JP2903473B2 - Compact high-magnification zoom lens - Google Patents

Description

The present invention relates to a compact high-magnification zoom lens.

[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 zoom lens built-in 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.

This type of lens system does not need to consider disposing a mirror as in a so-called single-lens reflex camera, and can shorten the back focus. for that reason,
For a lens system with a wide angle of view, such as for a single-lens reflex camera, it is not necessary to arrange the rear principal plane position on the rear side of the optical system with a retrofocus type. Conversely, as a telephoto type, The refractive power arrangement can be such that the position of the rear principal plane is somewhat toward the object side.

Basically, a multifocal switching type variable magnification optical system such as a single focus lens and a two-unit zoom as described in JP-A-57-201213 are also telephoto type lens systems. Further, as an advanced type of the two-group zoom lens, an attempt was made to improve the aberration correction by dividing the specific lens group,
A three-unit zoom lens having a variable magnification ratio is provided. Japanese Patent Application Laid-Open No. Sho 60-57814 discloses a four-group zoom lens comprising four lens groups and three movable groups.

[Problems to be Solved by the Invention] The zoom lens described above has a zoom ratio of 1.5 to 2 at most.
And the aperture ratio is too small to be practical.

On the other hand, the present applicant has developed a four-group zoom lens described in JP-A-63-43115 with the aim of improving the zoom ratio and the optical performance. Further, as a simplified mechanism of the zoom lens, a lens system and the like described in Japanese Patent Application Laid-Open No. 63-153511 have been 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 zoom range in order to satisfy practical demands by further utilizing the change in perspective for the purpose of drawing. It is intended to reduce the size.

Accordingly, an object of the present invention is to provide a compact, high-magnification zoom lens of a three-group zoom system with a comprehensive angle of view of about 76 ° to 18 ° and an optical performance of about 3 to 4 with good optical performance over the entire zoom range. To provide.

[Means for Solving the Problems] The zoom lens according to the present invention basically includes
Starting from the development of the lens system of No. 153511, the objective was achieved as a three-unit zoom type lens system in consideration of simplification of the lens frame structure and compactness by optimizing the focusing method.

The lens configuration and the behavior of the lens unit during zooming are originally positive and negative from the object side in order from the object side in order to correct the magnification load and aberration correction during zooming, particularly to correct the field curvature, and to reduce the size of the lens system. , 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 second lens group and the third lens group can perform almost the same zooming movement while improving the optical performance. In other words, 3 as a special solution in the 4-group zoom method
A group zoom method was found.

As described above, the zoom lens according to the present invention is a single lens having a positive refractive power as a whole of the second lens group having a negative refractive power and the third lens group having a positive refractive power in a four-unit zoom type lens system. The second lens group is a group. In this manner, the zoom ratio is 3 to 3 as a three-group zoom method.
In order to achieve about 4, it is important to properly arrange the refractive power of each lens group in reducing the size of the lens system.
Further effects can be further improved by using an optimal thick lens structure and using new materials.

The zoom lens of the present invention is based on the above idea, and includes, in order from the object side, 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 zooming is performed by changing the distance between the lens groups. The following conditions (1), (2) and (3)
Is satisfied.

(1) 0.05 < ₁ / _W <0.9 (2) 1.0 < _12W / _W <2.0 (3) 3.5 < _β3T <5.0 where ₁ is the refractive power of the first lens unit, and _12W is the first lens unit at the wide-angle end. And the combined refractive power of the second lens group,
_W is the refractive power of the entire system at the wide-angle end, and β _3T is the lateral magnification of the third lens unit at the telephoto end.

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 achieve a higher magnification. Like that.

As described above, the present invention analyzes the lens system of the four-unit zoom system as shown in FIG. 15, and based on the result of the study on the mechanism and structure as well as the compactness of the lens system. There is a solution in which the third lens unit has a relatively small magnification during zooming from the wide-angle end to the telephoto end, and the role of the third lens unit at that time is to perform the curvature of the image plane rather than the magnification. It has been found that the optical performance is improved, such as performing 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, in the third lens group zoom lens, the action of correcting the field curvature provided by the third lens group is to adjust the interval on the optical axis, that is, to give a margin of the telephoto ratio to the lens configuration on the telephoto side, A convex meniscus-shaped air lens is provided in the thick lens constituting the lens to generate higher-order aberrations.

The three-unit zoom type lens system configured as described above has the first lens unit G _{1 at} the wide-angle end as shown in FIG.
If the refractive power of its synthesis by the second lens G ₂ can be considered as positive 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 basically a telephoto type, and 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 main 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.

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 the second zoom lens as shown in FIG, the refractive power at the wide-angle end _W, the following expression holds when the total length of the lens system and L _{W. W} = ₁ (1−e _2W · ₃ ) + (1−e _1W · ₁ ) + ( <sub>2
+ 3 -e '2W 2 3)</sub> (i) L W = e 1W + e 2W + l' W (ii) l 'W = {- 1 e 2W + (1-e 1W · 1) (1-e 2W ·
₂ )｝ / _W (iii) where ₁ , ₂ , and ₃ are the first lens group G ₁ and the second lens group, respectively.
The refractive power of the lens group G ₂ and the third lens group G ₃ , e _1W is the distance between the principal points of the first lens group G ₁ and the second lens group G _{2 at} the wide angle end, e
_1T The first lens group G ₁ and second main point interval of the lens group G ₂ at the telephoto end, e _2W and the second lens group G ₂ at the wide angle end 3
The main point interval of lens groups G _3, e _2T is in the second lens group G ₂ and the principal point distance between the third lens group G _3, l _'W back at the wide-angle end focus, l' _T telephoto end in the telephoto end Back focus.

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 determined as a specification is constant, so that the refractive power of the first lens unit is increased, and the movement amount during zooming is reduced, so that the entire lens system is reduced in size. It is preferred. However, the present invention
Since the main purpose is to increase the magnification, the telephoto side necessarily enters the telephoto region 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.

When the value goes below the lower limit of the condition (1), the refractive power of the first lens unit becomes weak, so that the zooming movement amount 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 an important condition for determining the refractive power arrangement that balances the optical performance and the overall length of the lens system in the zoom lens of the present invention having a zoom ratio of 3 to 4.

Condition (2) is that the first lens group G ₁ and the second lens group
It is obtained by defining a combined refractive power of the lens unit G _2. 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 group is set and its lateral magnification is set, the refractive power of the third lens group 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.

Exceeding the upper limit of the condition (2) is effective in shortening the overall length of the lens system at the wide-angle end, and requires a relatively small amount of movement during zooming to the telephoto end. But first lens group G ₁ and tends to the refractive power of the second lens group G ₂ are both strong, it is difficult to balance the aberrations including the correction of image plane Curved, eventually shooting It is not preferable because sensitivity due to eccentricity in the performance and quality of the lens increases.

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 refractive power of the third lens group G ₃ to the subsequent weak Therefore, it is necessary to balance the aberration correction, and the back focal length of the lens system is shortened 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 group and the second lens group, 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 refractive power distribution of the third lens group, 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 is important, and also significant in obtaining good performance. That is, the paraxial lateral magnification (hereinafter, referred to as the magnification) which the third lens group bears.
Is the condition (3).

The magnification of the third lens group is directly linked 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 paraxial layout is provided by giving the magnification of the third lens group at the telephoto end where the magnification should be set under the condition (3). 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 becomes high, which is preferable for obtaining a high magnification ratio.
The amount of movement of the lens group 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 increase the zoom ratio.

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

(1 ') 0.05 < ₁ / _W <0.6 These conditions define the refractive power of the first lens unit. To achieve a high magnification, the first lens unit and the second lens unit must be used.
It is preferable that each of the 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 '), there is 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 consider using the first lens group as the focusing group. A very high performance and high zoom ratio zoom lens 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, if the condition (3) is limited as in the following condition (3 '), the magnification can be set to 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. If the lower limit of the condition (3 ') is exceeded, it becomes difficult to increase the magnification as described above.

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

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

Although the refractive power of the first lens group is given by the above-mentioned condition, the first lens group basically has 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 based on its role, and includes a negative front group _G2F and a positive rear group _G2R .

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. An aberration having a sign opposite to those of the aberrations generated by one 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 disposing a positive lens and a negative lens from the object side, and a positive lens or a negative lens may be further disposed depending on required imaging performance. . Or an air lens therebetween by dividing the positive lens or a negative lens of the front group G _2F, the front group G _2F
The performance can be further improved by using an aspherical surface for the middle lens.

