JP2006350051A - Variable power optical system and imaging apparatus equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact and high-performance variable power optical system or the like whose variable power ratio is extremely large. <P>SOLUTION: The variable power optical system is constituted by disposing: at least a first lens group GR1 having positive power; a second lens group GR2 having negative power; and a third lens group GR3 having positive power from an object side to an image side, and the first lens group GR1 is equipped with a first optical prism PR, while the third lens group GR3 is equipped with a second optical prism PR'. Then, a lens nearest to the image side (eleventh lens L11) in the third lens group GR3 is made aspherical. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a variable magnification optical system used for a lens unit and the like, and an imaging apparatus including the variable magnification optical system.

  In recent years, with the widespread use of personal computers (PCs), digital cameras (imaging devices) that can easily capture images have become widespread. And for such digital cameras as well as cameras using silver halide films (silver halide cameras), miniaturization (thinning) and high performance (for example, high zooming function and high aberration correction function) are desired. Has been.

In order to meet these demands, an imaging device (video camera or the like) has been developed in which a variable power optical system (zoom lens) including a right-angle prism is mounted on the lens group (first lens group) closest to the object side (see FIG. For example, Patent Documents 1 and 2). In these imaging apparatuses, the length of the first lens group is suppressed by bending the optical axis with a right-angle prism (and thus the total length of the zoom lens is suppressed). Therefore, a zoom lens with a reduced overall length can be appropriately disposed in a limited space of the housing of the image pickup apparatus, and as a result, the size of the housing (and thus the size of the image pickup apparatus) is small and thin.
JP-A-8-248318 (refer to claim 1 etc.) Japanese Patent Laid-Open No. 9-146000 (see FIG. 5 etc.)

  However, the imaging devices of Patent Documents 1 and 2 have a variable magnification optical system including a plurality of lens groups having positive, negative, positive, and positive power arrangements. Therefore, at the time of zooming, for example, the second lens group must move relatively large. Then, the total length of the variable magnification optical system (zoom lens) may be increased (lengthened) due to the amount of movement of the second lens group. For this reason, it is difficult to say that the effects of downsizing and the like are sufficiently exhibited in the imaging apparatuses disclosed in Patent Documents 1 and 2.

  In particular, there is a growing demand for downsizing of recent imaging devices (digital cameras, video cameras, etc.), and accordingly, downsizing of the variable magnification optical system itself is also required. For this reason, there is a fact that there is a very high demand for a high-performance variable magnification optical system as well as miniaturization by bending the optical axis.

  The present invention has been made in view of the above-mentioned problems and the current state of the art, and an object thereof is to provide a high-performance and miniaturized variable magnification optical system and an imaging apparatus including the same. .

  The variable magnification optical system of the present invention includes a plurality of lens groups that form an image of light rays from the object side on an image sensor. Further, the plurality of lens groups include at least a first lens group having a positive power, a second lens group having a negative power, and a third lens group having a positive power from the object side to the image side. And. In this zoom optical system, the first lens group includes a first optical axis changing element that changes the optical axis, while the third lens group includes a second optical axis changing element that changes the optical axis. Furthermore, in the variable magnification optical system of the present invention, the most image side lens in the third lens group has at least one aspherical surface.

  When the variable magnification optical system is reduced in size, for example, the distance between groups (interval between lens groups) is shortened. In such a case, the power (refractive power) required for each lens group is relatively increased. In particular, in a variable power optical system having positive, negative, and positive power arrangement, the power required for each lens group tends to increase. Thus, when the power of the lens group is increased, various aberrations (off-axis aberrations and the like) are likely to occur.

  However, when the most image side lens in the third lens group has at least one aspherical surface as in the variable power optical system of the present invention, this aspherical surface is used to effect off-axis aberrations and the like. Can be corrected manually. Therefore, the present invention provides a small-sized (compact) variable magnification optical system with high performance (while having a high aberration correction function).

In addition, it is preferable that the aspherical surface located on the image side in the most image side lens satisfies the following conditional expression (1).
2 <(| X | − | X ₀ |) × 100 / {C ₀ × (N′−N) × f3} <100
... Conditional expression (1)
However,
X: aspherical surface shape X _0: surface shape C ₀ aspheric reference spherical surface curvature of the aspherical surface of the reference sphere N: refractive power of the object side in the aspheric medium N ': the image side in the aspheric medium Refracting power of f3: focal length of the third lens unit.

  This conditional expression (1) defines a range for harmonizing the miniaturization of the variable magnification optical system and the high performance of aberration correction based on the power of the most image side lens of the third lens group. Yes. When the lower limit of conditional expression (1) is exceeded, the occurrence of various aberrations is suppressed, while when the lower limit of conditional expression (1) is exceeded, excessive enlargement of the variable magnification optical system is suppressed. It has come to be. Therefore, within the range of conditional expression (1), the present invention becomes a miniaturized variable magnification optical system while suppressing the occurrence of aberrations (while improving performance).

  Further, the third lens group may include at least four or more lenses. This is because aberration correction can be effectively performed with a plurality of lenses.

  In general, in a variable power optical system having a “positive / negative / positive” power arrangement as in the present invention, divergent light is emitted from the second lens group. Therefore, in order to effectively converge the emitted divergent light, a plurality of lenses may be positioned closer to the object side than the second optical axis changing element in the third lens group.

  With such a configuration, each lens can converge the diverging light stepwise and guide it to the second optical axis changing element. For this reason, the distance from the second lens group to the second optical axis changing element is relatively short, and as a result, the total length of the variable magnification optical system is shortened.

Moreover, it is preferable that the zoom optical system of the present invention satisfies the following conditional expression (2) when zooming.
0.1 ≦ MV2 / Lw ≦ 0.5 Conditional expression (2)
However,
MV2: Movement amount of the second lens group Lw: Total length of the variable magnification optical system in the wide-angle end state

  Conditional expression (2) defines a range for achieving harmony between miniaturization of the variable magnification optical system and higher performance of aberration correction (for example, higher magnification) based on the amount of movement of the second lens group. is doing. Further, when the upper limit value of conditional expression (2) is not reached, excessive enlargement of the variable power optical system is suppressed. On the other hand, when the lower limit value of conditional expression (2) is exceeded, there are various types of variable power optical systems. The magnification can be secured. Therefore, within the range of conditional expression (2), the present invention becomes a miniaturized variable magnification optical system while ensuring the type of magnification.

The present invention is a variable magnification optical system having a high variable magnification ratio that satisfies the following conditional expression (3).
5.0 <ft / fw ... conditional expression (3)
However,
ft: focal length of the entire variable magnification optical system at the telephoto end fw: focal length of the entire variable magnification optical system at the wide angle end.

  In the zoom optical system of the present invention, when the first lens group and the third lens group move for zooming, the inter-group distance between the first lens group and the third lens group remains unchanged. It may be. For example, the first lens group and the third lens group may be coupled (connected) via a coupling unit, and may be moved simultaneously when the both lens groups are zoomed. In such a case, the configuration (arrangement configuration) for arranging these both lens groups is simplified. Then, both lens groups can be accommodated in, for example, the same lens barrel. As a result, the size of the lens barrel is relatively reduced.

  In order to improve the telecentricity of the light finally emitted from the variable magnification optical system, in the variable magnification optical system of the present invention, a fourth lens group having a positive power is provided on the image side of the third lens group. It may be arranged.

  The material of the lens of the present invention is not particularly limited. Therefore, each lens in the variable magnification optical system of the present invention may be formed of a resin (plastic or the like). In particular, it is preferable that the most image side lens in the third lens group GR3 is formed of resin. This is because if the lens material is made of resin, it is easy to form an aspherical surface.

  Note that the imaging device of the present invention including the above-described zooming optical system has a very high zooming ratio, and is a high-performance and compact imaging device.

  Even in the case where the power required for each lens group is increased and the distance between the groups is shortened for the purpose of miniaturization, according to the present invention, various aberrations caused by the power increase can be reduced by the third lens group. Can be effectively corrected by the aspherical surface of the most image side lens. Therefore, a variable power optical system that has high performance and is miniaturized, and an imaging apparatus including the same are realized.

