Abstract:
Disclosed are a bifocal lens having two focal distances to enable near image capturing and far image capturing and capable of being manufactured to have a thin profile, and an imaging device including same. A bifocal lens according to disclosed embodiments may include: a refractive optical system having at least one refractive lens element and having a first focal distance; and a reflective optical system having multiple reflective surfaces and having a second focal distance that is different from the first focal distance. Because the refractive optical system and the reflective optical system have mutually different focal distances, the bifocal lens according to an embodiment may be capable of both near image capturing and far image capturing.

Description:
TECHNICAL FIELD 
       [0001]    One or more embodiments of the present disclosure relate to a dual focus lens having two focal lengths and an image pickup apparatus including the dual focus lens, and more particularly, to a dual focus lens which may be thinly manufactured having two focal lengths for short distance and long distance photography, and an image pickup apparatus including the dual focus lens. 
       BACKGROUND ART 
       [0002]    Due to a recent trend in reducing sizes of not only compact cameras and cameras in mobile devices, but also sizes of mirrorless cameras and single-lens reflex cameras, there is a demand for the development of small camera lenses. In general, the small camera lenses are designed as single focus lenses. However, since the single focus lenses have fixed viewing angles, it is difficult to capture images with various photography effects by using the single focus lenses. In particular, the compact cameras and the cameras in the mobile devices are mostly designed to be appropriate for short distance photography, but not for long distance photography. 
         [0003]    Among lenses for short distance and long distance photography, a multifocal lens having a plurality of focal lengths or a zoom lens having a variable focal length is mostly used. However, the zoom lens used in the compact cameras usually includes at least six lenses, thereby causing cameras to be long and heavy. Although the mirrorless cameras and the single-lens reflex cameras may be used by changing various single focus lenses having different focal lengths, there are still problems in that long focus lenses for long distance photography are long and large, and there are also inconveniences of having to change lenses. Furthermore, since the cameras in the mobile devices are relatively small, it is difficult to apply the zoom lens in the cameras in the mobile devices. Even when an additional lens may be externally attached to a camera in a mobile device by using an adapter so as to perform long distance photography, the camera in the mobile device may increase in size. Recently, lenses in which two optical systems having different focal lengths are integrated are being developed. However, such lenses require two image sensors, thereby causing an increase in a manufacturing cost and a size of a camera. 
       DETAILED DESCRIPTION OF THE INVENTION 
     Technical Problem 
       [0004]    One or more embodiments include a dual focus lens which may be thinly manufactured having two focal lengths for short distance and long distance photography, and an image pickup apparatus including the dual focus lens. 
       Technical Solution 
       [0005]    According to one or more embodiments, a dual focus lens includes a refractive optical system having a first focal length, the refractive optical system including at least one refractive lens element; and a reflective optical system having a second focal length that is different from the first focal length, the reflective optical system including a plurality of reflection surfaces. The refractive optical system and the reflective optical system respectively have a first image plane and a second image plane, and the refractive optical system and the reflective optical system are both located at an object side with respect to the first and second image planes. 
         [0006]    The refractive optical system and the reflective optical system may be located having a common optical axis in the center. 
         [0007]    The refractive optical system may be located at the object side and the reflective optical system is located at an image side, and the center of the reflective optical system may include a first light incident region on which light emitted from the refractive optical system is incident, and a light emission region which emits light incident on the first light incident region to the image side. 
         [0008]    The dual focus lens may further include at least one common lens element located at the image side with respect to the refractive optical system and the reflective optical system, the at least one common lens element focusing light emitted from the refractive optical system on the first image plane and light emitted from the reflective optical system on the second image plane. 
         [0009]    The at least one common lens element may be designed to be movable in a direction of an optical axis or a direction perpendicular to the optical axis. 
         [0010]    In a direction from the object side to the image side, the refractive optical system may include a meniscus lens having a negative refractive power that includes a concave surface facing the object side and a convex surface facing the image side, and a biconvex lens. The at least one common lens element may include a meniscus lens having a negative refractive power that includes a concave surface facing the object side and a convex surface facing the image side. 
         [0011]    In a direction from the object side to the image side, the refractive optical system may include a meniscus lens having a negative refractive power that includes a convex surface facing the object side and a concave surface facing the image side, and a biconvex lens. In a direction from the object side to the image side, the at least one common lens element may include first and second meniscus lenses having a positive refractive power that includes a concave surface facing the object side and a convex surface facing the image side, and a third meniscus lens having a negative refractive power that includes a concave surface facing the object side and a convex surface facing the image side. 
         [0012]    Respective locations of the first and second image planes with respect to an optical axis may be the same. 
         [0013]    Respective locations of the first and second image planes with respect to an optical axis may be different. 
         [0014]    The reflective optical system may have a folded optics structure in which a light path is bent a plurality of times between the plurality of reflection surfaces. 
         [0015]    The reflective optical system may include a second light incident region formed in a ring shape around a circumference of the reflective optical system. The plurality of reflection surfaces may be optically facing each other so that light incident through the second light incident region is emitted to the light emission region. 
         [0016]    For example, the plurality of reflection surfaces may be formed in a ring shape having an optical axis in the center, and radii of the plurality of reflection surfaces with respect to the optical axis may decrease in a direction to which light incident through the second light incident region proceeds. 
         [0017]    The dual focus lens may further include a first coating layer located in the first light incident region, the first coating layer transmitting light having a first wavelength and blocking light having other wavelengths; and a second coating layer located on at least one of the plurality of reflection surfaces, the second coating layer reflecting light having a second wavelength which is different from the first wavelength and absorbing or transmitting light having other wavelengths. 
         [0018]    For example, any one of the first and second wavelengths may be in a visible light range and the other is in an infrared light range. 
         [0019]    The dual focus lens may further include a transparent substrate on which the plurality of reflection surfaces are fixed. 
         [0020]    The first and second light incident regions, and the light emission region may be formed on a surface of the transparent substrate. 
         [0021]    Surface regions of the transparent substrate respectively corresponding to the first light incident region and the light emission region may be curved surfaces. 
         [0022]    The plurality of reflection surfaces may be curved, and surface regions of the transparent substrate on which the plurality of the reflection surfaces are fixed may have shapes that correspond to respective curved shapes of the plurality of reflection surfaces. 
         [0023]    The transparent substrate may include a first surface and a second surface that are facing each other and parallel with each other. 
         [0024]    The dual focus lens may further include a first shutter transmitting or blocking light incident on the refractive optical system, and a second shutter transmitting or blocking light incident on the reflective optical system. 
         [0025]    The first and second shutters may be configured such that one transmits light and the other blocks light, selectively. 
