1111111111111111 IIIIII IIIII 111111111111111 111111111111111 IIIII IIIII IIIII IIIIII IIII 11111111
`US 20120147249Al
`
`c19) United States
`c12) Patent Application Publication
`Okano
`
`c10) Pub. No.: US 2012/0147249 Al
`Jun. 14, 2012
`(43) Pub. Date:
`
`(54)
`
`IMAGING LENS AND IMAGING APPARATUS
`
`(75)
`
`Inventor:
`
`Hideaki Okano, Aichi (JP)
`
`(73) Assignee:
`
`Sony Corporation, Tokyo (JP)
`
`(21) Appl. No.:
`
`13/302,655
`
`(22) Filed:
`
`Nov. 22, 2011
`
`(30)
`
`Foreign Application Priority Data
`
`Dec. 14, 2010
`
`(JP) ................................. 2010-278528
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`H04N 51225
`G02B 9/34
`
`(2006.01)
`(2006.01)
`
`(52) U.S. Cl. .................. 348/340; 359/773; 348/E05.024
`ABSTRACT
`(57)
`
`An imaging lens includes: an aperture stop; a first lens having
`a positive refractive power; a second lens having a negative
`refractive power which is formed in a concave shape on both
`sides thereof; a third lens having a positive refractive power
`which is formed in a meniscus shape in which a concave
`surface is directed toward the side of an object; and a fourth
`lens having a negative refractive power in which a convex
`surface is directed toward the object side, which are sequen(cid:173)
`tially disposed from the object side to the image side, wherein
`the imaging lens satisfies the following conditional expres(cid:173)
`sions (1), (2), (3), (4) and (5):
`
`0.40<fl/!f21<0.80
`
`0.80<[/21/}3<1.50
`
`0.90<fl!f41<2.00
`
`2.60<1(R2-R3)ljl 1<4.00
`
`vdl-vd2>25.
`
`(1)
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`(2)
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`(4)
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`(5)
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`AOET, Ex. 1011
`Page 1
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`

`

`Patent Application Publication
`
`Jun. 14, 2012 Sheet 1 of 23
`
`US 2012/0147249 Al
`
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`AOET, Ex. 1011
`Page 2
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`

`

`Patent Application Publication
`
`Jun. 14, 2012 Sheet 2 of 23
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`US 2012/0147249 Al
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`AOET, Ex. 1011
`Page 3
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`

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`Patent Application Publication
`
`Jun. 14, 2012 Sheet 3 of 23
`
`US 2012/0147249 Al
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`FIG.3
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`AOET, Ex. 1011
`Page 4
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`AOET, Ex. 1011
`Page 5
`
`

`

`Patent Application Publication
`
`Jun. 14, 2012 Sheet 5 of 23
`
`US 2012/0147249 Al
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`AOET, Ex. 1011
`Page 6
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`

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`Patent Application Publication
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`AOET, Ex. 1011
`Page 7
`
`

`

`Patent Application Publication
`
`Jun. 14, 2012 Sheet 7 of 23
`
`US 2012/0147249 Al
`
`FIG.7
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`SG
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`AOET, Ex. 1011
`Page 8
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`

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`AOET, Ex. 1011
`Page 9
`
`

`

`Patent Application Publication
`
`Jun. 14, 2012 Sheet 9 of 23
`
`US 2012/0147249 Al
`
`FIG.9
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`AOET, Ex. 1011
`Page 10
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`AOET, Ex. 1011
`Page 11
`
`

`

`Patent Application Publication
`
`Jun. 14, 2012 Sheet 11 of 23
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`US 2012/0147249 Al
`
`FIG.11
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`AOET, Ex. 1011
`Page 12
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`

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`AOET, Ex. 1011
`Page 13
`
`

`

`Patent Application Publication
`
`Jun. 14, 2012 Sheet 13 of 23
`
`US 2012/0147249 Al
`
`FIG.13
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`SG
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`AOET, Ex. 1011
`Page 14
`
`

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`AOET, Ex. 1011
`Page 15
`
`

`

`Patent Application Publication
`
`Jun. 14, 2012 Sheet 15 of 23
`
`US 2012/0147249 Al
`
`FIG.15
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`AOET, Ex. 1011
`Page 16
`
`

`

`Patent Application Publication
`
`Jun. 14, 2012 Sheet 16 of 23
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`US 2012/0147249 Al
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`Page 17
`
`

