# Patent

## Title
Imaging lens, and portable electronic apparatus including the same

## Abstract

An imaging lens includes a first lens element, a second lens element, an aperture stop, a third lens element, a fourth lens element, and a fifth lens elements arranged from an object side to an image side in the given order. Through designs of surfaces of the lens elements and relevant optical parameters, a short system length of the imaging lens may be achieved while maintaining good optical performance.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to Taiwanese Application No. 102135349, filed on Sep. 30, 2013.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an imaging lens and a portable electronic apparatus including the same.
2. Description of the Related Art
In recent years, as use of portable electronic devices (e.g., mobile phones and digital cameras) becomes ubiquitous, much effort has been put into reducing dimensions of portable electronic devices. Moreover, as dimensions of charged coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) based optical sensors are reduced, dimensions of imaging lenses for use with the optical sensors must be correspondingly reduced without significantly compromising optical performance.
A conventional imaging lens that includes four lens elements is no longer able to fulfill customers' requirements for higher image quality. Development of imaging lens with a small size and good image quality is required.
In addition to pixel requirement, large field of view is also required in the market. Each of U.S. application publication nos. 20110249346 and 20120087019, and U.S. Pat. No. 7,911,711 discloses a conventional imaging lens with five lens elements, which has an HFOV (half field-of-view) smaller than 40 degrees. Each of U.S. application publication nos. 20110316969 and 20120069140 discloses an imaging lens with greater HFOV, but a system length thereof is longer than 9 mm, which cannot meet requirement of miniaturization.
Reducing the system length of the imaging lens while maintaining satisfactory optical performance is always a goal in the industry.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an imaging lens having a shorter overall length while maintaining good optical performance.
According to one aspect of the present invention, an imaging lens comprises a first lens element, a second lens element, an aperture stop, a third lens element, a fourth lens element and a fifth lens element arranged in order from an object side to an image side along an optical axis of the imaging lens. Each of the first lens element, the second lens element, the third lens element, the fourth lens element and the fifth lens element has an object-side surface facing toward the object side and an image-side surface facing toward the image side.
The first lens element has a negative refractive power.
The object-side surface of the second lens element has a convex portion in a vicinity of the optical axis.
The image-side surface of the third lens element has a convex portion in a vicinity of the optical axis.
The image-side surface of the fourth lens element has a convex portion in a vicinity of the optical axis.
The fifth lens element is made of a plastic material.
The imaging lens satisfies AAG/CT1≦5.500, where AAG represents a sum of a distance between the image-side surface of the first lens element and the object-side surface of the second lens element at the optical axis, a distance between the image-side surface of the second lens element and the object-side surface of the third lens element at the optical axis, a distance between the image-side surface of the third lens element and the object-side surface of the fourth lens element at the optical axis, and a distance between the image-side surface of the fourth lens element and the object-side surface of the fifth lens element at the optical axis; and CT1 represents a distance between the object-side surface and the image-side surface of the first lens element at the optical axis.
The imaging lens does not include any lens element with refractive power other than the first lens element, the second lens element, the third lens element, the fourth lens element and the fifth lens element.
Another object of the present invention is to provide a portable electronic apparatus having an imaging lens with five lens elements.
According to another aspect of the present invention, a portable electronic apparatus includes a housing and an imaging module. The imaging module is disposed in the housing, and includes the imaging lens of the present invention, a barrel on which the imaging lens is disposed, a holder unit on which the barrel is disposed, and an image sensor disposed at the image side of the imaging lens.



