JP2003156686A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact and inexpensive zoom lens keeping a high zoom ratio while realizing the appropriate compensation of aberration. SOLUTION: This zoom lens 1 has a 1st lens group 11 having negative refractive power, a 2nd lens group 12 having positive refractive power, and a 3rd lens group 13 having positive refractive power in order from an object side. In the lens 1, a positive lens 31, a negative lens 32, a negative meniscus lens 33 whose concave surface faces to an image surface side and a 2nd positive lens 34 are arranged in order from the object side as the 2nd lens group 12. Furthermore, an air gap is made to exist between the lenses 33 and 34. One aspherical lens 41 is provided as the 3rd lens group 13. Thus, the compact and inexpensive zoom lens 1 keeping the high zoom ratio while realizing the appropriate compensation of aberration is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens used in a digital still camera, a video camera, a silver salt film camera and the like.

[0002]

2. Description of the Related Art Conventionally, various zoom lenses used in cameras have been known. In a camera using a solid-state image sensor such as a digital still camera and a video camera, a low-pass filter, a color correction filter, etc. are arranged in front of the solid-state image sensor. Therefore, a zoom lens of a camera using a solid-state image sensor requires a long back focus and a certain degree of telecentricity on the image plane side.

Such a zoom lens is composed of a first lens group having a negative refracting power, a second lens group having a positive refracting power, and a third lens group having a positive refracting power from the object side. Are disclosed in, for example, JP-A-7-261083, JP-A-11-52246, and JP-A-2001-66503.

[0004]

SUMMARY OF THE INVENTION By the way, Japanese Patent Laid-Open No. 7-
When only a spherical lens is used like the zoom lens described in Japanese Patent No. 261083, only about 2 × zoom magnification can be realized in consideration of the compactness of the zoom lens and aberration characteristics.

On the other hand, in the zoom lens disclosed in Japanese Unexamined Patent Publication No. 2001-66503, aberration characteristics are improved by incorporating an aspherical lens in each of the three lens groups. In recent years, as a zoom lens for a digital still camera, one that uses many glass mold aspherical lenses and pursues compactness and high performance has become mainstream. However, since an aspherical lens is difficult to process and expensive, using three aspherical lenses as in Japanese Patent Laid-Open No. 2001-66503 causes a problem that the price of the zoom lens becomes very high.

Japanese Unexamined Patent Publication No. 11-52246 discloses a zoom lens using only one aspherical lens. However, the zoom lens described in this publication is not designed with emphasis on compactness, and therefore the total length of the zoom lens is longer than the focal length when only one aspherical lens is used.

The present invention has been made in view of the above problems, and an object thereof is to realize a compact and inexpensive high-performance zoom lens by paying attention to the second lens group.

[0008]

According to a first aspect of the present invention, there is provided a zoom lens comprising a first lens group having a negative refracting power and a second lens having a positive refracting power in order from the object side. And a third lens group having a positive refractive power,
When changing from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group decreases, and the distance between the second lens group and the third lens group decreases. Increased,
The second lens group has a first positive lens, a negative lens, a negative meniscus lens having a concave surface facing the image plane side, and a second positive lens in this order from the object side, and the negative meniscus lens and the An air gap exists between the second positive lens.

A second aspect of the present invention is the zoom lens according to the first aspect, wherein the second lens group includes the first positive lens, the negative lens, the negative meniscus lens, and the second positive lens. It consists of a lens.

A third aspect of the present invention is the zoom lens according to the first or second aspect, wherein the focal point of the air lens between the negative meniscus lens and the second positive lens of the second lens group. The distance is f _2A , the focal length of the third lens group is f ₃ , the sum of the axial core thicknesses of the second lens group is Σ _2d , the total focal length at the telephoto end is f _T , the negative meniscus lens and the Let d _{2A be} the axial distance from the second positive lens, and let L _{T be} the total length from the first lens group at the telephoto end to the in-focus position.

[0011]

[Equation 3]

[0012] is satisfied.

The invention described in claim 4 is the zoom lens described in claim 3,

[0014]

[Equation 4]

Is satisfied.

