Patent Abstract:
A parallax compensation system and method is provided for a camera including an independent viewfinder. For close focus pictures, the camera&#39;s taking lens is shifted towards the viewfinder. In one embodiment, for far focus pictures the camera&#39;s taking lens is moved away from the viewfinder and is not centered on the image recording medium axis. The lens shifting is accomplished by mounting the taking lens eccentrically in a lens barrel. Rotation of the lens barrel shifts the taking lens towards the independent viewfinder for close focus shots. In one embodiment, the viewfinder axis is tilted towards the taking lens to help eliminate parallax in close focus pictures.

Full Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of cameras and, more particularly, to a parallax compensation system for a camera. 
     BACKGROUND OF THE INVENTION 
     Cameras having non-through the lens viewfinders, that is, viewfinders with an optical axis distanced from the image capture optical axis, exhibit a problem with parallax error at close shooting distances. At normal shooting distances (1.5 m to infinity) the parallax error is negligible. However, at very close shooting distances (i.e. 0.25 m), the parallax error causes unacceptable aiming mistakes. There are several existing methods to address this problem: 1) ignore it for very low-end cameras and simply accept aiming errors; 2) add so-called parallax markings in the bright frame mask, which require the user to remember to use those markings to recompose the subject if it is at close distance; 3) use a bright frame viewfinder with parallax markings and control the visibility of those markings automatically with moving masks or with liquid crystal panels; 4) employ an elaborate mechanism to couple the viewfinder mask or bright frame to the focusing movement of the lens, which mechanism typically comprises cams and levers and even motors in some high-end cameras. 
     A number of patents have tried different means for addressing the parallax error in cameras at close shooting distances. U.S. Pat. No. 6,243,539 to Chen provides a parallax compensation apparatus for a camera which comprises a viewfinder pivotally connected to a camera for locating objects to be taken. A follower link connected to the camera and having one end pivotally connected to the viewfinder causes the viewfinder to pivot, moving the adjusting device such that the optical axis of the viewfinder meets the optical axis of the lens in the subject to be taken. 
     U.S. Pat. No. 4,924,247 to Suzuki et al., relates to an apparatus and method for correcting and adjusting parallax in an electronic camera. Suzuki provides a parallax correcting apparatus which comprises an imaging device driving mechanism for supporting and moving an imaging device away from and towards the optical axis of the finder optical system. 
     Although somewhat effective for their intended purpose, the prior art devices are complicated and expensive. What is needed is a mechanically simple, inexpensive system for correcting parallax in a camera having an independent viewfinder. This object, as well as others, is satisfied by the present invention. 
     SUMMARY OF THE INVENTION 
     A parallax compensation system and method is provided for a camera including a non-through the lens viewfinder. The taking lens of a camera is mounted eccentrically in a cylindrical lens barrel. The lens barrel is rotated to shift the taking lens towards the viewfinder for close focus shots. Additionally, in one particular embodiment, the viewfinder axis is tilted towards the rotated taking lens axis to help eliminate parallax in close focus pictures. 
     These and other objects and advantages of the present invention will become more readily apparent in the description which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing summary, as well as the following detailed description of the preferred embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings an exemplary embodiment that is presently preferred it being understood, however, that the invention is not limited to the specific methods and instrumentality&#39;s disclosed. Additionally, like reference numerals represent like items throughout the drawings. In the drawings: 
     FIG. 1A is a perspective view from the front, right side of an exemplary camera useful with the present invention. 
     FIG. 1B is a perspective view from the rear, right side of the camera of FIG.  1 A. 
     FIG. 2A demonstrates the parallax encountered at close range with a standard camera having an independent viewfinder. 
     FIGS. 2B-2D demonstrates the elimination of parallax at close range in a camera made in accordance with various embodiments of the present invention. 
     FIG. 3A is a front plan view of an eccentric lens barrel in accordance with one embodiment of the present invention. 
     FIG. 3B is a side perspective view of the eccentric lens barrel of FIG.  3 A. 
     FIG. 4A is a front partial cut-away view of a camera made in accordance with one embodiment of the present invention. 
     FIG. 4B is an enlarged view of the cut away portion of FIG.  4 A. 
     FIG. 4C is a side perspective, partial exploded view of the camera of FIG. 4A 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before explaining the disclosed embodiments of the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the particular arrangement shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation. 
     The present invention relate to a camera with a first fixed-focus setting for normal shooting distances and a separate fixed-focus setting for close-up pictures. The fixed-focus setting for close distances is used to shift the center of the lens relative to the center of the image frame so as to help compensate for the parallax error of the viewfinder. 
