For using Canon EOS R (RF) mount mirrorless digital cameras with all Pentax K mount manual lenses.
Switching on "Release shutter without lens" in C.Fn5 is recommended.
Allows focus infinity.
Not suitable for Canon EOS film / digital SLR cameras and EOS M series EF-M mount mirrorless cameras.
Since there is no diaphram control, you can use the maximum aperture of Canon EF / EF-S lens only.