JPH04301811A - rear focus zoom lens - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[0001] The present invention relates to a rear focus type zoom lens, and in particular, a zoom lens with a variable magnification ratio of 8 to 10, used in photographic cameras, video cameras, broadcast cameras, etc. The present invention relates to a rear focus type zoom lens suitable for a zoom lens having a large aperture ratio with an F number of about 2.0 and a high zoom ratio. [0002] Conventionally, various types of zoom lenses for photographic cameras, video cameras, etc. have adopted the so-called rear focus type, in which focusing is performed by moving lens groups other than the first lens group on the object side. It is proposed that In general, rear focus type zoom lenses have a smaller effective diameter of the first group than zoom lenses that focus by moving the first group, making it easier to downsize the entire lens system, and making it easier to take close-up shots. In particular, very close-up photography is facilitated, and since the relatively small and lightweight lens group is moved, the driving force for the lens group is small and quick focusing is possible. As such a rear focus type zoom lens, for example, Japanese Patent Application Laid-open No. 63-44614 discloses, in order from the object side, a first group with positive refractive power, a second group with negative refractive power for variable magnification, and a second group with negative refractive power for variable magnification. In a so-called four-group zoom lens, which consists of four lens groups: a third group with negative refractive power to correct image field fluctuations associated with magnification, and a fourth group with positive refractive power, the third group is moved. Focus is on. However, this zoom lens has a tendency to increase the overall length of the lens because it is necessary to secure a movement space for the third group. [0005] In Japanese Patent Application Laid-open No. 136012/1982, a variable power section is composed of three or more lens groups, and focusing is performed by moving some of the lens groups. [0006] In JP-A-63-247316, in order from the object side, a first group with positive refractive power, a second group with negative refractive power,
It has four lens groups: a third group with positive refractive power and a fourth group with positive refractive power.The second group is moved to change the magnification, and the fourth group is moved to accompany the change in magnification. Performs image plane fluctuation and focus. In JP-A-58-160913, in order from the object side, a first group with positive refractive power, a second group with negative refractive power,
It has four lens groups: a third group with positive refractive power and a fourth group with positive refractive power.The first and second groups are moved to change the magnification, and the image plane changes due to the change in magnification. This is done by moving the fourth group. Focusing is performed by moving one or more of these lens groups. [0008] In JP-A-58-129404 and JP-A-61-258217, from the object side, the first group has a positive refractive power, the second group has a negative refractive power, and the third group has a positive refractive power. group, a fourth group with positive refractive power, and a fifth group with negative refractive power.
In a five-group zoom lens consisting of two lens groups, the fifth
Focusing is performed by moving the lens group or a plurality of lens groups including the fifth lens group. Japanese Unexamined Patent Publication No. 60-6914 discloses a 5-group zoom lens similar to the one described above, which has a property that the position of the focus lens group on the optical axis is constant for a specific finite distance object regardless of zooming. is proposed. Problems to be Solved by the Invention Generally, when a rear focus method is adopted in a zoom lens, the entire lens system becomes smaller as described above, and quick focusing becomes possible, and close-up photography becomes easier. is obtained. On the other hand, however, there is a problem in that aberration fluctuations during focusing become large, making it extremely difficult to obtain high optical performance while downsizing the entire lens system over the entire object distance range from infinity to close objects. A point appears. Particularly in the case of a zoom lens with a large aperture ratio and a high zoom ratio, a problem arises in that it is very difficult to obtain high optical performance over the entire zoom range and over the entire object distance. [0012] The present invention employs a rear focus system, and when achieving a large aperture ratio and high variable power, it prevents the overall size of the lens system from increasing, and can cover the entire variable power range from the wide-angle end to the telephoto end. Another object of the present invention is to provide a rear focus type zoom lens having a simple configuration and having good optical performance over the entire range of object distances, from objects at infinity to objects at short distances. Means for Solving the Problems The rear focus type zoom lens of the present invention includes, in order from the object side, a first group with a positive refractive power, a second group with a negative refractive power, and a second group with a positive refractive power. It has five lens groups: a third group, a fourth group with positive refractive power, and a fifth group with negative refractive power, and the first group is moved toward the object side and the second group is moved toward the image plane side. to change the magnification from the wide-angle end to the telephoto end, move the fourth group to correct the image plane fluctuation caused by the change in magnification, move the fourth group to focus, and adjust the focal length of the i-th group. When fi is the focal length of the entire system at the wide-angle end and telephoto end, respectively, fw and fT, and the imaging magnification of the fifth group is β5.
