JP2009229516A - Zoom lens and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens that is made compact, has a wide viewing angle and a high zoom ratio, and to provide an imaging apparatus. <P>SOLUTION: The zoom lens includes, in order from an object side: a first lens group G1 having a negative refractive power; a second lens group G2 having a positive refractive power; and a third lens group G3 having a positive refractive power. In the zoom lens, at zooming from a wide angle end to a telephoto end, each of the lens groups is moved in the optical axis direction so that an aerial space between the first lens group and the second lens group may decrease, and an aerial space between the second lens group and the third lens group may increase, the first lens group is constituted by arranging in order from the object side, a negative meniscus lens with a convex surface facing the object side, a negative meniscus lens with a convex surface facing the object side and a positive meniscus lens with a convex surface facing the object side. Either of the negative meniscus lenses in the first lens group includes at least one aspherical surface facing the image side, and the positive meniscus lens in the first lens group includes an aspherical surface whose positive refractive power is made weaker toward the periphery farther from the optical axis. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a zoom lens and an imaging apparatus. Specifically, the present invention relates to a technical field of a zoom lens and an image pickup apparatus that are small in size, have a wide angle of view, and have a high zoom ratio.

  In recent years, an imaging apparatus using a solid-state imaging device such as a digital still camera has been spreading. In such an image pickup apparatus, there is a high demand for higher image quality along with the spread, and particularly in a digital still camera having a large number of pixels, the imaging performance corresponding to a solid-state image sensor having a large number of pixels is excellent. There is a need for zoom lenses.

  In addition to the above-described improvement in image quality, there is a high demand for a wide angle of view along with a recent demand for miniaturization, and a zoom lens having a wide angle of view with a small size and a high zoom ratio is demanded. In particular, in a so-called collapsible image pickup apparatus in which a lens barrel is expanded and contracted in accordance with a zoom operation, it is desired to increase the angle of view and reduce the size while securing a zoom ratio of at least about four times. ing.

  As a type of zoom lens that realizes a reduction in size and a wide angle of view, for example, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a first lens group having a positive refractive power. A three-group zoom optical system in which three lens groups are arranged in order from the object side is known (see, for example, Patent Document 1 and Patent Document 2).

  In addition, as a type of zoom lens that realizes a high zoom ratio, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power And a fourth group zoom optical system in which a fourth lens group having a positive refractive power is arranged in order from the object side is known (for example, see Patent Document 3).

  In Patent Document 1, a zoom lens is proposed in which a half field angle at the wide angle end exceeds 40 ° and a wide field angle is achieved.

  Patent Document 2 proposes a zoom lens having a zoom ratio of 3 to 4 times.

  Patent Document 3 proposes a zoom lens that achieves both a wide angle of view in which the half angle of view exceeds 40 ° at the wide angle end and a high zoom ratio having a zoom ratio of 4 times or more.

JP 2003-35868 A JP 2006-49536 A JP 2005-283648 A

  However, in the zoom lens described in Patent Document 1, since the zoom ratio is as small as about 2.4 times, it does not satisfy the requirement for high zoom ratio that requires a zoom ratio of at least about 3 times.

  In the zoom lens described in Patent Document 2, the half angle of view at the wide angle end is less than 40 °, and it is difficult to say that the wide angle of view is sufficiently satisfied.

  Furthermore, the zoom lens described in Patent Document 3 has a four-group configuration. Since the number of lenses is correspondingly large, the total optical length becomes long, and the size reduction requirement is not satisfied. In particular, when used in a retractable image pickup apparatus, the length of the image pickup apparatus in the depth direction is long even when the lens barrel is stored, which is insufficient in terms of miniaturization.

  Therefore, an object of the zoom lens and the imaging apparatus of the present invention is to overcome the above-described problems and achieve a small size, a wide angle of view, and a high zoom ratio.

  In order to solve the above-described problem, the zoom lens includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. Are arranged in order from the side, and at the time of zooming from the wide-angle end to the telephoto end, the air gap between the first lens group and the second lens group decreases and the second lens group and the third lens group The first lens group, the second lens group, and the third lens group are movable in the direction of the optical axis so that the air space between the first lens group and the first lens group is convex on the object side. A negative meniscus lens, a negative meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side are sequentially arranged from the object side, and the negative meniscus lens of the first lens group is the image side. Have at least one aspherical surface , In which the positive meniscus lens of the first lens group has to have a non-spherical surface, such as positive refractive power becomes weaker toward the periphery from the optical axis.

  Therefore, in the zoom lens, the amount of various aberrations generated is reduced, and in particular, the amount of negative distortion and astigmatism at the wide-angle end is reduced.

  In order to solve the above-described problem, the imaging apparatus includes a zoom lens and an imaging element that converts an optical image formed by the zoom lens into an electrical signal, and the zoom lens has a negative refractive power. One lens group, a second lens group having a positive refractive power, and a third lens group having a positive refractive power are arranged in order from the object side, and at the time of zooming from the wide angle end to the telephoto end, The first lens group and the second lens group so that the air gap between the first lens group and the second lens group decreases and the air gap between the second lens group and the third lens group increases. And the third lens group is movable in the optical axis direction. The first lens group includes a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and an object side. Positive meniscus lens with convex surface Are arranged in order from the object side, the negative meniscus lens of the first lens group has at least one aspheric surface on the image side surface, and the positive meniscus lens of the first lens group is peripheral from the optical axis. An aspherical surface in which the positive refractive power is weakened toward the surface.

  Therefore, in the imaging apparatus, the amount of various aberrations that occur is reduced, and in particular, the amount of negative distortion and astigmatism at the wide-angle end is reduced.

  In the zoom lens or the imaging device described above, it is desirable that the aspherical surface formed on the image side surface of the negative meniscus lens in the first lens group is a composite aspherical surface.

  By making the aspherical surface formed on the image side surface of the negative meniscus lens into a composite aspherical surface, the selection range of the glass material of the negative meniscus lens is expanded.

  In the zoom lens or the imaging device described above, it is desirable that the aspherical surface of the positive meniscus lens in the first lens group is formed on the object side surface.

