Optical writing device and image forming apparatus

An optical writing device, comprising:

• first and second light source units each of which includes one or more light sources;
• a single polygon mirror that deflects a light beam emitted from each of the first and second light source units;
• a first scanning optical system that includes one or more reflective optical elements to reflect a light beam and one or more transmissive optical elements to transmit a light beam and forms an image with a light beam emitted from the first light source unit and deflected by the polygon mirror;
• a second scanning optical system that includes one or more reflective optical elements to reflect a light beam and one or more transmissive optical elements to transmit a light beam and forms an image with a light beam emitted from the second light source unit and deflected by the polygon mirror;
• and
• a plurality of first light detecting sensors that are disposed so as to correspond to respective light beams emitted from the first and second light source units and are used for controlling a writing start timing;
• wherein the first and second light source units, the first and second scanning optical systems, and a housing for holding these components are constituted plane symmetrically relative to a plane including a rotation axis of the polygon mirror and being parallel to a scanning line,
• in the reflective optical elements held at both end sides in the main scanning direction in the first and second scanning optical systems, a number of hold points for positioning is different between a writing start side and a writing end side in scanning of a light beam,
• in the reflective optical elements of the first and second scanning optical systems disposed in the optical axis direction from after the polygon mirror to before a separation mirror to guide a light beam to the first light detecting sensor, a number of hold points on each of a writing start side and a writing end side in scanning is same, and
• in the reflective optical elements disposed from after the separation mirror up to a surface to be scanned, a number of hold points on the writing start side of the first scanning optical system is same with a number of hold points on the writing end side of the second scanning optical system, and a number of hold points on the writing end side of the first scanning optical system is set to same with a number of hold points on the writing start side of the second scanning optical system.