Lens for reading an original image

摘要

A lens for reading an original has first to third lens groups sequentially arranged from an object side toward an image side. The first lens group is constructed by a first lens as a positive meniscus lens having a convex face on the object side. The second lens group is constructed by a second lens as a biconcave lens. The third lens group is constructed by a third lens as a biconvex lens. The first lens is constructed by a refractive index distribution type lens having a refractive index changed in a direction perpendicular to an optical axis of the original reading lens. Each of the second and third lenses is constructed by a refractive index distribution type lens having a refractive index changed in a direction of the optical axis. Otherwise, at least one of the first, second and third lenses may be constructed by a refractive index distribution type lens. In this lens construction, the original reading lens can be made compact and a field angle of this lens can be easily widened and high performance of the original reading lens can be easily realized.