JPH0253017A - Aspherical zoom lens - Google Patents

Abstract

PURPOSE:To obtain high performance with a small number of elements by composing the aspherical zoom lens of a 1st group which performs image forming operation, a 2nd group which performs power varying operation, a 3rd group which consists of an aspherical lens, and a 4th group which has positive refracting power and makes a focus adjustment. CONSTITUTION:This zoom lens consists of the 1st group 1 which has positive refracting power, the 2nd group 2 which has negative refracting power and performs the power varying operation by moving on the optical axis, the 3rd group 3 which consists of an aspherial lens with positive refracting power and performs converging operation, and the 4th group 4 which moves on the optical axis so as to hold an image plane shifting owing to the movement of the 2nd group and the movement of a body at a constant position from a reference surface in order from the object side. A lens type which is most suitable to the 1st group 1 is a cemented lens and a meniscus lens with positive refracting power in order from the object side and a lens type which is most suitable to the 2nd group 2 is a meniscus lens with negative refracting power and a cemented lens. Consequently, the aspherical zoom lens for a video camera with good performance is composed of a small number of elements or 10 elements.

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 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.
+A inches) and high-resolution devices are becoming mainstream. In addition, there is a strong demand for zoom lenses that have a large aperture ratio, are compact, lightweight, and have high performance.Furthermore, there is also a strong demand for cost reduction (while maintaining high performance,
There is a strong need to create a zoom lens with a reduced number of lenses. F number is approximately 1.2, zoom ratio is approximately 6
A conventional zoom lens of this size 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 bidet 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 has the function of moving the image plane formed by the first, second, and third groups 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 the image changes 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 problems, 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. Consisting of a second group that has a variable magnification effect by moving on the optical axis, a third group that is made of an aspherical lens with positive refractive power, and a fourth group that has positive refractive power and performs focus adjustment. In addition, 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, 1. In particular, a compact aspherical zoom lens with excellent aberration performance can be realized with a small number of components.

(1) 4.0<f+/fs<7.
0(2nd 1.0< 1 f z 1/f
Ko-〈1.6(3) 3.0〈f z/ f w
<7.0(4) 2.0< f a/f
w <3.0(5) 0.3< d I! /
f 4 <1.0(6) 0.4< r II/
f 2 <1.5 (7) 0.5 < r la
/ f 4 <1.2 (8) 0.6 < 716
/ f 4 <1.8 Effect The present invention solves the conventional problems with the above-described configuration. In other words, it is close to the image plane. Therefore, a light lens group with a small outer diameter 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 performance with a small number of lenses.

Furthermore, by appropriately selecting the positive refractive power of the third group, the combined refractive power of the first, second, and third groups can be reduced, and image fluctuations that occur during the focusing process due to movement of the fourth group can be effectively suppressed. I've made it so small that it doesn't become a problem.

Furthermore, by introducing an aspherical lens into the third group, the number of lenses can be significantly reduced while maintaining high performance.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a configuration diagram of an embodiment of an aspherical zoom lens according to 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. Condition (1) above, condition (
2), condition (3), and condition (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 type for the first group 1 is a cemented lens and a meniscus lens with positive refractive power in order from the object side, and the optimal lens type for the second group 2 is a meniscus lens with negative refractive power and a cemented lens. It's a lens.

The condition that the third group 3 has an aspherical shape is essential for correcting various aberrations of a large aperture with an F number of 1.degree. 2 with an extremely small number of 10 lenses. It is particularly effective in correcting spherical aberration.

Next, each conditional expression will be explained in 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 l 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 lens deviates from the lower limit, it can be made compact, but the Petzval sum of the entire system becomes large and negative, and the curvature of field cannot be corrected only by selecting the glass material. If the upper limit is exceeded, aberrations can be easily corrected, but the variable magnification system becomes long, making it impossible to make the entire system compact.

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 movement of the fourth group 4 during the focusing process becomes 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 achieve compactness of the entire system, but also makes it difficult to achieve close-up distances and far-field shots. It becomes difficult to correct the imbalance of off-axis aberrations during side shadows.

Condition (5) is a conditional expression regarding the air distance between the third group 3 and the fourth group 4. If 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,
A sufficiently close shooting distance cannot be achieved. If the upper limit is exceeded, it is 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.

