JP2811950B2 - Zoom lens having simple configuration and camera having the same - Google Patents

Description

The present invention relates to a zoom lens having a simple configuration suitable for a photographic camera, a video camera, and the like, and a camera having the same.
In particular, a lens unit having a negative refractive power precedes and has three lens units as a whole. The lens configuration of these three lens units is appropriately configured, and zooming is performed by changing the air spacing of each of the three lens units. The present invention relates to a zoom lens having a small lens length of about 4 to 4.5 and a zoom ratio of about 2.4 to 3, which has a good optical performance and a simple configuration, and a camera having the same.

(Prior Art) Conventionally, there are three lens groups of a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a negative refractive power in order from the object side. The applicant of the present invention has disclosed a zoom lens in which zooming is performed by moving a lens group, for example, in Japanese Patent Laid-Open No.
No. 14, JP-A-64-72114, and the like.

This type of zoom lens is relatively widely used as a photographing system for a wide angle of view because it is relatively easy to widen the angle of view.

In this publication, the first, second, and third groups are moved under a certain condition to perform zooming, and the lens configuration of the three lens groups is specified to correct aberration fluctuations accompanying zooming well. 8 to 9 as a whole with a zoom ratio of 2 to 3 times having optical performance
A relatively compact zoom lens, particularly a lens shutter camera, consisting of two lenses has been achieved.

(Problems to be Solved by the Invention) The zoom lenses proposed in the above-mentioned JP-A-63-271214 and JP-A-64-72114 each comprise two or more lenses in each lens group. For example, the chromatic aberration is corrected within each lens unit, and the refractive power of each lens unit is increased to shorten the overall optical length (the distance from the first lens surface to the imaging surface).

The present invention makes use of the refractive power arrangement of the zoom lens proposed earlier by the present applicant, further improves the lens configuration of each lens group, particularly aims at ultimate reduction of the number of lenses, and a zoom ratio of 2.
It is an object of the present invention to provide a zoom lens having a good optical performance over the entire zoom range of about 4 to 3 and an F number of about 4 to 4.5, and particularly having a simple configuration suitable for a lens shutter camera and a camera having the same. .

(Means for Solving the Problems) The zoom lens having a simple configuration according to the present invention includes, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a zoom lens having a negative refractive power. A first meniscus negative lens having a convex surface facing the object side; The second group is a positive second lens having a stronger refracting surface on the image surface side than the object side, and the third group is a meniscus positive 31st lens having a convex surface facing the image surface side, and a positive second lens on the image surface side. A negative 32nd lens with a strong refracting surface facing the object side, the focal length of the i-th lens unit is Fi, and the focal length at the wide-angle end of the entire system is FW.
The back focus at the wide-angle end and the telephoto end is set to SKW and SK respectively.
T, when the average value of the refractive indices of the materials of the first lens and the 32nd lens is ▼, and the Abbe number of the material of the second lens is ν2, 1.1 <(SKT−SKW) / FW <1.91.9 (1) −5 <F1 / FW <−3 (2) -1 <F2 / F3 <−0.8 (3) 1.75 <▲ ▼ <1.9 (4) 75 <ν2 <85 ‥‥‥ (5) The following condition is satisfied.

A camera having a zoom lens having a simple configuration according to the present invention includes, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. A first meniscus negative first lens having a convex surface directed toward the object side, and a second lens group disposed on the object side. A positive second lens having a stronger refracting surface directed toward the image surface side than the above, a meniscus-shaped positive 31st lens having the third group having a convex surface directed toward the image surface side, and a refracting surface stronger toward the object side than the image surface side , The focal length of the i-th lens unit is Fi, the focal length at the wide-angle end of the entire system is FW, and the back focus at the wide-angle end and the telephoto end is SKW, SKT, respectively. The average value of the refractive indices of the materials of the lens and the 32nd lens is ▲, the Abbe number of the material of the second lens is ν2, and the material of the first lens is An aspherical lens surface side, an aspherical lens surface on the image plane side of the second lens,
An aspheric surface is applied to the lens surface on the image plane side of the 31st lens, and the fourth order aspheric surface coefficients of the aspheric surfaces of these lenses are sequentially denoted by B1, B2,
B31, when the diagonal length of the effective screen is Y 1.1 <(SKT-SKW) / FW <1.9 (1) -5 <F1 / FW <-3 (2) -1 <F2 / F3 <−0.8 (3) 1.75 <▲ ▼ <1.9 (4) 75 <ν2 <85 (5) −7 <B1 · Y ³ <−2 (6) 1 < B2 · Y ³ <3 (7) −3 <B31 · Y ³ <−1 (8)

(Example) FIGS. 1 and 2 are lens cross-sectional views of Numerical Examples 1 and 2 of the present invention, respectively. In the figure, I is a first group having a negative refractive power, II is a second group having a positive refractive power, III is a third group having a negative refractive power, and arrows are each when zooming from the wide-angle side to the telephoto side. 3 shows a moving direction of a lens group.

