Complete with built-in radio transmission wireless functionality the Speedlite 600EX II-RT sits at the top of Canon's on-camera E-TTL / E-TTL II compatible flash lineup with a powerful guide number of 197' at ISO 100 and 200mm. This revision improves continuous flash performance by 1.1-1.5x or up to 2.0x with optional battery pack simplifies the menu system for faster operation and includes a specially designed bounce adapter a hard color filter and an updated soft case. The two-way 2.4 GHz radio system provides added reliability and a range up to 98.4' among up to 5 groups with a total of 15 individual Speedlites. This system also does not need direct line-of-site like traditional optical-based transmission and will work through obstacles.For added coverage and functionality the flash's zoom head can reach from 20-200mm with the option for wide 14mm coverage when the built-in diffusion panel is. Also the unit can tilt from -7 to +90 and rotate 180 either left or right for complete bounce capabilities. On the back of the 600EX II-RT is a backlit dot-matrix LCD panel that displays the status and allows users to easily access and change settings. Additionally the flash is durable with a redesigned contact construction and improved dust and water resistant sealing.Other capabilities of the 600EX II-RT include a stroboscopic mode as well as high-speed first and second curtain sync settings for more control over your image's final look. The flash is powered by 4 AA batteries and has a port for an optional external power pack. The rated recycle time is 0.1-5.5 seconds but can be sped up to 0.1-3.3 seconds in Quick Flash mode. It comes with a bounce adapter a hard CTO filter set a mini stand and an updated soft case that holds the flash and accessories.