JPS61140913A - High variable power system zoom lens - Google Patents

Abstract

PURPOSE:To make a titled zoom lens small in size and light in weight, and to improve its operability by providing at least one aspherical surface on each of the first and the second lens groups, and providing at least two aspherical surfaces on the fourth group, in a lens system constituted of four groups. CONSTITUTION:A titled high variable power system zoom lens is provided with the first lens group having a positive focal distance, the second lens group having a negative focal distance, the third lens group having a negative focal distance, and the fourth lens group having a positive focal distance, successively in order from an object side, and executes zooming, by moving the second lens group and the third lens group, and at least one aspherical surface is provided on each group of the first and the second lens groups, and also at least two aspherical surfaces are provided on the fourth group. By providing the aspherical surface on the first, the second and the fourth lens groups, respectively, these lens groups can be constituted of an extremely small number of lenses, also various aberrations generated in each group can be corrected satisfactorily, this zoom lens becomes small in size and light in weight, and the high variable power system zoom lens having a good operability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a zoom lens, and particularly to a small, lightweight, and compact lens used in video cameras, cine cameras, etc.
Regarding double zoom lenses.

Problems to be Solved by the Prior Art and the Invention Conventionally, many high-power zoom lenses have been designed to have positive,
It is known that the lens has a four-group configuration having negative, negative, positive or positive, negative, positive, and positive focal lengths, and that the second and third lens groups are moved during zooming. In such a configuration, the first lens group is moved to perform force shooting, which tends to increase the lens outer diameter of the first lens group, increase the weight of the zoom lens, and impair operability. there were. In addition, aberration fluctuations due to object distance are large,
In particular, there was a tendency for fluctuations in spherical aberration and astigmatism to be large at the telephoto end.

In order to make the total lens length compact in such a zoom lens having a four-group structure, it is possible to reduce the thickness of each lens group and the interval between each lens group, and to introduce an aspheric surface.

Devices employing these ideas are known, such as those described in Japanese Patent Application Laid-Open No. 56-147113 and Japanese Patent Application Laid-Open No. 59-28120. Of these, the first one is
, a compact zoom lens has been proposed by introducing an aspherical surface into the second lens group to reduce the number of lenses. However, this zoom lens has a low magnification of 11'1.6 and a zoom ratio of 3 times, and cannot be said to have very high performance as a zoom lens for a general video camera at present. In addition, the latter type is characterized by moving part or all of the fourth lens group to perform force shifting, which complicates aberration correction and causes large aberration fluctuations due to changes in object distance, which is not very desirable in terms of performance. . Furthermore, since the first, second, and third lens groups are moved to perform zooming, the cam mechanism becomes complicated, which causes problems such as the total length of the lens being different at both end focal lengths during zooming, which is not very desirable in terms of operation.

Structure of the Invention The high variable power zoom lens of the present invention comprises, in order from the object side, a lens group having a positive focal length, a second lens group having a negative focal length, a third lens group having a negative focal length, and A fourth lens group having a positive focal length is sequentially arranged, and g
A high variable power zoom lens that performs zooming by moving a second lens group and a third lens group, wherein each of the first and second lens groups is provided with at least one aspherical surface, and further comprises an aspherical surface. At least two aspheric surfaces are provided in four lens groups.

Function The present invention provides an aspheric surface for each of the first, second, and fourth lens groups of a conventional zoom lens having a four-group configuration.
, the second and fourth lens groups can be configured with an extremely small number of lenses, and various aberrations occurring in each group can be well corrected. Furthermore, each group provided with an aspherical surface is small and lightweight, making it possible to create a high-power zoom lens with good operability.

In addition, the present invention aims to introduce an aspherical surface in order to suppress the deterioration of various aberrations due to the reduction in the number of lens elements, and by increasing the degree of freedom in design, various aberrations can be reduced over the entire zoom range without having a large effect on aberration correction. It is designed to improve the That is, by giving appropriate negative aspherical amounts to the first lens group and positive aspherical amounts to the second lens group, aberration fluctuations due to zooming, especially spherical aberration, coma aberration, distortion aberration, By suppressing fluctuations in astigmatism and coma aberration in the second lens group, and by providing an appropriate amount of negative aspherical surface to the fourth lens group, the high performance required for this lens group can be maintained. However, it has a significant effect in suppressing all aberrations that affect imaging performance.

Embodiment FIG. 1 shows a lens cross section of an embodiment of the high-power zoom lens according to the present invention.