         [0026]    At least one of the first and second shutters may be divided into at least two segments that are independently driven in a circumference direction 
         [0027]    For example, the second focal length may be longer than the first focal length. 
         [0028]    The dual focus lens may further include at least one light source that is located in a space surrounding the refractive optical system. 
         [0029]    According to one or more embodiments, an image pickup apparatus includes the dual focus lens having the aforementioned structure, and an image sensor located at an image side of the dual focus lens. 
         [0030]    The image sensor may be divided into at least two independent segments. 
         [0031]    Respective locations of the first and second image planes with respect to an optical axis may be different. The image sensor may move to the first image plane while the refractive optical system is photographing, and move to the second image plane while the reflective optical system is photographing. 
         [0032]    The image sensor may be designed to be movable in a direction of an optical axis or a direction perpendicular to the optical axis. 
         [0033]    At least one selected from the refractive optical system and the reflective optical system may be configured to have a zoom function. 
         [0034]    The refractive optical system may be configured to form a first image having a first magnification, and the reflective optical system may be configured to form a second image having a second magnification that is greater than the first magnification. 
         [0035]    The image pickup apparatus may be configured to form a third image having a magnification between the first magnification and the second magnification by cropping and magnifying the first image, reducing the second image, and synthesizing the first image and second images. 
       Advantageous Effects of the Invention 
       [0036]    A dual focus lens according to the disclosed embodiments may include a refractive optical system including at least one refractive lens element and a reflective optical system including a plurality of reflection surfaces. Since the refractive optical system and the reflective optical system have different focal lengths, the dual focus lens of the present embodiments may be capable of both short distance and long distance photography. For example, the refractive optical system having a short focal length may be used for short distance photography, and the reflective optical system having a long focal length may be used for long distance photography. 
         [0037]    Also, the reflective optical system may have a folded optics structure in which a light path bends a plurality of times between the reflection surfaces, and thus be short in a direction of an optical axis. Therefore, the dual focus lens according to the present embodiments may have two different focal lengths and also be thinly manufactured. 
         [0038]    Furthermore, since the refractive optical system and the reflective optical system are located having a common optical axis in the center and image planes thereof are located at a substantially identical location, an image pickup device including the dual focus lens according to the present embodiments may use only one image sensor. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0039]      FIG. 1  is a schematic cross-sectional view of a dual focus lens and an image pickup apparatus including the dual focus lens, according to an embodiment; 
           [0040]      FIG. 2  is an enlarged partial sectional view of the center of a refractive optical system and a reflective optical system adjacent to the refractive optical system, which are included in the dual focus lens of  FIG. 1 ; 
           [0041]      FIG. 3  is an exemplary graph of transmittance per wavelength of a transmission coating layer located in a light transmission region of the reflective optical system; 
           [0042]      FIG. 4  is an exemplary graph of reflectance per wavelength of a reflection coating layer located in a reflection region of the reflective optical system; 
           [0043]      FIG. 5  is a view of the dual focus lens when a shutter of the refractive optical system is open, and a shutter of the reflective optical system is closed; 
           [0044]      FIG. 6  is an exemplary view of a path of light incident on the dual focus lens in the case of  FIG. 5 ; 
           [0045]      FIG. 7  is a view of the dual focus lens when the shutter of the refractive optical system is closed, and the shutter of the reflective optical system is open; 
           [0046]      FIG. 8  is an exemplary view of a path of light incident on the dual focus lens in the case of  FIG. 7 ; 
           [0047]      FIG. 9  is a schematic cross-sectional view of a dual focus lens and an image pickup apparatus including the dual focus lens, according to another example embodiment; 
           [0048]      FIGS. 10A to 10D  are exemplary views of various divided image sensors; 
           [0049]      FIGS. 11A to 11E  are exemplary views of various operations of a shutter; 
           [0050]      FIG. 12  is a table of specific optical data of a refractive optical system of a dual focus lens, according to a first embodiment; 
           [0051]      FIG. 13  is a table of aspheric coefficients of aspheric surfaces of the refractive optical system of the dual focus lens, according to the first embodiment; 
           [0052]      FIG. 14  is a table of specific optical data of a reflective optical system of the dual focus lens, according to the first embodiment; 
           [0053]      FIG. 15  is a table of aspheric coefficients of aspheric surfaces of the reflective optical system of the dual focus lens, according to the first embodiment; 
           [0054]      FIG. 16  is a table of diameters of a plurality of reflection surfaces of the reflective optical system of the dual focus lens, according to the first embodiment; 
           [0055]      FIG. 17  is a schematic cross-sectional view of a dual focus lens, according to a second embodiment; 
           [0056]      FIG. 18  is a cross-sectional view of a refractive optical system of the dual focus lens, according to the second embodiment; 
           [0057]      FIG. 19  is a table of specific optical data of the refractive optical system of the dual focus lens, according to the second embodiment; 
           [0058]      FIG. 20  is a table of aspheric coefficients of aspheric surfaces of the refractive optical system of the dual focus lens, according to the second embodiment; 
           [0059]      FIG. 21  is a cross-sectional view of a reflective optical system of the dual focus lens, according to the second embodiment; 
           [0060]      FIG. 22  is a table of specific optical data of the reflective optical system of the dual focus lens, according to the second embodiment; 
           [0061]      FIG. 23  is a table of aspheric coefficients of an aspheric surface of the reflective optical system of the dual focus lens, according to the second embodiment; 
           [0062]      FIG. 24  is a table of diameters of each of a plurality of reflection surfaces of the reflective optical system of the dual focus lens, according to the second embodiment; and 
           [0063]      FIG. 25  is a schematic cross-sectional view of a dual focus lens and an image pickup apparatus including the dual focus lens, according to another embodiment. 
           [0064]      FIGS. 26 and 27  are conceptual views describing a principle of a digital zoom function by using two images respectively obtained from a refractive optical system and a reflective optical system of a dual focus lens. 
       
    
    
     MODE OF THE INVENTION 
       [0065]    Hereinafter, a dual focus lens and an image pickup apparatus including the same will be described in detail with reference to the accompanying drawings, wherein like reference numerals refer to like elements throughout. Sizes of components in the drawings may be exaggerated for convenience of explanation. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Also, in the case where a position relationship between two items is described with the terms “on,” “on the top of,” or the like, one or more items may be interposed therebetween unless the term “directly” is used in the expression. 
         [0066]      FIG. 1  is a schematic cross-sectional view of a dual focus lens  100  and an image pickup apparatus including the dual focus lens  100 , according to an embodiment. Referring to  FIG. 1 , the dual focus lens  100  according to the present embodiment may include a refractive optical system  110  having a first focal length, and a reflective optical system  120  having a second focal length that is different from the first focal length. The refractive and reflective optical systems  110  and  120  may have a first image plane IP 1  and a second image plane IP 2 , respectively. Although  FIG. 1  illustrates an example in which respective locations of the first and second image planes IP 1  and IP 2  with respect to an optical axis OX are different, the respective locations of the first and second image planes IP 1  and IP 2  with respect to the optical axis OX may be the same depending on respective designs of the refractive and reflective optical systems  110  and  120 . 
