SPECIFICATION
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`Title
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`ZOOM LENS SYSTEM, IMAGE CAPTURE DEVICE, AND CAMERA SYSTEM
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`Cross-Reference to Related Applications
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`[0001] This application is based on, and claims the benefit of foreign priority to, Japanese Patent
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`Application No. 2020-085568 filed on May 15, 2020, the entire disclosure of which is hereby
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`incorporated by reference.
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`Technical Field
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`[0002] The present disclosure relates to a zoom lens system with the ability to compensate for
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`various types of aberrations sufficiently, and also relates to an image capture device and camera
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`system including such a zoom lens system.
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`Background Art
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`[0003]
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`JP 2006-178244 A discloses a zoom lens system including: a first lens group I having
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`positive refractive power; a second lens group II having negative refractive power; a third lens
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`groupII havingpositive refractive power; a fourth lens group IV having negative refractive power,
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`and a fifth lens group V having positive refractive power, wherethese first through fifth lens groups
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`I-V are arrangedin this order suchthat the first lens group I is located closer to an object than any
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`other lens group IJ-V is andthat the fifth lens group V is located closer to an image than any other
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`lens group I-IV is. The zoom lens system performs zooming from a wide-angle end toward a
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`telephoto end by moving the secondlens group II in a direction pointing from the object end toward
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`the image end with the first lens group I fixed and compensates for an aberration involved with
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`zooming by movingthethird lens group III, the fourth lens group IV, and thefifth lens group V.
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`Summary
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`[0004] The present disclosure provides a zoom lens system with the ability to compensate for
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`various types of aberrations sufficiently and also provide an image capture device and camera
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`system including such a zoom lens system.
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`[0005] A zoom lens system according to an aspect of the present disclosure includes: a first lens
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`group having positive power; a secondlens group having negative power; a third lens group having
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`

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`2
`positive power; a fourth lens group having negative power; and a fifth lens group havingpositive
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`power.
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`Thefirst, second, third, fourth, and fifth lens groups are arranged in this order such that
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`the first lens group is located closer to an object than any of the second, third, fourth, or fifth lens
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`group is, and that the fifth lens group is located closer to an image than any ofthe first, second,
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`third, or fourth lens groupis. The first lens group is made up of asingle lens. The second lens
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`group is made up of four lenses. While the zoom lens system is zooming from a wide-angle end
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`toward a telephoto end during a shooting session, the fifth lens group does not move butthefirst
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`to fourth lens groups moveto change intervals betweenall of the first, second, third, fourth, and
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`fifth lens groups.
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`Brief Description of Drawings
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`[0006] The figures depict one or more implementations in accordance with the present teaching,
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`by way of example only, not by way of limitations.
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`In the figures, like reference numerals refer
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`to the same or similar elements.
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`[0007] FIG.1 illustrates lens arrangements showing what state a zoom lens system according to
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`a first embodiment (corresponding to a first example of numerical values) assumes at an infinity
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`focus point;
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`FIG. 2 illustrates longitudinal aberration diagrams showing what state the zoom lens
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`system assumesat the infinity focus point in the first example of numerical values;
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`FIG.3 illustrates lens arrangements showing what state a zoom lens system according to
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`a second embodiment (corresponding to a second example of numerical values) assumes at an
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`infinity focus point;
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`FIG. 4 illustrates longitudinal aberration diagrams showing what state the zoom lens
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`system assumesat the infinity focus point in the second example of numerical values;
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`FIG. 5 illustrates lens arrangements showing what state a zoom lens system according to
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`a third embodiment (corresponding to a third example of numerical values) assumesat an infinity
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`focus point;
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`FIG. 6 illustrates longitudinal aberration diagrams showing what state the zoom lens
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`system assumesat the infinity focus point in the third example of numerical values;
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`FIG.7 illustrates lens arrangements showing what state a zoom lens system according to
`
`a fourth embodiment (corresponding to a fourth example of numerical values) assumes at an
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`infinity focus point;
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`FIG. 8 illustrates longitudinal aberration diagrams showing what state the zoom lens
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`system assumesat the infinity focus point in the fourth example of numerical values;
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`

