JPH01178913A - Aspherical zoom lens - Google Patents

Abstract

PURPOSE:To realize a large aperture ratio of F number 1.2, superior aberration compensation, and low cost at a time although the zoom lens consists of a small number of, e.g. 11 lens elements unlike conventional one by utilizing aspherical surface shapes and selecting a proper lens type. CONSTITUTION:Inequalities I-V hold and a 4th and a 5th group each have one aspherical surface. In the inequalities I-IV, f4, f5 and fR are the focal lengths of the 4th group, 5th group, and a relay lens system, d45 the air gap between the 4th and 5th groups, upsilon4a and upsilon4b the Abbe numbers of the negative lens and positive lens forming the cemented lens in the 4th group, and upsilon5a and upsilon5b the Abbe numbers of the negative lens and positive lens forming the cemented lens in the 5th group. Namely, the 4th group 4 and 5th group 5 use aspherical and spherical lenses as their cemented lenses to widen the permissible ranges of the shape and thickness accuracy of the aspherical lenses. Consequently, the compact, inexpensive zoom lens is obtained which consists of the small number of elements, but is bright with the F number 1.2 and has a X6 zoom ratio.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to a zoom lens for a video camera, and in particular to a high-performance aspheric lens that utilizes an aspheric surface to reduce the number of lens elements and increase the aperture ratio, thereby realizing a reduction in size and weight. This relates to zoom lenses.

Conventional technology Recent video cameras place emphasis on operability and mobility.
Small size (inches) is becoming mainstream. Along with this, there is a strong demand for zoom lenses with large aperture ratios, high magnification, small size and light weight, 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. Conventional zoom lenses have an F number of 1.4 and a zoom ratio of about 6, and each group that makes up the variable power section has a focusing section with three lenses,
In the case of zoom lenses for video cameras, which often have three variator parts, one compensator part, and six to eight relay lens systems, the exit pupil position is constant from the image plane to prevent color shading. In addition, since the crystal plate is placed in front of the image plane, a lens system with a long back focus is required.To realize a high-performance zoom lens, it is necessary to use a large number of 6 to 8 spherical surfaces. A relay lens system consisting of lenses was essential.

Problems to be Solved by the Invention However, with the above configuration, there are limits even if the spherical lens material, spherical lens arrangement, etc. are optimally designed.
However, it has been difficult to reduce the number of constituent elements while maintaining the aperture ratio, zoom ratio, and imaging performance.

The present invention takes advantage of the aspherical shape, and 1) has an unprecedentedly small number of elements, and is extremely bright with an F number of 1.2 (although it is compact with a 6x zoom ratio, and is inexpensive). The objective is to provide a high-performance zoom lens for video cameras.

In addition, it is difficult to obtain the necessary shape precision with conventional aspherical lenses, and those with good precision are very expensive, making it difficult to apply them to zoom lenses for video cameras where low cost is desired.

Means for Solving the Problems The configuration of the aspherical zoom lens of the present invention is as follows from the object side:
The first group is a focusing unit with positive refractive power, the second group is part of a variator that changes magnification by moving on the optical axis and has negative refractive power, and the magnification changes due to movement of part of the variator. a third group as a part of a compensator that keeps the image plane to be at a constant position from the reference plane, and the first group described above.
．． The 2nd and 3rd groups consist of a relay lens system connected to the variable power system formed by the 3rd group, and the relay lens system includes a 4th group consisting of an aspherical joint lens with positive refractive power, and a large air gap from the 4th group. It is composed of a fifth lens group consisting of an aspherical cemented lens having a positive refractive power, which is provided at a distance from the lens, and satisfies the following conditions.

+1) 0.8JR<j, <1.5j.

(21L, 2f, <f5<2.Of.

+3) 0.4 f R<d4s<1.0 J
R(41 shi 4h-shi 4m>15 (5) sisb-shi SS>25 (6) The fourth group and the fifth group each have at least one aspherical surface.

However, f=, fs, fR are the focal lengths of the fourth group, the fifth group, and the relay lens system, respectively, and d4. is the air distance between the fourth and fifth groups, and C1. ．． 4b indicates the Atsube number of the negative lens and positive lens forming the cemented lens of the fourth group,
C2. ．． 0 indicates the Abbe number of the negative lens and positive lens forming the cemented lens of the fifth group.

Further, the negative lenses constituting the fourth group and the fifth group have an aspherical shape on the surface opposite to the cemented surface, and are formed from an SF glass type.

Effect The present invention has the above-described configuration, that is, by utilizing the aspherical shape and selecting an appropriate lens type and lens material,
Despite having an unprecedentedly small number of lenses (1), it simultaneously achieves a large aperture ratio with an F number of 1.2, excellent aberration correction, and a low price.

