The Vivitar 285HV Flash is a powerful non-dedicated shoe-mount unit with a Guide Number of 141' at ISO 100 and 105mm and has an auto exposure range up to 70'. This flash unit has four 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°, and 90°. The unit has an easy-to-read lighted calculator dial so you can work under most lighting conditions, and it accepts optional high-voltage power sources for faster recycle time and more flashes.