     Referring now to FIGS. 1A and 1B, the camera  10  includes an outer housing  11  having a front portion  12   a  and a back portion  12   b.  The front portion  12   a  and the back portion  12   b  are made as two separate pieces to facilitate manufacturing of the housing  11 . It should be appreciated, however, that the housing may, alternatively, be comprised of any number of pieces. Additionally, the outer surfaces of the front  12   a  and back  12   b  portions may be contoured, if desired, to improve gripping capabilities and provide a more ergonomic and aesthetically pleasing design. In the preferred embodiment, the housing  11  is constructed of a lightweight, yet rugged plastic material, but may, alternatively, be constructed of an alloy material, a metallic material or any other suitable material. 
     Front portion  12   a  of housing  11  is adapted for connective engagement with the corresponding back portion  12   b  using conventional fastening means. The two halves form a substantially light tight connection when assembled together. In the present embodiment, the front and rear portions  12   a  and  12   b  are secured together using screws  14 . 
     The front and back portions  12   a,    12   b  include a plurality of openings integrally formed therein. The openings are structured and disposed to accept the taking lens (opening  16 )defining an image capture optical axis and a viewfinder assembly (openings  18   a  and  18   b ) defining an image framing optical path, the viewfinder assembly disposed apart from the taking lens. Other openings may also be included to accommodate other features, such as a battery door, function select controls, a flash and/or an external connector. 
     A trigger button  13  is accessible through an opening disposed on the top face  12   c  of the housing  11 . 
     An external interface cavity  30  is also integrally formed in the camera housing  11  and is accessible by moving the interface door  31 . External interfaces are disposed within the external interface cavity  30  for interconnection with an external device, such as a computer, printer, television or video monitor, imaging device, etc. 
     A status indicator opening  40  is provided through the rear housing  12   b.  A status LCD  41  is mounted on the rear housing  12   b.  Additional openings for a number of user select buttons  42  are additionally provided through the rear housing, and are disposed in close proximity to the status indicator. The number and orientation of the user select buttons  42  may vary to accommodate the particular camera  10  layout. Similarly, the functions provided may vary. Typical function selects include, on/off, timer on/off, etc. Additionally, the status LCD  41  may provide a variety of desired information including timer indication, battery status, number of remaining pictures, mode indicator, etc. 
     The present exemplary camera additionally includes a mirror slide switch  60  slideably engaged with the top face  12   c  of the housing  11 . Further, as will be described more filly herein, camera  10  includes a wiper switch  50  that slides in a groove formed in the front housing  12   a  and which switches the camera mode between normal and macro. 
     Referring now to FIG. 2A, there is shown a schematic illustration showing parallax error in a close focus picture taken with a conventional camera. A viewfinder optical axis  100  is defined through the center of the viewfinder of the camera. An image capture optical axis  110  is defined through the center of the camera image sensor. The viewfinder optical axis  100  and the image capture optical axis  110  are fixed parallel to each other. Objective taking lens  112  is centered on the sensor axis  110 . Parallax is defined as the difference between the area taken in by a camera lens and the area seen in the viewfinder. The closer the subject is to the camera, the greater the parallax. As such, at close range, the image recorded by the sensor is shifted as compared to the image framed in the viewfinder. 
     Referring now to FIG. 2B, there is shown a schematic illustration using a camera in accordance with one embodiment of the present invention. To compensate for parallax in the present embodiment, objective taking lens  112  is shifted towards the viewfinder axis. Although the image sensor is not shifted, shifting the lens alters the focus of the sensor. Once shifted, the parallax between the viewfinder and the taking lens is eliminated at a relatively close focal length, where the newly defined optical center axis  114  converges with the viewfinder axis  100 . The amount of lens shift needed can be described by the following equation: 
     
       
         Lens Shift=Parallax Distance×Focal Length/Subject Distance   (1)  
       
     
     where, parallax distance is the distance between the taking lens center and the viewfinder center. 
     In one particular implementation shown in FIG. 2B, the taking lens  112  was shifted 0.39 millimeters causing the lens axis  114  to converge with the viewfinder axis  100  at 380 mm, thus eliminating parallax at this distance. However, it has been found that shifting the lens center  112  too far from the sensor center can cause degradation in the corners of the picture. 
