Surveying instrument

Abstract

A surveying instrument includes a sighting telescope having an objective lens and an eyepiece; an erecting optical system functioning so that an image formed by said objective lens is viewed as an erect image through the eyepiece; and a light shield device, positioned in an optical path extending from an incident surface of the erecting optical system to an exit surface of the erecting optical system, for preventing an off-field light bundle which is incident on the erecting optical system from reaching the eyepiece.

1 . A surveying instrument comprising: 
 a sighting telescope having an objective lens and an eyepiece;    a semitransparent film positioned between said objective lens and said eyepiece;    a focus detecting device which receives light which is passed through said semitransparent film to detect a focus state of said sighting telescope; and    a light shield device, positioned in an optical path extending from said semitransparent film to said focus detecting device, for preventing an off-field light bundle which is incident on said semitransparent film from reaching said focus detecting device.    
   
   
       2 . The surveying instrument according to  claim 1 , further comprising an erecting optical system functioning so that an image formed by said objective lens is viewed as an erect image through the eyepiece, said semitransparent film being formed on a reflection surface of said erecting optical system.  
   
   
       3 . The surveying instrument according to  claim 2 , wherein said light shield device comprises a light shield mask fixed to an incident surface of said erecting optical system.  
   
   
       4 . The surveying instrument according to  claim 2 , further comprising a beam splitting prism which is provided separately from said erecting optical system and cemented to said semitransparent film, said light shield device being fixed to said beam splitting prism.  
   
   
       5 . The surveying instrument according to  claim 4 , wherein said semitransparent film is formed on a first reflection surface of said erecting optical system, said beam splitting prism being cemented to said first reflection surface wherein said semitransparent film being positioned between said beam splitting prism and said first reflection surface.  
   
   
       6 . The surveying instrument according to  claim 4 , wherein said semitransparent film is formed on a second reflection surface of said erecting optical system, said beam splitting prism being cemented to said second reflection surface wherein said semitransparent film being positioned between said beam splitting prism and said second reflection surface.  
   
   
       7 . The surveying instrument according to  claim 4 , wherein said beam splitting prism comprises a right-angle prism.  
   
   
       8 . The surveying instrument according to  claim 1 , further comprising an erecting optical system functioning so that an image formed by said objective lens is viewed as an erect image through the eyepiece; and 
 a beam splitting prism provided separately from said erecting optical system;    wherein said semitransparent film is formed on said beam splitting prism.    
   
   
       9 . The surveying instrument according to  claim 8 , wherein said light shield device is fixed to an exit surface of said beam splitting prism.  
   
   
       10 . The surveying instrument according to  claim 8 , wherein said beam splitting prism comprises a right-angle prism.  
   
   
       11 . The surveying instrument according to  claim 1 , wherein said focus detecting device comprises a phase-difference detection focus detecting device.  
   
   
       12 . The surveying instrument according to  claim 1 , wherein said focus detecting device comprises a contrast detecting focus detecting device.  
   
   
       13 . The surveying instrument according to  claim 1 , wherein said erecting optical system comprises a Porro prism.  
   
   
       14 . The surveying instrument according to  claim 13 , wherein said Porro prism comprises three right angle prisms.  
   
   
       15 . The surveying instrument according to  claim 1 , wherein said erecting optical system comprises a roof prism.  
   
   
       16 . The surveying instrument according to  claim 1 , wherein said sighting telescope comprises a focus adjustment lens positioned between said objective lens and said erecting optical system.