JPH0943513A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens of a low cost having a variable power ratio of about 3, an F number of about 1.8 and well compensated aberration and composed of only spherical lenses. SOLUTION: This zoom lens arranges, in order from the object side, a first lens group Gr1 having a positive refractive power, a second lens group Gr2 having a negative refractive power, a third lens group Gr3 having a positive refractive power and a fourth lens group Gr4 having a positive refractive power and power variation and focusing are performed by moving the second lens group Gr2 and the fourth lens group Gr4. All the first to the fourth lens groups Gr1-Gr4 are composed of spherical lenses and satisfy the following condition. Relation: 0.45<|f2 |/(fw .f1 )<1/2> <0.7, where f2 : the focal distance of the second lens group, f.: the focal distance of the whole system at the wide-angle end of the zoom lens and f1 : the focal distance of the whole system at the telescopic end of the zoom lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens used in a video camera or the like.

[0002]

2. Description of the Related Art In recent years, image pickup devices such as video cameras equipped with a zoom lens are required to have high image quality and high magnification, and at the same time, demands for downsizing and cost reduction.

Therefore, in order to meet the demand for miniaturization of the image pickup apparatus, the image pickup device used in the image pickup apparatus has been reduced in size from 1/3 inch to 1/4 inch, for example. The zoom lens used in the above has been downsized by using an aspherical lens. Specifically, a large aperture ratio zoom lens with a zoom ratio of about 10
By using an aspherical lens, it has come to be composed of about 9 to 10 lenses.

As such a zoom lens, for example, in Japanese Patent Laid-Open No. 5-323194, a zoom ratio of 9.5 and an F value of 1.85 are realized by nine lenses including an aspherical lens. A four-group zoom lens including first to fourth lens groups is shown. However, this zoom lens has a problem that it is difficult to assemble the fourth lens group with high precision. That is, the fourth of this zoom lens
In the lens group, a negative lens and a positive lens are arranged at a minute interval to form a so-called air lens. However, such an air lens is greatly affected by decentering and has poor assemblability. Further, in this zoom lens, there is a problem that the fluctuation of the distortion aberration becomes large as a result of the higher magnification.

Further, in Japanese Unexamined Patent Publication No. 5-297275, a zoom ratio of 10.0 and an F value of 1.85 are realized by ten lenses including an aspherical lens. A four-group zoom lens is shown. However, since this zoom lens uses three aspherical surfaces, there is a problem that the manufacturing cost becomes very high.
Further, also in this zoom lens, as a result of increasing the magnification, the fluctuation of the distortion becomes large.

[0006]

Generally, the aspherical shape of an aspherical lens is molded by a mold or a hybrid. However, such an aspherical lens has a very high manufacturing cost as compared with a spherical lens. Has become. Therefore, in the zoom lens using the aspherical lens as described above, the cost is not reduced because the cost of the aspherical lens is high even though the number of lenses can be reduced.

Therefore, the present invention has been proposed in view of such a conventional situation, and an object thereof is to provide a compact and high-performance zoom lens composed only of a spherical lens.

[0008]

The zoom lens according to the present invention completed in order to achieve the above object is a first lens having a positive refracting power, which is fixed to an image plane in order from the object side. A group, a second lens group having a negative refracting power, a third lens group having a positive refracting power fixed to the image plane, and a fourth lens group having a positive refracting power, and Second
A zoom lens that performs zooming from a wide-angle end to a telephoto end by moving a lens group, corrects an image point position shift during zooming by moving a fourth lens group, and focuses on an object at a finite distance, The first lens group, the second lens group, the third
The lens group and the fourth lens group are all spherical lenses,
It is characterized in that the condition of the following formula (1) is satisfied.

0.45 <| f ₂ | / ( _fw · _ft ) ^1/2 <0.7 (1) where f ₂ is the focal length of the second lens group, and f _w is the zoom The focal length of the entire system at the wide-angle end of the lens, and f _t is the focal length of the entire system at the telephoto end of the zoom lens.

The second lens group of the zoom lens includes, in order from the object side, a meniscus negative lens L4 having a convex surface on the object side,
It is preferably composed of a cemented lens including a biconcave negative lens L5 and a positive lens L6, and the meniscus negative lens L4 and the positive lens L6 are preferably made of the same material. By doing so, the spherical aberration generated on the concave surface of the meniscus negative lens L4 is corrected by the spherical aberration generated on the cemented surface of the cemented lens including the negative lens L5 and the positive lens L6.

The third lens group of the zoom lens is composed of a cemented lens composed of a positive lens L7 and a negative lens L8 in order from the object side, and the following formulas (2) and (3) are used.
It is preferable to satisfy the condition of.

