JP2784942B2 - Compact high-magnification 4-group zoom lens - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-magnification four-unit zoom lens having a simple structure used for a compact camera or the like.

[Conventional technology]

In recent years, it has been demanded that a wide-angle to telephoto image can be captured by using a zoom lens even in a compact camera or the like having good portability, and various zoom lenses for the compact camera have been developed accordingly.
As this zoom lens, a two-group type or three-group type zoom lens has been developed because its structure is simplified. However, it is not only difficult to obtain a high magnification, but it is also necessary to correct various aberrations for zooming. There was a drawback that it was difficult. Therefore, as the demand for higher-grade compact cameras increases, four-group zoom lenses have been widely adopted. However, although the four-group zoom lens has the advantage that aberrations can be satisfactorily corrected and a high magnification can be obtained, the structure becomes complicated, the size becomes large, and the advantages inherent in a compact camera may be impaired. There was a problem.

[Means for solving the problem]

In view of the current situation, the present invention provides, in order from the object side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power. For zooming from the wide-angle end to the telephoto end, the first
The lens group and the fourth lens group are moved integrally to the object side, the second lens group is moved so as to correct the image plane variation, and the third lens group is moved.
The first lens group includes at least one positive lens and one negative lens, and the second lens group has a convex surface facing at least one object side. The third lens group comprises at least one positive lens and one negative lens, and the fourth lens group comprises at least one negative lens having a concave surface facing the object side. This is a compact, high-magnification four-group zoom lens.

[Action]

In the present invention, the positive first lens unit, the positive second lens unit, the positive third lens unit, and the negative fourth lens unit are used during zooming.
By moving the lens group along the optical axis, the focal length can be continuously changed from wide angle to telephoto, and the second lens group is moved so as to correct the image plane fluctuation, and the first lens group is moved. Since the amount of movement of the group and the fourth lens group by zooming can be the same, the structure can be simplified.

FIG. 1 is a diagram illustrating a movement mode diagram of a zoom lens system according to the present invention.
In the figure, reference numeral 1 denotes a first lens group having a positive combined focal length,
2 is a second lens group having a positive combined focal length, 3 is a third lens group having a positive combined focal length, and 4 is a fourth lens group having a negative combined focal length.
A lens group, X is an optical axis, and P 'is an image forming position.

The first lens group 1 is a lens group for correcting spherical aberration particularly on the telephoto side, and includes at least one positive lens and at least one negative lens.

The second lens group is a lens group for correcting a variation in curvature of field due to zooming, and includes at least one positive meniscus lens.

The third lens group 3 includes an aberration variation due to focusing,
In particular, this is a lens group for correcting field curvature aberration, wherein at least one positive lens and at least one negative lens are located forward and at least one positive lens and at least one negative lens are located behind the stop S. Consists of a lens.

The fourth lens group 4 includes at least one positive lens and at least one negative lens.

In FIG. 1, during zooming from the wide-angle end (W) to the telephoto end (T), the first lens unit 1, the third lens unit 3, and the fourth lens unit 4 are monotonously moved to the object side, and The lens group 2 is monotonously moved toward the object side so as to correct the image plane fluctuation. At this time, the first lens group 1 and the fourth lens group 4 are integrally moved with the same amount of movement. This movement may be other than linear movement. Therefore, the structure of the four-unit zoom lens system can be simplified.

During zooming from the wide-angle end (W) to the telephoto end (T), spacing D ₁ of the first lens group 1 and the second lens group 2 is reduced after increasing once, the second lens group 2 and the third lens Group 3
Spacing D ₂ is increased between, and the third lens group 3 distance D ₃ between the fourth lens group 4 decreases.

At this time, focusing may be performed by any of the first lens group 1, the third lens group 3, and the fourth lens group 4.

In the present invention, it is desirable to satisfy the following conditions.

(1) 0.3 <f _W / f ₂ <0.45 This conditional expression is for correcting a field curvature aberration or the like generated during zooming, where f _W is the focal point of the entire system at the wide-angle end (W). distance, f ₂ is the focal length of the 2 second lens group.

