The Sigma MC-21 Mount Converter/Adapter gives shooters using L-Mount  cameras such as the Panasonic S1 , a wider range of lens options by allowing Sigma EF-Mount and SA-Mount lenses to be used.
Attaching the MC-21 to an existing Sigma SA or EF mount compatible lens will allow them to be used as L-Mount system lenses.
The MC-21 features a small LED light on the outer part of the ring that changes colour depending on the compatibility of the attached lens.
A green light indicates full compatibility, orange indicates compatibility, but that the lens requires a firmware update and no light at all indicates that the lens is not compatible at all.
There are over 29 lens profiles, (including full-frame and APS-C lenses) pre-loaded on to the MC-21 that optimize the autofocus and aperture control for each lens. The MC-21 also supports camera correction functions such as peripheral illumination, chromatic abberation of magnification and distortion.
Information such as lens type, focal length, F number, and other tags are embedded as Exif data in each image file.
The MC-21 also comes equipped with a socket for mounting a tripod and the inside of the barrel is covered with flocking to prevent internal reflections from reducing lens performance.
The Sigma MC-21 Mount Converter (Canon EF Lens to L-Mount Body) ships towards the end of May and retails for $329.99 CDN.
 – March 29, 2019 Update from Sigma – “When we announced the MC-21 on February 26th, 2019, we mentioned that it was compatible with cameras manufactured by Leica Camera AG. However, the specifications have changed and it will not be compatible with Leica’s existing L-Mount cameras. We sincerely apologize for the inconvenience this situation may have caused.”
- Only AF-S works in Autofocus Mode. AF-C cannot be selected.
- The Auto continuous operation cannot be used during video shooting.
- Touch AF cannot be used
- With lenses incorporating MO (Manual Override), operation in manual mode is possible only after focusing.
- MF guide is not available.
- The image stabilization function inside the camera body and the lens cannot be used simultaneously. Please ensure only one of these is selected.
- The AF Function Button and the Focus Preset Button incorporated on some lenses cannot be used.
Also published on Medium.