US007777972B1
`
`(12) United States Patent
`Chen et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,777,972 B1
`Aug. 17, 2010
`
`(54) IMAGING OPTICAL LENS ASSEMBLY
`(75) Inventors: Chun-Shan Chen, Taichung (TW);
`Hsiang-Chi Tang, Taichung (TW)
`
`(*) Notice:
`
`(73) Assignee: Largan Precision Co., Ltd., Taichung
`(TW)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`(21) Appl. No.: 12/483,748
`
`Jun. 12, 2009
`(22) Filed:
`Foreign Application Priority Data
`(30)
`Feb. 19, 2009
`(TW) .............................. 98105232A
`
`(51) Int. Cl.
`(2006.01)
`GO2B 9/34
`(2006.01)
`GO2B I3/18
`(52) U.S. Cl. ........................ 359/773: 359/715:359/740
`(58) Field of Classification Search ................. 359/715,
`359/738, 740, 773
`See application file for complete search history.
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`7,477.459 B2 *
`1/2009 Liao ........................... 3597773
`7,492,532 B2 * 2/2009 Shin ........................... 3597773
`2004/O136097 A1* 7/2004 Park ........................... 3597773
`2007/0188890 A1* 8, 2007 Jo et al. ...................... 3597773
`
`
`
`
`
`1/2009 Teraoka et al. .............. 3597773
`2009,0009889 A1
`2009/00 15944 A1* 1/2009 Taniyama ......
`... 359,773
`2009/0207507 A1* 8, 2009 Shinohara ................... 3597773
`* cited by examiner
`Primary Examiner Evelyn A. Lester
`(74) Attorney, Agent, or Firm—Birch, Stewart, Kolasch &
`Birch, LLP
`
`ABSTRACT
`(57)
`The present invention provides an imaging optical lens
`assembly including, in order from the object side to the image
`side: a first lens group comprising a first lens element with
`positive refractive power, no lens element with refractive
`power being disposed between the first lens element and an
`imaged object, the first lens element being the only lens
`element with refractive power in the first lens group; and a
`second lens group comprising, in order from the object side to
`the image side: a second lens element with negative refractive
`power; a third lens element; and a fourth lens element;
`whereinfocusing adjustment is performed by moving the first
`lens element along an optical axis, such that as a distance
`between the imaged object and the imaging optical lens
`assembly changes from far to near, a distance between the
`first lens element and an image plane changes from near to
`far; and wherein the number of the lens elements with refrac
`tive power in the imaging optical lens assembly is N, and it
`satisfies the relation: 4sNs5. The abovementioned arrange
`ment of optical elements and focusing adjustment method
`enable the imaging optical lens assembly to obtain good
`image quality and consume less power.
`
`19 Claims, 16 Drawing Sheets
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`U.S. Patent
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`Aug. 17, 2010
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`Sheet 1 of 16
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`140
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`100
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`101 102
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`131
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`132
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`Fig. 1
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`U.S. Patent
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`Aug. 17, 2010
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`Sheet 4 of 16
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`US 7,777,972 B1
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`340
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`300
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`3O 302
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`321-1322
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`331
`
`332
`350
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`360
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`370
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`Fig. 3
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`U.S. Patent
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`Aug. 17, 2010
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`Sheet 7 of 16
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`US 7,777,972 B1
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`531 Y532
`
`550
`
`560 570
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`Fig. 5
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`U.S. Patent
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`Aug. 17, 2010
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`Sheet 8 of 16
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`US 7,777.972 B1
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`
`
`W N 0 0 0 1 ( 98 #7 -------------------
`?^NN () 0.09' ?. 8 §
`}^NN ()()() £ º 9 § 9 …………………………………………….
`
`
`
`8842S
`
`I L '0
`
`
`
`
`
`
`
`
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`U.S. Patent
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`Aug. 17, 2010
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`Sheet 10 of 16
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`US 7,777,972 B1
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`TABLE
`(Embodiment 1)
`f- 4.33 mm, Fno - 2.90. HFOV = 33.5 deg.
`Material
`Index
`Curvature Radius
`Thickness
`
`Abbe H
`
`Focal
`length
`
`Plano
`Piano
`2.16949 (ASP)
`-5,88250 (ASP)
`100.00000 (ASP)
`3.21670 (ASP)
`-2.18540 (ASP)
`-1.04238 (ASP)
`2.90877 (ASP)
`0.96623 (ASP)
`Plano
`Plano
`Plano
`Plano
`Plano
`
`Infinity
`-0.089
`0.900
`0.200
`0.383
`0.64
`0.766
`0.070
`0.581
`0.300
`0.200
`0.500
`0.300
`0.484
`
`Plastic
`
`1.544
`
`55.9
`
`303
`
`Plastic
`
`1632
`
`234
`
`-5.27
`
`Plastic
`
`1530
`
`55.8
`
`3.05
`
`Plastic
`
`1530
`
`55.8
`
`Glass
`
`1517
`
`64.2
`
`Glass
`
`1517
`
`64.2
`
`Surface #
`
`Object
`Ape. Stop
`Lens 1
`
`Lens 2
`
`Lens 3
`
`Lens 4
`
`10
`
`R-fter
`
`Cover Glass
`
`14
`
`Image
`*Object Distance 100mm: surface 3 thickness =
`
`0.287 mm, f- 4.23 mm
`
`Fig.7
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`APPL-1008 / Page 11 of 23
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`U.S. Patent
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`Aug. 17, 2010
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`Sheet 11 of 16
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`US 7,777,972 B1
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`TABLE 2.
`Aspheric Coefficients
`3
`
`4
`
`5
`
`Surface #
`
`2
`
`k = -6.42.322E--00 0.00000E--00 - 1.00000E--03 - 1.63883E--01
`A4 -
`541140E-02 - 1,09227E-02 6.01 150E-02
`.5692OE-01
`A6 = -1964.45E-02 -5.15556E-02 - 82457E-01 - 1.94068E-01
`A8 = -1.14833E-O
`2.49347E-02 2,74168E-OI 2.21 72E-0
`A10 = 7.09572E-01 2.44208E-02 - 1.16446E-01 -1.06404E-01
`A12 = -2.3223OE-00 -4.66235E-02 -2.68287E-01 -4.40642E-02
`A14 it
`3.542.79E-00 -3.82606E-04 4.12009E-01 8.18527E-02
`A16- -2.03569E-00
`-1.82905E-01 -2.86683E-02
`
`Surface it
`
`6
`
`7
`
`8
`
`9
`
`k = -2.29304E+01 -4.53794E--00 -3.30328E-00 -5.73407E-HOO
`A4 = -1.16793E-01 - 19883E-01 -2.18847E-0 -113293E-01
`A6 =
`94.942E-01 3.5878E-02 7.07747E-O2 4.13104E-02
`A8 = -3.69015E-01 3.08158E-03 -489029E-03 -1.28908E-02
`A10= 2.56431E-01 -2.21268E-02 -2.898.61E-03 2.95065E-03
`A12 = 5.959E-02
`13277E-02 346094E-04 -5.61966E-04
`A14= -1.65957E-0
`1865O2E-03 1.72668E-04 7.44048E-05
`A 6= 6.38640E-02 -9.98190E-04 -3.06196E-05 -4.89505E-06
`
`Fig.8
`
`APPL-1008 / Page 12 of 23
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`U.S. Patent
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`Aug. 17, 2010
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`Sheet 12 of 16
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`US 7,777,972 B1
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`TABLE 3
`(Embodiment 2)
`f = 4.25 mm, Fino - 2.90, HFOW - 33.5 deg.
`Curvature Radius Thickness Material
`Index
`
`Abbe if RG
`
`Surface it
`
`O
`1.
`2
`3.
`4
`5
`6
`7
`8
`9
`10
`11
`
`12
`13
`4
`
`Object
`Ape. Stop
`Lens
`
`Lens 2
`
`Lens 3
`
`Lens 4
`
`IR-filter
`
`Cover Glass
`
`Image
`
`Plano
`Plano
`1.89503 (ASP)
`-9.59770 (ASP)
`-21.59870 (ASP)
`4.01330 (ASP)
`-3.30370 (ASP)
`-1.55897 (ASP)
`2.57806 (ASP)
`1.10343 (ASP)
`Plano
`Plano
`
`Piano
`Plano
`Plano
`
`Infinity
`-0.102
`0,900
`0.200
`0.346
`0.504
`0.76
`0.600
`0.350
`0.300
`0.200
`0.500
`
`0.300
`0.089
`
`Plastic
`
`1.544
`
`55.9
`
`2.99
`
`Plastic
`
`1632
`
`234
`
`-533
`
`Plastic
`
`1.544
`
`55.9
`
`4.70
`
`Plastic
`
`1530
`
`55.8
`
`-397
`
`Glass
`
`1.57
`
`642
`
`Glass
`
`517
`
`642
`
`*Object Distance 100mm: surface 3 thickness = 0.283 mm, f = 4.36 mm
`
`Fig.9
`
`APPL-1008 / Page 13 of 23
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`U.S. Patent
`
`Aug. 17, 2010
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`Sheet 13 of 16
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`US 7,777,972 B1
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`TABLE 4
`Aspheric Coefficients
`3
`
`4.
`
`5
`
`Surface #
`
`2
`
`k = -3.87349E-HOO O.OOOOOE-HOO 1.25366E--O2 -3.52526E--0
`A4 r.
`6.3258E-02 5.09.665E-03 8,4381E-02 178238E-01
`A6 = -40087OE-02 -4.18441E.02 - 59342E-01 - 184920E-01
`A8 -
`-5.03443E-02 3,3522OE-02 235534E-OI 2.13392E-0
`AO = 7.6422E-O
`2.23277E-02 - 18827E-01 - 1.04308E-0
`A12 = -2.58.608E--OO 8.2294OE-03 -2.4982E-01 -4.03773E-02
`Al4 = 3,71028E-00 -2.02587E-02 4.34.601E-01 8.43271E-02
`A16= -98.86E-HOO
`-2.097.16E-O -3.19236E-02
`
`Surface #
`
`6
`
`7
`
`8
`
`9
`
`k = -6-08404E01 -3.51853E--00-68.0667E-HO -760755EHOO
`
`A4 -
`
`-9086OE-0 -9. 19376E-02 -2.22385E-01 - 12575OE-0
`
`2.04732E-O2 747643E-O2 4,7329E-02
`A6 = 2.58744E-O
`A8 - -3.73925E-01 5.82878E-03 -4.26 188E-03 - 149248E-02
`A10= 2.464.79E-01 - 172439E-02 -3.05562E-03 3.37376E-03
`A12 - 6.78949E-02 1.26764E-O2 2.692,55E-04 -5.75776E-04
`A 14-c
`- 56664E-01 1.5695E-03 164291E-04 6.22629E-05
`A16= 5.4883 OE-02 - 171070E-03 -2.55825E-05 -347004E-06
`
`Fig.10
`
`APPL-1008 / Page 14 of 23
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`U.S. Patent
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`Aug. 17, 2010
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`Sheet 14 of 16
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`US 7,777,972 B1
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`TABLES
`(Embodiment 3)
`f 4.23 mm, Fno - 2.90. HFOV = 33.5 deg.
`Curvature Radius Thickness Material
`Index
`
`Abbe it fG
`
`Surface #
`
`O
`1
`2
`3
`4
`5
`6
`7
`8
`9
`O
`11
`12
`
`Object
`Ape. Stop
`Lens 1
`
`Lens 2
`
`Lens 3
`
`Lens 4
`
`IR-filter
`
`Cover Glass
`
`Plano
`Plano
`1.83571 (ASP)
`-9.26100 (ASP)
`-6.73390 (ASP)
`6.20280 (ASP)
`-2.4.1850 (ASP)
`-1.12530 (ASP)
`190758 (ASP)
`0.85107 (ASP)
`Plano
`Plano
`Plano
`
`Infinity
`-0.102
`0.900
`0.200
`0.311
`0.555
`0.736
`0.26
`0.320
`O.300
`0.200
`0.500
`0.300
`
`Plastic
`
`1.544
`
`55.9
`
`2.90
`
`Plastic
`
`1.632
`
`23.4
`
`-5.06
`
`Plastic
`
`1544
`
`55.9
`
`3.22
`
`Plastic
`
`1.544
`
`55.9
`
`-3.16
`
`Glass
`
`1517
`
`64.2
`
`Glass
`
`1517
`
`64.2
`
`13
`Plano
`4.
