JPH04338910A - High variable power rate zoom lens with small short-distance aberration variation - Google Patents

Abstract

PURPOSE:To obtain excellent performance from infinity to a short distance by stabilizing the performance of a three-group zoom lens and a four-group zoom lens in short-distance focusing. CONSTITUTION:The zoom lens consists of a 1st positive lens group I, a 2nd positive lens group II, and a 3rd negative lens group III and the power is varied from a wide-angle end to a telephoto end by moving the respective lens groups toward an object. While the most image-side lens element LF among lens elements constituting the 2nd lens group is fixed at a constant position, the remaining lens elements of the 2nd lens group are moved toward the object and the lens system consists of the 1st positive lens group I, the 2nd positive or negative lens group II, the 3rd negative lens group III, and a 4th negative lens group IV; and the power is varied from the wide-angle end to the telephoto end by moving the respective lens groups along the optical axis respectively. The most image-side lens element LF among elements constituting the 3rd lens group is fixed at a constant position and the remaining lens elements of the 2nd and 3rd lens groups are moved toward the object to put the lens system in focus.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens with a high zoom ratio, and more particularly to a zoom lens with a high zoom ratio that exhibits little variation in aberrations even when focusing at short distances and is designed to shorten the shortest photographing distance.

0002

BACKGROUND OF THE INVENTION In recent years, fully automatic cameras equipped with zoom lenses with high variable magnification are being commercialized as new concept cameras. Among these, when the variable power ratio exceeds about 3, it is difficult to realize it with a simple two-group zoom lens, so new lens types have been devised.

Under these circumstances, the present applicant developed a high variable magnification 3-group zoom lens developed from the original 4-group zoom lens (Japanese Patent Application Laid-Open No. 63-43115) in JP-A-63-1.
53511, and a focusing method that reduces aberration fluctuations at close distances was proposed in Japanese Patent Application Laid-Open No. 1-20401.
This was proposed in issue 3.

[0004] This focusing method requires only a small amount of focusing movement up to short distances, and has relatively little variation in aberrations, so it was an indispensable technology for realizing the above-mentioned zoom lens.

[0005] By the way, focusing of a conventional zoom lens is generally performed by moving the first lens group, and many focusing methods have been proposed that do not take much account of aberration fluctuations as a paraxial solution. ing.

[0006]

[Problems to be Solved by the Invention] On the other hand, there is a desire to further shorten the close-up distance, and in the above-mentioned invention of the applicant, aberration fluctuations are suppressed near the telephoto end where the amount of focusing movement becomes large, and high performance has been achieved. To do so, newer technology is required.

The present invention has been made in view of the above circumstances, and its object is to provide, in order from the object side, a first lens group with positive refractive power and a second lens group with positive refractive power, as proposed by the applicant. and a third lens group with negative refractive power, and a first lens group with positive refractive power in order from the object side.
During close-range focusing, a 4-group zoom lens consisting of a lens group, a second lens group with positive refractive power or negative refractive power, a third lens group with positive refractive power, and a fourth lens group with negative refractive power is used. The object of the present invention is to provide a zoom lens that has stable optical performance and can provide satisfactory performance from infinity to close range.

[0008]

[Means for Solving the Problems] A high-power zoom lens with little variation in close-range aberrations of the present invention, which achieves the above objects, has the following features:
Consisting of, in order from the object side, a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group with negative refractive power,
Changing the magnification from the wide-angle end to the telephoto end is performed by moving each lens group toward the object side.The second lens group is used as a focusing lens group, and the lens component closest to the image side that makes up this second lens group is fixed. This is characterized in that focusing is performed by fixing the lens component at a fixed position and moving the remaining lens components of the second lens group toward the object side.

Another invention provides, in order from the object side, a first lens group with positive refractive power, a second lens group with positive refractive power or negative refractive power,
Consisting of a third lens group with positive refractive power and a fourth lens group with negative refractive power, zooming from the wide-angle end to the telephoto end is performed by moving each lens group along the optical axis, and the second lens group The lens group and the third lens group are used as focusing lens groups, and the lens component closest to the image side constituting the third lens group is fixed at a fixed position, and the remaining lens components of the second lens group and the third lens group are focused on the object. The feature is that focusing is performed by moving to the side.

0010

[Operation] As mentioned above, many focusing methods have been proposed in the past, but in reality, it is extremely important to suppress aberration fluctuations, and the driving method and control means related to the focusing lens group are also important. It has meaning.

The present invention mainly focuses on suppressing fluctuations in spherical aberration and astigmatism caused by focusing near the telephoto end, and it is aimed at suppressing fluctuations in spherical aberration and astigmatism caused by focusing near the telephoto end. It was designed to be shortened. That is, as a method for achieving this, the concept of floating is introduced here using a so-called internal focusing method, and the degree of aberration fluctuation is reduced with a simple lens configuration, with the intention of stabilizing performance.

As mentioned above, focusing in a zoom lens has generally been carried out by moving the first lens group, but in recent years, an autofocus method has been adopted, and the focus position during zooming is moved by electrical means. It is possible to solve the problem by Therefore, we need a method to determine the power arrangement so that the focal position is within a nearly constant depth of focus,
It has become technically possible to mechanically correct the focal position, and it can be considered that the degree of freedom in optical design has increased.

Under these circumstances, in the present invention, first, in order from the object side, the first lens group has a positive refractive power, the second lens group has a positive refractive power, and the third lens group has a negative refractive power. We investigated a method for focusing at short distances without changing aberrations using a three-group zoom lens. In addition, there are four-group zoom lenses that form the basic configuration of this optical system, including a type in which the second lens group is a negative front group and a positive rear group, and a type in which the front group of the second lens group is a positive group. It was confirmed that the focusing method can be applied to a similar optical system with a refractive power of .

