JP3352265B2 - 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 zoom lens, and more particularly to a photographic field of view 62 preceded by a lens group having a negative refractive power having high optical performance over the entire zoom range suitable for a photographic camera, a video camera, and the like. About ~ 31 °, zoom ratio of about 2,
The present invention relates to a compact zoom lens having at least two lens groups, for example, having a short total lens length and having three lens groups.

[0002]

2. Description of the Related Art Usually, a focal length range which is easy to use as a zoom lens is a range sandwiching a diagonal size of a screen, for example, 35 m
The m-film version is a zoom lens having a focal length of 35 mm to 70 mm.

This type of zoom lens is composed of two lens units, a first unit having a negative refractive power and a second unit having a positive refractive power.
There is a group zoom lens (usually a short zoom), for example, Japanese Patent Application Laid-Open No. 61-87118 and Japanese Patent Application Laid-Open No. Hei 5-24937.
No. 3 has been proposed.

In general, in a two-unit zoom lens, there is a limit in reducing the overall length of the lens while maintaining a predetermined zoom ratio. For this reason, a so-called three-group zoom lens in which a third group having a negative refractive power is newly disposed on the image plane side in the two-group zoom lens to shorten the entire length of the lens while securing a predetermined zoom ratio is provided. For example, JP-A-58-9016 and JP-A-5-9016
It has been proposed in, for example, JP-A-8-111013.

In a three-unit zoom lens, by appropriately setting the refractive power and the lens configuration of each lens unit,
Ones that achieve high optical performance over the entire zoom range while achieving high zoom ratio are disclosed in, for example, JP-A-61-183613, JP-A-61-240217, and JP-A-62-8.
7925, JP-A-62-112115, JP-A-1-189622, and the like.

[0006]

Recently, in a photographic camera, a video camera, and the like, as the size of the camera has been reduced, there has been a demand for a zoom lens in which the entire lens system is reduced in size. Also, in a camera having an automatic focus detection device, electronic components and actuators for performing a focusing operation can be arranged in a part of an optical system, for example, a part of a lens barrel, in addition to downsizing of the entire lens system. There is a demand for an optical system having a space. Also, since the aperture mechanism provided in the optical system is relatively large, the aperture mechanism is provided, for example, at a position distant from the camera mount so as not to interfere with other components.

In general, for example, a method of using a glass material having a high refractive index for a lens on the image plane side of the stop constituting the optical system in order to secure a spatial area wider on the image plane side than the stop in the optical system.

Next, the optical function of this method will be described.

In general, the distance between two adjacent lens surfaces a and b in the optical system is D _ab , the refractive index of the medium between the lens surfaces a and b is N _ab , and the air conversion distance between the lens surfaces a and b is e. When _{ab e ab = D ab / N} ab ‥‥‥ the (a). As is clear from the equation (a), if the space between the lens surfaces a and b is filled with a medium having a high refractive power, the distance D _ab between the lens surfaces a and b, that is, the air area is increased while the air conversion distance e _ab is kept constant. Can be done.

In the above-mentioned Japanese Patent Application Laid-Open No. 61-87118, the highest refractive index of the glass material of the lens on the image side of the stop is about 1.8. For this reason, it is difficult to obtain a sufficient space area. Further, in Japanese Patent Publication No. 61-61653, a lens using a glass material having a refractive index of 1.85 is arranged on the image plane side of the stop, but since the axial thickness of the lens is relatively thin, a sufficient spatial area is provided. There was a problem that it was difficult to secure.

On the other hand, a negative lead type zoom lens, which is preceded by a lens group having a negative refractive power, has features that it is relatively easy to widen the angle of view and that a predetermined back focus can be easily obtained. However, since the entire lens system is asymmetric, unless the refractive power arrangement and the lens configuration of each lens group are properly set, the aberration fluctuation accompanying zooming increases,
It becomes difficult to obtain high optical performance over the entire zoom range.

