JPH0333710A - Aspherical zoom lens - Google Patents

Abstract

PURPOSE:To obtain high performance with a small constituting number of lens elements by making the most of an aspherical surface shape. CONSTITUTION:A lens group which is close to an image plane and, therefore, small in lens external diameter and light weight are used for focus adjustment. Further, a 3rd group is provided with positive refracting power to reduce the load of aberration compensation on a 4th group. Further, the composite refracting power of the 1st, 2nd, and 3rd groups is reduced by selecting the positive refracting power of the 3rd group properly, and variation of an image which is generated in a focusing process by the movement of the 4th group is reduced until no practical problem is generated. Further, at least one lens which has an aspherical surface shape is used in the 3rd and 4th groups. Consequently, the high performance is maintained and the number of elements is decreased greatly.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a compact, high-performance aspherical zoom lens with a zoom ratio of about 6 times for use in video cameras.

Conventional technology Recent video cameras are required to have high image quality as well as operability and mobility.
Alternatively, small 1/3-inch devices with high resolution are becoming mainstream. In addition, along with this, large aperture ratio and
There is a strong demand for a compact, lightweight, and high-performance zoom lens. Furthermore, there is a strong desire to reduce costs, and there is a strong need to realize a zoom lens that reduces the number of lenses while maintaining high performance. F number is approximately 1.2 to 1.4
A conventional zoom lens with a zoom ratio of about 6 times is composed of 13 or more lenses.

An example of the conventional zoom lens for a video camera described above will be described below with reference to the drawings. (for example,
(Japanese Patent Application No. 62-85019) FIG. 2 shows a configuration diagram of a conventional zoom lens for a video camera. In FIG. 2, 11 is a first group as a focus section, 12 is a second group as a variable power section, 13 is a third group as a compensator section, and 14 is a fourth group as a relay section.

The operation of the video camera zoom lens configured as described above will be explained below.

First, by moving on the optical axis, the first group 11 has a focusing effect that adjusts a shift in the focus position due to the object position. The second group 12 moves on the optical axis to change the magnification and change the focal length of the entire system. The third group 13 has a convencator effect that keeps the image plane, which changes due to the movement of the second group 12, at a constant position from the reference plane, and moves on the optical axis while maintaining a constant relationship with the second group 12. The fourth group 14 is the first group.

It has the function of moving the image plane formed by the second group and the third group to a desired position.

Problems to be Solved by the Invention However, the zoom lens configured as described above has a problem in that the first lens group 11, which has a large outer diameter and is heavy, must be moved for focus adjustment. . Furthermore, the movement of the first group 11 causes a change in the focal length of the entire system, that is, a change in the angle of view, resulting in a problem in that image fluctuation occurs during the focusing process. Furthermore, in order to make the zoom lens system compact, it is necessary to provide the third group 13 with negative refractive power, and the burden on the fourth group 14 to correct aberrations becomes extremely large. The problem was that it was difficult to realize.

The present invention employs a new lens type and utilizes an aspherical shape to provide an aspherical zoom lens that solves these problems.

Means for Solving the Problems In order to solve the above problem, the aspherical zoom lens of the present invention has, in order from the object side, a first group having a positive refractive power and an imaging function, and a first group having a negative refractive power. A second group that moves on the optical axis and has a variable power function, a third group that consists of an aspherical lens with positive refractive power, and an aspherical lens that has positive refractive power and performs focus adjustment. It is composed of a fourth group consisting of a cemented lens, and each group has a preferable lens type and image shape in terms of aberration performance.

Furthermore, in a configuration that satisfies the following conditions (1) to (7), a compact aspherical zoom lens with particularly excellent aberration performance can be realized with a small number of components.

