# Patent

## Title
Imaging lens

## Abstract

An imaging lens for a solid-state image sensor includes five lenses, arranged in order from an object side to an image side, a first lens with positive refractive power having a convex surface on the object side, a second lens with negative refractive power, a third lens with positive or negative refractive power having a meniscus shape with a convex surface on the object side and a concave surface on the image side near an optical axis, a fourth lens as a double-sided aspheric lens, having a concave surface on the image side near the optical axis, and a fifth lens as a double-sided aspheric lens, having a concave surface on the image side near the optical axis; wherein the first to fifth lenses are made of plastic materials.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation of U.S. application Ser. No. 13/853,359, filed on Mar. 29, 2013, the contents of which are incorporated herein by reference.


The present application is based on and claims priority of Japanese patent application No. 2012-085263 filed on Apr. 4, 2012, the entire contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to imaging lenses which form an image of an object on a solid-state image sensor such as a CCD sensor or C-MOS sensor used in a compact image pickup device and more particularly to imaging lenses composed of five lenses which are built in image pickup devices mounted in mobile terminals such as mobile phones and smart phones, which are becoming increasingly compact and thin, and PDAs (Personal Digital Assistances), game machines and information terminals such as PCs.
Description of the Related Art
In recent years, the market of mobile terminals with an image pickup device has been expanding increasingly. Today, most of such mobile terminals have a camera function. Nowadays, as for the camera performance of these mobile terminals, a high pixel density camera function comparable to a digital still camera is becoming mainstream. Furthermore, for the reasons of convenience and appearance, the demand for thinner models is growing, leading to a stronger need for smaller and thinner built-in image pickup devices. With this background, an imaging lens built in an image pickup device using a high pixel density image sensor is expected to provide higher resolution and be more compact and thinner and also to be a fast lens (namely a lens with a small F-value). At the same time, the imaging lens is strongly anticipated to provide a wide angle of view so that an image of a wide object can be taken.
Generally an imaging lens which copes with the need for compactness, thinness, and high performance is composed of a plurality of lenses. Conventionally, in order to deal with VGA up to 1 megapixel, an imaging lens composed of two or three lenses has been widely used for its advantage in terms of size and cost. Also, many types of imaging lenses composed of four lenses which are intended to cope with the need for an increase in the number of pixels have been proposed. Recently, imaging lenses composed of five lenses which can provide higher performance than those composed of four lenses have also been proposed in order to cope with the need for compactness and increase in the number of pixels as mentioned above. The present invention provides an imaging lens which is composed of five lenses to meet the above needs.
JP-A-2009-294528 (Patent Document 1) discloses an imaging lens composed of five lenses which are arranged in order from the object side as follows: a first lens with positive power having a convex surface on the object side, an aperture stop, a second lens with a meniscus shape near the optical axis, a third lens having a convex surface on the image side near the optical axis, a fourth lens in which both surfaces are aspheric and the peripheral area of the image side surface is convex, and a fifth lens in which both surfaces are aspheric and the peripheral area of the image side surface is convex, and among the second to fifth lenses there is only one negative lens with an Abbe number of 30 or less.
JP-A-2010-026434 (Patent Document 2) discloses an imaging lens composed of five lenses in which a positive first lens, a positive second lens, a negative third lens, a positive fourth lens, and a negative fifth lens are arranged in order from the object side.
The imaging lens described in Patent Document 1 has a ratio of total track length (TTL) to maximum image height (IH) (TTL/2IH) of about 1.0, so it is relatively compact. However, since its F-value is about 3.0, therefore, the imaging lens is not considered to provide enough brightness to cope with the increasing trend toward image sensors with a larger number of pixels. Although the imaging lens described in Patent Document 2 is a lens system which has an F-value of 2.05 to 2.5 to ensure sufficient brightness and provides high aberration correction capability, the power of its first lens is weak, so it is disadvantageous in order to achieve thinness.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above problem and has an objective to provide an imaging lens composed of five lenses which can achieve compactness and thinness, has a small F-value and corrects various aberrations properly and provides a relatively wide angle of view and also meets the need for cost reduction.
According to an aspect of the present invention, there is provided an imaging lens composed of five lenses which are arranged in order from the object side to the image side as follows: a first lens with positive refractive power having a convex surface on the object side, a second lens with negative refractive power, a third lens with positive or negative refractive power having a meniscus shape with a concave surface on the image side and a convex surface on the object side near an optical axis, a fourth lens having a concave surface on the image side near the optical axis, and a fifth lens having a concave surface on the image side near the optical axis. The both surfaces of the fourth and fifth lenses are aspheric (double-sided aspheric lenses). The first to fifth lenses are made of plastic materials.
Preferably, in the imaging lens according to the present invention, the second lens has a concave surface on the image side.
Preferably, the imaging lens according to the present invention satisfies conditional expressions (1), (2), and (3) below:

45<ν1<90  (1)

22<ν2<35  (2)

2.0<ν1/ν2<2.6  (3)

where
ν1: Abbe number of the first lens
ν2: Abbe number of the second lens.
Preferably, in the imaging lens according to the present invention, the fourth lens has a positive refractive power and the fifth lens has a negative refractive power.
In the imaging lens configured as mentioned above, among the five constituent lenses, the first lens has a strong positive refractive power so as to facilitate shortening of the total track length, and the second and fifth lenses have negative refractive power surfaces which have a diffuse effect to facilitate proper correction of aberrations on the image plane including the peripheral area. Also, the fourth lens is a lens with positive refractive power having a concave surface on the image side, so as to ensure an appropriate back focus. The both surfaces of the fourth lens and fifth lens have adequate aspheric shapes to control the angle of light rays incident on the image sensor.
The conditional expression (1) defines the Abbe number of the first lens and the conditional expression (2) defines the Abbe number of the second lens and these expressions both indicate conditions to correct chromatic aberration properly. If the Abbe number of the first lens is below the lower limit in the conditional expression (1) and if the Abbe number of the second lens is above the upper limit in the conditional expression (2), the difference between the variance values of the first lens and second lens would be smaller, resulting in insufficient correction of chromatic aberration. If the Abbe number of the first lens is above the upper limit in the conditional expression (1) and if the Abbe number of the second lens is below the lower limit in the conditional expression (2), the balance between axial chromatic aberration and chromatic aberration of magnification would deteriorate, resulting in performance decrease in the peripheral area. When both the conditional expressions (1) and (2) are satisfied and the Abbe number ratio is within the range indicated in the conditional expression (3), chromatic aberration is able to be corrected properly.
Preferably the imaging lens according to the present invention satisfies a conditional expression (4) below:

0.6<f1/f<0.9  (4)

where f represents the focal length of the overall optical system of the imaging lens and f1 represents the focal length of the first lens.
The conditional expression (4) defines the positive power of the first lens relative to the power of the overall optical system and indicates a condition to achieve compactness and correct aberrations properly. If the ratio is above the upper limit in the conditional expression (4), the positive power of the first lens relative to the power of the overall optical system would weaken, which would lead to a disadvantage in shortening the total track length. On the other hand, if it is below the lower limit, undesirably the power of the first lens would be too strong, making it difficult to correct aberrations and causing an increase in manufacturing tolerance sensitivity.
Preferably the imaging lens according to the present invention satisfies a conditional expression (5) below:

−1.0<f2/f<−0.8  (5)

where f2 represents the focal length of the second lens.
The conditional expression (5) defines the negative power of the second lens relative to the power of the overall optical system and indicates a condition to ensure that spherical aberration, coma aberration, and axial chromatic aberration are corrected properly.
If the ratio is above the upper limit in the conditional expression (5), it would be difficult to correct spherical aberration and coma aberration. On the other hand, if it is below the lower limit in the conditional expression (5), the negative power of the second lens would be too weak, making it difficult to correct axial chromatic aberration.
Preferably, in the imaging lens according to the present invention, an aperture stop is located on the object side of the first lens. By locating the aperture stop on the object side of the first lens, the exit pupil can be set away from the image plane, and consequently, the angle of light rays incident on the image sensor can be restrained adequately to ensure a good telecentricity on the image side.
Here the aperture stop located on the object side of the first lens is in either of the following two ways: it is located nearer toward the object and farther from the point where the object side surface of the first lens crosses the optical axis, or it is located anywhere in the area from the point where the object side surface of the first lens crosses the optical axis to the peripheral edge thereof.
In the imaging lens according to the present invention, preferably the fourth lens and the fifth lens have a meniscus shape with a concave surface on the image side near the optical axis and have a pole-change point other than on the optical axis on their object side surface and image side surface. Due to this aspheric shape, field curvature can be properly corrected while the angle of light rays incident on the image sensor is restrained to enhance telecentricity. “Pole-change point” here means a point on an aspheric surface where a tangential plane crosses the optical axis perpendicularly.
Preferably the imaging lens according to the present invention satisfies a conditional expression (6) below:

1.1<TTL/f<1.3  (6)

where TTL represents the distance on the optical axis from the imaging lens' surface nearest to the object side to the image plane without the filter being placed.
The conditional expression (6) defines the ratio of the total track length to the focal length of the overall optical system and indicates a condition to shorten the total track length and correct various aberrations properly.
If the ratio is above the upper limit in the conditional expression (6), it would facilitate correction of various aberrations due to increased freedom in shaping of each lens; however, it leads to a longer total track length, creating difficulty in achieving thinness. On the other hand, if the ratio is below the lower limit in the conditional expression (6), the total track length would be too short and it leads to reduction of the freedom in shaping of each lens, making it difficult to correct various aberrations.
Preferably the imaging lens according to the present invention satisfies a conditional expression (7) below:

−0.40<r1/r2<−0.08  (7)

where r1 represents the curvature radius of the object side surface of the first lens and r2 represents the curvature radius of the image side surface of the first lens.
The conditional expression (7) defines the shape of the first lens near the optical axis and indicates a condition to shorten the total track length and suppress spherical aberration.
If the ratio is above the upper limit in the conditional expression (7), the power of the object side surface of the first lens would be stronger than the power of its image side surface, undesirably resulting in increased spherical aberration. On the other hand, if the ratio is below the lower limit in the conditional expression (7), the power of the object side surface of the first lens would be too weak as compared with the power of its image side surface, which would be disadvantageous in shortening the total track length.
Preferably the imaging lens according to the present invention satisfies a conditional expression (8) below:

1.6<f4/f<3.8  (8)

where f4 represents the focal length of the fourth lens.
The conditional expression (8) defines the power of the fourth lens relative to the power of the overall optical system and indicates a condition to shorten the total track length while ensuring an adequate back focus.
If the ratio is above the upper limit in the conditional expression (8), the positive power of the fourth lens relative to the power of the overall optical system would weaken, which would make it easy to ensure an adequate back focus; however, it would bring a disadvantage in shortening the total track length. On the other hand, if the ratio is below the lower limit in the conditional expression (8), the positive power of the fourth lens relative to the power of the overall optical system would be too strong, and consequently, it would be advantageous in shortening the total track length; however, it would be difficult to ensure back focus.
Preferably the imaging lens according to the present invention satisfies a conditional expression (9) below:

−9.0<f5/f<−1.4  (9)

where f5 represents the focal length of the fifth lens.
The conditional expression (9) defines the negative power of the fifth lens relative to the power of the overall optical system.
If the ratio is above the upper limit in the conditional expression (9), the negative power of the fifth lens relative to the power of the overall optical system would be stronger, and consequently, it would be disadvantageous in shortening the total track length. On the other hand, if the ratio is below the lower limit in the conditional expression (9), the negative power of the fifth lens relative to the power of the overall optical system would be too weak, and consequently it would be advantageous in shortening the total track length; however, it would be difficult to correct distortion and field curvature.
In the imaging lens according to the present invention, preferably all the constituent lenses are made of plastic material. When all the lenses are made of plastic material, mass production at low cost is achievable. Specifically cycloolefin plastic material is used for the first lens, the third lens, the fourth lens, and the fifth lens and polycarbonate is used for the second lens.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view showing the general configuration of an imaging lens according to Embodiment 1 of the invention;
FIG. 2 shows spherical aberration, astigmatism and distortion of the imaging lens according to the Embodiment 1;
FIG. 3 is a view showing the general configuration of an imaging lens according to Embodiment 2 of the invention;
FIG. 4 shows spherical aberration, astigmatism and distortion of the imaging lens according to the Embodiment 2;
FIG. 5 is a view showing the general configuration of an imaging lens according to Embodiment 3 of the invention;
FIG. 6 shows spherical aberration, astigmatism and distortion of the imaging lens according to the Embodiment 3;
FIG. 7 is a view showing the general configuration of an imaging lens according to Embodiment 4 of the invention; and
FIG. 8 shows spherical aberration, astigmatism and distortion of the imaging lens according to the Embodiment 4.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Next, the preferred embodiments of the present invention will be described in detail referring to the accompanying drawings. FIGS. 1, 3, 5, and 7 are views showing the general configurations of imaging lenses according to Embodiments 1 to 4 of the present invention respectively. Since all these Embodiments have the same basic lens configuration, the lens configuration of an imaging lens according to the present invention is explained below referring to the view of the Embodiment 1.
As shown in FIG. 1, in the imaging lens according to the present embodiment, lenses are arranged in the following order from the object side to the image side: a first lens L1 with positive refractive power, a second lens L2 with negative refractive power, a third lens L3 with positive or negative refractive power, a fourth lens L4 with positive refractive power, and a fifth lens L5 with negative refractive power. Aperture stop ST is located on the object side of the first lens L1. Filter IR is located between the fifth lens L5 and image plane IM. This filter IR is omissible.
In this imaging lens composed of five lenses, the first lens L1 is a biconvex lens in which the object side surface r1 and image side surface r2 are both convex; the second lens L2 is a meniscus lens in which the object side surface r3 is convex and the image side surface r4 is concave; the third lens L3 is a meniscus lens in which the object side surface r5 is convex near the optical axis X and the image side surface r6 is concave; the fourth lens L4 is a meniscus lens in which the object side surface r7 is convex near the optical axis X and the image side surface r8 is concave; and the fifth lens L5 is a meniscus lens in which the object side surface r9 is convex and the image side surface r10 is concave.
The third lens L3 is a lens which has weak positive power or negative power relative to the power of the overall optical system and in the Embodiment 1, it has negative power and in the Embodiments 2 to 4, it has positive power.
In this configuration, among the five constituent lenses L1 to L5, the first lens has a strong positive refractive power so as to facilitate shortening of the total track length, and the second and fifth lenses have negative refractive power surfaces with a diffuse effect to facilitate proper correction of aberrations on the image plane including the peripheral area. The third lens L3 has a weak positive or negative power and is mainly responsible for correction of off-axial aberrations. The both surfaces of the fourth lens L4 and fifth lens L5 have adequate aspheric shapes, thereby enhancing the telecentricity of light rays incident on the image sensor.
The imaging lenses according to the preferred embodiments of the invention are all made of plastic material. In all the Embodiments, cycloolefin plastic material is used for the first lens L1, third lens L3, fourth lens L4, and fifth lens L5 and polycarbonate is used for the second lens L2.
Since all the lenses are made of plastic material, stable mass production is attainable and cost reduction is easy. In addition, since the first lens L1, third lens L3, fourth lens L4, and fifth lens L5 are made of the same material, it is attainable to manufacture the imaging lens easily.
The imaging lens according to the present invention satisfies the following conditional expressions:

45<ν1<90  (1)

22<ν2<35  (2)

2.0<ν1/ν2<2.6  (3)

0.6<f1/f<0.9  (4)

−1.0<f2/f<−0.8  (5)

1.1<TTL/f<1.3  (6)

−0.40<r1/r2<−0.08  (7)

1.6<f4/f<3.8  (8)

−9.0<f5/f<−1.4  (9)

where:

ν1: Abbe number of the first lens
ν2: Abbe number of the second lens
f: focal length of the overall optical system of the imaging lens
f1: focal length of the first lens
f2: focal length of the second lens
f4: focal length of the fourth lens
f5: focal length of the fifth lens
TTL: distance on the optical axis from the object side surface of the first lens to the image plane without the filter
r1: curvature radius of the object side surface of the first lens
r2: curvature radius of the image side surface of the first lens
In this embodiment, all the lens surfaces are aspheric. The aspheric shape of the lens surfaces is expressed by the following equation, where Z represents an axis in the optical axis direction, H represents height perpendicular to the optical axis, k represents conic constant, and A4, A6, A8, A10, A12, A14, and A16 represent aspheric surface coefficients:




  
    
      
        Z
        =
        
          
            
              
                H
                2
              
              R
            
            
              1
              +
              
                
                  1
                  -
                  
                    
                      (
                      
                        k
                        +
                        1
                      
                      )
                    
                    ⁢
                    
                      
                        H
                        2
                      
                      
                        R
                        2
                      
                    
                  
                
              
            
          
          +
          
            
              A
              4
            
            ⁢
            
              H
              4
            
          
          +
          
            
              A
              6
            
            ⁢
            
              H
              6
            
          
          +
          
            
              A
              8
            
            ⁢
            
              H
              8
            
          
          +
          
            
              A
              10
            
            ⁢
            
              H
              10
            
          
          +
          
            
              A
              12
            
            ⁢
            
              H
              12
            
          
          +
          
            
              A
              14
            
            ⁢
            
              H
              14
            
          
          +
          
            
              A
              16
            
            ⁢
            
              H
              16
            
          
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        1
      
    
  




Next, the imaging lenses according to the preferred embodiments of the invention will be explained. In each Embodiment, f represents the focal length of the overall optical system of the imaging lens, Fno represents F-number, ω represents half angle of view, and IH represents maximum image height. i represents a surface number counted from the object side, r represents curvature radius, d represents the distance between lens surfaces on the optical axis (inter-surface distance), Nd represents refractive index with respect to d-ray (reference wavelength), and νd represents Abbe number with respect to d-ray. An asterisk (*) after surface number i indicates that the surface is aspheric.
Embodiment 1
The basic lens data of the Embodiment 1 is shown below in Table 1.







TABLE 1





Unit mm


f = 4.160


Fno = 2.20


ω(°) = 34.49


IH = 2.856







Surface data











Surface
Curvature
Surface
Refractive
Abbe No.


No. i
radius r
distance d
index Nd
νd





(Object surface)
Infinity
Infinity


Stop
Infinity
−0.225


1*
1.754
0.655
1.535
56.16


2*
−5.259
0.025


3*
18.175
0.270
1.635
23.91


4*
2.111
0.350


5*
49.667
0.516
1.535
56.16


6*
9.971
0.187


7*
3.479
0.605
1.535
56.16


8*
21.778
0.573


9*
2.402
0.800
1.535
56.16


10* 
1.334
0.3


11 
Infinity
0.3
1.517
64.20


12 
Infinity
0.607


Image plane
Infinity










Single lens data









Lens
Start plane
Focal length





1
1
2.533


2
3
−3.746


3
5
−23.343


4
7
7.624


5
9
−7.565










Aspheric data













First
Second
Third
Fourth
Fifth



surface
surface
surface
surface
surface





k
−1.898E+00
−1.818E+00
 0.000E+00
−2.723E−01
 0.000E+00


A4
 3.822E−02
 1.288E−01
 4.814E−02
−8.944E−02
−1.060E−01


A6
−2.809E−02
−1.343E−01
 6.037E−02
 2.532E−01
 5.779E−02


A8
 4.970E−02
 1.978E−02
−1.838E−01
−3.068E−01
 1.251E−03


A10
−5.149E−02
 3.399E−04
 1.217E−01
 2.175E−01
−3.017E−02


A12
 4.628E−03
−6.173E−04
−1.665E−02
−5.539E−02
 6.065E−02


A14
 4.215E−03
−5.735E−04
−5.234E−04
 3.281E−03
−1.536E−02


A16
−3.450E−03
 8.520E−12
 2.394E−04
−6.552E−07
−2.048E−03






Sixth
Seventh
Eighth
Ninth
Tenth



surface
surface
surface
surface
surface





k
 3.438E+00
−3.702E+01
−3.345E+04
−1.855E+01
−4.858E+00


A4
−1.142E−01
 5.323E−02
−3.596E−02
−1.503E−01
−9.165E−02


A6
−2.103E−02
−7.412E−02
 9.066E−02
 4.478E−02
 4.113E−02


A8
 7.808E−03
−1.800E−02
−1.026E−01
−7.829E−03
−1.389E−02


A10
 2.283E−02
 1.682E−02
 4.108E−02
−1.119E−03
 2.647E−03


A12
 5.590E−05
 4.538E−03
−5.778E−03
 2.461E−04
−2.445E−04


A14
−1.053E−03
−2.738E−03
−5.187E−05
 0.000E+00
 3.564E−06


A16
−1.525E−04
−1.886E−05
−6.175E−06
 0.000E+00
 6.120E−07









As shown in Table 5, the imaging lens in the Embodiment 1 satisfies all the conditional expressions (1) to (9).
FIG. 2 shows spherical aberration (mm), astigmatism (mm), and distortion (%) of the imaging lens in the Embodiment 1. The spherical aberration diagram shows the amount of aberration at wavelengths of g-ray (436 nm), F-ray (486 nm), e-ray (546 nm), d-ray (588 nm), and C-ray (656 nm). The astigmatism diagram shows the amount of aberration on sagittal image surface S and the amount of aberration on tangential image surface T. FIG. 2 suggests that aberrations are properly corrected.
The total track length TTL is as short as 4.899 mm and its ratio to maximum image height IH (TTL/2IH) is 0.858, indicating that the imaging lens is thin enough though it is composed of five lenses. In addition, its F-value of 2.20 assures brightness and the half angle of view is relatively wide at about 35 degrees.
Embodiment 2
The basic lens data of the Embodiment 2 is shown below in Table 2.







TABLE 2





Unit mm


f = 4.159


Fno = 2.20


ω(°) = 34.50


IH = 2.856







Surface data











Surface
Curvature
Surface
Refractive
Abbe No.


No. i
radius r
distance d
index Nd
νd





(Object surface)
Infinity
Infinity


Stop
Infinity
−0.225


1*
1.874
0.584
1.535
56.16


2*
−21.965
0.100


3*
33.438
0.260
1.635
23.91


4*
2.343
0.238


5*
3.866
0.610
1.535
56.16


6*
11.067
0.386


7*
4.133
0.505
1.535
56.16


8*
41.270
0.460


9*
2.315
0.723
1.535
56.16


10* 
1.261
0.4


11 
Infinity
0.3
1.517
64.20


12 
Infinity
0.486


Image plane
Infinity










Single lens data









Lens
Start plane
Focal length





1
1
3.244


2
3
−3.939


3
5
10.749


4
7
8.515


5
9
−6.788










Aspheric data













First
Second
Third
Fourth
Fifth



surface
surface
surface
surface
surface





k
−1.886E+00
4.388E+02
3.059E−02
−1.458E+00 
 0.000E+00


A4
 3.969E−02
1.085E−01
3.059E−02
−1.085E−01 
−1.362E−01


A6
−2.319E−02
−1.011E−01 
3.157E−02
2.070E−01
 3.780E−02


A8
 5.384E−02
2.255E−02
−1.821E−01 
−3.220E−01 
 4.319E−03


A10
−4.879E−02
−1.427E−02 
1.166E−01
2.360E−01
−2.479E−02


A12
 3.911E−03
−2.987E−03 
−1.491E−02 
−5.626E−02 
 6.121E−02


A14
 5.711E−03
4.239E−03
1.644E−03
2.691E−03
−1.878E−02


A16
−8.275E−04
6.893E−03
2.378E−03
7.048E−05
−3.516E−03






Sixth
Seventh
Eighth
Ninth
Tenth



surface
surface
surface
surface
surface





k
 2.833E+01
−2.537E+01 
−7.621E+04 
−1.432E+01 
−4.589E+00


A4
−1.136E−01
4.457E−02
−2.654E−02 
−1.977E−01 
−1.031E−01


A6
−2.293E−03
−4.656E−02 
8.015E−02
7.206E−02
 4.359E−02


A8
−1.024E−03
−2.172E−02 
−9.668E−02 
−1.899E−02 
−1.337E−02


A10
 2.075E−02
1.441E−02
4.170E−02
2.427E−03
 2.537E−03


A12
 3.672E−03
4.481E−03
−6.034E−03 
0.000E+00
−2.484E−04


A14
 0.000E+00
−2.487E−03 
−1.193E−04 
0.000E+00
 5.549E−06


A16
−8.156E−04
5.868E−05
1.723E−05
0.000E+00
 5.752E−07









As shown in Table 5, the imaging lens in the Embodiment 2 satisfies all the conditional expressions (1) to (9).
FIG. 4 shows spherical aberration (mm), astigmatism (mm), and distortion (%) of the imaging lens in the Embodiment 2. The spherical aberration diagram shows the amount of aberration at wavelengths of g-ray (436 nm), F-ray (486 nm), e-ray (546 nm), d-ray (588 nm), and C-ray (656 nm). The astigmatism diagram shows the amount of aberration on sagittal image surface S and the amount of aberration on tangential image surface T. FIG. 4 suggests that aberrations are properly corrected.
The total track length TTL is as short as 4.962 mm and its ratio to maximum image height IH (TTL/2IH) is 0.869, indicating that the imaging lens is thin enough though it is composed of five lenses. In addition, its F-value of 2.20 assures brightness and the half angle of view is relatively wide at about 35 degrees.
Embodiment 3
The basic lens data of the Embodiment 3 is shown below in Table 3.







TABLE 3





Unit mm


f = 4.142


Fno = 2.20


ω(°) = 34.75


IH = 2.856







Surface data











Surface
Curvature
Surface
Refractive
Abbe No.


No. i
radius r
distance d
index Nd
νd





(Object surface)
Infinity
Infinity


Stop
Infinity
−0.200


1*
1.872
0.591
1.535
56.16


2*
−5.548
0.047


3*
6.355
0.276
1.635
23.91


4*
1.710
0.458


5*
8.500
0.392
1.535
56.16


6*
9.600
0.338


7*
7.528
0.523
1.535
56.16


8*
736.753
0.248


9*
1.973
0.848
1.535
56.16


10* 
1.509
0.4


11 
Infinity
0.3
1.517
64.20


12 
Infinity
0.600


Image plane
Infinity










Single lens data









Lens
Start plane
Focal length





1
1
2.682


2
3
−3.733


3
5
122.879


4
7
14.164


5
9
−33.034










Aspheric data













First
Second
Third
Fourth
Fifth



surface
surface
surface
surface
surface





k
−2.217E+00 
0.000E+00
0.000E+00
−9.585E−01 
0.000E+00


A4
3.626E−02
1.141E−01
2.186E−02
−9.693E−02 
−1.324E−01 


A6
−2.837E−02 
−1.313E−01 
5.007E−02
2.423E−01
5.992E−02


A8
3.465E−02
4.347E−02
−1.746E−01 
−3.158E−01 
3.496E−03


A10
−3.540E−02 
−1.263E−02 
1.461E−01
2.226E−01
−3.148E−02 


A12
0.000E+00
0.000E+00
−3.230E−02 
−5.368E−02 
5.376E−02


A14
0.000E+00
0.000E+00
0.000E+00
0.000E+00
−1.885E−02 


A16
0.000E+00
0.000E+00
0.000E+00
0.000E+00
0.000E+00






Sixth
Seventh
Eighth
Ninth
Tenth



surface
surface
surface
surface
surface





k
−2.594E+02 
−3.680E+01 
0.000E+00
0.000E+00
−2.505E+00 


A4
−1.128E−01 
5.806E−02
−4.213E−02 
−2.636E−01 
−1.306E−01 


A6
−1.993E−02 
−6.128E−02 
1.010E−01
8.066E−02
4.791E−02


A8
7.347E−03
−2.306E−02 
−1.037E−01 
−1.206E−02 
−1.380E−02 


A10
2.043E−02
1.553E−02
4.024E−02
−3.810E−03 
2.514E−03


A12
0.000E+00
4.864E−03
−5.715E−03 
9.779E−04
−2.677E−04 


A14
0.000E+00
−2.728E−03 
0.000E+00
0.000E+00
8.035E−06


A16
0.000E+00
0.000E+00
0.000E+00
0.000E+00
7.957E−07









As shown in Table 5, the imaging lens in the Embodiment 3 satisfies all the conditional expressions (1) to (9).
FIG. 6 shows spherical aberration (mm), astigmatism (mm), and distortion (%) of the imaging lens in the Embodiment 3. The spherical aberration diagram shows the amount of aberration at wavelengths of g-ray (436 nm), F-ray (486 nm), e-ray (546 nm), d-ray (588 nm), and C-ray (656 nm). The astigmatism diagram shows the amount of aberration on sagittal image surface S and the amount of aberration on tangential image surface T. FIG. 6 suggests that aberrations are properly corrected.
The total track length TTL is as short as 4.931 mm and its ratio to maximum image height IH (TTL/2IH) is 0.863, indicating that the imaging lens is thin enough though it is composed of five lenses. In addition, its F-value of 2.20 assures brightness and the half angle of view is relatively wide at about 35 degrees.
Embodiment 4
The basic lens data of the Embodiment 4 is shown below in Table 4.







TABLE 4





Unit mm


f = 4.000


Fno = 2.20


ω(°) = 35.5


IH = 2.856







Surface data











Surface
Curvature
Surface
Refractive
Abbe No.


No. i
radius r
distance d
index Nd
νd





(Object surface)
Infinity
Infinity


Stop
Infinity
−0.225


1*
1.714
0.617
1.535
56.16


2*
−7.181
0.023


3*
7.867
0.280
1.635
23.91


4*
1.864
0.377


5*
6.208
0.436
1.535
56.16


6*
7.014
0.278


7*
6.053
0.550
1.535
56.16


8*
50.000
0.263


9*
2.227
0.840
1.535
56.16


10* 
1.456
0.3


11 
Infinity
0.3
1.517
64.20


12 
Infinity
0.550


Image plane
Infinity










Single lens data









Lens
Start plane
Focal length





1
1
2.652


2
3
−3.916


3
5
85.058


4
7
12.825


5
9
−12.688










Aspheric data













First
Second
Third
Fourth
Fifth



surface
surface
surface
surface
surface





k
−1.660E+00 
0.000E+00
0.000E+00
−3.348E−01
0.000E+00


A4
3.944E−02
1.223E−01
4.176E−02
−9.291E−02
−1.365E−01 


A6
−3.645E−02 
−1.438E−01 
4.942E−02
 2.739E−01
8.053E−02


A8
5.301E−02
5.707E−03
−1.905E−01 
−3.065E−01
7.214E−03


A10
−5.023E−02 
1.473E−02
1.167E−01
 1.623E−01
−4.762E−02 


A12
0.000E+00
0.000E+00
1.130E−03
−1.734E−02
5.334E−02


A14
0.000E+00
0.000E+00
0.000E+00
 0.000E+00
−1.668E−02 


A16
0.000E+00
0.000E+00
0.000E+00
 0.000E+00
0.000E+00






Sixth
Seventh
Eighth
Ninth
Tenth



surface
surface
surface
surface
surface





k
−8.949E+01 
−2.128E+01 
0.000E+00
 0.000E+00
−3.428E+00 


A4
−1.148E−01 
5.853E−02
−4.184E−02 
−3.015E−01
−1.315E−01 


A6
−3.033E−02 
−9.973E−02 
9.287E−02
 9.151E−02
5.033E−02


A8
1.765E−03
−1.736E−02 
−1.040E−01 
−4.778E−03
−1.433E−02 


A10
2.057E−02
1.296E−02
4.104E−02
−4.021E−03
2.562E−03


A12
0.000E+00
9.310E−04
−6.824E−03 
−6.595E−04
−2.475E−04 


A14
0.000E+00
−1.363E−03 
0.000E+00
 0.000E+00
4.770E−06


A16
0.000E+00
0.000E+00
0.000E+00
 0.000E+00
6.120E−07









As shown in Table 5, the imaging lens in the Embodiment 4 satisfies all the conditional expressions (1) to (9).
FIG. 8 shows spherical aberration (mm), astigmatism (mm), and distortion (%) of the imaging lens in the Embodiment 4. The spherical aberration diagram shows the amount of aberration at wavelengths of g-ray (436 nm), F-ray (486 nm), e-ray (546 nm), d-ray (588 nm), and C-ray (656 nm). The astigmatism diagram shows the amount of aberration on sagittal image surface S and the amount of aberration on tangential image surface T. FIG. 8 suggests that aberrations are properly corrected.
The total track length TTL is as short as 4.712 mm and its ratio to maximum image height IH (TTL/2IH) is 0.825, indicating that the imaging lens is thin enough though it is composed of five lenses. In addition, its F-value of 2.20 assures brightness, and the half angle of view is relatively wide at about 35 degrees.
It is known that the imaging lenses according to the preferred embodiments of the present invention achieve a ratio of total track length to maximum image height (TTL/2IH) of about 0.85 and their total track length is short though they are each composed of five lenses. Furthermore, their F-value of about 2.20 assures brightness and their half angle of view ω is about 35 degrees so that imaging can be performed with a relatively wide angle of view and aberrations are corrected properly.
Table 5 shows data on the Embodiments 1 to 4 relating to the conditional expressions (1) to (9).











TABLE 5








Embodiment
Embodiment
Embodiment
Embodiment



1
2
3
4





f
4.160
4.159
4.142
4.000


f1
2.533
3.244
2.682
2.652


f2
−3.746
−3.939
−3.733
−3.916


f3
−23.343
10.749
122.879
85.058


f4
7.624
8.515
14.164
12.825


f5
−7.565
−6.788
−33.034
−12.688


v1
56.16
56.16
56.16
56.16


v2
23.91
23.91
23.91
23.91


TTL
4.899
4.962
4.931
4.712


r1
1.754
1.874
1.872
1.714


r2
−5.259
−21.965
−5.548
−7.181


IH
2.856
2.856
2.856
2.856


ω
34.49
34.499
34.750
35.536


Fno
2.20
2.20
2.20
2.20










Value of conditional expressions














(1)45 < v1 < 90
56.16
56.16
56.16
56.16


(2)22 < v2 < 35
23.91
23.91
23.91
23.91


(3)2.0 < v1/v2 < 2.6
2.349
2.349
2.349
2.349


(4)0.6 < f1/f < 0.9
0.609
0.780
0.648
0.663


(5)−1.0 < f2/f < −0.8
−0.901
−0.947
−0.901
−0.979


(6)1.1 < TTL/f < 1.3
1.178
1.193
1.191
1.178


(7)−0.40 < r1/r2 < −0.08
−0.334
−0.085
−0.337
−0.239


(8)1.6 < f4/f < 3.8
1.833
2.047
3.420
3.207


(9)−9.0 < f5/f < −1.4
−1.819
−1.632
−7.976
−3.173


TTL/2IH
0.858
0.869
0.863
0.825









As explained so far, when the imaging lenses composed of five lenses according to the aforementioned Embodiments are used for optical systems which are built in mobile terminals such as mobile phones and smart phones, PDAs (Personal Digital Assistances) and image pickup devices mounted in game machines or the like, their camera system is able to provide high performance and also achieve compactness.
The effects of the present invention are as follows.
According to the present invention, it is attainable to provide an imaging lens which corrects various aberrations properly and provides a relatively wide angle of view and brightness in response to the need for compactness and thinness.
Since all the constituent lenses are made of plastic material, an imaging lens suitable for mass production is obtainable at low cost.

