Patent Publication Number: US-9841576-B2

Title: System for parallax correction

Description:
GOVERNMENT RIGHTS STATEMENT 
     This invention was made with government support under contract number HR0011-13-C-0068 awarded by Defense Advanced Research Projects Agency. The government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to optics, and more particularly to parallax correction between two lenses. 
     2. Description of Related Art 
     Night vision systems include image intensification, thermal imaging, and fusion monoculars, binoculars, and goggles, whether hand-held, weapon mounted, or helmet mounted. Infrared imagers allow an operator to see people and objects. With the use of multiple infrared imagers and therefore more than one lens the need for correcting parallax between the lenses exist. Specifically, a remote object can be observed without any problem, because the image of the object is formed substantially at the center of the field of view of each of the right and left optical systems. However, as the object comes closer, its image moves away from the center, and at the extreme, the image of a very close object is formed out of the field of view of each of the optical systems. This problem is due to parallax, and can be solved by various methods. Typical methods which correct for parallax are manual and demand a great deal of time and effort, but also tend to leave small alignment errors, making it difficult to realize the optical performance as designed. 
     Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved system for parallax correction. The present disclosure provides a solution for this need. 
     SUMMARY OF THE INVENTION 
     A system for parallax correction includes a rotatable focus adjuster having a longitudinal axis. A lens retainer is engaged with the focus adjuster. A first lens is housed within the lens retainer aligned with the longitudinal axis. A second lens is positioned parallel to the first lens within the lens retainer. The second lens is configured to move laterally with respect to the first lens to correct for parallax between the first and second lenses. 
     The focus adjuster can include a set of circumferential threads that engage the lens retainer and are configured to urge the lens retainer along the longitudinal axis towards and away from an object of focus upon rotation of the focus adjuster. The focus adjustor can also include a set of gear teeth that engage gear teeth of the first lens such that rotation of the focus adjustor causes simultaneous rotation of the first lens. The lens retainer can include castellation&#39;s that mesh with the gear teeth of the focus adjuster to maintain position of the lens retainer when the focus adjuster is rotated. The gear teeth disposed on the first lens can have a predetermined length to facilitate calibration based on movement of the focus adjuster. 
     A cam can extend circumferentially about the first lens. The cam can have a profile configured to engage and laterally move the second lens upon rotation of the first lens for parallax correction between the first and second lenses. A spring mechanism can be included between the first and second lens configured to maintain the first and second lenses in parallel with one another. 
     The gear teeth of the first lens and the threads of the focus adjuster are keyed to each other such that parallax correction between the first and second lenses is keyed to a focal distance of the first and second lenses. The first lens can be a long wave infrared lens and the second lens can be a short wave infrared lens. 
     A method for correcting for parallax includes rotating a focus adjuster to advance and retract a lens retainer engaged with the focus adjuster towards and away from an object of focus. A first lens within the lens retainer is simultaneously rotated. A second lens positioned parallel to the first lens within the lens retainer is moved laterally to correct for parallax between the first and second lenses. The steps of rotating and laterally moving can include advancing a cam to force lateral movement of the second lens. 
     These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein: 
         FIG. 1  is a perspective view of an exemplary embodiment of a system for parallax correction constructed in accordance with the present disclosure, showing a focus adjuster and lens retainer housing a first and second lens; 
         FIG. 2  is an exploded view of the system of parallax correction of  FIG. 1 , showing threading for movement of the lens retainer; 
         FIG. 3  is a partially cut-away perspective view showing a gear mechanism between the focus adjuster and the first lens; and 
         FIG. 4  is a rear view of the system of parallax correction of  FIG. 1 , showing a cam circumferentially around the first lens. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a system for parallax correction in accordance with the disclosure is shown in  FIG. 1  and is designated generally by reference character  100 . Other embodiments of the system in accordance with the disclosure, or aspects thereof, are provided in  FIGS. 2-4 , as will be described. The system and method described herein can be used to correct for parallax between two lenses, e.g., between dual infrared lens such as for long wave infrared and a short wave infrared. 
     With reference to  FIGS. 1-4 , a system for parallax correction  100  is shown including a focus adjuster  102  defining a longitudinal axis A-A engaged with a lens retainer  104 . A first lens  106  is aligned with the longitudinal access A-A and a second lens  108  is positioned parallel with the first lens  106  within the lens retainer  104 . An optional protective cover  110  can be disposed adjacent the focus adjuster  102  surrounding the first and second lenses  106 , 108 . The focus  15  adjuster  102  engages with the lens retainer  104  using a common thread between two pieces. During operation, rotational movement of the focus adjuster  102  by the user urges the lens retainer  104  along the longitudinal axis A-A towards and away from an object of focus. The lens retainer  104  may be externally or otherwise supported to maintain position of the lens retainer  104  when the focus adjuster  102  is rotated. The focus adjuster  102  includes gear teeth  112  that mesh with gear teeth  130  of the first lens  106  to rotate the lens about its axis. 
     The first and second lenses  106 , 108  housed within the lens retainer  104  move in conjunction with the lens retainer  104  along the longitudinal axis A-A changing focus of the first and second lenses  106 , 108 . As the focus adjuster  102  is rotated the first lens  106  rotates simultaneously. As shown in  FIG. 4 , a cam  140  is positioned extending circumferentially about the first lens  106 . Upon rotation of the first lens  106 , the cam  140  rotates and causes lateral movement of the second lens  108  to correct for parallax between the first and second lenses  106 ,  108 . In other words, as the user rotates the focus adjuster  102  to focus on an object, the first lens  106  rotates and moves the second lens  108  laterally within the lens retainer  104 . This lateral movement of the second lens  108  corrects for parallax between the first and second lenses. The gear teeth  130  of the first lens  106  and threads of the focus adjuster  120  are keyed to a focal distance of each of the first and second lenses  106 ,  108 . Furthermore, the gear teeth  130  of the first lens  106  are predetermined length to facilitate calibration based on movement of the focus adjuster  102 . The system  100  includes a spring mechanism  150  between the first and second lens configured to maintain the first and second lenses  106 ,  108  in parallel with one another. 
     A method of correcting for parallax between two lenses using the system of  FIGS. 1-4  includes rotating a focus adjuster (e.g., focus adjuster  102 ) engaged with a lens retainer (e.g., lens retainer  104 ). Rotating of the focus adjuster urges the advancing and retracting of a lens retainer towards and away from an object of focus. The method continues by rotating a first lens (e.g., first lens  106 ) positioned within the lens retainer. With the step of rotating the first lens a cam (e.g., cam  140 ) is advanced to force lateral movement of a second lens (e.g., second lens  108 ) positioned parallel to the first lens to correct for parallax between the first and second lenses. 
     The methods and systems of the present disclosure, as described above and shown in the drawings, provide for a system for parallax correction with superior properties including laterally displacing at least one of two lenses. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.