JPH07287167A - Zoom lens with high power variation rate - Google Patents

Abstract

PURPOSE:To obtain a zoom lens small in size and in image forming performance by employing four-group constitution and satisfying specific conditions. CONSTITUTION:This zoom lens consists of a 1st negative lens group G1, a 2nd positive lens group G2, a 3rd negative lens group G3, and a 4th positive lens group G4 and a stop S is positioned between the 2nd lens group G2 and 3rd lens group G3 and moves together with the 3rd lens group G3 in one body at the time of zooming. Then -0.45<f1/fT<-0.15, 0.2<f4/fT<0.35, -4.0<B2T<-1.6, etc., are satisfied, where f1 is the focal length of the 1st lens group, f4 is the focal length of the 4th lens group, and B2T is the image formation power of the 2nd lens group at the telephoto end. Consequently, the field angle at the wide-angle end is >=80 deg., a>=X4 power variation rate is obtained, and the image forming performance is superior.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens having a high zoom ratio suitable for single-lens reflex cameras, compact cameras, video cameras, etc. The present invention relates to a high variable power zoom lens having a ratio.

[0002]

2. Description of the Related Art Conventionally, a wide angle of view of about 70 ° is included,
Many zoom lenses having a zoom ratio of about 3 have been proposed, most of which have a negative first lens group, a positive second lens group, a negative third lens group, and a positive fourth lens group. Is. By arranging the negative lens group closest to the object side, it is possible to widen the angle of view, and by forming the four-group structure, the degree of freedom of aberration correction is secured and high zooming is possible. As an example of such a zoom lens, Japanese Patent Application Laid-Open No. 62-6390
There is No. 9 publication.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention JP-A-62-6390
The angle of view at the wide-angle end of the zoom lens proposed in Japanese Patent No. 9 is about 70 °, and the zoom ratio is about 3 times. However, in recent years, as a standard zoom lens for a single-lens reflex camera, there is an increasing demand for a wider angle and a higher zoom ratio, and the zoom lens proposed in Japanese Patent Laid-Open No. 62-63909 is sufficient for this requirement. I couldn't answer.

In response to the demand for such a wide angle, Japanese Patent Laid-Open No.
Japanese Patent Laid-Open No. 173071 proposes a zoom lens including a wide angle of view of 80 ° or more, but the zoom ratio is as small as 2 times or less, and it has not been possible to meet the demand for high zooming. Further, in response to a request for high zoom ratio, Japanese Patent Application Laid-Open No. 5-31
Japanese Patent No. 3065 proposes a zoom lens having a zoom ratio of more than 4 times, but the angle of view at the wide-angle end is about 70 °, which does not sufficiently meet the requirement for widening.

The object of the present invention is to obtain a field angle of 80 ° at the wide-angle end.
As described above, it is to provide a zoom lens having a zoom ratio of 4 times or more, a smaller size, and excellent image forming performance.

[0006]

To achieve the above object, in a zoom lens according to the present invention, a first lens group having a negative refractive power and a second lens group having a positive refractive power are arranged in order from the object side. And a third lens group having a negative refracting power and a fourth lens group having a positive refracting power, and reducing an air gap between the first lens group and the second lens group, A zoom lens for performing zooming from a wide-angle end to a telephoto end by expanding an air space between a lens group and the third lens group and reducing an air space between the third lens group and the fourth lens group. , The focal length of the zoom lens at the telephoto end is fT, the focal length of the first lens unit is f1, the focal length of the fourth lens unit is f4, and the second distance at the telephoto end is
When the image forming magnification of the lens unit is B2T, the following conditions are satisfied.

−0.45 <f1 / fT <−0.15 0.2 <f4 / fT <0.35−4.0 <B2T <−1.6

[0008]

In the zoom lens having the negative first lens group, the positive second lens group, the negative third lens group, and the positive fourth lens group, the positive second lens group and the negative second lens group at the wide angle end are used. The distance between the third lens group is narrowed, the distance between the negative third lens group and the positive fourth lens group is widened, and the composite principal point from the second lens group to the fourth lens group is relatively shifted to the image plane. On the contrary, at the telephoto end, the distance between the positive second lens group and the negative third lens group is widened, and the distance between the negative third lens group and the positive fourth lens group is narrowed. By locating the composite principal point from the lens group to the fourth lens group relatively to the object, the negative principal point of the first lens group and the fourth principal point of the second lens group
It is possible to increase the change in the distance from the synthetic principal point to the lens group, and it is possible to achieve high zooming.

