# Patent

## Title
Optical system

## Abstract

There is provided an optical system including: a first lens having negative refractive power and having a meniscus shape of which an object-side surface is convex; a second lens having positive refractive power; a third lens having refractive power; and a fourth lens having positive refractive power and having a meniscus shape of which an object-side surface is convex, wherein the first to fourth lenses are sequentially disposed from an object side, whereby an aberration improvement effect, a wide field of view and a high degree of resolution may be realized.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority and benefit of Korean Patent Application No. 10-2014-0113300 filed on Aug. 28, 2014, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND
The present disclosure relates to an optical system.
Recent mobile communications terminals have commonly been provided with camera modules, allowing users to make video calls, as well as to capture still and moving images. In addition, as the degree of functionality of camera modules included in mobile communications terminals has gradually increased, camera modules for mobile communications terminals have come to be required to have high levels of resolution and high degrees of performance.
However, since there is a trend for mobile communications terminals to be miniaturized and lightened, there are limitations in implementing camera modules having the high levels of resolution and high degrees of performance.
In order to solve these problems, recently, lenses included in such camera modules have been formed of plastic, a material lighter than glass, and lens modules have been configured with five or more lenses, in order to achieve high levels of resolution in images captured thereby.
SUMMARY
An aspect of the present disclosure may provide an optical system in which an aberration improvement effect, a high degree of resolution, and a wide field of view are realized.
According to an aspect of the present disclosure, an optical system may include: a first lens having negative refractive power and having a meniscus shape of which an object-side surface is convex; a second lens having positive refractive power; a third lens having refractive power; and a fourth lens having positive refractive power and having a meniscus shape of which an object-side surface is convex, wherein the first to fourth lenses are sequentially disposed from an object side, whereby an aberration improvement effect, a wide field of view and a high degree of resolution may be realized.



BRIEF DESCRIPTION OF DRAWINGS
The above and other aspects, features and advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a configuration diagram of an optical system according to a first exemplary embodiment of the present disclosure;
FIG. 2 is graphs having curves representing aberration characteristics of the optical system shown in FIG. 1;
FIG. 3 is a table illustrating respective characteristics of lenses in the optical system illustrated in FIG. 1;
FIG. 4 is a table illustrating respective aspherical surface coefficients of lenses in the optical system illustrated in FIG. 1;
FIG. 5 is a configuration diagram of an optical system according to a second exemplary embodiment of the present disclosure;
FIG. 6 is graphs having curves representing aberration characteristics of the optical system illustrated in FIG. 5;
FIG. 7 is a table illustrating respective characteristics of lenses in the optical system illustrated in FIG. 5;
FIG. 8 is a table illustrating respective aspherical surface coefficients of lenses in the optical system illustrated in FIG. 5;
FIG. 9 is a configuration diagram of an optical system according to a third exemplary embodiment of the present disclosure;
FIG. 10 is graphs having curves representing aberration characteristics of the optical system illustrated in FIG. 9;
FIG. 11 is a table illustrating respective characteristics of lenses in the optical system illustrated in FIG. 9; and
FIG. 12 is a table illustrating respective aspherical surface coefficients of lenses in the optical system illustrated in FIG. 9.



DETAILED DESCRIPTION
Exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings.
The disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
In the drawings, the shapes and dimensions of elements may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like elements.
In the following lens configuration diagrams, thicknesses, sizes, and shapes of lenses may be exaggerated for clarity. Particularly, the shapes of spherical surfaces and aspherical surfaces, as illustrated in the lens configuration diagrams, are only illustrated by way of example, but are not limited to those illustrated in the drawings.
In addition, a first lens refers to a lens that is the closest to an object side, and a fourth lens refers to a lens that is the closest to an imaging surface.
Further, a first surface of each lens refers to a surface thereof closest to an object (or an object-side surface) and a second surface of each lens refers to a surface thereof closest to an imaging surface (or an image-side surface). Further, all numerical values of radii of curvature, thicknesses, and the like, of lenses are represented by millimeters (mm).
An optical system according to exemplary embodiments in the present disclosure may include four lenses.
That is, the optical system may include a first lens, a second lens, a third lens, and a fourth lens.
However, the optical system is not limited to including only the four lenses, but may further include other components, if necessary. For example, the optical system may include an aperture stop controlling an amount of light. In addition, the optical system may further include an infrared cut-off filter filtering infrared light. Further, the optical system may further include an image sensor converting an image of a subject incident thereon into an electrical signal. Further, the optical system may further include a gap maintaining member adjusting a gap between lenses.
The first to fourth lenses configuring the optical system according to exemplary embodiments may be formed of plastic.
In addition, at least one of the first to fourth lenses may have an aspherical surface. Alternatively, each of the first to fourth lenses may have at least one aspherical surface.
Here, the aspherical surfaces of the first to fourth lenses may be represented by the following Equation 1:




