Building on the design and popularity of its predecessor, the second version of the Canon Speedlite Transmitter ST-E3-RT can help you take full advantage of all the features on flashes such as the Speedlite EL-1, 600EX-RT, and 430EX III-RT. Version two of the ST-E3-RT makes complex lighting setups simple by facilitating radio-controlled, two-way wireless transmission at distances up to 98.4' among up to five groups or 15 individual Speedlites. Updates include Wireless Rear Curtain Synchronization for the look of motion in your subjects and a remarkable minimum power range of 1/81922 for very low light shooting. Another outstanding feature is FE Memory that allows you to lock-in an E-TTL flash exposure level, even in complex multi-flash setups, and subsequently continue to use it for the same scene or subject. Yet another upgrade is eight types of custom functions and three types of personal functions. Compact design with highly reliable construction combined with a clearly laid-out information panel and buttons with back lighting make this an indispensable tool for advanced professional flash photography.