Is Yongnuo RF 603NII N3 compatible with YN-565EX III.
If yes, how should you proceed?
Is Yongnuo RF 603NII N3 compatible with YN-565EX III.
If yes, how should you proceed?
Depends on your definition of "compatible."
The RF-603 II transceivers are manual-only triggers and can tell any ISO-compliant speedlight to fire off-camera. They cannot, however, communicate anything but the fire signal and the wake-up signal. They do not communicate TTL, HSS, Zoom, Group, or M power control signals. So they are not fully compatible, as TTL-triggers (e.g., YN-622N, Godox X1R/X-Pro, Phottix Odin II, etc.) would be.
Use is pretty typical as with most radio triggers:
Make sure the batteries are good in everything.
Make sure the transceivers are set to the same channel.
Attach the speedlight to the hotshoe of one unit to act as a receiver. Make sure the receiver unit is set to TRX mode. Be sure the flash is oriented correctly and fully forward in the hotshoe so all the pins on the foot make contact with the pads on the hotshoe.
Attach one to the hotshoe of the camera to act as a transmitter. (Make sure the unit is set to TRX or TX mode). Again, make sure the transmitter is properly seated in the hotshoe.
Turn everything on.
Make sure the camera is set as if to fire an on-camera flash at every shot.
Firing the camera should fire the flash.