Abstract:
An optical imaging system includes a first lens group and a second lens group. The first lens group includes a first lens and a second lens. The second lens group includes a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens. The first to seventh lenses are sequentially disposed from an object side toward an imaging plane. The optical imaging system satisfies TL/2Y&lt;1.3, where TL is a distance from an object-side surface of the first lens to the imaging plane, and 2Y is a diagonal length of the imaging plane.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims the benefit under 35 USC 119(a) of Korean Patent Application No. 10-2015-0145259, filed on Oct. 19, 2015 in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The following description relates to an optical imaging system including seven lenses. 
         [0004]    2. Description of Related Art 
         [0005]    A monitoring camera for an unmanned aerial vehicle that monitors a wide region and distance from the monitoring camera to a target is significantly large in size. The monitoring camera requires an optical imaging system that has a wide field of view to achieve high resolution. Similarly, to photograph the front and rear areas of a vehicle moving relatively fast with a monitoring camera requires an optical imaging system with a high resolution. 
         [0006]    An optical imaging system formed of glass can achieve a camera having a high level of resolution. However, the optical imaging system formed of glass weighs significantly more than an optical imaging system formed of plastic. Therefore, it is difficult to mount the optical imaging system formed of glass in a small unmanned aerial vehicle, a small terminal, or the like. 
         [0007]    Conversely, an optical imaging system formed of plastic may be lighter than one formed of glass. However, the optical imaging system formed of plastic has a lower resolution level than that of the optical imaging system formed of glass. Therefore, there is a need for a lightened optical imaging system capable of having a high resolution level. 
       SUMMARY 
       [0008]    This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
         [0009]    In one general aspect, an optical imaging system includes a first lens group and a second lens group. The first lens group includes a first lens and a second lens. The second lens group includes a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens. The first to seventh lenses are sequentially disposed from an object side toward an imaging plane. The optical imaging system satisfies TL/2Y&lt;1.3, where TL is a distance from an object-side surface of the first lens to the imaging plane, and 2Y is a diagonal length of the imaging plane. 
         [0010]    The second lens group may be movable in an optical axis direction. 
         [0011]    The first lens may have a negative refractive power. 
         [0012]    The second lens may have a positive refractive power. 
         [0013]    The third lens may have a negative refractive power. 
         [0014]    The fourth lens may have a positive refractive power. 
         [0015]    The fifth lens may have a positive refractive power. 
         [0016]    The sixth lens may have a negative refractive power. 
         [0017]    The seventh may have has a positive refractive power. 
         [0018]    The optical imaging system may satisfy −80&lt;{(1/f)*(Y/tan θ)−1}*100&lt;−20, where f is an overall focal length of the optical imaging system, Y is ½ of a diagonal length of the imaging plane, and θ is a half of a field of view of the optical imaging system. 
         [0019]    The optical imaging system may satisfy 1.0&lt;tan θ&lt;4.0, where θ is a half of a field of view of the optical imaging system. 
         [0020]    The optical imaging system may satisfy 0.4&lt;R2/f&lt;1.5, where f is an overall focal length of the optical imaging system, and R2 is a radius of curvature of an image-side surface of the first lens. 
         [0021]    The optical imaging system may satisfy −1.5&lt;f/f1&lt;−0.05, where f is an overall focal length of the optical imaging system, and f1 is a focal length of the first lens. 
         [0022]    The optical imaging system may satisfy 0.3&lt;f/f2&lt;0.8, where f is an overall focal length of the optical imaging system, and f2 is a focal length of the second lens. 