`

`Patent Application Publication
`
`Jun. 14, 2012 Sheet 17 of 23
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`US 2012/0147249 Al
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`AOET, Ex. 1011
`Page 18
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`AOET, Ex. 1011
`Page 19
`
`

`

`Patent Application Publication
`
`Jun. 14, 2012 Sheet 19 of 23
`
`US 2012/0147249 Al
`
`FIG.19
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`G4
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`AOET, Ex. 1011
`Page 20
`
`

`

`Patent Application Publication
`
`Jun. 14, 2012 Sheet 20 of 23
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`US 2012/0147249 Al
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`AOET, Ex. 1011
`Page 21
`
`

`

`Patent Application Publication
`
`Jun. 14, 2012 Sheet 21 of 23
`
`US 2012/0147249 Al
`
`FIG.21
`
`10
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`AOET, Ex. 1011
`Page 22
`
`

`

`Patent Application Publication
`
`Jun. 14, 2012 Sheet 22 of 23
`
`US 2012/0147249 Al
`
`FIG.22
`
`22
`
`jo
`
`21
`
`32
`
`40
`
`AOET, Ex. 1011
`Page 23
`
`

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`....
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`I COMMUNICATION I
`
`INFRARED
`
`SECTION
`
`23
`
`55
`
`31
`
`INFRARED LIGHT
`
`INTERFACE
`
`OPERATION KEY
`
`40
`
`MEMORY CARD
`
`MEMORY CARD
`
`INTERFACE
`
`1 MICROPHONE r----32
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`41
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`
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`
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`I
`SECTION
`IMAGING UNIT t----"1 CONTROL
`CAMERA
`
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`
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`
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`AOET, Ex. 1011
`Page 24
`
`

