JPH0980308A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens which never impairs its optical performance although the lens is compact. SOLUTION: The zoom lens consists of a 1st lens group Gr1 with positive refracting power and a 2nd lens group Gr2 with negative refracting power in order from an object side and varies in power from the wide-angle end to the telephoto end by narrowing down the interval between the 1st lens group Gr1 and 2nd lens group Gr2, and the 1st lens group Gr1 consists of a 1st lens L1, a 2nd lens L2 with negative refracting power, and a 3rd lens L3 with positive refracting power and satisfies a conditional expression 0.15<ϕ1×23<0.25. Here, ϕ1 is the refracting power of the 1st lens group and T23 is the air space between the 2nd lens and 3rd lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to a zoom lens suitable as a photographing lens for a lens shutter camera.

[0002]

2. Description of the Related Art Conventionally, there has been a demand for a compact zoom lens as a photographing lens for a lens shutter camera. As such a compact zoom lens,
From the object side, various zoom lenses including a first lens group having a positive refractive power and a second lens group having a negative refractive power have been proposed.

[0003]

However, in the zoom lens having the two-group structure, it is impossible to satisfactorily correct lateral chromatic aberration and distortion while ensuring a lens back necessary as a camera taking lens, especially at the wide-angle end. There was a problem. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a zoom lens that is compact and does not impair optical performance.

[0004]

In order to achieve the above object, in the zoom lens according to the present invention, in order from the object side,
It is composed of a first lens group having a positive refracting power and a second lens group having a negative refracting power. By narrowing the distance between the first lens group and the second lens group, from the wide-angle end to the telephoto end. In the zoom lens for performing zooming, the first lens group includes a first lens, a second lens having a negative refractive power, and a third lens having a positive refractive power. It is characterized by satisfying the formula. 0.15 <φ1 × T23 <0.25 (1) Further, in the zoom lens according to claim 2, in the zoom lens according to claim 1, the first lens is not formed on at least one surface. It is characterized by being a plastic lens having a spherical surface.

A zoom lens according to a third aspect is the zoom lens according to the first aspect, wherein the first lens has a negative refracting power.

[0006]

EXAMPLES Examples of zoom lenses according to the present invention will be shown below. However, in each embodiment, ri (i = 1, 2,
3. . . ) Is the radius of curvature of the i-th surface counted from the object side,
di (i = 1, 2, 3 ...) Indicates the i-th axial upper surface distance counted from the object side, and Ni (i = 1, 2,
3. . . ), Νi (i = 1, 2, 3 ...) Indicates the refractive index and Abbe number of the i-th lens from the object side for the d-line. The values of the axial distance d7 between the first lens group and the second lens group, the focal length f of the entire system, and the F number Fno are
It corresponds to the wide-angle end (W), the intermediate focal length (M), and the telephoto end (T) in order from the left. Further, the surface having the value of the radius of curvature written as INF indicates that it is a plane perpendicular to the optical axis (the radius of curvature is infinite).

In each of the examples, the surface with the radius of curvature marked with * indicates that it is a surface composed of an aspherical surface, and is defined by the following formula (A) representing the surface shape of the aspherical surface. It shall be. X = C · Y ² / {1 + √ (1-ε · Y ² · C ² )} + ΣAi · Yi (A) where, X: displacement from the reference plane in the optical axis direction, Y : Height in a direction perpendicular to the optical axis, C: reference curvature of an aspherical surface, ε: quadric surface parameter, Ai (i = 1, 2, 3 ...): aspherical coefficient, Yi (i = 1, 2, 1) , 3 ...): Y-th power of i. The letter E attached to the numerical value indicating the aspherical coefficient corresponds to the exponent part of each coefficient, for example, 1.0 × 1.
If it is 0E02, it means 1.0 × 10 ² .

[0008]

[Table 1]

[0009]

[Table 2]

[0010]

[Table 3]

FIGS. 1 to 3 are lens configuration diagrams corresponding to the first to third embodiments, showing the lens arrangement at the wide-angle end (W). The arrows m1 and m2 in FIGS. 1 to 3 indicate the first lens group (Gr1) and the second lens group (Gr2), respectively.
The movement from the wide-angle end (W) to the telephoto end (T) is schematically shown.

The zoom lens of each embodiment has, in order from the object side, a meniscus-shaped first lens L1 having a convex surface facing the object side (object-side surface is an aspherical surface), and negative refraction having a convex surface facing the object side. It has a meniscus-shaped second lens L2 having a power, a biconvex third lens L3 having a positive refractive power, a first lens group Gr1 including a diaphragm A, and a positive refractive power having a convex surface directed toward the image side. It is composed of a fourth lens L4 having a meniscus shape (a surface on the object side is an aspherical surface), and a second lens group Gr2 having a fifth lens L5 having a negative refractive power and having a concave surface facing the object side. . Of these, the first lens L1 has a negative meniscus shape in the first and third embodiments.
In Example 2, the shape is a positive meniscus shape. In each embodiment, the first lens L1 and the fourth lens L4 are lenses made of plastic.

In the zoom lens of each embodiment, the first lens group Gr1 has, in order from the object side, a first lens L1 that does not exert a strong refracting effect on a light beam that passes therethrough, a second lens L2 that has a negative refracting power, and a positive lens. The third lens L3 having a refractive power of By adopting such a configuration, the arrangement of the refracting power of the entire system becomes similar to that of the retrofocus type lens arrangement, so that the lens back at the wide-angle end is secured. Accordingly, the second lens group Gr2
The outer diameter of the lens can be reduced, and the entire system can be made compact. In addition, by using the first lens L1 having a weak refractive power as a negative lens, it is possible to further resemble a retrofocus type lens arrangement, and it is effective to secure a lens back at the wide-angle end. .