When the lower limit of the conditional expression is not satisfied, the spherical aberration at the intermediate focal length is under. When the upper limit of the conditional expression is not satisfied, the spherical aberration is over.

〔Example〕

Hereinafter, numerical examples of the present invention having the basic lens configuration shown in FIG. 2 will be described.

 The lens configuration in FIG. 2 is as follows.

The first lens group 1 is composed of a negative meniscus lens L ₁ and the biconvex positive lens L ₂ Metropolitan having a convex surface facing the object. The second lens group 2 includes a positive meniscus lens having a convex surface facing the object side.
Consisting of L _3. The third lens group 3 is composed of a negative lens L ₄ biconcave,
A cemented lens L ₅ + L _6, a negative meniscus lens L ₇ having a convex surface directed toward the object side and a negative meniscus lens L ₆ having a convex surface directed toward the positive lens L ₅ and the image side of the biconvex, biconvex positive lens and L _8, a cemented lens L ₉ + L ₁₀ Metropolitan of a negative meniscus lens L ₉ having a convex surface on the object side and a positive lens L ₁₀ of a biconvex. The fourth lens unit 4 includes a positive meniscus lens L having a concave surface facing the object side.
_11, a negative lens L ₁₂ and a bi-concave. Third lens group 3
Stop S is disposed between the the lens L ₇ and the lens L _8.

In the following description of the numerical examples, m: surface number sequentially counted from the object side r _i : radius of curvature of the i-th lens surface counted from the object side d _i : i-th lens component counted from the object side N _i : the refractive index of the i-th lens component counted from the object side with respect to the d-line ν _i : the Abbe number of the i-th lens component counted from the object side f ′: composite focal point of the whole system Distance Bf ': Back focus.

 The specific configuration of the first embodiment is as shown in the table below.

f 'Bf' angle W 39.20 8.73 58.0 ° N 60.00 25.85 38.6 ° T 111.40 57.31 21.4 ° _{d 4 d 6 d 18 W 1.03} 4.32 18.13 N 6.19 6.67 10.62 T 4.37 17.06 2.05 aberration curves FIG. 3 according to the specific structure It looks like

Next, the specific configuration of the second embodiment is as shown in the table below.

f 'Bf' angle W 39.26 8.66 59.2 ° N 60.00 25.92 39.0 ° T 111.40 57.40 21.6 ° _{d 4 d 6 d 18 W 1.04} 4.65 18.08 N 6.01 7.13 10.63 T 4.30 17.32 2.15 aberration curves Figure 4 according to the specific structure It looks like

FIG. 12 is an aberration curve diagram of each of the first and second embodiments.
Each of the aberrations in FIGS. 3 and 4 indicate that they are sufficiently practical.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, the first lens unit to the fourth lens unit are formed to have a convex-convex structure, and the first lens unit and the fourth lens unit are moved toward the object side along the optical axis. The second lens group, which is made of a positive meniscus lens having at least one convex surface facing the object side, is moved along the optical axis so as to correct the image plane fluctuation. , Compact 4 with good correction of aberration
It became possible to provide a group zoom lens.

[Brief description of the drawings]

FIG. 1 is a view showing the movement of a compact high-magnification four-unit zoom lens according to the present invention. FIG. 3 is an aberration curve diagram of the first embodiment, and FIG. 4 is an aberration curve diagram of the second embodiment. L ₁ , L ₁₂ : first to twelfth lenses X: optical axis, S: stop P ′: imaging position r ₁ , r ₂ ,... R ₂₂ : radius of curvature d ₁ , d ₂ ,. d ₂₁ : Thickness of each lens or air gap

Claims (1)

(57) [Claims] 1. A first lens group having a positive refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power are arranged in this order from the object side. In zooming from the wide-angle end to the telephoto end, the first lens unit and the fourth lens unit are integrally moved toward the object side, and the second lens unit is moved so as to correct image plane variation. The first lens group includes at least one positive lens and one negative lens, and the second lens group has a convex surface facing at least one object side. The third lens group includes at least one positive lens and one negative lens, and the fourth lens group includes at least one negative lens having a concave surface facing the object side. Compact high-magnification 4-group zoom lens 'S.