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`3
`FIG. 9 illustrates a schematic configuration for a digital camera according to the first
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`embodiment; and
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`FIG. 10 illustrates a schematic configuration for a lens interchangeable digital camera
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`accordingto the first embodiment.
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`Detailed Description
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`[0008] Embodiments of the present disclosure will now be described in detail with reference to
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`the accompanying drawings as appropriate. Note that unnecessarily detailed description may be
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`omitted.
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`For example, detailed description of already well-known matters and redundant
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`description of substantially the same configuration may be omitted. This is done to avoid making
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`the following description overly redundant and thereby to help one of ordinary skill in the art
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`understand the present disclosureeasily.
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`[0009]
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`In addition, note that the accompanying drawings and the following description are
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`provided to help one of ordinary skill in the art understand the present disclosure fully and should
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`not be construed as limiting the scope of the present disclosure, which is defined by the appended
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`claims.
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`[0010]
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`(First to fourth embodiments)
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`FIGS. 1, 3, 5, and 7 illustrate lens arrangement diagramsaccordingtofirst, second, third,
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`and fourth embodiments, each showing what state a zoom lens system assumesat an infinity focus
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`point.
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`[0011]
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`In FIGS. 1, 3, 5, and 7, portion (a) illustrates a lens arrangement at the wide-angle end
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`(which is a state with the shortest focal length fW); portion (b) illustrates a lens arrangement at a
`middle position (which is a state with a middle focal length f{M = V (£W * fT)); and portion (c)
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`illustrates a lens arrangement at the telephoto end (whichis a state with the longest focal length
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`fT). Note that portions (a), (b), and (c) of FIGS. 1, 3, 5, and 7 have the sameaspectratio.
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`[0012] Also, in FIGS. 1, 3, 5, and 7, the polygon arrows shown between portions (a) and (b)
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`thereof each connect together the respective positions of the lens groups at the wide-angle end
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`(Wide), middle position (Mid), and telephoto end (Tele) from top to bottom. Note that these
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`polygon arrowsjust connect the wide-angle end to the middle position and the middle position to
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`the telephoto end with the curves, and do not indicate the actual movementof the lens groups.
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`[0013] Also, the arrows added to the lens groups in FIGS. 1, 3, 5, and 7 each indicate the direction
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`of movement while the zoom lens system is focusing to makeatransition from the infinity in-
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`focus state toward the close-object in-focus state. Note that in FIGS. 1, 3, 5, and 7, the reference
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`signs of respective lens groups are shown underthe respective lens groups in portion (a) thereof,
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`