[Embodiment 1]
An embodiment of the present invention will be described below with reference to the drawings.

[1. About digital cameras)
5 and 6 are schematic configuration diagrams of a digital camera 29 which is an example of the imaging apparatus of the present invention. FIG. 5 shows the configuration of the internal block of each part, and also shows the lens unit 1 (a configuration including the variable magnification optical system 11 and the image sensor SR) built in the digital camera 29. On the other hand, FIG. 6 shows a side surface of the digital camera 29. In particular, FIG. 6 shows an example of the variable magnification optical system 11 constituting the lens unit 1. The height direction of the digital camera 29 is referred to as a height direction U, the horizontal direction is referred to as a horizontal direction V, and the depth direction is referred to as a depth direction Z.

  As shown in FIG. 5, the digital camera 29 includes a variable power optical system 11, an optical system drive unit 13, an image sensor SR, a signal processing unit 14, a display unit 15, a recording unit 16, a recording medium 17, an operation unit 18, and The control unit 19 is configured to be included.

  The variable magnification optical system 11 is an optical system that guides light from the imaging target to the image sensor SR and forms an image of the light on the light receiving surface (image surface) of the image sensor SR. Therefore, the variable magnification optical system 11 may be expressed as an imaging optical system or an imaging optical system. Details of the variable magnification optical system 11 will be described later.

  The optical system drive unit 13 has several drive motors (optical system drive motors) and a transmission mechanism (optical system transmission mechanism) that transmits the driving force to the lens group constituting the variable magnification optical system 11. (The drive motor and transmission mechanism are not shown). The optical system driving unit 13 sets the focal length and the focal position of the variable magnification optical system 11 using a drive motor and a transmission mechanism. Specifically, the optical system driving unit 13 sets a focal length and a focal position in response to an instruction from the control unit 19.

  The imaging element SR is, for example, a CCD (Charge Coupled Device) area sensor, a CMOS (Complementary Metal Oxide Semiconductor) sensor, or the like, and receives the light beam that has passed through the variable magnification optical system 11 and converts it into an electrical signal (imaging data). . Then, the imaging element SR outputs this imaging data to the signal processing unit 14.

  The signal processing unit 14 generates captured image data based on the imaging data by processing electronic data (imaging data) from the imaging element SR. The signal processing unit 14 turns the processing operation ON or OFF in accordance with an instruction from the control unit 19. In response to an instruction from the control unit 19, the signal processing unit 14 outputs the captured image data to the display unit 15 and the recording unit 16.

  The display unit 15 is configured by, for example, a liquid crystal panel, and displays captured image data from the signal processing unit 14, usage status of the digital camera 29, and the like.

  The recording unit 16 records the captured image data generated by the signal processing unit 14 on the recording medium 17 in accordance with an instruction from the control unit 19. In addition, the recording unit 16 reads captured image data from the recording medium 17 in accordance with an instruction from the control unit 19 according to an operation by the operation unit 18 or the like.

  The recording medium 17 may be incorporated in the digital camera 29, for example, or may be removable such as a flash memory. In short, any medium (such as an optical disk or semiconductor memory) that can record captured image data or the like may be used.

  The operation unit 18 outputs various operation instructions by a user or the like to the control unit 19 and includes, for example, a shutter release button and an operation dial.

  The control unit 19 is a central part that performs operation control and the like of the entire digital camera 29, and organically controls the driving of each member of the digital camera 29 to control the operation in an integrated manner.

[2. Lens unit)
Here, the lens unit 1 including the variable magnification optical system 11 and the image sensor SR will be described with reference to FIGS. 1, 5, and 6. An example of the lens unit 1 shown in FIGS. 5 and 6 is accommodated in the digital camera 29. The lens unit 1 bends the light beam using the optical prism PR and the reflection mirror MR.

  However, the member (optical axis changing element) that bends the light beam (optical axis) may be the optical prism PR or the reflection mirror MR. Therefore, in FIG. 1 (lens configuration diagram) showing a state in which the lens units 1 are expanded in a line, the variable magnification optical system 11 in which the third lens group GR3 includes the optical prism PR ′ (second optical axis changing element). Will be described as an example. The optical axis in the lens unit 1 is denoted as AX (AX1 to AX3; see FIGS. 5 and 6).

  In FIG. 1, “GRi” indicates a lens group, and “Li” indicates a lens. Further, “si” indicates a surface (transmission surface or the like). The numbers (i) given to “GRi”, “Li”, and “si” indicate the order from the object side to the image side. An aspheric surface is marked with “*” (asterisk). The variable magnification optical system 11 (and hence the lens unit 1) shown in FIG.

<2-1. Configuration of Lens Unit (Example 1)>
The variable magnification optical system 11 of the lens unit 1 includes a first lens group GR1, a second lens group GR2, a third lens group GR3, a fourth lens group GR4, and an image sensor unit SU in order from the object to be imaged. In addition, since this image pick-up element unit SU is the 5th position in order from the object side, below may be described as SU5.

<About the first lens group>
The first lens group GR1 includes, in order from the object side, a first lens L1, an optical prism (first optical prism) PR, a second lens L2, and a third lens L3. The first lens group GR1 as a whole has a “positive” optical power (refractive power). The power is defined as the reciprocal of the focal length.

  The first lens (front lens) L1 is a negative meniscus lens convex on the object side.

  The first optical prism (first optical axis changing element) PR is a prism that can bend a light beam from the object side to a right angle or the like (for example, a right angle prism). In the optical prism PR, s3 is a light incident surface, and s4 is a light exit surface.

  The second lens L2 is a biconvex positive lens (biconvex lens), and the third lens L3 is a positive meniscus lens convex to the object side.

<About the second lens group>
The second lens group GR2 includes a fourth lens L4, a fifth lens L5, and a sixth lens L6 in order from the object side. The second lens group GR2 as a whole has “negative” optical power.

  The fourth lens L4 is an object side convex negative meniscus lens. Note that s10 of the fourth lens L4 is an aspherical surface (aspherical refractive optical surface, a surface having a refractive action equivalent to an aspherical surface, etc.).

  The fifth lens L5 is a negative lens concave on both sides, and the sixth lens L6 is a positive lens convex on both sides. The fifth lens L5 and the sixth lens L6 constitute a cemented lens by cementing s12 and s13. In addition, as a bonding method, bonding with an adhesive or the like can be given (in addition, bonding with an adhesive or the like can be similarly mentioned as a bonding method of a bonded lens described later).

<About the third lens group>
The third lens group GR3 includes, in order from the object side, an optical aperture stop ST, a seventh lens L7, an optical prism (second optical prism) PR ′, an eighth lens L8, a ninth lens L9, a tenth lens L10, and an eleventh lens. A lens (most image side lens) L11 is included. The third lens group GR3 as a whole has “positive” optical power.

  The optical aperture stop ST is an aperture that can vary the aperture diameter RS. The optical aperture stop ST is formed integrally with the third lens group GR3. In FIG. 1, the optical aperture stop ST itself is denoted as s15 for convenience.

  The seventh lens L7 is an object side convex plano-convex lens. Note that s16 of the seventh lens L7 is an aspherical surface.

  The second optical prism (second optical axis changing element) PR ′ is a prism that can bend a light beam to approximately 90 ° (right angle or the like), for example, like the first optical prism PR. The seventh lens L7 and the second optical prism PR 'are joined via s17 and s18.

  The eighth lens L8 is a positive lens convex on both sides, and the ninth lens L9 is a negative lens concave on both sides. The eighth lens L8 and the ninth lens L9 constitute a cemented lens by cementing s21 and s22.

  The tenth lens L10 is a negative lens that is concave on both sides, and the eleventh lens L11 is a negative meniscus lens that is convex on the object side. Note that s26 (object side surface) and s27 (image side surface) of the eleventh lens L11 are aspherical surfaces.

