JPH1031155A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high optical performance over a specified photographic viewing angle and a specified variable power range by constituting a zoom lens of four lens group as a whole and properly setting the moving conditions and the refractive power of the respective lens groups at the time of a variable power action. SOLUTION: This zoom lens is provided with four lens groups L1-L4 of the first group L1 having the negative refractive power, the second group L2 having the positive refractive power, the third group L3 having the positive refractive power and the fourth group L4 having the negative refractive power in order from an object side. When the moving quantity of the first and the second groups L1 and L2 are respectively set to M1 and M2 when the variable power action is executed to a telephoto end from a wide-angle end, the condition of 1.1<M1/M2<1.6 is satisfied. Besides, the fourth group L4 is constituted of a single negative lens whose concave surface faces the object side and at least one surface of the negative lens is formed to be aspherical so that the negative refractive power becomes weak according as it approaches the peripheral part of the lens from the center thereof. Thus, the photographic viewing angle of bout 70 deg. and the variable power ratio of about 3.0 are secured at the wide-angle end and fluctuation in aberration accompanying the variable power action is excellently corrected. As the result, the high performance is obtained extending over the whole variable power range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small, high-magnification, wide-angle zoom lens suitable for a lens shutter camera, a video camera, and the like. The present invention relates to a zoom lens which is excellent in portability and has a reduced length (distance from one lens surface to an image surface).

[0002]

2. Description of the Related Art Recently, in a lens shutter camera, a video camera, and the like, a small zoom lens having a short overall lens length has been demanded with the downsizing of the camera.

In particular, lens shutter cameras have been increasingly miniaturized due to the development of peripheral technologies such as electric circuits for driving the zoom, and the photographing lenses provided therewith require high zoom ratio and compact zoom lenses. Have been.

Conventionally, as a zoom lens for a lens shutter, a so-called two-group zoom lens comprising two lens groups having positive and negative refractive power has been mainly used. Since the two-unit zoom lens has a simple lens configuration and a moving mechanism at the time of zooming, it has advantages such as downsizing of the camera and relatively low cost.

However, since the zooming operation must be performed by only one lens group, the zooming ratio is 1.6 to 1.6.
It is about twice, and forcibly increasing the zoom ratio causes an increase in the size of the lens system, and at the same time, it is difficult to maintain high optical performance.

On the basis of a two-unit zoom lens, the first unit is divided into two lens units having a positive refractive power.
A three-unit zoom lens which aims at high zoom ratio as a three-unit configuration having positive and negative refractive powers is disclosed in, for example, JP-A-3-282409, JP-A-4-37810, and JP-A-4-7651.
No. 1 publication and the like.

However, if an attempt is made to achieve a zoom lens system having a wide angle of view of, for example, a half angle of view of 35 ° or more with this lens group configuration, a change in the position of the entrance pupil during zooming becomes large. For this reason, it is very difficult to suppress aberration fluctuations due to zooming when achieving high zooming.

[0008] In addition, a zoom lens having a wide angle of view and a high zoom ratio by increasing the half angle of view at the wide angle end to about 38 ° and the zoom ratio by about 3.5 times by grouping multiple lenses has been proposed. JP 2
-72316 and Japanese Patent Laid-Open Publication No. 3-249614.

However, these zoom lens systems both have a large front lens diameter and a large total lens length, and are not always sufficient as a photographing lens for a compact camera.

In particular, when applied to a camera using an external finder, there is a problem that the lens barrel covers the field of view of the finder at the wide angle end. As a result, there is also a problem that the arrangement of the viewfinder and the form of the camera are restricted.

A four-group zoom lens having a relatively wide angle of view and a high zoom ratio, which comprises four lens groups of negative, positive, positive, and negative refractive power in order from the object side, is disclosed in, for example, Japanese Patent Application Laid-Open No. H4-2370.
No. 09 publication. However, this four-group zoom lens has a large number of lenses, and the front lens diameter tends to increase.