According to the present invention, in a zoom lens composed of three lens groups having a predetermined refractive power, a lens barrel component is disposed in a part of an optical system by appropriately setting the refractive power of each lens group, the lens configuration, and the like. The objective is to provide a zoom lens suitable for a photographic camera or a video camera and the like having high optical performance over the entire zooming range, and an optical apparatus using the zoom lens, while ensuring sufficient space and having little aberration fluctuation due to zooming. And

[0013]

Means for Solving the Problems] have a third group of the second group and the negative refractive power of the zoom lens of the invention of claim 1 includes a first unit having a negative refractive power in order from the object side positive refractive power Then, the zooming from the wide-angle end to the telephoto end is performed by moving the first lens unit with a convex locus toward the image plane, and moving the second lens unit so that the distance between the first lens unit and the first lens unit decreases. The first group includes a meniscus negative eleventh lens and a negative twelfth lens with a convex surface facing the object side, and a meniscus positive thirteenth lens with a convex surface facing the object side Wherein the second group is a positive twenty-first lens,
A positive twenty-second lens, a negative twenty-third lens, a positive twenty-fourth lens, and an aperture on the object side of the twenty-second lens;
The combined focal length of the first and second units at the wide-angle end is f
12W, the focal length of the entire system at the wide-angle end and the telephoto end is represented by f
W, fT, the refractive index and Abbe number of the material of the ij-th lens are Nij and vij, the axial thickness of the 23rd lens is D23, and the focal length of the first group is f1.

(Equation 2) It is characterized by satisfying certain conditions.

The invention of claim 2 is the invention of claim 1
The third group has at least one aspheric surface;
It is characterized by.

A camera according to a third aspect of the present invention is the camera according to the first or second aspect.
Is characterized by having a zoom lens.

[0016]

[0017]

1 to 3 show a numerical embodiment 1 of the present invention described later.
FIGS. 4A to 4C are lens cross-sectional views. In the lens cross-sectional views, (A) shows the zoom position at the wide angle end, (B) shows the middle position, and (C) shows the zoom position at the telephoto end. In the figure, L1 is a first group having a negative refractive power,
In order to correct the image plane fluctuation due to the zooming, the lens is moved and focused while having a convex locus on the image plane side as shown by an arrow. L2 is a second unit having a positive refractive power and has a zooming effect. When zooming from the wide-angle end to the telephoto end, the distance from the first unit decreases in the object side direction as indicated by the arrow. You are moving monotonously. L3 is a third group of negative refractive power having a fixed imaging action. SP is an aperture stop.

In general, in a zoom lens including three lens units having negative, positive, and negative refractive powers in this order from the object side as in the present embodiment, while reducing the overall length of the lens,
In order to obtain high optical performance over the entire zoom range, it is necessary to appropriately set the lens configurations of the first and second units that move, particularly during zooming.

Therefore, in this embodiment, as described above, the first group is composed of three lenses having a predetermined shape, and the second group is composed of four lenses having a predetermined shape.
The zoom lens is constituted by one lens and each element is set so as to satisfy the conditional expressions (1) to (6), thereby realizing a zoom lens having good optical performance in the entire zoom range. Also, during zooming, by providing the third group having a fixed negative refractive power, the principal point position is displaced toward the object side while preventing the lens barrel structure from becoming complicated, thereby obtaining an appropriate back focus.

Next, the technical meaning of the conditional expressions (1) to (6) will be described.

The conditional expressions (1) and (2) relate to the refractive index and the axial thickness (center thickness) of the material of the negative twenty-third lens constituting the second lens unit, and are provided mainly on the object side with respect to the twenty-second lens. The distance from the aperture stop to the mount when the zoom lens of the present invention is mounted on the camera body is widened to secure a large space area in a part of the lens barrel, and various components are easily mounted in the space area. It is to be able to do.

If a low refractive index glass material is used for the 23rd lens out of the conditional expression (1), it becomes difficult to increase the distance from the stop to the mount.

If the center thickness becomes smaller than the lower limit of conditional expression (2), it becomes difficult to increase the distance from the stop to the mount, and if the center thickness becomes larger than the upper limit, the lens thickness of the 23rd lens becomes too thick. As the total length of the lens increases, it becomes difficult to satisfactorily correct chromatic aberration.

Conditional expression (3) is for appropriately setting the Abbe number of the material of the twenty-third lens and favorably correcting axial chromatic aberration mainly due to zooming. If conditional expression (3) is not satisfied, axial chromatic aberration will be insufficiently corrected in the second lens unit, and fluctuation of axial chromatic aberration due to zooming will increase.

Conditional expression (4) is for appropriately setting the refractive indices of the materials of the eleventh lens and the twelfth lens in the first lens unit and obtaining high optical performance over the entire screen.

In general, the Pebbal sum P, which greatly affects the curvature of field of an optical system, is given assuming that the focal length of the i-th lens and the refractive index of the material are fi and ni, respectively, and the total number of lenses is K.

