JP2811828B2 - Zoom lens having simple configuration and camera having the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens having a simple configuration including two lens groups suitable for a lens shutter camera, a video camera, and the like, and a camera having the same, and in particular, to each lens. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens having a simple structure and a short overall lens length (distance from a first lens surface to an image plane), in which the number of lenses in a group is extremely reduced and aberration correction is performed satisfactorily, and a camera having the zoom lens.

(Prior Art) Conventionally, various zoom lenses having a short overall length have been proposed as the size of lens shutter cameras, video cameras and the like becomes smaller.

The present applicant has previously disclosed JP-A-57-201213 and JP-A-60-201213.
No. 170816, JP-A-60-191216, JP-A-62-56
In the 917 publication, etc., the first positive refractive power from the object side
We have proposed a small zoom lens that consists of two lens groups, a group and a second group with a negative refractive power, and changes the magnification by changing the distance between both lens groups.

In this publication, a positive / negative refractive power arrangement is adopted in order from the object side to achieve a zoom lens having a high optical performance with a relatively short back focus and a short overall lens length.

In addition, a zoom lens comprising a first group having a positive refractive power and a second group having a negative refractive power and performing zooming by changing the distance between both lenses has been proposed in, for example, JP-A-62-251710. I have. In this publication, the first group is composed of a triplet type composed of three lenses, the second group is composed of two lenses of a positive lens and a negative lens, and has a simple configuration with a total zoom ratio of about 1.5 composed of five lenses. A zoom lens is proposed.

In Japanese Patent Application Laid-Open No. 63-276013, the first group is composed of two lenses, a negative lens and a positive lens, and the second group is composed of two lenses, a positive lens and a negative lens. In addition, a zoom lens having a simple configuration with a zoom ratio of about 2 using a gradient index lens for a plurality of lenses has been proposed.

(Problems to be Solved by the Invention) In general, in a zoom lens composed of the two lens groups described above, in order to simplify the lens configuration, it is preferable to configure each lens group with as few lenses as possible.

However, in order to secure a predetermined zoom ratio and a shooting angle of view, the lens configuration of each lens group is not appropriately set, and fluctuations of various aberrations due to zooming increase, making it difficult to satisfactorily correct these. come.

Also, as proposed in the above-mentioned Japanese Patent Application Laid-Open No. 63-276013, the method of simplifying the lens configuration using the gradient index lens is said to make it difficult to accurately manufacture the gradient index lens. There is a problem.

The present invention is a zoom lens having two lens groups, using a lens made of a normal uniform material and appropriately setting the lens configuration of each lens group, while having a predetermined zoom ratio and a shooting angle of view, It is an object of the present invention to provide a zoom lens having a simple configuration having good optical performance over the entire zoom range in which the lens configuration is simplified and a camera having the same.

(Means for Solving the Problems) (1-1) 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 positive refractive power and a second lens unit having a negative refractive power. When performing zooming by changing the distance between both lens groups, the first group has a meniscus negative eleventh lens with the convex surface facing the object side, and both lens surfaces have a positive convex surface. No.
The second group is composed of a positive twenty-first lens and a negative twenty-second lens. The focal lengths of the first and second groups are F1 and F2, respectively. The Abbe numbers of the lens materials are ν11 and ν12, respectively, and the focal length at the wide-angle end of the entire system is F
W, the refractive index of the material of the eleventh lens and the twelfth lens is n1
0.4 <F1 / FW <1.2 (1) -1.5 <F2 / FW <-1.5 (2) ν11 <40 (3) 50 <ν12 (1) 4) 1.56 <n11 <1.65 (6) n12 <1.52 (7) The following condition is satisfied.

