This close-up accessory is placed between the camera body and lens to enable high-magnification photography. Eight electronic contact points allow communication between the camera and lens to continue as usual. The magnification differs according to the lens.
This is the magnifying factor of a lens. Macro lenses will often be described by their “magnification factor”. A lens with a 1:1 magnification factor produces a projected image on the sensor which is the same as the subject.