"New optical design: advanced 5-element/4-group optical design incorporating ultra-high index tanatalum-based optical glass to achieve extraordinary optical performance with improved corner sharpness, distortion and reduced vignetting. Industry's best aperture ring covers a 8-stop range markings, clearly indicating actual number of f-stops. No more guesswork! (Patent pending). Compatible with both Nikkor G lens and F lens (include non-AI and AI lens mounts). Advanced 5-element/4-group optical design incorporating ultra-high index tanatalum-based optical glass by Caldwell Photographic in the USA (patent pending). Increase maximum aperture by 1 stop. Increase MTF. Makes lens 0.71x wider. The tripod foot is detachable and compatible with Arca Swiss, Markins, Photo Clam ball heads. Tips: Before mounting your lens to the adaptor, please make sure that the f-stop of aperture ring on the adaptor is turned to ""7"" (i.e. mounting your lens to the adaptor while only the aperture ring in the adaptor is full closed.). Remark: This mount is manual aperture control. It does NOT support electronic aperture control. Like the revolutionary original Metabones Speed Booster announced in January 2013, the Speed Booster ULTRA has a magnification of 0.71x, and so it effectively reduces the crop factor of mirrorless cameras with DX-sized sensors, such as Sony E-mount and Fuji X-Mount cameras, from 1.5x to 1.07x. Howev"