A device for expanding the effective width Of an image forming surface, such as the face of a cathode ray tube, on which characters are formed in proper succession to make up lines of composition includes a carriage supporting photographic material, which is in optical alignment with the image forming surface, for permanently recording the images thus formed on the display surface, the carriage being movable from a first position, where a large portion of the photographic material is exposed to the image formed on the tube, to a second position where the remainder of the photographic material is placed within the field of view of the image forming surface.