The four-group zoom lens proposed in Japanese Patent Application Laid-Open No. 64-15610 has a zoom ratio of about 3, but
The angle of view was not always sufficient.

[0013]

In general, if the refractive power of each lens unit is increased in a zoom lens, the amount of movement of each lens unit for obtaining a predetermined zoom ratio is reduced, and the overall length of the lens is reduced. High magnification can be achieved. However, if the refractive power of each lens group is simply increased, aberration fluctuations accompanying zooming increase, and it is difficult to obtain good optical performance over the entire zoom range, especially when achieving high zooming and widening the angle of view. There is a problem of becoming.

The present invention comprises four lens groups as a whole, and by appropriately setting the moving conditions, refractive power, etc. of each lens group during zooming, the shooting angle of view at the wide-angle end is reduced to 70.
It is an object of the present invention to provide a zoom lens having high optical performance over the entire zoom range of about ° and a zoom ratio of about 3.0.

[0015]

A zoom lens according to the present invention comprises, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power, and a negative lens unit. 4th of refractive power
The zoom lens has four lens groups, and when zooming from the wide-angle end to the telephoto end, the distance between the first and second groups and the distance between the second and third groups increase. Each of the lens units moves on the optical axis so that the distance between the fourth unit and the fourth unit decreases.
It is characterized in that the group and the group move integrally.

[0016]

1 to 3 are sectional views of lenses according to numerical examples 1 to 3 of the present invention. 1A to 3A show the wide angle end, FIG. 1B shows the middle position, and FIG. 1C shows the telephoto end. 4 to 6 show various aberration diagrams of Numerical Embodiment 1 of the present invention, FIGS. 7 to 9 show various aberration diagrams of Numerical Embodiment 2 of the present invention, and FIGS. 10 to 12 show numerical aberrations of Numerical Embodiment 3 of the present invention. It is a some aberration figure.

In the figure, L1 is a first group having a negative refractive power, L2 is a second group having a positive refractive power, L3 is a third group having a positive refractive power, L4
Denotes a fourth unit having a negative refractive power. Arrows indicate the moving direction of each lens group when zooming from the wide-angle side to the telephoto side. SP
Is an aperture, and IP is an image plane.

In this embodiment, at the time of zooming from the wide-angle end to the telephoto end, the distance between the first and second units and the distance between the second and third units are increased, and the distance between the third and fourth units is increased. Each lens group is moved to the object side on the optical axis so that is reduced. As a result, a predetermined zoom ratio and a wide angle of view are effectively achieved, and the size of the entire lens system is reduced.

In particular, in the present invention, the first lens unit L1 having a negative refractive power is composed of two lenses, a positive lens having both convex surfaces and a negative lens having a concave surface facing the object side, in order from the object side. The second lens unit L2 having a refractive power is composed of one meniscus positive lens having a convex surface facing the object side, and the third lens unit L3 having a positive refractive power is a meniscus lens having a convex surface facing the image surface. The fourth lens unit L4 having a negative refractive power is constituted by one lens of a meniscus-shaped negative lens having a convex surface facing the image surface side. doing. As a result, while maintaining a predetermined zoom ratio, aberration fluctuations caused by zooming are corrected well, and high optical performance is obtained over the entire zoom range.

The fourth lens unit comprises a single negative lens having a concave surface facing the object side. At least one lens surface of the negative lens has a weak negative refractive power from the center of the lens toward the periphery of the lens. It is composed of aspherical surfaces having different shapes, and corrects aberration fluctuations due to zooming, and particularly favorably corrects off-axis aberrations such as field curvature and distortion. The third lens unit has at least one aspherical surface. As a result, aberration fluctuations during zooming and focusing are favorably corrected.

The stop SP is moved integrally with the third unit as the magnification changes, thereby preventing the lens outer diameter of each lens unit from increasing. Also, focusing is performed by moving the third lens unit, so that fluctuations in aberrations during focusing are reduced.

