Certification of Translation
`
`I, Teresa Sumiyoshi, do hereby certify that:
`
`1.
`
`I am fluent in the English and Japanese languages, and have worked as an interpreter and
`translator of these two languages for over 25 years.
`
`2. The attached English translation is a true and accurate translation of the original Japanese
`document, identified as WO2013125248.
`
`I declare under penalty of perjury under the laws of the United States of America and the State of
`California that the foregoing are true and correct and that this Certification was executed on this
`20th day of July, 2020, in Moraga, California.
`
`I declare that these statements are made with the knowledge that willful false statements and the
`like so made are punishable by fine or imprisonment, or both, under Section 1001 of Title 18 of
`the United States Code.
`
`____________________________
`
`Teresa Sumiyoshi
`
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`WO 2013/125248
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`PCT/JP2013/001035
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` Ex. 1013
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`(12) International Application Published Under The Patent Cooperation Treaty (PCT)
`(19) World Intellectual Property Organization International Bureau
`(10) International Publication Number WO 2013/125248 Al
`(43) International Publication Date August 29, 2013 (29.08.2013)
`WIPO I PCT
`(51) International Patent Classification: G02B 13/04 (2006.01) G02B 13/18 (2006.01)
`(21) International Application Number: PCT/JP2013/001035
`(22) International Filing Date: February 22, 2013 (22.02.2013)
`(25) Filing Language: Japanese
`(26) Publication Language: Japanese
`(30) Priority Data: 2012-039330 February 24, 2012 (24.02.2012)
`JP
`(71) Applicant: HITACHI MAXELL, LTD. [JP]/[JP]; 1-88 Ushitora 1-chome, Ibaraki-shi, Osaka
`5678567 Osaka (JP)
`(72) Inventors: Sugiyama, Takashi, c/o HITACHI MAXELL, LTD., 1-88 Ushitora 1-chome, Ibaraki-
`shi, Osaka 5678567 Osaka (JP); Yamazaki, Masaki, c/o HITACHI MAXELL, LTD.,
`1-88 Ushitora 1-chome, Ibaraki-shi, Osaka 5678567 Osaka (JP)
`(74) Agent: Yokozawa, Shiro et al, 1132-18 Shimadachi, Matsumoto-shi, Nagano-ken 3900852
`Nagano (JP)
`(81) Designated States (unless otherwise indicated, for every kind of national protection available):
`AE, AG, AL, AM, AO, AT, AU, AZ, BA, BB, BG, BH, BN, BR, BW, BY, BZ, CA, CH, CL, CN, CO, CR,
`CU, CZ, DE, DJ, DK, DM, DO, DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT, HN, HR, HU, ID,
`IL, IN, IR, IS, JO, JP, KE, KG, KH, KN, KP, KR, KW, KZ, LA, LC, LK, LR, LS, LU, LY, MA, MD, ME,
`MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI, NO, NZ, OM, PA, PE, PG, PH, PL, PT, QA, RO, RS,
`RU, RW, SA, SC, SD, SE, SG, SK, SL, SM, ST, SV, SY, TH, TJ, TM, TN, TR, TT, TZ, UA, UG, US,
`UZ, VC, VN, ZA, ZM, ZW.
`(84) Designated States (unless otherwise indicated, for every kind of regional protection available):
`ARIPO (BW, GH, GM, KE, LR, LS, MW, MZ, NA, RW, SD, SL, ST, SZ, TZ, UG, ZM, ZW), Eurasian
`(AM, AZ, BY, KG, KZ, RU, TJ, TM), European (AL, AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI,
`FR, GB, GR, HR, HU, IE, IS, IT, LT, LU, LV, MC, MK, MT, NL, NO, PL, PT, RO, RS, SE, SI, SK, SM,
`TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW, KM, ML, MR, NE, SN, TD, TG).
`Published:
`- with international search report (Article 21(3))
`- with amended claims (Article 19(1))
`(5
`4) Title: WIDE-ANGLE LENS AND IMAGING DEVICE
`

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`WO 2013/125248
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`57) Abstract: An imaging lens (10) is formed from a first group lens (11) having negative power, a
`second group lens (12) having positive power, a third group lens (13) having negative power, and a
`fourth group lens (14) having positive power, disposed in order from the subject side to the image
`side. Letting f be the focal distance for the entire lens system and ff2 the focal distance for the
`second group lens (12), 1.0 ≤ ff2/f ≤ 2.0 is satisfied; therefore, the entire length of the lens system
`can be kept short and image curvature can be suppressed. In addition, each of the subject side len
`s
`su
`rfaces and the image side lens surfaces for the second group lens (12), third group lens (13), and
`fourth group lens (14) are provided with aspherical surface shapes; therefore, the imaging lens (10)
`is constituted to be bright.
`[TN: Original document includes Japanese-language abstract, which is duplicative of the above
`English-language abstract]
`

`

`WO 2013/125248
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`PCT/JP2013/001035
`
`Specification
`
`Title of the Invention: Wide-angle lens and imaging device
`
`Technical Field
`[0001]
`The present invention relates to a compact, high resolution,
`wide-angle lens composed of four to six lenses.
`Background Art
`[0002]
`Patent document 1 discloses a wide-angle lens mounted on, for
`example, a vehicle camera or a monitoring camera. The wide-angle lens
`of document 1 is formed from a first lens having negative power, a
`second lens having positive power, a third lens having negative power,
`and a fourth lens having positive power, arranged in order from the
`object side to the image side. The wide-angle lens of document 1 has a
`diagonal viewing angle of about 65°.
`Prior Art Documents
`Patent Documents
`[0003]
`Patent document 1: JP 2009-14947 A
`Summary of the Invention
`Problem to be Solved by the Invention
`[0004]
` For a wide-angle lens mounted in an imaging device, such as
`an on-vehicle camera or monitoring camera, there is a demand for
`compactness, and for higher resolution in conjunction with an
`increase in the number of pixels of imaging elements incorporated
`into such imaging devices. It then becomes necessary to suppress,
`more than up to now, aberration such as curvature of field, in
`order to improve the resolution of a wide-angled lens.
`
`[0005]
` In light of such matters, the problem addressed by the
`present invention is to provide a compact and higher resolution
`wide-angle lens, and to provide an imaging device incorporating
`such a wide-angle lens.
`Means for Solving the Problem
`[0006]
`In order to solve the above-mentioned problem, a wide-angle lens
`of the present invention is characterized by:
`
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`2
`comprising a first group lens having negative power, a second
`group lens having positive power, a third group lens having negative
`power, and a fourth group lens having positive power arranged in order
`from an object side toward an image side;
`the first group lens comprising one lens having negative power or
`two lenses both having negative power;
`the second group lens comprising one lens having positive power
`or two lenses both having positive power;
`the third group lens comprising one lens having negative power;
`the fourth group lens comprising one lens having positive power;
`the lens constituting the first group lens being provided with a
`concave shape for the image-side lens surface;
`the lens, in the second group lens, disposed adjacent to the
`third group lens being provided with a convex shape for the image-side
`lens surface;
`the third group lens being provided with a concave shape for the
`object-side lens surface;
`at least one lens among the lenses constituting the second group
`lens, the third group lens, and the fourth group lens being made to
`have an aspherical shape for at least one lens surface among the
`object-side lens surface and the image-side lens surface; and
`the following conditional expression (1) being satisfied when f
`is the focal distance of the entire lens system, and ff2 is the focal
`distance of the second group lens:
` 1.0 ≤ ff2/f ≤2.0
` (1).
`
`[0007]
`Because the wide-angle lens of the present invention satisfies
`the conditional expression (1), the total length of the lens system
`can be kept short, and curvature of field can be suppressed. In
`addition, providing the lenses constituting the second group lens, the
`third group lens, and the fourth group lens with an aspherical shape
`makes it easy to increase the numerical aperture. If the upper limit
`of the conditional expression (1) is exceeded, curvature of field
`increases on the positive side and becomes difficult to correct. Below
`the lower limit of the conditional expression (1), curvature of field
`increases on the negative side and becomes difficult to correct. In
`addition, if the upper limit of the conditional expression (1) is
`exceeded, the positive power of the second group lens becomes
`relatively weaker, making it difficult to keep the total length of the
`lens system short. Note that “wide-angle lens” refers to an imaging
`lens with a diagonal angle of view of 60° or greater.
