Scanning optical system

Abstract

A scanning optical system has an object side lens unit for condensing light from an object, a mirror for performing a main scan to read the image of the object by deflecting the light transmitted through the object side lens and an image side lens unit for forming an image on the image sensing surface using both the extra-axial light and axial light in a subscan direction deflected by the mirror. The scanning optical system satisfies the predetermined condition defined by lenses of Abbe number.

What is claimed is:  
     
         1 . A scanning optical system comprising: 
 an object side lens unit for condensing light from an object;    a mirror for performing a main scan to read the image of the object by deflecting the light transmitted through the object side lens; and    an image side lens unit for forming an image on the image sensing surface using both the extra-axial light and axial light in a subscan direction deflected by the mirror; and    wherein the following condition is satisfied:    0.1<|(Σν fp−Σνfm )/ Lf|< 20.0    where Σνfp represents the sum of the Abbe numbers of the positive optical power lenses within the object side lens unit, Σνfm represents the sum of the Abbe numbers of the negative optical power lenses within the object side lens unit, and Lf represents the number of lenses in the object side lens unit.    
     
     
         2 . The scanning optical system according to  claim 1 , wherein the following condition is satisfied:  
       10.0<|(Σν rp−Σνrm )/ Lr|< 50.0  where Σνrp represents the sum of the Abbe numbers of the positive optical power lenses within the image side lens unit, Σνrm represents the sum of the Abbe numbers of the negative optical power lenses within the image side lens unit, and Lr represents the number of lenses in the image side lens unit.    
     
     
         3 . The scanning optical system according to  claim 1 , wherein the object side lens unit has a cemented lens comprising a negative lens element and a positive lens element on the outermost object side.  
     
     
         4 . The scanning optical system according to  claim 3 , wherein the cemented lens satisfies the following condition:  
       |φ f− 1/φ f|< 1.0  where φf−1 represents the optical power of the cemented lens on the outermost object side within the object side lens unit, and φf represents the optical power of the object side lens unit.    
     
     
         5 . The scanning optical system according to  claim 1 , wherein the object side lens unit comprises sequentially from the object side an object side front lens unit and an object side back lens unit arranged with a relatively large spacing therebetween.  
     
     
         6 . The scanning optical system according to  claim 5 , wherein the outermost image side lens element within the object side front lens unit and the outermost object side lens element within the object side back lens unit satisfy the condition below:  
       0.4< Rf− 1 r/Rf− 2 f< 5.0  where Rf−1r represents the radius of curvature of the image side surface of the outermost image side lens element within the object side front lens unit, and Rf−2f represents the radius of curvature of the object side surface of the outermost object side lens element within the object side back lens unit.    
     
     
         7 . The scanning optical system according to  claim 5 , wherein the object side front lens unit satisfies the following condition:  
       0.05< Tf− 12×φ f< 0.4  where Tf−12 represents the distance between the object side front lens unit and the object side back lens unit, and φf represents the optical power of the object side lens unit.