(1) 3.0 < fw / (21
0,5< r2 7 (3) 2.0 < f3/ (4) 2.0 < fw / (5) 0.05
< d, / (6) 0.4 < ru / (7)
0.2 < r14/Effect The present invention has the above configuration, so that f < 7. O fw <1.6 fw <7. O fw <4. O fw <1. O fw <1.5 f4 <1.5 The conventional problems have been solved. That is, a lens group that is close to the image plane and therefore has a small outer diameter and is light is used for focus adjustment. In addition, by giving the third group a positive refractive power,
This reduces the burden of aberration correction on the fourth group and achieves high performance with a small number of elements.

Furthermore, by appropriately selecting the positive refractive power of the third group, the first lens group. Second. The focusing refractive power of the third group is made small, and the fluctuation of the image that occurs during the focusing process due to the movement of the fourth group is made small to the extent that it does not pose a problem in practice.

Furthermore, by introducing at least one lens having an aspherical shape into the third and fourth groups, the number of lenses can be significantly reduced while maintaining high performance.

Example Below, regarding an aspherical zoom lens according to an example of the present invention,
This will be explained with reference to the drawings.

FIG. 1 shows the constituent countries of an embodiment of the aspherical zoom lens of the present invention. In FIG. 1, 1 is the first group;
2 is a second group, 3 is a third group, 4 is a fourth group, and 5 is an equivalent glass plate corresponding to a crystal filter, a face plate of an imaging device, etc.

In order to make a zoom lens compact, it is necessary to increase the refractive power of each group. Above condition (1) 1 condition (
2) Condition 1 (3) and Condition 2 (4) are conditional expressions that define the refractive power of each group, and provide strong refractive power to achieve compactness, but it is important to optimize the lens type, surface shape, etc. of each group. This setting is within a range that satisfies good aberration performance.

In particular, the optimal lens types for the first group 1 are, in order from the object side, a cemented lens and a meniscus lens with positive refractive power.
The optimal lens type for the second R2 is a meniscus lens with negative refractive power and a cemented lens.

The condition that the third group 3 has an aspherical shape is essential for constructing the third group 3 with a single lens and for correcting various aberrations of a large aperture with an F number of approximately 1.4. . In particular, the aspherical shape of the third group 3 has a great effect on correcting spherical aberration.

The condition that the fourth group 4 is a cemented lens having at least one aspherical surface is such that it can correct axial and off-axis chromatic aberrations with as few as two lenses, and correct monochromatic off-axis aberrations, especially coma aberration. This is essential for correcting.

Next, each condition will be explained in more detail.

Condition (1) is a condition regarding the refractive power of the first group 1.

If the lower limit is exceeded, the refractive power of the first group 1 becomes too large, making it difficult to correct spherical aberration on the long focal point side. If the upper limit is exceeded, the lens length will increase, making it impossible to create a compact zoom lens.

Condition (2) is a condition regarding the refractive power of the second group 2.

When the lower limit is exceeded, the system can be made compact, but the Petzval sum of the entire system becomes large and negative, and field curvature cannot be corrected only by selecting the glass material. becomes long, making it impossible to achieve compactness of the entire system.

Condition (3) is a condition regarding the refractive power of the third group 3.

If the lower limit is exceeded, the refractive power of the third group 3 becomes too large, making it difficult to correct spherical aberration on the short focus side. If the upper limit is exceeded, the synthetic groups of the first, second, and third groups will become divergent, so the outer diameter of the lens of the fourth group 4 located after it cannot be made small, and condition (3) is not met. Outside the upper and lower limits, changes in the angle of view due to movement of the fourth group 4 during the focusing process become large, making it impossible to reduce image fluctuations.

Condition (4) is a condition regarding the refractive power of the fourth group 4.

When it deviates from the lower limit, the screen coverage range becomes narrower, and in order to obtain the desired range, it is necessary to increase the lens diameter of the first group 1, making it impossible to achieve a reduction in size and weight.

If the upper limit is exceeded, it is easy to correct aberrations, but the amount of movement of the fourth group 4 becomes large when shooting at close range, which not only makes it impossible to make the entire system compact, but also when shooting at close and long distances. It becomes difficult to correct the imbalance of off-axis aberrations.