         [0023]    In another general aspect, an optical imaging system includes a first lens having a negative refractive power, a second lens having a positive refractive power, a third lens having a refractive power, a fourth lens having a refractive power, a fifth lens having positive a refractive power, a sixth lens having a negative refractive power and an object-side surface thereof being convex, and a seventh lens having a refractive power and having an inflection point formed on an image-side surface thereof. The first to seventh lenses are sequentially disposed from an object side toward an imaging plane. 
         [0024]    Both surfaces of the second lens may be convex. 
         [0025]    In another general aspect, an optical imaging system includes a first and second lens groups. The first and second lens groups is sequentially disposed from an object side toward an imaging plane. The first lens group is fixedly disposed at the object-side. The second lens group is slidably disposed relative to the first group. The optical imaging system satisfies 0.4&lt;f/fG2&lt;1.1, where f is an overall focal length of the optical imaging system and fG2 is a synthetic focal length of the second lens group. 
         [0026]    The optical imaging system may satisfy −80&lt;{(1/f)*(Y/tan θ)−1}*100&lt;−20, where f is an overall focal length of the optical imaging system, 2Y is a diagonal length of the imaging plane, and θ is half of a field of view of the optical imaging system. 
         [0027]    The first group of lens may include a first lens and a second lens. 
         [0028]    The second group of lens may include a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens. 
         [0029]    Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0030]      FIG. 1  is a diagram illustrating an example of an optical imaging system. 
           [0031]      FIG. 2  is a graphical illustration of aberration curves in an example of the optical imaging system illustrated in  FIG. 1 . 
           [0032]      FIG. 3  is a table of an example of characteristics of lenses of the optical imaging system illustrated in  FIG. 1 . 
           [0033]      FIG. 4  is a table of an example of aspherical characteristics of the optical imaging system illustrated in  FIG. 1 . 
           [0034]      FIG. 5  is a diagram illustrating another example of an optical imaging system. 
           [0035]      FIG. 6  is a graphical illustration of aberration curves in an example of the optical imaging system illustrated in  FIG. 5 . 
           [0036]      FIG. 7  is a table of an example of characteristics of lenses of the optical imaging system illustrated in  FIG. 5 . 
           [0037]      FIG. 8  is a table of an example of aspherical characteristics of the optical imaging system illustrated in  FIG. 5 . 
           [0038]      FIG. 9  is a graphical illustration of another example of an optical imaging system. 
           [0039]      FIG. 10  is a graphical illustration of aberration curves of the optical imaging system illustrated in  FIG. 9 . 
           [0040]      FIG. 11  is a table of an example of characteristics of lenses of the optical imaging system illustrated in  FIG. 9 . 
           [0041]      FIG. 12  is a table of an example of aspherical characteristics of the optical imaging system illustrated in  FIG. 9 . 
           [0042]      FIG. 13  is a diagram illustrating another example of an optical imaging system. 
           [0043]      FIG. 14  is a graphical illustration of aberration curves of the optical imaging system illustrated in  FIG. 13 . 
           [0044]      FIG. 15  is a table of an example of characteristics of lenses of the optical imaging system illustrated in  FIG. 13 . 
           [0045]      FIG. 16  is a table of an example of aspherical characteristics of the optical imaging system illustrated in  FIG. 13 . 
           [0046]      FIG. 17  is a diagram illustrating another example of an optical imaging system. 
           [0047]      FIG. 18  is a graphical illustration of aberration curves of the optical imaging system illustrated in  FIG. 17 . 
           [0048]      FIG. 19  is a table of an example of characteristics of lenses of the optical imaging system illustrated in  FIG. 17 . 
           [0049]      FIG. 20  is a table of an example of aspherical characteristics of the optical imaging system illustrated in  FIG. 17 . 
       
