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 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

• New positive-lock EF lens mount. 
• Detachable tripod foot compatible with Arca Swiss, Markins and Photo Clam ball heads.
• Rubber gasket protects MTF mount connection from dust and moisture.
• 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.     
• EF-S lenses require modification to fit or may remain incompatible even after modification (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
• AF may not work if the maximum aperture of the lens plus any EF Extender or other teleconverter attached is smaller than f/8 before boost or smaller than f/5.6 after boost.
• AFC (continuous AF) and AFF (flexible AF) modes are not supported, except on Olympus OM-D E-M1.
• Panasonic video AF may hunt more than a native lens or have unsatisfactory performance.
• Some Tamron lenses may have unsatisfactory AF accuracy.
• 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.
• Use of Canon Cinema lenses such as CN-E 18-80mm T4.4L IS KAS S for still photography is not supported.
• Iris changes are 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. This limitation does not apply to Cinema EOS lenses which permit fine resolution iris control, such as CN-E 18-80mm T4.4 L IS KAS S.
• No support for in-camera correction such as peripheral shading, CA and distortion
• Designed to cover a 24mm image circle, JVC GY-LS300 needs to have VSM configured to 86% (4k) when using a true Super 35 lens such as Canon CN-E 18-80mm T4.4L IS KAS S. Higher VSM settings is possible with full-frame lenses, but will be operating outside of the design parameters of the ULTRA optical formula. Many APS-C/DX lenses do not have adequate coverage at 86% (4k) and on JVC with ULTRA the use of full-frame or true Super 35 lenses is advised.