JPH08106048A - Zoom lens - Google Patents

Abstract

PURPOSE: To provide a zoom lens having a wide viewing angle and a high variable power ratio by comprising four lens groups as a whole and properly setting the refractive powers of respective lens groups and the moving conditions of respective lens groups at the time of varying the power. CONSTITUTION: This zoom lens comprises, in order from the object side, four lens groups of a first group L1 of a negative refractive power, a second group L2 of a positive refractive power, a third group L3 of a negative refractive power and a fourth group L4 of a positive refractive power, the fluctuation of an image plane by the power variation is compensated by moving the first group L1 to the side of the image plane while plotting a projected locus, the second group L2 is moved so that an interval between the second group L2 and the first group L1 is decreased and the lens constitution of the fourth group L4 is properly set in the case of power variation from wide angle end to the telescopic end.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens suitable for a photographic camera for 35 mm film, a video camera of an electronic recording system, an SV camera, and the like. Has a lens group,
By appropriately setting the lens configuration of these four lens groups, the overall zoom ratio is reduced to 3.5-
The present invention relates to a negative lead type zoom lens having an F number of about 5.8 at the wide-angle end and a shooting angle of view of about 74 ° at the wide-angle end.

[0002]

2. Description of the Related Art A so-called negative lead type zoom lens in which a lens unit having a negative refracting power precedes has been conventionally used, because a close-up shooting distance is relatively short and a wide angle of view is relatively easy. It is often used in wide-angle zoom lenses having an angle of 70 ° or more. For example, Japanese Patent Publication Sho-49-239
No. 12, JP-A-57-163213, etc., the first group having negative refracting power and the second group having positive refracting power are arranged in this order from the object side.
It has four lens units, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power, and moves the first lens unit toward the image side when zooming from the wide-angle end to the telephoto end. , A zoom lens in which the second group and the fourth group are moved to the object side and the third group is fixed or moved is proposed.

A negative lead type zoom lens in which such a lens unit having a negative refracting power precedes has features that it is relatively easy to widen the angle of view and that the close-up distance is shortened. On the other hand, it has drawbacks such as an increased aperture diameter and difficulty in achieving a high zoom ratio.

Zoom lenses which have been improved in view of these drawbacks and have been made compact and have a high zoom ratio are disclosed in, for example, JP-A-55-14403, JP-A-57-11315, and JP-A-57-11315. 58-4113 and JP-A-58-58
It is proposed in Japanese Patent Publication No.-95315.

In each of these publications, a zoom lens is composed of four lens groups as a whole, in order from the object side, negative, positive, negative and positive, and a predetermined lens group is appropriately moved. I am changing the magnification.

[0006]

In recent years, a standard zoom lens used for a single-lens reflex camera, a video camera or the like is required to have a wide field angle and a high zoom ratio.
For example, in a single-lens reflex camera for 35 mm film, the focal length is 35 mm to 70 mm and the focal length is 28 mm to 80 mm.
A wide-angle zoom lens of about mm is used as a standard zoom lens.

More recently, the focal length is 28 mm to 105 m.
There is a demand for a zoom lens for standard use which has a zooming range of m or a focal length of 28 mm to 135 mm and which has a zooming range expanded to the telephoto side.

However, in general, at such a photographing field angle and at a high zoom ratio, the total lens length becomes long, and complicated zoom movement is required for zooming, resulting in a multiple lens barrel construction. There arises a problem that the lens barrel becomes large and complicated.

According to the present invention, the zoom lens is composed of four lens groups as a whole, and by appropriately setting the refracting power of each lens group and the moving conditions of each lens group due to zooming,
The objective of the present invention is to provide a zoom lens with a relatively wide angle of view, which shortens the overall lens length, prevents the lens barrel from becoming large and complicated, and has high optical performance over the entire zoom range with a high zoom ratio. To do.

[0010]

A zoom lens according to the present invention comprises, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, a third group having a negative refractive power, and a positive group. The fourth of refractive power
When the magnification is changed from the wide-angle end to the telephoto end, the first lens unit is moved while having a convex locus on the image surface side to reduce the image plane variation due to the magnification change. Correcting and moving the second group so that the distance between the second group and the first group becomes small,
The third group is moved so that the distance between the third group and the second group becomes large, and the fourth group is moved so that the distance between the fourth group and the third group becomes small, The fourth group has a positive refractive power group 41, a positive group 42, and a negative group 43,
The 41st group has a cemented lens in which a lens 41P and a negative lens 41N are cemented, and the cemented lens surface has a convex surface directed toward the image surface side, and the 43rd group has a meniscus whose convex surface faces the image surface side. Negative lens 43N, the refractive index and Abbe number of the material of the positive lens 41P are N41P and ν41P, and the refractive index and Abbe number of the material of the negative lens 41N are N41.
When N and ν41N, 25 <ν41P-ν41N <61 (1) 0.06 <N41N-N41P <0.36 (2) is satisfied.

[0011]

FIG. 1 is a numerical example 1 of the zoom lens of the present invention.
3 is a lens cross-sectional view of FIG. In the figure, (A) is the wide-angle end, (B)
Shows the middle and (C) shows the telephoto end. 2 and 3 are lens cross-sectional views at the wide-angle end of zoom lenses according to Numerical Embodiments 2 and 3 of the present invention.

1 to 3, L1 is a first group having a negative refracting power, L2 is a second group having a positive refracting power, L3 is a third group having a negative refracting power, and L4 is a positive refracting power. It is the fourth group. L41 is the 41st group of positive refractive power, L42 is the 42nd group of positive refractive power
The group L43 is a 43rd group having a negative refractive power. SP is an aperture and IP is an image plane. The arrows indicate the movement loci of the respective lens groups when zooming from the wide-angle end to the telephoto end.

The 41st lens unit L41 is composed of a cemented lens in which a positive lens 41P having a convex surface directed toward the image surface side and a meniscus negative lens 41N having a convex surface directed toward the image surface side are cemented, and the cemented lens surface is the image surface. The convex surface is directed to the side. The 42nd lens unit L42 is composed of a positive lens whose both lens surfaces are convex. The 43rd lens unit L43 includes a meniscus-shaped negative lens 43N having a convex surface directed toward the image side.

In the present embodiment, as shown in FIG. 1, during zooming from the wide-angle end to the telephoto end, the first lens unit L1 is moved while having a convex locus on the image plane side, and the image accompanying zooming is changed. Correct the surface variation, move the second lens unit L2 so that the distance between the second lens unit and the first lens unit becomes small, and move the third lens unit L3 so that the distance between the third lens unit and the second lens unit becomes large. Then, the fourth lens unit L4 is moved so that the distance between the fourth lens unit and the third lens unit becomes small. or,
Focusing is performed by moving the first group.

In this embodiment, as described above, the refractive power of each lens group, the moving condition of each lens group upon zooming, and the fourth condition
The lens configuration of the group is set, the positive lens 41P and the negative lens 41N that form the 41st group are cemented, and the refractive indexes and Abbe numbers of the materials of both lenses are expressed by conditional expression (1),
It is set to satisfy (2). As a result, the zoom that has excellent optical performance over the entire zoom range with a wide angle of view and a high zoom ratio while satisfactorily compensating for variations in chromatic aberration when achieving high zoom power and shortening the overall lens length. I'm getting a lens.

In particular, this embodiment is characterized in that the lens structure of the fourth lens unit is set as described above. The 41st group and the 42nd group in the 4th group are both lens groups having a positive refractive power. Thereby, the light flux is gradually converged and the spherical aberration is satisfactorily corrected.

Further, as shown in FIG. 13, the 41st lens unit L41 on the most object side where both the incident height h of the on-axis ray and the incident height ha of the off-axis ray to the fourth lens group L4 are relatively high is made by the cemented lens. The cemented lens surface of the cemented lens has a convex surface facing the image plane side. Thereby, the spherical aberration generated in the first lens unit L1 to the third lens unit L3 is satisfactorily corrected.

The 43rd lens unit is composed of a meniscus negative lens whose convex surface faces the image plane side. As a result, the negative distortion produced by the first lens group at the wide-angle end is well corrected. Moreover, the principal point position of the entire system is located on the object side by the 43rd group. Thus, when the first lens unit has a negative refracting power and the fourth lens unit has a positive refracting power, it is possible to prevent the principal point position from moving relatively to the image side and to increase the total lens length. The total length is effectively shortened.

Next, the technical meaning of the conditional expressions (1) and (2) will be described. Conditional expressions (1) and (2) are the 41st
This is to appropriately set the refractive index and Abbe number of the materials of the positive lens 41P and the negative lens 41N of the group, mainly to favorably correct the variation of chromatic aberration due to zooming and to shorten the total lens length. .

If the upper limit of conditional expression (1) is exceeded, both axial chromatic aberration and lateral chromatic aberration will be overcorrected on the telephoto side.
On the other hand, when the value goes below the lower limit, the variation of chromatic aberration due to zooming becomes large. If the upper limit of conditional expression (2) is exceeded, the negative refractive power of the cemented lens surface becomes too strong, and it becomes difficult to maintain the back focus properly. On the other hand, when the value goes below the lower limit, the negative refractive power of the cemented lens surface becomes too weak, and it becomes difficult to position the principal point of the entire system on the object side to shorten the total lens length.

In the present invention, it is more preferable to set the numerical ranges of the conditional expressions (1) and (2) as follows in terms of aberration correction and shortening of the total lens length.

31 <ν41P-ν41N <61 (1a) 0.14 <N41N-N41P <0.36 (2a) In the present invention, the first group has the convex surface closest to the object side and toward the object side. The lens has a negative meniscus lens directed to it, a positive meniscus lens having a convex surface directed toward the object side closest to the image surface, and a negative lens on the object side of the positive lens. This mainly corrects distortion aberration at the wide-angle end, but also corrects various aberrations such as spherical aberration and coma aberration when the close-up distance is shortened, and reduces the lens outer diameter. . The second lens unit having a positive refractive power has a cemented lens of a negative lens and a positive lens and at least two positive lenses, and the third lens unit having a negative refractive power has a cemented lens of a positive lens and a negative lens. I am trying. This reduces variations in various aberrations over the entire zoom range and obtains high optical performance.

Next, numerical examples of the present invention will be shown. In the numerical examples, ri is the radius of curvature of the i-th lens surface in order from the object side, di is the i-th lens thickness and air gap from the object side, and ni and νi are the values of the i-th lens in order from the object side, respectively. The refractive index of glass and the Abbe number.

The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis, a positive light traveling direction, and R as paraxial radiuses of curvature A, B, C, D, and E, respectively. When

[0025]

[Equation 1] It is expressed by Table 1 shows the relationship between the above-mentioned conditional expression and various numerical values in the numerical examples.

[0026]

[Outside 1]

[0027]

[Outside 2]

[0028]

[Outside 3]

[0029]

[Table 1]

[0030]

As described above, according to the present invention, the total lens length can be shortened and the lens barrel structure can be realized by specifying the refractive powers of the four lens groups and the moving conditions of each lens group due to zooming. It is possible to achieve a zoom lens having a relatively wide angle of view and a high optical performance over the entire zooming range with a high zooming ratio while being simple.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 2 of the present invention.

FIG. 3 is a lens sectional view of Numerical Example 3 of the present invention.

FIG. 4 is an aberration diagram at the wide-angle end according to Numerical Example 1 of the present invention.

FIG. 5 is an intermediate aberration diagram of Numerical example 1 of the present invention.

FIG. 6 is an aberration diagram at a telephoto end according to Numerical Example 1 of the present invention.

FIG. 7 is an aberration diagram at the wide-angle end according to Numerical Example 2 of the present invention.

FIG. 8 is an intermediate aberration diagram of Numerical example 2 of the present invention.

FIG. 9 is an aberration diagram at a telephoto end according to Numerical Example 2 of the present invention.

FIG. 10 is an aberration diagram at a wide-angle end according to Numerical Example 3 of the present invention.

FIG. 11 is an intermediate aberration diagram of Numerical Example 3 of the present invention.

FIG. 12 is an aberration diagram at a telephoto end according to Numerical Example 3 of the present invention.

13 is an optical path diagram of the fourth group in FIG.

[Explanation of symbols]

 L1 1st group L2 2nd group L3 3rd group L4 4th group IP image plane SP Aperture ΔS Sagittal image plane ΔM Meridional image plane d d line g g line S.I. C sine condition

Claims (3)

[Claims] 1. Four lens groups, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, a third group having a negative refractive power, and a fourth group having a positive refractive power. At the time of zooming from the wide-angle end to the telephoto end, the first lens group is moved while having a convex locus on the image surface side to correct the image plane variation due to zooming, and The group is moved so that the distance between the second group and the first group becomes small, the third group is moved so that the distance between the third group and the second group becomes large, and the fourth group is moved. The fourth lens unit and the third lens unit are moved so that the distance between the fourth lens unit and the third lens unit becomes small, and the fourth lens unit is the fourth lens unit having the positive refractive power, the fourth lens unit having the positive refractive power, and the fourth lens unit having the negative refractive power.
The 41st group includes a lens 41P and a negative lens 41N.
And the cemented lens surface has a convex surface facing the image side, and the 43rd group has a meniscus negative lens 43N having a convex surface facing the image side. The refractive index and the Abbe number of the material of the lens 41P are N41P and ν, respectively.
41P, where the refractive index and Abbe number of the material of the negative lens 41N are N41N and ν41N, respectively, 25 <ν41P-ν41N <61 0.06 <N41N-N41P <0.36 are satisfied. Zoom lens. 2. The positive lens 41P has a shape with a convex surface facing the image surface side, the negative lens 41N has a meniscus shape with a convex surface facing the image surface side, and both lens surfaces of the 42nd lens group are convex surfaces. 2. The zoom lens according to claim 1, wherein the zoom lens is a positive lens. 3. The first lens unit includes a meniscus negative lens whose convex surface faces the object side closest to the object side, a meniscus positive lens whose convex surface faces the object side closest to the image side, and a positive lens of the positive lens. The zoom lens according to claim 1, further comprising a negative lens on the object side.