JPH11295595A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the compact zoom lens of a small lens number provided with high optical performance over the entire variable power range for which the photographing viewing angle of a wide angle end is a wide angle and a variable power ratio is high by appropriately setting mainly the moving condition of respective lens groups accompanying variable magnification, the refractive power of the respective lens groups and the variable power ratio of the respective lens groups, etc., in a 5-group zoom lens. SOLUTION: This zoom lens is provided with the five lens groups of the first group L1 of positive refractive power, the second group L2 of negative refractive power, the third group L3 of the positive refractive power, the forth group L4 of the positive refractive power and the fifth group L5 of the negative refractive power in order from an object side. At the time of the variable magnification from the wide angle end to a tele end, the respective lens groups are moved to the object side so as to increase the interval of the first group and the second group, increase the interval of the second group and the third group from the wide angle end to a middle zoom position, then reduce it to the tele end, increase the interval of the third group and the forth group and reduce the interval of the forth group and the fifth group. At the time of defining the image formation magnifications of the wide angle end and the tele end of the fifth group L5 as β5W and β5T, 2.5<β5T/β5W<5 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly, to a shooting angle of view of about 60 to 65 degrees at the wide angle end, an F number of about 3.5 to 4.5 at the wide angle end, and a zoom ratio of 4.3. ~
A portable photographic camera or video camera with a shortened overall length of the lens (distance from the first lens surface to the image surface) having good optical performance over the entire zoom range of about 4.7; and The present invention relates to a zoom lens suitable for an electronic still camera or the like.

[0002]

2. Description of the Related Art Heretofore, one of the photographing systems required for a photographic camera, a video camera, and the like has a high zoom ratio, a wide angle of view, and high optical performance over the entire zoom range. There is.

[0003] As a zoom lens, positive and negative in order from the object side
A zoom lens composed of five lens units having negative, positive, positive, and negative refractive powers and having a plurality of lens units moved at the time of zooming has a relatively high zoom ratio, which is relatively easy. JP-A-2-167520, JP-A-3-168
No. 214, JP-A-3-225307, JP-A-4-293007, JP-A-5-181061, JP-A-7-294817, JP-A-7-279
No. 79, JP-A-7-35979, JP-A-7-359
These are proposed in, for example, JP-A-151968 and JP-A-7-151969.

In Japanese Patent Application Laid-Open No. 63-195618, there are five lens units having positive, negative, positive, positive and negative refractive power in order from the object side, and lens units other than the first unit are moved. A zoom lens that performs focusing has been proposed.

In Japanese Patent Application Laid-Open No. 58-17981, there are four lens units having positive, negative, positive, and positive refractive power in this order from the object side. A zoom lens that divides into a lens unit having a negative refractive power and moves the lens unit having the negative refractive power to perform focusing has been proposed.

[0006]

Generally, in a five-unit zoom lens having five lens units having positive, negative, positive, positive, and negative refractive powers in order from the object side, a zoom ratio of 3.5 to 4.
In order to maintain a high optical performance over the entire zoom range while achieving a high zoom ratio of about 5, it is important to appropriately set the optical constants of each lens group constituting the lens system.

For example, in the above-described five-unit zoom lens,
Unless the moving conditions of each lens group during zooming, the refractive power of each lens group, and the zoom ratio of each lens group, etc. are not properly set, the occurrence of various aberrations due to zooming will increase, and images with good image quality will be produced. It becomes difficult to obtain.

In general, in order to increase the zoom ratio of a zoom lens, the number of lens units contributing to zooming is increased, or the refractive power of each lens unit is increased to increase the zooming effect. It is necessary to increase the amount of movement of the lens group that contributes to the magnification.
However, for example, in the method of strengthening the refractive power of the lens units, it is necessary to increase the number of lens components of each lens unit in order to satisfactorily correct fluctuations of various aberrations caused by zooming. A problem arises in that it becomes difficult.

In the method of increasing the amount of movement of the lens group,
It is necessary to secure a lot of space for the movement of the lens group due to zooming, and the overall length of the lens becomes longer. Especially when the movement form of the lens group is complicated, it is difficult to support the moving lens group in the lens barrel. As a result, it becomes difficult to reduce the size of the entire lens system.

According to the present invention, in a five-unit zoom lens, the moving conditions of the respective lens units, the refractive power of each of the lens units, the magnification ratio of each of the lens units, and the like are set appropriately. The object of the present invention is to provide a compact zoom lens having a high optical performance and a small number of lenses over the entire zoom range in which the shooting angle of view at the wide-angle end is about 60 to 65 degrees and the zoom ratio is about 3.5 to 4.5. I do.

[0011]

According to the present invention, there is provided a zoom lens system comprising: (1-1) a first unit having a positive refractive power, a second unit having a negative refractive power, and a third unit having a positive refractive power in order from the object side. Group, fourth group of positive refractive power,
The zoom lens system has five lens units of a fifth group having a negative refractive power. When zooming from the wide-angle end to the telephoto end, the distance between the first and second units increases, and the second and third units increase. The group spacing increases from the wide-angle end to an intermediate zoom position, then decreases to the telephoto end,
Each lens group is moved to the object side such that the distance between the third group and the fourth group increases and the distance between the fourth group and the fifth group decreases.

[0012]

1 to 3 are sectional views of a lens according to Numerical Examples 1 to 3 of the present invention, which will be described later. In the figure, W indicates the wide-angle end, M indicates the middle position, T indicates the zoom position at the telephoto end, and arrows indicate the movement trajectories of the respective lens units as the magnification changes from the wide-angle end to the telephoto end.