         [0067]    The dual focus lens  100  may further include at least one common lens element  130  that is used in both of the refractive and reflective optical systems  110  and  120 . The first focal length of the refractive optical system  110  is formed by functional actions of the refractive optical system  110  and the common lens element  130 , and the second focal length of the reflective optical system  120  is formed by functional actions of the reflective optical system  120  and the common lens element  130 . The common lens element  130  may be located at an image side with respect to the refractive and reflective optical systems  110  and  120 . Although  FIG. 1  illustrates an example in which there is only one common lens element  130 , two or more common lens elements  130  may be used depending on designs of the dual focus lens. The common lens element  130  may be designed such that light emitted from the refractive optical system  110  is focused on the first image plane IP 1 , and light emitted from the reflective optical system  120  is focused on the second image plane IP 2 . 
         [0068]    The image pickup apparatus according to the present embodiment may include the dual focus lens  100 , and an image sensor  140  that is located at any one of the first and second image planes IP 1  and IP 2 . For example, the image sensor  140  may be a charge-coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS) image sensor. A cover layer  141  may be additionally located on a light incident surface of the image sensor  140  so as to protect color filters and pixels of the image sensor  140 . 
         [0069]    As illustrated in  FIG. 1 , the refractive and reflective optical systems  110  and  120  may both be located at an object side with respect to the first and second image planes IP 1  and IP 2 . In other words, the first image plane IP 1  of the refractive optical system  110  and the second image plane IP 2  of the reflective optical system  120  may be located in the same direction with respect to the refractive and reflective optical systems  110  and  120 . Therefore, since the refractive and reflective optical systems  110  and  120  may form images on the same image sensor  140 , the image pickup apparatus may capture images at different viewing angles by using only the image sensor  140  and without separate image sensors for each of the refractive and reflective optical systems  110  and  120  that have different focal lengths. 
         [0070]    The refractive optical system  110  may include at least one refractive lens element disposed along the optical axis OX. Although  FIG. 1  illustrates two refractive lens elements  111  and  112 , the refractive optical system  110  may include only one, or three or more refractive lens elements depending on the design of the refractive optical system  110 . The first and second refractive lens elements  111  and  112  may be formed of materials having different refractive indexes so as to suppress chromatic aberration of the dual focus lens  100 . 
         [0071]    A first shutter  119 , which transmits or blocks light that is incident toward the refractive optical system  110 , may be located in a light path of the refractive optical system  110 . Although  FIG. 1  illustrates that the first shutter  119  is located in front of the refractive optical system  110 , a location of the first shutter  119  is not limited thereto. For example, the first shutter  119  may be located between the first and second refractive lens elements  111  and  112 , or between the second refractive lens element  112  and the reflective optical system  120 . 
         [0072]    The reflective optical system  120  may be located along the same optical axis OX as the refractive optical system  110 . In other words, the refractive and reflective optical systems  110  and  120  may be located having a common optical axis OX in the center. For example, as illustrated in  FIG. 1 , the refractive optical system  110  is located near the object side with respect to the optical axis OX, and the reflective optical system  120  is located near the image side with respect to the optical axis OX. Therefore, with respect to a direction from the object side to the image side, the refractive optical system  110  may be located at a front side and the reflective optical system  120  may be located at a rear side. 
         [0073]    Referring to  FIG. 1 , the reflective optical system  120  may include a first light incident region  125  on which light emitted from the refractive optical system  110  is incident, a light emission region  127  which emits light incident to the first light incident region  125  to the image side, a second light incident region  126  formed in a ring shape around a circumference of the reflective optical system  120 , and first to fourth reflection surfaces  121  to  124  disposed between the first and second light incident regions  125  and  126  in a radius direction having the optical axis OX in the center. The first light incident region  125  and the light emission region  127  may be located such that they face each other in the center of the reflective optical system  120 . The first light incident region  125  is a region on which light to be imaged by the refractive optical system  110  is incident, and the second light incident region  126  is a region on which light to be imaged by the reflective optical system  120  is incident. Light incident on the first light incident region  125  and light incident on the second light incident region  126  may both be emitted to the image side through the light emission region  127 . 
         [0074]    The first to fourth reflection surfaces  121  to  124  of the reflective optical system  120  may optically face each other so that light incident on the second light incident region  126  is emitted toward the light emission region  127 . The term “optically facing” indicates that the first to fourth reflection surfaces  121  to  124  are not physically facing one another, but are located such that light reflected from a reflection surface proceeds to another reflection surface. For example, the first reflection surface  121  reflects light incident on the second light incident region  126  to the second reflection surface  122 . Then, the second reflection surface  122  reflects light to the third reflection surface  123 , and the third reflection surface  123  reflects light to the fourth reflection surface  124 . Lastly, reflected light from the fourth reflection surface  124  proceeds to the image side through the light emission region  127 . Although  FIG. 1  illustrates an example of four reflection surfaces  121  to  124 , the present embodiment is not limited thereto, and at least two reflection surfaces may be used depending on the designs of the dual focus lens. 
         [0075]    The first to fourth reflection surfaces  121  to  124  may have a ring shape having the optical axis OX in the center. Also, as illustrated in  FIG. 1 , radii of the first to fourth reflection surfaces  121  to  124  with respect to the optical axis OX may decrease in a direction to which light incident through the second light incident region  126  proceeds. For example, the first reflection surface  121  may have the largest radius with respect to the optical axis OX, and the fourth reflection surface  124  may have the smallest. 
         [0076]    As described above, the reflective optical system  120  of the dual focus lens  100  according to the present embodiment may have a folded optics structure in which a light path bends a plurality of times between the first to fourth of reflection surfaces  121  to  124 . In the folded optics structure, the light path may be extended by using the first to fourth reflection surfaces  121  to  124  so that a thickness (or a length in a direction of the optical axis OX) of the reflective optical system  120  may be greatly reduced regardless of the second focal length of the reflective optical system  120 . Therefore, when the second focal length of the reflective optical system  120  is longer than the first focal length of the refractive optical system  110 , the dual focus lens  100  may have two different focal lengths and also be thinly manufactured. The dual focus lens  100  according to the present embodiment may be used for both short distance and long distance photography by selectively using the refractive optical system  110  having the first focal length and the reflective optical system  120  having the second focal length. For example, the refractive optical system  110  having a short focal length may be used for short distance photography (wide angle), and the reflective optical system  120  having a long focal length may be used for long distance photography (telephoto). If a magnification between a wide angle position of the refractive optical system  110  and a telephoto position of the reflective optical system  120  is obtained by digitally zooming using an image signal processor (not shown) of the image pickup apparatus, it is possible to continuously zoom from the wide angle position to the telephoto position. 
