JPH11133304A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a photographing viewing angle at a wide-angle end include a standard photographing viewing angle and to obtain high optical performance over an entire variable power range by providing five lens groups, moving them so that an interval between specified groups may be increased or decreased in the case of varying power and making the refractive power of each group satisfy specified conditions. SOLUTION: This zoom lens is provided with five lens groups L1 to L5. In the case of varying the power from a wide-angle end to a telephoto end, the 1st, the 3rd and the 5th groups L1, L3 and L5 are moved to an object side so that the interval between the 1st and the 2nd groups L1 and L2 may be increased, the interval between the 2nd and the 3rd groups L2 and L3 may be decreased, the interval between the 3rd and the 4th groups L3 and L4 may be increased, and the interval between the 4th and the 5th groups L3 and L4 may be decreased. Assuming that the focal distance of an i-th group is (fi) and the focal distance of an entire system at the wide-angle end is (fw), the lens satisfies the conditions; 1.2<f1/fw<2.6, 0.4<|f2/fw|<1.2, 0.75<f3/fw<1.8, 0.95<f4/fw<2.4 and 0.6<|f5/fw|<1.7.

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 full zoom range in which a photographing angle of view at the wide angle end is about 40 degrees, an F number is about 4.7 to 5.9, and a zoom ratio is about 3.5. The present invention relates to a telephoto zoom lens having a high zoom ratio including a standard angle of view suitable for a photographic camera, a video camera, an electronic still camera, and the like having excellent optical performance.

[0002]

2. Description of the Related Art Conventionally, 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 a standard angle of view, and has high optical performance over the entire zoom range. There is a telephoto end zoom lens.

As a telephoto type zoom lens, there are five lens units having positive, negative, positive, positive, and negative refractive power in order from the object side, and a plurality of lens units are moved during zooming. Is relatively easy to achieve a high zoom ratio. For example, Japanese Patent Application Laid-Open Nos. 2-167520 and 3-16821.
No. 4, JP-A-3-225307, JP-A-4-29300
No. 7, JP-A-5-181061, JP-A-7-29481
No. 7 has been proposed.

[0004]

Generally, in a five-unit zoom lens comprising five lens units having positive, negative, positive, positive, and negative refractive powers in order from the object side, a zoom ratio of 3 including a standard angle of view is included. In order to maintain a high optical performance over the entire zoom range while achieving a high zoom ratio of about 0.5, 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.

According to the present invention, in a five-unit zoom lens, by appropriately setting the moving conditions of each lens unit, the refractive power of each lens unit, the zoom ratio of each lens unit, etc. , Including a shooting angle of view at the wide-angle end of about 40 degrees, including a standard shooting angle of view, and a zoom ratio of about 3.5 over the entire zoom range,
It is intended to provide a zoom lens having high optical performance.

[0007]

According to the present invention, there is provided a zoom lens comprising: (1-1) a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power in order from the object side. Group, fourth with positive refractive power
A fifth lens unit having a negative refractive power and a fifth lens unit having a negative refractive power. Upon zooming from the wide-angle end to the telephoto end, the distance between the first and second units increases. The distance between the third group and the fourth group decreases, the distance between the third group and the fourth group increases, and the distance between the fourth group and the fifth group increases.
When the first, third, and fifth groups are moved to the object side so that the distance between the groups is reduced, the focal length of the i-th group is fi, and the focal length of the entire system at the wide-angle end is fW. .2 <f1 / fw <2.6 (1) 0.4 <| f2 / fw | <1.2 (2) 0.75 <f3 / fw <1.8 ( 3) 0.95 <f4 / fw <2.4 ‥‥‥ (4) 0.6 <| f5 / fw | <1.7 ‥‥‥ (5)

[0008]

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

FIGS. 2 to 4 are lens sectional views at the wide-angle end of Numerical Examples 2 to 4 of the present invention. In the figure, L1 is a first group having a positive refractive power, L2 is a second group having a negative refractive power, L3 is a third group having a positive refractive power, L4 is a fourth group having a positive refractive power, and L5 is a negative group. A fifth group SP having a refractive power is a stop, which is provided in front of the third group. 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 increases, the distance between the second and third units decreases, and The first, third, and fifth groups are moved to the object side such that the distance between the fourth group increases and the distance between the fourth group and the fifth group decreases. The second and fourth units are fixed during zooming.

The stop SP is moved integrally with the third lens unit. Focusing from an object at infinity to an object at a short distance is performed by moving the first lens unit to the object side.

In this embodiment, focusing may be performed by moving the fourth lens unit to the object side or moving the fifth lens unit to the image plane side. In addition, floating which is performed by moving a plurality of lens groups by different amounts may be used.