  By forming the aspherical surface of the positive meniscus lens on the object-side surface, high-order positive distortion that is likely to occur when correcting negative distortion at the wide-angle end is favorably corrected.

The zoom lens or the imaging apparatus described above is preferably configured so as to satisfy the following conditional expression.
(1) 2.0 <| f1 / fw | <3.5
However,
f1: The focal length of the first lens unit fw: The focal length of the entire lens system at the wide-angle end.

  By satisfying conditional expression (1), the negative distortion occurring at the wide-angle end is corrected well, and the diameter of the lens disposed closest to the object side in the first lens group is reduced.

The zoom lens or the imaging apparatus described above is preferably configured so as to satisfy the following conditional expression.
(2) 1.2 <L1 / fw <1.7
However,
L1: Thickness fw on the optical axis of the first lens group: The focal length of the entire lens system at the wide-angle end.

  By satisfying conditional expression (2), the sensitivity to decentering error and spacing error in the first lens group is suppressed, and the first lens group is reduced in thickness.

In the zoom lens and the imaging device described above, it is desirable that each lens except the composite aspherical resin of the negative meniscus lens in the first lens group is configured to satisfy the following conditional expression.
(3) N1n> 1.75
(4) N1p> 1.75
(5) ν1n−ν1p> 17
However,
N1n: Average value of refractive index at d line of two negative meniscus lenses in the first lens group N1p: Refractive index at d line of positive meniscus lens in the first lens group ν1n: Two refractive indices at the first lens group in the first lens group Average Abbe number ν1p of negative meniscus lens: The Abbe number of the positive meniscus lens in the first lens group.

  By satisfying conditional expression (3), conditional expression (4) and conditional expression (5), a decrease in refractive power of each lens is suppressed and lateral chromatic aberration is corrected well.

  In the present invention, a small size, a wide angle of view, and a high zoom ratio can be achieved.

  The best mode for carrying out the zoom lens and the imaging apparatus of the present invention will be described below with reference to the drawings.

  First, the zoom lens of the present invention will be described.

  The zoom lens according to the present invention includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power arranged in order from the object side. In the zooming operation from the wide-angle end to the telephoto end, the air interval between the first lens unit and the second lens unit decreases and the air interval between the second lens unit and the third lens unit increases. The lens group, the second lens group, and the third lens group are movable in the optical axis direction. The first lens group includes a negative meniscus lens having a convex surface facing the object side and a negative meniscus having a convex surface facing the object side. A lens and a positive meniscus lens having a convex surface directed toward the object side are sequentially positioned from the object side; the negative meniscus lens of the first lens group has at least one aspheric surface on the image side surface; The positive meniscus lens in the lens group moves from the optical axis to the periphery. Positive refractive power is designed to have an aspheric surface that is weakened.

  As described above, in the zoom lens according to the present invention, the first lens unit is provided with the two negative meniscus lenses having the convex surface facing the object side, so that the first lens becomes strong when zooming to the wide angle side. It is possible to disperse the negative refractive power of the group and reduce various aberrations that occur.

  The negative meniscus lens constituting the first lens group has at least one aspheric surface on the image side surface, and the positive meniscus lens constituting the first lens group has an aspheric surface. In addition, the negative distortion and astigmatism generated in the lens can be corrected well, and the spherical aberration generated on the telephoto end side can be corrected well.

  In particular, the positive meniscus lens has an aspherical surface whose positive refractive power decreases from the optical axis toward the periphery, so that higher-order positive distortion that is likely to occur when correcting negative distortion at the wide-angle end. The aberration can be corrected satisfactorily. That is, the shape of the distortion that tends to become a Jinkasa shape can be made a more preferable barrel shape.

Further, at the time of zooming, by moving not only the second lens group and the third lens group but also the first lens group in the optical axis direction, high zooming can be achieved without increasing the optical total length.
In addition, when the negative refractive power of the first lens unit is increased in order to increase the field angle, the amount of aberration is likely to increase. However, as described above, by providing two negative meniscus lenses. Various aberrations that occur can be reduced, and the negative meniscus lens has at least one aspheric surface, so that negative distortion can be corrected well, and the positive meniscus lens has an aspheric surface. Since the positive distortion aberration can be corrected satisfactorily, a wide angle of view can be achieved without degrading the optical performance.

  As described above, in the zoom lens of the present invention, the first lens group, the second lens group, and the third lens group are arranged in order from the object side, and the negative meniscus lens of the first lens group is located on the image side. The surface has at least one aspheric surface, and the positive meniscus lens of the first lens group is configured to have an aspheric surface whose positive refractive power decreases from the optical axis toward the periphery. A wide angle of view and high zooming can be achieved.

  In the zoom lens according to an embodiment of the present invention, the aspherical surface formed on the image side surface of the negative meniscus lens in the first lens group is a composite aspherical surface, that is, one of lens bodies formed of a glass material. It is desirable to form an aspherical surface with a resin material on the surface.

  By making the image side surface of the negative meniscus lens in the first lens group a composite aspherical surface, the glass material selection range of the lens body can be made wider than when one surface of the lens is aspherical by a glass material. As a result, astigmatism and distortion on the wide angle side can be corrected well.

  In particular, when a glass mold lens is used, the thickness of the center portion of the lens is reduced and distortion is likely to occur. When a negative meniscus aspheric lens is formed by such molding, it is formed by polishing. Compared to a spherical lens, the thickness of the central portion is required to be twice or more. Therefore, as described above, by forming a composite aspheric surface on the negative meniscus lens, the thickness of the lens can be reduced. For example, even when used in a retractable imaging device, the total optical length is shortened. Miniaturization can be achieved.

  Further, the negative meniscus lens used in the first lens group of the wide-angle lens of the type in which the lens group having negative refractive power is disposed closest to the object side tends to have a large aperture, but forms a composite aspherical surface by a resin material. As a result, the aspherical surface can be easily formed, and the manufacturing cost can be reduced.

  The composite aspherical surface may be formed on any of the two negative meniscus lenses in the first lens group, but the first lens group is a negative lens disposed on the image side of the negative meniscus lens disposed on the object side. Since the diameter of the meniscus lens is smaller, by providing a composite aspherical surface on the negative meniscus lens located on the image side in the first lens group, it becomes easy to form the aspherical surface and further reduce the manufacturing cost. be able to.

