Metabones Speed Booster Ultra uses an advanced 5-element 4-group optical design incorporating ULTRA-high index tantalum-based optical glass. The new design of Ultra version is specifically optimized for the Micro Four Thirds sensor and filter stack, and as a result achieves an astonishing level of performance that sets a new standard for focal reducers. The Speed Booster is essentially a backwards teleconverter, effectively shortening the focal length of the lens that's attached. This model act as a 0.71x focal length multiplier lens.