`[0008]
`In the present invention, when ff3 is the focal distance of the
`third group lens,
`
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`3
`the following conditional expression (2) is preferably satisfied:
` −2.0 ≤ ff2/ff3 ≤−1.0
` (2)
`[0009]
`The upper limit of the conditional expression (2) is for
`suppressing chromatic aberration. If the upper limit of the conditional
`expression (2) is exceeded, the negative power of the third group lens
`provided with a concave shape becomes too weak compared to the positive
`power of the second group lens provided with a convex shape, so chromatic
`aberration increases and becomes difficult to correct. Therefore, the
`upper limit is set to −1.0 or less to suppress chromatic aberration. The
`lower limit of the conditional expression (2) is for suppressing
`curvature of field and for keeping the total length of the lens system
`short. Below the lower limit of the conditional expression (2), the
`negative power of the third group lens provided with a concave shape
`becomes too strong compared to the positive power of the second group
`lens provided with a convex shape, leading to an increase in curvature of
`field. Therefore, the lower limit is set to −2.0 or greater to suppress
`curvature of field. In addition, below the lower limit of the conditional
`expression (2), the positive power of the second group lens becomes weak
`compared to the negative power of the third group lens, making it
`difficult to keep the total length of the lens system short. A balance
`between chromatic aberration and curvature of field can be achieved by
`setting the range of the conditional expression (2) to −1.9 to −1.3.
`[0010]
`In the present invention, when ff4 is the focal distance of the
`fourth group lens, the following conditional expression (3) is
`preferably satisfied:
` 0.5 ≤ ff4/f≤ 2.0
`[0011]
`The conditional expression (3) is for suppressing curvature of
`field. In other words, if the upper limit of the conditional
`expression (3) is exceeded, curvature of field increases on the
`positive side and becomes difficult to correct. Below the lower limit
`of the conditional expression (3), curvature of field increases on the
`negative side and becomes difficult to correct. Therefore, this range
`is set to 0.5 to 2.0 to better suppress curvature of field. An image
`surface balance can be achieved by setting the range of the
`conditional expression (3) to 0.7 to 1.7.
`[0012]
` To correct chromatic aberration well in the present invention,
`the second group lens preferably comprises a lens having an Abbe
`number of 40 or greater, and the third group lens preferably comprises
`a lens having an Abbe number of 35 or less.
`[0013]
`
` (3)
`
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`A configuration having a diagonal angle of view of 100° or
`
`greater may be employed in the present invention.
`4
`
`
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`PCT/JP2013/001035
`
`
`In other words, curvature of field can be suppressed even with a wide-
`angle lens having such a large angle of view.
`[0014]
` Next, an imaging device of the present invention is
`characterized by including the above-mentioned wide-angle lens, and an
`imaging element disposed at a focal position of the wide-angle lens.
`[0015]
` With the present invention, the wide-angle lens has high
`resolution, so a high-resolution imaging device can be achieved by
`using an imaging element with a large pixel number as an imaging
`element. In addition, the total length of the wide-angle lens can be
`shortened, so the imaging device can be made compact.
`Effect of the Invention
`[0016]
` With a wide-angle lens of the present invention, the total
`length of the lens system can be kept short, and curvature of field
`can be suppressed. In addition, it is easy to increase the numerical
`aperture.
`Brief Description of the Drawings
`[0017]
`FIG. 1 is a block diagram of an imaging lens of Embodiment 1 with the
`present invention applied thereto.
`FIG. 2A is an axial chromatic aberration diagram of the imaging lens
`of FIG. 1.
`FIG. 2B is a lateral aberration diagram of the imaging lens of FIG. 1.
`FIG. 2C is a curvature of field diagram of the imaging lens of FIG. 1.
`FIG. 2D is a distortion aberration diagram of the imaging lens of FIG. 1.
`FIG. 3 is a block diagram of an imaging lens of Embodiment 2 with the
`present invention applied thereto.
