Metabones Canon EF Lens to Micro Four Thirds Speed Booster T Ultra 0.71x

Features and Benefits
Optical
Increase maximum aperture by 1 stop
Increase MTF of any lens attached
Makes lens 0.71x wider
Patented 5-element/4-group optical design incorporating ultra-high index tanatalum-based optical glass by Caldwell Photographic in the USA
Supports 16:9 video with DX lenses.

Electronic
Autofocus capabilities on certain lenses/bodies
Can be powered either by camera body or by third-party external 5V power source (not included)
Iris/aperture controlled by the camera body
Image stabilization (IS) lens support
Electronic manual focusing (e.g. EF 85/1.2L II and discontinued EF 50/1.0L)
EXIF (focal length, aperture, zoom range)
Distance and zoom display on camcorders (requires lenses supporting distance information)

Other
Detachable tripod foot compatible with Arca Swiss, Markins and Photo Clam ball heads.
The opening is flocked with felt material coating to reduce internal reflection.
Compatible with all MFT mount cameras, including GH4, OM-D, Blackmagic Cinema Camera, Blackmagic Pocket Cinema Camera and JVC GY-LS300.

Limitations
EF-S lenses require modification to fit (but third party DX lenses can be used without modification)
Some EF-S and DX lenses may not have enough coverage of the entire image circle for stills after widening by 0.71x (but video will have enough coverage).
No video AF for Olympus
AFC (continuous AF) and AFF (flexible AF) modes are not supported
Panasonic video AF may hunt more than a native lens or have unsatisfactory performance.
Tamron lenses may have unsatisfactory video AF accuracy. Canon and Sigma lenses are fine.
No support for Focus Stacking and Focus Bracketing on Olympus.
On Olympus, other than E-M1, you may move the single AF point among any of the 81, but you may not multi-point AF. There is no restriction on E-M1 and Panasonic.
Very early Olympus models (e.g. E-PL1) have no autofocus support.
EF-mount lenses are not silent but may make audible click noises during autofocus operation and iris changes which may be picked up by the built-in microphone of the camera. An external microphone is recommended for video.
Iris changes are unsmooth but in 1/8 stop steps which may be noticeable in video recordings. Programmed exposure mode and shutter priority exposure mode should not be used for video.
No support for in-camera correction such as peripheral shading, CA and distortion
Designed to cover a 24mm image circle but not enough to cover Super35 so JVC GY-LS300 needs to have VSM configured to 86% (4k)