JP2003177314A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens whose entire length is short and whose distance from an exit pupil to an image surface is long. <P>SOLUTION: In this zoom lens equipped with a 1st lens group having negative refractive power, a 2nd lens group having positive refractive power, and a 3rd lens group having positive refractive power in order from an object side, the 1st and 3rd lens groups are constituted of one lens respectively, and the focal distance is changed by moving the 1st and the 2nd lens groups. Then, the ratio of the focal distance of the 2nd lens group to the focal distance of the 3rd lens group is set to ≥0.4 and ≤0.7. <P>COPYRIGHT: (C)2003,JPO

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 zoom lens suitable for a compact camera.

[0002]

2. Description of the Related Art In recent years, personal digital assistants and mobile phones called PDAs have been remarkably spread, and these devices are often equipped with compact digital cameras and digital video units. In such compact digital cameras and digital video units,
An image pickup device having a relatively small light receiving area is used, and a zoom lens having a simple structure is also used as an image pickup optical system.

As one of the zoom lenses having a simple structure, a first lens group having a negative refracting power, in order from the object side, is positive, as proposed in JP-A-11-21984 and US Pat. No. 5,745,301. A second lens group having a refractive power of
There is a so-called negative / positive / three-component zoom lens including a third lens group having a positive refractive power. The zoom lens having this configuration is expected to be suitable for a compact camera because it has a small number of lens groups that are moved to change the focal length and the moving mechanism is relatively simple.

[0004]

However, the conventional negative / positive / positive three-component zoom lens is compact enough in terms of its overall length, that is, the size in the optical axis direction, for use in a camera incorporated in a portable device. It's hard to say. For example, in the zoom lens of Japanese Patent Laid-Open No. 11-21984, the second lens group is composed of four lenses, so that the total length is long. The zoom lens of US Pat. No. 5,745,301 has a small total number of lenses of 3 to 4, but has a long total length because the refractive power of each lens is weak.

When it is attempted to shorten the total length of the zoom lens, the exit pupil tends to be close to the image plane. When the exit pupil is close to the image plane, the amount of light incident on the pixels in the peripheral portion of the image sensor is reduced, and the brightness of the captured image becomes uneven. Therefore, in order to obtain a good image, it is necessary to secure a certain distance or more between the exit pupil and the image plane.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a zoom lens having a short total length and an exit pupil sufficiently separated from the image plane.

[0007]

To achieve the above object, in the present invention, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a positive lens group are provided. In a zoom lens including a third lens group having a refracting power of, the first lens group and the third lens group each include only one lens, and at least the first lens group and the second lens group move in the optical axis direction. By doing so, the overall focal length changes, and the focal length of the second lens group is changed to f2,
When the focal length of the lens group is represented by f3, it is assumed that the relationship of Expression 1 is satisfied. 0.4 ≦ f2 / f3 ≦ 0.7 ... Expression 1

This zoom lens includes a first lens group and a third lens group.
Each lens group is composed of one lens, and therefore the total length is easily shortened. Further, by satisfying the expression 1, it is possible to increase the distance between the exit pupil and the image plane while suppressing the distortion due to the third lens group.

According to the present invention, a zoom lens including, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. The first lens group, the second lens group, and the third lens group each include only one lens, and at least the first lens group and the second lens group move in the optical axis direction, so that the entire focal length is The radius of curvature of the two surfaces of the second lens group closer to the first lens group is CR2f, the radius of curvature of the two surfaces of the second lens group closer to the third lens group is CR2r, and When the focal length of the second lens group is represented by f2 and the focal length of the third lens group is represented by f3, it is assumed that the expressions 2 and 3 are satisfied. −5.0 ≦ (CR2f−CR2r) / (CR2f + CR2r) ≦ −0.5 ... Equation 2 0.3 ≦ f2 / f3 ≦ 1.2 Equation 3

This zoom lens includes a first lens group, a second lens group
All of the lens group and the third lens group are composed of one lens, and it is easy to shorten the total length. Further, by satisfying the expression 2, it is possible to reduce the thickness of the lens forming the second lens group while suppressing astigmatism. Further, by satisfying Expression 3, it is possible to increase the distance between the exit pupil and the image plane while suppressing distortion.