`

`US 2012/0147249 Al
`
`Jun. 14,2012
`
`1
`
`IMAGING LENS AND IMAGING APPARATUS
`
`FIELD
`
`[0001] The present disclosure relates to an imaging lens
`and an imaging apparatus. More particularly, the present dis(cid:173)
`closure relates to a technical field of an imaging lens which is
`suitable for a small sized apparatus such as a digital still
`camera or a mobile phone mounted with a camera including
`an imaging device, and an imaging apparatus including the
`imaging lens.
`
`BACKGROUND
`
`[0002] A mobile phone with an attached camera, a digital
`still camera or the like including an imaging device (solid
`state imaging device) such as a CCD (Charge Coupled
`Device) or a CMOS (Complementary Metal Oxide Semicon(cid:173)
`ductor) has been used as an imaging apparatus.
`[0003]
`In such an imaging apparatus, there is demand for
`miniaturization. Further, in an imaging lens mounted in the
`imaging apparatus, there is also demand for a small size and
`a short total optical length.
`[0004] Further, in recent years, in a small sized imaging
`apparatus such as a mo bile phone with an attached camera, as
`miniaturization has been facilitated and a high pixel density
`imaging device has been developed, imaging apparatus mod(cid:173)
`els mounted with an imaging device of a high pixel density
`which is equivalent to a digital still camera have become
`widespread. Thus, a high pixel density lens performance cor(cid:173)
`responding to the high pixel density imaging device is
`demanded in an imaging lens to be mounted.
`[0005] Further, in order to prevent deterioration of image
`quality due to noise in photographing in dark places, there is
`demand for a lens with a bright F-number.
`[0006] Under these circumstances, in the related art, the
`following imaging lenses have been proposed (for example,
`JP-A-2004-4566, JP-A-2002-365530, JP-A-2002-365531,
`JP-A-2006-293324, JP-A-2007-219079, and JP-A-2009-
`69163).
`
`SUMMARY
`
`[0007] An imaging lens disclosed in JP-A-2004-4566 has a
`three-lens structure and a short total optical length is advan(cid:173)
`tageous. However, with the three-lens structure, it is difficult
`to satisfy the demand for a high resolution lens due to the high
`pixel density imaging device as described above and of small
`chromatic aberration, and to secure excellent optical perfor(cid:173)
`mance corresponding to an imaging device with a high pixel
`density.
`[0008] An imaging lens disclosed in JP-A-2002-365530
`and JP-A-2002-365531 has a four-lens structure and is
`capable of reliably correcting various aberrations, but has a
`long total optical length and thus does not satisfy the demand
`for miniaturization. Further, since the positive refractive
`power of the first lens and the negative refractive power of the
`second lens are strong, the eccentric sensitivity is high and
`assembly efficiency is lowered, which may result in deterio(cid:173)
`ration of optical performance.
`[0009] An imaging lens disclosed in JP-A-2006-293324
`has a four-lens structure and has a high aberration correction
`capability, but has a long total optical length and thus does not
`satisfy the demand for miniaturization. Further, since a third
`lens has a convex shape on both sides, it is difficult to correct
`aberration. Further, ghosting may occur when peripheral light
`beams are totally reflected, which may result in deterioration
`of optical performance to lower image quality.
`
`[0010] An imaging lens disclosed in JP-A-2007-219079
`has a four-lens structure and is capable of reliably correcting
`various aberrations, and particularly, field curvature, but has a
`long total optical length and thus does not satisfy the demand
`for miniaturization. Further, since the second lens is formed
`in a concave meniscus shape in which a convex portion is
`directed toward the object side, ghosting may occur, which
`may result in deterioration of optical performance so as to
`lower image quality. Further, since the refractive power of the
`second lens is weak, chromatic aberration is not sufficiently
`corrected, which may cause deterioration of optical perfor(cid:173)
`mance. In addition, since the positive refractive power of the
`third lens and a negative refractive power of the fourth lens are
`strong, the eccentric sensitivity between the first lens and the
`second lens is high and assembly efficiency is lowered, which
`may result in deterioration of optical performance. Further(cid:173)
`more, reflection ghosting occurring in a peripheral section of
`the fourth length may enter an imaging device, which may
`result in deterioration of optical performance so as to lower
`image quality.
`[0011] An imaging lens disclosed in JP-A-2009-69163 has
`a four-lens structure and has a high aberration correction
`capability, but has a long total optical length and thus does not
`satisfy the demand for miniaturization. Further, since the
`refractive power of the second lens is weak, chromatic aber(cid:173)
`ration is not sufficiently corrected, which may cause deterio(cid:173)
`ration of optical performance. Further, since the positive
`refractive power of the third lens and the negative refractive
`power of the fourth lens are strong, the eccentric sensitivity
`between the first lens and the second lens is high and assem(cid:173)
`bly efficiency is lowered, which may result in deterioration of
`optical performance. Furthermore, reflection ghosting occur(cid:173)
`ring in a peripheral section of the fourth length may enter an
`imaging device, which may result in deterioration of optical
`performance to lower image quality.
`[0012] Accordingly, it is desirable to provide an imaging
`lens and an imaging apparatus which are capable of securing
`an excellent optical performance corresponding to a high
`pixel density imaging device and of achieving miniaturiza(cid:173)
`tion.
`[0013] An embodiment of the present disclosure is directed
`to an imaging lens including an aperture stop, a first lens
`having a positive refractive power, a second lens having a
`negative refractive power which is formed in a concave shape
`on both sides thereof, a third lens having a positive refractive
`power which is formed in a meniscus shape in which a con(cid:173)
`cave surface is directed toward the object side, and a fourth
`lens having a negative refractive power in which a convex
`surface is directed toward the object side, which are sequen(cid:173)
`tially disposed from the object side to the image side. Here,
`the imaging lens satisfies the following conditional expres(cid:173)
`sions (1), (2), (3), (4) and (5):
`
`0.40</1/121<0.80
`
`0.80< [/2 l;fl<l.50
`
`0.90<fl!f41<2.00
`
`2.60<1(R2-R3)ljl 1<4.00
`
`vdl-vd2>25
`
`(1)
`
`(2)
`
`(3)
`
`(4)
`
`(5)
`
`where fl is the focal length of the first lens, f2 is the focal
`length of the second lens, f3 is the focal length of the third
`lens, f4 is the focal length of the fourth lens, f is the focal
`
`AOET, Ex. 1011
`Page 25
`
`