A fifth aspect of the present invention is the zoom lens according to any one of the first to fourth aspects, wherein:
The lens group and the second lens group are composed of only spherical lenses, and the third lens group has only one aspherical lens.

The sixth aspect of the present invention is the zoom lens according to the fifth aspect, wherein the third lens group is the aspherical lens.

The seventh aspect of the present invention is the zoom lens according to the fifth or sixth aspect, wherein the aspherical lens is molded of resin.

[0019]

1 shows a zoom lens 1 according to an embodiment of the present invention, a low-pass filter 91 and an image plane 92 (that is, an image pickup plane of a solid-state image pickup device of a digital still camera or a digital video camera). ) Is a cross-sectional view of a zoom lens of Example 1 described later.

The zoom lens 1 includes a first lens group 11 having a negative refracting power, a second lens group 12 having a positive refracting power, and a third lens having a positive refracting power in order from the object side toward the image plane side. A lens group 13 is provided. In the zoom lens 1, the distance between the first lens group 11 and the second lens group 12 decreases when changing from the wide-angle end (state during wide-angle shooting) to the telephoto end (state during telephoto shooting). , The distance between the second lens group 12 and the third lens group 13 increases. At this time,
The first lens group 11 reciprocates.

The first lens group 11 is composed of only three or four spherical lenses. Zoom lens 1 shown in FIG.
Then, from the object side, a positive lens 21 having a convex surface on the object side, a negative meniscus lens 22 having a small radius of curvature on the image side, a negative lens 23, and a positive lens 24 are provided. The negative meniscus lens 22, the negative lens 23, and the positive lens 24 are a combination of positive and negative lenses for reducing various aberrations, and further, a negative refracting power is shared by the two negative lenses. The most object-side positive lens 21 is provided to further improve optical characteristics such as distortion. When the positive lens 21 is omitted, the first lens group 11 is composed of three lenses.

The second lens group 12 is composed of only 4 or 5 lenses (see FIGS. 17 and 21 for the configuration of 5 lenses). In the zoom lens 1 shown in FIG. 1, a biconvex positive lens 31 and a negative lens 3 are arranged from the object side.
2. A negative meniscus lens 33 having a concave surface facing the image plane side and a positive lens 34 are arranged in order. Second lens group 1
Each lens of 2 is also a spherical lens. When the second lens group 12 is composed of five lenses,
A positive lens is added to the most object side.

Here, in the zoom lens composed of the first lens group having negative refractive power and the second and third lens groups having positive refractive power, the off-axis light flux from the first lens group is the optical axis. It is flipped up from and enters the second lens group. Therefore, in the zoom lens having such a configuration,
Generally, the second lens group becomes a cause of spherical aberration,
If the lens group is composed of three lenses, it becomes difficult to increase the zoom magnification of the zoom lens. Furthermore, the first
Distortion aberrations that cannot be corrected by the lens group are also preferably corrected by the second lens group.

Therefore, in the zoom lens 1 shown in FIG.
The second lens group 12 is composed of 4 or 5 lenses. In addition, when the compactness of the zoom lens 1 is given the highest priority, it is preferable that the second lens group 12 is composed of four lenses.

In the second lens group 12 of the zoom lens 1,
A biconvex positive lens 31 and a negative lens 32 are arranged close to each other, and a negative meniscus lens 33 and a positive lens 34 are arranged close to each other with a predetermined space therebetween. By configuring the second lens group 12 with (single) lenses having positive, negative, negative, and positive refracting power, the Betzval sum of the second lens group 12 is suppressed to a small value. Furthermore, by providing a predetermined interval between two lenses having negative refractive power, it is possible to correct the field curvature to a high off-axis image height.