In the present embodiment, as described above, the refractive power of each lens group is set so as to satisfy the conditional expressions (1) to (5), and each lens group is zoomed based on the above-described conditions upon zooming. By moving the zoom lens, zooming is performed by effectively assigning zooming to each lens group.
Aberration correction is performed satisfactorily over the entire zoom range, including the degree and standard angle of view.

Next, the technical meaning of each of the above conditional expressions will be described. Conditional expression (1) is a condition for appropriately setting the focal length of the first lens unit. Generally, like the zoom lens according to the present invention, a zoom lens of a so-called positive lead type, which is preceded by a convex lens group (a lens group having a positive refractive power), increases the overall optical length by increasing the positive refractive power of the first group. This is advantageous for shortening, and furthermore, it is easy to obtain a telephoto type refractive power arrangement at the telephoto end, so that it is easy to secure a bright FNo.

However, if the positive refracting power of the first lens unit is excessively increased, it becomes difficult to correct the spherical aberration particularly at the telephoto end, and it becomes difficult to obtain the retrofocus type refracting power at the wide-angle end. It is difficult to widen the angle of view.

Conditional expression (1) is set in view of the above-mentioned reason. If the value exceeds the upper limit, it becomes difficult to reduce the size of the entire optical system, secure a bright FNo, and exceed the lower limit. In addition, it becomes difficult to correct spherical aberration at the telephoto end, or it is difficult to arrange a retrofocus type refractive power at the wide-angle end.

Conditional expression (2) is a condition for appropriately setting the focal length of the second lens unit and for favorably correcting mainly distortion. When the value exceeds the upper limit of conditional expression (2), it becomes difficult to arrange the retrofocus type refractive power at the wide-angle end, which is not good. If the lower limit value is exceeded, it becomes difficult to correct negative distortion at the wide-angle end.

Conditional expression (3) is a condition for appropriately setting the focal length of the third lens unit and for favorably correcting mainly spherical aberration. If the value exceeds the upper limit of conditional expression (3), spherical aberration tends to be overcorrected, which is not good. Conversely, if the value exceeds the lower limit, spherical aberration tends to be insufficiently corrected, which is not preferable.

Conditional expression (4) is a condition for appropriately setting the focal length of the fourth lens unit and for mainly maintaining good image plane characteristics. When the value exceeds the upper limit of conditional expression (4), spherical aberration tends to be overcorrected, and at the same time, it becomes difficult to correct positive distortion at the telephoto end. If the value exceeds the lower limit, the Petzval sum increases in the positive direction, which is not good.

Conditional expression (5) is a condition for properly setting the focal length of the fifth lens unit and for mainly correcting distortion well. When the value exceeds the upper limit of conditional expression (5), it becomes difficult to correct negative distortion at the wide-angle end. Also, if the lower limit is exceeded, it becomes difficult to correct positive distortion at the telephoto end, and at the same time,
It becomes difficult to secure a sufficient back focus at the wide angle end.

In this embodiment, it is more preferable that the numerical range of the conditional expressions (1) to (5) is set as follows: 1.5 <f1 / fw <1.9１ (1a) 0.5 <| f2 / fw | <0.9 ‥‥‥ (2a) 1.0 <f3 / fW <1.3 ‥‥‥ (3a) 1.3 <f4 / fw <1.7 ‥‥‥ (4a) 0.8 <| f5 /Fw|<1.3‥‥‥(5a).

The zoom lens according to the present invention is achieved by satisfying the above-mentioned conditions. However, the zoom lens can satisfactorily correct aberration fluctuations at the time of achieving a higher zoom ratio, and can achieve high optical performance over the entire screen. To achieve this, it is preferable to satisfy at least one of the following conditions.

(A1) The i-th unit has at least two positive lenses and one negative lens. When the zoom ratio of the i-th group is Zi and the zoom ratio of the entire system is Z, 1 <logZ2 / LogZ <2 ‥‥‥ (6) 0.15 <logZ5 / logZ <0.25 ‥‥‥ (7)

At the telephoto end, the first group has a higher amount of land rays (rays emitted from an axis at infinity and most distant from the optical axis) at the telephoto end. large.

On the other hand, at the wide-angle end, the off-axis principal ray passes through a relatively high position, so that it has a large effect on astigmatism and field curvature. As described above, since the first group is a positive lens group that is greatly affected by various aberrations in the entire optical system, the positive refractive power of the first group is dispersed into at least two positive lenses, and at least one more lens is dispersed. The residual aberration is corrected by the negative lens, and as a result, various aberrations of the entire optical system are favorably corrected.

Conditional expression (6) is a condition for appropriately setting the zoom ratio of the second lens unit to the zoom ratio of the entire zoom lens system. If the upper limit value is exceeded, it becomes difficult to correct the variation in aberration of the second unit due to zooming. If the lower limit value is exceeded, the burden of zooming on lens units other than the first and second units becomes too large. Therefore, it becomes difficult to correct aberration fluctuations in the entire zoom lens system.

Conditional expression (7) is a condition for appropriately setting the zooming ratio of the fifth unit to the zooming ratio of the entire zoom lens system. If the upper limit value is exceeded, it becomes difficult to correct the variation in aberration of the fifth unit due to zooming. If the lower limit value is exceeded, the burden of zooming on the lens units other than the first and fifth units increases. If it is too long, it becomes difficult to correct aberration fluctuations in the entire zoom lens system.

In this embodiment, it is more preferable that the numerical ranges of the conditional expressions (6) and (7) are set as follows: 1.3 <logZ2 / logZ <1.7 (6a) 0.17 <logZ5 / It is preferable to set logZ <0.2０．２ (7a).

(A2) The second group has at least two negative lenses and one positive lens, the fourth group has at least one positive lens and a negative lens, and the fifth group has at least one It has a positive lens and a negative lens.

By dispersing the negative refracting power of the second lens unit into at least two negative lenses and correcting the residual aberration with at least one negative lens, it is possible to correct the negative distortion particularly at the wide angle end. Have gone to.

A negative aberration correcting lens is arranged in the fourth lens unit having a positive refractive power to facilitate spherical aberration correction. A positive aberration correction lens is arranged in the fifth unit having a negative refractive power, and the correction of the positive distortion at the telephoto end is particularly excellent.

(A3) The first unit is composed of a negative meniscus lens having a convex surface facing the object side and two positive lenses having a strong convex surface on the object side. Thereby, good optical performance is obtained over the entire zoom range.

(A4) The second group is composed of a negative lens with both lens surfaces concave, a positive lens with both lens surfaces convex, and a negative lens with both lens surfaces concave.

(A5) The third unit is a single positive lens having a convex surface facing the image surface side or a meniscus-shaped negative lens having a convex surface facing the image surface side, and a meniscus-shaped positive lens having a convex surface facing the image surface side. Three lenses, a lens and a positive lens, or a meniscus-shaped positive lens with the convex surface facing the image side, and two positive lenses
It consists of two lenses.

(A6) The fourth unit is composed of two lenses: a positive lens having both convex surfaces and a negative lens having a concave surface facing the object side.

(A7) The fifth unit is composed of a positive lens having a convex surface facing the image plane side and a negative lens having both lens surfaces concave. Thereby, good optical performance is obtained over the entire zoom range.

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

[0038]

[Outside 1]

[0039]

[Outside 2]

[0040]

[Outside 3]

[0041]

[Outside 4]

[0042]

[Table 1]

[0043]

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. The shooting angle of view at the wide-angle end is 4
A zoom lens having high optical performance can be achieved over the entire zoom range including about 0 degrees, the standard photographing angle of view, and a zoom ratio of about 3.5.

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

FIG. 5 is an aberration diagram of Numerical Example 1 of the present invention.

FIG. 6 is an aberration diagram of a numerical example 2 of the present invention.

FIG. 7 is an aberration diagram of a numerical example 3 of the present invention.

FIG. 8 is an aberration diagram of a numerical example 4 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 (3)

[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 decreases. However, the distance between the third group and the fourth group increases, and the distance between the fourth group and the fifth group increases.
When the first, third, and fifth groups are moved to the object side so that the distance between the groups is reduced, the focal length of the i-th group is fi, and the focal length of the entire system at the wide-angle end is fW. .2 <f1 / fw <2.6 0.4 <| f2 / fw | <1.2 0.75 <f3 / fw <1.8 0.95 <f4 / fw <2.4 0.6 <| 2. The zoom lens according to claim 1, wherein a condition of f5 / fw | <1.7 is satisfied. 2. The ith group has at least two positive lenses and one negative lens, and the zoom ratio of the ith group is Zi,
2. The zoom lens according to claim 1, wherein a condition of 1 <logZ2 / logZ <2 0.15 <logZ5 / logZ <0.25 is satisfied, where Z is the zoom ratio of the entire system. 3. 3. The second group has at least two negative lenses and one positive lens, the fourth group has at least one positive lens and a negative lens, and the fifth group is at least one positive lens. 3. The zoom lens according to claim 1, further comprising a lens and a negative lens.