JPS61296319A - Small-sized zoom lens - Google Patents

Abstract

PURPOSE:To shorten the overall length of a lens system consisting of four lens groups and to reduce the weight by arranging a fixed stop between the 2nd and the 3rd groups and satisfying a specific condition between the on-axis gap between the 2nd and the 3rd groups at a wide-angle zoom end and the on-axis gap between the 2nd group and stop. CONSTITUTION:The lens system consists of the 1st group 31 for focusing which has positive refracting power, the 2nd group 32 which moves monotonously during power variation and has negative refracting power, the 3rd group 33 which moves monotonously in the opposite direction from the 2nd group 32 during power variation and has positive refracting power, and the 4th group 34 which performs fixed image forming operation and has positive refracting power successively fro an object side and when the fixed stop 35 is arranged between the 2nd and the 3rd groups, an inequality holds, where 1w is the on-axis gap between the 2nd and the 3rd groups at the wide-angle zoom end and 1s is the on-axis gap between the 2nd group and stop. Then, the 2nd group, the 3rd group, and the stop are so arranged as to satisfy the inequality to realize high power variable power without mechanical interference between both groups and the stop. Consequently, the overall length of the lens system is shortened and the diameter of the front lens of the 1st group 31 is decreased to reduce the size of the whole lens system.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a compact zoom lens, and in particular to a compact zoom lens that is suitable for photo cameras, video cameras, etc. and is designed to reduce the weight of the entire lens system with a high zoom ratio. This relates to zoom lenses.

(Prior Art) As a zoom lens with a relatively high zoom ratio that has been conventionally used in photographic cameras, video cameras, etc., there is a zoom lens having the configuration shown in FIG. In the figure, 11 is the first group with positive refractive power for focusing, 12 is the second group with negative refractive power that mainly functions to change the magnification and moves monotonically, and 13 is the correction for image plane fluctuations associated with changing the magnification. In order to do this, the third group 14 with negative refractive power, which moves convexly back and forth toward the object side, is arranged as necessary to make the light beam from the first group to the third group a substantially parallel light beam. The fourth group having a fixed positive refractive power and 15 are the fifth group having a fixed positive refractive power which performs an imaging function.

Reference numeral 16 denotes a diaphragm, which is often arranged between the third and fourth groups or between the fourth and fifth groups. In the zoom lens shown in Figure 1, the second and third groups share the moving space when changing magnification, so the overall lens length can be relatively short and the entire lens system can be made compact. In order to reduce the overall size, the refractive power of the second group should be made as strong as possible.
It is necessary to reduce the amount of movement of the group. However, if the refractive power of the second group is strengthened, aberration fluctuations due to zooming will increase,
Another problem arises in that manufacturing accuracy must be improved. In addition, the inventor's long-term research results show that if the refractive power of the second group is made too strong, the lens thickness must be increased to ensure the edge thickness of the convex lens, and as a result, the overall length of the lens becomes longer. There are cases. Therefore, the refractive power of the second group cannot be made very strong.

Also, if you try to widen the angle of view by shortening the focal length at the wide-angle end, the diameter of the front lens of the first group or the oblique light beam will be determined, so the wider the angle of view, the larger the diameter of the front lens and the larger the diameter of the entire lens system. is becoming larger. On the other hand, if you shift the focal length at the wide-angle end to a longer one, the diameter of the front lens is determined by the larger diameter of the oblique light flux near the wide-angle end or the maximum axial light flux at the telephoto end, so the predetermined zoom ratio If you try to achieve this, the focal length at the telephoto end will become too long, and the diameter of the front lens will increase accordingly. Also, in the zoom lens shown in Figure 1, both the second and third groups have negative refractive power, so
The axial light beam diverges, and the diameter of the aperture disposed after it tends to increase. Generally, in a zoom lens, as the focal length increases, the aperture diameter increases. Further, the aperture unit requires a diameter approximately twice the maximum aperture diameter. Therefore, a lens configuration in which the focal length at the telephoto end is long is not preferable for downsizing the lens system.