  In the zoom lens according to the embodiment of the present invention, it is desirable to form the aspherical surface of the positive meniscus lens in the first lens group on the object side surface.

  By forming the aspherical surface of the positive meniscus lens on the object-side surface, higher-order positive distortion that tends to occur when correcting negative distortion at the wide-angle end can be corrected more satisfactorily. The shape of the aberration can be a barrel shape.

In the zoom lens according to an embodiment of the present invention, it is preferable that the zoom lens is configured to satisfy the following conditional expression.
(1) 2.0 <| f1 / fw | <3.5
However,
f1: The focal length of the first lens unit fw: The focal length of the entire lens system at the wide-angle end.

  Conditional expression (1) defines the ratio of the focal lengths at the wide angle end of the first lens group.

  If | f1 / fw | in conditional expression (1) exceeds the lower limit, the focal length of the first lens group becomes too short, and it becomes difficult to correct negative distortion occurring at the wide angle end.

  Conversely, when | f1 / fw | in conditional expression (1) exceeds the upper limit value, the focal length of the first lens group becomes too long, and the diameter of the lens disposed closest to the object side in the first lens group increases. It is difficult to reduce the size.

  Therefore, the zoom lens can satisfactorily correct negative distortion occurring at the wide-angle end by satisfying conditional expression (1), and the diameter of the lens disposed closest to the object side in the first lens group. Can be reduced and the size can be reduced.

Furthermore, the zoom lens according to an embodiment of the present invention is preferably configured to satisfy the following conditional expression.
(2) 1.2 <L1 / fw <1.7
However,
L1: Thickness fw on the optical axis of the first lens group: The focal length of the entire lens system at the wide-angle end.

  Conditional expression (2) defines the thickness of the first lens group on the optical axis.

  If L1 / fw in conditional expression (2) exceeds the lower limit, the sensitivity to the eccentricity error and the distance error in the first lens group becomes too high, and a very high accuracy is required for assembling the zoom lens.

  On the other hand, if L1 / fw in conditional expression (2) exceeds the upper limit, the thickness of the first lens group becomes thick and it is difficult to reduce the size. In particular, when the zoom lens is used in a retractable lens barrel, size reduction during storage is hindered.

  Therefore, the zoom lens satisfies the conditional expression (2), so that the assembly accuracy of the zoom lens can be relaxed and the workability in the assembling work can be improved, and the thickness of the first lens group can be reduced and the size can be reduced. Can be achieved.

Furthermore, in the zoom lens according to an embodiment of the present invention, it is preferable that each lens excluding the composite aspheric resin of the negative meniscus lens in the first lens group is configured to satisfy the following conditional expression. .
(3) N1n> 1.75
(4) N1p> 1.75
(5) ν1n−ν1p> 17
However,
N1n: Average value of refractive index at d line of two negative meniscus lenses in the first lens group N1p: Refractive index at d line of positive meniscus lens in the first lens group ν1n: Two refractive indices at the first lens group in the first lens group Average Abbe number ν1p of negative meniscus lens: The Abbe number of the positive meniscus lens in the first lens group.

  Conditional expression (3), conditional expression (4), and conditional expression (5) define the refractive index and Abbe number of each lens of the negative meniscus lens and the positive meniscus lens in the first lens group.

  If N1n in Conditional Expression (3) or N1p in Conditional Expression (4) exceeds the lower limit, the refractive power of each lens will decrease, resulting in an increase in the total optical length and a decrease in the curvature of each surface of the lens. The amount of aberration increases.

  On the other hand, if ν1n−ν1p in the conditional expression (5) exceeds the lower limit value, it becomes difficult to correct lateral chromatic aberration, resulting in a decrease in optical performance.

  Accordingly, the zoom lens can satisfy the conditional expression (3), the conditional expression (4), and the conditional expression (5), thereby reducing the total optical length without reducing the refractive power of each lens. At the same time, the curvature of each surface of the lens is not reduced, the amount of various aberrations is reduced, and various aberrations can be corrected favorably, so that the optical performance can be improved.

  In the conditional expressions (3), (4) and (5), the negative ameniscus lens composite aspherical resin in the first lens group is excluded because the refractive index in the composite aspherical resin portion is This is because the change in refractive index and Abbe number is very small and the influence on the change in refractive power and aberration of the entire lens system is very small.

  In the zoom lens of the present invention, any one of the first lens group, the second lens group, and the third lens group, or a part of each of these lens groups can be shifted in a direction substantially orthogonal to the optical axis. It is possible to function as an anti-vibration optical system. When the zoom lens functions as such an anti-vibration optical system, the image pickup apparatus has a detection system for detecting image blur, a drive system for shifting the lens group, and a shift amount for the drive system based on the output of the detection system. What is necessary is just to provide the control system to give.

  In particular, in the zoom lens of the present invention, it is possible to shift an image with a small aberration fluctuation by shifting the entire second lens group in a direction substantially perpendicular to the optical axis.

  Next, specific embodiments of the zoom lens according to the present invention and numerical examples obtained by applying specific numerical values to the embodiments will be described with reference to the drawings and tables.

  The meanings of the symbols shown in the following description are as shown below.

  “Ri” is the radius of curvature of the i-th surface (i-th surface) from the object side to the image side, and “Di” is the surface distance between the i-th surface and the (i + 1) -th surface (lens of the lens). (Distance between centers or air spacing), “Ni” is the refractive index of the material constituting the i-th lens at the d-line, and “νi” is the Abbe number of the material constituting the i-th lens at the d-line. “INF” for the radius of curvature indicates that the surface is a plane, “ASP” for the radius of curvature indicates that the surface is an aspheric surface, and “Variable” for the surface interval is a variable interval. It shows that.

  Some lenses used in each numerical example have an aspheric lens surface. In the aspherical shape, “X” is the distance in the optical axis direction from the apex of the lens surface, “Y” is the height in the direction perpendicular to the optical axis, and “C” is the paraxial curvature (curvature radius of curvature) at the apex of the lens. Inverse number), “K” is a conic constant, and “Ai” is an i-th aspherical coefficient.

