Abstract:
An improved lens mounting systems for use in lens relay systems in disclosed. The lens mounting system includes at least one lens and a tubular lens mount. The tubular lens mount is portion of a cylinder with a cross section slightly larger than a semicircle. The edges of the tubular lens mount may be beveled. The inner diameter of the tubular lens mount may be equal to, or slightly smaller than, the outer diameter of the lens. In addition, the tubular lens mount may be in three point contact with the mounted lens.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates generally to an improved lens mounting system for use in field and lens relay systems. Such systems are used in endoscopes and similar optical instruments. 
         [0002]    A lens relay system is an optical system consisting of a sequence of lenses that relays the viewed image from lens to lens. Typically each lens relay set in the sequence takes the image from the preceding lens relay set and forms a new image, used as the input to the next lens relay set. The use of a field and lens relay system in an endoscope or other medical device is well known. One well known lens relay system is described in U.S. Pat. No. 3,257,902 and is referred to as the “Hopkins” relay lens system. This system transfers an optical image developed by an objective lens to an adjacent relay lens system or an eyepiece lens and achieves an acceptable level of transfer of a high brightness image with correction of optical aberrations. 
         [0003]    One particular challenge in manufacturing such a lens relay system is the mounting of the series of lens such that the lenses are held in the correct position relative to one another and that the lens centerlines remain collinear. One method of mounting a series of lenses is to use a cylindrical mounting tube. Each lens is placed, in order and with spacers, in the mounting tube and slid down to the lens or spacer below it prior to being secured in place. However, this process requires that the outer diameter of each lens to be slightly smaller that the inner diameter of the mounting tube to allow for the lens to be slid down the mounting tube into position. This, in turn, means that the level of precision in mounting each lens is less than ideal as the lens centerlines may not be exactly collinear due to the required space between the lens outer diameter and the mounting tube inner diameter. 
         [0004]    There is a need for an improved lens mounting system for use in devices that require a field and lens relay system. In particular, there is a need for a lens mounting system in which lenses can be held in position relative to each other with a high degree of precision such that the lens centerlines remain collinear. In this specification and in the appended claims the term “endoscope” means and should be interpreted to include an endoscope or any other similar optical instrument, whether used for surgery or other applications. In addition the improved lens mounting system is not limited to endoscopes and may be used in any optical application requiring a series of mounted lenses. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    An improved lens mounting system in accordance with the present invention includes a tubular lens mount. The tubular lens mount is a hollow approximately half-cylindrical structure with an inner diameter equal to or smaller than the outer diameter of the lenses. In certain embodiments the edges of tubular lens mount are beveled to prevent damage to the lenses where the tubular lens mount and lenses are in contact. The improved lens mounting system may itself be sheathed in an outer cylinder for protection of the lenses. 
         [0006]    Other features and advantages of the present disclosure will become apparent from the following description of the disclosure that refers to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    For a fuller understanding of the present invention, reference should be made to the following detailed description taken in connection with the accompanying drawings, not drawn to scale, in which the same reference numerals indicate the same or similar parts, wherein: 
           [0008]      FIG. 1  is a perspective view of a conventional lens relay system. 
           [0009]      FIG. 2  is a perspective view of an improved lens mounting system according to an embodiment of the present invention. 
           [0010]      FIG. 3  is a perspective view of a tubular lens mount used in an embodiment of the present invention. 
           [0011]      FIG. 4  is a front view of a tubular lens mount used in an embodiment of the present invention 
           [0012]      FIG. 5  shows the insertion of a lens into an improved lens mounting system according to an embodiment of the present invention. 
           [0013]      FIG. 6  is a front view of the tubular lens mount with a lens fully inserted with detailed views of the points of contact between the fully mounted lens and the tubular lens mount. 
