The Canon 2478A002 Speedlite Transmitter ST-E2 is a dedicated clip-on transmitter for E-TTL / E-TTL II wireless flash system. The auto flash transmitter can control an unlimited number of 420EX, 430EX, 550EX and 580EX flashes, in two separate groups; A and B. It sets and controls all functions of its slave units. The flash output ratio between groups A and B can also be adjusted from 8:1 to 1:1 or from 1:1 to 1:8. Under low-light or low-contrast conditions it emits an AF-assist beam linked to the EOS-3's 45 focusing points.Features:
- Wireless flash controller for the Canon 420EX and 550EX and other Canon flashes.
- Indoor transmission range of approximately 40 to 50 feet
- Outdoor transmission range of approximately 26 to 33 feet
- 1,500-transmission battery life
- Turns off after 90-second idle