The Metabones T Speed Booster Ultra 0.71x Adapter for Canon Full-Frame EF-Mount Lens to Sony E-Mount APS-C Camera allows a full-frame Canon EF-mount lens to be mounted onto a Sony E-mount camera. While doing so, the adapter's optics help to maximize the connected lens's apparent angle of view while providing a 1-stop increase for the camera over the lens's aperture range.

If a lens intended for 35mm film or similarly sized full-frame camera sensors is connected to a camera with a Sony E-mount APS-C-sized sensor, it would project an image larger than the Sony E-mount APS-C sensor was built to accept. Able to capture only the center portion of the projected image, the effective angle of view of the lens would be narrowed, creating an in-camera "crop factor." The T Speed Booster Ultra 0.71x Adapter for Canon Full-Frame EF-Mount Lens to Sony E-Mount APS-C Camera condenses the light from a lens designed for 35mm film or "full frame" camera sensors and projects it onto a Sony E-mount APS-C sensor. This allows a Sony E-mount APS-C sensor to utilize more of the light gathered by a connected lens, which effectively reduces the crop factor while making available to the sensor an additional 1 stop of light for each of the lens's f/stop settings.