Abstract: A linear printhead writer assembly includes a linear source of radiation such as an LED printhead, and an elongated linear focusing device such as a linear lens array, and a support housing for supporting both the source of radiation and focusing device in a fixed relation with respect to each other and to an exposure locus. A positioning bar is supported by the support housing and engages a web image member to position the image member with respect to the exposure locus. The writer is preferably used with an image member having a radiation-sensitive layer on a side opposite the writer and is particularly adapted for exposing a charged image member already containing a toner image as part of a process to create a two-color image on the image member. The focusing device is held in the writer assembly by a coupling with a pair of end supports, each coupling allowing thermal expansion of the lens support and also isolating the lens support from vibration transmitted through the support housing.