A restitution instrument for measuring and evaluating picture plates. The instrument includes a mounting stage for mounting the plate. The stage has two edges forming a 90.degree. angle. A carriage means attached to the stage, is used for guiding the stage free of rotation in directions parallel to the edges, i.e., X and Y directions. A drive means is attached to the stage for driving the stage in the X and Y directions along the carriage means. The drive means includes a drive unit slidably mounted to each of the edges and a drive member driven by a drive motor. The member is mounted at 90.degree. to the edge. The member drives the stage in a line of motion perpendicular to the edge. The lines of motion of each of the members intersects at a fixed point whose projection on to the stage falls upon an image point under observation. The drive means includes a measuring means for determining the distance the stage is driven in each of the X and Y directions. A stationary support member is located in close proximity to the image point. The drive members are braced against the member. The apparatus includes an optical observation system for viewing the image point. The system has a measuring mark and a beam splitter prism supported by the support member. The instrument provides increased accuracy and stability when compared with known restitution instruments.