It is preferable that each of the zoom lenses described above also satisfies the relation of Expression 4 when the focal length of the entire system at the wide-angle end is represented by fw. 1.0 ≦ f2 / fw ≦ 2.0 Equation 4

By satisfying the expression 4, it is possible to reduce the amount of movement of the second lens group while suppressing the axial chromatic aberration due to the second lens group.

Further, the focal length of the entire system at the wide-angle end is f
w, when the radius of curvature of one of the two surfaces of the first lens group which is closer to the second lens group is represented by CR1r, the relationship of Expression 5 may be satisfied. 0.8 ≦ CR1r / fw ≦ 1.6 Equation 5

By satisfying the expression 5, it is possible to suppress the distortion and the field curvature due to the first lens group.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the zoom lens of the present invention will be described below with reference to the drawings. The configuration of the zoom lens 1 of the present embodiment is schematically shown in FIG. The zoom lens 1 includes a first lens group 11, a second lens group 12, and a third lens group 13 in order from the object side. The first lens group 11 is composed of only one lens and has a negative refracting power. The second lens group 12 is composed of one or more lenses and has a positive refractive power. The third lens group is composed of one lens and has a positive refractive power.

In the zoom lens 1, the first lens group 11 and the second lens group 12 are moved in the optical axis direction to change the distance between the lens groups, thereby changing the entire focal length and the focal position. Is immutable. Third lens group 13
Is fixed.

The movement of the lens group for changing the focal length is schematically shown in FIG. 1 (b). In FIG. 1B, the symbol W indicates the state at the wide-angle end with the shortest focal length, that is, the largest angle of view, and the symbol T indicates the state at the telephoto end with the longest focal length, that is, the smallest angle of view. Is shown. Reference symbol M indicates a state in which the focal length is between the wide-angle end and the telephoto end (hereinafter, referred to as an intermediate point). While the focal length changes from the wide-angle end W to the telephoto end T, the first lens group 11 moves backward, or moves backward and moves forward, and the second lens group 12 moves forward.

The zoom lens 1 is set so as to satisfy the relationship of Expression 1. 0.4 ≦ f2 / f3 ≦ 0.7 Equation 1 (reprinted) Here, f2 is the focal length of the second lens group 12, and f3 is the focal length of the third lens group 13.

If the focal length ratio f2 / f3 does not reach the lower limit of Expression 1, the exit pupil will be close to the image plane. If the focal length ratio f2 / f3 exceeds the upper limit of Expression 1, the third lens group 13
The positive refracting power of becomes large, and the negative distortion becomes large.
By satisfying the relationship of Expression 1, it is possible to increase the distance between the exit pupil and the image plane for the entire length while suppressing the distortion due to the third lens group 13 while shortening the overall length of the zoom lens 1. Become.

The second lens group 12 can be composed of two or more lenses, but from the viewpoint of shortening the overall length of the zoom lens 1, it is preferably composed of one lens.
In that case, it sets so that the relationship of Formula 2 may be satisfy | filled. −5.0 ≦ (CR2f−CR2r) / (CR2f + CR2r) ≦ −0.5 (Expression 2) Here, CR2f and CR2r are the first of the two surfaces of the lenses forming the second lens group 12, respectively. 1 lens group 1
The radius of curvature closer to 1 (front surface) and the third lens group 11
Is the radius of curvature of the side closer to (rear surface). The radius of curvature of a surface is negative when the center of curvature is located on the object side of that surface, and is positive when the center of curvature is located on the image plane side of that surface, in accordance with general optical notation. To do.

