JP4027335B2 - Small zoom lens - Google Patents

Description

  The present invention relates to a compact and lightweight zoom lens compatible with high-order megapixels used in in-vehicle cameras, surveillance cameras, digital cameras, mobile phone cameras, and the like using light receiving elements such as CCDs and CMOSs. is there.

  In recent years, light receiving elements such as a CCD and a CMOS have been put into practical use at a fast tempo of miniaturization and high definition. Along with this, zoom lens systems used in digital cameras and mobile phone mounted cameras in which they are used are inevitably required to be small in size and high in performance.

  Conventionally, in order to achieve such high performance, the fact is that aberration correction has been performed using a large number of lenses. In addition, in order to achieve miniaturization of the camera, it is desired to make the zoom lens thinner, and it becomes necessary to make the total length of each lens group constituting the zoom lens shorter than before.

  In addition, as a feature of a light receiving element such as a CCD or CMOS, there is a restriction on the angle of the light beam taken into each pixel. If this is ignored, the amount of peripheral light decreases, resulting in a so-called dark camera in the peripheral part. Conventionally, in order to cope with such a phenomenon, an electric correction circuit is provided or a microlens that is paired with a light receiving element is arranged to increase the amount of light on the element surface.

Based on such a background, a high-performance negative, positive, and positive three-group zoom lens having a zoom ratio of about 2 to 3 times is disclosed in, for example, Patent Documents 1, 2, and 3 below. It is disclosed.
JP 2002-196240 A JP 2002-323654 A JP 2002-372667 A

  However, according to these proposals, the second lens group has a positive, positive, negative, and positive configuration, and two positive lenses are arranged in the front. The power becomes strong, which makes it difficult to correct various aberrations satisfactorily.

  In view of the problems as described above, the object of the present invention is to provide a compact, compact, and high zoom ratio suitable for a thin camera using a light receiving element such as a CCD or CMOS using high-definition pixels. The second lens group is configured to be negative, positive, positive, and negative, and the negative power is divided into two to facilitate correction of various aberrations and to provide a high-resolution zoom lens. .

  In order to solve the above problems, the zoom lens of the present invention has a three-group configuration, and is a first lens group having a negative power and a second lens having a positive power from the object side toward the imaging surface. The groups and the third lens group having a positive power are arranged in this order. The first lens group includes a first meniscus lens having a negative power with a convex surface facing the object side and a first meniscus lens having a positive power with a convex surface facing the object side, arranged in order from the object side. It consists of two lenses. Further, the second lens group includes a front group lens and a rear group lens arranged in order from the object side, and the front group lens is arranged in order from the object side and has a negative surface with a convex surface facing the object side. It comprises a third meniscus lens having power, a fourth lens having positive power, and a fifth lens having positive power, and the rear lens group has a negative power with a strong concave surface facing the image plane side. It is comprised from the 6th lens or the 6th lens which has negative power, and the 7th lens which has negative power. Furthermore, the third lens group is composed of an eighth lens having a positive power.

  In the zoom lens according to the present invention, since the second lens group has a power distribution divided into negative, positive, positive, and negative, it is easy to correct various aberrations. In particular, by arranging the third lens having the negative power closest to the object side, the exit pupil position and the back focus in the entire zoom lens can be kept long.

The zoom lens according to the present invention satisfies the following conditional expressions (1) to (4).
1.2 <| f1 / f2 | <1.8 (1)
1.0 <f2 / FW <2.0 (2)
0.5 <| fA / fB | <1.5 (3)
| F2 / fC | <1.5 (4)
FW: Focal length at the wide end of all optical systems
f1: Focal length of the first lens group
f2: Focal length of the second lens group
fA: Focal length of front lens group
fB: Focal length of the rear lens group
fC: focal length of the third lens from the most object side of the second lens group

Conditional expression (1) is a condition for keeping the entire length of the entire optical system from the wide end to the tele end stable. If the upper limit of 1.8 is exceeded, the total length on the telephoto side becomes shorter than that on the wide side. It will not meet the original purpose of miniaturization and thinning. In addition, the power of the second lens group becomes strong, and it becomes difficult to obtain stable aberrations over the entire zoom range. If the lower limit of 1.2 is not reached, the total length of the telephoto end becomes longer than the wide end, which also hinders downsizing and thinning.

Conditional expression (2) is a condition for suppressing the enlargement of the entire lens system and performing good aberration correction. When the upper limit of 2.0 is exceeded, the power of the entire lens system becomes weak, and various aberration characteristics can be kept stable, but the size cannot be reduced. If the lower limit of 1.0 is not reached, the power of the entire lens system becomes too strong even if the entire optical system can be miniaturized, and it becomes extremely difficult to balance aberrations in the entire zoom range.

Conditional expression (3) is a condition for reducing the total length of the entire optical system. If the upper limit of 1.5 is exceeded, the total length can be shortened, but the power of the rear lens of the second lens group becomes stronger, making it difficult to correct curvature of field and chromatic aberration over the entire zoom range, and shorten the back focus. Thus, it becomes impossible to secure a space for an insert such as a filter disposed behind the lens. Below the lower limit of 0.5, the total length of the entire optical system becomes longer, the field curvature becomes insufficiently corrected, and chromatic aberration of magnification becomes difficult to correct.

Conditional expression (4) reduces the Petzval sum of the second lens group and suppresses field curvature and coma aberration by disposing the third lens having the negative power closest to the object side of the second lens group. In addition, this is also a condition for stably maintaining astigmatism, axial chromatic aberration, and lateral chromatic aberration in the entire zoom range. If this condition of 1.5 is exceeded, the power of the third lens becomes too strong, and if the axial chromatic aberration and spherical aberration are corrected optimally, the curvature of field and the chromatic aberration of magnification cannot be corrected well. In addition to this, by disposing the negative third lens, the back focus can be kept long over the entire zoom range regardless of the small zoom lens.

Next, the zoom lens of the present invention can satisfy 0.1 <FW / f3 <0.5 when the focal length of the third lens group is f3. As a characteristic of a light receiving element such as a CCD or CMOS, the maximum emission angle of the optical system is important. The condition for keeping the exit angle small is 0.1 <FW / f3 <0.5, where f3 is the focal length of the third lens group. If the upper limit of 0.5 of this conditional expression is exceeded, the maximum emission angle can be reduced, but the power of the third lens group becomes too strong, and it becomes difficult to satisfactorily correct lateral chromatic aberration and curvature of field. On the other hand, if the lower limit of 0.1 is not reached, the power of the third lens group becomes weak, so that each aberration can be easily balanced, but the maximum emission angle cannot be reduced.

Here, at least one of the lens surfaces of the first lens group is an aspherical surface, at least one of the lens surfaces of the second lens group is an aspherical surface, and the lens of the third lens group. It is preferable that at least one of the surfaces is an aspherical surface because the number of lenses can be reduced.

  In the zoom lens according to the present invention, the configuration of the second lens group is negative, positive, positive, and negative power distribution, so that various aberrations can be easily corrected. Further, by using an aspheric surface for each group, there is an effect that it is possible to obtain a good aberration correction with a small number of lenses. Therefore, according to the present invention, it is possible to realize a compact, high-resolution three-group zoom lens that is relatively bright, compact, lightweight, and compact with a high zoom ratio corresponding to a light receiving element of a high-definition pixel.

  Embodiments of a zoom lens to which the present invention is applied will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram illustrating a zoom lens according to the first embodiment.

  The zoom lens 100 includes a first lens group I having negative power, a second lens group II having positive power, and a third lens group III having positive power from the object side toward the image plane 10. The zoom lens has a three-group configuration arranged in this order. In zooming from wide to tele, the third lens group III is fixed, the first lens group I moves on the optical axis from the object side to the image plane side, and moves from the image plane side to the object side from the middle. It moves along a trajectory that has a concave surface on the object side. On the other hand, the second lens group II is zoomed by moving on the optical axis sequentially from the image plane side to the object side.

  The first lens group I includes a first meniscus lens 1 having a negative power with a convex surface facing the object side and a second meniscus lens having a positive power with a convex surface facing the object side. It consists of a lens 2. The second lens group II includes a front group lens A and a rear group lens B arranged in order from the object side. The front lens group A is arranged in order from the object side, the meniscus third lens 3 having negative power with the convex surface facing the object side, the fourth lens 4 having positive power, and both having positive power. Consists of a convex fifth lens 5. The rear lens group B is composed of a sixth meniscus lens having a negative power with a strong concave surface facing the image surface side. On the other hand, the third lens group III includes a biconvex eighth lens 8 having positive power.

  The second lens 2, the sixth lens 6, and the eighth lens 8 are resin lenses, and both surfaces of the lens surfaces are aspherical surfaces. A cover glass 9 is disposed between the eighth lens 8 and the imaging plane 10.

The lens data of the entire optical system of the zoom lens 100 is as follows.
F-number: 2.85 4.03 5.49
Focal length: 3.48 6.74 10.47mm
f1: −8.064 mm fA: 3.830 mm
f2: 5.778 mm fB: -4.974 mm
f3: 12.704 mm fC: -7.159 mm

  Table 1A shows lens data of each lens surface of the zoom lens 100, and Table 1B shows aspheric coefficients for defining the aspherical shape of the aspherical lens surface.

  In Table 1A, i represents the order of the lens surfaces counted from the object side, R represents the radius of curvature of the lens surfaces, d represents the distance between the lens surfaces, Nd represents the refractive index of each lens, and νd represents Represents the Abbe number of each lens. The lens surface with a star on the number i is aspheric.

  Note that the aspherical shape adopted for the lens surface is that the axis in the optical axis direction is X, the height in the direction orthogonal to the optical axis is H, the conic coefficient is K, and the aspherical coefficients are A, B, C, and D. Can be expressed by the following equation.

  The meaning of each of these symbols and the expression representing the aspherical shape are the same in Examples 2 and 3 described later.

The zoom lens 100 according to the first embodiment satisfies the following conditional expressions (1) to (4).
1.2 <| f1 / f2 | <1.8 (1)
1.0 <f2 / FW <2.0 (2)
0.5 <| fA / fB | <1.5 (3)
| F2 / fC | <1.5 (4)
FW: Focal length at the wide end of all optical systems
f1: Focal length of the first lens group
f2: Focal length of the second lens group
fA: Focal length of front lens group
fB: Focal length of the rear lens group
fC: focal length of the third lens closest to the object side in the second lens group

  That is, | f1 / f2 | = 1.4, f2 / FW = 1.66, fA / fB = 0.77, f2 / fC = 0.8, which satisfies the conditional expressions (1) to (4). ing.

  FIG. 4 is an aberration diagram illustrating various aberrations in the zoom lens 100 according to the first example. In the figure, (W) is an aberration diagram for wide, (N) is normal, and (T) is an aberration diagram for tele. SA represents spherical aberration, AS represents astigmatism, and DIST represents distortion. Of the astigmatism, T represents a tangential image and S represents a sagittal image surface. The meanings of these symbols are the same in the aberration diagrams showing various aberrations in Examples 2 and 3 described later.

  FIG. 2 is a configuration diagram illustrating the zoom lens 200 according to the second embodiment. The zoom lens 200 has a three-group configuration including a first lens group I having negative power, a second lens group II having positive power, and a third lens group III having positive power, which are arranged in order from the object side. The power distribution and scaling method are the same as in the first embodiment.

  The first lens unit I includes a first meniscus lens 11 having a negative power with a convex surface facing the object side and a first meniscus lens having a positive power with a convex surface facing the object side. It consists of two lenses 12. The second lens group II includes a front group lens A and a rear group lens B arranged in order from the object side. The front lens group A is arranged in order from the object side, and has a positive power with the third lens 13 of the meniscus having a negative power with the convex surface facing the object side and the fourth lens 14 of the biconvex lens having a positive power. The rear lens group B is composed of a biconcave sixth lens 16 having a strong concave surface facing the image plane side. The third lens group III is composed of an eighth lens 18 having positive power by a biconvex lens.

  The second lens 12, the fifth lens 15, the sixth lens 16, and the eighth lens 18 are resin lenses, and both surfaces of each lens are aspheric. A cover glass 9 is disposed between the eighth lens 18 and the imaging plane 10.

The lens data of the entire optical system of the zoom lens 200 is as follows.
F-number: 3.02 4.39 5.95
Focal length: 3.50 6.76 10.50mm
f1: −8.110 mm fA: 3.738 mm
f2: 5.790 mm fB: -5.101 mm
f3: 12.704 mm fC: -10.929 mm

Table 2A shows lens data of each lens surface of the zoom lens 200, and Table 2B shows aspheric coefficients for defining the aspheric shape of the aspheric lens surface. FIG. 5 is an aberration diagram illustrating various aberrations of the zoom lens 200 according to the second example.

  The zoom lens 200 according to Example 2 satisfies the conditional expressions (1) to (4). That is, | f1 / f2 | = 1.4, f2 / FW = 1.65, fA / fB = 0.73, f2 / fC = 0.54, which satisfies the conditional expression.

  FIG. 3 is a configuration diagram illustrating the zoom lens 300 according to the third embodiment. The zoom lens 300 is a zoom lens having the same three-group configuration as in the first and second embodiments, except that the rear lens of the second lens group II is configured by two concave lenses. Yes. That is, the power distribution for each group and the movement method for zooming are the same as in the previous two examples.

  The first lens group I includes a first meniscus lens 21 having a negative power with a convex surface facing the object side and a first meniscus lens having a positive power with a convex surface facing the object side. It consists of two lenses 22. The second lens group II includes a front group lens A and a rear group lens B arranged in order from the object side. The front group lens A is a third meniscus lens having a negative power with a convex surface facing the object side. 23, a fourth lens 24 composed of a biconvex lens having a positive power, and a fifth lens 25 having a positive power with a strong convex surface facing the object side. The rear lens group B has a strong concave surface on the image surface side. The sixth lens 26 of meniscus having negative power directed toward the image and the seventh lens 27 of meniscus having negative weak power with the convex surface directed toward the image surface side. The third lens group III includes an eighth lens 28 having a positive power.

  The second lens 22, the fifth lens 25, the seventh lens 27, and the eighth lens 28 are resin lenses, and both surfaces of the second lens 22, the fifth lens 25, the eighth lens 28, and the image plane of the seventh lens 27. The side lens surface is aspherical. A cover glass 9 is disposed between the eighth lens 28 and the imaging plane 10.

The lens data of the entire optical system of the zoom lens 300 is as follows.
F number: 2.80 3.91 5.31
Focal length: 3.50 6.77 10.51 mm
f1: −8.330 mm fA: 3.563 mm
f2: 5.783 mm fB: −4.585 mm
f3: −11.079 mm fC: −13.260 mm

  Table 3A shows lens data of each lens surface of the zoom lens 300, and Table 3B shows aspheric coefficients for defining the aspheric shape of the aspheric lens surface. FIG. 6 shows various aberrations of the zoom lens 300 according to the third example.

  The zoom lens 300 according to Example 3 satisfies the conditional expressions (1) to (4). That is, | f1 / f2 | = 1.44, f2 / FW = 1.65, fA / fB = 0.78, and f2 / fC = 0.44, which satisfy the conditional expressions.

1 is a configuration diagram of a zoom lens 100 according to Embodiment 1 of the present invention. FIG. It is a block diagram of the zoom lens 200 which concerns on Example 2 of this invention. It is a block diagram of the zoom lens 300 which concerns on Example 3 of this invention. FIG. 2 is an aberration diagram of the zoom lens 100 in FIG. 1. FIG. 3 is an aberration diagram of the zoom lens 200 in FIG. 2. FIG. 4 is an aberration diagram of the zoom lens 300 in FIG. 3.

Explanation of symbols

I First lens group
II Second lens group
III Third lens group A Front group lens B Rear group lenses 1, 11, 21 First lens 2, 12, 22 Second lens 3, 13, 23 Third lens 4, 14, 24 Fourth lens 5, 15, 25 Fifth lens 6, 16, 26 Sixth lens 27 Seventh lens 8, 18, 28 Eighth lens 9 Cover glass 10 Imaging surface 100, 200, 300, Zoom lens

Claims (6)

