Yongnuo trigger flash trigger YN-E3-RT E3-RT E3RT TTL Flash Speedlite Wireless Transmitter for Canon 600EX-RT as ST-E3-RT with Two Free OOPSTEK Cleaning Cloths For Camera lenses canon lenses Two-way 2.4G radio communication,fully compatible with ST-E3-RT/ 600EX-RT Supports ETTL Ratio, Flash Exposure Compensation,Flash Exposure Lock, Flash Exposure Bracket, Modeling Flash Power Source: 2 AA/LR6 alkaline batteries Ni-MH batteries Transmission Range: 100M Flash Mode: ETTL/M/Multi/GR 4 flash modes