On the other hand, Japanese Patent Publication No. 51-12424 proposes a zoom lens consisting of five groups similar to that shown in FIG. 1, as shown in FIG. In the figure, the third lens group 23 has a positive refractive power and is moved monotonically in the opposite direction to the movement direction of the second lens group 22 that has a negative refractive power to achieve a high zoom ratio. In the figure, 21 is a first group for focusing, 24 is a fourth group for converting the light beam that has passed from the first group to the third group into a substantially parallel light beam, 25 is a fifth group that performs an imaging function, 27 is an optical member for extracting the finder light beam, and 26 is an aperture. In the zoom lens shown in FIG. 2, the light beam converges somewhat after passing through the third group, so the aperture system becomes relatively small. However, in order to reduce the diameter of the front lens of the first group, it is necessary to increase the distance between the second and third groups to some extent, and as a result, the overall length of the lens increases. Furthermore, the lens system of the third group is also increased. In order to shorten the overall length of the lens, it is possible to increase the refractive power of the second and third groups and reduce the amount of movement of both groups, but increasing the refractive power increases aberration fluctuations that occur with zooming. , it is not possible to make the refractive power too strong.

(Problems to be Solved by the Invention) The present invention aims to reduce the weight of the entire lens system by shortening the overall length of the lens and reducing the diameter of the front lens of the first group, which is particularly suitable for photographic cameras and video cameras. The objective is to provide a compact zoom lens with a high zoom ratio.

(Means for solving the problem) In order from the object side, a first group with positive refractive power for focusing, a second group with negative refractive power that moves monotonically when changing magnification, and the second group when changing magnification. It has four lens groups: a third group with a positive refractive power that moves monotonically in the opposite direction to the lens group, and a fourth group with a positive refractive power that performs a fixed imaging function, and the second group and the third group When arranging a fixed aperture between them, the axial distance between the second group and the third group at the wide-angle end zoom position is 1w, and the axial distance between the second group and the Tateki diaphragm is 1s. Then 0, 4< I s / 1w <0.75 ・-”・
- The setting was made to satisfy (1).

Other features of the invention are explained in the examples.

(Embodiment) FIG. 3 is a schematic diagram of an optical system according to an embodiment of the present invention. In the figure, 31 is a first group with positive refractive power for focusing, 32 is a second group with negative refractive power that moves monotonically toward the image plane during zooming,
33 is a third group with a positive refractive power that moves monotonically toward the object in the opposite direction to the second group when changing the magnification; 34 is a fourth group with a positive refractive power that performs a fixed imaging action; and 35 is a fourth group with a positive refractive power. This is a fixed diaphragm placed between the second group and the third group.

In this example, when changing the magnification of the second and third groups with the aperture in between,
By moving monotonically in one direction and further setting the second group, third group, and diaphragm to satisfy equation (1) above, the diameter of the front lens of the first group can be reduced, and the overall length of the lens can be shortened. We are trying to make this happen. Generally, in the zoom lens shown in Fig. 3, even if the aperture is placed between the second and third groups, the third
If a zoom system is adopted in which the group is reciprocated in a convex manner toward the object side, the advantage of sharing the space between the second and third groups will be lost, and the overall length of the lens will become longer. In other words, in a zoom system in which the third group moves back and forth, the second and third groups come closest at an intermediate position during zooming, so an extra space is provided in advance to prevent mechanical interference between the two groups. Therefore, the total length of the lens becomes longer. In contrast, in this embodiment, an aperture is placed between the second and third groups, and the magnification is changed by moving the second and third groups monotonically in opposite directions so as not to interfere with the aperture. Since the zoom method is adopted, no extra space is required. By providing the second group with a variable power effect and also providing a variable power effect with the third group, a predetermined variable power ratio can be efficiently obtained. Achieved double ratio. Also, the second group and the third group
The overall length of the lens is shortened by making effective use of the space between the lens groups and by reducing the overall amount of movement of the second and third groups on the optical axis. In addition, in a typical zoom lens, the first group often accounts for 50 to 80 percent of the weight of the entire zoom lens. Therefore, in order to reduce the weight of a zoom lens, it is effective to reduce the volume by reducing the specific gravity of the material of the first lens group or by reducing the diameter of the front lens of the first group. Among these materials, it is difficult to select a material with a small specific gravity because it reduces the degree of freedom in optical design. Therefore, in order to reduce the weight of the lens while maintaining good optical performance, it is effective to reduce the diameter of the front lens in the first group.