When zooming from the wide-angle end to the telephoto end, the zoom lens according to the present embodiment moves all three lens groups independently in the object side direction as shown in each figure. In particular, a predetermined zoom ratio is effectively obtained by greatly changing the distance between the second and third lens units. An aperture stop SP is arranged on the image plane side of the second lens unit, and moves integrally with the second lens unit during zooming.

As shown in FIGS. 1 and 2, the zoom lens of the present invention is composed of three lens units of negative, positive, and negative refractive power in order from the object side, that is, on both sides of the second group of positive refractive power. The first and third groups having negative refractive power are arranged, and the refractive power arrangement during zooming is negative,
A substantially symmetrical lens configuration is provided so as to be positive and negative. In the first group, high refractive index and high dispersion glass (N1> 1.
8, ν1 <25) The second group has a low refractive index, low dispersion glass (N2 <1.5
2,75 <ν2 <85).

By using such a substantially symmetrical lens arrangement and using glass of an appropriate material, the method of correcting chromatic aberration in each lens group as in the related art is not used, and chromatic aberration is corrected in a well-balanced manner as a whole lens system. Like that. That is, the three lens groups cancel each other out. The first lens unit has a meniscus negative first lens with a convex surface facing the object side, and the second lens unit has a convex positive lens surface with both lens surfaces having a higher refractive index on the image surface side than the object side. The second lens unit is composed of a meniscus positive 31st lens having a convex surface facing the image surface side and a negative 32nd lens having a stronger negative refraction surface facing the object side than the image surface side. However, even if the zoom lens is shortened, various aberrations including chromatic aberration can be corrected in a well-balanced manner over the entire zoom range, and a zoom lens with high optical performance can be obtained.

 Next, the technical meaning of each of the above conditional expressions will be described.

Conditional expression (1) appropriately sets the difference between the back focus at the wide-angle end and the telephoto end, that is, the amount of movement of the third lens unit toward the object side due to zooming from the wide-angle end to the telephoto end. This is for shortening.

If the amount of movement of the third lens unit is too large beyond the upper limit of conditional expression (1), the third lens unit will mechanically interfere with the second lens unit near the telephoto end. On the other hand, if the amount of movement of the third lens unit is too small below the lower limit, it becomes difficult to obtain a predetermined zoom ratio (about 2.4 to 3), which is not good.

Conditional expression (2) appropriately sets the negative refractive power of the first group,
This is for properly correcting various aberrations.

If the refractive power of the first lens unit becomes too strong beyond the upper limit of conditional expression (2), the balance of the refractive power arrangement of the entire system will be lost, and various aberrations such as coma will be corrected in a well-balanced manner over the entire zoom range. Becomes difficult. If the refractive power of the first lens unit is too weak below the lower limit, it becomes difficult to satisfactorily correct axial chromatic aberration on the wide-angle side.

Conditional expression (3) is for appropriately setting the ratio between the refractive powers of the second group and the third group to effectively obtain a predetermined zoom ratio.

If the upper limit of conditional expression (3) is exceeded and the refractive power of the third lens unit becomes too weak, the amount of movement of the third lens unit for securing a predetermined zoom ratio increases, and the overall length of the lens increases. If the refractive power of the third lens unit becomes too strong beyond the lower limit, it becomes difficult to satisfactorily correct off-axis aberrations such as field curvature.

Conditional expression (4) appropriately sets the average value 屈折 of the refractive indices of the materials of the lenses having the negative refractive power (the first lens and the thirty-first lens) among the lenses constituting the zoom lens, and the Petzval sum is appropriate. In order to maintain good image surface characteristics. When the value exceeds the upper limit, the Petzval sum increases in the positive direction, and when the value exceeds the lower limit, the Petzval sum increases in the negative direction, and in any case, the image surface characteristics are maintained well and the astigmatism is improved. It becomes difficult to correct for

Conditional expression (5) is for appropriately setting the Abbe number of the material of the second lens and mainly for correcting axial chromatic aberration well over the entire zoom range.

If the upper limit is exceeded, the axial chromatic aberration will be overcorrected on the telephoto side, and if the lower limit is exceeded, it will be difficult to satisfactorily correct the axial chromatic aberration in the zoom range from the wide-angle end to the intermediate zoom range.