  
    
      
        Z
        =
        
          
            
              cY
              2
            
            
              1
              +
              
                
                  1
                  -
                  
                    
                      (
                      
                        1
                        +
                        K
                      
                      )
                    
                    ⁢
                    
                      c
                      2
                    
                    ⁢
                    
                      Y
                      2
                    
                  
                
              
            
          
          +
          
            AY
            4
          
          +
          
            BY
            6
          
          +
          
            CY
            8
          
          +
          
            DY
            10
          
          +
          
            EY
            12
          
          +
          
            FY
            14
          
          +
          ...
        
      
    
    
      
        [
        
          Equation
          ⁢
          
            
          
          ⁢
          1
        
        ]
      
    
  




Here, c is curvature (the inverse of a radius of curvature) at an apex of the lens, K is a conic constant, and Y is a distance from a certain point on the aspherical surface of the lens to an optical axis in a direction perpendicular to the optical axis. In addition, constants A to F refer to aspherical surface coefficients. In addition, Z is a distance between the certain point on the aspherical surface at the distance Y and a tangential plane meeting the apex of the aspherical surface of the lens.
The optical system including the first to fourth lenses may have negative refractive power/positive refractive power/positive or negative refractive power/positive refractive power in respective lenses thereof, sequentially from the object side.
The optical system configured as described above may have a wide field of view and improve optical performance through aberration improvement.
The optical system according to exemplary embodiments may satisfy Conditional Expression 1.

FOV≧80  [Conditional Expression 1]

Here, FOV is a field of view of the optical system.
The optical system according to exemplary embodiments may satisfy Conditional Expression 2.

FOV/TTL>25  [Conditional Expression 2]

Here, FOV is the field of view of the optical system, and TTL is a distance from the object-side surface of the first lens to an imaging surface of the image sensor.
The optical system according to exemplary embodiments may satisfy Conditional Expression 3.

TTL/F≦2.30  [Conditional Expression 3]

Here, TTL is the distance from the object-side surface of the first lens to the imaging surface of the image sensor, and F is an overall focal length of the optical system.
The optical system according to exemplary embodiments may satisfy Conditional Expression 4.

−2.3<F1/F<−2.0  [Conditional Expression 4]

Here, F1 is a focal length of the first lens, and F is the overall focal length of the optical system.
The optical system according to exemplary embodiments may satisfy Conditional Expression 5.

F2/F≧0.73  [Conditional Expression 5]

Here, F2 is a focal length of the second lens, and F is the overall focal length of the optical system.
The optical system according to exemplary embodiments may satisfy Conditional Expression 6.

−5.0<F3/F<20.0  [Conditional Expression 6]

Here, F3 is a focal length of the third lens, and F is the overall focal length of the optical system.
The optical system according to exemplary embodiments may satisfy Conditional Expression 7.

4.0<F4/F<8.0  [Conditional Expression 7]

Here, F4 is a focal length of the fourth lens, and F is the overall focal length of the optical system.
The optical system according to exemplary embodiments may satisfy Conditional Expression 8.

2.1<TTL/ImgH<2.7  [Conditional Expression 8]

