Sharper corners, less distortion, reduced vignettingMetabones EF-RF Speed Booster ULTRA 0.71x - to adapt Canon EF mount full-frame lenses to the new Canon RF mount. Filmmakers are now able to mitigate most of the 4k video crop factor of EOS R (1.75x) and EOS RP (1.63x) and reduce it to 1.24x and 1.15x respectively. The field of view is now much closer to still photo mode. This new Speed Booster is not intended for still photography but will work if the camera is configured to APS-C mode.Speed Booster ULTRA uses an advanced 5-element/4-group optical design by Caldwell Photographic Inc., incorporating ultra-high index tantalum-based optical glass to achieve extraordinary optical performance with improved corner sharpness, distortion and reduced vignetting. Speed Booster ULTRA has a magnification of 0.71x, effectively reducing the crop factor of 4k video on EOS R and EOS RP from 1.75x to 1.24x. The Speed Booster ULTRA design makes very effective use of exotic materials at the furthest limit of glassmaking technology, and as a result is well corrected for use with virtually all full-frame SLR lenses regardless of exit pupil distance. Thus, the Speed Booster ULTRA performs extremely well with professional-grade f/2.8 zoom lenses such as the 24-70mm f/2.8 and 70-200mm f/2.8 zooms by Canon to produce 17-50mm f/2.0 and 50-142mm f/2.0 high-speed zooms, respectively. Similarly, high-speed fixed focal length lenses such as a 50mm f/1.2 will be transformed into a 35.5