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`4
`and therefore, an arrow indicating focusing is shown under the sign of each lens group for
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`convenience’s sake. The directions of movementof the respective lens groups during focusing
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`will be described more specifically later with respect
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`to each of the first
`
`through fourth
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`embodiments.
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`[0014] Furthermore, in FIGS. 1, 3, 5, and 7, the asterisk (*) attached to a particular surface
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`indicates that the surface is an aspheric surface.
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`Furthermore, the signs (+) and (-) addedto the
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`reference signs of the respective lens groups in FIGS. 1, 3, 5, and 7 indicate the powers of the
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`respective lens groups.
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`Furthermore, in FIGS. 1, 3, 5, and 7, the straight line drawn at the right
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`end indicates the position of the image planeS(i.e., a surface, facing the object, of the image
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`sensor).
`
`[0015]
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`(First embodiment)
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`FIG. 1 illustrates a zoom lens system according to a first embodiment.
`
`[0016] The zoom lens system includes: a first lens group G1 having positive power; a second
`
`lens group G2 having negative power; a third lens group G3 having positive power; a fourth lens
`
`
`
`group G4 having negative power; andafifth lens group G5 having positive power. Thefirst,
`
`second, third, fourth, and fifth lens groups G1—GSare arrangedin this order such that thefirst lens
`
`group G1 is located closer to an object than any other lens group is and that the fifth lens group
`
`G5 is located closer to an image than any other lens groupis.
`
`[0017]
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`Thefirst lens group G1 is made up ofa first lens L1 having positive power.
`
`[0018] The second lens group G2 is made up of: a second lens L2 having negative power; a third
`
`lens L3 having negative power; a fourth lens L4 having positive power, and a fifth lens L5 having
`
`negative power, which are arranged in this order such that the second lens L2 1s located closer to
`
`the object than any other memberof this second lens group G2 is and that the fifth lens L5 is
`
`located closer to the image than any other memberof this second lens group G2is.
`
`[0019] The third lens group G3 is made upof: an aperture stop A; a sixth lens L6 having positive
`
`power; a seventh lens L7 having positive power; an eighth lens L8 having negative power, and a
`
`ninth lens L9 having positive power, which are arrangedin this order such that the aperture stop A
`
`is located closer to the object than any other memberofthis third lens group G3 is and that the
`
`ninth lens L9 is located closer to the image than any other memberofthis third lens group G3is.
`
`[0020] The fourth lens group G4 is made up of a tenth lens L10 having negative power.
`
`[0021]
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`Thefifth lens group G5 is made up of an eleventh lens L11 having positive power.
`
`[0022] The respective lenses will be described.
`
`[0023] First of all, the lens that forms the first lens group G1 will be described.
`
`Thefirst lens
`
`L]1 is a meniscus lens having a convex surface facing the object.
`
`

`

`5
`[0024] Next, the respective lenses that form the second lens group G2 will be described. The
`
`second lens L2 is a meniscuslens having a convex surface facing the object. The third lens L3
`
`isabiconcavelens. The fourth lens L4is a biconvex lens.
`
`Thefifth lens L5 is a biconcavelens.
`
`The third lens L3 and the fourth lens L4 together form a bondedlens by being bonded together
`
`with an adhesive, for example. The second lens L2 is an example of a negative lens L2a. The
`
`third lens L3 is an example of anegative lens L2b. The fourth lens L4 is an example of a positive
`
`lens L2c.
`
`Thefifth lens L5 is an example of a negative lens L2d.
`
`[0025] Next, the respective lenses that form the third lens group G3 will be described. The sixth
`
`lens L6 is a meniscus lens having a convex surface facing the object. Both surfaces of the sixth
`
`lens L6 are aspheric surfaces. The seventh lens L7 is a biconvex lens. The eighth lens L8 is a
`
`plano-concave lens, of which a surface facing the image is a concave surface. The ninth lens L9
`
`is abiconvex lens. The eighth lens L8 and the ninth lens L9 together form a bonded lens by being
`
`bonded together with an adhesive, for example. The sixth lens L6 is an example of a positive
`
`lens L3a. The seventh lens L7 is an example of a positive lens L3b. The eighth lens L8 is an
`
`example of anegative lens L3c. The ninth lens L9 is an exampleof a positive lens L3d.
`
`[0026] Next, the lens that forms the fourth lens group G4 will be described. The tenth lens L10
`
`is a biconcave lens, both surfaces of which are aspheric surfaces.
`
`[0027] Next, the lens that forms the fifth lens group G5 will be described. The eleventh lens
`
`L11 is a meniscus lens having a convex surface facing the image. The eleventh lens L11 is an
`
`example of a single lens L5a.
`
`[0028] While the zoom lens system is zooming from the wide-angle end toward the telephoto
`
`end during a shooting session, the fifth lens group G5 does not movebutthefirst to fourth lens
`
`groups G1—G4 move toward the object.
`
`In addition, as the zoom lens system is zooming, the
`
`respective lens groups move along the optical axis such that the interval between the first lens
`
`group G1 and the second lens group G2 increases, the interval between the second lens group G2
`
`and the third lens group G3 decreases, the interval between the third lens group G3 and the fourth
`
`lens group G4 increases, and the interval between the fourth lens group G4 andthe fifth lens group
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`GS increases.
`
`[0029] While the zoom lens system is focusing to make a transition from the infinity in-focus
`
`state toward the close-object in-focus state, the fourth lens group G4 movesalongthe optical axis
`
`toward the imageplane.
`
`[0030]
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`(Second embodiment)
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`FIG.3 illustrates a zoom lens system according to a second embodiment.
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`[0031] The zoom lens system includes: a first lens group GI having positive power; a second
`
`

