Patent Publication Number: US-8967803-B2

Title: Image capturing apparatus and auto-focusing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 101125132, filed on Jul. 12, 2012. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to an image capturing apparatus and an auto-focusing method of the image capturing apparatus. More particularly, the invention relates to an image capturing apparatus applied for fundus examination and an auto-focusing method of the image capturing apparatus. 
     2. Background 
     The saying goes that human eyes are the window to the soul, and thus eye health is vital to human beings. The blood vessels may be directly seen from observing the fundus of an eye, such that the fundus examination may be performed periodically to track and inspect systematic disease, especially blood vessel lesions (e.g., diabetic retinopathy). Common ocular inspection apparatuses include pneumatonometers, refracting instruments, fundus cameras, and so on. Here, the fundus camera is an image capturing apparatus for capturing an image of the fundus of an eye, so as to facilitate diagnosis of ocular lesions. 
     A conventional image capturing apparatus for fundus examination is required to be able to adjust an imaging focal distance to the fundus of an eye in compliance with curvatures of different eye surfaces to be tested, and thereby the clear fundus image can be captured. For instance, according to the related art, light beams generated by two rectangular illuminating slits are refracted to an image sensor to be detected. The light beams enter a crystalline lens of an eye in parallel, and the light beams are refracted and focused on locations around the retina of the fundus. After the locations of two light points obtained by refracting the light beams back to the image sensor are calculated, the location of the focal point may be acquired for moving the lens and focusing on the retina of the fundus. 
     However, according to the related art, the image sensor need be aligned to the pupil manually, and the image sensor can focus on the fundus of an eye after the pupil is already aligned to the image sensor. The manual alignment of the image sensor to the pupil during the fundus examination is inconvenient and consumes significant time. 
     SUMMARY OF THE INVENTION 
     The invention is directed to an auto-focusing method of an image capturing apparatus. The auto-focusing method allows an image capturing apparatus to focus on a cornea and simultaneously obtain a distance from a fundus to the cornea, so as to reduce the time spent on focusing on the fundus. 
     The invention is further directed to an image capturing apparatus that is able to focus on the cornea and simultaneously obtain the distance from the fundus to the cornea, so as to reduce the time spent on focusing on the fundus. 
     In an embodiment of the invention, an auto-focusing method of an image capturing apparatus is provided. The auto-focusing method includes following steps. A plurality of light beams is transmitted from a plurality of light sources to an eye. The eye includes a cornea, a pupil, a crystalline lens, and a fundus. The light beams are transmitted to the fundus through the cornea. A plurality of first light point images on the cornea are detected by an image sensor through a lens module. Here, the first light point images are generated by transmitting the light beams to the cornea, and the lens module has a first lens and a second lens. According to the first light point images and focal adjustment data, the light sources and the first lens are moved simultaneously to focus on the cornea. A plurality of second light point images on the fundus are detected by the image sensor through the lens module. Here, the second light point images are generated by substantially intersecting the light beams at the pupil and transmitting the light beams to the fundus. According to the second light point images and the focal adjustment data, the first lens of the lens module is moved to focus on the fundus. 
     According to an embodiment of the invention, the step of moving the first lens of the lens module according to the first light point images and the focal adjustment data to focus on the cornea includes calculating a first set of location data of the first light point images. A first displacement corresponding to the first set of location data is obtained from the focal adjustment data according to the first set of location data. The first lens and the light sources are adjusted according to the first displacement. 
     According to an embodiment of the invention, the auto-focusing method of the image capturing apparatus further includes following steps. A cornea image of the cornea is detected, and a reflection difference of the cornea image is obtained according to distribution of the cornea image. The first lens is adjusted according to the reflection difference and correction data, and the reflection difference is obtained every other time sequence according to the distribution of the cornea image. 
     According to an embodiment of the invention, the step of detecting the second light point images on the fundus by the image sensor through the lens module includes obtaining a distance from the cornea to the fundus according to the second light point images and the focal adjustment data. 
     According to an embodiment of the invention, the step of detecting the second light point images on the fundus by the image sensor through the lens module further includes calculating a second set of location data of the second light point images. A second displacement corresponding to the second set of location data is obtained from the focal adjustment data according to the second set of location data. The first lens is adjusted according to the second displacement. 