[014] It is characterized by satisfying the following condition. DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of an embodiment of the paraxial refractive power arrangement of a rear focus type zoom lens according to the present invention. 2 and 3 are cross-sectional views of lenses of Numerical Examples 1 and 2 of the present invention, which will be described later. FIGS. 4 to 6 are various aberration diagrams at the wide-angle end, intermediate, and telephoto end of Numerical Example 1 of the present invention, which will be described later. be. 7 to 9 are various aberration diagrams at the wide-angle end, intermediate, and telephoto end of Numerical Example 2, which will be described later, of the present invention. 10 to 12 are various aberration diagrams at the wide-angle end, intermediate, and telephoto end of Numerical Example 3, which will be described later, of the present invention. 13 to 15 are numerical example 4 of the present invention, which will be described later.
FIG. 3 is a diagram of various aberrations at the wide-angle end, intermediate, and telephoto end. In the figure, 1 is the first group with positive refractive power, 2 is the second group with negative refractive power, 3 is the third group with positive refractive power, 4 is the fourth group with positive refractive power, 5 is the fifth group having negative refractive power. SP is an aperture stop, which is arranged in front of the third group 3. When changing the magnification from the wide-angle end to the telephoto end, the first group is moved toward the object side and the second group is moved toward the image plane side as shown by the arrows, and the fourth group is moved to compensate for the fluctuations in the image plane due to the change in magnification. It has been corrected. Further, a rear focus type is adopted in which focusing is performed by moving the fourth group on the optical axis. The solid line curve 4a and the dotted line curve 4b of the fourth group shown in the figure represent image plane fluctuations when changing the magnification from the wide-angle end to the telephoto end when focusing on an object at infinity and a close object, respectively. It shows the movement trajectory for correction. Note that the third group and the fifth group are fixed during zooming and focusing. In this embodiment, the fourth group is moved to correct image plane fluctuations caused by zooming, and the fourth group is also moved to perform focusing. Especially curve 4 in the same figure.
As shown in FIGS. a and 4b, when changing the magnification from the wide-angle end to the telephoto end, the lens is moved so as to have a convex locus toward the object side. This makes effective use of the space between the third and fourth groups and effectively shortens the overall length of the lens. In this embodiment, for example, when focusing from an object at infinity to a close object at the telephoto end, the fourth group is moved forward as shown by a straight line 4c in the figure. In this embodiment, compared to a conventional four-group zoom lens in which focusing is performed by extending the first group, the effective diameter of the first group can be increased by adopting the rear focusing method as described above. This is effectively prevented. By arranging the aperture diaphragm immediately before the third group, aberration fluctuations caused by the movable lens group can be reduced, and by shortening the distance between the lens groups in front of the aperture diaphragm, the diameter of the front lens can be reduced. easily achieved. By specifying the optical constants of each lens group as described above, a zoom lens with a high zoom ratio is obtained which has good optical performance over the entire zoom range and over the entire object distance. Next, the technical meaning of each of the above-mentioned conditional expressions will be explained. Conditional expression (1) relates to the refractive power of the second group, and is intended to effectively obtain a predetermined zoom ratio while reducing fluctuations in aberrations accompanying zooming. If the refractive power of the second group exceeds the lower limit and becomes too strong, it will be easier to downsize the entire lens system, but the Petzval sum will increase in the negative direction, the curvature of field will increase, and aberrations will fluctuate with zooming. becomes larger. If the upper limit is exceeded and the refractive power of the second group becomes too weak, aberration fluctuations due to zooming will decrease, but the amount of movement of the second group to obtain a predetermined zoom ratio will increase, and the overall length of the lens will become longer. It's not good because it's getting worse. Conditional expression (2) relates to the imaging magnification of the fifth group,