`

`lens group G2 having negative power; a third lens group G3 having positive power; a fourth lens
`
`
`
`group G4 having negative power; andafifth lens group G5 having positive power. Thefirst,
`
`second, third, fourth, and fifth lens groups G1—GSare arrangedin this order such that thefirst lens
`
`group G1 is located closer to an object than any other lens group is and that the fifth lens group
`
`G5 is located closer to an image than any other lens groupis.
`
`[0032]
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`Thefirst lens group G1 is made up ofa first lens L1 having positive power.
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`[0033] The second lens group G2 is made up of: a second lens L2 having negative power; a third
`
`lens L3 having negative power; a fourth lens L4 having positive power, and a fifth lens L5 having
`
`negative power, which are arranged in this order such that the second lens L2 1s located closer to
`
`the object than any other memberof this second lens group G2 is and that the fifth lens L5 is
`
`located closer to the image than any other memberof this second lens group G2is.
`
`[0034] The third lens group G3 is made upof: an aperture stop A; a sixth lens L6 having positive
`
`power; a seventh lens L7 having positive power; an eighth lens L8 having negative power, and a
`
`ninth lens L9 having positive power, which are arrangedin this order such that the aperture stop A
`
`is located closer to the object than any other memberofthis third lens group G3 is and that the
`
`ninth lens L9 is located closer to the image than any other memberofthis third lens group G3is.
`
`[0035] The fourth lens group G4 is madeup of a tenth lens L10 having negative power.
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`[0036]
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`Thefifth lens group G5 is made up of an eleventh lens L11 having positive power.
`
`[0037] The respective lenses will be described.
`
`[0038] First of all, the lens that formsthe first lens group G1 will be described.
`
`Thefirst lens
`
`L]1 is a meniscus lens having a convex surface facing the object.
`
`[0039] Next, the respective lenses that form the second lens group G2 will be described. The
`
`second lens L2 is a meniscuslens having a convex surface facing the object. The third lens L3
`
`isabiconcavelens. The fourth lens L4is a biconvex lens.
`
`Thefifth lens L5 is a biconcavelens.
`
`The third lens L3 and the fourth lens L4 together form a bondedlens by being bonded together
`
`with an adhesive, for example. The second lens L2 is an example of a negative lens L2a. The
`
`third lens L3 is an example of anegative lens L2b. The fourth lens L4 is an example of a positive
`
`lens L2c.
`
`Thefifth lens L5 is an example of a negative lens L2d.
`
`[0040] Next, the respective lenses that form the third lens group G3 will be described. The sixth
`
`lens L6 is a meniscus lens having a convex surface facing the object. Both surfaces of the sixth
`
`lens L6 are aspheric surfaces. The seventh lens L7 is a biconvex lens. The eighth lens L8 is a
`
`plano-concave lens, of which a surface facing the image is a concave surface. The ninth lens L9
`
`is abiconvex lens. The eighth lens L8 and the ninth lens L9 together form a bonded lens by being
`
`bonded together with an adhesive, for example. The sixth lens L6 is an example of a positive
`
`