Further, by changing the distances between the second lens group and the third lens group and between the third lens group and the fourth lens group in this way, the curvature of field is favorably corrected from the wide-angle end to the telephoto end. It is possible to obtain good imaging performance even when a high zoom ratio is achieved. In the above configuration, the present invention has found the following conditional expressions (1) to (3) in order to achieve high zooming and widening of the zoom lens at the same time.

(1) -0.45 <f1 / fT
<-0.15 (2) 0.2 <f4 / fT <0.35 (3) -4.0 <B2T <-1.6 where fT is the focal length at the telephoto end of the zoom lens, f1
Is the focal length of the first lens group, f4 is the focal length of the fourth lens group, and B2T is the imaging magnification of the second lens group at the telephoto end.

Conditional expression (1) defines the optimum range of the focal length of the first lens group. When the lower limit of conditional expression (1) is exceeded, the negative refractive power of the first lens group becomes small, and it becomes difficult to obtain a high zoom ratio. On the other hand, if the upper limit of conditional expression (1) is exceeded, the negative refracting power of the first lens group will increase, and the negative distortion at the wide-angle end that occurs in the first lens group will become excessive, and in particular widening of the angle of view will occur. It becomes difficult to correct when trying.

Conditional expression (2) defines the optimum range of the focal length of the fourth lens group. When the upper limit of conditional expression (2) is exceeded, the positive refractive power of the fourth lens unit becomes small, and the back focus at the wide-angle end becomes small. As a result, 1
In a zoom lens for an eye reflex camera, it interferes with a mirror, and in a compact camera or the like having less restrictions on back focus, the lens diameter of the fourth lens group becomes large, which is a problem against miniaturization. On the other hand, when the value goes below the lower limit of the conditional expression (2), the positive refractive power of the fourth lens group becomes excessive, and it becomes necessary to complicate the configuration of the fourth lens group for aberration correction. Therefore, the total length of the zoom lens becomes large, which is against the downsizing.

Conditional expression (3) defines an optimum range of the imaging magnification of the second lens group at the telephoto end. If the lower limit of conditional expression (3) is exceeded, the imaging magnification of the second lens group will increase, and the various aberrations that occur in the first lens group will increase, so that the various aberrations that occur in the first lens group will be kept extremely small. It is not preferable because the first lens group becomes complicated and the size of the first lens group becomes large. On the other hand, if the upper limit of conditional expression (3) is exceeded, the total length of the zoom lens at the wide-angle end (the distance from the lens surface closest to the object side to the lens surface closest to the image side) and the first
The increase in the effective diameter of the lens group is contrary to the miniaturization.

As more preferable conditions, the following conditional expressions (4) to (6) have been found. (4) -0.30 <f3 / fT <-0.
15 (5) 2.8 <B2T / B2W <6.0 (6) -3.0 <Δe2 / Δe3 <-
0.9 where f3: focal length of the third lens group, B2W
: Imaging magnification of the second lens group at the wide-angle end, Δe
2: The second lens at the telephoto end and the wide-angle end of the zoom lens
Δe3: difference in distance between the lens and the third lens group, Δe3: difference in distance between the third lens and the fourth lens group at the telephoto end and the wide-angle end of the zoom lens, conditional expression (4) is the focal point of the third lens group. It defines an appropriate range of distances. When the lower limit of conditional expression (4) is exceeded, the negative refractive power of the third lens group becomes small, and the change in the position of the combined principal point from the second lens group to the fourth lens group during zooming becomes small, resulting in a high variation. It is difficult to double. On the other hand, if the upper limit of conditional expression (4) is exceeded, the negative refractive power of the third lens group will become large, and the total length of the zoom lens will become large, which is contrary to downsizing.

