includes, in order from the object side, a first lens group having a negative refractive power, an open / close diaphragm , and a second lens group having a positive refractive power, and is moved by moving the first lens group and the second lens group. In the zoom lens system, the first lens group includes, in order from the object side, a positive first lens, a negative second lens, a negative third lens, a positive fourth lens, and a positive or negative first lens. 5 lenses are provided, and the following conditional expressions (1) to (3) are satisfied.
(1) 1.5 <| f1 / fw | <1.8
(2) 1.0 <f2 / (fw × ft) ^1/2 <1.3
(3) 1.0 <| f2 / f1 | <1.2
However,
f1: the focal length of the first lens group ,
f2: focal length of the second lens group ,
fw: focal length of the entire system at the short focal length end,
ft: focal length of the entire system at the long focal length end,
It is.

In the zoom lens system of the present invention, a flare cut stop is disposed between the first lens unit and the stop,
It is preferable to fix the second lens group during focusing and move the flare cut stop integrally with the first lens group.

In the zoom lens system of the present invention, it is preferable that the flare cut stop disposed between the first lens unit and the stop moves independently with respect to the first lens unit and the open / close stop during zooming.

According to the present invention, in a negative-positive two-group zoom lens system, even a camera using a small image sensor has a sufficient angle of view of 75 ° or more and a zoom ratio of about three times. A compact and low-cost zoom lens system can be obtained.

As shown in the simplified movement diagram of FIG. 21, the zoom lens system of the present embodiment is in order from the object side.
The first lens group 10 having a negative refractive power, the open / close stop S, and the second lens group 20 having a positive refractive power, and in zooming from the short focal length end (W) to the long focal length end (T), 1 lens group 1
0 once moves to the image side, then makes a U-turn and moves to the object side, and the second lens group 20 moves monotonously to the object side. The open / close diaphragm S moves together with the second lens group 20. Focusing is performed by the first lens group 10. During the focusing, the second lens group 20 is not movable. Apart from the open / close stop S, a flare cut stop FC1 is provided in front of the open / close stop S and behind the first lens group 10, and a flare cut stop FC2 is provided behind the second lens group 20. Yes. The flare cut stop FC1 once moves to the image side, then makes a U-turn and moves to the object side, and the flare cut stop FC2 moves fixedly or monotonously to the object side. The chain line in FIG. 21 is a locus when the flare cut stop FC2 monotonously moves toward the object side. The flare cut stop FC1 may move to the object side without moving to the image side as long as it does not contact the first lens group 10 and the open / close stop S.

In the zoom lens system of the present embodiment, the first lens group 10 includes at least two positive lenses and two negative lenses. By including two positive lenses and two negative lenses, various aberrations can be favorably corrected while securing a zoom ratio of about 3 times. In particular, in order from the object side, it is preferable to include a positive first lens, a negative second lens, a negative third lens, and a positive fourth lens. The first lens group can mainly correct distortion mainly by disposing a positive fourth lens. If a fifth lens having a weak power (regardless of positive or negative) is disposed behind the positive fourth lens, various aberrations can be corrected more favorably.

Conditional expression (1) is a condition for correcting the aberration while ensuring the back focus. By satisfying this condition, not only the back focus can be secured, but also the aberration can be corrected well even if the lens system is downsized. If the upper limit of conditional expression (1) is exceeded, the power of the first lens group becomes insufficient, and it becomes difficult to correct distortion. If the power of the first lens unit is increased beyond the lower limit of conditional expression (1), it is advantageous to ensure the back focus, but coma and astigmatism increase, which is necessary to obtain good performance. Will increase the number of lenses. For this reason, cost increases and the enlargement is caused.

Conditional expression (2) defines the power of the second lens group mainly responsible for the zooming action. Conditional expression (
If the upper limit of 2) is exceeded, the power of the second lens group is weak and the zooming action is insufficient. Therefore, in order to obtain a predetermined zoom ratio, it is necessary to increase the amount of movement of the second lens group, and the number of lenses in the first lens group must be reduced. This makes it difficult to correct off-axis aberrations by the first lens group. If the lower limit of conditional expression (2) is exceeded, the power of the second lens group is too strong, so that the variation in spherical aberration and coma due to zooming is large, making it difficult to achieve sufficient optical performance.

