JPS6224213A - Zoom lens - Google Patents

Abstract

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

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a zoom lens, which has a high zoom ratio suitable for still cameras, video cameras, broadcast TV cameras, etc. and employs a rear focus method with a large aperture ratio. This relates to zoom lenses.

(Prior Art) A 14-group zoom lens has been conventionally used in still cameras, video cameras, and the like, and has a relatively high variable power ratio and a large aperture ratio. This 4-group zoom lens consists of, in order from the object side, the first lens group for focusing, and the second lens group for zooming.
It consists of a V/Z group, a third lens group to correct image plane fluctuations associated with zooming, and a fourth lens group to balance the focal length and aberration correction of the entire system.4 groups A zoom lens uses a configuration in which a total of three lens groups are moved: two lens groups for zooming and one lens group for focusing.For this reason, the lens barrel tends to be relatively complex. Furthermore, when focusing on a short-distance object, the first lens group is extended toward the object side, so if an attempt is made to secure a sufficient amount of off-axis light, the diameter of the front lens tends to increase.

For this reason, various zoom lenses have been proposed that utilize a so-called rear focus system in which focusing is achieved by moving lens groups other than the first lens group.

For example, in US Pat. No. 4,364,642, focusing is performed by moving the third lens group in a four-group zoom lens.

Further, in US Pat. No. 4,460,251, focusing is performed by moving the second lens group and the third lens group integrally in a four-group zoom lens. Also, JP-A-58-136012
The publication proposes a zoom lens in which the variable magnification unit is composed of three or more lens groups, and focusing is achieved by moving some of the lens groups. However, although the front lens diameter of these zoom lenses is small, the movement trajectory of the focusing lens group changes greatly between objects at infinity and close objects, so extra space must be secured in the lens system in advance. There is a tendency for the total length of the lens to increase. In addition, in Japanese Utility Model Application Publication No. 59-63314, the fourth lens group of a four-group zoom lens is divided into two lens groups, and focusing is performed by moving one of the lens groups.

However, this zoom lens requires a total of three lens groups to be moved, and the lens barrel tends to become complicated.

(Problems to be Solved by the Invention) It is an object of the present invention to provide a zoom lens using a rear focus system with a simple structure and a high variable power ratio and a large aperture ratio, thereby reducing the overall size of the lens system.

(Means for solving the problem) In order from the object side, a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a third lens group with positive refractive power. It has four lens groups: the first lens group. The third lens group is fixed, the second lens group is moved in one direction to change the magnification, and the fourth lens group is moved to correct image plane fluctuations due to the change in magnification.
There are nine things you can do by moving the lens group.

Features of this other invention are described in the implementation section.

(Example) FIG. 19 shows a schematic diagram of the basic configuration of an optical system according to one embodiment of the present invention. In the figure, I is the first lens group with positive refractive power, ■ is the second lens group with negative refractive power, ■ is the third lens group with positive refractive power, and ■ is the fourth lens group with positive refractive power. It is. The magnification is changed by moving the second and fourth lens groups in the direction of the arrow.

Among these, the second lens group mainly performs zooming and the fourth lens group
The lens group corrects one-plane fluctuations that occur when changing the magnification.
□Focusing is performed by further moving the fourth lens group. Note that the first and third lens groups are fixed during zooming and focusing.

In this implementation row, the second lens group with negative refractive power, which is disposed between the first lens group with positive refractive power and the third lens group corresponding to the relay lens group, is moved in the -□ direction. 1. Third lens: This lens forms images of the □ group and efficiently changes the magnification. □Then, the variable power @4th lens group is moved non-linearly toward the 3rd lens group as shown in the same figure to correct the image plane fluctuation, and the 3rd and 4th lenses are Figure 9 shows the effective use of space with groups.
The overall length of the lens has been shortened.

