Patent ID: 7071957

Claim:
An image forming apparatus comprising: a first optical system comprising a first light beam generator, a second light beam generator, and a first scanner adapted to scan a first photosensitive member with a light beam from said first light beam generator to form a first color image on the first photosensitive member and to scan a second photosensitive member with a light beam from said second light beam generator to form a second color image on the second photosensitive member; a second optical system comprising a third light beam generator, a fourth light beam generator, and a second scanner adapted to scan a third photosensitive member with a light beam from said third light beam generator to form a third color image on the third photosensitive member and to scan a fourth photosensitive member with a light beam from said fourth light beam generator to form a fourth color image on the fourth photosensitive member; a transfer unit adapted to transfer images formed on each photosensitive member to a common transfer medium; a control unit adapted to control each of said light beam generators to form a pattern for correcting a color mis-registration; a position detector capable of detecting a position in a conveyance direction of patterns formed by each of the light beam generators, even where the position is less than one scan line; and a correcting unit adapted to correct a color mis-registration whose magnitude is less than one scan line in a conveyance direction by adjusting a relational phase of said first scanner and said second scanner according to detection results of said position detector.