Patent ID: 7202985

Claim:
An inner drum exposure apparatus comprising: a light source side optical system for polarizing and combining two laser beams emitted from the light source side, each independently modulated based on an image signal, by using a polarized light beam splitter, and for changing said two laser beams to right circular polarized light and left circular polarized light so as to be emitted toward a reflection surface of a light deflector serving as a scanning portion; a quarter wave plate integrally arranged on the rotation axis of said light deflector provided with the reflection surface, for converting said two laser beams constituted by right circular polarized light and left circular polarized light input from said light source side optical system into mutually orthogonal linear polarized light; an optical element of uniaxial crystal that is integrally arranged on the rotation axis of said light deflector provided with the reflection surface, and emits said two laser beams converted into mutually orthogonal linear polarized light by said quarter wave plate at different respective positions enabling switching resolution within a narrow range of 10% or less, whereby a division width D 3 of beam spots in a sub-scanning direction on a scanning surface is set according to the following expression: D 3=( D 1 +D 2)/2 ±D 4 wherein an interval of first beam spots corresponding to a first resolution is D 1 , an interval of second beam spots corresponding to a second resolution is D 2 at a time of switching resolution within a narrow range of 10% or less, and a design tolerance in the sub-scanning direction is D 4 ; and a sub-scan moving portion controlling so as to move said scanning portion in correspondence to the resolution.