In this embodiment, the first lens group is always fixed without being moved out during focusing to prevent an increase in lens diameter caused by moving it forward. When focusing, the fourth lens group, which is part of the variable magnification system, is moved instead of the first lens group, thereby reducing the overall number of movable lens groups and simplifying the mechanism. Efforts are being made to downsize the entire system. In other words, the space within the lens system can be effectively utilized by allowing the fourth lens group to have both the functions of zooming and focusing, and by moving the space between the third and fourth lens groups. In this way, the overall length of the lens has been shortened.

Note that the eleventh and third lens groups adjust paraxial quantities such as the focal length, angle of view, and pack focus of the entire system, and also satisfactorily correct aberration fluctuations caused by the movable lens group. In addition, in this embodiment, the diaphragm is placed in or near the third lens group to reduce fluctuations in aberration due to the movable lens group, and to maintain a good balance between the lens diameters of the first and fourth lens groups. preferred to maintain.

The zoom lens which is the object of the present invention is achieved by the above configuration, but it is preferable that the first lens group is made up of at least two positive lenses and one negative lens, and the second lens group is made up of at least one negative lens. By configuring the third lens group to have at least one positive lens and two negative lenses, and the fourth lens group to have at least one positive lens and one negative lens. be.

This effectively corrects chromatic aberration within each lens group, and also corrects spherical aberration on the telephoto side in the first lens group, and astigmatism and distortion on the wide-angle side in the second lens group. are doing.

Furthermore, in the present invention, in order to reduce aberration fluctuations due to zooming and to downsize the entire lens system, α7 is Ge2//W+ < 11 ・・−・−・・
・il+L2 < /4//W < 40 ・
−・−−−−−−+2) recognition < V, /f2) <λ6
・・−・−・・(3) 0.72 < /1//3
< 2h9 ・-・-・141L8 ＜ /3/
/ W <42 ・ ・ ・ ・ ・ (5) is a storm to be satisfied.

Conditional expression (1) relates to the refractive power of the second lens group.If the refractive power of the second lens group exceeds the lower limit and becomes stronger, it is desirable for proving the lens system, but the Petzval sum increases in the negative direction. The curvature of field increases. If the upper limit is exceeded and the refractive power of the second lens group becomes weaker, aberration fluctuations due to zooming will decrease, but the amount of movement must be increased to obtain a predetermined zoom ratio, and the overall length of the lens will become longer. It's coming.

Conditional expression (2) relates to the refractive power of the fourth lens group, and if the refractive power of the fourth lens group exceeds the lower limit and becomes strong, the axial spherical aberration on the wide-angle side will be undercorrected and will extend over the entire 9-fold magnification range. External coma aberration often occurs. Also, the 4th V exceeds the upper limit.
As the refractive power of the lens group becomes weaker, the amount of movement associated with zooming increases, the overall length of the lens increases, and aberration fluctuations during focusing increase.

Conditional expression (3) concerns the refractive power ratio between the second lens group and the fourth lens group. It becomes difficult to correct, and conversely, the upper limit value is exceeded and the refractive power of the 4th lens group becomes too weak.Then, the amount of movement increases, and...the focus becomes longer than 1, and the image from the 1st lens group becomes too weak. This is not desirable because the optical total length up to the surface is too long. Conditional expression (4) is
Regarding the refractive power ratio of the lens groups, if the lower limit value is exceeded and the refractive power of the first lens group becomes too strong, axial aberrations at the telephoto end tend to be undercorrected, and if the upper limit value is exceeded, the refractive power of the first lens group becomes too strong. If the distance becomes too weak, the distance between the first lens group and the third lens group becomes too wide than the amount of movement of the second lens group, which is not preferable because an unnecessary space is created.