    
    
       [0050]    Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience. 
       DETAILED DESCRIPTION 
       [0051]    The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. However, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be apparent to one of ordinary skill in the art. The sequences of operations described herein are merely examples, and are not limited to those set forth herein, but may be changed as will be apparent to one of ordinary skill in the art, with the exception of operations necessarily occurring in a certain order. Also, descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted for increased clarity and conciseness. 
         [0052]    The features described herein may be embodied in different forms, and are not to be construed as being limited to the examples described herein. Rather, the examples described herein have been provided so that this disclosure will be thorough and complete, and will convey the full scope of the disclosure to one of ordinary skill in the art. 
         [0053]    Spatially relative terms, such as “above,” “upper,” “below,” and “lower” and the like, may be used herein for ease of description to describe one element&#39;s relationship to another element(s) as shown in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures, for example, if the device in the figures is turned over, elements described as “above,” or “upper” other elements would then be oriented “below,” or “lower” the other elements or features. Thus, the term “above” can encompass both the above and below orientations depending on a particular direction of the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may be interpreted accordingly. 
         [0054]    The terminology used herein is for describing particular embodiments only and is not intended to be limiting of the present inventive concept. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” and/or “comprising” when used in this specification, specify the presence of stated features, integers, steps, operations, members, elements, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, elements, and/or groups thereof. 
         [0055]    As used herein, a first lens refers to a lens closest to an object (or a subject), while a seventh lens refers to a lens closest to an imaging plane (or an image sensor). In addition, all of radii of curvature and thicknesses of lenses, a TTL, an ImgH (½ of a diagonal length of the imaging plane), and focal lengths are represented by millimeters (mm). Further, thicknesses of the lenses, gaps between the lenses, and the TTL are distances in optical axes of the lenses. Further, in a description for shapes of the lenses, the meaning that one surface of a lens is convex is that an optical axis portion of a corresponding surface is convex, and the meaning that one surface of a lens is concave is that an optical axis portion of a corresponding surface is concave. Therefore, although it is described that one surface of a lens is convex, an edge portion of the lens may be concave. Likewise, although it is described that one surface of a lens is concave, an edge portion of the lens may be convex. 
         [0056]    An optical imaging system may include an optical system including a plurality of lenses, for example, the optical system of the optical imaging system may include seven lenses having refractive power. However, the optical imaging system is not limited to including only the lenses having the refractive power, for example, the optical imaging system may include a stop for controlling an amount of light. In addition, the optical imaging system may further include an infrared cut-off filter filtering infrared light. Further, the optical imaging system may further include an image sensor (that is, an imaging device) converting an image of a subject incident thereto through the optical system into electrical signals. Further still, the optical imaging system may include a gap maintaining member adjusting a gap between lenses. 
         [0057]    First to seventh lenses may be formed of materials having a refractive index different from that of air, for example, the first to seventh lenses may be formed of plastic or glass. At least one of the first to seventh lenses may have an aspherical shape. As an example, only the seventh lens of the first to seventh lenses may have the aspherical shape. In addition, at least one surface of all of the first to seventh lenses may be aspherical. Here, an aspherical surface of each lens may be represented by the following Equation 1: 
         [0000]    
       
         
           
             
               
                 
                   Z 
                   = 
                   
                     
                       
                         cr 
                         2 
                       
                       
                         1 
                         + 
                         
                           
                             1 
                             - 
                             
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   k 
                                 
                                 ) 
                               
                                
                               
                                 c 
                                 2 
                               
                                
                               
                                 r 
                                 2 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       Ar 
                       4 
                     