`

`7
`lens L3a. The seventh lens L7 is an example of a positive lens L3b. The eighth lens L8 is an
`
`example of anegative lens L3c. The ninth lens L9 is an exampleof a positive lens L3d.
`
`[0041] Next, the lens that forms the fourth lens group G4 will be described. The tenth lens L10
`
`is a biconcave lens, both surfaces of which are aspheric surfaces.
`
`[0042] Next, the lens that forms the fifth lens group G5 will be described. The eleventh lens
`
`L11 is a meniscus lens having a convex surface facing the image. The eleventh lens L11 is an
`
`example of a single lens L5a.
`
`[0043] While the zoom lens system is zooming from the wide-angle end toward the telephoto
`
`end during a shooting session, the fifth lens group G5 does not movebutthefirst to fourth lens
`
`groups G1—G4 move toward the object.
`
`In addition, as the zoom lens system is zooming, the
`
`respective lens groups move along the optical axis such that the interval between the first lens
`
`group G1 and the second lens group G2 increases, the interval between the second lens group G2
`
`and the third lens group G3 decreases, the interval between the third lens group G3 and the fourth
`
`lens group G4 increases, and the interval between the fourth lens group G4 andthe fifth lens group
`
`GS increases.
`
`[0044] While the zoom lens system is focusing to make a transition from the infinity in-focus
`
`state toward the close-object in-focus state, the fourth lens group G4 movesalongthe optical axis
`
`toward the imageplane.
`
`[0045]
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`(Third embodiment)
`
`FIG.5 illustrates a zoom lens system according to a third embodiment.
`
`[0046] The zoom lens system includes: a first lens group G1 having positive power; a second
`
`lens group G2 having negative power; a third lens group G3 having positive power; a fourth lens
`
`
`
`group G4 having negative power; andafifth lens group G5 having positive power. Thefirst,
`
`second, third, fourth, and fifth lens groups G1—GSare arrangedin this order such that thefirst lens
`
`group G1 is located closer to an object than any other lens group is and that the fifth lens group
`
`G5 is located closer to an image than any other lens groupis.
`
`[0047]
`
`Thefirst lens group G1 is made up ofa first lens L1 having positive power.
`
`[0048] The second lens group G2 is made up of: a second lens L2 having negative power; a third
`
`lens L3 having negative power; a fourth lens L4 having positive power, and a fifth lens L5 having
`
`negative power, which are arranged in this order such that the second lens L2 1s located closer to
`
`the object than any other memberof this second lens group G2 is and that the fifth lens L5 is
`
`located closer to the image than any other memberof this second lens group G2is.
`
`[0049] The third lens group G3 is made upof: an aperture stop A; a sixth lens L6 having positive
`
`power; a seventh lens L7 having positive power; an eighth lens L8 having negative power, and a
`
`

`

`8
`ninth lens L9 having positive power, which are arrangedin this order such that the aperture stop A
`
`is located closer to the object than any other memberofthis third lens group G3 is and that the
`
`ninth lens L9 is located closer to the image than any other memberofthis third lens group G3is.
`
`[0050] The fourth lens group G4 is madeup of a tenth lens L10 having negative power.
`
`[0051] The fifth lens group G5 is made up of an eleventh lens L11 having positive power.
`
`[0052] The respective lenses will be described.
`
`[0053] First of all, the lens that forms the first lens group G1 will be described.
`
`Thefirst lens
`
`L]1 is a meniscus lens having a convex surface facing the object.
`
`[0054] Next, the respective lenses that form the second lens group G2 will be described. The
`
`second lens L2 is a meniscuslens having a convex surface facing the object. The third lens L3
`
`isabiconcavelens. The fourth lens L4is a biconvex lens.
`
`Thefifth lens L5 is a biconcavelens.
`
`The third lens L3 and the fourth lens L4 together form a bondedlens by being bonded together
`
`with an adhesive, for example. The second lens L2 is an example of a negative lens L2a. The
`
`third lens L3 is an example of anegative lens L2b. The fourth lens L4 is an example of a positive
`
`lens L2c.
`
`Thefifth lens L5 is an example of a negative lens L2d.
`
`[0055] Next, the respective lenses that form the third lens group G3 will be described. The sixth
`
`lens L6 is a meniscus lens having a convex surface facing the object. Both surfaces of the sixth
`
`lens L6 are aspheric surfaces. The seventh lens L7 is a biconvex lens. The eighth lens L8 is a
`
`plano-concave lens, of which a surface facing the image is a concave surface. The ninth lens L9
`
`is abiconvex lens. The eighth lens L8 and the ninth lens L9 together form a bonded lens by being
`
`bonded together with an adhesive, for example. The sixth lens L6 is an example of a positive
`
`lens L3a. The seventh lens L7 is an example of a positive lens L3b. The eighth lens L8 is an
`
`example of anegative lens L3c. The ninth lens L9 is an exampleof a positive lens L3d.
`
`[0056] Next, the lens that forms the fourth lens group G4 will be described. The tenth lens L10
`
`is a biconcave lens, both surfaces of which are aspheric surfaces.
`
`[0057] Next, the lens that forms the fifth lens group G5 will be described. The eleventh lens
`
`L11 is a meniscus lens having a convex surface facing the image. The eleventh lens L11 is an
`
`example of a single lens L5a.
`
`[0058] While the zoom lens system is zooming from the wide-angle end toward the telephoto
`
`end during a shooting session,the fifth lens group G5 does not move,the first lens group G1 moves
`
`toward the object, the second lens group G2 movesto draw a locus that is convex toward the image,
`
`and the third and fourth lens groups G3, G4 move toward the object.
`
`In addition, as the zoom
`
`lens system is zooming, the respective lens groups move along the optical axis such that the
`
`interval between the first lens group G1 and the second lens group G2 increases, the interval
`
`

`

`9
`between the second lens group G2 andthe third lens group G3 decreases, the interval between the
`
`third lens group G3 and the fourth lens group G4 increases from the wide-angle end through a
`
`middle position but decreases from the middle position through the telephoto end, and the interval
`
`between the fourth lens group G4 andthefifth lens group GS increases.
`
`[0059] While the zoom lens system is focusing to make a transition from the infinity in-focus
`
`state toward the close-object in-focus state, the fourth lens group G4 movesalongthe optical axis
`
`toward the imageplane.
`
`[0060]
`
`(Fourth embodiment)
`
`FIG.7 illustrates a zoom lens system according to a fourth embodiment.
`
`[0061] The zoom lens system includes: a first lens group G1 having positive power; a second
`
`lens group G2 having negative power; a third lens group G3 having positive power; a fourth lens
`
`
`
`group G4 having negative power; andafifth lens group G5 having positive power. Thefirst,
`
`second, third, fourth, and fifth lens groups G1—GSare arrangedin this order such that thefirst lens
`
`group G1 is located closer to an object than any other lens group is and that the fifth lens group
`
`G5 is located closer to an image than any other lens groupis.
`
`[0062]
`
`Thefirst lens group G1 is made up ofa first lens L1 having positive power.
`
`[0063] The second lens group G2 is made up of: a second lens L2 having negative power; a third
`
`lens L3 having negative power; a fourth lens L4 having positive power, and a fifth lens L5 having
`
`negative power, which are arranged in this order such that the second lens L2 1s located closer to
`
`the object than any other memberof this second lens group G2 is and that the fifth lens L5 is
`
`located closer to the image than any other memberof this second lens group G2is.
`
`[0064] The third lens group G3 is made upof: an aperture stop A; a sixth lens L6 having positive
`
`power; a seventh lens L7 having positive power; an eighth lens L8 having negative power, and a
`
`ninth lens L9 having positive power, which are arrangedin this order such that the aperture stop A
`
`is located closer to the object than any other memberofthis third lens group G3 is and that the
`
`ninth lens L9 is located closer to the image than any other memberofthis third lens group G3is.
`
`[0065] The fourth lens group G4 is madeup of a tenth lens L10 having negative power.
`
`[0066]
`
`Thefifth lens group G5 is madeup of an eleventh lens L11 having positive power.
`
`[0067] The respective lenses will be described.
`
`[0068] First of all, the lens that forms the first lens group G1 will be described.
`
`Thefirst lens
`
`L]1 is a meniscus lens having a convex surface facing the object.
`
`[0069] Next, the respective lenses that form the second lens group G2 will be described. The
`
`second lens L2 is a meniscuslens having a convex surface facing the object. The third lens L3
`
`is abiconcavelens. The fourth lens L4is a biconvex lens.
`
`Thefifth lens L5 is a biconcavelens.
`
`

