The Canon EF Lens to FUJIFILM X-Mount Camera Speed Booster ULTRA from Metabones improves upon the original Metabones Speed Booster with a 5 element/4 group optical design that incorporates ultra-high refractive index tantalum-based glass for improved sharpness and reduced distortion and vignetting. The Speed Booster ULTRA allows a full frame Canon EF lens to be mounted to an APS-C format X-Mount camera and in doing so, increases the angle of view and increases the maximum aperture by approximately one f/stop. 

When a lens intended for full frame sensors or 35mm film is mounted to a camera with an APS-C sized sensor, it transmits a larger area of light than the smaller sensor was built to accept and therefore the effective angle of view of the lens increases. The Speed Booster condenses light from the lens and projects it onto the APS-C sensor allowing the sensor to utilize all of the lens' light and effectively reduces the crop factor of and APS-C E-Mount camera from 1.5x to 1.07x, producing a full-frame angle of view with an APS-C sensor. A corresponding increase in the maximum aperture of one f/stop makes the lens more effective in low-light situations and able to create a shallow depth of field. 

Although the lens will fit physically, automatic diaphragm (AE metering), or other auto functions are not retained using this speed booster.  Metabones Speed Boosters are quality made, using precision-machined brass with chromium plating on both the camera body and the lens side of the booster in order to ensure smooth mounting, quality aesthetic, and durability. A matte black interior reduces internal reflections and a black satin finish external surface matches with most camera bodies and lenses. This adapter has a tripod foot that is compatible with Arca Swiss, Markins, and Photo Clam ball heads, and can be removed if needed with an included hex key.

• Allows a full frame Canon EF lens to be mounted to an FUJIFILM X-mount APS-C format camera and in doing so, increases the angle of view and increases the maximum aperture by one f/stop.
• The Speed Booster ULTRA design incorporates ultra-high index tantalum-based optical glass for enhanced optical performance with improved corner sharpness and reduced distortion and vignetting. This glass technology and optical design perform extremely well with professional-grade f/2.8 zoom lenses and high-speed fixed focal length
• lenses such as a 50mm f/1.2 which will perform as a 35.5mm f/0.9 lens with high contrast and resolution from the center to the edges of the image.
• Precise fit and solid connection - lens has no play, gap or wiggling when mounted on speed booster and no adjustments are required to fit your lens. Both the camera-side and the lens-side of the speed booster are made of brass which is precision-machined and chrome-plated.
• The Speed Booster uses matte-black treatment to keep internal reflection to a minimum in order to maintain the maximum optical quality possible with the lens. The exterior features a black satin surface finish.
• Designed to reach infinity focus while maintaining the correct registration distance required to maintain optical quality of CRC lenses or lenses with floating elements.
• The speed booster features a detachable tripod foot which is compatible with Arca Swiss, Markins, Photo Clam ball heads. The booster may attach to a quick release plate or tripod using a 1/4"-20 screw.
• Although the lens will fit physically, automatic diaphragm (AE metering), or other auto functions will not be retained using this speed booster.
• Two hex keys included with the product, one to detach the tripod foot and another to tighten a mounting screw