Condition (6) relates to the radius of curvature of the aspherical lens constituting the third group 3. By appropriately setting the shape of the aspherical surface, various aberrations can be well corrected even though it is a single lens. However, when the lower limit is exceeded, it becomes difficult to correct spherical aberration, and when the upper limit is exceeded, it becomes difficult to correct comatic aberration of rays below the principal ray.

Conditions (9) and 00) are conditional expressions regarding the radius of curvature of the lens constituting the fourth group 4. Condition (9), condition 0ω
If the lower limit of is exceeded, 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 materials. 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. γ1 in the table,
T2... is the radius of curvature of each lens surface counted in order from the object side, dl, L,... is the wall thickness or air gap between lens surfaces, nl, n21,... is the d-line of each lens The refractive indexes ν1, ν2, . . . are Abbe numbers for the d-line. f is the focal length of the entire system, and F/No is the F number.

Furthermore, surfaces having an aspherical shape (indicated by *) are defined by the following indications.

+E-y6+F-y" +c-y10, Z: Distance from the tangential plane of the aspheric apex of a point on the aspheric surface with height y from the optical axis y: Height from the optical axis C: Aspheric apex curvature (=1/r) k: conic constant, E, F, G: aspherical coefficient (Example 1) r = 9180 to 52.826 F / No = 2.23 to 1.65, = 55, 210 d, = 1.20 n, = 1.8
0518 ci, = 25.5, = 30,212 d 2
=7. lOn z=1.58913 v ,=61.2
i=-125,367d3=0.20 ==24,819 d4=3.00 n3=1
．． 589131/3=61.2,=38,228
ds (variable),"'37.183 d,=0.90 n 4=
1.58913 v, =61.2γff=10,1
02 r s = -14,559 γ9 13,149 r +o-251,794 T I+ = 26,297 * T1 = -119,015 T I 3 = -323,142 γ,, =t6,996 γ, 5=-28,738 T +b=23.512 T1F" (1) T18; ■ T192 ■ Note that.

K = -1,61659 D = 1.60396 E = 5.99131 F = 4.90798 G = -2,04801 at = 5.08 d , = 0.90 n , = 1.66672 v
5=48.4d l""3.10n,=1.80
518 v a=25.5d,. (Variable) dz=3.10 nt=1.59981 sit=5
6.4d1□ (variable) dl3=0.90 nI! =1.80518 1/e
=25.5d, =5.50 n+=1.67790
C,=55.5d15=0.20 d+,=2.80 n to=1.71300
ν1°=53.9d1. (variable) d+s=8. o.

*The 12 marked surfaces are aspherical and have the following constant x 102 XIO-' Xl0-” ×1Q-11 Xl0-th next, show.

For an object point at infinity: f　　　d.

9.180 1,000 27.960 17,000 52.826 23.450 T1 surface at the tip of the lens When: Wide-angle example of variable air spacing by zooming standard Telephoto dl.

26.000 10.000 3.550 Measure it Wide angle 9,178 Standard 30,578 Telephoto 52.40 l lens tip When: s d 1.000 26,000 18.000 9,000 23.450 3,550 Measure from the 13th side wide angle standard Telephoto f　　　　　d.

9.172 1,000 40.513 21,000 51.629 23.45O f r / f w = 5.20 26.000 6.000 3.555 If.

d 12 d 17 14.165 2.000 11.682 4.483 14.144 2.021 dl dot of object point at 2m position 14.122 2 043 11.277 4,888 12.837 3,328 0.6m Object point at position d rz d If 14.028 2,137 10.111 6,054 10.407 5,758 1 / f w =1.23 f z / f w = 3.94 f a /
f w=2.39d1□/f,=0.53~0.65
γ,,/f, =0.73114/ f a
=0.78 T Ib/ f a =1.
07 Here, the standard position is the fourth group 4 at each object point position.
is the zoom position closest to the third group 3.