Further, the zoom lens of each embodiment satisfies the following conditional expression (1). 0.15 <φ1 × T23 <0.25 (1) where φ1 is the refracting power of the first lens group, and T23 is the air gap between the second lens and the third lens.

Conditional expression (1) is the second lens of the first lens group Gr1.
The air gap between the lens L2 and the third lens L3 is a condition to be satisfied, and relates to correction of lateral chromatic aberration and distortion. If the lower limit of conditional expression (1) is exceeded, the negative lens and the positive lens will come too close to each other, making it difficult to correct distortion. Conversely, conditional expression (1)
When the upper limit of the above is exceeded, the refractive power of the negative lens in the first lens group becomes large, and it becomes difficult to correct lateral chromatic aberration in particular.

Further, in the zoom lens of the embodiment, the first lens L1 of the first lens group Gr1 is a plastic lens having an aspherical surface on the object side. Generally, in the lens arranged closest to the object side, as compared with, for example, a lens arranged in the vicinity of a diaphragm, a light ray incident on an arbitrary point on the lens surface passes through various optical paths according to the change in the angle of view. . Further, this optical path depends on the surface shape of the lens arranged closest to the object side. Therefore, the optical path can be largely changed by changing the lens surface shape of the lens arranged closest to the object side. Therefore, by providing at least one aspherical surface in the first lens L1, it is possible to effectively correct spherical aberration and off-axis coma. Further, by using the plastic lens for the first lens L1 having an aspherical surface, it is possible to reduce the cost as compared with the case where the glass lens has an aspherical surface.

Further, the zoom lenses of the examples satisfy the following conditional expressions (2) and (3). -0.4 <fT × φL1 <0.4 ····· (2) -2.5 <φL1 × fT 2 × (βT-βW) / FnT + φL4 × fT 2 /FnT<2.5 ···· (3) where φL1: refractive power of the first lens L1, fT: focal length of the entire system at the telephoto end (T), βT: magnification of the second lens group at the telephoto end (T), βW: wide angle Magnification of the second lens unit at the end (W), FnT: F number at the telephoto end (T), φL4: Refracting power of the fourth lens L4.

Conditional expressions (2) and (3) represent conditions when plastic lenses are used for the first lens L1 in the first lens group Gr1 and the fourth lens L4 in the second lens group Gr2, It relates to changes in the focal position of the entire system due to changes in temperature.

Conditional expression (2) defines the refractive power of the first lens L1 which is a plastic lens in the first lens group Gr1. If the upper limit of conditional expression (2) is exceeded, the refractive power of the first lens L1 in the first lens group Gr1 will fluctuate due to temperature changes, and as a result, the focal position of the entire system will change significantly toward the image side. If the lower limit is exceeded, on the other hand, if the lower limit is exceeded, similarly, the focal position of the entire system largely changes toward the object side due to fluctuations in the refractive power of the first lens L1, and stable performance cannot be obtained.

Conditional expression (3) defines the relationship between each parameter of the plastic lens L4 in the second lens group Gr2 and the refractive power. If the upper limit of conditional expression (2) is exceeded, the refracting power of the fourth lens L4 in the second lens group Gr2 will fluctuate due to temperature changes, and as a result, the focal position of the entire system will change significantly toward the image side. , Stable performance cannot be obtained. On the other hand, when the value goes below the lower limit, the focal position of the entire system largely changes toward the object side due to the fluctuation of the refractive power of the fourth lens L4, and stable performance cannot be obtained.

Examples 1 to 3 according to the present invention are conditional expressions
Satisfies (1) to (3). The following table shows the values corresponding to the conditional expressions (1) to (3) in each example. However, T23 in the table
Corresponds to d4.

[0022]

[Table 4]

4 to 6 show the first to third embodiments, respectively.
FIG. 9 is an aberration diagram corresponding to FIG. In each figure, (W) shows the aberration at the wide-angle end (short focal end) focal length, (M) shows the intermediate focal length state (middle), and (T) shows the aberration at the telephoto end (long focal end) focal length. . Also, the solid line (d) represents the aberration for the d line, and the broken line (SC) represents the sine condition. Further broken line (DM)
And solid line (DS) represent astigmatism on the meridional surface and the sagittal surface, respectively.

[0024]

As described above, according to the present invention,
It is possible to provide a zoom lens that is compact and low in cost, but that does not impair optical performance.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a first embodiment of the present invention.

FIG. 2 is a lens configuration diagram of a second embodiment of the present invention.

FIG. 3 is a lens configuration diagram of Example 3 of the present invention.

FIG. 4 is an aberration diagram of Example 1 of the present invention.

FIG. 5 is an aberration diagram of Example 2 of the present invention.

FIG. 6 is an aberration diagram of Example 3 of the present invention.

[Explanation of symbols]

 Gr1: Positive lens group Gr2: Negative lens group L1: First lens L2: Second lens L3: Third lens L4: Fourth lens L5: Fifth lens

Claims (3)

[Claims] 1. A space between the first lens group and the second lens group, which comprises, in order from the object side, a first lens group having a positive refractive power and a second lens group having a negative refractive power. Is a zoom lens that performs zooming from the wide-angle end to the telephoto end by narrowing the lens, wherein the first lens group has a first lens, a second lens having a negative refractive power, and a positive refractive power. A zoom lens comprising a third lens and satisfying the following conditional expression: 0.15 <φ1 × T23 <0.25 where φ1: the refractive power of the first lens group, T23: the first lens group The air gap between two lenses and the third lens. 2. The zoom lens according to claim 1, wherein the first lens is a plastic lens having at least one aspherical surface. 3. The zoom lens according to claim 1, wherein the first lens has a negative refractive power.