JPH0534598A - Compact zoom lens - Google Patents

Abstract

PURPOSE:To obtain the zoom lens having high variable power and high performance, and also, being compact, which is suitable for a video camera, etc. CONSTITUTION:This zoom lens is provided with a first positive lens group fixed at the time of variable power, a second lens group for moving in connection with variable power, a third positive lens group fixed at the time of variable power, a fourth positive lens group for moving in connection with variable power, and a fifth positive lens group fixed at the time of variable power in order from an object side, and in this compact zoom lens, a second lens group is constituted of a negative meniscus single lens whose convex surface is turned to the object side, and a stuck doublet of a negative lens and a positive lens, and a fourth group is constituted of a stuck doublet of a positive lens and a negative lens, having at least one aspherical surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-performance, high-magnification, relatively compact zoom lens suitable for video cameras and the like.

[0002]

2. Description of the Related Art In recent years, home-use integrated video cameras have become widespread. Among them, small ones with excellent portability are becoming mainstream. Against this background, there is a technology for making a zoom lens with high zoom ratio and high performance to be compact, which makes it possible to realize a more compact camera.

6 with such a compact lens type
In the case of a zoom lens with a magnification of up to 8 times, the positive first lens is fixed as shown in JP-A-62-24213 and JP-A-2-311811.
Known are a group, a second group that moves negatively, a third group that is positive and fixed, and a fourth group that moves positively. However, there are many demands for a zoom lens that has a higher zoom ratio and a more compact size. With the known lenses described above, if the zoom ratio is further increased and the zoom lens is made compact, the exit pupil becomes shorter as the master system becomes compact. In addition, there is a drawback that the negative Petzval sum is increased, and it becomes difficult to correct the distortion.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to obtain a zoom lens having high zoom ratio, high performance and compact size.

[0005]

According to the present invention, in order from the object side, the first lens group is fixed and is positive during zooming, the second lens group is moved with zooming, the third lens group is fixed and positive during zooming, and zooming is performed. It has a positive fourth lens group that moves in accordance with the above, and a positive fifth lens group that is fixed during zooming. The second lens group has a negative meniscus single lens with a convex surface facing the object side, and a negative lens and a positive lens group. A zoom lens comprising a cemented doublet of lenses, a fourth lens group having at least one aspherical surface, and comprising a cemented doublet of a positive lens and a negative lens.

Further, it is desirable to carry out the present invention that the following conditions are satisfied. (1) In the present invention, the third lens group should have at least one aspherical surface.

(2) In the present invention, the fifth lens group should have at least one aspherical surface.

(3) In the present invention, 0.1 <F _W · | f ₂ | / (f _W · Z) <0.4 is satisfied.

However, F _W : F number at wide end f ₂ : Focal length of second lens group f _W : Focal length of entire system at wide end Z: Zoom ratio (4) In the present invention, n ₄₊ / n _4- <1.0 1.1 <ν ₄₊ / ν _4- is satisfied.

Where n _{4+ is} the refractive index of the positive lens in the fourth lens group n _4- : is the refractive index of the negative lens ν ₄₊ : is the Abbe number of the positive lens ν _{4+ is} the Abbe number of the negative lens

[0011]

The present invention has, in order from the object side, a positive lens group which is fixed during zooming, and a negative second lens group which has a zooming effect and moves with zooming. Then, a negative meniscus single lens with the second lens group having a convex surface facing the object side, a negative lens,
Further, by using a positive lens, a change in distortion due to zooming and a chromatic aberration of magnification are corrected well. The third lens group, which is fixed and positive at the time of zooming, is used for guiding the divergent light emitted from the second lens group to the fourth lens group. The fourth lens group has a positive refracting power, is used for an image forming action, and moves so as to correct the fluctuation of the image forming position which occurs during zooming. The fourth lens group is composed of a cemented doublet of a positive lens and a negative lens, which makes it possible to reduce aberration fluctuations due to errors such as decentering as compared with the case where the cementing is not used. Further, the use of an aspherical surface in the fourth lens group does not impair the ability of aberration correction reduced by using a cemented lens, and in particular, spherical aberration and astigmatism are satisfactorily corrected, which is such a simple configuration. However, it has achieved compactness of the lens system and good performance. Fifth
The lens group has a fixed and positive refractive power at the time of zooming, and by arranging this group on the most image plane side of the lens system, the negative Petzval sum increases and the exit pupil increases as the lens system becomes more compact. It is possible to obtain a good image even if the size is shortened and the zoom ratio is high.

