JP2879463B2 - Zoom lens - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens having a small variation in various aberrations used in a general user video camera and the like.

[Conventional technology]

In recent years, as a zoom lens used for a general user video camera or the like, a four-group zoom lens having a relatively large zoom ratio has been widely used.

In general, in this type of four-unit zoom lens, the second lens unit and the third lens unit move during zooming to perform a zooming operation when taught from the object side, and the first lens unit and the fourth lens unit are fixed. I have. The fixed fourth lens group includes a type composed of one group and a type composed of two groups.

[Problems to be solved by the invention]

When the fourth lens group is composed of one group, the length of the entire zoom lens system can be reduced, but it is difficult to correct aberration, and it is not expected to improve the brightness, zoom ratio, aberration correction, and the like of the lens. Was.

Further, when the fourth lens group is composed of two groups, it is advantageous in terms of aberration correction, but there is a disadvantage that the total length of the zoom lens system cannot be shortened as the length of the fourth lens group increases. Was.

SUMMARY OF THE INVENTION An object of the present invention is to provide a zoom lens in which the above-mentioned disadvantages are improved and the overall length of the zoom lens is short, the lens outer diameter is small, and various aberrations are satisfactorily corrected while having a high zoom ratio. .

[Means for solving the problem]

In order to achieve the above object, the present invention comprises, in order from the object side, a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group. The lens group is fixed during zooming, the second lens group,
A zoom lens in which a focal length is continuously changed by moving a lens group and a fourth lens group along an optical axis to change a mutual air space, and for zooming from a wide angle side to an image side. The second lens group and the third lens group are moved toward the image side such that the air gap between the lenses is reduced, and the diaphragm is located between the second lens group and the third lens group or the third lens group. A zoom lens is provided between a group and a fourth lens group, and is moved integrally with the third lens group for zooming.

[Action]

In the present invention, by moving the second lens group, the third lens group, and the fourth lens group along the optical axis to change the air gap between the lens groups, zooming from a wide angle to a telephoto state is achieved. It can be carried out.

During zooming from the wide-angle side to the telephoto side, the second lens group and the third lens group are moved toward the image side, and the diaphragm is moved integrally with the third lens group. The zoom lens can be moved in a wide range without being hindered by the three lens groups and the aperture, and while being a zoom lens with a high zoom ratio, the overall length of the zoom lens can be shortened and the size can be reduced. Can be maintained in a relatively weak state, thereby preventing the aberration from deteriorating. Also, during zooming, the stop is moved along the optical axis integrally with the third lens group, so that the height of off-axis rays can be prevented from increasing and the lens outer diameter can be reduced. Variation in aberration can be reduced.

In FIG. 1 showing a lens configuration and a moving mode of a zoom lens according to the present invention, reference numeral 1 denotes a first lens group having a positive combined focal length, 2 denotes a second lens group having a negative combined focal length, and 3 denotes a combined focal length. Is a third lens group having a positive focal length, 4 is a fourth lens group having a positive combined focal length, S is an aperture, O is an image plane, and X is an optical axis.

In FIG. 1, the first lens group 2, the third lens group 3, and the fourth lens group 4 are moved along the optical axis to zoom from the wide-angle end (W) to the telephoto end (T). air space D ₁ of the between the lens group 1 and the second lens group 2 increased, the air spacing between the second lens group 2 and the third lens group 3
D ₂ decreases. The third lens group 3 and the fourth lens group 4
Air space D ₃ and decreases once increases. During the zooming, the first lens group 1 is fixed.

The stop S is disposed before (object side) or after (image side) the third lens group 3 and is moved integrally with the third lens group 3.
When the stop S moves immediately after the second lens group 2 immediately after the second lens group 2, the off-axis ray height in the fourth lens group 4 increases on the wide angle side, and the ray on the telephoto side increases. The difference from the height is increased, and it is difficult to suppress the fluctuation of the field curvature aberration and the distortion. When the stop S is located immediately before the fourth lens group 4,
In the case of moving integrally with the lens group 4, the height of the light beam of the off-axis light beam with respect to the first lens group 1 on the wide-angle side increases, and the outer diameter of the first lens group 1 must be increased. It will be.