`

`US 2012/0147249 Al
`
`Jun. 14,2012
`
`2
`
`length of an entire lens system, R2 is a paraxial curvature
`radius of a surface on the object side of the first lens, R3 is a
`paraxial curvature radius of a surface on the image side of the
`first lens, vdl is the Abbe number of the first lens, and vd2 is
`the Abbe number of the second lens.
`[0014] With this configuration, focal lengths are appropri(cid:173)
`ately distributed between the first lens having the positive
`refractive power, the second lens having the negative refrac(cid:173)
`tive power, the third lens having the positive refractive power
`and the fourth lens having the negative refractive power, in the
`imaging lens.
`[0015]
`In the above-described imaging lens, it is preferable
`that the imaging lens satisfy the following conditional expres(cid:173)
`sion (6):
`
`0.30<1(R6-R7)/j31<1.50
`
`(6)
`
`where R6 is a paraxial curvature radius of the surface on the
`object side of the third lens, and R7 is a paraxial curvature
`radius of a surface on the image side of the third lens.
`[0016] As the imaging lens satisfies the conditional expres(cid:173)
`sion ( 6), the size of the paraxial curvature radii of the surface
`on the object side of the third lens and the surface on the image
`side thereof become optimal, and the difference between the
`paraxial curvature radii of the surface on the object side of the
`third lens and the surface on the image side thereof is pre(cid:173)
`vented from being large.
`[0017]
`In the above-described imaging lens, it is preferable
`that the aperture stop be disposed between the top of the
`surface on the object side of the first lens and the effective
`diameter thereof.
`[0018] As the aperture stop be disposed between the top of
`the surface on the object side of the first lens in the optical axis
`direction and the effective diameter thereof, the amount of
`peripheral light entering the first lens is increased.
`[0019]
`In the above-described imaging lens, it is preferable
`that the imaging lens satisfy the following conditional expres(cid:173)
`sion (7):
`
`3.00<!f41/D8<7.00
`
`(7)
`
`where D8 is a center thickness of the fourth lens.
`[0020] As the imaging lens satisfies the conditional expres(cid:173)
`sion (7), the center thickness of the fourth lens becomes
`optimal.
`[0021]
`In the above-described imaging lens, it is preferable
`that the imaging lens satisfy the following conditional expres(cid:173)
`sion (8):
`
`1.00<R4;f.1<30.00
`
`where R4 is a paraxial curvature radius of a surface on the
`object side of the second lens.
`[0022] As the imaging lens satisfies the conditional expres(cid:173)
`sion (8), the size of the paraxial curvature radius of the surface
`on the object side of the second lens becomes optimal.
`[0023] Another embodiment of the present disclosure is
`directed to an imaging apparatus including an imaging lens
`and an imaging device which converts an optical image
`formed by the imaging lens into an electrical signal. The
`imaging lens includes an aperture stop, a first lens having a
`positive refractive power, a second lens having a negative
`refractive power which is formed in a concave shape on both
`sides thereof, a third lens having a positive refractive power
`which is formed in a meniscus shape in which a concave
`surface is directed toward the side of an object, and a fourth
`lens having a negative refractive power in which a convex
`surface is directed toward the object side, which are sequen-
`
`tially disposed from the object side to the image side. The
`imaging lens satisfies the following conditional expressions
`(1), (2), (3), (4) and (5):
`
`0.40</1/121<0.80
`
`0.80<[/21/}3<1.50
`
`0.90<fl!f41<2.00
`
`2.60<1(R2-R3)ljl 1<4.00
`
`vdl-vd2>25
`
`(1)
`
`(2)
`
`(3)
`
`(4)
`
`(5)
`
`where fl is the focal length of the first lens, f2 is the focal
`length of the second lens, f3 is the focal length of the third
`lens, f4 is the focal length of the fourth lens, f is the focal
`length of an entire lens system, R2 is a paraxial curvature
`radius of a surface on the object side of the first lens, R3 is a
`paraxial curvature radius of a surface on the image side of the
`first lens, vdl is the Abbe number of the first lens, and vd2 is
`the Abbe number of the second lens.
`[0024] With this configuration, focal lengths are appropri(cid:173)
`ately distributed between the first lens having the positive
`refractive power, the second lens having the negative refrac(cid:173)
`tive power, the third lens having the positive refractive power
`and the fourth lens having the negative refractive power, in the
`imaging lens of the imaging apparatus.
`[0025] According to the imaging lens and the imaging
`apparatus of the embodiment of the present disclosure, it is
`possible to secure an excellent optical performance corre(cid:173)
`sponding to an imaging device of a high pixel density and to
`achieve miniaturization.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0026] FIG. 1 is a diagram illustrating a lens configuration
`of an imaging lens according to a first embodiment;
`[0027] FIG. 2 is a diagram illustrating spherical aberration,
`astigmatism and distortion of a value example obtained by
`applying specific values to the first embodiment;
`[0028] FIG. 3 is a diagram illustrating a lens configuration
`of an imaging lens according to a second embodiment;
`[0029] FIG. 4 is a diagram illustrating spherical aberration,
`astigmatism and distortion of a value example obtained by
`applying specific values to the second embodiment;
`[0030] FIG. 5 is a diagram illustrating a lens configuration
`of an imaging lens according to a third embodiment;
`[0031] FIG. 6 is a diagram illustrating spherical aberration,
`astigmatism and distortion of a value example obtained by
`applying specific values to the third embodiment;
`[0032] FIG. 7 is a diagram illustrating a lens configuration
`of an imaging lens according to a fourth embodiment;
`[0033] FIG. 8 is a diagram illustrating spherical aberration,
`astigmatism and distortion of a value example obtained by
`applying specific values to the fourth embodiment;
`[0034] FIG. 9 is a diagram illustrating a lens configuration
`of an imaging lens according to a fifth embodiment;
`[0035] FIG. 10 is a diagram illustrating spherical aberra(cid:173)
`tion, astigmatism and distortion of a value example obtained
`by applying specific values to the fifth embodiment;
`[0036] FIG. 11 is a diagram illustrating a lens configuration
`of an imaging lens according to a sixth embodiment;
`[0037] FIG. 12 is a diagram illustrating spherical aberra(cid:173)
`tion, astigmatism and distortion of a value example obtained
`by applying specific values to the sixth embodiment;
`
`AOET, Ex. 1011
`Page 26
`
`