Conditional expression (3) defines the balance of the refractive powers of the first lens group and the second lens group. In the negative positive two-group zoom lens system, the axial luminous flux is higher in the second lens group than in the first lens group, and spherical aberration is more likely to occur in the second lens group. . In this zoom lens system, by making the power of the second lens group slightly weaker than the power of the first lens group,
A balance is established so that aberrations generated by the first lens group (particularly spherical aberration) and aberrations generated by the second lens group cancel each other.

If the upper limit of conditional expression (3) is exceeded, the power of the first lens group is equal to or greater than that of the second lens group, and aberrations (especially spherical aberration) occurring in the first lens group are reduced to the second lens group. It becomes difficult to counteract with a group. When the lower limit of conditional expression (3) is exceeded, the power of the second lens group becomes too strong compared to the first lens group, and aberrations (especially spherical aberration) generated in the second lens group cancel out in the first lens group. It becomes difficult.

In this zoom lens system, a flare cut stop FC1 for limiting off-axis light flux at the short focal length end is disposed on the object side of the second lens group. If the flare-cut stop FC1 is arranged on the object side of the second lens group in this way, it is easy to correct off-axis aberrations at the short focal length end.
Further, even when the first lens group is a focusing lens, a decrease in peripheral light amount due to focusing is reduced. It is also advantageous for reducing the diameter of the first lens group.

The flare cut stop FC1 moves together with the first lens group which is a focus lens group during focusing. When the flare-cut stop FC1 is arranged in this way, unnecessary light rays can be effectively excluded while securing a necessary peripheral light amount during short-distance focusing. Also,
The flare-cut stop FC1 is disposed near the intermediate position between the first lens group and the second lens group in order to reduce the decrease in peripheral light amount by excluding diagonal rays and intermediate high-image rays at the short focal length end. Is done. With this arrangement, the flare-cut diaphragm FC1 can be used during zooming.
Since there is a possibility of colliding with the first lens group and the second lens group, they move independently of each other.

The flare cut stop FC2 is arranged behind the second lens group (on the image plane side). As described above, when the flare cut stop FC2 is arranged, unnecessary off-axis rays on the long focal length side can be effectively excluded.

  An aspheric surface is preferably disposed in the first lens group. By disposing an aspheric surface, it is possible to satisfactorily correct distortion and astigmatism particularly at the short focal length end.

Next, specific examples will be described. In the various aberration diagrams and tables, SA is spherical aberration, SC is a sine condition, chromatic aberration (axial chromatic aberration) diagram represented by spherical aberration, and d-line, g-line, and C-line are chromatic aberrations for each wavelength. , S for sagittal, M for meridional, W for half angle of view (°), FNO.
F-number, f is the focal length of the entire system, fB back focus, r is the radius of curvature, d is the lens thickness or distance between lens, N _d is the refractive index of the d line, [nu denotes the Abbe number.

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 c is the curvature (1 / r), y is the height from the optical axis, K is the conic coefficient, A4, A6, A8
, ... are aspheric coefficients of each order)

1 to 4 and Table 1 show Example 1 of the zoom lens system according to the present invention. FIG. 1 is a lens configuration diagram at the short focal length end, FIG. 2 is a diagram of various aberrations thereof, FIG. 3 is a lens configuration diagram at the long focal length end, FIG. 4 is a diagram of the various aberrations, and Table 1 is numerical data thereof.

The negative first lens group 10 includes, in order from the object side, a positive first lens 11, a negative second lens 12, a negative third lens 13, a positive fourth lens 14, and a negative first lens . The positive second lens group 20 includes a positive lens 21, a positive lens 22, a negative lens 23, and a positive lens 24 in order from the object side. The open / close stop S is 0.60 forward from the pole of the eleventh surface (second lens group 20), and moves together with the second lens group 20 during zooming. The flare cut stop FC1 is located at 16.23 and 1.07 rearward from the pole of the tenth surface (first lens group 10) at the short focal length end and the long focal length end, and the height from the optical axis is 9.0. The flare-cut stop FC2 is located at the rear 0.42 and 11.45 from the pole of the 18th surface (second lens group 20) at the short focal length end and the long focal length end, the height from the optical axis is 7.3, and moves during zooming. To do.
(Table 1)
FNO. = 1: 3.5-5.8
f = 18.50-53.30
W = 38.7-15.0
fB = 37.42-74.16
Surface NO. R d N _d ν
1 509.738 3.06 1.62004 36.3
2 -509.738 0.10--
3 47.626 1.20 1.71300 53.9
4 16.299 7.36--
5 57.087 1.00 1.69680 55.5
6 18.500 3.63--
7 39.626 4.04 1.69895 30.1
8 -497.937 0.20--
9 71.551 1.90 1.52538 56.3
10 * 58.318 38.83-2.63--
11 36.551 2.15 1.58913 61.2
12 -167.832 0.10--
13 22.262 6.27 1.51633 64.1
14 -238.944 1.78--
15 -38.429 6.00 1.67270 32.1
16 18.321 0.80--
17 36.503 5.30 1.51742 52.4
18 -21.620---
* Is a rotationally symmetric aspherical surface.
Aspheric data (Aspheric coefficient not shown is 0.00):
Surface NO K A4 A6 A8
10 0.00 -0.27724 × 10 ^-4 -0.40939 × 10 ^-8 -0.84597 × 10 ^-9
A10 A12
0.48 128 × 10 ^-11 -0.13019 × 10 ^-13

