In a previous article I wrote about recording 5K ProRes RAW with the Atomos Ninja V and the Canon EOS R5 by enabling crop mode, but this mode introduces a 1.6x crop, which can be mitigated with the Metabones EF to RF speed booster 0.71x, and by the way, has the same crop factor as the Canon EF-RF 0.71x Adapter.
Just like with the Canon EOS R that has a 1.83x crop, the math should be simple, multiplying the sensor crop factor by the focal reducer crop factor, in the case of the Canon EOS R 1.75x × 0.71x ≈ 1.24x, and in the case of the case of the Canon EOS R5 1.6x × 0.71 ≈ 1.13x, but empirical testing shows that is more like 1.15x
I know, in paper 1.13x vs 1.15x doesn’t look like much, but in practice, it is a huge difference. So after taking some snapshots with and without the focal reducer, there are the visual results, in yellow the 1.13x crop factor:
Also notice, the camera crops while recording UHD instead of DCI: