JPS6332513A - Zoom lens - Google Patents

Abstract

PURPOSE:To easily obtain a wide view angle, to miniaturize the whole lens system, and to correct an aberration in a high level by specifying a refractive power and a lens arrangement of each lens group of four lens groups, and an image forming magnification of a fourth group, extending over the whole variable power range. CONSTITUTION:The titled zoom lens is provided with four lens groups of a first group I of a negative refractive power, a second group II of a positive refractive power, a third group III of a negative refractive power, and the fourth group IV in order from an object side, and the variable power is executed by fixing the first group and the fourth group and moving the second group and the third group onto an optical axis. In this zoom lens, a composite focal distance of the first group, the second group and the third group is positive within the whole variable power range, and a composite focal distance of the third group and the fourth group is negative, and when an image forming magnification at an arbitrary position in the whole variable power range of the fourth group is denoted as beta4, this zoom lens is constituted so as to a condition of the inequality. In this way, a wide view angle is easily obtained, and also, the whole lens system is miniaturized, and an aberration can be corrected in a high level.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a zoom lens suitable for photographic cameras, video cameras, etc., and particularly has at least four lens groups preceded by a lens group with negative refractive power. The present invention relates to a zoom lens having a wide angle of view, a short overall lens length, and good optical performance.

(Prior Art) There is a so-called four-group zoom lens, which has been conventionally used in still cameras, video cameras, etc., and is preceded by a negative lens group with a relatively high zoom ratio and a wide angle of view. For example, as proposed in British Patent No. 91522, this four-group zoom lens consists of a first group with negative refractive power for focusing, a second group with positive refractive power for zooming, and a second group with positive refractive power for zooming. group, ¥J3 group with negative refractive power to correct image plane fluctuations due to zooming, and the focal point of the system! It consists of four lens groups, the fourth group being used to maintain a good balance between distance and aberration correction.

This four-group zoom lens has a feature that by providing the first group with negative refractive power, it is possible to relatively easily achieve a high zoom ratio and a wide angle of view.

However, since this 4-group zoom lens is preceded by a lens group with negative refractive power, the total length of the lens inevitably increases compared to a zoom lens that is preceded by a lens group with positive refractive power, and the refractive power of the 4th group is strengthened. In other words, since the imaging magnification is increased to form an image, the number of lenses in the fourth group must be increased in order to correct aberrations, which inevitably tends to increase the overall length of the lens.

(Problems to be Solved by the Invention) The present invention aims to provide a four-group type zoom lens with a short overall lens length, which can easily widen the angle of view, and can also provide a relatively high zoom ratio of about 2. Particularly, it is an object of the present invention to provide a zoom lens suitable for photographic cameras, video cameras, etc., which has a lens configuration in which a lens group having a negative refractive power precedes the zoom lens, and has good optical performance.

(Means for solving the problem) From the object side, the first group has negative refractive power, and the second group has positive refractive power.
lens group, a third group with negative refractive power, and a fourth group, the first group and the fourth group are fixed, and the second group and the third group are moved on the optical axis to change the lens group. In a zoom lens that performs magnification, the composite focal length of the first group, the second group, and the third group is positive in the entire magnification range, and the combined focal length of the third group and the fourth group is positive.
When the combined focal length of the group is negative and the imaging magnification at any position in the entire zoom range of the fourth group is β4, then 0.8<β4<2.0 ( 1) Satisfy the following conditions.

Other features of the invention are described in the Examples.

(Example) FIG. 1 is a schematic diagram of a lens configuration of a zoom lens according to the present invention.

The figure (A) shows the wide-angle end, and the figure (B) shows the telephoto end.

In the figure, the first group has negative refractive power for focusing, ■ is the second group with positive refractive power for zooming, and ■ has negative refractive power to correct image plane fluctuations due to zooming. The third group is the fourth group having a positive or negative refractive power for image formation. The magnification is changed from the wide-angle end to the telephoto end by moving the second and third groups in the direction of the arrow. Nao S
T is a diaphragm, which is provided in or near the second group, and is moved together with the second group during zooming.

In this embodiment, the combined focal length of the first, second, and third groups is made positive over the entire zoom range, and
The refracting power of each lens group and the res group are arranged so that the combined focal length of the group and the fourth group is negative.

In other words, the overall configuration is of a telephoto type consisting of two lens groups with positive and negative refractive powers.

This makes it easy to widen the photographing angle of view at the wide-angle end by making the first group a lens group with negative refractive power. By making the entire lens a telephoto type, it is easy to shorten the overall lens length.

