JP3032955B2 - Compact high-magnification zoom lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact high-magnification zoom lens.

[0002]

2. Description of the Related Art In recent years, a camera has been fully automated, and a compact camera which is excellent in portability while being multifunctional has a built-in zoom lens to broaden a photographing area. Therefore, a compact lens system is necessary because the zoom lens itself is incorporated in the camera system as a photographing optical system.

In this type of lens system, there is no need to consider disposing a mirror as in a so-called single-lens reflex camera, and the back focus can be shortened. Therefore, for a lens system with a wide angle of view, such as for a single-lens reflex camera, it is not necessary to use a retrofocus type and arrange the rear main plane position behind the optical system. As a type, it is possible to adopt a refractive power arrangement in which the rear main plane position is positioned somewhat toward the object side.

[0004] Basically, a variable power optical system of a multifocal switching type including a single focus lens, and Japanese Patent Application Laid-Open No. 57-2012.
The two-unit zoom as described in Japanese Patent Publication No. 13 is also a telephoto type lens system. Further, as a development of the two-unit zoom lens, there has been provided a lens in which a specific lens unit is divided to improve aberration correction, and a three-unit zoom lens in which the magnification is shared. In addition, it consists of four lens groups,
JP-A-60-57 discloses a four-group zoom lens with three movable groups.
No. 814.

[0005]

The zoom lens described above has a zoom ratio of 1.5 to at most about 2, and has a small aperture ratio, which is insufficient in practical use.

On the other hand, the present applicant has developed a four-group zoom lens described in Japanese Patent Application Laid-Open No. 63-43115 with the aim of improving the zoom ratio and optical performance. Japanese Patent Application Laid-Open No. 63-153511 discloses a simplified structure of the zoom lens.
A lens system and the like described in Japanese Patent Application Laid-Open No. H10-209,837 were proposed. These zoom lenses are lens systems having a zoom ratio of about 3 and excellent optical performance over the entire zoom range.

The present invention intends to increase the magnification with great difficulty in optical design, and further expands the magnification range in order to satisfy practical demands by making use of changes in perspective for drawing purposes. It is intended to further reduce the size of the system.

Accordingly, it is an object of the present invention to provide an image having a comprehensive angle of view of 7
It is an object of the present invention to provide a compact, high-magnification zoom lens of a three-group zoom system in which the optical performance of about 6 ° to 18 ° and a zoom ratio of about 3 to 4 is excellent over the entire zoom range.

[0009]

The zoom lens system according to the present invention is basically based on the development of the lens system of the above-mentioned Japanese Patent Application Laid-Open No. 63-153511, and further has a simplified lens frame structure and a focusing system. The objective was achieved as a three-unit zoom type lens system in consideration of compactness due to optimization of.

The lens configuration and the behavior of the lens group during zooming are originally described from the object side in order from the point of view of the magnification burden and the aberration correction, especially the correction of the curvature of field during zooming, and to reduce the size of the lens system. A lens configuration having positive, negative, positive, and negative refractive power is used as a basic refractive power distribution. When this four-group zoom method is used as a general solution of the zoom equation,
It has been found that the lens group and the third lens group can perform the same zooming movement while improving the optical performance. That is, a three-group zoom system as a special solution among the four-group zoom system was found.

The zoom lens according to the present invention has a 4
The second lens group having a negative refractive power and the third lens group having a positive refractive power in the lens system of the group zoom system are combined into one lens group having a positive refractive power, which is referred to as a second lens group. is there. In order to achieve a zoom ratio of about 3 to 4 as a three-group zoom system in this manner, it is important to appropriately arrange the refractive power of each lens group in reducing the size of the lens system, and more optimally. The effect can be further enhanced by the construction of a thick lens having a large thickness and the use of a new material.

The zoom lens of the present invention is based on the above idea, and includes, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a positive refractive power, and a second lens unit having a negative refractive power. 3
It is more configuration and lens group, those with varying distances between the lens units performing zooming, the first lens County negative lens
A negative lens, a first positive lens and a second positive lens.
Between the lens and the first positive lens.
And the second lens group has a negative refractive power.
The former county and the rear county with positive refractive power, and between the previous county and the rear county
It is composed of the arranged aperture and the following condition (1),
Characterized by satisfying (2), (3) and (4)
It is.

