For heavy medium format lenses like telephoto lens, we suggest to use with a telephoto bracket and a tripod to balance its weight when shoot

1. As Canon’s EOS lenses are electronically controlled，most Canon EF mount lenses do not feature a manual aperture ring，so when used on our EOS-M4/3, which is a full manual operation adapter ring, the aperture could not be transferred to the camera, it will stop down to its smallest f/stop by default.
2. Some buyer mentioned could not adjust the aperture, actually this is because your lens does not have the aperture control function, If your lens does not have a manual aperture control ring, it will stop down to its smallest f/stop by default
3. You could set your aperture via this way, but we do not suggest to use this way: You can control the f-stop by putting the lens on an EOS body, stop it down using the DOF preview button, and while holding the button down taking the lens off the camera. You can then transfer the lens to the M4/3 camera, and it will retain the f-stop.