Canon's EF lenses are designed to work natively with its DSLRs (and film SLRs if you're still shooting analog). There are tons of EF lens options out there, many of which are still fantastic. The RF lens line represents glass made specifically for Canon's newer mirrorless cameras. You can very easily adapt EF lenses to RF bodies with a $99 adapter. RF lenses will not work on DSLRs, however, because there's no way to adapt the lens mount due to the difference in flange distance.