The basic focusing method is as shown in FIG.
), a second lens group with positive refractive power (power is φ2), and a third lens group with negative refractive power (power is φ3), in which the second lens group is moved toward the object side. This method attempts to focus on a nearby object point. According to this method, the distance between the first lens group and the second lens group and the distance between the second lens group and the third lens group change, making it possible to utilize the effect of compensating for variations in aberrations. .

On the other hand, when the close distance is further shortened, although the focal length of the focusing lens at a specific focal length remains constant, the amount of focusing movement generally increases significantly on the long focal length side. Therefore, there is a need to take further measures to reduce aberration fluctuations.

Furthermore, when focusing, it is easy to think of the idea of correcting field curvature by subtly changing the distance between lens groups, which is used in wide-angle lenses, etc., but due to the variable power of zoom lenses, It is not very desirable to have separate cams for the movement of the lens and for the movement of the focusing, both from a mechanical standpoint and from the standpoint of accumulating manufacturing errors.

Therefore, in the present invention, as shown in FIG. 2, in a three-group zoom lens having a power arrangement similar to that in FIG.
The closest to the image plane of the second group forming the focusing lens group,
Lens component LF with relatively small power (power is φ
LF) and fixed it during focusing.
By moving the remaining lens group (power: φ2F) toward the object side, a floating effect is obtained.

Now, Table 1 below shows the aberration coefficients of each lens group with respect to an object point at infinity at the telephoto end in the fourth embodiment, which will be described later, in which the variable power ratio is not so large, and is used as a reference value. In Table-1, SA3, SA5, and SA7 are the 3rd, 5th, and 7th order spherical aberration coefficients, respectively, and CMA3, C
MA5 is the third-order and fifth-order coma aberration coefficients, respectively,
AST3 and AST5 are 3rd and 5th order astigmatism coefficients, respectively, and DIS3 and DIS5 are 3rd and 5th order astigmatism coefficients, respectively.
It is the following distortion aberration coefficient (the same applies hereinafter).

Table-1
Infinity object point (∞) lens group SA3
SA5 SA7
CMA3 CMA5 1
-0.08670 -0.00
974 -0.00132 0.12667
0.02527 2
-0.02523 0.04735
0.02241 -0.05921 0.
00013 3 0.11
403 -0.03713 -0.02335
-0.06568 -0.03619 Total sum 0.00210 0.
00048 -0.00226 0.001
79 -0.01078 Lens group
AST3 AST5 D
IS3 DIS5 1
-0.03661 -0.00235
0.05643 0.00245 2
0.05276 0.00
227 -0.07744 -0.00097
3 -0.01668
-0.00010 0.04883 0
．． 00071 Total sum -0.000
53 -0.00018 0.02782
0.00219.

Next, Table 2 shows the aberration coefficients at short distance (-0.5 m) when using the conventional focusing method in the optical system of the present invention shown in FIG. is the short distance (
-0.5m). Here, higher-order aberration coefficients are also shown so that the comparison of both coefficients can be made strictly at the aberration level. From the characteristic coefficients of each group in these tables and the sum on the image plane, it is possible to evaluate the state of an object point at infinity and the change in performance at short distances.

Table-2
Near-distance object point (-0.5m) Conventional focusing method lens group SA3 SA
5 SA7 CMA3
CMA5 1
-0.05798 -0.00507 -0
．． 00055 0.05811 0.0
1023 2 -0.042
58 0.04639 0.02411
-0.00529 0.01410
3 0.08671 -0
．． 02459 -0.01352 -0.04
602 -0.03094 Total sum
-0.01385 0.01674
0.01004 0.00680 -0
．． 00661 Lens group AST3
AST5 DIS3
DIS5 1 -0.0
1779 -0.00093 0.0365
7 0.00110 2
0.03422 0.00135 −
0.06202 -0.00039 3
-0.01551 -0.000
01 0.04547 0.00035
Total sum 0.00092 0
．． 00041 0.02003 0.00
107.

Table-3
Near-distance object point (-0.5m) Invention focusing method lens group SA3 SA
5 SA7 CMA3
CMA5 1
-0.05872 -0.00517 -0
．． 00056 0.06027 0.0
1063 2 -0.057
37 0.04083 0.02244
0.00358 0.01954
3 0.08715 -0.
02486 -0.01334 -0.046
37 -0.03083 Total sum
-0.02894 0.01080
0.00854 0.01747 -0.
00067 Lens group AST3
AST5 DIS3
DIS5 1 -0.01
822 -0.00096 0.03716
0.00114 2
0.03399 0.00139 -0
．． 06226 -0.00041 3
-0.01553 -0.0000
4 0.04553 0.00037 Total sum 0.00024 0.
00039 0.02043 0.001
10.

From these tables, it is clear that the focusing method of the present invention is effective in suppressing significant fluctuations in higher-order aberrations including spherical aberrations on the telephoto side. The difference in the aberration correction state is particularly remarkable for spherical aberration. In Table 2, the higher orders (SA5, 7) are larger than the third order, and the overall balance is disrupted. On the other hand, this is not the case in Table 3, and the balance is good. The aberration diagrams are as shown in A and B in FIG. 3, respectively. At A in the figure, the aberration tilts toward the + side due to higher-order effects, and the balance with other aberrations is not good.

At this time, it is desirable to use the power φLF of the lens component LF disposed closest to the image plane in the second group within the following range.

φLF/φW <1.5
...
(1) However, φW is the refractive power (
power).

If conditional expression (1) is not satisfied, the power of this lens component LF becomes large, and it becomes necessary to construct the lens component with a plurality of lenses. As a result, the total length of the lens system increases, which is undesirable. If the value of equation (1) can be appropriately selected in order to configure the focusing lens group without increasing its power as a whole,
This is extremely advantageous in terms of overall aberration correction. Since this lens component LF is fixed during focusing, FIG.
This can be easily achieved by configuring the lens holding frame to be held separately from the focusing unit, as shown in the cross section of the lens barrel. Here, the configuration and operation of FIG. 4 will be briefly explained.