When changing the magnification from the wide-angle end to the telephoto end, the first and fourth groups
By fixing the group and moving both the second and third groups toward the object in the direction of the arrow, the variable power effect is increased and a variable power ratio of approximately 2 is easily obtained.

In this example, the refractive power of the fourth group is made weak overall, that is, it has a refractive power that satisfies conditional expression (1) when converted to imaging magnification, and the combined focal length with the third group is is set to be negative. Further, as a result, various aberrations caused by the variable power system can be effectively corrected with a small number of lenses, about 1 to 2 lenses.

If the lower limit of conditional expression (+) is exceeded and the positive refractive power of the fourth group becomes too strong, the overall negative refractive power will be too weak when combined with the third group, and the telephoto ratio will be insufficient. As the number of lenses increases, the total length of the lens also increases.

If the upper limit of conditional expression (1) is exceeded and the negative refractive power of the fourth group becomes too strong, the telephoto ratio will not be sufficient or the number of lenses will have to be increased to correct the aberrations generated by the fourth group. ,
As a result, the total length of the lens increases, which is not good.

In this example, in order to achieve a wide angle of view and good optical performance over the entire zoom range while further reducing the overall length of the lens, the focal length of the first group was set to fl, and the entire system at the wide-angle end 1 and the telephoto end was When the focal lengths of are f, , fT, respectively, 0.5fw < l f+ l <4fT..." (2
) It is better to satisfy the following conditions.

Conditional expression (2) relates to the negative refractive power of the first group; if the negative refractive power of the first group exceeds the lower limit and becomes too strong, the telephoto ratio at the telephoto end will increase and the overall length of the lens will increase. .

In addition, in order to keep the overall lens length short when the lower limit is exceeded, it is necessary to strengthen the positive refractive power of the second group, which results in large aberration fluctuations due to zooming, and it is important to properly correct this. It's going to be difficult. In particular, it becomes difficult to satisfactorily correct spherical aberration at the telephoto end.

If the negative refractive power of the first group exceeds the upper limit and becomes too weak, the magnification change effect of the second group becomes weak, and the amount of movement of the second and third groups must be adjusted to obtain a predetermined magnification ratio. As a result, the inclination of the variable power cam becomes steeper, and the sensitivity of the second lens group also increases, which is not good.

In this embodiment, the diaphragm is placed in or near the second group and moved together with the second group during zooming, thereby reducing the effective diameter of each lens group and making the entire lens system more compact. There is. That is, in a conventional four-group zoom lens, the aperture is placed in or near the fourth group. This is effective in reducing the effective diameter of the fourth group, which has a large number of lenses, but on the contrary, the effective diameters of the first and second groups become larger. In this embodiment, since the refractive power of the fourth group is weaker than that of a conventional four-group zoom lens, relatively good aberration correction can be achieved even if the number of lenses is reduced. Therefore, in this embodiment, by arranging the diaphragm as described above, the effective diameter of the lens of the first and second groups as well as the fourth group is reduced, thereby achieving miniaturization of the entire lens system.

In this example, in order to reduce aberration fluctuations during zooming and shorten the overall length of the lens, the focal length of the second group is f2, which is 0.5fw<f2<2f, -, ... (3) It is better to set it like this.

Conditional expression (2) relates to the refractive power of the second group; if the refractive power exceeds the lower limit and becomes too strong, aberration fluctuations due to zooming will increase, making it difficult to properly correct spherical aberration, especially at the telephoto end. It's coming. Moreover, if the upper limit is exceeded and the refractive power of the second revision becomes too weak, the amount of movement of the second lens group must be increased to obtain a predetermined variable power ratio, which is not good because the overall length of the lens increases.

In the compact zoom lens of this example, aberration fluctuations during zooming are reduced and aberrations are well corrected, especially spherical aberration at telephoto (!11). It is preferable to have at least one negative lens with a convex surface facing the object side and at least one positive lens with a meniscus shape with a convex surface facing the object side.

Further, it is preferable that the fourth group has at least one single lens or a laminated lens with a convex surface facing the object side.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the i-th lens surface in order from the object side, D
i is the first lens thickness and air gap from the object side, Ni
and νi are the refractive index and Abbe number of the glass of the i-th lens in order from object n1, respectively.

The aspherical shape is X@ in the optical axis direction and H@1 in the direction perpendicular to the optical axis.
1. Let the traveling direction of light be positive, and R is the paraxial curvature half, radius, al
When +a2+a3+a and t are aspherical coefficients, it is expressed by the following formula: +a,)(4+a2H'+a3H8+34H").

