The ProMaster 170SL Speedlight works with your camera to add light where you want it. It automatically adjusts its exposure and light beam to match your camera and lens settings. The articulating head can be adjusted for a variety of swivel and bounce positions; and is compatible with many light modifiers. The 170SL's powerful guide number of 52m/171ft combined with 180mm zoom head can illuminate subjects from afar. The built-in wireless TTL system provides expanded off-camera lighting options (functions as a master of slave).