The PowerST4 Receiver enables remote power control of Elinchrom RX flashes with a camera-mounted PocketWizard MiniTT1 Transmitter or FlexTT5 Transciever. PocketWizard ControlTL technology allows you to control the flash power level using the camera’s Flash Exposure Control (FEC). The PowerTracking feature automatically adjusts flash power to maintain the photographer-established level and thus proper exposure when the aperture and/or ISO is changed. Slide the new PocketWizard AC3 ZoneController into the shoe of the camera-mounted MiniTT1 or FlexTT5 and ST4 linked Elinchrom RX flashes can be controlled in three zones: A, B, and C in 1/3-stop increments over a six-stop range. The ST4 can also receive standard PocketWizard signals from a Plus, Plus II and MultiMAX transmitter. Set for Channel 1 at the factory, the ST4 can be easily set for any of the 20 ControlTL or 32 standard channels using the units' LEARN function or by USB connection with the PocketWizard Utility software. The PowerST4 draws its power directly from the Elinchrom RX flash remote control socket; there’s no need to install or replace batteries. The PocketWizard PowerST4 is a must-have for Canon photographers using PocketWizard with Elinchrom RX flash units.