<About the fourth lens group>
The fourth lens group GR4 includes, in order from the object side, a twelfth lens L12 and a thirteenth lens L13. The fourth lens group GR4 as a whole has a “positive” optical power.

  The twelfth lens L12 is a positive lens convex on both sides. Note that s28 and s29 are aspherical surfaces. The thirteenth lens L13 is an object side concave negative meniscus lens.

<About the imaging unit>
The image sensor unit SU5 includes a cover glass CG having a two-surface configuration (s32 / s33) and a fixedly arranged image sensor SR. A cover glass CG is attached to the image sensor SR. Specifically, the cover glass CG s33 and the light receiving surface of the image sensor SR are disposed so as to be extremely close to each other. The cover glass CG may serve as an optical filter (for example, an infrared cut filter) having a predetermined cutoff frequency characteristic determined by the pixel pitch of the image sensor SR.

<2-2. Construction data of variable magnification optical system (Example 1)>
Next, construction data of the variable magnification optical system 11 of Example 1 will be described with reference to Tables 1 and 2.

  “Ri” in Table 1 indicates a radius of curvature [unit: mm] on each surface (si). An aspheric surface is marked with an asterisk (*). “Di” represents an axial upper surface distance [unit: mm] between the i-th surface (si) and the i + 1-th surface (si + 1). In addition, when the axial top surface distance changes (fluctuates) due to zooming, di in the wide-angle end state (W), di in the intermediate focal length state (M), di in the telephoto end state (T) are in this order. It is written.

  “Ni” and “υi” indicate the refractive index (Nd) and the Abbe number (νd) of the medium at the axial upper surface spacing (di). The refractive index (Nd) and Abbe number (νd) are for the d-line (wavelength 587.56 nm).

  The “focal length state” means a wide angle end state (W: shortest focal length state) to an intermediate focal length state (M) to a telephoto end state (T: longest focal length state). “F” and “FNO” indicate the focal length [unit: mm] and the F number of the entire system corresponding to the respective focal states (W), (M), and (T).

By the way, the aspheric surface is defined by the following equation (definition equation 1).
X (H) = C ₀ · H ² / {1 + √ (1−ε · C ₀ ² · H ² )} + ΣAj · H ^j (Definition Formula 1)
However, in definition formula 1,
H: Height in the direction perpendicular to the optical axis AX X (H): Displacement amount in the optical axis AX direction (sag) at the position of the height H C ₀ : Paraxial curvature (= 1 / ri)
ε: quadratic surface parameter j: degree of aspheric surface,
Aj: j-th order aspheric coefficient.

Therefore, data relating to the aspheric surface (aspherical surface data) is shown in Table 2 below. However, the coefficient of the term which is not described is “0” (zero), and “E−n” = “× 10 ⁻ⁿ ” for all data.

<2-3. Movement of each lens group in the variable magnification optical system (Example 1)>
About zooming
Here, the movement of each lens group (GR1 to GR4) will be described with reference to FIG. Usually, during zooming or the like (magnification or the like), the zooming optical system 11 changes the interval between the lens groups along the optical axis AX. For example, the zooming optical system 11 in FIG. 1 moves at least some of the lens groups in each lens group during zooming. Specifically, the first lens group GR1 to the fourth lens group GR4 (that is, all the lens groups) move toward the object side (however, the second lens group GR2 moves toward the image side and then moves toward the image side) To do).

  During such zooming, the distance between the lens groups (inter-group distance) varies. Therefore, in FIG. 1, only the shaft upper surface interval (di) in which the interval variation occurs with zooming is numbered. Specifically, d8, d14, d27, and d31 are illustrated. Further, an arrow “MMi” in the drawing indicates movement of each lens group from the telephoto end state (W) to the intermediate focus state (M), and further from the intermediate focus state (M) to the telephoto end state (T). This is shown schematically. Note that i of MMi indicates the order from the object side to the image side. Therefore, it corresponds to the order of each lens group.

  2 to 4 show aberrations of the variable magnification optical system 11 during zooming. Specifically, FIG. 2 (FIGS. 2A to 2C) shows aberration in the wide-angle end state (W), FIG. 3 (FIGS. 3A to 3C) shows aberration in the intermediate focal length state (M), and FIG. 4A to 4C) show aberrations in the telephoto end state (T).

  2A, 3A, and 4A show spherical aberration (SA) and sine condition (SC). The line d in the figure indicates the spherical aberration [unit; mm] with respect to the d line, and the broken line SC indicates the unsatisfactory sine condition [unit; mm]. In these figures, FNO (F number) is also indicated.

  2B, 3B and 4B show astigmatism. A broken line DM in the figure indicates astigmatism [unit: mm] with respect to the d-line on the meridional surface. A line DS indicates astigmatism [unit: mm] with respect to the d line on the sagittal surface. In these drawings, “Y ′” [unit: mm] which is the maximum image height (distance from the optical axis AX) on the light receiving surface of the image sensor SR is also described.

  2C, FIG. 3C, and FIG. 4C show distortion. The solid line in the figure indicates the distortion [unit:%] with respect to the d line. In these figures, “Y ′” is also written.

[3. Example of various features of the present invention]
As described above, according to the present invention, from the object side to the image side, at least the first lens group GR1 having positive power, the second lens group GR2 having negative power, and the first lens group having positive power. A variable magnification optical system having three lens groups GR3. The first lens group GR includes a first optical prism PR, while the third lens group GR3 includes a second optical prism PR ′.

  Furthermore, in the variable magnification optical system of the present invention, the most image side lens (the eleventh lens L11) in the third lens group GR3 has at least one aspherical surface (in Example 1, s26 and s27 are aspherical surfaces). ).

  When trying to meet the recent demand for downsizing of the imaging device (digital camera 29, etc.), the variable magnification optical system 11 in the imaging device can be downsized by various methods. However, when the variable magnification optical system 11 is reduced in size, the distance between the groups is generally shortened, so that the power (refractive power) required for each lens group is relatively increased. In particular, as in the variable power optical system 11 of the present invention, when the first lens group GR1 to the third lens group GR3 have a positive, negative, and positive power arrangement, the power required for each lens group increases. It's easy to do.

  As described above, when the power of the lens group is increased, various aberrations are easily generated. In particular, off-axis aberrations (coma aberration, astigmatism, etc.) due to off-axis rays separated from the optical axis AX are remarkable. However, when the most image side lens (the eleventh lens L11) in the third lens group GR3 has at least one aspherical surface as in the variable magnification optical system 11 of the present invention, this aspherical surface is used. Thus, off-axis aberrations can be effectively corrected (aberration correction) (see FIGS. 2 to 4). Therefore, the present invention provides a small (compact) variable magnification optical system 11 while effectively correcting aberrations.

The aspherical surface (s27) on the image side of the most image side lens (the eleventh lens L11) only needs to satisfy the conditional expression (1).
2 <(| X | − | X ₀ |) × 100 / {C ₀ × (N′−N) × f3} <100
... Conditional expression (1)
However,
X: aspherical surface shape X _0: surface shape C ₀ aspheric reference spherical surface curvature of the aspherical surface of the reference sphere N: refractive power of the object side in the aspheric medium N ': the image side in the aspheric medium Refracting power of f3: focal length of the third lens unit [unit: mm]
It is.

  Conditional expression (1) is an expression relating to the aspherical shape required for the positive power adjustment in the third lens group GR3. That is, the conditional expression (1) represents a shape capable of exhibiting positive power necessary for aberration correction (correction of off-axis aberration and the like). This conditional expression (1) is based on the power of the most image side lens (eleventh lens 11) of the third lens group GR3, and the variable magnification optical system 11 is reduced in size (for example, the total length of the variable magnification optical system 11). The range for harmonizing the high performance of the aberration correction and the aberration correction is specified.

  When the upper limit value is exceeded (when exceeding) in this conditional expression (1), it means that the aspherical surface has a relatively strong power (that is, the third lens group GR3 can exhibit a relatively large power). Therefore, the total length of the variable magnification optical system 11 is relatively short.

