The Speedlite Transmitter ST-E3-RT (Ver.2) provides some much anticipated upgrades from professionals to make it an even more appealing resource for flash photography when used with the Speedlite EL-1. This updated version allows for wireless rear curtain synchronization to capture ambient light trails and convey a sense of speed for moving subjects. The expansive minimum output range (down to 1/8192 power) gives you increased opportunity for creativity over the flash output from brightest to dimmest. And you now have FE Memory as part of the radio transmitter, so you can lock-in an E-TTL flash exposure level, even in complex multi-flash setups, and continue to use it for the same scene or subject. These improvements combine with the previous benefits of its predecessor including radio controlled, two-way wireless transmission up to 98.4 ft., among up to five groups or fifteen individual Speedlites, a dot matrix LCD with backlighting, intuitive controls and more.