Each lens 14 of the first group is attached to the lens holding frame 1.
Fixed. Each lens 15 except for the lens component LF of the second group is fixed to the lens holding frame 4. Furthermore, each lens 16 of the third group is similarly fixed to the lens holding frame 7. The second group lens component LF is fixed to the lens holding frame A. The lens holding frame 1 is a moving frame 10
Fixed. The moving frame 10 has a pin 3 and a lens holding frame A.
A pin 6 is installed in the lens holding frame 7, and a pin 9 is installed in the lens holding frame 7, respectively. The fixed frame 11 is provided with a long hole in the optical axis direction, and each pin 3, 6, and 9 is slidable in the axial direction. The cam ring (zoom ring) 12 is provided with a zoom cam groove, and by rotating the cam ring 12 around its axis, each pin 3, 6, and 9 moves, and each group changes accordingly. By moving in a zoom trajectory,
Zooming is performed.

By the way, a focusing rod 13 is attached to the lens holding frame A, and the focusing rod 13 is fitted into a hole provided in the lens holding frame 4. A spring 17 wound around the focusing rod 13 presses the lens holding frame 4 against the lens holding frame A, so that both move together during zooming.

During focusing, the focusing member (not shown) is moved by the focusing motor and pushes the lens holding frame 4 to the left, so that only the lens holding frame 4 moves along the focusing rod 13 independently of the lens component LF. The lens is extended and focusing is performed. spring 17
If you stop pushing it, the lens holding frame 4 will naturally return to the right, so that it can move freely back and forth. From the object side, the first lens group with positive refractive power, the first lens group with positive refractive power, or negative refractive power. Even in a four-group zoom lens consisting of a second lens group with refractive power, a third lens group with positive refractive power, and a fourth lens group with negative refractive power, the effect on the image plane due to the change in the distance between the lens groups is basically It has the same optical properties as the above-mentioned three-group zoom lens, and the same method can be applied to the same lens component as the above-mentioned lens component LF.

In order to show this, first, FIG. 5 shows the first lens group with positive refractive power (power is φ1), the second lens group with negative refractive power (power is φ2), and the third lens group with positive refractive power. A four-group zoom lens consisting of a lens group (power is φ1), and a fourth lens group with negative refractive power (power is φ4), and a first lens group with positive refractive power (power is φ1),
A four-group zoom lens consisting of a second lens group with positive refractive power (power is φ2), a third lens group with positive refractive power (power is φ1), and a fourth lens group with negative refractive power (power is φ4). Showing power arrangement. Focusing is performed by providing a lens component LF (power is φLF) with relatively small power on the closest to the image plane side of the third group constituting the focusing lens group, and keeping this component fixed during focusing. A similar floating effect can be obtained by moving the lens group and the second group together.

In order to show this, the variable power ratio 4, which will be described later, will be described below.
．． Regarding the second example of the high variable power zoom lens No. 63,
Tables 4 to 6 showing aberration coefficients similar to Tables 1 to 3 above are shown.

Table-4
Infinity object point (∞) lens group SA3
SA5 SA7
CMA3 CMA5 1
-0.04682 -0.00
671 -0.00112 0.04417
0.01216 2
0.24511 0.04398
0.00840 -0.09794 -0.
02170 3 -0.25
298 -0.01759 0.00057
0.10612 0.02488
4 0.05368 -
0.01927 -0.00739 -0.0
4908 -0.01836 Total sum
-0.00101 0.00040
0.00046 0.00327 −
0.00303 Lens group AST3
AST5 DIS3
DIS5 1 -0.
01074 -0.00012 0.020
40 0.00018 2
0.01932 0.00035
-0.01654 -0.00016 3
0.00084 0.00
005 -0.01358 0.00001
4 -0.00940
-0.00012 0.01614 -0.
00003 Total sum 0.0000
0 0.00016 0.00643
-0.00001.

Table-5
Near-distance object point (-0.5m) Conventional focusing method lens group SA3 SA
5 SA7 CMA3
CMA5 1
-0.03080 -0.00323 -0
．． 00039 0.01211 0.0
0400 2 0.222
31 0.04147 0.00851
-0.06510 -0.01445
3 -0.23046 -0
．． 01451 0.00078 0.09
470 0.02065 4
0.03604 -0.01075
-0.00342 -0.03104
-0.01387 Total sum -0.0
0291 0.01297 0.0054
8 0.01067 -0.00368
Lens group AST3 AS
T5 DIS3 DIS5
1 -0.00358
-0.00002 0.01217 0.
00009 2 0.01
239 0.00018 -0.01157
-0.00010 3
-0.00167 0.00000 -0
．． 01034 0.00005 4
-0.00882 -0.0001
4 0.01415 -0.00007 Total sum -0.00168 0.
00002 0.00440 -0.000
03.

Table-6
Near-distance object point (-0.5m) Invention focusing method lens group SA3 SA
5 SA7 CMA3
CMA5 1
-0.03159 -0.00336 -0
．． 00041 0.01392 0.0
0440 2 0.222
81 0.04140 0.00846
-0.06560 -0.01453
3 -0.24356 -0
．． 01785 0.00011 0.10
232 0.02389 4
0.03658 -0.01094
-0.00332 -0.03169
-0.01381 Total sum -0.0
1577 0.00925 0.0048
4 0.01894 -0.00005
Lens group AST3 AS
T5 DIS3 DIS5
1 -0.00375 -
0.00002 0.01245 0.0
0009 2 0.012
51 0.00018 -0.01170
-0.00010 3
-0.00194 0.00001 -0.
01045 0.00004 4
-0.00883 -0.00014
0.01423 -0.00007 Total
Sum -0.00201 0.0
0003 0.00454 -0.0000
3.

These tables clearly demonstrate the effectiveness of the focusing method of the present invention. In particular, fluctuations in higher-order spherical aberration can be suppressed. That is, in Tables 5 and 6,
Compared to the cases in Tables 1 to 3, this is a zoom lens with a higher zoom ratio, so the difference due to the focusing method becomes clearer. In Table 5, the higher-order spherical aberration is very large, and when shown in an aberration diagram, the aberration curve tilts significantly to the right as shown in FIG. 7A. In Table 6, the overall balance is maintained, and this is also reflected in the aberration diagram shown in FIG. 7B.

In this case, the second lens group and the third lens group basically move together during focusing, and by independently extending the zoom cam mechanism of the second and third groups toward the object side, This will focus on the distance object point. Therefore, the second and third groups can be realized by another mechanism that integrates only focusing. In addition, the fixed lens component LF, which has a field flattening effect,
is disposed closest to the image plane side of the third group, and is fixed at a specific position and does not move during focusing. On the other hand, during zooming, the lens moves as part of the third lens group together with the remaining lens components of the third lens group. Note that the above conditional expression (1) is also applied to this four-group zoom lens.

On the other hand, on the aberration correction surface, the lens component L
Since F has the effect of correcting the flatness of the image plane, even if the aberration balance is such that the field curvature is large to some extent not only at a specific focal position but up to the front of the lens component LF, this lens component LF Therefore, it is possible to obtain image plane flatness, and the burden of aberration correction can be reduced. This point is a big advantage, and it has great significance in that it improves the drawbacks of conventional zoom lenses, which had good performance for distant objects but had a noticeable performance deterioration when it came to close objects. There is. In particular, optical systems for applications other than single-lens reflex cameras have tended to be compromised in terms of optical performance. However, according to the present invention, by making major improvements in design and providing leeway in terms of performance, the product can be improved. It is possible to provide satisfactory image quality during image processing.

Further, it is desirable that a zoom lens to which the focusing method of the present invention is applied satisfies the following paraxial conditional expression.

Regarding the 3-group zoom lens, 0
．． 4<φ1/φW<1.25
...(2) 1.1
<φ12/φW <3.0
...(3) 1.5<
β3T/β3W<4.0
...(4) However, φ1 is
The refractive power φW of the first lens group is the refractive power φ12 of the entire system at the wide-angle end, and the composite refractive power β3W of the first and second lens groups at the wide-angle end is the near-refractive power of the third lens group at the wide-angle end. Axial horizontal magnification β3T
is the paraxial lateral magnification of the third lens group at the telephoto end.

Regarding the four-group zoom lens, φ12 in the above equation (3) can be considered as a similar relationship by expressing it as the following relationship.

[0041] φ2 = φ2 + φ3 −e'23 φ2 φ3 φ12=
φ1 +φ2 −e'12φ1 φ2 Here, φ2
, Φ3 are respectively the second of the four-group zoom lens for convenience.
The power of the group and the third group, e'23 is the interval between them, and φ2 is the combined power of the second group and the third group. Further, e'12 is the distance between the first lens group and the group synthesized above.

However, it should be noted that in the four-group zoom lens, the distance between the second and third groups, which corresponds to the second group of the three-group zoom lens, is variable. Because of this relationship, a four-group zoom lens can be configured to have a shorter overall lens system length at the telephoto end.

The above equation (2) defines the power of the first lens group, and this value can be particularly large when the variable power ratio is small. Further, under such conditions, it is also possible to configure the first lens group with a single lens made of a special low dispersion glass material. If the lower limit of conditional expression (2) is exceeded,
This leaves a problem with chromatic aberration of magnification at the wide-angle end. Also,
If the upper limit is exceeded, the amount of movement of the first lens group during zooming increases, which is undesirable because the overall length of the lens system at the telephoto end becomes longer. Further, there are restrictions on optical system design such as simplifying the lens frame configuration by making the first lens group and the third lens group have the same amount of movement during zooming.

According to the above equation (3), the first lens group and the second lens group
It defines the combined power of the lens group and is related to the total length of the lens system at the wide-angle end, which determines the size of the camera. Shortening the total length of this type of optical system largely depends on the size of the second lens group. After the power of the first lens group is determined within the range of equation (2), the power of the second lens group is determined using equation (3). The power of the group and the principal point spacing between the first and second lens groups are determined. Exceeding the lower limit of conditional expression (3) is undesirable because it causes difficulties in correcting aberrations and necessitates increasing the number of constituent lenses and using new materials for the purpose of miniaturization. Furthermore, if the upper limit value, which is advantageous for correcting aberrations, is exceeded, the amount of movement during zooming and the overall length of the lens system will increase, which deviates from the purpose of the present invention, which is miniaturization.

Equation (4) above is based on the third lens group (in the case of a four-group zoom lens, the fourth lens group), which is characteristic of the optical system to which the present invention is applied.
This is a formula that limits the magnification load when changing the magnification of the lens group (lens group) as the ratio of the values at the telephoto end and the wide-angle end. If the value is significantly below this lower limit, a zoom system with a simpler configuration is more suitable than the zoom lens type of the present invention (however, this may not necessarily be true if the ultra-wide angle is used as the wide-angle end). do not have.). In addition, if the upper limit is exceeded, the manufacturing error sensitivity may exceed the machining accuracy due to the mechanism configuration, and the aperture ratio will become smaller.As a result of considering the practicality of the lens system, It is a restriction.

