Makes Lens 0.71x Wider, Aluminum Alloy and Brass Construction, Satin Surface Finish, Positive-Lock EF Lens Mount, LED Indicator, Image Stabilization Lens Support, Autofocus Speed is Properly Adjusted, Increase Maximum Aperture by 1 Stop Use this Metabones Canon EF Lens to RF-Mount T CINE Speed Booster Ultra 0.71x (EOS-R) 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 to support the newly EOS C70 (Super 35mm sensor). The field of view is now much closer to still photo mode. The Speed Booster is not intended for still photography but will work if the camera is configured to APS-C mode. It uses an advanced 5-element/4-group optical design by Caldwell Photographic incorporating ultra-high index tantalum-based optical glass to achieve extraordinary optical performance with improved corner sharpness distortion and reduced vignetting. The 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. It has a design that 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. 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 35.5mm f/0.9 lens with excellent contrast and resolution from the center all the way to the edges of the image.