The new MC-21 mount adapter allows the use of interchangeable lenses with Sigma SA and Sigma EF mounts on camera bodies with the L-Mount. The MC-21 mount adapter is not compatible with Leica SL, CL, and TL2. When used with the Panasonic Lumix S1 and S1R, only the AF-S function operates in autofocus mode. The AF-C function cannot be selected. In the past, there were various methods that allowed lenses from one camera system to be used on a body with a different system. However, today's digital camera systems are much more complex, making it a challenging task to develop a mount adapter that aligns both the mechanical components and the software requirements of lenses and cameras. Even greater difficulties arise when developing an adapter that allows the attachment of lenses for DSLR cameras to the bodies of mirrorless interchangeable lens cameras. There is a significant demand in today's photography market for such an adapter that not only adjusts the flange focal distance but also maintains full functionality.