[0046]

[Embodiments] Next, first to sixth embodiments of the present invention will be described. Lens data for each example will be described later, but the first example is an optical system with a focal length of 39 mm to 148 mm, and belongs to a fairly high variable power zoom lens in this class. Therefore, if not only the aberration fluctuations during zooming but also the aberration fluctuations during focusing are not kept small, even if the product is commercialized, it will lead to unsatisfactory performance and will not be accepted in the market. As shown in FIG. 8, which shows lens cross-sectional views at the wide-angle end and the telephoto end, lens groups I to III
It is a three-group zoom lens consisting of a lens component LF, which is located closest to the image plane in the second lens group, and is arranged to suppress aberration fluctuations during focusing, and a lens component LF in the second lens group II. By extending the lens components other than the component LF during focusing, it is possible to focus on a short distance object point. It can be seen that the focal length fLF of the lens component LF at this time is fLF≈∞, that is, this lens component LF is a substantially powerless lens component. At the wide-angle end, intermediate focal length, and telephoto end, spherical aberration, astigmatism, at infinity object point and at close distance -2.0 m,
FIG. 14 shows a comparison of lateral chromatic aberration and distortion.

Now, returning to the first example, the total length of the lens system at the wide-angle end (distance from the first surface to the film surface) is just under 82 mm, and the spherical aberration at the telephoto end is slightly smaller at close distances. However, although the astigmatism is large in the annular zone, the fluctuation of astigmatism is similar to this, so the optical performance is stable and good.

Furthermore, an aspherical surface made of resin is used in the third lens group, and this has a great effect in correcting field curvature. Note that if an aspherical surface is used in the second lens group,
It is clear that this can be effective in correcting spherical aberration.

The second embodiment has a focal length of 38 mm to 176 mm.
This is a four-group zoom lens optical system consisting of lens groups I to IV of mm, and the variable power ratio is slightly increased to reduce the aperture ratio at the telephoto end. The configuration of the lens system is
This is almost the same as the example. A cross-sectional view of the lens is shown in FIG.
FIG. 15 shows an aberration diagram similar to FIG. 14 corresponding to an object point at infinity and an object point at a short distance of -2.0 m. Focusing is performed by the method shown in FIG. fLF at this time = -199
It is 8.96. As is clear from the aberration diagram, aberration fluctuations are kept small. In particular, it has good balance at short distances at the telephoto end, making it effective for high-magnification photography.

In the third embodiment, the focal length is 38.0 mm or more.
This is a four-group zoom lens optical system consisting of 150 mm lens groups I to IV, and is intended to be a zoom lens with high performance and versatility within the range that satisfies normal photography. FIG. 10 shows a cross-sectional view of the lens, and FIG. 16 shows an aberration diagram. The configuration of the lens system is almost the same as in the previous embodiment. From the aberration diagram, it can be seen that the optical performance is stable and at a practical level in any focal range and at short distances. A feature of this embodiment is that the aperture ratio at the telephoto end is large.

In the fourth embodiment, the focal length is 36.2 mm.
It is a three-group zoom lens optical system consisting of lens groups I to III of ~131 mm, and by reducing the variable power ratio, it is possible to obtain stable performance in the variable power range. FIG. 11 shows a cross-sectional view of the lens, and FIG. 17 shows an aberration diagram. At this time, the focal length of the lens component LF is fLF=-5459.76.

In the fifth embodiment, the focal length is 29.2 mm.
This is a 4-group zoom lens optical system consisting of ~54mm lens groups I to IV, and the angle of view at the wide-angle end is wide, which may cause difficulties in correcting lateral chromatic aberration at this focal length. The aim is to achieve high performance by adopting the configuration shown in Figure 12 and making effective use of the aspherical surface. This example is also 4
It is a group zoom lens, and the seventh surface (in the second lens group II)
The 18th surface (in the fourth lens group IV) is an aspherical surface. At this time, fLF=77.294, and the power is larger than that of the previous embodiments, and the aberration correction surface also plays a correction function at each focal position. As shown in the aberration diagram in FIG. 18, it can be seen that the aberration balance at each focal length and short distance is good, and the aberration fluctuations are extremely small.

The sixth embodiment has a focal length of 36 mm to 131 mm.
．． This is an example in which a 5mm optical system is configured with a four-group zoom lens consisting of lens groups I to IV, with the second lens group II and the third lens group
Since the amount of change in the distance between lens group III during zooming is small, this contributes to aberration correction, and it is easy to
As can be inferred that it can be constructed as a group zoom lens, it can be seen that basically the same effect can be obtained. here,
FIG. 13 shows a cross-sectional view of the lens, and FIG. 19 shows an aberration diagram.

The lens data of each example is shown below.
In the following, the symbols are as follows: f is the focal length of the entire system, FNO is the F number, ω is the half angle of view, fB is the back focus, r1, r2... are the radius of curvature of each lens surface,
d1, d2... are the distances between each lens surface, nd1, nd
2... is the d-line refractive index of each lens, νd1, νd2... are the Abbe numbers of each lens, and the aspherical shape is as follows: When the optical axis direction is x and the direction orthogonal to the optical axis is y, It is expressed by the following formula.

x=(y2/r)/[1+{1-P(y
2/r2)}1/2 ] +A4y4 +A6y6 +A8y8 +A10 y1
0 However, r is the paraxial radius of curvature, P is the conic coefficient, A4, A
6. A8 is the aspheric coefficient.