Conditional expression (5) relates to the refractive power of the third lens group; if the refractive power of the third lens group exceeds the lower limit and becomes strong, spherical aberration on the wide-angle side tends to be undercorrected, and furthermore, the refractive power of the fourth lens group increases. The force must be weakened, and the amount of movement of the fourth lens group increases accordingly. Furthermore, if the upper limit is exceeded and the refractive power of the third lens group becomes too weak (p), the spherical aberration on the wide-angle side tends to be overcorrected, which is undesirable.

Next, a numerical implementation 91 of the present invention is shown. In the numerical implementation sequence, R1 is the radius of curvature of the first lens surface I@ from the object side, Di is the thickness and air gap of the first lens from the object side,
N1 and yi are each in order from the object side! These are the refractive index and Atsube number of the glass of the i-th lens. Table 1 also shows the focal length of each lens group in each numerical value implementation column.

Numerical implementationflI41 Ri Di Ni ν11 13
6.36 10 1.8G518 25.4z
3 (t81 7.6 L60311 6
α73 -90.12 0. I t4 2
&5G 4. SL69680 5&55
6L46 tI t 6 70.26 G, 9 1.7?250
49.67 1L38 λ6L 8 -IL15 α9 L73500 4
9.89 1? , 37 λ2 L8466
6 2λ910 -5L64 t2 Ll
l Shibori D! I L 12 -67.81 t9 L7440G
44713 -41.04 αIL 14 546B! LOL55963 6L2
)5-1λ47 LOL75520 27.51
6 -55.70 α2L 17 2 (t95 19 L72916 5
4718 60.51 t3 t19 2
G, 27 LOL84666 2L92G
147 14 1゜2) -24 t54 2.9 t48749
7 (t222 -2JLO1α11゜23 14.49 4.2 L6968Q
55.524 -30L46 t4 t2
5 - 5.0 1.51633 64.
126 4XI L S7-3.7 Numerical implementation sequence 2 R1Di Ni νt 1 127.43 2.0 1.80518
2&42 39.78 7.6 L6031
1 60.73 -89.19 α
I t4 2a44 5L6 1.69
680 55.55 57.17 tx
t6 12 t77 (t9 t7725
0 49.67 1L94 14 1゜8 -HL55 α9 L7350G
49.89 1a49 λ4 1.8466
6 23.910 -6104 t2 L
ll-6L53 t9 L72600
5λ512 -35.59 1.5
1゜13 Aperture L5
L14 5 & 78 5. OL55963 61
．． 2Is-11531OL75520 27.
516 -67.37 αIL17
2Z27 2.9 L7440G 447
18 8Lal t3 t 19 2Z11 1.0 1.84666
23.920 1124 2.4
12) -2)140 2.9 L4874
9 70.222 -2a98 αI
t23 1! L35 42 L69
680 55ju -31λ6? t4L 25 5L
51633 64126 ω
L1゛ Numerical implementation sequence 3 Ri Di Ni ν11 13
9.84 1G 1.80518 25.42
40.50 7.6 160311 6(
L73 -91.03 αI
L4 25.60 4.5 169680
55.55 5fi, 91 tI L6
119.9B 0.9 1.7?250 4
9.67 1L72 λ9L 8 -16.04 α9 173500 4
9.89 2). 35 12 1.84666
2) 910-4λ2) t2L 11 11! Li 2. I
L12 40.88 1J L7
4400 44713 -30119
0. I L14 11174 4!
1.55963 6L2)5 -1167 1.
0 1.75520 27516 -4L13
0.2 L17 2 turtle 20 LOL729
16 54.718 4Z2) 13 1゜19 30.40 0.8 1.740?7
27.820 1LO44,51,559636L2
2) -39.91 0.1 1
゜22 1a81 :lL2 1.51633
64123 87.27 t4 1°24
1) &0 capture 1633 6 tons 125
=o 1° Numerical implementation column 4 Ri D i N i y negative 1
13! L73 2AL80518 2) 42
40.01? , 6 1.60311 6α7
3 -10149 (LX L429.30
&6 1.69680 55.55 8
9.72 tI L6 11fu24 α
9 L77250 49.67 12.34
11 L 8 -1a27 (LOL73500 4Q,
89 17.02 &4 1.84666
2) 91O-7α53 12 L ll Aperture J) Zl 1゜12 5 & 41 Z85 1.74400
44713 -15 Table 83 FuIL 14 -1424 0.9 1.84666
2) 915-2L49 αI
Lrs 3Q, 533.7 L6968
