The YN565EX III is equipped with the USB interface, you can download the latest firmware from YONGNUO official website to upgrade the speedlite. The recycling time for full output just takes 2 seconds; you can get high speed current-return experience even without using brand new batteries, which will only takes 3-4 seconds. It is equipped with the battery electric power display function, allows you to check the battery remaining capacity easily. It also can be triggered by the camera set-top, PC synchronization trigger and wireless optical trigger off the camera. The YN565EX III is equipped with the AF-assist beam emitter, allows you to focus easily in dark environment. Supports automatic and manual zooming, the focal length can be varied between 24?105mm. Specifications: Circuit design: Insulated Gate Bipolar Transistor(IGBRT) Guide No: 58 meters (ISO 100, 105mm) Flash mode: TTL, M, Multi Wireless mode: Set-top /S1/S2 pre-flash-canceled mode Wireless triggering distance: 20-25m indoor, 10-15m outdoor Slave groups: 3 (A, B and C) Channels: 4 Zoom range: auto,24,28,35,50,70,80,105mm Vertical rotation angle: -7--90 degrees Horizontal rotation angle: 0-270 degrees Power supply: 4 * AA size batteries (Alkaline or Ni-MH are usable) (not included) Lighting times: 100-1500 times(AA alkaline cell used)