Abstract:
A lens module has a plurality of lens units which have focal lengths different from each other; an imaging device which focuses a subject light passing through one lens unit selected from the plurality of lens units on a common imaging plane to conduct photoelectric conversion; and a lens base which houses the plurality of lens units so that tip&#39;s faces of lenses at subject side in the plurality of lens units are disposed at the same position, wherein switching of light paths in the plurality of lens units is conducted by moving the entire lens base.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2004-19906 filed on Jan. 28, 2004, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a lens module and a camera capable of switching two focal length. Especially, the present invention relates a lens module and a camera capable of being embedded in thin type electronics devices such as a cellular phone or a digital camera.  
         [0004]     2. Related Art  
         [0005]     Recently, a cellular phone and a thin type digital camera which embeds an imaging device having one or more million pixels. The cellular phone is required to be size and thinness capable of housing in pockets of clothes and bags. Since users prefer the cellular phone having big size display screen and good operationality, flip type cellular phones became widespread. The flip type cellular phones have more severe limitation against thickness of the imaging device, and the thickness thereof has to be only 10 mm or less at the maximum.  
         [0006]     The imaging device has a lens and an image sensor such as a CCD (Charge Coupled Device) and a CMOS sensor. It is not easy to shorten a distance from the lens to the image sensor. The distance in a light axis direction is decided by a focal length of the lens and the thickness of the image sensor. If the focal length of the lens is shortened with respect to a size (about 1/3-1/2 inch) of the imaging phase of the image sensor, an image magnification becomes short too much. Therefore, ordinary users may not be able to take pictures they want (see article of http://www.zdnet.co.jp/mobile/0304/14).  
         [0007]     As resolution of the image sensor becomes high, size of the image sensor also becomes larger. The reason is that if only the resolution is raised without changing size of the image sensor, pixel size becomes small, the imaging data saturates easily, and image quality of the image deteriorates.  
         [0008]      FIG. 10  is a diagram showing a relationship between a size of the image sensor and a field edge of the lens. As the resolution of the image sensor becomes high and a size of the imaging area also becomes large, the focal length becomes long. That is, when the image sensor of high resolution and large size is used, it is necessary to enlarge the distance between the image sensor and the lens.  
         [0009]     The thickness of the image sensor includes the thickness of a protection glass and a package of a chip. Therefore, there is a physical limitation to reduce the thickness.  
         [0010]     By the above-mentioned reasons, when the imaging device having more than one million pixels is used for the cellular phone, design of the cellular phone is limited by the thickness of the imaging device, and portability is also damaged. Moreover, if optical zoom lens is used for the cellular phone, it is necessary to change the focal length from wide-angle to telephoto angle. Therefore, the thickness of the cellular phone becomes further thick and downsizing becomes further difficult. By such a reason, there is no cellular phone which has the imaging device having one or more million pixels and full-fledged optical zoom function.  
       SUMMARY OF THE INVENTION  
       [0011]     In order to solve the above-described problem, an object of the present invention is to provide a lens module and a camera capable of switching focal lengths, downscaling a size and reducing a thickness.  
         [0012]     A lens module according to one embodiment of the present invention, comprising:  
         [0013]     a plurality of lens units which have focal lengths different from each other;  
         [0014]     an imaging device which focuses a subject light passing through one lens unit selected from said plurality of lens units on a common imaging plane to conduct photoelectric conversion; and  
         [0015]     a lens base which houses said plurality of lens units so that tip&#39;s faces of lenses at subject side in said plurality of lens units are disposed at the same position,  
         [0016]     wherein switching of light paths in said plurality of lens units is conducted by moving the entire lens base. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a cross-section diagram of the lens module in the case of using the TELE lens to take images.  
         [0018]      FIG. 2  is a cross-section diagram of the lens module in the case of using the WIDE lens to take images.  
         [0019]      FIG. 3  is a plan view of the lens module according to the embodiment.  
         [0020]      FIG. 4  is a cross-section diagram at line B-B′ in  FIG. 3 .  
         [0021]      FIG. 5  is a cross-section diagram at line C-C′ in  FIG. 3 .  
         [0022]      FIG. 6A  is an appearance diagram as seen from the above,  FIG. 6B  is an appearance diagram as seen from the X direction, and  FIG. 6C  is an appearance diagram as seen from the Y direction.  
         [0023]      FIG. 7  is a plan view when the WIDE actuator and the TELE actuator  34  are integrated.  