The rear group G _2R of the second lens group is disposed at a distance D from the front group G _2F on the optical axis, and basically has one negative lens and two positive lenses like a triplet or a Tessar type. Consists of lenses. Here, the first lens group and the second lens group form an image forming system as a whole.
The _G2R can be considered to constitute a so-called relay system.

This rear group G _2R is located at a position where the marginal luminous flux diameter is large in the telephoto range, and it is necessary to greatly contribute to the correction of spherical aberration.Also, there is little difficulty in manufacturing including eccentric sensitivity. It is necessary to take care not to increase the incident angle or the outgoing angle on each surface.

In the zoom lens of the present invention, in order to realize further miniaturization, the value of the principal point interval e ′ ₂ between the front group G _2F and the rear group G _2R of the second lens group G ₂ is set within a certain range. It is necessary to reduce the dead space by allocating a thick lens so as to satisfy the paraxial configuration.

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

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 of 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, it is possible to configure a small zoom lens with a high zoom ratio, which is an object of the present invention.

EXAMPLES Next, examples of the compact high-magnification zoom lens of the present invention will be described.

Example 1 Example 2 Example 3 Example 4 Where r ₁ , r ₂ , ... are the radii of curvature of the respective surfaces of the lens, d ₁ , d ₂ ,
... the thickness and lens distance of each lens, n _1, n _2, ... is the refractive index of each lens, ν _1, ν _2, ... is the Abbe number of each lens.

Embodiments 1 to 4 also cover the lens configuration shown in FIG. 1 from an angle of view of about 58 ° at the wide angle end to about 18 ° at the telephoto end. In these embodiments, not only the overall length is short, but also the outer diameter of the lens is small, so that the configuration is convenient for carrying.

The aberrations at the wide-angle end, the intermediate focal length, and the telephoto end of the first embodiment are respectively shown in FIGS. 3, 4, and 5, and the aberrations at the wide-angle end, the intermediate focal length, and the telephoto end of the second embodiment are respectively. 6, 7, and 8 show the aberrations at the wide angle end, the intermediate focal length, and the telephoto end of the third embodiment, respectively, as shown in FIGS.
In FIG. 11, the aberrations at the wide-angle end, the intermediate focal length, and the telephoto end of the fourth embodiment are as shown in FIGS. 12, 13, and 14, respectively.

In the lens system of the present invention, it is effective to provide an aspheric surface in order to further increase the zoom ratio and further improve the performance. That first lens group G ₁ and the second lens group
It is possible to weaken the lightly refractive power burden of the lens component by employing an aspherical surface in G ₂ can improve the optical performance can be designed with a margin.

When the aspherical surface shape of the optical axis direction to the x-axis, taking the direction perpendicular to the optical axis in the y-axis, the radius of curvature at the optical axis near the surface (the radius of the reference sphere) was r _k, It is shown by the following equation.

Where A _k , B _k , C _k , and D _k are aspherical coefficients, and k is k
Indicates that this is the th plane.

[Effects of the Invention] The present invention has a three-group configuration of positive, positive, and negative. Each lens group moves during 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. In addition, the structure of the second lens group has a special feature to make it even smaller, and the angle of view at the wide-angle end is 76 °.
It is possible to realize a lens system having a degree of view or a lens system having a field angle of about 18 ° at the telephoto end.

[Brief description of the drawings]

FIG. 1 is a sectional view of the first to fourth embodiments of the present invention, and FIG.
FIG. 3 shows the basic configuration of the present invention and the movement of each group. FIGS. 3 to 14 show aberration curves of each embodiment of the present invention. FIG. 15 shows the configuration of a conventional four-group zoom lens and each group. FIG. 6 is a diagram showing the movement of the image.

Claims (2)

(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. A compact high-magnification zoom lens, which is a lens system that performs zooming by changing the interval on each optical axis and satisfies the following conditions. (1) 0.05 < ₁ / _W <0.9 (2) 1.0 < _12W / _W <2.0 (3) 3.5 < _β3T <5.0 where ₁ is the refractive power of the first lens unit, and _12W is the first lens unit at the wide-angle end. And the combined refractive power of the second lens group,
_W is the refractive power of the entire system at the wide-angle end, and β _3T is the lateral magnification of the third lens unit at the telephoto end. 2. The compact high-magnification zoom lens according to claim 1, wherein said first lens group or said second lens group includes an aspherical surface.