                     + 
                     
                       Br 
                       6 
                     
                     + 
                     
                       Cr 
                       8 
                     
                     + 
                     
                       Dr 
                       10 
                     
                     + 
                     
                       Er 
                       12 
                     
                     + 
                     
                       Fr 
                       14 
                     
                     + 
                     
                       Gr 
                       16 
                     
                     + 
                     
                       Hr 
                       18 
                     
                     + 
                     
                       
                         Jr 
                         20 
                       
                       . 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
         [0058]    In Equation 1, c is the inverse of a radius of curvature of the lens, k is a conic constant, r is a distance from a certain point on an aspherical surface of the lens to an optical axis, A to J are aspherical constants, and Z (or SAG) is a distance between the certain point on the aspherical surface of the lens at the distance Y and a tangential plane meeting the apex of the aspherical surface of the lens. 
         [0059]    An optical imaging system may include seven lenses, a filter, an image sensor, and a stop. Next, the above-mentioned components will be described. 
         [0060]    The first lens may have refractive power, for example, the first lens may have negative refractive power. 
         [0061]    At least one surface of the first lens may be concave, for example, an image-side surface of the first lens may be concave. 
         [0062]    The first lens may have a spherical surface, such as, both surfaces of the first lens being spherical. The first lens may be formed of a material having high light transmissivity and excellent workability, for example, the first lens may be formed of glass. However, a material of the first lens is not limited to glass and may be another material such as plastic. 
         [0063]    The second lens may have refractive power, such as, the second lens having positive refractive power. 
         [0064]    At least one surface of the second lens may be convex, for example, both surfaces of the second lens may be convex. 
         [0065]    The second lens may have an aspherical surface, such as, an object-side surface of the second lens being aspherical. The second lens may be formed of a material having high light transmissivity and excellent workability, for example, the second lens may be formed of plastic. However, a material of the second lens is not limited to plastic and may be formed of other materials including glass. 
         [0066]    The third lens may have refractive power, for instance, the third lens may have positive or negative refractive power. 
         [0067]    One surface of the third lens may be convex, such as, an image-side surface of the third lens being convex. 
         [0068]    The third lens may have an aspherical surface, for example, an image-side surface of the third lens may be aspherical. The third lens may be formed of a material having high light transmissivity and excellent workability, and may be formed of other materials including plastic. However, a material of the third lens is not limited to plastic and could be formed of glass. 
         [0069]    The fourth lens may have refractive power, such as, the fourth lens having positive or negative refractive power. 
         [0070]    The fourth lens may have a meniscus shape, for example, an object-side surface of the fourth lens may be concave. 
         [0071]    The fourth lens may have an aspherical surface, such as, both surfaces of the fourth lens being aspherical. The fourth lens may be formed of a material having high light transmissivity and excellent workability, for example, like being formed of plastic. However, a material of the fourth lens is not limited to plastic and may be other materials including glass. 
         [0072]    The fifth lens may have refractive power, for example, the fifth lens may have positive refractive power. 
         [0073]    At least one surface of the fifth lens may be convex, for example, both surfaces of the fifth lens may be convex. 
         [0074]    The fifth lens may have an aspherical surface, for example, both surfaces of the fifth lens may be aspherical. The fifth lens may be formed of a material having high light transmissivity and excellent workability, for example, the fifth lens may be formed of plastic. However, a material of the fifth lens is not limited to plastic, for example, the fifth lens may be formed of glass. 
         [0075]    The sixth lens may have refractive power, for example, the sixth lens may have negative refractive power. 
         [0076]    The sixth lens may have a meniscus shape, for example, an image-side surface of the sixth lens may be concave. 
         [0077]    The sixth lens may have inflection points, for example, the inflection points may be formed on both surfaces of the sixth lens. 
         [0078]    The sixth lens may have an aspherical surface, for example, both surfaces of the sixth lens may be aspherical. The sixth lens may be formed of a material having high light transmissivity and excellent workability, for example, the sixth lens may be formed of plastic. However, a material of the sixth lens is not limited to plastic, for example, the sixth lens may be formed of glass. 
         [0079]    The seventh lens may have refractive power, for example, the seventh lens may have positive or negative refractive power. 
         [0080]    The seventh lens may have a meniscus shape, for example, an image-side surface of the seventh lens may be concave. 
         [0081]    The seventh lens may have inflection points, for example, the inflection points may be formed on both surfaces of the seventh lens. 
         [0082]    The seventh lens may have an aspherical surface, for example, both surfaces of the seventh lens may be aspherical. The seventh lens may be formed of a material having high light transmissivity and excellent workability, for example, the seventh lens may be formed of plastic. However, a material of the seventh lens is not limited to plastic, for example, the seventh lens may be formed of glass. 
         [0083]    The lenses of the optical imaging system configured as described above may be grouped into two lens groups, for example, the first lens and the second lens may form a first lens group, and the third to seventh lenses may form a second lens group. The first lens group may be fixed to an object side. The second lens group may be movable, for example, the second lens group may move between the first lens group and the imaging plane in order to focus the lenses. 
         [0084]    The filter may filter a partial wavelength from light incident through the first to seventh lenses, for example, the filter may filter infrared wavelengths of the incident light. 
         [0085]    The thickness of the filter may be reduced during manufacturing by being formed of plastic. 
         [0086]    The image sensor may be configured to have a high resolution, for example, a unit size of pixels configuring the image sensor may be 1.12 μm or less. 
         [0087]    The stop may be positioned to adjust the amount of light incident on the lenses, for example, the stop may be disposed between the second and third lenses. 
         [0088]    The optical imaging system may satisfy the following Conditional Expressions: 
         [0000]      −80&lt;{(1/ f )*( Y /tan θ)−1}*100&lt;−20  [Conditional Expression]
 
         [0000]        TL/ 2 Y&lt; 1.3  [Conditional Expression]
 
         [0000]      1.0&lt;tan θ&lt;4.0  [Conditional Expression]
 
         [0000]      0.4&lt; R 2/ f&lt; 1.5  [Conditional Expression]
 
         [0000]      −1.5&lt; f/f 1&lt;−0.05  [Conditional Expression]
 
         [0000]      0.3&lt; f/f 2&lt;0.8  [Conditional Expression]
 
         [0000]      1.5&lt; f/EPD&lt; 3.2  [Conditional Expression]
 
         [0000]      0.4&lt; f/fG 2&lt;1.1.  [Conditional Expression]
 