       
    
    
       [0014]    With reference to the drawings, the features thereof are described below. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIG. 1  shows a conventional lens mounting system  10  for use in a field and relay lens system. As discussed above, one method of mounting a series of lenses is to use a cylindrical mounting tube  11 . Each lens  22  is placed, in order, in the mounting tube and slid down to the lens or spacer below it prior to being secured in place. However, this process requires that the outer diameter of each lens is slightly smaller that the inner diameter of the mounting tube  11  to allow for the lens  22  to be slid down the mounting tube  11  into position. This, in turn, means that the level of precision in mounting each lens is less than ideal as the lens centerlines by not be exactly collinear due to the space between the outer diameter of the lens and the inner diameter the mounting tube. 
         [0016]      FIG. 2  shows an improved lens mounting system  20  for use in a field and relay lens system. Unlike a conventional designs, the improved tubular lens mount  21  is constructed in the shape of a hollow cylinder that has been cut parallel to the longitudinal axis of the cylinder. This results in a shape approximating a hollow half cylinder and, unlike conventional designs, allows full access to what was previously the interior of the cylinder. The full access to the interior of the cylindrical shell allows for the precise placement and alignment of individual lenses  22  in the tubular lens mount  21 . In addition, unlike conventional designs, the inner diameter of the hollow cylinder is equal to or slightly smaller that the diameter of the lenses to be mounted. 
         [0017]      FIG. 3  shows an perspective view of the improved tubular lens mount  21 . The tubular lens mount  21  is in the shape of a hollow cylinder that that been cut parallel to the longitudinal axis. The tubular lens mount  21  may be constructed of any suitable material including metals, such as stainless steel or aluminum, plastics, or various composite material. The material should have sufficient flexibility to allow for the expansion of edges  23  during the insertion of the lenses  22 . The material should also have sufficient rigidity such that after the lenses  22  have been inserted the edges  23  return close to their original location and the tubular lens mount  21  returns close to its original diameter to hold the lenses  22  in place. The thickness of the tubular lens mount  21  will depend on the material selected for construction and must allow for the required flexibility (during insertion) and rigidity (while holding) the lens. In addition, the edges  23  of the tubular lens mount  21  are preferably beveled so as to not scratch or chip the lenses  23 . 
         [0018]    As will be shown in more detail below, the diameter of the tubular lens mount  21  is preferably equal to or slight less than the diameter of the lenses  22  to allow for a solid three point suspension of the lenses  22 . However, additional mounting means are contemplated. For example, the lenses could be installed using a bonding agent (e.g. glue), screws and/or pins inserted tangentially through the tubular lens mount  21 , soldering, or other conventional mounting means. Using any of these mounting methods, the ability to have access to the interior of the original cylindrical shell allows for more precise placement of the individual lenses  22 . In addition, the completed assembly, including the tubular lens mount  21  and lenses  22 , may itself be mounted in a outer cylinder or sheath to protect the lenses from dirt, dust, and other foreign objects. 
         [0019]      FIG. 4  is a front view of the tubular lens mount  21  as seen looking down the longitudinal axis. This more clearly shows the preferred beveling of the edges  23  of the tubular lens mount  21 . In addition it can be seen that the cut along the longitudinal axis of the full hollow cylinder is not at the equator  41  of the cylinder. The cut is made above the equator  41 , and the resulting shape has the beveled edges  23  separated by a distance smaller than the inner diameter of the tubular lens mount  21 . In an exemplary embodiment the inner diameter of the tubular lens mount  21  is 2.2 mm and the beveled edges  23  extend 0.4 mm above the longitudinal equator  41  of the tubular lens mount  21 . While described as a hollow cylinder that has been cut, any method of manufacturing (e.g. extruding) the resulting hollow half cylinder shape of the tubular lens mount  21  is acceptable. 
         [0020]      FIG. 5  is a front view of the tubular lens mount  21  with a lens  22  partially inserted. Prior to the insertion of a lens  22 , the distance between the two edges  23  of the tubular lens mount  21  is less than the outer diameter of the lens  22 . The lens  22  is mounted in the tubular lens mount  21  by first forcing the edges  23  of the tubular lens mount  21  apart. This momentarily increases the effective diameter of the tubular lens mount  21 , and increases the distance between edges  23  to allow for the insertion of lens  22 . The lens  22  is inserted parallel to the longitudinal axis of the tubular lens mount  21 . 