When the second lens group 12 is composed of one lens, the ratio of the difference in the radius of curvature to the sum of the radiuses of curvature is expressed by the formula 2
If the lower limit of is not reached, it becomes a biconvex lens having a small difference in absolute value of curvature between the front surface and the rear surface, and it becomes difficult to correct astigmatism. Further, when the ratio of the difference in the radius of curvature to the sum of the radiuses of curvature exceeds the upper limit of Expression 2, the meniscus lens has a small difference in the curvature between the front surface and the rear surface, and in order to have a necessary refractive power, a thick lens is used. And you have to By satisfying the expression 2, it becomes possible to make the second lens group 12 a single relatively thin lens while suppressing astigmatism.

When the second lens group 12 is composed of one lens and the relationship of the expression 2 is satisfied, the relationship of the expression 3 is satisfied instead of the relationship of the expression 1. May be. 0.3 ≦ f2 / f3 ≦ 1.2 ... Equation 3 (repost)

As described above, in the zoom lens 1, the focal length is changed by the movement of the first lens group 11 and the second lens group 12, but the movement amount of the second lens group 12 is the main factor that determines the total length. Therefore, it is desirable to satisfy the relationship of Expression 4. 1.0 ≦ f2 / fw ≦ 2.0 Equation 4 (reprinted) Here, fw is the focal length of the entire zoom lens 1 at the wide-angle end W.

The smaller the ratio f2 / fw of the focal length of the second lens group 12 to the focal length at the wide-angle end W, the larger the refractive power of the second lens group 12, and the smaller the moving amount of the second lens group 12. However, on the other hand, the axial chromatic aberration increases. If the ratio f2 / fw does not reach the lower limit of Expression 4, it becomes necessary to increase the number of lenses forming the second lens group 12 in order to correct the axial chromatic aberration, and conversely the total length of the zoom lens 1 increases. Becomes Further, when the focal length ratio f2 / fw exceeds the upper limit of Expression 4, the refractive power of the second lens group 12 becomes small and the axial chromatic aberration is easily corrected, but the movement amount increases. Limiting the movement amount of the second lens group 12 makes it difficult to obtain a desired zoom magnification. By satisfying the relation of Expression 4, it becomes possible to reduce the movement amount of the second lens group 12 while suppressing the axial chromatic aberration.

Generally, in a zoom lens in which a lens unit having negative refracting power is located closer to the object side than a lens unit having positive refracting power, it is necessary to increase the negative refracting power. However, when the first lens group having negative refracting power is composed of only one lens, if an attempt is made to obtain a large refracting power at the object-side surface (front surface), the incident light ray is bent too much. Off-axis aberrations, especially distortions and field curvatures, occur and are difficult to correct. Therefore, when the first lens group is composed of only one lens, the front surface has a small refracting power, and the rear surface having a small off-axis ray height has a relatively large negative refracting power.
It is desirable to be able to favorably correct off-axis aberrations.
For this purpose, it is preferable to satisfy the relationship of Expression 5. 0.8 ≦ CR1r / fw ≦ 1.6 Formula 5 (repost) Here, CR1r is 2 of the lenses that form the first lens group 11.
It is the radius of curvature of one of the two surfaces closer to the second lens group 12 (rear surface).

The ratio CR1r / f of the radius of curvature of the rear surface of the lens forming the first lens group 11 to the focal length at the wide-angle end W.
When w exceeds the upper limit of Expression 5, the curvature of the rear surface becomes small and the curvature of the front surface must be increased, and it becomes difficult to correct distortion and curvature of field. On the contrary, if the ratio CR1r / fw does not reach the lower limit of Expression 5, the curvature of the rear surface becomes too large and the negative distortion increases. By satisfying the relationship of Expression 5, it is possible to give the front surface a small negative refractive power or a positive refractive power, and it becomes possible to satisfactorily correct distortion and field curvature.

[0027]

EXAMPLES Four examples of the zoom lens 1 will be shown below. In each embodiment, the first lens group 11 and the second lens group 1
Each of the second and third lens groups 13 is composed of one lens, and the protective glass 14 of the image pickup element when used in a compact camera is also shown. The surface of the protective glass 14 of each lens and the image sensor is represented by S1 to S8 in order from the object side. The unit of length such as focal length and radius of curvature is mm.