         [0024]      FIG. 8  depicts one example of an individual shutter  13 ′.  
         [0025]      FIG. 9  is a diagram for explaining one example of switching of the zoom amount.  
         [0026]      FIG. 10  is a diagram showing a relationship between a size of the image sensor and a field edge of the lens. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     Hereinafter, one embodiment of the present invention will be explained, with reference to the drawings.  
         [0000]     First Embodiment  
         [0028]      FIGS. 1 and 2  are cross-section diagrams for explaining the outline of a lens module according to one embodiment of the present invention. The lens module according to this embodiment adopts a bifocal switching manner that can switch and use a wide-angle lens (hereinafter, “WIDE lens”) and a telephoto lens (hereinafter, “TELE lens”).  
         [0029]      FIG. 1  is a cross-section diagram of the lens module in the case of using the TELE lens to take images.  FIG. 2  is a cross-section diagram of the lens module in the case of using the WIDE lens to take images.  
         [0030]     In both cases of  FIGS. 1 and 2 , the installation position of an image sensor is the same, and an optical axis of light incident on the image sensor is common. That is, in the embodiment, the WIDE lens and the TELE lens use the same optical axis.  
         [0031]     As shown in  FIGS. 1 and 2 , the lens module according to this embodiment is largely divided into two, that is, a fixed sensor holder  1 , and a lens base  2  movable according to the lens to be used. The lens base  2  is arranged on a subject side, and the sensor holder  1  is arranged on a photographer side.  
         [0032]     The sensor holder  1  has an image sensor  3  formed of a CCD, a CMOS sensor or the like. The image sensor  3  is assumed to have a high resolution exceeding one million pixels, but there is no particular limitation on the resolution.  
         [0033]     A protective glass  4  is attached on the upper surface of an imaging plane of the image sensor  3 . A first mirror  5  is provided obliquely above the image sensor  3 . The first mirror  5  is provided in the sensor holder  1 , and is used only when the TELE lens is used. Since the sensor holder  1  is always fixed, the first mirror  5  does not move. However, the first mirror  5  may be provided on the lens base  2 , and in this case, the first mirror  5  also moves.  
         [0034]     The lens base  2  has a WIDE lens  6 , a WIDE lens frame  7 , a WIDE lens holder  8  for holding the WIDE lens frame  7 , a TELE lens  9 , a TELE lens frame  10 , a TELE lens holder  11  for holding the TELE lens frame  10 , a second mirror  12 , and a shutter  13 . The lens base  2  can move in a direction substantially parallel to the imaging plane of the image sensor  3 . When the TELE lens  9  is used, the lens base  2  moves to the position shown in  FIG. 1 , and when the WIDE lens  6  is used, the lens base  2  moves to the position shown in  FIG. 2 .  
         [0035]     When the TELE lens  9  is used, as shown in  FIG. 1 , subject light passing through the TELE lens  9  is reflected by the first mirror  5  and guided to the second mirror  12 , and reflected by the second mirror  12  to enter into the image sensor  3 .  
         [0036]     On the other hand, when the WIDE lens  6  is used, as shown in  FIG. 2 , the subject light directly enters into the image sensor  3 , without passing through the first mirror  5  and the second mirror  12 . That is, the first mirror  5  and the second mirror  12  are used only at the time of using the WIDE lens  6 .  
         [0037]     Thus, in this embodiment, the optical length is changed according to whether the subject light is guided to the first or second mirror  5  or  12 , thereby increasing the optical length at the time of using the TELE lens  9 . By providing the first and the second mirrors  5  and  12 , the optical path can be provided in a direction substantially parallel to the imaging plane of the image sensor  3 , thereby decreasing the length in the direction of the optical axis.  
         [0038]      FIG. 3  is a plan view of the lens module according to the embodiment.  FIGS. 1 and 2  respectively show the cross-section diagram at line A-A′ in  FIG. 3 .  FIG. 4  is a cross-section diagram at line B-B′ in  FIG. 3 , and  FIG. 5  is a cross-section diagram at line C-C′ in  FIG. 3 .  
         [0039]     A shift mechanism of the lens base  2  will be explained first. The lens base  2  is, as shown in  FIG. 3 , can shift in the right and left direction in the figure, along guide rods  21  and  22 . The guide rod  21  is inserted and fitted into a hole  23  formed at one end of the lens base  2 . The guide rod  22  is inserted and fitted into a hole  24  formed at the other end of the lens base  2 . The lens base  2  is suspended from the sensor holder  1 , by the guide rods  21  and  22 .  