5 to 8 and Table 2 show Example 2 of the zoom lens system according to the present invention. 5 is a lens configuration diagram at the short focal length end, FIG. 6 is a diagram of various aberrations, FIG. 7 is a lens configuration diagram at the long focal length end, FIG. 8 is a diagram of the various aberrations, and Table 2 is numerical data thereof. The basic lens configuration is the same as in the first embodiment. The open / close stop S is located at a distance from the pole of the eleventh surface (second lens group 20) to the front.
At 60. The flare cut stop FC1 has a tenth position at the short focal length end and the long focal length end.
It is located behind 19.34 and 1.00 from the pole of the surface (first lens group 10), and the height from the optical axis is 8.0. The flare-cut stop FC2 is 0.63 and 37.34 rearward from the pole of the 18th surface (second lens group 20) at the focal length end and the long focal length end, and the height from the optical axis is 9.0, and does not move during zooming. (Fixed).
(Table 2)
FNO. = 1: 3.5-5.8
f = 18.50-53.30
W = 38.7-15.0
fB = 37.63-74.34
Surface NO. R d N _d ν
1 444.292 3.06 1.69895 30.1
2 -444.292 0.10--
3 42.708 1.20 1.80 400 46.6
4 15.736 8.17--
5 3776.523 1.00 1.69680 55.5
6 22.220 1.84--
7 31.745 5.22 1.66680 33.0
8 -140.405 0.20--
9 64.463 1.90 1.52538 56.3
10 * 62.546 39.43-2.60--
11 54.135 2.49 1.58913 61.2
12 -87.008 0.10--
13 18.098 3.40 1.51633 64.1
14 304.893 3.19--
15 -48.503 5.90 1.67270 32.1
16 17.164 1.15--
17 37.978 5.30 1.51742 52.4
18 -22.940---
* Is a rotationally symmetric aspherical surface.
Aspheric data (Aspheric coefficient not shown is 0.00):
Surface NO K A4 A6 A8
10 0.00 -0.20822 × 10 ^-4 0.19203 × 10 ^-7 -0.94078 × 10 ^-9
A10 A12
0.56152 × 10 ^-11 -0.13718 × 10 ^-13

9 to 12 and Table 3 show Example 3 of the zoom lens system according to the present invention. FIG.
Is a lens configuration diagram at the short focal length end, FIG. 10 is a diagram of various aberrations, FIG. 11 is a lens configuration diagram at the long focal length end, FIG. 12 is a diagram of the various aberrations, and Table 3 is numerical data thereof.

