Image forming apparatus with resolution control

Abstract

An image forming apparatus which enables resolution modes to be readily changed over has a light-emitting element for irradiating a polygonal mirror with a light beam and a controller for controlling the light-emitting element. The controller is connected to an image clock signal changeover circuit that changes the period of an image clock signal to a period which is n (a positive integer) times the former. The controller is arranged such that the image recording density in the horizontal scanning direction can be changed by the image clock signal changeover circuit and/or the controller judges the pulses of a horizontal synchronizing signal output from a photosensor to be valid at intervals of (n-1) pulses, thereby enabling control of the recording density in the vertical scanning direction. An electrostatic latent image with the desired recording density can be obtained on a photosensitive member by selecting a combination of an image recording density changeover operation for the horizontal scanning direction in which the period of the image clock signal is multiplied by n and an image recording density changeover operation for the vertical scanning direction in which the pulses of the horizontal synchronizing signal are judged to be valid at intervals of (n-1) pulses.