The new MC-21 mount adapter makes it possible to use interchangeable lenses with Sigma SA mount and SIGMA EF mount on camera bodies with the L-mount. The MC-21 mount adapter is not compatible with Leica SL, CL and TL2. When used with Panasonic Lumix S1 and S1R, only the AF-S function works in AF-on mode. The AF-C function cannot be selected. There have been various methods in the past that allowed lenses from a particular camera system to be used on a body with another system. However, today's digital camera systems are much more complex and it is a difficult task to develop a connection adapter that matches both the mechanical components and the software requirements of lenses and cameras. Even greater difficulties arise in the development of an adapter that should allow lenses for DSLR cameras to be attached to the bodies of mirrorless interchangeable lens cameras. There is a great demand in today's photographic market for such an adapter, which not only adapts the flange focal length, but also maintains full functionality.