Abstract: A document scanner carriage housing contains a pair of spaced mirrors whose spacing and parallelism is precisely maintained by floating metal spacer plates which are not affixed to the housing. Spaced springs urge one of the mirrors into engagement with the spacer plates, the other mirror being referenced to the molded plastic housing. The parallel facing image plane sides of the mirrors are substantially unobstructed by the spacer plates which contact them thus allowing the scanner to efficiently use a substantial proportion of the image planes of the mirrors and occupy a comparatively small footprint. The floating spacer plates and mirrors are cushioned against shock and vibration by compressed elastomeric pads on the underside of the housing cover which allows the spacing and parallelism of the mirrors to be maintained without direct affixation of the mirrors or spacer plates to the housing.