     According to an embodiment of the invention, the auto-focusing method further includes detecting the first light point images by the image sensor through the first lens and detecting the second light point images by the image sensor through the first lens. 
     In an embodiment of the invention, an image capturing apparatus that includes a plurality of light sources, an image sensor, a lens module, and a control unit is provided. The light sources transmit a plurality of light beams to an eye. Here, the eye includes a cornea, a pupil, a crystalline lens, and a fundus, and the light beams are transmitted to the fundus through the cornea. The lens module is disposed between the light sources and the image sensor and has a first lens and a second lens. The control unit is coupled to the image sensor and the lens module. The image sensor detects a plurality of first light point images on the cornea through a lens module, and the first light point images are generated by transmitting the light beams to the cornea. The control unit simultaneously moves the light sources and the first lens according to the first light point images and focal adjustment data, such that the image sensor focuses on the cornea. The image sensor detects a plurality of second light point images on the fundus through the lens module, and the second light point images are generated by substantially intersecting the light beams at the pupil and transmitting the light beams to the fundus. The control unit moves the first lens of the lens module according to the second light point images and the focal adjustment data, such that the image sensor focuses on the fundus. 
     According to an embodiment of the invention, the control unit calculates a first set of location data of the first light point images, obtains a first displacement corresponding to the first set of location data from the focal adjustment data according to the first set of location data, and adjusts the first lens and the light sources according to the first displacement. 
     According to an embodiment of the invention, the image sensor detects a cornea image of the cornea, and the control unit obtains a reflection difference of the cornea image according to distribution of the cornea image and adjusts the first lens according to the reflection difference and correction data. 
     According to an embodiment of the invention, the image capturing apparatus further includes a time sequence control unit coupled to the control unit, and the time sequence control unit informs the control unit every other time sequence to obtain the reflection difference of the cornea image according to the distribution of the cornea image. 
     According to an embodiment of the invention, the control unit obtains a distance from the cornea to the fundus according to the second light point images and the focal adjustment data. 
     According to an embodiment of the invention, the control unit calculates a second set of location data of the second light point images, obtains a second displacement corresponding to the second set of location data from the focal adjustment data according to the second set of location data, and adjusts the first lens according to the second displacement. 
     According to an embodiment of the invention, the image sensor detects the first light point images and the second light point images through the first lens. 
     In view of the above, the image capturing apparatus may focus on the cornea by detecting the first light point images that are obtained by transmitting the light beams to the cornea and may then focus on the fundus by detecting the second light point images transmitted to the fundus. Thereby, when the image capturing apparatus completely focuses on the cornea, the image capturing apparatus may also obtain the distance from the fundus to the cornea through moving the lens to acquire the location data of the second light point images, and the image capturing apparatus then completely focuses on the fundus. As a result, by applying the image capturing apparatus described herein, the time spent on focusing on the fundus may be reduced. 
     Several exemplary embodiments accompanied with figures are described in detail below to further explain the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments and, together with the description, serve to explain the principles of the disclosure. 
         FIG. 1  is a block diagram illustrating an image capturing apparatus according to an embodiment of the invention. 
         FIG. 2  is a flow chart illustrating an auto-focusing method of an image capturing apparatus according to an embodiment of the invention. 
         FIG. 3A ,  FIG. 3C , and  FIG. 3E  are block diagrams illustrating an image capturing apparatus that detects first light point images according to an embodiment of the invention. 
         FIG. 3B  is a schematic diagram illustrating distribution of the first light point images correspondingly depicted in  FIG. 3A . 
         FIG. 3D  is a schematic diagram illustrating distribution of the first light point images correspondingly depicted in  FIG. 3C . 
         FIG. 3F  is a schematic diagram illustrating distribution of the first light point images correspondingly depicted in  FIG. 3E . 
         FIG. 4A  to  FIG. 4C  are schematic views illustrating tracking of a cornea image according to an embodiment of the invention. 
