JPH0255308A - 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 Field of Industrial Application The present invention relates to a high-power, high-performance zoom lens with a zoom ratio of 8 times for use in video cameras.

Conventional technology Recent video cameras are required to have high image quality as well as operability and mobility.
Small (1/2 inch) and high resolution devices are becoming mainstream. In addition, there is a strong demand for a zoom lens with a large aperture ratio, small size, light weight, high magnification, and high performance. 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. A conventional zoom lens with an F number of about 1.4 and a zoom ratio of about 8 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,
(Application No. Sho 62-296501) FIG. 2 shows a configuration diagram of a conventional zoom lens for a video camera. In FIG. 2, reference numeral 11 denotes a first group as a focusing section;
2 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 part.

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 compensator function 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 includes the first, second and second groups. It has the function of moving the image plane formed by 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 in order to adjust the focus. . 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 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 fourth group 13 is required to have negative refractive power.
This poses a problem in that the load on the group 14 becomes extremely large, making it difficult to achieve high performance with a small number of components.

The present invention provides a zoom lens that solves these problems by adopting a new lens type.

Means for Solving the Problems In order to solve the above problems, the zoom lens of the present invention has the following features:
In order from the object side, the first group has a positive refractive power and has an imaging function, the second group has a negative refractive power and has a variable power function by moving the optical axis, and the second group has a positive refractive power. the third with
and a fourth group that has positive refractive power and performs focus adjustment, and each group has a lens type and surface shape that are preferable in terms of aberration performance.

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

(114,0<f, /fW<7.0(2)
1.0<l f21/fW<1.6 (3) 3.0<r3
/rv<6゜0 (4) 2.0<fW/fW<4.0(5) 0.
3<a, /f4<1.0(6) 0.6<l r,
l/f3<2.0 (7) 0.6<rn/f8<2.0 (8) 0.3< l r, I/f3<0.7(
9) 0.5<r3/fW<1.00ff) 0
．． 6<rll/f4<1.8 Effect The present invention solves the conventional problems with the above-described configuration. 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. Furthermore, by providing the third group with positive refractive power, the burden of aberration correction on the fourth group is reduced, achieving high magnification and high performance with a small number of constituent elements. Furthermore, by appropriately selecting the positive refractive power of the third group, the first lens group. Second. The composite 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.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration diagram of an embodiment of a zoom lens according to the present invention. In FIG. 1, 1 is the first group, 2 is the second group, 3 is the third group, 4 is the fourth group, and 5 is an equivalent glass plate corresponding to the crystal filter 2 or the face plate of the imaging device. be.

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) 5 conditions (3) 1 conditions (4) are conditional expressions that define the refractive power of each group, and provide strong refractive power to achieve compactness, but it is necessary 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 l are a cemented lens and a meniscus lens with positive refractive power, starting from the object side.
The optimal lens type for the second group 2 is a meniscus lens with negative refractive power and a cemented lens. Next, each condition will be explained in more detail.

Condition (]) 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 it is outside the lower limit, it can be made compact, but the Benzbar sum of the entire system becomes large and negative, and field curvature cannot be corrected by selecting the glass material alone.When it exceeds the upper limit, it is easy to correct aberrations, but the variable magnification system is This makes 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 combined system of the first, second, and third groups becomes a divergent system, and therefore the outer diameter of the lens of the fourth group 4 located after it cannot be made small.

Furthermore, if the upper and lower limits of condition (3) are exceeded, the change in the angle of view due to the movement of the fourth group 4 during the focusing process becomes wide, 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 makes it difficult to correct the aberrations when shooting at close and long distances. It becomes difficult to correct the imbalance of off-axis aberrations.

Condition (5) is a condition 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 sufficient imaging distance. exceed the upper limit. This makes it difficult to downsize the entire system. Furthermore, when securing a sufficient amount of light around the screen, the outer diameter of the lens of the fourth group 4 cannot be made small.

Conditions (6), 9, (7), and (8) relate to the radius of curvature of the lens constituting the third group 3. Condition (6)
.

When the lower limit of condition (7) is exceeded, the angle of incidence of off-axis rays on these surfaces increases, making it difficult to correct off-axis coma.When the upper limit of condition (6) and condition (7) is exceeded, If the lower limit of condition (8) is exceeded, spherical aberration will be under-corrected, and conversely, if the lower limit of condition (8) is exceeded, spherical aberration will be over-corrected. When the lower limit of condition (8) is exceeded, it becomes difficult to correct comatic aberration for off-axis rays below the chief ray.

Condition (9) 3 Condition 00) is a conditional expression regarding the radius of curvature of the lens constituting the fourth group 4. Condition (9) 1 condition 00
), the angle of incidence on these surfaces becomes large, making it difficult to correct comatic aberration for off-axis rays above the principal ray. Moreover, when the lower limit of condition (9) is exceeded, the spherical aberration of the g-line becomes overcorrected. If the upper limit of condition (9) is exceeded, axial and lateral chromatic aberrations cannot be corrected within the range of practically usable glass H. If the upper limit of condition 00) is exceeded, it becomes difficult to correct spherical aberration.

