Abstract:
A relay set ( 1, 11, 23 ) for the optical system of a rigid endoscope, the optical system comprising an objective ( 20 ) at the distal end, an ocular ( 22 ) at the proximal end and between them a relay lens system consisting of several relay sets ( 1, 11, 21, 23 ), the relay set ( 1, 11, 23 ) consisting of two half sets ( 2   a   , 2   b ) having the same lens units ( 3   a   1, 3   a   2, 3   a   3, 3   a   4; 3   b   1, 3   b   2, 3   b   3, 3   b   4 ) arranged in symmetrical sequence with respect to the center ( 5 ) of the set, wherein each half set ( 2   a   , 2   b ) consists of four lens units ( 3   a   1, 3   a   2, 3   a   3, 3   a   4; 3   b   1, 3   b   2, 3   b   3, 3   b   4 ) having in the sequence of raising distance from the center ( 5 ) the refracting powers Positive, Negative, Positive, Positive (P, N, P, P).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Rigid endoscopes usually have an optical system consisting of an objective, an ocular and between them a relay lens system consisting of several relay sets. Because the objective and each relay set is producing an image which is turned up-side down, and because a standard endoscope should produce an upright image, usually an odd number of relay sets is used so that the image produced by the optical system is upright. 
         [0002]    Generic relay sets, as shown in U.S. Pat. No. 4,676,606 and U.S. Pat. No. 4,693,568, have a symmetrical arrangement of lens units so that the relay set is consisting of two symmetric half sets. 
         [0003]    Known relay sets have the disadvantage that they need highly complicated calculations to design a relay set with desired optical properties, i.e. with corrected lens aberrations. If a relay set is correctly designed, it has a fixed configuration and it is mass produced in this configuration to be used several times in an optical system. 
         [0004]    The disadvantage of the relay set, according to the state of the art, is that according to its fixed configuration it also has a fixed overall length. This means that an optical system; at reasonable costs, can only be produced having a length that is a multiple (normally odd multiple) of the length of the relay set. If a standard resectoscope has three relay sets and a longer resectoscope is needed, it is necessary to use five relay sets so that the overall length of the ocular is almost double. If an only slightly elongated endoscope is needed, a relay set with a length other than the standard length is needed and has to be completely redesigned. Such a complete redesign of a relay set is extremely complicated and expensive. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    The objective of the present invention is to make the design of endoscope with different lengths easier and less expensive. 
         [0006]    According to the invention, the lens units in each half set of the relay set and seen from the center are having the following refractive power (Positive and Negative in the following are called P and N): P,N,P,P. For the complete relay set this is P,P,N,P, (center), P,N,P,P. To make a relay set according to the state of the art with a new length, requires a complete recalculation of all distances of the lens units and also of the lens units themselves. Quite to the contrary, according to the invention a recalculation of the overall length of the relay set requires only finding new distances of the lens units. No changes with the lens units themselves are necessary. The correction of lens aberrations remains unaffected by the change of overall length. With the same set of lens units, using only different distances, a new overall length of the relay set can be achieved. Finding the correct placement of the lens units for a new overall length of the relay set is quite simple. For a given set of lens units simple formulas or curves can be given according to which all the places of the lens units for a desired overall length easily can be found. With the relay set according to the invention, therefore, it is an easy design step to change the overall length of the set. If an endoscope with a special overall length is needed, the invention allows for the simple design of relay sets of an appropriate length. The relay set according to the invention can be mixed in an optical system with conventional relay sets. If a given endoscope having three conventional relay sets each 60 mm long, has to be made 10 cm longer, one additional conventional relay set and one relay set according to the invention with a length of 40 mm can be added. 
         [0007]    It is advantageous to have the corresponding lens units of the two half sets at symmetrical distances from the center. With this design the magnification of the lens unit is 1 as it is generally required. 
         [0008]    Having the outer lenses in an asymmetrical position, the magnification is different from 1. The advantages of previous embodiments of the invention with respect to easy calculation of the overall length remain also with this embodiment. 
         [0009]    It is advantageous to place a glass rod in the middle of the relay set. This is a well known measure to reduce the air length. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    In the drawings examples of the invention are schematically shown. 
           [0011]      FIGS. 1   a - d  show the arrangement of the lens units of a relay set in four different overall lengths; 
           [0012]      FIGS. 2   a - c  show the lens units of a relay set having the same length but three different magnifications; 
           [0013]      FIG. 3  shows a conventional optical system with three conventional relay sets; and 
           [0014]      FIGS. 4   a - c  show an optical system having four conventional relay sets and one relay set according to the invention in three different lengths. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIGS. 1   a - d  show relay sets according to the invention in different lengths. 
         [0016]    In  FIG. 1   a , a relay set  1   a  is shown which, according to the invention, has two half sets  2   a  and  2   b  being symmetrically arranged with respect to the center of the relay set  1  which in the drawing is indicated by a center line  5 . From the center line  5  to the outside, the half set  2   a  has lens units  3   a   1 ,  3   a   2 ,  3   a   3  and  3   a   4 . The half set  2   b  has lens units  3   b   1 ,  3   b   2 ,  3   b   3  and  3   b   4 . The lenses of the pairs  3   a   1 - 3   b   1 ,  3   a   2 - 3   b   2 ,  3   a   3 - 3   b   3  and  3   a   4 - 3   b   4  are identical and are symmetrically placed with respect to the center line  5 . According to the invention, the refractive powers of the lens units are:  3   a   1  and  3   b   1  positive,  3   a   2  and  3   b   2  negative,  3   a   3  and  3   b   3  positive and  3   a   4  and  3   b   4  positive. This is indicated with the letters P and N underneath  FIG. 1   a.    