  FIG. 1 is a diagram showing a lens configuration of a zoom lens 1 according to the first embodiment of the present invention.

  As shown in FIG. 1, the zoom lens 1 according to the first embodiment is composed of eight lenses.

  The zoom lens 1 includes a first lens group G1, a second lens group G2, and a third lens group G3 arranged in order from the object side. When zooming from the wide angle end to the telephoto end, The first lens group G1, the second lens group G2, and the third lens group G3 so that the air gap between the second lens group G2 decreases and the air gap between the second lens group G2 and the third lens group G3 increases. Is moved in the direction of the optical axis.

  The first lens group G1 has a negative refractive power, a negative meniscus lens L1 having a convex surface facing the object side, a negative meniscus lens L2 having a compound aspheric surface on the image side surface and a convex surface facing the object side, A positive meniscus lens L3 having an aspherical surface on the object side and a convex surface facing the object side is sequentially arranged from the object side.

  The second lens group G2 has a positive refractive power, a biconvex lens L4 having an aspheric surface on the object side surface, a biconcave lens L5, a negative meniscus lens L6 having a convex surface facing the object side, and an image side surface. And a biconvex lens L7 having an aspherical surface are sequentially arranged from the object side. The biconvex lens L4 and the biconcave lens L5 constitute a cemented lens having a cemented surface R10 in which a convex surface and a concave surface having the same radius of curvature facing the image side of the biconvex lens L4 and the object side of the biconcave lens L5 are cemented. The negative meniscus lens L6 and the biconvex lens L7 constitute a cemented lens having a cemented surface R13 in which a concave surface and a convex surface having the same radius of curvature facing the image side of the negative meniscus lens L6 and the object side of the biconvex lens L7 are cemented. Yes.

  The third lens group G3 is composed of a biconvex lens L8 having positive refractive power and having aspheric surfaces on both sides.

  A diaphragm IR (a diaphragm surface R8) is disposed between the first lens group G1 and the second lens group G2, and the diaphragm IR is fixed.

  A filter FL such as a low-pass filter or an infrared cut filter is disposed between the third lens group G3 and the image plane IMG.

  Table 1 shows lens data of Numerical Example 1 in which specific numerical values are applied to the zoom lens 1 according to the first embodiment.

  When the zoom lens 1 is zoomed from the wide-angle end state to the telephoto end state, the surface distance D7 between the first lens group G1 and the second lens group G2 (aperture stop IR), the second lens group G2 and the third lens group G3. The surface distance D14 between the lens group G3 and the surface distance D16 between the third lens group G3 and the filter FL change. The variation in the wide-angle end state (focal length f = 5.34), the intermediate focal length state (focal length f = 10.47), and the telephoto end state (focal length f = 21.31) of each surface interval in Numerical Example 1 The interval is set to F number Fno. And Table 2 together with the half angle of view ω.

  In the zoom lens 1, the most image side surface (R5) of the negative meniscus lens L2 of the first lens group G1, the object side surface (R6) of the positive meniscus lens L3 of the first lens group G1, and the second lens group G2. The object-side surface (R9) of the biconvex lens L4, the image-side surface (R14) of the biconvex lens L7 of the second lens group G2, the object-side surface (R15) of the biconvex lens L8 of the third lens group G3, and the third The image side surface (R16) of the biconvex lens L8 of the lens group G3 is formed as an aspherical surface. Table 3 shows the fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients A4, A6, A8, and A10 of the aspherical surface in Numerical Example 1 together with the conic constant K.

In Table 3 and the table showing the aspherical coefficient described later, “E-i” represents an exponential expression with 10 as the base, that is, “10 ⁻ⁱ ”, for example, “0.12345E-05”. Represents “0.12345 × 10 ⁻⁵ ”.

  Table 4 shows values of the conditional expressions (1) to (5) in the zoom lens 1, that is, f1, fw, | f1 / fw | of the conditional expression (1), L1, fw of the conditional expression (2). , L1 / fw, N1n in conditional expression (3), N1p in conditional expression (4), and ν1n, ν1p, and ν1n−ν1p in conditional expression (5) are shown.

  As apparent from Table 4, the zoom lens 1 satisfies the conditional expressions (1) to (5).

  FIGS. 2 to 4 show various aberration diagrams of the numerical example 1 in the infinite focus state, FIG. 2 is a wide angle end state (f = 5.34), and FIG. 3 is an intermediate focal length state (f = 10. 47) and FIG. 4 are graphs showing various aberrations in the telephoto end state (f = 21.31).

  In the spherical aberration diagrams shown in FIGS. 2 to 4, the solid line indicates the d-line value, the dotted line indicates the c-line value, and the alternate long and short dash line indicates the g-line value. Further, in the astigmatism diagrams shown in FIGS. 2 to 4, solid lines indicate values on the sagittal image plane, and broken lines indicate values on the meridional image plane.

  From each aberration diagram, it is clear that Numerical Example 1 has excellent imaging performance with various aberrations corrected well.

  FIG. 5 is a diagram showing a lens configuration of the zoom lens 2 according to the second embodiment of the present invention.

  The zoom lens 2 in the second embodiment is composed of seven lenses as shown in FIG.

  The zoom lens 2 includes a first lens group G1, a second lens group G2, and a third lens group G3 arranged in order from the object side. When zooming from the wide angle end to the telephoto end, The first lens group G1, the second lens group G2, and the third lens group G3 so that the air gap between the second lens group G2 decreases and the air gap between the second lens group G2 and the third lens group G3 increases. Is moved in the direction of the optical axis.

  The first lens group G1 has a negative refractive power, a negative meniscus lens L1 having a convex surface facing the object side, a negative meniscus lens L2 having a compound aspheric surface on the image side surface and a convex surface facing the object side, A positive meniscus lens L3 having an aspherical surface on the object side and a convex surface facing the object side is sequentially arranged from the object side.

  The second lens group G2 has a positive refractive power, and includes a biconvex lens L4 having an aspheric surface on both sides, a biconvex lens L5, and a biconcave lens L6, which are sequentially positioned from the object side. The biconvex lens L5 and the biconcave lens L6 constitute a cemented lens having a cemented surface R12 in which a convex surface and a concave surface having the same radius of curvature facing the image side of the biconvex lens L5 and the object side of the biconcave lens L6 are cemented.

