Abstract: A reading optical system for projecting a document image on a CCD in an image reading device, providing, sequentially from the document side, a symmetrical lens group rotatable about the optical axis, and a free curved mirror. Reflective surface shape of the free curved mirror is symmetrical in a plane perpendicular to the linear layout direction of the line CCD and includes the intersection of the optical axis of the lens group and the reflective surface of the free curved mirror. The reflective surface shape of the free curved mirror is asymmetrical in a plane parallel to the linear layout direction of the line CCD and includes the normal line (NL) at the intersection. The number of lenses of the lens group structure can be reduced to three lenses while maintaining a high optical performance by using such a free curved mirror.

Abstract: A reading optical system for projecting a document image on a CCD in an image reading device, providing, sequentially from the document side, a symmetrical lens group rotatable about the optical axis, and a free curved mirror. Reflective surface shape of the free curved mirror is symmetrical in a plane perpendicular to the linear layout direction of the line CCD and includes the intersection of the optical axis of the lens group and the reflective surface of the free curved mirror. The reflective surface shape of the free curved mirror is asymmetrical in a plane parallel to the linear layout direction of the line CCD and includes the normal line (NL) at the intersection. The number of lenses of the lens group structure can be reduced to three lenses while maintaining a high optical performance by using such a free curved mirror.

Abstract: A zoom lens system consists of, in order from the enlargement side to the reduction side, a first lens unit having a negative optical power and a second lens unit having a positive optical power. In the zoom lens system, either the first or the second lens unit has at least one surface having an optical power of diffraction.

Abstract: A zoom lens system is provided with first, second, and third lens units from an enlargement side. The first, second, and third lens units have a negative refractive power, positive refractive power, and negative refractive power, respectively. The first lens unit has a first doublet lens composed by a biconvex lens and a biconcave lens. The second lens unit has a second doublet lens composed by a biconvex lens and a negative meniscus lens. During zooming from the longest focal length end to the shortest focal length end, the first lens unit is kept stationary and the second and third lens units are each moved monotonically.

Abstract: A radial gradient index lens system has a refractive index distribution. The refractive index decreases from an optical axis along a height. The lens system has two meniscus lens elements whose convex surfaces have a larger radius of curvature than concave surfaces. The meniscus lens elements are arranged symmetrically with respect to an aperture stop so that the convex surfaces thereof face an object side and an image side, respectively. The gradient index lens system is for use in a copying apparatus or as a reading optical system.