Abstract: An anti-backlash means, particularly adapted for photographic enlargers including a channel shaped optical bench having a pair of guideways; a frame movable along the guideways, having a pair of tracks, a pair of rack elements, and leaf springs supporting the rack elements in continuous relation; a gear rotatably supported by the optical bench including a pair of gear elements engageable with the rack elements, and wheels riding on the tracks to maintain a fixed minor spacing between the pitch plane of the rack elements at the pitch radius of the gear elements; either the gear elements or the rack elements having offset teeth to eliminate backlash.