Conditional expression (5) defines an appropriate range of the ratio of the imaging magnification of the second lens group at the telephoto end and the wide-angle end. If the upper limit of conditional expression (5) is exceeded, the change in the imaging magnification of the second lens group will become large, and the changes in various aberrations due to zooming, especially the changes in spherical aberration and coma will become large, making correction difficult. . On the other hand, when the value goes below the lower limit of the conditional expression (5), the change in the image forming magnification of the second lens group becomes small and it becomes difficult to achieve a high zoom ratio.

Conditional expression (6) defines an appropriate range of the ratio of the change in the distance between the second lens group and the third lens group and the change in the distance between the third lens group and the fourth lens group due to zooming. There is. If the lower limit of conditional expression (6) is exceeded, the change in the distance between the third lens group and the fourth lens group becomes relatively small, and it becomes difficult to correct the fluctuation of the field curvature due to zooming, which is not preferable. If the upper limit of conditional expression (6) is exceeded, the second
The change in the distance between the lens group and the third lens group becomes relatively small, which undesirably increases the effective diameter and diaphragm diameter of the third lens group at the telephoto end. In order to reduce the aperture diameter, it is more desirable to set the upper limit of conditional expression (6) to -1.2.

Further, in order to achieve both compactness of the zoom lens and excellent aberration correction, it is desirable to provide an aspherical surface in the first lens group. At that time, it is desirable to have an aspherical shape such that the negative refractive power becomes smaller toward the periphery. Further, in order to correct well-balanced spherical aberration and distortion that tend to occur in the fourth lens group, it is desirable to provide an aspherical surface in the fourth lens group. At that time, it is desirable that an aspherical surface is provided on the boundary surface with the air, and the aspherical shape is such that the positive refractive power becomes smaller toward the peripheral portion.

[0018]

EXAMPLE 1 FIG. 1 is a lens configuration diagram of Example 1 of the present invention. Examples according to the present invention will be described below. In the first embodiment, as shown in FIG. 1, the negative first lens group G1
Is a biconcave negative lens whose image side surface is aspherical, and a cemented lens of a biconvex positive lens and a biconcave negative lens in order from the object side. The positive second lens group G2 is, in order from the object side, an object side. The negative third lens group G3 is composed of a cemented lens of a negative meniscus lens with a convex surface facing to and a biconvex positive lens, a cemented lens of a biconvex positive lens and a biconcave negative lens, and a biconvex positive lens.
The positive fourth lens group G includes, in order from the object side, a cemented lens of a positive meniscus lens having a concave surface facing the object side and a biconcave negative lens, and a negative meniscus lens having a concave surface facing the object side.
4 is composed of, in order from the object side, a biconvex positive lens having an aspherical image side surface, and a cemented lens having a biconvex positive lens and a biconcave negative lens. Further, the diaphragm S includes the second lens group G2 and the third lens group G.
Located between 3 and the third lens group G3 for zooming.
Move together with.

The values of the specifications and the numerical values corresponding to the conditions of the embodiment of the present invention are listed below. In the specification table of the embodiment, f is the focal length, F is the F number, and 2ω is the angle of view. The leftmost number represents the order from the object side, r is the radius of curvature of the lens surface, d is the lens surface spacing, and n and ν are d lines (wavelength λ = 58
7.6 nm) and the Abbe number. The surface marked with * at the left end is an aspherical surface, and the aspherical shape is the distance along the optical axis from the tangent plane of the vertex of the aspherical surface at the height h in the vertical direction from the optical axis. X (h)
Where r is the paraxial radius of curvature, k is the conic constant, and Cn is the aspherical coefficient of degree n, then X (h) = (h ² / r) / [1+ (1-kh ² / r ² ).
^1/2] + C4 is expressed by ^{h 4 + C6 h 6 + C8} h 8 + C10h 10.