  The third lens group G3 is composed of a biconvex lens L7 having positive refractive power and aspheric surfaces on both sides.

  A diaphragm IR (a diaphragm surface R8) is disposed between the first lens group G1 and the second lens group G2, and the diaphragm IR is fixed.

  A filter FL such as a low-pass filter or an infrared cut filter is disposed between the third lens group G3 and the image plane IMG.

  Table 5 shows lens data of Numerical Example 2 in which specific numerical values are applied to the zoom lens 2 according to the second embodiment.

  When the zoom lens 2 is zoomed from the wide-angle end state to the telephoto end state, the surface distance D7 between the first lens group G1 and the second lens group G2 (aperture stop IR), the second lens group G2 and the third lens group The surface distance D13 between the lens group G3 and the surface distance D15 between the third lens group G3 and the filter FL change. The variation in the wide-angle end state (focal length f = 5.33), the intermediate focal length state (focal length f = 10.69), and the telephoto end state (focal length f = 21.30) of each surface interval in Numerical Example 2 The interval is set to F number Fno. And Table 6 together with the half angle of view ω.

  In the zoom lens 2, the most image side surface (R5) of the negative meniscus lens L2 of the first lens group G1, the object side surface (R6) of the positive meniscus lens L3 of the first lens group G1, and the second lens group G2. The object side surface (R9) of the biconvex lens L4, the image side surface (R10) of the biconvex lens L4 of the second lens group G2, the object side surface (R14) of the biconvex lens L7 of the third lens group G3, and the third The image side surface (R15) of the biconvex lens L7 of the lens group G3 is formed as an aspherical surface. Table 7 shows the fourth-order, sixth-order, eighth-order and tenth-order aspheric coefficients A4, A6, A8 and A10 of the aspherical surface in Numerical Example 2 together with the conic constant K.

  Table 8 shows values of the conditional expressions (1) to (5) in the zoom lens 2, that is, f1, fw, | f1 / fw | of the conditional expression (1), L1, fw of the conditional expression (2). , L1 / fw, N1n in conditional expression (3), N1p in conditional expression (4), and ν1n, ν1p, and ν1n−ν1p in conditional expression (5) are shown.

  As is apparent from Table 8, the zoom lens 2 satisfies the conditional expressions (1) to (5).

  FIGS. 6 to 8 show various aberration diagrams of the numerical example 2 in the infinite focus state. FIG. 6 shows the wide-angle end state (f = 5.33), and FIG. 7 shows the intermediate focal length state (f = 10. 69) and FIG. 8 are graphs showing various aberrations in the telephoto end state (f = 21.30).

  In the spherical aberration diagrams shown in FIGS. 6 to 8, the solid line indicates the d-line value, the dotted line indicates the c-line value, and the alternate long and short dash line indicates the g-line value. In the astigmatism diagrams shown in FIG. 6 to FIG. 8, values on the sagittal image plane are shown by solid lines, and values on the meridional image plane are shown by broken lines.

  From each aberration diagram, it is clear that Numerical Example 2 has excellent imaging performance with various aberrations corrected well.

  FIG. 9 is a diagram showing a lens configuration of the zoom lens 3 according to the third embodiment of the present invention.

  As shown in FIG. 9, the zoom lens 3 according to the third embodiment is composed of eight lenses.

  The zoom lens 3 includes a first lens group G1, a second lens group G2, and a third lens group G3 arranged in order from the object side. When zooming from the wide angle end to the telephoto end, The first lens group G1, the second lens group G2, and the third lens group G3 so that the air gap between the second lens group G2 decreases and the air gap between the second lens group G2 and the third lens group G3 increases. Is moved in the direction of the optical axis.

  The first lens group G1 has a negative refractive power, a negative meniscus lens L1 having a convex surface facing the object side, a negative meniscus lens L2 having a compound aspheric surface on the image side surface and a convex surface facing the object side, A positive meniscus lens L3 having an aspherical surface on the object side and a convex surface facing the object side is sequentially arranged from the object side.

  The second lens group G2 has a positive refractive power, a biconvex lens L4 having an aspheric surface on the object side surface, a biconcave lens L5, a negative meniscus lens L6 having a convex surface facing the object side, and an image side surface. And a biconvex lens L7 having an aspherical surface are sequentially arranged from the object side. The biconvex lens L4 and the biconcave lens L5 constitute a cemented lens having a cemented surface R10 in which a convex surface and a concave surface having the same radius of curvature facing the image side of the biconvex lens L4 and the object side of the biconcave lens L5 are cemented. The negative meniscus lens L6 and the biconvex lens L7 constitute a cemented lens having a cemented surface R13 in which a concave surface and a convex surface having the same radius of curvature facing the image side of the negative meniscus lens L6 and the object side of the biconvex lens L7 are cemented. Yes.

  The third lens group G3 is composed of a biconvex lens L8 having positive refractive power and having aspheric surfaces on both sides.

  A diaphragm IR (a diaphragm surface R8) is disposed between the first lens group G1 and the second lens group G2, and the diaphragm IR is fixed.

  A filter FL such as a low-pass filter or an infrared cut filter is disposed between the third lens group G3 and the image plane IMG.

  Table 9 shows lens data of a numerical example 3 in which specific numerical values are applied to the zoom lens 3 according to the third embodiment.

  When zooming from the wide-angle end state to the telephoto end state in the zoom lens 3, the surface distance D7 between the first lens group G1 and the second lens group G2 (aperture stop IR), the second lens group G2 and the third lens group The surface distance D14 between the lens group G3 and the surface distance D16 between the third lens group G3 and the filter FL change. The variation in the wide-angle end state (focal length f = 5.34), the intermediate focal length state (focal length f = 10.74), and the telephoto end state (focal length f = 21.33) of each surface interval in Numerical Example 3 The interval is set to F number Fno. And Table 10 together with the half angle of view ω.

