The AF540FGZ Electronic-Flash unit features a large guide number of 54 (at ISO 100) and provides a variety of advanced flash applications, including advanced P-TTL auto flash, high-speed synchronisation and wireless P-TTL auto flash (when mounted on a Pentax SLR camera). When mounted on a Pentax Auto-focus SLR (after the Z-10 and including Digital Format models) equipped with an FA-, FA J-, DFA- or DA- series lens, the AF540FGZ automatically adjusts its angle of discharge to the lens' focal length. The AF540FGZ auto-flash unit also features a newly provided 'Digital' position on the focal-length conversion scale of the Zoom Head which can accommodate digital SLRs, Bounce Flash function with adjustable angles of -10 to 90 degrees vertically and up to 180 degrees horizontally, and Power-zoom flash head to cover angles of view for 24mm to 85mm lenses (in 35mm format).