(1-2) 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 positive refractive power and a second lens unit having a negative refractive power. When zooming is performed by changing the distance between both lens groups, the first group is composed of a meniscus negative eleventh lens with a convex surface facing the object side and a positive twelfth lens with both lens surfaces convex. , The second group
The first lens unit and the second lens unit comprise a 21st lens and a negative 22nd lens.
The focal length of the group is F1, F2, the Abbe number of the material of the eleventh lens and the twelfth lens is ν11, ν12, the focal length at the wide angle end of the entire system is FW, the material of the eleventh lens and the twelfth lens. N11, n12, an aspherical surface is provided on the object side or the image surface side of the eleventh lens, the fourth order aspherical coefficient of the aspherical surface is B, and the diagonal length of the effective screen is Y. 0.4 <F1 / FW <1.2 (1) -1.5 <F2 / FW <-1.5 (2) ν11 <40 (3) 50 <ν12 (4) 1.56 < n11 <1.65 (6) n12 <1.52 (7) 1 <| B · Y ³ | <15 (9)

(Example) FIGS. 1 and 2 are lens cross-sectional views of Numerical Examples 1 and 2 of the present invention. In the figure, (A) shows the zoom position at the wide angle end, (B) shows the middle position, and (C) shows the zoom position at the telephoto end.

In the figure, I is a first group having a positive refractive power, and II is a second group having a negative refractive power. By moving both lens groups toward the object side as indicated by arrows while reducing the distance between the two lens groups. Zooming is performed from the wide-angle end to the telephoto end. SP is the aperture.

In the present embodiment, the overall length of the lens is shortened, particularly the overall length of the lens at the wide-angle end, by employing such a zoom system and refractive power arrangement. Then, the lens configuration of each lens group, the lens shape of each lens group, and the like are configured as described above so that the entire lens system has a symmetrical arrangement at the time of zooming. A zoom lens having a simple configuration in which the first group has two lenses and the second group has two lenses having a total of four lenses having good optical performance over the entire zoom range of about 62 to 35 degrees. ing.

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

Conditional expression (1) relates to the refractive power of the first lens unit, and conditional expression (2) relates to the refractive power of the second lens unit. Conditional expressions (1) and (2)
When the zooming is performed by moving both lens groups, the size of the entire lens system is reduced, and the variation in aberration is reduced while a predetermined zooming ratio is secured.

If the refractive power of each lens unit becomes too strong beyond the lower limit value of conditional expression (1) or the upper limit value of conditional expression (2), a predetermined zoom ratio can be easily obtained. It becomes difficult to satisfactorily correct curvature and coma.

If the upper limit of conditional expression (1) or the lower limit of conditional expression (2) is exceeded and the refractive power of each lens unit becomes too weak, the back focus becomes too short, and the effective diameter of the second unit increases. . In addition, the amount of movement of each lens unit for securing a predetermined zoom ratio increases, and the overall length of the lens becomes longer.

Conditional expressions (3) and (4) are satisfied when the first lens unit is composed of a negative meniscus eleventh lens having a convex surface facing the object side and a positive twelfth lens having both convex surfaces. The purpose is to appropriately set the Abbe number of the material of both lenses to favorably correct axial chromatic aberration.

If conditional expressions (3) and (4) are not satisfied, the fluctuation of the axial chromatic aberration accompanying zooming becomes large, which is not good.

The conditional expressions (6) and (7) relate to the refractive index of the material of the eleventh lens and the twelfth lens. If the conditional expressions (6) and (7) are not satisfied, the Petzval sum increases and the astigmatism also increases. Not good because it comes.

Conditional expression (9) is for maintaining good optical performance of the entire screen over the entire zoom range in a camera having a simple configuration of a zoom lens. Specifically, it is preferable to provide an aspherical surface on the object side or image plane side of the eleventh lens in the first group, the shape of which has a shape in which the negative refractive power increases from the center to the periphery of the lens.

In the conditional expression (9), when the aspherical surface is applied to the object-side lens surface of the eleventh lens, the aspherical surface coefficient B has a negative sign, and when it is applied to the image-side lens surface, the aspherical surface coefficient B has a positive sign.

If the upper limit of conditional expression (9) is exceeded, the aspherical effect will be insufficient and it will be difficult to satisfactorily correct the curvature of field. If the lower limit is exceeded, the aspherical effect will be too strong and the curvature of field will be corrected. It is not good because it becomes excessive.

In the present invention, while reducing the overall length of the lens,
In order to easily obtain a predetermined zoom ratio, when the principal point intervals at the wide-angle end and the telephoto end of the first and second units are eW and eT, respectively, 1.7 <eW / eT <2.7 (5) It is better to satisfy the conditions.

Conditional expression (5) sets the distance between the principal points of the first lens unit and the second lens unit at the wide-angle end and the telephoto end appropriately, and reduces the total length of the lens based on the conditional expressions (1) and (2). , For example, to obtain a zoom ratio of about 2.

