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. The popularity of its predecessor, 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 individuals 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. Up to five groups or 15 individual flashes can be controlled via one transmitter 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. Its Dot Matrix LCD Panel displays all pertinent information simultaneously and backlit control panel means easy operation. Upgraded with Eight types of custom functions, three types of personal functions, this upgraded flash is a 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 for reliable information transmission and operation.