## Claims

1. An imaging lens for a solid-state image sensor, comprising, from an object side to an image side of the imaging lens:
a first lens with positive refractive power having a convex surface facing the object side;
a second lens with negative refractive power;
a third lens with positive or negative refractive power having a meniscus shape with a convex surface facing the object side and an image-side surface that is concave near an optical axis of the imaging lens;
a fourth lens that is a double-sided aspheric lens having an image-side surface that is concave near the optical axis; and
a fifth lens that is a double-sided aspheric lens having an image-side surface that is concave near the optical axis,
wherein the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are made of plastic materials, and the imaging lens contains only five lenses.

2. The imaging lens according to claim 1, wherein the second lens has a concave surface facing the image side.

3. The imaging lens according to claim 1, wherein when ν1 is an Abbe number of the first lens and ν2 is an Abbe number of the second lens, the first lens and the second lens satisfy conditional expressions (1), (2), and (3) below:


45<ν1<90  (1)



22<ν2<35  (2)



2.0<ν1/ν2<2.6.  (3)

4. The imaging lens according to claim 1, wherein the fourth lens has positive refractive power, and the fifth lens has negative refractive power.

5. The imaging lens according to claim 1, wherein when f is an overall focal length of the imaging lens and f1 is a focal length of the first lens, a conditional expression (4) below is satisfied:


0.6<f1/f<0.9.  (4)

6. The imaging lens according to claim 1, wherein when f is an overall focal length of the imaging lens and f2 is a focal length of the second lens, a conditional expression (5) below is satisfied:


−1.0<f2/f<−0.8.  (5)

7. The imaging lens according to claim 6, wherein when f4 is a focal length of the fourth lens, a conditional expression (8) below is satisfied:


1.6<f4/f<3.8.  (8)

8. The imaging lens according to claim 7, wherein when f5 is a focal length of the fifth lens, a conditional expression (9) below is satisfied:


−9.0<f5/f<−1.4.  (9)

9. The imaging lens according to claim 1, wherein an aperture stop is located on an object side of the first lens.

10. The imaging lens according to claim 1, wherein the fourth lens and the fifth lens each have a meniscus shape and pole-change points separated from the optical axis on an object-side surface and the image-side surface.

11. The imaging lens according to claim 1, wherein when f is an overall focal length of the imaging lens and TTL is a distance along the optical axis from an image plane of the imaging lens to an object-side surface of the first lens, a conditional expression (6) below is satisfied:


1.1<TTL/f<1.3.  (6)

12. The imaging lens according to claim 1, wherein the first lens is a biconvex lens, and when r1 is a curvature radius of an object-side surface of the first lens and r2 is a curvature radius of an image-side surface of the first lens, a conditional expression (7) below is satisfied:


−0.40<r1/r2<−0.08.  (7)

13. The imaging lens according to claim 1, wherein cycloolefin plastic material is used for the first lens, the third lens, the fourth lens, and the fifth lens, and polycarbonate is used for the second lens.

14. An imaging lens for a solid-state image sensor, comprising, from an object side to an image side of the imaging lens:
a first lens with positive refractive power having a convex surface facing the object side;
a second lens with negative refractive power;
a third lens with positive or negative refractive power having a meniscus shape with a convex surface facing the object side and an image-side surface that is concave near an optical axis of the imaging lens;
a fourth lens that is a double-sided aspheric lens having an image-side surface that is concave near the optical axis; and
a fifth lens that is a double-sided aspheric lens having an image-side surface that is concave near the optical axis,
wherein the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are made of plastic materials, and
when f is an overall focal length of the imaging lens and f2 is a focal length of the second lens, a conditional expression (5) below is satisfied:


−1.0<f2/f<−0.8.  (5)

15. The imaging lens according to claim 14, wherein when f4 is a focal length of the fourth lens, a conditional expression (8) below is satisfied:


1.6<f4/f<3.8.  (8)

16. The imaging lens according to claim 15, wherein when f5 is a focal length of the fifth lens, a conditional expression (9) below is satisfied:


−9.0<f5/f<−1.4.  (9)

17. The imaging lens according to claim 14, wherein the second lens has a concave surface facing the image side.

18. An imaging lens for a solid-state image sensor, comprising, from an object side to an image side of the imaging lens:
a first lens with positive refractive power having a convex surface facing the object side;
a second lens with negative refractive power;
a third lens with positive or negative refractive power having a meniscus shape with a convex surface facing the object side and an image-side surface that is concave near an optical axis of the imaging lens;
a fourth lens that is a double-sided aspheric lens having an image-side surface that is concave near the optical axis; and
a fifth lens that is a double-sided aspheric lens having an image-side surface that is concave near the optical axis,
wherein the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are made of plastic materials, and cycloolefin plastic material is used for the first lens, the third lens, the fourth lens, and the fifth lens, and polycarbonate is used for the second lens.

19. The imaging lens according to claim 18, wherein the second lens has a concave surface facing the image side.

20. The imaging lens according to claim 18, wherein the fourth lens has positive refractive power, and the fifth lens has negative refractive power.