The Speedlite 600EX-RT features a wireless multiple flash system using radio wave communication that provides precise control over as many as five groups or fifteen individual flashes at a distance of up to 98.4'. Communicating on 2.4 GHz frequency, it will not be interrupted by physical barriers. It is also very powerful, with a guide number of 197' (60 m) at ISO 100 and a zoom flash head that covers a 20-200mm range. It provides full swivel movement of 180° in both directions. Compatible with the AF frame of all EOS cameras, the Speedlite 600EX-RT even works perfectly with the 61-Point High Density Reticular AF found in the EOS-1D X and the EOS 5D Mark III. It supports all current versions of TTL, including evaluative E-TTL II.