JPH11223772A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a four-group zoom lens with portability in which a photographic field angle can be widened, and lens full length (a distance from the first lens face to an image face) can be shortened. SOLUTION: This zoom lens is provided with four lens groups, that is, a first group L1 with a power refractive power, second group L2 with a positive refractive power, third group L3 with a positive refractive power, and fourth group with a negative refractive power successively from an objective side. In this case, at the time of varying a power from a field angle edge to a telephoto edge, each lens group is moved on an optical axis so that an interval between the first group L1 and the second group L2 can be increased, and an interval between the third group L3 and the fourth group L4 can be decreased. When a focal distance of the first group L1 is f1, and the synthetic focal distance at the telephoto edges of the first group L1 and the second group L2 are respectively f1 and 2T, a condition that 3<f1/f1 and 2T<50 is fulfilled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact zoom lens having a high zoom ratio and a wide angle of view 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 reduces the total lens length (distance from the first lens surface to the image surface).

[0002]

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

In particular, the lens shutter camera has been increasingly miniaturized due to the development of peripheral technology such as an electric circuit for driving a zoom, etc., and a photographic lens provided for the camera has been required to have a high zoom ratio and a compact zoom lens. Have been.

As a zoom lens, positive and negative in order from the object side
Consists of four lens groups of positive, positive, and negative refractive power,
A four-group zoom lens having a relatively wide angle of view and a high zoom ratio is disclosed in, for example, JP-A-3-208004 and JP-A-3-24961.
4, JP-A-3-50516, JP-A-3-8
It has been proposed in, for example, US Pat.

[0005]

Problems to be Solved by the Invention Japanese Patent Laid-Open No. Hei 3-208
The zoom lenses proposed in Japanese Patent Application Laid-Open No. 004 and JP-A-3-249614 have a relatively wide angle of view, but have a large front lens diameter and the entire lens system is not always small.

The zoom lens proposed in JP-A-3-50516 and JP-A-3-85508 has a telephoto ratio (ratio of the total length of the lens at the telephoto end to the focal length at the telephoto end) of 1 which is large. It exceeded, and the whole lens system was big.

A conventional four-unit zoom lens, which includes four lens units having positive, positive, positive, and negative refractive powers in order from the object side, has a high refractive power because the first group has a relatively narrow positive refractive power. Although it is preferable as a telephoto zoom lens with a variable magnification ratio, it is difficult to increase the angle of view at the wide-angle end.

Further, these four-group zoom lenses tend to have a large number of lenses, a large front lens diameter, and a large overall lens system.

The present invention comprises four lens groups as a whole, and by appropriately setting the moving conditions and the refractive power of each lens group during zooming, the photographic angle of view at the wide-angle end is increased to 70.
A telephoto ratio of 0.95 or less for reducing the overall length of the lens at the telephoto end, which has high optical performance over the entire zoom range with a zoom ratio of about 3.5 and a high zoom ratio with a wide angle of view of about The purpose of the present invention is to provide a compact zoom lens.

[0010]

The zoom lens according to the present invention comprises: (1-1) a first unit having a positive refractive power, a second unit having a positive refractive power, and a third unit having a positive refractive power in order from the object side. And a fourth lens unit having a negative refractive power, the fourth lens unit having a fourth lens unit. When zooming from the wide-angle end to the telephoto end, the distance between the first unit and the second unit increases. Each lens group moves on the optical axis so that the distance between the groups decreases, and the focal length of the first group is f1, and the first group and the second group
When the combined focal length at the telephoto end of the group is f1, 2T, 3 <f1 / f1, 2T <50 (1) is satisfied.

(1-2) In order from the object side, a first lens unit having a positive 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. Each lens group has two lens groups such that at the time of zooming from the wide-angle end to the telephoto end, the distance between the first and second groups increases and the distance between the third and fourth groups decreases. Moving on the optical axis, the focal length of the first lens unit is f1, the focal length at the wide angle end of the entire system is fW, and the effective screen size of the image plane is φ.
Where 3 <f1 × fW / φ ² <50 (2).

