JP2621454B2 - Zoom lens - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a zoom lens suitable for a photographic camera, a video camera, and the like, and in particular, has three lens groups preceding a lens group having a negative refractive power, The present invention relates to a zoom lens having good optical performance with a short overall length of a high-magnification lens in which zooming is performed by moving these three lens groups.

(Prior Art) Conventionally, there are three lens groups of a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a negative refractive power. A zoom lens in which zooming is performed by moving two lens groups is disclosed in, for example,
JP 11260, JP-A-56-159614, JP-B-58-503
No. 27, British Patent No. 398307 and the like.

This type of zoom lens is relatively widely used as a photographing system for a wide angle of view because it is relatively easy to widen the angle of view.

However, Japanese Patent Publication No. 58-50327 and British Patent No. 3
The zoom lens of No. 98307 has the full length at the wide-angle end (No. 1
The distance from the lens surface to the image surface) is relatively long, and the diameter of the front lens is large, which is not always enough to reduce the size of the camera.

The zoom lenses disclosed in JP-A-55-11260 and JP-A-56-159614 are photographic lenses for copiers that change the photographic magnification from a low magnification to a high magnification including an equal magnification at a finite photographing distance. Yes, it does not actively change the focal length. This zoom lens is used in a so-called conjugate relationship by reversing the lens system as a whole at low magnification and high magnification, and the focal lengths at low magnification and high magnification are substantially equal, and at the intermediate magnification. Since the focal length is changed, it is not a zoom lens suitable for a photographic camera or a video camera.

The applicant of the present invention has proposed a zoom lens of the same type as that described above, which is suitable for a photographic camera, a video camera, or the like, for these zoom lenses in Japanese Patent Application Laid-Open No. 58-200208. In this publication, the first, second, and third groups of negative, positive, and negative
High optics in which the first and second groups of the two lens groups are moved under certain conditions to perform zooming, and the lens configuration of the three lens groups is specified so that aberration fluctuations caused by zooming are corrected well. Achieving a high-performance zoom lens.

(Problems to be Solved by the Invention) The present invention utilizes a refractive power arrangement of a zoom lens proposed in Japanese Patent Application Laid-Open No. Sho 58-200208 of the present applicant to provide a zoom type and a lens configuration of each lens group. It is another object of the present invention to provide a zoom lens which is further improved, in particular, shortens the overall length of the lens and achieves a high zoom ratio of about 3 and has high optical performance over the entire zoom range.

(Means for Solving the Problems) The present invention provides three lens groups of a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a negative refractive power in order from the object side. When performing zooming from the wide-angle end to the telephoto end by moving the three lens units, both the second and third units are in the object side direction, and the third unit is more than the second unit. Is moved more, and the surface distance between the first and second units and the surface distance between the second and third units at the wide angle end are S1w and S2w, respectively, and the focal length of the third unit is f3. When the focal lengths of the entire system at the wide-angle end and the telephoto end are respectively FW and FT, 1.5 <S1w / S2w <3.2 ＜ (1) 0.2 <| f3 | / FT <0.35 ‥‥‥‥ (2) 3.00 <FT / FW <5 (3) It is characterized by satisfying the following condition.

(Example) FIGS. 1 to 4 are lens cross-sectional views of Numerical Examples 1 to 4, respectively, of the present invention. In the figure, I is the first group of negative refractive power, II
Indicates a second group having a positive refractive power, III indicates a third group having a negative refractive power, and arrows indicate moving directions of the respective lens groups when zooming from the wide-angle side to the telephoto side.

When zooming from the wide-angle end to the telephoto end, the zoom lens according to the present embodiment moves three lens groups as shown in each figure, and at this time, both the second and third groups are moved in the object side direction. The third group is moved more than the second group.

Also, at the time of zooming from the wide-angle end to the telephoto end, the first unit is moved together with the second and third units as shown in FIG. By moving the first unit in this manner, the overall length of the lens at the wide-angle end is effectively reduced. That is, a refractive power arrangement is adopted in which the entire length of the lens is short on the wide-angle side and long on the telephoto side.

In particular, when the zoom lens is composed of the three lens units having the above-described refractive power, the ratio of the surface distance S1w between the first and second units and the surface distance S2w between the second and third units at the wide angle end is large. It is set so as to satisfy the conditional expression (1).