At the time of zooming from the wide-angle end to the telephoto end, the first
The entire length of the lens at the wide-angle end is shortened by moving all of the fourth group from the group to the object side, thereby reducing the size of the entire camera when not used.

At the time of zooming from the wide-angle end to the telephoto end, when the moving amounts of the first and second units are M1 and M2, respectively, 1.1 <M1 / M2 <1.6 (1) We are trying to satisfy the conditions.

Conditional expression (1) relates to the ratio of the amount of movement between the first lens unit and the second lens unit during zooming, and is mainly used to shorten the overall length of the lens while favorably correcting field curvature. is there. If the upper limit of conditional expression (1) is exceeded and the amount of movement of the first lens unit is larger than that of the second lens unit, the overall length of the lens at the telephoto end becomes longer.

If the amount of movement of the first lens unit becomes smaller than the lower limit of conditional expression (1), it becomes difficult to satisfactorily correct aberration fluctuations caused by zooming, particularly fluctuations in chromatic aberration of magnification. come.

It is more preferable to set the numerical range of conditional expression (1) as follows: 1.2 <M1 / M2 <1.4 (1a).

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air spacing from the object side, and Ni and νi are the i-th lens surfaces in order from the object side. The refractive index and Abbe number of glass. In the aspherical shape, the radius of curvature at the center of the lens surface is R, the optical axis direction (the traveling direction of light) is the X axis, the direction perpendicular to the optical axis is the Y axis,
When B, C, D and E are each aspheric coefficients

[0028]

(Equation 1) It is represented by the following expression. “E−X” means “× 10 ^−X ”.

[0029]

[Outside 1]

[0030]

[Outside 2]

[0031]

[Outside 3]

[0032]

As described above, according to the present invention, the wide-angle end photographing is performed by appropriately configuring the moving conditions and the refracting power of each lens unit during zooming, as constituted by four lens units as a whole. It is possible to achieve a zoom lens having high optical performance over the entire zoom range with an angle of view of about 70 ° and a zoom ratio of about 3.0.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 4 is an aberration diagram at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 5 is an intermediate aberration diagram of the numerical example 1 of the present invention.

FIG. 6 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention;

FIG. 7 is an aberration diagram at a wide-angle end according to Numerical Example 2 of the present invention.

FIG. 8 is an intermediate aberration diagram of the numerical example 2 of the present invention.

FIG. 9 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention;

FIG. 10 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 11 is an intermediate aberration diagram of the numerical example 3 of the present invention.

FIG. 12 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

[Explanation of symbols]

 L1 First lens unit L2 Second lens unit L3 Third lens unit L4 Fourth lens unit SP Aperture IP image plane d d-line g g-line S Sagittal image plane M Meridional image plane

Claims (7)

[Claims] 1. A first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a negative refractive power. The distance between the first unit and the second unit and the second unit during zooming from the wide-angle end to the telephoto end.
Each lens group moves on the optical axis such that the distance between the third group and the third group increases, and the distance between the third group and the fourth group decreases, and the second group and the fourth group move integrally. Zoom lens. 2. The fourth group comprises a single negative lens having a concave surface facing the object side, and at least one lens surface of the negative lens has a weak negative refractive power from the center of the lens toward the periphery of the lens. The zoom lens according to claim 1, wherein the zoom lens has an aspherical shape. 3. The zoom lens according to claim 1, wherein said third group has at least one aspherical surface. 4. The zoom lens according to claim 1, wherein the third lens unit has a stop that moves integrally with zooming. 5. The zoom lens according to claim 4, wherein focusing is performed by moving said third lens unit. 6. The zoom lens system according to claim 1, wherein when zooming from the wide-angle end to the telephoto end, the first to fourth units are all moved to the object side. Zoom lens. 7. The zoom lens system according to claim 1, wherein when moving from the wide-angle end to the telephoto end, the first and second lens groups have a moving amount of M1 and M2, respectively, and satisfy the following condition: 1.1 <M1 / M2 <1.6. The zoom lens according to claim 1, wherein: