Take your creativity further with the Canon Speedlite 600EX-RT Flashgun, a powerful flashgun with built-in wireless radio control for use both on and off the camera. The built-in radio triggering offers remote lighting control over distances up to an impressive 30m and unlike IR control you don’t have to worry whether you are in direct line of sight. The Canon ST-E3-RT Speedlite Transmitter can be used in conjunction with the 600EX to trigger up to 15 Speedlites from up to an impressive 30metres. The Canon Speedlite 600EX-RT Flashgun features an AF assist beam to help focus in the dark and a guide no of 60m (ISO 100, at 200mm setting) to ensure long-range flash and wide-area coverage. The 600EX Flashgun takes four AA batteries