A single pass highlight color printer is disclosed which utilizes two pairs of Raster Output Scan (ROS) systems mounted symmetrically about a common polygon motor assembly (38,40). Four identical optical systems (30,32,34,36) are thus provided , with diode laser outputs (6,8,10,12) directed from a ROS frame (4') parallel and separated to allow the appropriate spacing for xerographic components situated adjacent the xerographic belt. Each ROS unit includes a 90° mirror pair (36D1,36D2) which is mounted on a roof mirror carriage (36F) which in turn is connected to a focus carriage (36G) via a flexible guide system (50,52,54; 58,60,62). The interaction between the focus carriage and the roof mirror carriage enables a skew alignment and process (beam steering) adjustment to be accomplished with a high degree of precision.