  In the zoom lens 3, the most image side surface (R5) of the negative meniscus lens L2 of the first lens group G1, the object side surface (R6) of the positive meniscus lens L3 of the first lens group G1, and the second lens group G2. The object-side surface (R9) of the biconvex lens L4, the image-side surface (R14) of the biconvex lens L7 of the second lens group G2, the object-side surface (R15) of the biconvex lens L8 of the third lens group G3, and the third The image side surface (R16) of the biconvex lens L8 of the lens group G3 is formed as an aspherical surface. Table 11 shows the fourth-order, sixth-order, eighth-order and tenth-order aspheric coefficients A4, A6, A8 and A10 of the aspherical surface in Numerical Example 3 together with the conic constant K.

  Table 12 shows values of the conditional expressions (1) to (5) in the zoom lens 3, that is, f1, fw, | f1 / fw | of the conditional expression (1), L1, fw of the conditional expression (2). , L1 / fw, N1n in conditional expression (3), N1p in conditional expression (4), and ν1n, ν1p, and ν1n−ν1p in conditional expression (5) are shown.

  As can be seen from Table 12, the zoom lens 3 satisfies the conditional expressions (1) to (5).

  FIGS. 10 to 12 show various aberration diagrams of the numerical example 3 in the infinite focus state. FIG. 10 shows the wide-angle end state (f = 5.34), and FIG. 11 shows the intermediate focal length state (f = 10. 74) and FIG. 12 are graphs showing various aberrations in the telephoto end state (f = 21.33).

  In the spherical aberration diagrams shown in FIGS. 10 to 12, the solid line indicates the d-line value, the dotted line indicates the c-line value, and the alternate long and short dash line indicates the g-line value. In the astigmatism diagrams shown in FIGS. 10 to 12, the solid line shows the value on the sagittal image plane, and the broken line shows the value on the meridional image plane.

  From each aberration diagram, it is clear that Numerical Example 3 has excellent imaging performance with various aberrations corrected well.

  FIG. 13 is a diagram showing a lens configuration of the zoom lens 4 according to the fourth embodiment of the present invention.

  As shown in FIG. 13, the zoom lens 4 in the fourth embodiment is composed of eight lenses.

  The zoom lens 4 includes a first lens group G1, a second lens group G2, and a third lens group G3 arranged in order from the object side. When zooming from the wide angle end to the telephoto end, The first lens group G1, the second lens group G2, and the third lens group G3 so that the air gap between the second lens group G2 decreases and the air gap between the second lens group G2 and the third lens group G3 increases. Is moved in the direction of the optical axis.

  The first lens group G1 has a negative refractive power, a negative meniscus lens L1 having a convex surface facing the object side, a negative meniscus lens L2 having a compound aspheric surface on the image side surface and a convex surface facing the object side, A positive meniscus lens L3 having an aspherical surface on the image side and a convex surface facing the object side is sequentially arranged from the object side.

  The second lens group G2 has a positive refractive power, a biconvex lens L4 having an aspheric surface on the object side surface, a biconcave lens L5, a negative meniscus lens L6 having a convex surface facing the object side, and an image side surface. And a biconvex lens L7 having an aspherical surface are sequentially arranged from the object side. The biconvex lens L4 and the biconcave lens L5 constitute a cemented lens having a cemented surface R10 in which a convex surface and a concave surface having the same radius of curvature facing the image side of the biconvex lens L4 and the object side of the biconcave lens L5 are cemented. The negative meniscus lens L6 and the biconvex lens L7 constitute a cemented lens having a cemented surface R13 in which a concave surface and a convex surface having the same radius of curvature facing the image side of the negative meniscus lens L6 and the object side of the biconvex lens L7 are cemented. Yes.

  The third lens group G3 is composed of a biconvex lens L8 having positive refractive power and having aspheric surfaces on both sides.

  A diaphragm IR (a diaphragm surface R8) is disposed between the first lens group G1 and the second lens group G2, and the diaphragm IR is fixed.

  A filter FL such as a low-pass filter or an infrared cut filter is disposed between the third lens group G3 and the image plane IMG.

  Table 13 shows lens data of a numerical example 4 in which specific numerical values are applied to the zoom lens 4 according to the fourth embodiment.

  When the zoom lens 4 is zoomed from the wide-angle end state to the telephoto end state, the surface distance D7 between the first lens group G1 and the second lens group G2 (aperture stop IR), the second lens group G2, and the third lens group G3. The surface distance D14 between the lens group G3 and the surface distance D16 between the third lens group G3 and the filter FL change. In the numerical value example 4, the distance between the surfaces in the wide angle end state (focal length f = 5.35), the intermediate focal length state (focal length f = 10.30), and the telephoto end state (focal length f = 22.66) are variable. The interval is set to F number Fno. And Table 14 together with the half angle of view ω.

  In the zoom lens 4, the most image side surface (R5) of the negative meniscus lens L2 of the first lens group G1, the image side surface (R7) of the positive meniscus lens L3 of the first lens group G1, and the second lens group G2. The object-side surface (R9) of the biconvex lens L4, the image-side surface (R14) of the biconvex lens L7 of the second lens group G2, the object-side surface (R15) of the biconvex lens L8 of the third lens group G3, and the third The image side surface (R16) of the biconvex lens L8 of the lens group G3 is formed as an aspherical surface. Table 15 shows the fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients A4, A6, A8, and A10 of the aspheric surface in Numerical Example 4 together with the conic constant K.

  Table 16 shows values of the conditional expressions (1) to (5) in the zoom lens 4, that is, f1, fw, | f1 / fw | of the conditional expression (1), L1, fw of the conditional expression (2). , L1 / fw, N1n in conditional expression (3), N1p in conditional expression (4), and ν1n, ν1p, and ν1n−ν1p in conditional expression (5) are shown.

  As is apparent from Table 16, the zoom lens 4 satisfies the conditional expressions (1) to (5).

  FIGS. 14 to 16 show various aberration diagrams of Numerical Example 4 in the infinite focus state. FIG. 14 shows the wide-angle end state (f = 5.35), and FIG. 15 shows the intermediate focal length state (f = 10. 30) and FIG. 16 are graphs showing various aberrations in the telephoto end state (f = 21.26).

