Laser scanning unit and method and apparatus for calibrating a post-scan assembly in a laser scanning unit

A laser scanning unit comprising:

• a separate upper housing portion and a separate lower housing portion;
• means attaching said upper housing portion and said lower housing portion to for a housing for said laser scanning unit,
• a scanning assembly including a scanning device;
• a first light beam source directing a first light beam toward said scanning device;
• a second light beam source directing a second light beam toward said scanning device;
• and
• first and second post-scan optical assemblies located to receive first and second scanning beams reflected from said scanning device, each said post-scan optical assembly comprising a first, second and third fold mirror, a first f-theta lens located between said first and said second fold mirrors, and a second f-theta lens located to receive light reflected from said third fold mirror and output a compensated scanning beam for generating a scan line on a corresponding photoconductive member, each said first and second fold mirror and said first f-theta lens being mounted in said upper housing portion and each said fold mirror and said second f-theta lens being mounted in said lower housing portion.