Sigma EM-140 DG Macro Ring Flash for Nikon SLR Cameras Fully dedicated with the latest TTL auto exposure systems Flash tubes can be switched on or off for creative flash control Wireless flash control; high-speed synchro flash Guide number of 14 (ISO 100) Guide number of 14 (ISO 100) Ideal for close-up photography, especially medical and scientific applications.55mm and 62mm adapter rings are included with the flash