0 55.51? -67,12) 3L 18 35w1l LOL84666 23
．． 919 1aO02 8 L2
0 13494 Z9 L48741i1
7(L22) -2a20 0. IL22
17.12 42 L69680 5&
523 -959.83 t4L 24 Korea 5.5 L51633 6
4125 a-L Numerical implementation sequence 5 R1Di Nl yL l 134.55 L80 La0S18
2&42 35.69 7.60 L6
0311 6α73 -9L53 0.1OL 4 25.84 5.40 1.69680
5155 76.47 tX L6
．． 9Z12 0.9OL77250 49.67
LL37 3.5OL 8 -13.51 0.85 1.73500
4g, 89 16.95'L75 1.
84666 23.910 -15180 L
2 Lll Aperture 1.76 1°12 6a51 120 L74400 4
Table 713 -26.45 110 1゜14
-1162 α9G 1.84666 2)
915-2ch, 25 α10 L16
95.64 440 1.69680 5&
517 -2431 13 L 18 50.44 (L90 1.84666
2) 919 1a32 R701゜20 -64Z63 150 L48749
71122) -26.00 0.10 1゜22 15.93 42OL72000 5α2
23 -515.13 14 1゜24 -
ago L51633 64125
oo L l 20Z83 L8 La0
S18 2L42 4&49 7.5
160311 60.73 -10
&71 α11゜4 3LOa
L9 1.69680 5&55
11L86 tl 1゜6 -52
! L29 0.8 L7725G
49.67 17.44 Fu6
L8 -19.00 α75
L73500 4J, 89 2!96
LOLa4S66 23.910 -1
45.50 12 Lll Aperture j)
1.2 L 12 -10130 2.9 L72
916 54713 -3λ99 16
L14-15J4 α9
1.84666 23.915 -I
Q, 96 αI L16 26λ
54 λ6 La1S00 6
3.417 -3a52 L3・
L18 3L75 LOLa2S3(>
2) 919 17.71 (
L5 L20 1a+34 5
．． 4 La9S80 5&52)
-6:1L85 L4 1°22
(To) 55 L5163
3 6 melon 123 ψ
L numerical implementation column 7 R1Di Ni ν1 1 16427 L8 L8051g
25.42 45.42 7.2 L603
11 6α73 -10a65 α1 1゜4 3L99 5.4 1.69680 5
L55 101L34 11L 6 14442 0.8 1.77250 4
9.67 1&48 λ6L 8 -124 0.75 1.73500 4
9.89 19.67 10 1.84666
2)910 -32)61 t2 Ll
l Aperture 1.2L 12 5&65 3.7 L61800
64413 -25L78 L4 Li2
-17.99 0.9 1.84666 2
&915 -2)09 t3 Li2
2&59 10 L84666 2)917
1a51 0.8 Li2 1&73
4.5 16 (168055, 519-4 to 16
t4 L 20 - 5.5 1.51633 64
12) c1!11°8' -14167 Numerical implementation sequence 8 Ri Di Ni ν11 41
9.63 1S L8051B 25.42
7444 λ2L a 35174 7. a L43387
Q&14 -64.63 0.1
1゜5 39.51? , 9 L4
9700 8L66 -461.44 α1
1°? 27.47 2.9 L696
8Q 55.58 39.14 tI
LO2) 610,9S L88300 40.
810 1408 Yu18 Lll
-46,190,701,8040046,6122&
94 λ15 1゜13 -10.82 0.70 1.77250
49.614 -220.28 2h70
L92286 2L315 -17.37 12
1゜16 32422 LO1,72600
51517-87,0115L i2 Aperture 19
1゜19 -227.37 5.4 L5
5963 6L220-Li91
LOL75520 27.52) -37.
99 0.1 1゜22 2m31 2.9
L74400 1723 13:L72
t3 L24 2L45 LOL8466
6 2) 925 1λ14 2h4
L26 -147.37 λ9 L
48749 7α227-2fu71 0. I
L 28 11456 4.2 1.69680
5 & 529 91.27 t4 L30
(To) L50 1.5
1633 64.131 ψ
L Numerical implementation sequence 9 Ri Di Ni yil 1
57.87 L91.80518 2&42
5&68 λ2L 319″L60 &7 L43387 9&
14-6104 0. I L 5 3 & 22 7.4 L49700 8
L66 171&55 (LX L7
2&73 19 L69680 55.58
3 & 51 /, I LO5 & 35 G
, 9 L, 77250 49.610 1L
70 λ8L 11 -1415 α9 L73500
49.812 1a63 2ja L846
66 23.913 -5N41 tZ
Li2 5Q, 44 LOL72600 5
1515 90 & 88 L5 Li2 Aperture f) 19 L 17 -20.83! L4 L55963
6L, 2) 8 -9.27 LOL755
20 27.519 -19L80 αIL 20 2L15 2. Q L74400
4472) 194.27 tZ L22
20.43 1.0 1.84666 2)
923 1L93 14 L u -2L9 148749 70.225
-19.53 0. l L26 12.
00 42 L69680 55.527
2&65/J L2B-5,5L
51633 6419ooL S, <-19904 Table 1 Effects of the Invention) According to the present invention, the entire lens system with a variable power ratio of 6 and an F number of L2 can be miniaturized and aberrations can be suppressed well. It is possible to achieve the correction or to achieve a zoom lens using a focus method.