[0012]

1 to 6 are sectional views of lenses according to numerical examples 1 to 6 of the present invention. 1 to 6, (A) shows the wide-angle end, (B) shows the middle, and (C) shows the telephoto end. FIGS. 7 to 9 show the wide-angle end of Numerical Embodiment 1 of the present invention.
It is an aberration figure of a middle and a telephoto end. 10 to 12 are aberration diagrams at the wide-angle end, at the middle, and at the telephoto end according to Numerical Embodiment 2 of the present invention. FIGS. 13 to 15 show the wide-angle end of Numerical Embodiment 3 of the present invention.
It is an aberration figure of a middle and a telephoto end. 16 to 18 are aberration diagrams at the wide-angle end, at the middle, and at the telephoto end in Numerical Embodiment 4 of the present invention. FIGS. 19 to 21 show the wide-angle end of Numerical Embodiment 5 of the present invention.
It is an aberration figure of a middle and a telephoto end. 22 to 24 are aberration diagrams at the wide-angle end, at the middle, and at the telephoto end in Numerical Example 6 of the present invention.

In the drawing, L1 is a first lens unit having a positive refractive power, L2 is a second lens unit having a positive refractive power, L3 is a third lens unit having a positive refractive power, and L4 is a positive lens.
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 a stop provided between the second and third units. 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 as to reduce the interval. This effectively achieves a predetermined zoom ratio and wide angle of view,
The entire lens system is downsized.

The aperture stop SP moves together with the fourth lens unit in the first and second numerical embodiments shown in FIGS.
In Numerical Examples 3 to 6, the lens unit moves integrally with the third lens unit. As described above, the stop SP is moved in accordance with zooming, thereby preventing an increase in the lens outer diameter of each lens unit.

Focusing from an object at infinity to an object at a close distance is performed by moving a third lens unit, which will be described later, to the object side to reduce fluctuations in aberrations during focusing.

In the present invention, the first lens unit L1 having a positive 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 includes a single meniscus positive lens having a convex surface facing the object side.
The group L3 is composed of a meniscus negative lens having a convex surface facing the image surface side and a positive lens having both lens surfaces convex. The fourth lens unit L4 having a negative refractive power has a convex surface facing the image surface side. It is composed of a single meniscus negative lens. 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 third lens unit has at least one aspherical surface. As a result, aberration fluctuations during zooming and focusing are favorably corrected.

The fourth lens unit is composed of a single negative lens having a concave surface facing the object side, and at least one lens surface of the negative lens has a weaker negative refractive power from the center of the lens toward the periphery of the lens. It is made up of an aspherical surface and corrects aberration fluctuations due to zooming, and particularly favorably corrects off-axis aberrations such as field curvature and distortion.

A zoom lens according to a first aspect of the invention is characterized by having the above-described configuration (1-1).

Of these, conditional expression (1) is for reducing the overall length of the lens at the telephoto end without excessively increasing the diameter of the front lens, even though the zoom lens is a high-power zoom lens starting from the wide-angle end. That is, it relates to the tele ratio. When the focal length f1 becomes shorter than the lower limit of conditional expression (1),
If the diameter of the front lens becomes excessively large, and if the diameter exceeds the upper limit, the telephoto ratio becomes large, which is an obstacle to downsizing the camera.

A zoom lens according to a second aspect of the present invention is characterized by having the above-described configuration (1-2).

As described above, in order to reduce the telephoto ratio, it is preferable that the focal length f1 is short (the refractive power of the first lens unit is strong), but if the focal length f1 is too short, the zoom including the wide-angle system is reduced. In the case of a lens, the front lens diameter becomes large. Conditional expression (2) indicates that, in the zoom type of the present invention, the condition of the balance should be substantially inversely proportional to the focal length f1 of the image circle as well as the width having a relationship with the focal length fW at the wide-angle end. That is what I found. If the lower limit value of conditional expression (2) is exceeded, the front lens diameter becomes too large, and if the upper limit value is exceeded, the telephoto ratio does not decrease, which is not good.

In the present invention, in order to further effectively obtain the zoom lens aimed at by the present invention, it is preferable to satisfy at least one of the following constitutions.

