The Metabones Speed Booster Ultra 0.71x F-Mount to RF-Mount Lens Adapter mounts F-Mount lenses on an RF-Mount camera body. Its optical group compresses the image circle to 0.71x, which widens the field of view and adds one stop of light. An aperture ring on the adapter sets the diaphragm, which keeps a lens with no aperture ring of its own controllable. A tripod foot carries the weight of the lens instead of hanging it off the camera mount.