Apparatus for shifting a lens carriage including a variable magnification pancratic lens assembly having a plurality of relatively movable optical elements. The lens carriage is mounted to move a first lens element to a plurality of discrete positions along a travel path (oblique to the optical axis established at the 1:1 magnification ratio) for maintaining registration of the light image projected by the lens assembly in the image plane when the image-to-object distance is fixed. A second element of the lens assembly is carried by the first element and is longitudinally movable to a plurality of discrete positions relative to the first element. An arm is positioned in the path of movement of the second lens element to engage the second element to effect particular longitudinal movement thereof relative to the first lens element as the carriage is moved. A series of stops interact with the lens elements to establish specific optical relationships therebetween at discrete positions of the second lens element and discrete positions of the first lens element to provide the varying magnifications.