For example, considering the volume of a lens proportionally, it is proportional to the cube of the lens diameter, so if the lens diameter can be reduced by 10%, the volume can be reduced by about 27% from (0,9)'. In this embodiment, the diameter of the front lens of the first group is prioritized in order to reduce the weight of the entire lens system. In other words, compared to a zoom lens in which the aperture is located behind the fourth group as shown in Figures 1 and 2, an optical system with an aperture located closer to the first group between the second and third groups By arranging it at a substantially intermediate position, priority is given to reducing the diameter of the front lens of the first group. In this embodiment, the effective diameter of the front lens becomes smaller in both the diameter of the front lens of the first group determined by the oblique light flux on the wide-angle side and the diameter of the front lens of the first group determined by the axial light flux on the telephoto side. The aperture and lens groups are arranged like this. Furthermore, while preventing the front lens effective diameter from increasing due to oblique light flux when widening the field of view, the front lens effective diameter is partially determined by the axial light flux on the telephoto side, and the F number on the telephoto side is increased. This regulation allows the size of the front lens effective diameter to be arbitrarily determined, thereby controlling the size of the entire lens system in a well-balanced manner.

By arranging the second group, third group, and diaphragm so as to satisfy equation (1), mechanical interference between the two groups and the diaphragm can be prevented, and the overall length of the lens can be shortened while achieving a high zoom ratio. The aim is to reduce the diameter of the front lens of the first group.

As mentioned above, moving the aperture close to the first group is advantageous in reducing the diameter of the front lens of the first group, but on the other hand, the rear lens system behind the aperture, for example the lens system of the fourth group, increases. I'll come. Conditional expression (1) is intended to reduce the size of the entire lens system while maintaining a good balance between the effective diameters of the front lens diameter and the rear lens diameter of the first group.

If the lower limit of conditional expression (1) is exceeded, the diameter of the front lens of the first group becomes smaller, but on the contrary, the effective diameter of the rear lens increases, especially since the third group moves relative to the aperture when changing the magnification. The position of the off-axis oblique light beam incident on the fourth group fluctuates greatly, and it becomes difficult to satisfactorily correct the aberration fluctuations at this time. On the other hand, if the aperture position moves away from the first group by exceeding the upper limit of conditional expression (1), the diameter of the front lens of the first group will increase, and the amount of increase will be particularly noticeable when widening the angle of view, which is not preferable.

The compact zoom lens that is the object of the present invention is achieved by satisfying the above conditions, but furthermore,
In order to reduce aberration fluctuations over the entire zooming range and to downsize the entire lens system, the total amount of movement of the second and third groups during zooming is set to ξ.

It is desirable to satisfy the condition (2) where η is 0.5<lη/ζl<1.3. If the lower limit of conditional expression (2) is exceeded and the amount of movement of the third group is reduced, the refractive power of the second group to obtain a predetermined variable power ratio can be weakened, which is advantageous in terms of manufacturing and aberration correction. However, the amount of movement of the second group increases relatively.