         FIG. 5A  to  FIG. 5C  are schematic views illustrating detection of a fundus image according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED EXEMPLARY EMBODIMENTS 
     During fundus examination, if the apparatus used for the examination may rapidly focus on the cornea and the fundus of an eye in response to various curvatures of different eye surfaces and may further capture clear images on the fundus, the efficiency of fundus examination may be ameliorated. Accordingly, the invention is directed to an image capturing apparatus and an auto-focusing method of the image capturing apparatus. In order to make the invention more comprehensible, embodiments are described below as examples to demonstrate that the invention can actually be implemented. 
       FIG. 1  is a block diagram illustrating an image capturing apparatus according to an embodiment of the invention. The image capturing apparatus  100  described in the present embodiment is a fundus camera or any other optometry instruments. With reference to  FIG. 1 , the image capturing apparatus  100  includes a plurality of light sources  110 ,  120 , and  130 , a lens module  140 , an image sensor  150 , and a control unit  160 . According to the present embodiment, the image capturing apparatus  100  serves to detect an eye  200  that has a cornea  210 , a pupil  220 , a crystalline lens  202 , and a fundus  230 . The fundus  230  has a retina, optic nerves, a choroid, and other tissues (not shown). 
     Specifically, the light sources  110 ,  120 , and  130  emit a plurality of light beams L 1 , L 2 , and L 3  that are transmitted to the fundus  230  through the cornea  210 . In the present embodiment, the light sources  110 ,  120 , and  130  are invisible light sources (e.g., far infrared light sources), and the light beams L 1 , L 2 , and L 3  are invisible light beams (e.g., far infrared light beams). Besides, the light sources  110 ,  120 , and  130  described in the present embodiment may provide the light beams characterized by favorable rectilinearity. Particularly, the light beam L 1  is substantially transmitted along a direction V 1 , the light beam L 2  is substantially transmitted along a direction V 2 , and the light beam L 3  is substantially transmitted along a direction V 3 . The directions V 1 , V 2 , and V 3  are not parallel to one another. In the present embodiment, each light source  110 ,  120 , and  130  may respectively emit the light beams L 1 , L 2 , and L 3  at fixed projection angles, such that the light beams L 1 , L 2 , and L 3  are intersected at an intersection point G, and a focusing distance D 1  from a center location Go of each light source  110 ,  120 , and  130  to the intersection point G may be determined. In other embodiments, the projection angles at which the light sources  110 ,  120 , and  130  emit the light beams L 1 , L 2 , and L 3  may be adjusted according to the images captured by the image capturing apparatus  100 , and thereby the location of the intersection point G of the light beams L 1 , L 2 , and L 3  may be controlled. To better illustrate the invention, only three light sources are shown in  FIG. 1 . However, the number of the light sources is not limited in the present embodiment. A person having ordinary skill in the art may change the number of the light sources in the image capturing apparatus  100  based on actual design demands with reference to the teachings of the present embodiment. 
     The lens module  140  is configured between the image sensor  150  and the light sources  110 ,  120 , and  130 . Here, the lens module  140  has a first lens  142  and a second lens  144 , and the second lens  144  represents a combination of basic lenses. In the present embodiment, the first lens  142  of the lens module  140  may be coupled to or separated from the fixing base (not shown) of each light source  110 ,  120 , and  130 , such that the first lens  142  may be moved together or not together with the light sources  110 ,  120 , and  130 . In particular, when the light sources  110 ,  120 , and  130  emit the light beams L 1 , L 2 , and L 3  at the fixed angles, the first lens  142  may be moved back and forth on a light axis C together with the light sources  110 ,  120 , and  130 , such that the intersection point G of the light beams L 1 , L 2 , and L 3  is located at the pupil  220  of the eye  200 . Thereby, the image sensor  150  may focus on the cornea  210 , and a cornea image may be clearly displayed on the image sensor  150 . After the image sensor  150  completely focuses on the cornea  210 , the arrangement of the first lens  142  will no longer be subject to the light sources  110 ,  120 , and  130 . Namely, the first lens  142  is separated from the fixing base of each light source  110 ,  120 , and  130 , and the first lens  142  may be moved back and forth or rotated on the light axis C, such that the image sensor  150  may further focus on the fundus  230 . The collaborative configurations of the first lens  142 , the second lens  144 , and the light sources  110 ,  120 , and  130  allow the image capturing apparatus  100  to focus on the fundus  230  in an expedited manner, and the clarity of the captured fundus image may be enhanced. 