         [0077]    The first to fourth reflection surfaces  121  to  124  may be individually assembled and fixed in the image pickup apparatus. In this case however, a manufacturing process may be complicated, and a great amount of time may be necessary to accurately locate the first to fourth reflection surfaces  121  to  124  at their respective positions. Therefore, the first to fourth reflection surfaces  121  to  124  may be fixed onto a transparent substrate  128  and then located in the image pickup apparatus. The transparent substrate  128  may be formed of, for example, glass or a transparent material such as polymethylmethacrylate (PMMA). According to the present embodiment, in order to suppress chromatic aberration of the dual focus lens  100 , a refractive index of the transparent substrate  128  may differ from that of the common lens element  130 . For example, the transparent substrate  128  may be formed of PMMA and the common lens element  130  may be formed of a glass material having a refractive index different from that of PMMA. When using the transparent substrate  128  on which the first to fourth reflection surfaces  121  to  124  are fixed, the first light incident region  125 , the second light incident region  126 , and the light emission region  127  may be formed on a surface of the transparent substrate  128 . 
         [0078]    As illustrated in  FIG. 1 , a shape of the transparent substrate  128  may be complicated according to respective locations and shapes of the first to fourth reflection surfaces  121  to  124 , the first light incident region  125 , the second light incident region  126 , and the light emission region  127 . For example, when the first to fourth reflection surfaces  121  to  124  have respective curved shapes, surface regions of the transparent substrate  128  on which the first to fourth of reflection surfaces  121  to  124  are fixed may have shapes that respectively correspond to the respective curved shapes of the first to fourth reflection surfaces  121  to  124 . The first to fourth reflection surfaces  121  to  124  may be reflection coatings formed by coating the corresponding surface regions of the transparent substrate  128 . In order to assist image forming operations of the refractive and reflective optical systems  110  and  120 , surface regions of the transparent substrate  128  that respectively correspond to the first light incident region  125  and the light emission region  127  may be curved surfaces having a refractive power. Although  FIG. 1  illustrates that a surface region of the transparent substrate  128  corresponding to the second light incident region  126  is a plane, but the surface region of the transparent substrate  128  corresponding to the second light incident region  126  may also be a curved surface having a refractive power. 
         [0079]    The dual focus lens  100  may additionally include a second shutter  129  that transmits or block light that is incident on the reflective optical system  120 . For example, the second shutter  129  may be facing the second light incident region  126 . The first shutter  119  that transmits or blocks light incident on the refractive optical system  110  and the second shutter  129  that transmits or blocks light incident on the reflective optical system  120  may be located at different locations with respect to the optical axis OX, but on the same plane. When the first and second shutters  119  and  129  are located on the same plane, the first and second shutters  119  and  129  may be formed on a single substrate. The first and second shutters  119  and  129  may be designed such that one transmits light and the other blocks light when necessary. For example, the first shutter  119  may be open and the second shutter  129  may be closed, or vice versa. The first and second shutters  119  and  129  may be, for example, mechanical shutters that mechanically open and close, electronic shutters that open and close by using polarized light or liquid crystal, or electrostatic shutters that open and close by using non-transmission ink layer. 
         [0080]      FIG. 2  is an enlarged partial sectional view of the center of the refractive and reflective optical systems  110  and  120  adjacent to the refractive optical system  110 , which are included in the dual focus lens  100  of  FIG. 1 . Referring to  FIG. 2 , the first light incident region  125  of the reflective optical system  120  is facing the refractive optical system  110 . Also, the fourth reflection surface  124  is located at a circumference of the first light incident region  125 . For example, the first light incident region  125  and the fourth reflection surface  124  may be located in the same surface region of the transparent substrate  128 . That is, the first light incident region  125  and the fourth reflection surface  124  may be respectively located in the center and a circumference of a surface region of the transparent substrate  128  facing the refractive optical system  110 . Since the first light incident region  125  is a region for the refractive optical system  110  and the fourth reflection surface  124  is a region for the reflective optical system  120 , the first light incident region  125  and the fourth reflection surface  124  may have different surface characteristics. For example, the first light incident region  125  and the fourth reflection surface  124  may be curved surfaces having different radius of curvature. Alternatively, the first light incident region  125  and the fourth reflection surface  124  may be aspheric surfaces having the same radius of curvature but different aspheric coefficients. 
         [0081]    A high transmission coating layer may be formed in the first light incident region  125  so that light emitted from the refractive optical system  110  may transmit the first light incident region  125 . Also, a high reflection coating layer may be formed on the fourth reflection surface  124  so as to reflect light reflected from the third reflection surface  123 . The high transmission coating layer and the high reflection coating layer may be formed to transmit or reflect light having the same wavelengths (e.g., visible light). However, the refractive and reflective optical systems  110  and  120  may form images by using light having different wavelengths. In this case, the high transmission coating layer and the high reflection coating layer may be formed to transmit or reflect light having different wavelengths. The high reflection coating layer may not only be formed on the fourth reflection surface  124 , but on any one of the first to third reflection surfaces  121  to  123 . 
         [0082]    For example, as shown in a graph of transmittance per wavelength of  FIG. 3 , the high transmission coating layer may transmit light in having a wavelength in a visible light range and block light having other wavelengths. Also, as shown in a graph of reflectance per wavelength of  FIG. 4 , the high reflection coating layer may reflect light having a wavelength in an infrared light range and absorb or transmit light having other wavelengths. Alternatively, the high transmission coating layer may transmit light having the wavelength in the infrared light range or a wavelength in an ultraviolet light range, and the high reflection coating layer may reflect light having the wavelength in the visible light range. For example, when the refractive optical system  110  uses visible light and the reflective optical system  120  uses infrared light to form images, the refractive optical system  110  may capture a usual color image, and the reflective optical system  120  may provide functions such as iris recognition, blood vessel recognition, subject distance estimation, infrared signal detection, infrared thermal imaging, and night vision. 
         [0083]    Hereinafter, operations of the dual focus lens  100  according to the present embodiment will be described with reference to  FIGS. 5 to 8 . 
         [0084]      FIG. 5  is a view of the dual focus lens  100  when the first shutter  119  of the refractive optical system  110  is open, and the second shutter  129  of the reflective optical system  120  is closed.  FIG. 6  is an exemplary view of a path of light incident on the dual focus lens  100  in the case of  FIG. 5 . Only elements related to the refractive optical system  110  are illustrated in  FIG. 6 , and elements related to the reflective optical system  120  are omitted. As illustrated in  FIG. 5 , the first shutter  119 , formed in a circular shape in the center, is open, and the second shutter  129 , formed in a ring shape in a periphery region, is closed. In this case, light is incident only on the refractive optical system  110 . Accordingly, only the refractive optical system  110  contributes to an image formed on the image sensor  140 . Then, the image pickup apparatus may perform short distance photography. The image sensor  140  of the image pickup apparatus may be located at the first image plane IP 1 . 
         [0085]      FIG. 7  is a view of the dual focus lens  100  when the first shutter  119  of the refractive optical system  110  is closed, and the second shutter  129  of the reflective optical system  120  is open.  FIG. 8  is an exemplary view of a path of light incident on the dual focus lens  100  in the case of  FIG. 7 . In  FIG. 8 , the elements related to the reflective optical system  120  are only illustrated, and the elements related to the refractive optical system  110  are omitted. As illustrated in  FIG. 7 , the first shutter  119 , formed in a circular shape in the center, is closed, and the second shutter  129 , formed in a ring shape in the periphery region, is open. In this case, light is incident only on the reflective optical system  120 . Accordingly, only the reflective optical system  120  may contribute in forming of an image by the image sensor  140 . Then, the image pickup apparatus may perform long distance photography. The image sensor  140  of the image pickup apparatus may be located at the second image plane IP 2 . Therefore, the image sensor  140  may move to the first image plane IP 1  when the refractive optical system  110  is photographing, and may move to the second image plane IP 2  when the reflective optical system  120  is photographing. However, according to embodiments, when the first and second image planes IP 1  and IP 2  are the same, the image sensor  140  may be fixed. 
         [0086]      FIG. 9  is a schematic cross-sectional view of a dual focus lens  200  and an image pickup apparatus including the dual focus lens  200 , according to another embodiment. Referring to  FIG. 9 , the dual focus lens  200  according to the present embodiment may include the refractive optical system  110  having a first focal length, and a reflective optical system  150  having a second focal length that is different from the first focal length. Unlike the dual focus lens  100  of  FIG. 1 , the reflective optical system  150  included in the dual focus lens  200  of  FIG. 9  has a flat shape. 
         [0087]    In the present embodiment, the reflective optical system  150  may include a first light incident region  155  on which light emitted from the refractive optical system  110  is incident, a light emission region  157  which emits light incident to the first light incident region  155  to the image side, a second light incident region  156  formed in a ring shape around a circumference of the reflective optical system  150 , and first to fourth reflection surfaces  151  to  154  disposed between the first and second light incident regions  155  and  156  in a radius direction having the optical axis OX in the center. The first to fourth reflection surfaces  151  to  154  may be fixed onto a transparent substrate  158  that is flat. For example, the second and fourth reflection surfaces  152  and  154  may be located on a first surface of the transparent substrate  158 , and the third reflection surface  153  may be located on a second surface of the transparent substrate  158 . The first and second surfaces of the transparent substrate  158  are facing each other, and a perpendicular direction of the first and second surfaces may be in parallel with the optical axis OX. The first light incident region  155  and the light emission region  157  that are located in the center of the reflective optical system  150  may have curved surfaces. Also, the first reflection surface  151  facing the second light incident region  156  may be inclined so that light reflected by the first reflection surface  151  is inclined and thus proceeds to the second reflection surface  152 . 
         [0088]    The image sensor  140  may be divided into at least two separate segments, and at least one of the first and second shutters  119  and  129  may be divided into at least two separate segments that are independently driven. For example,  FIGS. 10A to 10D  are exemplary views of various divided image sensors  140  and  FIGS. 11A to 11E  are exemplary views of various operations of the first and second shutters  119  and  129 . 
         [0089]    Referring to  FIG. 10A , the image sensor  140  may include two segments  140   a  and  140   b  that are vertically divided. The segments  140   a  and  140   b  may be physically divided, or be logically divided by using the image signal processor of the image pickup apparatus. For example, the image signal processor may separately process signals that are generated from the segments  140   a  and  140   b  and thus form two images, or alternatively, merge and process the signals and thus form one image. Alternatively, as in  FIG. 10B , the image sensor  140  may include two segments  140   a  and  140   b  that are horizontally divided. Alternatively, as in  FIG. 10C , the image sensor  140  may include four segments  140   a ,  140   b ,  140   c , and  140   d  that are vertically and horizontally divided. 
         [0090]    When the image sensor  140  is divided into the segments  140   a ,  140   b ,  140   c , and  140   d , the image pickup apparatus may obtain stereo images having different parallaxes. For example, when the image sensor  140  is vertically divided, stereo images having parallaxes of a horizontal direction may be obtained; when the image sensor  140  is horizontally divided, stereo images having parallaxes of a vertical direction may be obtained; and when the image sensor  140  is horizontally and vertically divided, stereo images having parallaxes of the horizontal and vertical directions may be obtained. 
         [0091]    In order to obtain such stereo images, the reflective optical system  120  may be used by closing the first shutter  119  in the center and opening the second shutter  129  in the periphery region, as illustrated in  FIG. 7 . In this case, the image signal processor of the image pickup apparatus may separately process signals generated from the segments  140   a ,  140   b ,  140   c , and  140   d  and thus generate a plurality of images. Alternatively, in order to obtain a usual image, the refractive optical system  110  may be used by opening the first shutter  119  and closing the second shutter  129 , as illustrated in  FIG. 5 . In this case, the image signal processor of the image pickup apparatus may merge and process the signals generated from the segments  140   a ,  140   b ,  140   c , and  140   d  and thus form one image 
         [0092]    At least one of the first and second shutters  119  and  129  may be divided into at least two segments that are independently driven in a circumference direction. For example, the second shutter  129  may be vertically divided into two segments  129   a  and  129   b  as illustrated in  FIGS. 11A and 11B , or be horizontally divided into the segments  129   a  and  129   b  as illustrated in  FIGS. 11C and 11D . When the second shutter  129  is divided into the segments  129   a  and  129   b , while the first shutter  119  in the center is closed, the segments  129   a  and  129   b  of the second shutter  129  may be operated such that one is open and the other is closed. As illustrated in  FIG. 5 , while the first shutter  119  is open, the segments  129   a  and  129   b  of the second shutter  129  may both be closed. 
