After the Canon 5D Mark II was introduced to the professional world of video production, there was a creative rebirth in the film and video community. It gave us a system that was similar to motion picture cameras by offering a large sensor, shallow depth of field and interchangeable lenses. Like many motion picture cameras, the Canon 5D Mark III is modular. It can interface with a variety of lenses, video monitors, magazines, support rods, follow focus, etc.
Very early on, it became apparent that there was a need to adapt different combinations of lenses to camera bodies. The design for these adapters appear relatively simple (a metal ring that allows one mount to connect to another), but the difficulty was introducing the pass through of the data in the electronics of the lens mounts. For instance, the Canon EF mount uses an electronic contact to open and close the iris. Metabones is a company that specializes in electronic adapters for a variety of still and motion cameras.
Metabones has different types of adapters for everything from Micro 4/3 to PL to Sony E, and even their brand new FE for the Sony A7s. Not only can these widely used smart adapters pass through auto focus and aperture, they also pass through important IS information that allows you to take advantage of image stabilization features in a Canon EF lens when mounted to a Sony FS700. These adapters are incredibly capable, but Metabones took it to the next level when they introduced the Speed Booster adapters, which not only increases your light output by a full stop, but can also reverse your crop factor. This effectively increases the field of view on your Sigma 18-35 mm f1.8 to almost a full frame viewing perspective with a wide open aperture of f1.2. These adapters are made specifically for cameras like the Black Magic Pocket Cinema Camera, Panasonic GH4, Sony FS700 and many more.