Condition (5) is a conditional expression regarding the air distance between the third group 3 and the fourth group 4. When the lower limit is exceeded, the height of off-axis rays becomes small, and it becomes difficult to correct lateral chromatic aberration only by selecting the glass material.

In addition, there are restrictions on the amount of movement of the fourth group 4 during close-range shooting,
It is not possible to achieve a sufficiently close shooting distance, it is difficult to make the entire system compact if the upper limit is exceeded, and it is not possible to reduce the outer diameter of the 4th lens group 4 when ensuring sufficient light intensity around the screen. .

Condition (6) relates to the radius of curvature of the object side surface of the aspherical lens constituting the third group 3. Introducing an aspheric surface on either the object side, the image side, or both,
By setting its shape optimally, various aberrations can be well corrected even though it is a single lens. but,
When the lower limit of condition (6) is exceeded, it becomes difficult to correct spherical aberration, and when the upper limit is exceeded, it becomes difficult to correct comatic aberration for off-axis rays below the principal ray.

Condition (7) is a conditional expression regarding the radius of curvature of the cemented surface of the lens constituting the fourth group 4. By introducing an aspheric surface on at least one of the object side surface or cemented surface of the negative refractive power lens that constitutes the cemented lens, or the image side surface of the positive refractive power lens, and setting the shape optimally, it is possible to , monochromatic aberration can be well corrected while correcting chromatic aberration of magnification. However, if the lower limit of condition (7) is exceeded, the angle of incidence on these surfaces becomes large, making it difficult to correct comatic aberration for off-axis rays above the chief ray, and causing overcorrection of spherical aberration of the F-line. Become. If the upper limit is exceeded, axial and lateral chromatic aberrations cannot be corrected within the range of practically usable glass materials.

An example that satisfies these conditions is shown below.

In the table, rI, r2. . . . is the radius of curvature of each lens surface counted in order from the object side, d11d2. . . . is the wall thickness or air gap between lens surfaces, nl, n2.・・・・・・
... is the refractive index of each lens for the d-line; C2.・
... is the Atsbe number for the d-line. f is the focal length of the entire system, and F/No is the F number.

Further, a surface having an aspherical shape is defined by the following formula.

+D-Y4 +E-Y6 +F-Y8 +G-Y
However, Z: distance from the tangential plane of the aspherical surface vertex of a point on the aspherical surface whose height from the optical axis is Y; Y: height from the optical axis C: curvature of the aspherical vertex (-1/r) K: conic constant, E, F, G: aspheric coefficient (Example 1) f = 5.964 ~ 35.709 F/No = 1.45 ~ 1.94 r, = 40.151 d 1-0 .9 n
, =1.80518 v , -25,5r 2=
19.849 d 2 = 4.8 n 2 - 1.5
8913 v 2 = 61.2r --76,574
d3=0.2rs□14-954 da・2.2
n3-1.58913 shea=61-2r ・2
7-879 d s (variable) r 6 = 17.49
6 d 6=0.7 n , =1.58913
v4-61.2r-5,468d, =3.2-r8'! -8,045do =0.7n5=1.66
672 115□48.4r e □ 6.929
d e =2.4 na -1-80518v
a -25,5r -97,444d, (variable) r 11 = 12.857 d 11 -2,9n
, -1,59561v 7-56.6r I! -3
8,011d 12 (variable) r , -23,160d
1l-0,7n, -1,84666y 8-23.
9r, -7,750d M-3,7n, -1,6
7790y, -55,5r --17,412d
, (variable) rpeng=ω d , =8.0 ``n−■ Note that the 12th surface and the 15th surface are aspheric surfaces, and are expressed by the following aspheric coefficients.

12th side 15th side K -2,809E1 3.950E-1D 1
．． 195E-46, 307E-523, 230E-71
,494E-6 F 1.137g-8-8,021E-8C-3,4
43E-101,744[! -9 Next, an example of the air spacing that can be changed by zooming will be shown.