     Referring now to FIGS. 2C and 2D, there is shown another embodiment of the camera of the present invention. In the embodiment of FIGS. 2C and 2D, to prevent the lens from shifting too far from the center of the sensor, the taking lens  112  is shifted a small distance away from the viewfinder axis  100  for far focus shots, but is shifted towards the viewfinder axis  100  for close focus shots. Additionally in this embodiment, the viewfinder is tilted towards the sensor axis  110 . To reduce cost, the viewfinder of the present embodiment is permanently angled towards the taking lens, defining an adjusted viewfinder axis  116 . 
     For far focus shots, the taking lens  112  is shifted away from the adjusted viewfinder axis  116 , defining an adjusted far focus lens axis  118 . For close focus shots, the taking lens  112  is shifted towards the adjusted viewfinder axis  116 , defining the adjusted viewfinder close focus axis  118 ′. 
     In one particular implementation having the viewfinder permanently tilted, as shown in FIG. 2C, shifting the taking lens  112  away from the viewfinder axis  100  by 0.15 millimeters from the original lens axis  110  resulted in a far focus convergence of the adjusted viewfinder axis  116  with the adjusted far focus lens axis  118  at 1700 millimeters. In the same embodiment, as shown in FIG. 2D, shifting the taking lens  112  towards the viewfinder axis  100  by 0.15 millimeters from the original lens axis  110  resulted in a close focus convergence of the adjusted viewfinder axis  116  with the adjusted close focus lens axis  118 ′ at 380 millimeters, thus eliminating parallax at that distance. 
     Referring now to FIGS. 3A and 3B, there is shown one embodiment of an eccentric taking lens barrel  130  which may be used to implement the lens shift described in connection with the FIGS. 2B-2D. An eccentric taking lens barrel  130  is shown such that the barrel includes a bore  131 . Although the lens barrel  130  is cylindrical in shape in this particular embodiment, the bore  131  is located off center in the lens barrel  130  such that the length R 1  is significantly greater than length R 2 , where R 1  is measured from the center of the bore to the furthest outer edge of the lens barrel  3 O and R 2  is measured from the center of the bore to the closest outer edge of the lens barrel  130 . The lens assembly  140 , including the taking lens group  142 , is mounted in the bore  131 . The taking lens barrel  130  additionally includes cam arms  132 ,  134  and  136 , which engage cam surfaces on the body of the camera to limit the range of motion, when the lens barrel is rotated. Cam arm  136  further includes the wiper post  138 . Wiper post  138  interfaces with a wiper or switch outside the camera housing to permit the user to manually rotate the lens assembly  140 . 
     Referring now to FIGS. 4A,  4 B and  4 C, there is shown a camera  150  that incorporates one embodiment of the present invention. Camera  150  includes a viewfinder assembly  160  having lenses  162  and  164  and a taking lens assembly  140  seated in an eccentric taking lens barrel  130 . In the present embodiment, the viewfinder assembly of camera  150  is permanently tilted towards the taking lens  142  such that the vector  165  (FIG. 4A) defines the tilted viewfinder axis. Additionally, the eccentric lens barrel  130  is free to rotate only a prescribed amount in the camera body. Rotating the lens barrel  130  clockwise (as shown in shadow by the displacement  136 ′,  140 ′ of arm  136  and taking lens assembly  140 , respectively) brings the taking lens  142  ( 142 ′) closer to the viewfinder. Line D 1  is the distance from the center of the viewfinder to the center of the unshifted taking lens  142 . Line D 2  is the distance from the center of the viewfinder to the center of the shifted taking lens  142 ′. As can be seen, when the eccentric lens barrel  130  is shifted the taking lens  142  is shifted ( 142 ′) closer to the viewfinder. As described in connection with FIGS. 2B-2D, this reduces the parallax of the camera for close focus pictures, while having a negligible effect on far focus pictures. A sensor  170  seated in the body of camera  150  behind the taking lens  130  captures the image when the trigger ( 13  of FIGS. 1A and 1B) is depressed. An internal coupling ring  185  couples the eccentric lens barrel  130  to the front cover wiper  180  on the outside of the housing. 
     Note that the disclosed method of shifting the taking lens can be applied to all kinds of image capture devices including cameras wherein the image recording media is photographic film, or wherein the image recording media includes a CMOS or CCD sensor as described herein. The present invention is particularly suitable for digital cameras due to the small size of the image frame on the sensor and therefore the small amount the lens needs to shift sideways for parallax compensation. It is understood that the lens shift must be limited to the maximum extent of the image circle (maximum coverage of the lens) to avoid poor image quality in the corners. 
     While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Technology Classification (CPC): 6