JPS6435523A - Light scanning device - Google Patents

Abstract

PURPOSE:To prevent influence to light scanning caused by the stain and the scratch of a deflecting surface by specifying the shapes of the incident surface of an image-formation lens in a main scanning direction and the projectile surface of the said lens in the main and sub scanning direction. CONSTITUTION:The incident surface of the image-formation lens which is a single lens has a negative toric surface in the sub scanning direction and the shapes of the incident surface in the main scanning direction and the projectile surface in the main and sub scanning direction are decided according to a formula I. Supposing that compound focal distance of the image-formation lens and a positive anamorphic lens in the main scanning direction is fm, the compound focal distance in the sub scanning direction is fs, the radius of curvature near the optical axis of the projectile surface is R3, refractive index is (n) and the diameter of a beam waist is BW(=4lambdafm/pid), (d) means the diameter of an incident beam and lambda means a wavelength), the image-formation lens and the positive anamorphic lens are made to satisfy the condition of inequalities II and III. In the formula I, H means the height from the optical axis, K means the constant of a cylinder, A means the curvature near the optical axis, B and C mean the constants and X means a distance from the plane close to an apex to the lens surface in the height H from the optical axis. Thus, the light scanning does not easily receive the influence by the scratch and the stain of the deflecting surface and the printing of reflection on the deflecting surface can be solved.