For an object point at infinity: f　　　d, dゎ　dI! d.

Wide angle 5.966 1.000 15.894 4.4
22 2.000 standard 19.108 10.150
6.744 2.252 4.170 Telephoto 36.2
06 13.871 3.023 4.422 2.
000 When the object point is located 2 m from the lens tip r1 surface: fd5d, d12dIs 5.965 1.000 15.894 4.4
01 2.021 standard 20.320 10.550
6.344 2.049 4.373 Telephoto 35.
705 13.871 3.023 3.703 2
．． 719 When the object point is 0.6 m measured from the r1 surface at the tip of the lens: Wide angle f d5 d, d, d.

Wide angle 5.958 1.000 15.894 4.3
55 2.067 standard 23.620 11.520
5.374 1.516 4.906 Telephoto 34.7
56 13.871 3.023 2.284 4.
138rj /fw -4,68f2/fw -1,0
5f3/fw=2.76 fw/Iw=3.
21d12/f, =0.08~0.23r1
1 / f 3 = 0.78r M / f 4 ””0.
40 Here, the standard position is the zoom position where the fourth group 4 approaches the third group 3 at each object point position.

Other examples satisfying the above conditions will be shown below.

(Example 2) f 5.968-36.103 F/No-1, 45-1.95 r, -42,958d, -0,9n, -1
,80518v 1-25.5rz ・20.407
d2・4.8 12-1.58913 v2 =6
1.2r s □-62.676 d s J, 2r
j-15,802d,-2,2n,=1.58913
shi, = 61.2r5 ” 30.976 d, (
variable) r6 = 28.571 d6 J, 7 n
4d, 58913 v4-61.2r 7!6.01
2 d, 112.9rs □ -8,31d
de -0,7n, -1,66672175□48.
4to dew? , 421 de ・2-4 n, =
1.80518 μs = 25.5r, -118
, 398d, (variable) rj, s 15.271
d11 -2,6n, -1,60311v, =6
0.7r cL-53,111d, (variable) r,
-14,368d, -0,7n 8=1.8051
8v8=25.5rll-6,282d,
-4,9n, =1.67790 v9=55.
5r, m-23,114dll (variable) rilI
oo d,=8.0 rrl-■ Note that the 12th surface and the 15th surface are aspheric surfaces, and are expressed by the following aspheric coefficients.

12th page 15th page 2.073f! 1 2.509 1.483E-51,085B-4 -1,188E-75,003 [! -72.112E-
8-7,835E-8 -3,638 [! -101,158E-9 An example of variable air spacing by zooming is shown below.

When the object point is at infinity: f d5dゎ wide angle 5.970 1.000 15.894 standard 1
8.895 10.190 6.704 Telephoto 36.
420 13.914 2.980 Measured from the lens tip r1 surface 2 When: dI! dS 8.180 2.000 6.128 4.052 B, 179 2.000 Wide angle f d of object point at m position When the object point is at a position of 0.6 m: f d, dゎ d12d65.96
5 1.000 15.894 8.119
2.060 standard 23.373 11.510 5.
384 5.453 4.727 Telephoto 35.48?
13.914 2.980 6.212 3.96
7fw/fw=4.61 f2/fw=
1.05fw 71w-3, 35fw /fw -2,
71d12/f, =0.34~0.51 rj
, /r3-0.76r,1/r, =0.
39 Here, the standard position is the zoom position where the fourth group 4 approaches the third group 3 at each object point position.

Other examples satisfying the above conditions will be shown below.

In this embodiment, the first group and the second group are the same as in the first embodiment.