First Example f = 39.0 to 80
．． 9~148.5 FNO=
4.58~6.20~8.68
ω = 28.9~14.9~8
．． 3° fB = 9.68~
40.53~91.44r1 = -316.3
761 d1 = 1.3400
nd1 = 1.83400 νd1 = 37.16
r2 = 37.7799
d2 = 0.8432 r3 = 55
．． 0945 d3 = 3.1600
nd2 =1.61405 νd2 =54.
95 r4 = -586.4745
d4 = 0.1847 r5 =
29.8948 d5 = 4.90
00 nd3 =1.53996 νd3 =5
9.57 r6 = -115.6637
d6 = (variable) r7 = −
37.4745 d7 = 1.18
00 nd4 =1.78590 νd4 =4
4.18 r8 = 21.1223
d8 = 0.9701 r9 =
36.2884 d9 = 2.
6500 nd5 = 1.78472 νd5
=25.71 r10= -45.5730
d10= 2.3180 r11=
−22.6975 d11=
1.3000 nd6 = 1.63854 νd
6 =55.38 r12= -27.7381
d12= 4.0650 r13
= ∞． (Aperture) d13= 4
．． 0859 r14=-182.3473
d14= 2.0800 nd7
=1.68893 νd7 =31.08 r15=
-194.6074 d15=
0.4088 r16= 100.1782
d16=2.3800n
d8 =1.54739 νd8 =53.55 r1
7=-36.4417 d1
7= 1.3474 r18= 112.24
52 d18= 1.2900
nd9 =1.78472 νd9 =25.71
r19= 19.0879
d19=4.2650 nd10=1.583
13 νd10=59.36 r20=-28
．． 1382 d20= 1.6500
r21=-20.0777
d21=1.7100 nd11=1.7
2600 νd11=53.56 r22= −
20.7925 d22=(variable)
r23=-42.0853
d23=3.1200 nd12=1.8
4666 νd12=23.78 r24= −
22.8307 d24= 2.32
87 r25= -18.1063 (aspherical surface)
d25=0.8600 nd13=1.51
742 νd13=52.41 r26= -1
8.2961 d26= 1.500
0 nd14=1.77250 νd14=49
．． 66 r27= 89.0676 Aspheric coefficient 25th surface P = 1 A4 = 0.15094×10-4A6 = 0
．． 36466×10-7A8 =-0.40180×
10-10 A10 = 0.56431×10-12
.

Second Example f = 38.0 to 82
．． 8~176.0 FNO=
4.62~ 7.53~ 11.15
ω = 29.6~14.6~6
．． 9° fB = 6.18~
38.03~106.05r1 = -8204.4
298 d1 = 1.4500
nd1 = 1.83400 νd1 = 37.16
r2 = 32.1497
d2 = 0.8500 r3 = 47
．． 5851 d3 = 3.2000
nd2 =1.61405 νd2 =54.
95 r4 = -1942.9777
d4 = 0.2150 r5 =
26.3265 d5 = 5.00
00 nd3 =1.53996 νd3 =5
9.57 r6 = -200.2508
d6 = (variable) r7 = −
39.1402 d7 = 1.30
00 nd4 =1.78590 νd4 =4
4.18 r8 = 20.1050
d8 = 0.6478 r9 =
33.8748 d9 = 2.
6500 nd5 = 1.78472 νd5
=25.68 r10= -38.3830
d10= 1.2259 r11=
−29.0561 d11=
1.3000 nd6 = 1.61405 νd
6 =54.95 r12= -36.4855
d12=(variable) r13=
∞． (Aperture) d13= 4.0
000 r14=-92.6144
d14= 2.1000 nd7=
1.68893 νd7 =31.08 r15=
-322.7288 d15= 0
．． 3250 r16= 88.7094
d16= 2.2000 nd8
=1.54739 νd8 =53.55 r17=
-33.9960 d17=
0.5862 r18= 209.5506
d18= 1.3000n
d9 =1.78472 νd9 =25.71 r1
9 = 21.0222 d1
9=4.0000 nd10=1.58913
νd10=60.97 r20=-25.0
062 d20= 1.0000
r21=-19.2691
d21=1.7000 nd11=1.741
00 νd11=52.68 r22=-20
．． 2562 d22=(variable)
r23=-36.6191
d23=3.1500 nd12=1.846
66 νd12=23.78 r24= -21
．． 2860 d24= 2.7816
r25= -16.1349 (aspherical surface) d
25=0.1000 nd13=1.5174
2 νd13=52.41 r26= -16.
8308 d26= 1.5000
nd14=1.77250 νd14=49.6
6 r27= 177.9701 Aspheric coefficient 25th surface P = 1 A4 = 0.25779×10-4A6 =
0.78006×10-7A8 =-0.1503
3×10-9A10 = 0.17915×10-11
.

Third embodiment f = 38.0~81.5~150.0F
NO=4.62~6.24~8.81ω
= 29.6~14.9~8.2°fB
= 9.46~41.78~93.55r1
= -531.9150 d1
= 1.4500 nd1 = 1.83400
νd1 = 37.16r2 = 36.758
1 d2 = 0.8500 r3
= 54.0975 d3
= 3.2000 nd2 = 1.61405
νd2 = 54.95 r4 = -710.7
728 d4 = 0.2150
r5 = 28.8796
d5 = 5.0000 nd3 = 1.539
96 νd3 = 59.57 r6 = -126
．． 5198 d6 = (variable)
r7 = -35.3558
d7 = 1.3000 nd4 = 1.785
90 νd4 = 44.18 r8 = 20
．． 9761 d8 = 1.0031
r9 = 40.6555
d9 = 2.6500 nd5 = 1.7
8472 νd5 =25.71 r10= −
41.9853 d10= 2.21
55 r11=-23.5923
d11=1.3000 nd6=1
．． 63854 νd6 =55.38 r12=
-27.9570 d12=(variable) r13= ∞. (aperture)
d13= 4.0000 r14= -167
．． 5276 d14= 2.1000
nd7 =1.68893 νd7 =31.
08 r15=-192.1174
d15= 0.3250 r16= 1
44.5763 d16= 2.20
00 nd8 =1.54739 νd8 =5
3.55 r17=-35.1160
d17= 1.3859 r18=
99.6476 d18=1.
3000 nd9 = 1.78472 νd9
=25.71 r19= 19.5849
d19= 4.0000 nd1
0=1.58313 νd10=59.36 r20=
−26.8188 d20=
1.0000 r21=-20.3106
d21= 1.7000n
d11=1.74100 νd11=52.68 r2
2=-20.9455 d2
2=(variable) r23= -39.8644
d23=3.1500n
d12=1.84666 νd12=23.78 r2
4=-22.9355 d2
4 = 2.3185 r25 = -18.82
12 (aspherical surface) d25= 0.8500 nd
13=1.51742 νd13=52.41 r26
= -19.0277 d26
= 1.5000 nd14=1.77250
νd14=49.66 r27=85.36
32 Aspheric coefficient 25th surface P = 1 A4 = 0.12231×10-4A6 =
0.29324×10-7A8 =-0.9160
2×10-10 A10 = 0.62671×10-
12.

