JPS6049885B2 - Wide-angle zoom lens system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens preceded by a diverging lens group.

Conventionally, zoom lenses that are preceded by this type of diverging lens group have an inverted telephoto power arrangement, which is advantageous for wide-angle applications, but on the other hand, spherical aberration and coma aberration fluctuate greatly, and distortion aberration occurs. tended to be significantly negative at short focal lengths.

In order to effectively correct all aberrations, it is considered necessary to increase the focal length of the diverging lens group and the converging lens group that follows it to reduce the burden of aberration correction for each component of the revision. Ta. As a result, the overall shape became larger and the amount of movement during revision increased, making it difficult to put it into practical use. By adopting a new and different type of lens configuration, the present invention eliminates the above-mentioned drawbacks and corrects various aberrations in a well-balanced manner while keeping the lens shape small. The objective is to provide a zoom lens with a significantly reduced weight compared to the conventional zoom lens, and furthermore, it has a minimum focal length of 740 mm, a zoom ratio of 2 times or more, an aperture ratio of 3, and a progressive speed. The lens system according to the present invention is composed of two groups, the front group of the diverging lens group and the rear group of the converging lens group, when viewed from the object side, and the lens system can be changed by mechanically moving the lens along the optical axis. It is a double act.

Then, sequentially insert the front lens group, which is the diverging lens group, from the object side.
A first negative meniscus lens with a concave surface facing the image side, a second negative meniscus lens with a concave surface facing the image side, and a first positive meniscus lens with a convex surface facing the object side, separated from each other.
The rear group consists of a convergent lens group consisting of the component D, which includes, in order from the object side, a second positive lens, a second positive meniscus lens convex to the object side, and a third positive meniscus lens convex to the object side. It is composed of six components separated from each other: a lens, a double lens, a fourth positive meniscus lens convex toward the image side, and a third positive lens. The significance of the arrangement of these lens components will be described below.

The first positive lens in the diverging lens group is the most important feature of the zoom lens according to the present invention, and is an indispensable component for correcting distortion on the short focal length side. If the focal length of the first positive lens is FlF, and the focal length of the entire diverging lens group is f1, it is desirable to satisfy the following.

If the lower limit is less than 1.2, the power of the first positive lens becomes too strong, making it impossible to correct spherical aberration on the long focal length side. If it is larger than the upper limit, the desired distortion cannot be obtained even if the pending effects of the first positive lens and the subsequent negative lens are taken into consideration. In order to further widen the angle of view, it is necessary to correct distortion, which increases in proportion to the cube of the angle of view. For this purpose, two of the diverging lens groups
All of the two negative components must have a meniscus shape that is concave with respect to the line side, and when the radii of curvature on the image side of these two negative components are R4 and R6 in order from the object side, IR4l<1R61
By doing so, it is possible to configure a diverging lens group that is compatible with a wide angle. Furthermore, if the distance between the second negative lens and the first positive meniscus lens is DF, then 0.05≦DF.
Satisfying /1f11≦0.2 makes it possible to simultaneously correct variations in spherical aberration and variations in field curvature at the shortest focal length and longest focal length by making the diverging lens group a thick lens.

If the lower limit is exceeded, this effect disappears and the shortest and longest distances cannot be balanced, and if the upper limit is exceeded, the diverging lens group becomes too thick and the principal plane penetrates deep into the diverging lens, limiting the range of movement of the converging ν lens group. and the zoom ratio cannot be adjusted. Additionally, as a result, the rear convergent lens group must also be made capable of withstanding wider angles. Based on this requirement, in the convergent group, the positive meniscus lens convex to the image side and the third positive lens are divided into two components, which could have been combined into one positive lens component. This produces a positive effect on distortion,
In addition, it was possible to satisfactorily correct field curvature. With the above configuration, the basic shape of this type of zoom lens is determined, and furthermore, in order to correct the high-order chromatic aberration that tends to occur with wide-angle lenses, it is possible to create a zoom lens by simply changing the fine structure of each component. So layer can achieve high performance wide-angle zoom lens.

Preferred embodiments according to the present invention will be described below. Example 1 is the basic of the invention.

Figure 1 shows the shortest focal length state of the lens configuration according to this example, and Figure 4 shows various aberrations at the shortest focal length state, longest focal length state, and intermediate focal length state.The various aberrations are very well balanced. It can be seen that distortion aberration in particular has become extremely small. The specifications of this example are as follows. FIG. 2 shows the shortest focal length state of the lens configuration.

In Example 2, the first lens in the diverging lens group, which is the front group,
By increasing the Atsube number of the positive lens, high-order chromatic aberrations, especially on the shortest focal length side, can be corrected, and the achromatization of the entire diverging group can be achieved by using the second negative lens as a bonding component. This has been achieved by Furthermore, by creating a difference in the refractive index of both the positive and negative lenses that make up the laminated lens, the Petzval sum is made positive and the curvature of field is appropriately balanced. The third negative lens component in the convergent lens group, which is the rear group, is a composite component of a positive lens and a negative lens, and the refractive index of the positive lens is Npl, the Abbe number is νP1, and those of the negative lens are NN, ν, respectively. By doing so, it is possible to satisfactorily correct the color change due to spherical aberration on the long focal length side, contributing to improved performance on the long focal length side.

The specifications of the lens system according to this example are shown below, and the various aberrations at each focal length state are shown in FIG. In addition, in each specification table,
r is the radius of curvature of each lens surface, d is the center thickness and air gap of each lens, n is the refractive index of each lens, ν is the Atsube number of each lens, and the subscript number represents the order from the object side. shall be taken as a thing.

Further, in the aberration diagram, the solid line in the spherical aberration diagram represents spherical aberration, and the dotted line represents the amount of violation of the sine condition. FIG. 3 shows the shortest focal length state of the lens configuration.

In Example 3, the second positive lens of the convergent lens group, which is the rear group, is added as a bonded component to the lens system in Example 2. This makes it possible to easily correct axial chromatic aberration and also correct color changes due to spherical aberration, reducing the burden of correcting aberrations for other components and making it possible to achieve even better performance. Ta. The specifications of the lens system according to this example are shown below, and the various aberrations in each focal length state are shown in FIG.

[Brief explanation of the drawing]

1 to 3 are lens configuration diagrams in the state of the shortest focal length of the lens system in Example 1 and Example 3, respectively, and FIGS. 4 to 6 are lens configuration diagrams of Example 1 and 3, respectively.
FIG. 6 is an aberration diagram at each focal length state of the lens system in Example 3.

Claims (1)

[Claims] 1. Consists of two groups in order from the object side: a front group of diverging lens groups and a rear group of convergent lens groups, and magnification can be changed by mechanically moving both groups. In the zoom lens, the diverging group includes, in order from the object side, a first positive lens, a first negative meniscus lens with a concave surface facing the image side, and a second negative meniscus lens also with a concave surface facing the image side. , a first positive meniscus lens convex toward the object side, four components separated from each other, and the convergent group consists of, in order from the object side, a second positive meniscus lens, a second positive meniscus lens convex toward the object side, and a second positive meniscus lens convex toward the object side. It is composed of six components separated from each other: a third positive meniscus lens convex to the side, a biconcave negative lens, a fourth positive meniscus lens convex to the image side, and a third positive lens.
And when the radius of curvature of the image side surface of the second negative meniscus lens is r_4 and r_6 in order from the object side, |r_4|<
A wide-angle zoom lens system characterized by satisfying the following conditions: |r_6|