Abstract:
A rod lens comprises a tubular body having a first end, a second end, a length and a diameter, a first optically transparent closing element, tightly sealing the first end of the tubular body, a second optical transparent closing element, tightly sealing the second end of the body. The rod lens further comprises n further optical elements being positioned within the tubular body defining n+1 chambers in the tubular body, with n being an integer &gt;0, and n+1 optical fluids being positioned in the n+1 chambers, with each of the n+1 optical fluids being positioned in one of the n+1 chambers, whereby at least one of the n+1 optical fluids having a refractive index different from the other n+1 optical fluids.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority of German patent application No. 10 2005 027 880.9 filed on Jun. 9, 2005. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a rod lens and an endoscope comprising at least one such rod lens. 
   Rod lenses per se are known and are for example used by the applicant under the designation “Hopkins Optics” in rigid endoscopes. 
   Rod lenses in general consist of a cylindrical body made from glass whereby the opposite circular ends are machined in order to form optical elements. The length of their body is usually many times bigger than their diameter. 
   Rod lenses have got the advantage that they conduct light for example in an endoscope with a higher efficiency than can be achieved with conventional plate-shaped lenses between which relatively large pockets of air exist. 
   Rod lenses made of glass have got the disadvantage, though, that they always form rigid bodies and cannot be used in flexible endoscopes. Therefore, in general, bundles of fiber optic picture guides are used in flexible endoscopes. Such bundles of fiber optic picture guides have got the disadvantage that they create a pixelated picture which reduces the precision of the representation notably. 
   Rod lenses made from glass further have got the disadvantage that they are made from a brittle material. During their daily use for example in an optical system of an endoscope, they will be dropped every now and then, leading to splinters coming off or even to the breakage of the rod lens. Such damage renders the optical system unusable. In such cases usually the complete optical system must be replaced. 
   In order to compensate for those disadvantages of rod lenses made of glass, flexible liquid filled rod lenses have been developed. 
   One example for such a flexible rod lens is known from U.S. Pat. No. 5,892,625. Such a rod lens comprises a tubular body which is tightly sealed on both ends by closing elements. Between those closing elements there is disposed a transparent fluid such as water or an optical fluid. In this way rod lenses are created which show at least some degree of flexibility. It has often proven difficult though to adjust such rod lenses to the desired optical characteristics. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the invention to describe a fluid-filled rod lens with which optical aberrations can be corrected in a simple and economical fashion. 
   The applicant has now found that through the formation of different chambers in such a fluid-filled rod lens which are filled with liquid or gel-like optical media having different refractive indices the optical characteristics of a fluid-filled rod lens can be adjusted in a simple but highly precise fashion. In this way optical aberrations e.g. in an endoscope can be corrected. 
   According to one aspect of the invention, a rod lens is provided comprising a tubular body having a first end, a second end, a length and a diameter, a first optically transparent closing element, tightly sealing said first end of said tubular body, a second optically transparent closing element, tightly sealing said second end of said tubular body, n further optical elements being positioned within said tubular body defining n+1 chambers in said tubular body, with n being an integer &gt;0, and n+1 optical fluids being positioned in said n+1 chambers, with each of said n+1 optical fluids being positioned in one of said n+1 chambers, whereby at least one of the n+1 optical fluids has a refractive index different from the other n+1 optical fluids. 
   According to another aspect of the invention an endoscope comprising at least one such rod lens is provided. 
   The expression “optical fluid” as used herein comprises all liquid and gel-like optical media. 
   The expressions “first optically transparent closing element”, “second optically transparent closing element”, “first further optical element”, “second further optical element”, “first optical fluid” “second optical fluid” etc. as used herein solely serve to distinguish the closing elements, further optical elements or the optical fluids respectively from each other and they are no indications towards their position relative to one another or other characteristics. 
   The expression “further optical element” as used herein designates every transparent element which can tightly separate two chambers within the tubular body. 
   Since the refractive index of optical fluids can be precisely controlled and since the optical fluids can easily be introduced into the rod lens or removed therefrom, the rod lenses according to the invention can be adjusted to the desired optical characteristics in a notably simpler and more precise fashion. 
   Therefore in many cases the use of such rod lenses can make the use of expensive optical elements such as achromatic lenses redundant. 
   The tubular body of the rod lens can hereby have any shape as long as it comprises an internal hollow space and two openings opposite to each other. The cross-section of the tubular body will usually be circular but it can also be oval, elliptical or polygonal. 
   The tubular body can be made from any material as long as this material is impervious towards the optical fluid contained therein. Examples for materials used for making the tubular body include plastics or metals. 
   The closing elements and the further optical elements can also be made from any material as long as it is impervious towards the optical fluid contained within the tubular body as well as optically transparent. Examples for materials used for making the closing elements or the further optical elements include glasses or plastics. 
   The tubular body can be connected to the closing elements and the further optical elements by all means known to a man of the art as long as a connection is formed which is impervious against the enclosed optical fluids. Examples for connections include those that can be achieved by gluing, cementing, welding, crimping or by shrinking the tubular body onto the closing elements or the further optical elements respectively. 
   The closing elements and the further optical element can also be first inserted into a metallic tube and a tube-like shrinkable material can be mounted on top of the assembly in order to improve the seal. 
   The optical fluid can be any known liquid or gel-like optical medium as long as its refractory index is bigger than that of air. Examples for such optical fluids include materials such as those commercially available from Cargille Laboratories Cedar Grove, N.J., USA. 
   Preferably the optical media should comprise substances which are stable over long periods of time. 
   The n+1 optical fluids contained in the n+1 chambers can be exclusively liquid or exclusively gel-like optical media as well as any combination of liquid and gel-like media. 
   In an embodiment of the invention the tubular body consists of a flexible material. 
   This measure increases the fracture-resistance of a rod lens. 
   Due to the construction of the body from a flexible material the whole rod lens can be made flexible and used for example in flexible endoscopes instead of bundles of optical fibers. 
   In a further embodiment of the invention tubular body is made from plastic. 
   This has got the advantage that the tubular body is light as well as highly fracture-resistant. 
   In a further embodiment of the invention the length of the tubular body is bigger than the diameter of the tubular body especially at least three times as big. 
   Such ratios of length of the tubular body to diameter result especially in their use in an endoscope in particularly advantageous optical characteristics. 
   In a further embodiment of the invention at least one of n+1 the optical fluids has a refractive index of more than 1.3, preferably all of the n+1 optical fluids have a refractive index of more than 1.3. 
   The conduction of light in an optical medium is proportional to the square of the refractive index of that optical medium. This means that the higher the refractive index the better the transmission of light. Through the above measure the transmission of light in the rod lens is notably improved. 
   In a further embodiment at least one of the closing elements is designed as an optical element and preferably both closing elements are designed as optical elements. 
   This measure has got the advantage that the closing elements can not only be used to contain the optical media within the tubular body but they can also be used to adjust the optical characteristics of the rod lens to the respective application. 
   In a further embodiment of the invention at least one of the n further optical elements is a lens. 
   This measure has got the advantage that the further optical elements cannot only be used to separate the optical fluids but they can also be used to adjust the optical characteristics of the rod lens to the respective application. 
   In a further embodiment of the invention at least one of the n further optical elements is an optically transparent membrane. 
   Such an optically transparent membrane can thereby be curved or planar. 
   This measure has got the advantage that an optically transparent membrane is very light leading to a notably lighter rod lens. The use of a curved membrane further provides another possibility for optical corrections. 
   Such an optically transparent membrane itself further has got only very little influence on the optical characteristics of the rod lens so no additional errors are generated thereby which would then have to be corrected again with other optical elements or the optical fluids. 
   In an endoscope with several further optical elements these can be any combination of lenses, optically transparent membranes and other optical elements. 
   In a further embodiment of the invention n=1. 
   It has been found that in many cases one further optical element and therefore two chambers for the optical fluids are sufficient to achieve the desired characteristics. 
   Therefore this creates a constructively simple and easy to manufacture rod lens. 
   It will be appreciated that the features mentioned above and those still to be mentioned below can be used not only in the cited combination but also in other combinations or on their own without departing from the scope of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Illustrative embodiments of the invention are now explained in more detail in the following description and depicted in the drawings in which: 
       FIG. 1  shows a longitudinal section of a first embodiment of a fluid-filled rod lens, and 
       FIG. 2  shows an endoscope comprising fluid-filled rod lenses in a partial section. 
       FIG. 3  shows a longitudinal section of a further embodiment of a fluid-filled rod lens. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   In  FIG. 1  a fluid-filled rod lens in its entirety is designated with the reference numeral  10 . 
   The rod lens  10  comprises a tubular body  12  with a first end  14  and a second end  16 . The tubular body  12  is hereby made from a shrinkable plastic. 
   On the first end  14  the body  12  is sealed by a first optically transparent closing element  18  which is designed here as a lens. The body  12  was connected tightly to the closing element  18  by shrinking the plastic onto the closing element  18 . 
   On the second end  16  the body  12  is sealed by a second optically transparent closing element  20 . This second closing element  20  was also connected tightly to the body  12  by shrinking the plastic of body  12  onto the second closing element  20 . 
   The second closing element  20  is here designed as an achromatic lens and comprises a collecting lens  22  and a dispersing lens  24 . The collecting lens  22  is thereby made from crown glass and the dispersing lens  24  is made from flint glass. This combination of lens and lens material leads to chromatic aberrations which can occur when polychromatic light is transmitted through a rod lens being corrected. 
   Between the first closing element  18  and the second closing element  20  a further optical element  25  is positioned within the body  12  which is here designed as a lens. Since only one further optical element  25  is present n=1. This optical element  25  has also been connected tightly to the tubular body  12  by shrinking the plastic of the tubular body  12  onto the optical element  25 . Through this tight connection two (n+1) chambers are created which are completely separated from each other. The two chambers are in their circumference delimited by the tubular body  12 . A first chamber  26  is on one side delimited by the first closing element  18  and on the other side by the further optical element  25 . A second chamber  27  is delimited on one side by the further optical element  25  and on the other side by the second closing element  20 . 
   In the instance shown here the two chambers  26  and  27  have different sizes but it is obvious to a man of the art that the dimensions of the two chambers  26  and  27  can have any ratio to each other. 
   A first optical fluid  28  is filled into the first chamber  26  and a second optical fluid  29  is filled into the second chamber  27 . 
   The two optical fluids  28  and  29  are in this instant both optical liquids. These optical liquids are immersion liquids which are commercially available from Cargille Laboratories Cedar Grove, N.J., USA under formula codes 4550 and 50350. 
   The dimensions of the chambers  26  and  27  as well as the refractive indices of the optical fluids  28  and  29  are hereby matched in such a way that the desired optical characteristics of the rod lens  10  are achieved. 
   The body  12  has got a length L and an internal diameter D. Length L is about 3.5 times bigger than diameter D so that for use in a shaft of an endoscope a suitable cylindrical shape and excellent optical performance is achieved. 
   In  FIG. 2  an endoscope in its entirety is designated with the reference numeral  30 . 
   The endoscope  30  comprises a shaft  32  with a distal end  34  and a proximal end  36 . 
   Shaft  32  is sealed tightly at its distal end  34  by a closing element  38 , the closing element  38  being designed as a lens here. 
   At its proximal end  36  shaft  32  terminates in a head  40  of the endoscope  30  to which is connected an ocular  42 . 
   The inside of the shaft  32  forms an optical tube  44  of the endoscope  30 . Through the optical tube  44  light from the distal end  34  of the shaft is conducted to the ocular  42 . 
   Fluid-filled rod lenses are positioned within the optical tube  44 , two of which  50  and  50 ′ are shown here which are of identical design. Rod lens  50 ′ is turned 180° in relation to rod lens  50 . It is also possible to have more rod lenses which can be the same or different. 
   One of the two rod lenses  50  and  50 ′ will now be described as an example. 
   The rod lens  50  comprises a tubular body  52  consisting here of metal. The tubular body  52  comprises a first end  54  and a second end  56 . 
   The tubular body  52  is sealed off at its first end  54  by a first optically transparent closing element  58  which is here designed as a lens. The first closing element  58  is thereby cemented into the tubular body  52  in order to create a tight connection. 
   The tubular body  52  is sealed off at its second end with a second optically transparent closing element  60  which is here also designed as a lens. The second closing element  60  is hereby cemented into the tubular body  52  in order to create a tight connection. 
   Within the tubular body  52  there is further disposed a further optical element  65  which is here designed as a curved optically transparent membrane. This optically transparent membrane is glued to the tubular body  52  in order to form a tight connection between the tubular body  52  and the further optical element  65 . The further optical element  65  divides the tubular body  52  into a first chamber  66  and a second chamber  67 . Therefore n=1 in this case. 
   The two chambers  66  and  67  are in their circumference delimited by the tubular body  52 . The first chamber  66  is delimited on one side by the first closing element  58  and on the other side by the further optical element  65 . The second chamber  67  is delimited on one side by the further optical element  65  and on the other side by the second closing element  60 . 
   A first optical fluid  68  is disposed in the first chamber  66  and a second optical fluid  69  is disposed in the second chamber  67 . 
   The two optical fluids are transparent optical gels which are commercially available from Cargille Laboratories Cedar Grove, N.J., USA under gel codes 0607 and 0608. 
   The optical characteristics of the two optical fluids are adjusted to each other so that optical aberrations such as chromatic aberrations are corrected and an achromatic lens is no longer needed in this rod lens. 
   In order to produce such a rod lens  50  the further optical element  65  is glued into the tubular body  52 . After that the first optical fluid  68  is filled into the first chamber  66  on the right hand side of this drawing. After that the first closing element  58  is inserted into the tubular body  52  making sure that no air bubbles are present in this first optical fluid  68 . The closing element  58  is then tightly cemented into the tubular body  52 . 
   In a second step the second optical fluid  69  is filled into the second chamber  67  on the left hand side of this drawing. After this the second closing element  60  is inserted into the tubular body  52  making sure that no air bubbles are present in the second optical fluid  69 . The second closing element  60  is then cemented tightly into the tubular body  52  so that in all a tight optically transparent fluid-filled rod lens  50  is formed. Such a rod lens can be built into the endoscope  30  in the same way as a known rod lens made from glass. 
   The filling of the rod lens can also take place after inserting and connecting the two closing elements and the further optical element with body  52  for example by radial openings in body  52  which are then closed. 
   Furthermore a tube can be shrunk onto the rod lens  50  in order to provide further measures to ensure lasting seal. 
   In  FIG. 3  a rod lens is designated in its entirety with the reference numeral  80 . 
   Rod lens  80  comprises a tubular body  82  made from a flexible plastic having a first end  84  and a second end  86 . 
   At the first end  84  the tubular body is tightly sealed by a first closing element  88  which is here designed as a lens. The first closing element  88  has been glued into the tubular body  82  in order to provide a tight connection. 
   At the second end  86  the tubular body  82  is tightly closed by a second closing element  90  which is here designed as a lens. The second closing element  90  has been glued into tubular body  82  in order to ensure a tight connection. 
   Arranged within the tubular body  82  is a first further optical element  90  and a second further element  94 . Therefore in this case n=2. The first optical element  92  and the second optical element  94  have been both glued into the tubular body  82  in order to provide a tight connection. 
   The first closing element  88  and the first further optical element  92  together with the tubular body  82  define a first chamber  96 . The first further optical element  92  and the second further optical element  94  together with the tubular body  82  define a second chamber  98 . The second further optical element  94  and the second closing element  90  together with the tubular body  82  define a third chamber  100 . 
   The first chamber  96  is filled with a first optical fluid  102  which in this case is an immersion liquid commercially available from Cargille Laboratories, Cedar Grove, N.J., USA under code number 50350 with a refractive index of 1.475. 
   The second chamber  98  is filled with a second optical fluid  104 . The second optical fluid  104  is an optical gel which is commercially available from Cargille Laboratories, Cedar Grove, N.J., USA under code number 0607. This optical gel has a refractive index of 1.457. 
   The third chamber  100  is filled with a third optical fluid  106  which in this case is the same immersion liquid as has been used for the first optical fluid  102 . 
   This leads to a symmetrical rod lens with three fluid-filled chambers. 
   The first closing element  88 , the first optical fluid  102  in the first chamber and the first further element  92  form a lens triplet which acts as an achromatic lens. The second further optical element  94 , the third optical fluid  106  in this third chamber  100  and the second closing element  90  also form a lens triplet which acts as an achromatic lens. 
   Although the three-chambered rod lens  80  here is symmetrical it is obvious to a man of the art that this must not necessarily be the case and the ratio of the dimensions of the first chamber  96 , the second chamber  98  and the third chamber  100  relative to each other can be varied in order to adapt the rod lens to the desired optical properties.