Scanning and imaging optical system, optical scanner, and image forming apparatus with lenses of different signs and refractive index distribution increasing toward rim

Abstract

A scanning and imaging optical system that condenses beams of light deflected by an optical deflector toward a surface to be scanned to form a light spot for optical scanning on the surface includes plurality of scanning lenses. Among the scanning lenses, at least two of the scanning lenses are resin lenses that are formed by plastic molding, and where a position coordinate in a horizontal scanning direction or in a vertical scanning direction is X, refractive index distribution in a cross-section with respect to the position coordinate X is Δn(X), the refractive index distribution in a cross-section in the horizontal scanning direction that includes an optical axis or in the vertical scanning direction of the resin lenses, signs of the refractive index distribution Δn(X) at least in the vertical scanning direction are not identical for all of the resin lenses.