WO2013058534A1

WO2013058534A1 - Imaging lens

Info

Publication number: WO2013058534A1
Application number: PCT/KR2012/008471
Authority: WO
Inventors: Kyung Hwan Lee
Original assignee: Lg Innotek Co., Ltd.
Priority date: 2011-10-21
Filing date: 2012-10-17
Publication date: 2013-04-25
Also published as: KR101933960B1; TW201329494A; TWI585445B; KR20130043998A

Abstract

The present invention relates to an imaging lens, the imaging lens including, in an ordered way from an object side, a first lens having a positive (+) refractive power and convexly formed at an object side surface, a second lens having a negative (-) refractive power and concavely formed at an object side surface, a third lens of meniscus form having a positive (+) refractive power and having an inflection point on both surfaces, and a fourth lens having a negative (-) refractive power.

Description

IMAGING LENS

The teachings in accordance with exemplary embodiments of this invention relate generally to an imaging lens.

Recently, vigorous research efforts are being made in the field of a mobile phone-purpose camera module, a digital still camera (DSC), a camcorder, and a PC camera (an imaging device attached to a person computer) all connected with an image pick-up system. One of the most important components in order that a camera module related to such an image pickup system obtains an image is an imaging lens producing an image.

An imaging lens is recently constructed with 3 pieces or 4 pieces of lenses for compactness and low cost.

However, although the 4-piece lens system may be advantageous in terms of price, but in some cases, an image lens of the above-mentioned structure fails to show satisfactory optical properties or aberration properties, and thus, an optical system with high resolution and high power structure is required.

Accordingly, embodiments of the present invention may relate to an imaging lens that substantially obviates one or more of the above disadvantages/problems due to limitations and disadvantages of related art, and it is an object of the present invention to provide an imaging lens configured to realize a compact imaging lens with a high resolution and a high power structure.

In one general aspect of the present invention, there is provided an imaging lens, the imaging lens comprising, in an ordered way from an object side: a first lens having a positive (+) refractive power and convexly formed at an object side surface; a second lens having a negative (-) refractive power and concavely formed to an object direction; a third lens of meniscus form having a positive (+) refractive power and having an inflection point on both surfaces; and a fourth lens having a negative (-) refractive power.

Preferably, but not necessarily, the second lens has an inflection point on an image side surface.

Preferably, but not necessarily, an aperture is positioned at a front end of an object side surface of the first lens.

Preferably, but not necessarily, the fourth lens has an inflection point on at least one or more surfaces.

Preferably, but not necessarily, one surface or both surfaces of the first, second, third and fourth lenses is an aspheric shape.

Preferably, but not necessarily, the imaging lens meets one or more conditional expressions of 0.6 < │f/f2 │< 1, 1.2 < f/f3 < 1.8, 0.6 < │f/f4 │< 1, 0.3 < │f3/f4 │< 0.8, 0.8 < │f1/f2 │< 1.3, 0.8 < │f1/f │< 1.2, 1 < │f2/f │< 1.5, 0.85 < │f/f1 │< 1.15, where f is an entire focus distance (focal length) of the imaging lens, and f1, f2, f3 and f4 are focus distances of the first, second, third and fourth lenses.

Preferably, but not necessarily, the imaging lens meets a conditional expression of 1.2 < L/f1 < 1.4, where f is an entire focus distance (focal length) of the imaging lens, and f1 is a focus distance of the first lens, and a distance on an optical axis from an object side surface of the first lens to an image side surface is L.

Preferably, but not necessarily, the imaging lens meets a conditional expression of 4.3 < L < 4.5, where a distance on an optical axis from an object side surface of the first lens to an image side surface is L.

Preferably, but not necessarily, the imaging lens meets a conditional expression of 70 < FOV < 90, where FOV is a diagonal Field Of View.

Preferably, but not necessarily, the imaging lens meets a conditional expression of 1.6 < n2 < 1.7, 1.5 < n1 < 1.6, 1.5 < n3 < 1.6, 1.5 < n4 < 1.6, where each refractive index of the first, second, third and fourth lenses is n1, n2, n3 and n4.

Preferably, but not necessarily, the imaging lens meets a conditional expression of 22 < V2 < 32, 50 < V1 < 60, 50 < V3 < 60, 50 < V4 < 60, where V1, V2, V3, and V4 are Abbe's numbers of the first, second, third and fourth lenses.

Preferably, but not necessarily, the imaging lens meets a conditional expression of 2.0 < F/# < 3.0, where F/# is an F-number.

Preferably, but not necessarily, the imaging lens meets a conditional expression of 0 < (r3+r4)/(r3-r4) < 1, where r3 and r4 are respectively radius of curvature of an object side surface of the second lens and radius of curvature of an image side surface.

Preferably, but not necessarily, the imaging lens meets a conditional expression of L3R2 ＞-1, L4R2 ＜ 1, where a radius of curvature of a second surface of the third lens is L3R2, and a radius of curvature of a second surface of the fourth lens is L4R2.

In another general aspect of the present invention, there is provided an imaging lens, the imaging lens comprising, in an ordered way from an object side: a first lens having a positive (+) refractive power and convexly formed at an object side surface; a second lens having a negative (-) refractive power and concavely formed to an object direction; a third lens having a positive (+) refractive power and convexly formed at a center of an image side surface; and a fourth lens having a negative (-) refractive power.

The imaging lens according to the present invention has an advantageous effect in that a compact and high resolution imaging lens having a high power structure can be realized.

FIG. 1 is a constructional view illustrating a camera module lens according to an exemplary embodiment of the present invention.

FIGS. 2a and 2b are graphs measuring a coma aberration according to an exemplary embodiment of the present invention.

FIG.3 is a graph illustrating an aberration according to an exemplary embodiment of the present invention.

FIGS.4a and 4b are graphs illustrating an MTF (Modulation Transfer Function) characteristic relative to spatial frequency on a zoom position, and an MTF characteristic relative to a defocusing position at a zoom position.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In describing the present invention, detailed descriptions of constructions or processes known in the art may be omitted to avoid obscuring appreciation of the invention by a person of ordinary skill in the art with unnecessary detail regarding such known constructions and functions. Accordingly, the meaning of specific terms or words used in the specification and claims should not be limited to the literal or commonly employed sense, but should be construed or may be different in accordance with the intention of a user or an operator and customary usages. Therefore, the definition of the specific terms or words should be based on the contents across the specification.

Now, the imaging lens according to exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a constructional view illustrating an imaging lens according to an exemplary embodiment of the present invention.

The imaging lens formed with a plurality of lenses is arranged about an optical axis (ZO), where thickness, size, and shape of each lens are rather overdrawn in FIG.1 for description, and a spherical shape or an aspheric shape has been only presented as one exemplary embodiment, but obviously not limited to this shape.

Referring to FIG.1, a camera lens module according to an exemplary embodiment of the present invention includes, in an ordered way from an object side, a first lens (10), a second lens (20), a third lens (30), a fourth lens (40), a filter (50) and a photo-detector (light receiving element, 60).

Light corresponding to image information of a subject is incident on the photo-detector (60) by passing the first lens (10), the second lens (20), the third lens (30), the fourth lens (40) and the filter (50).

Hereinafter, in the description of the construction of each lens, "object side surface" means a surface of a lens facing an object side with respect to an optical axis, and "image side surface" means a surface of a lens facing a capturing surface with respect to an optical axis.

A first lens (10) has a positive (+) refractive power and is convexly formed at an object side surface (S1). A second lens (20) is a concave lens having a negative (-) refractive power, has a concave surface to an object direction and has an inflection point at an image side surface (S4). Furthermore, a separate aperture may be positioned at a front end of the object side surface (S1) of the first lens (10).

In addition, a third lens (30) takes a shape of a meniscus form having a positive (+) refractive power with an inflection point on all surfaces, and a center of an image side surface is convexly formed. A fourth lens (40) has a negative (-) refractive power, and has an inflection point on at least one or more surfaces.

One surface or both surfaces of the first, second, third and fourth lenses (10, 20, 30, 40) is aspheric.

For information, 'S2' of FIG.1 is an image side surface of the first lens (10), 'S3' is an object side surface of the second lens (20), 'S5' is an object side surface of the third lens (30), 'S6' is an image side surface of the third lens (30), and 'S7' and 'S8' are respectively an object side surface and an image side surface of the fourth lens (40), and 'S9' and 'S10' are respectively an object side surface and an image side surface of the filter (50).

The filter (50) may be any one optical filter selected from an infrared filter and a cover glass. The filter (50), if applied with the infrared filter, prevents radiant heat emitted from external light from being transferred to the photo-detector (60). Furthermore, the infrared filter transmits visible light and reflects and outputs infrared rays to the outside. The photo-detector (60) is an image sensor, for example, CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), etc.

Because the later-described conditional expressions and exemplary embodiments are preferred embodiments enhancing an effect of interaction, it would be obvious to those skilled in the art that the present invention is not necessarily comprised of the following conditions. For example, only by satisfying some conditions of later-described conditional expressions, the lens construction (framework) of the present invention may have an enhanced effect of interaction.

[Conditional expression 1] 0.6 < │f/f2 │< 1, 1.2 < f/f3 < 1.8, 0.6 < │f/f4 │< 1

[Conditional expression 2] 0.3 < │f3/f4 │< 0.8, 0.8 < │f1/f2 │< 1.3

[Conditional expression 3] 0.8 < │f1/f │< 1.2, 1 < │f2/f │< 1.5

[Conditional expression 4] 0.85 < │f/f1 │< 1.15

[Conditional expression 5] 1.2 < L/f1 < 1.4

[Conditional expression 6] 4.3 < L < 4.5

[Conditional expression 7] 70 < FOV < 90

[Conditional expression 8] 1.6 < n2 < 1.7, 1.5 < n1 < 1.6, 1.5 < n3 < 1.6, 1.5 < n4 < 1.6

[Conditional expression 9] 22 < V2 < 32, 50 < V1 < 60, 50 < V3 < 60, 50 < V4 < 60

[Conditional expression 10] 2.0 < F/# < 3.0

[Conditional expression 11] 0 < (r3+r4)/(r3-r4) < 1

[Conditional expression 12] L3R2＞-1, L4R2 ＜ 1

where, f: an entire focus distance (focal length) of the imaging lens

f1, f2, f3, f4: a focus distance of the first, second, third and fourth lenses

D12, D23, D34: a distance between first/second lenses on an optical axis, a distance between second/third lenses on an optical axis and a distance between third/fourth lenses on an optical axis

D1, D2, D3, D4: a center thickness of first, second, third and fourth lenses

L: a distance on an optical axis from an object side surface of first lens to an image side surface

n1, n2, n3, n4 : refractive index of first, second, third and fourth lenses

V1, V2, V3, V4: an Abbe's number of the first, second, third and fourth lenses

bf2, bf3, bf4 : a distance on an optical axis from an image side surface of second, third and fourth lenses to an image side surface

FOV: Diagonal Field of View

L3R2: radius of curvature of second surface of the third lens

L4R2: radius of curvature of second surface of the fourth lens

F/#: F-number

r3,r4: radius of curvature of an object side surface of second lens and radius of curvature of an image side surface

Conditional expression 8 specifies refractive powers of the first, second, third and fourth lenses (10, 20, 30, 40), the first, second, third and fourth lenses (10, 20, 30, 40) have refractive powers each having an appropriate compensation of spherical aberration and appropriate chromatic aberration according to the conditional expression 8, and conditional expression 9 specifies Abbe's number of first, second, third and fourth lenses (10, 20, 30, 40). The specification of Abbe's number of each lens is a condition for better compensation of chromatic aberration.

Hereinafter, the action and effect of the present invention will be described with reference to a specific exemplary embodiment. Aspheric mentioned in a later- exemplary embodiment is obtained from a known Equation 1, and `E and its succeeding number` used in Conic constant k and aspheric coefficient A, B, C, D, E, F indicates 10's power. For example, E+01 denotes 10.sup.1, and E-02 denotes 10.sup.-2.

MathFigure 1

where, z: distance from the lens's top-point to an optical axis direction,

c: basic curvature of a lens , Y: distance towards a direction perpendicular to an optical axis, K: conic constant, and A, B, C, D, E, F: aspheric coefficients

[EXEMPLARY EMBODIMENTS]

The following Table 1 shows an exemplary embodiment matching the aforementioned conditional expressions.

Table 1

	Exemplary embodiments
f	2.8600
f1	3.1736
f2	-3.5966
f3	1.8987
f4	-2.9509
V1	56.5
V2	23.9
V3	56.5
V4	56.5
n1	1.5350
n2	1.6340
n3	1.5350
n4	1.5310
D12	0.377
D23	0.132
D34	0.100
D1	0.596
D2	0.348
D3	0.890
D4	0.530
L	4.360
f/f1	0.901
L/f1	1.374
bf2	3.387
bf3	2.907
bf4	1.917

Referring to Table 1, it can be noted that │f/f1 │ is 0.90 that matches the conditional expression 4, and L/F1 is 1.37 that matches the conditional expression 5.

The following Table 2 shows an exemplary embodiment which is a more detailed exemplary embodiment over that of Table 1.

Table 2

Surfacenumber	Curvature radius (R)	Thickness or distance(d)	Refractive index (N)
Stop*	2.53	0.596	1.537
2*	-4.78	0.377
3*	-4.97	0.348	1.634
4*	4.43	0.132
5*	-4.63	0.890	1.537
6*	-0.89	0.100
7*	1.50	0.530	1.531
8*	0.67	0.953
9	Infinity	0.300	1.52
10	Infinity	0.118
image	Infinity	0.017

The notation * in the above Table 2 and following Table 3, which is further written near the surface number, indicates aspheric. The following Tables 3 and 4 respectively show a value of aspheric coefficient of each lens in the exemplary embodiment of Table 2.

Table 3

Surface number	k	A	B	C	D	E
1*	-3.9254	-0.0451	-0.0497	-0.1754	0.0800	-0.0711
2*	28.3069	-0.1739	0.0500	-0.3034	0.4228	-0.1819
3*	-22.1905	-0.4794	0.2440	-0.4502	1.0276	-0.5663
4*	-169.7252	-0.1200	0.0182	0.0848	-0.0510	0.0091
5*	-9.6926	0.0274	0.0265	-0.0356	0.0318	-0.0084
6*	-0.6198	0.1626	-0.0283	0.0129	0.0205	-0.0003

Table 4

Surface number	k	3rd	4th	5th	6th	7th	8th	9th	10th	11th	12th
1*	-7.3113	-0.0854	-0.0280	-0.0265	0.0465	-0.0093	-0.0069	0.0020	-0.0003	0.0005	-0.0001
2*	-2.6912	-0.1566	-0.0249	0.1017	-0.0683	0.0234	-0.0039	-0.0003	-0.0003	0.0003	-0.0001

FIGS.2a and 2b are graphs illustrating coma aberration according to an exemplary embodiment of the present invention, where tangential aberration and sagittal aberration of each wavelength based on a field height are measured. In FIGS.2a and 2b, it is interpreted that a coma aberration correcting function is good as curves approach the X axis from a positive axis and a negative axis. In the measurement examples of FIGS. 2a and 2b of shown aberration diagrams, because values of images in nearly all fields proximate to the X axis, coma aberration correction function demonstrates a superior figure.

FIG.3 is a graph illustrating spherical aberration according to an exemplary embodiment of the present invention. That is, FIG.3 is a graph measuring longitudinal spherical aberration, astigmatic field curves and distortion in order from left side. In FIG.3, a Y axis means size of an image, and an X axis means focal distance (unit: mm) and distortion degree (unit: %). In FIG.3, it is interpreted that an aberration correcting function is good as curves approach the Y axis. In the shown aberration diagram, because values of images in nearly all fields appear proximate to the Y axis, spherical aberration, astigmatic field curves and distortion all demonstrate a superior figure.

That is, a range of the longitudinal spherical aberration is -0.029㎜ ~ +0.0125㎜, a range of astigmatic field curves is -0.015㎜ ~ +0.01㎜, and a range of distortion is -0.90㎜ ~ +0.15㎜, such that the imaging lens according to the present invention can correct the characteristics of spherical aberration, astigmatic field curves and distortion, whereby the imaging lens according to the present invention has an excellent lens characteristics.

FIGS.4 is a graph illustrating an MTF (Modulation Transfer Function) characteristic relative to spatial frequency on a zoom position. FIG. 4 has measured an MTF characteristic depending on a variation of spatial frequencies at cycle per millimeter (cycle/mm). Here, an MTP characteristic refers to a rate obtained by calculating a difference between light starting from an original subject surface and a formed image that passes through a lens, wherein a case of MTF figure `1` is the most idealistic, and as MTF values decrease, resolution falls down.

Referring to FIG. 4a, since FIG. 4a indicating that an MTF value is high, it can be known that the imaging lens according to an embodiment is superior in optical performance.

FIG.4b is a graph illustrating an MTF characteristic relative to a defocusing position at a zoom position, where a frequency is 143 c/mm of through focus MTF.

The previous description of the present invention is provided to enable any person skilled in the art to make or use the invention. Various modifications to the invention will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the invention. Thus, the invention is not intended to limit the examples described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

As apparent from the foregoing, the imaging lens according to the exemplary embodiments of the present invention has an industrial applicability in that a compact and high resolution imaging lens having a power structure can be realized.

