AF assist beam works with up to 61-point High Density Reticular AF system There are 15 custom functions and 6 personal functions for maximum customization. Optical transmission is available in addition to radio transmission Quick Flash settings speeds up recycle time and flash duration. Manual power settings from 1/1 to 1/128 power in 1/3-stop increments Flash color temperature information is automatically transmitted to the camera. Flash duration of 1.8 ms or less, or 2.3 ms or less in Quick Flash mode Stroboscopic setting from 1-500 Hz, or 1-199 Hz during optical transmission wireless shooting. Compatible with ST-E3 Speedlite Transmitter Approximately 100-700 flashes with AA alkaline batteries