     The sensing region of the image sensor  150  may have an imaging surface (not shown). The cornea image on the cornea  210  and the fundus image on the fundus  230  may be imaged on the imaging surface of the image sensor  150  through the lens module  140 . The image sensor  150  described in the present embodiment is, for instance, a charge coupled device (CCD), a complementary metal-oxide semiconductor (CMOS) device, a photo-sensing film, and so on. 
     The control unit  160  is coupled to the image sensor  150 , the first lens  142 , and the second lens  144 . In the present embodiment, the control unit  160  controls the arrangement of the first lens  142  and the light sources  110 ,  120 , and  130  on the light axis C according to the image of the eye  200  detected by the image sensor  150  and focal adjustment data, such that the image sensor  150  focuses on the cornea  210 . Besides, the control unit  160  controls the arrangement of the first lens  142  on the light axis C, such that the image sensor  150  focuses on the fundus  230 . 
     The auto-focusing method of the image capturing apparatus is described below in view of the aforesaid image capturing apparatus  100  and the eye  200 .  FIG. 2  is a flow chart illustrating an auto-focusing method of an image capturing apparatus according to an embodiment of the invention. The auto-focusing method described in the present embodiment is suitable for detecting the eye  200  through the image capturing apparatus  100 . 
     With reference to  FIG. 1  and  FIG. 2 , in step S 201 , the light sources  110 ,  120 , and  130  emit the light beams L 1 , L 2 , and L 3  to the eye  200 . Here, the light beams L 1 , L 2 , and L 3  are transmitted to the fundus  230  through the cornea  210  of the eye  200 . In the present embodiment, the light sources  110 ,  120 , and  130  may be arranged in a triangular manner and may emit the light beams L 1 , L 2 , and L 3  that are not parallel to one another. 
     In step S 203 , the image sensor  150  detects a plurality of first light point images on the cornea  210  through the lens module  140 . Here, the first light point images are generated by transmitting the light beams L 1 , L 2 , and L 3  to the cornea  210 . The image sensor  150  may also detect the first light point images directly through the first lens  142  and the second lens  144  of the lens module  140 . 
     Particularly,  FIG. 3A ,  FIG. 3C , and  FIG. 3E  are block diagrams illustrating an image capturing apparatus that detects first light point images according to an embodiment of the invention.  FIG. 3B  is a schematic diagram illustrating distribution of the first light point images correspondingly depicted in  FIG. 3A .  FIG. 3D  is a schematic diagram illustrating distribution of the first light point images correspondingly depicted in  FIG. 3C .  FIG. 3F  is a schematic diagram illustrating distribution of the first light point images correspondingly depicted in  FIG. 3E . It is assumed herein that the non-parallel light beams L 1 , L 2 , and L 3  emitted from the light sources  110 ,  120 , and  130  are distributed in a regular-triangular manner and transmitted toward the eye  200  before the light beams L 1 , L 2 , and L 3  are intersected. With reference to  FIG. 3A  and  FIG. 3B , when the light beams L 1 , L 2 , and L 3  detected by the image sensor  150  through the lens module  140  are intersected at a intersection point P 1  between the cornea  210  and the light sources  110 ,  120 , and  140  (i.e., in front of the cornea  210 ), the distribution of the first light point images  212 ,  214 , and  216  which are transmitted to the cornea  210  and detected by the image sensor  150  is shaped as a regular triangle T 1 , and the images  52 ,  54 , and  56  located on the imaging surface of the image sensor  150  respectively correspond to the first light point images  212 ,  214 , and  216 . With reference to  FIG. 3C  and  FIG. 3D , when the light beams L 1 , L 2 , and L 3  detected by the image sensor  150  through the lens module  140  are intersected at a intersection point P 2  between the cornea  210  and the fundus  230  (i.e., on back of the cornea  210 ), the distribution of the first light point images  210 ′,  212 ′, and  214 ′ which are transmitted to the cornea  210  and detected by the image sensor  150  is shaped as an inverted triangle T 2 , and the images  52 ′,  54 ′, and  56 ′ located on the imaging surface of the image sensor  150  respectively correspond to the first light point images  212 ′,  214 ′, and  216 ′. Note that each first light point image described above has a nearly circular shape, and the area and the shape of the first light point images are not limited in the present embodiment. 
