If you own a BMPCC4K it is safe to say that one of the most purchased accessories for it, and some would say essential, is a Speed Booster of some kind, whether it's from Metabones or from a company like Viltrox. These new models from the former have had their optics redesigned to account for the filter stack thickness of the BMPCC4K, which Metabones says is substantially thinner than standard M43 cameras.
According to the company this is particularly important when the camera is used with extremely large apertures. As many users will know, some of the less expensive Speed Boosters out there can become extremely soft when the aperture is wide open.
In addition to the new optical tuning, the adaptors feature a tripod mount that lines up precisely with the bottom of the BMPCC4K itself, so that the camera and the Speed Booster can both be attached to the same quick release plate.
There are two new models, the Ultra 0.71x, which is the one you'll need if you have a lot of APS-C or DX lenses, and the XL 0.64x, which is better suited to full-frame lenses. Both adaptors are available for EF, EF Cine, and Nikon G mounts. The 0.71x Ultra is also available in PL mount form.