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 an aspherical 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, 5 is the fifth group, 6
is an equivalent glass plate that corresponds to a crystal filter or a face plate of an imaging device.

Condition (1) is a condition regarding the power of the fourth group 4 of the relay lens system. If the lower limit is exceeded, the bank focus becomes short, and under the condition that the power of the relay lens system is constant, the focal length f5 of the fifth group 5 increases, making it impossible to secure the necessary exit pupil position.

When the upper limit is exceeded, the power and ray height of the fifth group 5 become too large, making it impossible to maintain good aberrations.

Condition (2) is a condition regarding the power of the fifth group 5.

When f is larger than the upper limit, the position of the exit pupil is closer to the image sensor, making it undesirable as a video camera lens. When r5 exceeds the lower limit, the refractive power of the fifth group 5 becomes too strong, resulting in aberrations. Correction becomes difficult.

Condition (3) is the air distance d4 between the fourth group 4 and the fifth group 5.
This defines S. If the lower limit is exceeded, astigmatism becomes too negative, making it difficult to correct field curvature. If the upper limit is exceeded, the height of the upper ray of the off-axis beam becomes high and the angle of incidence becomes large, making it difficult to correct off-axis aberrations.

Furthermore, the lens length becomes long, making it impossible to realize a compact relay lens system.

Conditions (4) and (5) are related to the correction of chromatic aberration.0Condition (4) specifies the difference in Abbe number between the positive and negative lenses that constitute the cemented lens of the fourth group 4.0
Condition (5) is the 0 condition (
Outside the range of condition (4), it becomes difficult to correct longitudinal chromatic aberration, and outside the range of condition (5), it is impossible to satisfactorily correct lateral chromatic aberration.

The condition (6) that the fourth group 4 and the fifth group 5 have aspherical surfaces means that the number of constituent elements is extremely small (1).
This lens is indispensable for correcting various aberrations with a large aperture of number 1.2. Of these, the aspherical surface of the fourth group 4 is mainly effective in correcting on-axis spherical aberration, and the aspherical surface of the fifth group 5 is mainly effective in correcting off-axis aberration.

In the fourth group 4 and the fifth group 5, by using an aspherical lens cemented with a spherical lens, the allowable range of shape, thickness, and darkness of the aspherical lens is widened, and manufacturing of the aspherical lens is facilitated. Become. In addition, S, which is a low melting point glass,
By using an aspherical lens made of F-based glass,
The glass molding method, which is a highly productive method, can be easily applied, and aspherical lenses can be produced in large quantities with high precision and at low cost.

Under the lens configuration and conditions based on the present invention, a compact, high-performance, and inexpensive zoom lens for video cameras with an F number of approximately 1.2 and a zoom ratio of approximately 6 times is realized with a 1) lens configuration; I was able to do that.

Examples satisfying these conditions are r1 in Table 0 below.
r,... are the radius of curvature of each surface of the lens counted in order from the object side, dl, d2... are the wall thickness or air gap between the lens surfaces, n 1 , n 2...・・・・・・
is the refractive index of each lens for the d-line; C2...
... is the Abbe number for the d-line. Furthermore, surfaces having an aspherical shape (indicated by *) are defined by the following indications.

+G-y” However, Z: Distance from the tangential plane of the aspherical vertex of a point on the aspherical surface with height y from the optical axis y: Height from the optical axis C: Curvature of the aspherical vertex (-1 /R) k: conic constant, E, F, G: aspherical coefficients (blank below) (Example 1) f = 9.22 to 52.77 F/No-1, 23 to 1.75 rs = 60 .517 dt −1,20J =
1.80518 Us =25.5r2- 30.
312 62= 2.33r8- 60.517 d
s=3.55n, =1.58913y
2=61.2r, =-356,772da -0,2
0r5-28.073 d5-7.2On3=1.
58913 ν, -61,2r6 =-137,
399d6= (variable) r7--72.734 d,
-0,90n4-1.83400 shi,,37.2
r8- 14.680 d8-2.51rg” -
23,512do -0,90ns -1,69100
W s =54.8r, = 1). 866 d,=3.
30 n6-1.80518 Shiro=25.5r1
) = -382,252dll = (variable) ra =
-26-400% = 0.90 17 = 1-72
342't=38. Or,=-460,18
96tI” (variable) r” = 24.019 6
=1.0On =1.80328 νs□25.
5+4 approval
Brl5- 22.165 d, -7
,6On,=1.71300 shi,=53.9r
= 28.487 di -15,60 ivy r” = 20.793 d = 1.0 On
=1-80328 νe=25.5ff
ff m
+r -10,825d =7.1On =1.
58913 v =61.2 proverb
II
II
IIr--35,910d, =1. OO4 − r, = oe d, =6.7On+! =
1.51633 v , =64.1r machine・■ Note that the surface marked with this mark is an aspherical surface and has the following constant.