     With reference to  FIG. 1  and  FIG. 2 , in step S 205 , the control unit  160  moves the first lens  142  according to the first light point images and focal adjustment data, so as to focus on the cornea  210 . In particular, to allow the light beams L 1 , L 2 , and L 3  to be intersected at the cornea  210  and enter the eye  200 , the control unit  160  calculates a first set of location data of the first light point images. According to the first set of location data, the control unit  160  may obtain a first displacement corresponding to the first set of location data from the focal adjustment data. Here, the focal adjustment data are, for instance, stored in a storage apparatus (not shown) coupled to the control unit  160 . To be specific, the first light point images detected by the image sensor  150  through the lens module  140  may be distributed in a different manner by simultaneously adjusting the light sources  110 ,  120  and  130  and the first lens  142 , and therefore the focal adjustment data may include parameters required by the image sensor  150  for focusing on the cornea  210 . For instance, the focal adjustment data includes a plurality of differences between the predetermined location data O 1  and different first sets of location data as well as the first displacements of the first lens  142  (i.e., the moving distance of the first lens  142  on the light axis C) corresponding to the differences. That is, when the light sources  110 ,  120 , and  130  respectively emit the light beams L 1 , L 2 , and L 3  at the fixed angles, the control unit  160  adjusts the first lens  142  according to the first displacement. At the same time, the light sources  110 ,  120 , and  130  and the first lens  142  are simultaneously moved on the light axis C, and the light beams L 1 , L 2 , and L 3  are then intersected at the pupil  220  and transmitted to the fundus  230 , such that the image sensor  150  may focus on the cornea  210 . Certainly, in other embodiments, when the projection angles at which the light sources  110 ,  120 , and  130  respectively emit the light beams L 1 , L 2 , and L 3  are adjustable, the control unit  160  may also adjust the projection angle of each light source  110 ,  120 , and  130  according to the first displacement, and the light beams L 1 , L 2 , and L 3  are then intersected at the pupil  220  and transmitted to the fundus  230 . Thereby, the image sensor  150  may still focus on the cornea  210 . 
     In particular, as illustrated in  FIG. 3A  and  FIG. 3B , the distribution of the first light point images  212 ,  214 , and  216  detected by the image sensor  150  is shaped as a regular triangle T 1 . Here, the control unit  160  calculates a first set of location data R 1  of the first light point images  212 ,  214 , and  216 , and the control unit  160  may, based on the first set of location data R 1 , calculate distance and vector difference among the first light point images  212 ,  214 , and  216 . In addition, the control unit  160  obtains a first displacement X 1  corresponding to the first set of location data R 1  from the focal adjustment data and adjusts the first lens  142  according to the first displacement X 1 . As shown in  FIG. 3E  and  FIG. 3F , the image sensor  150  detects the first light point images  212 ″,  214 ″, and  216 ″ that are intersected at the pupil  220 , i.e., the first light point images  212 ″,  214 ″, and  216 ″ are overlapped. Here, the light beams L 1 , L 2 , and L 3  are intersected at the pupil  220  and enter the eye  200 , and the images  52 ″,  54 ″, and  56 ″ located on an imaging surface of the image sensor  150  respectively correspond to the first light point images  212 ″,  214 ″, and  216 ″. 
     From another perspective, as illustrated in  FIG. 3C  and  FIG. 3D , the distribution of the first light point images  212 ′,  214 ′, and  216 ′ detected by the image sensor  150  is shaped as an inverted triangle T 2 . Likewise, the control unit  160  calculates a first set of location data R 1 ′ of the first light point images  212 ′,  214 ′, and  216 ′, and the control unit  160  may, based on the first set of location data R 1 ′, calculate distance and vector difference among the first light point images  212 ′,  214 ′, and  216 ′. In addition, the control unit  160  obtains a first displacement X 1 ′ corresponding to the first set of location data R 1 ′ from the focal adjustment data and adjusts the first lens  142  according to the first displacement X 1 ′. At this time, as illustrated in  FIG. 3E  and  FIG. 3F , the image sensor  150  detects the first light point images  212 ″,  214 ″, and  216 ″ that are intersected at the pupil  220  and overlapped with one another. 
