JP3301815B2 - 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 zoom lens.

[0002]

2. Description of the Related Art In recent years, a lens-mounted compact camera equipped with a zoom lens has become widespread as a photographing lens.

Further, a camera capable of performing pseudo panoramic photographing in which the upper and lower portions of a Leica format screen are cut has been commercialized, and it is desired that the zoom lens be further widened.

A wide-angle zoom lens of this kind is disclosed in, for example, Japanese Patent Application Laid-Open No. 3-204608 or Japanese Patent Application Laid-open No. 3-2.
As described in Japanese Patent No. 40013, almost all are positive component leading two-group zoom lenses.

However, the configuration described in Japanese Patent Application Laid-Open No. 3-204608 has a relatively large number of lens elements of eight, and a variable magnification ratio of about 1.7 times.

The configuration described in Japanese Patent Application Laid-Open No. Hei 3-240013 has a high zoom ratio of about 2.4 times, but has a large number of lens elements of eleven.

For these reasons, it is desired to reduce the number of lens components together with a high zoom ratio.

In response to the demand for reducing the number of lens components together with these high zoom ratios, for example, Japanese Patent Laid-Open No.
As described in JP-A-200913, JP-A-3-274516 or JP-A-4-178608, there is an image sensor in which the number of lens components is reduced by employing an aspherical lens. In particular, Japanese Patent Application Laid-Open
Japanese Patent Application Laid-Open No. 274516/1992 and Japanese Patent Application Laid-Open No. 4-178608 realize a wide angle with a small number of four lenses by using a plurality of aspherical lenses.

[0009] However, aspherical lenses are generally made by glass molding. However, glass molding is more expensive than spherical lenses with current technology, including running costs. In addition, aspheric lenses
Optical axis decentering has a greater effect on optical performance than a general spherical lens. Therefore, the use of a plurality of aspherical lenses causes a significant increase in manufacturing costs.

By the way, in recent years, with the progress of photosensitive materials,
High-sensitivity, high-resolution films have become widespread, and the ISO film speed of common-use films for compact cameras has become 400. For this reason, it has become possible to sufficiently shoot with a lens having a small aperture ratio.

On the other hand, the two-unit zoom lens preceding the positive component is composed of a first positive lens unit having a positive refractive power and a second negative lens unit having a negative refractive power. Magnification is performed by changing the relative distance between the group and the second negative lens group. However, since the first positive lens group has a stop, the diameter of the entrance pupil generally varies during magnification. In particular, it has more brightness than necessary for general shooting at the wide-angle end.

[0012]

As described above, in this type of zoom lens, it is desired to further reduce the size of the zoom lens by increasing the angle of view and reducing the number of lens components. Despite the fact that the aperture ratio of the lens can be reduced by improving the sensitivity, there is room for improvement in reducing the overall size, such as having more brightness than necessary for shooting at the wide-angle end.

An object of the present invention is to change the aperture diameter by changing the magnification and to secure the minimum necessary aperture ratio in the entire zooming range, thereby achieving a wider angle of view, and at the same time, making it inexpensive and compact. It is to provide a zoom lens that can be used.

[0014]

A zoom lens according to the present invention comprises a first positive lens group having a positive refractive power and a second negative lens group having a negative refractive power which are sequentially arranged from the object side. In a zoom lens that performs zooming by relatively changing the distance between the first positive lens group and the second negative lens group, the first positive lens group is arranged on the object side, which is sequentially arranged from the object side. The first negative meniscus lens having a concave surface, the second positive lens having a convex surface having a larger curvature than the image side on the object side, a third negative lens, and a fourth positive lens, wherein the second negative lens group has a convex surface on the image side. A first positive meniscus lens and a second negative meniscus lens having a concave surface on the object side.
Is formed by a spherical surface having a radius of curvature, lens thickness of the first positive lens group D1, and the sum of the distance between the lenses,
fw is the focal length of the entire system at the wide-angle end, and f1 is the first focal length.
The focal length of the positive lens group, fG4, is the focal length of the fourth positive lens in the first positive lens group, and R1 is the object-side radius of curvature of the first negative meniscus lens in the first positive lens group, n1 Is the refractive index at the d-line of the first negative meniscus lens in the first positive lens group, and ν2 is the Abbe number of the second positive lens in the first positive lens group.
D1 / fw <0.75, 0.7 <f1 / fw <0.8
5, 0.5 <fG4 / fw <0.65, 0.6 <fw (n
1-1) / | R1 | <1.1 and v2 <40.

[0015]

According to the present invention, a wide angle of view exceeding 70 ° at the wide-angle end can be obtained with a small number of lens components, and good imaging performance can be obtained. Here, each conditional expression will be described.

