Light interception structure for an automatic focus detection surveying instrument

Abstract

A light interception structure for an automatic focus detection surveying instrument that includes a telescopic optical system having an objective optical system and an ocular optical system. A beam splitting optical element splits object light transmitted through the objective optical system of the telescopic optical system and includes a splitting surface. A focus detection device has a light receiving device for receiving light split by the beam splitting optical element. One surface of the beam splitting optical element is provided with an anti-reflection treatment. The one surface is a surface upon which external light entering the telescopic optical system through the ocular optical system is first incident after passing through or being reflected by the beam splitting surface of the beam splitting optical element.

What is claimed is:  
     
         1 . A light interception structure for an automatic focus detection surveying instrument comprising: 
 a telescopic optical system having an objective optical system and an ocular optical system;    a beam splitting optical element which splits object light transmitted through the objective optical system of the telescopic optical system, said beam splitting optical element including a splitting surface; and    a focus detection device having a light receiving device for receiving light split by the beam splitting optical element;    wherein one surface of the beam splitting optical element is provided with an anti-reflection treatment to provide light diffusion, said one surface comprising a surface upon which external light entering the telescopic optical system through the ocular optical system is first incident after passing through or being reflected by the beam splitting surface of the beam splitting optical element.    
     
     
         2 . The light interception structure for an automatic focus detection surveying instrument according to  claim 1 , wherein said anti-reflection treatment provides light diffusion such that a substantial portion of the external light entering the telescopic optical system is diffused.  
     
     
         3 . The light interception structure for an automatic focus detection surveying instrument according to  claim 2 , wherein said anti-reflection treatment for light diffusion is surface polishing.  
     
     
         4 . The light interception structure for an automatic focus detection surveying instrument according to  claim 2 , wherein the surface of the beam splitting optical element which is subject to the anti-reflection treatment is coated with an anti-reflection paint.  
     
     
         5 . The light interception structure for an automatic focus detecting surveying instrument according to  claim 1 , said beam splitting optical element comprising a Porro prism with a prism attached to a reflection surface of said Porro prism, a boundary between said Porro prism and said prism comprising said splitting surface.  
     
     
         6 . The light interception structure for an automatic focus detection surveying instrument according to  claim 1 , said splitting surface comprising a reflecting surface of a Porro prism.  
     
     
         7 . The light interception structure for an automatic focus detection surveying instrument according to  claim 1 , at least one surface of said beam splitting optical element being free of said anti-reflection treatment.