Here, TTL is the distance from the object-side surface of the first lens to the imaging surface of the image sensor, and ImgH is a diagonal length of the imaging surface of the image sensor.
Next, the first to fourth lenses configuring the optical system according to exemplary embodiments will be described.
The first lens may have negative refractive power. In addition, the first lens may have a meniscus shape of which an object-side surface is convex. In detail, first and second surfaces of the first lens may be convex toward the object.
At least one of the first and second surfaces of the first lens may be aspherical.
The second lens may have positive refractive power. In addition, both surfaces of the second lens may be convex.
At least one of first and second surfaces of the second lens may be aspherical. For example, both surfaces of the second lens may be aspherical.
The third lens may have positive or negative refractive power. In addition, the third lens may have a meniscus shape of which an image-side surface is convex. In detail, first and second surfaces of the third lens may be convex toward the imaging surface.
At least one of the first and second surfaces of the third lens may be aspherical. For example, both surfaces of the third lens may be aspherical.
The fourth lens may have positive refractive power. In addition, the fourth lens may have a meniscus shape of which an object-side surface is convex. In detail, first and second surfaces of the fourth lens may be convex toward the object.
At least one of the first and second surfaces of the fourth lens may be aspherical. For example, both surfaces of the fourth lens may be aspherical.
In addition, the fourth lens may have at least one inflection point formed on the first surface thereof, and also have at least one inflection point formed on the second surface thereof. For example, the second surface of the fourth lens may be concave in the paraxial region and become convex at an edge thereof.
In the optical system configured as described above, a plurality of lenses perform an aberration correction function, whereby aberration performance may be improved.
In addition, the optical system may have a wide field of view (FOV).
In addition, in the optical system, all of the lenses are formed of plastic, whereby costs associated with lens module manufacturing may be decreased and efficiency in the lens module manufacturing may be increased.
An optical system according to a first exemplary embodiment of the present disclosure will be described with reference to FIGS. 1 through 4.
The optical system according to the first exemplary embodiment may include a first lens 110, a second lens 120, a third lens 130, and a fourth lens 140, and may further include an infrared cut-off filter 150 and an image sensor 160.
Here, as shown in Table 1, a field of view (FOV) of the optical system may be 90 degrees, a distance (TTL) from an object-side surface of the first lens 110 to a first surface (imaging surface) of the image sensor 160 may be 3.04 mm, and a diagonal length (ImgH) of the first surface (imaging surface) of the image sensor 160 may be 1.39 mm.
In addition, a focal length (F1) of the first lens 110 may be −2.83 mm, a focal length (F2) of the second lens 120 may be 1.02 mm, a focal length (F3) of the third lens 130 may be 20.10 mm, a focal length (F4) of the fourth lens 140 may be 10.04 mm, and an overall focal length (F) of the optical system may be 1.36 mm.










TABLE 1









FOV
90



TTL
3.04



ImgH
1.39



F 
1.36



F1
−2.83



F2
1.02



F3
20.1



F4
10.04










In addition, respective characteristics (radii of curvature, thicknesses of lenses or distances between the lenses, refractive indices, and Abbe numbers) of lenses are shown in FIG. 3.
In the first exemplary embodiment, the first lens 110 may have negative refractive power, and have a meniscus shape of which an object-side surface is convex. The second lens 120 may have positive refractive power and both surfaces thereof may be convex. The third lens 130 may have positive refractive power and have a meniscus shape of which an image-side surface is convex. The fourth lens 140 may have positive refractive power and have a meniscus shape of which an object-side surface is convex. In addition, the fourth lens 140 may have at least one inflection point formed on each of first and second surfaces thereof.
Meanwhile, the respective surfaces of the first to fourth lenses 110 to 140 may have aspherical surface coefficients as shown in FIG. 4. That is, the first to fourth lenses 110 to 140 may have aspherical surfaces, respectively.
In addition, the optical system configured as described above may have aberration characteristics shown in FIG. 2.
An optical system according to a second exemplary embodiment of the present disclosure will be described with reference to FIGS. 5 through 8.
The optical system according to the second exemplary embodiment of the present disclosure may include a first lens 210, a second lens 220, a third lens 230, and a fourth lens 240, and may further include an infrared cut-off filter 250 and an image sensor 260.
Here, as shown in Table 2, a field of view (FOV) of the optical system may be 100 degrees, a distance (TTL) from an object-side surface of the first lens 210 to a first surface (imaging surface) of the image sensor 260 may be 3.13 mm, and a diagonal length (ImgH) of the first surface (imaging surface) of the image sensor 260 may be 1.39 mm.
In addition, a focal length (F1) of the first lens 210 may be −2.96 mm, a focal length (F2) of the second lens 220 may be 1.01 mm, a focal length (F3) of the third lens 230 may be −22.74 mm, a focal length (F4) of the fourth lens 240 may be 6.46 mm, and an overall focal length (F) of the optical system may be 1.36 mm.