In the drawing, L1 is a first lens unit having a positive refractive power, L2 is a second lens unit having a negative refractive power, L3 is a third lens unit having a positive refractive power, and L4 is a positive lens.
Is a fourth unit having a positive refractive power, L5 is a fifth unit having a negative refractive power, S
P denotes an aperture, which is provided behind the third lens group. IP is an image plane.

In this embodiment, when zooming from the wide-angle end to the telephoto end, the distance between the first and second units increases, and the distance between the second and third units extends from the wide-angle end to the intermediate zoom position. Increases and decreases from the intermediate zoom position to the telephoto end,
Each lens group is moved to the object side so that the distance between the group and the fourth group increases and the distance between the fourth group and the fifth group decreases.

The amount of change in the distance between the lens units due to the magnification change is relatively largest in the first and second units, and then in the third and third units.
The change in the distance between the fourth lens group and the distance between the fourth and fifth lens groups is substantially the same, the change in the distance between the second lens group and the third lens group is the smallest, and the air distance is the largest at almost the middle zoom position.

In the present embodiment, the first lens unit is composed of a negative meniscus lens having a convex surface on the object side and a positive lens having a sharper curvature on the object side than on the image side. The second group is composed of a cemented lens in which a negative lens and a positive lens, both lens surfaces of which are concave, are cemented. The third group is composed of a positive single lens having a sharper curvature on the object side than on the image plane side. The third group is provided with a stop and moves by itself during zooming.

The fourth unit includes independent two lenses of a negative lens and a positive lens.
It consists of two lenses. An aspherical surface is provided on the lens surface closest to the object and the lens surface closest to the image in the fourth unit. The fifth unit includes a single negative lens having an aspheric surface with a concave surface facing the object side.

Focusing from an object at infinity to an object at a short distance is performed by moving the fourth unit to the object side. In the present embodiment, a floating operation in which a plurality of lens groups are moved by different amounts may be used.

The zoom lens according to the present invention can be achieved by satisfying the above-mentioned conditions. However, the zoom lens system can satisfactorily correct aberration fluctuations at the time of achieving a high zoom ratio, and can achieve high optical performance over the entire zoom range. It is preferable to satisfy at least one of the following conditions in order to obtain.

(A) When the imaging magnifications of the fifth lens unit at the wide-angle end and the telephoto end are β5W and β5T, the condition that 2.5 <β5T / β5W <5 (1) is satisfied. .

If the zoom ratio of the fifth lens unit becomes too large beyond the upper limit value of the conditional expression (1), it is not good because aberration fluctuations caused by zooming occurring in the fifth lens unit cannot be corrected.

If the lower limit value of the conditional expression (1) is exceeded and the zoom ratio of the fifth lens unit becomes too small, the variable power sharing of the other lens units becomes large, and the whole lens system becomes large. Absent.

It is more preferable in terms of aberration correction if the numerical range of conditional expression (1) is set as follows.

2.7 <β5T / β5W <3.5 (1a) (a) The distance between the second lens unit and the third lens unit at the wide-angle end is D2W, and the distance between the lens units at the intermediate zoom position is D2W. When the maximum lens group distance is D2M and the lens group distance at the telephoto end is D2T, the following condition is satisfied: D2W <D2M ‥‥‥ (2) D2T <D2M ‥‥‥ (3)

Conditional expression (2) relates to the distance at the zoom position where the distance between the second and third lens groups is maximized at an intermediate zoom position between the distance between the second and third lens groups at the wide-angle end. Deviates from the distance, the distance between the second lens unit and the third lens unit at the wide-angle end increases, and the overall length and the front lens diameter at the wide-angle end increase.

Condition (3) relates to the distance between the zoom position where the distance between the second lens unit and the third lens unit becomes maximum at the intermediate zoom position and the distance between the second lens unit and the third lens unit at the telephoto end. If it is out of the range, it becomes difficult to correct the coma flare in the middle range when high zooming is performed.

It is more preferable to set the conditional expressions (2) and (3) as follows.

2 × D2W <D2M ‥‥‥ (2a) 2 × D2T <D2M ‥‥‥ (3a) 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. Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

[0029]

[Outside 1]

[0030]

[Outside 2]

[0031]

[Outside 3]

[0032]

[Table 1]

[0033]

As described above, according to the present invention, in the five-unit zoom lens, the movement condition of each lens unit, the refracting power of each lens unit, and the zoom ratio of each lens unit are mainly associated with zooming. By appropriately setting the shooting angle of view at the wide-angle end,
A compact zoom lens having high optical performance and a small number of lenses can be achieved over the entire zoom range of about 0 to 65 degrees and a zoom ratio of about 3.5 to 4.5.

[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 group L2 Second group L3 Third group L4 Fourth group L5 Fifth group SP Aperture IP image plane d d-line g g-line ΔS Sagittal image plane ΔM Meridional image plane

Claims (6)

[Claims] 1. A first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power, and a negative refractive power in order from the object side. In zooming from the wide-angle end to the telephoto end, the distance between the first and second groups increases, and the distance between the second and third groups becomes wide-angle. Each lens group is increased such that the distance from the end increases to an intermediate zoom position, then decreases to the telephoto end, the distance between the third group and the fourth group increases, and the distance between the fourth group and the fifth group decreases. A zoom lens that is moved to the object side. 2. The zoom according to claim 1, wherein when the imaging magnification of the fifth lens unit at the wide-angle end and the telephoto end is β5W and β5T, the following condition is satisfied: 2.5 <β5T / β5W <5. lens. 3. The zoom lens according to claim 1, wherein focusing from an object at infinity to an object at a short distance is performed by moving the fourth unit to the object side. 4. The zoom lens according to claim 1, wherein the first group has at least one positive lens and at least one negative lens. 5. The zoom lens according to claim 1, wherein the lens closest to the object in the fifth group is a negative lens. 6. The zoom lens according to claim 5, wherein said fifth group includes a single negative lens.