(Example 2) f = 9.249-53,227 F / No = 1.25-1.70 r + = 64.104 d 1 = 1.20 n 1
=1.80518 v +=25.5r z=33,8
06 d , = 6.80 n z = 1.58913
v, =61.2γz=-128,303dff=
0.20'r 4=28.212 d4=3.0O
n3=1.58913! ' :1=61.2r 5
=45,317 d s (variable) r 6=39.7
87 d , = 1.0 On , = 1.58913 v
,=61.21? =11.518d? =5. O
Or a=-16,396d s=1. OONS
=1.69700, =48.579=13,356
d9=3.20n&=1.80518v
&=25.5r +o=283,205 d to
(Variable) *r++=43.158 dz=3.00 nt=1
．． 60311 Schiff=6o,'7γ,,=-60,67
6dl□ (variable) 12=-109,219 d 13
=1.00 n a = 1.80518 V 5 = 2
5.54=19,119 d 14=6.0On!
=1.71300 99=53.9.5=-26,64
9d,,=0.206=25,718d+6=2
．． 6On to=1.77250 1/to=49.
6+y=348,967 d 17 (variable)+s=
00 d + s = 8.0019 = ω Note that the 11 surfaces marked with * are aspheric surfaces and have the following constants.

K=　　5.66204 D-”-3,08908xlo-s E=2.19517Xl0-' F = -1,07562X 10-” G=　　　　　6.32638　Xl0-” Next, an example of an air interval that can be changed by zooming will be shown.

When the object point is at infinity: f di d,, d, Z d9.2
49 1,800 29,800 16,455 2
．． 00027.550 19,400 12,200
14,209 4.245 wide-angle standard telephoto 53,277 26,700 4,900 16
,478 1.976 2m measured from the 11th surface of the lens tip
For object point at position: r ds d+o d+z dew wide angle 9,247 1,800 29,800 16,
412 2.043 standard 30,872 20,800
10,800 13,810 4.645 Telephoto 52
,947 26,700 4,900 15,175
3.279For an object point located 0.6 m from the γ1 plane of the tip of the lens: fd, d,. d1□ dl? Wide angle 9,243 1,800 29,800 16
,318 2.137 standard 42,221 24,40
0 7,200 12,640 5.815 Telephoto 52
,360 26.700 4,900 12.824
5.631f + / f w=5.69 1 f
z 1/ r w = 1.36 f 3/ f w = 4.
57 f a / f w = 2.40d 12
/f a =0.64~0.74 γ, +/f
3=1.02r+a/ra=0.86
γ+h/f a =1.1, and the standard position is the zoom position where the fourth group 4 is closest to the third group 3 at each object point position.

Figure 3 (a) (b) (C), Figure 4 (a) (b) (C)
, FIGS. 5(a), 5(b), and 5(C) show the aberration performance of Example 1 at the wide-angle end, standard, and telephoto end, respectively. Similarly, Figures 6 (a) (b) (C) and Figure 7 (a) (b) (C
), FIGS. 8(a), (b), and (C) show the aberration performance of Example 2 at the wide-angle end, standard, and telephoto end, 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, the F number is approximately 1.2 and the zoom ratio is approximately 6.
An aspherical zoom lens for video cameras that is twice as compact and has good performance can be realized with as few as 10 lenses.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an aspherical 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 are diagrams of a first embodiment of the present invention. various aberration diagrams,
FIG. 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 sagittal image plane, and the dotted line shows the meridional image plane. 1... 1st group, 2... 2nd group, 3... 3rd group, 4... 4th group, 5...・Crystal filter, etc.

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. It consists of an aspherical lens with a refractive power of
It consists of a third group that has a light condensing effect, and a fourth group that moves on the optical axis so as to keep the image plane, which changes due to the movement of the second group and the movement of the object, at a constant position from the reference plane. An aspherical zoom lens that is a spherical 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.
The aspherical zoom lens according to 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 and a single lens with positive refractive power. . (3) The zoom lens according to claim 2, wherein the third group is an aspherical lens having a positive refractive power with the convex surface facing the object side. (4) Claim (2) characterized in that the cemented lens of the fourth group has a cemented surface with the 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) The zoom lens according to claim (2), which satisfies the following conditions. (1) 4.0<f_1/fw<7.0 (2) 1.0<|f_2|/fw<1.6 (3) 3.0<f_3/fw<7.0 (4) 2.0 <f_4/fw<3.0 (5) 0.3<d_1_2/f_4<1.0 (6) 0.4<γ_1_1/f_3<1.5 (7) 0.5<γ_1_4/f_4<1.2 (8) 0.6<γ_1_6/f_4<1.8 where fw is the focal length of the entire system at the wide-angle end, fi (i=1, 2
, 3, 4) is the focal length of the i-th group, d_1_2 is the 12th air gap counting from the object side, γj (j = 11, 14
, 16) indicates the radius of curvature of the j-th lens surface.