The second lens group 12 is composed of a positive lens 31 and a negative lens 32.
In the case of a single lens, a front lens group in which a positive lens is further provided on the object side of the positive lens 31) and a negative meniscus lens 3
By dividing it into a rear group consisting of 3 and a positive lens 34, image plane correction is realized while correcting chromatic aberration in each of the front group and the rear group. In the front lens group, an air gap is provided between the positive lens 31 and the negative lens 32 to obtain a spherical aberration correction effect. Further, by using the negative meniscus lens 33 as the third lens, it is possible to suppress the height at which the light from the front group is incident, and it is possible to obtain the effect of correcting spherical aberration.

Further, there is an air gap between the negative meniscus lens 33 and the positive lens 34, and by bringing these lenses close to each other, an air lens having a stronger refractive power than usual is formed, and the effect of correcting distortion aberration is formed. Is obtained. By directing the concave surface of the negative meniscus lens 33 toward the image plane side, the telecentricity required for image formation on the solid-state image sensor is ensured while maintaining compactness.

The third lens group 13 is a lens group having only one aspherical lens, and in the zoom lens 1 shown in FIG. 1, the third lens group 13 is composed of only one aspherical lens 41. The third lens group 13 is provided for the purpose of correcting various aberrations, and a large refractive power is not required. Therefore, the processing accuracy of the aspherical lens 41 can be stabilized. Further, since the difference in wall thickness of the aspherical lens 41 can be reduced, it is possible to reduce the cost in processing the aspherical surface.

When the compactness of the zoom lens 1 is emphasized, it is preferable that the third lens group 13 is one aspherical lens, but a combination of an aspherical lens and another spherical lens is the first. It may be a three-lens group 13. By using only one aspherical lens, the performance of the zoom lens 1 can be kept high and the size and manufacturing cost can be reduced.

First lens group 11 and second lens group 12
Is composed of only a spherical lens, and stability in terms of performance of the entire zoom lens 1 is secured. On the other hand, by using an aspherical lens for the third lens group 13 that does not require a large refractive power, it is possible to reduce the difference in wall thickness of the aspherical lens. It need not be molded by a mold, but may be molded by a resin. As a result, it is possible to further reduce the cost and stabilize the performance.

The zoom lens 1 further includes a second lens.
Between the negative meniscus lens 33 and the positive lens 34 of the group 12
The focal length of the air lens of f_2AOf the third lens group 13
F is the focal length_Three, Σ is the sum of the axial core thicknesses of the second lens group 12.
_2d, The total focal length at the telephoto end is f_T, Negative menis
The axial distance between the cas lens 33 and the positive lens 34 is d
_2A, From the first lens group 11 at the telephoto end to the in-focus position.
The total length at_TAs a result, Expressions 5 to 7 are satisfied.

[0032]

[Equation 5]

[0033]

[Equation 6]

[0034]

[Equation 7]

The sum of the on-axis core thickness Σ _2d is obtained by omitting the diaphragm, and the distance in the low-pass filter 91 in the total length L _T is the air-converted distance.

The number 5 indicates the condition of the value of the focal length f _2A of the air lens is normalized by the focal length f ₃ of the third lens group 13 between the negative meniscus lens 33 and the positive lens 34, air The conditions for ensuring distortion correction and telecentricity by making the focal length of the lens appropriate are shown.

That is, if f _2A / f ₃ exceeds the upper limit of the expression (5), it becomes difficult to correct distortion at the wide-angle end, and it becomes difficult to secure telecentricity. Further, the spherical aberration at the telephoto end is insufficiently corrected. On the other hand, if f _2A / f ₃ is less than the lower limit of Expression 5, the rear group of the second lens group 12 for forming the air lens will be large. Further, the divergence of the upper light flux at the wide-angle end becomes excessive, and it becomes difficult to correct the positive deviation of the image plane, and the spherical aberration at the telephoto end becomes excessively corrected.

Equation 6 shows the condition of the value obtained by dividing the sum Σ _2d of the on-axis core thicknesses of the second lens group 12 by the total focal length f _T at the telephoto end, and when the zoom ratio is large. Is also a condition for making the zoom lens 1 compact.