An example that satisfies these conditions is shown below.

r1 in the table. "... is the radius of curvature of each lens surface counted in order from the object side, d,, d2... is the wall thickness or air gap between the lens surfaces, n1=12... is the d-line of each lens. The refractive index, C1, C2, .

(Example 1) r=8.671~(i6.287 F/N0=1.44~2.06 r, = 58.943 d, = 1.40 n
, J, 80518 v , =25.5r2-32.
691 d2-8.3012-1.58913 v2=
61.2r 3*-143,751d , 0,20r
t ・29.049 d a □2.9On3□1.
589131/3 =61.2r, *46-391
d5 (variable) r6-37.820 d6=0.9
0 n, =1.58913 v, =61.2r
-10,392d, =5.58F r o Tan -14,859(1B =0.90.ns
□1.66672 v s =48.4r, -1
2,782d, = 3.40 n6 = 1.80518 v
6-25.5r l,! 193°767 da (
variable) r,, =275.142 d++ -2,
00n 7=1. tl+7790 Schiff=55.5r
, -55,015d , =0.20r, -53,24
3du-2,10n8=1.67790v. =55
．． 5r --144,250d 14-1.40 rlS-23,13t3 d, -1,0On, =1.8
0518 v, =25.5r, ! -31,372
d, (variable) r n -81,765d 174
．． 0On +o = 1.80518 Sil1-25.5
rll= 17.152 d, -5,0On,, -
1,67790y,, =55.5r, 9=-40,
626d 1950.20r n □ 26-0(io
d a, 2. son 12=1-71300
v I! -53,9 "□・IO2,025d, (variable) r, = (X) dt1=8.0Ora
-■ Next, an example of an air interval that can be changed by zooming will be shown.

For an object point at infinity: r d5 dl, d.

Wide angle 8. G71 1.0000 29.162
7 17.5050 marks 7 31.8, 17 21.20
00 8.9G27 13.9885 telephoto 6G,
2) 37 21+, 5000 1.6627 17.
4948 Lens tip r, when the object point is 2m measured from the surface, 2 f d5 d, d wide angle 8
．． 670 1.0000 29.1627 17.4
676B! ? 1! 36.127 22.6000
? , 5627 13.4449 Telephoto 65.6
98 28.5000 1.6627 15.516
5 When the object point is 0.6 m measured from the r1 plane at the tip of the lens: f d5 dゎ d5 wide angle 8
．． 666! ,0000 29.1627 17.
3846 standard 51.636 26.3000 3
．． 8627 11.8110 Telephoto 64.697 2
B, 5000 1.6 (i27 12.0773fW
/fW =6.09 1 r21/fW =1
．． 32r9/rv-4,9OfW/l, =2.75
di / r t −0,59 ~ 0.73 l rn
l/f a -1,30rl,/rl =1=
25 1 r, l/r3=o, s4r, /
r, =0.72 r, / f 4
=1.09 Here, the target <1ζ position is the zoom position where the fourth group 4 approaches the third group 3 at each object point position.

(Example 2) f-8,675 to 65.135 F/N0 = 1.44 to 1.84 r, = 56.129 d, = 1.50 n
1 = 1.80518 v, = 25.5r2 =
31.021 d2=8.3012 =1.58913
172 =61.2r --130,145d3=0
．． 20r, -26,459d, =3.2On, -
1,58913y3=61.2r, -41,702d
, (variable) r, = 61.481 66=0.9
0 n, =1.58913 v, =61.2r
, = 10.579 d 7 = 5.45 r a =
-15,281d a J, 90ns □1-6
7003 νs = 47.2to = 13.265
d9□3.70 n6. t, eosta I/
6 = 25.5r, -854,208d, (variable)
r,, -co d,, =2.50 n7=1.
67790 Schiff=55.5r l! =-50,06
8d u =0.20r,, = 49.3546
,, =2.50 n8=1.67790 v. =
55.5r --128,964d, =1.52
-r5=-22,506dIS=1.0On, =1.8
0518 v, =25.5r, =-31,257d
16 (variable) r, -81,648d, =1.0O
n, =1.80518v, =25.5r,
-16,780d, =5.0On,, =1.67
790 v,, =55.5r =-37,215d
, =0.20ra= 24.401 d! I=2.
6 On! =1.71300y, =53.9r,
=125.385 d, (variable)j, =
(X) d, =8. o.

ra=　　ω Next, an example of an air interval that can be changed by zooming will be shown.

When the object point is at infinity: f d5 dIll d Wide angle 8.6
76 1.0000 27.3627 8.622
8 standard 26.768 17.8500 10.51
27 6.1986 Telephoto 66.109 26.1
000 2.2627 10.6223 Lens tip
When the object point is 2m measured from the first plane: f d5
dwa d.