First, 0.5 <D ₁ /fw<0.75
Conditional expression for making the lens system compact, D ₁ /
When fw ≧ 0.75, that is, when the total length of the first positive lens unit is long, the refractive power of each lens element is weakened, which is advantageous for aberration correction. However, the entrance pupil is far away, the front lens diameter is increased, and the lens system is large. Become Conversely, when 0.5 ≧ D ₁ / fw, the refractive power of each element in the first positive lens unit increases, and the fluctuation of spherical aberration and curvature of field due to zooming increases.

Also, 0.7 <f ₁ /fw<0.85
A conditional expression for achieving a compact lens system and ensuring a back focus at the wide-angle end, where f ₁ / fw ≧
When the value is 0.85, the lateral magnification of the second negative lens unit decreases, and the amount of movement of each of the first positive lens unit and the second negative lens unit during zooming increases, resulting in an increase in the size of the lens system. Further, it becomes difficult to sufficiently secure the back focus at the wide-angle end. On the other hand, when 0.7 ≧ f ₁ / fw, the refractive power of the first positive lens unit is increased, and the fluctuation of coma aberration particularly due to zooming becomes large, and the field curvature is insufficiently corrected over the entire zooming range. Becomes

Further, 0.5 <f _G4 /fw<0.65
Is a conditional expression regarding power distribution in the first positive lens unit,
0.7 <f ₁ /fw<0.85, and f _G4 / fw ≧
At 0.65, the refractive power of each element in the first positive lens group is weakened, which is advantageous for aberration correction. However, the image-side principal point of the first positive lens group moves forward, and at the telephoto end, It becomes difficult to secure the interval between the first positive lens unit and the second negative lens unit. On the other hand, when 0.5 ≧ f _G4 / fw, when the third positive lens and the fourth negative lens in the first positive lens group
The refractive power of the positive lens increases, and the fluctuation of spherical aberration, curvature of field, and coma due to zooming increases, making it difficult to correct the entire zooming range in a well-balanced manner.

Then, 0.6 <fw (n ₁ -1) / | R
₁ | <1.1 is a conditional expression relating to the correction of distortion occurring in a wide-angle range, and specifies the curvature of the object-side surface of the first negative meniscus lens in the first positive lens group, and reduces the negative distortion. By causing this, the positive distortion generated in the second negative lens group is canceled and corrected with good balance. For this reason, fw
When (n ₁ -1) / | R ₁ | ≧ 1.1, distortion generated on the object side of the first negative meniscus lens decreases, and positive distortion increases in a wide-angle range, which is not preferable. Conversely, when 0.6 <fw (n ₁ -1) / | R ₁ |, the curvature of both surfaces of the first negative meniscus lens becomes large, and the fluctuation of astigmatism particularly during zooming becomes large.

Ν ₂ <40 is a conditional expression relating to correction of chromatic aberration of magnification, and is set so as to cancel out chromatic aberration of magnification which is excessively corrected by the second negative lens unit. ν ₂ ≧
At 40, the chromatic aberration of magnification changes from undercorrection to overcorrection during zooming from the wide-angle range to the telephoto range.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the zoom lens according to the present invention will be described below with reference to the drawings.

First, as shown in FIG. 1, the zoom lens shown in the first embodiment has a first positive lens group 1 having a positive refractive power, which is sequentially arranged from an object side (not shown), and a negative refractive power. The second negative lens group 2 has the following configuration. The magnification is changed by relatively changing the distance between the first positive lens group 1 and the second negative lens group 2. The first positive lens group 1 includes a first negative meniscus lens 11 having a concave surface on the object side and a convex surface having a larger curvature on the object side, that is, having a larger curvature on the object side than the image side.
The lens comprises a second positive lens 12, a third negative lens 13, and a fourth positive lens 14, each having a sharp convex surface . An aperture surface 15 is provided between the third negative lens 13 and the fourth positive lens 14. Further, the second negative lens group 2 includes a first positive meniscus lens 21 having a convex surface on the image side and a second negative meniscus lens 22 having a concave surface on the object side.

Then, numerical values of respective parts are set as shown in Table 1, and various aberrations are set as shown in FIGS.

Note that d indicates a d-line, g indicates a g-line, S indicates a sagittal image plane, and M indicates a meridional image plane.

Further, r is the radius of curvature of each lens surface, d is the lens thickness or lens surface interval, nd is the refractive index of the lens, and νd is the Abbe number of the lens.

In addition, 1: 8.2, f = 28.8-40.
9-58.2, 2w = 72.7 ° -56.5 ° -41.
4 °.

[0027]

[Table 1] According to the above numerical relationships, the values in the respective conditional expressions are as follows, and all satisfy the respective conditional expressions.

D ₁ /fw=0.599 f ₁ /fw=0.755 f _G4 /fw=0.590 fw (n ₁ −1) / | R ₁ | = 0.988 ν ₂ = 35.5 The spherical aberration, astigmatism, and distortion in the first embodiment are shown in FIGS.
8, f = 40.9 and f = 58.2 are shown.

