Engineered for fast frame rate shooting the canon speedlite 600ex ii rt improves on the older 600ex model with faster continuous firing and up to 50 more flashes during high framerate shooting use it off camera or in the hotshoe the 600ex ii rt is extremely versatile and offers wireless shooting via radio and optical transmission and performs in the most demanding situations making it an ideal companion for the eos 1d x mark ii the unit features a 60 m iso 100 guide number and recycles