Compatible with radio triggering Guide number of 60 metres 20-200mm zoom compatibility The Canon Speedlite 600EX-RT is a professional-level flashgun designed for use with a Canon full frame DSLR, such as the EOS 5D Mark III. Thanks to the 60m guide number at ISO 100 low light conditions can be tackled with ease, whether indoors or outside, and the zoom head can cover a 20-200mm focal length. The Canon Speedlite 600EX-RT can also function as the trigger for up to 15 other compatible flashguns, making it the potential hub of a portable studio lighting system. The Canon Speedlite 600EX-RT is compatible with the E-TTL II metering system, allowing any compatible digital SLR to accurately adjust power and distribution of light automatically. With an ST-E3-RT unit mounted to a DSLR the Canon Speedlite 600EX-RT can even be triggered off-camera to allow for creative lighting techniques. The bounce and swivel features allow for the flash to be redirected, giving a more balanced or diffused light source where required. The Speedlite 600EX-RT can be part of a 15-unit setup, giving you the opportunity to light an outdoor shoot without needing a power source other than four AA batteries per flash. As a result the Speedlite 600EX-RT is an excellent choice for the professional photographer, replacing the Speedlite 580EX with an improved feature set and longer guide number.