Sigma EF-530 DG ST Flashgun - Pentax DedicatedFlashgun features a powerful Guide Number of 53 and is designed to work with the latest TTL auto exposure systems of all popular manufacturers' digital and film SLR cameras. It features TTL automatic flash exposure control for easy operation, while the autozoom function automatically sets the optimum illumination angle in accordance with the lens' focal length in a range from 24mm to 105mm.