Document density detector apparatus

Abstract

A document density detector apparatus to be used for an image forming apparatus in which a focal lens is disposed in an optical pass for guiding light reflected from the surface of a document, to the surface of a light receiving body, and a light sensor for detecting the density of the document is fixed outside of an area through which the light reflected from the surface of the document passes before illuminating a predetermined surface of the light receiving body, and in which an image of the document formed on the light receiving body may be enlarged or reduced at the desired magnification by moving the focal lens along the optical pass in the direction toward the document or toward the light receiving body. When an image forming mode is set at magnification which causes the focal lens to be moved to a position nearer to the document from the reference position, the focal lens is moved such that the density of a document is detected with the focal lens moved to the reference position, and when a mode for automatic detection of the density of a document is set before image forming, for an image forming apparatus capable of selecting the mode for automatic detection, or at any time for an image forming apparatus so arranged as to always execute automatic detection of the density of a document, before image forming.