Close-up lens attachment that, shorten close-focusing distance of lenses by shortening the focal length of the optical system. The higher the strength the shorter the focal length and shorter the focusing distance.

The strength is given as reciprocal of focal length in meter. That means a +1 diopter puts the focus plane to 1m. Enables the user to take macro images without using a dedicated macro lens. By shorten the focal length of taking lens the magnification increases while the field of view decreases but keeping the depth of field.

Popular to reduce the close focus distance using vintage lenses especially anamorphic lenses and zooms that do not focus as close as primes. Offers several effects for storytelling, from miniaturizing look when put on a wide field lens with large aperture to very close distance images taken showing little details on small objects when used with a long focal length.