The new connection adapter MC-21 allows to use interchangeable lenses with SIGMA SA connection and SIGMA EF connection on camera bodies with the L-mount. The MC-21 adapter is not compatible with Leica SL, CL and TL2. In conjunction with Panasonic LUMIX S1 and S1R, only the AF-S function works in the AF mode. The AF-C function cannot be selected. In the past, there have been various methods that made it possible to use lenses from a certain camera system on a housing 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 will allow lenses for DSLR cameras to be attached to the housings of mirrorless interchangeable lens cameras. In today's photographic market there is a great demand for such an adapter that not only adjusts the flange focal length but also maintains full functionality.