`

`10
`The third lens L3 and the fourth lens L4 together form a bondedlens by being bonded together
`
`with an adhesive, for example. The second lens L2 is an example of a negative lens L2a. The
`
`third lens L3 is an example of anegative lens L2b. The fourth lens L4 is an example of a positive
`
`lens L2c.
`
`Thefifth lens L5 is an example of a negative lens L2d.
`
`[0070] Next, the respective lenses that form the third lens group G3 will be described. The sixth
`
`lens L6 is a meniscus lens having a convex surface facing the object. Both surfaces of the sixth
`
`lens L6 are aspheric surfaces. The seventh lens L7 is a biconvex lens. The eighth lens L8 is a
`
`biconcave lens. The ninth lens L9 is a biconvex lens. The eighth lens L8 andthe ninth lens L9
`
`together form a bondedlens by being bonded together with an adhesive, for example. The sixth
`
`lens L6 is an example of a positive lens L3a. The seventh lens L7 is an example ofa positive
`
`lens L3b. The eighth lens L8 is an example of a negative lens L3c. The ninth lens L9 is an
`
`example of a positive lens L3d.
`
`[0071] Next, the lens that forms the fourth lens group G4 will be described. The tenth lens L10
`
`is a biconcave lens, both surfaces of which are aspheric surfaces.
`
`[0072] Next, the lens that forms the fifth lens group G5 will be described. The eleventh lens
`
`L11 is a meniscus lens having a convex surface facing the image. The eleventh lens L11 is an
`
`example of a single lens L5a.
`
`[0073] While the zoom lens system is zooming from the wide-angle end toward the telephoto
`
`end during a shooting session, the fifth lens group G5 does not movebutthefirst to fourth lens
`
`groups G1—G4 move toward the object.
`
`In addition, as the zoom lens system is zooming, the
`
`respective lens groups move along the optical axis such that the interval between the first lens
`
`group G1 and the second lens group G2 increases, the interval between the second lens group G2
`
`and the third lens group G3 decreases, the interval between the third lens group G3 and the fourth
`
`lens group G4 increases, and the interval between the fourth lens group G4 andthe fifth lens group
`
`GS increases.
`
`[0074] While the zoom lens system is focusing to make a transition from the infinity in-focus
`
`state toward the close-object in-focus state, the fourth lens group G4 movesalongthe optical axis
`
`toward the imageplane.
`
`[0075]
`
`(Conditions and advantages)
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`Next, conditions for implementing the zoom lens systems accordingto the first to fourth
`
`embodiments, for example, will be described. That is to say, a plurality of possible conditions
`
`are defined for the zoom lens systems according to each of these four embodiments.
`
`In that case,
`
`a zoom lens system, of which the configuration satisfies all of these possible conditions, is most
`
`advantageous. Alternatively, a zoom lens system that achieves its expected advantages by
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`11
`satisfying the individual conditions to be described below mayalso be obtained.
`
`[0076] For example, as in the zoom lens system accordingto the first to fourth embodiments
`
`described above, a zoom lens system according to an aspect of the present disclosure includes: a
`
`first lens group G1 having positive power; a second lens group G2 having negative power; a third
`
`lens group G3 having positive power; a fourth lens group G4 having negative power; anda fifth
`
`lens group G5 having positive power.
`
`Thefirst, second, third, fourth, and fifth lens groups G1—
`
`G5 are arranged in this order such that the first lens group G1 is located closer to an object than
`
`any of the second, third, fourth, or fifth lens group G2, G3, G4, GS is and that the fifth lens group
`
`G5 is located closer to an image than any of the first, second, third, or fourth lens group G1, G2,
`
`G3, G4 is.
`
`Thefirst lens group G1 is made up of a single lens. The second lens group G2 is
