Abstract: In an optical scanner, coupling lens system 3 includes a first optical element as at least one optical element other than the optical element located the farthest away from a light source, the first optical element being made of a material having substantially no power and a negative temperature coefficient of refractive power, and scanning lens system 5 includes at least one second optical element made of a material having positive power and a negative temperature coefficient of refractive index.

Abstract: An image formation method for forming an image of a plurality of colors through a charging step, an image exposing step, a developing step and a transferring step, wherein the image exposing step is made up of a first image exposing step and a second image exposing step, the developing step of at least one color is carried out after the first image exposing step, and in the subsequent second image exposing step, the toner image area formed by the developing step is exposed and charge latent images for forming toner images of the rest of the colors are formed while a potential of the toner image area is selectively shifted.