[Brief explanation of the drawing]

1st, 3rd, 5th, 7th, 9th, 11th, 13th, 1st
5 and 17 are cross-sectional views of lenses of numerical implementation columns 1 to 9 of the present invention, respectively, and figures 2, 4, 6, 8, 10, 12, 14, 16, and 18 respectively Numerical implementation sequence 1 of the present invention ~
9 and 19 are schematic diagrams of the basic configuration of an optical system according to an embodiment of the present invention. In the various aberration diagrams, (6) is the aberration diagram for the wide-angle side, d is the d-line, g is tla, M is the meridional image plane, and S is the aberration diagram for the telephoto side.
is the sagittal image plane, 1. I[, 1, lV are the first, 2.3g3, and fourth lens groups, respectively.

Claims (1)

[Claims] (1) In order from the object side, the first lens group has a positive refractive power, the second lens group has a negative refractive power, the third lens group has a positive refractive power, and the fourth lens group has a positive refractive power. It has four lens groups,
The first and third lens groups are fixed, the second lens group is moved in one direction to change the magnification, and the fourth lens group is moved to correct image plane fluctuations due to the change in magnification. A zoom lens characterized in that focusing is performed by moving the fourth lens group. (2) The first lens group includes at least two positive lenses and one negative lens, the second lens group includes at least one positive lens and two negative lenses, and the third lens group includes at least one positive lens and two negative lenses. Claim 1, wherein each lens group has at least one positive lens and one negative lens, and the fourth lens group has at least one positive lens and at least one negative lens. Zoom lens listed. (3) When the focal length of the i-th lens group is f_i and the focal length of the entire system at the wide-angle end is f_W, then 0.7<|f_2/f_W|<2.1 1.2<f_4/f_W<4. Claims characterized by satisfying the following conditions: 0 1.2<|f_4/f_2|<3.6 0.72<f_1/f_3<2.9 1.8<f_3/f_W<4.2 The zoom lens described in item 2.