`
`made up of four lenses. While the zoom lens system is zooming from a wide-angle end toward
`
`a telephoto end during a shooting session, the fifth lens group G5 does not movebutthe first to
`
`fourth lens groups G1—G4 move to change intervals between all of the first through fifth lens
`
`groups G1-G5. This provides a zoom lens system with the ability to compensate for various
`
`types of aberrations sufficiently over the entire zoom range while obtaining a wide angle of view
`
`at the wide-angle end.
`
`[0077] Also, in the zoom lens system, for example, the second lens group G2 suitably includes a
`
`negative lens L2d whichis located closer to the image than any other member of the second lens
`
`group G2 is. This allows the zoom lens system to be downsized.
`
`[0078] Furthermore, in the zoom lens system, for example, the second lens group G2 is suitably
`
`made up of: a negative lens L2a; a negative lens L2b; a positive lens L2c; and the negative lens
`
`L2d. The negative lens L2a, the negative lens L2b, the positive lens L2c, and the negative lens
`
`L2d are arrangedin this order such that the negative lens L2a is located closer to the object than
`
`any other memberof the second lens group G2is and that the negative lens L2d is located closer
`
`to the image than any other memberof the second lens group G2 is. This allowsthe refractive
`
`angle of a light beam incident on the negative lens L2d to be decreased, thus reducing various
`
`types of aberrations(e.g., the field curvature, in particular).
`
`[0079] Furthermore, the zoom lens system suitably satisfies the following Inequality (1), for
`
`example:
`
`[0080] vL2b > 62
`
`(1)
`
`where vL2b is an abbe numberwith respect to a d—line of the negative lens L2b.
`
`[0081] The condition expressed by this inequality (1) defines the abbe numberwith respect to a
`
`d-line of the negative lens L2b.
`
`Ifthe abbe number wereless than the lowerlimit defined by this
`
`Inequality (1), then it would be difficult to compensate for various types of aberrations (such as a
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`12
`chromatic aberration of magnification and an axial chromatic aberration, among other things).
`
`[0082] To enhance the advantage described above, the condition expressed by the following
`
`Inequality (1a) is suitably satisfied:
`
`[0083] vL2b>65
`
`(la)
`
`Moresuitably, to further enhance the advantage described above, the condition expressed
`
`by the following Inequality (1b) maybesatisfied:
`
`[0084] vL2b > 67
`
`(1b)
`
`Furthermore, in the zoom lens system, for example, the second lens group G2 suitably
`
`includes a negative lens L2a which is located closer to the object than any other memberof the
`
`second lens group G2is, and the zoom lens system suitably satisfies the following Inequality (2):
`
`[0085] nL2a> 1.9
`
`(2)
`
`where nL2ais a refractive index with respect to a d-line of the negative lens L2a.
`
`[0086] The condition expressed by this Inequality (2) defines a refractive index with respect to a
`
`d-line of the negative lens L2a.__If the refractive index were less than the lower limit defined by
`
`this Inequality (2), then it would be difficult to compensate for the field curvature at the wide-
`
`angle end, in particular.
`
`[0087] To enhance the advantage described above, the condition expressed by the following
`
`Inequality (2a) is suitably satisfied:
`
`[0088] nL2a> 1.95
`
`(2a)
`
`Moresuitably, to further enhance the advantage described above, the condition expressed
`
`by the following Inequality (2b) maybesatisfied:
`
`[0089] nL2a> 2.00
`
`(2b)
`
`Furthermore, in the zoom lens system, for example, the third lens group G3 is suitably
`
`madeupof: a positive lens L3a; a positive lens L3b; a negative lens L3c; and a positive lens L3d.
`
`Thepositive lens L3a, the positive lens L3b, the negative lens L3c, and the positive lens L3d are
`
`suitably arranged in this order such that the positive lens L3a is located closer to the object tha