(Example 3) f beak 5.961-35.802 F/No = 1.44-1.94 r □18.528 d = 2-6 n, -1
, 59561 Schiff 56.6 II
11r, --25,947d ll (variable) r = 16.225d, 7n -1
-84666νs□23.9U
a a wide angle r 14= 6-821 d u □4-2 n,
□1-67790 νg = ss, 5r +s =
-20,544d! s (variable) r response = ■ d
, , 8.0 rj=■ Note that the 11th surface and the 15th surface are aspherical surfaces, and are expressed by the following aspherical surface coefficients.

11th page 15th page K -1,2932,278 D-7,135B-58,665F! , -5E-9,3
10E-8-7, 322E-7F-1, 395E-8-
1,070E-8G 2.803E-10-9,90
3[! -11 Next, an example of the air spacing that can be changed by zooming will be shown.

When the object point is at infinity: f d s d v d , dr
55.962 1.000 15.894 6.545
2.000 standard 18.929 10.150 6
．． 744 4.514 4.031 Telephoto 36.185
13.871 3.023 6.545 2.00
0 At the wide angle of an object point at a position of 2 m measured from the lens front @r1 plane: f '5 'I) '4
'I55.961 1.000 15.894
6.526 2.019 Standard 20.152 10.
550 6.344 4.324 4.222 Telephoto
35.79'6 13.871 3.023 5.8
74 2.671 0.6m measured from the r1 surface of the lens tip
For object points at positions: Wide angle f d5 dv d12 d.

Wide angle 5°956 1.000 15.894 6.4
83 2.062 standard 23.479 11.510
5.384 3.822 4.723 Telephoto 35.0
48 13.871 3.023 4.544 4.
001f8/fw=3.11 f4/fw=2
．． 89d, /fw-0,22~0.38 fw, /f
3=1.0Or, t/r 4-0.40 Here, the standard position is the zoom position where the fourth group 4 approaches the third group 3 at each object point position.

Other examples satisfying the above conditions will be shown below.

In this embodiment, the first group and the second group are the same as in the first embodiment.

(Example 4) f = 5.962 to 35.694 F/N O = 1.43 to 1.94 r 11 = 13.238 d 11 = 2.9
n 7=1.59561 "□=-35,018d 1
2 (variable) r , = 22.075 d , = 0.
7 n 8=1.84666r 17.500 d
, 1 □3.1 n , = 1.67790r 1K
=-17,473d, (variable) rIl, oo
d, =8.0rj= ■ Note that the 11th surface and the 13th surface are aspherical surfaces, and are expressed by the following aspherical surface coefficients.

11th page 13th page K -9,974-2,498 D 1.217E-4-2,0141! -5E 1
．． 640E-7-4, 821E-7F 2.638E
-83,190E-8G-6,005E-10-6,8
65E-10 Next, an example of the air spacing that can be changed by zooming is shown as ν8·23.9 ν,·55.5 ν, , 56.6.

When the object point is at infinity: f d5 dtl d□ 'Is5
．． 965 1.000 15.894 5.06
6 2.000 standard 1B, 996 10.150
6.744 2.910 4.156 Telephoto 36.1
98 13.871 3.023 5.066 2.
000 When the object point is at a position of 2 m measured from the rI plane at the tip of the lens: Wide angle f d5dゎ d12d.

5.962 1.000 15.894 5.0
46 2.021 standard 20.202 10.550
6.344 2.710 4.357 Telephoto 35.
690 13.871 3.023 4.349 2
．． 717 When the object point is 0.6 m measured from the r3 surface at the tip of the lens: Wide angle Is 2.067 4.882 4.125 -3.16 =0.80 f d5dゎ d□ Wide angle 5.957 1.000 15 .894 5.0
00 standard 23.455 11.510 5.384
2.184 Telephoto 34.733 13.871 3
．． 023 2.942f8/fw-2,77fw/f.

d, /f4-0.12~0.27 r++/fsr
, / r 4-0.40 Here, the standard position is the zoom position where the fourth group 4 approaches the third group 3 at each object point position.

Figure 3 (a), (b), (C), Figure 4 (a),
(b), (C), Figure 5 (a), (b), (c)
are the wide-angle end of Example 1 at the object point position of 2 m, the standard, and
This shows the aberration performance at the telephoto end.

