Close-up lens attachment that, shorten close-focusing distance of lenses by shortening the focal length. The higher the strength the shorter the focal length and the shorter the focusing distance. The strength is given as reciprocal of focal length in meter.
A Split diopter is a standard diopter element which is precision-cut in half and mounted in a ring. It creates a shot with two planes of focus rather than one. Makes a sharp image of the foreground (captured through the diopter) and the background (captured through the uncovered half of your camera’s lens).