"This 16-channel, 5-group wireless speedlight transmitter from Yongnuo lives up to the brand's reputation for making accessible and high-quality camera gear. With a straightforward interface, push-button operation, and a whole pile of helpful features for a photographer with varying needs, the E3-RT is a great addition to anyone's gear bag. The wireless range on this transmitter is rated to over 100 meters, or 328 feet. Some features include AF beam focus-assist, a modeling strobe, flash exposure lock, and up to 9 custom functions you can set to your preferences. It's also capable of E-TTLII and E-TTL auto flash, manual flash, strobe, and multiple metering modes as well as advanced flash control (in one-third and half stops) via the push-button interface. A large LCD display lets you keep an eye on all your settings and control groups, and confirmation LED indicators let you know when you're correctly paired with external flashes or additional cameras for shutter triggering. The unit runs on AA or LR6 alkaline batteries for up to 10 hours at a time, and a power-saving function puts it to sleep after 5 minutes idle to conserve battery life.|Two-way 2.4G radio communication, fully compatible with ST-E3-RT/600EX-RT|15 Physical Channels, 1 Auto Channel, Up to 10,000 customizable photographer ID|Transmission Range: 100M|Multi YN-E3-RT can share slave flashes|Display group/charge status of slave flashes|Firmware can be upgraded via USB|High resolution Dot-Matrix LCD, Backlight for LCD/keys|Fast lock mechanism|Built-in AF assist beam emitter, buzzer|Remote shutter release, Linked Shot|Flash Mode: ETTL/M/Multi/GR 4 flash modes|A/B/C/D/E 5 groups|Supports 1st Curtain, 2nd Curtain (Only in M mode),High speed Sync|Supports ETTL Ratio, Flash Exposure Compensation,|Flash Exposure Lock, Flash Exposure Bracket, Modeling Flash|9 Custom Functions|Settings saved automatically"