Each lens group includes a first lens group having a negative power, a second lens group having a positive power, and a third lens group having a positive power, arranged from the object side toward the imaging surface. 3 groups of zoom lenses that perform zooming by changing the air spacing of
The first lens group includes a first meniscus lens having a negative power with a convex surface facing the object side and a second meniscus lens having a positive power with a convex surface facing the object side, which are arranged in order from the object side. Composed by
The second lens group is composed of a front group lens and a rear group lens arranged in order from the object side,
The front lens group includes a third lens having a negative power, a fourth lens having a positive power, and a fifth lens having a positive power, which are arranged in order from the object side and have a convex surface facing the object side. Become
The rear lens group comprises a sixth lens having negative power;
The third lens group Ri Do eighth lens having a positive power,
The focal length of the entire optical system at the wide end is FW, the focal length of the first lens group is f1, the focal length of the second lens group is f2, the focal length of the third lens group is f3, and the second lens group is A zoom lens that satisfies the following conditional expression where fC is a focal length of three lenses, fA is a focal length of a front lens group, and fB is a focal length of a rear lens group.
1.2 <| f1 / f2 | <1.8
1.0 <f2 / FW <2.0
0.5 <| fA / fB | <1.5
| F2 / fC | <1.5 Each lens group includes a first lens group having a negative power, a second lens group having a positive power, and a third lens group having a positive power, arranged from the object side toward the imaging surface. 3 groups of zoom lenses that perform zooming by changing the air spacing of
The first lens group includes a first meniscus lens having a negative power with a convex surface facing the object side and a second meniscus lens having a positive power with a convex surface facing the object side, which are arranged in order from the object side. Composed by
The second lens group is composed of a front group lens and a rear group lens arranged in order from the object side,
The front lens group includes a third lens having a negative power, a fourth lens having a positive power, and a fifth lens having a positive power, which are arranged in order from the object side and have a convex surface facing the object side. Become
The rear lens group comprises a sixth lens having negative power;
The third lens group includes an eighth lens having a positive power,
A zoom lens satisfying the following conditional expression, where FW is the focal length of the entire optical system at the wide end, and f3 is the focal length of the third lens group.
0.1 <FW / f3 <0.5 Each lens includes a first lens group having a negative power, a second lens group having a positive power, and a third lens group having a positive power, which are arranged in order from the object side toward the imaging surface. A zoom lens of three groups that performs zooming by changing the air interval of the group,
The first lens group includes a first meniscus lens having a negative power with a convex surface facing the object side and a second meniscus lens having a positive power with a convex surface facing the object side, which are arranged in order from the object side. Composed by
The second lens group is composed of a front group lens and a rear group lens arranged in order from the object side,
The front lens group includes a third lens having a negative power, a fourth lens having a positive power, and a fifth lens having a positive power, which are arranged in order from the object side and have a convex surface facing the object side. Become
The rear lens group includes a sixth lens having negative power and a seventh lens having negative power.
The third lens group includes an eighth lens having a positive power,
The focal length of the entire optical system at the wide end is FW, the focal length of the first lens group is f1, the focal length of the second lens group is f2, the focal length of the third lens group is f3, and the second lens group is A zoom lens that satisfies the following conditional expression where fC is a focal length of three lenses, fA is a focal length of a front lens group, and fB is a focal length of a rear lens group.
1.2 <| f1 / f2 | <1.8
1.0 <f2 / FW <2.0
0.5 <| fA / fB | <1.5
| F2 / fC | <1.5 Each lens includes a first lens group having a negative power, a second lens group having a positive power, and a third lens group having a positive power, which are arranged in order from the object side toward the imaging surface. A zoom lens of three groups that performs zooming by changing the air interval of the group,
The first lens group includes a first meniscus lens having a negative power with a convex surface facing the object side and a second meniscus lens having a positive power with a convex surface facing the object side, which are arranged in order from the object side. Composed by
The second lens group is composed of a front group lens and a rear group lens arranged in order from the object side,
The front lens group includes a third lens having a negative power, a fourth lens having a positive power, and a fifth lens having a positive power, which are arranged in order from the object side and have a convex surface facing the object side. Become
The rear lens group includes a sixth lens having negative power and a seventh lens having negative power.
The third lens group includes an eighth lens having a positive power,
A zoom lens satisfying the following conditional expression, where FW is the focal length of the entire optical system at the wide end, and f3 is the focal length of the third lens group.
0.1 <FW / f3 <0.5 In claim 1 or 3,
A zoom lens satisfying the following conditional expression, where FW is the focal length of the entire optical system at the wide end, and f3 is the focal length of the third lens group.
0.1 <FW / f3 <0.5 In any of claims 1 to 5,
At least one of the lens surfaces of the first lens group is an aspheric surface,
Of the lens surfaces of the second lens group, at least one surface is an aspheric surface,
A zoom lens according to claim 3, wherein at least one of the lens surfaces of the third lens group is an aspherical surface.

Images