In the present invention, it is desirable that condition (1) to condition (4) is secondarily satisfied. In condition (1), the third lens group has an aspherical surface, so that spherical aberration from wide to middle is corrected, and coma flare from wide to tele is suppressed, further improving performance is expected. . Under the condition (2), by having at least one aspherical surface in the fifth lens group, which is closest to the image plane, it is possible to correct astigmatism and distortion without affecting other aberrations. it can.
Condition (3) is a condition related to the refractive power of the second lens group, and is the present condition.
Satisfying (3) is advantageous for obtaining a highly variable and compact lens system. That is, when the value goes below the lower limit, the focal length of the second lens unit becomes too short for a certain appropriate F number, and fluctuations in distortion and coma due to zooming become too large. Also, if the upper limit is exceeded, the amount of movement during zooming becomes large, which is disadvantageous for compactness. The condition (4) relates to the refractive indices and Abbe numbers of the positive lens and the negative lens of the fourth lens group, and it is desirable to satisfy these conditions for correcting axial chromatic aberration and lateral chromatic aberration at a large angle of view.

[0013]

EXAMPLES Examples of the zoom lens of the present invention will be shown below.

In the examples, R is the radius of curvature of the surface, D is the surface spacing, N is the refractive index, and ν is the Abbe number (wavelength is d-line = 58).
7.56 nm). In addition, various values described in the present specification in each example are shown in a separate table. In the examples, a low pass filter, an infrared cut filter, and a cover glass corresponding to a face plate are provided between the final lens surface and the image forming surface. Each symbol in the table is R: radius of curvature of each refracting surface D: distance between refracting surfaces N: refractive index of glass material of lens ν: Abbe number of glass material of lens f: focal length of entire lens system 2ω: angle of view F: F Show each number. The specific configuration of the embodiment is as follows.

The aspherical surface shape in the embodiment is represented by the following formula.

[0016]

[Equation 1]

However, each symbol in the formula is as follows.

C = 1 / R: Paraxial curvature of aspherical surface h: Height from optical axis K: Cone constant φ: Deformation amount of aspherical surface measured in optical axis direction from surface vertex (including displacement amount by spherical surface) ) also the D-PQ is 10 ^-PQ in example, D + PQ represents 10 ^{+ PQ.}

(Embodiment 1) A lens having the lens structure shown in FIG. 1 and the following (lens numerical values in Table 1, Table 2 and Table 3 are taken).

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

FIGS. 2, 3 and 4 are aberration diagrams of the first embodiment, FIG. 2 is a wide, FIG. 3 is a middle, and FIG. 4 is a teleposition.

(Embodiment 2) The lens having the lens structure shown in FIG. 1 is used, and the lens values shown in the following (Table 4, Table 5 and Table 6) are taken.

[0025]

[Table 4]

[0026]

[Table 5]

[0027]

[Table 6]

FIGS. 5, 6, and 7 are aberration diagrams of the second embodiment. FIG. 5 is a wide lens, FIG. 6 is a middle lens, and FIG.

[0029]

According to the present invention, as shown in the aberration charts shown in the first and second embodiments and the drawings, it has a high zoom ratio of about 10 times or more, yet has good performance and is compact. We were able to realize a zoom lens.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a lens configuration of Examples 1 and 2 of the present invention.

FIG. 2 is an aberration diagram of Example 1 at a wide position.

FIG. 3 is an aberration diagram of Example 1 at a middle position.

FIG. 4 is an aberration diagram at a teleposition of the first example.

FIG. 5 is an aberration diagram at a wide position in Example 2.

FIG. 6 is an aberration diagram for Example 2 at a middle position.

FIG. 7 is an aberration diagram for Example 2 at the teleposition.

Claims (1)

Claims: 1. A fixed first positive lens unit during zooming in order from the object side.
A lens unit, a second negative lens unit that moves with zooming, a third positive lens unit that is fixed during zooming, a positive fourth lens unit that moves with zooming, and a fixed positive lens unit during zooming. Fifth
The second lens group includes a negative meniscus single lens having a convex surface facing the object side, a negative lens, and a positive lens, and the fourth lens group includes a cemented doublet of the positive lens and the negative lens. , A compact zoom lens having at least one aspherical surface in the fourth lens group.