The BMPCC4K Speed Booster ULTRA 0.71x and XL 0.64x are similar to the standard M43 Speed Booster adapters (MB_SPEF-m43-BT3 and MB_SPEF-m43-BT4) but the optics have been re-designed to optimise for the filter stack thickness of 2.4mm found in Blackmagic cameras rather than the 4mm of a standard Micro Four Thirds.