`FIG. 4A is an axial chromatic aberration diagram of the imaging lens
`of FIG. 3.
`FIG. 4B is a lateral aberration diagram of the imaging lens of FIG. 3.
`FIG. 4C is a curvature of field diagram of the imaging lens of FIG. 3.
`FIG. 4D is a distortion aberration diagram of the imaging lens of FIG. 3.
`FIG. 5 is a block diagram of an imaging lens of Embodiment 3 with the
`present invention applied thereto.
`FIG. 6A is an axial chromatic aberration diagram of the imaging lens
`of FIG. 5.
`FIG. 6B is a lateral aberration diagram of the imaging lens of FIG. 5.
`FIG. 6C is a curvature of field diagram of the imaging lens of FIG. 5.
`FIG. 6D is a distortion aberration diagram of the imaging lens of FIG. 5.
`
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`
`FIG. 7 is a block diagram of an imaging lens of Embodiment 4 with the
`present invention applied thereto.
`FIG. 8A is an axial chromatic aberration diagram of the imaging lens
`of FIG. 7.
`FIG. 8B is a lateral aberration diagram of the imaging lens of FIG. 7.
`FIG. 8C is a curvature of field diagram of the imaging lens of FIG. 7.
`FIG. 8D is a distortion aberration diagram of the imaging lens of FIG. 7.
`FIG. 9 is a block diagram of an imaging lens of Embodiment 3 with the
`present invention applied thereto.
`FIG. 10A is an axial chromatic aberration diagram of the imaging lens
`of FIG. 9.
`FIG. 10B is a lateral aberration diagram of the imaging lens of FIG.
`9.
`FIG. 10C is a curvature of field diagram of the imaging lens of FIG.
`9.
`FIG. 10D is a distortion aberration diagram of the imaging lens of FIG.
`9.
`FIG. 11 is a diagram illustrating an imaging device incorporating an
`imaging lens.
`Mode for Implementing the Invention
`[0018]
` An imaging lens to which the present invention has been applied
`will be described hereinafter with reference to the drawings.
`[0019] Embodiment 1
` FIG. 1 is a block diagram of the imaging lens of Embodiment 1.
`As shown in FIG. 1, an imaging lens 10 comprises a first group lens 11
`having negative power, a second group lens 12 having positive power, a
`third group lens 13 having negative power, and a fourth group lens 14
`having positive power, arranged in order from the object side toward
`the image side. The imaging lens 10 of the present embodiment is
`composed of four lenses, with a first group lens 11 comprising one
`first lens 111, a second group lens 12 comprising one second lens 121,
`a third group lens 13 comprising one third lens 131, and a fourth
`group lens 14 comprising one fourth lens 141. A diaphragm 17 is
`disposed between the first group lens 11 and the second group lens 12,
`in other words, between the first lens 111 and the second lens 121. A
`cover glass 18 is disposed on the image side of the fourth lens 141.
`An image forming surface 19 is positioned with a gap between the image
`forming surface 19 and the cover glass 18.
`[0020]
` The first lens 111 is provided with a planar shape for the
`object-side lens surface 111a, and with a concave shape for the image-
`side lens surface 111b.
`
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`6
`The second lens 121 is provided with a convex shape for both the
`object-side lens surface 121a and the image-side lens surface 121b.
`The third lens 131 is provided with a concave shape for the object-
`side lens surface 131a, and a convex shape for the image-side lens
`surface 131b. The fourth lens 141 is provided with a convex shape for
`both the object-side lens surface 141a and the image-side lens surface
`141b.
`[0021]
` Where Fno. is the numerical aperture of the imaging lens 10, ω
`is the half viewing angle, and L is the total length of the lens
`system, these values are as follows:
` Fno.=2
` ω=57.5°
` L=12.303 mm
`[0022]
` In addition, where f is the focal distance of the entire lens
`system, ff1 is the focal distance of the first group lens 11 (the
`first lens 111), ff2 is the focal distance of the second group lens 12
`(the second lens 121), ff3 is the focal distance of the third group
`lens 13 (the third lens 131), and ff4 is the focal distance of the
`fourth group lens 14 (the fourth lens 141), these values are as
`follows:
` f=1.9748
` ff1=−7.394
` ff2=2.019
` ff3=−1.089
` ff4=1.545
`[0023]
`
`The imaging lens 10 of the present embodiment satisfies the
`following conditional expressions (1)-(3):
` 1.0 ≤ ff2/f ≤2.0
`
`(1)
` −2.0 ≤ ff2/ff3 ≤−1.0
` (2)
` 0.5 ≤ ff4/f ≤2.0
`
`(3)
`[0024]
` In other words, ff2/f=1.02, ff2/ff3=−1.85, and ff4/f=0.78.
`[0025]
`The imaging lens 10 of the present embodiment satisfies the
`conditional expression (1), so the total length of the lens system can
`be kept short, and curvature of field can be suppressed.
`
`
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`7
`
`In other words, if the upper limit of the conditional expression (1)
`is exceeded, curvature of field increases on the positive side and
`becomes difficult to correct. Below the lower limit of the conditional
`expression (1), curvature of field increases on the negative side and
`becomes difficult to correct. In addition, if the upper limit of the
`conditional expression (1) is exceeded, the positive power of the
`second group lens 12 becomes relatively weaker, making it difficult to
`keep the total length of the lens system short.
`[0026]
`In addition, the imaging lens 10 satisfies the conditional
`expression (2), so the total length of the lens system can be kept
`short, and curvature of field can be suppressed, while suppressing
`chromatic aberration. In other words, if the upper limit of the
`conditional expression (2) is exceeded, the negative power of the third
`group lens provided with a concave shape 131 becomes too weak compared
`to the positive power of the second group lens provided with a convex
`shape 12, so chromatic aberration increases and becomes difficult to
`correct. Therefore, the upper limit is set to −1.0 or less to suppress
`chromatic aberration. The lower limit of the conditional expression (2)
`is for suppressing curvature of field and keeping the total length of
`the lens system short. Below the lower limit of the conditional
`expression (2), the negative power of the third group lens provided
`with a concave shape 131 becomes too strong compared to the positive
`power of the second group lens provided with a convex shape 12, leading
`to an increase in curvature of field. Therefore, the lower limit is set
`to −2.0 or greater to suppress curvature of field. Below the lower
`limit of the conditional expression (2), the positive power of the
`second group lens 12 becomes weak compared to the negative power of the
`third group lens 13, making it difficult to keep the total length of
`the lens system short. A balance between chromatic aberration and
`curvature of field can be achieved by setting the range of the
`conditional expression (2) to −1.9 to −1.3.
`[0027]
` Furthermore, the imaging lens 10 satisfies the conditional
`expression (3), so curvature of field can be better suppressed. In
`other words, if the upper limit of the conditional expression (3) is
`exceeded, curvature of field increases on the positive side and
`becomes difficult to correct. Below the lower limit of the conditional
`expression (3), curvature of field increases on the negative side and
`becomes difficult to correct. Therefore, this range is set to 0.5 to
`2.0 to better suppress curvature of field. A balance of the image
`surface can be achieved by setting the range of the conditional
`expression (3) to 0.7 to 1.7.
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`8
`
`[0028]
` In addition, the following conditional expressions (4) and (5)
`are satisfied in the present embodiment, where νd2 is the Abbe number
`of the second group lens 12 (the second lens 121) and νd3 is the Abbe
`number of the third group lens 13 (the third lens 131):
` νd2 ≥ 40
`(4)
` νd3 ≤ 35
`(5)
`
`[0029]
` In the present embodiment, νd2=52 and νd3=23.4. As a result,
`chromatic aberration can be corrected well with the imaging lens 10
`because the second lens 121, which is made of a low-dispersion
`material, is arranged adjacent to the third lens 131, which is made of
`a high-dispersion material.