In each of the embodiments, the lens surfaces S1 to S6 are all aspherical surfaces. The aspherical surface is defined by Equation 6. X = C · Y ² / {1+ (1−ε · C ² · Y ² ) ^1/2 } + ΣA ⁱ · Y ⁱ Equation 6 Here, X is the displacement amount in the optical axis direction, and Y is perpendicular to the optical axis. Direction height, C is paraxial curvature, ε is conic coefficient, A _i is order i
Is the coefficient of the Y term of. Note that the Y term is up to the 10th order, and the coefficient A _i of the odd-order Y term is 0.

<First Embodiment> FIG. 2 shows a sectional view of the zoom lens of the first embodiment including the optical axis. Further, the construction data are listed in Table 1 and the aspherical surface coefficients are listed in Table 2. The axial upper surface spacing that changes when changing the focal length indicates the values at the wide-angle end W, the intermediate point M, and the telephoto end T.

[0030] Table 1    Surface radius of curvature Axial upper surface spacing Refractive index (Nd) Abbe number (νd)                         W M T   S1 550.549                       0.800 1.52200 52.20   S2 2.150                       2.309 1.630 0.378   S3 1.850                       2.600 1.52200 52.20   S4 -4.614                       1.157 1.579 3.058   S5 9.677                       0.980 1.52200 52.20   S6 -3.713                       0.900   S7 ∞                       0.400 1.51680 64.20   S8 ∞

Table 2 surface S1: ε = 1.0 A2 = 0.0 A4 = 0.54950x10 ^-2 A6 = -0.31896x10 ^-2 A8 = 0.80326x10 ^-3 A10 = -0.75268x10 ^-4 S2: ε = 1.0 A2 = 0.0 A4 = 0.44341x10 ^-2 A6 = -0.16536x10 ^-1 A8 = 0.78162x10 ^-2 A10 = -0.15165x10 ^-2 S3: ε = 1.0 A2 = 0.0 A4 = -0.14386x10 ^-1 A6 = -0.83531x10 ^-3 A8 = -0.27278 x10 ^-2 A10 = 0.28917x10 ^-3 S4: ε = 1.0 A2 = 0.0 A4 = 0.32612x10 ^-1 A6 = -0.10095x10 ⁰ A8 = 0.32080x10 ⁰ A10 = -0.40210x10 ⁰ S5: ε = 1.0 A2 = 0.0 A4 = ^{0.37575x10 -1 A6 = -0.46849x10 -1 A8 =} 0.18563x10 -1 A10 = -0.21170x10 -2 S6: ε = 1.0 A2 = 0.0 A4 = 0.81783x10 -1 A6 = -0.55045x10 -1 A8 = 0.12803x10 - ¹ A10 = 0.0

Table 3 shows the focal lengths at the wide-angle end W, the intermediate point M and the telephoto end T, the F value, the distance between the surface S1 and the image plane, and the distance between the exit pupil and the image plane.

In this embodiment, the following settings are made and the equation 1
~ All relationships of Expression 5 are satisfied. f2 / f3 = 0.56 (CR2f-CR2r) / (CR2f + CR2r) =-2.
34 f2 / fw = 1.36 CR1r / fw = 1.00

The distance from the front surface S1 of the first lens group to the image plane is about 9.2 mm at maximum, and the total length is short. The distance between the exit pupil and the image plane is the shortest at the wide-angle end W, 3.7 mm, but the total length is relatively short.

FIG. 3 shows spherical aberration, astigmatism and distortion. In FIG. 3, the upper stage is the wide-angle end W, the middle stage is the midpoint M,
The lower part is the aberration at the telephoto end T. The solid line (d) in spherical aberration represents the d line, and the broken line (SC) represents the sine condition. Further, the solid line (DS) and the broken line (D
M) represents a sagittal surface and a meridional surface, respectively.
By satisfying the relationships of Expressions 1 to 5, various aberrations are suppressed well.

