JPH0968652A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a zoom lens of 5-element constitution which has a variable power ratio of about 1.7 times, is small in size, light in weight and low in cost and is well corrected of various aberrations. SOLUTION: This zoom lens consists, successively from an object side, a first lens group A which has a negative first lens 1 having a concave face on the object side, a positive second lens 2 of a meniscus shape having a convex face on the object side and a positive third lens 3 having a biconvex face and has positive refracting power over the entire part and a second lens group B which has a positive fourth lens 4 of a meniscus shape having a concave shape on the object side and a negative fifth lens 5 having a concave face on the object side and has negative refracting power as a whole. Further, the zoom lens has a variable power effect by changing the spacing between both lens groups and has at least one synthetic resin lens and at least one aspherical face in the respective lens groups and satisfies the conditions (a) to (c). (a) 0.6<f1/fW<1.0, (b) -1.4<f2/fW<-0.7. (c) ν3-ν1>20. In the equations, fw: the focal length over the entire part of the lens system at the wide angle end, f1: the focal length over the entire part of the first lens group, f2: the focal length over the entire part of the second lens group, ν1: the Abbe number of the first lens, ν3: The Abbe number of the third lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact, lightweight, and low-cost zoom lens suitable for small-lens shutter cameras, video cameras, etc., having a short back focus and a short overall lens length.

[0002]

2. Description of the Related Art In recent years, as lens shutter cameras, video cameras, etc. have become smaller and lighter and their prices have become lower, there has been a strong demand for the lenses used therein to be smaller and lighter as well as costly. Further, it is strongly desired to mount a compact and lightweight zoom lens as a lens used for this type of application, and a zoom lens having a length comparable to that of a conventionally used single focus lens is demanded. Generally, in order to reduce the size of the zoom lens, it is necessary to increase the refractive power of each group including the amount of movement for zooming. However, in order to increase the refractive power while maintaining the lens performance, it is necessary to increase the number of lenses and select a high refractive index optical material.

In order to reduce weight and cost,
It is known as a very effective means to reduce the number of lenses and to use a lens having a synthetic resin which is easy and inexpensive to injection-mold. However, currently existing optical plastic materials have a low refractive index of about 1.5 to 1.6, and their types are limited. In this way, downsizing of the lens,
There are many contradictory factors in achieving weight reduction and cost reduction, and it is not easy to adopt synthetic resin lenses in lens design.

Further, for example, as an example of a conventional compact zoom lens having five lenses, there is a compact zoom lens disclosed in Japanese Patent Application No. 57-201213. In this conventional small-sized zoom lens, a first lens group having a positive first lens, a negative second lens, and a positive third lens in order from the object side, and having a positive refracting power as a whole, , Positive fourth
The second lens group has a lens and a negative fifth lens and has a negative refracting power as a whole, and the magnification is changed by changing the distance between the two lens groups. And thus the first
The lens structure in which the lens group is composed of positive, negative, and positive, and the second lens group is composed of positive and negative is a very advantageous lens structure for downsizing of the lens system.

[0005]

However, as described above, the first problem
In a small zoom lens in which the lens group is composed of positive, negative, and positive, and the second lens group is composed of positive and negative, the distortion at the wide-angle end tends to be large, and this is corrected well. The problem was that it was difficult. Further, in the conventional compact zoom lens of this type, since the first lens group having a positive refractive power is composed of three lenses, positive, negative and positive, in order to secure the light rays in the peripheral portion, Especially, it is necessary to increase the effective diameters of the first lens, the fourth lens, and the fifth lens, which is a bottleneck in downsizing.

[0006]

The present invention has been made to solve such a problem, and is suitable for a lens shutter camera, a video camera, etc. having a zoom ratio of about 1.7 times. The objective is to obtain a zoom lens that is compact, lightweight, and cost-effective at the same time, and that has various aberrations corrected well.

In order to achieve the above object, the zoom lens of the present invention comprises, as shown in FIG. 1, a negative first lens 1 having a concave surface facing the object side and a convex surface facing the object side in order from the object side. A positive meniscus second lens 2 and a positive third lens 3 having convex lens surfaces on both sides, and a first lens group A having a positive refracting power as a whole, and a concave surface on the object side. A positive meniscus-shaped fourth lens 4 and a negative fifth lens 5 having a concave surface facing the object side, and a second lens group B having a negative refracting power as a whole. In a zoom lens having a zooming effect by changing the distance between the groups AB, each lens group AB has at least one synthetic resin lens and at least one aspherical surface, and the following (a) to (a) It is characterized by satisfying various conditions defined in C). (A) 0.6 <f1 / fW <1.0 (b) -1.4 <f2 / fW <-0.7 (c) ν3-ν1> 20 where fW: focus of the entire lens system at the wide-angle end Distance f1: focal length of the entire first lens group f2: focal length of the entire second lens group ν1: Abbe number of the first lens ν3: Abbe number of the third lens

