The Sunpak 555 is a powerful professional-grade automatic handle mount electronic flash. It is capable of TTL dedication with the EXT-11 PC cord. It features bounce and swivel, a guide number of 150 feet with ISO 100 film, and an auto range that extends from 1.6 to 107 feet (over a 7 aperture range), making the 555 a good choice when shooting over large distances. In addition to TTL and auto capability, the 555 features manual flash control from full to 1/64 power. It accepts a number of power sources, such as the CL-2 NiCd battery cluster and the high voltage TR-PakII NiCd power pack or an AC adapter. The 555 is often used with the bracket attached to the base of the camera, but is becoming more popular with off-camera lighting, due to the tripod/light stand threaded bottom and because of it's powerful lighting. The Sunpak 555 is extremely popular among extreme sports photographers, particularly skateboard photographers.