As a result, the back focus at the wide-angle end is shortened, and the overall length of the lens at the wide-angle end is significantly reduced.

If the upper limit of conditional expression (1) is exceeded, the back focus will increase more than necessary. If the lower limit is exceeded, the back focus will be too short, and the third lens unit will be too close to the imaging surface. Defects such as dust adhering to the lens surface appearing on the photosensitive surface and ghosting due to reflection on each lens surface are likely to occur. In this embodiment, it is more preferable to set the conditional expression (1) as 2.5 <S1w / S2w <2.8.

Further, by setting the ratio between the focal length f3 of the third lens unit and the focal length FT of the entire system at the telephoto end as in the conditional expression (2), it is possible to maintain good optical performance over the entire zoom range, The overall system is downsized.

That is, by increasing the refractive power of the third lens unit to some extent, the entire lens system is slightly telephoto-type on the telephoto side to increase the focal length and to reduce the size of the entire lens system.

Beyond the upper limit, the tendency to telephoto is reduced and the entire lens system becomes larger. If the lower limit is exceeded, on the contrary, the telephoto tendency becomes too strong and the size of the entire lens system can be easily reduced, but the curvature of field tends to be overcorrected, making it difficult to obtain good optical performance. In this embodiment, it is more preferable to set the conditional expression (2) as 0.2 <| f3 | / FT <0.35.

Conditional expression (3) is a condition for appropriately setting the zoom ratio in the zoom lens of the present invention and maintaining good optical performance over the entire zoom range.

That is, in the above-described lens configuration, by setting each element so as to fall within the zoom range, high optical performance is obtained over the entire zoom range while miniaturizing the entire lens system.

The zoom lens aimed at by the present invention can be achieved by satisfying the above conditions, but in order to further reduce the size of the lens system and obtain good optical performance, the following conditions must be satisfied. good.

When the focal length of the first lens unit is f1, and the distance from the first lens surface on the object side at the wide-angle end to the image plane is Lw, 0.4 <Lw / FT <0.9 (4) 0.25 <| f1 | / FT <0.53 (5) The following condition must be satisfied.

If the upper limit of conditional expression (4) is exceeded, the entire lens system will be large. If the lower limit is exceeded, it will be difficult to obtain a predetermined zoom ratio.

Conditional expression (5) is for appropriately setting the amount of movement when performing focusing by the first lens unit, and for reducing fluctuations in aberrations during focusing. If the negative refractive power of the first lens unit becomes too weak beyond the upper limit value of the conditional expression (5), it is not preferable because the amount of extension at the time of focusing increases and the diameter of the front lens increases. On the other hand, if the refractive power of the first lens unit becomes too strong beyond the lower limit, the diameter of the front lens becomes small, but the fluctuation of aberrations during focusing increases, which is not good.

In this embodiment, more preferably, conditional expression (4) is satisfied.
0.5 <Lw / FT <0.8, and conditional expression (5) is set to 0.3 <
It is better to set as | f1 | / FT <0.45.

In the present embodiment, the first lens unit is moved together with the second and third lens units so as to reduce the size of the entire lens system while ensuring a predetermined zoom ratio.

At this time, in order to move the first group and easily secure a predetermined zoom ratio, when the moving amounts of the second group and the third group accompanying zooming are s and t, respectively, 0.7 <s / t < 0.95 It is better to satisfy (6). By moving the third lens unit more than the second lens unit so as to satisfy the conditional expression (6), it is easy to reduce the size of the entire lens system while securing a predetermined zoom ratio.

Exceeding the lower limit of conditional expression (6), the amount of movement of the third lens unit becomes
If the amount of movement of the group is too large, the second and third groups mechanically interfere on the telephoto side, which is not good. On the other hand, if the amount of movement of the third unit exceeds the upper limit and the amount of movement of the third unit is too small, it is difficult to effectively reduce the size of the entire lens system when the first unit is moved. Come.

In the present embodiment, while miniaturizing the entire lens system,
In order to satisfactorily correct the aberration fluctuation during zooming, the second group is composed of two or more positive lenses, negative lenses, and positive lenses in order from the object side. In particular, the amount of aberration generated in the second group is small. I can do it.