It is also conceivable to fix the stop S between the second lens group 2 and the third lens group 3 or between the third lens group 3 and the fourth lens group 4, but disposing the fixed group in the movable group. Causes problems in mechanism and operation.

On the other hand, by arranging the stop S before or after the third lens group 3 and moving it together with the third lens group 3, fluctuations of various aberrations can be reduced while keeping the optical system compact. can do.

Focusing in the range from the wide-angle end (W) to the telephoto end (T) is mainly performed by moving a part of the fourth lens unit 4 or the first lens unit 1 along the optical axis.

In the present invention, it is desirable that the third lens group 3 or the fourth lens group 4 has at least one aspheric surface. This is to minimize the lens configuration. Generally, this kind of zoom lens has 12 lenses.
Generally, the number is up to 13, but in recent years, in order to reduce costs, the use of aspherical lenses tends to simplify the lens configuration. In the case of the present invention, the third lens group 3
Denotes a moving group, and when the third lens group 3 is a single lens, it is particularly desirable to make the third lens group 3 aspherical in order to suppress variations in various aberrations. That is, by using an aspheric lens for the third lens group 3, spherical aberration and distortion in the entire zoom lens system can be corrected well. When an aspheric lens is used for the fourth lens group 4, it is possible to satisfactorily correct curvature of field.

In the present invention, when zooming from the wide-angle side to the telephoto side, the second lens group 2 and the third lens group 3 are moved toward the image side so that the air gap between them is reduced, and the second lens group 2 and the third lens group 3 are moved toward the image side.
Since the position of the lens unit 2 at the telephoto end (T) can be located closer to the image side than the position of the third lens unit 3 at the wide-angle end (W), the overall length of the zoom lens can be made shorter and more compact. A high zoom ratio of up to eight times is obtained. Note that the third lens group 3 may be moved toward the object side near the telephoto end (T) from the viewpoint of aberration correction or zoom ratio.

Further, the third focal length of the lens unit 3 f _3, when the focal length of the entire system at the wide-angle end to the _{f w, 2.5 <f 3 /} f w <4.5 is satisfied the condition of ... (1) Is desirable.

When the value goes below the lower limit of the condition (1), the positive refractive power of the fourth lens unit 4 can be weakened, which is advantageous for aberration correction.
The positive refractive power of the third lens group 3 becomes large, and it becomes difficult to configure the third lens group 3 with a single lens. If the lower limit of the condition (1) is exceeded, the amount of movement of the third lens unit 3 and the fourth lens unit 4 due to zooming becomes large, and a problem in mechanism occurs. On the other hand, when the value exceeds the upper limit of the condition (1), the positive refractive power of the fourth lens unit 4 becomes strong, and it becomes difficult to satisfactorily correct the aberration of the fourth lens unit 4 with a small number of lenses.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Here, 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 : thickness or air gap n _{i of} the i-th lens component counted from the object side : Refractive index for the d-line of the i-th lens component counted from the object side ν _i : Atsube number of the i-th lens component counted from the object side f ′: Composite focal length of the whole system M: Wide-angle end W: An intermediate position between the wide-angle end and the telephoto end T: telephoto end The aspherical surface is represented by *, and its shape is represented by X in the optical axis direction.
When the height on the axis and optical axis is h, It is represented by

Here, c is the reciprocal of the radius of curvature on the paraxial axis, K is the eccentricity, and a ₁ , a ₂ , a ₃ ,...

The lens configuration of the first embodiment shown in FIG. 2 is as follows.