14th surface 17th surface k 1.37013 X 100-2.12547 X
104[1-5,54507X104-1.0281
)X10UE-2,90015X10" 2.87
426X10"F-1, 15024X1041.271
47xlO (G-1゜30862 x 104 2.
07954 x 104 The air spacing that can be changed by zooming is shown by the following value.

f d, d, d.

9.22 1.5000 22.4702 1.9
85430.86 18.2000 3.5820
4.173652.77 22.5500 2.8
023 0.6033f 4-19.71f
5 29.49 f R Seal 20.09d 4s-1
5,2 shi 1-shi,, = 28.4νsb V 5
a-35,7 (Example 2) f -9, 22 to 52.76 F/No-1, 23 to 1.75 (1st group 1, 2nd group 2, 3rd group 3 are the same as Example 1) common.) r”, =26.122 d14= 1.00 n
8=1.68893y 8=31.1rIs=2
0.933 d, = 7.50 n9=1.71
300y, =53.9r, =-29,687
di =16.38r”, =19.979d,
= 1.50 n, = 1.80328 y,
=25.5r@=10.720d, =8
．． 0On,, =1.5B913y,, =6
1.2r, =-35,409d, = 1.00r3
1 = oo dB = 6.70 ”t!
=1.51633! ',! =64.1rδ
・ ■ Note that the surface marked with * is an aspherical surface and has the following constant.

14th side 17th side k 1.27287x100 -2.46159xl
OID -5,26693x104 -8.21845
x104E 1.34562 x 104 2.19
464 x 10@F -2,82955X10”
1.38914X10'G -7,72896xlO
'2.02375xlO' Note that the air spacing that can be changed by zooming is the same as in the first embodiment.

f −20,72f =28.39 f, −
21,33d 4s-16,38si1. -shi,, -22
,8ν1. -%, -35.7 Figures 2, 3, and 4 are wide-angle views of Example 1.

Similarly, Figures 5, 6, and 7 show the aberration performance at the standard and telephoto ends, respectively, from Figure 0 showing the aberration performance at the wide-angle, standard, and telephoto ends of Example 2, and each example is good. It can be seen that it has excellent optical performance.

Effects of the Invention As is clear from the above explanation, under the lens configuration and conditions of the present invention, 1) a compact camera with an F number of about 1.2 and a zoom ratio of about 6 times, with a very small number of lenses; A zoom lens with good performance has been created.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an aspherical zoom lens according to an embodiment of the present invention, Figs. 2, 3, and 4 are various aberration diagrams of embodiment 1, and Figs. 5, 6, and 7. are various aberration diagrams of Example 2. In the diagram of spherical aberration, the solid line is dvA, the dotted line is the spherical aberration with respect to 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...
- 5th group, 6...crystal filter, etc. Name of agent: Patent attorney Toshio Nakao
i Hand-Pack 4) t￥ Figure 2 f -9,2! O IA@JIJJ(mm) IFJ[,t(m+
n+ 'Lnlli''4.m, Fig. 3 f-jO, 85δ Fig. 4 f=52.773
Strain j Yuri 4th surface L (ms + 1 4th, 9th person 7u E (super possible historical sunu name ((4th figure 7 f = 52.1) 5

Claims (2)

[Claims] (1) In order from the object side, a first group as a focusing section having a positive refractive power, a second group as a variator section having a negative refractive power and changing magnification by moving on the optical axis, The third group serves as a compensator that keeps the image plane, which changes due to the movement of the variator, at a constant position from the reference plane, and the relay lens system connects to the variable power system formed by the first, second, and third groups. The relay lens system has a positive refractive power and a fourth group consisting of an aspherical cemented lens, and a positive refracting lens system provided with a large air gap from the fourth group. An aspherical zoom lens that is composed of a fifth group consisting of a strong aspherical cemented lens and satisfies the following conditions: [
1] 0.8f_R<f_4<1.5f_R[2] 1.2
f_R<f_5<2.0f_R[3]0.4f_R<d
_4_5<1.0f_R[4]ν_4_b−ν_4_a
>15 [5] ν_5_b−ν_5_a>25 [6] The fourth group and the fifth group each have at least one aspherical surface. However, f_4, f_5, and f_R are the fourth and fifth groups, respectively.
The focal length of the group and relay lens system, d_4_5 is the fourth
The air distance between the group and the fifth group, ν_4_a, ν_4_b, indicate the Abbe numbers of the negative lens and positive lens forming the cemented lens of the fourth group, and ν_5_a, ν_5_b represent the negative lens forming the cemented lens of the fifth group. and the Abbe number of the positive lens. (2) Claim (1) characterized in that the negative lenses constituting the fourth group and the fifth group have an aspherical shape on the surface opposite to the cemented surface, and are made of SF glass type. The aspherical zoom lens described.