  However, if the power exhibited by the third lens group GR3 is high, various aberrations (coma aberration and the like) are likely to occur. Then, when the upper limit value of the conditional expression (1) is exceeded, the variable magnification optical system 11 can relatively easily generate aberrations, but the total length can be reduced.

  On the other hand, when the lower limit value is exceeded (lower) in the conditional expression (1), it means that the aspherical surface has a relatively weak power (that is, the third lens group GR3 can exhibit only a relatively small power). In such a case, an aberration caused by off-axis rays from the third lens group GR3 is less likely to occur due to a small power.

  However, if the power exerted by the third lens group GR3 is weak, the total length of the variable magnification optical system 11 also becomes long. Then, when the lower limit of conditional expression (1) is exceeded, the variable magnification optical system 11 can be relatively large in size, but can suppress the occurrence of various aberrations.

  From the above, when the lower limit value of conditional expression (1) is exceeded, the occurrence of various aberrations is suppressed. On the other hand, when the lower limit value of conditional expression (1) is exceeded, excessive enlargement of the lens unit is suppressed. The For this reason, within the range of conditional expression (1), the present invention provides a miniaturized variable magnification optical system 11 while suppressing the occurrence of aberrations (while improving performance).

  As described above, when the upper limit value is exceeded in the conditional expression (1), the third lens group GR3 exhibits a relatively large power. For this reason, the light beam passing position in the second optical prism PR ′ is relatively close to the optical axis AX, and the size of the second optical prism PR ′ itself is reduced. However, the focal length becomes shorter as the power of the third lens group GR3 increases. Therefore, although the second optical prism PR 'is reduced in size, it is difficult to secure a space for arranging the second optical prism PR' in the third lens group GR3.

  On the other hand, when the lower limit is exceeded in this conditional expression (1), the third lens group GR3 can exhibit only a relatively small power. For this reason, the light beam passing position in the second optical prism PR ′ is relatively distant from the optical axis AX, and the size of the second optical prism PR ′ itself is increased. However, the focal length increases as the power of the third lens group GR3 decreases. Therefore, it becomes easy to secure a space for arranging the enlarged second optical prism PR ′ in the third lens group GR3. However, the total length of the variable magnification optical system 11 itself becomes long.

  As described above, when the upper limit value of the conditional expression (1) is not reached, a space for disposing the second optical prism PR ′ can be easily secured, whereas when the lower limit value of the conditional expression (1) is exceeded, the variable power optical system An excessive increase in size of the system 11 itself can be suppressed. Therefore, within the range of the conditional expression (1), the present invention is a variable power optical system that can easily secure the arrangement space for the second optical prism PR ′ while allowing the second optical prism PR ′ to be designed in a relatively small size. It becomes system 11. That is, the variable magnification optical system 11 of the present invention has a second optical prism PR ', but is downsized.

  Further, the number of aspheric surfaces is not limited. In other words, the aspheric surfaces may be formed on the object side surface (s26) and the image side surface (s27) of the most image side lens (the eleventh lens L11) in the third lens group GR3. However, various aberration corrections can be effectively performed as long as at least the image side surface (s27) of the eleventh lens L11 satisfies the conditional expression (1).

  Further, in the vicinity of the image side surface (s27) that is further away from the optical aperture stop ST, the on-axis light beam and the off-axis light beam are dissociated. Therefore, astigmatism or the like is likely to occur. However, astigmatism can be effectively corrected if the image side surface (s27) has an aspherical shape as in the present invention.

Note that the variable magnification optical system 11 of Example 1 [image side surface (s27) of the eleventh lens 11] corresponds to the conditional expression (1) as follows (see FIG. 23 described later). .
(| X | − | X ₀ |) × 100 / {C ₀ × (N′−N) × f3} = 42.9 on the image side surface (s27)

The values of X, X ₀ , C ₀ , N, N ′, and f3 in the conditional expression (1) are as follows (see FIG. 24 described later).
X = 0.059491
X ₀ = 0.149167
C ₀ = 0.02336734
N = 1.62017
N ′ = 1.00000
f3 = 14.443653

  In the variable magnification optical system 11 of the present invention, the third lens group GR3 may include at least four or more lenses. With such a configuration, even if the power of the third lens group GR3 increases and various aberrations are likely to occur due to downsizing (compacting), the aberrations are effectively reduced by a plurality of lenses. This is because it can be corrected. In other words, with this configuration, the present invention provides a variable magnification optical system 11 that can disperse the burden of aberration correction among a plurality of lenses.

[Embodiment 2]
A second embodiment of the present invention will be described. In addition, about the member which has the same function as the member used in Embodiment 1, the same code | symbol is attached and the description is abbreviate | omitted.

  In the variable magnification optical system 11 (Example 1) in Embodiment 1, the third lens group GR3 includes at least four or more lenses. As shown in FIG. 1, one lens (seventh lens L7) is positioned on the object side of the second optical prism PR ′, and four lenses (eighth lens L8 to eleventh lens 11) are positioned on the image side. ) Is located.

[1. About other variable magnification optical systems)
However, the variable magnification optical system 11 of the present invention is not limited to such a position (arrangement position). Therefore, a variable magnification optical system 11 (Example 2) having an arrangement position different from that of Example 1 will be described below with reference to FIG.

  In FIG. 7, the second optical prism PR ′ in the first embodiment (see FIG. 1) is omitted, and the air interval is clearly shown. In addition, the variable magnification optical system 11 of Example 2 includes, in order from the object to be imaged, a first lens group GR1, a second lens group GR2, a third lens group GR3, and a stationary fourth lens group GR4. The optical power arrangement is “positive / negative / positive / positive”. Further, the image sensor SR is fixed to the cover glass CG included in the fourth lens group GR4 (the image sensor SR is stationary).

<About the variable magnification optical system of Example 2 (see FIG. 7)>
<About the first lens group>
The first lens group GR1 includes, in order from the object side, a first lens L1, an optical prism PR, a second lens L2, and a third lens L3. Each lens has the following characteristics.
First lens L1: Negative meniscus lens convex on the object side Second lens L2 Positive lens convex on both sides Third lens L3: Positive meniscus lens convex on the object side

<About the second lens group>
The second lens group GR2 includes a fourth lens L4, a fifth lens L5, and a sixth lens L6 in order from the object side. Each lens has the following characteristics.
Fourth lens L4: negative lens concave on both sides (s10 is aspheric)
・ Fifth lens L5: negative lens concave on both sides ・ Sixth lens L6: positive lens convex on both sides Note that the fifth lens L5 and the sixth lens L6 constitute a cemented lens by cementing s12 and s13. Yes.

<About the third lens group>
The third lens group GR3 includes, in order from the object side, an optical aperture stop ST (also expressed as s15, integrated with the third lens group GR3), a seventh lens L7, an eighth lens L8, a ninth lens L9, a tenth lens L10, And an eleventh lens (most image side lens) L11. Each lens has the following characteristics.
Seventh lens L7: Positive lens convex on both sides (s16 is aspheric)
Eighth lens L8: negative meniscus lens concave on the object side ninth lens L9 positive positive lens on both sides tenth lens L10 negative negative lens on both sides eleventh lens L11 negative negative meniscus lens on the object side (s24・ S25 is aspheric)
The seventh lens L7 and the eighth lens L8 constitute a cemented lens by cementing s17 and s18, and the ninth lens L9 and the tenth lens L10 are cemented lenses by cementing s21 and s22. Is configured.

  Although not shown, an optical prism, a reflection mirror, or the like that bends the light beam emitted from the eighth lens L8 is provided between the eighth lens L8 and the ninth lens L9 (air interval). ing.

<About the fourth lens group>
The fourth lens group GR4 includes, in order from the object side, a twelfth lens L12 and a cover glass CG (a glass having a two-surface structure having s28 and s29). The twelfth lens L12 has the following characteristics.
Twelfth lens L12: positive meniscus lens convex on the object side (s26 and s27 are aspheric surfaces)

<< Construction data of variable magnification optical system (Example 2) >>
Next, construction data of the variable magnification optical system 11 of Example 2 will be described with reference to Tables 3 and 4. Tables 3 and 4 are expressed in the same manner as Tables 1 and 2 above.