         [0021]    The distance between the edges  23  must allow for the insertion of the lenses  22 , and this provides an upper limit on how far the edges  23  of the tubular lens mount  21  may extend above the equator  41 . In addition, the selection of the material used and the thickness of the tubular lens mount  21  will impact how far the edges  23  of the tubular lens mount  21  may extend above the equator  41 . As noted above, the tubular lens mount  21  needs to have sufficient flexibility to allow for the expansion of edges  23  during the insertion of the lenses  22  and sufficient rigidity to hold the lenses  22  in place. The distance between the edges  23  is reduced the farther the edges  23  extend above the equator  41 , requiring a more flexible material. The distance between the edges  23  is increased the closer the edges  23  are to the equator  41 , allowing for the use of a less flexible material. If the edges  23  extend too far above the equator the tubular lens mount  21  will either be too rigid or too flexible. If the lens mount  21  is too rigid, the edges  23  will not flex apart far enough to allow the insertion of the lenses  22 . If the lens mount  21  is too flexible, the edges  23  will not have sufficient rigidity to hold the lenses  22  in place after insertion. 
         [0022]      FIG. 6  is a front view of the tubular lens mount  21  with a lens  22  fully inserted. As noted in the discussion of  FIG. 5 , a lens  22  is mounted in the tubular lens mount  21  by first forcing the edges  23  of the tubular lens mount  21  apart. This results in an increased effective diameter of the tubular lens mount  21 . Once in place, as shown in Detail B of  FIG. 6 , the lens  22  will now be in contact with the tubular lens mount  21  at a single point of contact  24  between the base of lens  22  and the center of the tubular lens mount  21 . The force holding the edges  23  of the tubular lens mount  21  apart is then removed. This results in two additional points of contact  25  as shown in Detail A of  FIG. 6 . Specifically the lens  22  will now be in contact with the tubular lens mount  21  at each edge  23 . This results in the lens  22  being held in suspension with three contacts points. 
         [0023]      FIG. 6  shows that the outer circumference of lens  22  is not in complete contact with the inner surface of the tubular lens mount  21 . As mentioned above, unlike conventional designs, the inner diameter of the tubular lens mount  21  is equal to or slightly smaller that the diameter of the lenses to be mounted. This prevents full circumferential contact between the lens  22  and the tubular lens mount  21 . Instead, as the force holding the edges  23  apart is removed, the edges  23  will come in contact with the lens  22 . This results in a slight bowing of the tubular lens mount  21  as shown in  FIG. 6 . 
         [0024]    The tubular lens mount  21  may be used with any number or type of lenses that have a circular or cylindrical shape that is parallel to the direction of the light. These could include rod lenses, concave lenses, convex lenses, or doublets. In addition spacers may be used in the tubular lens mount  21  to separate individual lenses  22  by desired distances. 
         [0025]    There are numerous advantages to this approach of constructing a field and relay lens system. First, lenses  22  may be installed and/or reinstalled in any order. With conventional designs, each lens  22  would have to be installed in sequence as there is no access to the interior of the full cylinder. This means that with conventional designs any repairs potentially require removing a large number of lenses  22  to obtain access to the correct lens  22 . Second, because the outer diameter of the lenses  22  is not required to be smaller than the inner diameter of the mounting tube, precise placement of the lenses  22  is now possible. This allows for improved optical quality of the image, as the lens centerlines can be collinear. In addition the distance between each lens  22  in the field and relay lens system can be guaranteed. The combination of precise mounting of lenses  22  with the ability to mount lenses  22  in any order allows for great control over the optical quality of the images produced with a field and relay lens system of this type. In addition, if the lenses  22  in a field and relay lens system of this type become unaligned, easier access for realignment is possible. 
         [0026]    Although the present disclosure has been described in relation to particular embodiments thereof, many other variations, modifications, combination of features, and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present disclosure be limited not by the specific disclosure herein, but only by the appended claims.