`

`US 2012/0147249 Al
`
`Jun. 14,2012
`
`3
`
`[0038] FIG.13 is a diagram illustrating a lens configuration
`of an imaging lens according to a seventh embodiment;
`[0039] FIG. 14 is a diagram illustrating spherical aberra(cid:173)
`tion, astigmatism and distortion of a value example obtained
`by applying specific values to the seventh embodiment;
`[0040] FIG.15 is a diagram illustrating a lens configuration
`of an imaging lens according to an eighth embodiment;
`[0041] FIG. 16 is a diagram illustrating spherical aberra(cid:173)
`tion, astigmatism and distortion of a value example obtained
`by applying specific values to the eighth embodiment;
`[0042] FIG.17 is a diagram illustrating a lens configuration
`of an imaging lens according to a ninth embodiment;
`[0043] FIG. 18 is a diagram illustrating spherical aberra(cid:173)
`tion, astigmatism and distortion of a value example obtained
`by applying specific values to the ninth embodiment;
`[0044] FIG.19 is a diagram illustrating a lens configuration
`of an imaging lens according to a tenth embodiment;
`[0045] FIG. 20 is a diagram illustrating spherical aberra(cid:173)
`tion, astigmatism and distortion of a value example obtained
`by applying specific values to the tenth embodiment;
`[0046] FIG. 21 is a perspective view illustrating a mobile
`phone in a closed state to which an imaging apparatus accord(cid:173)
`ing to another embodiment of the present disclosure is
`applied, which will be more apparent in cooperation with
`FIGS. 22 and 23;
`[0047] FIG. 22 is a perspective view illustrating the mobile
`phone in an open state; and
`[0048] FIG. 23 is a block diagram thereof.
`
`DETAILED DESCRIPTION
`
`[0049] Hereinafter, preferred embodiments for an imaging
`lens and an imaging apparatus of the present disclosure will
`be described.
`
`[Configuration oflmaging Lens]
`
`[0050] The imaging lens according to the embodiment of
`the present disclosure includes an aperture stop, a first lens
`having a positive refractive power, a second lens having a
`negative refractive power which is formed in a concave shape
`on both sides thereof, a third lens having a positive refractive
`power which is formed in a meniscus shape in which a con(cid:173)
`cave surface is directed toward the side of an object, and a
`fourth lens having a negative refractive power in which a
`convex surface is directed toward the object side, which are
`sequentially disposed from the object side to the image side.
`[0051] Accordingly, the positive, negative, positive and
`negative refractive powers are disposed in the imaging lens, to
`form an arrangement configuration in which the positive
`refractive power proceeds.
`[0052] By forming the second lens in the concave shape on
`both sides, total reflection ghosting due to off-axis light
`beams diffuses in a peripheral portion of the lens, so that the
`ghosting light is prevented from being incident to an imaging
`device such as a CCD or CMOS, which is effective in correc(cid:173)
`tion of coma aberration.
`[0053] Forming the third lens in the meniscus shape having
`the positive refractive power is effective in aberration correc(cid:173)
`tion, and particularly, is effective in field curvature and astig(cid:173)
`matism correction.
`[0054] By forming the fourth lens having the negative
`refractive power in the shape of which the convex surface is
`directed toward the object side, ghosting light which enters a
`peripheral portion of the fourth lens is prevented from being
`
`incident to the imaging device such as a CCD or CMOS by
`being reflected from the surface thereof on the object side.
`[0055] Further, the imaging lens according to the embodi(cid:173)
`ment of the present disclosure satisfies the following condi(cid:173)
`tional expressions (1), (2), (3), (4) and (5).
`
`0.40<fl/!f21<0.80
`
`0.80< [/2 l;fl<l.50
`
`0.90<fl!f41<2.00
`
`2.60<1(R2-R3)ljl 1<4.00
`
`vdl-vd2>25
`
`(1)
`
`(2)
`
`(3)
`
`(4)
`
`(5)
`
`[0056] Here, fl is the focal length of the first lens, f2 is the
`focal length of the second lens, f3 is the focal length of the
`third lens, f4 is the focal length of the fourth lens, fis the focal
`length of an entire lens system, R2 is a paraxial curvature
`radius of a surface on the object side of the first lens, R3 is a
`paraxial curvature radius of a surface on the image side of the
`first lens, vdl is the Abbe number of the first lens, and vd2 is
`the Abbe number of the second lens.
`[0057] The conditional expression (1) is a conditional
`expression relating to an appropriate refractive power distri(cid:173)
`bution of the second lens in the refractive power of the first
`lens. The reason why the absolute value is used in the focal
`length of the second lens is because the second lens has the
`negative refractive power. By setting the first lens and the
`second lens to have the refractive power arrangement shown
`in the conditional expression (1), it is possible to obtain an
`excellent aberration correction effect.
`[0058]
`Iffl/lf21 is beyond the upper limit of the conditional
`expression (1 ), the refractive power of the second lens
`becomes excessively strong, and it is thus difficult to correct
`off-axis aberration, and particularly to correct astigmatism
`and field curvature, which consequently lowers assembly
`efficiency at the time of manufacturing.
`[0059] On the other hand, if fl/I f2 I is beyond the lower limit
`of the conditional expression (1), the refractive power of the
`second lens becomes excessively weak, and it is thus disad(cid:173)
`vantageous in terms of reduction of the total optical length,
`which is disadvantageous in terms of miniaturization. Fur(cid:173)
`ther, it is disadvantageous in terms of correction of chromatic
`aberration, which makes it difficult to secure an excellent
`optical performance suitable for an imaging device of a high
`pixel density.
`[0060] For this reason, the imaging lens satisfies the con(cid:173)
`ditional expression (1 ), and thus, it is possible to achieve
`miniaturization and to secure an excellent optical perfor(cid:173)
`mance suitable for an imaging device of a high pixel density.
`[0061] The conditional expression (2) is a conditional
`expression relating to an appropriate refractive power distri(cid:173)
`bution of the third lens in the refractive power of the second
`lens. The reason why the absolute value is used in the focal
`length of the second lens is because the second lens has the
`negative refractive power.
`[0062]
`If lf21/f3 is beyond the upper limit of the conditional
`expression (2), the refractive power of the third lens becomes
`excessively strong, and it is thus difficult to correct off-axis
`aberration, and particularly to correct astigmatism and field
`curvature, which consequently lowers assembly efficiency at
`the time of manufacturing.
`
`AOET, Ex. 1011
`Page 27
`
`