     During the detection of the eye  200  by the image sensor  150 , the relative position of the eye  200  and the light axis C does not necessarily remain unchanged; therefore, in order for the image sensor  150  to keep the light beams L 1 , L 2 , and L 3  to be intersected at the pupil  220 , the control unit  160  may obtain a reflection difference of a cornea image according to distribution of the cornea image. Besides, the control unit  160  may adjust the first lens according to the reflection difference and correction data. Here, the correction data may include parameters respectively corresponding to various reflection differences; thereby, the control unit  160  may adjust the first lens  142  to track the cornea image, the light beams L 1 , L 2 , and L 3  detected by the image sensor  150  may be intersected at the pupil  220 , and thus the image sensor  150  may consistently focus on the cornea  210 . 
       FIG. 4A  to  FIG. 4C  are schematic views illustrating tracking of a cornea image according to an embodiment of the invention. Here,  FIG. 4A  shows an image captured by the image sensor  150  when the pupil  220  is shifted toward a first direction E 1 ;  FIG. 4B  shows an image captured by the image sensor  150  when the pupil  220  remains not shifted;  FIG. 4C  shows an image captured by the image sensor  150  when the pupil  220  is shifted toward a second direction E 2 . For the purpose of clear illustration, in  FIG. 4A  to  FIG. 4C , the cornea image captured by the image sensor  150  is divided into regions A and B by dotted lines S 1  and S 2 , and the region A and the region B are respectively located at two sides of the dotted lines S 1  and S 2 . 
     Specifically, after the image sensor  150  focuses on the cornea  210 , as illustrated in  FIG. 4B , the reflection of the cornea image  40  at the regions A and B is equal (e.g., the circular area  400  is equally distributed in the regions A and B). When the cornea  210  and the light axis C of the image sensor  150  are relatively moved, and the pupil  220  detected by the image sensor  150  is shifted toward the first direction E 1 , the reflection of the cornea image  42  (i.e., the circular area  420 ) is mainly located in the region A, as shown in  FIG. 4A . Hence, the control unit  160  obtains a reflection difference by calculating the difference in reflection at the regions A and B. The control unit  160  may further compare the reflection difference with correction data, so as to adjust the first lens  142  and further equalize the reflection at the regions A and B. When the eye  200  and the light axis C of the image sensor  150  are relatively moved, and the pupil  220  detected by the image sensor  150  is shifted toward the second direction E 2 , the reflection of the cornea image  44  (i.e., the circular area  440 ) is mainly located in the region B, as shown in  FIG. 4C . Similarly, the control unit  160  may obtain a reflection difference by calculating the difference in reflection at the regions A and B and compare the reflection difference with the correction data, so as to adjust the first lens  142  and further equalize the reflection at the regions A and B. As such, in case of external disturbance, the control unit  160  may timely adjust the first lens  142  by tracking the reflection difference of the cornea image. Thereby, the image sensor  150  may keep the light axis of the first lens  142  to be located at the center position of the pupil  220 . 
     The control unit  160  may be coupled to a time sequence control unit (not shown), and the time sequence control unit informs the control unit  160  every other time sequence to obtain the difference in reflection at the regions A and B, so as to obtain the reflection difference of the cornea image. Thereby, the control unit  160  may, according to the time sequence, examine whether the light beams L 1 , L 2 , and L 3  are constantly intersected at the pupil  220  and transmitted to the fundus  230 , such that the image sensor  150  may consistently focus on the cornea  210 . 
     In step S 207 , the image sensor  150  detects a plurality of second light point images on the fundus  230  through the lens module  140 . Here, the second light point images are generated by substantially intersecting the light beams L 1 , L 2 , and L 3  at the pupil  220  and transmitting the light beams L 1 , L 2 , and L 3  to the fundus  230 . Specifically, as shown in  FIG. 5A  to  FIG. 5C , the distances from the pupils  220  to the fundus  230  in different eyes  210  are different, and therefore the distribution of the second light point images detected by the image sensor  150  through the lens module  140  is different. 
