Schneiders Diopter Full Gen2 are close-up lens attachments that reduce the near focus distance. The higher the strength, the shorter the focusing distance (MOD). The strength is given as reciprocal of focal length in meters. This means a +1 Diopter brings the plane of focus to 1 meter. Diopter shorten the focal length of the optical system.
Using Schneiders Diopter Full Gen2 filters macro images can be taken without using a special macro lens. By increasing the magnification while the field of view decreases but keeping the depth of field. These filters are popular to reduce the MOD of vintage lenses. Especially anamorphic lenses and zooms. They provide various effects for storytelling, from a miniaturized look on a wild field lens with a large aperture to very close-up images showing small details on small objects when used with a long focal length.