<About the movement of each lens group in the variable magnification optical system (Example 2)>
About zooming
As shown in FIG. 7, the zoom optical system 11 of Example 2 moves at least a part of the lens groups in each lens group in zooming. Specifically, the first lens group GR1 to the third lens group GR3 move toward the object side (however, the second lens group GR2 moves toward the object side and then moves toward the image side). Therefore, in FIG. 7, only the shaft upper surface interval (di) in which the interval variation occurs with zooming is numbered. Specifically, d8, d14, and d25 are illustrated.

  8 to 10 show aberrations of the variable magnification optical system 11 of Example 2 during zooming. 8 to 10 are expressed in the same manner as in FIGS.

[2. Example of various features of the present invention]
As described above, the variable magnification optical system 11 according to the second embodiment includes at least four or more lenses (specifically, the seventh lens L7 to the eleventh lens L11) as in the first embodiment. Has GR3. Both surfaces (s24 and s25) of the most image side lens (the eleventh lens L11) of the third lens group GR3 are aspheric. In addition, the image side surface (s25) satisfies the condition of the conditional expression (1) (see FIG. 23). Therefore, the variable magnification optical system 11 of Example 2 has the same effects as the variable magnification optical system 11 of Embodiment 1.

  Furthermore, the variable magnification optical system 11 of Example 2 includes an optical prism, a reflecting mirror, etc. (second optical axis changing element; non-optical element) in the third lens group GR3 (between the eighth lens L8 and the ninth lens L9). (Shown) is provided. The seventh lens L7 and the eighth lens L8 are located on the object side such as the optical prism. That is, the variable magnification optical system 11 of the present invention includes a plurality of lenses on the object side of the third lens group GR3 relative to the optical prism or the like.

  In general, in the variable magnification optical system 11 having the “positive / negative / positive / positive” power arrangement as in the present invention, the light beam immediately after the second lens group GR2 is converged by the first lens group GR1. Must be released. Therefore, the second lens group GR2 has a relatively strong negative power. As a result, the combined power of the second lens group GR2 and the first lens group GR1 becomes negative. Then, divergent light is emitted from the second lens group GR2.

  Therefore, in order to effectively converge the emitted diverging light, in the variable magnification optical system 11 of the present invention, a plurality of lenses are positioned closer to the object side than the optical prism or the like in the third lens group GR3. It has become. With such a configuration, each lens can converge the diverging light step by step and guide it to an optical prism or the like. Therefore, the distance from the second lens group GR2 to the third lens group GR3 (particularly, the distance from the second lens group GR2 to the optical prism of the third lens group GR) is relatively short. Therefore, the present invention as in the second embodiment is a variable magnification optical system 11 in which the distance between the second lens group GR2 and the third lens group GR3 is narrow.

  Further, when such a variable magnification optical system 11 is accommodated in the housing of the digital camera 29 as shown in FIGS. 5 and 6, the height direction U of the digital camera 29 is shortened. That is, the digital camera 29 including the variable magnification optical system 11 of the present invention is downsized.

[Embodiment 3]
Embodiment 3 of the present invention will be described. In addition, about the member which has the same function as the member used in Embodiment 1 * 2, the same code | symbol is attached and the description is abbreviate | omitted.

[1. About other variable magnification optical systems)
There is another configuration in which the height direction U of the digital camera 29 is further shortened. For example, the second lens group GR2 does not move excessively during zooming (magnification). First, a variable magnification optical system (Examples 3 to 5) having such a configuration will be described below.

  As in the second embodiment, the variable magnification optical system 11 according to the third to fifth embodiments sequentially includes the first lens group GR1, the second lens group GR2, the third lens group GR3, and the stationary first lens group GR1 in order from the object to be imaged. It has four lens groups GR4 and has an optical power arrangement of “positive / negative / positive / positive”. The second optical prism included in the third lens group GR3 is also omitted as in the second embodiment.

<Variation Optical System of Example 3 (see FIG. 11)>
<About the first lens group>
The first lens group GR1 includes, in order from the object side, a first lens L1, an optical prism PR, a second lens L2, and a third lens L3. Each lens has the following characteristics.
First lens L1: Negative meniscus lens convex on the object side Second lens L2 Positive lens convex on both sides Third lens L3: Positive meniscus lens convex on the object side

<About the second lens group>
The second lens group GR2 includes a fourth lens L4, a fifth lens L5, and a sixth lens L6 in order from the object side. Each lens has the following characteristics.
Fourth lens L4: negative lens concave on both sides (s10 is aspheric)
・ Fifth lens L5: negative lens concave on both sides ・ Sixth lens L6: positive lens convex on both sides Note that the fifth lens L5 and the sixth lens L6 constitute a cemented lens by cementing s12 and s13. Yes.

<About the third lens group>
The third lens group GR3 includes, in order from the object side, an optical aperture stop ST (also expressed as s15, integrated with the third lens group GR3), a seventh lens L7, an eighth lens L8, a ninth lens L9, a tenth lens L10, And an eleventh lens (most image side lens) L11. Each lens has the following characteristics.
Seventh lens L7: Positive lens convex on both sides (s16 is aspheric)
The eighth lens L8: a negative meniscus lens concave on the object side. The ninth lens L9: a negative meniscus lens convex on the object side. A tenth lens L10: a positive meniscus lens convex on the object side. An eleventh lens L11: positive positive on the object side. Meniscus lens (s24 and s25 are aspherical)
The seventh lens L7 and the eighth lens L8 constitute a cemented lens by joining s17 and s18, and the ninth lens L9 and the tenth lens L10 are joined by joining s21 and s22. It constitutes a cemented lens.

  Although not shown, an optical prism, a reflection mirror, or the like that bends the light beam emitted from the eighth lens L8 is provided between the eighth lens L8 and the ninth lens L9 (air interval). ing.

<About the fourth lens group>
The fourth lens group GR4 includes, in order from the object side, a twelfth lens L12 and a cover glass CG (a glass having a two-surface structure having s28 and s29). The twelfth lens L12 has the following characteristics.
Twelfth lens L12: positive lens convex on the object side (s26 and s27 are aspheric surfaces)

<< Construction data of variable magnification optical system (Example 3) >>
Next, construction data of the variable magnification optical system 11 of Example 3 will be described with reference to Tables 5 and 6. Tables 5 and 6 are expressed in the same manner as Tables 1 and 2 above.

<< About the movement of each lens group in the variable magnification optical system (Example 3) >>
<< About zooming >>
As shown in FIG. 11, the zoom optical system 11 of Example 3 moves at least a part of the lens groups (first lens group GR1 to third lens group GR3) in each lens group to the object side in zooming. It is moved. Therefore, in FIG. 11, only the shaft upper surface interval (di) in which the interval variation occurs with zooming is numbered. Specifically, d8, d14, and d25 are illustrated.

  12 to 14 show aberrations of the variable magnification optical system 11 of Example 3 during zooming. 12 to 14 are expressed in the same manner as in FIGS.

<About the variable magnification optical system of Example 4 (see FIG. 15)>
<About the first lens group>
The first lens group GR1 includes, in order from the object side, a first lens L1, an optical prism PR, a second lens L2, and a third lens L3. Each lens has the following characteristics.
First lens L1: Negative meniscus lens convex on the object side Second lens L2: Positive lens convex on both sides Third lens L3: Positive lens convex on both sides

<About the second lens group>
The second lens group GR2 includes a fourth lens L4, a fifth lens L5, and a sixth lens L6 in order from the object side. Each lens has the following characteristics.
Fourth lens L4: negative lens concave on both sides (s10 is aspheric)
・ Fifth lens L5: negative lens concave on both sides ・ Sixth lens L6: positive lens convex on both sides Note that the fifth lens L5 and the sixth lens L6 constitute a cemented lens by cementing s12 and s13. Yes.

<About the third lens group>
The third lens group GR3 includes, in order from the object side, an optical aperture stop ST (also expressed as s15, integrated with the third lens group GR3), a seventh lens L7, an eighth lens L8, a ninth lens L9, a tenth lens L10, And an eleventh lens (most image side lens) L11. Each lens has the following characteristics.
Seventh lens L7: Positive lens convex on both sides (s16 is aspheric)
The eighth lens L8: a negative meniscus lens concave on the object side. The ninth lens L9: a negative meniscus lens convex on the object side. A tenth lens L10: a positive meniscus lens convex on the object side. An eleventh lens L11: positive positive on the object side. Meniscus lens (s24 and s25 are aspherical)
The seventh lens L7 and the eighth lens L8 constitute a cemented lens by cementing s17 and s18, and the ninth lens L9 and the tenth lens L10 are cemented lenses by cementing s21 and s22. Is configured.

  Although not shown, an optical prism, a reflection mirror, or the like that bends the light beam emitted from the eighth lens L8 is provided between the eighth lens L8 and the ninth lens L9 (air interval). ing.

<About the fourth lens group>
The fourth lens group GR4 includes, in order from the object side, a twelfth lens L12, a thirteenth lens L13, and a cover glass CG (a glass having a two-surface structure having s30 and s31). Each lens has the following characteristics.
The twelfth lens L12: a positive lens convex on both sides (s26 and s27 are aspheric surfaces)
-13th lens L13: negative lens concave on both sides

<< Construction data of variable magnification optical system (Example 4) >>
Next, construction data of the variable magnification optical system 11 of Example 4 will be described with reference to Tables 7 and 8. Tables 7 and 8 are expressed in the same manner as Tables 1 and 2 above.

<< About the movement of each lens group in the variable magnification optical system (Example 4) >>
<< About zooming >>
As shown in FIG. 15, in the zooming optical system 11 of Example 4, at least a part of the lens groups (the first lens group GR1 to the third lens group GR3) in each lens group is moved to the object side during zooming. It is moved. Accordingly, in FIG. 15, only the shaft upper surface distance (di) where the distance variation occurs with zooming is numbered. Specifically, d8, d14, and d25 are illustrated.

  16 to 18 show aberrations of the zoom optical system 11 of Example 4 during zooming. 16 to 18 are expressed in the same manner as FIGS. 2 to 4.

<Variation Optical System of Example 5 (see FIG. 19)>
<About the first lens group>
The first lens group GR1 includes, in order from the object side, a first lens L1, an optical prism PR, a second lens L2, and a third lens L3. Each lens has the following characteristics.
First lens L1: Negative meniscus lens convex on the object side Second lens L2 Positive lens convex on both sides Third lens L3: Positive meniscus lens convex on the object side

<About the second lens group>
The second lens group GR2 includes a fourth lens L4, a fifth lens L5, and a sixth lens L6 in order from the object side. Each lens has the following characteristics.
Fourth lens L4: negative meniscus lens convex on the object side (s10 is aspheric)
・ Fifth lens L5: negative lens concave on both sides ・ Sixth lens L6: positive lens convex on both sides Note that the fifth lens L5 and the sixth lens L6 constitute a cemented lens by cementing s12 and s13. Yes.

<About the third lens group>
The third lens group GR3 includes, in order from the object side, an optical aperture stop ST (also expressed as s15, integrated with the third lens group GR3), a seventh lens L7, an eighth lens L8, a ninth lens L9, a tenth lens L10, And an eleventh lens (most image side lens) L11. Each lens has the following characteristics.
Seventh lens L7: Positive lens convex on both sides (s16 is aspheric)
The eighth lens L8: a negative meniscus lens concave on the object side. The ninth lens L9: a negative meniscus lens convex on the object side. A tenth lens L10: a positive meniscus lens convex on the object side. An eleventh lens L11: positive positive on the object side. Meniscus lens (s24 and s25 are aspherical)
The seventh lens L7 and the eighth lens L8 constitute a cemented lens by cementing s17 and s18, and the ninth lens L9 and the tenth lens L10 are cemented lenses by cementing s21 and s22. Is configured.

  Although not shown, an optical prism, a reflection mirror, or the like that bends the light beam emitted from the eighth lens L8 is provided between the eighth lens L8 and the ninth lens L9 (air interval). ing.

<About the fourth lens group>
The fourth lens group GR4 includes, in order from the object side, a twelfth lens L12, a thirteenth lens L13, and a cover glass CG (a glass having a two-surface structure having s30 and s31). Each lens has the following characteristics.
The twelfth lens L12: a positive lens convex on both sides (s26 and s27 are aspheric surfaces)
13th lens L13: negative meniscus lens concave on the object side

<< Construction data of variable magnification optical system (Example 5) >>
Next, construction data of the variable magnification optical system 11 of Example 5 will be described with reference to Tables 9 and 10. Tables 9 and 10 are expressed in the same manner as Tables 1 and 2 above.

<< About the movement of each lens group in the variable magnification optical system (Example 5) >>
<< About zooming >>
As shown in FIG. 19, in the zooming optical system 11 of the fifth embodiment, at the time of zooming, at least a part of the lens groups (the first lens group GR1 to the third lens group GR3) in each lens group is moved to the object side. It is moved. Accordingly, in FIG. 19, only the shaft upper surface distance (di) in which the distance variation occurs with zooming is numbered. Specifically, d8, d14, and d25 are illustrated.

  20 to 22 show aberrations of the variable magnification optical system 11 of Example 6 during zooming. 20 to 22 are expressed in the same manner as FIGS. 2 to 4.

[2. Example of various features of the present invention]
As described above, the variable magnification optical system 11 of Examples 3 to 5 includes at least four or more lenses (specifically, the seventh lens L7 to the eleventh lens L11), as in Examples 1 and 2. A third lens group GR3 is included. At least one surface (s24 / s25) of the most image side lens (eleventh lens L11) of the third lens group GR3 is aspheric. In addition, the image side surface (s25) satisfies the condition of the conditional expression (1) (see FIG. 23). Therefore, the variable magnification optical system 11 of Examples 3 to 5 achieves the same effects as the variable magnification optical system 11 of the first embodiment.

  Further, the variable magnification optical system 11 of the third to fifth embodiments, like the second embodiment, includes an optical prism, a reflecting mirror, and the like (first lens) in the third lens group GR3 (between the eighth lens L8 and the ninth lens L9). 2 optical axis changing elements) are provided, and the seventh lens L7 and the eighth lens L8 are positioned on the object side such as the optical prism. Therefore, the variable magnification optical system 11 of Examples 3 to 5 also exhibits the same function and effect as the variable magnification optical system 11 of Embodiment 2.

In particular, the zoom optical system 11 of Examples 3 to 5 satisfies the following conditional expression (2) during zooming (magnification).
0.1 ≦ MV2 / Lw ≦ 0.5 Conditional expression (2)
However,
MV2: Amount of movement of the second lens group GR2 [unit: mm]
Lw: Full length of the variable magnification optical system 11 in the wide-angle end state (W) [unit: mm]
It is.

  Conditional expression (2) defines the moving amount MV2 of the second lens group GR2 by the total length Lw of the variable magnification optical system 11 in the wide-angle end state (W). This conditional expression (2) is based on the amount of movement MV2 of the second lens group GR2, and is used to reduce the size of the variable magnification optical system 11 (for example, shorten the overall length of the variable magnification optical system 11) and to correct aberrations. A range for harmony with high performance is defined.

  When the ratio of the movement amount MV2 of the second lens group GR2 to the total length Lw of the variable magnification optical system 11 exceeds the upper limit value of the conditional expression (2), the second lens group GR2 has a relatively long distance for zooming. Moving. In such a case, the variable magnification optical system 11 can exhibit various magnifications as the movement amount MV2 increases.

  However, if the movement amount MV2 of the second lens group GR2 is too long, it is necessary to secure a front-rear (object-side / image-side) interval of the second lens group GR2. Therefore, when the upper limit value of conditional expression (2) is exceeded, the variable magnification optical system 11 exhibits various magnifications, although the total length is relatively long.

  On the other hand, when the ratio of the movement amount MV2 of the second lens group GR2 to the total length Lw of the variable magnification optical system 11 exceeds the lower limit value of the conditional expression (2), the second lens group GR2 is relatively short for zooming. Move only distance. In such a case, the front-rear distance (space) of the second lens group GR2 can be shortened as the movement amount MV2 decreases. Therefore, the total length of the variable magnification optical system 11 is also shortened.

  However, if the distance between the front and rear of the second lens group GR2 is shortened, the magnification setting range of the variable magnification optical system 11 based on the movement of the second lens group GR2 is narrowed. That is, the variable magnification optical system 11 cannot exhibit various magnifications. For this reason, when the lower limit value of conditional expression (2) is exceeded, the variable magnification optical system 11 has a relatively short overall length, although the width of magnification setting is narrowed.

  From the above, when the conditional expression (2) is below the upper limit value, an excessive enlargement of the variable magnification optical system 11 is suppressed, whereas when the conditional expression (2) is above the lower limit value, the variable magnification optical system 11. Various magnifications can be secured. Therefore, within the range of conditional expression (2), the present invention provides a variable magnification optical system 11 that is downsized while ensuring the type of magnification.

  As described above, when the upper limit value is exceeded in this conditional expression (2), the second lens group GR2 moves relatively long distance, which is advantageous in correcting various aberrations. However, as described above, as the movement amount MV2 increases, the total length of the variable magnification optical system 11 also increases. On the other hand, if the lower limit is exceeded in conditional expression (1), the second lens group GR2 moves only a relatively short distance, which is disadvantageous in correcting various aberrations. However, as described above, as the movement amount MV2 decreases, the total length of the variable magnification optical system 11 also decreases. For this reason, within the range of the conditional expression (2), the present invention becomes a miniaturized variable magnification optical system 11 while performing good aberration correction.

In addition, it is as follows when the lens unit 1 of Examples 3-5 is made to correspond to conditional expression (2) (refer FIG. 23).
-MV2 / Lw of Example 3 = 0.19
-MV2 / Lw = 0.20 in Example 4
-MV2 / Lw of Example 5 = 0.26

Further, the value of MV2 · Lw in the conditional expression (2) is as follows (see FIG. 24 described later).
-MV2 of Example 3 = 14.349, Lw of Example 3 = 75.347
-MV2 of Example 4 = 15.165, Lw of Example 4 = 75.000
-MV2 of Example 5 = 16.950, Lw of Example 5 = 65.470

[Other embodiments]
The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the zoom ratio (magnification ratio) in the lens unit 1 of the present invention is not particularly limited, but it is preferable that the following conditional expression (3) is satisfied.

Conditional expression (3) is as follows.
5.0 <ft / fw
However,
ft: focal length of the entire variable magnification optical system at the telephoto end fw: focal length of the entire variable magnification optical system at the wide angle end.

  Conditional expression (3) represents the zoom ratio of the variable magnification optical system 11 (and thus the lens unit 1). Then, satisfying this conditional expression (3) has a considerably higher zoom ratio than the zoom ratio (for example, about 3 times) of the conventional digital camera 29. That is, the present invention is a lens unit 1 that exhibits the above-described effects while having a high zoom ratio. This increases the significance of the zoom performance (magnification performance) in the variable magnification optical system 11 of the present invention, and makes it possible to achieve user benefits.

In the above description, conditional expressions (1) to (3) have been described. Accordingly, FIG. 23 shows values of the conditional expressions (1) to (3) corresponding to the first to fifth embodiments. FIG. 24 shows the values of X, X ₀ , C ₀ , N, N ′, f3, MV2, Lw, ft, and fw necessary for obtaining the values of conditional expressions (1) to (3). Then, as shown in FIG. 23, the variable magnification optical system 11 of Examples 1 and 2 of the present invention satisfies the conditional expressions (1) and (3). It can be seen that the variable power optical system 11 of No. 5 satisfies the conditional expressions (1) to (3).

  Further, the zoom optical system 11 according to the present invention has an inter-group distance between the first lens group GR1 and the third lens group GR3 when the first lens group GR1 and the third lens group GR3 are moved by zooming. May be left unchanged. For example, the first lens group GR1 and the third lens group GR3 may be integrated with each other via a lens frame (connecting portion; not shown), so that both may move simultaneously.

  As described above, when the first lens group GR and the third lens group GR are connected (linked), the configuration (arrangement configuration) required for disposing both the lens groups GR1 and GR3 is simplified. Is done. Therefore, both lens groups GR1 and GR3 can be accommodated in, for example, the same lens barrel (not shown). As a result, the lens barrel tends to be relatively compact.

  In addition, a power source for movement (such as a motor) corresponding to each of the first lens group GR1 and the third lens GR3 is not required (a configuration required for movement (movement configuration) is simplified). That is, the two lens groups of the first lens group GR1 and the third lens GR3 can be moved with only a single power source.

  Further, in order to make the light incident on the image pickup element SR light with high telecentricity, the variable magnification optical system 11 of the present invention includes the first lens group GR1 to the third lens having a positive, negative, and positive power arrangement. Next to GR3 (on the image side), a positive fourth lens group GR4 is disposed (arranged). With such a configuration, shading that can occur in the image sensor SR can be suppressed.

  Further, each lens (Li) of the lens group (GRi) in the variable magnification optical system 11 may be formed of a resin (plastic or the like). In particular, it is preferable that the most image side lens in the third lens group GR3 is made of resin. This is because if the lens is made of resin, it is easy to form an aspherical surface. In addition, mass production of lenses is possible, leading to cost reduction of the variable magnification optical system 11 (and thus the digital camera 29). In addition, although the material of resin is not specifically limited, For example, a polycarbonate etc. are mentioned.

  By the way, the compact variable magnification optical system 11 of the present invention is used in various imaging devices (silver halide photographic cameras, digital still cameras, etc.) and digital input devices (for example, digital devices equipped with imaging devices). Therefore, the imaging apparatus using the variable magnification optical system 11 of the present invention is compact. Further, the ratio of the variable magnification optical system 11 occupying the limited volume in the housing of the imaging apparatus or the like is relatively small. For this reason, various components (electronic components and the like) can be arranged in a housing with a margin such as an imaging device (effective utilization of the housing volume can be achieved). Therefore, a high-performance imaging device equipped with various components can be realized.

  5 and 6 includes a first lens group GR1 and a third lens group GR3 that fix the imaging element SR and include an optical axis changing element (optical prism PR or reflecting mirror MR). A configuration in which zooming or the like is performed so as to be moved may be used. Further, the imaging device 29 may be configured to perform zooming or the like by fixing the first lens group GR1 and the third lens group GR3 including the optical axis changing element and moving the imaging element SR.

  Recently, various digital cameras and video cameras that can handle both moving images and still images have been developed. Therefore, the present invention means all image pickup apparatuses that can convert an optical image formed on the light receiving surface of the image pickup device into an electric signal. Therefore, for example, a digital camera, a digital movie camera, a web camera, a mobile phone, a personal digital assistant (PDA) and the like are assumed. A web camera is a camera connected to an electronic device that can send and receive images via a network. However, either an open type or a private type may be used, and either a method of directly connecting to a network or a method of connecting via a personal computer or the like may be used.