         [0093]    Alternatively, referring to  FIG. 10D , the image sensor  140  may be divided into five segments  140   a ,  140   b ,  140   c ,  140   d , and  140   e . For example, the image sensor  140  may include the segments  140   a ,  140   b ,  140   c ,  140   d , and  140   e  at the top, the bottom, the right, the left, and the center. In this case, the image pickup apparatus may obtain not only stereo images by using the reflective optical system  120 , but also wide angle images by using the refractive optical system  110 . Therefore, as illustrated in  FIG. 11E , the first and second shutters  119  and  129  may both be horizontally divided into upper and lower segments  119   a ,  119   b ,  129   a , and  129   b . The segments  119   a  and  119   b  of the first shutter  119  and the segments  129   a  and  129   b  of the second shutter  129  may open in an opposite direction. For example, the upper segment  119   a  of the first shutter  119  and the lower segment  129   b  of the second shutter  129  may open simultaneously. Alternatively, the lower segment  119   b  of the first shutter  119  and the upper segment  129   a  of the second shutter  129  may open simultaneously. Although  FIG. 11E  illustrates that the first and second shutters  119  and  129  are both horizontally divided, the present embodiment is not limited thereto, and the first and second shutters  119  and  129  may be vertically divided. 
       First Embodiment 
       [0094]    The dual focus lens  100  having the structure illustrated in  FIG. 1  is manufactured according to a first embodiment.  FIG. 12  is a table of specific optical data of the refractive optical system  110  of the dual focus lens  100 , according to the first embodiment. In  FIG. 12 , surfaces S 0  and S 1  indicate both surfaces of the first shutter  119 . Surfaces S 2  to S 12  are shown in  FIG. 6 . For example, the surfaces S 2  and S 3  indicate both surfaces of the first refractive lens element  111 , the surfaces S 4  and S 5  indicate both surfaces of the second refractive lens element  112 , the surfaces S 6  and S 7  respectively indicate the first light incident region  125  and the light emission region  127 , the surfaces S 8  and S 9  indicate both surfaces of the common lens element  130 , the surfaces S 10  and S 11  indicate both surfaces of the cover layer  141 , and the surface S 12  indicate a surface of the image sensor  140 . 
         [0095]    As shown in  FIG. 12 , the first refractive lens element  111  is a meniscus lens having a negative refractive power that includes a concave surface facing the object side and a convex surface facing the image side. The second refractive lens element  112  is a biconvex lens. The first light incident region  125  and the light emission region  127  both have concave surfaces. Also, the common lens element  130  is a meniscus lens having a negative refractive power that includes a concave surface facing the object side and a convex surface facing the image side. 
         [0096]    The surfaces S 2  to S 9  are aspheric surfaces.  FIG. 13  is a table of aspheric coefficients of the aspheric surfaces of the refractive optical system  110  of the dual focus lens  100  according to the first embodiment. The aspheric coefficients may satisfy Equation 1. 
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         [0097]    In the refractive optical system  110  of the dual focus lens  100  according to the first embodiment, an effective focus length (EFL) is 5.967 mm, and an entrance pupil diameter (EPD) is 0.88 mm, and an f-number is 6.7. 
         [0098]      FIG. 14  is a table of specific optical data of the reflective optical system  120  of the dual focus lens  100 , according to the first embodiment. In  FIG. 14 , surfaces S 20  and S 21  indicate both surfaces of the second shutter  129 . Surfaces S 22  to S 25  and surfaces S 6  to S 12  are shown in  FIG. 8 . For example, the surface S 22  indicates the second light incident region  126 , and the surfaces S 23  to S 25  respectively indicate the first to third reflection surfaces  121 ,  122 , and  123 . The surfaces S 6  to S 12  are common surfaces of the refractive and reflective optical systems  110  and  120 . The fourth reflection surface  124  is formed on the surface S 6 . As shown in  FIG. 14 , the surfaces S 23  to S 25  and the surfaces S 6  to S 9  are aspheric surfaces.  FIG. 15  is a table of aspheric coefficients of the aspheric surfaces of the reflective optical system  120  of the dual focus lens  100  according to the first embodiment. Since the aspheric coefficients of the surfaces S 6  to S 9  are already shown in  FIG. 13 , detailed description thereof will be omitted. 
         [0099]    As shown in  FIG. 14 , the transparent substrate  128  and the common lens element  130  may be formed of different materials so as to suppress chromatic aberration of the dual focus lens  100 . In  FIG. 14 , the transparent substrate  128  is formed by using PMMA, and the common lens element  130  is formed by using glass having a refractive index of 1.744992, and dispersive power of 42.404%. 
         [0100]      FIG. 16  is a table of effective external and internal diameters of the second light incident region  126  and the first to third reflection surfaces  121  to  123  of the reflective optical system  120  of the dual focus lens  100 , according to the first embodiment. The effective external and internal diameters shown in the table of  FIG. 16  are determined with respect to a distance from the optical axis OX. The values of  FIG. 16  are shown in “mm.” 
         [0101]    In the reflective optical system  120  of the dual focus lens  100  according to the first embodiment, an EFL is 27.65 mm, an EPD is 10.64 mm, and an f-number is 2.6. 
       Second Embodiment 
       [0102]      FIG. 17  is a schematic cross-sectional view of a dual focus lens  300 , according to a second embodiment. The dual focus lens  300  according to the second embodiment includes the refractive optical system  110  having a first focal length, the reflective optical system  120  having a second focal length that is different from the first focal length, and first to third common lens elements  131 ,  132 , and  133 . Difference between the first and second embodiments is in that the dual focus lens  300  according to the second embodiment includes the first to third common lens elements  131 ,  132 , and  133 , and image planes of the refractive and reflective optical systems  110  and  120  are the same. 
         [0103]      FIG. 18  is a cross-sectional view of the refractive optical system  110  of the dual focus lens  300 , according to the second embodiment.  FIG. 19  is a table of specific optical data of the refractive optical system  110  of the dual focus lens  300 , according to the second embodiment. In the table of  FIG. 19 , surfaces S 0  and S 1  indicate both surfaces of the first shutter  119 . Surfaces S 2  to S 15  are shown in  FIG. 18 . For example, the surfaces S 2  and S 3  indicate both surfaces of the first refractive lens element  111 , the surface S 4  and S 5  indicate both surfaces of the second refractive lens element  112 , the surfaces S 6  and S 7  respectively indicate the first light incident region  125  and the light emission region  127 , the surfaces S 8  and S 9  indicate both surfaces of the first common lens element  131 , the surfaces S 10  and S 11  indicate both surfaces of the second common lens element  132 , the surfaces S 12  and S 13  indicate both surfaces of the third common lens element  133 , and the surfaces S 14  and S 15  indicate both surfaces of the cover layer  141 . 