         [0017]    To the left and to the right of the relay set  1   a  image planes  6   a  and  6   b  are shown. Because of its symmetrical arrangement, the relay set  1  is transporting an image from  6   a  to  6   b  or vice versa with the magnification  1 . 
         [0018]    In  FIG. 1 , the relay set  1   a  is shown with a certain overall length. 
         [0019]    In  FIG. 1   b  and in  FIG. 1   c , relay sets  1   b  and  1   c  are shown having different overall lengths. As can be seen from  FIG. 1 , for all three lens sets  1   a ,  1   b  and is exactly the same lens units are used. Only their relative distances from the center line  5  are varied. In all three configurations the magnification is 1. Only the overall length is different. Also the correction of lens aberrations remains the same. All major lens aberrations are sufficiently corrected. 
         [0020]    If the relay set  1   a  is correctly designed in one overall length as shown in  FIG. 1   a , the variation of overall length is easily achieved. As can be seen from  FIGS. 1   a  to  1   c , the variation of lens positions follows simple relations. 
         [0021]    The lens units  3   a   1  to  3   b   4  do not require any redesign. According to the invention, it is only necessary to have the lens units chosen with proper refractive power, namely  3   a   1  and  3   b   1  with positive power,  3   a   2  and  3   b   2  with negative power,  3   a   3  and  3   b   3  with positive power and  3   a   4  and  3   b   4  with positive power. 
         [0022]    Following the before mentioned rule, the lens units can vary in shape from the embodiment shown in  FIGS. 1   a  to  1   c . Instead of the simple lenses shown in the drawing lens units of cemented type, composed of several different glasses can also be used. 
         [0023]      FIG. 1   d  shows an alternative relay set  1   d . The lenses  3   a   1  to  3   a   4  and  3   b   1  to  3   b   4  are the same as with  1   a . In the center gap between lenses  3   a   1  and  3   b   1 , a glass rod  7  with parallel end faces is placed in order to reduce in the big center gap between the half-sets  2   a  and  2   b , the distance through which the light has to travel through air. 
         [0024]    According to  FIGS. 1   a  to  1   d , the arrangement of lenses in the two half sets  2   a  and  2   b  is symmetrical with respect to the center line  5 . Due to this symmetrical arrangement of lens units the magnification of the relay sets  1   a  to  1   c  is  1 . An alternative possibility is shown in  FIG. 2 . 
         [0025]      FIG. 2   a  shows a relay set  11   a  having a similar design as relay set  1   a  of  FIG. 1   a . According to the invention, is the relay set  11   a  again has a symmetrical arrangement of lens units with a sequence of refractive power P,N,P,P in each half set. 
         [0026]      FIG. 2   b  shows a relay set  11   b  using exactly the same lens units as in relay set  11   a . As shown in  FIG. 2 , the overall length of relay set  11   a  and relay set  11   b  are the same. But in the relay set  11   b , the outermost lenses  14   a  and  14   b  are shifted asymmetrically. Due to this asymmetrical arrangement of lenses the magnification is different. In this case it is 0.75. 
         [0027]      FIG. 2   c  shows relay set  11   c  again having the same lenses as relay set  11   a . The outermost lenses  14   a  and  14   b , as can be seen in  FIG. 2   c , even more shifted asymmetrically as with lens unit  11   b . The overall length again is the same as that of the relay sets  11   a  and  11   b . The magnification of the relay set  11   c  is 0.5. It has to be remarked that in the examples shown in  FIGS. 2   a  to  2   c , the magnifications given as 1 for  FIG. 2   a,  0.75 for  FIG. 2   b  and 0.5 for  FIG. 2   c , are valid for rays passing the lens units from left to right. If the light goes from right to left the magnifications are 1 in  FIG. 2   a,  1.33 for  FIGS. 2   b  and  2  for  FIG. 2   c.    
         [0028]    The relay sets  11   a ,  11   b  and  11   c  of  FIG. 2  have the same advantage as the lens unit  1  shown in  FIG. 1  with respect to the possibility to easily change the overall length. 
         [0029]    The relay sets shown in  FIGS. 1 and 2  are used in rigid endoscopes as shown, for example, in FIG. 13 of U.S. Pat. No. 4,693,568. According to the standard design of rigid endoscopes, a rigid metal tube, not shown, is enclosing an optical system as shown in  FIG. 3 . 
         [0030]    The optical system of  FIG. 3  is of a conventional design having an objective  20 , three relay sets  21  and an ocular  22 . The relay sets  21  are identical. They may be of any conventional design according to the state of the art as mentioned in the introduction. To keep the image upright, the number of relay sets  21  is odd. 
         [0031]    If a longer endoscope is needed, additional relay sets can be added. This is shown in  FIG. 4   a . To the right of the optical system, two additional relay sets are added. One of them is another conventional relay set  21 . The other one is a relay set  23   a  designed according to the present invention, e.g. a relay set as shown in  FIG. 1  or  2 . As can be seen from  FIG. 4   a , the relay set  23   a  is shorter than the relay set  21  so that a desired specific overall length of the endoscope results. As shown in  FIGS. 4   b  and  4   c , relay sets  23   b  or  23   c  of different lengths can replace  23   a  so that any required overall length of the endoscope is possible. 
         [0032]    Additionally, it is possible to replace any of the conventional relay sets  21  by a relay set  23   a , according to the present invention, so that the overall length of the endoscope can be adjusted to any required length. For special purposes, a relay set according to  FIG. 2 , having a magnification smaller or bigger than 1, can be used.