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 tantalum-based optical glass by Caldwell Photographic in the USA
Supports 16:9 video with DX lenses.
Electronic

Autofocus
Can be powered either by camera body or by third-party external 5V power source (not included)
Iris/aperture controlled by the camera body
Smooth iris support with the latest Canon (2009+), Tamron (SP series 2013+) and Sigma (2016+) lenses
Image stabilization (IS) lens support
Support for cameras with in-body image stabilization (IBIS), including Panasonic GX7, GX8, GX80/85 and Olympus cameras
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)
Cinema EOS lens support (CN-E 18-80mm T4.4 L), including AF (requires external 5V power via micro USB port), auto iris and servo zoom
Other

Detachable tripod foot compatible with Arca Swiss, Markins and Photo Clam ball heads.
The opening is flocked with felt material 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.