Next, a second embodiment will be described with reference to FIG.

The second embodiment shown in FIG. 5 has the same configuration as the lens configuration of the first embodiment shown in FIG.

Note that 1: 8.2, f = 28.8-40.
9-58.2, 2w = 72.7 ° -56.4 ° -41.
4 °.

[0032]

[Table 2] According to the above numerical relationships, the values in the respective conditional expressions are as follows, and all satisfy the respective conditional expressions.

D ₁ /fw=0.626 f ₁ /fw=0.799 f _G4 /fw=0.556 fw (n ₁ −1) / | R ₁ | = 0.997 v ₂ = 32.2 The spherical aberration, astigmatism, and distortion in the second embodiment are shown in FIGS.
8, f = 40.9 and f = 58.2 are shown.

Next, a third embodiment will be described with reference to FIG.

The third embodiment shown in FIG. 9 has the same configuration as the lens configuration of the first embodiment shown in FIG.

Note that 1: 8.2, f = 28.8-40.
9-58.2, 2w = 72.7 ° -56.4 ° -41.
4 °.

[0037]

[Table 3] According to the above numerical relationships, the values in the respective conditional expressions are as follows, and all satisfy the respective conditional expressions.

D ₁ /fw=0.652 f ₁ /fw=0.754 f _G4 /fw=0.590 fw (n ₁ -1) / | R ₁ | = 0.768 v ₂ = 36.3 The spherical aberration, astigmatism, and distortion in the third embodiment are shown by the focal length f = 2 according to FIGS.
8.8, f = 40.9, and f = 58.2 are shown.

Here, each embodiment satisfies the respective conditional expressions, so that various aberrations are corrected in a well-balanced manner.

[0040]

According to the zoom lens of the present invention, it is possible to further increase the angle of view with a small number of lens components, and it is not necessary to use an aspherical lens .

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a zoom lens according to a first embodiment of the present invention at the wide-angle end.

FIG. 2 is a characteristic diagram showing various aberrations of the first embodiment at f = 28.8.

FIG. 3 is a characteristic diagram showing various aberrations of the first embodiment at f = 40.9.

FIG. 4 is a characteristic diagram showing various aberrations at f = 58.2 in the first embodiment.

FIG. 5 is an explanatory diagram showing a lens at a wide-angle end according to the second embodiment.

FIG. 6 is a characteristic diagram showing various aberrations at f = 28.8 in the second embodiment.

FIG. 7 is a characteristic diagram showing various aberrations of the second embodiment at f = 40.9.

FIG. 8 is a characteristic diagram showing various aberrations at f = 58.2 in the second embodiment.

FIG. 9 is an explanatory diagram showing a lens at the wide-angle end according to the third embodiment.

FIG. 10 is a characteristic diagram showing various aberrations of the third embodiment at f = 28.8.

FIG. 11 is a characteristic diagram showing various aberrations at f = 40.9 in the third embodiment.

FIG. 12 is a characteristic diagram showing various aberrations at f = 58.2 in the third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st positive lens group 2 2nd negative lens group 11 1st negative meniscus lens 12 2nd positive lens 13 3rd negative lens 14 4th positive lens 21 1st positive meniscus lens 22 2nd negative meniscus lens

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (1)

(57) [Claims] 1. A first positive lens group having a positive refractive power and a second negative lens group having a negative refractive power, which are sequentially arranged from the object side, wherein the first positive lens group and the second negative lens group are arranged. In a zoom lens that performs zooming by relatively changing the distance between lens groups, the first positive lens group is a first negative meniscus lens that is sequentially arranged from the object side and concave on the object side, Image side
A second positive lens having a convex surface with a large curvature, a third negative lens, and a fourth positive lens. The second negative lens group includes a first positive meniscus lens convex on the image side and a concave positive lens on the object side. 2. Each of the lenses has a predetermined radius of curvature on the object side and the image side.
Is formed by a spherical surface having the lens thickness of the first positive lens group D1, and the sum of the distance between the lenses, the focal length of the entire system and fw at the wide-angle end, said f1 the focal length of the first positive lens group, the fG4 The focal length of the fourth positive lens in the first positive lens group, R1 is the radius of curvature of the first negative meniscus lens in the first positive lens group on the object side, and n1 is the radius of curvature in the first positive lens group. When the refractive index at the d-line of the first negative meniscus lens, ν2, is the Abbe number of the second positive lens in the first positive lens group, 0.5 <D1 / fw <0.7
5, 0.7 <f1 / fw <0.85, 0.5 <fG4 / fw <0.65, 0.6 <fw (n1-1) / | R1 | <1.1, .nu.2 <40 A zoom lens characterized in that: