JP2007219040A - Variable power optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable power optical system which has a high variable power ratio in spite of being high in performance and compact and further has a blurring correction function, and an imaging apparatus equipped therewith. <P>SOLUTION: The variable power optical system having the blurring correction function and forming the optical image of an object on an imaging device so as to vary power includes a first lens group Gr1 having positive power, a second lens group Gr2 having negative power, a third lens group Gr3 having positive power, and at least one following lens group having positive power or negative power in order from an object side. When varying the power from a wide angle end (W) to a telephoto end (T), the first lens group Gr1 moves to the object side (m1), the second lens group Gr2 is positionally fixed (m2) and the third lens group Gr3 moves to the object side (m3). When dividing the third lens group Gr3 to an object side part and an image side part, the image side part is set as a blurring correction group GrV and made to be eccentric in a perpendicular direction to an optical axis AX, whereby blurring is corrected. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a variable magnification optical system, for example, a variable magnification optical system having a camera shake correction function suitable for a digital camera, a video camera, a digital device with an image input function, etc. It is related with the imaging device provided with.

In recent years, downsizing of digital cameras and camera-equipped mobile phones has been progressing, and an image pickup apparatus mounted thereon is required to have a camera shake correction function as well as downsizing and thinning. In order to meet these demands, various types of zoom lens systems have been proposed. For example, in the zoom lens systems described in Patent Documents 1 and 2, the entire second lens group or the entire third lens group with respect to the optical axis in a positive / negative / positive / negative / positive five-group zoom configuration from the object side. By moving it vertically, it has a function of correcting blurring of the captured image due to camera shake. In the zoom lens system described in Patent Document 3, camera shake correction is performed in a partial group of the third lens group in a positive / negative / positive / positive four-group zoom configuration from the object side. The zoom lens system described in Patent Document 4 achieves compactness with high magnification by arranging a bent portion that bends the optical path in the second lens group in a zoom configuration having positive, negative, and positive zoom groups. is doing.
JP-A-10-111455 JP-A-10-111456 Japanese Patent Laid-Open No. 10-260355 Japanese Patent Laid-Open No. 2004-102809

  In the zoom lens systems proposed in Patent Documents 1 and 2, camera shake correction is performed by moving the second lens group or the third lens group as a camera shake correction group perpendicularly to the optical axis. For this reason, there is a problem that an actuator and a mechanical mechanism necessary for camera shake correction are increased, and as a result, the size of the imaging lens unit is increased. In the zoom lens system described in Patent Document 3, camera shake correction is performed in a partial group of the third lens group. However, since the first lens group is fixed during zooming, the diameter of the first lens group is large. . Therefore, it is not suitable for downsizing the lens unit. Patent Document 4 describes a compact zoom lens system with a high magnification, but does not have a camera shake correction function and does not include any description regarding camera shake correction.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a variable power optical system having a high zoom ratio while having high performance and compactness, and further having a camera shake correction function. It is to provide an imaging apparatus provided.

  In order to achieve the above object, a variable magnification optical system according to a first aspect of the present invention is a variable magnification optical system having a camera shake correction function and capable of forming an optical image of an object on an image sensor so that the magnification can be changed. In order from the side, the first lens group having a positive power, the second lens group having a negative power, the third lens group having a positive power, and at least one subsequent lens group having a positive power or a negative power, and having a wide-angle end In zooming from the telephoto end to the telephoto end, the first lens group moves to the object side, the second lens group is fixed in position, the third lens group moves to the object side, and the third lens group is moved When the object-side portion and the image-side portion are divided, the image-side portion is used as a camera-shake correction group, and camera shake correction is performed by decentering in the direction perpendicular to the optical axis.

The variable magnification optical system according to a second aspect of the present invention is characterized in that, in the first aspect, the camera shake correction group has a positive power and satisfies the following conditional expression (1).
0.9 <fas / f3 <3.5 (1)
However,
fas: focal length of the image stabilization group,
f3: focal length of the third lens group,
It is.

A variable magnification optical system according to a third aspect of the invention is characterized in that, in the first or second aspect of the invention, the following conditional expression (2) is satisfied.
0.3 <f3 / √ (fw × ft) <1.3… (2)
However,
f3: focal length of the third lens group,
fw: focal length of the entire system at the wide-angle end,
ft: focal length of the entire system at the telephoto end,
It is.

  A variable magnification optical system according to a fourth invention is characterized in that, in any one of the first to third inventions, the camera shake correction group includes a single lens.

  A variable magnification optical system according to a fifth aspect of the present invention is the optical system according to any one of the first to fourth aspects, wherein the third lens group and the third lens group are interposed between the second lens group and the third lens group. It has the aperture stop which moves integrally.

  A variable magnification optical system according to a sixth aspect of the present invention is the zoom lens system according to any one of the first to fifth aspects, wherein the third lens group includes a positive meniscus lens that is convex toward the object side in order from the object side, and is positive as a whole. It is composed of a cemented lens of power, a single lens of negative power, and a single lens of positive power, and the single lens of positive power is the camera shake correction group.

  A variable magnification optical system according to a seventh invention is characterized in that, in any one of the first to sixth inventions, focusing is performed by moving the subsequent lens group.

  A variable magnification optical system according to an eighth invention is characterized in that, in any one of the first to seventh inventions, the second lens group has a reflecting surface for bending an optical path.

A variable magnification optical system according to a ninth invention is characterized in that, in any one of the first to eighth inventions, the following conditional expression (3) is satisfied.
0.4 <ΔT (3Gr) / ΔT (1Gr) <1.7 (3)
However,
ΔT (1Gr): Amount of movement of the first lens unit during zooming from the wide-angle end to the telephoto end,
ΔT (3Gr): the amount of movement of the third lens unit during zooming from the wide-angle end to the telephoto end,
It is.

  A variable magnification optical system according to a tenth aspect of the present invention is the optical system according to any one of the first to ninth aspects, wherein the second lens group includes, in order from the object side, a negative power front group and a negative power or a positive power. It consists of two subgroups, the rear group, and one of the subgroups performs a non-monotonous movement in zooming.

  An image pickup apparatus according to an eleventh aspect includes the variable power optical system according to any one of the first to tenth aspects.

  According to the present invention, it is possible to achieve a high zoom ratio with high performance and compactness by the characteristic movement of each lens group, and by using the image side portion of the third lens group as a camera shake correction group, Effective camera shake correction is possible while maintaining good optical performance and compactness. The configuration for correcting camera shake is effective for downsizing the actuators and mechanical mechanisms necessary for camera shake correction. Therefore, in a bending optical system that bends the optical path closer to the object side than the third lens group, even better optical performance can be obtained. Effective camera shake correction can be performed while maintaining performance and compactness. Accordingly, it is possible to realize a variable power optical system having a high zoom ratio and a camera shake correction function while being high performance and compact, and an image pickup apparatus including the same. If the imaging apparatus according to the present invention is used in devices such as a digital camera, it can contribute to thinning, lightening, compactness, cost reduction, high performance, high functionality, etc. of these devices.

  Hereinafter, a variable magnification optical system, an imaging apparatus, and the like embodying the present invention will be described with reference to the drawings. An imaging apparatus according to the present invention is an optical apparatus that optically captures an image of a subject and outputs it as an electrical signal, and constitutes a main component of a camera used for still image shooting and moving image shooting of a subject. is there. Examples of such cameras include digital cameras, video cameras, surveillance cameras, in-vehicle cameras, video phone cameras, door phone cameras, etc., and personal computers, portable information devices (mobile computers, mobile phones, mobile phones). Cameras that are built in or externally attached to information terminals (PDA: Personal Digital Assistant) and other small and portable information device terminals, peripheral devices (mouse, scanner, printer, memory, etc.), and other digital devices Can be mentioned. As can be seen from these examples, it is possible not only to configure a camera by using an imaging apparatus, but also to add a camera function by mounting the imaging apparatus on various devices. For example, a digital device with an image input function such as a mobile phone with a camera can be configured.

  The term “digital camera” used to refer to the one that records optical still images exclusively, but digital still cameras and home digital movie cameras that can handle still images and movies simultaneously have also been proposed. In particular, it has become difficult to distinguish. Therefore, the term “digital camera” means a digital still camera, digital movie camera, or web camera (whether an open type or a private type, a camera that is connected to a network and connected to a device that enables image transmission / reception). , And the like, including those directly connected to a network and those connected via a device having an information processing function such as a personal computer.) It is assumed that all cameras having an imaging device including an imaging device or the like for converting a video signal as an electric video signal as main components are included.

  21 and 22 are schematic cross-sectional views showing a schematic optical configuration example of a camera CU (corresponding to a digital camera, a digital device with an image input function, etc.). The imaging device LU mounted on the camera CU shown in FIG. 21 has a straight type optical configuration without bending of the optical path, and the imaging device LU mounted on the camera CU shown in FIG. 22 is bent with the bending of the optical path. It has a type optical configuration. These imaging devices LU correspond to a zoom lens system ZL (a variable magnification optical system as a photographing lens system) that forms an optical image (IM: image plane) of an object in order from the object (namely, subject) side so that the magnification can be changed. ST: Diaphragm, parallel plane plate PT (optical filter such as an optical low-pass filter and infrared cut filter arranged as necessary; corresponding to the cover glass of the image sensor SR), and zoom lens system An image sensor SR that converts an optical image IM formed on the light receiving surface SS by ZL into an electrical signal is included, and forms a part of a camera CU corresponding to a digital camera or the like. When a digital camera is configured with these imaging devices LU, the imaging device LU is usually arranged inside the body of the camera, but it is possible to adopt a form as necessary when realizing the camera function. It is. For example, the unitized imaging device LU may be configured to be detachable or rotatable with respect to the camera body, and the unitized imaging device LU may be detachable with respect to a portable information device (cell phone, PDA, etc.) or You may comprise so that rotation is possible.

  In the imaging device LU shown in FIG. 22, a planar reflection surface RL is disposed in the middle of the optical path in the zoom lens system ZL, and at least one lens is disposed on each of the front side and the rear side of the reflection surface RL. ing. By this reflection surface RL, the optical path for using the zoom lens system ZL as a bending optical system is bent, and at this time, the optical axis AX is bent approximately 90 degrees (that is, 90 degrees or substantially 90 degrees). Thus, the light beam is reflected. If the reflection surface RL that bends the optical path is provided in the optical path of the zoom lens system ZL in this way, the degree of freedom of arrangement of the imaging device LU is increased, and the size of the imaging device LU in the thickness direction is changed, so that the imaging device It is possible to achieve an apparent thinning of the LU. For example, when the reflecting surface RL is arranged in the second lens group Gr2 as in the second to fourth embodiments (FIGS. 6 to 8) described later, the camera thickness can be effectively shortened. it can. The bending position of the optical path is not limited to the middle of the zoom lens system ZL, and may be further set on the front side or the rear side of the zoom lens system ZL as necessary. Appropriate bending of the optical path makes it possible to effectively reduce the apparent thickness and size of the camera CU on which the imaging device LU is mounted.

  The reflection surface RL is constituted by a reflection member such as a prism (right angle prism or the like), a mirror (plane mirror or the like). In each embodiment described later (FIGS. 2 to 4 and FIGS. 6 to 8), the prism PR, which is a reflecting member, is used as a bending means for bending the optical axis AX. The light beam is reflected by one reflecting surface RL so that the optical axis AX of the zoom lens system ZL is bent by approximately 90 degrees. The bending means may have two or more reflecting surfaces. That is, a reflecting member that reflects a light beam so that the optical axis AX of the zoom lens system ZL is bent by approximately 90 degrees with two or more reflecting surfaces may be used. The optical action for bending the optical path is not limited to reflection, but may be refraction, diffraction, or a combination thereof. That is, you may use the bending means which has a reflective surface, a refractive surface, a diffraction surface, or those combined. Further, the prism PR used in each embodiment described later does not have optical power (power: an amount defined by the reciprocal of the focal length), but is optically used as a bending means for bending the optical path. You may have power. For example, if the optical power of the zoom lens system ZL is partially borne by the reflecting surface RL of the prism PR, the light incident side surface, the light emitting side surface; the mirror reflecting surface RL, etc., the power burden on the lens element is reduced. Optical performance can be improved.

  The zoom lens system ZL includes a plurality of lens groups, and the plurality of lens groups moves along the optical axis AX and performs zooming (ie, zooming) by changing the lens group interval. In the first and second embodiments described later, the zoom lens system ZL has a positive / negative / positive / positive four-group zoom configuration, and in the third embodiment, the zoom lens system ZL has a positive / negative / The zoom lens system ZL has a positive / negative (negative / negative) / positive / positive four-group zoom configuration in the fourth embodiment. Further, the first embodiment to be described later has a straight type optical configuration without bending of the optical path shown in FIG. 21, and the second to fourth embodiments are bent types with bending of the optical path shown in FIG. It has an optical configuration. Note that the photographing lens system used in the imaging device LU is not limited to the zoom lens system. Instead of the zoom lens system, another type of variable magnification optical system (for example, a variable focal length imaging optical system such as a varifocal lens system or a multiple focal length switching type lens) may be used as the photographing lens system.

  An optical image to be formed by the zoom lens system ZL corresponds to an optical low-pass filter having a predetermined cutoff frequency characteristic determined by the pixel pitch of the image sensor SR (parallel plane plate PT in FIGS. 21 and 22). ), The spatial frequency characteristics are adjusted so that the so-called aliasing noise that occurs when converted into an electrical signal is minimized. Thereby, generation | occurrence | production of a color moire can be suppressed. However, if the performance around the resolution limit frequency is suppressed, there is no need to worry about the occurrence of noise without using an optical low-pass filter, and the display system where the noise is not very noticeable (for example, the liquid crystal of a mobile phone) When a user performs shooting or viewing using a screen or the like, it is not necessary to use an optical low-pass filter in the shooting lens system.

  As the optical low-pass filter, a birefringence low-pass filter, a phase low-pass filter, or the like can be applied. Examples of the birefringent low-pass filter include those made of a birefringent material such as quartz whose crystal axis direction is adjusted to a predetermined direction, and those obtained by laminating wave plates that change the polarization plane. Examples of the phase type low-pass filter include those that achieve the required optical cutoff frequency characteristics by the diffraction effect.

  As the imaging element SR, for example, a solid-state imaging element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) sensor having a plurality of pixels is used. The optical image formed by the zoom lens system ZL (on the light receiving surface SS of the image sensor SR) is converted into an electrical signal by the image sensor SR. The signal generated by the image sensor SR is subjected to predetermined digital image processing, image compression processing, etc. as necessary, and recorded as a digital video signal in a memory (semiconductor memory, optical disk, etc.), or in some cases via a cable. Or converted into an infrared signal and transmitted to another device.

  In the image pickup apparatus LU shown in FIGS. 21 and 22, the zoom lens system ZL performs reduction projection from the enlargement subject to the reduction side image pickup element SR, but displays a two-dimensional image instead of the image pickup element SR. If the zoom lens system ZL is used as a projection lens system using a display element (for example, a liquid crystal display element), an image projection apparatus that performs an enlarged projection from the reduced image display surface to the enlarged screen surface is configured. Can do. That is, the zoom lens system ZL of each embodiment described below is not limited to use as a photographing lens system, but can also be suitably used as a projection lens system.

  1 to 4 are lens configuration diagrams respectively corresponding to the zoom lens systems ZL constituting the first to fourth embodiments, and the lens arrangement at the wide angle end (W) is shown in an optical section (second to second). The fourth embodiment is shown as an optical section of the bent optical system in the optical path development state). 5 to 8 are optical path diagrams respectively corresponding to the zoom lens systems ZL constituting the first to fourth embodiments. The optical arrangement at the wide-angle end (W) is shown as an optical section (second to second). The fourth embodiment is shown by an optical section in a bent optical system in an optical path bent state).

  1 to 4, the surface with ri (i = 1, 2, 3,...) Is the i-th surface counted from the object side (the surface with ri marked with * is an aspheric surface). The axial top surface interval with di (i = 1, 2, 3,...) Is a variable interval that changes during zooming among the i-th axial top surface intervals counted from the object side. In each lens configuration diagram, arrows m1, m2, m2a, m2b, m3, m4, and m5 indicate the first lens group Gr1, the second lens group Gr2, and the front in zooming from the wide-angle end (W) to the telephoto end (T). The movement of the group Gr2a, the rear group Gr2b, the third lens group Gr3, the fourth lens group Gr4, and the fifth lens group Gr5 (that is, the change in the relative position with respect to the image plane IM) is schematically shown, and the arrow mP Indicates that the plane-parallel plate PT is fixed in position during zooming. 1 to 3, the arrow m2 is the second lens group Gr2, the arrow m4 in FIG. 3 is the fourth lens group Gr4, and the arrow m2a in FIG. 4 is the front group Gr2a. It is shown that. An arrow mF indicates a focus lens group from infinity shooting to short-distance shooting (fourth lens group Gr4 in the first, second and fourth embodiments, and fifth lens group Gr5 in the third embodiment). The arrow mV schematically shows the movement of the camera shake correction group for performing camera shake correction (that is, eccentricity in the direction perpendicular to the optical axis AX). In any of the embodiments, a stop (that is, an aperture stop) ST is disposed between the second lens group Gr2 and the third lens group Gr3, and the stop ST is integrated with the third lens group Gr3. It is configured to zoom (arrow m3).

  The zoom lens system ZL of the first to fourth embodiments is a variable magnification optical system that has a camera shake correction function and forms an optical image IM of an object on the image sensor SR so that the magnification can be changed. The first lens group Gr1 having positive power (power: an amount defined by the reciprocal of the focal length), the second lens group Gr2 having negative power, and the third lens group Gr3 having positive power in order from And at least one subsequent group having positive or negative power, and has a zoom configuration in which zooming is performed by changing the interval between the lens groups. The zoom lens systems ZL of the second to fourth embodiments have a configuration of a bending optical system having a prism PR that bends the optical axis AX in the second lens group Gr2. The lens configuration of each embodiment will be described in detail below.

  In the first embodiment (FIGS. 1 and 5), a stop ST is disposed between the second lens group Gr2 and the third lens group in a positive / negative / positive / positive straight type four-group zoom configuration. Each lens group is configured as follows. The first lens group Gr1 includes, in order from the object side, a negative meniscus lens that is concave on the image side, a biconvex positive lens, and a positive meniscus lens that is convex on the object side. The second lens group Gr2 includes, in order from the object side, a negative meniscus lens that is concave on the image side whose image side surface is an aspheric surface, and a cemented lens that includes a biconcave negative lens and a biconvex positive lens. Yes. The third lens group Gr3 includes, in order from the object side, a positive meniscus lens convex on the object side whose object side surface is an aspheric surface, a cemented lens including a biconvex positive lens and a negative meniscus lens concave on the object side, and an image. It is composed of a biconcave negative lens whose side surface is an aspheric surface and a positive meniscus lens convex on the object side that constitutes the camera shake correction group GrV. The fourth lens group Gr4 includes, in order from the object side, a biconvex positive lens and a negative meniscus lens concave on the object side whose object side surface is an aspheric surface.

  In the first embodiment (FIGS. 1 and 5), the first lens group Gr1 monotonically (that is, substantially linearly) toward the object side during zooming from the wide-angle end (W) to the telephoto end (T). The third lens group Gr3 moves monotonously (that is, substantially linearly) to the object side, and the fourth lens group Gr4 moves U-turns from the object side to the image side after moving to the object side (that is, Move to draw a convex trajectory on the object side.) The second lens group Gr2 is a fixed group. Focusing is performed by the fourth lens group Gr4. That is, a system is adopted in which the fourth lens group Gr4 is moved to the object side to perform focusing from an object at infinity to a close object. Further, a system that corrects camera shake by decentering in the vertical direction with respect to the optical axis AX is adopted, with one positive lens closest to the image side as the camera shake correction group GrV in the third lens group Gr3.

  In the second embodiment (FIGS. 2 and 6), a stop ST is provided between the second lens group Gr2 and the third lens group in a positive / negative / positive / positive bending type four-group zoom configuration. Each lens group is configured as follows. The first lens group Gr1 includes, in order from the object side, a cemented lens including a negative meniscus lens concave on the image side and a biconvex positive lens, and a positive meniscus lens convex on the object side. The second lens group Gr2 includes, in order from the object side, a biconcave negative lens whose image side surface is an aspheric surface, a prism PR, and a cemented lens composed of a biconcave negative lens and a biconvex positive lens. ing. The third lens group Gr3 includes, in order from the object side, a positive meniscus lens convex on the object side whose object side surface is an aspheric surface, a cemented lens including a biconvex positive lens and a negative meniscus lens concave on the object side, and an image. It is composed of a biconcave negative lens whose side surface is an aspheric surface and a positive meniscus lens convex on the object side that constitutes the camera shake correction group GrV. The fourth lens group Gr4 includes, in order from the object side, a biconvex positive lens whose both surfaces are aspheric surfaces and a negative meniscus lens concave on the object side.

  In the second embodiment (FIGS. 2 and 6), in zooming from the wide-angle end (W) to the telephoto end (T), the first lens group Gr1 is monotonically (that is, substantially linear) toward the object side. The third lens group Gr3 moves monotonously (that is, substantially linearly) to the object side, and the fourth lens group Gr4 moves U-turns from the object side to the image side after moving to the object side (that is, Move to draw a convex trajectory on the object side.) The second lens group Gr2 is a fixed group. Focusing is performed by the fourth lens group Gr4. That is, a system is adopted in which the fourth lens group Gr4 is moved to the object side to perform focusing from an object at infinity to a close object. Further, a system that corrects camera shake by decentering in the vertical direction with respect to the optical axis AX is adopted, with one positive lens closest to the image side as the camera shake correction group GrV in the third lens group Gr3.

  In the third embodiment (FIGS. 3 and 7), in a positive / negative / positive / negative / positive bending type five-group zoom configuration, there is a diaphragm between the second lens group Gr2 and the third lens group. The ST is arranged, and each lens group is configured as follows. The first lens group Gr1 includes, in order from the object side, a cemented lens including a negative meniscus lens concave on the image side and a biconvex positive lens, and a positive meniscus lens convex on the object side. The second lens group Gr2 includes, in order from the object side, a biconcave negative lens whose image side surface is an aspheric surface, a prism PR, and a cemented lens composed of a biconcave negative lens and a biconvex positive lens. ing. The third lens group Gr3 includes, in order from the object side, a biconvex positive lens whose object side surface is an aspheric surface, a cemented lens composed of a biconvex positive lens and a biconcave negative lens, and an image side surface which is an aspheric surface. The lens includes a negative meniscus lens that is concave on the image side and a positive meniscus lens that is convex on the object side that constitutes the image stabilization group GrV. The fourth lens group Gr4 includes one negative meniscus lens that is concave on the object side. The fifth lens group Gr5 is composed of, in order from the object side, a positive meniscus lens convex on the image side whose both surfaces are aspheric surfaces, and a positive meniscus lens convex on the image side.

  In the third embodiment (FIGS. 3 and 7), during zooming from the wide-angle end (W) to the telephoto end (T), the first lens group Gr1 is monotonically (that is, substantially linear) toward the object side. The third lens group Gr3 moves monotonously (that is, substantially linearly) to the object side, and the fifth lens group Gr5 moves monotonously (that is, substantially linearly) to the image side. The second lens group Gr2 and the fourth lens group Gr4 are fixed groups. Focusing is performed by the fifth lens group Gr5. That is, a system is adopted in which the fifth lens group Gr5 is moved to the object side to perform focusing from an object at infinity to a close object. Further, a system that corrects camera shake by decentering in the vertical direction with respect to the optical axis AX is adopted, with one positive lens closest to the image side as the camera shake correction group GrV in the third lens group Gr3.

  In the fourth embodiment (FIGS. 4 and 8), in a four-unit zoom configuration of positive / negative (negative / negative) / positive / positive bending type, between the second lens group Gr2 and the third lens group. Is provided with a stop ST, and each lens group is configured as follows. The first lens group Gr1 includes, in order from the object side, a negative meniscus lens that is concave on the image side and two positive meniscus lenses that are convex on the object side. The second lens group Gr2 includes, in order from the object side, two subgroups of a negative power front group Gr2a and a negative power rear group Gr2b. The front group Gr2a includes, in order from the object side, a biconcave negative lens whose image side surface is an aspheric surface, and a prism PR. The rear group Gr2b includes a biconcave negative lens in order from the object side. And a biconvex positive lens. The third lens group Gr3 includes, in order from the object side, a positive meniscus lens convex on the object side whose object side surface is an aspheric surface, a cemented lens including a biconvex positive lens and a negative meniscus lens concave on the object side, and an image. It is composed of a biconcave negative lens whose side surface is an aspheric surface and a biconvex positive lens constituting the camera shake correction group GrV. The fourth lens group Gr4 includes, in order from the object side, a positive meniscus lens convex on the image side whose both surfaces are aspheric surfaces, and a negative meniscus lens concave on the object side whose image side surfaces are aspheric surfaces. .

  In the fourth embodiment (FIGS. 4 and 8), during zooming from the wide-angle end (W) to the telephoto end (T), the first lens group Gr1 is monotonically (that is, substantially linear) toward the object side. The rear lens group Gr2b of the second lens group Gr2 moves from the image side to the object side after moving to the image side (that is, moves so as to draw a convex locus on the image side), and moves to the third lens. The group Gr3 moves monotonously (that is, substantially linearly) toward the object side, and the fourth lens group Gr4 moves U-turns from the object side to the image side after moving toward the object side (that is, a locus convex toward the object side). Move to draw.) The front group Gr2a of the second lens group Gr2 is a fixed group. Focusing is performed by the fourth lens group Gr4. That is, a system is adopted in which the fourth lens group Gr4 is moved to the object side to perform focusing from an object at infinity to a close object. Further, a system that corrects camera shake by decentering in the vertical direction with respect to the optical axis AX is adopted, with one positive lens closest to the image side as the camera shake correction group GrV in the third lens group Gr3.

  As described above, in any of the embodiments, in order from the object side, the first lens group having the positive power, the second lens group having the negative power, the third lens group having the positive power, and the subsequent of the positive power or the negative power. And at the time of zooming from the wide-angle end to the telephoto end, the first lens unit moves to the object side, the second lens unit is fixed in position, and the third lens unit moves to the object side. When the third lens unit is moved and divided into an object side part and an image side part, the image side part is used as a camera shake correction group to decenter the lens in the direction perpendicular to the optical axis, thereby performing camera shake correction. Yes. The variable magnification optical system has three lens groups of positive, negative, and positive in order from the object side, and the first lens group moves to the object side during variable magnification from the wide angle end to the telephoto end. Therefore, a compact variable power optical system having a small lens diameter of the first lens group while having a high magnification and a high zoom ratio can be provided. Since the position of the second lens group is fixed during zooming, the number of moving lens groups can be reduced, and the number of lens moving actuators can be reduced. In addition, since the third lens unit is configured to move toward the object side during zooming from the wide-angle end to the telephoto end, it can contribute to high magnification and high zooming.

  By performing camera shake correction by moving the camera shake correction group perpendicular to the optical axis, it is possible to perform camera shake correction while suppressing aberration deterioration due to lens movement (ie, eccentricity). By using the image side part of the third lens group (that is, the part of the third lens group including the most image side lens) as the camera shake correction group, the lens diameter and the amount of lens eccentricity are reduced and the weight is reduced. can do. As a result, the camera shake correction actuator and the mechanical mechanism can be reduced. Since the third lens group can reduce the lens diameter, if a part of the third lens group is used as a camera shake correction group, the camera shake correction can be performed more than when other lens groups (for example, the second lens group and the fourth lens group) are used. The movement space at the time is small. Although the lens diameter of the object side portion of the third lens group is small, if it is used as a camera shake correction group, the performance deterioration at the time of camera shake correction due to decentering becomes large. That is, since aberration correction (chromatic aberration correction, etc.) in the third lens group can be performed on the object side portion of the third lens group, performance degradation occurs even when the image side portion of the third lens group is used as a camera shake correction group. It becomes possible to suppress.

  The power of the image side portion used as the camera shake correction group may be positive or negative. However, when negative power is given to the image side portion, it is necessary to increase the positive power of the object side portion, which makes it difficult to correct aberrations. If positive power is given to the image side portion, the positive power of the third lens group can be compensated, so that favorable aberration correction can be performed. In other words, the zoom type that has positive, negative, and positive on the object side is advantageous for higher magnification and higher magnification. By providing positive power to the image side portion of the third lens group, good optical performance is achieved. It is possible to effectively correct camera shake while holding the image. Therefore, it is preferable that the power of the image side portion used as the camera shake correction group is positive.

  By having a lens group having positive or negative power on the image side of the third lens group (that is, a subsequent lens group), it is possible to increase the sensitivity of image movement due to decentering of the camera shake correction group. It is possible to perform camera shake correction with a short movement distance. Therefore, the mechanical mechanism for correcting camera shake can be reduced. In each zoom type, after the fourth lens group, it is possible to increase the sensitivity of image movement due to decentering of the camera shake correction group (that is, to reduce the decentering amount). For example, the positive, negative, positive, and positive four-group zoom is a zoom type that is advantageous for high magnification and can obtain stable performance, but the positive power fourth lens group is the amount of decentering of the image stabilization group. Acts to decrease As the image stabilization group moves away from the image plane, the bent light beam bends more greatly at the same power and reaches the image plane. Therefore, the distance from the image stabilization group to the image plane is increased, and at least one lens group is provided in the interval. If arranged, a large camera shake correction effect can be obtained.

  As described above, it is possible to achieve a high zoom ratio with high performance and compactness by the characteristic movement of each lens group, and it is good by using the image side portion of the third lens group as a camera shake correction group. Effective camera shake correction is possible while maintaining excellent optical performance and compactness. The configuration for correcting camera shake is effective for downsizing the actuators and mechanical mechanisms necessary for camera shake correction. Therefore, in a bending optical system that bends the optical path closer to the object side than the third lens group, even better optical performance can be obtained. Effective camera shake correction can be performed while maintaining performance and compactness. Therefore, it is possible to achieve a high zoom ratio and a camera shake correction function while achieving high performance and compactness. If an imaging device equipped with the variable magnification optical system is used in a device such as a digital camera, it can contribute to its thinness, light weight, compactness, low cost, high performance, high functionality, and the like. Conditions for obtaining these effects in a well-balanced manner and achieving higher optical performance and the like will be described below. In addition, the zoom ratio when satisfying the conditions described below is preferably 7 times or more, more preferably 7 to 10 times, from the balance between high performance and downsizing.

It is desirable that the camera shake correction group have positive power and satisfy the following conditional expression (1).
0.9 <fas / f3 <3.5 (1)
However,
fas: focal length of the image stabilization group,
f3: focal length of the third lens group,
It is.

  Conditional expression (1) defines a preferable condition range regarding the power of the camera shake correction group. If the upper limit of conditional expression (1) is exceeded, the sensitivity of the image plane movement amount to the lens movement amount of the camera shake correction group becomes small. For this reason, it is necessary to increase the lens movement amount for camera shake correction, which increases the camera shake correction mechanism. In other words, when the power of the image stabilization group becomes weaker, the lens movement amount (i.e., the eccentricity amount) increases, and as a result, it is necessary to secure a large space for the eccentric movement including the surrounding mechanical configuration, The imaging device is not suitable for downsizing. On the other hand, if the lower limit of conditional expression (1) is exceeded, performance degradation due to axial coma and peripheral blurring increases due to lens decentering during camera shake correction.

It is more desirable to satisfy the following conditional expression (1a).
1.4 <fas / f3 <2.9 (1a)
The conditional expression (1a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (1).

It is desirable to satisfy the following conditional expression (2).
0.3 <f3 / √ (fw × ft) <1.3… (2)
However,
f3: focal length of the third lens group,
fw: focal length of the entire system at the wide-angle end,
ft: focal length of the entire system at the telephoto end,
It is.

  Conditional expression (2) defines a preferable condition range regarding the power of the third lens group. If the upper limit of conditional expression (2) is exceeded, the amount of movement of the three groups becomes large in order to increase the zoom ratio, and the total lens length becomes long, which is disadvantageous for making compact. If the movement amount of the third lens group is not increased, the zoom ratio earned by the change in the distance between the second and third lens groups is reduced, and the power and movement amount of the first lens group must be greatly increased. As a result, deterioration of aberration performance (for example, image surface performance) occurs. On the other hand, if the lower limit of conditional expression (2) is exceeded, spherical aberration occurring inside the third lens group cannot be suppressed and the MTF deteriorates.

It is more desirable to satisfy the following conditional expression (2a).
0.5 <f3 / √ (fw × ft) <1.0… (2a)
The conditional expression (2a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (2).

  In the first to fourth embodiments (FIGS. 1 to 4), the camera shake correction group GrV is composed of one single lens. As in each embodiment, it is preferable that the camera shake correction group includes one single lens. By configuring the camera shake correction group with a single lens, the camera shake correction group can be further reduced in weight, and the actuator that drives the camera shake correction group can be made smaller. Further, by using a single lens, the mechanical structure for holding the lens can be simplified, and the peripheral mechanical members can be reduced in weight and size.

  In the first to fourth embodiments (FIGS. 1 to 4), an aperture stop ST that moves integrally with the third lens group Gr3 during zooming is provided between the second lens group Gr2 and the third lens group Gr3. Has been placed. As in each embodiment, it is preferable to have an aperture stop that moves integrally with the third lens group during zooming between the second lens group and the third lens group. By arranging an aperture stop on the object side of the third lens group (that is, between the second and third lens groups) and moving the third lens group and the aperture stop integrally during zooming, camera shake may occur. The lens diameter of the correction group can be reduced, and the camera shake mechanism can be further downsized.

  In the first, second, and fourth embodiments (FIGS. 1, 2, and 4), the third lens group Gr3 includes, in order from the object side, a positive meniscus lens that is convex on the object side, and positive power as a whole. The positive power single lens constitutes an image stabilization group GrV. The cemented lens is a negative power single lens and a positive power single lens. As described above, the third lens unit includes, in order from the object side, a positive meniscus lens convex toward the object side, a positive power cemented lens as a whole, a negative power single lens, and a positive power single lens. It is preferable that the positive power single lens is the image stabilization group. By separating positive power into a positive meniscus lens convex on the object side and a cemented lens having positive power as a whole, strong positive power as a whole can be arranged while suppressing the occurrence of spherical aberration. Further, by making the cemented lens convex on the object side, it is possible to suppress the occurrence of spherical aberration, and chromatic aberration correction by the cemented lens is also possible. A negative power single lens can improve Petzval sum, and a positive power single lens can correct camera shake. By disposing an aspherical surface on a single lens with negative power, it is possible to correct aberrations at the object side portion of the third lens group. If an aspherical surface is provided up to a single lens of positive power that is a camera shake correction group, deterioration of MTF on the axis is unavoidable during camera shake correction. By correcting the aberration generated in the positive meniscus lens and the cemented lens up to the single lens of negative power, it is possible to prevent the camera shake correction group from being adversely affected.

  In the first to fourth embodiments (FIGS. 1 to 4), the succeeding lens group (fourth lens group Gr4 in the first, second and fourth embodiments, fifth in the third embodiment). Focusing is performed by moving the lens group Gr5). As in each embodiment, it is preferable to perform focusing by moving the subsequent lens group. That is, it is preferable to employ a method of performing focusing from an infinitely distant object to a close object by moving a lens group located closer to the image side than the third lens group to the object side. In each embodiment, focusing from an infinite object to a close object is performed by moving the fourth lens group Gr4 or the fifth lens group Gr5 to the object side as indicated by an arrow mF (FIGS. 1 to 4). It is configured. If focusing is performed with the first lens group, the lens diameter of the first lens group becomes large, and the variable magnification optical system cannot be miniaturized. If focusing is performed with the second lens group or the third lens group, the change in image magnification during focusing becomes large, which is not preferable. If focusing is performed with a subsequent lens group positioned on the image side of the third lens group, a change in image magnification is reduced, and a variation in field curvature due to zooming can be reduced.

  In the second to fourth embodiments (FIGS. 2 to 4 and FIGS. 6 to 8), the second lens group Gr2 has a reflecting surface RL that bends the optical path. As described above, it is preferable to have a reflecting surface that bends the optical path in the second lens group. Since the second lens group is fixed during zooming, a bending means (for example, a prism or a mirror) can be fixedly arranged inside the second lens group or in the vicinity of the second lens group. If the lens group has a fixed position in zooming, it is not necessary to move the bending means having a large volume during zooming, so that the variable magnification optical system can be made compact.

It is desirable to satisfy the following conditional expression (3).
0.4 <ΔT (3Gr) / ΔT (1Gr) <1.7 (3)
However,
ΔT (1Gr): Amount of movement of the first lens unit during zooming from the wide-angle end to the telephoto end,
ΔT (3Gr): the amount of movement of the third lens unit during zooming from the wide-angle end to the telephoto end,
It is.

  Conditional expression (3) defines a preferable condition range regarding the movement amount balance between the first lens group and the third lens group. If the amount of movement of the third lens unit relative to the amount of movement of the first lens unit exceeds the upper limit of conditional expression (3), the total length of the variable magnification optical system cannot be shortened, resulting in compactness. It becomes difficult to achieve. Conversely, if the amount of movement of the third lens group relative to the amount of movement of the first lens group becomes too small beyond the upper limit of conditional expression (3), the contribution of the third lens group to the zoom will be insufficient, resulting in high magnification. And high zoom ratio cannot be achieved.

It is more desirable to satisfy the following conditional expression (3a).
0.6 <ΔT (3Gr) / ΔT (1Gr) <1.4 (3a)
The conditional expression (3a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (3).

  In the fourth embodiment (FIGS. 4 and 8), the second lens group Gr2 is composed of two partial groups of a negative power front group Gr2a and a negative power rear group Gr2b. The rear group Gr2b moves U-turns so that the distance from the front group Gr2a is slightly changed. That is, the rear group Gr2b moves from the wide-angle end (W) to the middle (M) toward the image side (increase in the distance from the front group Gr2a), and moves from the middle (M) to the telephoto end (T) toward the object side (front). Move U-turn so that the distance to the group Gr2a decreases. In this way, the second lens group is composed of two subgroups, the negative power front group and the negative power or positive power rear group, in order from the object side, and any one of the subgroups is in magnification. It is preferable that the movement is not monotonous. In zooming, it is preferable that one of the front group and the rear group is fixed in position and the other is moved by a small amount in the optical axis direction. By changing the distance between the front group and the rear group of the second lens group by a small amount during zooming, aberration variation during zooming of the second lens group (for example, an image plane such as a tilt of the image plane on the wide angle side). (Degradation of performance) can be suppressed, and the performance at the time of zooming can be further improved.

The change in the lens interval in the second lens group (that is, the change in the interval between the front group and the rear group) is very small compared to the change in the interval of the zooming group. As the degree of the change, it is desirable to satisfy the following conditional expression (4).
ΔT2max / ΔT (3Gr) <0.25 (4)
However,
ΔT2max: Maximum displacement (absolute value) of the lens interval during zooming in the second lens group,
ΔT (3Gr): the amount of movement of the third lens unit during zooming from the wide-angle end to the telephoto end,
It is.

  The zoom lens system ZL constituting each embodiment uses a refractive lens that deflects incident light by refraction (that is, a lens that deflects at the interface between media having different refractive indexes). However, the usable lens is not limited to this. For example, a diffractive lens that deflects incident light by diffracting action, a refractive / diffractive hybrid lens that deflects incident light by combining diffractive action and refracting action, and a refractive index distribution that deflects incident light by a refractive index distribution in the medium A mold lens or the like may be used. However, it is desirable to use a homogeneous material lens having a uniform refractive index distribution, because the refractive index distribution type lens whose refractive index changes in the medium increases the cost of its complicated manufacturing method. Further, in the zoom lens system ZL constituting each embodiment, a stop ST is used as an optical element in addition to the lens, but a light flux restricting plate (for example, a flare cutter) or the like for cutting unnecessary light is used. You may arrange | position as needed.

  Hereinafter, the configuration of the zoom lens system embodying the present invention will be described more specifically with reference to construction data and the like. Examples 1 to 4 listed here are numerical examples corresponding to the first to fourth embodiments, respectively, and are optical configuration diagrams showing the first to fourth embodiments (FIGS. 1 to 4). 8) shows the lens configuration, optical path, and the like of the corresponding first to fourth embodiments.

  Tables 1 to 8 show construction data of Examples 1 to 4, and Table 9 shows data such as values corresponding to conditional expressions of each example. In the basic optical configurations (i: surface number) shown in Table 1, Table 3, Table 5, and Table 7, ri (i = 1, 2, 3,...) Is the i-th surface counted from the object side. The radius of curvature (mm) and di (i = 1, 2, 3,...) Indicate the axial distance (mm) between the i-th surface and the (i + 1) -th surface counted from the object side. (Here, the state before eccentricity is shown.), Ni (i = 1, 2, 3,...) And νi (i = 1, 2, 3,. The refractive index (Nd) and Abbe number (νd) of the optical material for the d-line are shown. Further, the axial top surface distance di that changes during zooming is a variable air distance from the wide-angle end (shortest focal length state, W) to the middle (intermediate focal length state, M) to the telephoto end (longest focal length state, T). , F, FNO respectively indicate the focal length (mm) and the F number of the entire system corresponding to each focal length state (W), (M), (T).

The surfaces marked with * in the data of the radius of curvature ri are aspherical surfaces (aspherical refractive optical surfaces, surfaces having a refractive action equivalent to aspherical surfaces, etc.), and represent the following aspherical surface shapes: It is defined by the formula (AS). In Table 2, Table 4, Table 6, and Table 8, aspherical data of each example are shown. However, the coefficient of the term without description is 0, and E−n = × 10 ⁻ⁿ for all data.
X (H) = (C0 · H ² ) / {1 + √ (1−ε · C0 ² · H ² )} + Σ (Aj · H ^j ) (AS)
However, in the formula (AS)
X (H): Amount of displacement in the optical axis AX direction at the position of height H (based on the surface vertex),
H: height in a direction perpendicular to the optical axis AX,
C0: paraxial curvature (= 1 / ri),
ε: quadric surface parameter,
Aj: j-order aspheric coefficient,
It is.

  FIGS. 9 to 12 are longitudinal aberration diagrams before decentering (normal state) and infinite focus state corresponding to Examples 1 to 4, respectively. (W) is the wide-angle end, and (M) is the middle. , (T) are various aberrations at the telephoto end (in order from the left, spherical aberration, astigmatism, distortion aberration, FNO is F number, Y ′ (mm) is the maximum on the light receiving surface SS of the image sensor SR. The image height (corresponding to the distance from the optical axis AX). In the spherical aberration diagram, a solid line d represents spherical aberration (mm) with respect to the d line, and a broken line SC represents an unsatisfactory sine condition (mm). In the astigmatism diagram, the broken line DM represents the meridional surface, and the solid line DS represents each astigmatism (mm) with respect to the d-line on the sagittal surface. In the distortion diagram, the solid line represents the distortion (%) with respect to the d-line.

  13 to 20 are lateral aberration diagrams in the infinite focus state before eccentricity (normal state) and after eccentricity (camera shake correction state) corresponding to Examples 1 to 4, respectively. 14 corresponds to the first embodiment, FIGS. 15 and 16 correspond to the second embodiment, FIGS. 17 and 18 correspond to the third embodiment, and FIGS. 19 and 20 correspond to the fourth embodiment. 13 to 20, (A) and (B) are lateral aberration diagrams before decentering, and (C) to (E) are lateral aberration diagrams after decentering (y ′ (mm) is imaging. Maximum image height on the light receiving surface SS of the element SR (corresponding to a distance from the optical axis AX). FIGS. 13, 15, 17, and 19 show the lateral aberrations on the axis and at the maximum image height when a camera shake of 0.4 degrees at the wide-angle end (W) is corrected by the eccentricity of the camera shake correction group. 14, 16, 18, and 20 show on-axis and maximum images when camera shake at an angle of 0.1 degrees is corrected by eccentricity of the camera shake correction group at the telephoto end (T). It represents the degradation of lateral aberration at high. As can be seen from FIG. 13 to FIG. 20, aberration deterioration is small and good performance can be ensured even in the camera shake correction state.

  Table 10 shows the amount of lens eccentricity when correcting camera shake in each example (unit: mm, eccentric direction: direction perpendicular to the optical axis AX). In Table 10, Wide indicates the amount of lens eccentricity when the tilt of 0.4 degrees is corrected at the wide angle end (W), and Tele indicates when the tilt of 0.1 degrees is corrected at the telephoto end (T). The amount of lens eccentricity is shown.

The lens block diagram of 1st Embodiment (Example 1). The lens block diagram of 2nd Embodiment (Example 2). The lens block diagram of 3rd Embodiment (Example 3). The lens block diagram of 4th Embodiment (Example 4). The optical path figure of 1st Embodiment (Example 1). The optical path figure of 2nd Embodiment (Example 2). The optical path figure of 3rd Embodiment (Example 3). The optical path figure of 4th Embodiment (Example 4). FIG. 4 is a longitudinal aberration diagram of Example 1 before decentration. FIG. 5 is a longitudinal aberration diagram of Example 2 before decentration. FIG. 6 is a longitudinal aberration diagram of Example 3 before decentration. FIG. 6 is a longitudinal aberration diagram of Example 4 before decentration. FIG. 4 is a lateral aberration diagram before and after decentration and at the wide-angle end in Example 1. FIG. 5 is a lateral aberration diagram before and after decentration and at the telephoto end in Example 1. FIG. 5 is a lateral aberration diagram before and after decentration and at the wide-angle end in Example 2. FIG. 5 is a lateral aberration diagram before and after decentration and at the telephoto end in Example 2. FIG. 4 is a lateral aberration diagram before and after decentration and at the wide-angle end in Example 3. FIG. 5 is a lateral aberration diagram before and after decentration and at the telephoto end in Example 3. FIG. 6 is a lateral aberration diagram before and after decentering and at the wide-angle end in Example 4. FIG. 6 is a lateral aberration diagram before and after decentration and at the telephoto end in Example 4. The side view which shows the example of schematic optical structure of the camera carrying an imaging device of an optical path straight type in a typical cross section. FIG. 3 is a side view schematically showing a cross section of a schematic optical configuration example of a camera equipped with an optical path bending type imaging apparatus.

Explanation of symbols

CU camera LU imaging device ZL zoom lens system (variable magnification optical system)
Gr1 First lens group Gr2 Second lens group Gr3 Third lens group Gr4 Fourth lens group Gr5 Fifth lens group GrV Camera shake correction group Gr2a Front group Gr2b Rear group PR Prism (bending means)
RL Reflecting surface ST Aperture (aperture stop)
PT Parallel plane SR Image sensor SS Photosensitive surface IM Image plane AX Optical axis

Claims (11)

  A variable magnification optical system having a camera shake correction function and capable of forming an optical image of an object on an image sensor so that the magnification can be changed, and in order from the object side, a first lens unit having a positive power and a second lens having a negative power And a third lens group having a positive power and at least one subsequent lens group having a positive power or a negative power, and the first lens group moves toward the object side upon zooming from the wide-angle end to the telephoto end. When the second lens group is fixed, the third lens group moves to the object side, and the third lens group is divided into an object side part and an image side part, the image side part is shaken. A variable power optical system characterized in that camera shake correction is performed by decentering the correction group in a direction perpendicular to the optical axis. The zoom optical system according to claim 1, wherein the camera shake correction group has positive power and satisfies the following conditional expression (1):
0.9 <fas / f3 <3.5 (1)
However,
fas: focal length of the image stabilization group,
f3: focal length of the third lens group,
It is. The variable magnification optical system according to claim 1, wherein the following conditional expression (2) is satisfied:
0.3 <f3 / √ (fw × ft) <1.3… (2)
However,
f3: focal length of the third lens group,
fw: focal length of the entire system at the wide-angle end,
ft: focal length of the entire system at the telephoto end,
It is.   The variable power optical system according to claim 1, wherein the camera shake correction group includes a single lens.   The aperture stop which moves integrally with a 3rd lens group in the said variable magnification is provided between the said 2nd lens group and the said 3rd lens group, The any one of Claims 1-4 characterized by the above-mentioned. Variable magnification optical system.   The third lens group includes, in order from the object side, a positive meniscus lens convex toward the object side, a positive power cemented lens as a whole, a negative power single lens, and a positive power single lens. The variable power optical system according to claim 1, wherein a power single lens is the image stabilization group.   The variable power optical system according to claim 1, wherein focusing is performed by moving the subsequent lens group.   The variable power optical system according to claim 1, further comprising a reflecting surface that bends an optical path in the second lens group. The variable magnification optical system according to claim 1, wherein the following conditional expression (3) is satisfied:
0.4 <ΔT (3Gr) / ΔT (1Gr) <1.7 (3)
However,
ΔT (1Gr): Amount of movement of the first lens unit during zooming from the wide-angle end to the telephoto end,
ΔT (3Gr): the amount of movement of the third lens unit during zooming from the wide-angle end to the telephoto end,
It is.   The second lens group, in order from the object side, includes two subgroups, a negative power front group and a negative power or positive power rear group, and one of the subgroups is not monotonous in zooming. The variable magnification optical system according to claim 1, wherein the zoom lens system moves.   An imaging apparatus comprising the variable magnification optical system according to claim 1.