         [0089]    Here, f is an overall focal length of the optical imaging system, 2Y is a diagonal length of the imaging plane, Y is ½ of 2Y, θ is half of a field of view of the optical imaging system, R2 is a radius of curvature of the image-side surface of the first lens, f1 is a focal length of the first lens, f2 is a focal length of the second lens, EPD is an entrance pupil diameter, and fG2 is a synthetic focal length of the second lens group. 
         [0090]    The optical imaging system satisfying the above Conditional Expressions may be miniaturized, and may realize high resolution. 
         [0091]    Next, optical imaging systems according to several embodiments will be described. 
         [0092]    First, an optical imaging system according to an embodiment will be described with reference to  FIG. 1 . 
         [0093]    The optical imaging system  100  includes an optical system including a first lens  110 , a second lens  120 , a third lens  130 , a fourth lens  140 , a fifth lens  150 , a sixth lens  160 , and a seventh lens  170 . 
         [0094]    In the configurations of the lenses as described above, the first lens  110  and the second lens  120  form a first lens group G 1 , and the third to seventh lenses  130  to  170  form a second lens group G 2 . 
         [0095]    The optical imaging system  100  includes a filter  180 , an image sensor  190 , and a stop ST. The filter  180  is disposed adjacently to an image-side surface of the seventh lens  170 , and the stop ST is disposed between the second lens  120  and the third lens  130 . 
         [0096]    In the present embodiment, the first lens  110  has a negative refractive power. An object-side and image-side surfaces of the first lens  110  are concave. The second lens  120  has a positive refractive power, and both surfaces are convex. The third lens  130  has a negative refractive power. An object-side surface of third lens  130  is concave and the image-side surface is convex. The fourth lens  140  has a positive refractive power. An object-side surface of the fourth lens  140  is concave and an image-side surface is convex. The fifth lens  150  has a positive refractive power and both surfaces the fifth lens  150  are convex. The sixth lens  160  has a negative refractive power. An object-side surface of the sixth lens  160  is convex and an image-side surface is concave. In addition, inflection points are formed on both surfaces of the sixth lens  160 . The seventh lens  170  has a positive refractive power. The object-side surface of the seventh lens  170  is convex and the image-side surface is concave. In addition, inflection points are formed on both surfaces of the seventh lens  170 . 
         [0097]    The optical imaging system configured as described above has aberration characteristics as illustrated in  FIG. 2 .  FIGS. 3 and 4  are tables representing characteristics of lenses and aspherical characteristics of the optical imaging system illustrated in  FIG. 1 . 
         [0098]    An optical imaging system according to another embodiment will be described with reference to  FIG. 5 . 
         [0099]    The optical imaging system  200  according to the embodiment includes an optical system having a first lens  210 , a second lens  220 , a third lens  230 , a fourth lens  240 , a fifth lens  250 , a sixth lens  260 , and a seventh lens  270 . 
         [0100]    The first lens  210  and the second lens  220  form a first lens group G 1 , and the third to seventh lenses  230  to  270  may form a second lens group G 2 . 
         [0101]    The optical imaging system  200  includes a filter  280 , an image sensor  290 , and a stop ST. The filter  280  is disposed adjacently to an image-side surface of the seventh lens  270 , and the stop ST is disposed between the second lens  220  and the third lens  230 . 
         [0102]    The first lens  210  has a negative refractive power, and an object-side surface thereof is convex and an image-side surface thereof is concave. The second lens  220  has a positive refractive power, and both surfaces are convex. The third lens  230  has a negative refractive power, and an object-side surface is concave and an image-side surface is convex. The fourth lens  240  has a positive refractive power, and an object-side surface thereof is concave and an image-side surface thereof is convex. The fifth lens  250  has a positive refractive power, and both surfaces thereof are convex. The sixth lens  260  has a negative refractive power, and an object-side surface thereof is convex and an image-side surface thereof is concave. In addition, inflection points are formed on both surfaces of the sixth lens  260 . The seventh lens  270  has a positive refractive power, and an object-side surface thereof is convex and an image-side surface thereof is concave. In addition, inflection points are formed on both surfaces of the seventh lens  270 . 
         [0103]    The optical imaging system configured as described above represents aberration characteristics as illustrated in  FIG. 6 .  FIGS. 7 and 8  are tables representing characteristics of lenses and aspherical characteristics of the optical imaging system according to the embodiment illustrated in  FIG. 6 . 
         [0104]    An optical imaging system according to another embodiment will be described with reference to  FIG. 9 . 
         [0105]    The optical imaging system  300  according to the embodiment includes an optical system including a first lens  310 , a second lens  320 , a third lens  330 , a fourth lens  340 , a fifth lens  350 , a sixth lens  360 , and a seventh lens  370 . 
         [0106]    In the configuration of the lenses described above, the first lens  310  and the second lens  320  form a first lens group G 1 , and the third to seventh lenses  330  to  370  form a second lens group G 2 . 
         [0107]    The optical imaging system  300  includes a filter  380 , an image sensor  390 , and a stop ST. The filter  380  is disposed adjacently to an image-side surface of the seventh lens  370 , and the stop ST is disposed between the second lens  320  and the third lens  330 . 
         [0108]    In the present embodiment, the first lens  310  has a negative refractive power, and an object-side surface thereof is convex and an image-side surface thereof is concave. The second lens  320  has a positive refractive power, and both surfaces thereof are convex. The third lens  330  has a positive refractive power, and both surfaces thereof are convex. The fourth lens  340  has a negative refractive power, and both surfaces thereof are concave. The fifth lens  350  has a positive refractive power, and both surfaces thereof are convex. The sixth lens  360  has a negative refractive power, and an object-side surface thereof is convex and an image-side surface thereof is concave. In addition, inflection points are formed on both surfaces of the sixth lens  360 . The seventh lens  370  has a positive refractive power, and an object-side surface thereof is convex and an image-side surface thereof is concave. In addition, inflection points are formed on both surfaces of the seventh lens  370 . 