`

`US 2012/0147249 Al
`
`Jun. 14,2012
`
`4
`
`[0063] On the other hand, if lf2 l/f3 is beyond the lower limit
`of the conditional expression (2), the refractive power of the
`third lens becomes excessively weak, and it is thus disadvan(cid:173)
`tageous in terms of reduction of the total optical length, which
`is disadvantageous in terms of miniaturization.
`[0064] For this reason, the imaging lens satisfies the con(cid:173)
`ditional expression (2), and thus, it is possible to achieve
`miniaturization and to secure an excellent aberration correc(cid:173)
`tion performance to thereby secure an excellent optical per(cid:173)
`formance.
`[0065] The conditional expression (3) is a conditional
`expression relating to an appropriate refractive power distri(cid:173)
`bution of the fourth lens in the refractive powers of the lenses
`of the entire system. The reason why the absolute value is
`used in the focal length of the fourth lens is because the fourth
`lens has the negative refractive power.
`[0066]
`Iff/lf41 is beyond the upper limit of the conditional
`expression (3), the refractive power of the fourth lens
`becomes excessively strong, and it is thus difficult to correct
`off-axis aberration, and particularly to correct field curvature
`and distortion, which consequently lowers assembly effi(cid:173)
`ciency at the time of manufacturing.
`[0067] On the