The main objective is to maintain good optical performance over the entire screen while shortening the overall length of the lens. If the imaging magnification of the fifth group becomes too small beyond the lower limit, the overall length of the lens will not be shortened enough. If the imaging magnification becomes too large beyond the upper limit, the overall length of the lens will be shortened, but it will be difficult to obtain a predetermined back focus, and the distance from the exit pupil to the image plane will also become short, which is not good. Conditional expression (3) concerns the ratio of the refractive powers of the third group and the fourth group, and is mainly used to shorten the total length of the lenses after the third group while maintaining good optical performance of the entire screen. be. If the refractive power of the third group exceeds the lower limit and becomes too strong, the overall length of the lens will become shorter, but it will become difficult to properly correct spherical aberration and coma, and it will also become difficult to secure a predetermined back focus. . Furthermore, if the upper limit is exceeded and the refractive power of the third group becomes too weak, the overall length of the lens will not be shortened enough. The rear focus type zoom lens, which is the object of the present invention, can be achieved by satisfying the above conditions, but it also reduces aberration fluctuations accompanying zooming, and has a high level of stability over the entire zooming range. In order to obtain good optical performance, it is preferable to satisfy the following conditions. The zoom ratio is z, the imaging magnification of the second group at the telephoto end is β2T, and the amount of movement of the first and second groups when changing from the wide-angle end to the telephoto end is V1 and V2, respectively. It is necessary to satisfy the following condition. Conditional expression (4) relates to the ratio of the amount of movement of the first group and the second group when changing magnification from the wide-angle end to the telephoto end. This is to achieve a good balance between reducing the diameter of the front lens and shortening the overall length of the lens. If the lower limit is exceeded and the amount of movement of the first group becomes too small, it becomes difficult to effectively shorten the overall lens length at the wide-angle end, and if the upper limit is exceeded and the amount of movement of the first group becomes too large. This is not a good idea because the diameter of the front lens increases to ensure off-axis light in the zoom range from intermediate to telephoto end. Conditional expression (5) relates to the imaging magnification of the second group at the telephoto end relative to the zoom ratio. If the lower limit is exceeded and the imaging magnification becomes too small, the amount of movement of the second group to obtain a predetermined variable power ratio becomes large, resulting in an increase in the overall length of the lens. Conversely, if the imaging magnification exceeds the upper limit and the imaging magnification becomes too large, the overall length of the lens will be shortened, but the movement trajectory of the fourth group near the telephoto end for an object at infinity will change rapidly, and the driving means such as a motor will This is not a good idea because the load on the system will increase. In the present invention, it is particularly preferable that the zoom lens has the following relationship: 1.8<|f5/f3|<2.6
It is better to satisfy the condition (6). Conditional expression (6) relates to the refractive powers of the fifth group and the third group, and is intended to obtain good optical performance while shortening the lens lengths of the third and subsequent groups. If the lower limit of conditional expression (6) is exceeded and the refractive power of the fifth group becomes too strong, the negative Petzval sum increases, making it difficult to correct field curvature. On the other hand, if the upper limit is exceeded and the refractive power of the fifth group becomes too weak, a sufficient overall length shortening effect cannot be obtained. Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the i-th lens surface from the object side, Di is the thickness and air gap of the i-th lens from the object side, and Ni and νi are the curvature radius of the i-th lens from the object side, respectively. These are the refractive index and Abbe number of glass. [0036] In addition, R19 and R in Numerical Examples 1 and 3
20. R20 and R21 in Numerical Examples 2 and 4 are glass materials such as a face plate. The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis, a positive direction of light propagation, R0 is the paraxial radius of curvature, and B, C, D, and E are the aspherical coefficients. When [003
[8] [Equation 5] Table 1 shows the relationship with each conditional expression in each numerical example. Numerical Example 1 F= 1 ~ 9.51 FNO=
1:2.05~2.88 2ω=56.1°
~ 6.4° R 1 = 9.167
D1=0.166 N1=1.80
518 ν 1= 25.4 R 2=
3.363 D2= 0.658
N2=1.51633 ν2=6
4.1 R3=-38.490D
3=0.025
R4=
3.548 D4= 0.475
N 3 = 1.80400 ν 3 = 46.
6 R 5 = 17.348 D 5
= variable
R6=24.0
92 D 6 = 0.083 N 4
=1.83400 ν 4= 37.2
R7=0.749 D7=0
．． 275
R8=-1.352
D8=0.083 N5=1
．． 51742 ν 5= 52.4 R
9= 0.988 D 9= 0.3
25 N 6 = 1.80518 ν 6
= 25.4 R10 = -16.201
D10= variable
R11=
Aperture D11 = 0.170