The first lens group 1 is composed of a negative meniscus lens L ₁ and a convex surface directed toward the positive biconvex lens L ₂ and the object side positive meniscus lens L ₃ Metropolitan having a convex surface directed toward the object side. Second lens group 2
Includes a negative meniscus lens L ₄ with a convex surface toward the object side,
A cemented lens L ₅ + L ₆ Metropolitan a positive meniscus lens L ₆ having a convex surface directed toward the negative lens L ₅ and the object side of the biconcave. The third lens group 3 is composed of a positive lens L ₇ biconvex. Fourth lens group 4
Is composed of a positive meniscus lens L ₈ and a negative meniscus lens L ₉ and a biconvex positive lens L ₁₀ Metropolitan having a convex surface directed toward the object side. L ₁₁ is a low pass filter consisting of a plane-parallel plate. The stop S is disposed between the third lens unit 3 and the fourth lens unit 4 behind the third lens unit 3 and moves together with the third lens unit 3 during zooming. Focusing in the range wherein the wide-angle end (W) to the telephoto end (T), either by moving the optical axis of the positive lens L ₈ of the fourth lens group 4 and the negative lens L ₉ and the positive lens L ₁₀ integrally, Alternatively, the first lens group 1 is moved along the optical axis, or both are moved along the optical axis. However, if the positive lens L ₈ of the fourth lens group 4 and the negative lens L ₉ and the positive lens L ₁₀ can focusing by moving together, the first lens group 1
Is preferable because the outer diameter of the first lens unit 1 can be made smaller than when focusing is performed.

Eleventh surface and the thirteenth surface of the glass lens L ₈ of the fourth lens group 4 of the glass lens L ₇ of the third lens group 3 is an aspherical surface. Eleventh
The aspheric surface can favorably correct spherical aberration and distortion in the entire zoom lens system. The aspheric surface of the thirteenth surface can favorably correct field curvature aberration.

 The specific configuration is as shown in the table below.

The aberration curve according to this specific configuration is as shown in FIG.

Lens configuration of the second embodiment shown in Fig. 4, the diaphragm S is disposed in front of the third lens group 3, the glass lens L ₇ of the third lens group 3 of the 11th surface and the fourth lens group 4 except that aspheric surface is used in the seventeenth surface of the plastic lens L ₁₀ is first
This is the same as the embodiment. The function and effect of the aspherical surface are the same as in the first embodiment.

 The specific configuration is as shown in the table below.

An aberration curve according to this specific configuration is as shown in FIG.

The various aberrations in the aberration curve diagrams of the above embodiments indicate that they are sufficiently practical.

The aspheric lens in the first and second embodiments is made of a glass lens or a plastic lens.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, a zoom lens that has a high zoom ratio, can reduce the overall length of the lens, can be made compact, and can reduce variations in various aberrations. Is now available.

[Brief description of the drawings]

FIG. 1 is a view showing the manner of movement of a zoom lens according to the present invention. FIG. 2 is a layout diagram of each lens when the lens groups of the first embodiment are set at a wide-angle end (W) and a telephoto end (T). Figure 3 is the first
FIG. 4 is an aberration curve diagram of the embodiment, FIG. 4 is a layout diagram of each lens when the lens units of the second embodiment are at the wide-angle end (W) and the telephoto end (T), and FIG. FIG. 4 is an aberration curve diagram of FIG. L ₁ ... L ₁₀ : first lens to tenth lens L ₁₁ : low-pass filter X: optical axis, S: stop O: imaging surface r ₁ , r ₂ ,..., R ₂₀ : each surface of lens and low-pass filter curvature radius _{d 1, d 2, ...... d} 19: thickness or air space of the lens and the low-pass filter

Claims (2)

(57) [Claims] 1. A zoom lens system comprising: a first positive lens unit, a second negative lens unit, a third positive lens unit, and a fourth positive lens unit in order from the object side, wherein the first lens unit is fixed during zooming. A zoom lens system in which a focal length is continuously changed by moving a second lens group, a third lens group, and a fourth lens group along an optical axis to change an air gap therebetween, During zooming from the zoom lens to the telephoto side, the second lens group and the third lens group are moved toward the image side such that the air gap between the lenses is reduced,
The diaphragm is disposed between the second lens group and the third lens group or between the third lens group and the fourth lens group, and is moved integrally with the third lens group for zooming. Zoom lens system. 2. A patent characterized by satisfying 2.5 <f ₃ / f _w <4.5, where f _{3 is} the focal length of the third lens group and f _w is the focal length of the entire system at the wide-angle end. The zoom lens according to claim 1.