`[0030]
` Next, Table 1A shows lens data of the lens surfaces of the
`imaging lens 10. Table 1A specifies the lens surfaces in order
`counting from the object side. Lens surfaces marked with an asterisk
`are aspherical surfaces. In the present embodiment, the object-side
`lens surfaces 121a, 131a and 141a, and the image-side lens surfaces
`121b, 131b and 141b of each of the second lens 121 (the second group
`lens 12), the third lens 131 (the third group lens 13), and the fourth
`lens 141 (the fourth group lens 14) are provided with an aspherical
`shape. S indicates the diaphragm 17. The 9th and 10th surfaces are
`glass surfaces of the cover glass 18. The units for the radius of
`curvature and the spacing are millimeters.
`[0031] Table 1A
`
`Surface No.
`
`Curvature
`Radius
`Infinity
`1st surface
`3.835
`2nd surface
`3rd surface S Infinity
`4th surface * 2.106
`5th surface * −1.760
`6th surface * −0.633
`7th surface * −8.915
`8th surface * 0.949
`9th surface * −3.890
`10th surface
`Infinity
`11th surface
`Infinity
`
`Spacing Nd (refractive
`index)
`1.000
`1.15168
`4.726
`−0.036
`1.279
`0.513
`0.431
`0.057
`1.108
`0.631
`0.300
`0.872
`
`1.5346
`
`1.5168
`
`1.5346
`
`1.6319
`
`νd (Abbe
`number)
`64.2
`
`56.0
`
`23.4
`
`56.0
`
`64.2
`
`[0032]
`Next, Table 1B shows aspherical coefficients for defining the
`aspherical shape of a lens surface made to be aspherical. Table 1B
`also specifies the lens surfaces in order counting from the object
`side.
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`9
`
`Table 1B
`6th Surface 7th Surface 8th Surface 9th Surface
`5th Surface
`4th Surface
`−2.355196
`50.90771
`−11.43756
`−4.732964
`1.00817
`−27.28282
`K
`A4 2.89094E−01 −4.91304E−02 −2.41659E−01 −5.11864E−01 8.08884E−03 9.15869E−02
`−6.14929E−02
`A6 −6.15595E−01 5.14099E−02 3.16267E−01 1.43965E+00 4.3844E−02
`A8 7.23663E−01 −6.30732E−02 1.31348E−01 −2.05869E+00 −5.83106E−02 3.51186E−02
`A10 −4.60752E−01 2.37616E−02 −8.28993E−01 1.78101E+00 3.22554E−02 −1.26469E−02
`A12 0.00000E+00 0.00000E+00 8.33710E−01 −8.46702E−01 −7.77033E−03 1.74905E−03
`A14 0.00000E+00 0.00000E+00 −2.59305E−01 1.71228E−01 −1.21963E−04 2.83005E−05
`A16 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 2.25513E−04 −2.22343E−05
`
`[0033]
`Note that the aspherical shape used for a lens surface is
`expressed by the following formula, where Y is the sag, c is the
`inverse of the curvature radius, K is the conic constant, h is the ray
`height, and A4 is the fourth-order, A6 the sixth-order, A8 the eighth-
`order, A10 the tenth-order, A12 the twelfth-order, A14 the fourteenth-
`order, and A16 the sixteenth-order aspherical coefficient;
`[0034] Numerical formula 1
`
`[0035] (Effect)
`FIG. 2A-2D are an axial chromatic aberration diagram, a lateral
`aberration diagram, a curvature of field diagram, and a distortion
`aberration diagram of the imaging lens 10. The axial chromatic
`aberration diagram of FIG. 2A shows focal shift, with the vertical
`axis showing the wavelength. In the lateral aberration diagram of FIG.
`2B, the horizontal axis shows the coordinates of the entrance pupil,
`and the vertical axis shows the aberration amount. FIG. 2B shows the
`results of a simulation carried out for a plurality of rays of
`different wavelengths. In the curvature of field diagram of FIG. 2C,
`the horizontal axis shows the distance in the optical axis direction,
`and the vertical axis shows the height of the image. In FIG. 2C, S
`indicates the curvature of field aberration in the sagittal plane, and
`T indicates the curvature of field aberration in the tangential plane.
`In the distortion aberration diagram of FIG. 2D, the horizontal axis
`shows the image strain, and the vertical axis shows the height of the
`image. As shown in FIG. 2A, axial chromatic aberration is corrected
`well with the imaging lens 10 of the present embodiment. In addition,
`as shown in FIG. 2B, color bleeding is suppressed. Furthermore, as
`shown in FIGS. 2C and 2D, curvature of field is corrected well.