R12= Aspherical surface D12=
0.450 N 7=1.58913
ν7=61.2 R13=-18.788
D13 = variable
R14=
2.200 D14=0.083
N 8 = 1.80518 ν 8 = 2
5.4 R15=0.980D
15=0.566 N 9=1.58313
ν 9= 59.4 R16= Aspheric D16= Variable

R17=-32.161 D17=0.
083 N10=1.76182 ν1
0=26.5 R18= Aspherical surface
D18=0.500
R19=
∞ D19= 0.933
N11=1.51633 ν11=64.
1 R20= ∞

[Table 1] R12 surface R0=1.552
B = −4.528×10−2 C
= −1.663×10−2 D = 6.6
60×10-3R16 surface R0= -2.505
B = 6.627×10-2C
= −5.766×10−2 D = 4.47
5×10-2R18 surface R0=4.493
B = 7.893×10-4C =
1.279×10−1 D = −8.64
2×10-2 Numerical Example 2 F= 1 ~ 9.51 FNO=
1:2.05~2.88 2ω=56.1°
~ 6.4° R 1 = 9.165
D1=0.166 N1=1.80
518 ν 1= 25.4 R 2=
3.363 D2= 0.650
N2=1.51633 ν2=6
4.1 R3=-39.307D
3=0.025
R4=
3.567 D4= 0.483
N 3 = 1.80400 ν 3 = 46.
6 R 5 = 17.872 D 5
= variable
R6=21.5
03 D 6= 0.083 N 4
=1.83400 ν 4= 37.2
R7=0.749 D7=0
．． 275
R8=-1.346
D8=0.083 N5=1
．． 51742 ν 5= 52.4 R
9= 0.990 D 9= 0.3
33 N 6=1.80518 ν 6
= 25.4 R10 = -16.474
D10= variable
R11=
Aperture D11 = 0.170

R12= Aspherical surface D12=
0.450 N 7=1.60311
ν7=60.7 R13=-48.791
D13 = variable
R14=
2.337 D14= 0.083
N8=1.84666 ν8=2
3.8 R15= 1.102D
15=0.025
R16=
1.167 D16= 0.516
N9=1.58313 ν9=59.
4 R17= Aspherical surface D17= Variable
R18=-10.862
D18=0.083 N10=1.
78472 ν10= 25.7 R1
9= Aspherical surface D19= 0.500

R20=∞ D2
0=0.933 N11=1.51633
ν11= 64.1 R21= ∞ 0040] [Table 2] R12 surface R0= 1.498
B = −4.890×10−2 C
= −1.704×10−2 D = 4.4
39×10-3R16 surface R0= -2.200
B = 6.534×10-2C
= −5.194×10−2 D = 2.19
6×10-2R19 surface R0= 7.340
B=-2.842×10-3C=
1.017×10−1 D = −4.73
8×10-2 Numerical Example 3 F= 1 ~ 7.59 FNO=
1:2.05~2.88 2ω=52.4°
~7.4° R1=6.162
D1=0.138 N1=1.80
518 ν 1= 25.4 R 2=
2.524 D2= 0.568
N2=1.51633 ν2=6
4.1 R3= 106.969 D
3=0.023
R4=
2.827 D4= 0.422
N 3 = 1.80400 ν 3 = 46.
6 R 5 = 15.628 D 5
= variable
R6=17.7
83 D 6 = 0.076 N 4
=1.83400 ν 4= 37.2
R7=0.637 D7=0
．． 238
R8=-0.973
D8=0.076 N5=1
．． 51742 ν 5= 52.4 R
9= 0.917 D 9= 0.2
94 N 6 = 1.80518 ν 6
= 25.4 R10 = -6.370
D10= variable
R11=
Aperture D11 = 0.150

R12= Aspherical surface D12=
0.437 N7=1.58913
ν7=61.2 R13=-6.246
D13 = variable
R14=
2.108 D14= 0.092
N 8 = 1.80518 ν 8 = 2
5.4 R15=0.874D
15=0.537 N 9=1.58313
ν 9= 59.4 R16= Aspheric D16= Variable

R17=-55.890 D17=0.
076 N10=1.78472 ν1
0=25.7 R18= Aspherical surface
D18=0.460
R19=
∞ D19=0.860
N11=1.51633 ν11=64.
1 R20= ∞

[Table 3] R12 surface R0=1.409
B = −7.693×10−2 C
= −1.925×10−2 D = 6.6
23×10-3R16 surface R0= -2.145
B = 8.329×10-2C
= −7.255×10−2 D = 4.39
9×10-2R18 surface R0= 3.563
B=1.052×10-2C=
2.346×10−1 D = −2.47
0x10-1 Numerical Example 4 F= 1 ~ 7.59 FNO=
1:2.05~2.88 2ω=52.4°
~7.4° R1=6.342
D1=0.138 N1=1.80
518 ν 1= 25.4 R 2=
2.527 D2= 0.568
N2=1.51633 ν2=6
4.1 R3= 101.290D
3=0.023
R4=
2.873 D4= 0.414
N 3 = 1.80400 ν 3 = 46.
6 R 5 = 17.266 D 5
= variable
R6=21.8
63 D 6= 0.076 N 4
=1.88300 ν 4= 40.8
R7=0.686 D7=0
．． 238
R8=-1.103
D8=0.076 N5=1
．． 51742 ν 5= 52.4 R
9= 0.931 D 9= 0.2
76 N 6 = 1.80518 ν 6
= 25.4 R10 = -7.556
D10= variable
R11=
Aperture D11 = 0.150

