`

`Patent Application Publication
`
`Jan. 22, 2004 Sheet 1 of 11
`
`US 2004/0012861 Al
`
` Ex. 1006
`Page 2
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`IMAGE PICKUP
`
`UNIT
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` Ex. 1006
`Page 5
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`US 2004/0012861 Al
`
`Jan.22,2004
`
`1
`
`IMAGE PICKUP LENS, IMAGE PICKUP UNIT
`AND PORTABLE TERMINAL
`
`BACKGROUND OF THE INVENTION
`
`[0001] 1. Field of the Invention
`[0002] The invention relates to an image pickup lens
`preferable as an optical system of a solid state pickup
`element such as a CCD type image sensor or a CMOS type
`image sensor, an image pickup unit having the image picl'"t1p
`lens, and a portable terminal having the image pickup unit.
`[0003] 2. Description of Related Art
`[0004]
`In recent years, with the heightened performance
`and the miniaturization of an image pickup device using a
`solid-state image pickup element such as a CCD (charge
`coupled device) type image sensor or a CMOS (comple(cid:173)
`mentary metal oxide semiconductor) type image sensor, a
`portable terminal and a personal computer respectively
`having the image pickup device have spread to users.
`[0005] Also, with the miniaturization and
`the dense
`arrangement of pixels of the element due to the increase of
`functions in the portable terminal and the personal computer,
`the further miniaturization of an image pickup lens mounted
`on the image pickup device is strongly required for the
`miniaturization of the image pick7.1p device.
`[0006]
`In recent years, because a triplet lens structure can
`have higher performance as compared with a single lens
`structure and a doublet lens structure, the triplet lens struc(cid:173)
`ture composed of a first lens having the positive refractive
`power, a second lens having the negative refractive power
`and a third lens having the positive refractive power
`arranged in that order from an object side has been generally
`used as an image pickup lens of a small-sized image pickup
`device. This triplet type image pickup lens is disclosed in
`Published Unexamined Japanese Patent Application (Toku(cid:173)
`kai) No. 2001-75006.
`[0007] However, in the image pickup lens disclosed in the
`Application No. 2001-75006, though various types aberra(cid:173)
`tion are preferably corrected while maintaining the ,vide
`angle of view, the image pickup lens is not appropriate to the
`shortening of a total lens length (that is, a distance from an
`aperture stop to a focal point on an image side) along an
`optical axis.
`
`SUMMARY OF THE INVENTION
`
`[0008]
`In an order to solve the above problem, an object
`of the present invention is to provide an image pickup lens
`which is composed of a plurality of lenses and is miniatur(cid:173)
`ized, an image pickup unit and a portable terminal.
`[0009]
`In an order to accomplish the above-mentioned
`object, in accordance ,vith the first aspect of the present
`invention, an image pickup lens comprising four lenses
`arranged in an order of a first lens, a second lens, a third lens
`and a fourth lens from an object side,
`[0010] wherein the first lens has positive refractive power
`and has a convex surface facing toward the object side, the
`second lens has the positive refractive power, the third lens
`has negative refractive power and has a concave surface
`facing toward the object side to be formed in a meniscus
`shape, and the fourth lens has the positive or negative
`
`refractive power and has a convex surface facing toward the
`object side to be formed in the meniscus shape.
`[0011]
`In the above configuration, four lenses are arranged
`in an order of the first, second, third and fourth lenses. In use,
`the first lens is placed on the object side, and the fourth lens
`is placed on an image side. In this use condition, the positive
`lens group and the negative lens respectively having the
`comparatively strong refractive power are arranged in that
`order from the object side, and the convex surface of the first
`lens faces toward the object side. Therefore, a total lens
`length is shortened. Here, the total lens length denotes a
`distance on an optical axis from the object side surface of the
`first lens to an image side focal point of the whole image
`pickup lens. However, in the image pickup lens having an
`aperture stop arranged nearest to the object side, the total
`lens length denotes a distance on an optical axis from the
`aperture stop to the image side focal point of the whole
`image pickup lens. This definition of the total lens length is
`effective in this specification including claims.
`[0012] Also, the concave surface of the third lens formed
`in the meniscus shape faces toward the object side, and the
`convex surface of the fourth lens formed in the meniscus
`shape faces toward the object side. Therefore, an air lens
`having the positive refractive power is formed between the
`third and fourth lenses. Accordingly, the total lens length can
`be further shortened, and a telecentric characteristic can be
`maintained in the periphery of an image screen.
`[0013] Here, the fourth lens has the shape and orientation
`of the convex surface described above and can have the
`positive or negative refractive power. Hereinafter, "positive
`or negative refractive power" denotes that any of the posi(cid:173)
`tive refractive power and the negative refractive power is
`allowed.
`[0014] Preferably, following conditional formulas (1), (2)
`and (3) are satisfied:
`
`L/2Y<1.60
`
`0.40<{12/f<0.70
`
`(1)
`(2)
`
`(J),
`25<{(v1+v2)/2}-v1
`[0015] where L denotes a distance on an optical axis from
`the object side surface of the first lens to an image side focal
`point ~f the whole image pickup lens, 2Y denotes the length
`of a diagonal line on an effective image screen, fl2 denotes
`a combined focal length of the first lens and the second lens,
`f denotes a focal length of the whole image pickup lens, vl
`denotes an Abbe number of the first lens, v2 denotes an Abbe
`number of the second lens, and v3 denotes an Abbe number
`of the third lens.
`[0016] The conditional formulas (1) to (3) indicate con(cid:173)
`ditions for obtaining a miniaturized image pickup lens in
`which aberration is preferably corrected. Here, L of the
`conditional formula (1) denotes a distance on an optical axis
`from the object side surface of the first lens to the image side
`focal point of the whole image pickup lens. The "image side
`focal point" denotes an image point obtained when a parallel
`ray parallel to the optical axis is incident on the image
`pickup lens. Also, when an optical member of a plane
`parallel plate shape such as a low pass filter is arranged in
`a space between the surface of the image pickup lens nearest
`to the image side and the image side focal point, the distance
`L is converted into a distance L in air, and the distance Lin
`air satisfies the formula (1).
`
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`Page 13
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`US 2004/0012861 Al
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`Jan.22,2004
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`2
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`[0017] The conditional formula (1) indicates a condition
`for achieving the shortening of the total lens length. When
`L/2Y is lower than the upper limit of the conditional formula
`(1), the total lens length is directed to be shortened.
`
`[0018] Also, as to the conditional formula (2) for appro(cid:173)
`priately setting the combined focal length of the first lens
`and the second lens, when f2/f is set to be higher than the
`lower limit, the combined positive refractive power of the
`first lens and the second lens is not excessively enlarged, the
`generation of both the high-order spherical aberration and
`the coma can be suppressed. Also, when f2/f is set to be
`lower than the upper limit, the combined positive refractive
`power of the first lens and the second lens is appropriately
`obtained, and the total lens length can be shortened.
`
`[0019] Also, as to the conditional formula (3) for the
`correction of the chromatic aberration in the first and second
`lenses having the positive refractive power and the third lens
`having the negative refractive power, when {(vl+v2)/2}-v3
`is set to be higher than the lower limit, the axial chromatic
`aberration and the lateral chromatic aberration can be cor(cid:173)
`rected.
`
`[0020] Preferably, an aperture stop is arranged nearest to
`the object side. Because of the configuration of the aperture
`stop arranged nearest to the object side, the position of an
`exit pupil can be set away from an image surface. Therefore,
`a principal ray of a light flux emerging from the final surface
`of the lenses is incident on a solid-state image pick-up
`element at an angle near a right angle. That is, the image side
`telecentric characteristic required for the image pickup lens
`of the solid-state image pickup element can be preferably
`obtained, and a shading phenomenon in the periphery of an
`image screen can be reduced.
`
`[0021] Preferably, the image pickup lens satisfies follow(cid:173)
`ing conditional formulas (4), (5) and (6):
`
`L'/2Y<1.60
`
`0.40<f12//<0.70
`
`(4)
`
`(5)
`
`25<{(v1+v2)/2}-v3
`(6),
`[0022] where L' denotes a distance on an optical axis from
`the aperture stop to an image side focal point of the whole
`image pickup lens, 2Y denotes the length of a diagonal line
`on an effective image screen, f12 denotes a combined focal
`length of the first lens and the second lens, f denotes a focal
`length of the whole image pickup lens, vl denotes an Abbe
`number of the first lens, v2 denotes an Abbe number of the
`second lens, and v3 denotes an Abbe number of the third
`lens.
`
`[0023] The conditional formulas (4) to (6) indicate con(cid:173)
`ditions for obtaining a miniaturized image pickup lens in
`which aberration is preferably corrected. Here, L' of the
`conditional formula ( 4) denotes a distance on an optical axis
`from the aperture stop to the image side focal point of the
`whole image pickup lens. The "image side focal point"
`denotes an image point obtained when a parallel ray parallel
`to the optical axis is incident on the image pick-up lens. Also,
`when an optical member of a plane parallel plate shape such
`as a low pass filter is arranged in a space between the surface
`of the image pickup lens nearest to the image side and the
`image side focal point, the distance L' is converted into a
`distance L' in air, and the distance L' in air satisfies the
`formula (4).
`
`[0024] The conditional formula (4) indicates a condition
`for achieving the shortening of the total lens length. When
`L'/2Y is lower than the upper limit of the conditional
`formula (4), the total lens length is directed to be shortened.
`[0025] Also, as to the conditional formula (5) for appro(cid:173)
`priately setting the combined focal length of the first lens
`and the second lens, when f2/f is set to be higher than the
`lower limit, the combined positive refractive power of the
`first lens and the second lens is not excessively enlarged, the
`generation of both the high-order spherical aberration and
`the coma can be suppressed. Also, when f2/f is set to be
`lower than the upper limit, the combined positive refractive
`power of the first lens and the second lens is appropriately
`obtained, and the total lens length can be shortened.
`[0026] Also, as to the conditional formula ( 6) for the
`correction of the chromatic aberration in the first and second
`lenses having the positive refractive power and the third lens
`having the negative refractive power, when { (vl +v2 )/2}-v3
`is set to be higher than the lower limit, the axial chromatic
`aberration and the lateral chromatic aberration can be cor(cid:173)
`rected.
`[0027] When an aperture stop is arranged nearest to the
`object side, the total lens length can be set to a distance from
`the aperture stop to the image side focal point of the whole
`image pickup lens, and the calculation based on the total lens
`length is preferred.
`[0028] Preferably, follmving conditional formulas (7) and
`(8) are satisfied:
`
`-0.40<1?5/ ((N3-1)-f) <-0.20
`
`(7)
`
`(8),
`0.30<fa/f<D.50
`[0029] where f denotes a focal length of the whole image
`pickup lens, RS denotes a curvature radius of the object side
`surface of the third lens facing, N3 denotes a refractive index
`of the third lens at a d-line, and fa denotes a focal length of
`an air lens formed by an image side surface of the third lens
`and the object side surface of the fourth lens.
`
`[0030] When the negative refractive power of the object
`side surface of the third lens is appropriately set, the
`conditional formula (7) indicates a condition for easily
`correcting a curvature of the image surface and flattening the
`image surface. Here, the focal length of the object side
`surface of the third lens is expressed by R5/(N3-l) by using
`the curvature radius RS and the refractive index N3 of the
`third lens. The conditional formula (7) indicates a ratio of the
`focal length of the object side surface of the third lens to the
`focal length of the whole image pickup lens.
`
`[0031] When R5/((N3-l)·f) is lower than the higher limit
`of the conditional formula (7), the negative refractive power
`of the object side surface of the third lens is not excessively
`enlarged, and the generation of excessive spherical aberra(cid:173)
`tion and the generation of coma flare of an abaxial light flux
`can be suppressed. When R5/((N3-l)·f) is higher than the
`lower limit, the negative refractive power of the object side
`surface of the third lens is maintained. Therefore, a positive
`Petzval's sum is lowered, the axial chromatic aberration and
`the lateral chromatic aberration can be preferably corrected
`in addition to the correction of the curvature of the image
`surface.
`
`[0032] The conditional formula (8) indicates a condition
`for appropriately setting the positive refractive power of the
`
` Ex. 1006
`Page 14
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`US 2004/0012861 Al
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`Jan.22,2004
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`3
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`air lens formed between the image side surface of the third
`lens and the object side surface of the fourth lens. The focal
`length fa of the air lens can be calculated according to a
`formula:
`
`fa=R6-R7/ [R7·(1-N3 )+R6·(N4-1 )-D6·(1-N3)-(N4-
`1)],
`[0033] where N3 denotes the refractive index of the third
`lens at the d-line. N4 denotes a refractive index of the fourth
`lens at the d-line, R6 denotes a curvature radius of the image
`side surface of the third lens, R7 denotes a curvature radius
`of the object side surface of the fourth lens, and D6 denotes
`an interval of an air space on the optical axis between the
`third and fourth lenses.
`[0034] When the conditional formula (8) is satisfied, the
`curvature of the image surface and the distortion can be
`corrected. and the telecentric characteristic of the light flux
`on the image side can be maintained.
`[0035] Further preferably, in place of the conditional for(cid:173)
`mula (8), a follmving conditional formula (9) is satisfied:
`
`(9).
`-0.40<R5/((N3-1 )f)<-0.25
`[0036] Preferably, an image side surface of the fourth lens
`satisfies a following conditional formula (10):
`
`X-Xll<O
`(10)
`[0037]
`for a displacement value X of an aspherical surface
`expressed in the formula (11):
`
`h2 i RS
`X = --====== + LA;h'
`I+ ✓ I - (I+ KS)h2 / RS2
`
`(11)
`
`[0038] and a displacement value XO of a rotational qua(cid:173)
`dratic surface component of the aspherical surface expressed
`in the formula (12):
`
`shape satisfying the formulas (10), (11) and (12). Therefore,
`the telecentric characteristic particularly for the light flux at
`the high angle of view can be maintained.
`
`[0042] Preferably, the first lens is formed out of glass
`material, and the second, third and fourth lenses are formed
`out of plastic material.
`
`[0043] The term "formed out of plastic material" includes
`that the coating processing is performed on the surface of a
`substance including the plastic material as base material for
`the purpose of the anti-reflection or the improvement of
`surface hardness. This definition is available for following
`all description.
`
`[0044] Plastic lenses made by the injection molding are
`used as the lenses composing the image pickup lens, the
`miniaturized lightweight image pickup lens is advanta(cid:173)
`geously obtained at low cost. However, the refractive index
`of the plastic material considerably changes with the tem(cid:173)
`perature. Therefore, assuming that plastic lenses are used for
`all lenses of the image pickup lens, a problem has arisen that
`the position of an image point of the whole image pickup
`lens changes with the temperature.
`
`[0045] The configuration of the present invention uses
`many plastic lenses and compensates the change of the
`position of the image point of the whole image pickup lens
`caused by the temperature change. That is, the first positive
`lens is formed out of the glass material of which the
`refractive index hardly changes with the temperature, and
`the second, third and fourth lenses are formed out of the
`plastic material. The second lens has the comparatively
`strong positive refractive power, and the third lens has the
`comparatively strong negative refractive power. Therefore,
`the influence of the second lens on the position of the image
`point changing with the temperature cancels out that of the
`third lens, and the positional change of the image point in the
`whole image pickup lens caused by the temperature change
`can be suppressed to a low degree.
`
`Ii° /RS
`XO=---;=======
`I + V I - (I + KS)h 2 / RS2
`
`(12)
`
`[0046] Preferably, a following conditional formula (13) is
`satisfied:
`
`in a range of h satisfying hmax X 0.5<h<hmax,
`[0039]
`where a vertex of the image side surface of the fourth lens
`is set as an origin, a direction of an optical axis is set as an
`X-axis, h denotes a height in an arbitrary direction perpen(cid:173)
`dicular to the optical axis, Ai denotes an i-th order coefficient
`of the aspherical surface for the image side surface of the
`fourth lens, hmax denotes a maximum effective radius, RS
`denotes a curvature radius of the image side surface of the
`fourth lens, and KS denotes a conic constant for the image
`side surface of the fourth lens.
`
`[0040] Here, the vertex of the image side surface denotes
`the intersection of the surface and the optical axis.
