JP2010160275A - Zoom lens system, imaging device and camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens system, an imaging device and a camera, suitable for wide angle photography not only with high resolution but also with a wide field angle at a wide angle end, and having respectively a short total lens length, a very small size and high performance, while keeping a high zooming ratio exceeding three times. <P>SOLUTION: In the zoom lens system including successively from the object side to the image side, at least the first lens group having a negative power, the second lens group having a positive power, an aperture diaphragm, and the third lens group having a negative power, when zooming from the wide angle end to a telescopic end at the imaging time, at least the second lens group and the third lens group among the first lens group, the second lens group and the third lens group are moved along an optical axis, to thereby perform variable magnification, and when performing variable magnification, the aperture diaphragm is moved along the optical axis independently of the second lens group and the third lens group. The imaging device and the camera are also provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a zoom lens system, an imaging apparatus, and a camera. In particular, the present invention has a high resolution, a wide angle of view at the wide-angle end, and is suitable for wide-angle shooting. The present invention relates to a high-performance zoom lens system, an imaging device including the zoom lens system, and a thin and compact camera including the imaging device.

  There is an extremely strong demand for compactness and high performance of a camera having an image sensor that performs photoelectric conversion (hereinafter simply referred to as a digital camera) such as a digital still camera or a digital video camera. In particular, in recent years, there has been a demand for a thin digital camera with the highest priority on storage and portability. As one of means for realizing such a thin digital camera, various zoom lens systems for bending light rays from an object have been proposed.

  In Patent Document 1, in order from an object, a first lens group having a negative refractive power that is fixed during zooming, a second lens group that includes a prism for bending an optical path that is fixed and does not have a refractive power during zooming, and moves during zooming. A third lens group having a positive refractive power; a fourth lens group that moves during zooming and has a negative refractive power; and a fifth lens group that is fixed during zooming and has a positive refractive power; A zoom lens having a diaphragm between the four lens groups is disclosed.

  Patent Document 2 has a positive lens group, a negative lens group, and a diaphragm, a negative lens group is disposed on the object side of the diaphragm, and the negative lens group has a cemented lens in which a plurality of lenses are cemented. Regarding at least one lens constituting the cemented lens, the physical properties of the glass material are specified under two conditions, and an imaging optical system having a prism for bending the optical path of the optical system is disclosed.

Patent Document 3 has a positive lens group, a negative lens group, and a diaphragm, a negative lens group is disposed on the image plane side from the diaphragm, and the negative lens group has a cemented lens in which a plurality of lenses are cemented. Further, the physical properties of the glass material of at least one lens constituting the cemented lens are specified under three conditions, and an imaging optical system having a prism for bending the optical path of the optical system is disclosed.
JP 2008-197594 A JP 2008-191306 A JP 2007-108715 A

  However, although the zoom lenses and optical systems disclosed in Patent Documents 1 to 3 are all downsized to a certain extent, the zooming ratio is about 3 times or less and the angle of view at the wide-angle end is also insufficient. Therefore, it cannot satisfy the recent demand for a digital camera that is not only very thin and compact but also sufficiently applicable to wide-angle shooting while having a high zooming ratio.

  The object of the present invention is not only high in resolution, but also suitable for wide-angle shooting with a wide angle of view at the wide-angle end, while maintaining a high zooming ratio exceeding 3 times and a very small lens length. To provide a high-performance zoom lens system, an imaging device including the zoom lens system, and a thin and compact camera including the imaging device.

One of the above objects is achieved by the following zoom lens system. That is, the present invention
In order from the object side to the image side, at least a first lens group having a negative power, a second lens group having a positive power, an aperture stop, and a third lens group having a negative power,
During zooming from the wide-angle end to the telephoto end during imaging, at least the second lens group and the third lens group of the first lens group, the second lens group, and the third lens group are moved along the optical axis. Let ’s zoom in,
The present invention relates to a zoom lens system in which an aperture stop moves along an optical axis independently of a second lens group and a third lens group when performing the zooming.

One of the above objects is achieved by the following imaging device. That is, the present invention
An imaging apparatus capable of outputting an optical image of an object as an electrical image signal,
A zoom lens system that forms an optical image of the object;
An image sensor that converts an optical image formed by the zoom lens system into an electrical image signal;
The zoom lens system is
In order from the object side to the image side, at least a first lens group having a negative power, a second lens group having a positive power, an aperture stop, and a third lens group having a negative power,
During zooming from the wide-angle end to the telephoto end during imaging, at least the second lens group and the third lens group of the first lens group, the second lens group, and the third lens group are moved along the optical axis. Let ’s zoom in,
The present invention relates to an imaging apparatus that is a zoom lens system in which an aperture stop moves along an optical axis independently of a second lens group and a third lens group when performing the zooming.

One of the above objects is achieved by the following camera. That is, the present invention
A camera that converts an optical image of an object into an electrical image signal, and displays and stores the converted image signal;
An image pickup apparatus including a zoom lens system that forms an optical image of an object, and an image sensor that converts an optical image formed by the zoom lens system into an electrical image signal;
The zoom lens system is
In order from the object side to the image side, at least a first lens group having a negative power, a second lens group having a positive power, an aperture stop, and a third lens group having a negative power,
During zooming from the wide-angle end to the telephoto end during imaging, at least the second lens group and the third lens group of the first lens group, the second lens group, and the third lens group are moved along the optical axis. Let ’s zoom in,
The present invention relates to a camera which is a zoom lens system in which an aperture stop moves along an optical axis independently of a second lens group and a third lens group when performing the zooming.

  According to the present invention, not only the resolution is high, but the angle of view at the wide-angle end is large, which is suitable for wide-angle shooting, while maintaining a high zooming ratio exceeding 3 times, An extremely small and high-performance zoom lens system having a short distance from the most object side surface to the image plane, an imaging device including the zoom lens system, and a thin and compact camera including the imaging device can be provided. .

(Embodiments 1 to 4)
1, 3, 5 and 7 are lens arrangement diagrams of the zoom lens systems according to Embodiments 1 to 4, respectively.

FIGS. 1, 3, 5 and 7 all show a zoom lens system in an infinitely focused state. In each figure, (a) shows the lens configuration at the wide angle end (shortest focal length state: focal length f _W ), and (b) shows the intermediate position (intermediate focal length state: focal length f _M = √ (f _W * f). _T )) shows a lens configuration, and FIG. 8C shows a lens configuration at the telephoto end (longest focal length state: focal length f _T ). Also, in each figure, the broken line arrows provided between FIGS. (A) and (b) are obtained by connecting the positions of the lens groups in the wide-angle end, the intermediate position, and the telephoto end in order from the top. Straight line. Therefore, between the wide-angle end and the intermediate position, and between the intermediate position and the telephoto end are simply connected by a straight line, which is different from the actual movement of each lens group. Furthermore, in each figure, the arrow attached to the lens group represents the focusing from the infinite focus state to the close object focus state. That is, the moving direction during focusing from the infinitely focused state to the close object focused state is shown.

  The zoom lens system according to each embodiment includes, in order from the object side to the image side, a first lens group G1 having a negative power, a second lens group G2 having a positive power, an aperture stop A, and a negative A third lens group G3 having a positive power and a fourth lens group G4 having a positive power. The second lens element L2 (prism) in the first lens group G1 corresponds to a lens element that has a reflecting surface that bends light rays from an object, for example, an axial principal ray from an object, and bends approximately 90 °. The position is omitted. In the zoom lens system according to each embodiment, the lens element having a reflective surface is a prism, but the lens element having the reflective surface may be, for example, a mirror element. In addition, as will be described later, the prisms arranged in the zoom lens system according to each embodiment are both flat on the entrance surface and the exit surface, but at least one of the entrance surface and the exit surface depends on the lens configuration. It may be convex or concave.

  During zooming, the distance between each lens group and the aperture stop, that is, the distance between the first lens group G1 and the second lens group G2, the distance between the second lens group G2 and the aperture stop A, and the aperture stop A and the third lens. The second lens group G2, the third lens group G3, and the fourth lens group G4 are arranged on the optical axis so that the distance between the group G3 and the distance between the third lens group G3 and the fourth lens group G4 change. The aperture stop A moves in the direction along the optical axis independently of each lens group. The zoom lens system according to each embodiment can reduce the size of the entire lens system while maintaining high optical performance by arranging these lens groups in a desired power arrangement.

  In FIGS. 1, 3, 5 and 7, an asterisk * attached to a specific surface indicates that the surface is an aspherical surface. In each figure, a symbol (+) and a symbol (−) attached to a symbol of each lens group correspond to a power symbol of each lens group. In each figure, the straight line described on the rightmost side represents the position of the image plane S, and is located on the object side of the image plane S (between the image plane S and the most image side lens surface of the fourth lens group G4). Are provided with a parallel plate P equivalent to an optical low-pass filter, a face plate of an image sensor, or the like.

  As shown in FIG. 1, in the zoom lens system according to Embodiment 1, the first lens group G1 includes, in order from the object side to the image side, a biconcave first lens element L1, an entrance surface, and an exit surface. Both of the second lens element L2 (prism) having a reflecting surface and a flat surface, a biconvex third lens element L3, and a biconcave fourth lens element L4. Among these, the third lens element L3 and the fourth lens element L4 are cemented. Further, both the first lens element L1 and the fourth lens element L4 have an aspheric image side surface.

  In the zoom lens system according to Embodiment 1, the second lens unit G2 includes, in order from the object side to the image side, a biconvex fifth lens element L5 and a negative meniscus first lens with a convex surface facing the image side. The fifth lens element L5 and the sixth lens element L6 are cemented with each other. The fifth lens element L5 has an aspheric object side surface.

  In the zoom lens system according to Embodiment 1, the third lens unit G3 includes, in order from the object side to the image side, a positive meniscus seventh lens element L7 with a convex surface facing the image side, and a biconcave shape. The seventh lens element L7 is joined to the eighth lens element L8. The eighth lens element L8 has an aspheric image side surface.

  In the zoom lens system according to Embodiment 1, the fourth lens unit G4 includes, in order from the object side to the image side, a biconvex ninth lens element L9 and a negative meniscus shape having a convex surface directed toward the image side. The ninth lens element L10 and the tenth lens element L10 are cemented with each other. The ninth lens element L9 has an aspheric object side surface.

  In the zoom lens system according to Embodiment 1, a parallel plate P is provided on the object side of the image plane S (between the image plane S and the tenth lens element L10).

  In the zoom lens system according to Embodiment 1, during zooming from the wide-angle end to the telephoto end during imaging, the second lens group G2 is positioned closer to the object side at the telephoto end than at the wide-angle end. The third lens group G3 moves in a convex locus on the object side, and the fourth lens group G4 is positioned so that the position at the telephoto end is closer to the image side than the position at the wide-angle end. The first lens group G1 moves and is fixed with respect to the image plane. An aperture stop A disposed between the second lens group G2 and the third lens group G3 is used for the second lens group G2 and the third lens during zooming from the wide-angle end to the telephoto end during imaging. Independently of any of the groups G3, the lens moves so that the position at the telephoto end is closer to the object side than the position at the wide-angle end. That is, during zooming, the distance between the first lens group G1 and the second lens group G2 decreases, the distance between the second lens group G2 and the aperture stop A, the distance between the aperture stop A and the third lens group G3, The second lens group G2, the aperture stop A, the third lens group G3, and the fourth lens group G4 are each along the optical axis so that the distance between the third lens group G3 and the fourth lens group G4 changes. Moving.

  As shown in FIG. 3, in the zoom lens system according to Embodiment 2, the first lens group G1 is a negative meniscus first lens element L1 having a convex surface directed toward the object side in order from the object side to the image side. A second lens element L2 (prism) that is flat on both the incident surface and the output surface and has a reflecting surface, a positive meniscus third lens element L3 having a convex surface facing the object side, and a convex surface facing the object side. It comprises a negative meniscus fourth lens element L4. Among these, the third lens element L3 and the fourth lens element L4 are cemented. Further, both the first lens element L1 and the fourth lens element L4 have an aspheric image side surface.

  In the zoom lens system according to Embodiment 2, the second lens group G2 includes, in order from the object side to the image side, a biconvex fifth lens element L5 and a negative meniscus first lens with a convex surface facing the image side. The fifth lens element L5 and the sixth lens element L6 are cemented with each other. The fifth lens element L5 has an aspheric object side surface.

  In the zoom lens system according to Embodiment 2, the third lens unit G3 includes, in order from the object side to the image side, a positive meniscus seventh lens element L7 having a convex surface directed toward the image side, and a biconcave shape. The seventh lens element L7 is joined to the eighth lens element L8. The eighth lens element L8 has an aspheric image side surface.

  In the zoom lens system according to Embodiment 2, the fourth lens unit G4 includes, in order from the object side to the image side, a biconvex ninth lens element L9 and a negative meniscus shape having a convex surface directed toward the image side. The ninth lens element L9 and the tenth lens element L10 are cemented with each other. The ninth lens element L9 has an aspheric object side surface.

  In the zoom lens system according to Embodiment 2, a parallel plate P is provided on the object side of the image plane S (between the image plane S and the tenth lens element L10).

  In the zoom lens system according to Embodiment 2, when zooming from the wide-angle end to the telephoto end during imaging, the second lens group G2 is positioned closer to the object side than the position at the wide-angle end at the telephoto end. The third lens group G3 moves in a convex locus on the object side, and the fourth lens group G4 is positioned so that the position at the telephoto end is closer to the image side than the position at the wide-angle end. The first lens group G1 moves and is fixed with respect to the image plane. An aperture stop A disposed between the second lens group G2 and the third lens group G3 is used for the second lens group G2 and the third lens during zooming from the wide-angle end to the telephoto end during imaging. Independently of any of the groups G3, the lens moves so that the position at the telephoto end is closer to the object side than the position at the wide-angle end. That is, during zooming, the distance between the first lens group G1 and the second lens group G2 decreases, the distance between the second lens group G2 and the aperture stop A, the distance between the aperture stop A and the third lens group G3, The second lens group G2, the aperture stop A, the third lens group G3, and the fourth lens group G4 are each along the optical axis so that the distance between the third lens group G3 and the fourth lens group G4 changes. Moving.

  As shown in FIG. 5, in the zoom lens system according to Embodiment 3, the first lens group G1 includes, in order from the object side to the image side, a biconcave first lens element L1, an entrance surface, and an exit surface. Both of the second lens element L2 (prism) having a reflecting surface and a flat surface, a biconvex third lens element L3, and a biconcave fourth lens element L4. Among these, the third lens element L3 and the fourth lens element L4 are cemented. The first lens element L1 has an aspheric image side surface, and the third lens element L3 has an aspheric object side surface.

  In the zoom lens system according to Embodiment 3, the second lens unit G2 includes, in order from the object side to the image side, a biconvex fifth lens element L5 and a negative meniscus first lens with a convex surface facing the image side. The fifth lens element L5 and the sixth lens element L6 are cemented with each other. The fifth lens element L5 has an aspheric object side surface.

  In the zoom lens system according to Embodiment 3, the third lens unit G3 includes, in order from the object side to the image side, a positive meniscus seventh lens element L7 with a convex surface facing the image side, and a biconcave shape. The seventh lens element L7 is joined to the eighth lens element L8. The eighth lens element L8 has an aspheric image side surface.

  In the zoom lens system according to Embodiment 3, the fourth lens unit G4 includes, in order from the object side to the image side, a biconvex ninth lens element L9 and a negative meniscus shape having a convex surface directed toward the image side. The ninth lens element L10 and the tenth lens element L10 are cemented with each other. The ninth lens element L9 has an aspheric object side surface.

  In the zoom lens system according to Embodiment 3, a parallel plate P is provided on the object side of the image plane S (between the image plane S and the tenth lens element L10).

  In the zoom lens system according to Embodiment 3, during zooming from the wide-angle end to the telephoto end during imaging, the second lens group G2 is positioned more on the object side at the telephoto end than at the wide-angle end. The third lens group G3 moves in a convex locus on the object side, and the fourth lens group G4 is positioned so that the position at the telephoto end is closer to the image side than the position at the wide-angle end. The first lens group G1 moves and is fixed with respect to the image plane. An aperture stop A disposed between the second lens group G2 and the third lens group G3 is used for the second lens group G2 and the third lens during zooming from the wide-angle end to the telephoto end during imaging. Independently of any of the groups G3, the lens moves so that the position at the telephoto end is closer to the object side than the position at the wide-angle end. That is, during zooming, the distance between the first lens group G1 and the second lens group G2 decreases, the distance between the second lens group G2 and the aperture stop A, the distance between the aperture stop A and the third lens group G3, The second lens group G2, the aperture stop A, the third lens group G3, and the fourth lens group G4 are each along the optical axis so that the distance between the third lens group G3 and the fourth lens group G4 changes. Moving.

  As shown in FIG. 7, in the zoom lens system according to Embodiment 4, the first lens unit G1 includes, in order from the object side to the image side, a negative meniscus first lens element L1 having a convex surface directed toward the object side. And a second lens element L2 (prism) having both a reflecting surface and a reflecting surface, a biconvex third lens element L3, and a biconcave fourth lens element L4. Among these, the third lens element L3 and the fourth lens element L4 are cemented. Further, both the first lens element L1 and the third lens element L3 have an aspheric object side surface.

  In the zoom lens system according to Embodiment 4, the second lens unit G2 includes, in order from the object side to the image side, a biconvex fifth lens element L5 and a negative meniscus first lens with a convex surface facing the image side. The fifth lens element L5 and the sixth lens element L6 are cemented with each other. The fifth lens element L5 has an aspheric object side surface.

  In the zoom lens system according to Embodiment 4, the third lens unit G3 includes, in order from the object side to the image side, a positive meniscus seventh lens element L7 having a convex surface directed toward the image side, and a biconcave shape. The seventh lens element L7 is joined to the eighth lens element L8. The eighth lens element L8 has an aspheric image side surface.

  In the zoom lens system according to Embodiment 4, the fourth lens unit G4 includes, in order from the object side to the image side, a biconvex ninth lens element L9 and a negative meniscus shape having a convex surface directed toward the image side. The ninth lens element L9 and the tenth lens element L10 are cemented with each other. The ninth lens element L9 has an aspheric object side surface.

  In the zoom lens system according to Embodiment 4, a parallel plate P is provided on the object side of the image plane S (between the image plane S and the tenth lens element L10).

  In the zoom lens system according to Embodiment 4, during zooming from the wide-angle end to the telephoto end during imaging, the second lens group G2 is positioned on the object side at the telephoto end relative to the position at the wide-angle end. The third lens group G3 moves in a convex locus on the object side, and the fourth lens group G4 is positioned so that the position at the telephoto end is closer to the image side than the position at the wide-angle end. The first lens group G1 moves and is fixed with respect to the image plane. An aperture stop A disposed between the second lens group G2 and the third lens group G3 is used for the second lens group G2 and the third lens during zooming from the wide-angle end to the telephoto end during imaging. Independently of any of the groups G3, the lens moves so that the position at the telephoto end is closer to the object side than the position at the wide-angle end. That is, during zooming, the distance between the first lens group G1 and the second lens group G2 decreases, the distance between the second lens group G2 and the aperture stop A, the distance between the aperture stop A and the third lens group G3, The second lens group G2, the aperture stop A, the third lens group G3, and the fourth lens group G4 are each along the optical axis so that the distance between the third lens group G3 and the fourth lens group G4 changes. Moving.

  In the zoom lens systems according to Embodiments 1 to 4, in order from the object side to the image side, at least a first lens group G1 having negative power, a second lens group G2 having positive power, and an aperture stop A and a third lens group G3 having negative power are arranged, and at the time of zooming from the wide-angle end to the telephoto end during imaging, at least the second lens group G2 and the third lens group G3 are along the optical axis. Since the aperture stop A moves along the optical axis independently of the second lens group G2 and the third lens group G3 when zooming is performed by moving the zoom lens at the wide-angle end, Although the angle of view is large and the zooming ratio is high, a very compact configuration with a short overall lens length can be achieved.

  In the zoom lens systems according to Embodiments 1 to 4, the first lens group G1 has a reflecting surface that can bend light rays from an object, for example, can bend an axial principal ray from an object by approximately 90 °. Since the second lens element L2 (prism) is included, the zoom lens system can be made thin in the optical axis direction of the axial ray from the object in the imaging state.

  In the zoom lens systems according to Embodiments 1 to 4, the second lens group G2 includes only a cemented lens element composed of a lens element having a negative power and a lens element having a positive power. For example, the lens barrel can be easily incorporated into the lens holding frame, and the lens system including the peripheral lens holding frame member can be further reduced in size. .

  The zoom lens systems according to Embodiments 1 to 4 have the four-group configuration of the first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4. The number of lens groups is not particularly limited as long as the lens system includes at least a first lens group having negative power, a second lens group having positive power, and a third lens group having negative power. It may be a three-group configuration, a four-group configuration, or any other configuration. Further, when there is a lens group located on the image side with respect to the third lens group, there is no particular limitation on its power.

  The following description is given for conditions preferred to be satisfied by a zoom lens system like the zoom lens systems according to Embodiments 1 to 4. A plurality of preferable conditions are defined for the zoom lens system according to each embodiment, but a zoom lens system configuration that satisfies all of the plurality of conditions is most desirable. However, by satisfying individual conditions, it is possible to obtain a zoom lens system that exhibits the corresponding effects.

For example, as in the zoom lens systems according to Embodiments 1 to 4, in order from the object side to the image side, at least a first lens group having negative power, a second lens group having positive power, and an aperture A diaphragm and a third lens group having negative power, and at the time of zooming from the wide-angle end to the telephoto end during imaging, at least the first lens group, the second lens group, and the third lens group The second lens group and the third lens group are moved along the optical axis for zooming. When zooming is performed, the aperture stop is positioned on the optical axis independently of the second lens group and the third lens group. It is preferable that the zoom lens system that moves along (hereinafter, this lens configuration is referred to as a basic configuration of the embodiment) satisfies the following condition (1).
_{1.5 <(L AT -L AW)} / f W <4.0 ··· (1)
(However, f _T / f _W ≧ 3.2)
here,
L _AT : Distance from the aperture stop to the image plane at the telephoto end,
L _AW : Distance from the aperture stop to the image plane at the wide-angle end,
f _T : focal length of the entire system at the telephoto end,
f _W : the focal length of the entire system at the wide angle end.

  The condition (1) is a condition related to the position of the aperture stop. If the lower limit of the condition (1) is not reached, the aperture stop approaches the image plane at the telephoto end, and the distortion may be deteriorated. On the contrary, when the value exceeds the upper limit of the condition (1), the image surface property at the telephoto end may be deteriorated.

In addition, the above effect can be further achieved by satisfying at least one of the following conditions (1) ′ and (1) ″.
_{2.0 <(L AT -L AW)} / f W ··· (1) '
_{(L AT -L AW) / f} W <3.4 ··· (1) ''
(However, f _T / f _W ≧ 3.2)

The conditions (1), (1) ′, and (1) ″ are more preferably satisfied under the following conditions.
f _T / f _W ≧ 4.0

For example, a zoom lens system having a basic configuration like the zoom lens systems according to Embodiments 1 to 4 preferably satisfies the following condition (2).
2.5 <β _2T / β _2W <4.6 (2)
(However, f _T / f _W ≧ 3.2)
here,
β _2T : Lateral magnification of the second lens group at the telephoto end and at infinity in-focus state,
β _2W : lateral magnification of the second lens group at the wide-angle end and at infinity in-focus state,
f _T : focal length of the entire system at the telephoto end,
f _W : the focal length of the entire system at the wide angle end.

  The condition (2) is a condition relating to the lateral magnification of the second lens group. If the lower limit of condition (2) is not reached, the change in magnification of the second lens group is small, and the zooming ratio of the entire zoom lens system may be small. On the other hand, if the upper limit of condition (2) is exceeded, the power of the second lens group becomes too large, and it may be difficult to sufficiently suppress the occurrence of spherical aberration at the telephoto end.

In addition, the above effect can be further achieved by further satisfying at least one of the following conditions (2) ′ and (2) ″.
2.9 <β _2T / β _2W (2) ′
β _2T / β _2W <4.2 (2) ''
(However, f _T / f _W ≧ 3.2)

The conditions (2), (2) ′ and (2) ″ are more preferably satisfied under the following conditions.
f _T / f _W ≧ 4.0

For example, the zoom lens system having the basic configuration like the zoom lens systems according to Embodiments 1 to 4 preferably satisfies the following condition (3).
0.23 <T _G2 / L _W <0.37 (3)
(However, f _T / f _W ≧ 3.2)
here,
T _G2 : the amount of movement of the second lens group on the optical axis during zooming from the wide-angle end to the telephoto end during imaging,
L _W : total lens length at the wide-angle end (distance from the most object side surface of the first lens group to the image plane),
f _T : focal length of the entire system at the telephoto end,
f _W : the focal length of the entire system at the wide angle end.

  The condition (3) is a condition relating to the amount of movement of the second lens group on the optical axis. If the lower limit of the condition (3) is not reached, the power of the second lens group becomes too large, and spherical aberration may occur and the performance at the telephoto end may deteriorate. On the other hand, if the upper limit of condition (3) is exceeded, the amount of movement of the lens group located closer to the image side than the second lens group will be small, and it may be difficult to ensure a sufficient focus range.

The above effect can be further achieved by further satisfying at least one of the following conditions (3) ′ and (3) ″.
0.26 <T _G2 / L _W (3) '
T _G2 / L _W <0.33 (3) ''
(However, f _T / f _W ≧ 3.2)

The conditions (3), (3) ′ and (3) ″ are more preferably satisfied under the following conditions.
f _T / f _W ≧ 4.0

  Each lens group constituting the zoom lens system according to Embodiments 1 to 4 includes a refractive lens element that deflects incident light by refraction (that is, a type in which deflection is performed at an interface between media having different refractive indexes). However, the present invention is not limited to this. For example, a diffractive lens element that deflects incident light by diffraction, a refractive / diffractive hybrid lens element that deflects incident light by a combination of diffractive action and refractive action, and a refractive index that deflects incident light according to the refractive index distribution in the medium Each lens group may be composed of a distributed lens element or the like. In particular, in a refractive / diffractive hybrid lens element, it is preferable to form a diffractive structure at the interface of media having different refractive indexes, since the wavelength dependency of diffraction efficiency is improved.

  Furthermore, in each embodiment, an optical low-pass filter, a face plate of an image sensor, or the like is equivalent to the object side of the image plane S (between the image plane S and the most image side lens surface of the fourth lens group G4). Although the configuration in which the parallel plate P is arranged is shown, as this low-pass filter, a birefringent low-pass filter made of quartz or the like whose predetermined crystal axis direction is adjusted, or a required optical cutoff frequency. A phase type low-pass filter or the like that achieves the characteristics by the diffraction effect can be applied.

(Embodiment 5)
FIG. 9 is a schematic configuration diagram of a digital still camera according to the fifth embodiment. In FIG. 9, the digital still camera includes an image pickup apparatus including a zoom lens system 1 and an image pickup device 2 that is a CCD, a liquid crystal monitor 3, and a housing 4. As the zoom lens system 1, the zoom lens system according to Embodiment 1 is used. In FIG. 9, the zoom lens system 1 includes a first lens group G1, a second lens group G2, an aperture stop A, a third lens group G3, and a fourth lens group G4. In the housing 4, the zoom lens system 1 is disposed on the front side, and the imaging element 2 is disposed on the rear side of the zoom lens system 1. A liquid crystal monitor 3 is disposed on the rear side of the housing 4, and an optical image of the subject by the zoom lens system 1 is formed on the image plane S.

  Thus, by using the zoom lens system according to Embodiment 1 for a digital still camera, it is possible to provide a small digital still camera that has a high ability to correct resolution and curvature of field and has a short overall lens length when not in use. it can. Note that the digital still camera shown in FIG. 9 may use any of the zoom lens systems according to Embodiments 2 to 4 instead of the zoom lens system according to Embodiment 1. Further, the optical system of the digital still camera shown in FIG. 9 can be used for a digital video camera for moving images. In this case, not only a still image but also a moving image with high resolution can be taken.

  In the digital still camera according to the fifth embodiment, the zoom lens system according to the first to fourth embodiments is shown as the zoom lens system 1, but these zoom lens systems need to use all zooming areas. There is no. That is, a range in which the optical performance is ensured may be cut out according to a desired zooming area, and used as a zoom lens system having a lower magnification than the zoom lens system described in the first to fourth embodiments.

  In addition, an imaging apparatus including the zoom lens system according to Embodiments 1 to 4 described above and an imaging element such as a CCD or a CMOS is used as a monitoring camera in a mobile phone device, a PDA (Personal Digital Assistance), or a monitoring system. It can also be applied to Web cameras, in-vehicle cameras, and the like.

ここで、κは円錐定数、Ａ４、Ａ６、Ａ８及びＡ１０は、それぞれ４次、６次、８次及び１０次の非球面係数である。 Hereinafter, numerical examples in which the zoom lens systems according to Embodiments 1 to 4 are specifically implemented will be described. In each numerical example, the unit of length in the table is “mm”, and the unit of angle of view is “°”. In each numerical example, r is a radius of curvature, d is a surface interval, nd is a refractive index with respect to the d line, and vd is an Abbe number with respect to the d line. In each numerical example, the surface marked with * is an aspherical surface, and the aspherical shape is defined by the following equation.

Here, κ is a conic constant, and A4, A6, A8, and A10 are fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients, respectively.

  2, 4, 6 and 8 are longitudinal aberration diagrams of the zoom lens systems according to Embodiments 1 to 4, respectively.

  In each longitudinal aberration diagram, (a) shows the aberration at the wide angle end, (b) shows the intermediate position, and (c) shows the aberration at the telephoto end. Each longitudinal aberration diagram shows spherical aberration (SA (mm)), astigmatism (AST (mm)), and distortion (DIS (%)) in order from the left side. In the spherical aberration diagram, the vertical axis represents the F number (indicated by F in the figure), the solid line is the d line (d-line), the short broken line is the F line (F-line), and the long broken line is the C line (C- line). In the astigmatism diagram, the vertical axis represents the image height (indicated by H in the figure), the solid line represents the sagittal plane (indicated by s), and the broken line represents the meridional plane (indicated by m in the figure). is there. In the distortion diagram, the vertical axis represents the image height (indicated by H in the figure).

(Numerical example 1)
The zoom lens system of Numerical Example 1 corresponds to Embodiment 1 shown in FIG. Table 1 shows surface data of the zoom lens system of Numerical Example 1, Table 2 shows aspheric data, and Table 3 shows various data.

Table 1 (surface data)

Surface number rd nd vd
Object ∞
1 -250.13498 0.50000 1.77788 45.7
2 * 7.57756 2.59400
3 ∞ 8.78000 1.84666 23.8
4 ∞ 0.30000
5 9.25321 2.19000 1.85468 23.5
6 -113.04902 0.40000 1.70476 29.0
7 * 7.29683 Variable
8 * 12.15635 5.78400 1.70710 54.9
9 -6.39724 1.00000 1.84564 24.1
10 -14.18617 Variable
11 (Aperture) ∞ Variable
12 -21.20432 1.34500 1.84666 23.8
13 -5.57181 5.38700 1.71278 34.3
14 * 13.82072 Variable
15 * 15.77991 4.18900 1.48890 70.2
16 -7.01341 0.40000 1.75520 27.6
17 -9.81575 Variable
18 ∞ 0.78000 1.51633 64.1
19 ∞ (BF)
Image plane ∞

Table 2 (Aspheric data)

Second side
K = 0.00000E + 00, A4 = -1.70407E-04, A6 = 1.40966E-06, A8 = -1.24793E-07
A10 = 0.00000E + 00
7th page
K = 0.00000E + 00, A4 = -7.29024E-05, A6 = -3.44168E-06, A8 = 1.23828E-07
A10 = 0.00000E + 00
8th page
K = 0.00000E + 00, A4 = -1.16507E-04, A6 = -1.11724E-06, A8 = 1.43004E-08
A10 = 2.65611E-09
14th page
K = 0.00000E + 00, A4 = 4.83763E-04, A6 = -8.94594E-07, A8 = 1.16986E-06
A10 = -5.97662E-08
15th page
K = 0.00000E + 00, A4 = -6.36530E-05, A6 = 3.53841E-06, A8 = -1.34086E-07
A10 = 1.92460E-09

Table 3 (various data)

Zoom ratio 4.70027
Wide angle Medium telephoto Focal length 5.0601 14.2696 23.7836
F number 3.45000 4.20000 6.10000
Angle of View 41.5019 15.4685 9.1053
Image height 3.8300 3.8300 3.8300
Total lens length 62.3774 62.3389 62.3639
BF 0.87599 0.83759 0.86237
d7 18.0934 2.3517 0.9824
d10 1.0000 1.0607 5.8276
d11 1.1859 7.5533 8.3450
d14 1.0131 7.8942 11.1975
d17 6.5600 8.9924 1.5000

Zoom lens group data Group Start surface Focal length
1 1 -9.73266
2 8 11.45158
3 12 -14.13599
4 15 15.01092

(Numerical example 2)
The zoom lens system of Numerical Example 2 corresponds to Embodiment 2 shown in FIG. Table 4 shows surface data of the zoom lens system of Numerical Example 2, Table 5 shows aspheric data, and Table 6 shows various data.

Table 4 (surface data)

Surface number rd nd vd
Object ∞
1 1200.00000 0.50000 1.72343 42.7
2 * 7.77026 2.51400
3 ∞ 8.30 200 1.83522 24.7
4 ∞ 0.30000
5 8.55428 1.53200 1.87879 25.5
6 37.41771 0.40000 1.73284 37.7
7 * 7.06197 Variable
8 * 12.25017 8.09100 1.70398 55.0
9 -5.95538 1.00000 1.83903 26.0
10 -15.07924 Variable
11 (Aperture) ∞ Variable
12 -38.37396 2.41500 1.82357 24.4
13 -5.46267 0.40000 1.70143 32.9
14 * 17.58057 variable
15 * 39.05647 2.48600 1.57109 63.1
16 -7.01341 1.23100 1.72452 28.9
17 -12.13158 Variable
18 ∞ 0.78000 1.51633 64.1
19 ∞ (BF)
Image plane ∞

Table 5 (Aspheric data)

Second side
K = 0.00000E + 00, A4 = -1.46343E-04, A6 = 1.19212E-06, A8 = -9.85093E-08
A10 = 0.00000E + 00
7th page
K = 0.00000E + 00, A4 = -6.82772E-05, A6 = -2.06898E-06, A8 = 6.55329E-08
A10 = 0.00000E + 00
8th page
K = 0.00000E + 00, A4 = -7.10639E-05, A6 = -2.42961E-08, A8 = 5.84728E-09
A10 = 2.49106E-09
14th page
K = 0.00000E + 00, A4 = 4.56907E-04, A6 = -1.94139E-05, A8 = 5.26366E-06
A10 = -3.80048E-07
15th page
K = 0.00000E + 00, A4 = -1.43386E-05, A6 = 1.55630E-06, A8 = 4.49001E-08
A10 = -2.13104E-09

Table 6 (various data)

Zoom ratio 3.42898
Wide angle Medium telephoto Focal length 5.8998 12.1382 20.2303
F number 3.45000 4.20000 6.10000
Angle of view 35.8270 17.7827 10.5321
Image height 3.8300 3.8300 3.8300
Total lens length 59.5224 59.4886 59.5175
BF 0.87847 0.84472 0.87360
d7 15.6345 5.0901 0.8845
d10 1.0000 4.2691 4.6300
d11 1.3317 2.2065 11.9357
d14 2.9726 9.0130 7.3978
d17 7.7541 8.1142 3.8449

Zoom lens group data Group Start surface Focal length
1 1 -10.87028
2 8 12.46938
3 12 -25.32546
4 15 19.27566

(Numerical Example 3)
The zoom lens system of Numerical Example 3 corresponds to Embodiment 3 shown in FIG. Table 7 shows surface data of the zoom lens system of Numerical Example 3, Table 8 shows aspheric data, and Table 9 shows various data.

Table 7 (surface data)

Surface number rd nd vd
Object ∞
1 -514.73620 0.50000 1.80420 46.5
2 * 8.48905 2.52500
3 ∞ 8.97500 1.84665 23.8
4 ∞ 0.30000
5 * 10.65048 1.74000 1.90813 21.2
6 -89.72368 0.40000 1.82192 27.0
7 8.68706 Variable
8 * 12.69300 6.89200 1.70617 54.9
9 -6.65750 1.00000 1.84666 23.8
10 -13.94982 Variable
11 (Aperture) ∞ Variable
12 -44.62836 2.21200 1.84666 23.8
13 -5.11647 1.20200 1.73009 33.3
14 * 9.84672 Variable
15 * 16.47205 5.71400 1.48700 70.4
16 -7.01341 0.40100 1.75520 27.6
17 -10.13009 Variable
18 ∞ 0.78000 1.51633 64.1
19 ∞ (BF)
Image plane ∞

Table 8 (Aspherical data)

Second side
K = 0.00000E + 00, A4 = -1.08830E-04, A6 = 2.77108E-06, A8 = -1.01686E-07
A10 = 0.00000E + 00
5th page
K = 0.00000E + 00, A4 = 5.93065E-05, A6 = 1.40474E-06, A8 = -3.77922E-08
A10 = 0.00000E + 00
8th page
K = 0.00000E + 00, A4 = -1.28181E-04, A6 = -8.20548E-07, A8 = -2.80970E-10
A10 = 1.68599E-09
14th page
K = 0.00000E + 00, A4 = 4.49362E-04, A6 = 1.01928E-05, A8 = 1.77989E-07
A10 = 1.73892E-08
15th page
K = 0.00000E + 00, A4 = -4.53632E-05, A6 = 6.65272E-06, A8 = -2.99741E-07
A10 = 5.81681E-09

Table 9 (various data)

Zoom ratio 4.90001
Wide angle Medium telephoto Focal length 5.0600 14.8761 24.7942
F number 3.45000 4.20000 6.10000
Angle of View 41.4475 14.8061 8.7324
Image height 3.8300 3.8300 3.8300
Total lens length 64.3677 64.3469 64.3625
BF 0.88473 0.86386 0.87945
d7 20.0293 3.0002 0.8698
d10 1.0000 1.0000 3.1306
d11 1.9768 8.8588 14.4177
d14 1.1120 7.9696 9.8611
d17 6.7239 10.0134 2.5628

Zoom lens group data Group Start surface Focal length
1 1 -9.49017
2 8 11.75957
3 12 -14.02980
4 15 16.17519

(Numerical example 4)
The zoom lens system of Numerical Example 4 corresponds to Embodiment 4 shown in FIG. Table 10 shows surface data of the zoom lens system of Numerical Example 4, Table 11 shows aspheric data, and Table 12 shows various data.

Table 10 (surface data)

Surface number rd nd vd
Object ∞
1 * 630.01820 0.50000 1.80420 46.5
2 8.52870 3.11940
3 ∞ 9.38060 1.84666 23.8
4 ∞ 0.30000
5 * 18.10220 2.55350 1.91315 23.6
6 -27.48010 0.40000 1.66937 31.2
7 10.43090 Variable
8 * 11.88240 6.04440 1.61091 60.8
9 -7.85790 0.74350 1.84666 23.8
10 -13.76870 Variable
11 (Aperture) ∞ Variable
12 -104.13360 2.00000 1.76792 26.2
13 -4.00000 3.98370 1.75091 32.3
14 * 12.93720 variable
15 * 34.77360 3.04210 1.48700 70.4
16 -6.00000 1.00000 1.75520 27.6
17 -8.37360 Variable
18 ∞ 0.78000 1.51633 64.1
19 ∞ (BF)
Image plane ∞

Table 11 (Aspheric data)

First side
K = 0.00000E + 00, A4 = 3.40812E-05, A6 = -7.90600E-07, A8 = 2.21406E-08
A10 = -1.49414E-10
5th page
K = 0.00000E + 00, A4 = 8.18443E-05, A6 = 9.78340E-07, A8 = -3.23064E-08
A10 = 3.06117E-10
8th page
K = 0.00000E + 00, A4 = -1.17268E-04, A6 = -1.41778E-06, A8 = 5.40104E-08
A10 = -5.52566E-10
14th page
K = 0.00000E + 00, A4 = 4.42039E-04, A6 = -5.88231E-06, A8 = 2.91170E-06
A10 = -2.18270E-07
15th page
K = 0.00000E + 00, A4 = -6.50354E-05, A6 = 4.00067E-08, A8 = 1.15937E-07
A10 = -3.17546E-09

Table 12 (various data)

Zoom ratio 5.88981
Wide angle Medium telephoto Focal length 5.0598 14.3700 29.8016
F number 3.30012 4.20044 6.10014
Angle of View 40.5362 15.1534 7.2564
Image height 3.8300 3.8300 3.8300
Total lens length 68.9968 68.9994 69.0426
BF 0.86698 0.86945 0.91267
d7 22.1205 4.1827 0.7310
d10 1.0000 9.5000 9.5000
d11 2.6479 1.0253 14.5060
d14 0.7364 8.0595 9.0457
d17 7.7778 11.5152 0.5000

Zoom lens group data Group Start surface Focal length
1 1 -9.83551
2 8 13.13113
3 12 -16.12353
4 15 16.75009

  Table 13 below shows the corresponding values for each condition in the zoom lens system of each numerical example.

Table 13 (corresponding values of conditions)

  The zoom lens system according to the present invention is applicable to digital input devices such as a digital camera, a mobile phone device, a PDA (Personal Digital Assistance), a surveillance camera in a surveillance system, a web camera, an in-vehicle camera, etc. It is suitable for a photographing optical system that requires high image quality.

Lens arrangement diagram showing an infinitely focused state of the zoom lens system according to Embodiment 1 (Example 1) Longitudinal aberration diagram of the zoom lens system according to Example 1 in an infinitely focused state Lens arrangement diagram showing an infinitely focused state of the zoom lens system according to Embodiment 2 (Example 2) Longitudinal aberration diagram of the zoom lens system according to Example 2 in an infinitely focused state Lens arrangement diagram showing an infinitely focused state of the zoom lens system according to Embodiment 3 (Example 3) Longitudinal aberration diagram of the zoom lens system according to Example 3 in an infinitely focused state Lens arrangement diagram showing an infinitely focused state of the zoom lens system according to Embodiment 4 (Example 4) Longitudinal aberration diagram of the zoom lens system according to Example 4 in an infinitely focused state Schematic configuration diagram of a digital still camera according to Embodiment 5

G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group L1 First lens element L2 Second lens element (prism)
L3 3rd lens element L4 4th lens element L5 5th lens element L6 6th lens element L7 7th lens element L8 8th lens element L9 9th lens element L10 10th lens element A Aperture stop P Parallel plate S Image plane 1 Zoom lens system 2 Image sensor 3 LCD monitor 4 Case

Claims (8)

In order from the object side to the image side, at least a first lens group having a negative power, a second lens group having a positive power, an aperture stop, and a third lens group having a negative power,
During zooming from the wide-angle end to the telephoto end during imaging, at least the second lens group and the third lens group of the first lens group, the second lens group, and the third lens group are moved along the optical axis. Let ’s zoom in,
A zoom lens system in which an aperture stop moves along the optical axis independently of the second lens group and the third lens group when performing the zooming. The zoom lens system according to claim 1, wherein the zoom lens system satisfies the following condition (1):
_{1.5 <(L AT -L AW)} / f W <4.0 ··· (1)
(However, f _T / f _W ≧ 3.2)
here,
L _AT : Distance from the aperture stop to the image plane at the telephoto end,
L _AW : Distance from the aperture stop to the image plane at the wide-angle end,
f _T : focal length of the entire system at the telephoto end,
f _W : the focal length of the entire system at the wide angle end. The zoom lens system according to claim 1, satisfying the following condition (2):
2.5 <β _2T / β _2W <4.6 (2)
(However, f _T / f _W ≧ 3.2)
here,
β _2T : Lateral magnification of the second lens group at the telephoto end and at infinity in-focus state,
β _2W : lateral magnification of the second lens group at the wide-angle end and at infinity in-focus state,
f _T : focal length of the entire system at the telephoto end,
f _W : the focal length of the entire system at the wide angle end. The zoom lens system according to claim 1, wherein the zoom lens system satisfies the following condition (3):
0.23 <T _G2 / L _W <0.37 (3)
(However, f _T / f _W ≧ 3.2)
here,
T _G2 : the amount of movement of the second lens group on the optical axis during zooming from the wide-angle end to the telephoto end during imaging,
L _W : total lens length at the wide-angle end (distance from the most object side surface of the first lens group to the image plane),
f _T : focal length of the entire system at the telephoto end,
f _W : the focal length of the entire system at the wide angle end.   The zoom lens system according to claim 1, wherein the first lens group includes a lens element having a reflecting surface that bends a light beam from an object.   2. The zoom lens system according to claim 1, wherein the second lens group includes only a cemented lens element of a lens element having a negative power and a lens element having a positive power. An imaging apparatus capable of outputting an optical image of an object as an electrical image signal,
A zoom lens system that forms an optical image of the object;
An image sensor that converts an optical image formed by the zoom lens system into an electrical image signal;
The zoom lens system is
In order from the object side to the image side, at least a first lens group having a negative power, a second lens group having a positive power, an aperture stop, and a third lens group having a negative power,
During zooming from the wide-angle end to the telephoto end during imaging, at least the second lens group and the third lens group of the first lens group, the second lens group, and the third lens group are moved along the optical axis. Let ’s zoom in,
An image pickup apparatus, which is a zoom lens system in which an aperture stop moves along the optical axis independently of the second lens group and the third lens group when performing the zooming. A camera that converts an optical image of an object into an electrical image signal, and displays and stores the converted image signal;
An image pickup apparatus including a zoom lens system that forms an optical image of an object, and an image sensor that converts an optical image formed by the zoom lens system into an electrical image signal;
The zoom lens system is
In order from the object side to the image side, at least a first lens group having a negative power, a second lens group having a positive power, an aperture stop, and a third lens group having a negative power,
During zooming from the wide-angle end to the telephoto end during imaging, at least the second lens group and the third lens group of the first lens group, the second lens group, and the third lens group are moved along the optical axis. Let ’s zoom in,
A camera which is a zoom lens system in which an aperture stop moves along an optical axis independently of the second lens group and the third lens group when performing the zooming.

Images