Scale-focus or zone-focus is a type of focusing system used by many inexpensive cameras from the 1940s and 1950s. These cameras have an adjustable focus, but lack a focusing aid such as a rangefinder. You had to determine the distance to the subject and set the focus using a scale printed on the lens. If you are good at estimating distances, or have a tape measure at hand, you can get precise, sharp focus with one of these cameras.