| 摘要 |
PROBLEM TO BE SOLVED: To control the fluctuation of diameters of light spot within tolerance by constituting a lens so as to be provided with the depth margin so that the fluctuation due to an image height of diameters of the light spot caused by ununuformity of refractive index in the lens is controlled within the tolerance in an actual use. SOLUTION: A luminous flux from a light source 10 is coupled with a succeeding optical system by a coupling lens 12 and is formed into a proper luminous flux cross sectional shape with an aperture 14 for forming a beam, and converged in a subscanning direction with a cylinder lens 16, and when it is reflected on a mirror 18, it is formed into a line image long in a main scanning corresponding direction near the deflecting reflection surface of the optical deflector 20 of a polygon mirror. The deflected luminous flux deflected in a constant angular velocity with the optical deflector 20 transmits a lens 30 for optical scanning to be converged on the surface to be scanned 40 as a light spot, which optically scans the surface 40 at a constant velocity. The lens 30 is formed by a plastic molding method, and however it has a refractive index distribution in its inside, the fluctuation due to the image height of the diameters of the light spot is controlled within the tolerance in actual use by designing the lens having the depth margin. |
