Canon EF lenses optically behave very similarly to the newer RF Mirrorless range of lenses, so putting EF lenses onto Canon R Bodies such as the R5 Mk II  is incredibly popular. Autofocus is still fully supported however the RF lenses use newer technology to have a much faster responding autofocus system. Where superfast autofocus is critical RF lenses are far ahead of EF, however for a majority of cases using the more inexpensive EF lenses are a very suitable alternative, and this adapter makes that possible.