[0020]

[Table 1] Specifications of Example 1 f = 24.70 to 117.00 F = 3.63 to 5.74 2ω = 85.8 to 2
0.6 ° Second surface aspherical coefficient k = 1.000 C4 = -0.1019 × 10 ^-4 C6 = -0.7017 ×
10 ^-8 C8 = 0.7760 x 10 ^-11 C10 = -0.1534 x 10 ^-13 21st surface aspheric surface k = 1.000 C4 = 0.8640 x 10 ^-5 C6 = 0.2559 x 10 ^-7 C8 = -0.5444 x 10 ^-10 C10 = -0.6038 × 10 ^-13 Change in interval during zooming f 24.6998 48.9998 117.0017 D5 32.4458 11.2472 1.0000 D13 1.0000 9.7032 25.3695 D19 13.8542 7.4402 1.0000 Bf 38.1001 53.7971 96.0334 Condition corresponding numerical value (1) f1 / fT = -0.275 (2) f4 / FT = 0.286 (3) B2T = -2.535 (4) f3 / fT = -0.232 (5) B2T / B2W = 3.658 (6) Δe2 / Δe3 = -1.896 Figure 2 3 is a diagram of various types of aberration at the wide-angle end in Example 1, and FIG.
[Fig. 6A] is an aberration diagram of Example 1 in the intermediate focal length state,
FIG. 4 is a diagram of various types of aberration at the telephoto end of the first embodiment. In each aberration diagram, H is the incident ray height, Y is the image height, d is the d line (λ
= 587.6 nm) and g indicate the g-line (λ = 435.8 nm). In the astigmatism diagram, the dotted line indicates the meridional image plane and the solid line indicates the sagittal image plane.

From each aberration diagram, it is clear that various aberrations are satisfactorily corrected and that the embodiment of the present invention has excellent imaging performance.

[0022]

As described above, according to the present invention, the zoom lens having an angle of view at the wide-angle end of 80 ° or more, a zoom ratio of 4 × or more, a small size, and excellent image forming performance. Can be provided. Further, the image can be deflected by moving any one of the first to fourth lens groups or a part of the lens group in the direction perpendicular to the optical axis, and the image stabilizing optical system can be used. It can be applied to systems. Focusing is preferably performed by moving the first lens group, but it is also possible to perform focusing by moving the third lens group or the fourth lens group.

[Brief description of drawings]

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

FIG. 2 is a diagram of various types of aberration at the wide-angle end according to the first exemplary embodiment of the present invention.

FIG. 3 is a diagram of various types of aberration in an intermediate focal length state of Example 1 according to the present invention.

FIG. 4 is a diagram of various types of aberration at the telephoto end of Embodiment 1 according to the present invention.

[Explanation of the sign of the main part]

 G1 ・ ・ ・ First lens group G2 ・ ・ ・ Second lens group G3 ・ ・ ・ Third lens group G4 ・ ・ ・ Fourth lens group S ・ ・ ・ Aperture

Claims (6)

[Claims] 1. A first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a positive refractive power in order from the object side. A fourth lens group having an air gap between the first lens group and the second lens group is reduced, and an air gap between the second lens group and the third lens group is enlarged, In a zoom lens that performs zooming from the wide-angle end to the telephoto end by reducing the air space between the third lens unit and the fourth lens unit, the focal length of the zoom lens at the telephoto end is fT,
When the focal length of the lens unit is f1, the focal length of the fourth lens unit is f4, and the imaging magnification of the second lens unit at the telephoto end is B2T, the following conditions are satisfied: Magnification zoom lens. -0.45 <f1 / fT <-0.15 0.2 <f4 / fT <0.35 -4.0 <B2T <-1.6 2. The focal length of the third lens group is f
The high-variation-magnification zoom lens according to claim 1, wherein the following condition is satisfied when the value is 3. -0.30 <f3 / fT <-0.15 3. The high zoom ratio zoom lens according to claim 1, wherein the following condition is satisfied when the image forming magnification of the second lens group at the wide-angle end of the zoom lens is B2W. 2.8 <B2T / B2W <6.0 4. A difference in distance between the second lens group and the third lens group at the telephoto end and the wide-angle end of the zoom lens is Δe.
2. The high variable power zoom lens according to claim 1, wherein the following condition is satisfied, where Δe3 is a difference in distance between the third lens group and the fourth lens group. -3.0 <Δe2 / Δe3 <-0.9 5. The first lens group has at least one aspherical surface.
The high variable power zoom lens according to claim 1, further comprising a surface. 6. The high variable power zoom lens according to claim 1, wherein at least one aspherical surface is included in the fourth lens group.