  In the spherical aberration diagrams shown in FIGS. 14 to 16, the solid line indicates the d-line value, the dotted line indicates the c-line value, and the alternate long and short dash line indicates the g-line value. Further, in the astigmatism diagrams shown in FIGS. 14 to 16, the values on the sagittal image plane are indicated by solid lines, and the values on the meridional image plane are indicated by broken lines.

  From each aberration diagram, it is clear that Numerical Example 4 has excellent imaging performance with various aberrations corrected well.

  Next, the imaging apparatus of the present invention will be described.

  The imaging device of the present invention is an imaging device that includes a zoom lens and an imaging device that converts an optical image formed by the zoom lens into an electrical signal.

  The zoom lens provided in the imaging apparatus includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power in order from the object side. At the time of zooming from the wide-angle end to the telephoto end, the air gap between the first lens group and the second lens group decreases and the air gap between the second lens group and the third lens group increases. As described above, the first lens group, the second lens group, and the third lens group are movable in the optical axis direction. The first lens group includes a negative meniscus lens having a convex surface facing the object side, and a convex surface facing the object side. A negative meniscus lens directed toward the object side and a positive meniscus lens having a convex surface directed toward the object side. The negative meniscus lens of the first lens group has at least one aspheric surface on the image side surface. The positive meniscus lens in the first lens group Positive refractive power toward the periphery is to have an aspheric surface that is weakened from.

  As described above, in the imaging apparatus of the present invention, the zoom lens is provided with two negative meniscus lenses having a convex surface facing the object side in the first lens group, so that the zoom lens is strong at the time of zooming toward the wide angle side. The negative refracting power of the first lens unit can be dispersed to reduce various aberrations that occur.

  The negative meniscus lens constituting the first lens group has at least one aspheric surface on the image side surface, and the aspheric surface on the object side surface of the positive meniscus lens constituting the first lens group. Thus, it is possible to satisfactorily correct negative distortion and astigmatism that occur at the wide-angle end, and it is possible to satisfactorily correct spherical aberration that occurs on the telephoto end side.

  In particular, the positive meniscus lens has an aspherical surface whose positive refractive power decreases from the optical axis toward the periphery, so that higher-order positive distortion that is likely to occur when correcting negative distortion at the wide-angle end. The aberration can be corrected satisfactorily. That is, the shape of the distortion that tends to become a Jinkasa shape can be made a more preferable barrel shape.

  Further, at the time of zooming, by moving not only the second lens group and the third lens group but also the first lens group in the optical axis direction, high zooming can be achieved without increasing the optical total length.

  In addition, when the negative refractive power of the first lens unit is increased in order to increase the angle of view, the amount of aberration is likely to increase, but as described above, by providing two negative meniscus lenses Various aberrations can be reduced, and the negative meniscus lens has at least one aspherical surface, so that negative distortion can be corrected well, and the positive meniscus lens has an aspherical surface. Since the positive distortion aberration can be corrected satisfactorily, a wide angle of view can be achieved without degrading the optical performance.

  As described above, in the imaging apparatus of the present invention, the zoom lens includes the first lens group, the second lens group, and the third lens group arranged in order from the object side, and the negative meniscus lens of the first lens group. Has at least one aspheric surface on the image side surface, and the positive meniscus lens of the first lens group has an aspheric surface whose positive refractive power decreases from the optical axis toward the periphery. Accordingly, it is possible to achieve a small size, a wide angle of view, and a high zoom ratio.

  FIG. 17 is a block diagram of a digital still camera according to an embodiment of the imaging apparatus of the present invention.

  An imaging apparatus (digital still camera) 100 performs a camera block 10 that performs an imaging function, a camera signal processing unit 20 that performs signal processing such as analog-digital conversion of a captured image signal, and recording and reproduction processing of the image signal. An image processing unit 30, an LCD (Liquid Crystal Display) 40 for displaying captured images, an R / W (reader / writer) 50 for writing and reading image signals to and from the memory card 1000, and an imaging device A CPU (Central Processing Unit) 60 for controlling the whole, an input unit 70 composed of various switches and the like that are operated by a user, and a lens drive control unit for controlling the driving of the lenses arranged in the camera block 10 80.

  The camera block 10 includes an optical system including a zoom lens 11 (zoom lenses 1, 2, 3, 4 to which the present invention is applied), and an image sensor 12 such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS). Etc.

  The camera signal processing unit 20 performs various signal processing such as conversion of the output signal from the image sensor 12 into a digital signal, noise removal, image quality correction, and conversion into a luminance / color difference signal.

  The image processing unit 30 performs compression encoding / decompression decoding processing of an image signal based on a predetermined image data format, conversion processing of data specifications such as resolution, and the like.

  The LCD 40 has a function of displaying various data such as an operation state of the user input unit 70 and a photographed image.

  The R / W 50 writes the image data encoded by the image processing unit 30 to the memory card 1000 and reads the image data recorded on the memory card 1000.

  The CPU 60 functions as a control processing unit that controls each circuit block provided in the imaging apparatus 100, and controls each circuit block based on an instruction input signal or the like from the input unit 70.

  The input unit 70 includes, for example, a shutter release button for performing a shutter operation, a selection switch for selecting an operation mode, and the like, and outputs an instruction input signal corresponding to an operation by a user to the CPU 60.

  The lens drive control unit 80 controls a motor (not shown) that drives each lens of the zoom lens 11 based on a control signal from the CPU 60.

  The memory card 1000 is a semiconductor memory that can be attached to and detached from a slot connected to the R / W 50, for example.

  Hereinafter, an operation in the imaging apparatus 100 will be described.

  In a shooting standby state, under the control of the CPU 60, an image signal shot by the camera block 10 is output to the LCD 40 via the camera signal processing unit 20 and displayed as a camera through image. In addition, when an instruction input signal for zooming is input from the input unit 70, the CPU 60 outputs a control signal to the lens drive control unit 80, and a predetermined value of the zoom lens 11 is controlled based on the control of the lens drive control unit 80. The lens is moved.

  When a shutter (not shown) of the camera block 10 is operated by an instruction input signal from the input unit 70, the captured image signal is output from the camera signal processing unit 20 to the image processing unit 30, and is subjected to compression coding processing. Converted to digital data in data format. The converted data is output to the R / W 50 and written to the memory card 1000.

