Optical scanning apparatus

Abstract

The present invention has as its object to provide a compact optical scanning apparatus of high performance. So, in the present invention, an optical scanning apparatus comprised of two or more reflecting mirrors is of a construction in which the optical characteristics of the mirrors are made different from each other, and an unevenness in light quantity on a surface to be scanned is corrected.

1 . An optical scanning apparatus comprising: 
 light source means having a light emitting portion emitting light beam;    deflecting means;    an imaging optical system for causing the light beam deflected by the deflecting means to be imaged into a spot shape on a surface to be scanned; and    a plurality of mirrors provided in an optical path between the deflecting means and the surface to be scanned,    wherein at least two of the plurality of mirrors differ in reflectance for an on-axial ray from each other, and reflectance for the on-axial ray and reflectance for an off-axial ray of each of the at least two of the plurality of mirrors are different from each other.    
   
   
       2 . An optical scanning apparatus according to  claim 1 , wherein the reflectance for the on-axial ray and the reflectance for the off-axial ray of each of said at least two of said plurality of mirrors are made different from each other in order to compensate for unevenness in image plane illuminance on said surface to be scanned.  
   
   
       3 . An optical scanning apparatus comprising: 
 light source means having a light emitting portion emitting light beam;    deflecting means;    an imaging optical system for causing the light beam deflected by the deflecting means to be imaged into a spot shape on a surface to be scanned; and    a plurality of mirrors provided in an optical path between the deflecting means and the surface to be scanned,    wherein at least two of the plurality of mirrors differ in reflectance for an on-axial ray from each other, and reflectance for the on-axial ray and reflectance for an off-axial ray of a mirror having the lowest reflectance among the plurality of mirrors are different from each other.    
   
   
       4 . An optical scanning apparatus according to  claim 3 , wherein reflectance for the on-axial ray and reflectance for the off-axial ray of said mirror having the lowest reflectance among said plurality of mirrors are made different from each other in order to compensate for unevenness in image plane illuminance on said surface to be scanned.  
   
   
       5 . An optical scanning apparatus according to  claim 3 , 
 wherein light beam emitted from said light source means is P-polarized with respect to and incident on an incidence surface of an fθ lens constituting said imaging optical system; and    wherein reflectance for the on-axial ray of said mirror of the lowest reflectance among said plurality of mirrors than that for the off-axial ray thereof.    
   
   
       6 . An optical scanning apparatus comprising: 
 light source means having a light emitting portion emitting a beam;    deflecting means,    an imaging optical system for causing the beam deflected by the deflecting means to be imaged into a spot shape on a surface to be scanned; and    a plurality of mirrors provided in an optical path between the deflecting means and the surface to be scanned,    wherein a width of the light beam incident on a deflecting surface of the deflecting means in a main scanning direction is greater than the width of the deflecting surface in the main scanning direction;    wherein at least two of the plurality of mirrors differ in reflectance for an on-axial ray from each other; and    wherein reflectance for the on-axial ray of a mirror having the lowest reflectance among the plurality of mirrors is smaller than reflectance for an off-axial ray thereof.    
   
   
       7 . An optical scanning apparatus according to  claim 6 , wherein reflectance for the on-axial ray of said mirror of the lowest reflectance among said plurality of mirrors is made smaller than that for the off-axial ray thereof in order to compensate for unevenness in image plane illuminance on said surface to be scanned.  
   
   
       8 . An optical scanning apparatus comprising: 
 light source means having a light emitting portion emitting a beam;    deflecting means;    an imaging optical system for causing the beam deflected by the deflecting means to be imaged into a spot shape on a surface to be scanned; and    a plurality of mirrors provided in an optical path between the deflecting means and the surface to be scanned,    wherein reflectance for an on-axial ray of each of at least two of the plurality of mirrors is 90% or less, and reflectance for the on-axial ray thereof and reflectance for an off-axial ray thereof are different from each other.    
   
   
       9 . An optical scanning apparatus according to  claim 8 , wherein said reflectance for the on-axial ray of each of said at least two of said plurality of mirrors and said reflectance for the off-axial ray thereof are made different from each other in order to compensate for unevenness in image plane illuminance on said surface to be scanned.  
   
   
       10 . An optical scanning apparatus according to  claim 1 , wherein an fθ lens constituting said imaging optical system is a plastic lens.  
   
   
       11 . An image forming apparatus comprising: 
 an optical scanning apparatus according to  claim 10;     a photosensitive member disposed on said surface to be scanned;    a developing device for developing an electrostatic latent image formed on said photosensitive member by the beam scanned by said optical scanning apparatus as a toner image;    a transferring device for transferring said developed toner image to a transfer material; and    a fixing device for fixing the transferred toner image on the transfer material.    
   
   
       12 . An image forming apparatus comprising: 
 the optical scanning apparatus set out in  claim 11;  and    a printer controller for converting code data inputted from an external device into an image signal and inputting it to the optical scanning apparatus.    
   
   
       13 . A color image forming apparatus comprising: 
 a plurality of optical scanning apparatuses comprises the optical scanning apparatus set out in  claim 10;  and    a plurality of image bearing members disposed on the surfaces to be scanned of the respective optical scanning apparatuses for forming images of different colors thereon.    
   
   
       14 . A color image forming apparatus according to  claim 13 , further comprising a printer controller for converting a color signal inputted from an external device into image data of different colors and inputting them to the respective optical scanning apparatuses.  
   
   
       15 . An optical scanning apparatus according to  claim 2 , wherein an fθ lens constituting said imaging optical system is a plastic lens.  
   
   
       16 . An optical scanning apparatus according to  claim 3 , wherein an fθ lens constituting said imaging optical system is a plastic lens.  
   
   
       17 . An optical scanning apparatus according to  claim 4 , wherein an fθ lens constituting said imaging optical system is a plastic lens.  
   
   
       18 . An optical scanning apparatus according to  claim 5 , wherein an fθ lens constituting said imaging optical system is a plastic lens.  
   
   
       19 . An optical scanning apparatus according to  claim 6 , wherein an fθ lens constituting said imaging optical system is a plastic lens.  
   
   
       20 . An optical scanning apparatus according to  claim 7 , wherein an fθ lens constituting said imaging optical system is a plastic lens.  
   
   
       21 . An optical scanning apparatus according to  claim 8 , wherein an fθ lens constituting said imaging optical system is a plastic lens.  
   
   
       22 . An optical scanning apparatus according to  claim 9 , wherein an fθ lens constituting said imaging optical system is a plastic lens.