Fourth embodiment f=36.2~68.0~131.0F
NO=3.60~5.65~7.42ω
= 30.8~17.6~9.4°fB
= 9.78~32.68~81.23r1
= −86.8576 d1
= 0.9500 nd1 = 1.83400
νd1 = 37.16r2 = 41.411
0 d2 = 0.9080 r3
= 51.8432 d3
= 3.2800 nd2 = 1.65844
νd2 = 50.86 r4 = -137.6
627 d4 = 0.1200
r5 = 33.2481
d5 = 4.5600 nd3 = 1.518
23 νd3 = 58.96 r6 = -86
．． 0513 d6 = (variable)
r7 = -56.6012
d7 = 0.5000 nd4 = 1.785
90 νd4 = 44.18 r8 = 19
．． 1893 d8 = 0.8890
r9 = 36.0325
d9 = 2.7900 nd5 = 1.7
8470 νd5 =26.22 r10= −
47.5157 d10= 3.23
80 r11=-21.0043
d11=1.3300 nd6=1
．． 65830 νd6 =53.44 r12=
-26.9041 d12=4.
5520 r13=∞. (aperture)
d13= 4.1200 r14= -1
10.2549 d14= 2.13
00 nd7 =1.68893 νd7 =3
1.08 r15=-69.7784
d15= 0.5940 r16=
139.7565 d16=2.
9700 nd8 = 1.54739 νd8
=53.55 r17= -32.6632
d17= 1.2060 r18=
161.2610 d18=
1.1100 nd9 = 1.78472 νd
9 = 25.71 r19 = 18.7929
d19=5.1500n
d10=1.58313 νd10=59.36 r2
0=-28.0029 d2
0 = 0.7190 r21 = -20.98
45 d21= 1.6700
nd11=1.74100 νd11=52.68
r22=-21.8084
d22=(variable) r23=-49.73
66 d23= 3.0300
nd12=1.84666 νd12=23.78
r24=-24.4370
d24=2.7250 r25=-17.
5797 (aspherical surface) d25= 0.6500
nd13=1.52492 νd13=51.77 r
26=-18.2786 d
26=1.0000 nd14=1.7725
0 νd14=49.66 r27=71.
7600 Aspheric coefficient 25th surface P = 1 A4 = 0.21637×10-4A6 =
0.49594×10-7A8 =-0.1022
8×10-11 A10 = 0.56359×10-
12.

Fifth embodiment f = 29.2~37.0~54.0F
NO=4.60~5.11~6.30ω
= 36.5~30.3~21.8°fB
= 5.02~11.53~27.41r1
= −26.4534 d1
= 1.0000 nd1 = 1.83400
νd1 = 37.16r2 = -881.877
4 d2 = 0.4200 r3
= −278.5753 d3
= 3.6189 nd2 = 1.69680
νd2 = 56.49 r4 = -24.7
811 d4 = 0.5000
r5 = 27.8321
d5 = 1.6197 nd3 = 1.696
80 νd3 = 56.49 r6 = 67
．． 7204 d6 = (variable)
r7 = -54.9522 (aspherical surface) d7
= 3.0703 nd4 = 1.78800
νd4 = 47.38 r8 = 9.98
82 d8 = 4.4827
nd5 = 1.83400 νd5 = 37.16
r9 = -111.8670
d9 = (variable) r10 = ∞. (Aperture) d10= 4.1130 r11=
−530.8542 d11=
3.8073 nd6 =1.61405 ν
d6 = 54.95 r12 = -8.819
7 d12= 0.5000
nd7 = 1.84666 νd7 = 23.88 r
13=-17.3752 d
13= 0.5000 r14= -42.6
880 d14= 1.1971
nd8 =1.64000 νd8 =60.09
r15=-23.1652
d15=(variable) r16= -23.7
219 d16= 2.3041
nd9 = 1.84666 νd9 = 23.88
r17=-15.7393
d17= 2.3156 r18= -14
．． 1806 (aspherical surface) d18= 0.5000
nd10=1.64000 νd10=60.09
r19=-87.5074
d19=2.0761 r20=-27.
9339 d20= 0.5500
nd11=1.60311 νd11=60.7
0 r21= 334.4222
Aspheric coefficient 7th surface P = 1 A4 = -0.24960×10-4 A6 = 0
．． 97359×10-7A8 =-0.34211×
10-8A10 = 0.24291×10-10
18th surface P = 1 A4 = 0.76581×10-5A6 =
-0.54028×10-7A8 = 0.1498
5 x 10-8 A10 = -0.73315 x 10-11
.

