The MC-21 Mount Converter enables the use of Sigma EF-mount lenses on L-mount mirrorless camera bodies, and maintains full lens performance, including autofocus in AF-S mode and auto-exposure, as well as in-camera correction and image stabilization technologies. An integrated LED can be used to display select Sigma lens compatibility with the adapted camera body, and the adapter also has pre-loaded lens data to support peripheral illumination, chromatic aberration, and distortion corrective functions. In order to maintain a high degree of image quality, the interior of the adapter is flocked to reduce reflections, and it also retains full EXIF data to benefit post-production and file management. Additionally, a removable tripod mount is included for more stable mounting when working with heavier lenses.

Per Sigma, this Mount Converter/Lens Adapter is compatible with a select number of Sigma's own EF-mount lenses, and may or may not be suitable for use with other manufacturers' EF-mount lenses.