For this reason, even if the diaphragm is disposed close to the second group, the distance between the first group and the diaphragm at the wide-angle end increases, which is not preferable because the diameter of the front lens of the first group increases. Conversely, if the amount of movement of the third group is increased beyond the upper limit of conditional expression (2), the amount of movement of the second group can be relatively reduced, and the diameter of the front lens of the first group can be reduced. However, since the variable power effect of the second lens group decreases, it becomes difficult to obtain a predetermined variable power ratio. In addition, in the case of the zoom lens of the present invention, since the diverging light beam from the second group enters the third group, the incident position of the axial light beam to the third group is higher than that of the second group, and if the change is large, the change will occur. It becomes difficult to satisfactorily correct aberrations associated with magnification, especially fluctuations in spherical aberration.

In addition, in the present invention, in order to further reduce aberration fluctuations during zooming and to perform zooming efficiently under the above-mentioned conditional expression (2), the focal lengths of the second and third groups should be set separately. f2. When f3 is set, 1< l fs /f2 l <2"...(3
) is desirable. If the lower limit of conditional expression (3) is exceeded and the refractive power of the third group becomes too strong, it will be difficult to satisfactorily correct aberration fluctuations for the diverging light flux incident from the second group. If this is exceeded and the refractive power of the third group becomes weaker, the amount of movement of the third group during zooming must be increased, which is undesirable because the overall length of the lens increases.

In addition, in a zoom system in which the front and rear lens groups are moved during zooming with an aperture unit in between, as in the present embodiment, if the lens barrel is configured with a conventional cylindrical cam, the outer diameter of the lens barrel increases. For this reason, in this embodiment, it is preferable to construct the lens barrel by arranging a cam space in front or behind the diaphragm unit, or by arranging a plate cam on one side of the diaphragm unit. In addition, in the case of a bar-type positioning system for guiding a movable lens in a straight line, simply arranging it outside the diaphragm unit is disadvantageous in terms of external dimensions. For this reason, instead of using a circular iris diaphragm system, the diaphragm unit itself uses a slide system that uses two blades and slides in the left and right directions to form a space in the vertical direction, and bars, etc. are placed in this space. With this configuration, it is possible to obtain a lens barrel that is both simple and compact. Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the first lens surface from the object side, Di is the thickness of the first lens from the object side, and air intervals Ni and νi are the radius of curvature of the first lens surface from the object side, respectively. These are the refractive index and Atsube number of glass. ■, ■, III, rV are respectively 1st. Second.
Third. The fourth group is shown, and f1+f2. f3. f4 is the first . Second. Third. This is the focal length of the fourth group.

Numerical Example I F-1,00~5.52 FNO Maro 1:1.25~
R27-oo D27-0. ．． 4724R28-0
0 1,752ω-57,b~11.0°N 1=1.8051s ν 1- 25.4N
2-1.60311 ν 2- 60.7N
3s1.62299 v 3-58.2N
4-1.6968 ν 4- 55.5N 7
-1.7495 ν 7- 35.3N 8-
1.62299 ν 8- 58.2N 9-1
．． 84666 v 9= 23.9NIO-1
,5927ν10- 35.3Nil-1,72υ11
- 50.2 N12-1.84666 y12= 23.9N
13-1.64 ν13- 60. lN14
J, 60311 v 14- 60.7N15=1
．． 51633 ν15- 64.1 Numerical Example 3 F-1,00~5.52 FNO-1:1.40~R
25-01:l D25-0.6627R261
-ω L, 75 2 ω-51,5°~1O10°2-1.
60311 ν 2- 60. ．． 73-1.622
99 ν 3- 58.24-1.7725
υ 4- 49.67-1.71300 2/
7 Proverbs 53.88-1.69680 υ 8- 5
5-59-1.84666 ν 9- 23.91
0J, 60311 v 10- 60.711-1
．． 69680 ν11- 55.512 dew 1.84
666 υ12- 23.913-1.77250
ν13- 49.8N14=1.5+633
ν14- 64.1 Numerical Example 5 F-1,00~5.52 FNO=l:1.25~R
27= ■ D27=0.6640R28−■ 1.75 2 ω=51.6°~l000°N I
-1,805+8 ν 1- 25.4N 2=
1.60311 ν 2- 60.7N 3-1
．． 89680 v 3- 55.5N 4-1
．． 77250 ν 4- 49.6N 7-1.
7725 ν 7= 49.6N 8-1.
69700 ν 8- 48.5N 9-1.8
4666 ν 9- 23.9NIO-1,696
80v IO = 55.5N11-1.80610
υ11- 40.9N12J, 84868 v
12-23.9N! 3=1.56384 y1
3-60.7N14-1.603] 1 υ14
- 60.7N15=1.51633 b15=
64.1 (Effects of the Invention) According to the present invention, a compact zoom lens with a high zoom ratio is achieved by reducing the overall length of the lens and the diameter of the front lens of the first group, thereby reducing the weight of the entire lens system. can be achieved.