[0013] _{(1) 0.05 <φ 1 /} φ W <0.9 (2) 1.0 <φ 12W / φ W <2.0 (3) 2.0 <β 3T <5.0 (4 5 <e ′ ₂ <20 where φ ₁ is the refractive power of the first lens group, φ _12W is the combined refractive power of the first and second lens groups at the wide-angle end,
phi _W is the refractive power of the entire system at the wide angle end, beta _3T is a lateral magnification of the third lens group at the telephoto end, e _'2 is mainly of the front and rear groups
The point interval .

The zoom lens according to the present invention is characterized by the above-described configuration. However, the overall length and the outer diameter of the lens system are reduced as described below to achieve a compact configuration and further increase the magnification. To achieve.

As described above, the present invention analyzes the lens system of the four-unit zoom system as shown in FIG. 15 and examines not only the compactness of the lens system but also the mechanism and structure. Based on the fact that there is a solution with a relatively small zoom ratio that is borne during zooming from the wide-angle end to the telephoto end of the third lens unit, and the role of this third lens unit at that time is to focus on the image plane rather than the zooming. It was found that the optical performance was improved, such as being responsible for music correction.

In this manner, the second lens group and the third lens group of the four-group zoom can be formed as one lens group with an appropriate interval on the optical axis.

On the other hand, the function of correcting the field curvature provided by the third lens group is to adjust the interval on the optical axis, that is, to provide a margin of the telephoto ratio in the lens configuration on the telephoto side in the three-unit zoom lens. Alternatively, a convex meniscus air lens is provided in a thick lens constituting each lens to generate higher-order aberrations.

In the three-unit zoom type lens system configured as described above, the combined refractive power of the first lens unit G ₁ and the second lens unit G ₂ is positive at the wide-angle end as shown in FIG. Can be considered as one lens group. And it constitutes a so-called telephoto type in the third lens group G ₃ having a negative refractive power followed it.

As described above, the refractive power arrangement at the wide-angle end is as follows.
Basically, it is a telephoto type, which is optimal for forming a wide-angle end with a short back focus. On the other hand, at the wide-angle end,
Since the focal length is short, it is possible to arrange the refractive power such that the rear principal plane position is relatively behind the lens system. In other words, a compact paraxial arrangement with good performance can be obtained.

Conditions (1) and (2) are provided for the above reasons.

The condition (1) is a condition for defining the refractive power of the first lens group. The first lens group basically considers the influence on the telephoto ratio at the telephoto end, the aberration correction situation in the entire zoom range, and the focusing method, rather than the entire length of the lens system at the wide-angle end. There is a need. That is, this condition (1) is a condition for determining an important factor in obtaining compact and good optical performance while achieving a high magnification ratio.

Here, in a three-unit zoom lens as shown in FIG. 4, the refractive power at the wide-angle end is φ _W , and the total length of the lens system is L _W.
Then, the following equation is established. φ _W = φ ₁ (1-e _2W・ φ ₃ ) + (1-e _1W・ φ ₁ ) (φ ₂ + φ ₃ -e ' _2W φ ₂ φ ₃ ) (a) L _W = e _1W + e _2W + l' _W (b) l ′ _W = {− φ ₁ e _2W + (1-e _1W · φ ₁ ) (1-e _2W · φ ₂ )} / φ _W (c) where φ ₁ , φ ₂ , φ ₃ Is the refractive power of the first lens group G ₁ , the second lens group G ₂ , and the third lens group G ₃ , respectively, e _1W is the principal point distance between the first lens group G ₁ and the second lens group G _{2 at} the wide angle end, e _1T is the distance between the first lens group G ₁ and the second lens group at the telephoto end.
The main point interval of the lens group G _2, e _2W second lens group G ₂ and the main point interval of the third lens group G _3, e _2T and the second lens group G ₂ at the telephoto end the third lens group at the wide-angle end the main point interval of G _3, l _'W back at the wide-angle end focus, l'
_T is the back focus at the telephoto end.

As can be seen from these paraxial relational expressions, when it is clear that the overall length of the lens system is the shortest at the wide-angle end as in the present invention, attention should be paid only to the wide-angle end.
Therefore, for the total length at the telephoto end, a thick configuration is assigned in consideration of the zooming movement trajectory and the movement amount based on the refractive power arrangement.

When the value exceeds the upper limit of the condition (1), the focal length at the wide-angle end, which is determined as a specification, is constant, so that the refractive power of the first lens unit becomes strong and the amount of movement during zooming becomes small. This is preferable because the size is reduced. However, since the present invention mainly aims to increase the magnification, the telephoto side necessarily enters the telephoto range where the angle of view exceeds about 24 °, so that chromatic aberration occurs and the flatness of the image plane cannot be maintained. . Therefore, it is conceivable to achieve the object of the present invention while paying attention to the configuration of the thick lens in the first lens group. However, in this case, the number of lenses increases and the thickness of the lens increases, which is not preferable.

If the lower limit of the condition (1) is exceeded, the refractive power of the first lens unit becomes weak, so that the zooming movement from the wide-angle end to the telephoto end becomes large, and the total length of the lens system becomes large.
This is advantageous in terms of aberration correction, but is contrary to the object of the present invention, that is, downsizing.

As described above, the condition (1) is that the zoom ratio is 3-4.
This is an important condition in determining the refractive power arrangement that balances the optical performance of the zoom lens of the present invention with the overall length of the lens system.

Condition (2) defines the combined refractive power of the first lens group G ₁ and the second lens group G ₂ at the wide-angle end. Then, a so-called telephoto type is constituted by the positive combining system and the negative third lens group, thereby achieving compactness of the entire system.

When the paraxial back focus of the third lens unit is set and its lateral magnification is set, the refractive power of the third lens unit is determined. That is, when the magnification is given, the refractive power arrangement is almost determined by the condition (2), and the paraxial arrangement of the entire system can be set.

When the value exceeds the upper limit of the condition (2), it is effective in shortening the total length of the lens system at the wide-angle end, and a relatively small amount of movement during zooming to the telephoto end is required. However, the refractive powers of the first lens group G ₁ and the second lens group G ₂ both tend to be strong, and it becomes difficult to balance the aberrations including the correction of the image surface curvature. It is not preferable because sensitivity due to eccentricity in the performance and quality of the lens increases.

[0030] Condition (2) for aberration correcting the lower limit of is advantageous, not only it is difficult to shorten the overall length of the lens system at the wide angle end, the refraction of the third lens group G ₃ to the subsequent Since the force becomes weak, it is necessary to balance aberration correction, and the back focus of the lens system becomes short because the rear principal plane position enters the thick lens system of the third lens unit. Therefore, the lens diameter becomes large, which is contrary to the object of the present invention.

When the conditions (1) and (2) described above are satisfied, the refractive power arrangement of the first lens unit and the second lens unit, which are the basic framework of the lens system of the present invention, is set.

Further, if the distribution of the refractive power of the third lens group is determined, the paraxial layout of the lens system of the present invention will be determined.

In order to determine the distribution of the refractive power of the third lens unit, it is important to bear the magnification during zooming from the wide-angle end to the telephoto end. In consideration of this and the paraxial back focus, the refractive power arrangement of the entire system can be determined.

Here, considering compactness and high magnification at the wide-angle end, the paraxial lateral magnification borne by the third lens group has an important meaning, and also has a great significance in obtaining good performance. . That is, the condition (3) defines the paraxial lateral magnification (hereinafter, referred to as the magnification) which the third lens group bears.

The magnification of the third lens group is directly related to the magnification from the wide-angle end to the telephoto end, and is also related to the amount of movement of the third lens group during zooming. Therefore, when trying to obtain the same magnification, the magnification carried by the second lens group also changes depending on how the magnification carried by the third lens group is given, the movement locus during zooming changes, and the situation of aberration correction also changes. .

That is, the basic refractive power arrangement is determined by the conditions (1) and (2), and the basic near power is provided by giving the magnification of the third lens unit at the telephoto end where the magnification should be set under the condition (3). The axial layout is almost determined. Further, by allocating the thick configuration of each lens unit, the objective is realized by repeatedly revising the paraxial configuration so as to achieve good imaging performance, a desired magnification, and downsizing of the lens system.

When the value exceeds the upper limit of the condition (3), the magnification of the third lens unit increases, which is preferable for obtaining a high zoom ratio. However, the moving amount of the third lens unit during zooming increases. In addition, it is not preferable to exceed the upper limit of the condition (3) in order to achieve a thick lens configuration with a small number of lenses and to increase the amount of movement of the lens unit to increase the telephoto ratio from the viewpoint of performance. In addition, the lens frame and the driving mechanism become complicated and cost increases. If the lower limit is exceeded, the magnification borne by the second lens group becomes high in order to achieve a high zoom ratio, and the total length of the lens system from the wide-angle end to the telephoto end changes relatively little, and the lens system can be made compact. Correction becomes difficult. Therefore, in order to perform aberration correction satisfactorily, a gradient index lens must be used together. Since it is difficult to correct aberrations in this way, it is practically difficult to achieve a high zoom ratio, and the zoom ratio becomes about 2, making it more difficult.

In the zoom lens according to the present invention,
In particular, in order to further increase the magnification, it is desirable to limit the condition of the condition (1) to the range of the following condition (1 ′).

(1 ′) 0.05 <φ ₁ / φ _W <0.6 These conditions define the refractive power of the first lens group. It is preferable that each of the group, the second lens group, and the third lens group has a large degree of freedom for independently moving during zooming from the wide-angle end to the telephoto end. In order to provide this degree of freedom, it is preferable to limit the range to the above condition (1 ′).

If the value falls within the lower limit of the condition (1 '), the lens system has a margin at the telephoto end with respect to the entire length of the lens system. In terms of optical performance, it is necessary to use the first lens unit as the focusing unit. If it is not considered, it can be performed very well and a high-performance zoom lens with high magnification can be obtained. If the upper limit is not exceeded, it is possible to reduce the size of the lens system, particularly, to achieve a refractive power distribution that can reduce the overall length on the telephoto side. In addition, a small high-magnification zoom lens can be obtained in accordance with the distribution of the refractive power of the second lens group.

Further, regarding the condition (3), the following condition (3 ′)
By limiting as described above, the magnification can be made about 3 to 4.

(3 ′) 2.5 <β _3T <5.0 In order to increase the magnification, it is important to appropriately select the lateral magnification of the third lens unit in terms of both optical performance and manufacturing. Condition (3 ')
If the lower limit is exceeded, it becomes difficult to increase the magnification as described above.

The basic distribution of refractive power of each lens group can be determined by the above conditions.

Next, the structure of an actual thick lens will be described.

The refractive power of the first lens group is given by the above condition, but the lens configuration is basically composed of a cemented lens of a positive lens and a negative lens.
However, a positive lens may be further added thereto. Further, by separating the cemented lens and forming a meniscus air lens therebetween, the aberration correction effect can be increased.

The second lens group is considered to be composed of two groups because of its role, and includes a negative front group G _2F and a positive rear group G _2R .

The front group G _2F in the second lens group is used to correct distortion and field curvature which are difficult to correct with the rear group G _2R alone among the off-axis aberrations generated in the first lens group. First,
An aberration having a sign opposite to those of the aberrations generated in the lens group is generated. Further, correction of spherical aberration has an important role in correcting chromatic spherical aberration particularly in a telephoto region where a marginal light beam diameter becomes large.

The lens configuration of the front group G _2F is based on the arrangement of a negative lens and a positive lens from the object side, and further includes a positive lens or a negative lens according to the required imaging performance. You may. Or an air lens therebetween by dividing the positive lens or a negative lens of the front group G _2F, it is possible to improve further the performance by using an aspherical lens in the front group G _2F.

The rear group G _2R of the second lens group is the same as the front group G _2F
And a distance D on the optical axis, and is basically composed of one negative lens and two positive lenses like a triplet or a Tessar type. Here, since the first lens group and the second lens group form an imaging system as a whole, the rear group G _2R can be considered to constitute a so-called relay system.

The rear group G _2R is located at a position where the diameter of the marginal luminous flux becomes large in the telephoto range, and it is necessary to greatly contribute to the correction of spherical aberration. It is necessary to take care not to increase the incident angle or the outgoing angle on each surface so as to reduce the angle.

In the zoom lens according to the present invention, in order to realize further miniaturization, the front group G _{2F of} the second lens group G ₂ is required.
It is necessary to reduce the dead space by setting the value of the principal point interval e ′ ₂ of the rear group G _2R within a certain range and allocating a thick lens so as to satisfy this paraxial configuration.

Also, by reducing the size of the lens system,
In some cases, the refractive power of either the front group G _2F or the rear group G _2R of the lens group G ₂ becomes strong, leading to performance degradation. In that case, it is effective to use an aspherical surface or a gradient index lens.

The second lens group of the zoom lens according to the present invention includes:
The lens system is composed of a front group G _2F having a negative refractive power and a rear group G _2R having a positive refractive power. If a margin is not given and high image quality is taken into consideration, or if a beam splitter or the like is provided and a light path is branched to a light receiving element or a finder optical system, a smaller lens system can be realized. In other words, this can further reduce the size as in Examples 8 to 11 described later.

[0054] In order to realize this way miniaturization of the two lens groups of the optical power phi _2F front group G _2F and the rear group G _2R of the front group G _2F in the second lens group G ₂ main The point interval e ′ ₂ or the like may be appropriately selected. Here, the refractive power φ ₂ of the second lens group G ₂ is defined within a certain range according to the condition (2).

The refractive power φ of the rear group G _2R of the second lens group G _2.
2R is defined based on the following equation.

Φ _2R = (φ ₂ −φ _2F ) / (1−φ _2F · e ′ ₂ ) The refractive power arrangement of the second lens group G ₂ itself can be regarded as a so-called retrofocus type. That is, by arranging the front group G _2F having a negative refractive power in front of the rear group G _2R having a positive refractive power, the position of the image forming point from the second lens group G ₂ is lengthened. The position of the object point with respect to the third lens group is lengthened, and the arrangement is advantageous for aberration correction.

Here, the principal point interval e ′ between the front group G _2F and the rear group G _2R.
By strengthening the refractive power phi ₂₁ of the front group G _2F with a shorter _2, results in a substantial aperture ratio of the front group G _2F becomes large, somewhat disadvantageous mainly correct spherical aberration at the telephoto end However, it is not so disadvantageous for correcting off-axis aberrations.

Further, since the overall length of the lens system is shortened, the outer diameter generally tends to increase. However, since the entrance pupil distance of the first lens unit is shortened, downsizing can be achieved, and the overall size can be reduced.

[0059] To achieve further miniaturization From the above, it is desirable to select within a range showing a principal point interval e _'2 the following conditions (4).

(4) 5 <e ′ ₂ <20 The condition (4) is to achieve a reduction in the overall size of the lens system by reducing the overall length at the wide-angle end and the outer diameter of the lens.

Exceeding the upper limit of this condition is preferred for optical performance, but the overall length is somewhat longer. If the lower limit is exceeded, the front group G _2F and the rear group G _2R interfere with each other, which is not preferable.

The third lens group has negative refractive power, and can be regarded as a rear group of negative refractive power in a so-called telephoto type lens system. At the wide-angle end, the position of the rear principal plane is relatively close to the image plane, so that the optical system as a whole does not have its principal plane positioned in front of the lens system as in the original telephoto type. However, as it approaches the telephoto end, telephoto-type features become more pronounced. As described in the description of the condition (3), considering that the third lens group has an effect as a rear conversion lens having a large lateral magnification on the telephoto side, the effect in the vertical direction at the image plane position is not effective. Since it acts as a vertical magnification, it is important to take advantage of this and control it at the same time.

In the lens system according to the present invention, the back focus at the wide-angle end can be shortened by the third lens group, and conversely, the back focus can be extremely short. Therefore, care must be taken so that the rear principal plane position of the third lens group does not enter the object side very much. For this purpose, the third lens group is basically composed of a positive lens and a negative lens. Although it is possible to form this with only one negative lens, the imaging performance cannot be sufficiently improved unless the refractive power is weakened. However, if the refractive power is weakened, the amount of movement during zooming becomes large, which is not preferable.

With the above-described configuration, a compact zoom lens with a high zoom ratio, which is the object of the present invention, can be configured.

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a compact high-magnification zoom lens according to the present invention will be described.
Examples of each lens are shown below. Example 1

Embodiment 2

Embodiment 3

Embodiment 4 Where r ₁ , r ₂ ,... Are the radii of curvature of the respective surfaces of the lens, d ₁ ,
d _2, ... is the thickness and lens distance of each _{lens, n} 1, n
_2, ... is the refractive index of each lens, [nu _1, [nu _2, ... is the Abbe number of each lens.

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

Example 1 has the lens configuration shown in FIG. 1 and is very small and has good imaging performance.

The aberrations at the wide-angle end, the intermediate focal length, and the telephoto end of this embodiment are as shown in FIGS. 3, 4, and 5 , respectively.

Embodiments 2 and 4 also have the lens configuration shown in FIG. 1 and have an angle of view of about 73 ° at the wide-angle end, which is the widest angle for this type of zoom lens. The aberrations at the wide-angle end, the intermediate focal length, and the telephoto end in the second embodiment are shown in FIGS.
7 and 8, and the aberrations at the wide-angle end, intermediate focal length, and telephoto end of the fourth embodiment are as shown in FIGS. 12, 13, and 14 , respectively.

Embodiment 3 is a high-magnification zoom lens having the lens configuration shown in FIG. 1 and having an angle of view at the wide-angle end of about 62 ° and a magnification of about 3, and is characterized by miniaturization and imaging performance. . The aberrations at the wide-angle end, the intermediate focal length, and the telephoto end of this embodiment are as shown in FIGS. 9, 10, and 11 , respectively.