Numerical Example I F-1oo~188.9 FNo-1: 3.6~4
．． 6 2ω-62,1'~35.4'R2 surface; aspherical shape a, =2.875 xlO-', β2=8.4
76 Xl0-”.

a' = 1.547 XIO", β4 = 7.948
xlO-1af, 2. =97.4~184 f, =-179.9 β4=1.03 Numerical Example 2 FJOO~188.9 FNO-1: 4.1~5.
8 2 (&1-62.0' ~ 35.3' mountain 14-5
358.40 014・6.90 N 7-1.5
3980 Schiff 34,5R2 surface; aspherical shape a, =7.311 Xl0-8. β2=1.693
xio-”.

a3=-5,180xlO-+6. β4=3.728
xlO-"f1□, =101.0~190.7 f, knee 147.9 β4=0.99 Numerical Example 3 F=100~188.9 FNo-1: 4.1~5
．． 8 2ω-82,0'~35.30f 12+
=100.5~190. .

f, = -145.5 β4.0.99 Numerical Example 4 F-100~187 FNo=l: 3.9~5.
8 2ω-61,7°~35.4° (R4-162,
35D 4. Variable RI field; spherical shape a, =1.89] Xl0-', R2=-2
,872x10-th.

a3=2.658 x+o-15, a4=2.646
xlO-18a, =2.591 xlO-',
a2=5.386 Xl0-”.

a3=4.319 Xl0-15. a4=1.06
4 xlO-18f 123 =103.7~194
．． 0f, =-123.4 β, =0.96 Numerical Example 5 F-100 to 188.9 FNo-1: 3.6 to 4
．． 6 2ω=61.9' ~35.2゜1R12=
4100 D12-2.911, R15-(aperture) D15/Variable 18=-39,49DI8-4.16 89-1
．． 60311 ν 9-60.719=-349,
52019-Variable■■τ0--129.76 D20=4.9
9 N 9-1.19171 ν 9-57.
49=-154,35 R2 surface: aspherical shape a, =2.972 xlo-', a2=8.
684 xlo-eyes.

a 3 =1.594 XIO-1', a
4 = 8.167 Xl0-18f! 23 = 9
8.0 to 185.1 f, = -192.4 β4 = 1.02 For reference, Table 1 shows the relationship between each of the above-mentioned conditional expressions and each numerical example of the present invention. In Table-1, f123W
+f123T are the 1st. Composite wide-angle end and telephoto end focal length of the second and third groups, fff4W+f 34T
are the composite focal lengths of the third group and the fourth group at the wide-angle end and the telephoto end, respectively.

Table 1 (Effects of the Invention) According to the present invention, as described above, by specifying the refractive power and lens arrangement of each of the four lens groups and the imaging magnification of the fourth group over the entire magnification range, a wide image can be obtained. It is possible to achieve a zoom lens in which angularization can be easily obtained, the entire lens system is miniaturized, and aberrations are well corrected.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an optical system according to an embodiment of the present invention, Figs. 2 to 6 are cross-sectional views of lenses of numerical embodiments 1 to 5 of the present invention, and Figs. Numerical Example 1 of the Invention
5 is a diagram showing various aberrations of No. 5. In Figures 1 to 6 (A)
(B) is a cross-sectional view of the lens at the wide-angle end, (B) is an aberration diagram at the telephoto end, and (A) is an aberration diagram at the wide-angle end, (B) is an intermediate view, and (C) is an aberration diagram at the telephoto end. In the figure, ■, ■, ■ are the 1st group and the 2nd group.
The groups, the third group, the fourth group, and the arrows indicate the directions of movement during zooming. Patent Applicant: Canon Co., Ltd. No. 1 Usagi 2 Kuchi (A) Ryo 3 times (A) 5th Kuchi (A> Kabuto 6 Ro (A) See 7 times Houki 8 times Man 9 Kuchi 10 times See 11 times

Claims (2)

[Claims] (1) It has four lens groups: a first group with negative refractive power, a second group with positive refractive power, a third group with negative refractive power, and a fourth group in order from the object side, and the first group and the fourth group is fixed, and the second group is fixed.
In a zoom lens that changes magnification by moving a group and a third group on the optical axis, the combined focal length of the first group, second group, and third group is positive over the entire zoom range, and the third group and the composite focal length of the fourth group is negative, and when the imaging magnification at any position in the entire zooming range of the fourth group is β_4, the following condition is satisfied: 0.8<β_4<2.0 A zoom lens that is characterized by: (2) Claim 1, characterized in that a diaphragm that moves with zooming is provided in or near the second group.
Zoom lens described in section.