     In step S 209 , the control unit  160  moves the first lens  142  according to the focal adjustment data as well as the second light point images detected by the image sensor  150 , so that the image sensor  150  can focus on the fundus  230 . In particular, the control unit  160  calculates a second set of location data of the second light point images, e.g., distance and vector difference among the second light point images. Besides, the control unit  160  may obtain a second displacement corresponding to the second set of location data from the focal adjustment data. Here, the focal adjustment data may include parameters required by the image sensor  150  for focusing on the fundus  230 , such that the control unit  160  may calculate the distance from the fundus  230  to the cornea  210  and thereby control the image sensor  150  to focus on the fundus  230 . For instance, the focal adjustment data include a plurality of differences between the predetermined location data O 2  and different second sets of location data as well as the second displacements of the first lens  142  (i.e., the moving distance of the first lens  142  on the light axis C or the angle at which the first lens  142  rotates on the light axis C) corresponding to the differences. Therefore, the control unit  160  allows the image sensor  150  to detect clear fundus images after the control unit  160  adjusts the first lens  142  according to the second displacement. 
     In particular, as shown in  FIG. 5A , the image sensor  150 , after focusing on the cornea  210 , simultaneously detects the second light point images  232 ,  234 , and  236  on the fundus  230 . At this time, the control unit  160  may obtain the distance D 2  from the cornea  210  to the fundus  230  according to the second set of location data R 2  of the second light point images  232 ,  234 , and  236  and obtain the second displacement X 2  corresponding to the second lens  144 . For instance, as indicated in  FIG. 5B , in the eye  200  where the distance from the cornea  210  to the fundus  230  is relatively long, the control unit  160  may obtain the distance D 2 ′ from the cornea  210  to the fundus  230  according to the second displacement X 2 ′ and move the first lens  142  on the light axis C. At this time, there is a displacement y′ between the light axis C′ of the image sensor  150  and the light axis C located at the pupil  220 . In another aspect, as indicated in  FIG. 5C , in the eye  200  where the distance from the cornea  210  to the fundus  230  is relatively short, the control unit  160  may obtain the distance D 2 ″ from the cornea  210  to the fundus  230  according to the second displacement X 2 ″ and move the first lens  142  on the light axis C. At this time, there is a displacement y″ between the light axis C″ of the image sensor  150  and the light axis C located at the pupil  220 . In another embodiment of the invention, the control unit  160  may allow the first lens  142  and the light axis C to have a viewing angle therebetween, such that the image sensor  150  may focus on the fundus  230 . Thereby, the control unit  160  may adjust the first lens  142  according to the distribution of the second light point images detected by the image sensor  150 , such that the image sensor  150  may obtain the clear fundus images after focusing on the cornea  210 . 
     In the present embodiment, the first lens  142  is disposed between the second lens  144  and the light sources  110 ,  120 , and  130 , and the second lens  144  is disposed between the first lens  142  and the image sensor  150 , for instance. However, in another embodiment, the first lens  142  may be disposed between the second lens  144  and the image sensor  150 , and the second lens  144  may be disposed between the first lens  142  and the light sources  110 ,  120 , and  130 . Other components, the material thereof, the arrangement thereof, each step in the auto-focusing method, the functions of said steps, and the effects achieved thereby are all similar to those described in the embodiment of the image capturing apparatus  100  shown in  FIG. 1 , and thus no further description is provided hereinafter. 
     To sum up, according to the descriptions of the image capturing apparatus and the auto-focusing method of the image capturing apparatus, the image capturing apparatus may focus on the cornea by detecting the first light point images that are obtained by transmitting the light beams to the cornea and may then focus on the fundus by detecting the second light point images on the fundus. Here, the second light point images are generated by substantially intersecting the light beams at the pupil and transmitting the light beams to the fundus. As a result, by applying the image capturing apparatus described herein, the time spent on focusing on the fundus may be reduced, and the clear fundus images may be obtained. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.