When the third lens unit has a positive lens and at least one negative lens, and when each lens unit is composed of one lens, at least one lens surface in the third lens unit is negatively refracted toward the lens periphery. It is preferable to use an aspherical surface having a weaker power (higher positive refractive power). According to this, it is possible to satisfactorily correct the fluctuation of the distortion and the chromatic aberration of magnification due to zooming.

Further, the first group has at least one negative lens and one positive lens. For example, in the case of two negative lenses and one positive lens, one lens surface in the first group becomes positive as it goes to the periphery of the lens. It is preferable to use an aspherical surface having a shape in which the refractive power of the lens is weak (the negative refractive power is strong). According to this, barrel distortion generated from the second lens unit can be favorably corrected.

In addition to the lens configuration of each lens group shown in Numerical Examples 1 to 4 described below, the following configuration is preferable.

The first group is composed of three meniscus negative lenses having a convex surface facing the object side, a negative lens, and a positive lens in order from the object side, and the second group is composed of a positive lens, a positive lens (or a cemented positive lens). Lens), a positive lens, an aperture stop, a negative lens, and a positive lens. The third group is a meniscus positive lens having a convex surface facing the image surface side, and a meniscus-shaped lens having a convex surface facing the image surface side. It is better to have two negative lenses.

Next, numerical examples of the present invention will be described. In numerical examples
Ri is the radius of curvature of the i-th lens surface in order from the object side,
Is the i-th lens thickness and air gap from the object side, Ni and ν
i is the refractive index and Abbe number of the glass of the i-th lens in order from the object side.

Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

The aspherical shape has an x-axis in the direction of the optical axis, an H-axis in the direction perpendicular to the optical axis, a positive traveling direction of light, and R is a paraxial radius of curvature, A, B,
When C, D, E, ... are each aspheric coefficients It is represented by the following equation.