Since this embodiment is intended for a zoom lens for a video camera, a parallel plane plate is arranged behind the final lens. Furthermore, the reason why bonded lenses are used for the first, second, and fourth lens groups is not only to solve manufacturing problems but also to satisfactorily correct chromatic aberrations that occur in these groups.

In this embodiment, bonded lenses are used for the first, second, and fourth lens groups, but a combination of single lenses may be used. Further, in this embodiment, a case of a zoom type in which the second and third lens groups are moved is shown, but it goes without saying that the present invention can be applied to other zoom types, such as a zoom type in which the second lens group is moved.

Further, in this embodiment, the C-force focusing is performed by moving the fourth lens group, but it is also possible to perform the focusing by moving all or part of the fourth lens group.

The formula for determining the basic shape of an aspherical surface will be explained in FIG.

As shown in Figure 2, the optical axis direction is the X axis, the direction perpendicular to it is the Y axis, and the paraxial radius of curvature is R1, the height from the optical axis is H.
The amount of displacement in the optical axis direction from the lens surface apex reference O is X. Then, it is expressed as . Here, K is the conic constant, A, B.

0 and D are aspheric coefficients. In the above equation, the first term defines the basic shape of the aspheric surface.

Next, numerical examples of the present invention will be shown. In the numerical examples, R1 is the radius of curvature of the first lens surface in order from the object side,
di is the thickness of the first lens and the air gap in order from the object side, and ni and ν1 are the refractive index and Abbe number of the glass of the first lens, respectively, in order from the object side.

Numerical example f = 9.17 to 52.21 F number = 1:
1.4 Zoom ratio = 5.69R1 = 35.584
dl= 1.2 n1=1.84666 ν1=
23.9R2=21.346 d2=14. On2=
1.71285 $72=43.2R3=-1331
．． 98 d3=variable R4=-34,059 d4=o,
8 n: (-1,7725J/3=49.6R5=
10.206 d5=3.9i n4=1.922
86 ν4=21.3R@= 12.914 d
6=variable R7”-10,888d7=0.8n
5=:1.48749 5=70.1R8=-
26.36 48=Variable R9= 16.692 d9=5.5 n6=
1.618 316=63.4RIO=-4
1,358dlo = 1.5Ru = (aperture) 0.0
dll=t, 52fl12=17.025 d12=
0.8 n7=1.80518 y1=25
．． 4RI3=8.523 13=12. On8
=1.6583ull=53.4RI4=-
32,672d14=3.0R15=0.0
d15=5.4 n9=1.51633
G = 64.1R S = O, O *Aspherical coefficient Water surface number Figure 3 is a diagram of various aberrations of each part of an embodiment of the present invention, (B) is the wide end, (B) is the standard part, ( 0) indicates the tele end.

In the figure, the d-line has a wavelength of 587.56 nm.
.

The second line shows the case where the wavelength is 435.784 nm.

Effects of the Invention The present invention provides at least one aspherical surface in each of the first and second lens groups, and provides at least two aspherical surfaces in the fourth lens group, thereby making the entire zoom lens smaller and lighter. It has great practical effects that can be used in actual industry, such as easy to use, good operability, and good aberration correction.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of an embodiment of a high-power zoom lens according to the present invention, Figure 2 is a diagram showing an aspherical shape, Figure 3 is a diagram of various aberrations of an embodiment of the present invention, and cA) is The wide end, (E) shows the standard part, and (C) shows the tele end. R: Radius of curvature of the forward axis H: Height from the optical axis S: Sagittal image surface ΔM = Meridional image surface d: Lens thickness and air spacing Figure 1

Claims (3)

[Claims] (1) In order from the object side, the first lens group has a positive focal length, the second lens group has a negative focal length, the third lens group has a negative focal length, and the fourth lens group has a positive focal length.
In a zoom lens in which lens groups are sequentially arranged and zooming is performed by moving a second lens group and a third lens group, each of the first and second lens groups has at least one aspherical surface. A high variable power zoom lens further comprising at least two aspherical surfaces in the fourth lens group. (2) The high variable power system according to claim 1, wherein the first and second lens groups each include two lenses, and the fourth lens group includes at least three lenses. zoom lens. (3) The high variable power system according to claim 1 or 2, wherein the first and second lens groups each include a bonded lens, and the fourth lens group has at least one bonded surface. zoom lens.