It might seem strange to produce a speed booster that converts full-frame lenses to full-frame. But with the Canon EOS R and EOS RP mirrorless cameras, when you’re shooting 4K video, you’re not exactly using the entire full-frame view of the sensor. The Canon EOS R has about a 1.75x crop factor, and the EOS RP has a 1.64x crop factor (similar to APS-C).
The new Metabones EF-RF Speed Booster ULTRA 0.71x, however, helps to reverse this problem. It widens the view when EF lenses are used on the EOS R and EOS RP to 1.24x and 1.15x respectively when shooting 4K video.