[0027]

(Equation 5) Becomes

In the above-mentioned conditional expression (1), the refractive index of the material of the negative twenty-third lens is set higher than a predetermined value 1.83. According to the expression (b), the Petzval sum is positive. It gets bigger in the direction.

Therefore, in the present invention, a glass material having a small refractive index satisfying conditional expression (4) is used for the materials of the eleventh lens and the twelfth lens which are negative lens components in order to make the Petzval sum well-balanced.

When the value exceeds the upper limit of conditional expression (4), it becomes difficult to reduce the Petzval sum, and the field curvature increases. If the lower limit is exceeded, the curvature of each lens surface becomes strong, and as a result, distortion increases in the negative direction at the wide-angle end, which is not good.

Conditional expression (5) appropriately sets the Abbe number of the material of the three lenses in the first group, that is, uses a glass material having a large Abbe number for the negative lens component and a small Abbe number for the positive lens component. By using a glass material, the chromatic aberration in the first lens group is mainly satisfactorily corrected. If conditional expression (5) is not satisfied, it becomes difficult to satisfactorily correct chromatic aberration in the first lens unit.

Conditional expression (6) is for appropriately setting the refractive power of the first lens unit, reducing the effective diameter of the first lens unit, and correcting various aberrations in a well-balanced manner. When the value exceeds the upper limit of conditional expression (6), the effective diameter of the first lens unit increases. If the lower limit value is exceeded, the distortion increases in the negative direction on the wide-angle side and the spherical aberration increases on the telephoto side, making it difficult to satisfactorily correct this.

In the present invention, in order to favorably correct negative distortion on the wide-angle side, curvature of field in the intermediate area, and coma flare on the telephoto side, at least one aspherical surface is provided in the third lens unit. Is good.

In the present invention, to obtain good optical performance over the entire zoom range while further increasing the distance from the stop to the mount, the numerical ranges of the above-mentioned conditional expressions (1) to (6) are set as follows. Good to do.

[0035]

(Equation 6) Next, numerical examples of the present invention will be described. In the numerical examples, r
i is the radius of curvature of the i-th lens surface in order from the object side, d
i is the i-th lens thickness and air space in order from the object side,
ni and νi are the refractive index and Abbe number of the glass of the i-th lens in order from the object side. Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples. 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 traveling direction of light, and R represents a paraxial radius of curvature, A, B, C,
When D is each aspheric coefficient

[0036]

(Equation 7) It is represented by the following expression.

[0037]

[Outside 1]

[0038]

[Outside 2]

[0039]

[Outside 3]

[0040]

[Table 1]

According to the present invention, as described above, the predetermined refraction
In a zoom lens consisting of three lens groups of power, by appropriately setting the refractive power of each lens group, the lens configuration, and the like, a sufficient space for disposing the lens barrel part in a part of the optical system and zooming is achieved. A zoom lens suitable for a photographic camera, a video camera, or the like having little accompanying aberration fluctuation and high optical performance over the entire zoom range can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 3 of the present invention.

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

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

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

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

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

FIG. 9 is an aberration diagram at a telephoto end in 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 the numerical example 3 of the present invention.

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

[Explanation of symbols]

 L1 First lens unit L2 Second lens unit L3 Third lens unit SP Aperture d d line gg line ΔS Sagittal image plane ΔM Meridional image plane

──────────────────────────────────────────────────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 (3)

(57) [Claims] 1. A first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power in order from the object side, and perform zooming from a wide-angle end to a telephoto end. The first group is moved with a locus convex toward the image plane side, and the second group is moved toward the object side so as to reduce the distance from the first group. The second lens unit comprises a meniscus negative eleventh lens and a negative twelfth lens with a convex surface facing the object side, and a meniscus positive thirteenth lens with a convex surface facing the object side. , Positive 22nd lens, negative 23rd lens, positive 2nd lens
4 lenses, and a stop on the object side of the 22nd lens. The combined focal length of the first and second units at the wide-angle end is f12W, and the focal length of the entire system at the wide-angle end and the telephoto end is fW. , FT, the refractive index and Abbe number of the material of the ij-th lens are Nij and vij, and the axial thickness of the 23rd lens is D2.
3. When the focal length of the first lens unit is f1. A zoom lens that satisfies certain conditions. 2. The zoom lens according to claim 1 , wherein said third group has at least one aspheric surface. 3. A camera comprising the zoom lens according to claim 1 .