Further, in the present invention, even if the angle of view is widened, the height of incidence of the oblique light beam on the first group on the wide-angle side can be made relatively low, so it is possible to prevent the diameter of the front lens of the first group from increasing. Furthermore, since the effective diameters of the third and fourth groups behind the aperture do not increase much, it is easy to create a compact zoom lens with a wide angle of view and a smaller overall lens diameter. can.

In addition, the positional sensitivity of each lens group is reduced, making assembly easier. Furthermore, since the angle of view is generally narrow at the telephoto end and is often taken outdoors, it is possible to use the telephoto end to the extent that there is no practical problem. By regulating the F number, the diameter of the front lens of the first group can be controlled, and a compact zoom lens can be easily achieved.

[Brief explanation of drawings]

Figures 1 and 2 are schematic diagrams of the optical system of a conventional zoom lens, Figure 3 is a schematic diagram of the optical system of a zoom lens according to the present invention, and Figures 4 to 9 are numerical values of the present invention. Example 1~
6 and FIGS. 10 to 15 are aberration diagrams of numerical examples 1 to 6 of the present invention, respectively. In the aberration diagrams, (A), (B), and (C) respectively show aberrations at the wide-angle end, middle, and telephoto end when an object is at infinity. In the figure, arrows indicate the moving direction of the lens group during zooming, d indicates the d-line, g indicates the g-line, ΔS indicates the sagittal image plane, and ΔM indicates the meridional image plane. Patent Applicant: Canon Co., Ltd. Ei 1. Product 2. Monju 3. Circle 4th Child O Father Rabbit 9. Zuhatsu 7. Article 6. Zuo 9. Mahiro 12th Fuyoku Kuneho Seisho (self-published) July 7, 1986 Commissioner of the Japan Patent Office, Mr. 2. Name of the invention: Small zoom lens 3. Relationship with the person making the correction case. Patent applicant address: 3-30-2 Shimomaruko, Ota-ku, Tokyo. Name (100)
) Canon Co., Ltd. Representative Ryuzo Kaku
Part 4. Agent address: 301 Jiyukaoka, Belheim, 2-17-3 Okusawa, Setagaya-ku, Tokyo 158 (Telephone: 71s-5814) 5.
Target of correction (
Column 6 of detailed explanation of the invention in the requested specification, contents of amendment

Claims (1)

[Scope of Claims] (1) In order from the object side, a first group with a positive refractive power for focusing, a second group with a negative refractive power that moves monotonically when changing magnification, and the second group when changing magnification. It has four lens groups: a third group with a positive refractive power that moves monotonically in the opposite direction to the above, and a fourth group with a positive refractive power that performs a fixed imaging function. When arranging a fixed aperture between the two, when the axial distance between the second group and the third group at the wide-angle end zoom position is 1_w, and the axial distance between the second group and the aperture is 1_s. A small zoom lens characterized by being set to satisfy 0.4<1_s/1_w<0.75. (2) The second lens group and the third lens group are set to satisfy 0.5<|η/ξ|<1.3, where ξ and η are the total amount of movement during zooming of the second and third groups, respectively. A compact zoom lens according to claim 1.