Numerical Example 1 F = 36.13 FNo = 1: 3.6 2ω = 61.8 ゜ to 18.8
13 0.6130.6 to 8.1 R 1 = 82.24 D 1 = 1.30 N 1 = 1.81600 v 1 = 46.6 R 2 = 33.31 D 2 = 4.00 R 3 = -166.93 D 3 = 1.30 N 2 = 1.77250 v 2 = 49.6 R 4 = 37.25 D 4 = 0.15 R 5 = 20.78 D 5 = 3.30 N 3 = 1.64769 v3 = 33.8 R 6 = 65.32 D 6 = variable R 7 = 191.31 D 7 = 2.40 N 4 = 1.49700 v4 = 81.6 R 8 = -40.65 D 8 = 0.15 R 9 = 39.53 D 9 = 1.83 N 5 = 1.49700 ν 5 = 81.6 R10 = 123.79 D10 = 0.15 R11 = 13.99 D11 = 4.00 N 6 = 1.49700 ν6 = 81.6 R12 = 152.76 D12 = 2.50 R13 = Aperture D13 = 1.00 R14 = -48.19 D14 = 2.04 N7 = 1.83400 ν7 = 37.
2 R15 = 15.76 D15 = 1.00 R16 = 28.18 D16 = 3.00 N 8 = 1.56732 ν8 = 42.8 R17 = -25.02 D17 = variable R18 = -27.86 D18 = 2.70 N 9 = 1.64769 ν3 = 33.
8 R19 = -16.28 D19 = 3.72 R20 = -15.12 D20 = 1.20 N10 = 1.80400 ν4 = 46.
6 R21 = -26.35 D21 = 2.53 R22 = -16.27 D22 = 1.20 N11 = 1.69680 ν5 = 55.
5 R23 = −32.50 R5: Aspheric surface A = 0 B = −1.777632 × 10 ⁻⁵ C = −2.92211 × 10 ⁻⁸ D = −5.46454 × 10 ⁻¹¹ E = 1.79023 × 10 ⁻¹³ Numerical example 2 F = 36.26 FNo = 1: 3.6 2ω = 61.6 ゜ ～ 18.5
133 133 to 8.1 R 1 = 52.72 D 1 = 1.20 N 1 = 1.81600 ν 1 = 46.6 R 2 = 31.48 D 2 = 4.00 R 3 = -163.89 D 3 = 1.20 N 2 = 1.77250 ν 2 = 49.6 R 4 = 44.88 D 4 = 0.15 R 5 = 19.20 D 5 = 3.00 N 3 = 1.64769 v 3 = 33.8 R 6 = 34.68 D 6 = Variable R 7 = 87.36 D 7 = 2.80 N 4 = 1.49700 v 4 = 81.6 R 8 = -34.28 D 8 = 0.15 R 9 = 33.44 D 9 = 1.80 N 5 = 1.49700 ν 5 = 81.6 R10 = 87.98 D10 = 0.15 R11 = 12.07 D11 = 3.00 N 6 = 1.49700 ν 6 = 81.6 R12 = 25.37 D12 = 3.00 R13 = Aperture D13 = 0.80 R14 = -85.21 D14 = 2.00 N 7 = 1.83400 ν 7 = 37.
2 R15 = 14.01 D15 = 0.61 R16 = 21.22 D16 = 2.60 N 8 = 1.56732 ν 8 = 42.8 R17 = -29.97 D17 = Variable R18 = -25.51 D18 = 2.70 N 9 = 1.64769 ν 9 = 33.
8 R19 = -14.95 D19 = 2.87 R20 = -14.06 D20 = 1.20 N10 = 1.80400 ν10 = 46.
6 R21 = -26.35 D21 = 1.72 R22 = -14.17 D22 = 1.20 N11 = 1.69680 ν11 = 55.
5 R23 = -23.08 R5: Aspheric surface A = 0 B = −1.667165 × 10 ⁻⁵ C = −2.59916 × 10 ⁻⁸ D = −1.86464 × 10 ⁻¹⁰ E = 2.69112 × 10 ⁻¹³ Numerical example 3 F = 36.13 FNo = 1: 3.6 2ω = 61.8 ゜ ～ 18.8
13 0.6130.6 to 8.1 R 1 = 75.20 D 1 = 1.30 N 1 = 1.81600 ν 1 = 46.6 R 2 = 32.04 D 2 = 3.70 R 3 = -183.91 D 3 = 1.30 N 2 = 1.77250 ν 2 = 49.6 R 4 = 32.19 D 4 = 0.15 R 5 = 19.70 D 5 = 3.60 N 3 = 1.58347 ν 3 = 30.2 R 6 = 105.20 D 6 = Variable R 7 = 289.44 D 7 = 2.85 N 4 = 1.49700 ν 4 = 81.6 R 8 = -31.11 D 8 = 0.16 R 9 = 27.68 D 9 = 3.06 N 5 = 1.48749 ν 5 = 70.2 R10 = -122.87 D10 = 1.02 N 6 = 1.84666 ν 6 = 23.9 R11 = 153.05 D11 = 0.15 R12 = 13.13 D12 = 2.70 N 7 = 1.60311 ν 7 = 60.7 R13 = 26.31 D13 = 3.00 R14 = Aperture D14 = 0.70 R15 = -167.10 D15 = 2.04 N 8 = 1.83400 ν 8 = 37.2 R16 = 14.07 D16 = 1.22 R17 = 26.97 D17 = 2.60 N 9 = 1.62606 ν 9 = 39.2 R18 = -33.53 D18 = Variable R19 = -28.69 D19 = 2.70 N10 = 1.59270 ν10 = 35.
3 R20 = -16.21 D20 = 3.70 R21 = -15.48 D21 = 1.20 N11 = 1.69680 ν11 = 55.
5 R22 = -26.35 D22 = 1.34 R23 = -16.62 D23 = 1.20 N12 = 1.69680 ν12 = 55.
5 R24 = -39.59 R5: Aspheric surface A = 0 B = −1.996935 × 10 ⁻⁵ C = −4.2762 × 10 ⁻⁸ D = −2,11643 × 10 ⁻¹¹ E = −1.02294 × 10 ⁻¹³ Numerical example 4 F = 36.13 FNo = 1: 3.6 2ω = 61.8 ゜ to 18.8
13 13130.6 to 8.1 R 1 = 54.79 D 1 = 1.30 N 1 = 1.77250 ν 1 = 49.6 R 2 = 31.74 D 2 = 3.70 R 3 = -134.69 D 3 = 1.30 N 2 = 1.77 250 ν 2 = 49.6 R 4 = 28.67 D 4 = 0.15 R 5 = 18.26 D 5 = 4.00 N 3 = 1.58347 ν 3 = 30.2 R 6 = 86.80 D 6 = Variable R 7 = 272.00 D 7 = 2.85 N 4 = 1.49700 ν 4 = 81.6 R 8 = -30.92 D 8 = 0.16 R 9 = 44.19 D 9 = 3.06 N 5 = 1.51742 ν 5 = 52.4 R10 = -42.15 D10 = 1.02 N 6 = 1.84666 ν 6 = 23.
9 R11 = -301.92 D11 = 0.15 R12 = 13.37 D12 = 2.70 N 7 = 1.61700 ν 7 = 62.8 R13 = 31.74 D13 = 3.00 R14 = Aperture D14 = 0.70 R15 = -107.11 D15 = 2.04 N 8 = 1.83400 ν 8 = 37.2 R16 = 14.89 D16 = 1.22 R17 = 31.32 D17 = 2.60 N 9 = 1.62045 ν 9 = 38.1 R18 = -28.74 D18 = Variable R19 = -41.58 D19 = 3.00 N10 = 1.59270 ν10 = 35.
3 R20 = -17.65 D20 = 3.27 R21 = -16.61 D21 = 1.20 N11 = 1.79216 ν11 = 54.
7 R22 = -70.11 D22 = 3.27 R23 = -15.01 D23 = 1.20 N12 = 1.48749 ν12 = 70.
2 R24 = −24.63 R5: Aspheric surface A = 0 B = −2.00504 × 10 ⁻⁵ C = −5.8775 × 10 ⁻⁸ D = 7.79387 × 10 ⁻¹¹ E = −5.00224 × 10 ⁻¹³ (Effects of the Invention) According to the present invention, by specifying the refractive power and the lens configuration of the three lens groups as described above, the entire lens system can be reduced in size and have a high zoom ratio of about 4 and a high zoom ratio. In addition, a zoom lens having good optical performance over the entire zoom range can be achieved.

[Brief description of the drawings]

1 to 4 are lens sectional views of Numerical Examples 1 to 4 of the present invention, respectively, and FIGS. 5 to 8 are various aberration diagrams of Numerical Examples 1 to 4 of the present invention, respectively. In the lens cross-sectional view, I, II, and III represent the first group, the second group,
In the third group, the arrows indicate the moving direction of each lens group during zooming from the wide-angle end to the telephoto end, and (A), (B),
(C) shows aberrations at the wide-angle end, the middle, and the telephoto end, respectively, and d is d.
Line, g is g line, SC is sine condition, ΔS is sagittal image plane,
ΔM is a meridional image plane.

Claims (5)

(57) [Claims] 1. An optical system comprising: a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. When performing zooming from the wide-angle end to the telephoto end by moving the second lens unit and the third lens unit, both the second lens unit and the third lens unit are moved toward the object side, and the third lens unit is moved more than the second lens unit. The surface distance between the first and second lens units at the wide-angle end and the surface distance between the second lens unit and the third lens unit are S1w and S2w, respectively, the focal length of the third lens unit is f3, and the entire system at the wide-angle end and the telephoto end. 1.5 <S1w / S2w <3.2 0.2 <| f3 | / FT <0.35 3.00 <FT / FW <5 When the focal lengths of the zoom lens are FW and FT, respectively, the following condition is satisfied. 2. When the focal length of the first lens unit is f1 and the distance from the first lens surface on the object side at the wide-angle end to the image plane is Lw, 0.4 <Lw / FT <0.9 0.25 <| f1 | / FT The zoom lens according to claim 1, wherein the following condition is satisfied. 3. The zoom lens according to claim 2, wherein said second group includes at least two positive lenses, a negative lens, and a positive lens in order from the object side. 4. The third group has a positive lens and at least one negative lens in order from the object side, and at least one lens surface in the third group is aspherical. 2. The zoom lens according to 2. 5. The apparatus according to claim 1, wherein the first lens group includes at least one lens in order from the object side.
3. The zoom lens according to claim 2, further comprising a negative lens and a positive lens, wherein at least one lens surface in the first group is aspheric.