Optical printer
Common optical effects include fade outs and fade ins, dissolves, slow motion, fast motion, and matte work. More complicated work needs dozens of elements, all combined into a single scene. Ideally, the audience in a theater should not be able to notice any optical printers work, but this is not always the case. For economical reasons, especially in the 1950s, and later in TV series produced on movie, printer work was limited to only the actual parts of a scene needing the effect, so there is a clear change in the image quality when the transition occurs.