TABLE 2









FOV
100



TTL 
3.13



ImgH
1.39



F 
1.36



F1
−2.96



F2
1.01



F3
−22.74



F4
6.46










In addition, respective characteristics (radii of curvature, thicknesses of lenses or distances between the lenses, refractive indices, and Abbe numbers) of lenses are shown in FIG. 7.
In the second exemplary embodiment, the first lens 210 may have negative refractive power, and have a meniscus shape of which an object-side surface is convex. The second lens 220 may have positive refractive power and both surfaces thereof may be convex. The third lens 230 may have negative refractive power and have a meniscus shape of which an image-side surface is convex. The fourth lens 240 may have positive refractive power and have a meniscus shape of which an object-side surface is convex. In addition, the fourth lens 240 may have at least one inflection point formed on each of first and second surfaces thereof.
Meanwhile, the respective surfaces of the first to fourth lenses 210 to 240 may have aspherical surface coefficients as shown in FIG. 8. That is, the first to fourth lenses 210 to 240 may have aspherical surfaces, respectively.
In addition, the optical system configured as described above may have aberration characteristics shown in FIG. 6.
An optical system according to a third exemplary embodiment in the present disclosure will be described with reference to FIGS. 9 through 12.
The optical system according to the third exemplary embodiment may include a first lens 310, a second lens 320, a third lens 330, and a fourth lens 340, and may further include an infrared cut-off filter 350 and an image sensor 360.
Here, as shown in Table 3, a field of view (FOV) of the optical system may be 80 degrees, a distance (TTL) from an object-side surface of the first lens 310 to a first surface (imaging surface) of the image sensor 360 may be 3.11 mm, and a diagonal length (ImgH) of the first surface (imaging surface) of the image sensor 360 may be 1.17 mm.
In addition, a focal length (F1) of the first lens 310 may be −2.88 mm, a focal length (F2) of the second lens 320 may be 0.99 mm, a focal length (F3) of the third lens 330 may be −6.07 mm, a focal length (F4) of the fourth lens 340 may be 5.63 mm, and an overall focal length (F) of the optical system may be 1.36 mm.










TABLE 3









FOV
80



TTL
3.11



ImgH
1.17



F 
1.36



F1
−2.88



F2
0.99



F3
−6.07



F4
5.63










In addition, respective characteristics (radii of curvature, thicknesses of lenses or distances between the lenses, refractive indices, and Abbe numbers) of lenses are shown in FIG. 11.
In the third exemplary embodiment, the first lens 310 may have negative refractive power, and have a meniscus shape of which an object-side surface is convex. The second lens 320 may have positive refractive power and both surfaces thereof may be convex. The third lens 330 may have negative refractive power and have a meniscus shape of which an image-side surface is convex. The fourth lens 340 may have positive refractive power and have a meniscus shape of which an object-side surface is convex. In addition, the fourth lens 340 may have at least one inflection point formed on each of first and second surfaces thereof.
Meanwhile, the respective surfaces of the first to fourth lenses 310 to 340 may have aspherical surface coefficients as shown in FIG. 12. That is, the first to fourth lenses 310 to 340 may have aspherical surfaces, respectively.
In addition, the optical system configured as described above may have aberration characteristics shown in FIG. 10.










TABLE 4






First Exemplary 
Second Exemplary 
Third Exemplary 



Embodiment
Embodiment
Embodiment


















FOV/TTL
29.61
31.95
25.72


TTL/F
2.24
2.30
2.29


F1/F
−2.08
−2.18
−2.12


F2/F
0.75
0.74
0.73


F3/F
14.78
−16.72
−4.46


F4/F
7.38
4.75
4.14


FOV
90
100
80


TTL/ImgH
2.18705036
2.25179856
2.6581197









Meanwhile, it may be appreciated from Table 4 that the optical systems according to the first to third exemplary embodiments satisfy Conditional Expressions 1 to 8 described above. Therefore, a wide field of view may be obtained, and optical performance may be improved.
As set forth above, with the optical systems according to exemplary embodiments of the present disclosure, the wide field of view may be broadened, and the aberration improvement effect may be increased to improve optical performance.
While exemplary embodiments have been shown and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present invention as defined by the appended claims.

## Claims

1. An optical system comprising:
a first lens having negative refractive power and having a meniscus shape of which an object-side surface is convex;
a second lens having positive refractive power;
a third lens having refractive power; and
a fourth lens having positive refractive power and having a meniscus shape of which an object-side surface is convex,
wherein the first to fourth lenses are sequentially disposed from an object side, and a focal length of the first lens F1 and an overall focal length of the optical system F satisfy Conditional Expression 1:


−2.3<F1/F<−2.0.  [Conditional Expression 1]

2. The optical system of claim 1, wherein both surfaces of the second lens are convex.

3. The optical system of claim 1, wherein the third lens has negative refractive power.

4. The optical system of claim 1, wherein the third lens has a meniscus shape of which an image-side surface is convex.

5. The optical system of claim 1, wherein Conditional Expression 2 is satisfied:


FOV≧80  [Conditional Expression 2]


where FOV is a field of view of the optical system.

6. The optical system of claim 1, further comprising an image sensor converting an image of a subject incident through the first to fourth lenses into an electrical signal,
wherein Conditional Expression 3 is satisfied:


FOV/TTL>25  [Conditional Expression 3]


where FOV is a field of view of the optical system, and TTL is a distance from the object-side surface of the first lens to an imaging surface of the image sensor.

