Speed booster to full frame? What at first sight seems to make little sense, can be very helpful in some cases: Because the mirrorless Canon R has a full frame image sensor, but this is not completely usable for filmmakers in 4K mode -- as known, only a section is read out. This disadvantage can now be circumvented to some extent with a new Metabones Speedbooster adapter.
The Canon EF to RF-Mount T Speed Booster ULTRA 0.71x reduces the focal length of the used EF lens and thus effectively reduces the 4K video crop factor of the Canon EOS R from about 1.75x to 1.24x, with the EOS RP the crop factor shrinks from 1.63x to 1.15x. As always, this also adds about one f-stop to the light intensity.
The dual-pixel autofocus is also supported, one of the advantages of the Canon camera(s). The optical image stabilization should also work.
Note that the adapter is only designed for 4K video and should not be used in FullHD mode, where the full sensor area is already active.
The Metabones Speedbooster Canon EF to RF-Mount T Speed Booster ULTRA 0.71x costs 479 dollars.