[0012] _{-0.42 <r c / f 3 <} -0.34 ··· (2) ν L7 -ν L8 <15 ··· (3) where, r _c is a positive lens L7 negative lens L8 radius of curvature of the cemented surface of, f ₃ is the focal length of the third lens group, [nu _L7 is the Abbe number at the d-line of the positive lens L7, [nu _L8 is d of the negative lens L8
It is the Abbe number on the line.

The meaning of each conditional expression in the zoom lens will be described below.

The conditional expression (1) defines the refractive power of the second lens group. Then, in the conditional expression (1), when | f ₂ | / ( _fw / _ft ) ^1/2 exceeds the lower limit value, the aberration variation during zooming becomes large, and it becomes difficult to correct coma flare. Become. There is also a problem that the first lens group becomes large. On the other hand, in the conditional expression (1), when | f ₂ | / ( _fw / _ft ) ^1/2 exceeds the upper limit value, the movement amount of the second lens group during zooming becomes large,
The overall length of the zoom lens becomes longer.

The conditional expression (2) defines the cemented surface of the cemented lens of the third lens group. In conditional expression (2), when r _c / f ₃ exceeds the lower limit value, spherical aberration and axial chromatic aberration are undercorrected, and conversely, when r _c / f ₃ exceeds the upper limit value, spherical aberration In addition to overcorrection, the edge thickness of the positive lens becomes small and the workability deteriorates.

The above conditional expression (3) defines the Abbe number of the cemented lens of the third lens group. If ν _L7 −ν _L8 exceeds the upper limit value, it becomes impossible to maintain the balance of chromatic aberration correction. .

[0017]

EXAMPLES Specific examples to which the present invention is applied will be described below. In the following examples, i is the surface number of the lens counted from the object side, r is the radius of curvature of the lens, d is the wall thickness of the lens or the axial upper surface spacing, and n is the lens spacing. The refractive index of each lens with respect to the e-line is shown, and ν is the Abbe number of each lens with respect to the e-line. Also,
f is the focal length of the entire zoom lens system at the wide-angle end zoom position, the intermediate zoom position, and the telephoto end zoom position, and FNo is the opening F at the wide-angle end zoom position, the intermediate zoom position, and the telephoto end zoom position. Shows the number.

Example 1 Table 1 shows lens data of the zoom lens of Example 1.

[0019]

[Table 1]

FIG. 1 shows a lens configuration diagram corresponding to the zoom lens of the present embodiment. That is, in the zoom lens of this embodiment, the first lens group Gr1, the second lens group Gr2, the diaphragm S, the third lens group Gr3, the fourth lens group Gr5, the filter F and the image plane Z are arranged in this order from the object side. Is configured.

Here, in the first lens group Gr1, a cemented lens in which a meniscus negative lens L1 having a convex surface on the object side and a meniscus positive lens L2 having a convex surface on the object side are cemented, and a meniscus positive lens L3 having a convex surface on the object side. And the second lens group Gr2 includes a meniscus negative lens L4 having a convex surface on the object side.
And a cemented lens in which a biconcave negative lens L5 and a convex meniscus positive lens L6 on the object side are cemented. Here, the negative meniscus lens L4 and the positive meniscus lens L6
Are made of the same material.

The third lens group Gr3 has a biconvex positive lens L7 and a meniscus negative lens L8 concave on the object side.
And the fourth lens group G.
r4 is composed of a cemented lens in which a meniscus negative lens L9 having a convex surface on the object side and a biconvex positive lens L10 are cemented.

Example 2 Table 2 shows lens data of the zoom lens of the second example.

[0024]

[Table 2]

FIG. 2 shows a lens configuration diagram corresponding to the zoom lens of the present embodiment. That is, in the zoom lens of this embodiment, the first lens group Gr1, the second lens group Gr2, the diaphragm S, the third lens group Gr3, the fourth lens group Gr5, the filter F and the image plane Z are arranged in this order from the object side. Is configured.

Here, in the first lens group Gr1, a cemented lens in which a negative meniscus negative lens L1 convex to the object side and a positive meniscus positive lens L2 to the object side are cemented, and a positive meniscus lens L3 convex to the object side. And the second lens group Gr2 includes a meniscus negative lens L4 having a convex surface on the object side.
And a cemented lens in which a biconcave negative lens L5 and a biconvex positive lens L6 are cemented. Here, the meniscus negative lens L4 and the positive lens L6 are made of the same material.

The third lens group Gr3 includes a biconvex positive lens L7 and a meniscus negative lens L8 concave on the object side.
And the fourth lens group G.
r4 is composed of a cemented lens in which a meniscus negative lens L9 having a convex surface on the object side and a biconvex positive lens L10 are cemented.