Sixth embodiment f = 36.0~68.8~131.5F
NO=4.62~5.80~7.50ω
= 30.9~17.5~9.3°fB
= 9.78~34.28~83.34r1
= −179.8187 d1
= 1.0919 nd1 = 1.83400
νd1 = 37.16r2 = 38.465
1 d2 = 0.8788 r3
= 49.9828 d3
= 3.1628 nd2 = 1.61720
νd2 = 54.04 r4 = -279.9
562 d4 = 0.1998
r5 = 30.1522
d5 = 4.7290 nd3 = 1.518
23 νd3 =58.96 r6 = -112
．． 6403 d6 = (variable)
r7 = -42.9353
d7 = 0.7101 nd4 = 1.785
90 νd4 = 44.18 r8 = 19
．． 2434 d8 = 1.0696
r9 = 38.2064
d9 = 2.7010 nd5 = 1.7
8472 νd5 =25.71 r10= −
44.0457 d10= 2.67
89 r11=-21.2365
d11=1.2931 nd6=1
．． 63854 νd6 =55.38 r12=
−27.2568 d12=(variable) r13= ∞. (aperture)
d13= 4.0108 r14= -402
．． 5078 d14= 2.1024
nd7 =1.68893 νd7 =31.
08 r15=-97.7116
d15= 0.3479 r16= 1
07.4156 d16= 2.63
54 nd8 = 1.54739 νd8 = 5
3.55 r17=-33.2395
d17= 1.5238 r18=
193.3836 d18=1.
2076 nd9 = 1.78472 νd9
=25.71 r19= 18.0304
d19= 4.6310 nd1
0=1.58313 νd10=59.36 r20=
−27.2813 d20=
0.9453 r21=-19.4411
d21= 1.6868 n
d11=1.74100 νd11=52.68 r2
2=-20.1265 d2
2 = (variable) r23 = -47.2575
d23=3.0383n
d12=1.84666 νd12=23.78 r2
4=-23.6858 d2
4 = 2.4178 r25 = -17.74
64 (aspherical surface) d25= 0.7957 nd
13=1.50137 νd13=56.40 r26
= −18.0796 d26
= 0.6371 nd14=1.77250
νd14=49.66 r27=74.51
22 Aspheric coefficient 25th surface P = 1 A4 = 0.19070×10-4A6 =
0.49353×10-7A8 =-0.1602
1×10-10 A10 = 0.58494×10-
12.

The refractive power φW of the entire system in the first to sixth embodiments, the refractive power φLF of the lens component LF, and the values of the parameters corresponding to the conditional expressions (1) to (4) above are as follows. It is shown in Table-7.

[0063]

[0064]

As explained above, according to the high variable magnification zoom lens of the present invention with little variation in near-field aberrations, the focusing group of the conventional high variable magnification zoom lens proposed by the present applicant has a fixed focus during focusing. By arranging the lens components, it is possible to easily realize an optical system that has extremely stable performance up to short distances. As a result, it is possible to improve the performance of zoom lenses for photo cameras, which are said to be weak at close range, and it is also possible to develop new markets.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the power arrangement of a three-group zoom lens for explaining a basic focusing method based on the premise of the present invention.

FIG. 2 is a diagram showing a power arrangement when the focusing method according to the present invention is applied to a three-group zoom lens.

FIG. 3 is an aberration diagram at close range when a conventional focusing method is applied to a three-group zoom lens and when a focusing method according to the present invention is provided.

[Figure 4] 3 using the focusing method according to the present invention
FIG. 2 is a cross-sectional view showing an example of a lens barrel structure of a group zoom lens.

FIG. 5 is a diagram showing a power arrangement when the focusing method according to the present invention is applied to a four-group zoom lens in which the second lens group is negative.

FIG. 6 is a diagram showing a power arrangement when the focusing method according to the present invention is applied to a four-group zoom lens in which the second lens group is positive.

FIG. 7 is an aberration diagram at close range when a conventional focusing method is applied to a four-group zoom lens and when a focusing method according to the present invention is provided.

FIG. 8 is a cross-sectional view of the lens at the wide-angle end and the telephoto end of the first embodiment.

FIG. 9 is a cross-sectional view of the lens at the wide-angle end and the telephoto end of the second embodiment.

FIG. 10 is a cross-sectional view of the lens at the wide-angle end and the telephoto end of the third embodiment.

FIG. 11 is a lens sectional view at the wide-angle end and the telephoto end of the fourth embodiment.

FIG. 12 is a sectional view of the lens at the wide-angle end and the telephoto end of the fifth embodiment.

FIG. 13 is a lens sectional view at the wide-angle end and the telephoto end of the sixth embodiment.

FIG. 14 is an aberration diagram of the first example.

FIG. 15 is an aberration diagram of the second example.

FIG. 16 is an aberration diagram of the third example.

FIG. 17 is an aberration diagram of the fourth example.

FIG. 18 is an aberration diagram of the fifth example.

FIG. 19 is an aberration diagram of the sixth embodiment.

[Explanation of symbols]

LF...Lens component I in the focusing group that is fixed during focusing...First lens group II...Second lens group III...Third lens group IV...Fourth lens group

Claims (2)

[Claims] Claim 1: Consisting of, in order from the object side, a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group with negative refractive power, and zooming from the wide-angle end to the telephoto end is , by moving each lens group toward the object side, using the second lens group as a focusing lens group, and fixing the lens component closest to the image side of the second lens group in a fixed position.
A high variable magnification zoom lens with little variation in short-range aberrations, characterized in that focusing is performed by moving the remaining lens component of the second lens group toward the object side. 2. In order from the object side, a first lens group with positive refractive power, a second lens group with positive refractive power or negative refractive power, a third lens group with positive refractive power, and a fourth lens group with negative refractive power. The zooming from the wide-angle end to the telephoto end is performed by moving each lens group along the optical axis, with the second and third lens groups serving as focusing lens groups, and the third lens group acting as a focusing lens group. A short-distance lens system characterized by focusing by fixing the constituent lens component closest to the image side in a fixed position and moving the remaining lens components of the second and third lens groups toward the object side. High magnification zoom lens with little variation in aberrations.