Patent ID: 7087892

Claim:
A light scanner comprising: a light source portion for emitting a light beam having a predetermined wavelength; an optical deflector for scanning the light beam from the light source portion; a first imaging optical system placed between the light source portion and the optical deflector for guiding the light beam from the light source portion to a deflection surface of the optical deflector; a second imaging optical system of a single curved mirror placed between the optical deflector and a surface to be scanned for guiding the light beam from the optical deflector to the surface to be scanned; a scanning start signal detector for detecting the light beam scanned by the optical deflector; and a detecting optical system placed between the optical deflector and the scanning start signal detector for guiding the light beam scanned by the optical deflector to the scanning start signal detector, wherein the first imaging optical system, the optical deflector and the second imaging optical system are located at different positions in a sub-scanning direction so that the light beam from the first imaging optical system enters obliquely with respect to a plane containing a normal to the deflection surface of the optical deflector and being parallel to a main scanning direction, and the light beam from the optical deflector enters obliquely with respect to a plane containing a normal to the curved mirror at its vertex and being parallel to the main scanning direction, an angle θM formed by an optical axis of the light beam traveling to the curved mirror and the plane containing the normal to the curved mirror at its vertex and being parallel to the main scanning direction satisfies 10<θM<35, the curved mirror also is part of the detecting optical system, and in the cross section taken along a sub-scanning direction, when the angle of a reflected light beam from the deflection surface of the optical deflector with respect to an incident light beam from the first imaging optical system is measured in a positive direction, the angle of a reflected light beam from the curved mirror with respect to an incident light beam from the deflection surface is measured in a negative direction.