Abstract:
An endoscope includes a shaft receiving at least a pair of the lens groups movable jointly to provide focusing of an image upon actuation of an adjusting wheel and adapted to be disengaged to have displacement of one of the pair of lens groups relative to the other lens group for adjusting a magnification of the image.

Description:
TECHNICAL FIELD 
     The present invention relates to an endoscope having variable magnification according to the generic part of claim 1. 
     Endoscopes of this type are employed for medical and technical applications. 
     STATE OF THE ART 
     A generic endoscope is known from FR A 2 648 920. This printed publication describes the optical construction of an endoscope having variable magnification. In order to change the magnification of the generated eyepiece image, the two groups of lenses comprising the eyepiece are moved differently. Focusing occurs by moving the eyepiece as one unit. 
     A mechanical construction with which the relatively complicated movements of the individual groups can be realized is not described in this printed publication although it would be necessary, particularly, in an endoscope to realize the individual possible adjustments by means of a compact construction in order to prevent the eyepiece region, which is essential for handling, of the endoscope from becoming too large and too heavy. 
     Another endoscope having variable magnification is known from U.S. Pat. No. 4,666,262. This endoscope is also provided with an endoscope objective lens attached to its distal end, with an image relay which transmits the image of the endoscope objective lens to the proximal end, and with an eyepiece through which the image transmitted by the image relay is observed. The eyepiece is composed of several groups of lenses, some of which are adjustable, therefore the magnification of the eyepiece image is adjustable. Although the mechanical construction of this known endoscope is relatively simple, the pupil changes due to the selected optical construction of the eyepiece, which is disturbing in a number of applications. 
     DESCRIPTION OF THE INVENTION 
     The object of the present invention is to provide an endoscope having variable magnification of the eyepiece image with no change in the state of the pupil and in which the required movements can be carried out with a light and compact mechanical construction. 
     In the invented solution, at least one of the lens groups continues to be moveable for adjusting the magnification of the eyepiece image, whereas for focusing the eyepiece respectively the lens groups are moved as a unit. These movements are realized in that the lenses of the eyepiece not moved for adjusting the magnification are contained in a first tube in which at least one other tube containing a lens group moved for adjusting the magnification is conveyed in a moveable manner. The result is a very simple construction of the eyepiece tube without needing to substantially enlarge the external diameter of the eyepiece in relation to the endoscope while maintaining constant magnification of the eyepiece. The increase in weight is minimal so that the invented endoscope is well balanced and therefore feels good &#34;in the hand&#34;. 
     The invented endoscope can, of course, possess variable magnification, thus be provided with a zoom eyepiece. Especially suited is the invented design, however, for two-position eyepieces. 
     In this case, the other tube can be retained in any of the magnification positions by a lock-in means in the first tube, in particular, by means of a spring-biased ball which engages in one of the two grooves in the first tube. 
     This embodiment has the particular advantage that it suffices to provide a single adjusting wheel with which magnification can be adjusted and the eyepiece image can be focused. For this purpose the adjusting wheel acts on the other tube in such a manner that when the adjusting wheel is rotated, first the first and the other tube are moved jointly. As the path of the movement of the first tube is limited on both sides by a stop respectively, when the adjusting wheel is rotated again, the other tube is conveyed from one magnification position to another magnification position. The adjusting wheel can act on the other tube via a worm wheel/gear engagement or a toothed rack/gear connection. 
     In the simplest embodiment of the present invention, only one lens group is moved to adjust the magnification of the eyepiece image. However, in order to improve image quality, it is an advantage if two lens groups are designed in a moveable manner. 
     For this purpose one of the two lens groups is contained in the other (second) tube, and the other moveable lens group is contained in a third tube. The third tube is pretensioned by a spring in the direction of the second tube with a stop limiting the movement path of the third tube. 
     As in the invented embodiment, the lens groups of the eyepiece are moved jointly in order to adjust focusing, it is especially advantageous if a glass cover is provided in the eyepiece which is preferably included in the optical calculation of the eyepiece elements. 
    
    
     A BRIEF DESCRIPTION OF THE DRAWING 
     The present invention is made more apparent in the following using preferred embodiments with reference to the drawing depicting in: 
     FIG. 1 a section through the proximal part of an invented endoscope, and 
     FIG. 2 the lenses of a preferred embodiment of a two-position eyepiece in both magnification positions. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     FIG. 1 shows the proximal part of a preferred embodiment of an invented endoscope. The endoscope is provided in an as such known manner with a light guide connection 1 through which the light from an illumination source, not depicted, is conveyed to the distal end of the endoscope, also not depicted. 
     The object field illuminated by this light is imaged by an endoscope objective lens (also not depicted) attached to the distal end and is transmitted by an image relay 2 to the proximal end. The image relay 2 can be, as in the shown preferred embodiment, composed of a relay lens system which is provided with a rod lens or a fiber bundle or a gradient lens system. 
     The (real) image transmitted to the proximal end is observed by means of an eyepiece optic 3 or imaged using a video camera flange-mounted to the eyepiece funnel 13. 
     The lens system 3 of the two-position eyepiece is depicted in more detail in FIG. 2. The following table shows the radii R 2  to R 20 , the air spaces respectively lens thicknesses including the materials for a preferred embodiment of the present invention and for one of the two magnification positions. The air spaces for the second magnification position are indicated in the lower section of FIG. 2. Surface R 1  is one of the two surfaces of the glass cover of the eyepiece. 
     In one position of the two-position eyepiece, magnification is 30-fold and in the other position 80-fold. 
     
         ______________________________________Surface No.Material   Radius      Airspace/thickness______________________________________1          plane       11.67   air2          62.64       3.50    SK53          -15.18      0.40    air4          17.53       5.50    SK165          -12.32      1.0     SFL66          -145.38     8.57    air7          plane       10.33   air8          20.54       2.50    S-SFL569          plane       0.20    air10         4.22        4.00    S-SF511         -11.63      1.0     S-SFL5612         1.94        3.391   air13         7.29        1.80    S-LAF314         -2.05       1.10    S-SF1015         -5.87       6.64    air16         -3.50       1.75    S-BAK417         -2.05       0.90    S-SFL5618         -4.47       0.20    air19         5.46        2.0     S-SF1020         plane       3.91    air______________________________________ 
    
     The lenses figures correspond to the ones selected by Schott, Mainz, Germany. 
     As FIG. 2 shows, in the depicted preferred embodiment of the present invention, two groups of lenses are moved for adjusting the magnification. The two moved groups of lenses are the two distal-end-facing groups of lenses, whose diameter are relatively small in such a manner that the moving mechanism for adjusting the magnification can be compact and light. 
     The mechanism is made more apparent in the following with reference to FIG. 1: 
     In order to realize the mentioned movements, the stationary lenses of the eyepiece are contained in a first tube 4, which is contained in a moveable manner in an external tube 5 of the eyepiece part of the endoscope. A second tube 6 and a third tube 7 are contained in a moveable manner in the first tube 4. The third tube 7 is pretensioned by a spring 8 in the direction of the second tube 6, with a stop 9 limiting the movement path of the third tube. 
     A single adjusting wheel 10, which acts on the second tube 6 and moves it when rotated, is provided for adjusting magnification and focusing. The second tube 6 is determined in the two magnification positions by a lock-in means in the first tube 4. The lock-in means is produced by a spring-biased ball 11 which can engage one of two grooves 12 in the first tube according to the respective set magnification. 
     When the adjusting wheel 10 is rotated, first the first and the second tube are moved jointly. As the movement path is limited on both sides by stops, when the adjusting wheel of the second tube is rotated again, the second tube is conveyed from one magnification position to the other magnification position. The third tube follows the movement of the second tube due to the pretensioning by the spring with a stop limiting the movement path of the third tube. 
     A glass cover 14, which is included in the optical calculation of the eyepiece, is provided in the eyepiece funnel 13 for sealing the endoscope. 
     In the preceding, the present invention is described using a preferred embodiment without the intention of limiting the scope or spirit of the overall inventive idea. Nonetheless, reference is made to the drawing for illustration of all the details not explained in more detail herein.