`
`[0041] Generally, a plurality oflenses combined with each
`other are used. When the total lens length is shortened, a
`back focal length is shortened. Therefore, it is difficult to
`obtain the telecentric characteristic of the light flux on the
`image side. In the present invention, the image side surface
`of the fourth lens and nearest to the image side among the
`surfaces of the lenses is formed in the aspherical surface
`
`(13),
`[0047] where f234 denotes a combined focal length of the
`second, third and fourth lenses, and f denotes a focal length
`of the whole image pickup lens.
`
`[0048] The conditional formula (13) prescribes the com(cid:173)
`bined focal length of the lenses formed out of the plastic
`material. Because the positional change of the image point
`of a plastic lens caused by the temperature change depends
`on a degree of the refractive power of the lens, the combined
`focal length of the first, second and third lenses formed out
`of the plastic material is set to a large value to suppress a
`sum of values of the refractive power of the lenses to a low
`value. Therefore, the positional change of the image point
`caused by the temperature change can be suppressed to a low
`degree.
`
`[0049] Preferably, a saturated water absorption rate of the
`plastic material is not more than 0.7%.
`
`[0050] Because the saturated water absorption rate of the
`plastic material is larger than that of the glass material, a
`non-uniform distribution of absorbed water occurs in the
`plastic lens due to a rapid change of humidity. Therefore, the
`
` Ex. 1006
`Page 15
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`US 2004/0012861 Al
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`Jan.22,2004
`
`4
`
`refractive index of the plastic lens cannot be uniformly set,
`and a preferable image forming performance cannot be
`obtained. In the present invention, the lenses are formed out
`of the plastic material having a low saturated water absorp(cid:173)
`tion rate, and the deterioration of the performance caused by
`the change of humidity is reduced.
`
`[0051]
`In accordance with the second aspect of the present
`invention, an image pickup lens comprising four lenses
`arranged in an order of a first lens, a second lens, a third lens
`and a fourth lens from an object side,
`
`[0052] wherein the first lens has positive refractive power
`and has a convex surface facing toward the object side, one
`lens or two lenses selected from the second, third and fourth
`lenses have the positive refractive power, at least one lens of
`the positive refractive power selected from the first, second,
`third and fourth lenses is formed out of glass material,
`
`[0053]
`another lens of the positive refractive power and
`one lens of negative refractive power selected from the first,
`second, third and fourth lenses are formed out of plastic
`material, and
`
`[0054]
`an image side surface of the fourth lens satisfies a
`following conditional formula (14):
`
`X-Xll<O
`(14)
`[0055]
`for a displacement value X of an aspherical surface
`expressed in the formula (15):
`
`h2 i RS
`X = ----====== + LA;h'
`I+ ✓ I - (I+ KS)h2 / RS2
`
`(15)
`
`[0056] and a displacement value XO of a rotational qua(cid:173)
`dratic surface component of the aspherical surface expressed
`in the formula (16):
`
`Ii° /RS
`XO=--;=======
`I + V I - (I + KS)h 2 / RS2
`
`(16)
`
`in a range of h satisfying hmax X 0.5<h<hmax,
`[0057]
`where a vertex of the image side surface of the fourth lens
`facing is set as an origin, a direction of an optical axis is set
`as an X-axis, h denotes a height in an arbitrary direction
`perpendicular to the optical axis, Ai denotes an i-th order
`coefficient of the aspherical surface for the image side
`surface of the fourth lens, hmax denotes a maximum effec(cid:173)
`tive radius, R8 denotes a curvature radius of the image side
`surface of the fourth lens, and K8 denotes a conic constant
`for the image side surface of the fourth lens.
`
`[0058] Here, the vertex of the image side surface denotes
`the intersection of the surface and the optical axis.
`
`[0059]
`In the above configuration, four lenses are arranged
`in an order of the first, second, third and fourth lenses. In use,
`the first lens is placed on the object side, and the fourth lens
`is placed on the image side. In this use condition, the first
`positive lens having the convex surface facing toward the
`image side and nearest to the object side is arranged.
`Therefore, as compared with the configuration having the
`
`first lens of a negative refractive power, the configuration
`advantageous to shorten the total lens length can be
`obtained.
`
`[0060] Also, in the configuration of the present invention,
`lenses selected from the first, second, third and fourth lenses
`are formed out of the plastic material. As described above,
`though the plastic lens is advantageous to make a miniatur(cid:173)
`ized lightweight image pickup lens at low cost, the plastic
`lens has a fault that the position of an image point of the lens
`considerably changes due to a large change of the refractive
`index of the lens caused by the temperature change.
`
`[0061] Therefore, the configuration of the present inven(cid:173)
`tion uses many plastic lenses and compensates the change of
`the position of the image point of the whole image pickup
`lens caused by the temperature change. In the present
`invention, one positive lens is formed out of the glass
`material of which the refractive index hardly changes with
`the temperature, and two lenses including at least one
`positive lens and at least one negative lens are formed out of
`the plastic material. Therefore, the large positive refractive
`power can be distributed to the glass lens and the plastic
`lenses. Also, because the plastic lenses include the positive
`lens and the negative lens of the comparatively strong
`refractive power, the influence of the positive lens on the
`positional change of the image point caused by the tempera(cid:173)
`ture change cancels out that of the negative lens, and the
`positional change of the image point in the whole image
`pickup lens caused by the temperature change can be
`suppressed to a low degree.
`
`[0062] Also, in the configuration of the present invention,
`the image side surface of the fourth lens is formed in the
`aspherical surface shape satisfying the formulas (14), (15)
`and (16). Therefore, the telecentric characteristic particu(cid:173)
`larly for the light flux at the high angle of view can be
`maintained.
`
`[0063] Preferably, the lenses other than the lens having the
`positive refractive power and formed out of the glass mate(cid:173)
`rial are formed out of the plastic material.
`
`[0064]
`In the above configuration, only one lens having
`the positive refractive power is formed out of the glass
`material, and the other three lenses are formed out of the
`plastic material. Therefore, many plastic lenses are used.
`Accordingly, the advantage of forming the lenses out of the
`plastic material can be effectively obtained.
`
`[0065] Preferably, the first lens is formed out of the glass
`material.
`
`[0066]
`In the above configuration, the first lens placed
`nearest to the object side and damaged most easily due to
`external causes is not formed out of the easily damaged
`plastic material but formed out of the glass material. There(cid:173)
`fore, the generation of flaws of the first lens can be reduced,
`and the first lens protects the other lenses formed out of the
`plastic material.
`
`[0067] Preferably, a following conditional formula (17) is
`satisfied:
`
`[fl/234[<0.7
`(17),
`[0068] where f234 denotes a combined focal length of the
`second, third and fourth lenses, and f denotes a focal length
`of the whole image pickup lens.
`
` Ex. 1006
`Page 16
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`US 2004/0012861 Al
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`Jan.22,2004
`
`5
`
`[0069] As described for the formula (9), the conditional
`formula (13) prescribes the combined focal length of the
`lenses formed out of the plastic material. Therefore, the
`combined focal length of the second, third and fourth lenses
`formed out of the plastic material is set to a high value
`according to the conditional formula (13) to suppress a sum
`of values of the refractive power of the lenses to a low value,
`and the positional change of the image point caused by the
`temperature change can be suppressed to a low degree.
`
`[0070] Preferably, a saturated water absorption rate of the
`plastic material is not more than 0.7%.
`
`[0071] Plastic having a low saturated water absorption rate
`is used as the lens material. Therefore, the performance of
`the plastic lenses does not deteriorate regardless of the
`change of humidity.
`
`[0072] Preferably, following conditional formulas (18),
`(19) and (20) are satisfied:
`
`Li2Y<l.60
`
`0.40<(12/f<D.70
`
`(18)
`
`(19)
`
`25<VP-vN
`(20),
`[0073] where L denotes a distance on an optical axis from
`the object side surface of the first lens to an image side focal
`point of the whole image picln1p lens, 2Y denotes the length
`of a diagonal line on an effective image screen, f12 denotes
`a combined focal length of the first lens and the second lens,
`f denotes a focal length of the whole image pickup lens, vP
`denotes an Abbe number of the lens having the strongest
`positive refractive power, v N denotes an Abbe number of the
`lens having the strongest negative refractive power.
`
`[0074] The conditional formulas (18), (19) and (20) indi(cid:173)
`cate conditions for obtaining a miniaturized image pickt1p
`lens in which the aberration is preferably corrected.
`
`[0075]
`In the same manner as the formula (1), the condi(cid:173)
`tional formula (18) indicates a condition for achieving the
`shortening of the total lens length.
`
`[0076] Also, in the same manner as the formula (2), the
`conditional formula (19) indicates a condition for appropri(cid:173)
`ately setting the combined focal length of the first lens and
`the second lens. When f2/f is set to be higher than the lower
`limit, the generation of both the high-order spherical aber(cid:173)
`ration and the coma can be suppressed. Also, when f2/f is set
`to be lower than the upper limit, the total lens length can be
`shortened.
`
`[0077] Also, the conditional formula (20) indicates a con(cid:173)
`dition for prescribing the Abbe number of the positive lens
`having the strongest positive refractive power and the Abbe
`number of the negative lens having the strongest negative
`refractive power to preferably correct the chromatic aberra(cid:173)
`tion. When vP-vN is set to be higher than the lower limit,
`the axial chromatic aberration and the lateral chromatic
`aberration can be corrected in good balance.
`
`[0078] Preferably, the second lens has the positive refrac(cid:173)
`tive power, and the third lens has the negative refractive
`power.
`
`[0079]
`In the above configuration, because the positive
`lenses and the negative lens having the comparatively strong
`refractive power are arranged in that order from the object
`side, the total lens length can be easily shortened.
`
`[0080]
`In accordance with the third aspect of the present
`invention, an image pickup unit comprises:
`
`[0081] a solid-state image pickup element having a
`photoelectric transfer unit;
`
`[0082] an image pickup lens for forming an image of
`an object in the photoelectric transfer unit of the
`solid-state image pickup element;
`
`[0083] a substrate for holding the solid-state image
`pickup element, the substrate comprising an external
`connection terminal through which an electric signal
`is transmitted or received; and
`
`[0084] a casing made of a light shielding substance
`and comprising an opening for incident light entering
`an object side,
`
`[0085] wherein the solid-state image pickup element,
`the image pickup lens, the substrate and the casing
`are combined with each other,
`
`[0086] a length of the image pickup unit in a direction
`of an optical axis of the image pickup lens is not
`more than 15 mm,
`
`[0087]
`the image pickup lens comprises four lenses
`arranged in an order from the object side, and
`
`[0088]
`the lens arranged nearest to the object side has
`the positive refractive power.
`
`[0089] The "opening for incident light" is not limited to a
`space forming means such as a hole and indicates a means
`for forming an area through which incident light entering the
`object side can be transmitted. This definition is available for
`the fourth aspect of the present invention described later.
`
`[0090] The image pickup unit having the configuration
`described above satisfies a request of the miniaturization and
`the lightening-in-weight and is used to be mounted on a
`small-sized portable electronic device. In this unit, the lens
`arranged nearest to the object side is set to a positive lens,
`and the structure advantageous for the shortening of the total
`lens length is adopted. The image pickup lens comprises
`four lenses while shortening the length of the whole image
`pickup unit in the direction of the optical axis.
`
`[0091] The description "the length of the image pickup
`unit in the direction of the optical axis is not more than 15
`mm" denotes a total length of the image pickup unit having
`all the above-described elements along the direction of the
`optical axis. For example, when the casing is placed on a
`front surface of the substrate and electronic parts are
`arranged on a back surface of the substrate, a distance from
`an end portion of the casing on the object side to an end
`portion of the electronic parts projecting from the back
`surface of the substrate is not more than 15 mm. This
`definition is available for the fourth aspect of the present
`invention.
`[0092]
`It is preferred that many lenses are arranged in the
`image pickt1p lens to correct various types aberration and
`improve the telecentric characteristic of the solid-state
`image pickup element and the quality of the formed image.
`However, the number of lenses of the image pickup unit
`mounted on a small-sized electronic device is generally
`three at most. Because four lenses are used for the image
`
` Ex. 1006
`Page 17
`
`HP,
`
`

`

`US 2004/0012861 Al
`
`Jan.22,2004
`
`6
`
`pickup unit of the present invention, the configuration of the
`present invention is advantageous