SCAN OPTICAL SYSTEM HAVING FALL COMPENSATING FUNCTION

摘要

PURPOSE:To compensate the fall of a deflector with a compact constitution, by adding a scan optical system including a single spherical lens and a Fresnel lens having a rotary asymmetrical refractive index from the side of the reflector between a medium to be scanned and the deflector. CONSTITUTION:The luminous flux given from a light source part 1 is linearly formed into an image at the area near the reflective surface 3a of a deflector 3 through the 1st image forming optical system 2 and then projected on a medium 6 to be scanned according to the rotary movement of the deflector 3 and via a single spherical lens 4 of the 2nd image forming optical system plus Fresnel lens systems 50a and 50b. The systems 50a and 50b contains a Fresnel lens 50a having the negative refractive power at the side of the deflector 3 and a Fresnel lens 50b having the positive refractive power at the side of the medium 6 and have the positive refractive power within a section including the optical axis of the lens 4 and vertical to the deflecting surface.