         [0104]    As shown in  FIG. 19 , the first refractive lens element  111  is a meniscus lens having a negative refractive power that includes a convex surface facing the object side and a concave surface facing the image side. The second refractive lens element  112  is a biconvex lens. The first light incident region  125  and the light emission region  127  both have concave surfaces. The first and second common lens elements  131  and  132  are meniscus lenses having a positive refractive power that includes a concave surface facing the object side and a convex surface facing the image side. Also, the third common lens element  133  is a meniscus lens having a negative refractive power that includes a concave surface facing the object side and a convex surface facing the image side. 
         [0105]    The surfaces S 2  to S 13  are aspheric surfaces.  FIG. 20  is a table of aspheric coefficients of the aspheric surfaces of the refractive optical system  110  of the dual focus lens  300 , according to the second embodiment. The aspheric coefficients may satisfy Equation 1. 
         [0106]    In the refractive optical system  110  of the dual focus lens  300  according to the second embodiment, an EFL is 8 mm, an EPD is 2.3 mm, and an f-number is 3.4. 
         [0107]      FIG. 21  is a cross-sectional view of the reflective optical system  120  of the dual focus lens  300 , according to the second embodiment.  FIG. 22  is a table of specific optical data of the reflective optical system  120  of the dual focus lens  300 , according to the second embodiment. In the table of  FIG. 22 , surfaces S 20  and S 21  indicate both surfaces of the second shutter  129 . Surfaces S 22  to S 25  and surfaces S 6  to S 15  are shown in  FIG. 21 . For example, the surface S 22  indicates the second light incident region  126 , and the surfaces S 23  to S 25  respectively indicate the first to third reflection surfaces  121 ,  122 , and  123 . The surfaces S 6  to S 15  are common surfaces of the refractive and reflective optical systems  110  and  120 . The fourth reflection surface  124  is formed on the surface S 6 . As shown in  FIG. 22 , the surfaces S 23  to S 25  and the surfaces S 6  to S 13  are aspheric surfaces.  FIG. 23  is a table of aspheric coefficients of the aspheric surfaces of the reflective optical system  120  of the dual focus lens  300  according to the second embodiment. Since the aspheric coefficients of the surfaces S 6  to S 13  are already shown in  FIG. 20 , detailed description thereof will be omitted. 
         [0108]    As shown in  FIGS. 19 and 22 , the first and second refractive lens elements  111  and  112 , the transparent substrate  128 , and the first to third common lens elements  131 ,  132 , and  133  may be formed of different materials so as to suppress chromatic aberration of the dual focus lens  300 . In  FIGS. 19 and 22 , the first refractive lens element  111  is formed by using a glass material having a refractive index of 1.65 and a dispersive power of 33.44%, the second refractive lens element  112  is formed by using a glass material having a refractive index of 1.67 and a dispersive power of 52.27%, the transparent substrate  128  is formed by using PMMA, the first and third common lens elements  131  and  133  are formed by using polycarbonate (PC), and the second common lens element  132  is formed by using PMMA. However, the present embodiment is not limited to the description above, and various materials may be used according to the designs of the dual focus lens  300 . 
         [0109]      FIG. 24  is a table of effective external and internal diameters of the first to third reflection surfaces  121 ,  122 , and  123  of the reflective optical system  120  of the dual focus lens  300 , according to the second embodiment. The values of  FIG. 24  are shown in “mm.” 
         [0110]    In the reflective optical system  120  of the dual focus lens  300  according to the second embodiment, an EFL is 25.2 mm, an EPD is 22 mm, and an f-number is 1.1. 
         [0111]    In general, the image pickup apparatus may use an illumination light to photograph in dark places or estimate distance. However, using the illumination light may increase a volume of the image pickup apparatus. Since there is a space between the refractive optical system  110  and the reflective optical systems  120  and  150  in the dual focus lenses  100 ,  200 , and  300  according to the above-described embodiments, it is possible to save an internal space of the image pickup apparatus by arranging a light source in the space between the refractive optical system  110  and the reflective optical systems  120  and  150 . 
         [0112]      FIG. 25  is a schematic cross-sectional view of a dual focus lens  300 ′ and an image pickup apparatus including the dual focus lens, according to another embodiment. Referring to  FIG. 25 , the dual focus lens  300 ′ may additionally include a light source  160  that is located in a space between the refractive and reflective optical systems  110  and  120  in a direction perpendicular to the optical axis OX in which the space surrounds the refractive optical system  110 . The light source  160  may be, for example, a light-emitting diode (LED). The light source  160  may be a linear light source that is formed in a ring shape and located having the optical axis OX in the center. Alternatively, one or more light sources  160  may be located around a circumference of the refractive optical system  110 .  FIG. 25  illustrates an example in which the light source  160  is located in the dual focus lens  300  of  FIG. 17 . However, the present embodiment is not limited thereto, and the light source  160  may be located around the refractive optical system  110  of the dual focus lenses  100  and  200  respectively illustrated in  FIGS. 1 and 9 . 
         [0113]    Since the reflective optical system  120  has a long focal length, the reflective optical system  120  may be sensitive to vibrations. In order to compensate the vibrations, at least one of the common lens elements  131 ,  132 , and  133 , which are located between the reflective optical system  120  and the image sensor  140 , or the image sensor  140  may be driven in a direction perpendicular to the optical axis OX. For example, any one of the common lens elements  131 ,  132 , and  133 , or all of the common lens elements  131 ,  132 , and  133 , or the image sensor  140  may be driven in a direction perpendicular to the optical axis OX to compensate the vibrations. The common lens element  130  illustrated in  FIGS. 1 and 9  may also be driven in the direction perpendicular to the optical axis OX. 
         [0114]    When a location of an object is changed (i.e., when a distance between the object and the image pickup apparatus is changed), at least one of the common lens elements  131 ,  132 , and  133 , or the image sensor  140  may be driven in a direction of the optical axis OX so as to control focus. For example, in order to accurately form an image of the object in the image sensor  140 , any one of the common lens elements  131 ,  132 , and  133  or all of the common lens elements  131 ,  132 , and  133  may be driven in the direction of the optical axis OX. Alternatively, the image sensor  140  may be driven in the direction of the optical axis OX. The common lens element  130  illustrated in  FIGS. 1 and 9  may also be driven in the direction of the optical axis OX. 
         [0115]    It is possible to integrate mechanisms for moving the common lens elements  130 ,  131 ,  132 , and  133  or the image sensor  140  in the direction of the optical axis OX or the direction perpendicular to the optical axis OX. In other words, the common lens elements  130 ,  131 ,  132 , and  133  or the image sensor  140  may all be designed such that they move to the direction of the optical axis OX or the direction perpendicular to the optical axis OX. 