The negative first lens group 10 includes, in order from the object side, a positive first lens 11, a negative second lens 12, a negative third lens 13, a positive fourth lens 14, and a positive first lens . The positive second lens group 20 includes a positive lens 21, a positive lens 22, a negative lens 23, and a positive lens 24 in order from the object side. The open / close stop S is 0.60 forward from the pole of the eleventh surface (second lens group 20). The flare cut stop FC1 is located behind 20.67 and 2.59 from the pole of the tenth surface (first lens group 10) at the short focal length end and the long focal length end, and the height from the optical axis is 7.7. The flare cut stop FC2 is located at 0.00 and 11.04 rearward from the pole of the 18th surface (second lens group 20) at the short focal length end and the long focal length end, and the height from the optical axis is 7.2, and moves during zooming. To do.
(Table 3)
FNO. = 1: 3.4-5.8
f = 18.60-53.00
W = 38.6-15.1
fB = 37.40-74.18
Surface NO. R d N _d ν
1 417.869 3.06 1.64769 33.8
2 -417.869 0.30--
3 52.769 1.20 1.71300 53.9
4 16.014 6.10--
5 40.377 1.00 1.78964 44.6
6 17.579 3.48--
7 33.220 3.68 1.80094 25.5
8 129.960 0.20--
9 58.685 1.90 1.52538 56.3
10 * 58.914 41.03-6.40--
11 33.947 2.31 1.60311 60.7
12 -150.945 0.28--
13 20.221 4.58 1.53005 65.2
14 3654.436 1.53--
15 -54.618 6.00 1.67270 32.1
16 16.779 1.13--
17 44.964 5.30 1.51742 52.4
18 -25.303---
* Is a rotationally symmetric aspherical surface.
Aspheric data (Aspheric coefficient not shown is 0.00):
Surface NO K A4 A6 A8
10 0.00 -0.29 175 × 10 ^-4 -0.36407 × 10 ^-7 -0.70866 × 10 ^-9
A10 A12
0.55257 × 10 ^-11 -0.19195 × 10 ^-13

FIGS. 13 to 16 and Table 4 show Example 4 of the zoom lens system according to the present invention. FIG. 13 is a lens configuration diagram at the short focal length end, FIG. 14 is a diagram of various aberrations, FIG. 15 is a lens configuration diagram at the long focal length end, FIG. 16 is a diagram of the various aberrations, and Table 4 is numerical data thereof.

The basic lens configuration is the same as in the third embodiment. The open / close stop S is 0.60 forward from the pole of the eleventh surface (second lens group 20). The flare cut stop FC1 is located 20.00 and 0.45 rearward from the pole of the tenth surface (first lens group 10) at the short focal length end and the long focal length end, and the height from the optical axis is 7.5. The flare-cut stop FC2 is located 0.42 and 38.01 behind the pole of the 18th surface (second lens group 20) at the short focal length end and the long focal length end, and the height from the optical axis is 9.0, and moves during zooming. No (fixed).
(Table 4)
FNO. = 1: 3.5-5.8
f = 18.50-53.30
W = 38.7-15.0
fB = 37.42-75.01
Surface NO. R d N _d ν
1 407.941 3.06 1.69895 30.1
2 -407.941 0.10--
3 48.376 1.20 1.78590 44.2
4 16.417 8.72--
5 1198.213 1.00 1.69680 55.5
6 21.285 2.09--
7 32.387 4.97 1.67270 32.1
8 -159.850 0.20--
9 67.012 1.90 1.52538 56.3
10 * 69.759 39.60-2.60--
11 53.885 3.38 1.58913 61.2
12 -90.697 1.33--
13 18.647 4.68 1.51633 64.1
14 3977.679 2.34--
15 -50.466 6.00 1.67270 32.1
16 17.241 1.05--
17 37.628 5.27 1.51742 52.4
18 -24.635---
* Is a rotationally symmetric aspherical surface.
Aspheric data (Aspheric coefficient not shown is 0.00):
Surface NO K A4 A6 A8
10 0.00 -0.21102 × 10 ^-4 0.27400 × 10 ^-7 -0.92284 × 10 ^-9
A10 A12
0.52448 × 10 ^-11 -0.12658 × 10 ^-13