FIG. 3 is a lens configuration diagram of a lens unit including the variable magnification optical system according to Example 1. FIG. 6 is a spherical aberration diagram of the variable magnification optical system (Example 1) in the wide-angle end state (W). FIG. 6 is an astigmatism diagram of the variable magnification optical system (Example 1) in the wide-angle end state (W). FIG. 6 is a distortion diagram of the variable magnification optical system (Example 1) in the wide-angle end state (W). FIG. 6 is a spherical aberration diagram of the variable magnification optical system (Example 1) in the intermediate focal length state (M). FIG. 6 is an astigmatism diagram of the variable magnification optical system (Example 1) in the intermediate focal length state (M). FIG. 6 is a distortion diagram of the variable magnification optical system (Example 1) in the intermediate focal length state (M). FIG. 6 is a spherical aberration diagram of the variable magnification optical system (Example 1) in the telephoto end state (T). FIG. 6 is an astigmatism diagram of the variable magnification optical system (Example 1) in the telephoto end state (T). FIG. 6 is a distortion diagram of the variable magnification optical system (Example 1) in the telephoto end state (T). It is a digital camera of each embodiment, and is a schematic structure figure from the back. It is a digital camera of each embodiment, and is a schematic structure figure from the side. FIG. 6 is a lens configuration diagram of a lens unit including the variable magnification optical system according to Example 2. FIG. 6 is a spherical aberration diagram of the variable magnification optical system (Example 2) in the wide-angle end state (W). FIG. 7 is an astigmatism diagram of the variable magnification optical system (Example 2) in the wide-angle end state (W). FIG. 6 is a distortion diagram of the variable magnification optical system (Example 2) in the wide-angle end state (W). FIG. 6 is a spherical aberration diagram of the variable magnification optical system (Example 2) in the intermediate focal length state (M). FIG. 6 is an astigmatism diagram of the variable magnification optical system (Example 2) in the intermediate focal length state (M). It is a distortion aberration figure of the variable magnification optical system (Example 2) which became the intermediate focal distance state (M). FIG. 6 is a spherical aberration diagram of the variable magnification optical system (Example 2) in the telephoto end state (T). FIG. 6 is an astigmatism diagram of the variable magnification optical system (Example 2) in the telephoto end state (T). FIG. 6 is a distortion diagram of the variable magnification optical system (Example 2) in the telephoto end state (T). FIG. 6 is a lens configuration diagram of a lens unit including the variable magnification optical system according to Example 3. FIG. 12 is a spherical aberration diagram of the variable magnification optical system (Example 3) in the wide-angle end state (W). FIG. 6 is an astigmatism diagram of the variable magnification optical system (Example 3) in the wide-angle end state (W). FIG. 6 is a distortion diagram of the variable magnification optical system (Example 3) in the wide-angle end state (W). FIG. 10 is a spherical aberration diagram of the variable magnification optical system (Example 3) in the intermediate focal length state (M). FIG. 6 is an astigmatism diagram of the variable magnification optical system (Example 3) in the intermediate focal length state (M). FIG. 12 is a distortion diagram of the variable magnification optical system (Example 3) in the intermediate focal length state (M). FIG. 12 is a spherical aberration diagram of the variable magnification optical system (Example 3) in the telephoto end state (T). FIG. 6 is an astigmatism diagram of the variable magnification optical system (Example 3) in the telephoto end state (T). FIG. 12 is a distortion diagram of the variable magnification optical system (Example 3) in the telephoto end state (T). FIG. 6 is a lens configuration diagram of a lens unit including the variable magnification optical system according to Example 4. FIG. 12 is a spherical aberration diagram of the variable magnification optical system (Example 4) in the wide-angle end state (W). FIG. 6 is an astigmatism diagram of the variable magnification optical system (Example 4) in the wide-angle end state (W). FIG. 12 is a distortion diagram of the variable magnification optical system (Example 4) in the wide-angle end state (W). FIG. 12 is a spherical aberration diagram of the variable magnification optical system (Example 4) in the intermediate focal length state (M). FIG. 6 is an astigmatism diagram of the variable magnification optical system (Example 4) in the intermediate focal length state (M). FIG. 12 is a distortion diagram of the variable magnification optical system (Example 4) in the intermediate focal length state (M). FIG. 12 is a spherical aberration diagram of the variable magnification optical system (Example 4) in the telephoto end state (T). FIG. 6 is an astigmatism diagram of the variable magnification optical system (Example 4) in the telephoto end state (T). FIG. 12 is a distortion diagram of the variable magnification optical system (Example 4) in the telephoto end state (T). FIG. 10 is a lens configuration diagram of a lens unit including the variable magnification optical system according to Example 5. FIG. 12 is a spherical aberration diagram of the variable magnification optical system (Example 5) in the wide-angle end state (W). FIG. 10 is an astigmatism diagram of the variable magnification optical system (Example 5) in the wide-angle end state (W). FIG. 12 is a distortion diagram of the variable magnification optical system (Example 5) in the wide-angle end state (W). FIG. 10 is a spherical aberration diagram of the variable magnification optical system (Example 5) in the intermediate focal length state (M). FIG. 10 is an astigmatism diagram of the variable magnification optical system (Example 5) in the intermediate focal length state (M). FIG. 12 is a distortion diagram of the variable magnification optical system (Example 5) in the intermediate focal length state (M). FIG. 10 is a spherical aberration diagram of the variable magnification optical system (Example 5) in the telephoto end state (T). FIG. 12 is an astigmatism diagram of the variable magnification optical system (Example 5) in the telephoto end state (T). FIG. 12 is a distortion diagram of the variable magnification optical system (Example 5) in the telephoto end state (T). It is explanatory drawing which shows the result of conditional expression (1)-conditional expression (3) corresponding to the variable magnification optical system of Examples 1-5. The values of | X |, | X ₀ |, C ₀ , N, N ′, f3, MV2, Lw, ft, and fw in the conditional expression (2) corresponding to the variable magnification optical systems of Examples 1 to 5 are shown. It is explanatory drawing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lens unit 11 Variable magnification optical system 29 Digital camera (imaging device)
GRi lens group GR1 first lens group GR2 second lens group GR3 third lens group GR4 fourth lens group SU imaging element unit Li lens si surface SR imaging element PR optical prism (first optical axis changing element)
PR 'optical prism (second optical axis changing element)
ST Optical aperture CG Cover glass AX Optical axis

Claims (11)

Provided with a plurality of lens groups that image light rays from the object side onto the image sensor,
The plurality of lens groups are at least from the object side to the image side,
A first lens group having positive power;
A second lens group having negative power;
A third lens group having positive power;
Contains
The first lens group includes a first optical axis changing element that changes the optical axis, while the third lens group includes a second optical axis changing element that changes the optical axis,
Further, the variable magnification optical system, wherein the most image side lens in the third lens group has at least one aspherical surface. 2. The variable magnification optical system according to claim 1, wherein an aspherical surface located on the image side in the most image side lens satisfies the following conditional expression (1):
2 <(| X | − | X ₀ |) × 100 / {C ₀ × (N′−N) × f3} <100
... Conditional expression (1)
However,
X: aspherical surface shape X _0: surface shape C ₀ aspheric reference spherical surface curvature of the aspherical surface of the reference sphere N: refractive power of the object side in the aspheric medium N ': the image side in the aspheric medium Refracting power of f3: focal length of the third lens unit.   The variable power optical system according to claim 1 or 2, wherein the third lens group includes at least four lenses.   4. The variable power optical system according to claim 1, wherein the third lens group includes a plurality of lenses closer to the object side than the second optical axis changing element. 5. The zoom optical system according to claim 1, wherein the following conditional expression (2) is satisfied when zooming:
0.1 ≦ MV2 / Lw ≦ 0.5 Conditional expression (2)
However,
MV2: Movement amount of the second lens group Lw: Total length of the variable magnification optical system in the wide-angle end state The zoom lens system according to claim 1, wherein the following conditional expression (3) is satisfied:
5.0 <ft / fw ... conditional expression (3)
However,
ft: focal length of the entire variable magnification optical system at the telephoto end fw: focal length of the entire variable magnification optical system at the wide angle end. When the first lens group and the third lens group move for zooming,
The variable magnification optical system according to any one of claims 1 to 6, wherein an inter-group distance between the first lens group and the third lens group is unchanged.   8. The zoom optical system according to claim 7, wherein the first lens group and the third lens group are in a connected state.   The variable power optical system according to any one of claims 1 to 8, wherein a fourth lens group having a positive power is disposed on the image side of the third lens group.   The variable magnification optical system according to any one of claims 1 to 9, wherein the most image side lens in the third lens group is formed of a resin.   An imaging apparatus comprising the variable magnification optical system according to claim 1.

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