  The focusing is performed by the lens drive control unit 80 based on a control signal from the CPU 60, for example, when the shutter release button of the input unit 50 is half pressed or when the shutter release button is fully pressed for recording (photographing). This is performed by moving a predetermined lens of the zoom lens 11.

  When reproducing the image data recorded on the memory card 1000, predetermined image data is read from the memory card 1000 by the R / W 50 according to the operation on the input unit 70, and decompressed and decoded by the image processing unit 30. After the processing is performed, the reproduction image signal is output to the LCD 40 and the reproduction image is displayed.

  In the above-described embodiment, an example in which the imaging device is applied to a digital still camera has been shown. However, the application range of the imaging device is not limited to a digital still camera, and a digital video camera and a camera are incorporated. The present invention can be widely applied as a camera unit of a digital input / output device such as a mobile phone or a PDA (Personal Digital Assistant) in which a camera is incorporated.

  The shapes and numerical values of the respective parts shown in each of the above embodiments are merely examples of embodiments for carrying out the present invention, and the technical scope of the present invention is interpreted in a limited manner by these. It must not be.

FIGS. 2 to 17 show the best mode for carrying out the imaging apparatus and the zoom lens according to the present invention, and this figure shows the lens configuration of the first embodiment of the zoom lens according to the present invention. . FIG. 3 and FIG. 4 show aberration diagrams of numerical examples in which specific numerical values are applied to the first embodiment, and this figure shows spherical aberration, astigmatism, and distortion in the wide-angle end state. . It is a figure which shows the spherical aberration, the astigmatism, and the distortion aberration in the intermediate focal length state. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration in a telephoto end state. It is a figure which shows the lens structure of 2nd Embodiment of this invention zoom lens. FIG. 7 and FIG. 8 show aberration diagrams of numerical examples in which specific numerical values are applied to the second embodiment, and this figure shows spherical aberration, astigmatism, and distortion in the wide-angle end state. . It is a figure which shows the spherical aberration, the astigmatism, and the distortion aberration in the intermediate focal length state. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration in a telephoto end state. It is a figure which shows the lens structure of 3rd Embodiment of this invention zoom lens. FIG. 11 and FIG. 12 show aberration diagrams of numerical examples in which specific numerical values are applied to the third embodiment, and this figure shows spherical aberration, astigmatism, and distortion aberration in the wide-angle end state. . It is a figure which shows the spherical aberration, the astigmatism, and the distortion aberration in the intermediate focal length state. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration in a telephoto end state. It is a figure which shows the lens structure of 4th Embodiment of the zoom lens of this invention. FIG. 15 and FIG. 16 show aberration diagrams of numerical examples in which specific numerical values are applied to the third embodiment, and this figure shows spherical aberration, astigmatism, and distortion in the wide-angle end state. . It is a figure which shows the spherical aberration, the astigmatism, and the distortion aberration in the intermediate focal length state. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration in a telephoto end state. It is a block diagram which shows one Embodiment of this invention imaging device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Zoom lens, 2 ... Zoom lens, 3 ... Zoom lens, 4 ... Zoom lens, G1 ... 1st lens group, G2 ... 2nd lens group, G3 ... 3rd lens group, 100 ... Imaging device, 11 ... Zoom lens , 12 ... Image sensor

Claims (7)

A first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power are sequentially arranged from the object side, and are telephoto from the wide-angle end. The first lens so that the air gap between the first lens group and the second lens group decreases and the air gap between the second lens group and the third lens group increases during zooming to the end. A zoom lens in which the group, the second lens group, and the third lens group are movable in the optical axis direction;
In the first lens group, a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side are sequentially positioned from the object side. Consisting of
The negative meniscus lens of the first lens group has at least one aspheric surface on the image side surface;
The zoom lens according to claim 1, wherein the positive meniscus lens of the first lens group has an aspherical surface in which the positive refractive power decreases from the optical axis toward the periphery. 2. The zoom lens according to claim 1, wherein the aspherical surface formed on the image side surface of the negative meniscus lens in the first lens group is a composite aspherical surface. The zoom lens according to claim 1, wherein an aspherical surface of a positive meniscus lens in the first lens group is formed on the object side surface. The zoom lens according to any one of claims 1 to 3, wherein the zoom lens is configured to satisfy the following conditional expression.
(1) 2.0 <| f1 / fw | <3.5
However,
f1: The focal length of the first lens unit fw: The focal length of the entire lens system at the wide-angle end. The zoom lens according to any one of claims 1 to 4, wherein the zoom lens is configured to satisfy the following conditional expression.
(2) 1.2 <L1 / fw <1.7
However,
L1: Thickness fw on the optical axis of the first lens group: The focal length of the entire lens system at the wide-angle end. 6. The zoom lens according to claim 2, wherein each of the lenses except the composite aspherical resin of the negative meniscus lens in the first lens group is configured to satisfy the following conditional expression.
(3) N1n> 1.75
(4) N1p> 1.75
(5) ν1n−ν1p> 17
However,
N1n: Average value of refractive index at d line of two negative meniscus lenses in the first lens group N1p: Refractive index at d line of positive meniscus lens in the first lens group ν1n: Two refractive indices at the first lens group in the first lens group Average Abbe number ν1p of negative meniscus lens: The Abbe number of the positive meniscus lens in the first lens group. An imaging apparatus comprising a zoom lens and an image sensor that converts an optical image formed by the zoom lens into an electrical signal,
The zoom lens is
A first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power are sequentially arranged from the object side, and are telephoto from the wide-angle end. The first lens so that the air gap between the first lens group and the second lens group decreases and the air gap between the second lens group and the third lens group increases during zooming to the end. The group, the second lens group, and the third lens group are movable in the optical axis direction;
In the first lens group, a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side are sequentially positioned from the object side. Consisting of
The negative meniscus lens of the first lens group has at least one aspheric surface on the image side surface;
The imaging apparatus according to claim 1, wherein the positive meniscus lens of the first lens group has an aspherical surface in which positive refractive power decreases from the optical axis toward the periphery.

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