Wide angle 8.675 1.0000 27.362
7 8.58544! :! Semi-29. 'Q3 19
．． +00 9.2627 5.8200 telephoto 6
5.135 26.1000 2.2627 8.
666 When the object point is 0.6 m measured from the r3 surface of the tip of the lens: d5 dゎ d6 1.0000 27. :T327 8.502B2
2.2000 6.1627 4.738326
．． 1000 2.2627 5.4789r21
/rvI=1.30 r4/fW -2,63 rl! l/f3=1.15 rlsl/fW -=o, st Wide angle 8.672 Standard 40.752 Telephoto 63.607 f, /fW -5,65 f3/fW =5.00 d, /r, =0. 60~0.73r, /
r, =1.14 r, /f, =0.74 r, /
r, -1,07 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), (C1, Figure 4 (a),
(b), (C), Figure 5 (a), (b), (C)
The wide-angle end of Example 1 is standard.

Similarly, FIG. 6(a) shows the aberration performance at the telephoto end.
, (b), (C), Fig. 7 (a), (b), (
C), Figures 8(a) and (b).

(C) shows the aberration performance at the wide-angle end, standard, and telephoto end of Example 2. 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, the F number is approximately 1.4. Zoom ratio is about 8
A zoom lens for large-diameter, high-magnification video cameras that is twice as compact and has good performance can be realized with as few as 12 lenses.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a zoom lens according to an embodiment of the present invention, Fig. 2 is a block diagram of a conventional zoom lens, and Figs. 3, 4, and 5 show various aberrations of Embodiment 1 of the present invention. Figure, Figure 6,
FIG. 7 and FIG. 8 are diagrams of various aberrations of Example 2. In the diagram of spherical aberration, the solid line shows the spherical aberration for the d-line, the dashed-dotted line shows the spherical aberration for the g-line, and in the diagram of astigmatism, the solid line shows the sasicle image plane, and the dotted line shows the meridional image plane. 1...First group, 2...Second group, 3...
...3rd group, 4...4th group, 5...
・Crystal filter, etc. Name of agent Patent attorney Shigetaka Awano Figure f = 65.697 pl, ac 36° - (+2 60 02 Spherical dinner -) (a) -0,20002 Astigmatism (1) ( b) -500,06,Q Mi back (horseback) (C) Figure 6 = 8.675 Fl, 42 262°E6.2 -02 00 6.2 Spherical aberration (ms) (Ct) -026, Q O, 2 9 spinning aberration -) (b) -so oo s,. Strain collection (%) (C) Figure f = a, er. (Ql (bl (C) Figure 46.12G ((Zl (b) Figure f = 2q, qq4 14.41 76'76'' -020,60,2 Uncollected difference (7nfR) ((Z) - 020,002 WOP aberration (π town (b) 15 o o, o s, Mi IJ! aberration (U4) (C) Fig. f = 6s, ts5 Fl, 85 86° 36° - (12QOα2 spherical surface Adjustment (mm) (a) -Q2 0.OQ2 1LA aberration (mm) (b) -s, o o, o 5. Distortion difference (C)

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 second group having a positive refractive power. a third group that has a refractive power and has a light-condensing effect, and a fourth group that moves on the optical axis so as to keep the image plane, which changes depending on the movement of the second group and the object position, at a constant position from the reference plane. 1. A zoom lens comprising: a zoom lens, wherein the third group and the fourth group have 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) characterized in that the group is composed of two single lenses with positive refractive power and two single lenses with negative refractive power, and the fourth group is composed of a cemented lens and a single lens with positive refractive power. 1
) Zoom lenses listed. (3) The first lens counting from the object side of the third group is a positive lens with a convex surface facing the image side, and the second lens is a positive lens with a convex surface facing the object side. 3. The zoom lens according to claim 2, wherein the third lens is a meniscus lens having a negative refractive power with a center of curvature on the object side on both surfaces. (4) Claim (2) characterized in that the cemented lens of the fourth group has a cemented surface with a convex surface facing the object side, and the single lens with positive refractive power is a lens with the convex surface facing the object side. ) Zoom lenses listed. (5) Claims characterized by satisfying the following conditions (
2) The zoom lens described. (1) 4.0<f_1/f_W<7.0 (2) 1.0<|f_2|/f_W<1.6 (3) 3.0<f_3/f_W<6.0 (4) 2.0 <f_4/f_W<4.0 (5) 0.3<d_1_6/f_4<1.0 (6) 0.6<|r_1_2|/f_3<2.0 (7) 0.6<r_1_3/f_8<2 .0 (8) 0.3<|r_1_5|/f_3<0.7 (9) 0.5<r_1_8/f_4<1.0 (10) 0.6<r_2_0/f_4<1.8 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, d_1_6 is the 16th air space counting from the object side, r_j (j = 12, 13,
15, 18, 20) indicate the radius of curvature of the j-th lens surface.