JP3245297B2 - Small 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 small zoom lens used for a lens shutter camera or the like.

[0002]

2. Description of the Related Art As a zoom lens of this kind, a lens in which the first group lens is a negative power lens is disclosed in
JP-A-3-27613 and JP-A-3-213814.

[0003]

However, the former is small in number, but expensive in material, and is not practical. The latter has a larger number of lenses and a longer overall lens length.
In addition, the back focus cannot be lengthened, and the diameter of the rear ball increases, making it impossible to make it compact.

The present invention provides a compact zoom lens having a short overall length by reducing the diameter of the front lens and the rear lens in order to reduce the size of the lens itself. Further, in order to reduce the size of the lens barrel, there is provided a compact zoom lens which has a small amount of extension during zooming despite having a magnification ratio of about 2.4.

[0005]

In order to achieve the above object, the present invention employs the following lens system. That is, in a two-group zoom lens in which a front group having a positive power and a rear group having a negative power are formed, and the distance between the two groups is reduced, the focal length is changed to the long focal length side. In order from the object side, the first lens unit is a cemented first lens unit having a negative power of a biconvex lens and a biconcave lens, the second lens unit is a negative lens having a concave surface on the object side, and the positive meniscus third lens unit has a convex surface facing the image side. Group lens, positive biconvex fourth lens group, rear meniscus positive meniscus fifth lens group whose convex surface faces the image side in order from the object side, negative sixth lens group having strong curvature on the object side, object The zoom lens includes a negative meniscus seventh lens group having strong curvature on the side, and eight lenses in seven groups in total. By adopting a lens system in which at least one surface of the first lens unit has an aspheric surface, and at least one of the third lens unit and the fourth lens unit has an aspheric surface,
In combination with the above structural features, it is possible to satisfactorily correct various aberrations.

[0006] In addition to the above-mentioned geometric features, it is necessary to satisfy the following constitutional conditions. -1.3 <f1 / 2 / fw <-0.8 (1) 0.63 <f1G / fw <0.89 (2) where f1.2 is the focal length of the first and second lens units, and fw is The focal length at the wide end, f1G, is the focal length of the front group.

The first group lens of such a positive / negative type two-group zoom lens is usually a positive lens, but starts with a negative lens in order to reduce the diameter of the front lens and further increase the back focus at the wide end. It has a retro focus configuration. In the case of a retrofocus type lens, the overall length of the lens tends to be longer than the focal length. However, by using an aspherical lens for the first lens unit and the third or fourth lens unit, the overall length is reduced. I have.

The conditional expression (1) relates to the power of the negative lens unit of the front group. If the lower limit is exceeded, aberration correction is easy, but the overall length of the lens becomes longer, the back focus becomes shorter, and the back lens diameter becomes larger. Become. If the upper limit is exceeded, the overall length of the lens will be short, but the back focus will be too long, which will cause the lens frame to become large.

The conditional expression (2) represents the limitation of the overall length of the lens system. If the lower limit of the conditional expression is exceeded, the back focus at the telephoto end becomes longer, so that the amount of extension by zooming increases and the lens frame does not become large. If the upper limit is exceeded, the distance between the front group and the rear group at the wide end becomes large, and the overall length of the lens becomes long.

In terms of aberration, when the value exceeds the upper limit of (1), coma increases and astigmatism in the negative direction increases.
Beyond the lower limit of (2), negative spherical aberration increases. Further, by applying an aspherical surface to the first, third or fourth lens group, it is possible to shorten the overall length of the front lens group without increasing the number of lenses in spite of the retrofocus type. , Corrects astigmatism in the minus direction and positive distortion, and the third or fourth lens unit corrects negative spherical aberration. The first group of cemented lenses has an appropriate refractive index difference, thereby correcting field curvature and astigmatism.

[0011]

EXAMPLES Tables 1 to 4 show four examples of the present invention. 1 to 5 show sectional views and aberration diagrams.
In the figure, the sign is negative when the space is on the left side of the previous surface, is positive when it is on the right, and the radius of curvature is negative when concave on the object side and positive when convex.

The aspheric surface used in the present invention is given by the following equation.

[0013]

(Equation 1)

Where z: depth from the tangent plane to the surface vertex c: paraxial curvature of the surface h: height from the optical axis k: conical constant A: fourth order aspherical coefficient B: sixth order non-spherical coefficient Spherical coefficient C: 8th order aspherical coefficient D: 10th order aspherical coefficient E: 12th order aspherical coefficient F: 14th order aspherical coefficient G: 16th order aspherical coefficient H: 18th order aspherical coefficient Hereinafter, examples of the zoom lens according to the present invention will be described.
In each embodiment, the surface numbers were counted in order from the object side,
The corresponding surface number of each lens is shown. The interval 10 and the interval 16 change due to zooming. The data of the aspherical surface is shown in the lowermost column together with the surface number. Also, surface number 1
0 corresponds to the stop surface, and a radius of curvature of 0 indicates that the radius of curvature is infinite. The refractive index is d-line (588n
m) indicates the refractive index, and dispersion indicates the Abbe number. The aspheric coefficient indicates the value of each coefficient shown in the equation.

The features of each embodiment will be described below. Example 1
Is a representative example of this embodiment.

Embodiment 2 is an example in which the back focus is long at the wide end.

Embodiment 3 is an example in which the back focus is short at the wide end and the total length is long.

Embodiment 4 is an example in which the feeding amount is large.

Tables show the configuration data of each embodiment.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

[Table 4]

[0024]

By using a negative lens for the first group lens and using an aspherical lens, it is possible to shorten the lens diameter and the overall length, and to provide a zoom lens with a small lens frame. Become.

[Brief description of the drawings]

FIGS. 1 to 5 show a sectional view on the short focus side and aberration diagrams on the short focus side and the long focus side corresponding to the first to fourth embodiments of the present invention.

FIG. 1 is a block diagram of the present invention.

FIG. 2 is a cross-sectional view and aberration diagrams of the first embodiment.

FIG. 3 is a sectional view and an aberration diagram of a second embodiment.

FIG. 4 is a cross-sectional view and aberration diagrams of a third embodiment.

FIG. 5 is a cross-sectional view and aberration diagrams of a fourth embodiment.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/18 G02B 21/02 G02B 25/00-25/04

Claims (1)

(57) [Claims] 1. A two-group zoom lens comprising a front group having a positive power and a rear group having a negative power and changing a distance between two groups to change a focal length. In order from the object side, a cemented first group lens having negative power of a biconvex lens and a biconcave lens, a second group lens of negative power having a concave surface on the object side, and a positive meniscus third group having a convex surface facing the image side Lens, positive biconvex fourth lens unit, rear meniscus fifth lens unit having a convex surface facing the image side in order from the object side, negative sixth lens unit having strong curvature on the object side, object side Negative meniscus seventh with strong curvature
The first lens unit includes at least one aspherical surface, and the third lens unit includes a third lens unit.
A small zoom lens that satisfies each of the following conditional expressions in a lens system in which at least one of the group lens and the fourth group lens has an aspheric surface. -1.3 <f1 / 2 / fw <-0.8 (1) 0.63 <f1G / fw <0.89 (2) where f1.2 is the focal length of the first and second lens units, and fw is The focal length at the wide end, f1G, is the focal length of the front group.