         [0040]     The shift of the lens base  2  is controlled by a switching mechanism and a switching actuator  25 . The switching actuator  25  is actuated when a user operates a zoom button (not shown). The zoom button is not necessarily a dedicated one, and a mode setting button provided originally in a mobile phone or the like can be used.  
         [0041]     The switching actuator  25  converts an electric signal due to the operation of the zoom button to a mechanical signal. That is, the switching actuator  25  rotates a reduction gear  27  via a switching actuator gear  26 . Since the reduction gear  27  engages with a disc  28 , the disc  28  also rotates. The disc  28  is formed with a drive pin  30 , which engages with a cam groove  29 . When the disc  28  rotates, the drive pin  30  also moves corresponding thereto, and the cam groove  29  moves in the right and left direction (in a direction of the imaging plane of the image sensor  3 ) in  FIG. 3 . As shown in  FIG. 4 , since the cam groove  29  is formed in a part of the lens base  2 , the entire lens base  2  shifts in the right and left direction in  FIG. 3  along the guide rods  21  and  22 , that is, substantially parallel to the imaging plane of the image sensor  3 , together with the movement of the drive pin  30 .  
         [0042]     As described in this embodiment, when the entire lens base  2  is shifted, since the movement of the lens base  2  is straight, as the weight of the lens base  2  increases, the noise and impact at the time of stopping becomes unignorable. In order to solve this problem without decreasing the switching speed, it is desired to control the movement of the lens base  2  at a switching speed such that the moving speed of the lens base  2  changes in a sine curve. At this time, if a speed reducer such as the reduction gear  27  is combined therewith, better noise reduction and impact-proofness can be achieved.  
         [0043]     There are two conditions for determining the shift amount of the lens base, that is, one condition is that as the shift amount increases, the size of the entire lens module increases, and the other is that when the shift amount is decreased, light leakage may occur from the WIDE lens  6  side at the time of using the TELE lens  9 .  
         [0044]     As a result of trial and error by the present inventor, it is found that the shift amount of the lens base is desirably larger than the length of the imaging plane, and within 1.5 times as large as the length thereof. This range can be considered to be a safety zone with respect to the light leakage from the WIDE lens  6 .  
         [0045]      FIG. 6  is an appearance diagram of the lens module in another embodiment.  FIG. 6A  is an appearance diagram as seen from the above,  FIG. 6B  is an appearance diagram as seen from the X direction, and  FIG. 6C  is an appearance diagram as seen from the Y direction. The lens module shifts in the Y direction in  FIG. 6 . In the lens module in  FIG. 6 , the guide rods  21  and  22  are arranged outside of a housing of the lens module.  
         [0046]     An automatic focusing mechanism of the WIDE lens  6  and the TELE lens  9  will be explained below.  FIG. 4  shows a sectional structure on the TELE lens  9  side, wherein a disc-like face cam  31  is provided on the imaging plane side of the TELE lens holder  11 . The TELE lens holder  11  is pressed against the face cam  31  by a pressure bar spring  32 . The face cam  31  engages with the TELE actuator gear  33 , and the TELE actuator gear  33  is rotated by a TELE actuator  34 .  
         [0047]     A difference in level is provided on a face of the face cam  31  to be contacted with the TELE lens holder  11 . When the TELE actuator  34  rotates the TELE actuator gear  33 , the face cam  31  also rotates, and the TELE lens holder  11  shifts in the direction of optical axis due to the difference in level in the face cam  31 , thereby performing focus adjustment.  
         [0048]     While a cross-section diagram of the WIDE lens  6  corresponding to  FIG. 4  is omitted in this specification, the WIDE lens  6  has the same structure as that shown in  FIG. 4 . The WIDE actuator  35  shifts in the direction of optical axis by the face cam for the WIDE lens  6 , to perform focus adjustment.  
         [0049]     The WIDE lens  6  and the TELE lens  9  may be driven by one actuator.  FIG. 7  is a plan view when the WIDE actuator and the TELE actuator  34  are integrated. The actuator in  FIG. 7  rotates/drives the WIDE actuator gear  39  and the TELE actuator gear  33  via fan-shape gears  37  and  38 .  
         [0050]     In the case of  FIG. 7 , when either the WIDE lens  6  or the TELE lens  9  is used, both lenses shift in the direction of optical axis, but there occurs no problem in photographing. By having the structure shown in  FIG. 7 , the number of actuators can be reduced, thereby realizing cost reduction and miniaturization.  