R12= Aspherical surface D12=
0.4147 N7=1.60311
ν 7= 60.7 R13= −14.337
D13 = variable
R14=
2.361 D14= 0.092
N8=1.84666 ν8=2
3.8 R15= 1.017D
15=0.023
R16=
1.103 D16= 0.483
N9=1.60311 ν9=60.
7 R17= Aspherical surface D17= Variable
R18=-17.020
D18=0.076 N10=1.
78472 ν10= 25.7 R1
9=5.079 D19=0.46
0
R20=∞
D20=0.860 N11=1.516
33 ν11= 64.1 R21=
∞ [0042] [Table 4] R12 surface R0= 1.318
B = −8.866×10−2 C
= −1.146×10−2 D = −1.0
61×10-2R17 surface R0= -1.903
B = 6.518×10-2C
= −1.462×10−2 D = −8.3
15×10-2R19 surface R0=5.079
B = 2.412×10-3C
= 2.134×10-1 D = -2.
856×10−1 Table 1 [0043] [Table 5] [Effects of the Invention] According to the present invention, as described above, the refractive power of the five lens groups and the movement of the first and second groups during zooming are By setting the conditions and adopting a lens configuration in which the fourth group is moved during focusing, the entire lens system is made smaller while achieving a zoom ratio of approximately 8 to 10 and excellent aberration correction over the entire zoom range. At the same time, it is possible to achieve a rear focus type zoom lens with an F number of 2.0 and a large aperture ratio, which has high optical performance with little aberration fluctuation during focusing.

[Brief explanation of the drawing]

[Fig. 1] A schematic diagram of an embodiment showing the paraxial power arrangement of the present invention.

[Figure 2] Lens cross-sectional view of Numerical Example 1 of the present invention

[Figure 3] Lens cross-sectional view of Numerical Example 2 of the present invention

[Figure 4]
Various aberration diagrams at the wide-angle end of Numerical Example 1 of the present invention

[Figure 5]
Intermediate aberration diagrams of Numerical Example 1 of the present invention

[Figure 6]
Various aberration diagrams at the telephoto end of Numerical Example 1 of the present invention

[Figure 7]
Various aberration diagrams at the wide-angle end of Numerical Example 2 of the present invention

[Figure 8]
Intermediate various aberration diagrams of numerical example 2 of the present invention

[Figure 9]
Various aberration diagrams at the telephoto end of Numerical Example 2 of the present invention

[Figure 10]
Various aberration diagrams at the wide-angle end of Numerical Example 3 of the present invention

[Figure 11]
Intermediate aberration diagrams of numerical example 3 of the present invention

[Figure 12]
Various aberration diagrams at the telephoto end of Numerical Example 3 of the present invention

[Figure 13
] Various aberration diagrams at the wide-angle end of Numerical Example 4 of the present invention

[Figure 1
4] Intermediate various aberration diagrams of Numerical Example 4 of the present invention

[Figure 1
5] Various aberration diagrams at the telephoto end of Numerical Example 4 of the present invention

[Explanation of symbols]

1 1st group 2 2nd group 3 3rd group 4 4th group 5 5th group d d line g g line ΔM Meridional image plane ΔS Sagittal image plane SP Aperture

Claims (3)

[Claims] Claim 1: A first group having positive refractive power in order from the object side,
It has five lens groups: a second group with negative refractive power, a third group with positive refractive power, a fourth group with positive refractive power, and a fifth group with negative refractive power, and the first group is used as an object. side, the second group is moved toward the image plane side to perform magnification change from the wide-angle end to the telephoto end, and the fourth group is moved to correct image plane fluctuations caused by the change in magnification. to perform focusing, and set the focal length of the i-th group to fi.
, the focal lengths of the entire system at the wide-angle end and the telephoto end are respectively fw,
fT, and the imaging magnification of the fifth group is β5, a rear focus type zoom lens that satisfies the following condition. 2. The zoom ratio is z, the imaging magnification of the second group at the telephoto end is β2T, and the amount of movement of the first group and the second group during zooming from the wide-angle end to the telephoto end is V1 and V2, respectively. 2. The rear focus type zoom lens according to claim 1, wherein the following condition is satisfied when . 3. In the zoom lens, 1.8
3. The rear focus type zoom lens according to claim 2, wherein the rear focus type zoom lens satisfies the following condition: <|f5/f3|<2.6.