If the upper limit or the lower limit of conditional expression (5) is exceeded, it becomes difficult to obtain a predetermined zoom ratio while shortening the overall length of the lens.

In addition, in the present invention, it is particularly preferable in terms of aberration correction that the radius of curvature of the object-side and image-surface-side lens surfaces of the 22nd lens constituting the second group having a negative refractive power is RA and RB, respectively. It is better to satisfy the following conditions.

Conditional expression (8) is for correcting various aberrations of the entire screen in a well-balanced manner over the entire zooming, and it becomes difficult to maintain the optical performance of the entire screen in a well-balanced state even if the upper limit or the lower limit is exceeded. come.

In Numerical Examples 1 and 2, which will be described later, the eleventh lens is formed of an aspherical lens made of plastic, and a zoom lens in which the curvature of field is well corrected is obtained.

In addition, in the present invention, in order to correct various aberrations in a well-balanced manner, particularly while miniaturizing the entire lens system, the above-mentioned conditional expressions (1) to (4) must be set to 0.6 <F1 / FW <1.2-1.3 <F2 / It is better to set as FW <−0.7 ν11 <3850 <ν12.

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, the lens shape, the refractive power, and the like of each lens group of a zoom lens that performs zooming by moving two lens groups having a predetermined refractive power are set as described above. It is possible to achieve a zoom lens having a simple configuration including four lenses as a whole and having a high optical performance over the entire zoom range of about 2 in which the overall length is reduced, 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, and FIGS. 3 and 4 are various aberration diagrams of Numerical Examples 1 and 2 of the present invention. In the lens cross-sectional view and the aberration diagram, (A) is an aberration diagram at a wide-angle end, (B) is an intermediate diagram, and (C) is an aberration diagram at a telephoto end. In the figure, I and II denote the first and second lens groups, SP denotes the aperture, and arrows denote the moving directions of the respective groups during zooming.

Claims (4)

(57) [Claims] 1. A zoom lens system comprising: a first lens unit having a positive refractive power and a second lens unit having a negative refractive power in order from the object side; The first lens unit includes a negative meniscus eleventh lens having a convex surface facing the object side and a positive twelfth lens whose both lens surfaces are convex. The second lens unit includes a positive lens.
The first lens unit and the second lens unit comprise a 21st lens and a negative 22nd lens.
The focal length of the group is F1, F2, the Abbe number of the material of the eleventh lens and the twelfth lens is ν11, ν12, respectively, the focal length at the wide-angle end of the entire system is EW, the material of the eleventh lens and the twelfth lens Where the refractive indices of n11 and n12 are respectively 0.4 <F1 / FW <1.2−1.5 <F2 / FW <−0.5 ν11 <40 50 <ν12 1.56 <n11 <1.65 n12 <1.52 Zoom lens with a simple configuration. 2. When the radii of curvature of the object-side and image-side lens surfaces of the 22nd lens are RA and RB, respectively. 2. A zoom lens having a simple configuration according to claim 1, wherein the following condition is satisfied. 3. The condition that 1.7 <eW / eT <2.7 is satisfied when the principal point intervals at the wide-angle end and the telephoto end of the first group and the second group are eW and eT, respectively. A zoom lens having a simple configuration according to 1. 4. A zoom lens system comprising: a first lens unit having a positive refractive power and a second lens unit having a negative refractive power in order from the object side; The first lens unit includes a negative meniscus eleventh lens having a convex surface facing the object side and a positive twelfth lens whose both lens surfaces are convex. The second lens unit includes a positive lens.
The first lens unit and the second lens unit comprise a 21st lens and a negative 22nd lens.
The focal length of the group is F1, F2, the Abbe number of the material of the eleventh lens and the twelfth lens is ν11, ν12, the focal length at the wide angle end of the entire system is FW, the material of the eleventh lens and the twelfth lens. N11, n12, an aspherical surface is provided on the object side or the image surface side of the eleventh lens, the fourth order aspherical coefficient of the aspherical surface is B, and the diagonal length of the effective screen is Y. 0.4 <F1 / FW <1.2−1.5 <F2 / FW <−0.5 ν11 <40 50 <ν12 1.56 <n11 <1.65 n12 <1.52 1 <| B · Y ³ | <15 A camera having a simple configuration of a zoom lens.