`Image
`Plano
`*Object Distance 100 mm: surface 3 thickness = 0.278 mm, f = 4.35 mm
`
`0.474
`
`Fig.11
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`APPL-1008 / Page 15 of 23
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`U.S. Patent
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`Aug. 17, 2010
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`Sheet 15 of 16
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`US 7,777.972 B1
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`TABLE 6
`Aspheric Coefficients
`3
`
`4
`
`5
`
`Surface #
`
`2
`
`k = -3.68354E--00 42.7537E-01 - 1.18048E -02 - 4.8668E-HO
`A4 = 6.6097OE-02 4.25004E-03 8.41 135E-02 1872O8E-O
`A6 F -3.9289E-O2 -4.02627E-02 - 16690E-0 - 184789E-01
`A8 or
`-5.48599E-02 3,32827E-02 2.46696E-01 2.09987E-01
`A10 = 7.67707E-01 -2.8444E-02 - 10007E-01 -1.0.0444E-01
`A12 = -2.57677E--00 9.96757E-03 -2.51777E-0 -3.2931E-02
`A14 = 3.69371E-00 -3.24649E-02 4.19955E-01 8.88264E-02
`A16= -198154E-HO0 -3.5583OE-04 -2.15316E-01 -4.33497E-02
`
`Surface #
`6
`7
`8
`9
`k = -3.22944E--0 -3.251.33E--00-40863OE-01 -6.51806E--00
`A4 = -2.08072E-01 -9.36284E-02 -2,08003E-01 - 143476E-01
`A6 -
`2.67223E-0
`147155E-02 7.38545E-02 5.61405E-02
`A8 -
`-3.84575E-01 5.87603E-03 -4.41204E-03 - 167975E-02
`A 10-
`2.37336E-01 -159335E-02 -3.08.231E-03 3.32273E-03
`A12 = 6.76477E-02
`.30256E-02 2.62777E-04 -528673E-04
`A 14-of
`-1.53505E-0
`156088E-03 E.639.16E-04 6.68925E-05
`A16- 5.58447E-02 - 182229E-03 -251552E-05 -5.25040E-06
`
`Fig. 12
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`APPL-1008 / Page 16 of 23
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`U.S. Patent
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`Aug. 17, 2010
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`Sheet 16 of 16
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`US 7,777.972 B1
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`TABLE 7
`Embodiment Embodiment Embodiment
`3
`1
`2
`
`f
`Fino
`HFOW
`N
`fmax/fmin
`|BFLl-BFL2
`(D1-D2)* 100/f
`V
`V2
`
`T34/T23
`TTL/ImgH
`
`4.33
`2.90
`33.5
`4
`1.02
`0.0
`2.02
`55.9
`23.4
`1.43
`1.42
`0.
`1.84
`
`4.25
`2.90
`33.5
`4
`1.03
`0.0
`1.98
`55.9
`23.4
`42
`0.90
`19
`1.75
`
`4.23
`2.90
`33.5
`4
`1.03
`0.0
`1.87
`55.9
`23.4
`1.46
`1.3
`0.47
`
`1.75
`
`Fig.13
`
`APPL-1008 / Page 17 of 23
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`1.
`MAGING OPTICAL LENS ASSEMBLY
`
`US 7,777,972 B1
`
`BACKGROUND OF THE INVENTION
`
`10
`
`15
`
`1. Field of the Invention
`The present invention relates to an imaging optical lens
`assembly, and more particularly, to an imaging optical lens
`assembly with focusing adjustment.
`2. Description of the Prior Art
`In recent years, with the popularity of camera mobile
`phones, the demand for compact photographing lenses is
`increasing, and the sensor of a general photographing camera
`is none other than CCD (charge coupled device) or CMOS
`device (Complementary Metal Oxide Semiconductor
`device). Furthermore, as advanced semiconductor manufac
`turing technology has allowed the pixel size of sensors to be
`reduced and compact photographing lenses have gradually
`evolved toward higher megapixels, there is an increasing
`demand for compact photographing lenses featuring better
`image quality.
`A conventional compact photographing lens equipped in a
`mobile phone is usually a single focus lens having a fixed
`focal length. For a specific object distance, since the photo
`graphing lens has a limited depth of field, it is apt to produce
`blurred images. Therefore, as the resolution of compact pho
`25
`tographing lenses increases, a focusing adjustment function
`becomes more and more indispensable as well. Generally, a
`photographing lens with focusing adjustment function per
`forms focusing adjustment by using a driving motor to move
`the entire photographing lens relative to the sensor. However,
`Such a photographing lens requires higher power consump
`tion because the driving motor is configured to drive the entire
`photographing lens. Moreover, the photographing lens has a
`relatively long total track length.
`
`30
`
`SUMMARY OF THE INVENTION
`
`35
`
`40
`
`45
`
`The present invention provides an imaging optical lens
`assembly including, in order from the object side to the image
`side: a first lens group comprising a first lens element with
`positive refractive power, no lens element with refractive
`power being disposed between the first lens element and an
`imaged object, the first lens element being the only lens
`element with refractive power in the first lens group; and a
`second lens group comprising, in order from the object side to
`the image side: a second lens element with negative refractive
`power; a third lens element; and a fourth lens element, focus
`ing is performed by moving the first lens element along the
`optical axis, Such that as a distance between the imaged object
`and the imaging optical lens assembly changes from far to
`near, a distance between the first lens element and the imaging
`Surface changes from near to far, and during focusing the
`other lens elements in the imaging optical lens assembly do
`not move relative to the imaging plane; and wherein the
`number of the lens elements with refractive power in the
`imaging optical lens assembly is N, and it satisfies the rela
`tion: 4sNs5.
`According to one aspect of the present invention, there is
`provided a method for performing focusing for an imaging
`optical lens assembly; wherein the lens assembly includes, in
`order from the object side to the image side: a first lens group
`comprising a first lens element with positive refractive power,
`no lens element with refractive power being disposed
`between the first lens element and an imaged object, the first
`lens element being the only lens element with refractive
`65
`power in the first lens group; and a second lens group com
`prising, in order from the object side to the image side: a
`
`50
`
`55
`
`60
`
`2
`second lens element with negative refractive power; a third
`lens element; and a fourth lens element; and wherein the
`method for performing focusing includes moving the first
`lens element along the optical axis, such that as a distance
`between the imaged object and the imaging optical lens
`assembly changes from far to near, a distance between the
`first lens element and the imaging Surface changes from near
`to far, and during focusing the other lens elements in the
`imaging optical lens assembly can either move or not move
`relative to the imaging plane.
`The aforementioned arrangement of lens groups can effec
`tively improve the image quality of the imaging optical lens
`assembly. In the present imaging optical lens assembly, a
`single lens element, the first lens element, is selected to move
`along the optical axis to perform the focusing adjustment so
`that less power will be consumed during the focusing process.
`In addition, by selecting the first lens element to perform
`focusing adjustment, the number of lens groups can be
`reduced to effectively reduce the variability in the assembly/
`manufacturing of the imaging optical lens assembly.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows an imaging optical lens assembly in accor
`dance with a first embodiment of the present invention.
`FIG.2 shows the aberration curves of the first embodiment
`of the present invention.
`FIG. 3 shows an imaging optical lens assembly in accor
`dance with a second embodiment of the present invention.
`FIG. 4 shows the aberration curves of the second embodi
`ment of the present invention.
`FIG. 5 shows an imaging optical lens assembly in accor
`dance with a third embodiment of the present invention.
`FIG. 6 shows the aberration curves of the third embodiment
`of the present invention.
`FIG. 7 is TABLE 1 which lists the optical data of the first
`embodiment.
`FIG. 8 is TABLE 2 which lists the aspheric surface data of
`the first embodiment.
`FIG.9 is TABLE3 which lists the optical data of the second
`embodiment.
`FIG.10 is TABLE 4 which lists the aspheric surface data of
`the second embodiment.
`FIG. 11 is TABLE5 which lists the optical data of the third
`embodiment.
`FIG. 12 is TABLE 6 which lists the aspheric surface data of
`the third embodiment.
`FIG. 13 is TABLE 7 which lists the data of the respective
`embodiments resulted from the equations.
`
`DETAILED DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`The present invention provides an imaging optical lens
`assembly including, in order from the object side to the image
`side: a first lens group comprising a first lens element with
`positive refractive power, no lens element with refractive
`power being disposed between the first lens element and an
`imaged object, the first lens element being the only lens
`element with refractive power in the first lens group; and a
`second lens group comprising, in order from the object side to
`the image side: a second lens element with negative refractive
`power; a third lens element; and a fourth lens element;
`wherein focusing is performed by moving the first lens ele
`ment along the optical axis, such that as a distance between
`the imaged object and the imaging optical lens assembly
`changes from far to near, a distance between the first lens
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`element and the imaging Surface changes from near to far, and
`wherein the number of the lens elements with refractive
`power in the imaging optical lens assembly is N, and it satis
`fies the relation: 4sNs5.
`When the relation of N=5 is satisfied, the fifth lens element
`can be disposed between the first and second lens elements,
`the third and fourth lens elements, or the fourth lens element
`and the image plane.
`In the aforementioned imaging optical lens assembly, the
`focallength of the imaging opticallens assembly is f when the
`first lens element is positioned closest to the image plane, the
`focal length of the first lens element is f1, the focal length of
`the third lens element is f3, and they satisfy the relations:
`1.0<f7f1<1.7, 0.6<f/f3<1.8.
`When f7fl satisfies the above relation, the displacement
`distance of the first lens element will not be too large, thus the
`total track length (TTL) of the imaging optical lens assembly
`will not become too long. This also ensures that the move
`ment of the first lens element relative to the image plane has
`enough sensitivity required for focusing adjustment. By hav
`ing the first lens element move along the optical axis to
`perform the focusing adjustment (the so-called internal
`focusing method), the total track length of the imaging optical
`lens assembly can be shortened effectively. TTL is defined as
`the on-axis spacing between the object-side Surface of the first
`lens element and the image plane when the first lens element
`is positioned closest to the imaged object.
`The relation 0.63/f3<1.8 enables the third lens element to
`effectively distribute the refractive power of the optical sys
`tem, reducing the sensitivity of the optical system.
`In the aforementioned imaging optical lens assembly, the
`on-axis spacing between the image-side surface of the first
`lens element and the image plane is D1 when the first lens
`element is positioned closest to the imaged object, the on-axis
`spacing between the image-side Surface of the first lens ele
`ment and the image plane is D2 when the first lens element is
`positioned closest to the image plane, the focal length of the
`imaging optical lens assembly is f when the first lens element
`is positioned closest to the image plane, and they satisfy the
`relation: 1.0<(D1-D2)*100/f-3.0.
`When the above relation is satisfied, the movement of the
`first lens element relative to the image plane has enough
`sensitivity required for focusing adjustment. The above rela
`tion also prevents the displacement distance of the first lens
`element from becoming too large.
`In the aforementioned imaging optical lens assembly, the
`on-axis spacing between the third lens element and the fourth
`lens element is T34, the on-axis spacing between the second
`lens element and the third lens element is T23, and they
`satisfy the relation: 0.2<T34/T23<1.6.
`When the above relation is satisfied, the off-axis aberration
`of the imaging optical lens assembly can be effectively cor
`rected. The above relation also prevents the back focal length
`from becoming too short and thus causing the rear end of the
`lens assembly to have insufficient space to accommodate
`mechanical components.
`In the aforementioned imaging optical lens assembly, the
`maximum focallength of the imaging opticallens assembly is
`f, the minimum focal length of the imaging optical lens
`assembly is f, and they satisfy the relation: 1sf/
`60
`fis1.05.
`The above relation prevents the displacement distance of
`the first lens element from becoming too large and keeps the
`magnifying power of the optical system within a proper
`range.
`In the aforementioned imaging optical lens assembly, the
`back focal length of the imaging optical lens assembly is
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`BFL1 when the first lens element is positioned closest to the
`imaged object, the back focal length of the imaging optical
`lens assembly is BFL2 when the first lens element is posi
`tioned closest to the image plane, and they satisfy the relation:
`BFL1-BFL2<0.1 mm.
`Preferably, BFL1 and BFL2 satisfy the relation: IBFL1
`BFL2|=0.
`When the above relation is satisfied, the image plane can be
`fixed and the number of moving elements can be reduced,
`thereby reducing the cost and the variability in the manufac
`turing of the lens assembly.
`In the aforementioned imaging optical lens assembly, it is
`preferable that the first lens element has a convex object-side
`surface so that the refractive power thereof can be enhanced to
`shorten the total track length of the imaging optical lens
`assembly.
`In the aforementioned imaging optical lens assembly, it is
`preferable that the fourth lens element has a concave image
`side Surface.
`In the aforementioned imaging optical lens assembly, it is
`preferable that the second lens element has a concave image
`side Surface and the third lens element has a concave object
`side Surface and a convex image-side Surface, so that accu
`mulation of aberrations can be avoided.
`In the present imaging optical lens assembly, the first lens
`element provides a positive refractive power, and the aperture
`stop is located near the object side of the imaging optical lens
`assembly, thereby the exit pupil of the imaging optical lens
`assembly can be positioned far away from the image plane.
`Therefore, the light will be projected onto the electronic
`sensor at a nearly perpendicular angle, and this is the telecen
`tric feature of the image side. The telecentric feature is very
`important to the photosensitive power of the current solid
`state electronic sensor as it can improve the photosensitivity
`of the electronic sensor to reduce the probability of the occur
`rence of shading.
`In addition, in optical systems with a wide field of view, the
`correction of distortion and chromatic aberration of magnifi
`cation is especially necessary, and the correction can be made
`by placing the aperture stop in a location where the refractive
`power of the optical system is balanced. In the present imag
`ing optical lens assembly, if the aperture stop is disposed
`between the first lens element and the imaged object, the
`telecentric feature will be enhanced to reduce the total track
`length of the optical system; if the aperture stop is disposed
`between the first lens element and the second lens element,
`the wide field of view is emphasized. Such an arrangement of
`the aperture stop also effectively reduces the sensitivity of the
`optical system.
`In the present imaging optical lens assembly, the lens ele
`ments can be made of glass or plastic material. If the lens
`elements are made of glass, there is more flexibility in dis
`tributing the refractive power of the optical system. If plastic
`material is adopted to produce lens elements, the production
`cost will be reduced effectively. Additionally, the surfaces of
`the lens elements can beformed to be aspheric and made to be
`non-spherical easily, allowing more design parameter free
`dom which can be used to reduce aberrations and the number
`of the lens elements, so that the total track length of the
`imaging optical lens assembly can be shortened effectively.
`In the aforementioned imaging optical lens assembly, it is
`preferable that the third lens element has a positive refractive
`power so that the refractive power of the optical system can be
`distributed effectively.
`In the aforementioned imaging optical lens assembly, it is
`preferable that the Abbe number of the second lens element is
`V2, and it satisfies the relation: V2<29.
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`The above relation facilitates the correction of the chro
`matic aberration of the optical system.
`And it will be more preferable that V2 satisfies the relation:
`V2<25.
`In the aforementioned imaging optical lens assembly, it is
`preferable that the Abbe number of the first lens element is
`V1, and it satisfies the relation: 50<V1<62.
`The above relation facilitates the correction of the astig
`matism of the optical system.
`In the aforementioned imaging optical lens assembly, it is
`preferable that the second lens element has a concave object
`side Surface.
`According to another aspect of the present invention, the
`aforementioned imaging optical lens assembly further com
`prises an electronic sensor on which an object is imaged.
`15
`When the first lens element is positioned closest to the imaged
`object, the total track length of the imaging optical lens
`assembly is TTL, which is defined as the on-axis spacing
`between the object-side surface of the first lens element and
`the image plane when the first lens element is positioned
`closest to the imaged object, and the maximum image height
`of the imaging optical lens assembly is ImgH, which is
`defined as half of the diagonal length of the effective pixel
`area of the electronic sensor, and they satisfy the relation:
`TTL/ImgH<1.95.
`The above relation enables the imaging optical lens assem
`bly to maintain a compact form.
`Preferred embodiments of the present invention along with
`the appended drawings will be described in the following
`paragraphs.
`FIG. 1 shows an imaging optical lens assembly in accor
`dance with a first embodiment of the present invention, and
`FIG. 2 shows the aberration curves of the first embodiment of
`the present invention. The imaging optical lens assembly of
`the first embodiment of the present invention, which mainly
`comprises two lens groups, includes, in order from the object
`side to the image side:
`a first lens group comprising a plastic first lens element 100
`with positive refractive power having a convex object-side
`surface 101 and a convex image-side surface 102, the object
`side and image-side surfaces 101 and 102 of the first lens
`element 100 being aspheric, no lens element with refractive
`power being disposed between the first lens element 100 and
`an imaged object, the first lens element being the only lens
`element with refractive power in the first lens group
`a second lens group comprising, in order from the object
`side to the image side:
`a plastic second lens element 110 with negative refractive
`power having a convex object-side surface 111 and a
`concave image-side Surface 112, the object-side and
`image-side surfaces 111 and 112 of the second lens
`element 110 being aspheric;
`a plastic third lens element 120 having a concave object
`side Surface 121 and a convex image-side Surface 122.
`the object-side and image-side surfaces 121 and 122 of
`the third lens element 120 being aspheric; and
`a plastic fourth lens element 130 having a convex object
`side Surface 131 and a concave image-side Surface 132,
`the object-side and image-side surfaces 131 and 132 of
`the fourth lens element 130 being aspheric;
`an aperture stop 140 disposed between the first lens ele
`ment 100 and the imaged object;
`an IR filter 150 disposed between the image-side surface
`132 of the fourth lens element 130 and the image plane 170,
`the IR filter 150 having no influence on the focal length of the
`imaging optical lens assembly:
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`a sensor cover glass 160 disposed between the IR filter 150
`and the image plane 170, the sensor coverglass 160 having no
`influence on the focal length of the imaging optical lens
`assembly; and
`an image plane 170 disposed behind the sensor cover glass
`160.
`Focusing is performed by moving the first lens element
`along the optical axis, such that as a distance between the
`imaged object and the imaging optical lens assembly changes
`from far to near, a distance between the first lens element and
`the imaging Surface changes from near to far, and during
`focusing the other lens elements in the imaging optical lens
`assembly do not move relative to the imaging plane.
`The equation of the aspheric Surface profiles is expressed
`as follows:
`
`wherein:
`X: the height of a point on the aspheric Surface at a distance
`Y from the optical axis relative to the tangential plane at the
`aspheric Surface vertex;
`Y: the distance from the point on the curve of the aspheric
`Surface to the optical axis;
`k: the conic coefficient;
`Ai: the aspheric coefficient of order i.
`In the first embodiment of the present imaging optical lens
`assembly, the maximum focal length of the imaging optical
`lens assembly is f, the minimum focal length of the imag
`ing optical lens assembly is f, and they satisfy the relation:
`f/ft, 1.02.
`In the first embodiment of the present imaging optical lens
`assembly, the back focal length of the imaging optical lens
`assembly is BFL1 when the first lens element 100 is posi
`tioned closest to the imaged object, the back focal length of
`the imaging optical lens assembly is BFL2 when the first lens
`element 100 is positioned closest to the image plane 170, and
`they satisfy the relation: IBFL1-BFL2|=0.0.
`In the first embodiment of the present imaging optical lens
`assembly, the on-axis spacing between the image-side Surface
`102 of the first lens element 100 and the image plane 170 is D1
`when the first lens element 100 is positioned closest to the
`imaged object, the on-axis spacing between the image-side
`surface 102 of the first lens element 100 and the image plane
`170 is D2 when the first lens element 100 is positioned closest
`to the image plane 170, the focal length of the imaging optical
`lens assembly is f when the first lens element 100 is posi
`tioned closest to the image plane 170, and they satisfy the
`relation: (D1-D2)*100/f-2.02.
`In the first embodiment of the present imaging optical lens
`assembly, the Abbe number of the first lens element 100 is V1,
`and it satisfies the relation: V1=55.9.
`In the first embodiment of the present imaging optical lens
`assembly, the Abbe number of the second lens element 110 is
`V2, and it satisfies the relation: V2=23.4.
`In the first embodiment of the present imaging optical lens
`assembly, the on-axis spacing between the third lens element
`120 and the fourth lens element 130 is T34, the on-axis
`spacing between the second lens element 110 and the third
`lens element 120 is T23, and they satisfy the relation: T34/
`T23=0.11.
`In the first embodiment of the present imaging optical lens
`assembly, the focal length of the imaging optical lens assem
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`bly is f when the first lens element 100 is positioned closest to
`the image plane 170, the focal length of the first lens element
`100 is fl, the focal length of the third lens element 120 is f3,
`and they satisfy the relations: f/fl=1.43, f/f3=1.42.
`In the first embodiment of the present imaging optical lens 5
`assembly, the image plane 170 is provided with an electronic
`sensor on which an object is imaged. When the first lens
`element 100 is positioned closest to the imaged object, the
`total track length of the imaging optical lens assembly is TTL
`and the maximum image height of the imaging optical lens
`assembly is ImgH, and they satisfy the relation: TTL/
`ImgH=1.84.
`The detailed optical data of the first embodiment is shown
`in FIG. 7 (