In each of Examples 2 to 4 , the axial distance is narrowed even at the wide-angle end, so that the overall length of the entire system is shortened and the outer diameter of the lens is reduced, thereby greatly reducing the size of the lens system.

In each of the above embodiments, the first lens group, the second lens group, and the third lens group are each provided with an air lens having a strong action, and a high-order aberration generating surface is obtained from the viewpoint of aberration correction. Thus, a delicate aberration balance is achieved while giving many degrees of freedom.

In the lens system of the present invention, it is effective to provide an aspherical surface in order to further increase the zoom ratio and further improve the performance. In other words, by adopting an aspherical surface for the first lens group G ₁ or the second lens group G ₂ , the load on the lens components can be reduced and the refracting power can be reduced, so that it is possible to design with margin and improve the optical performance. I can do it.

As the shape of the aspherical surface, the direction of the optical axis is taken as the x-axis, the direction perpendicular to the optical axis is taken as the y-axis, and the radius of curvature (radius of the reference spherical surface) near the optical axis of the surface is _defined as rk. Then, it is represented by the following equation.

Here, A _k , B _k , C _k , and D _k are aspherical coefficients, and k indicates that the aspherical surface is the k-th surface.

[0092]

According to the present invention, the three lens units of positive, positive and negative are arranged so that each lens unit moves at the time of zooming, thereby enabling downsizing and a high magnification ratio. Thus, a zoom lens having extremely good optical performance from the wide-angle end to the telephoto end can be realized. Further, the second lens group is provided with a special feature to make it more compact, and a lens system having a field angle of about 76 ° at the wide-angle end or a lens angle of view of 1 at the telephoto end.
It is possible to realize a lens system of about 8 °.

[Brief description of the drawings]

FIG. 1 is a sectional view of Embodiments 1 to 4 of the present invention.

FIG. 2 is a diagram showing a basic configuration of the present invention and a moving state of each group.

FIG. 3 is an aberration curve diagram at the wide angle end according to the first embodiment.

FIG. 4 is an aberration curve diagram at an intermediate focal length according to the first embodiment.

FIG. 5 is an aberration curve diagram at the telephoto end according to the first embodiment.

FIG. 6 is an aberration curve diagram at the wide angle end according to the second embodiment.

FIG. 7 is an aberration curve diagram at an intermediate focal length according to the second embodiment.

FIG. 8 is an aberration curve diagram at the telephoto end according to the second embodiment.

FIG. 9 is an aberration curve diagram at the wide angle end according to a third embodiment.

FIG. 10 is an aberration curve diagram at the intermediate focal length according to the third embodiment.

FIG. 11 is an aberration curve diagram at the telephoto end according to a third embodiment.

FIG. 12 is an aberration curve diagram at the wide angle end according to a fourth embodiment.

FIG. 13 is an aberration curve diagram at the intermediate focal length according to the fourth embodiment.

FIG. 14 is an aberration curve diagram at the telephoto end according to the fourth embodiment.

FIG. 15 is a diagram illustrating a configuration of a conventional four-group zoom lens and movement of each group.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-161423 (JP, A) JP-A-1-252916 (JP, A) JP-A-1-252917 (JP, A) JP-A-1- 314218 (JP, A) JP-A-2-16515 (JP, A) JP-A-2-16516 (JP, A) JP-A-2-73211 (JP, A) (58) Fields investigated (Int. Cl. ^7, DB name) G02B 9/00 - 17/08 G02B 21/02 - 21/04 G02B 25/00 - 25/04

Claims (1)

(57) [Claims] A first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. The first lens group includes a negative lens, a first positive lens, and a first lens unit. The first lens unit performs zooming by changing the interval on each optical axis .
Two positive lenses, the negative lens and the first positive lens.
A second lens group is disposed between the front group and the rear group, and the second lens group is disposed between the front group and the rear group having a negative refractive power and the rear group having a positive refractive power. A compact high-magnification zoom lens comprising an aperture and satisfying the following conditions. _{(1) 0.05 <φ 1 /} φ W <0.9 (2) 1.0 <φ 12W / φ W <2.0 (3) 2.0 <β 3T <5.0 (4) 5 < e ′ ₂ <20 where φ ₁ is the refractive power of the first lens group, φ _12W is the combined refractive power of the first and second lens groups at the wide-angle end, and φ _W is the refractive power of the entire system at the wide-angle end. , Β _3T is the lateral magnification of the third lens group at the telephoto end, and e ′ ₂ is the distance between the principal points of the front group and the rear group.