Similarly, Fig. 6(a), (b), (c), Fig. 7(
a), (b), (C), Figure 8 (a), (b),
(C) shows aberration performance at the wide-angle end, standard, and telephoto end of Example 2 at an object point position of 2 m, respectively. Figure 9(a)
, (b), (C), Figure 10 (a), (b),
(C), Fig. 11 (a), Φ), (C) show the aberration performance at the wide-angle end, standard, and telephoto end of Example 3 at an object point position of 2 m, respectively; Fig. 12 (a), (b) ), (C
), Figure 13 (a), (b).

(C), 14th W (a), (b), and (C) show aberration performance at the wide-angle end, standard, and telephoto end of Example 3 at an object point position of 32 m, respectively. From these figures, it can be seen that each example has good optical performance.

Effects of the Invention As is clear from the above explanation, under the lens configuration and conditions of the present invention, a compact and high-performance aspherical surface for video cameras with an F number of about 1.4 and a zoom ratio of about 6 times can be obtained. It is possible to realize a zoom lens with as few as nine lenses.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an aspherical zoom lens according to a first embodiment of the present invention, FIG. 2 is a configuration diagram of a conventional zoom lens,
3, 4, and 5 are various aberration diagrams of Example 1 of the present invention, FIG. 6, FIG. 7, and FIG. 8 are various aberration diagrams of Example 2 of the present invention, and FIG. 10 and 11 are various aberration diagrams of Example 3 of the present invention, and FIGS. 12, 13, and 14 are various aberration diagrams of Example 4 of the present invention. In the diagram of spherical aberration, the solid line is the d-line, the dotted line is the F-line, and the broken line is the spherical aberration with respect to the C-line. In the diagram of astigmatism, the solid line is the sagittal curvature of field, and the dotted line is the meridional curvature of field. 1...First group, 2...Second group, 3...
...3rd group, 4...4th group, 5...
・Crystal filter.

Claims (1)

[Claims] (1) In order from the object side, a first group having a positive refractive power, a second group having a negative refractive power and having a variable magnification effect by moving on the optical axis, and a positive refractive power. A third group consisting of an aspherical lens with a refractive power of a fourth lens that moves and includes an aspherical lens;
What is claimed is: 1. An aspherical zoom lens comprising a plurality of groups, the third group and the fourth group having a relatively large air gap. (2) The first group consists of a cemented lens and a meniscus lens with positive refractive power in order from the object side, the second group consists of a meniscus lens with negative refractive power and a cemented lens, and the third group consists of a meniscus lens with negative refractive power and a cemented lens.
Claim 1, wherein the group is composed of a single lens having at least one aspherical surface, and the fourth group is composed of a cemented lens having at least one aspherical surface.
) Aspherical zoom lens. (3) The aspherical zoom lens according to claim 2, wherein the third group is an aspherical lens with a positive refractive power and a convex surface facing the object side. (4) The aspherical zoom lens according to claim 2, wherein the cemented lens of the fourth group has a cemented surface with a convex surface facing the object side, and has at least one aspherical surface. (5) The aspherical zoom lens according to claim (2), wherein the following conditions (1) to (7) are satisfied. (1) 3.0<f_1/f_w<7.0 (2) 0.5<|f_2|/f_w<1.6 (3) 2.
0<f_3/f_w<7.0 (4) 2.0<f_4/f_w<4.0 (5) 0.05<d_1_2/f_4<1.0 (6) 0
．． 4<r_1_1/f_3<1.5 (7) 0.2<r_
1_4/f_4<1.5 However, f_w is the focal length of the entire system at the wide-angle end, f_i (i=1, 2, 3, 4) is the focal length of the i-th group, and d_1_2 is the 12th focal length counting from the object side. The air spacing, r_j (j=11, 14) indicates the radius of curvature of the jth lens surface.