Patent ID: 7247840

Claim:
An image forming apparatus, comprising: a plurality of optical systems and a plurality of image carriers, each optical system scanning a surface of a corresponding image carrier with a laser beam in a main scanning direction to form an image of a specific color on the image carrier; a plurality of first detecting units and a plurality of second detecting units, each first detecting unit being situated at a first position along the main scanning direction of a corresponding laser beam and each second detecting unit situated at a second position along the main scanning direction of the corresponding laser beam, wherein the first detecting unit and the second detecting unit detect the corresponding laser beam; clock generating units for each laser beam; and a plurality of third detecting units, each third detecting unit being situated at a third position along the main scanning direction of a corresponding laser beam, wherein the third detecting unit detects the corresponding laser beam, wherein a clock frequency adjusting unit configured (a) to count a number of clocks of a write clock during a period from when any of the first detecting units, the second detecting units, and the third detecting units detects the corresponding laser beam until any of an adjoining first detecting unit, second detecting unit, and third detecting unit detects the corresponding laser beam, (b) to take a count of the number of clocks for one laser beam as a reference value, and (c) to adjust a write clock frequency of each of the laser beams other than the one lased beam so as to coincide with the reference value.