More preferably, the zoom lens of the present invention is characterized by satisfying the conditions defined in the following (d) to (g) on the premise of the above. (D) -1.2 <R1 / f1 <-0.4 (e) -4.0 <R5 / R6 <-1.2 (f) 0.15 <(D3 + D4 + D5) / f1 <0.
5 (g) −0.3 <D9 / f2 <−0.05 where f1: focal length of the first lens group f2: focal length of the second lens group Ri: radius of curvature of the i-th surface from the object side ( i is 1,5
6) Dj: j-th axial upper surface distance from the object side (j is 3,
4, 5, 9)

[0009]

According to the present invention, as shown in FIG. 1, a negative first lens 1 having a concave surface facing the object side in order from the object side, a meniscus-shaped positive second lens 2 having a convex surface facing the object side, A first lens group A having a positive third lens 3 having convex surfaces on both sides, and having a positive refracting power as a whole, and a positive meniscus fourth lens 4 having a concave surface facing the object side; A negative fifth lens 5 having a concave surface facing the object side, and a second negative lens having a negative refracting power as a whole.
It is arranged in front of the lens group B, and the magnification is changed by changing the distance between the two lens groups.

According to the present invention, as described above, the first lens group A having a positive refracting power as a whole is composed of the negative lens 1, the positive lens 2 and the positive lens 3, and the second lens group having a negative refraction as a whole. B is composed of a positive lens 4 and a negative lens 5, and the first lens group A having the above-mentioned configuration is arranged in front of the second lens group B having the above-mentioned configuration, so that a conventional compact zoom lens having a five-element configuration. It reduces distortion more than
This makes it possible to obtain a compact zoom lens with various aberrations corrected well.

In the present invention, although at least one synthetic resin lens is used for each lens group, each lens group of the first lens group A and the second lens group B has at least one non-surface. By properly arranging the spherical surface, aberration fluctuations due to zooming are reduced and various aberrations are well corrected. Of the aspherical surfaces of each lens group, the aspherical surface used for the first lens group A is effective mainly for correcting spherical aberration. The aspherical surface used for the second lens group B is effective mainly for correcting astigmatism.

The condition (a) is for properly setting the refracting power of the first lens unit A, for downsizing the lens, and for satisfactorily correcting various aberrations. When the value exceeds the upper limit of the condition (a), the refractive power of the first lens unit A becomes too weak, and the back focus becomes too short. Furthermore, the amount of movement for zooming increases,
At the same time as the total length of the lens becomes longer, the effective diameter of the lens must be greatly expanded, which makes downsizing and weight reduction impossible. If the lower limit of the condition (a) is exceeded, the refracting power of the first lens unit A will become too strong, and the amount of movement for zooming will be small, but spherical aberration and astigmatism will be undercorrected. Therefore, it becomes difficult to correct even if an aspherical surface is used.

The condition (b) is for properly setting the refracting power of the second lens unit B, aiming at downsizing of the lens and satisfactorily correcting various aberrations. When the value exceeds the upper limit of the condition (b), the refracting power of the second lens unit B becomes too strong, and the amount of movement for zooming is small, but spherical aberration and astigmatism are undercorrected. However, it becomes difficult to correct even if an aspherical surface is used. When the lower limit of condition (b) is exceeded,
The refracting power of the second lens unit B becomes too weak and the back focus becomes too short. In addition, the amount of movement for zooming becomes large, the total length of the lens becomes long, and at the same time, the effective diameter of the lens must be greatly expanded, which leads to size reduction,
Lightening is hopeless.

The condition (c) relates to chromatic aberration,
If this condition is exceeded, it becomes difficult to correct the axial chromatic aberration.

Further, in order to satisfactorily correct various aberrations, (d)
It is preferable that the conditions defined in (g) to (g) are satisfied.

The condition (d) relates to the radius of curvature of the object-side lens surface R1 of the first lens 1 of the first lens group A, and is mainly used to favorably correct astigmatism and distortion. It is a thing. If the upper limit of condition (d) is exceeded, astigmatism will be overcorrected. In addition, the distortion becomes more barrel-shaped, making correction difficult. On the contrary, if the lower limit value of the condition (d) is exceeded, astigmatism will be undercorrected, and distortion will also be strong in the pincushion type, making correction difficult.

The condition (e) relates to the radius of curvature of the third lens 3, and is mainly for favorably correcting spherical aberration and astigmatism. If the upper limit of the condition (e) is exceeded, spherical aberration and astigmatism will be overcorrected, making correction difficult. When the value goes below the lower limit of the condition (e), spherical aberration and astigmatism are undercorrected, which makes correction difficult.