`Therefore, the imaging lens 10 has high resolution.
`[0036]
`
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`PCT/JP2013/001035
`
`
` In the present embodiment, the object-side lens surfaces 121a,
`131a and 141a, and the image-side lens surfaces 121b, 131b and 141b of
`the second lens 121 (the second group lens 12), the third lens 131
`(the third group lens 13), and the fourth lens 141 (the fourth group
`lens 14) are provided with aspherical shapes, so the imaging lens 10
`takes on a bright configuration. Furthermore, in the present
`embodiment, the total length Lof the lens system can be suppressed to
`a short 12.303 mm.
`[0037] Embodiment 2
`FIG. 3 is a block diagram of the imaging lens 20 of Embodiment 2.
`As shown in FIG. 3, the imaging lens 20 comprises a first group lens
`21 having negative power, a second group lens 22 having positive
`power, a third group lens 23 having negative power, and a fourth group
`lens 24 having positive power, arranged in order from the object side
`toward the image side. The imaging lens 20 of the present embodiment
`is composed of five lenses, with a first group lens 21 comprising one
`first lens 211, a second group lens 22 comprising two lenses, namely a
`second lens 221 and a third lens 222, a third group lens 23 comprising
`one fourth lens 231, and a fourth group lens 24 comprising one fifth
`lens 241. A diaphragm 27 is disposed between the second lens 221 and
`third lens 222 in the second group lens 22. A cover glass 28 is
`disposed on the image side of the fifth lens 241. An image forming
`surface 29 is positioned with a gap between the image forming surface
`29 and the cover glass 28.
`[0038]
` The first lens 211 is provided with a planar shape for the
`object-side lens surface 211a, and with a concave shape for the image-
`side lens surface 211b. The second lens 221 is provided with a convex
`shape for both the object-side lens surface 221a and the image-side
`lens surface 221b. The third lens 231 is provided with a concave shape
`for the object-side lens surface 231a, and a convex shape for the
`image-side lens surface 231b. The fourth lens 241 is provided with a
`convex shape for both the object-side lens surface 241a and the image-
`side lens surface 241b.
`[0039]
` Where Fno. is the numerical aperture of the imaging lens 20, ω
`is the half viewing angle, and L is the total length of the lens
`system, these values are as follows:
`
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`
` Fno.=2
` ω=69.0°
` L=12.300 mm
`[0040]
` In addition, where f is the focal distance of the entire lens
`system, ff1 is the focal distance of the first group lens 21 (the
`first lens 221), ff2 is the focal distance of the second group lens 22
`(the second lens 221 and the third lens 222), ff3 is the focal
`distance of the third group lens 23 (the fourth lens 231), and ff4 is
`the focal distance of the fourth group lens 24 (the fifth lens 241),
`these values are as follows:
` f=1.9055
` ff1=−3.430
` ff2=2.059
` ff3=−1.481
` ff4=2.451
`[0041]
` Note that if ff21 is the focal distance of the second lens 221
`constituting the second group lens 22, and ff22 is the focal distance
`of the third lens 222, these values are as follows:
` ff21=4.080
` ff22=2.685
`[0042]
` The imaging lens 20 of the present embodiment satisfies the
`following conditional expressions (1)-(3):
`(1)
` 1.0 ≤ ff2/f = 1.08≤2.0
`
` −2.0 ≤ ff2/ff3 = −1.39 ≤ −1.0 (2)
` 0.5 ≤ ff4/f = 1.29≤2.0
`
`(3)
`[0043]
` In addition, the following conditional expressions (4) and (5)
`are satisfied by the present embodiment, where νd2 is the Abbe number
`of the third lens 222, which has the higher Abbe number of the second
`lens 221 and the third lens 222 constituting the second group lens 22,
`and νd3 is the Abbe number of the third group lens 23 (the fourth lens
`231).
` νd2 = 56 ≥ 40
`
`
`
`(4)
`
`
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`12
`(5)
`
`
`
` νd3 = 23.4 ≤ 35
`[0044]
` Next, Table 2A shows lens data of each lens surface of the imaging
`lens 20. Table 2A specifies the lens surfaces in order counting from the
`object side. Lens surfaces marked with an asterisk are aspherical
`surfaces. In the present embodiment, the object-side lens surfaces 222a,
`231a and 241a, and the image-side lens surfaces 222b, 231b and 241b of
`each of the third lens 222, the fourth lens 231 (the third group lens
`23), and the fifth lens 241 (the fourth group lens 24) are provided with
`an aspherical shape. S indicates the diaphragm 27. The 12th and 13th
`surfaces are the glass surfaces of the cover glass 28. The units for the
`radius of curvature and the spacing are millimeters.
`[0045] Table 2A
`
`Surface No.
`
`1st surface
` 2nd surface
` 3rd surface
` 4th surface
` 5th surface S
` 6th surface *
` 7th surface *
` 8th surface *
` 9th surface *
`10th surface *
`11th surface *
`12th surface
`13th surface
`
`Curvature
`Radius
`Infinity
`2.029
`7.134
`−3.822
`Infinity
`44.135
`−1.473
`−0.828
`−8.142
`3.144
`−1.905
`Infinity
`Infinity
`
`Spacing
`
`1.005
`2.846
`1.804
`0.042
`0.058
`1.471
`0.386
`0.482
`0.100
`1.423
`0.100
`0.300
`2.207
`
`Nd (refractive
`index)
`1.5891
`
`
`νd (Abbe
`number)
`61.3
`
`
`1.6477
`
`
`
`1.5346
`
`
`1.6323
`
`
`1.5346
`
`
`1.5168
`
`
`33.8
`
`
`
`56.0
`
`
`23.4
`
`
`56.0
`
`
`64.2
`
`
`
`[0046]
`Next, Table 2B shows aspherical coefficients for defining the
`aspherical shape of a lens surface made to be aspherical. Table 2B
`also specifies the lens surfaces in order counting from the object
`side.
`Table 2B
`8th Surface 9th Surface 10th Surface 11th Surface
`7th Surface
`6th Surface
`
`K
`−0.6534266 14.03202
`2.128012
`0
`−4.524449
`−33.86235
`A4 −3.50474E−02 −1.27565E−01 3.64349E−01 3.25046E−02 −2.54735E−01 8.43204E−03
`A6 9.71551E−03 7.82738E−02 −1.21525E−01 8.10461E−02 3.12620E−01 1.06866E−02
`A8 −2.43483E−02 −5.46723E−02 −8.19386E−02 −1.01145E−01 −3.04821E−01 −1.15984E−02
`A10 7.63834E−04 1.26404E−02 1.54306E−01 4.57183E−02 2.00014E−01 7.74896E−03
`A12 5.97866E−03 0.00000E+00 −8.41133E−02 −8.55866E−03 −8.51187E−02 −2.07850E−03
`A14 −8.87636E−03 0.00000E+00 2.02896E−02 4.42919E−04 2.07222E−02 1.16093E−04
`A16 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 −2.15500E−03 3.42064E−05
`
`[0047] (Effect)
`
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`The imaging lens 20 of the present embodiment satisfies the
`
`conditional expressions (1)-(3), so the total length of the lens
`system can be kept short, and curvature of field and chromatic
`aberration can be suppressed. In addition, chromatic aberration can be
`corrected well in the present embodiment because the third lens 222,
`which is made of a low-dispersion material, is arranged adjacent to
`the fourth lens 231, which is made of a high-dispersion material.
`[0048]
` Furthermore, in the present embodiment, the object-side lens
`surfaces 222a, 231a and 241a, and the image-side lens surfaces 222b,
`231b and 241b of each of the third lens 222 of the second group lens
`22, the fourth lens 231 (the third group lens 23), and the fifth lens
`241 (the fourth group lens 24) are provided with an aspherical shape.
`As a result, the numerical aperture Fno. becomes 2, and the imaging
`lens 20 takes on a bright configuration. In addition, the total length
`L of the lens system can also be suppressed to a short 12.300mm in the
`present embodiment.
`[004