The conditional expressions (6) and (8) are mainly for favorably correcting the field curvature.

If the upper limit of conditional expression (6) or the upper limit of conditional expression (8) is exceeded, it becomes difficult to satisfactorily correct field curvature. If the lower limit of conditional expression (6) or the lower limit of conditional expression (8) is exceeded, the aspherical effect becomes too strong, and the field curvature becomes excessively corrected, which is not good.

If the upper limit of conditional expression (7) is exceeded, the aspherical effect will be too weak, making it difficult to satisfactorily correct spherical aberration. On the other hand, if the value exceeds the lower limit, spherical aberration will be overcorrected, which is not good.

Next, numerical examples of the present invention will be described. In numerical examples
Ri is the radius of curvature of the i-th lens surface in order from the object side,
Is the i-th lens thickness and air gap from the object side, Ni and ν
i is the refractive index and Abbe number of the glass of the i-th lens in order from the object side.

The aspheric surface has an X-axis in the optical axis direction and H in the direction perpendicular to the optical axis.
R and paraxial radius of curvature, A, B, C, D,
When E is each aspheric coefficient It is represented by the following equation.

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

(Effects of the Invention) According to the present invention, by specifying the refractive powers and the lens configurations of the three lens groups as described above, the entire zoom range of about 2.4 to 3 can be achieved in order to reduce the size of the entire lens system. Thus, it is possible to achieve a zoom lens having a simple configuration having good optical performance over a wide range and a camera having the same.

[Brief description of the drawings]

1 and 2 are lens sectional views of Numerical Examples 1 and 2 of the present invention, respectively, and FIGS. 3 and 4 are Numerical Examples 1 and 2 of the present invention, respectively.
FIG. 4 is a diagram of various aberrations of FIG. In the lens cross-sectional views, I, II, and III indicate the first, second, and third groups, respectively, and arrows indicate the moving direction of each lens group during zooming from the wide-angle end to the telephoto end. B) and (C) are aberration diagrams at the wide-angle end, the middle, and the telephoto end, respectively, d is d-line, g is g-line, SC is sine condition, ΔS
Is a sagittal image plane, and ΔM is a meridional image plane.

Claims (2)

(57) [Claims] 1. A lens system comprising: a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. The first unit is a negative meniscus first lens having a convex surface facing the object side, and the second unit is provided with a stronger refracting surface on the image surface side than the object side. A third positive lens having a meniscus-shaped positive first lens having a convex surface facing the image surface side and a negative second lens having a strong refraction surface facing the object side as compared with the image surface side. The focal length of the i-th lens unit is Fi, the focal length at the wide-angle end of the entire system is FW, the back focus at the wide-angle end and the telephoto end is SKW and SET, respectively, and the refractive index of the material of the first lens and the 32nd lens. Is the average value of ▲ and the Abbe number of the material of the second lens is ν2. 1.1 <(SKT−SKW) / FW <1.9−5 <F1 / FW <−3-1 <F2 / F3 < −0.8 1.75 <▲ ▼ <1.9 75 <ν2 <85 A zoom lens having a simple configuration characterized by satisfying the following condition. 2. A lens system comprising: a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. The first unit is a negative meniscus first lens having a convex surface facing the object side, and the second unit is provided with a stronger refracting surface on the image surface side than the object side. A third positive lens having a meniscus-shaped positive first lens having a convex surface facing the image surface side and a negative second lens having a strong refraction surface facing the object side as compared with the image surface side. The focal length of the i-th lens unit is Fi, the focal length at the wide-angle end of the entire system is FW, the back focus at the wide-angle end and the telephoto end is SKW, SKT, and the refractive index of the material of the first lens and the 32nd lens. , The Abbe number of the material of the second lens is ν2, the aspherical surface on the object side lens surface of the first lens is the second lens The aspherical surface is applied to the image-side lens surface of the lens, the aspherical surface is applied to the image-side lens surface of the 31st lens, and the fourth-order aspherical surface coefficients of the aspheric surfaces of these lenses are sequentially denoted by B1, B2, B31, When the diagonal length of the effective screen is Y, 1.1 <(SKT−SKW) / FW <1.9−5 <F1 / FW <−3-1 <F2 / F3 <−0.8 1.75 <▲ ▼ <1.975 <ν2 <85 ^{-7 <B1 · Y 3 <-2} 1 <B2 · Y 3 <3 -3 < camera having a zoom lens of a simple configuration which satisfies the B31 · Y ³ <-1 following condition.