As a Canon top-of-the-line flash, the Speedlite 600EX-RT takes the best features from existing models and adds functionality for enhanced digital photography. The 600EX features a new wireless multiple flash system using radio wave communication that provides more precise control over as many as five groups of flashes. There?s also more power, with a guide number of 197? (60 m) at ISO 100, a zoom flash head that covers a 20-200mm range. 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.