Example 3 Table 3 shows the lens data of the zoom lens of the third example.

[0029]

[Table 3]

FIG. 3 shows a lens configuration diagram corresponding to the zoom lens of the present embodiment. That is, in the zoom lens of this embodiment, the first lens group Gr1, the second lens group Gr2, the diaphragm S, the third lens group Gr3, the fourth lens group Gr5, the filter F and the image plane Z are arranged in this order from the object side. Is configured.

Here, in the first lens group Gr1, a cemented lens in which a negative meniscus lens L1 convex to the object side and a positive meniscus positive lens L2 to the object side are cemented, and a positive meniscus lens L3 to the object side is cemented. And the second lens group Gr2 includes a meniscus negative lens L4 having a convex surface on the object side.
And a cemented lens in which a biconcave negative lens L5 and a biconvex positive lens L6 are cemented. Here, the meniscus negative lens L4 and the positive lens L6 are made of the same material.

The third lens group Gr3 includes a biconvex positive lens L7 and a meniscus negative lens L8 concave on the object side.
And the fourth lens group G.
r4 is composed of a cemented lens in which a meniscus negative lens L9 having a convex surface on the object side and a biconvex positive lens L10 are cemented.

Example 4 Table 4 shows lens data of the zoom lens of the fourth example.

[0034]

[Table 4]

FIG. 4 shows a lens configuration diagram corresponding to the zoom lens of this embodiment. That is, in the zoom lens of this embodiment, the first lens group Gr1, the second lens group Gr2, the diaphragm S, the third lens group Gr3, the fourth lens group Gr5, the filter F and the image plane Z are arranged in this order from the object side. Is configured.

Here, the first lens group Gr1 includes a meniscus negative lens L1 which is convex toward the object side and a biconvex positive lens L.
The second lens group Gr2 is composed of a cemented lens in which 2 is cemented and a meniscus positive lens L3 having a convex surface on the object side.
It comprises a meniscus negative lens L4 that is convex on the object side, a cemented lens in which a biconcave negative lens L5 and a biconvex positive lens L6 are cemented. Here, the meniscus negative lens L4 and the positive lens L6 are made of the same material.

The third lens group Gr3 includes a biconvex positive lens L7 and a meniscus negative lens L8 concave on the object side.
And the fourth lens group G.
r4 is composed of a cemented lens in which a meniscus negative lens L9 having a convex surface on the object side and a biconvex positive lens L10 are cemented.

Here, | f ₂ | / (f _w · f in the conditional expressions (1) to (3) of the zoom lenses of Examples 1 to 4
The values of _t ) ^1/2 , r _c / f ₃ , and ν _L7 −ν _L8 are as shown in Table 5.

[0039]

[Table 5]

5 to 16 are aberration diagrams of the zoom lenses of Examples 1 to 4 described above. 5 to 7 are aberration diagrams of the zoom lens of Embodiment 1, FIG. 5 is an aberration diagram at the wide-angle end zoom position, FIG. 6 is an aberration diagram at the intermediate zoom position, and FIG. 7 is a telephoto end zoom. It is an aberration diagram in a position. Also,
8 to 10 are aberration diagrams of the zoom lens of Embodiment 2, FIG. 8 is an aberration diagram at a wide-angle end zoom position, FIG. 9 is an aberration diagram at an intermediate zoom position, and FIG. 10 is a telephoto end zoom position. It is an aberration diagram. 11 to 13 are aberration diagrams of the zoom lens of Embodiment 3, FIG. 11 is an aberration diagram at a wide-angle end zoom position, FIG. 12 is an aberration diagram at an intermediate zoom position, and FIG. 13 is a telephoto end zoom position. FIG. 14 to 16 are aberration diagrams of the zoom lens of Embodiment 4, and FIG.
Is an aberration diagram at the wide-angle end zoom position, FIG. 15 is an aberration diagram at the intermediate zoom position, and FIG. 16 is an aberration diagram at the telephoto end zoom position. 5 to 16, the solid line e represents the spherical aberration with respect to the e line, the broken line g represents the spherical aberration with respect to the g line, the solid line S represents the astigmatism on the sagittal surface, and the broken line M represents the meridional surface. Represents the astigmatism of.

From these figures, it can be seen that the zoom lenses of the respective examples are well corrected for aberrations and have excellent optical performance. In particular, in the zoom lenses of the respective embodiments to which the present invention is applied, the fluctuation of the distortion aberration at the time of zooming, which has been a serious problem in the conventional zoom lenses, is extremely suppressed.

[0042]

As is apparent from the above description, according to the present invention, a zoom lens having a zoom ratio of about 3 and an F value of about 1.8 and good aberration correction is provided with an aspherical surface. It can be realized without using a lens.

Since the spherical lens is much lower in manufacturing cost than the aspherical lens, the zoom lens of the present invention composed of only the spherical lens is lower in cost than the zoom lens using the aspherical lens. Can be manufactured in.

Moreover, the spherical lens can be manufactured by using the conventional production means for the spherical lens, and moreover, the lens surface can be easily measured and the quality can be easily evaluated. Therefore, according to the present invention in which a zoom lens is configured only with such a spherical lens, it is possible to provide a low-cost zoom lens with stable quality.

Further, in the zoom lens of the present invention, the fluctuation of the distortion aberration at the time of zooming is suppressed to a very small level.
Therefore, the zoom lens of the present invention is very suitable for applications in which variations in distortion are a problem, such as graphic input.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a zoom lens according to a first embodiment to which the present invention is applied.

FIG. 2 is a configuration diagram of a zoom lens according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a zoom lens according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram of a zoom lens according to a fourth embodiment of the present invention.

FIG. 5 is an aberration diagram at a wide-angle end zoom position of the zoom lens in the first embodiment to which the present invention is applied.

FIG. 6 is an aberration diagram at the intermediate zoom position of the zoom lens in the first embodiment to which the present invention is applied.

FIG. 7 is an aberration diagram at a telephoto end zoom position of the zoom lens in the first embodiment to which the present invention has been applied.

FIG. 8 is an aberration diagram at a wide-angle end zoom position of a zoom lens according to a second example of the present invention.

FIG. 9 is an aberration diagram at an intermediate zoom position of the zoom lens in the second embodiment to which the present invention has been applied.

FIG. 10 is an aberration diagram at a telephoto end zoom position of a zoom lens in a second embodiment to which the present invention has been applied.

FIG. 11 is an aberration diagram at a wide-angle end zoom position of a zoom lens according to a third embodiment of the present invention.

FIG. 12 is an aberration diagram at a middle zoom position of a zoom lens in a third embodiment to which the present invention has been applied.

FIG. 13 is an aberration diagram at a telephoto end zoom position of a zoom lens in a third embodiment to which the present invention has been applied.

FIG. 14 is an aberration diagram at a wide-angle end zoom position of a zoom lens according to a fourth example of the present invention.

FIG. 15 is an aberration diagram at a middle zoom position of the zoom lens in the fourth embodiment to which the present invention has been applied.

FIG. 16 is an aberration diagram at a telephoto end zoom position of a zoom lens according to a fourth example of the present invention.

[Explanation of symbols]

 Gr1 First lens group Gr2 Second lens group Gr3 Third lens group Gr4 Fourth lens group L1 Negative lens L2 Positive lens L3 Positive lens L4 Negative lens L5 Negative lens L6 Positive lens L7 Positive lens L8 Negative lens L9 Negative lens L10 Positive lens S Aperture F Filter Z Image plane

Claims (3)

[Claims] 1. A first lens group having a positive refractive power, which is fixed to an image plane, a second lens group having a negative refractive power, and a second lens group, which are fixed to an image plane, in this order from the object side. A third lens group having a positive refracting power and a fourth lens group having a positive refracting power are arranged, and the fourth lens group performs zooming from the wide-angle end to the telephoto end by moving the second lens group. In the zoom lens for correcting the image point position shift during zooming by moving the lens and focusing on an object at a finite distance, the first lens group, the second lens group, the third lens group and the fourth lens group are all spherical surfaces. A zoom lens comprising a lens and satisfying the condition of the following formula (1). _{0.45 <| f 2 | / (} f w · f t) 1/2 <0.7 ··· (1) where, f ₂ is the focal length of the second lens group, f _w is a wide-angle zoom lens The focal length of the entire system at the end, f _t is the focal length of the entire system at the telephoto end of the zoom lens. 2. The second lens group, in order from the object side,
It is composed of a meniscus negative lens L4 convex on the object side and a cemented lens composed of a biconcave negative lens L5 and a positive lens L6, and the meniscus negative lens L4 and the positive lens L6 are made of the same material. The zoom lens according to claim 1. 3. The third lens group is composed of a cemented lens including a positive lens L7 and a negative lens L8 in order from the object side, and satisfies the conditions of the following formulas (2) and (3). The zoom lens according to claim 1. -0.42 <junction surface _{r c / f 3 <-0.34 ···} (2) ν L7 -ν L8 <15 ··· (3) where, r _c is a positive lens L7 and a negative lens L8 Radius of curvature, f ₃ is the focal length of the third lens group, ν _L7 is the Abbe number of the positive lens L7 at the d line, and ν _L8 is the d of the negative lens L8.
It is the Abbe number on the line.