<Second Embodiment> FIG. 4 is a sectional view of the zoom lens of the second embodiment including the optical axis. Further, the construction data is listed in Table 4, and the aspherical surface coefficient is listed in Table 5.

[0037] Table 4    Surface radius of curvature Axial upper surface spacing Refractive index (Nd) Abbe number (νd)                         W M T   S1 60.926                       0.800 1.52200 52.20   S2 2.500                       2.727 1.873 0.300   S3 1.850                       2.600 1.52200 52.20   S4 -5.979                       1.272 1.637 2.912   S5 4.723                       0.800 1.52200 52.20   S6 -4.955                       0.700   S7 ∞                       0.400 1.51680 64.20   S8 ∞

Table 5 Surface S1: ε = 1.0 A2 = 0.0 A4 = 0.70699x10 ^-2 A6 = -0.24333x10 ^-2 A8 = 0.38742x10 ^-3 A10 = -0.25740x10 ^-4 S2: ε = 1.0 A2 = 0.0 A4 = 0.96012x10 ^-2 A6 = -0.84789x10 ^-2 A8 = 0.23315x10 ^-2 A10 = -0.33989x10 ^-3 S3: ε = 1.0 A2 = 0.0 A4 = -0.12594x10 ^-1 A6 = 0.29528x10 ^-2 A8 = -0.66655x10 ^-2 A10 = 0.15321x10 ^-2 S4: ε = 1.0 A2 = 0.0 A4 = 0.95562x10 ^-2 A6 = 0.16287x10 ⁰ A8 = -0.96355x10 ⁰ A10 = 0.18597x10 ¹ S5: ε = 1.0 A2 = 0.0 A4 = 0.32484x10 ^-1 A6 = -0.38292x10 ^-1 A8 = 0.11674x10 ^-1 A10 = -0.83065x10 ^-3 S6: ε = 1.0 A2 = 0.0 A4 = 0.88394x10 ^-1 A6 = -0.61840x10 ^-1 A8 = 0.12803x10 ^-1 A10 = 0.0

Table 6 shows the focal lengths at the wide-angle end W, the intermediate point M and the telephoto end T, the F number, the distance between the surface S1 and the image plane, and the distance between the exit pupil and the image plane.

In this embodiment, the following settings are made and equation 1
~ All relationships of Expression 5 are satisfied. Also in this embodiment, it is possible to increase the distance from the exit pupil to the image plane while shortening the overall length. f2 / f3 = 0.64 (CR2f-CR2r) / (CR2f + CR2r) =-1.
90 f2 / fw = 1.42 CR1r / fw = 1.16

FIG. 5 shows spherical aberration, astigmatism, and distortion. By satisfying the relationships of Expressions 1 to 5, various aberrations are suppressed well.

<Third Embodiment> FIG. 6 shows a sectional view of the zoom lens of the third embodiment including the optical axis. Further, the construction data are listed in Table 7 and the aspherical surface coefficients are listed in Table 8.

[0043] Table 7    Surface radius of curvature Axial upper surface spacing Refractive index (Nd) Abbe number (νd)                         W M T   S1 405.887                       0.800 1.52200 52.20   S2 2.500                       2.725 1.871 0.300   S3 1.850                       2.600 1.52200 52.20   S4 -4.901                       1.474 1.818 3.020   S5 3.780                       0.800 1.52200 52.20   S6 -10.969                       0.500   S7 ∞                       0.400 1.51680 64.20   S8 ∞