(A-1) When the focal length of the i-th lens unit is fi, the following condition is satisfied: 1 <f2 / f3 <5 (3)

Conditional expression (3) is for effectively performing focusing by moving the third lens unit in a zoom lens having a refractive power arrangement as described above. If the lower limit of conditional expression (3) is exceeded, the third condition will be satisfied during focusing.
The amount of movement of the group becomes too large, and as a result, problems such as an increase in the close distance or an increase in the overall length of the lens occur. On the other hand, when the value exceeds the upper limit, the focus sensitivity becomes too high and the focus control becomes difficult.

(A-2) When the distances between the wide-angle end and the telephoto end of the first and second units are d1W and d1T, respectively, and the focal length of the entire system at the telephoto end is fT.

[0028]

(Equation 3) Satisfying the following conditions.

Conditional expression (4) relates to the balance between the amount of movement during zooming of the first lens unit and the focal length at the telephoto end. The first lens unit moves relatively greatly during zooming, and greatly changes the distance between the first lens unit and the second lens unit. This is due to off-axis aberrations, particularly chromatic aberration of magnification, that occur with the movement of the fourth lens unit consisting of a single lens. This is to correct the fluctuation. At this time, if the lower limit of conditional expression (4) is exceeded, correction of the above-mentioned aberration fluctuations will be insufficient, and if the upper limit is exceeded, the overall length of the telephoto will be too long, which will be an obstacle to miniaturization.

(A-3) Assuming that the imaging magnifications of the fourth lens unit at the wide-angle end and the telephoto end are β4W and β4T, respectively, the following condition is satisfied: 2 <β4T / β4W <5 (5) It is.

Conditional expression (5) is the fourth factor which is responsible for the main variable power sharing.
It represents the degree of zooming in the group. If the lower limit of conditional expression (5) is exceeded, in order to achieve a high magnification as in the present invention, it is necessary to secure a variable power sharing by other lens groups, and the power arrangement of the present invention deviates from the power arrangement, and the entire lens system becomes large. On the other hand, if the upper limit value is exceeded, it becomes impossible to maintain good aberration when the fourth unit is constituted by a single lens.

(A-4) The second group has at least one positive lens L2P, and the radii of curvature of the object-side and image-side lens surfaces of the positive lens L2P are respectively R2P1, R2.
When P2

[0033]

(Equation 4) Satisfying the following conditions.

Conditional expression (6) is mainly for favorably correcting coma over the entire zoom range. If the condition is not satisfied, it becomes difficult to favorably correct coma.

(A-5) The second unit is a single lens L2
a, and the Abbe number of the material of the lens L2a is νda
20 <νda <26 (7) This condition must be satisfied.

Conditional expression (7) is mainly for favorably correcting magnification chromatic aberration at the telephoto end. Outside this range, it becomes difficult to correct lateral chromatic aberration.

In each of the above-mentioned conditional expressions (1) to (7), it is preferable to set the numerical value range as follows in view of aberration correction.

5 <f1 / f1, T <40 (1a) 5 <f1 · fW / φ ² <40 (2a) 1.5 <f2 / f3 <3.5 (3a) )

[0039]

(Equation 5) 2 <β4T / β4W <4 (5a)

[0040]

(Equation 6) 21 <νda <24 (7a) The conditional expression (3a) may be further set as follows.

2 <f2 / f3 <3 (3b) Next, numerical examples of the present invention will be described. In the numerical examples, R
i is the radius of curvature of the i-th lens surface in order from the object side, D
i is the i-th lens thickness and air gap from the object side, Ni
And νi are the refractive index and Abbe number of the glass of the i-th lens in order from the object side. 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, and B, C, D,
When E is each aspheric coefficient

[0042]

(Equation 7) It is represented by the following expression. Also, “eX” is “× 10^-XMeans
I taste.

Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

[0044]

[Outside 1]

[0045]

[Outside 2]

[0046]

[Outside 3]

[0047]

[Outside 4]

[0048]

[Outside 5]

[0049]

[Outside 6]

[0050]

[Table 1]

[0051]

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 the four lens units as a whole. The angle of view is as wide as 70 ° and the zoom ratio is 3.5
A telephoto ratio of 0.1 at the telephoto end, which has high optical performance over the entire zoom range of a high zoom ratio and a high zoom ratio.
A small zoom lens of 95 or less can be achieved.

[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 a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 5 is a sectional view of a lens according to a numerical example 5 of the present invention.