         [0109]    The optical imaging system configured as described above represents aberration characteristics as illustrated in  FIG. 10 .  FIGS. 11 and 12  are tables representing characteristics of lenses and aspherical characteristics of the optical imaging system according to the embodiment illustrated in  FIG. 10 . 
         [0110]    The optical imaging system may be focused, for example, the second lens group G 2  may be moved anywhere between the first lens group G 1  and an imaging plane  390 . Therefore, the distance D 1  between the second lens  320  and the third lens  330  may be changed to a number within a range of −0.025 to 0, and a distance D 2  between the seventh lens  370  and the imaging plane  390  may be changed to a number within in a range of 0.74 to 0.765. 
         [0111]    The optical imaging system configured as described above may perform high resolution photographing by changing a position of the second lens group G 2 . 
         [0112]    An optical imaging system according to another embodiment will be described with reference to  FIG. 13 . 
         [0113]    The optical imaging system  400  according to the embodiment includes an optical system including a first lens  410 , a second lens  420 , a third lens  430 , a fourth lens  440 , a fifth lens  450 , a sixth lens  460 , and a seventh lens  470 . 
         [0114]    In the configuration of the lenses as described above, the first lens  410  and the second lens  420  form a first lens group G 1 , and the third to seventh lenses  430  to  470  form a second lens group G 2 . 
         [0115]    The optical imaging system  400  includes a filter  480 , an image sensor  490 , and a stop ST. The filter  480  is disposed adjacently to an image-side surface of the seventh lens  470 , and the stop ST is disposed between the second lens  420  and the third lens  430 . 
         [0116]    In the present embodiment, the first lens  410  has a negative refractive power, and an object-side surface thereof is convex and an image-side surface thereof is concave. The second lens  420  has a positive refractive power, and both surfaces thereof are convex. The third lens  430  has a negative refractive power, and an object-side surface thereof is concave and an image-side surface thereof is convex. The fourth lens  440  has a positive refractive power, and an object-side surface thereof is concave and an image-side surface thereof is convex. The fifth lens  450  has a positive refractive power, and both surfaces thereof are convex. The sixth lens  460  has a negative refractive power, and an object-side surface thereof is convex and an image-side surface thereof is concave. In addition, inflection points are formed on both surfaces of the sixth lens  460 . The seventh lens  470  has a positive refractive power, and an object-side surface thereof is convex and an image-side surface thereof is concave. In addition, inflection points are formed on both surfaces of the seventh lens  470 . 
         [0117]    The optical imaging system configured as described above represents aberration characteristics as illustrated in  FIG. 14 .  FIGS. 15 and 16  are tables representing characteristics of lenses and aspherical characteristics of the optical imaging system according to the embodiment illustrated in  FIG. 14 . 
         [0118]    An optical imaging system according to another embodiment will be described with reference to  FIG. 17 . 
         [0119]    The optical imaging system  500  according to the embodiment includes an optical system including a first lens  510 , a second lens  520 , a third lens  530 , a fourth lens  540 , a fifth lens  550 , a sixth lens  560 , and a seventh lens  570 . 
         [0120]    In the configurations of the lenses as described above, the first lens  510  and the second lens  520  form a first lens group G 1 , and the third to seventh lenses  530  to  570  form a second lens group G 2 . 
         [0121]    The optical imaging system  500  includes a filter  580 , an image sensor  590 , and a stop ST. The filter  580  is disposed adjacently to an image-side surface of the seventh lens  570 , and the stop ST is disposed between the second lens  520  and the third lens  530 . 
         [0122]    In the present embodiment, the first lens  510  has a negative refractive power, and both surfaces thereof are concave. The second lens  520  has a positive refractive power, and both surfaces thereof are convex. The third lens  530  has a negative refractive power, and an object-side surface thereof is concave and an image-side surface thereof is convex. The fourth lens  540  has a positive refractive power, and an object-side surface thereof is concave and an image-side surface thereof is convex. The fifth lens  550  has a positive refractive power, and both surfaces thereof are convex. The sixth lens  560  has a negative refractive power, and an object-side surface thereof is convex and an image-side surface thereof is concave. In addition, inflection points are formed on both surfaces of the sixth lens  560 . The seventh lens  570  has a negative refractive power, and an object-side surface thereof is convex and an image-side surface thereof is concave. In addition, inflection points are formed on both surfaces of the seventh lens  570 . 
         [0123]    The optical imaging system configured as described above represents aberration characteristics as illustrated in  FIG. 18 .  FIGS. 19 and 20  are tables representing characteristics of lenses and aspherical characteristics of the optical imaging system according to the embodiment illustrated in  FIG. 18 . 
         [0124]    A half of a field of view of each of the optical imaging systems according to the first to fifth embodiments may be substantially 59 degrees or more. Therefore, the optical imaging system according to the present disclosure is useful for a device requiring a wide field of view, such as a monitoring camera for an unmanned aerial vehicle or a monitoring camera for a vehicle. 
         [0125]    Table 1 represents values of Conditional Expressions of the optical imaging systems according to the first to fifth embodiments. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 First 
                 Second 
                 Third 
                 Fourth 
                 Fifth 
               