         [0116]    So far, the refractive optical system  110  and the reflective optical systems  120  and  150  of the dual focus lenses  100 ,  200 ,  300 , and  300 ′ are described as having a fixed magnification. However, depending on the design, any one or all of the refractive optical system  110  and the reflective optical systems  120  and  150  may be configured to perform a zoom function with variable magnification. For example, the refractive optical system  110  may be designed such that the first and second lens elements  111  and  112  are used to perform a zoom function, or such that the common lens elements  130 ,  131 ,  132 , and  133  and the first and second refractive lens elements  111  and  112  of the refractive optical system  110  are used together to perform the zoom function. Also, the refractive optical system  110  may include additional lens elements other than the lens elements  111  and  112  to perform the zoom function. 
         [0117]    The reflective optical system  120  of  FIGS. 1 and 17  may be configured such that distances between the first to fourth reflection surfaces  121  to  124  are variable, or designed such that the distances between the first to fourth reflection surfaces  121  to  124  are variable and the first to third common lens elements  131 ,  132 , and  133  are used to perform the zoom function. The reflective optical system  150  of  FIG. 9  may be configured such that at least one selected from the first to fourth reflection surfaces  151  to  154  is a deformable mirror. The deformable mirror is a mirror having a variable curvature so that a focal length may be changed, and may be modified into various forms by mechanical or electrical manipulation. For example, the deformable mirror may include a flexible reflection surface formed of a flexible material, and a plurality of electrical or mechanical fine actuators that are 2-dimensionally arrayed to locally push or pull the flexible reflection surface and thus modify a form thereof. Also, the first to fourth reflection surfaces  121  to  124  of the reflective optical system  120  of  FIGS. 1 and 17  may be deformable mirrors. 
         [0118]    A digital zoom function may be implemented by using two images obtained from the refractive optical system  110  and the reflective optical systems  120  and  150  of the dual focus lenses  100 ,  200 ,  300 , and  300 ′. In other words, if respective magnifications between a wide angle position of the refractive optical system  110  and telephoto positions of the reflective optical systems  120  and  150  are obtained by digitally zooming using an image signal processor (not shown) of the image pickup apparatus, it is possible to continuously zoom from the wide angle position to the telephoto position.  FIGS. 26 and 27  are conceptual views describing a principle of a digital zoom function by using two images obtained from the refractive optical system  110  and the reflective optical systems  120  and  150  of the dual focus lenses  100 ,  200 ,  300 , and  300 ′. 
         [0119]    Referring to  FIG. 26 , it is supposed that the refractive optical system  110  forms, for example, a 1× zoom image  11 , and the reflective optical systems  120  and  150  form, for example, a 5× zoom image  15 . A 2× zoom image  12  may be obtained by cropping and then digitally magnifying a central portion of the 1× zoom image  11  obtained from the refractive optical system  110 . If only the central portion of the 1× zoom image  11  is magnified, an overall image quality of the 2× zoom image  12  may decrease. Therefore, the 5× zoom image  15  obtained from the reflective optical systems  120  and  150  is reduced, and a viewing angle area corresponding to a central portion  12   a  of the 2× zoom image  12  is replaced with a reduced version of the 5× zoom image  15 . As a result, the central portion  12   a  of the 2× zoom image  12  may be obtained by reducing the 5× zoom image  15  and a surrounding portion  12   b  may be obtained by magnifying the 1× zoom image  11 . Then, since at least an image quality of the central portion  12   a  of the 2× zoom image  12  did not decrease, the digital zoom function may be implemented according to the present embodiment while reducing image quality deterioration. 
         [0120]    According to this method, as illustrated in  FIG. 27 , a 3× zoom image  13  or a 4× zoom image  14  may be obtained by combining an image obtained by cropping and magnifying the central portion of the 1× zoom image  11  obtained from the refractive optical system  110 , and an image obtained by shrinking the 5× zoom image  15  obtained from the reflective optical systems  120  and  150 . Alternatively, in addition to zoom images obtained by zooming according to integer multiples, i.e., 2×, 3×, and 4×, it is possible to form a zoom image at any magnification. Also, a central portion of the 5× zoom image  15  may be cropped and magnified to obtain a zoom image of greater than a 5× zoom level. A 10× zoom image that is obtained by digitally zooming using a general image pickup apparatus may have a very low image quality. However, according to the present embodiment, since the 5× zoom image  15  is magnified, the quality of the 10× zoom image is not greatly decreased. Also, an overall clarity of the 1× zoom image  11  may be improved by replacing the central portion of the 1× zoom image  11  which corresponds to a viewing angle of the 5× zoom image  15  with the 5× zoom image  15 , or by correcting the 1× zoom image  11  with reference to the 5× zoom image  15 . 
         [0121]    There are a few aspects to regard when synthesizing the 1× zoom image  11  and the 5× zoom image  15 . For example, since the refractive optical system  110  and the reflective optical systems  120  and  150  have different optical properties, e.g., aberration and brightness, the 1× zoom image  11  and the 5× zoom image  15  may have different degrees of distortion, aberration, and brightness. Accordingly, a central portion and a surrounding portion of a synthesized image may have different degrees of distortion, aberration, and brightness. Also, since the 1× zoom image  11  is magnified and the 5× zoom image  15  is reduced, the respective resolutions of the central portion and the surrounding portion of the synthesized image may be different from each other. Therefore, image processing may be performed such that the central portion and the surrounding portion of the synthesized image are smoothly connected to each other. 
         [0122]    In performing the above image processing, based on information regarding degrees of distortion, aberration, brightness, and resolution of the 1× zoom image  11  and the 5× zoom image  15  which are obtained from the optical properties of the refractive optical system  110  and the reflective optical systems  120  and  150 , an image to be synthesized may be corrected by using interpolation methods so that a central portion and a surrounding portion of the image to be synthesized may be smoothly corrected. For example, in order to obtain the 2× zoom image  12  by synthesizing the 1× zoom image  11  and the 5× zoom image  15 , first, a brightness ratio between a central portion and a surrounding portion of the 1× zoom image  11  and a brightness ratio between a central portion and a surrounding portion of the 5× zoom image  15  are calculated. Next, a brightness ratio between a central portion and a surrounding portion of the 2× zoom image  12  is determined with reference to the two brightness ratios of the 1× zoom image  11  and the 5× zoom image  15 . Then, when generating the 2× zoom image  12  by synthesizing, image processing may be performed such that a brightness of the reduced 5× zoom image  15  that is to be located in the central portion of the 2× zoom image  12  and a brightness of the cropped and magnified 1× zoom image  11  that is to be located in the surrounding portion of the 2× zoom image  12  is equal to the determined brightness ratio. The image processing may also be performed with respect to a degree of distortion, aberration, and resolution of the image to be synthesized by following methods similar to the above-described method. 
         [0123]    It should be understood that the embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. While one or more embodiments of the present invention have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.