FIG. 6 is a sectional view of a lens according to a numerical example 6 of the present invention.

FIG. 7 is a diagram showing various aberrations at the wide-angle end according to Numerical Embodiment 1 of the present invention;

FIG. 8 is a diagram showing various aberrations in the middle of Numerical Embodiment 1 of the present invention.

FIG. 9 is a diagram showing various aberrations at the telephoto end according to Numerical Embodiment 1 of the present invention.

FIG. 10 is a diagram showing various aberrations at the wide-angle end according to Numerical Example 2 of the present invention.

FIG. 11 is a diagram showing various aberrations in the middle of Numerical Example 2 of the present invention;

FIG. 12 is a diagram illustrating various aberrations at the telephoto end according to Numerical Example 2 of the present invention;

FIG. 13 is a diagram showing various aberrations at the wide-angle end according to Numerical Example 3 of the present invention.

FIG. 14 is a diagram showing various aberrations in the middle of the numerical example 3 of the present invention;

FIG. 15 is a diagram showing various aberrations at the telephoto end according to Numerical Example 3 of the present invention;

FIG. 16 is a diagram showing various aberrations at the wide-angle end according to Numerical Example 4 of the present invention.

FIG. 17 is a diagram showing various aberrations in the middle of the numerical example 4 of the present invention;

FIG. 18 is a diagram showing various aberrations at the telephoto end according to Numerical Example 4 of the present invention.

FIG. 19 is a diagram illustrating various aberrations at the wide-angle end according to Numerical Example 5 of the present invention.

FIG. 20 is a diagram showing various aberrations in the middle of the numerical example 5 of the present invention;

FIG. 21 is a diagram illustrating various aberrations at the telephoto end according to Numerical Example 5 of the invention.

FIG. 22 is a diagram illustrating various aberrations at the wide-angle end according to Numerical Example 6 of the present invention;

FIG. 23 is a diagram showing various aberrations in the middle of the numerical example 6 of the present invention;

FIG. 24 is a diagram showing various aberrations at the telephoto end according to Numerical Example 6 of the present invention;

[Explanation of symbols]

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

Claims (8)

[Claims] 1. A first lens unit having a positive 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 increases upon zooming from the wide-angle end to the telephoto end,
Each lens unit moves on the optical axis so that the distance between the third unit and the fourth unit decreases, and the focal length of the first unit is f1, and the combined focal length of the first unit and the second unit at the telephoto end. Where f <1 / T and f <1T. 2. Four lens groups, in order from the object side, a first group having a positive refractive power, a second group having a positive refractive power, a third group having a positive refractive power, and a fourth group having a negative refractive power. The distance between the first unit and the second unit increases upon zooming from the wide-angle end to the telephoto end,
Each lens group moves on the optical axis so that the distance between the third group and the fourth group is reduced, the focal length of the first group is f1, the focal length of the entire system at the wide-angle end is fW, and the effective image plane. A zoom lens characterized by satisfying 3 <f1 × fW / φ ² <50 when a screen size is φ. 3. The zoom lens according to claim 1, wherein a condition of 1 <f2 / f3 <5 is satisfied when a focal length of the i-th lens unit is fi. 4. When the distance between the first lens unit and the second lens unit at the wide-angle end and the telephoto end is d1W and d1T, respectively, and the focal length of the entire system at the telephoto end is fT. 3. The zoom lens according to claim 1, wherein the following condition is satisfied. 5. The condition that 2 <β4T / β4W <5 when the imaging magnifications of the fourth lens unit at the wide-angle end and the telephoto end are β4W and β4T, respectively. Zoom lens. 6. The second group has at least one positive lens L2P, and the radii of curvature of the object-side and image-side lens surfaces of the positive lens L2P are R2P1 and R2P2, respectively. ] 3. The zoom lens according to claim 1, wherein the following condition is satisfied. 7. The zoom lens according to claim 3, wherein the third lens unit is moved to the object side when focusing from an object at infinity to a close object. 8. The lens system according to claim 6, wherein the second lens unit includes a single lens L2a, and satisfies the following condition: 20 <νda <26 when the Abbe number of the material of the lens L2a is νda. Zoom lens.