The second lens group 12 is a lens group that plays an important role in correcting spherical aberration and distortion. By increasing the sum Σ _2d of the core pressures of the second lens group 12, aberration correction is facilitated. You can However, the sum of core pressure Σ
_{If 2d} is increased, the zoom lens 1 becomes larger. That is, when Σ _2d / f _T exceeds the upper limit of the equation 6, the entire lens system becomes large, and Σ _2d / f _T
Is less than the lower limit of the equation 6, it becomes difficult to properly correct various aberrations.

Equation 7 is an axial distance d between the negative meniscus lens 33 and the positive lens 34 in the rear group of the second lens group 12.
_2A shows the condition of a value obtained by dividing _2A by the total length L _T from the first lens group 11 to the in-focus position at the telephoto end, and the aberration correction of the rear group of the second lens group 12 even if the zoom ratio is large. It is a condition for maintaining ability.

That is, when d _2A / L _T exceeds the upper limit of the expression 7, aberration correction is advantageous, but the entire zoom lens 1 becomes large, and when d _2A / L _T falls below the lower limit of the expression 7. This is advantageous for making the zoom lens 1 compact, but the second
It becomes difficult to form an air lens that satisfies the condition of Expression 5 by the rear group of the lens group 12. It can be said that the lower limit of Expression 7 is a condition that plays the same role as the upper limit of Expression 5.

For the above reasons, the zoom lens 1 has
To satisfying the condition (7), the second lens group 12 becomes 4
Alternatively, the zoom lens 1 includes five lenses and has a large zoom ratio (about 2 to 4 times), is compact, and has various aberrations appropriately corrected.
Is realized.

The conditions of the expressions 5 to 7 show the range of general preferable conditions when the second lens group 12 is composed of 4 or 5 lenses, and the embodiment 1 to be described later. It is more preferable that the conditions shown in Formula 8 are satisfied so as to be supported by Nos. 6 to 6.

[0044]

[Equation 8]

[0045]

EXAMPLE FIG. 1 is a diagram showing a lens configuration in Example 1. As shown in FIG. Table 1 is a table showing the design value of each lens, and Table 2 is substituted into the aspherical surface formula shown by the equation 9 when designing the aspherical lens (surface number 18 is an aspherical surface) which is the third lens group. It is a table showing the value of the parameter. In Expression 9, ε is a quadric surface parameter, which is set to 1 in this embodiment. A to E are parameters for determining the shape of the aspherical surface, and r is a paraxial radius of curvature. Table 3 is a table showing various numerical values relating to zooming of the zoom lens.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Equation 9]

[0049]

[Table 3]

2 to 4 are views showing, in order, various aberrations of the zoom lens according to Example 1 at the wide-angle end, the intermediate position and the telephoto end. FIGS. 2 (a), (b), (c),
(D) shows spherical aberration, field curvature aberration, distortion aberration, and chromatic aberration of magnification, respectively.

The solid line and the alternate long and short dash line in (a) show spherical aberration at the d and g lines, and the wavy line shows the amount of sine condition violation. The solid line and the alternate long and short dash line in (b) show the field curvature aberrations on the sagittal image planes of the d and g lines, and the short and long wavy lines show the field curvature aberrations on the meridional image planes of the d and g lines. The same applies to aberration diagrams of other examples.

FIG. 5 is a view showing the lens arrangement in the second embodiment. Table 4 is a table showing design values of each lens,
Table 5 is a table showing the values of the parameters substituted into the aspherical expression shown in Formula 9 when designing an aspherical lens (surface number 18 is an aspherical surface). Table 6 is a table showing various numerical values relating to zooming of the zoom lens.

[0053]

[Table 4]

[0054]

[Table 5]

[0055]

[Table 6]

FIGS. 6 to 8 are diagrams sequentially showing various aberrations at the wide-angle end, the intermediate position and the telephoto end of the zoom lens according to the second example, and FIGS. 6 (a), 6 (b) and 6 (c),
(D) shows spherical aberration, field curvature aberration, distortion aberration, and chromatic aberration of magnification, respectively.

FIG. 9 is a view showing the lens arrangement in the third embodiment. Table 7 is a table showing design values of each lens,
Tables 8 and 9 show parameters to be substituted into the aspherical surface formula shown in the equation 9 when designing an aspherical lens (surface number 18 is an aspherical surface according to Table 8 and surface number 19 is an aspherical surface according to Table 9). It is a table which shows a value. Table 10 is a table showing various numerical values relating to zooming of the zoom lens.

[0058]

[Table 7]

[0059]

[Table 8]

[0060]

[Table 9]

[0061]

[Table 10]

FIGS. 10 to 12 are views showing various aberrations at the wide-angle end, the intermediate position, and the telephoto end of the zoom lens according to the third embodiment, in order, respectively, (a), (b), (c),
(D) shows spherical aberration, field curvature aberration, distortion aberration, and chromatic aberration of magnification, respectively.

FIG. 13 is a view showing the lens arrangement in the fourth embodiment. Table 11 is a table showing design values of each lens, and Tables 12 and 13 are numerical values when designing an aspherical lens (surface number 18 is an aspherical surface according to Table 12 and surface number 19 is an aspherical surface according to Table 13). 11 is a table showing the values of parameters substituted into the aspherical surface formula shown in FIG. Table 14 is a table showing various numerical values relating to zooming of the zoom lens.

[0064]

[Table 11]

[0065]

[Table 12]

[0066]

[Table 13]

[0067]

[Table 14]

FIGS. 14 to 16 are diagrams showing various aberrations at the wide-angle end, the intermediate position and the telephoto end of the zoom lens according to the fourth embodiment. FIGS. 14 (a), (b), (c),
(D) shows spherical aberration, field curvature aberration, distortion aberration, and chromatic aberration of magnification, respectively.

FIG. 17 shows the lens arrangement of the fifth embodiment. In the zoom lens according to the fifth example, the second lens group includes five lenses, and the third lens group moves to the image plane side during zooming (the same applies to the sixth example). Table 15 is a table showing design values of each lens, and Tables 16 and 17 show aspherical lenses (surface number 2).
0 is an aspherical surface according to Table 16 and surface number 21 is an aspherical surface according to Table 17). Table 18 is a table showing various numerical values relating to zooming of the zoom lens.

[0070]

[Table 15]

[0071]

[Table 16]

[0072]

[Table 17]

[0073]

[Table 18]

18 to 20 are diagrams showing various aberrations at the wide-angle end, the intermediate position, and the telephoto end of the zoom lens according to the fifth embodiment. FIGS. 18 (a), (b), (c),
(D) shows spherical aberration, field curvature aberration, distortion aberration, and chromatic aberration of magnification, respectively.

FIG. 21 shows the lens arrangement of the sixth embodiment. Table 19 is a table showing design values of each lens, and Tables 20 and 21 are numerical values when designing an aspherical lens (surface number 20 is an aspherical surface according to Table 20 and surface number 21 is an aspherical surface according to Table 21). 11 is a table showing the values of parameters substituted into the aspherical surface formula shown in FIG. Table 22 is a table showing various numerical values relating to zooming of the zoom lens.

[0076]

[Table 19]

[0077]

[Table 20]

[0078]

[Table 21]

[0079]

[Table 22]

22 to 24 are diagrams showing various aberrations at the wide-angle end, the intermediate position and the telephoto end of the zoom lens according to the sixth embodiment, and FIGS. 22 (a), (b), (c),
(D) shows spherical aberration, field curvature aberration, distortion aberration, and chromatic aberration of magnification, respectively.

Table 23 is a table showing the values of the mathematical parts of the formulas 5 to 7 in the first to sixth embodiments.

[0082]

[Table 23]

[0083]

According to the present invention, it is possible to realize a compact zoom lens having a high zoom ratio while performing appropriate aberration correction. Further, by using one aspherical lens, the manufacturing cost of the zoom lens can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a zoom lens according to Example 1. FIG.

FIG. 2 is a diagram showing various aberrations at the wide-angle end of the zoom lens of Example 1. FIGS.

FIG. 3 is a diagram showing various aberrations at an intermediate position of the zoom lens of Example 1.