BRIEF DESCRIPTION OF THE DRAWINGS
Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which:
FIG. 1 is a schematic diagram to illustrate the structure of a lens element;
FIG. 2 is a schematic diagram that illustrates the first preferred embodiment of an imaging lens according to the present invention;
FIG. 3 shows values of some optical parameters corresponding to the imaging lens of the first preferred embodiment;
FIG. 4 shows values of some parameters of an optical relationship corresponding to the imaging lens of the first preferred embodiment;
FIGS. 5(a) to 5(d) show different optical characteristics of the imaging lens of the first preferred embodiment;
FIG. 6 is a schematic diagram that illustrates the second preferred embodiment of an imaging lens according to the present invention;
FIG. 7 shows values of some optical parameters corresponding to the imaging lens of the second preferred embodiment;
FIG. 8 shows values of some parameters of an optical relationship corresponding to the imaging lens of the second preferred embodiment;
FIGS. 9(a) to 9(d) show different optical characteristics of the imaging lens of the second preferred embodiment;
FIG. 10 is a schematic diagram that illustrates the third preferred embodiment of an imaging lens according to the present invention;
FIG. 11 shows values of some optical parameters corresponding to the imaging lens of the third preferred embodiment;
FIG. 12 shows values of some parameters of an optical relationship corresponding to the imaging lens of the third preferred embodiment;
FIGS. 13(a) to 13(d) show different optical characteristics of the imaging lens of the third preferred embodiment;
FIG. 14 is a schematic diagram that illustrates the fourth preferred embodiment of an imaging lens according to the present invention;
FIG. 15 shows values of some optical parameters corresponding to the imaging lens of the fourth preferred embodiment;
FIG. 16 shows values of some parameters of an optical relationship corresponding to the imaging lens of the fourth preferred embodiment;
FIGS. 17(a) to 17(d) show different optical characteristics of the imaging lens of the fourth preferred embodiment;
FIG. 18 is a schematic diagram that illustrates the fifth preferred embodiment of an imaging lens according to the present invention;
FIG. 19 shows values of some optical parameters corresponding to the imaging lens of the fifth preferred embodiment;
FIG. 20 shows values of some parameters of an optical relationship corresponding to the imaging lens of the fifth preferred embodiment;
FIGS. 21(a) to 21(d) show different optical characteristics of the imaging lens of the fifth preferred embodiment;
FIG. 22 is a schematic diagram that illustrates the sixth preferred embodiment of an imaging lens according to the present invention;
FIG. 23 shows values of some optical parameters corresponding to the imaging lens of the sixth preferred embodiment;
FIG. 24 shows values of some parameters of an optical relationship corresponding to the imaging lens of the sixth preferred embodiment;
FIGS. 25(a) to 25(d) show different optical characteristics of the imaging lens of the sixth preferred embodiment;
FIG. 26 is a table that lists values of parameters of other optical relationships corresponding to the imaging lenses of the first to sixth preferred embodiments;
FIG. 27 is a schematic partly sectional view to illustrate a first exemplary application of the imaging lens of the present invention; and
FIG. 28 is a schematic partly sectional view to illustrate a second exemplary application of the imaging lens of the present invention.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Before the present invention is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure.
In the following description, “a lens element has a positive (or negative) refractive power” means the lens element has a positive (or negative) refractive power in a vicinity of an optical axis thereof. “An object-side surface (or image-side surface) has a convex (or concave) portion at a certain area” means that, compared to a radially exterior area adjacent to said certain area, said certain area is more convex (or concave) in a direction parallel to the optical axis. Referring to FIG. 1 as an example, the lens element is radially symmetrical with respect to an optical axis (I) thereof. The object-side surface of the lens element has a convex portion at an area A, a concave portion at an area B, and a convex portion at an area C. This is because the area A is more convex in a direction parallel to the optical axis (I) in comparison with a radially exterior area thereof (i.e., area B), the area B is more concave in comparison with the area C, and the area C is more convex in comparison with an area E. “In a vicinity of a periphery” refers to an area around a periphery of a curved surface of the lens element for passage of imaging light only, which is the area C in FIG. 1. The imaging light includes a chief ray Lc and a marginal ray Lm. “In a vicinity of the optical axis” refers to an area around the optical axis of the curved surface for passage of the imaging light only, which is the area A in FIG. 1. In addition, the lens element further includes an extending portion E for installation into an optical imaging lens device. Ideally, the imaging light does not pass through the extending portion E. The structure and shape of the extending portion E are not limited herein. In the following embodiments, the extending portion E is not depicted in the drawings for the sake of clarity.
Referring to FIG. 2, the first preferred embodiment of an imaging lens 10 according to the present invention includes a first lens element 3, a second lens element 4, an aperture stop 2, a third lens element 5, a fourth lens element 6, a fifth lens element 7, and an optical filter 8 arranged in the given order along an optical axis (I) from an object side to an image side. The optical filter 8 is an infrared cut filter for selectively absorbing infrared light to thereby reduce imperfection of images formed at an image plane 9.
Each of the first, second, third, fourth and fifth lens elements 3-7 and the optical filter 8 has an object-side surface 31, 41, 51, 61, 71, 81 facing toward the object side, and an image-side surface 32, 42, 52, 62, 72, 82 facing toward the image side. Light entering the imaging lens 10 travels through the object-side and image-side surfaces 31, 32 of the first lens element 3, the object-side and image-side surfaces 41, 42 of the second lens element 4, the aperture stop 2, the object-side and image-side surfaces 51, 52 of the third lens element 5, the object-side and image-side surfaces 61, 62 of the fourth lens element 6, the object-side and image-side surfaces 71, 72 of the fifth lens element 7, and the object-side and image-side surfaces 81, 82 of the optical filter 8, in the given order, to form an image on the image plane 9. Each of the object-side surfaces 31, 41, 51, 61, 71 and the image-side surfaces 32, 42, 52, 62, 72 is aspherical and has a center point coinciding with the optical axis (I).
The lens elements 3-7 are made of a plastic material in this embodiment, and at least one of the lens elements 3-6 may be made of other materials in other embodiments.
In the first preferred embodiment, which is depicted in FIG. 2, the first lens element 3 has a negative refractive power. The object-side surface 31 of the first lens element 3 has a convex portion 311 in a vicinity of the optical axis (I), and a concave portion 312 in a vicinity of a periphery of the first lens element 3. The image-side surface 32 of the first lens element 3 is a concave surface.
The second lens element 4 has a positive refractive power. The object-side surface 41 of the second lens element 4 is a convex surface that has a convex portion 411 in a vicinity of the optical axis (I). The image-side surface 42 of the second lens element 4 is a convex surface.
The third lens element 5 has a positive refractive power. The object-side surface 51 of the third lens element 5 is a concave surface. The image-side surface 52 of the third lens element 5 is a convex surface that has a convex portion 521 in a vicinity of the optical axis (I).
The fourth lens element 6 has a positive refractive power. The object-side surface 61 of the fourth lens element 6 has a convex portion 611 in a vicinity of the optical axis (I), and a concave portion 612 in a vicinity of a periphery of the fourth lens element 6. The image-side surface 62 of the fourth lens element 6 is a convex surface that has a convex portion 621 in a vicinity of the optical axis (I).
The fifth lens element 7 has a negative refractive power. The object-side surface 71 of the fifth lens element 7 is a concave surface. The image-side surface 72 of the fifth lens element 7 has a convex portion 721 in a vicinity of the optical axis (I), a convex portion 722 in a vicinity of a periphery of the fifth lens element 7, and a concave portion 723 between the convex portions 721 and 722.
Shown in FIG. 3 is a table that lists values of some optical parameters corresponding to the surfaces 31-81, 32-82 of the first preferred embodiment. The imaging lens 10 has an overall system effective focal length (EFL) of 1.059 mm, a half field-of-view (HFOV) of 60.000°, an F-number of 2.775, and a system length of 5.097 mm. The system length refers to a distance between the object-side surface 31 of the first lens element 3 and the image plane 9.
In this embodiment, each of the object-side surfaces 31-71 and the image-side surfaces 32-72 is aspherical, and satisfies the optical relationship of




  
    
      
        
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where:
R represents a radius of curvature of the aspherical surface;
Z represents a depth of an aspherical surface, which is defined as a perpendicular distance between an arbitrary point on the aspherical surface that is spaced apart from the optical axis (I) by a distance Y, and a tangent plane at a vertex of the aspherical surface at the optical axis (I);
Y represents a perpendicular distance between the arbitrary point on the aspherical surface and the optical axis (I);
K represents a conic constant; and
a2i represents a 2ith aspherical coefficient.
Shown in FIG. 4 is a table that lists values of some optical parameters of the aforementioned optical relationship (1) corresponding to the first preferred embodiment.
Relationships among some of the aforementioned optical parameters corresponding to the first preferred embodiment are as follows:

CT5/CT4=0.559

AAG/CT5=2.633

CT5/AC23=0.701

CT5/(AC34+AC45)=3.439

CT4/CT1=1.645

AAG/CT1=2.423

CT1/(AC34+AC45)=3.738

AAG/AC12=2.875

AC12/AC23=0.642

AC12/(AC34+AC45)=3.150

ALT/CT4=4.652

ALT/AC23=5.830

ALT/(AC34+AC45)=28.607

CT2/AC23=1.430

CT2/(AC34+AC45)=7.019

CT3/CT4=1.343

AAG/CT3=1.096

CT3/AC23=1.684

CT3/(AC34+AC45)=8.262

where:
CT1 represents a distance between the object-side surface 31 and the image-side surface 32 of the first lens element 3 at the optical axis (I);
CT2 represents a distance between the object-side surface 41 and the image-side surface 42 of the second lens element 4 at the optical axis (I);
CT3 represents a distance between the object-side surface 51 and the image-side surface 52 of the third lens element 5 at the optical axis (I);
CT4 represents a distance between the object-side surface 61 and the image-side surface 62 of the fourth lens element 6 at the optical axis (I);
CT5 represents a distance between the object-side surface 71 and the image-side surface 72 of the fifth lens element 7 at the optical axis (I);
AC12 represents a distance between the image-side surface 32 of the first lens element 3 and the object-side surface 41 of the second lens element 4 at the optical axis (I);
AC23 represents a distance between the image-side surface 42 of the second lens element 4 and the object-side surface 51 of the third lens element 5 at the optical axis (I);
AC34 represents a distance between the image-side surface 52 of the third lens element 5 and the object-side surface 61 of the fourth lens element 6 at the optical axis (I);
AC45 represents a distance between the image-side surface 62 of the fourth lens element 6 and the object-side surface 71 of the fifth lens element 7 at the optical axis (I);
AAG represents a sum of the distance between the image-side surface 32 of the first lens element 3 and the object-side surface 41 of the second lens element 4 at the optical axis (I), the distance between the image-side surface 42 of the second lens element 4 and the object-side surface 51 of the third lens element 5 at the optical axis (I), the distance between the image-side surface 52 of the third lens element 5 and the object-side surface 61 of the fourth lens element 6 at the optical axis (I), and the distance between the image-side surface 62 of the fourth lens element 6 and the object-side surface 71 of the fifth lens element 7 at the optical axis (I); and
ALT represents a sum of the distance between the object-side surface 31 and the image-side surface 32 of the first lens element 3 at the optical axis (I), the distance between the object-side surface 41 and the image-side surface 42 of the second lens element 4 at the optical axis (I), the distance between the object-side surface 51 and the image-side surface 52 of the third lens element 5 at the optical axis (I), the distance between the object-side surface 61 and the image-side surface 62 of the fourth lens element 6 at the optical axis (I), and the distance between the object-side surface 71 and the image-side surface 72 of the fifth lens element 7 at the optical axis (I).
FIGS. 5(a) to 5(d) show simulation results corresponding to longitudinal spherical aberration, sagittal astigmatism aberration, tangential astigmatism aberration, and distortion aberration of the first preferred embodiment, respectively. In each of the simulation results, curves corresponding respectively to wavelengths of 470 nm, 555 nm, and 650 nm are shown.
It can be understood from FIG. 5(a) that, since each of the curves corresponding to longitudinal spherical aberration has a focal length at each field of view (indicated by the vertical axis) that falls within the range of ±0.025 mm, the first preferred embodiment is able to achieve a relatively low spherical aberration at each of the wavelengths. Furthermore, since a deviation in focal length among the curves at each field of view does not exceed the range of ±0.04 mm, the first preferred embodiment has a relatively low chromatic aberration.
It can be understood from FIGS. 5 (b) and 5 (c) that, since each of the curves falls within the range of ±0.20 mm of focal length, the first preferred embodiment has a relatively low optical aberration.
Moreover, as shown in FIG. 5 (d), since each of the curves corresponding to distortion aberration falls within the range of ±24%, the first preferred embodiment is able to meet requirements in imaging quality of most optical systems.
In view of the above, even with the system length reduced down to 5.097 mm, the imaging lens 10 of the first preferred embodiment is still able to achieve a relatively good optical performance.
Referring to FIG. 6, the differences between the first and second preferred embodiments of the imaging lens 10 of this invention reside in that: the object-side surface 61 of the fourth lens element 6 is a concave surface; the image-side surface 62 of the fourth lens element 6 has a convex portion 621 in a vicinity of the optical axis (I), and a concave portion 622 in a vicinity of a periphery of the fourth lens element 6; the object-side surface 71 of the fifth lens element 7 has a concave portion 711 in a vicinity of the optical axis (I), and a convex portion 712 in a vicinity of a periphery of the fifth lens element 7; and the image-side surface 72 of the fifth lens element 7 has a convex portion 721 in a vicinity of the optical axis (I), and a concave portion 724 in a vicinity of a periphery of the fifth lens element 7.
Shown in FIG. 7 is a table that lists values of some optical parameters corresponding to the surfaces 31-81, 32-82 of the second preferred embodiment. The imaging lens 10 has an overall system focal length of 1.018 mm, an HFOV of 58.000°, an F-number of 2.808, and a system length of 5.168 mm.
Shown in FIG. 8 is a table that lists values of some optical parameters of the aforementioned optical relationship (1) corresponding to the second preferred embodiment.
Relationships among some of the aforementioned optical parameters corresponding to the second preferred embodiment are as follows:

CT5/CT4=1.046

AAG/CT5=3.624

CT5/AC23=0.756

CT5/(AC34+AC45)=3.761

CT4/CT1=1.452

AAG/CT1=5.504

CT1/(AC34+AC45)=2.477

AAG/AC12=1.780

AC12/AC23=1.541

AC12/(AC34+AC45)=7.661

ALT/CT4=6.811

ALT/AC23=4.926

ALT/(AC34+AC45)=24.495

CT2/AC23=1.205

CT2/(AC34+AC45)=5.991

CT3/CT4=2.411

AAG/CT3-1.572

CT3/AC23=1.744

CT3/(AC34+AC45)=8.670

FIGS. 9(a) to 9(d) show simulation results corresponding to longitudinal spherical aberration, sagittal astigmatism aberration, tangential astigmatism aberration, and distortion aberration of the second preferred embodiment, respectively. It can be understood from FIG. 9(a) that, since the curves corresponding to longitudinal spherical aberration fall within the range of ±0.025 mm of focal length, the second preferred embodiment is able to achieve a relatively low spherical aberration at each of the wavelengths, and has a relatively low chromatic aberration. Referring to FIGS. 9(b), 9(c) and 9(d), since the curves corresponding to astigmatism aberrations fall within the range of ±0.15 mm of focal length, and the curves corresponding to distortion aberration fall within the range of ±21%, the second preferred embodiment is able to achieve a relatively good optical performance even with the system length reduced down to 5.168 mm.
Referring to FIG. 10, the differences between the first and third preferred embodiments of the imaging lens 10 of this invention reside in that: the object-side surface 61 of the fourth lens element 6 is a concave surface; and the image-side surface 72 of the fifth lens element 7 has a convex portion 721 in a vicinity of the optical axis (I), and a concave portion 724 in a vicinity of a periphery of the fifth lens element 7.
Shown in FIG. 11 is a table that lists values of some optical parameters corresponding to the surfaces 31-81, 32-82 of the third preferred embodiment. The imaging lens 10 has an overall system focal length of 1.028 mm, an HFOV of 58.000°, an F-number of 2.778, and a system length of 5.215 mm.
Shown in FIG. 12 is a table that lists values of some optical parameters of the aforementioned optical relationship (1) corresponding to the third preferred embodiment.
Relationships among some of the aforementioned optical parameters corresponding to the third preferred embodiment are as follows:

CT5/CT4=1.008

AAG/CT5=2.143

CT5/AC23=1.178

CT5/(AC34+AC45)=6.678

CT4/CT1=1.386

AAG/CT1=2.995

CT1/(AC34+AC45)=4.778

AAG/AC12=1.872

AC12/AC23=1.349

AC12/(AC34+AC45)=7.644

ALT/CT4=5.034

ALT/AC23=5.882

ALT/(AC34+AC45)=33.333

CT2/AC23=1.337

CT2/(AC34+AC45)=7.578

CT3/CT4=1.159

AAG/CT3=1.864

CT3/AC23=1.355

CT3/(AC34+AC45)=7.678

FIGS. 13(a) to 13(d) show simulation results corresponding to longitudinal spherical aberration, sagittal astigmatism aberration, tangential astigmatism aberration, and distortion aberration of the third preferred embodiment, respectively. It can be understood from FIG. 13 (a) that, since the curves corresponding to longitudinal spherical aberration fall within the range of ±0.035 mm of the focal length, the third preferred embodiment is able to achieve a relatively low spherical aberration at each of the wavelengths, and has a relatively low chromatic aberration. Referring to FIGS. 13(b), 13(c) and 13(d), since the curves corresponding to astigmatism aberrations fall within the range of ±0.25 mm of focal length, and the curves corresponding to distortion aberration fall within the range of ±12%, the third preferred embodiment is able to achieve a relatively good optical performance even with the system length reduced down to 5.215 mm.
FIG. 14 illustrates the fourth preferred embodiment of an imaging lens 10 according to the present invention, which has a configuration similar to that of the first preferred embodiment.
Shown in FIG. 15 is a table that lists values of some optical parameters corresponding to the surfaces 31-81, 32-82 of the fourth preferred embodiment. The imaging lens 10 has an overall system focal length of 1.044 mm, an HFOV of 60.000°, an F-number of 2.785, and a system length of 4.990 mm.
Shown in FIG. 16 is a table that lists values of some optical parameters of the aforementioned optical relationship (1) corresponding to the fourth preferred embodiment.
Relationships among some of the aforementioned optical parameters corresponding to the fourth preferred embodiment are as follows:

CT5/CT4=0.367

AAG/CT5=4.405

CT5/AC23-0.419

CT5/(AC34+AC45)=2.056

CT4/CT1=1.500

AAG/CT1=2.423

CT1/(AC34+AC45)=3.738

AAG/AC12=2.875

AC12/AC23=0.642

AC12/(AC34+AC45)=3.150

ALT/CT4=4.758

ALT/AC23=5.438

ALT/(AC34+AC45)=26.682

CT2/AC23=1.430

CT2/(AC34+AC45)=7.019

CT3/CT4=1.473

AAG/CT3=1.096

CT3/AC23=1.684

CT3/(AC34+AC45)=8.262

FIGS. 17(a) to 17(d) show simulation results corresponding to longitudinal spherical aberration, sagittal astigmatism aberration, tangential astigmatism aberration, and distortion aberration of the fourth preferred embodiment, respectively. It can be understood from FIG. 17 (a) that, since the curves corresponding to longitudinal spherical aberration fall within the range of ±0.02 mm of focal length, the fourth preferred embodiment is able to achieve a relatively low spherical aberration at each of the wavelengths, and has relatively low chromatic aberration. Referring to FIGS. 17 (b), 17 (c) and 17 (d), since the curves corresponding to astigmatism aberrations fall within the range of ±0.15 mm of focal length, and the curves corresponding to distortion aberration fall within the range of ±27%, the fourth preferred embodiment is able to achieve a relatively good optical performance even with the system length reduced down to 4.990 mm.
Referring to FIG. 18, the differences between the first and fifth preferred embodiments of the imaging lens 10 of this invention reside in that: the image-side surface 72 of the fifth lens element 7 has a convex portion 721 in a vicinity of the optical axis (I), and a concave portion 724 in a vicinity of a periphery of the fifth lens element 7.
Shown in FIG. 19 is a table that lists values of some optical parameters corresponding to the surfaces 31-81, 32-82 of the fifth preferred embodiment. The imaging lens 10 has an overall system focal length of 1.069 mm, an HFOV of 60.000°, an F-number of 2.794, and a system length of 5.074 mm.
Shown in FIG. 20 is a table that lists values of some optical parameters of the aforementioned optical relationship (1) corresponding to the fifth preferred embodiment.
Relationships among some of the aforementioned optical parameters corresponding to the fifth preferred embodiment are as follows:

CT5/CT4=0.375

AAG/CT5=3.650

CT5/AC23=0.675

CT5/(AC34+AC45)=2.645

CT4/CT1=1.570

AAG/CT1=2.148

CT1/(AC34+AC45)=4.495

AAG/AC12=2.037

AC12/AC23=1.210

AC12/(AC34+AC45)=4.738

ALT/CT4=3.838

ALT/AC23=6.916

ALT/(AC34+AC45)=27.084

CT2/AC23=1.573

CT2/(AC34+AC45)=6.159

CT3/CT4=0.954

AAG/CT3=1.435

CT3/AC23=1.718

CT3/(AC34+AC45)=6.729

FIGS. 21(a) to 21(d) show simulation results corresponding to longitudinal spherical aberration, sagittal astigmatism aberration, tangential astigmatism aberration, and distortion aberration of the fifth preferred embodiment, respectively. It can be understood from FIG. 21(a) that, since the curves corresponding to longitudinal spherical aberration fall within the range of ±0.035 mm of focal length, the fifth preferred embodiment is able to achieve a relatively low spherical aberration at each of the wavelengths, and has a relatively low chromatic aberration. Referring to FIGS. 21(b), 21(c) and 21(d), since the curves corresponding to astigmatism aberrations fall within the range of ±0.20 mm of focal length, and the curves corresponding to distortion aberration fall within the range of ±21%, the fifth preferred embodiment is able to achieve a relatively good optical performance even with the system length reduced down to 5.074 mm.
FIG. 22 illustrates the sixth preferred embodiment of an imaging lens 10 according to the present invention, which has a configuration similar to that of the first preferred embodiment.
Shown in FIG. 23 is a table that lists values of some optical parameters corresponding to the surfaces 31-81, 32-82 of the sixth preferred embodiment. The imaging lens 10 has an overall system focal length of 1.030 mm, an HFOV of 63.000°, an F-number of 2.710, and a system length of 5.050 mm.
Shown in FIG. 24 is a table that lists values of some optical parameters of the aforementioned optical relationship (1) corresponding to the sixth preferred embodiment.
Relationships among some of the aforementioned optical parameters corresponding to the sixth preferred embodiment are as follows:

CT5/CT4=0.400

AAG/CT5=3.380

CT5/AC23=0.717

CT5/(AC34+AC45)=2.561

CT4/CT1=1.713

AAG/CT1=2.315

CT1/(AC34+AC45)=3.738

AAG/AC12=2.119

AC12/AC23=1.144

AC12/(AC34+AC45)=4.084

ALT/CT4=4.301

ALT/AC23=7.712

ALT/(AC34+AC45)=27.533

CT2/AC23=1.953

CT2/(AC34+AC45)=6.972

CT3/CT4=1.228

AAG/CT3=1.101

CT3/AC23=2.202

CT3/(AC34+AC45)=7.860

FIGS. 25(a) to 25(d) show simulation results corresponding to longitudinal spherical aberration, sagittal astigmatism aberration, tangential astigmatism aberration, and distortion aberration of the sixth preferred embodiment, respectively. It can be understood from FIG. 25(a) that, since the curves corresponding to longitudinal spherical aberration fall within the range of ±0.02 mm of focal length, the sixth preferred embodiment is able to achieve a relatively low spherical aberration at each of the wavelengths, and has a relatively low chromatic aberration. Referring to FIGS. 25(b), 25(c) and 25(d), since the curves corresponding to astigmatism aberrations fall within the range of ±0.20 mm of focal length, and the curves corresponding to distortion aberration fall within the range of ±30%, the sixth preferred embodiment is able to achieve a relatively good optical performance even with the system length reduced down to 5.050 mm.
Shown in FIG. 26 is a table that lists the aforesaid relationships among some of the aforementioned optical parameters corresponding to the six preferred embodiments for comparison. When each of the optical parameters of the imaging lens 10 according to this invention satisfies the following optical relationships, the optical performance is still relatively good even with the reduced system length:

AAG/CT1≦5.500  (2)

AAG/CT3≦2.000  (3)

AAG/AC12≦3.000  (4)

CT4/CT1≦1.800  (5)

AAG/CT5≦4.800  (6)

1.300≦CT2/AC23  (7)

3.700≦ALT/CT4  (8)

0.500≦CT5/CT4  (9)

4.100≦ALT/AC23  (10)

22.000≦ALT/(AC34+AC45)  (11)

1.500≦CT3/AC23  (12)

6.500≦CT3/(AC34+AC45)  (13)

1.300≦CT3/CT4  (14)

2.100CT1/(AC34+AC45)  (15)

5.000≦CT2/(AC34+AC45)  (16)