Table 8 Surface S1: ε = 1.0 A2 = 0.0 A4 = 0.80360x10 ^-2 A6 = -0.24945x10 ^-2 A8 = 0.36749x10 ^-3 A10 = -0.22161x10 ^-4 S2: ε = 1.0 A2 = 0.0 A4 = 0.11298x10 ^-1 A6 = -0.78889x10 ^-2 A8 = 0.18107x10 ^-2 A10 = -0.23435x10 ^-3 S3: ε = 1.0 A2 = 0.0 A4 = -0.13293x10 ^-1 A6 = 0.28627x10 ^-2 A8 = -0.77053x10 ^-2 A10 = 0.19681x10 ^-2 S4: ε = 1.0 A2 = 0.0 A4 = 0.10874x10 ^-1 A6 = 0.13331x10 ⁰ A8 = -0.83192x10 ⁰ A10 = 0.16111x10 ¹ S5: ε = 1.0 A2 = 0.0 A4 = 0.36065x10 ^-1 A6 = -0.37253x10 ^-1 A8 = 0.96236x10 ^-2 A10 = -0.63540x10 ^-3 S6: ε = 1.0 A2 = 0.0 A4 = 0.10832x10 ⁰ A6 = -0.70698x10 ^-1 A8 = 0.12803x10 ^-1 A10 = 0.0

Table 9 shows the focal lengths at the wide-angle end W, the intermediate point M and the telephoto end T, the F value, the distance between the surface S1 and the image plane, and the distance between the exit pupil and the image plane.

In this embodiment, the following settings are made, and equation 1
~ All relationships of Expression 5 are satisfied. Also in this embodiment, it is possible to increase the distance from the exit pupil to the image plane while shortening the overall length. f2 / f3 = 0.54 (CR2f-CR2r) / (CR2f + CR2r) =-2.
21 f2 / fw = 1.38 CR1r / fw = 1.16

FIG. 7 shows the spherical aberration, astigmatism and distortion. By satisfying the relationships of Expressions 1 to 5, various aberrations are suppressed well.

<Fourth Embodiment> FIG. 8 shows a sectional view of the zoom lens of the fourth embodiment including the optical axis. Table 10 shows the construction data and Table 11 shows the aspherical coefficients.
Listed.

[0049] Table 10    Surface radius of curvature Axial upper surface spacing Refractive index (Nd) Abbe number (νd)                         W M T   S1 -180.030                       0.800 1.52200 52.20   S2 2.500                       2.739 1.881 0.300   S3 1.850                       2.600 1.52200 52.20   S4 -4.368                       1.601 1.929 3.077   S5 3.422                       0.800 1.52200 52.20   S6 -190.057                       0.450   S7 ∞                       0.400 1.51680 64.20   S8 ∞

Table 11 Surface S1: ε = 1.0 A2 = 0.0 A4 = 0.85323x10 ^-2 A6 = -0.27590x10 ^-2 A8 = 0.43578x10 ^-3 A10 = -0.27373x10 ^-4 S2: ε = 1.0 A2 = 0.0 A4 = 0.12243x10 ^-1 A6 = -0.89528x10 ^-2 A8 = 0.22540x10 ^-2 A10 = -0.29652x10 ^-3 S3: ε = 1.0 A2 = 0.0 A4 = -0.14236x10 ^-1 A6 = 0.22045x10 ^-2 A8 = -0.76496x10 ^-2 A10 = 0.19680x10 ^-2 S4: ε = 1.0 A2 = 0.0 A4 = 0.11968x10 ^-1 A6 = 0.14646x10 ⁰ A8 = -0.10474x10 ¹ A10 = 0.21996x10 ¹ S5: ε = 1.0 A2 = 0.0 A4 = 0.28159x10 ^-1 A6 = -0.29321x10 ^-1 A8 = 0.36815x10 ^-2 A10 = 0.35090x10 ^-3 S6: ε = 1.0 A2 = 0.0 A4 = 0.11598x10 ⁰ A6 = -0.77558x10 ^-1 A8 = 0.12803x10 ^-1 A10 = 0.0

Table 12 shows the focal lengths at the wide-angle end W, the intermediate point M and the telephoto end T, the F number, the distance between the surface S1 and the image plane, and the distance between the exit pupil and the image plane.

In this embodiment, the following settings are made, and equation 1
~ All relationships of Expression 5 are satisfied. Also in this embodiment, it is possible to increase the distance from the exit pupil to the image plane while shortening the overall length. f2 / f3 = 0.45 (CR2f-CR2r) / (CR2f + CR2r) =-2.
47 f2 / fw = 1.35 CR1r / fw = 1.16

FIG. 9 shows the spherical aberration, astigmatism and distortion. By satisfying the relationships of Expressions 1 to 5, various aberrations are suppressed well.