17 to 20 and Table 5 show Example 5 of the zoom lens system according to the present invention. 17 is a lens configuration diagram at the short focal length end, FIG. 18 is a diagram of various aberrations thereof, FIG. 19 is a lens configuration diagram at the long focal length end, FIG. 20 is a diagram of the various aberrations, and Table 5 is numerical data thereof. The basic lens configuration is the same as that of the first embodiment. The open / close stop S is 0.60 forward from the pole of the eleventh surface (second lens group 20). The flare cut stop FC1 is located behind 20.91 and 1.75 from the pole of the tenth surface (first lens group 10) at the short focal length end and the long focal length end, and the height from the optical axis is 7.6. The flare cut stop FC2 is located at 0.40 and 37.24 rearward from the pole of the 18th surface (second lens group 20) at the short focal length end and the long focal length end, and the height from the optical axis is 9.0, and moves during zooming. No (fixed).
(Table 5)
FNO. = 1: 3.4-5.8
f = 18.50-53.30
W = 38.7-15.0
fB = 37.40-74.24
Surface NO. R d N _d ν
1 312.109 3.01 1.69895 30.1
2 -312.109 0.10--
3 64.488 1.20 1.80610 40.9
4 18.469 5.94--
5 62.964 1.00 1.69680 55.5
6 19.094 4.46--
7 31.531 4.47 1.69895 30.1
8 944.830 0.20--
9 94.199 1.80 1.52538 56.3
10 * 53.793 41.51-4.59--
11 42.430 2.06 1.58913 61.2
12 -128.075 0.54--
13 21.280 6.75 1.51633 64.1
14 -190.813 1.63--
15 -41.497 6.00 1.67270 32.1
16 18.552 0.83--
17 42.120 4.37 1.51742 52.4
18 -23.252---
* Is a rotationally symmetric aspherical surface.
Aspheric data (Aspheric coefficient not shown is 0.00):
Surface NO K A4 A6 A8
10 0.00 -0.16052 × 10 ^-4 -0.27457 × 10 ^-7 0.20213 × 10 ^-10
A10 A12
-0.34272 × 10 ^-12 0.21019 × 10 ^-15
Table 6 shows values for each conditional expression in each example.
(Table 6)
Example 1 Example 2 Example 3 Example 4 Example 5
Conditional expression (1) 1.68 1.70 1.64 1.68 1.70
Conditional expression (2) 1.05 1.06 1.04 1.07 1.06
Conditional expression (3) 1.06 1.06 1.07 1.08 1.06
As is apparent from Table 6, Examples 1 to 5 satisfy the conditional expressions (1) to (3),
As is apparent from the various aberration diagrams, the various aberrations are also corrected relatively well.

It is a lens block diagram in the short focal distance end of Example 1 of the zoom lens system by this invention. FIG. 2 is a diagram illustrating various aberrations in the configuration of FIG. 1. FIG. 3 is a lens configuration diagram at a long focal length end of Example 1; FIG. 4 is a diagram illustrating various aberrations in the configuration of FIG. 3. It is a lens block diagram in the short focal distance end of Example 2 of the zoom lens system by this invention. FIG. 6 is a diagram illustrating various aberrations in the configuration of FIG. 5. FIG. 6 is a lens configuration diagram at a long focal length end in Example 2; FIG. 8 is a diagram illustrating various aberrations in the configuration of FIG. 7. It is a lens block diagram in the short focal distance end of Example 3 of the zoom lens system by this invention. FIG. 10 is a diagram of various aberrations in the configuration of FIG. 9. It is a lens block diagram in the long focal distance end of the Example 3. FIG. 12 is a diagram illustrating various aberrations in the configuration of FIG. 11. It is a lens block diagram in the short focal distance end of Example 4 of the zoom lens system by this invention. FIG. 14 is a diagram illustrating various aberrations in the configuration of FIG. 13. 6 is a lens configuration diagram at a long focal length end of Example 4. FIG. FIG. 16 is a diagram illustrating various aberrations in the configuration of FIG. 15. It is a lens block diagram in the short focal distance end of Example 5 of the zoom lens system by this invention. FIG. 18 is a diagram illustrating various aberrations in the configuration of FIG. 17. It is a lens block diagram in the long focal distance end of the Example 5. FIG. 20 is a diagram illustrating various aberrations in the configuration in FIG. 19. It is a simple movement figure of the zoom lens system by this invention.

Claims (3)

In a zoom lens system including a first lens unit having a negative refractive power, an open / close stop, and a second lens group having a positive refractive power in order from the object side, and zooming by moving the first lens unit and the second lens unit ,
The first lens group includes, in order from the object side, a positive first lens, a negative second lens, a negative third lens, a positive fourth lens, and a positive or negative fifth lens. And
A zoom lens system satisfying the following conditional expressions (1) to (3):
(1) 1.5 <| f1 / fw | <1.8
(2) 1.0 <f2 / (fw × ft) ^1/2 <1.3
(3) 1.0 <| f2 / f1 | <1.2
However,
f1: the focal length of the first lens group ,
f2: focal length of the second lens group ,
fw: focal length of the entire system at the short focal length end,
ft: focal length of the entire system at the long focal length end   2. The zoom lens system according to claim 1, wherein a flare cut stop is provided between the first lens group and the open / close stop, the second lens group is fixed during focusing, and the flare cut stop is connected to the first lens group. Zoom lens system that moves together.   3. The zoom lens system according to claim 1, wherein a flare-cut stop is provided between the first lens group and the open / close stop, and the flare-cut stop is independent of the first lens group and the open / close stop during zooming. Zoom lens system that moves.

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