               
                 Conditional 
                 Exemplary 
                 Exemplary 
                 Exemplary 
                 Exemplary 
                 Exemplary 
               
               
                 Expression 
                 Embodiment 
                 Embodiment 
                 Embodiment 
                 Embodiment 
                 Embodiment 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 {(1/f) * (Y/tanθ) − 1} * 100 
                 −47.70 
                 −36.30 
                 −30.20 
                 −53.30 
                 −46.80 
               
               
                 tanθ 
                 2.356 
                 1.678 
                 1.664 
                 2.356 
                 2.145 
               
               
                 TL/2Y 
                 1.260 
                 1.220 
                 1.210 
                 1.220 
                 1.160 
               
               
                 R2/f 
                 0.860 
                 0.880 
                 0.730 
                 0.990 
                 0.950 
               
               
                 f/f1 
                 −0.640 
                 −0.580 
                 −0.760 
                 −0.590 
                 −0.730 
               
               
                 f/f2 
                 0.540 
                 0.560 
                 0.560 
                 0.540 
                 0.590 
               
               
                 f/EPD 
                 2.990 
                 3.160 
                 2.760 
                 2.960 
                 3.160 
               
               
                 f/fG2 
                 0.700 
                 0.790 
                 0.780 
                 0.810 
                 0.820 
               
               
                   
               
             
          
         
       
     
         [0126]    As set forth above, according to the embodiments, an optical imaging system capable of being mounted in a small terminal and having a high level of resolution is realized. 
         [0127]    While this disclosure includes specific examples, it will be apparent to one of ordinary skill in the art that various changes in form and details may be made in these examples without departing from the spirit and scope of the claims and their equivalents. The examples described herein are to be considered in a descriptive sense only, and not for purposes of limitation. Descriptions of features or aspects in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if the described techniques are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined in a different manner, and/or replaced or supplemented by other components or their equivalents. Therefore, the scope of the disclosure is defined not by the detailed description, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents are to be construed as being included in the disclosure.