FIG. 4 is a diagram showing various aberrations at the telephoto end of the zoom lens according to Example 1;

FIG. 5 is a diagram showing a configuration of a zoom lens according to Example 2.

FIG. 6 is a diagram showing various aberrations at the wide-angle end of the zoom lens of Example 2.

FIG. 7 is a diagram showing various aberrations at the intermediate position of the zoom lens of Example 2.

FIG. 8 is a diagram showing various aberrations at the telephoto end of the zoom lens according to Example 2;

FIG. 9 is a diagram showing a configuration of a zoom lens according to Example 3.

FIG. 10 is a diagram showing various aberrations at the wide-angle end of the zoom lens of Example 3;

FIG. 11 is a diagram showing various aberrations at the intermediate position of the zoom lens of Example 3;

FIG. 12 is a diagram showing various aberrations at the telephoto end of the zoom lens of Example 3;

FIG. 13 is a diagram showing a configuration of a zoom lens according to Example 4.

FIG. 14 is a diagram showing various aberrations at the wide-angle end of the zoom lens of Example 4;

FIG. 15 is a diagram showing various aberrations at the intermediate position of the zoom lens of Example 4;

FIG. 16 is a diagram showing various aberrations at the telephoto end of the zoom lens of Example 4;

FIG. 17 is a diagram showing a configuration of a zoom lens according to Example 5.

FIG. 18 is a diagram showing various aberrations at the wide-angle end of the zoom lens of Example 5;

FIG. 19 is a diagram showing various aberrations at the intermediate position of the zoom lens of Example 5;

FIG. 20 is a diagram showing various aberrations at the telephoto end of the zoom lens of Example 5;

FIG. 21 is a diagram showing a configuration of a zoom lens according to Example 6.

FIG. 22 is a diagram showing various aberrations at the wide-angle end of the zoom lens of Example 6;

FIG. 23 is a diagram showing various aberrations at the intermediate position of the zoom lens of Example 6;

FIG. 24 is a diagram showing various aberrations at the telephoto end of the zoom lens of Example 6;

[Explanation of symbols]

1 zoom lens 11 First lens group 12 Second lens group 13 Third lens group 31 Positive lens 32 negative lens 33 negative meniscus lens 34 Positive lens 41 Aspherical lens

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H087 KA02 KA03 PA09 PA10 PA17                       PB09 PB10 QA02 QA07 QA14                       QA22 QA26 QA34 QA41 QA46                       RA05 RA12 RA13 RA36 RA42                       RA44 SA14 SA16 SA19 SA62                       SA63 SA64 SA74 SB05 SB15                       SB16 SB22 UA01

Claims (7)

[Claims] 1. A zoom lens, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. And, when changing from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group decreases, and the second lens group and the third lens group And the second lens group has a first positive lens, a negative lens, a negative meniscus lens having a concave surface facing the image plane side, and a second positive lens in this order from the object side. However, there is an air gap between the negative meniscus lens and the second positive lens. 2. The zoom lens according to claim 1, wherein the second lens group includes the first positive lens, the negative lens, the negative meniscus lens, and the second positive lens. Zoom lens to do. 3. The zoom lens according to claim 1, wherein the negative meniscus lens and the second lens of the second lens group are included.
The focal length of the air lens between the positive lens and the positive lens is f _2A , the focal length of the third lens unit is f ₃ , the sum of the axial core thicknesses of the second lens unit is Σ _2d , and the total focal length at the telephoto end. Let f _{T be} the axial distance between the negative meniscus lens and the second positive lens be d _2A , and the total length from the first lens group to the in-focus position at the telephoto end be L _T. The zoom lens is characterized in that 4. The zoom lens according to claim 3, wherein: The zoom lens is characterized in that 5. The zoom lens according to claim 1, wherein the first lens group and the second lens group are composed of spherical lenses only, and the third lens group is an aspherical surface. A zoom lens having only one lens. 6. The zoom lens according to claim 5, wherein the third lens group is the aspherical lens. 7. The zoom lens according to claim 5, wherein the aspherical lens is made of resin.