From the ManufacturerThe Electronic Flash Macro Ring EM-140 DG is designed to work with both AF 35mm film and digital SLR cameras of all popular manufactures. It is ideal for photographing subjects in fine detail when the shadowless mode is used and is extremely effective for scientific and medical applications. Dual flash tubes can fire simultaneously or separately. Using only one flashtube creates shadow, which can give a three-dimensional feeling to the subject. The flash features a guide number of 14 with ISO 100. The Modeling Flash function makes it possible to check for reflections and shadows before actually taking the flash picture. A wireless flash function is also available when the EM-140 DG is used as master and the EF-500 DG Super as a slave unit for creating fine shadow details. High-speed synchro and exposure compensation functions are also available for advanced flash photography. Ideal for close-up photography, especially medical and scientific applications 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)G/No. 46/ft, 14/m (ISO 100) Power Level 1/1 1/2 1/4 1/8 1/16 1/32 1/64 2 tubes (ft)463323171286 2 tubes (m)1410753.52.51.8Compatibility with Canon AF SLR and Digital SLR Cameras EM140 Ring FlashCanon EOS TTL 35 Film SLRETTL, ETT-II*1 TTL Digital SLRETTL, ETTL-II*1 Distance Priority Manual Flash- High Speed SynchroFPO*2 Multi FlashO Exposure Compensation FunctionO Modeling FlashO Wireless FlashTTLO*2*4 "O" Available, "-" Not available*1: Compatible with E-TTL and TTL. Please note A-TTL automatic exposure is not supported.*2: This function is not supported by some camera models.*3: Compatible with 3D-multi BL exposure.*4: Manual exposure is also possible.