AAG may be designed to be smaller for fulfilling requirement of miniaturization of the imaging lens 10. AAG may have a relatively large reducible ratio compared to CT1. Better arrangement may be achieved when the relationship (2) is satisfied. The relationship (2) may have a lower limit: 2.000≦AAG/CT1≦5.500.
AAG may be designed to be smaller for fulfilling requirement of miniaturization of the imaging lens 10. AAG may have a relatively large reducible ratio compared to CT3. Better arrangement may be achieved when the relationship (3) is satisfied. The relationship (3) may have a lower limit: 1.000≦AAG/CT3≦2.000.
AAG may be designed to be smaller for fulfilling requirement of miniaturization of the imaging lens 10. AAG may have a relatively large reducible ratio compared to AC12. Better arrangement may be achieved when the relationship (4) is satisfied. The relationship (4) may have a lower limit: 1.500≦AAG/AC12≦3.000.
Considering light transmission and difficulty in manufacturing when the imaging lens 10 has a reduced system length, better arrangement may be achieved when the relationship (5) is satisfied. The relationship (5) may have a lower limit: 1.000≦CT4/CT1≦1.800.
AAG may be designed to be smaller for fulfilling requirement of miniaturization of the imaging lens 10. AAG may have a relatively large reducible ratio compared to CT5. Better arrangement may be achieved when the relationship (6) is satisfied. The relationship (6) may have a lower limit: 2.000≦AAG/CT5≦4.800.
Since the object-side surface 41 of the second lens element 4 has the convex portion 411 in the vicinity of the optical axis (I), CT2 has a relatively small reducible ratio compared to AC23. Better arrangement may be achieved when the relationship (7) is satisfied. The relationship (7) may have an upper limit: 1.300≦CT2/AC23≦2.000.
Considering difficulty in manufacturing and image quality, CT4 has a relatively large reducible ratio compared to ALT. Better arrangement may be achieved when the relationship (8) is satisfied. The relationship (8) may have an upper limit: 3.700≦ALT/CT4≦7.000.
Considering light transmission, difficulty in manufacturing and image quality, CT4 has a relatively large reducible ratio compared to CT5. Better arrangement may be achieved when the relationship (9) is satisfied. The relationship (9) may have an upper limit: 0.500≦CT5/CT4≦1.100.
Although reduction of ALT may contribute to reduction of the overall system length, it is limited due to consideration of difficulty in manufacturing. Therefore, AC23 has a relatively large reducible ratio compared to ALT. Better arrangement may be achieved when the relationship (10) is satisfied. The relationship (10) may have an upper limit: 4.100≦ALT/AC23≦8.000.
Although reduction of ALT may contribute to reduction of the overall system length, it is limited due to consideration of difficulty in manufacturing. Therefore, AC34 and AC45 have a relatively large reducible ratio compared to ALT. Better arrangement may be achieved when the relationship (11) is satisfied. The relationship (11) may have an upper limit: 22.000≦ALT/(AC34+AC45)≦35.000.
Considering difficulty in manufacturing and image quality, AC23 has a relatively large reducible ratio compared to CT3. Better arrangement may be achieved when the relationship (12) is satisfied. The relationship (12) may have an upper limit: 1.500≦CT3/AC23≦2.500.
Since the image-side surface 52 of the third lens element 5 has the convex portion 521 in the vicinity of the optical axis (I), CT3 has a relatively small reducible ratio compared to AC34 and AC45. Better arrangement may be achieved when the relationship (13) is satisfied. The relationship (13) may have an upper limit: 6.500≦CT3/(AC34+AC45)≦9.000.
Considering difficulty in manufacturing and image quality, CT4 has a relatively large reducible ratio compared to CT3, and better arrangement may be achieved when the relationship (14) is satisfied. The relationship (14) may have an upper limit: 1.300≦CT3/CT4≦2.500.
Considering difficulty in manufacturing and image quality, AC34 and AC45 have a relatively reducible ratio compared to CT1, and better arrangement may be achieved when the relationship (15) is satisfied. The relationship (15) may have an upper limit: 2.100≦CT1/(AC34+AC45)≦5.000.
Considering difficulty in manufacturing and image quality, AC34 and AC45 have a relatively reducible ratio compared to CT2, and better arrangement may be achieved when the relationship (16) is satisfied. The relationship (16) may have an upper limit: 5.000≦CT2/(AC34+AC45)≦8.000.
To sum up, some of the effects and advantages of the imaging lens 10 according to the present invention are described hereinbelow:
1. Since the first lens element 3 has the negative refractive power and the aperture stop 2 is disposed between the second lens element 4 and the third lens element 5, the system length may be reduced while maintaining image quality.
2. By virtue of the convex portions 411, 521 and 621, image quality may be ensured.
3. Since the fifth lens element 7 is made of a plastic material, weight and cost of the imaging lens 10 may be reduced.
4. Through design of the relevant optical parameters, such as AAG/CT1, AAG/CT3, AAG/AC12, CT4/CT1, AAG/CT5, CT2/AC23, ALT/CT4, CT5/CT4, ALT/AC23, ALT/(AC34+AC45), CT3/AC23, CT3/(AC34+AC45), ALT/AC23, CT3/CT4, CT1/(AC34+AC45) and CT2/(AC34+AC45), optical aberrations, such as spherical aberration, may be reduced or even eliminated. Further, through surface design and arrangement of the lens elements 3-7, even with the system length reduced, optical aberrations may still be reduced or even eliminated, resulting in relatively good optical performance.
5. Through the aforesaid six preferred embodiments, it is apparent that the system length of this invention may be reduced down to below 6 mm, so as to facilitate developing thinner relevant products with economic benefits.
Shown in FIG. 27 is a first exemplary application of the imaging lens 10, in which the imaging lens 10 is disposed in a housing 11 of a portable electronic apparatus 1 (such as a mobile phone, but not limited thereto), and forms a part of an imaging module 12 of the portable electronic apparatus 1. The imaging module 12 includes a barrel 21 on which the imaging lens 10 is disposed, a holder unit 120 on which the barrel 21 is disposed, and an image sensor 130 disposed at the image plane 9 (see FIG. 2).
The holder unit 120 includes a first holder portion 121 in which the barrel 21 is disposed, and a second holder portion 122 having a portion interposed between the first holder portion 121 and the image sensor 130. The barrel 21 and the first holder portion 121 of the holder unit 120 extend along an axis (II), which coincides with the optical axis (I) of the imaging lens 10.
Shown in FIG. 28 is a second exemplary application of the imaging lens 10. The differences between the first and second exemplary applications reside in that, in the second exemplary application, the holder unit 120 is configured as a voice-coil motor (VCM), and the first holder portion 121 includes an inner section 123 in which the barrel 21 is disposed, an outer section 124 that surrounds the inner section 123, a coil 125 that is interposed between the inner and outer sections 123, 124, and a magnetic component 126 that is disposed between an outer side of the coil 125 and an inner side of the outer section 124.
The inner section 123 and the barrel 21, together with the imaging lens 10 therein, are movable with respect to the image sensor 130 along an axis (III), which coincides with the optical axis (I) of the imaging lens 10. The optical filter 8 of the imaging lens 10 is disposed at the second holder portion 122, which is disposed to abut against the outer section 124. Configuration and arrangement of other components of the portable electronic apparatus 1 in the second exemplary application are identical to those in the first exemplary application, and hence will not be described hereinafter for the sake of brevity.
By virtue of the imaging lens 10 of the present invention, the portable electronic apparatus 1 in each of the exemplary applications may be configured to have a relatively reduced overall thickness with good optical and imaging performance, so as to reduce cost of materials, and satisfy requirements of product miniaturization.
While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.

## Claims

1. An imaging lens comprising a first lens element, a second lens element, an aperture stop, a third lens element, a fourth lens element and a fifth lens element arranged in order from an object side to an image side along an optical axis of said imaging lens, each of said first lens element, said second lens element, said third lens element, said fourth lens element and said fifth lens element having an object-side surface facing toward the object side and an image-side surface facing toward the image side, wherein:
said first lens element has a negative refractive power;
said object-side surface of said second lens element has a convex portion in a vicinity of the optical axis;
said image-side surface of said third lens element has a convex portion in a vicinity of the optical axis;
said image-side surface of said fourth lens element has a convex portion in a vicinity of the optical axis;
said fifth lens element is made of a plastic material;
said imaging lens satisfies AAG/CT1≦5.500, where AAG represents a sum of a distance between said image-side surface of said first lens element and said object-side surface of said second lens element at the optical axis, a distance between said image-side surface of said second lens element and said object-side surface of said third lens element at the optical axis, a distance between said image-side surface of said third lens element and said object-side surface of said fourth lens element at the optical axis, and a distance between said image-side surface of said fourth lens element and said object-side surface of said fifth lens element at the optical axis; and CT1 represents a distance between said object-side surface and said image-side surface of said first lens element at the optical axis; and
said imaging lens does not include any lens element with refractive power other than said first lens element, said second lens element, said third lens element, said fourth lens element and said fifth lens element.

2. The imaging lens as claimed in claim 1, further satisfying AAG/CT3≦2.000, where CT3 represents a distance between said object-side surface and said image-side surface of said third lens element at the optical axis.

3. The imaging lens as claimed in claim 2, further satisfying AAG/AC12≦3.000, where AC12 represents the distance between said image-side surface of said first lens element and said object-side surface of said second lens element at the optical axis.

4. The imaging lens as claimed in claim 3, further satisfying CT4/CT1≦1.800, where CT4 represents a distance between said object-side surface and said image-side surface of said fourth lens element at the optical axis.

5. The imaging lens as claimed in claim 4, further satisfying AAG/CT5≦4.800, where CT5 represents a distance between said object-side surface and said image-side surface of said fifth lens element at the optical axis.

6. The imaging lens as claimed in claim 5, further satisfying 1.300≦CT2/AC23, where CT2 represents a distance between said object-side surface and said image-side surface of said second lens element at the optical axis; and AC23 represents the distance between said image-side surface of said second lens element and said object-side surface of said third lens element at the optical axis.

7. The imaging lens as claimed in claim 2, further satisfying CT4/CT1≦1.800, where CT4 represents a distance between said object-side surface and said image-side surface of said fourth lens element at the optical axis.

8. The imaging lens as claimed in claim 7, further satisfying 3.700≦ALT/CT4, where ALT represents a sum of the distance between said object-side surface and said image-side surface of said first lens element at the optical axis, a distance between said object-side surface and said image-side surface of said second lens element at the optical axis, a distance between said object-side surface and said image-side surface of said third lens element at the optical axis, the distance between said object-side surface and said image-side surface of said fourth lens element at the optical axis, and a distance between said object-side surface and said image-side surface of said fifth lens element at the optical axis.

9. The imaging lens as claimed in claim 8, further satisfying 0.500≦CT5/CT4, where CT5 represents the distance between said object-side surface and said image-side surface of said fifth lens element at the optical axis.

10. The imaging lens as claimed in claim 9, further satisfying 4.100≦ALT/AC23, where AC23 represents the distance between said image-side surface of said second lens element and said object-side surface of said third lens element at the optical axis.

11. The imaging lens as claimed in claim 10, further satisfying 22.000≦ALT/(AC34+AC45), where AC34 represents the distance between said image-side surface of said third lens element and said object-side surface of said fourth lens element at the optical axis; and AC45 represents the distance between said image-side surface of said fourth lens element and said object-side surface of said fifth lens element at the optical axis.

12. The imaging lens as claimed in claim 1, further satisfying AAG/AC12≦3.000, where AC12 represents the distance between said image-side surface of said first lens element and said object-side surface of said second lens element at the optical axis.

13. The imaging lens as claimed in claim 12, further satisfying 1.500≦CT3/AC23, where CT3 represents a distance between said object-side surface and said image-side surface of said third lens element at the optical axis; and AC23 represents the distance between said image-side surface of said second lens element and said object-side surface of said third lens element at the optical axis.

14. The imaging lens as claimed in claim 13, further satisfying 0.500≦CT5/CT4, where CT4 represents a distance between said object-side surface and said image-side surface of said fourth lens element at the optical axis; and CT5 represents a distance between said object-side surface and said image-side surface of said fifth lens element at the optical axis.

15. The imaging lens as claimed in claim 14, further satisfying 6.500≦CT3/(AC34+AC45), where AC34 represents the distance between said image-side surface of said third lens element and said object-side surface of said fourth lens element at the optical axis; and AC45 represents the distance between said image-side surface of said fourth lens element and said object-side surface of said fifth lens element at the optical axis.

16. The imaging lens as claimed in claim 1, further satisfying CT4/CT1≦1.800, where CT4 represents a distance between said object-side surface and said image-side surface of said fourth lens element at the optical axis.

17. The imaging lens as claimed in claim 16, further satisfying 4.100≦ALT/AC23, where ALT represents a sum of the distance between said object-side surface and said image-side surface of said first lens element at the optical axis, a distance between said object-side surface and said image-side surface of said second lens element at the optical axis, a distance between said object-side surface and said image-side surface of said third lens element at the optical axis, the distance between said object-side surface and said image-side surface of said fourth lens element at the optical axis, and a distance between said object-side surface and said image-side surface of said fifth lens element at the optical axis; and AC23 represents the distance between said image-side surface of said second lens element and said object-side surface of said third lens element at the optical axis.

18. The imaging lens as claimed in claim 17, further satisfying 1.300≦CT3/CT4, where CT3 represents the distance between said object-side surface and said image-side surface of said third lens element at the optical axis.

19. The imaging lens as claimed in claim 18, further satisfying 2.100≦CT1/(AC34+AC45), and 5.000≦CT2/(AC34+AC45), where AC34 represents the distance between said image-side surface of said third lens element and said object-side surface of said fourth lens element at the optical axis; AC45 represents the distance between said image-side surface of said fourth lens element and said object-side surface of said fifth lens element at the optical axis; and CT2 represents the distance between said object-side surface and said image-side surface of said second lens element at the optical axis.

20. A portable electronic apparatus comprising:
a housing; and
an imaging module disposed in said housing, and including an imaging lens as claimed in claim 1, a barrel on which said imaging lens is disposed, a holder unit on which said barrel is disposed, and an image sensor disposed at the image side of said imaging lens.