         [0051]     In this embodiment, as shown in  FIG. 1 , the WIDE lens holder  8  for holding the WIDE lens  6  and the TELE lens holder  11  for holding the TELE lens  9  are arranged such that the tips thereof on the subject side are substantially flush. Accordingly, the WIDE lens  6  and the TELE lens  9  do not protrude from the entire surface of the lens module, thereby obtaining a structure that can sufficiently withstand severe drop tests required for mobile phones. Further, since the lenses do not protrude from the entire surface, the design of the mobile phone and the like will not be damaged.  
         [0052]     The mechanism of the shutter  13  will be explained next. The shutter  13  according to the embodiment has, as shown in  FIG. 3 , a rectangular shape, and normally arranged at a position which does not close the optical axis. The shutter  13  rotates 180 degrees immediately after the user presses a shutter button (not shown). As a result, immediately after the user presses the shutter button, the subject light incident on the imaging plane of the image sensor  3  is intercepted only once. Accordingly, noise light does not enter into the image sensor  3  immediately after imaging, thereby improving the quality of the photographed image.  
         [0053]     More specifically, a shutter gear  40  is fitted to the shaft of the rectangular shutter  13 , and an idle gear  41  engages with the shutter gear  40 , and a shutter actuator gear  42  engages with the idle gear  41 . The shutter actuator gear  42  is rotated by a shutter actuator  43 . The shutter  13  rotates at a high speed by 180 degrees, when the user presses the shutter button (not shown). Accordingly, the subject light does not enter into the image sensor  3 , while the shutter  13  passes, and hence, noise light components are not included in the imaged data of the image sensor  3 .  
         [0054]     It is necessary to make the lens module small and thin as much as possible, and hence, the layout of respective members has to be worked out well. The structure of the lens module shown in FIGS.  1  to  5  is only one example, and the arrangement of members may be changed according to need. Taking effective use of the space into consideration, as shown in  FIGS. 1 and 2 , it is desired to arrange the switching actuator  25  for shifting the lens base  2  next to the image sensor  3 .  
         [0055]     Since the lens base  2  shifts every time switching of WIDE/TELE is performed, the shift mechanism has to have excellent durability. For the example of using the guide rods  21  and  22  according to this embodiment, the durability has been proven for a zoom lens and the like.  
         [0056]     However, when the lens base  2  is repeatedly shifted along the guide rods  21  and  22 , there is the possibility that the dust from the vicinity of the guide rods  21  and  22  enters into the sensor holder  1 , and adheres on the imaging plane of the image sensor  3 . In this embodiment, therefore, as shown in  FIG. 4 , a dustproof groove  51  extending substantially parallel to the guide rods  21  and  22  is formed obliquely below the guide rods  21  and  22 . The dustproof groove  51  can prevent dust and the like generated in the case where the lens base  2  shifts along the guide rods  21  and  22  from being intruded inside. Accordingly, there is no possibility that the dust and the like adhere on the imaging plane of the image sensor  3 .  
         [0057]     Thus, in this embodiment, since the WIDE lens holder  8  and the TELE lens holder  11  having a different focal length are arranged so that the tips thereof on the subject side are substantially flush, the lenses do not protrude from the housing, the lenses can withstand the drop tests, and the design will not be damaged.  
         [0058]     Further, since the optical length is made long by changing the angle of the subject light by the first and the second mirrors  5  and  12 , the thickness in the direction of optical axis can be sufficiently thin, thereby realizing a thin lens module.  
         [0059]     In the embodiment, an example in which the rectangular shutter  13 , which rotates 180 degrees about the axis, has been explained, but the form of the shutter  13  is not particularly limited, and an individual shutter generally used in a silver salt camera and the like may be used.  FIG. 8  depicts one example of an individual shutter  13 ′. One of two blade members  52  and  53  constituting the shutter  13 ′ is for the WIDE lens, and the other is for the TELE lens. These blade members  52  and  53  are normally sheltered at a position where they do not cover the optical axes of the both lenses, as shown in  FIG. 8 . Cam grooves  54  and  55  are formed in these blade members  52  and  53 , and drive pins  56  and  57  respectively engage with these cam grooves. These drive pins  56  and  57  are integrally formed on a disc  58 , and the disc  58  is rotated/driven by a shutter actuator (not shown).  
