The Vivitar 385HV Flash is a powerful non-dedicated shoe-mount unit with a guide number of 138' at ISO 100 and 85mm and has an auto exposure range up to 70' (21.3 m). This flash unit has 5 auto f/stop settings and built-in variable power to deliver accurate exposures and convenient fill-flash. The zoom head adjusts to 35mm, 50mm, and 105mm and can be set to bounce at 0°, 45°, 60°, 75° and 90°. The unit has an easy-to-read lighted calculator dial so you can work under most lighting conditions. It operates on 4 AA batteries, and it also accepts any 6v-3a external power pack for faster recycle times and more flashes.