7. The optical system of claim 1, further comprising an image sensor converting an image of a subject incident through the first to fourth lenses into an electrical signal,
wherein Conditional Expression 4 is satisfied:


TTL/F≦2.30  [Conditional Expression 4]


where TTL is a distance from the object-side surface of the first lens to an imaging surface of the image sensor, and F is an overall focal length of the optical system.

8. The optical system of claim 1, wherein Conditional Expression 5 is satisfied:


F2/F≧0.73  [Conditional Expression 5]

where F2 is a focal length of the second lens, and F is an overall focal length of the optical system.

9. The optical system of claim 1, wherein Conditional Expression 6 is satisfied:


−5.0<F3/F<20.0  [Conditional Expression 6]

where F3 is a focal length of the third lens, and F is an overall focal length of the optical system.

10. The optical system of claim 1, wherein Conditional Expression 7 is satisfied:


4.0<F4/F<8.0  [Conditional Expression 7]

where F4 is a focal length of the fourth lens, and F is an overall focal length of the optical system.

11. The optical system of claim 1, further comprising an image sensor converting an image of a subject incident through the first to fourth lenses into an electrical signal,
wherein Conditional Expression 8 is satisfied:


2.1<TTL/ImgH<2.7  [Conditional Expression 8]


where TTL is a distance from the object-side surface of the first lens to an imaging surface of the image sensor, and ImgH is a diagonal length of the imaging surface of the image sensor.

12. The optical system of claim 1, wherein the first to fourth lenses are plastic lenses.

13. The optical system of claim 1, wherein the fourth lens has at least one inflection point on the object-side surface thereof.

14. The optical system of claim 1, wherein the fourth lens has at least one inflection point on an image-side surface thereof.

15. An optical system comprising:
a first lens having negative refractive power and having a meniscus shape of which an object-side surface is convex;
a second lens having positive refractive power of which both surfaces are convex;
a third lens having refractive power; and
a fourth lens having positive refractive power,
wherein the first to fourth lenses are sequentially disposed from an object side, and
Conditional Expression 1 is satisfied:


FOV≧80  [Conditional Expression 1]


where FOV is a field of view of the optical system, and a wherein a focal length of the first lens F1 and an overall focal length of the optical system F satisfy Conditional Expression 2:


−2.3<F1/F<−2.0.  [Conditional Expression 2]

16. The optical system of claim 15, further comprising an image sensor converting an image of a subject incident through the first to fourth lenses into an electrical signal,
wherein Conditional Expression 3 is satisfied:


FOV/TTL>25  [Conditional Expression 3]


where TTL is a distance from the object-side surface of the first lens to an imaging surface of the image sensor.

17. The optical system of claim 15, further comprising an image sensor converting an image of a subject incident through the first to fourth lenses into an electrical signal,
wherein Conditional Expression 4 satisfied:


TTL/F≦2.30  [Conditional Expression 4]


where TTL is a distance from the object-side surface of the first lens to an imaging surface of the image sensor, and F is an overall focal length of the optical system.

18. The optical system of claim 15, wherein Conditional Expression 5 is satisfied:


F2/F≧0.73  [Conditional Expression 5]

where F2 is a focal length of the second lens, and F is an overall focal length of the optical system.

19. The optical system of claim 15, wherein Conditional Expression 6 is satisfied:


−5.0<F3/F<20.0  [Conditional Expression 6]

where F3 is a focal length of the third lens, and F is an overall focal length of the optical system.

20. The optical system of claim 15, wherein Conditional Expression 7 is satisfied:


4.0<F4/F<8.0  [Conditional Expression 7]

where F4 is a focal length of the fourth lens, and F is an overall focal length of the optical system.

21. The optical system of claim 15, further comprising an image sensor converting an image of a subject incident through the first to fourth lenses into an electrical signal,
wherein Conditional Expression 8 is satisfied:


2.1<TTL/ImgH<2.7  [Conditional Expression 8]


where TTL is a distance from the object-side surface of the first lens to an imaging surface of the image sensor, and ImgH is a diagonal length of the imaging surface of the image sensor.

22. The optical system of claim 15, wherein the third lens has negative refractive power.

23. The optical system of claim 15, wherein the third lens has a meniscus shape of which an image-side surface is convex.

24. The optical system of claim 15, wherein the fourth lens has a meniscus shape of which an object-side surface is convex.

25. The optical system of claim 15, wherein the fourth lens has at least one inflection point on each of an object-side surface and an image-side surface thereof.