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The WFT-E4 is effectively a 're-bodied' WFT-E3, it provides a vertical grip and controls as well as wireless image transfer to FTP or HTTP servers as well as remote wireless control using the EOS Utility software. It also provides connectivity for GPS and external USB Hard Disk (mass storage device).
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WFT-E4/E4A Wireless Battery Grip (optional)

With the new WFT-E4/E4A you can shoot wirelessly (802.11b/g) direct to FTP servers as well as have two-way communication over PTP and HTTP. In HTTP mode you can effectively remote control the camera, see a live view, change settings and take shots. The USB port can be used to store directly to external USB hard disks (although only small flash devices can be powered by the grip) or provide GPS data from USB GPS devices. The one thing the WFT-E4/E4A doesn't do is provide any extra power to the camera, as you can see it doesn't have a dummy battery stalk, instead the camera battery stays in the camera and the grip simply attaches to the bottom of the camera (and communicates through a new connector).