The condition (f) is for configuring the axial upper surface distance of the second lens 2 of the first lens group A, the air distance between the second lens 2 and the third lens 3, and the axial upper surface distance of the third lens 3. Is. When the value exceeds the upper limit of the condition (f), the total lens length becomes long and the lens effective diameter becomes large, so that it becomes impossible to make the lens compact and lightweight. When the value goes below the lower limit of the condition (f), it becomes difficult to correct spherical aberration and astigmatism.

The condition (g) relates to the air gap between the fourth lens 4 and the fifth lens 5 of the second lens group B. When the value exceeds the upper limit of the condition (g), it becomes difficult to correct spherical aberration particularly at the telephoto end. When the value goes below the lower limit of the condition (g), the total length of the lens becomes long, and the effective diameter of the lens becomes large, so that it is impossible to reduce the size and weight.

[0020]

EXAMPLES In the following, numerical examples of the present invention are shown in Table 1 and sectional views of the optical axes thereof are shown in FIGS. 1 to 3. FIG.
Shows the wide-angle end, FIG. 2 shows the intermediate focal length, and FIG. 3 shows the telephoto end. Also, in the table, ri (i is 1 to 11)
Is the radius of curvature of the i-th surface from the object side, and di (i is 1
10 to 10) is the i-th lens thickness or air space from the object side, ni (i is 1 to 5) is the refractive index of the i-th lens from the object side to the d-line, and νi (i is 1 to 5) is The respective Absolute numbers for the d-line of the i-th lens from the object side are shown. Further, in this embodiment, the second lens 2 and the fourth lens 4 are made of synthetic resin.

[0021]

[Table 1]

A surface having an aspherical shape is defined by the following equation 1.

[0023]

[Equation 1] However, Z: distance from the tangent plane of the aspherical vertex of a point on the aspherical surface whose height is y from the optical axis y: height from the optical axis C: curvature of the aspherical vertex (= 1 / r) S: Cone constants D, E, F, G: Aspherical surface coefficients.

FIGS. 4 to 6 are aberration diagrams of the above embodiment, in which FIG. 4 shows the wide-angle end, FIG. 5 shows the intermediate focal length, and FIG. 6 shows the telephoto end. In the diagram, d is the d line, F is the F line, C is the C line, SC is the sine condition, and astigmatism is divided into the sagittal direction DS and the meridional direction DT in order to complicate the drawing. Is shown.

[0025]

As can be seen from the embodiments and aberration diagrams described above, according to the present invention, a zoom having a zoom ratio of about 1.7 times, which is suitable for a lens shutter camera, a video camera, etc. With the lens, it was possible to achieve size reduction, weight reduction, and cost reduction at the same time, and it was possible to obtain a zoom lens with various aberrations corrected well.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical axis at a wide-angle end of a zoom lens according to an exemplary embodiment of the present invention.

FIG. 2 is a sectional view of the optical axis at the intermediate focal length in the above embodiment.

FIG. 3 is a sectional view of the optical axis at the telephoto end of the above embodiment.

FIG. 4 is an aberration diagram showing lens performance at the wide-angle end of the zoom lens of the above-described example.

FIG. 5 is an aberration diagram showing lens performance of the zoom lens of the above-described embodiment at an intermediate focal length.

FIG. 6 is an aberration diagram showing lens performance of the zoom lens of the above-described embodiment at the telephoto end.

[Explanation of symbols]

 1 1st lens 2 2nd lens 3 3rd lens 4 4th lens 5 5th lens A 1st lens group B 2nd lens group

Claims (2)

[Claims] 1. A negative first lens having a concave surface facing the object side, a positive meniscus lens having a convex surface facing the object side, and a positive lens having a convex surface on both lens surfaces. A first lens unit having a third lens and having a positive refracting power as a whole, and a meniscus-shaped positive fourth lens unit having a concave surface facing the object side.
It has a lens and a negative fifth lens having a concave surface directed toward the object side, and is composed of a second lens group having a negative refracting power as a whole. The zoom lens has a feature that each lens group has at least one synthetic resin lens and at least one aspherical surface, and satisfies various conditions defined in the following (a) to (C): Zoom lens to do. (A) 0.6 <f1 / fW <1.0 (b) -1.4 <f2 / fW <-0.7 (c) ν3-ν1> 20 where fW: focus of the entire lens system at the wide-angle end Distance f1: focal length of the entire first lens group f2: focal length of the entire second lens group ν1: Abbe number of the first lens ν3: Abbe number of the third lens 2. The zoom lens according to claim 1, wherein:
A zoom lens characterized by satisfying various conditions defined in the following (d) to (g). (D) -1.2 <R1 / f1 <-0.4 (e) -4.0 <R5 / R6 <-1.2 (f) 0.15 <(D3 + D4 + D5) / f1 <0.
5 (g) −0.3 <D9 / f2 <−0.05 where f1: focal length of the first lens group f2: focal length of the second lens group Ri: radius of curvature of the i-th surface from the object side ( i is 1,5
6) Dj: j-th axial upper surface distance from the object side (j is 3,
4, 5, 9)