         [0060]     When the user presses the shutter button, the shutter actuator immediately rotates the disc by 60 degrees counterclockwise, and immediately thereafter, rotates the disc by 60 degrees clockwise. Accordingly, the blade members  52  and  53  cover the optical axes of the both lenses  6  and  9  only for a short time. That is, imaging by the image sensor  3  is interrupted only for a short time.  
         [0061]     Even when the shutter  13 ′ of another type is used as shown in  FIG. 8  is used, the shutter  13 ′ can be driven by one actuator, thereby enabling miniaturization. The various types of shutter mechanism described above can be incorporated in the lens module according to the embodiment, since the tips on the subject side of the WIDE lens  6  and the TELE lens  9  are made flush.  
         [0062]     In the above embodiment, while an example in which the WIDE lens  6  and the TELE lens  9  are provided has been explained, a standard lens may also be provided. That is, the present invention is widely applicable when two or more lenses having a different focal length are provided.  
         [0063]     The lens module described above can be incorporated in portable equipment such as a mobile phone with camera function and a digital camera.  
         [0064]     Various types of portable equipment having a built-in camera are in many cases provided with a digital zoom function. However, the digital zoom has inferior image quality as compared to the optical zoom, and as the zoom magnification increases, the image quality deteriorates. Under such circumstances, the digital camera and the like use the optical zoom and the digital zoom together. However, in order to realize miniaturization, the optical zoom is approximately limited to tri-magnifications, and further zoom is performed by the digital zoom.  
         [0065]     In the portable equipment having the lens module according to this embodiment incorporated therein, the optical zoom and the digital zoom can be used together. Since the lens module according to this embodiment has two types of lenses having a different focal length, there are two zoom amounts capable of the optical zoom. When the user sets the zoom amount other than those two, the digital zoom is used.  
         [0066]     For example, a case where the user sets a zoom amount corresponding to the focal length of the WIDE lens  6  to gradually increase the zoom amount will be explained hereinafter. In this case, optical zoom is performed by using the WIDE lens  6 , and thereafter, digital zoom is performed with respect to the data imaged by using the WIDE lens  6 , up to the zoom amount corresponding to the focal length of the TELE lens  9 . When reaching the zoom amount corresponding to the focal length of the TELE lens  9 , digital zoom is suspended, to display the immediately preceding imaged data, and optical zoom is performed by switching to the TELE lens  9  by the lens base  2 . When the zoom amount is increased further, digital zoom is performed with respect to the data imaged by using the TELE lens  9 . On the contrary, when the zoom amount is decreased gradually, the similar operation is performed.  
         [0067]      FIG. 9  is a diagram for explaining one example of switching of the zoom amount. A hybrid processor in the portable equipment performs adjustment of the zoom amount in the following procedure. That is, as shown in the figure, when the zoom amount is changed from a short focus (WIDE) side to a long focus (TELE) side, the zoom amount changes by 1.2 magnifications. More specifically, the zoom amount changes by one step (1.2 magnifications) every time the user makes a short-press on the zoom button. On the other hand, when the user makes a long-press on the zoom button, the zoom amount changes by one step at an interval of 0.3 second.  
         [0068]     When the zoom amount is changed from the short focus side, optical zoom is performed by using the WIDE lens  6 , and the fifth magnification (2.1 magnifications) in  FIG. 9  becomes the maximum zoom amount by using the WIDE lens  6 .  
         [0069]     Subsequently, when the user presses the zoom button, the lens is switched to the TELE lens  9 , with the screen display of the portable equipment unchanged. When switching to the TELE lens  9  has finished, the screen display is changed to the one using the TELE lens  9 . At this stage, digital zoom is not performed, and a screen display by the optical zoom is conducted. The zoom amount at this stage is, as shown in  FIG. 9 , is 2.5 magnifications. In this state, when the user makes a long-press on the zoom button, the zoom amount changes by one step (1.2 magnifications) at an interval of 0.3 second. Finally, the maximum zoom amount becomes 5.2 magnifications.  
         [0070]     In contrast, when the zoom amount is changed from the long focus side toward the short focus side, zoom is switched in an order opposite to that explained above, and the zoom amount changes by 1/1.2 magnifications.  
         [0071]     Thus, even when the WIDE lens  6  and the TELE lens  9  are switched halfway, scaling of an image is performed smoothly, without interrupting the screen display.  
         [0072]     When the lens module according to this embodiment is assembled in the portable equipment such as a camera, a hybrid zoom camera that can achieve a seamless zoom function by combining the optical zoom and the digital zoom can be realized, as in the normal digital camera.