Claims

An imaging lens comprising, in an ordered way from an object side: a first lens having a positive (+) refractive power and convexly formed at an object side surface; a second lens having a negative (-) refractive power and concavely formed to an object direction; a third lens of meniscus form having a positive (+) refractive power and having an inflection point on both surfaces; and a fourth lens having a negative (-) refractive power.
The imaging lens of claim 1, wherein the second lens has an inflection point on an image side surface.
The imaging lens of claim 1, wherein an aperture is positioned at a front end of an object side surface of the first lens.
The imaging lens of claim 1, wherein the fourth lens has an inflection point on at least one or more surfaces.
The imaging lens of claim 1, wherein one surface or both surfaces of the first, second, third and fourth lenses is an aspheric shape.
The imaging lens of claim 1, wherein the imaging lens meets one or more conditional expressions of 0.6 < │f/f2 │< 1, 1.2 < f/f3 < 1.8, 0.6 < │f/f4 │< 1, 0.3 < │f3/f4 │< 0.8, 0.8 < │f1/f2 │< 1.3, 0.8 < │f1/f │< 1.2, 1 < │f2/f │< 1.5, 0.85 < │f/f1 │< 1.15, where f is an entire focus distance (focal length) of the imaging lens, and f1, f2, f3 and f4 are focus distances of the first, second, third and fourth lenses.
The imaging lens of claim 1, wherein the imaging lens meets a conditional expression of 1.2 < L/f1 < 1.4, where f is an entire focus distance (focal length) of the imaging lens, and f1 is a focus distance of the first lens, and a distance on an optical axis from an object side surface of the first lens to an image side surface is L.
The imaging lens of claim 1, wherein the imaging lens meets a conditional expression of 4.3 < L < 4.5, where a distance on an optical axis from an object side surface of the first lens to an image side surface is L.
The imaging lens of claim 1, wherein the imaging lens meets a conditional expression of 70 < FOV < 90, where FOV is a diagonal Field Of View.
The imaging lens of claim 1, wherein the imaging lens meets a conditional expression of 1.6 < n2 < 1.7, 1.5 < n1 < 1.6, 1.5 < n3 < 1.6, 1.5 < n4 < 1.6, where each refractive index of the first, second, third and fourth lenses is n1, n2, n3 and n4.
The imaging lens of claim 1, wherein the imaging lens meets a conditional expression of 22 < V2 < 32, 50 < V1 < 60, 50 < V3 < 60, 50 < V4 < 60, where v V1, V2, V3, and V4 are Abbe's numbers of the first, second, third and fourth lenses.
The imaging lens of claim 1, wherein the imaging lens meets a conditional expression of 2.0 < F/# < 3.0, where F/# is an F-number.
The imaging lens of claim 1, wherein the imaging lens meets a conditional expression of 0 < (r3+r4)/(r3-r4) < 1, where r3 and r4 are respectively radius of curvature of an object side surface and an imaging side surface.
The imaging lens of claim 1, wherein the imaging lens meets a conditional expression of L3R2 ＞-1, L4R2 ＜ 1, where a radius of curvature of a second surface of the third lens is L3R2, and a radius of curvature of a second surface of the fourth lens is L4R2.
An imaging lens, the imaging lens comprising, in an ordered way from an object side: a first lens having a positive (+) refractive power and convexly formed at an object side surface; a second lens having a negative (-) refractive power and concavely formed to an object direction; a third lens having a positive (+) refractive power and convexly formed at a center of an image side surface; and a fourth lens having a negative (-) refractive power.
The imaging lens of claim 15, wherein the imaging lens meets one or more conditional expressions of 0.6 < │f/f2 │< 1, 1.2 < f/f3 < 1.8, 0.6 < │f/f4 │< 1, 0.3 < │f3/f4 │< 0.8, 0.8 < │f1/f2 │< 1.3, 0.8 < │f1/f │< 1.2, 1 < │f2/f │< 1.5, 0.85 < │f/f1 │< 1.15, where f is an entire focus distance (focal length) of the imaging lens, and f1, f2, f3 and f4 are focus distances of the first, second, third and fourth lenses.
The imaging lens of claim 15, wherein the imaging lens meets a conditional expression of 1.2 < L/f1 < 1.4, where f is an entire focus distance (focal length) of the imaging lens, and f1 is a focus distance of the first lens, and a distance on an optical axis from an object side surface of the first lens to an image side surface is L.
The imaging lens of claim 15, wherein the imaging lens meets a conditional expression of 4.3 < L < 4.5, where a distance on an optical axis from an object side surface of the first lens to an image side surface is L.
The imaging lens of claim 15, wherein the imaging lens meets a conditional expression of 70 < FOV < 90, where FOV is a diagonal Field Of View.
The imaging lens of claim 15, wherein the imaging lens meets a conditional expression of 2.0 < F/# < 3.0, where F/# is an F-number.