Incidentally, here, the first lens group 11 and the second lens group 11
Although the example in which the focal length is changed by moving only the lens group 12 has been described, the third lens group 13 may also be moved to change the focal length.

[0055]

The zoom lens of the present invention has a short overall length and is compact, but since the distance between the exit pupil and the image plane is long, an image having no significant difference in brightness between the central portion and the peripheral portion is formed. be able to. Also, in spite of being compact, distortion,
Various aberrations such as astigmatism and field curvature are small. Therefore,
It is particularly suitable for a camera built in a mobile device.

[Brief description of drawings]

FIG. 1 is a configuration of a zoom lens according to an embodiment of the present invention,
FIG. 3 is a diagram schematically showing movement of lens groups during zooming.

FIG. 2 is a sectional view including the optical axis of the zoom lens according to the first embodiment.

FIG. 3 is a diagram showing spherical aberration, astigmatism, and distortion of the zoom lens of the first embodiment.

FIG. 4 is a sectional view including an optical axis of a zoom lens according to a second example.

FIG. 5 is a diagram showing spherical aberration, astigmatism, and distortion of the zoom lens of the second embodiment.

FIG. 6 is a sectional view including an optical axis of a zoom lens according to a third example.

FIG. 7 is a diagram showing spherical aberration, astigmatism, and distortion of the zoom lens of the third embodiment.

FIG. 8 is a sectional view including an optical axis of a zoom lens according to a fourth example.

FIG. 9 is a diagram showing spherical aberration, astigmatism, and distortion of the zoom lens of the fourth embodiment.

[Explanation of symbols]

1 zoom lens 11 First lens group 12 Second lens group 13 Third lens group 14 Image sensor protective glass

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshito Iwasawa             2-3-3 Azuchi-cho, Chuo-ku, Osaka             Kokusai Building Minolta Co., Ltd. (72) Inventor Tetsuo Kono             2-3-3 Azuchi-cho, Chuo-ku, Osaka             Kokusai Building Minolta Co., Ltd. F term (reference) 2H087 KA03 PA03 PA17 PB03 QA02                       QA03 QA07 QA17 QA18 QA21                       QA25 QA34 QA41 QA46 RA05                       RA12 RA13 RA42 SA14 SA16                       SA19 SA62 SA63 SA74 SB02                       SB12 SB22

Claims (4)

[Claims] 1. A zoom lens comprising, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. The first lens group and the third lens group each include only one lens, and the entire focal length is changed by moving at least the first lens group and the second lens group in the optical axis direction. A zoom lens characterized in that when the focal length of the group is f2 and the focal length of the third lens group is f3, the relationship of 0.4 ≦ f2 / f3 ≦ 0.7 is satisfied. 2. A zoom lens comprising, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. , The first lens group, the second lens group, and the third lens group each include only one lens, and the entire focal length is changed by moving at least the first lens group and the second lens group in the optical axis direction. Then, of the two surfaces of the second lens group, the radius of curvature closer to the first lens group is CR2f, and of the two surfaces of the second lens group, the radius of curvature closer to the third lens group is CR2r, and When the focal length of the lens group is f2 and the focal length of the third lens group is f3, -5.0≤ (CR2f-CR2r) / (CR2f + CR2
r) A zoom lens characterized by satisfying the relationships of ≤-0.5 and 0.3≤f2 / f3≤1.2. 3. The zoom according to claim 1, wherein when the focal length of the entire system at the wide angle end is represented by fw, the relationship of 1.0 ≦ f2 / fw ≦ 2.0 is satisfied. lens. 4. The focal length of the entire system at the wide-angle end is fw,
When the radius of curvature of one of the two surfaces of the first lens group which is closer to the second lens group is represented by CR1r, the relationship of 0.8 ≦ CR1r / fw ≦ 1.6 is satisfied. The zoom lens according to claim 2.