This T Speed Booster Ultra 0.71x Adapter from Metabones allows a full-frame Canon EF-mount lens to be used on a Canon RF-mount camera. While providing a one-stop increase for the camera over the lens's aperture range, up to a maximum output aperture of f/0.9, the adapter's optics help to maximize the connected lens's apparent angle of view during UHD 4K video capture.

When recording UHD 4K video, a Canon RF-mount camera is only able to capture the center portion of the image projected on its sensor, creating an in-camera "crop factor." A Canon EOS R Mirrorless Digital Camera Body and a Canon EOS RP Mirrorless Digital Camera Body feature a UHD 4K crop factor of 1.75x and 1.63x respectively. Inside this adapter, five optical elements in four groups condenses the light from the full-frame lens and effectively reduces the crop factor to 1.24x and 1.15x respectively. This also makes available to the sensor an additional one stop of light throughout the lens's aperture range.

This adapter is constructed from aluminum alloy for durability while minimizing weight and its mounting rings are made with brass to further prevent wear-and-tear. An internal, matte black coating prevents the appearance of reflections within the adapter barrel, and to help reduce stress on the camera mount when placed on a tripod, the adapter includes a detachable Arca-type compatible tripod foot with 1/4"-20 threads.

This T Speed Booster Ultra 0.71x Adapter supports electronic communication between an attached camera and lens. If the lens includes autofocus, image stabilization, as well as camera-controlled aperture functions, this adapter is intended to allow use of those features. Also, if an attached lens is capable of generating EXIF metadata when used with a directly compatible camera, this adapter is designed to transfer that information, so it can be saved along with image files generated the combined Canon EF-mount lens and Canon EF-M mount camera.